Metal deposition print head

From RepRapWiki
Revision as of 19:32, 2 September 2011 by Greenatolsecondtry (Talk | contribs)

Jump to: navigation, search

This page is the nucleus on this wiki for development of a metal depositing print head to go along with an XYZ Cartesian robot or robot arm.


The big picture

Machines are the main physical tools that allow material wealth creation. Good machines require precisely shaped metal parts, made to dimensional tolerances in the 10-30 micron range (roughly).

The MetalicaRap is moving forwards but there are many roads to glory :). Another particularly interesting and promising method is to form the metal object roughly and slightly oversized (near net shape) using a solid freeform fabrication method, and then machine the surfaces of the part that must be precisely shaped using a traditional subtractive method like EDM or milling, either after or during freeform fabrication.

While there do not seem to be any open precision cnc milling or EDM machines, the know how to make them is widely available, so a serviceably precise Open EDM or milling machine can certainly be made. Development of a suitable open freeform fabrication method suitable will enable the afor mentioned type of printer.

Such a machine would be relatively easy to have largely self replicating because it can print precision metal parts like a leadscrew, gears, linear journal bearings and fittings as well as snap together structural members, which is the bulk of the mechanical and structural components of such a machine. It could also print most of the parts for a Lister engine, hammer drill, a car (if the print volume was big enough), refrigerator etc.

Secondly, such a printer would probably have to already print in 2 different materials at least: a support material and a metal. Then, you could add an FDM head to the printer, allowing plastics to be printed onto the metal part as it is being made (within limits of not being exposed to excess heat). You would then have a multimaterial printer that could print the parts for even more of a car etc. Additional heads could be added like a head that deposited ceramic with the use of a diode laser, allowing you to produce parts mostly finished (including windings) for a stepper motor, most of an alternator, etc. Speed could be increased simply with multiple heads.

Existing freeform fabrication processes

See Comprehensive_search_for_full_strength_material_printers#Additive_processes_that_might_be_adaptable_to_printing See also the existing printer sections in that document. Ultrasonic consolidation is another particularly interesting one.

Proposed approaches

See . Essentially we are adding a small bit of metal to a much larger bit, ideally consolidating it into a perfectly contiguous mass, which is very similar to welding with filler, so that is what most processes will draw on.

There is so called "micro welding" which involves units that may be a suitable size. They might be adapted as a convenient starting point for the gun or power supply etc.

Methods of adding material indiscriminately like metal vapor deposition or Chemical Vapor Deposition or plasma sputtering could also be used and then followed by subtractive machining.

==Wire and induction heating==

Wire as a feedstock is a handy way to go, easy to transport and, for the prototyping process easier to buy and handle. Under atmospheric pressure argon.

Primer for uninitiated: Remember current is induced in such a way that it produces a field that counteracts the changes in the primary magnetic field. In the diagram of magnetic field lines, with the higher density of magnetic field lines indicates the areas that are heated more. The higher the frequency, the less the heating tends to penetrate the surface of the inductively heated metal.

Induction heating could either use a plain, rod shaped air core solenoid or non conductive ferrite core magnet, with one pole of the magnet close to the metal surface, and modulated at relatively high frequency (10s of khz) to achieve an annular shaped heating area on the surface of a metal object (the melt pool).

Another way which could give a more uniform, circular heated area could be to have the magnetic field enter the surface over a small area and exit over a large area. Heating occurs at a useful intensity at the small pole and the magnetic circuit is closed a bit better which helps increase coupling into the pool. The coil could be water cooled.

The surrounding area could also be pre-heated with radiant heating using a nichrome or, since it is argon atmosphere, tungsten element, or the melt pool could be assisted a bit (how much? What sort of energy flux do we need here for various sized melt pools?).

Resistive heating


Try to basically scale down and make open one of the freeform fabrication ones methods that use wire under argon, or another arc welding method. Remember precision is not critical since there will be a machining step later.

 There is a purely resistive, sans  arc method listed lower down in a patent.

Electron beam

Electron beam welding, basically. See documents at the main page on existing processes; nasa simply adapted a purchased electron beam welding system to use as a freeform fabricator.

The main problem is that their system used a vacuum of 5x 10-5 torr. While making a chamber for that level is doable, everything inside has to be compatible with that vacuum level too. Sensors, electronics, motors, lubricants, all become harder to integrate with the system inside the chamber when desirable, as buying off the shelf units specially made for high vacuum is probably very expensive. Could try to make our own but it's ultimately a real hurdle however you work it.

However strictly speaking only the electron gun itself needs to be under a high vacuum. There are many electron beam welding rigs that use low vacuum chambers and under normal atmospheric pressure (would still have to be argon though). Either a plasma window or even just a suitable arrangement of powerful pumps and narrow constrictions filled with gas is enough to keep the inside of the gun a vacuum while getting the electron beam out. A thin material though which the beam passes would probably not work due to overheating of it, or scattering or excess absorption of the beam? What if water cooled or it were moved (or the beam redirected) rapidly so the beam only passes through a given section very briefly? The thin material window can move relative to the electron gun easily; there are plastics and other materials which are sufficiently flexible and gas impermeable that they could be used to accommodate the motion while maintaining a seal. Or vacuum oil could be used with a metal to metal joint for a good seal.

Since we don't need a particularly well focused electron beam more research is needed on why NASA chose to use high vacuum in the entire chamber - money was no object maybe and they just didn't want to bother with plasma windows?

We could use the same gun as the MetalicaRap or a smaller one.

Ultimately the main benefit of electron beam for our purposes is probably only precision control of the energy into the melt pool? What else? The SMD and PTA FFF methods supposedly get full strength so it might not have much advantage but be more complex and expensive to prototype.

