MetalicaRap

MetalicaRap

Release status: Experimental

 Description An Electron Beam 3D Metal and Home Solar cell Printer, including microscope vision system (SEM) & Z axis metal correction in a vacuum.(Design stage). License GPL Author Rapatan Based-on Sui Generis Categories EBM,Powder CAD Models none External Link please contact us via mail forum below

MetalicaRap is an open 3D metal & home solar cell printer, based on the principles of electron beam welding and vapor deposition. MetalicaRap is currently in the design stage. The goal is to have affordable home-manufacturing of solar cells, key electrical parts and milled-quality metal parts[3][4][5].

An electron beam based printer was chosen due to the ability to print itself, the power efficiency of an electron gun versus a powerful laser at fusing metal, and the fact that an electron gun and vacuum chamber are the primary requirements for thin film solar cell printers. It was recognized that the printer did not require a new technological invention, but does require the existing solutions to become publicly accessible through grassroots research and re-engineering.

One of the goals is a solar cell production plant design that MetalicaRap will be able to print, that will utilize MetalicaRap's vacuum chamber and beam for the solar cell manufacturing processes[6]. For a typical family home electrical system we may bring the solar cell cost down from 10,000 euro to 400 euro by self printing. (Solar cell installation, inverter, and other costs would obviously be on top of this price).

21% of all solar cells manufactured used the CIGS process (2011) [7] [8], it works at the same vacuum of 10-4 Torr as the metal printer, by creating metal layers by directly co-evaporating readily available targets Video of; copper gallium mix, copper indium mix, selenium sulfur mix[9], molybdenum backing layer, tin oxide front contact onto a heated substrate with a chemically dipped buffer layer and a front copper alloy electrical collector strip. This CIGS [10] thin film manufacturing process will consist of electron beam physical vapor deposition[11] (EBPVD summary material [12])Other precursor choices including Indium Gallium Nitride may also be possible [13][14] [15].

MetalicaRap, Project overview

Congratulations Aleksander he has made the first home build electron beam welder!! See 27min 40Sec long video home page

Introduction

We are now 18 months into the development of a printer capable of printing in all common metals, which can largely print itself.

Why an Open Design?

Currently few commercial companies give away the ability to manufacture their own product to the customer (Google's "free search" business model comes closest and also Mendel – see below). MetalicaRap does, through self-printing, which is why this project needs volunteers initially giving their time, effort and charitable contributions via crowd funding. This price reduction method and empowerment model has been shown to work with a plastic printer in 2009 bringing the price down by a factor of 60 (30,000 euro to 500 euro kit price Mendel http://reprap.org/ http://en.wikipedia.org/wiki/Adrian_Bowyer award wining inventor).

What are the benefits?

Metal Fabricated Home Japan SANAA 2005

A home solar cell printer will enable a whole set of new possibilities via near free electricity including: Solar Jewelry , Solar Bike, Zero house utilizing self printed titanium Vacuum panels [16], water supply from air condensing, home tropical greenhouse/Plant factory, along with the well known environmental benefits of solar power for heating and lighting being a factor of 25-45 times cleaner than traditional fuels [17][18].

Metal printing has obvious benefits for reducing transport costs. Later MetalicaRap may effect accommodation costs Japanese metal home moving beyond high status cultural applications Walt Disney Concert Hall, through reducing metal refinement and manufacturing costs, by replacing foundry processes by processing its own billet metal in to metal powder through electron beam melting on to a spinning disk within MetalicaRap, an established method[19][20].

Titanium powder may come down to 6 euro per kilogram (2012) as titanium's last refining step is Electron beam melting of "Titanium Sponge" the identical process to MetalicaRap's.

Titanium's properties include: highest strength to weight ratio of any pure metal, corrosion resistance similar to platinum, can be nearly as hard as diamonds (this may lead to wearing component life times of over 70 years with a car body lasting 300 years), and with high recyclable factor of materials within MetalicaRap [21].

Few large commercial companies would compete with MetalicaRap products, as titanium's durability (hundreds of years) means that it is not in their interest to, as they may see it as "destroying" their own resale market. Yet, through branding and short-lived fashionable product design, some large companies will try to maintain high product redundancy rates.

MetalicaRap may be one of the very few environmental solutions that largely overcomes "energy cannibalism" Energy Cannibalism Explanation

Why should I help?

There is no technological block to the success of this project, but it requires the engineering solutions to happen within an open hardware cultural context to succeed, a group of technical specialists volunteering their time and effort, along with crowd funding. We have had the involvement of 6 part-time specialists based in Copenhagen, Geneva (ex-Cern), California (ex-Stanford) and Toronto, volunteering in areas including electron gun design. We currently have 2 specialists consulting for us. More people involved at a non-specialist task level will bring the project forward quicker.

Critically, MetalicaRap may offer the ability to largely print the most expensive parts. This may enable the price of the solar cell printer to fall by a factor of 100, to be within the home budget's grasp (printing the electron gun is equivalent to printing a 600W fiber laser in a Selective Laser Sintering machine; this gun's function is to melt metal on a build platform to producing metal thin film solar cells and metal parts).

For now, the self-replication will not include the vacuum chamber. The power supply is under construction from bought-in parts. One pump will initially be purchased, and, as the design progresses, further parts will be self-printed.

If you would like to help, knowing that MetalicaRap's design development details do not fit in one persons head, please specialize and take ownership of a specific task from below or contact us via the mail forum.

Towards this aim of reaching further volunteers, we would really appreciate the inclusion of the below within your member contact newsletter in a form that suits your organization.

Kind Regards MetalicaRap team

Design criteria

The printer should have the following characteristics:

• A build volume of about 30cm × 30cm × 30cm (prototype will be 24cm × 24cm × 24cm as this is minimum that can still print babies)
• Produces finished parts +/- 20 µm over 20mm
• Finished parts should be the metallurgical equivalent to wrought iron milled metal parts (full strength, >98% density)
• The printer is largely self reproducing (i.e. it can print many of its own parts)
• Single Phase electrical supply
• Minimum consumables beyond metal powder (avoiding need for e.g. argon gas would be an advantage for later designs)
• Cost for parts which it cannot itself print plus the raw material for printable parts is less than the cost of a used car (self replication plus self build kit may reduce the price by approximately 100 times i.e. from the existing price of a metal 3D printer or solar cell plant; 1,000,000 euro price tag, to 10,000 euro self print/kit price. historically the plastic printer went from 30,000 euro commercial price to 500 euro in 2009 via this approach)
• The build-rate can be slow i.e. 0.2 kg per hour.
• Max height should be 2.4m so it can fit in a home. ( first / simpler to construct prototype will be taller than this until we know how much we can bend beam while maintaining spot size, the bigger the bend the shorter it will become)
• Shape and size of vacuum chamber and electron gun power rating should be suitable for Solar Cell Printing(300W).

Introduction Existing Commercial Electron Beam 3D printer 2min video, Solar cells by co-evaporating 4 metals on top of each other & some ancillary layers video creating Copper/Indium/Gallium/Selenium layers , Factory at home,People locally developing solutions for local problems while being connected globally and for those who have everything developing technology for a market of one! personal fabrication as a way to take control and as an aid for identity [22] ,A commercially Printed Rocket Engine Takes Flight in USA! See here at 2:40.

Request for specialists and non specalists

We are looking for further technical people who are committed to empowering themselves and their environment through self motivated practical tasks in the following areas: Stainless steel metal prototype machining, High voltage power supply prototyping (75kV 1-5KW), vacuum instrumentation, mechanical drafting / design, and back-end software (specifically in unified accelerator library; a gcode to electron beam deflection coil data application) and electron optics design. We are now also looking for more people to chase non specialist tasks as well.

Crowd Funding Support of MetalicaRap

We are currently raising money to make a RepStrap version of MetalicaRap.

We need an estimated 50K euro, and have so far raised over 8000 euro. Donations over 100 euro recieve a MetalicaRap Printing Certificate. We are aiming for a final kit parts price of 9K to 13K euro.

You can donate money:

• via paypal to MetalicaRap@3iii.dk
• or bank transfer. Please write an email to MetalicaRap@3iii.dk for details of MetalicaRap committee managed account.

There are many other ways you can help further the development of MetalicaRap. Please read this page to get an idea of current development status. We can be contacted on the RepRap IRC channel, MetalicaRap@3iii.dk, or best at RepRap MetalicaRap forum.

Current status

We are based in Copenhagen Denmark at Labitat.dk and our main engineers are also in Lancashire UK. On Wednesday nights, you could come to Labitat in Frederiksberg, Denmark and meet the team. Electron gun test rig and repstrap vacuum chamber, including pumps and gauges, are currently under electrical maintenance.

Get involved! The current team donates their free time. Current tech team: 1 Administrator, 3 software developers UAL, 1 electrical engineer and 1 physicist (all part-time) (Very occasional advice from: 1 ultra-high vacuum metal deposition specialist, 2 physicists, 1 high-voltage system designer, 1 mechanical design engineer).

Do get in touch. See talk page and forum for more discussion.

General Design

Philosophy and technical considerations

"Since Jones and Swainson many other techniques for rapid prototyping have been developed. Three of the most significant are selective laser sintering (SLS), filament deposition modeling (FDM), and the MIT powder/ink-jet-glue process. A rapid prototyping machine that can make most of its own component parts will clearly be easier to design if one avoids things like high-powered lasers; having the machine make a laser from scratch would be difficult. More subtly, ink-jet print heads (though cheap) are intrinsically hard to make as they involve micro-fabrication, and so a machine based on them would be unlikely (in the medium term) to be able to liberate itself from that one bought-in part." [23] Adrian Bowyer

Even though SLS was one of the 3 major contenders for the reprap machine, it was rejected due to the difficulty of self manufacturing the laser. Using an electron beam may offer easier self manufacture, due to it largely consisting of 3 simple elements; a cathode metal ring, an anode metal tube and a hot wire.

Another key issue is producing verified, dimensionally finished parts. Commercial metal powder printers, both laser and electron based, can not measure the individual parts they produce during production, unlike conventional machining methods. MetalicaRap could due to the inclusion of a layer by layer measuring system (stereo, 3d scanning electron microscope).

The challenges of Z axis control is expected to be greatly helped by the vision system and z axis correction method EBM/vaporization (Vision systems are currently in development stage on state of the art commercial machines.)

It is important to point out that this is a complex and in the 1000's of euro price range project. Your largely self-producing printer is possible in the commercial setting with either laser or electron beam printing parts (as the commercial machines indicate), but due to the power transfer inefficiency from wall socket to most common metals via lasers being 50 times worse than in electron beams, available home lasers would print too slowly. A typical CO2 laser to copper energy transfer efficiency is 1.6%, so 400W energy into the metal therefore requires a 25000 W laser -- current home build lasers are considered large at 30W (an exception to this is laser to steel: 80%). Therefore lasers would limit the achievable part size to 10's of cm3 (e.g. 3cm x3cmx3cm) with a 2 day print duration, which makes it impracticably slow for self replicating printers. For further proof try our Laser 808 Build Speed Calculator from this [24].

So the electron gun is still likely to be quite a bit easier to build for the same power level. Especially as long as complications due to magnetic forces, grounding, X-ray radiation, and calibration do not turn out to unsurmountable problems. We do not expect them to. Also, its likely that subtractive machining is needed. Commercial printers report being able to produce finished parts for jet engines and medical implants etc. without it, but granted maybe there are details the manufacturers don't put on their web sites.