Summary of comparison between different approaches

I think we should steer clear of the high vacuum approaches anyway for this particular project, because of the cost and difficulty of prototyping and working with high vacuum. I think further research on the support materials will tell which is the best, but I am leaning towards induction if enough power can be coupled to the melt pool that way. GreenAtol 00:00, 14 August 2011 (UTC)

Argon supply

As mentioned in the reprap forum, Argon can be extracted from the air at a small scale economically and with relatively non expensive or complex machinery. So the cost or difficulty of obtaining Argon as a consumable is probably not a major issue ultimately, just the electricity cost. The documentation on the commercial FFF processes indicates high purity argon is desirable, (99.99%) and that 10 volumes of gas exchange in the chamber is typically needed to achieve good metallurgy. But even high purity Argon does not look too hard to make at a small scale. Seems unlikely that even if they start with 99.99% argon that the purity actually in the chamber after 10 exchanges will be near that, maybe though. Successive division operations can add (multiply) up pretty fast. Laminar flow rather than dilution flow in the chamber must be employed most likely.

Approaches include, may need to be combined or repeated for high purity:

  • Pressure swing adsorption.
  • Membrane separation (maybe with reverse osmosis membranes?)
  • Fractionation of air.

Existing open freeform fabrication processes or metal deposition heads

There are none known as far as I can tell right now.GreenAtol 00:11, 14 August 2011 (UTC)

Deposition speed

Obviously faster is better. However using thicker wire and more heat in the melt pool has limits and might have serious tradeoffs at some point. Using a row of identical deposition heads might be better. An array another step better still, as material could be deposited in a large number of places. An array of say 5 by 5 heads could be fixed relative to each other, and the motion required of the array to bring all the heads over the relevant points where material needs to be deposited could be either a scanning, raster approach, or there could be some performance enhancement possible using more complex motions that would be computed for each metal deposition layer. The melt pools could be sufficiently separated that they do not effect each other normally.


EDM is a nearly force free method. But milling entails significant force, though you can reduce the amount by moving the mill head more slowly.

So the object being fabricated needs to be firmly affixed to the rest of the printer somehow, the firmer the better. This is closely related to the support structure strategy. Options include, and these could be combined:

  • Have the bottom of the first print layer of metal stick to a ceramic baseplate, but not so much that it is impractical to remove. Could be removed by breaking the bond by differential thermal expansion or maybe just a good stiff whack. Limitations:
    • When the object first starts it's contact area with the base is small so it is poorly attached. Might have to be extra gentle with any milling, and/or maybe the process can be controlled to control the strength of the bond.
    • If the first print layer only touches the bottom of the chamber at a point or line you are probably out of luck, would have to use the support material approach along with in situ casting (see support section.)
  • The support material could be laid down in a single layer first as a sort of glue layer, if it had the right properties (has to stick to both metal and bottom of the print chamber of course and be adequately strong and temperature resistant WRT not burning and preferably not distorting (e.g. by melting) when the molten metal is deposited onto it). As the part is build up, the support material can be built up too, so it continues to provide a solid, rigid connection to the base. The corners of the build chamber could have vertical attachment points too, without interfering with the cartesian robot, which the support material can brace against. There may be a large amount of support material, if it can be reused in subsequent printings might as well go to town an fill any volume not filled with print metal with support material to provide quite solid support.
    • See support structure section.
  • There could be rods or pegs or wire sticking up from the base of the print chamber. Could be the same material as the print material. The metal could be deposited starting with welding it to the wire. Would provide grounding too for processes that require it.
    • Could either be 3 in a triangle shape and hold the object down just by being support pillars and through their own rigidity.
    • Could be only a single or 2 wires or pegs. The first bit of metal laid is welded to it/them, and then they are pulled downwards forcibly. This holds the object against the print chamber bottom and can continue to as the object grows if the support material surrounds it (or it supports it's self against the bottom of the chamber due to it's geometry of course). This could be combined well with the sticking to the bottom and corners of the chamber.
    • removing the pegs could be done by machining, or if the dimensioning is not critical there could be just a small mechanism built in to the printer base that cuts through the rod or wire, releasing the part. More wire or rod could then be fed up, and the printer can start a new cycle without manual intervention.

Support structures

For the uninitiated: When you print from the bottom up, layer by layer starting from the bottom, suppose you are printing a coat hanger, vertically, with the hook a the top. That is, viewing it in profile. The tip of the hook needs to be printed before it is connected in any way to the rest of the coat hanger. So it would need, in any case to be supported against gravity in the meantime. This bit may be called a "leader" before it is connected to the main object. Or you may be printing a large number of small unconnected objects... See fixturing and grounding sections too.

Patents reveal a lot of interesting information about possible materials and methods for support structures. Water soluble ceramics, structures that can be disintegrated with ultrasonic vibrations, high strength wax, and there is probably a lot more gold to be found.

If needed, more than one support structure could be used, each with their own strengths. So if a material was really good for attaching the metal to the base of the print chamber for instance for fixturing, but really slow to deposit.

Support structures perform the following functions/should have the following properties for the printers we are talking about here:

  • brace long thin vertical shafts and walls and parts that are not otherwise braced against the base of the print chamber (like the tip of the coat hanger hook before connected to the rest of the hanger, a leader) against the milling forces. This sort of entails being able to stick to the metal reasonably well and also be reasonably strong.
  • damp vibrations from the mill in long thin shafts and walls and floating points, again needs strength and stick
    • if it's a stout object with no overhangs and is not a leader it doesn't really need any bracing or support material since it can stand up by itself and would be affixed to the base of the print chamber. Those objects may still be useful so as a step of the dev process, printing these might make a good intermediate goal.
  • Act as a sort of in situ cast:
    • The subtractive machine tool will probably have a hard time in most cases machining the bottom surface of any perfectly horizontal overhangs of any significant length (a mill bit of the right shape or multi axis milling machine could help in many situations but there will still be a lot of geometries where it wouldn't be able to reach under there). In that case the support can be deposited, milled to the desired shape, and then the molten metal deposited on top. The precision would never be as good as milling the metal itself but it's better than nothing. Obviously this requires that it be heat resistant enough.
    • When printing a leader, the bottom of the leader would similarly be hard to machine, and could benefit from this.
    • Ultimately you still need to be able to machine under ledges at least a bit or you could only machine the top facing surface of any object which is an unacceptably severe limit on printable geometry. Suitable milling bits will probably suffice, or a "bit" with a small 90 degree gear built in, even, or the milling drive motor could be a water turbine or other quite small power plant (so it can reach in places reasonably), and the mill be a 5 axis mill.