Due to lack of control in metal powder deposition and molten metal forming droplet/distortions in conventional ebeam 3D printing (e.g Arcam 3d) a tolerance of 300µ in the Z axis is typical with 10µ powder. Finer powders are prone to magnetic forces and typically unwieldy, though powder demagnetization and non ferrous construction is a possibility. This demands an error correction which is based around a vision system using a 4-sector, independent channel axial Back Scatter Electron detection (BSE) Scanning Electron Microscope (SEM) combined with image processing. The pseudo stereo SEM picture data can be converted to true 3D dimensional data (asymmetrical 4-source BSE photometric stereo 3D-imaging), enabling sub µ metal height measurements. Z axis dimensional mistakes in any particular layer can be found and corrected by removal of high points through electron beam machining of the metal. From discussions with industry experts we may bring the XYZ axis error to 20µ over 20mm (IT grade 7 See IT grade table here.)

Advantages of current chosen design approach

• Fully functional parts directly from standard metals
• For most parts it may offer dimensionally finished metal parts IT grade 7
• Good metallurgy on all common metals (Melting process rather than sintering process ensures near 100% of solid material)
• Closed loop system
• Self measurement of finished part tolerances.
• May offer automatic self correction (subtractive machining steps during build process and feedback with compensation used in the additive process).
• Can print thin film CIGS Solar cells in existing 10$^- $$^4 vacuum chamber with existing electron gun. Will be able to self print additional required parts for solar cell printer. • Can create its own metal powder from scrap metal. • Can finish the refining process for titanium metal by melting titanium sponge, which may lead to a 25 fold reduction in the titanium price. Disadvantages of current chosen design approach • Vacuum chamber needs on going maintenance. • Given the quantity and quality of metal/materials used in 10-4 torr vacuum chamber construction they may have high cost or be hard to obtain. (Limited outgasing required, more info: [25][26]) • Difficultly in managing metal powders, indicated by the need to have layer error correction, Problem area's including; powder layer flatness, metal meniscus blob formation, metal powder trapped in work piece (i.e. designed internal closed cavities, designed internal porous or honeycomb structures most likely impossible without additional processing or work on the part after printing). • Quality Control may be a hurdle to overcome - on the fly heat treatment process development (to overcome residual stress present in the first few layers) may be desirable but optional. Layer by layer temperature measurement is one way for metallurgical quality assurance. Currently multiple printed and tested tensile test samples are used to prove most processes. This is a problem in general for additive manufacturing of all sorts at present. • Adequate surface finish may require post processing, depending on the purpose of the part. Later by the addition of argon we could do electronbeam polishing[27]. • Non-desktop size wardrobe size, chamber volume approx 0.3m cubed. MetalicaRapBaby Overwiev description of the prototype, actual builders should go to builders only section below. MetalicaRapBaby in it's current form has 8 main elements which form the printer hardware proper: • Triode electron gun within a 4 way reducer cross. • Electron optics assemply including deflection coils and magnetic lenses. • A metal powder dispensing trough hopper, with a cartesian 8cm diameter topological pick up ring. • Build platform in a 14 inch dia. build platform tube within outer glass tube chamber. • SEM for vision system for feedback regarding the shape of the part, using the 12kg trough, hopper pick up ring. • One roughing pump capable of 10-4 Torr • Switch Mode Power Supply -63kV up to 5kW series parallel resonant converter topology. A low power gun build example Low power gun in operation.. See [1] Electron Gun Elements Coil wiring diagram Electron Gun Static electron gun 1-5kW max (-63kV accelerating voltage) output approximately 1m above the build platform. The gun has a small filament chamber and a Whenelt electrode, i.e. a triode gun. A triode gun contains an anode with a hole in it, to accelerate the electrons from the filament. This anode will function as an electrostatic lens and form an image of the filament close to the gun. This image is known as the cross over. Out current design of the electron gun is based on an analytical model from Potapkin (2008). With our chosen parameters the the diameter of the cross over is about 120µ. This cross over will have to demagnified and reimaged onto the work surface by electron optics. • Electron Gun constructed from self printed Stainless steel 304L 6" 4.5" inch 4 way crosses reducer with ID 100.4mm beam pipe. Beam pipe terminates in joining adapter to glass chambers. The poteltial of the Wenelt electrode will be set by feedback through a resistor to the cathode to make the output form the electron gun self-stabilising. To set the dimension for the power supply and the feedback resistors we need a rough estimate of the perveance (current-voltage relation I=P*U^{3/2}) of the electron gun. The gun is to first order a triode, one of the mainstays of electronics in the first half of the 20th century (amplifier tubes). Hence there excists lots of literature on how to calculate the perveance of a triode. The number of electrons emitted from the cathod themionicaly is given by the Dushman Equation which is exponential with the temperature of the cathode. But must of these themionically emited electrons are pushed back by the electric field from space charge, so the important quantity is the space charge limited current, which is must often descriped with the Child-Langimur equation. This equation strightly only applys to diodes and we have to adapt it for our pourpose with is a triode with the Whenelt beeing the grid. Currently the distance from the cathode to the Wenelt is 1.175mm and the distance form the Whenelt to the anode is 29.3mm. The diameter of the cathode is 2mm.(Check I think the thickness of Wenelt is 1.175mm and its 0.3mm from cathode?) In the paper (VanDeBroek1986)on the emitting disk ratio the emmiting disk ratio is given in terms of the drive which is 1-(V_g1/V_co) (equation(1) VanDeBroek1986). Where V_co is the cut off potential (zero field strength right at the center of the filament, emitting area zero) which can be measured experimentially for a given electron gun. It can also be calculated from the Durchgriff, but the paper does not give the coefficeints for a triode with the ratios that we have designed. But the Durchgriff is probably somewhere between 0.02 and 0.01 times V_acc (Table 1 VanDeBroek1986). Some where between 600 and 1200V. At half the V_co we can expect to have approximately half of the emmitter area available, from which we can calculate the space charge limited current form Child's law. Child's law says that for a diode the current density is given by j[A/cm^2] = 2.33e-6 V^(3/2)[V]/d^2[cm] [28]. Where d is the distance between the cathode and the anode and V is the voltage across. For our case we get j=4A/cm^2. For a 2mm diameter cathode where all of it emits this gives current about I=0.1A. But for our desired optics which can achieve a small gun cross over diameter of 120µ Potapkin(2008) requires a wehnelt electrode nearly at cutoff voltage(i.e 97%) [Important note U_c in Potapkins paper probably means the cut-off voltage]. This means that emitting area of cathode is reduced, from fig 3(VanDeBroek1986) drive of 0.03 so emting disk ratio is 0.1, So that at our operating conditions we have about 10 percent of the emitting radius avaliable we get a radius of 0.1mm which corresponds to an area of 0.0003cm^2 and a limiting current of about 0.00125A allowing for 15% loss of beam in to anode. So the 47µ spot size beam would be at 65W. Assuming we desire this 1000V cut off we need a 2.4KOhm resistor between wehnelt and cathode.(Accepting L/R=10.99 in fig3 VanDeBroek1986)) Spangenberg page 416, formular 15.4 gives a way of calculating the amplification mu of en electron gun. Doing the calculation with the numbers of the current design we get mu=367. In formula 15.3 Spangenberg gives that the ratio of the Whenelt (V_2) and anode (V_3) potentials is related to mu at the cut-off mu=-V_3/V_2. Given this mu and V_3=62.5kV we get a cut-off potential of -170V. Currently 2x 430K ohm in parrallel or 215Kohm for 940W gun power level and 4x 430Kohm in series or 1720Kohm for 100W power level ( maintaining 3KV across resistor in both cases). Electron Optics Assembly The electron optics assembly reimage and demagnify the electron gun crossover onto the build platform to create the electron beam focal spot for melting metal powder for additive printing and melting targets for solar cell EBPVD process. The focus spot size should be 100µ for printing and 10µ for SEM imaging (to achive 20µ resoluton ie. the Nyquist limit), with a pointing accuracy 10µ. Additionally the focus spot size for providing micro vaporization of errors in the build should be in the range 10µ to 40µ, see gun layout page 3. Initially this would be used to flatten every tenth layer of the build through high points/blobs removal. Future software development could provide live modeling of build, so through the adjustment of beam melting path in the subsequent layers errors/blobs could be accounted for as they arise, thereby limiting the need for blob removal to critical surfaces. The electron optics assembly will take the form of a two lens demagnifying telescope with an interlens deflection system for moving the image. To first order electron optics can be designed as standard geometric optics, with a few modifications. We will need to reimage and demagnify the cross over onto the printing surface. It is important to note that rays around the crossover are not straight lines, only asymtotically so. This means that to consider the crossover in terms of geometric optics, we have to use the asymtotic position of the crossover, that is, the focal point where the asymtotically straight rays meet, when projected backwards. The smalles spot size need is around 10µ, which means that out optics will have to demagnify by a factor of about 0.1 given the cross over diameter of 120µ. The needed demagnification can be distributed over the two lenses and the total magnification will be given by M = M_1 M_2, where M is found from the thin lens formula 1/s_o + 1/s_i = 1/f and M = -s_i/s_o. We see that for a lens to be demagnifying M<1 the distance to the image (s_i) will be smaller that the conjugate distance to the object (s_o). In practical terms this means that it will be hard to have L2 be de-magnifying, it will have to be neutral (M=1) or magnifiying in order to leave room in the vacuum chamber and not having to bend the beam excessivly to achive a large printing area. Hence we will have to put all the de-magnification on L1. This leads to the complication of having a very divergent beam between L1 and L2, implying that the diameter of L2 will have to very much larger than the diameter of L1. The situation is illustrated in the figure. At precent we do not know how large diameter magnetic lenses are feasible? But figure 4.22 in W.D Riecke (1982) showes a realised lens with a diameter of 8cm. Overview of the optical design. CO = crossover, L1 is the first lens, the red dots the focal points of L1. L2 is the second lens with blue focal points. Im is the final image. The magnification of L2 is one. Overview of the quantities used for calculating the necessary magnetic field in the deflection coils. Another possibility would be an adjustable aperture in the beam. We note that the small spot (10µ) is only needed for SEM imaging, hence it will not require the energy of the full beam, we can afford to lose energy. We could then design the electron optics assembly to have a magnification M on the range 0.1 to 1, and then stop down the beam with the adjustable aperture when the small spot is needed. This procedure could also possibly reduce the aberrations when low aberrations are most need, ie. for SEM imaging. Maybe this could also be done by varying the lens current, hence changing the focal length? Assuming a two lens design we can write M_1 s_{o1} = - s_{i1} and M_2 s_{o2} = - s_{i2} for the two lenses respectively. (The magnification M is negative). We have some further constrains that we would like to add to the system. First the image from the first lens is the object of the second lens. Assuming a separation l between the two lenses we have l-s_{i1}=s_{o2} and we want a given total magnification M given by M=M_1 M_2. Further we could want to constrain the apature of L2. Given the maximum deflection of the beam required to realize a printing area of 24cm by 24cm is 14.65 degrees measured at L2 and 16mm is beam diameter of at max deflection 151mm before L2 and the baffel is situated at 30mm after L1. One appealing solution is M_1 = 0.3 \ M_2=1.25 \ s_{o1}=100mm \ s_{i1}=30mm \ {o2}= 459 mm \ s_{i2} = 573 mm. With this design the aperture radii of L1 and L2 have to be at least 3.8mm and 27.15mm, respectively but due to inter lens XY deflection of beam further space is required prior to L2. So minimum pipe diameter is 83mm thereby giving the space needed to deflect the 16mm diameter beam within to achieve 14.65 degrees deflection at L2. For this Print mode asymtotic focal lengths we get f_1 = 23.1mm and f_2=255mm. This design will give a total magnification of 0.38, which corresponds to a focal spot size of 45µ, which is good enough for printing but too large for the vision requirements. By changing the magnifications to M_1 = 0.08 \ M_2=1.2 with out changing any lengths we will achieve a total magnification of 0.096, corresponding to a spot size of 11µ which is sufficient for the SEM vision system. As lenses and baffel lengths stay the same, in this SEM configuration the intermediate image will be before the baffel instead at it, as the aperture radius of the baffel is 0.12mm, and the size the beam is 0.37mm going in to this aperture, we will lose 67% of beam power in to the baffel, but this should be acceptable or even preferably in the case of SEM imaging. The needed SEM mode asymtotic focal lenghts in this case are f_1 = 7.4mm and f_2 = 261mm. Compared to optical lenses magnetic lenses are very poor with large abarations. In essence we are building an SEM, and lots of research has been done on magnetic lenses for this pourpose. SEM operates with spot sizes on the order of 1µ or less, that is, 1 or two orders of magnitudes less than what we are aming for. Hence we do not have to optimise the design to the same extend as SEM designers do. One of the fundamental parameters in magnetic lens design is the gap to bore ratio S/D. According to W.D Riecke (1982) p. 179 we are free to choose this ratio is in the range 0.5 to 2, preferably in the range 0.7 to 1.5. The pole pices in an magnetic lens are tuncated cones the diameter at the truncations sould be 3 to 4 times the diameter of the bore, and the conic half angle should be 55 degrees. W.D Riecke (1982) p. 255. The magnetic lenses we have their magnetic flux carried on pole pices and cores. One important requirement is that we do not saturate the magnetic cores and theis will couse a large leak in magnetic field which will distrupt the magnetic lens. IN a classical magnetic lens the cores is connected to two flanges (top and bottom) which connects to the magnetic shielding which incases the electric coils. Theese two "flanges" will go through the pipe which contains the EOA. The minimum thickness can becalculated acording to formular 4.119 in Riecke (1982), given the need excitation and the saturation flux of the flange material. h_0 = \frac{\mu_0 NI}{B_0 |ln(tan(\theta_0/2))|} For soft iron we will assume a saturation B_0 = 1T and the cone angle is on the order of 50 degrees. So all four flanges needs to be at least 3mm thick. The minimum thickness of the encasing can be calculated from 4.125. The inductance of the proposed coil designs, assuming a an iron core, will be on the order of 1H, which is significant. Care will have to be taken to avoid transients, which could generate very high voltages and arching in the coil. Simple formula to calculate the temperature increase in the coils. NI=\sqrt{C_T h_{0}^3 sigma q \deltaT} \sqrt{eta +1/eta}, where C_T is the cooling efficiency of the coil, sigma is the specific electrical conductivity of the wire material; q=Na/A is the space factor of the coil windings, where a is the actual cross-sectional area of the copper wire employed; h_0 represents a charateristic length for the size of the coil cross-section and is defined by h^2_0 =A; and eta=h/h_0 specifies the shape of the coil cross-section with h as the extension of the coil in the direction of the lens axis. If b is the radial extencion of the cross-section of the (rectangular) coil, its 'aspect ration' h/b can be easily seen to be conected with eta by h/b = eta^2. The value eta=1 indicates a square cross-section. This formula can also be expressed in current density j_w=\sqrt{C_T sigma q (\deltaT/h_{0})} \sqrt{eta +1/eta}. It is not possible to change the cooling efficiency by very much by changing the aspect ratio of the coil cross-section. The space factor of the windings is generally about q=0.65. The value C_T is determined by the general properties of the coil and the cooling mechanism. If water cooling is incorporated in the external lens casing, C_T of 40-50Wm^{-2}C^{-1} can bee achieved corresponding to an average current density of j_w = 1.8A/mm^2 at a temperature rise of \delta T = 70C. So for L1 SEM mode we can choose design with S/D=1 and D=8mm, hence f_1/D=0.925 (f_1=7.4mm SEM). So D/f_1 = 1.08 According to Lenz (1982) figure 3.11 we then need an reduced excitation of 8.7AV^(1/2). The reduced excitation is defined as (NI)/(\sqrt{U}), p172, where U is the beam voltage. That is, sqrt{62500}*8.7 = 2175turns. In L1 Printing mode we need the asymtotic focal length of 23.08mm, this requires less turns hence f_1/D=2.89. So D/f_1 = 0.346 According to Lenz (1982) figure 3.11 we then need an reduced excitation of 5AV^(1/2)Thus we need a reduced excitation of 5*sqrt{62500}=5*250=1250 A-turns. We choose the demagnifying lens SEM mode design as this demads more turns, yet will also operate in print mode as well but at a lower current . For L2 in printing configuration we need a focal length of 255mm. At this position we need to accommodate the expanded beam and allow for delection of the beam in the lens. The needed lens diameter has been found to be 67mm at least.plus its 16mm beam thickness (See spread sheet K81) and clearance ie needs 83mm diameter. We would like to make this lens shorter to allow room for the deflection coils hence we will choose a S/D ratio of 0.7 D=90 so S=63mm. For L2 we found D/f_2 = 0.353 according to Lenz (1982) figure 3.11 which results in an reduced excitaiton of 5.0 or 1250A-turns. So coil dimensions allowing 180% space for wire packing density. For demagnifying lens SEM mode assume that we need 2000A-turns. The max current density we can accept with a temperature increse of 70C is 1.8A/mm^2. We then need a coil cross-section area of 2000/1.8 = 1052.6mm^2. Corresponding to 32.4mm x 32.4mm. Assuming that we can drive a max of 1A through the coil, we need a wire cross-sectional area of 0.52mm^2 or a side length of 0.73mm. This corresponds to a AWG 20 or 21. [29] If we take AWG 20 each wire will take up an area of 0.81^2mm^2 = 0.65mm^2. For 2000 wires we then need 1312.2mm^2 of coil cross sectional area. This corresponds to 36.2mm by 36.2mm. or with an extra margin 25 mm x 55mm. 1375mm^2. Demagnifyng lens Assume j_w = 1.8A/mm^2 max current/cm square is 180A/cm sq in coil, Assume wire crossection is square, and max current in an individual wire is 4A, therefore 67 wires per cm sq max., so round down to 8x8 wires in one cm sq diameter 10mm/52 =0.19mm from awg chart AWG 17 with varnish insulation, 2750 wires in probe forming lens so approx cross section area of coil 2750/64=43 sq cm 12 cm x 4cm. round up to 12 x 6 for tolerance. For demagnifying lens Print mode assume that we need 1500A-turns. The max current density we can accept with a temperature increse of 70C is 1.8A/mm^2. We then need a coil cross-section area of 1500/1.8 = 789.5mm^2. Corresponding to 28.1mm x 28.1mm. Assuming that we can drive a max of 1A through the coil, we need a wire cross-sectional area of 0.52mm^2 or a side length of 0.73mm. This corresponds to a AWG 20 or 21. If we take AWG 20 each wire will take up an area of 0.81^2mm^2 = 0.65mm^2. For 1500 wires we then need 975.0mm^2 of coil cross sectional area. This corresponds to 31.2mm by 31.2mm or with an extra margin 25 mm x 55mm. 1375mm^2. Probe forming lens Assume max current/cm square is 180A/cm sq in coil,Assume wire crossection is square, and max current in an individual wire is 4A, 67 wires per cm sq max. , , so round down to 8x8 wires in one cm sq diameter 10mm/8 =1.25mm from awg chart [30] AWG 17 with varnish insulation, 600 wires in probe forming lens so approx cross section area of coil 600/64=10 sq cm 4cm x 2.5cm. (Note Later we should consider whether we can use a permanet magnet design, W.D Riecke (1982) p. 168 writes that permanent magnets are can provide magnetic potentials up about 3000 Oe cm or about 2400 ampere turns, which is sufficient up to a beam voltage of 50kV, ours beam voltage is 62kV, so how does these figure compare with the values for modern neodymium magnets? The magnets must remain under their Curie temperature of 320C.) (Note reduced excitation is defined as (NI)/(\sqrt{U}) The minus disappears when the multiplication is turned into a division Then a reduced excitation of 8.7 AV^(1/2) corresponds to 2175A-turns.) (Note The asymtotic focus position will be 10.0mm form the lens midplane according to Lenz (1982) figure 3.12 from reduced excitment of 7.5 so from graph Zv/D =1.2, D=8 so Zv=1.2*8=10 . The real focus position will be about 9.1mm from the lens midplane acording to figure 3.10 as at reduced exicetment of 8.7, Zf /D =1.1 given D=8 so Zf=8*1.1=9.1. K: I currently have baffel at 29.3 not 9.1, in SEM mode the image should be before the appature. We have calculated abouve that the image sits at 30mm after the lens midplace in printing mode, so the apature placement should be alright.)) Simplificaton of the EOA design Given that we have taken our design principles form SEM designs, where the spotsize requirements are much more stringent than for our pourpuses we might be able to get by with some further simplifications that will make the machine much easier to build. The pole pieces are introduced to reduce the abarations, but they might not be needed. Also the deflection system we have chosen is selected because it reduces abarations, by making the electron beam pass through the center of L2. We might be able to get by with having the delections coils sit after L2 outside of the pipe for the EOA. We the delection coils outside the pipe and no requirement for the pole pieces and choosing a thin non-magnetic pipe, (about 1mm thinkness, 0.5 should be enough to hold the vacuum, but it would be very hard to weld. 1mm is more feasible.) we could place the magnetic lenses outside the pipe. This would make it much easier to acess and adjust the lenses, i.e. they can then be slid up and down the pipe. The only thing we would need to be inside the pipe is a baffle. If we make the baffle sit at the intermediate corss over and we can isolate the baffle electrically we could use the current from the baffle to ground as a measure of focus (if outside of focus electrons will be absorbed by the baffle), which would make it much easier to focus L1. Design of the deflection coils Out first choice of deflection systems is called a prelens double deflection system in P.Hawkes & E.Kasper volume 2 page 824. This system consists of two deflectors D1 and D2 at a distance 2a and a in from of L2, respectively. D2 has twice the amount of windings and the opposite polarization of D1. In this system D1 will deflect the beam out of the optical axis and D2 will deflected it back in such a way that the beam passes through the center of L2 to reduce aberrations. The deflectors consists of rings of a high permeability material like ferrite, with windings whos normal is perpendicular to the optical axis. From expanding the magnetic field in the interior of the deflector in Fourier terms one learns that the coefficients can be written as a_k = \frac{4}{\pi}\sum_{i=1}^{n} N_i sin(k\theta_i). By carefully choosing the number and angles of the windings on the ferrite ring the odd coefficients can be made to vanish, reducing the aberrations from the deflectors. Hawkes & Kasper p. 839. For instance n=2 and N_1 = N_2 leads to \theta_1 = 48 degrees and \theta_2 = 72 degrees, see figure 40.13 in Hawkes & Kasper. Calculation of the necessary field strength. Assuming the z axis to be the optical axis of the EOA, one would need a magnetic field purely in the x direction to deflect the beam in the y direction, i.e. the field is perpendicular to both the velocity of the electron and the direction of deflection. In this case the force on an electron can be written as F=evB. In the case where a force is perpendicular to the velocity one will obtain a circular motion, i.e. centripetal force. The radius of curvature will be given as R=(m/eB)\sqrt{2eV_acc/m}. With the definitions of the various lengths given in the figure to the right we can write the deflecton length x over the distance S as R=S^2 + x^2 / 2x \approx S^2/2x. Combining with the expression for the radius of curvature we get S^2/2x = (1/B)\sqrt{2mV_acc/e}. In our current design we would like to deflect the beam about 20 degrees over a distance of approximately 2cm, corresponding to x=7mm. Hence we can estimate the required B field from the above formulas. B = (2x/S^2)\sqrt{2mV_acc/e}. Setting V_acc = 62keV and S=2cm and x=7mm we get B=0.015T. For a circuit with an inductance the instantaneous current and voltage is given by i=I_p*sin(2*pi*f*t) and v=2*pi*f*L*cos(2*pi*f*t) where f is the frequency, I_p the peak current and L the inductance. To drive the coils at the frequency f we will then dissipate the power P=R*I_p^2*pi. And the peak voltage in the system will be V_p = 2*pi*f*L*I_p. Experiments with a mock up model of the deflection coil configuration has shown that a high permitivity material like ferrite is required. Because of the high frequencies the coil is required operate at a low conductivity material like ferrite should be used. The experiments showed that about 2500A-turns are needed to obtain a field of 15mT in the center of the deflector. A ferrite coil with 2500 windings will have an inductance of at least a few H, which could present a problem. Driving this coil at 10000 Hz would mean we would have to handle peak voltages on the order of 100kV. We might need another design of the defection coils. Maybe akin to a set of Helmholtz coils. This would also mean we should change the deflector design form a one deflector design to a one deflector design like in a tv. The expression for the field strength in the center of a pair of Helmholtz coils is B = (4/5)^(3/2)\mu_0NI/R. Setting R=4cm and B=0.01T we get NI=500. And because these coils are air coils we get much lower inductances. An air coil with a diameter of 8cm and 500 windings will have an inductance of about 50e-6H. By making the deflection zones longer, we can lower the requirements for the B field strength. Making the deflection coils 8cm long instead of 2cm we can lower the required field strength by a factor of 4^2 = 16. That is we need a field of 1mT. For a set of Helmholtz coils to give 1mT at the center, when the radius of the coils is 5cm, we need about 100 ampere turns. Such a coil will have an inductance of a few microH. And we would have to handle peak voltages of about 1V. Measurements in the lab has shown that for a traditional deflector design (not Helmholtz) we need 0.9A*2400 turns to achive a field strength of 1mT in the center 5 cm from the edge of the coils in the case of air coils. If we construct a yoke of laminated silicon iron we need 0.1 A*2400 turns to achive 1mT in the center. In this experiment the windings of the coils was 5cm by 5cm and the yoke was 2.5cm x 2.5cm. Helmholtz deflection coil assume max current/cm square is 250A/cm sq in coil,Assume wire crossection is square, and max current in an individual wire is 0.5A, 250/. =500 wires per cm sq max. , , so round down to 22x22 wires in one cm sq diameter 10mm/22 =0.45mmsquare from awg chart [105] AWG 25 with varnish insulation, NI required 200 per coil , (400 wires per pair) ,each helmholtz 400 wires so approx cross sction area of coil 400/500=0.8 sq cm thickness 2.cm x width 0.4 cm. coil groove is 2cm by 1cm (skin depth at 20K .9mm diameter so ok). For 1 m from platform to probe forming lens 11 deg interlens deflection required pipe radius 16mm I.D. SEM Vision System The 3d printed layer can be measured via a sensor pick up ring that's attached to gravity fed powder hopper just above the build surface with 2 powder wiper blades attached. The SEM Vision will be based topological mode SEM vision and provide µm resolution. Vacuum Chamber and Pump • Glass Chambers MetalicaRapBaby (3D printer prototype version) and MetalicaRapLight EBPVD (solar cell printing version) MetalicaRapBaby 3D printer: 3D print chamber based around large diameter borosilicate glass tube with aluminum plates on the top and bottom with L gasket seals (as used on vacuum bell jars). The bottom aluminum plate can be lowered to gain access to the attached build platform/motors/sensors and includes electrical feed through.A Stand will support the glass tube and the top aluminum plate with the gun and power supply attached via O rings above it, beam tube to gun/filament/anode chamber will need to be welded in mother chamber due to heat when printer is operating. Large diameter removable cement pipe used to shield around it all. MetalicaRapLight EBPVD ( Solar version) chamber based around a square bottom flask with metal vapor trap. Glass chambers are connected to electron gun tube via top Aluminum plate Tube/Glass adapter; with 5 o rings, 2 for gun tube sealing and 3 for top aluminium plate to square bottomed flask sealing, having 1 o-ring for cushioning end of glass and two for sealing each joint.Large diameter removable cement pipe used to shield around it all. • Pump is a roughing pump 2 stage Vane pump e.g.Leybold D4 D4B Trivac Rotary Vane Dual Stage 3.4cfm 2K euro new. to 1 x10-4 torr gas ballast off [31] [32][33] 1.0x 10^-$$ ^4$Torr )
• High vacuum $10^- $$^4 Torr to 10^-$$ ^5$
• Electrical feed-troughs ; For tungsten filament AC 6V 15W 50/60Hz heater power supply based around modified microscope flat wound bulb's body(sm8018) giving a -63 KV Wehnelt feedthrough which is within a test tube providing -60KV cathode feed-through, using large diameter glass cylinder chamber with L gaskets TV feedthrough seal with o rings or o ring to copper tube then connect TV neck to copper tube. Glass tube to metal tube connection video[34].
• Mechanical feed-troughs ; will be avoided by using periodically replaced cheap standard Nema motors within the chamber.
• Viewing & illumination windows ; As main chambers will be glass no others are needed beyond.a window in the surrounding shielding box of standard glass 70mm thick can be multiple sheets no seal required as outside main large diameter glass cylinder.
• Pirani vacuum gauge home build version (use google translate) [35]
• Outer box for shielding constructed of cheap material 3cm of concrete (or solidified sand or earth brick).