A good support structure strategy, in this case, would also entail:

  • structures are easy to remove, preferably completely and not damage the surface. Metals are usually soluble in other metals. So if the support material was another metal like a low melting point alloy, it might damage the precisely machined surface anywhere the molten material touches, either when it is being deposited or removed, which is probably not acceptable. Maybe some alloys to choose from that do not have this problem with certain metals though.
    • In many cases it will have to disintegrate to be removed.
  • structures are manageable cost. Material may be recycled in many cases probably.
  • main problem is desirable material combined with practical deposition and removal.

Possible materials

Add examples of the water soluble ceramics, low melting alloys, high strength wax, also some sort of fast set gypsum (crystal structure absorbs moisture into it, dissolve to remove? Even if it takes some time to set that may be okay slows things down a bit but they are already pretty slow), materials like concrete which are sort of like epoxy (hardening occurs due to chemical reaction), the roughened stainless steel foil material pressed together one, salt or another material deposited in a solvent and the solvent evaporated, ultrasonic powder consolidation could work (powder plus pressure plus ultrasound), high speed droplets or bits of metal or deformable material fired at the surface (that droplet spray method sometimes used for making liners on engine cylinders?)(coudl be released with ultrasonic shaking maybe), maybe could be electrolytically deposited but probably pretty slow, vaporized and then deposits on there. Anything that liquiefies with cold rather than heat?

Thixotropic materials. Materials which sublimate at low atmospheric pressures? (could pressurize the build chamber too).

Fundamentally it is of course printing all over again, but the precision can be very low and it only has to work with one material with the right properties (although more might be useful of course especially if no perfect material which can also be easily printed with and removed can be found though here's hoping).

Grounding and supports

Unless the support material is a metal, or perhaps a metal trace from the main object is made out to any leaders may be problems grounding the leaders. The deposition method could maybe be designed so that the connection to ground is made right close to the melt pool, so if a GTAW like process were used there might be 2 arcs rather than 1, hitting the workpiece half millimeter apart and with current going down one and up the other. Or maybe better yet the wire could be the ground (the molten metal might be hard to maintain in continuity with the wire though). Induction could avoid this problem maybe.

Also obviously something needs to be figured out even for the main, non leader part, but just a wire sticking up from the bottom of the plate, to which the first bit of metal is welded should be fine.

Approaches that do not require grounding or have the current collector very close to the heated area:

  • Induction
  • Non-transfer plasma arc welding - basically super hot gas directed at the workpiece. Gas is heated by the arc, arc does not extend to the workpiece so it does not need grounding.
* Other methods using suitable gas flow patterns could be used to get heating only on small spots where desired e.g. have the gas exit from a small tube which is concentric with another tube which vacuums the gas and plenty of nearby atmospheric gas, back up, or even direct gas in a sort of cone shape towards the same area that the hot gas is being directed, keeping nearby areas exposed only to colder gas? The colder gas acting as a sort of wedge to get the hot gas away from the surface as soon as it has served it's purpose. Relative gas velocities probably have to be appropriate, but the surface of the molten pool would be concave so that might help direct the gas away from the surface again.  One issue might be splashing or vaporization of metal from the surface of the melt pool.  Might also be possible to heat the gas stream with a tungsten filament?
Conceivably the entire process could be be done at a fraction of atmospheric pressure, so that instead of arcs you can get stable gas discharges.  That may allow reduced electrode wear in the case of non-transfer plasma welding, or it could allow the two discharges to be more easily directed to the workpiece without difficult to manage instabilities? 
  • Chemically heated gas like oxyhydrogen welding - not as hot and probably not as precise as plasma, plus complications of hydrogen or oxygen or other stuff contaminating workpiece.
  • Heat the wire not the melt pool directly - need more info on welding, most likely problem is that not enough energy can be transferred (heat capacity of metal is too low)
  • Solid state welding like ultrasonic, EM pulse and explosive
  • electron beam welding uses only very low currents so it would be relatively easy to ground the object with a small metal probe that touches the metal, which probably doesn't work really with arc welding because the currents are so high. So high pressure ebeam then.

General information on welding

There is available on the web free copies of the book "Principles of welding: processes, physics, chemistry and metallurgy" which is pretty good. There is also "materials science and engineering callister" available, which has more information on welding and the materials science involved.

Finite element analysis/simulation of the weld process we are thinking of would be a good idea to see what sort of residual stresses and distortion is involved if we can get access to the software tools for it, although the commercial processes like LENS do not seem to have a problem with it and use melt pools of what are probably comparable size compared with what we are likely to.

The main difference though is that if the machining is to be done at each step distortion from the welding process after machining might be a real problem. Smaller melt pools might help, as might keeping the z axis separation between the machining plane and the metal deposition plane high, and precomputed compensation for any distortion that is expected. Ultimately ultrasonic consolidation may end up being the way to go as it is essentially distortion free.


a camera like but smaller might be useful for prototyping, maybe made with a low cost camera plus filters. Feedback about melt pool temperature is not as critical when melting is done under atmospheric pressure as when under vacuum because the metal is not as prone to evaporation/boiling. A lot of information can be obtained from sensing the arc current, or by "ringing" the induction coil, etc. too so sensors per se may not be needed.

stress and strain

For the uninitiated: stress implies compression or tension in a material. Strain indicates actual flexing/distortion. So stress will cause strain because any force on an object will cause some flexing since nothing is perfectly rigid, and if you flex (strain) a part on purpose by say bending it with your hands, the strain implies that stress will appear in the object. So they always occur together and are closely linked.

For melting processes, the books on welding say substantial stress/strain is always substantial and due to both thermal expansion and change of volume when metal freezes. Stress may be relieved by heat treatment. Ultimately probably not a problem if you only wanted near net shape parts, but in out case we want finished parts so the amount by which the object is distorted *after machining* matters a lot. ,

Things may be reduced in severity by using smaller melt pool, and also by increasing the distance between the material addition zone and the final machining zone, keeping the entire object very hot during printing (reduces relative amount of expansion but then shape changes occur during cooling after printing) and maybe other means (use cold gas to get the heat out of the ibject as soon as possible after it leaves the melt pool?).