Metal powder dispenser

This will be a gravity fed split powder hopper.A small hopper will move in the x direction, intermittently refilled by main hopper situated besides electron gun tube. The small hopper will have a 12Kg powder capacity, this gravity fed powder hopper just above the build surface has two 1cm square section powder wiper blades attached wither side, leveling the roughly dispensed powder. The powder is released using two sliding slotted plates. A second main powder hopper will gravity feed the 12 kg hopper. The 12kg hopper will be sitting in a box created from a single 8cm thick sheet of aluminum self shaped to a box by MetalicaRap subtractive electron beam cutting.

Other dispensing considerations:

• clumping may be an obstacle at high vacuums, A better metal powder flow through the hopper could be achieved through a slight vacuum reduction during gravity hopper operation and then reevacuating again before bean melting resumes.
• SEM pickup PIN diodes protection cover will be used when printing.

Build platform

A 30cm vertical travel stepper motor driven circular platform within a 14 inch 304 tube printed in parts. Within the build platform is a built in ceramic insulation layer. Two felt or titanium metal brush o- rings seal to keep the metal powder from falling through build platform and build platform cylinder.

Power supply

Power supply Full Bridge LCC Series Resonant Converter with duty cycle switching variation control and above resonance frequency switching variation control, through this frequency variation maintaining Zero Current Switching during Coolmos switch ON and Zero Voltage switching during Coolmos OFF switching, with Arc sense, arc quench and arc count with output via a gun resistor, this gun resistor combined with the power supply itself will be used for beam current control .

High output series-parallel resonant DC-DC converter (search on this bold text string) -62.5KV 0 to 5KW running at 181.5KHz resonant up to 500Khz at idle/no load, with a -325V to -62.5KV transformer with voltage doubler on output, the transformer is designed for a specific value of inductance and capacitance to operate at the desired resonant frequency, as the load changes the parasitic capacitance of the transformer changes too, this means that at high load the series resonant converter topology dominates and light / no load the parallel resonant converter topology dominates. The change in load changes dramatically due to occasional arcing in the gun, This topology deals with these changes effectively. Each of the 178 PCB transformer secondary converter stages is a pcb with 1 turn coil track outputting -354 V d.c. via cheap rectifiers and voltage doublers/smoothing capacitors, when this is combined with the resonant tank gain of a range from 2.25 times to 6 times, the output voltage of 63KV is obtained. Along the stack of pcb's the voltage increases gradually keeping under the paschen air arc limit. Secondary converter stages are connected in series creating the -62.5 KV output,. Two C shaped transformer N87 ferite cores with 11 turn primary (54A) and a high voltage 178 PCB secondary insulated bobbin 4mm deep of UHMWPE seperates ferite core and PCB secondaries.

Power supply feedback control around transformer measures Output voltage feedback via 208 thick film resistors creating voltage divider. Output current sense feedback via measuring voltage either side of a temperature stable resistor. Input /Primary current sense via 2 "current transformers" in series in each leg of full bridge. Wehnelt voltage feed back via thick film voltage divider. These four signals go via signal reconditioning board then on to Field programmable gate array (FPGA) [36]via four channel analogue to digital converter (ADC) 12 bit 40Msps[37][38]. FPGA process maintains input and output current parity within acceptable current window values. Allows a small error signal from voltage output variations when within a narrower voltage output window values. FPGA drives 4 coolmos FET gates in full bridge topology via driver chip.

Solftware for the FPGA_High_Voltage_side is coding voltage feedback from linear to Log and then coding for sending over fibre optic to FPGA_Low_voltage_side. FPGA_Low_voltage_side software consists of feedback signal decode from optic fiber, Followed by low pass filter and PID controler d_controller and Digital pulse width modulator with 4 outputs to H bridge FETS. Along with a power supply user interface.

A separate housekeeping supply provides bias for all control circuitry, providing a 5V separate stand-by voltage which remains active when the power supply unit is shut down for any reason ( later once efficiency of power supply is assessed a Power Factor adjuster circuit may be added between rectifier and dc to dc converter). FPGA also checks for error conditions.

Beam current modulation options;

• Control via power supply feed back circuit, leaving gun cathode to Wehnelt electrode bias fixed via resistor. When at 1KW power and shut down in half a cycle ( 0.2MHz switch frequency) the resonant energy left in LCC circuit and output capacitance would lead to one extra 55micron cube of melted Titanium or 40 microns cube of melted steel which is workable .

Self replication

Self-replication of a vacuum chamber runs into the "how to make a match box inside a match box problem".

This will be overcome by purchasing a large diameter glass cylinder 406.4mm diameter 1130mm long and using Vacuum bell jar style Viton L gaskets top and bottom to aluminum top and bottom plates. All build platform parts can be printed in the mother machine in segments then assembled and fitted within the glass cylinder which provides the vacuum seal. This also means TIG welding gear is not needed as all parts can be electron beam welded together in mother machine. Later glass test tubes and ultimately glass cylinder can be manufactured in oversize machine by beam melting glass sand in contact with metal within chamber or in hotter climates by solarsintering[39][www.markuskayser.com].

Specialist Parts

Those which are not self printable or readily available;

• Transformer ferrite core ; Rectangular hollow section shape single phase style [40] but modified by a drill removing corners so circular cross section on secondary high voltage side.
• 4 toroid coil cores Material (?)
• Roughing pump capable of 10-4Torr
• long large diameter Flexible hose to reduce back streaming of oil from pump to gun (with end CF-16 hose to pump fitting)
• Priani vacuum gauge ( now home build version availible (use google translate) [41])
• Electrically operated CF-16 T valve
• Exhaust Valve
• Transformer varnish insulated wire for coils
• Viton o rings; 6 small for cathode, 3 small & 3 large for gun tube to glass chamber adapter, two large 18inch bell Jar L gasket seals with top and bottom aluminum plates.
• Carbon or ceramic high temperature washers 2000+C for Wehnelt support x 9 (3 support rods)
• Copper OPFC knfe edge flange sealing rings; 2x 6.34inch DN() , 1 x DN80 anode, electron gun tube flange 1.33inch DN() for 6.34 inch to 1.33inch reducer plate.
• Safety vacuum cleaner ( needed for cleaning up Aluminum and Titanium) Self printed.

Access to ; Vacuum leak detector Spot welder for in chamber electrical connections of OFPC copper conductors having glass beads as conductor insulation. Geiger counter eg Radiation Detector - Pocket Geiger Type 4 [42], Self-indicating instant radiation alert and dosimeter (SIRAD) [43] easily worn, result via comparison with color chart ( 4 - 25 Euro each SIRAD) [44] [45].

Avoid the need for TIG Welder in MetalicaRapBaby by bourgt in part electron gun beam tube being short enough to be able to fit in chamber of mother machine, (TIG welder for electron gun tube and tube to flange attachment for MetalicaRapBabe).

Background Technical design considerations

Construction Materials

Materials:

• Electron gun wall stainless 304 L: cold rolled, p.243
• Metals for cathode/1st anode-Wehnelt/anode electrodes (tungsten/molybdenum/tungsten) , curved steel cover for bulb filament.
• Metal for "soft iron core" surrounding the two lens coil windings: unalloyed soft iron. For yoke and polepices use a soft iron, like AISI 1006.
• Interlens X Y-deflection coils made from 3 ferite toroids. All the X deflection couils will be interconnected, with the first toroid wound in opposite direction from the second and third toroids and the Y deflection coils similarly connected.
• Thermal conducting material for anode support structure that extends through the middle of the anode support: Copper for Wehnelt support rods and water cooling core within 304L anode support rod, see p.246.
• Thermionic emission regime hot filament design: tungsten in the form of a light bulb sm8018, see cost saving approaches below. ( Or a tungsten ribbon 2mm wide 0.254mm thick (copper infused tungsten has also been mentioned as physically more stable)).
• Ceramic insulators, you can use either mullite or alumina. Avoid stuff like teflon (is a sponge for water, and outgasses too much) or macor (machinable glass -- too delicate). Your shoulder washers in electron gun support are standard commercial items. These are specialist items so we have tried to replace them with everyday glass items e.g. test tubes.

Finishes: Interior surface of vacuum chamber should be polished (..) and then cleaned acetone and ethyl alcohol.

Matirials to aviod:

• Avoid zinc, magnesium, and lead, as these don't have negligible equilibrium pressure at temperature, i.e. out gass too much at elevated temperature. For example avoid brass as out-gasses intensely when it gets hot, which can lead to ionization and flash overs, see p.237.

Powder and metalurgy issues

NASA is also making their own machine but with wire not powder. The 1 hour lecture is a good introduction to the metallurgy involved in EBM, see here. (If this does not work then go to http://www.aeronautics.nasa.gov/electron_beam.htm# Select windows streaming in main page, then Windows Streaming Video then +window streaming in pop up window, some other selection options come up with the wrong video).

Play with this Online Design Tool: Build Speed Calculator for metals build speed software we have written and then you get a good idea of which metal you want to start with.

The initial test run prints will be made in stainless steel 30µ (Pre cool final printed parts from this powder is therefore likely to achieve a tolerance of 250µ) and chromium cobalt under 50µ 30µ?( Pre cool final printed parts from this powder is therefore likely to achieve tolerance of 250µ)metal powder [46]supplier[47], and then later the challenges of Titanium 4µ powder will be considered (Pre cool final printed parts from this powder is therefore likely to achieve tolerance of 20µ). See article on micro sls [48]. See example machine [49],See example of twin chamber 3D printer[50]. Though through subtractive machining we may be able to bring critical surfaces of most of parts down to 20µ. stainless is 316L grain size -45µ+10µ product purpose 3D printing good fluibility, 60gbp a kilo best price 80 kg per buy delivery 3 month. Powder is manufactured from cold rolled metal (e.g. 304 approx 1.8 Euro a KG 07/20111) by Electron Beam Melting of a rod of feed material which then is momentarily caught on spinning plate and flung thereafter, thereby solidify by cooling. See[51] [52]

The magnetic metals lead to magnetizing of iron based metal powders so should be avoided where possible, the main magnetic metals are iron, nickel, cobalt and some of thier alloys.

The metal powders are not good to ingest or breath in so a mask should be worn. The metal powders may get caught in the fine folds of your skin so gloves should be worn.

All metal powders burns easier than solid blocks and some of them are a fire hazard. The active metals are most flammable and difficult to handle: Titanium 4µ, other active metals include aluminum, zirconium, then the moderate range metals e.g. cobalt chromium 50µ and finally low range stainless steel 30µ. General fire avoidance should be followed, avoid sparks and open flames, avoid dust clouds, e.g. through dumping action of powders, and use appropriate tools. Design principles of fire avoidance should include: appropriate grounding of equipment, avoiding excess mechanical friction in design. For active metals consider a glove box contained nitrogen clean up environment or just a liquid based vacuum cleaner. The number of electrons, the velocity of electrons and the beam diameter all effects the resultant melting and penetration. Putting the focal point within the metal gives more penetration, while placing it above the metal spreads the beam and gives a wider melt pool. Beams with higher electron current penetrates deeper and inputs more heat, yet less current with higher velocity electrons gives less heat input and less penetration.

The first layers are tricky to print; the first layer must weld well to metal base to stop part warping, because cold platform contact hot metal residual stress tries to snap build platform so build platform needs to be thick to resist this force, must also need to be reusable after each print must be milled. (Carification needed)

Cost reduction by pre-processing milling metal into metal powder within MetalicaRap through electron beam melting on to a spinning disk is also achievable later. For a particular steel unprocessed it costs about 0.5 Euro/kg, but traditional metal stock for milling machining costs 20 Euro/kg, for metal powder up to 60 euro/Kg, these raw material pre-processing costs may reduce to 1Euro/kg by self processing.

Pros and cons of 3d metal processes [53](see below for link comparing tool head processes for more detail)

Safety issues

Firing a high voltage highly accelerated electrons at a metal target will generate X-rays. This is essentially what the X-ray tube at the dentist's does. And so will MetalicaRap, so beware.

The penetrating ability of the generated X-rays is proportional to the acceleration voltage of the electron beam (electron energy). In your old fashioned television (C.R.T.) the acceleration voltage was 30kV, as long as you kept the electrons inside the tube it was not a problem, people sat in front of it for 40 years with no ill affects. But with with MetalicaRap precautions should be taken, like in the hospitals. MetalicaRap keeps the electrons and the targets within a glass or metal box surrounded by a further shielding concrete/sand container.

We can use this formula to calculate the dose rate,

R [rad/s] = 50 x V [kV] x I [mA] x Z_{target} / [r [cm]]2 x 74 where V is acceleration voltage, I beam current, Z_{target} is a constant for target metal, r distance from target. The formula is from the Radiation safety manuel page 11.

Lets calculate the dose inside the box we find;

The dose rate inside the chamber at 14 cm from a copper target operated at 100kV and 14 mA is: 50 x 100 x 14 x 29/ (7cm)2 x 74 = 560 rad/s.

The recommended shielding from this level of radiation for working hours use is 1.2mm of lead.

Comparing lead equivalent shielding in different materials ; 1mm lead equivalent by materials to ; 2.5mm steel , 6.1mm concrete , 9.1 mm packed soil, 50mm Borosilicate glass, [54] [55].

Our MetalicaRapBaby and MetalicaRapBabe chamber/gun area's made out of stainless steel 304 5mm thick, which is equivalent to 2mm thickness of lead shielding. Combined 12mm glass surrounded by a 30mm thick outer shielding concrete box equivalent to 0.24mm + 5 mm=5.24mm thickness of lead. So between nearly twice and four times the required shielding is provided by the chamber and shielding box. So plenty of shielding is evident.

General Information

Solar cell thin film deposition

Thin film deposition summary by material [56] RF sputter is another option for increased solar cell production rate [57] uses the electron beam to resonate a cavity to produce an RF magnetron) .

Green Tech./Solar Cell production cost calculation

To produce thin film CIGS solar cells at under 11 cents per Watt peak. So Solar cells cost for a family 3 Bed house; Average Electricity usage 4200KW per year, 4200KW/365days*4.93 Equivalent Hrs peak sunshine= 4200KW/1800Hrs=2.3KW peak of solar cell panels required, at 11 cents per Watt peak the solar cell's would cost 253 dollars from MetalicaRaps plant plus cost of backing material, cost of inverter plus extras 1300 dollar, so it may offer an uninstalled system at under 1,900 dollars,( current price for uninstalled system is around 14,000 dollars (jan 2011)). (Calculation based on cloudy areas of world, 1KWatt peak solar panel system under 4.9 hours peak sunshine per day gives approx 1800KWh per year, A desert area at low latitude would be up to twice as good as this.)( For reference in a hot climate a 1.25 dollar/W installed financed system gives ;0.07 dollar/KWh over 20yrs, 0.03dollar/kWh over 60 yrs [58])

EBM introduction [59]

Images EBM / EBW [60]

General background Videos EBW see here [61]

Back ground Information on Electron beam processes; electron beam welding / vaporization , EBM 3D printing,

Scanning electron microscope (3)(4).

More technical sites

General practical technical information; Power supply; Transfomer winding [62]

.General practical technical information; Feedthrough glass joining ways to adjust your glass items in your test tube based electrical feedthroughs and insulate/construct with bead glass between electrodes.[63], Glass tube to metal tube connection[64]

General practical technical information;Electron gun / CRT tube salvage ; Explanation of how to take apart a cathode ray tube electron gun to salvage Wehnelt molybdenum disk with hole in ( the first disk in front of the hot wire cathode) a tv CRT [65] note you can diamond file/diamond saw break the pip on the very back of tube to release the vacuum then reseal with blow torch to keep the electrical feed-throughs functional. Another example of a old CRT oscilloscope.[66] .

Conventional Helium detector explanation [67]

Self Replication Engineering Options See section 2. [68].

EBM technical background lecture See here [69]

General background Videos EBW see here [70]

Vacuum chamber principles; Essential reading before you weld/construct your vacuum chamber, Basic Vacuum technology by Varian

Maths behind vacuum processes (Not for the faint hearted )[71]

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MetalicaRapWin

A later innovative development could be the MetalicaRapWin with a beam window. A window between gun and build platform enables the use of high brightness small spot size LaBa6 filaments that last 1,000 hrs as opposed to 70 hrs for tungsten. Allows the use of barrier argon gas at atmospheric pressure surrounding build platform and associated mechanics so no pump down time after accessing build chamber. Will also offer large part manufacturing in inexpensive argon "tents" as only the gun requires a vacuum chamber. Disadvantages include; some ballooning of beam as it passes through approx 5mm's of argon atmosphere between build platform and window, lowing resolution of SEM vision system (x-ray sensing option may help or build platform chamber pump down for vision system and argon for printing), high tech stationary window will involve high tech manufacturing, Low tech aluminum slot window will reduce print speed and increase mechanical complexity as build platform to gun physical scanning motion will be required. Repeated door opening will be overcome through these windows and thus ion pumps or electron beam sublimation pumps will be less stressed.