Solid welding processes don't have the problem nearly as badly since no melting/freezing and usually lower temperatures (especially ultrasonic).

Plasma or vapor deposition may be another low distortion material addition method

Stresses produced during melt deposition

Melt deposition has many advantages in terms of speed and the ability to deposit any alloy with full strength and other good material properties, but the thermal distortion is one of the main problems involved with freeform fabrication with this method. There are other metal deposition methods that might turn out to be plenty good and workable like sintering followed by CVD PVD, plasma deposition or electrochemical deposition, and the 2 cold spraying methods EM gun and gas nozzle type. Those require more research too and might turn out to be promising.

  • more on trying to get low or stress free parts (need info on degree of random changes that occur with thermal cycling or just heat/cool, and also the degree of predictability and randomness (or otherwise unpredictable changes) of changes in shape during the printing processes (the various processes) )
      • method that anneals part as it is being made, heat it to above the cprrep point but below melting temp basically but plastic apparently , some basic info o ndistortion but may bot be the whole story as it does not factor in scan pattern etc. which we know makes a big diff , secondly does not adress the compensatability of this type of distortion which is obviously very high " Since most deposition materials change density with temperature, especially as they transition from a fluid to a solid, thermally solidifiable material rapid prototyping systems share the challenge of minimizing geometric distortions of the product prototypes that are produced by these density changes. Thermally solidifiable systems are subject to both "curl" and "plastic deformation" distortion mechanisms. Curl is manifest by a curvilinear geometric distortion which is induced into a prototype during a cooling period. The single largest contributor to such a geometric distortion (with respect to prototypes made by the current generation of rapid prototyping systems which utilize a thermally solidifiable material) is a change in density of the material as it transitions from a relatively hot flowable state to a relatively cold solid state.

For the simple case where an expansion coefficient is independent of temperature, the nature and magnitude of geometric distortion of sequentially applied planar layers can be estimated. Assume a linear thermal gradient dT/dz is present in a material when it is formed into a plate of thickness h in the z direction, and that the material has a constant thermal expansion coefficient α. The z direction is generally orthogonal to a support surface on which the plate is constructed. If the plate is subsequently allowed to come to some uniform temperature, it will distort, without applied stress, to form a cylindrical shell of radius r where: r=(α*dT/dz) -1 ( 1)

Curl C is defined as the inverse of the radius of curvature: C=1/r. An example of positive curl is shown in FIG. 1. Sequential layers of a thermoplastic material 104 are deposited on a base 102, using a moving extruder 106. As is typical in thermally solidified rapid prototypes, a series of layers are deposited sequentially in the z direction (i.e., the direction orthogonal to base 102), with the last layer deposited always having the highest temperature. Such an additive process typically results in a geometrically accurate part which contains a thermal gradient. As the part subsequently cools and becomes isothermal, the part distorts as a result of a curling of the ends of long features. "

  • search: no internal residual stress
    • from the EOS (DMLS system)site for the cobalt chrome material they sell to go with the printer, Stress relieving procedure:-

Stress relieving is done in a stress relieving furnace under argon atmosphere or in a vacuum furnace. The stress relieving sequence is as follows:- 1. ramp up to 650 °C in 60 minutes 2. hold for 3h 3. furnace heating power off and open the furnace door when temperature dropped down to approx. 400°C Annealing:- Specific properties can be modified by annealing the parts at various temperatures ranging from 650 to 850°C and for dwell times between 1 and 4h for DMLS printed parts, does not specify precision well DMLS so would be 50-25 micron according to prior research

 uses a shaker of sorts low freq but can be ultrasonic

Librar Vibratory Stress Relief y REPRINT: VIBRATORY STRESS RELIEF: A FUNDAMENTAL STUDY OF ITS EFFECTIVENESS" Says library so migh tbe more where that came from

Patent No. PCT/GB88/00136 describe in detail the relevant apparatus for using the thermal tensioning technique to eliminate buckling distortions for butt welding of thin plates. "

  • relieving stress in metal and other material layers
    • extremely powerful ultrasound to releive stress? other ways to rleive stress or produce compressive stress to coiunteract the tensile stresses in the deposited metal layer other
    • other extreme shocks waves traveling through the devicee produced by exposives etc?
    • powerful em pulses?
    • deposite ions with an ion beam? almost any element can be used and so the alloy could remain good composition

more research starting august 22

Okay at this point the note files I have been using have gotten very mixed up because there are issues that are often interconnected so notes are on a range of subjects. However it takes time to organize them that would be better spent on research. Don't forget to check out the other pages in the related pages section of the comprehensive search for a full strength material printer page for other pages with similar notes.

    • what are the stresses involved?
    • what sor to alloys? probably some pretty good alloys can be made
    • this coudl be used with the array of electrodes thing with the crt that mentioned perhaps if it is possible to build large objects that are low stress
    • ocudl use a strong electric feild vetically to encourage ions to go straight to the surface might help to allow increased standoff distances for a given precision
    • use an LCD screen or similar as the electrodes?
    • what are the electrodes made of ? We cant hav ethem dissolve whereas in normal process you prbably can, maybe we could make them from glassy carbon or something
    • could use stress modification techniques if there is tensile stress build up em peening, vibrational stress releive ultrasonic cavitation etc.
    • coudl print a shell of high melting point metal and then fill the shell with other material
      • they must have some way that is similar for the stamping things for dies made with electroformding, to give strength to the relatively thin layer
    • hav eto prevent the metal from contacting the other electrode obviously, could maybe use capacitance or other measures to see how close it is toa given electrode and compensate with reduced current
    • coudl be a cold deposition method for on top of plastic as an insulating layer maybe, have to coat plastic with something conductive first though coudl use electroless plating maybe
    • look more into electroless plating to build up a large object too
      • as mentioned in the microsintering thing, can sinter an object then deposit material electrolytically in the pores might work even if the layer has some stress, one main problem is the pores blocking themselves off might lead to porosity but maybe coudl eb solvedwell enough through some means,
      • also electroless, coudl have channels built into the sintered part much like capilliaries, with electroless fluid pumped through
      • also if water was left behind and trapped inside it coudl boil destroying the part but maybe coudl be removed with heating if there is even the slightest hole allowing it to escape. If there is not that could be a problem btu there would very rarely be pockets of any significant size
      • EFAB thing, saw it before, uses elecgtordeposition and says it can make stuff up to centimeters in size, true or not don't know, says good material properties, not clear how they do it thouth