Low tech option: Scanning aluminum slot beam window (14cm length x 100µ width)

A narrow slot window which is physically moved across the build area. Window will be cooled through thermal conduction to water channels surrounding the window. Requires minimum 100kV beam to penetrate a 20µ thick AL window, to keep beam losses below 21%. Beam loss is inversely proportional to acceleration voltage.

High tech option: Stationary window

A stationary high tech window that will be cooled through convection and radiation alone. "Transparency" of window enables the possibility of a less penetrating beam of 60kV. 400µ sheet with 50µ micro dead end holes creating an ebeam window.

Beam divergence at different atmospheric pressures beyond window, left at atmospheric pressure, middle at third of atmospheric pressure , right at a hundredth of atmospheric pressure

Software

MetalicaRap will be a software machine. Fast computers (and progamers) are easily avaliable where as high precision machining and calibration of components is relatively much harder. We hope to be able to control the build process to a high level of precision through software tracking, abarration correction and feedback. Belowe we have listed some of the processes that will require software control.

• Electron gun beam focus model: To highlight resolution operational compromises between; the higher the gun cathode voltage the tighter gun focus, so the smaller the beam spot size on the metal powder giving rise to a higher XY minimum feature size (lens adjustment can alleviate. [72] See lens simulation), yet also the higher cathode voltage the faster the electrons go, so the deeper the electron energy deposition/giving rise to deeper vaporization holes, giving less vertical Z resolution, (used during Z axis error correction mode). Also surface tension is correlated with temperature, and works in opposition to wetting effects flattening the surface of the melt pool (if the melt pool diameter is small compared to the thickness of the metal layer it may appear as a molten blob of metal). This model will receive an energy profile of the beam by pulling two wire prongs through the beam in the X and Y direction, The wire prongs attached to the end of the sensor ring will be pulled through the beam by the XY motor drives, thereby sensing the energy cross section through the electron beam, which will be radioed back to Unified accelerator Library control system, enabling automatic adjustment of beam focus, beam strength and beam spot size. This will also be used to compensate for ripple in the power supply and operational loss of beam alignment from for example filament variation and magnetic interference. All except the last of these effects should be predictable so most calculations for build can be done by the model prior to build in offline mode.
• Thermal Real Time Model: This allows us to keep track of the thermal changes across the build chamber or cooling path, as the electron gun pulses strike the build volume powder. Cooling rate controls the micro-structure which determins the mechanical properties of the final part. Defects include residual stress that can only be removed by removing the part from the chamber and heat treating before continuation of the build, so it is best avoided by temperature management. In vacuum there is no convection, only non air heat conduction and a little radiative cooling. The conduction path is only through metal to metal contact so as parts builds the cooling path changes continuously. Also each layer melts part of the previous layer.

We will have to consider the following 4 situations conduction rates:

• Metal powder and solid metal volumes experiencing direct electron energy deposition (i.e. heat around electron penetrated regions, the depth of these volumes increases with electron gun accelerating voltage and vary with metal type). See electron penetration model [73].
• Solid metal thermal conduction volumes (the completed elements of final metal part under construction).
• Metal powder conduction volumes (the surrounding powder).
• Chamber/boundary thermal conditions (vacuum region, build box). See electron strike model for different metals and different cathode voltages.

In general for any unit volume receiving an amount of energy per second, from a distant energy source, to increase in temperature by 1K (the metals specific heat capacity), the amount of energy (W or J/s) arriving from that energy source (the electron beam) via a path; The paths energy transit rate (the conduction rate) is dependent on the cross sectional area of path, the length of path and the temperature difference between the ends of the path, (thermal conductivity in units of W/K). The volume changes size by the surrounding pressure (atmospheric pressure, indicating the density of the material). So from known initial temperature conditions combining the specific heat capacity, thermal conductivity and density to calculate paths, then summing these paths leads to knowing the temperature of a specific unit piece of metal and its physical state, solid or liquid or vaporized (temperature above or below its melting point or vaporization point at any particular time). The following should be considered; variation of mass with scan speed, bed preheating scans. See for more background technical information. (Clarification needed) [74] [75].

• We may need a network structure to combine the different hardware elements.

"Unified accelerator library"

Our electron beam focus model and control software choice

Those looking for entertainment might look at the open source Unified Accelerator Library (UAL) that has a 30yr track record of simulation and control of electron beam movement , a Electron beam focus model and a Control/Simulation approach. But UAL lacks thermal models and metal powder melting modeling so it's main use may be to get the beam spot landing on the powder at the correct position and with the desired diameter defined in the G code from skeinforge. (You can down load UAL here [76], [77] Introduction here, [78]

Manuel for UAL's Design Toolkit called MADX where you can enter a hardware definition i.e. collection of coils along a beam start with two solenoids at 0.1m and -6 m, beam at 0m along latticeset, at 3kW 100 micron diameter (MetalicaRap will likely have 3 XY deflector coils for beam deflection, 2 "Solenoid" for beam lenses) then run simulation of beam with OFFLINE MODEL UAL 1.9 here.

The hardware definition of coil positions is called the "lattice". The control ONLINE UAL 1.11 will them apply this simulation to the control of the electron guns in real time. Ignore the following elements we don't have them in MetalicaRap: BeamBean, electric kicker,Kicker, RF cavity, taylor map, wake, wriggler .

This has the advantage of being a closed loop system, which while simulating the beam movement simultaneously records models coils, guns, motors inputs; voltage values, current values etc. Then when you run the real world machine these form the drive instructions to the machine, any sensors picking up deviations are resolved through alarms or the software "reality checking" and thus improving the model. It also is designed as a multi user, multi platform software environment. Some draw backs may be over complexity of the system.

Main Deflector Coil driver options; a.) Raster 30cmx30cm b.) point and shoot

"Code Aster"

Our thermal modeling software choice

Quick start instructions on thermal modeling software:

• Open Source thermal real time model software Code_aster Introduction here[80],
• Download extra element GetDP.exe here[85] (put GetDP.exe in c:\ASTER\OUTILS\gmsh\) once it is installed and extra element has been copied then as it finishs select option to run code aster.

First select your problem type definition files from the wiki i.e.Thermal program example See here (Use login user: getdp password: getdp) [86]

Second build your mesh of shape you require to be tested, with code_aster sub module Gmsh: you can find it In ASTK prg window under menu item Tools Gmsh \\\ then in Gmsh window select GEO in drop down sub menu //// or import shape via .stl file In ASTK prg window, menu item Tools, Gmsh , then in Gmsh window select; MESH submenu

Third run solver to solve the problem you have defined above by selecting the SOLVER submenu in the GetDP window and hit GetDP button. In GetDP window choose source files for problem; name.PRO file(the problem defined in an example text file from GetDP wiki ) Choose name.MSH ( mesh file defining geometry) Then in GetDP window select options and tick "display client messages" option, then hit Pre then Cal then Pos buttons and then see window called message console window and it will tell you what happened, the output results files name.PRE name.RES name.POS will be in the same directory as the name.PRO file you selected for input.

General info;(Gmsh is a three-dimensional finite element grid generator with a build-in CAD engine and post-processor) See here [87] Can access Gmsh through Graphic user interface or directly through unix or TCPIP socket via code_aster sub module getDP Download GetDP.exe here[88] (put GetDP.exe in c:\ASTER\OUTILS\gmsh\ or specify path to existing location) Overview here [89]See here [90]GetDP documentation here [91], Thermal program example See here (Use login user: getdp password: getdp) [92] Documentation for relevant thermal model calculations See Thermics module R5.02 booklet: / General Architecture D00301a.pdf In DDocsHTML (Down load following two links, unzip to same folder) [93] [94], Complete Guide to code_aster documentation here [95], Software Principles explained here[96] ,Aster documentation source here [97] , home page here [98] wiki[99],

Files and Parts

SMPS insulators ( ensure G code objects have solid walls) File:Nylon1 elements of smps assembly v1p00.stlFile:Nylon2 elements of smps assembly v1p00.stlFile:Nylon3 elements of smps assembly v1p00.stl

SMPS secondary transformer PCB boards Kicad file File:Secondary A smps assembly v1p00.kicad pcbFile:Secondary B smps assembly v1p00.kicad pcb

Freecad compatible file of Nylon parts File:Nylon 1 2 3 elements of smps assembly FreeCadFile v1p00.FCStd

MetalicaRap V2.00 (old)

File:Assembly1 MetalicaRap V2.04.stl Pre detailing chamber to scale (old)

Sub Assemblies and Related

EBS=Electron beam sinterer/melting.

sequence - electron gun parts repstrapped EBS. Assembled tested in repstrap vacuum chamber. Metal powder deposition mechanism parts repstraped EBS . Gun deposition assembled tested. MetalicarapVacuumChamber parts Electron beam sintered by our system. MetalicarapVacuumchamber assembled tested. 5 Elements assembled and tested.

MetalicaRap V2.00

Design review

Cost saving approaches

cost saving approaches List;