"Layerize exports files in GDSII format; these are then used to drive an e-beam or laser-based pattern generator, yielding a set of photomask tools that define each cross section with sub-micron resolution. The photomasks are used in the EFAB process to define the locations of selective material deposition on each layer of the device. The EFAB manufacturing process begins with a blank substrate (typically alumina) and grows devices layer-by-layer by depositing and planarizing at least two metals. One metal is structural,formingthefeatures ofthefinisheddevice. Theother metal is sacrificial, providing support during the layering process and eventually removed. Figure 7 show the layering process, involving three key steps. In Step 1, a first metal (e.g. the sacrificial metal as shown) is selectively electrodeposited onto the substrate in areas defined by the photomask, in a pattern corresponding to the first cross-section of the device. In Step 2, a second metal (e.g. the structural metal) is blanket deposited (typically by electrodeposition). The second metal covers the first metal and fills in the region where the first metal was not deposited. InStep3,thetwometalsareplanarizedviaaproprietaryprocess to form a two-material layer of precisely controlled thickness, flatness, and surface finish. These three steps are then repeated again and again until all layers have been formedand the desired device has been fully generated. Finally, the sacrificial metal is completely removed by a selective etching process, freeing the device for use. If the first layer is entirely sacrificial metal, then devices will be completely released from the substrate; this method is typically used for medical devices. However, electrically interfaced devices such as those shown in Figure 5 can also be built directly on the substrate and remain attached to it; dicing the substrate then singulates the individual “chips” for use"\

What is "planarization"? presumably a method of levellin/flattenign the surface to a known plane, but how? prpbably just or similar

Fast and Accurate Deposit Internal Stress Determination on the double disc sensor thing, maybe 2 of them coudl be used together to provide real time montioring, also says some guidelines recomendations for the stress level in deposits that need high precision, optical is 5 mpa , so with methods like the ones in the patents above maybe could do more. Welding would have higher internal stresses than that probably, remember the thermal stress docs were saying hundred MPa range.

        • so basically looks like just need some reasonably economical and tough metal alloys that can be deposited and a method to ensure the stress is tightly controlled in real time, an then the electrode array, maintain suitable spacing and that may wel lmake a good FFF method either to use with another method or to produce parts off the bat with all metal electrodeposited. Low temperature high strenght alloys like that zinc alloy stuff found in cars the multmachine people like coudl be used to do bulk filling, or even coudl be done just by printing a shell, heating everything up to a temp suitable for casting with low distortion(right below the melting point of the metal which is to be added) and putting the metal in the hollow shell.
          • need to check speed at which low stress material can be deposited
      • could use it as a bulk metal deposition method, simply mask off areas that you want to stop growing somehow, has to be done under water though. Can also print up a "cast" of sorts which will be filled with electodeposited metal
        • important:method of low temperature low stressmetal deposition
        • leaders would be a bit of a problem, maybe a conductive polymer coudl be used somehow, have it wired in so it can be swiched to ground or left floating, then ground it when you want deposition to start? Or just print a very thin shaft and surround it with the support/maskin/casting material for the very little bit of mechanical support it would need
    • 6457629 a mehtod of multimaterial fabricaton using ultrasonic joinin of different materials "More recently, nickel vapor deposition has been employed as a means of producing nickel shells for net shape fabrication applications. Nickel vapor deposition (NVD) allows thicker shells to be produced as deposition rates are higher than electroforming (Milinkovic, 1995). However, NVD involves the use of highly toxic gases and a specialized reaction chamber. The cost and risk of this technology are both very high. " proabbly nickel carbonyl, laser heating maybe.
      • interesting, describes putting a rod of material down to the surface and rotating it to add a layer of material, probably messes up the material properties thouh?important: low stress maybe low heat input method of deposition but looks like is not particularly low temperature as the temp gets to 0.7 to 0.9 of the melting point
      • Maybe carbonyls coudl be used effectively as a bulk deposition method in combination with inkjet masking/partialsequential layer casting it coudl be used with masking, the heatin gmethod probably does not have to be that intense, maybe coudl be used with halogen lamp as super broght projector etc.?
        • important: says is virtually stress free!
        • melting point of pure nickel is too close to that of steel though , maybe other materials that are depositable with carbonyl? Still coudl be used with lower temp alloys for bulk strength.
    • maybe can use magnetostrictive actuator for ultrasonic consolidation more fabricatiable coudl get the actuator from an old ultasonic impact (peening) gun maybe , go back and have a look at those papers on the material properties of the stuff with ultrasonic consolidation
    • one of those general roundup papers but looks liek a fairly good one, regarding combos of additive/subrtactive (hybrid) apparently sort of contradicts itself on that and nto really clear
    • more on thermal disortion and residual internally equilibriated stresses

One specific technique, referred to as Dynamically Controlled Low Stress No Distortion (DC-LSND) welding, was introduced by Guan et al. in 1993 and uses a localised cooling source, which trails the welding heat source at a short distance. Although the results produced are promising, the stress reduction mechanisms are still not fully understood. In this work, the three main fields of interest for the DC-LSND welding process, namely the thermal field, the residual stress field, and the buckling distortion, were investigated by means of conceptual, analytical and finite element models, and by experimental techniques, including thermocouple measurements, (synchrotron) X-ray residual stress measurements, residual deformation measurements, and microstructural evaluation. The combination of modelling and experimental work has provided valuable insight into the process of welding with a trailing heat sink. says it is open acess but don't seem to be able to download acopy


Shape Deposition Manufacturing probably already saw this and it is probably included above but searched and could not fidn it

      • A process is described in which a weld is produced without residual stresses; or with residual stresses reduced to a low value. Stress cycles of low value at low frequency are applied in the longitudinal direction of the weld by means of an air operated vibrator during welding. 4386727
      • use of dry ice basically to cool the trailin gendge of hte weld apparently greatly reduces distortion, not clear exactly how though To assess the cooling impact some thermal field measurements were made using a thermal imaging camera. The thermal profile of a weld is typified by a long "comet" like heat trail, which reflects the relatively slow cooling rate achieved from self-quench conduction and ambient radiation. However, the results revealed the effectiveness of the CO2 as a cooling medium. The truncation of the heat trail of the weld by the CO2 can be seen to be complete and almost instantaneous. Temperatures of more than 700°C are reduced to <100°C over a distance of about 6 mm, which corresponds to the width of the cooling jet (see Figure 3). Interestingly, the thermal profile and the temperature gradient in the actual molten weld zone remain unaltered, implying that the forced cooling does not significantly affect the actual welding process in terms of the solidification of the weld pool.
      • claims 90% less cracking and distortion but compared to what not clear looks like cold dip welding sort of thing and a pretty shady company
    • Benchmarking of Rapid Prototyping Techniques in Terms of Dimensional Accuracy and Surface Finish
    • mats allow machining more easoily and solve grounding maybe?
    • what about some sort of high precision investment casting thing? done under vacuum say? Have the casting material made from 2 different materials that can be mixed and matchded to match the coefficeint of thermal expansion to the part being made. Make the cast, heat it to the melting point under vacuum perhaps then add it.
      • had a look and coulnd't find anything on highly precise casting, 80 microns for premium investment casting that's it.
      • ultimately the problem with the cast them machine approach is taht you can't always reach in tthere to do machining expecially with a mill, so you would need part specific tooling. Theoretically maybe a mill head tha was very small and very accurate on a robot arm maybe with a wide range of attachments and milling bits and maybe micro milling attachments or something could be the next best thing
        • absolute positioning, xray or gamma (radioactive material but not scalable so no)
        • brace against swrokpeice ot the base
          • heavy on the comuputation extremely heavy even maybe. Mioght need extra computatioin hardware a GPU or even multiple, etc

.*****could be edm maybe or similar after investement casting, 80 microns is not much to remove and get good surface finish

        • could havae a mini microrobot or maybe many of them that do the EDM work attached to workpeice by suction, just a thin cable leading to each of htem, positionin gis the main problem though maybe they coudl get enough info from the surrounding geometry? A probe that does the positioning from could work, as long as the bot can see the probe maybe, or maybe arm based encoders, would agian limit reach. Ultimately the most important parts to machine are bearing surfaces so probably reachable. Plus anything that is made with conventional methods is machineable relatively easily and that is the real goal anyway.
        • the main thing is user intervention and knowledge needed, and speed, and indivisable cost
          • machinists always seem to say otherwise bitut it seems clear that the first 2 should be soluble even for conventional machining as long as people share their experiences and results and dimensional feedback is possible there shoul dbe no problem.
            • one problem with machining is the various bits etc that you need, also collissions, but collisions can be avoided almost absolutely by improved automation. You coudl make your own cobalt or hss bits and maybe with a grinding bit for the mill and some preceramic polymer or similar silicon carbide and other bits? but this is going down the conventional road again with a different way to do everything and a different tool for each job. Still if it worked it works. Need to focus on the end performance that is being obtained .
        • with precomputation maybe it is possible to improve on the precision of investment casting, also with vacuum and special cast materials?
          • Even if not, could deposit nickel on the inside of a cast by nvd or electro, then pour the metal in and even though the nickel shell would melt or not be strong enough that is manageable. Thermal distortions would probably still occur though, but unpredictably and to what degree is the question, als ohetting the nickel to physically stick to the cast might help hold it in place
        • 0.02620741394208896607141661280442 interesting doc o n nanofactoories, size of water molecule 18 grams water so a cube 2.6 cm on a side 6.2 x 10^23 atoms so maybe 4.2 x 10^-11 meters wide or so 50 th on a nanometer
**maybe more research needed for precision ceramic forming and also coating and bonding to metal, plastics not really a problem probably.

Advanced Manufacturing Applications capillary stream of liquid metal dropped onto the object, does not seem to adress stress though

Control of residual stresses in shape deposition manufacturing find it maybve also Control of Residual Thermal Stresses in Shape Deposition Manufacturing

IN SHAPE DEPOSITION MANUFACTURING OF METAL PARTS very interesting thesis on the stresses including prediction of it

    • thermal deposition, internal

residual stresses build up as each new layer is deposit- ed due to differential contraction and thermal gra- dients between the freshly deposited molten materi- al and the previously solidified layer. Individual lay- ers can be shot-peened at a peening station to con- trol the build up of stress.

    • maybe ask the authors how long it too k them when have time to do the various FEM analysis esp te SDM thermal stresses thesis one and what hardware they used, just to see if practical to predict and compensate
    • obtain ABACUS or similar FEM software and learn to use it
    • says plasma spray with full density?? probably exaggeration
    • kind of interesting didn't really read, invar and TiC as low CTE material for laser deposition to overcome thermal stress
    • lookup ballistic particle manufacturing again
    • print the mold, them mold stuff, what precision do they get?
    • interesting for machinign, machine, then measure the surface you got, then machine again allows much less precise machine tools plus you want to be able to measure the surface anyway, goes to show some of hte promise for more dependence on computation and measurement and less on rigidity etc. An alternate approach to free-form surface fabrication Surface milling and grinding are widely used for the fabrication of free-form surfaces for molds and dies. The continuous demand for better product quality has led to demand in higher surface accuracy. Limiting factors are the positioning accuracy of the tool and the accuracy of the manufacturing process. Computer controlled optical surfacing (CCOS) has been developed mainly for the fabrication of spherical and aspherical optics. The surface is repeatedly measured and corrected using abrasives until the target accuracy is attained. In principle, sub-micron accuracy is achievable. The accuracy is limited by surface measurement, and not by the processing equipment.