• Only control via power supply feed back circuit leaving gun cathode to Wehnelt electrode bias fixed via resistor. When at 1KW power and shut down in half a cycle ( 0.2MHz switch frequency) the resonant energy left in LCC circuit and output capacitance would lead to one extra 55micron cube of melted Titanium or 40 microns cube of melted steel. See problem C for calculation Physics Principles/Discussion Yes! big cost savings here!
• filament based around tungsten microscope bulb ( ie flat wound)( sm8018 6V 15W bayonet square filament towards top BA15D ) with top glass dome removed held on remaining glass, half in and out of chamber by 2 viton O rings in bespoke sealing fitting having 2 o rings on inside sealing to bulb glass and on outside 2 more o rings sealing to inside of 2 inch test tube. These o rings are supported by dual grooved on inner & outer aluminum o ring support cylinder which is situated in the 2 inch test tube and which also supports 3 x 304 pillars that attach and support the tungsten Wehnelt cylinder, via 9 in total 1000+ metling point carbon/ceramic/alumina washers, electrical connection must be maintained by tungsten bypass wire or washers being electrically conductive(one; wehnelt hole OD, support rod ID. 2; larger dia. than wehnelt hole OD, support rod ID )[101]The test tube which is half in and out of the chamber is held in its own compression fitting on the end vacuum flange, the test tube is modified with a hole in its end for the bulb filament to protrude out of. A threaded 2 wall cylinder that is clipped in to bulb stub ends on either side of bulb base at one end and pressed against dual grooved inner & outer aluminum o ring support cylinder at the other, and thus provides adjustment of Z position of filament with respect to Wehnelt, accessible from outside of the chamber. A coil surrounds the test tube and a small coil attached to the bulb completes the filament drive "core-less transformer" electrical circuit, when combined with a dimmer circuit connected to coil out side the test tube it replaces conventional filament current control. Thus using a test tube with a home wound coil round it and a modified light bulb provides; -80KV electrical feed-through, -77KV electrical wehnelt feed-through, filament transformer, filament , heat removal mechanism from bulb to test ube, support for wehnelt disc(adjustable height above filament aim 0.3mm) ( also covered with a cap so no pointy HV parts revealed). A user selectable resistor is also included between wehnelt and filament within the test tube. 6.5Keuro saved here.
• Two large TV tubes with screens drilled through with appox 16 inch circular holes enough for build platform, placed face to face with oring between screens, one neck removed where the electron gun is inserted via a o ring, maybe one path to save 2K euro of chamber metal and get 1 set of free electrical feedthroughs for motors (motors working in chamber).
• Since you can get an electron beam to operate in a vacuum of around 5x10^-3 Torr. Avoid metal sealed flanges such as the conflat or wheeler flange By Buna rubber seals and low out gassing glues can be used for sealing components and costly vacuum flanges can be avoided in much of the construction. Simple pipe threads sealed with teflon tape or even glues can be used along with cheaper KF flanges. ( status untested ).
• Avoid expensive vacuum specified water cooled motors operating in the vacuum ( heat dissipation problem) By using oversized normal NEMA motors to cope with overheating and replace any oil filled elements eg gear boxs with a higher temperature white grease. Out-gassing shouldn't be a big problem with grease.;( Status may only last 6 months at a time partially tested) //A hole should also be drilled into the gearbox to allow air to be evacuated.//
• Normally you use use pneumatic vacuum gate valves for the foreline and roughing valves and then a large pneumatic "angle" gate valve for the diffusion pump/ion pump inlet. Lastly, a pneumatic poppet type valve is used to vent the chamber to atmosphere. Avoid the expensive 25.4cm angle gate valve By home-brew using large plumbing valves gate or ball valves for 4 inch and smaller diffusion pumps. See how well home brew valves hold a vacuum BEFORE you put them onto your vacuum chamber. ( status untested).;
• MetalicaRapWin 2nd pump Oil diffusion or ion pumps may be replaced by MetalicaRaps electron beam heating a titanium block within the vacuum chamber, thereby creating a Titanium Sublimation Pump Or what I think we should name it the Electron beam titanium sublimation pump so avoids all gate valves to the second pump since titanium is replenished each atmospheric cycle by the beam melting it and thus also avoids ion pump refreshment /maintenance. ( this new method of pumping relies on a having a very good rough pump vacuum ie 1x10-3Torr so the beam can operate to raise titanium to 1300-1600 deg.C. its sublimation temperature. eg Leybold D4 D4B Trivac Rotary Vane Dual Stage 3.4cfm 2K euro new. to 1 x10-4 torr gas ballast off [102] [103][104] or Kinney KC Series KC-3 pump 2K euro recon. or e.g DS 102 Dual Stage Rotary Vane Vacuum Pump 2 x10-3torr 2K euro new. ( these pumps both use oil for lubrication, Oil free called dry pumps are better for EBPVD. (check which PVD metals deposit ok with oil around and which not? ) Dry pump options are currently too expensive eg 10K euro plus; Richards EPX or top end Dry Scroll pumps or Blower Booster paired with own Backing Pump) to protect the chamber put the titanium block in side a double walled box with a beam entry hole at the top, and offset breathing holes through to the rest of the chamber on the box sides, thereby protecting the main chamber from the condensed titanium on inside surfaces of the box and yet let chamber gas combine with titanium creating solid compounds/a chemical pump with inbuilt recovery. Pumping speed may be moderate; for a 13 inch long 1 inch wide by 3 inch high box surrounding the titanium bar , gives a Ti deposit area of 91square inchs, at 20 degC. given pumping speed is 25 litres per second per square inch of deposited Titanium, So Nitrogen pumping speed is 2275 litre per second or 136 m3 / min or 8191 m3 per hour, thus the beam creates its own high vacuum pump. (some tantalum will be advantageous for argon pumping). (Arcing is more likely at poorer vacuum pressures, from the paschen curve we can see that this may not be a problem[105] (should allow / avoid arcing between; cathode to wehnelt 3kV over 0.3mm (same as Pd 3x10-2Torr cm at 3KV See graph [106]) - welhnet to anode - 100KV over 34mm (same as Pd 2.9x10-4Torr cm at 100kV See graph [107])(note; may not work/ may arc at rough pumping pressure levels of 1x10-2 Torr for argon on wehnelt ( i.e. Pd 3x10-1Torr cm at 3KV See graph [108])))) ( untested but breakthrough if works and probably will especially for MetalicaRapWin with its 10-7Torr vac requiremnt !)

More Examples

Practical manufacturing walk through

Manufacturing walk through Time/Cost

Given Electricity is 2kwh per hour .5Euro/hr Part A Material; Stainless steal, Size; 300x300x200mm Weight; 15Kg 10µ Stainless powder (40 to 100Euro/kg) melt print 100µ Z layer thickness

1 minute per 100µ each layer See below; 1 minute per Z 100µ layer, each layer preheated 20 degrees Centigrade under melting-point followed by printed by beam5.33 minute per Every 10th layer Z axis correction see below ;

SEM ( part assumed to occupy 1/9 of whole print area; 1/9* 300*300=10 000$mm^2$ measurement at every 10µ, SEM picture 500x500 pixel so 5mmx5mm, So for 10,000$mm^2$ need 400 SEM pictures 10,000/25= 400 4x pictures from 4 picups gives effect of different angles? for 3D picture reconstruction so real distances, 400 5mmx5mm pictures, 250ms a picture = 100sec. plus time of mechanical movement of electron gun between .024m square patches at .03m per second is 12y strips each 0.3m strip takes 10 seconds to travel, so in all takes 120 seconds to cover build area( Risk of underestimate factor x100 ) 100+120=220 or 3.66 min flatten blobs through repeated surface spot melting 1ms per 70µ diameter spot area 4000x10-6$mm^2$ ( 850µs duration & 150µs beam movement) 1/10 of part high(Risk of underestimate factor x2) ( 1/10*10 000mm2/ 4000x10-6 $mm^2$= 1x105 spots 1x105 spots*1ms= 100Sec 1.66min

Time so far 200* Z correction layers 5.33 Min each 1066 + 1800 printed layer 1min each = 2866 min ( 2.0 days) Cost 690 Euro materials 600Euro Electricity 90

Critical Design Review, Review of decisions made so far

In chronological order

1.metal.......................... Vs ..composite. ........... .........Why .Metals needed for high stress high temp contexts , engines, solar plants.. -ve ........................ +ve metals 100 % recyclable fits Cradle to Cradle Design See [109]

2.additive.Sintering........ Vs Subtractive EDM?.................Why Tool path manual intervention required.Consumables......... -ve ..Powder management ............ +ve

3.ebeam..Vs laser .....Why A)laser below 50W,small size part 5x5x5cm,slow B) Laser above 150W cost, permit , Wall plug efficiency , optics .-ve .not so cool , difficulty diagnostics...+ve solar cell printer possible

4.powder...........................Vs foil..........................................Why foil waste removal.................................-ve .Harder solid parts.& powder management...... +ve

5.vision & correction sub. Vs one pass blind process ... ....Why .reliability Verifiable tolerance............................................. -ve ...Complexity..................... ................ +ve

6.gravity hopper................ Vs twin chamber........................ Why avoid old powder reuse fresh every time easier prep ............ -ve their must be a good reason to use 2 build chamber? e.g. EOS is. +ve

High Voltage for builders

The high voltage bobbin for transformer is an insulating material; HDPE 4mm or cheaper XLPE ( X indicates crosslinked LDPE) or nylon 6/6 insulation, This cross linked low density polyethylene XLPE is used in 11KV to 500KV cables where LPE is set to a fixed form by a process called curing or vulcanization, this can be done via chemical or electron beam radiation. This crosslinking process improves the mechanical stability of the cheaper XLPE products. Comparing the breakdown voltages on different Polyethylene we find that HDPE is 100KV/mm, LLDPE 75KV/mm LDPE 75KV/mm XLPE 50KV/mm p.8[179]]. Other materials include PVC, ceramics, glass, rubber, resins, reinforced plastics, polypropylene, impregnated paper, wood, cotton, mica, pressboards, Bakelite, Perspex, Ebonite, Teflon [180]

Introduction to HIgh Voltage [181]

Shielding Tech for builders

1mm lead shielding is equivalent to :3mm 304 stainless , ??mm sand, ??mm concrete,  ??mm standard glass ??mm leaded glass, external box with window cheap ideas?.

Argon gas cylinder needs to be protected from falling over, as long as their is some ventilation the argon gas is no problem, a 60 euro cylinder should provide 3000 chamber purges in window option design ( background info; oxygen 21% of air argon less than 1 %, if oxygen concentration falls below 17% than can effect ill people for healthy people its ok down till 12%, if trace element of CO2 is also present hyperventilation can be triggered which allows no ill effects down to 7% Oxygen. this C02 trace approach is added to argon fire extinguisher systems). For on beam path calculation target penetration based on NIST material testing calculater for 90KV 1.8 mm of lead gives 100% attenuation[182].

Other design options which other builders may choose to follow that we have rejected

Chamber & pumps & feedthroughs

The non window single chamber version can be adapted for Lanthanum hexaboride (LaB6) filaments ( lasting 1000 times longer than tungsten filaments but expensive and needing higher vacuum of 10-6Torr) through creating a dual pressure vacuum chamber design, dividing chamber up between filament/cathode/anode area and the main weld chamber with a mini "airlock" chamber which is high speed pumped. The existing single aperture/ baffle between L1 and L2 magnetic lenses can be cleaved/split in to two separate apertures in two disks thus creating an intermediate mini airlock chamber. The existing aperture size small apertures(100µ) thus doubles up as two air nozzles separating the electron gun from the weld chamber. These 100µ apertures (image size at baffle is 6% of 1mm emitter radius de-magnified by 0.3 so image height is 20µm so aperture will be about 100µ(check)) are suitable size as a pumping aperture/nozzle between electron gun chambers at 10-6 Torr and 10-4 Torr weld chambers. This adaption also requires additional vacuum pumps for each area and the intermediate mini chamber between the baffles.