The current research investigates the adoption of CCOS for the fabrication of free-form steel surfaces. This paper reports on the development of a test bed and initial experiment results.

The test bed is based on a six-axis RX robot as the motion platform with a spindle attached to the wrist of the robot. Surface measurement is carried out using a Talysurf surface profiler. Surface error correction is performed by abrasion of material from the surface. The amount of material to be removed is based on the measured surface error. Following a predetermined tool path, the feed rate along the tool path for surface correction is to be varied according to the required among of material to be removed locally.

A free-form surface specimen of mold steel of about 40 mm × 40 mm across is used for the initial experiment. The surface is prepared by CNC surface machining with the initial maximum error over 50 μm. The positioning accuracy of the motion system is estimated to be no better than 0.1 mm. Through surface measurement and correction, the surface accuracy is significantly improved.

Copyright © 1993-2001, Hugh Jack Engineer On a Disk Overview: This note set is part of a larger collection of materials available at nothign to do with what was looking for but interesitn ginfo on manufacturing processes more here

    • SDM for ceramic parts with the make a cast then inject the slurry method, supposedly dimensionally accurate in their view Fabrication of High Quality Ceramic Parts Using Mold SDM
    • patennt 5745834 says hot isostatic processing gets `1 to 55 micron accuracy?? it was mangled
    • 6450393 patent that describes the putting a whole layer of foild down then welding in the righ tspots approach for UC, also the author had a paper describing that system too doumandinis
    • precision investmetnt casting 3204303 need to know how predictable it is also maybe do it under vacuum, have integral coolign channels in the mold etc. Lots of options to improve precision but there is ultimately a random or unpredictable component in the thermal shrinkage just depends on how big it is, still the normal premium investment casting got 80 microns over an inch. Maybe have to talk to someone who knows or find docs on compensating for shrinkage or otherwise attempting to produce accurate castings.
    • Chapter 40. Design of a Laser CVD Rapid Prototyping System sounds iteresting but probably only very small scale due to low deposition rates
    • what about putting metal powder ina mold and applying pressure but not isostatically and then ultrasounding? hot isostatic processing produces fuly dens parts. Als omaybe the dimensional changes in hot isostatic processing are more predictable in casting due to less crystallization changes happening and therefore high precision could be acheived
    • interesting new method, uses 2 diff powders deposited in 3d next to each other, then subject then both to conditions that only cause sintering or other joining in one of the powders, which becomes the part
    • A comparative study of wire feeding and powder feeding in direct diode laser deposition for rapid prototyping Usig diode laser for full strength metal parts shows the brightnes is adequate don't need fiber or ndyag lasers

METAL AND CERAMIC COMPONENTS BY THE MULTIPHASE JET SOLIDIFICATION (MJS) PROCESS okay mildly interesting but uses binders, basically like fdm but mostly metal, then remove binders and sinter the object s

    • see wikipedia article on casting, what if you melt it twice to get the gas bubble sout ? Maybe coudl get a bunch of suitable molds of hemispheres made or maybe use a ceramic ball bearing and a way to scan in the resulting cast surface, and do experiments to try to make highly accurate castings, no might have to make the cast yourself to match the CTE etc. so taht woudl increset he cost of experimetn
      • Note that patternmaker's shrinkage does not take phase change transformations into account. For example, eutectic reactions, martensitic reactions, and graphitization can cause expansions or contractions.[19]
      • maybe not possible to do casting in a way that eliminates the need for machining, surely someone would have at least tried it by now and can find no eveidence that anyone has

make a separate category for metal printers

      • WATCHING SOME MIT MACHINING VIDS is clearly important to have the scanner to scan in oparts
    • add to the comprehensive search page in the proposed open printers section a lin to the metal depositon head and to the ultrasonic consolidation hybrid pritner page, also make sure it and both of them are suitable categorized and accessible from the righ tplaces and also the multimaterial printer page

More general research in august 30--------------
    • in situ fabrication of mechanisms (fully assemebled) and sources of error for dimensionality etc.
    • checked out the author Nickel, coudl not find any more stuff on thermal stress in SDM or anything else
    • for the fused block one could assemble a whole plane or line of blocks and then position over the existing object and weld, might be easier to apply force needed for ultrasonic weldign since can apply it on all 4 sides of the plane and also press down., maybe even coudl be weldied explosively woudl sove thermaldistortion issue , maybe they coudl actually be joined mechanically and still get good strength with some joint mechanism like screws or cold fitting or something?
      • another on digtial materials basically blocks
        • search "digital assembler" they say they made one that uses gik parts so see if it can be found that uses 20 micron gik blocks .
        • coudl use error detection on the blocks, then on the line, before deposition, also might be able to connect with mechanical connectors and then press and weld as with isostatic ultrasonic processing to get good bonding
        • also many ways to increase the speed, have an area instead of a line with multiple print heads working on the same object
        • could maybe use frequencies that only bond some types of blocks when desired? probably not much point
        • coudl do it assembly at low temps so grease and oil can be inserted as blocks maybe no need just leave channels
    • for scanning laser microscope thing coudl have a low res image roduced by largish spot size, then take multiple images at a slight offset and correlate to give higher res images that maybe much smaller than the spot size of th laser beam

K. P. Cooper and S. G. Lambrakos


MOLD SHAPE DEPOSITION MANUFACTURING thesis free and interesting and good mostly on material search and selection woul have thought that was the easy part maybe can do better by being more comprehensive and taking a higher level view, building a library of materials and their properties to choose from including many materials they did not consider and also compormising on e.g. the like of cutting heads is not such a big deal

Thin-Walled Structures

plasma-sprayed deposits undergo self-anneal- ing, which leads to stress-relief and recrystallization, causing fine, stress-free, and equiaxed microstructures" very interesting need to get the doc though