(Old option: Another option is using 2 recycled TV cathode ray tubes as main vacuum chamber, Leaving only the problem of the build chamber tube which can now self print in 7 pieces and assembled, which is achievable as no longer needs to be vacuum tight only metal powder tight as is within glass Cathode ray tube chambers and cutting the hardened screen glass is successfull. Finally a good way to reuse all those old TV's!) Pumping options ; diaphragm pump no oil Dry

Link to details of High vacuum chamber (initially welded then glued)

• Electrical feed-troughs ; For tungsten filament AC 10A 3V 30W ( NB SM8018 bulb for comparison is 6V 2.5A 15 W flat wound filament but nearly all energy is seen by gun where as only a 40th of ribbon is seen by gun but is 30W 2mm wide 50µ thick ( check)) 50/60Hz heater power supply electrical feed-through includes a oil immersed 100KV isolating transformer using a Pyrex and quartz tubing within CF pipe coupler with orings with oil imersion on outside [183] .By placing last stage of main 100KV power supply the cockcroftwalton ladder in its own vacuum chamber keeps all high voltage ( 100KV) within vacuum(except filament isolating transformer) which allows 15 KV sparkplug type electrical feedthroughs to be used [184] these are welded sparkplugs on CF flanges with out radio noise suppression carbon resistor . A further welded sparkplug type electrical feedthrough will be used for interconnection of 100KV from power supply sub vacuum chamber to main gun chamber. CF flange Electrical connectors, Other (1x 140KV 2KW , , 6x SEM PIN diode pickups low current low voltage,
• Mechanical feed-troughs ; 45Nm torque oring or more leak resistant magnetic feed-throughs 3x 12mm Motor shaft Vacuum chamber motion feed through. 10-5 Torr Low torque version and high torque for 700W build platform motor.
• a dry pump option is better for EBPVD but currently 10K plus euro so rely on back flow oil filtering. ( Aminor issue for metal printing but a problem for solar cell printing is the silicon oil vapor in to the chamber from the oil diffussion pump which will be cracked when in contact with tungsten filament (at 2600 C) producing oil by products that reduce the vacuum and affect the quality of EBPVD [185] melted metal depsoited layers (EBPVD summary by material [186]) .
• Alternative roughing pump is use an oil diffusion pump, there is an existing home build design, see here: [187],[188] (use google translate) though some people have had success with using the chilling unit from an air conditioner in-between pump and chamber [189]. Other electrical feedthrough options includes 100KV sparkplugs with out radio noise suppression carbon resistor [190] with oil immersion on outside. But many commercial machines use the diffusion pumps and cope with the oil issues;The cooled condensation baffles in between the pump and the chamber is adequate to prevent any significant amount of oil getting in the chamber at these pressures. The best way to do wire coils is to seal them into a stainless steel can, and allow a cooling medium like air to ventilate the can. You cannot hope to dissipate much heat from a coil in vacuum, and you don't want the coil to outgas into your vacuum anyway. For the prototype we suggest one gun in a chamber that can be used to test either guns design( Melting gun and vision gun).Once we see the outcome of the test we can decide to try two separate guns again if necessary.

Powder Deposition

• The Arcam EMB uses a "textured roller". Presumably a roller is textured with a pattern of holes which is loaded with powder, then the powder falls out of the holes, and a little random redistribution occurs on the way down to the workpiece surface for a reasonably uniform powder layer of repeatable thickness this design will likely operate at ultra high vacuum.
• Leveling the surface of the powder bed or enabling better flow through hopper at ultra high vacuums may be possible using ultrasonic lubrication to briefly fluidize the powder bed. It might cause unacceptable settling though.
• The density of the powder is lower than the density of the solid metal. So if the powder is only deposited using say the textured roller the upper level of the powder bed will get higher than the surface of the part being printed. How is this dealt with in the Arcam printers? More research needed
• Upon beam heating material loss in the form of evaporation and melting is released in to the chamber redepositing itself on windows and light optics and even chemically react with filament ( a minor effect with most materials but a major effect if used in electron beam machining mode where a non metallic backing material or axillary material which is ignited leading to rapid expulsion of auxiliary material that pushes up through the partially mellted hole in the metal work piece above thus causing expulsion of molten metal in the hole, thus creating a cleaner hole shape See 26min in [191]), a slotted disk in combination with a pulsed beam operation and a slotted disk can protect these windows / optics surfaces. (another approach is to use replaceable and disposable glass sheet covers).

Power supply and power control options

• control via power supply feed back circuit leaving gun cathode to Wehnelt bias fixed via gun resistor ( which includes inherent sensing of beam current; as too high beam current means more voltage drop across resistor so more beam pinching so reducing beam current so simple feed back control). When at 1KW power and shut down in half a cycle ( 0.2MHz switch frequency) the resonant energy left in LCC circuit and output capacitance would lead to one extra 55micron cube of melted Titanium or 40 microns cube of melted steel . . See problem C for calculation Physics Principles/Discussion These gun resistor values give 0.94 KW not 0.1 KW look again maybe .For electron optics precision 3KV across Fixed gun resistor (2x 430K Ohm Resistors making Total 215KOhm when arranged in parallel for printing mode (300W rated resistor 50mm x 373mm E12 values [192]), Or 1720 KOhm 4 resistors arranged in series SEM mode, situated in open air air cooling , So beam will run at 940W and 100W respectively 15mA and 1.6mA respectively ) selectable from outside test tube via 3 pole 2 way (6KV) switch solenoid powered by coil on long leads with rectified AC via core less transformer around test tube, ( will need to develop beam calibration current measurement method after filament change possible with 4 pin diode sensing spot size, this approach was found limiting by inability to pulse electron gun due to its parasitic capacitance.
• Use power supply only approach, but with a refinement of 8 fixed value /position adjustable gun resistor so you can put beam current in suitable range to allow for filament change variations, instead of manual rotation ,use fet 4KV & 8x ldr/resistor gate matrix & 8 x led outside test tube. This would make the change of gun resistor automatic. Rejected due to difficulty of finding a FET small enough to go in test tube, ( 200W 4KV up to 30mA)
• Current sensing methods; On transformer secondary (high voltage side) second FPGA on optical link via SFP gigabit modules can sit at -62.5KV and measure current via fixed 40K Ohm (40K non varying element of gun resistor it also has 0 to 140K ohm variable / or via 8 fixed resistors element in 20K ohm steps ) gun resistor their by gaining 30dB Signal noise, ( as opposed to second FPGA siting at 0V sensing beam current across gun resistor via two voltage dividers (-62.5KV to -2V voltage divider), as opposed to using separate (5W 100 ohm) current sensing resistor in earth return from chamber, even less noise but earthing complications with some motor types and requiring some low voltage secondary insulation of chamber) ( power to FPGA via low voltage rectifier and core less transformer via filament test tube ( same method as filament supply but additionally rectified).
• by control of the bias on the Wehnelt voltage in gun ; 0V( full beam wehnelt has same voltage as cathode filament No bias ) to - 3KV pinch off (cut off where wehnelt is at the lowest voltage and cathode filament is 3KV more positive ( i.e. more like anode) ). This bias is achieved via E130L vacuum tube acting as a voltage divider of the main output voltage thereby in effect creating a second voltage supply, OR via 2nd transformer isolated power-supply providing up to 3KV bias. This approach has poor short circuit protection and poor repeatability due to main filament replacement alignment variation).
• by control of the bias on the Wehnelt voltage in gun ; via a second power supply across cathode and Welneht. ( this option is not compatible with the o/p current sense via a ground path resistor as it places a parallel power supply, o/p current sense via a hall device Isolation via a led to photo-transistor 10cm light tube to bring signal to low voltage side/ FPGA side. High voltage side circuit powered by a second core-less transformer across glass test tube used in cathode filament assembly, primary is mains, secondary rectified 5V for LED driver circuit and 15 V for hall current sense device ).
• limit the control option to pulsed operation; use FET series each 800V with transient voltage protection regulator circuit for an x-ray tube with transient voltage protection
• A full high voltage drop across a tetrode ( triode limits bandwidth [193], this tetrode is a safety feature as it controls the current independently of gun but is expensive.
• Push the parallel series converters resonant tank current by 30% so get higher voltage output of 73KV instead of 63 KV. This requires n=19 Cp=18nF Cs=57nF alpha=0.3125 Ls=13.5µH. fo= 181.5Khz. Max duty cycle 0..8. Stress on components increases as Zs Series impedance drops from 333 Ohms to 236 Ohms.
• Voltage multiplier ladder version Cartesian 1kW gun power supply circuit construction will be based around 2 MOT serialized 100KV(1Kw) that gets feeded from a freqency controlled 3 phase switchmode powersupply range 100 Hz to 1 KHz and 8 stage Cockcroft walton ladder for the positive 15 Kv x8= 120KV un regulated, To avoid the need for both; expensive air tight 100KV connecters, and power supply oil immersion , the Cockcroft walton ladder will be situated within the vacuum tank (dead tank with the enclosure at earth potential) in a sub chamber sealed from the main chamber having its own small 8KV ion pump with some tantalum, slotted cathode cells for argon gas collection [194]. The intermediate wall between vacuum tank containing Cockroft walton ladder and main chamber containing gun will be constructed from copper with internal water cooling channels connected to exterior water supply to avoid Diode and resistor overheating problems. With the use of a one way valve between chambers the circuitry remains well insulated unaffected by vacuum loss in the main chamber. .( Cross linking machines already use this vacuum encased powersupply approach).

Cockcroft Walton ladder Calculator Help & Tool for any one who want's a fast overview [195]

Power supply functional diagram now full wave Cockcroft- Walton ladder
• You take heat out of assemblies like this by incorporating water cooling. If you use high purity water (80 meg-ohm) it is reasonably non-conducting electrically, though initially tests will be air cooled vanes on high voltage feed through copper bar.

Deflector coil options

Driver circuit choice Coil position options 1)7 degrees at bottom of gun 2)nearer build table. By rotating the scan raster by 45 degrees in the X Y plane means that we can increase scan speed by product of X and Y coils deflection speeds (in contrast to max X deflection speed equaling max X coil deflection speed), though we do get a lower pointing accuracy.

Specific's

• What motor power for build platform vertical motion see scale diagram below ? owned by username ;...........likely finish date :.........emotional status..........
• Which diameter for extension rod inside moterdriven sleeve. I.D. & O.D. sleeve diameters, I.D. & O.D for extention shaft? owned by username ;...........likely finish date :.........emotional status..........
• What motor size & minimum shaft O.D. for hopper X movement/powder deposition ? owned by username ;...........likely finish date :.........emotional status..........
• What is the best Main Deflector Coil driver topology options ; a) Raster 30cmx30cm b) point and shoot owned by username ;...........likely finish date :.........emotional status..........
• What solvent removes conductive coating on outside of salvaged TV tube? Best method to get a clear viewing / illumination window in CRT. Best way to cut hole in screen after pip breakage release of vacuum and capacitive discharge via shorting anode cap to earthing band on four corners of set ( use own cable as anode cable may have diode in[196][197][198]), be safe out there!. owned by username ;...........likely finish date :.........emotional status..........

Broader research (this is the difficult stuff) you need plenty of free time to do these

• ....................................................................................................................................................................................owned by username ;...........likely finish date :.........emotional status..........

None of the processes in themselves are new, they have all been done in other contexts. What is new is that it may offer finished parts requiring no further machining, verification of parts tolerance and bring error correction to metal powder 3D printing for the first time, thus enabling full-strength finished dimensional parts production.

(add your username, your likely Task completion date , and emotional status comment ;(possibles include " its fun" " its challenging" "wow" "----" "I feel like Robinson Crusoe" " I am so alve" "I am going to be wealthy" .... )

If these knowledge areas are new to you, remember to use your networking skills to talk to others, that friend or uncle may be just that expert!

Design/research questions:

• A. Possible pit falls of running an SEM at 100W in four-source photometric stereo Ruderford back scatter mode?
• B. Depth of field of measurements layer errors over 200µ height, typical SEM power is 0.1W?
• C. Target metal surface temperature measurement would be a big advantage, Do you know of a electron bombardment based remote temperature measurement approach?.
• D. Quantify relationship between cathode surface tolerances and electron gun performance, (spot size variation , 2nd order effects etc ) Quantify range of gun performance at cathode tolerances of IT 7.
• E. Which pattern of beam movement a "fixed raster pattern (like a TV scan )" or "point and fire where needed" in a) preheat stage? ( taking temp up to 20 C below melting pointas (commercial printers preheat and infill print method)) b)melting/sintering by following part shape? (scanning coil eddy currents overcome with delays?,scanning blanked out areas leads to time wasting?, variable shaped beam more efficient?, Interference from other signals- X ray , secondary electrons , luminescence , beam induced currents?, Clear path for beam? (commercial printers do edges of parts in this method)

MetalicaRap Construction; Physics Principles/Disscussion