      • has a section on counteracting stresses with shot peening and by surrounding the part in ceramic to prevent distortion and then annealing
      • example of using shot peenign with sdm
      • if the part was rotated around it's center of gravity that migth htelp a bit to reduce thermal distortion because the stress would be circular in some places cancelling itself out, i.e. for a cylindrical region of the part, also maybe if a support material that bonded extremely well were used it could pull on and stretch the part material due to it's own thermal shrinkage but probably no such material since has to be easy to remove too. Still for lathe or other concentric circle parts this could be a way to reduce distortion a lot, coudl then be embedded in ceramic and annealed or just left as is maybe if peening was used during deposition or residual stress is otherwise manageable
      • ultraprecision additive material 'manufacturing station with EDM sort of interesting' in that it is acheiving high precision though , looks like is only for repair of existing components, interesting that they developed a special diode laser of high brightness apparently also uses various methoids to reduce thermal sresses similar
      • probabl yalready added but good enoguh to be sure
      • what precision is acheived with gelcasting ?
      • Hybrid plasma deposition and milling for an aeroengine double helix integral impeller made of superalloy apparently got enough precision
      • also maybe coudl build up thin walls or pillars or similar and then join them together to reduce residual stress, much line printing separate lines then joioning but higer z component , and still all those other ways of changing the scan pattern, preheat, thermal pinch, peen, cryogenic treatment, both types of vibratory relief etc. too bad they don't quantify their attempts t reduce stress
        • vibratory releif thing said that did not change shape of part but must a little bit maybe check again, also how does it work again? maybe it coudl be done with the object embedded in water or other solvent soluble ceramic ot other extemely rigid material, or frozen material since vibration takes no heat coudl be ice even at very low temps
          • coudl be quite a large block of ceramic if it is reusable. Would take some time to deposit, but could spray it on and allow evaporation of solvent. Also if ice coudl be used then a very large block could be used though getting the vibes in there migh tbe an issue.
          • what about going to extremes - nanoparticles, extremely low temperatures or high temperatures, a salready said powerful vibrations or shock waves, what else?
      • maybe put the questio to enineering forum on how to reliev or reduce stress or a way to deposit metal without stress
      • very interesting: STRESS FREE DEposition of steel though has to be relatively high martensitic fraction probably manageable , plasma spray such that stress is controlled partly due to supercooling the metal, wonder how much it coudl eb supercooled? , what about if the layers peen each other low stress method of metal deposition maybe cermaics too? also saw a method advertizing stress free silicon carbide coating
        • ss of stress control can also be fine-tuned by the additional application of simultaneous spray peening (for example, as described in GB patent 1605035 ALSO CHECK
        • search stress control rather then remove/reduce
      • on laser consolidation comments on precision, was to within 25 microns for wall thickness and 50 micron for the diameter of a hollow cylinder
      • WO-A-96/09421 discloses a technique of producing

metallic articles by sprayforming wherein the conditions are tailored to ensure stress control

Residual Stress in Additive Manufacturing

      • similarly isostatic processing coudl be used with poorly bonded ultrasonic consolidation stuff etc. maybe to improve bonding

    • mayeb possible to produce blocks that woudl fall into place when vibrated or self assemble or something, if so then coudl use a mold, put the blocks in, then isostatic press and ultrasound with very little unpredictable distortion so make a net shape part high precision




ASSESSMENT OF CASTABILITY OF DENTAL CASTING ALLOYS some stuff on precision quality dental castings

Summary of current state of research

September 1: Okay so right now for a metal only printer it looks like the best way is to use a droplet on demand printer with molten metal. I think this could be done with induction heating and induction magnetic valves of a sort. The valves can be coils around the relatively narrow (like 0.5 mm) bore of the deposition nozzle section. AC current through them can be used to repel the metal inductively, and 2 of them can be used together to peristaltically pump small quantities of metal, which become the droplets.

This can give good metal deposition in terms of bonding/consolidation, material properties, strength, and variety of alloy that can be used. However the next main issue is residual stress reduction and releif.

For this the approaches, in terms of what should be implemented, in order, are preheating the substrate (build plate)(the dimensional changes that may occur with cooling need to be kept in mind though since the ultimate goal here is to make precision parts, more research is needed on how predictable such changes are), adjusting the deposition pattern and method (pillars or walls which the voids between are then filled in especially look interesting), other process parameters of all sorts, and then stress relief methods mentioned above and on the multimaterial page can hopefully be applied to remove or reduce production of most of the rest of the remaining stress.

EM peening, motorized peening hammer, ultrasonic vibrations either from the substrate or through ultrasonic peening, and low frequency vibrations, shot peening, thermal pinch, and quickly extracting excess heat from the welded area and more are all options. Then annealing or vibrational stress relief or other post production stress relief methods could be applied if needed after the build, one example is annealing while the object is embedded with ceramics (e.g. water soluble) to prevent dimensional changes similar perhaps, but ideally the stress really should be relieved and reduced during the build process because that makes it easier to get better precision for various reasons.

The ideal is a method to deposit stress free void free metal with good material properties at a reasonable rate. The precision does not have to be very good because it will most likely be combined with subtractive removal anyway.

A relatively large amount of support material is likely to be used so it would be nice if it were recyclable or low cost. The search for suitable materials is not trivial but there is such variety to choose from there is inevitably something that will do.

Essentially this deposition method could be either scaled down greatly to the extent where it can deposit with high precision on the order of 10 microns and get good surface finish, probably hard to do but possible with (high temperature for the metal) inkjet type technology, or it can be followed by machining for each layer or set of layers. There are many examples of such hybrid processes in the literature, see the multimaterial page for some more info on them. The most extensively developed and interesting is the Shape Deposition Manufacturing one from carnegie melon. They use it as a generalized term for hybrid FFF/printing and though a metal printing version is developed to a limited degree it is not done yet.

Supporting the leaders and other small parts against machining forces with the hybrid approach, as well as precisely forming bottom facing surfaces and the bottom of leaders is another, due to machine tool reach limitations and the difficulty of fixturing. One way to fixture is to surround the object with rigid support material. Another is to have the machine tool actually brace against the object being machined with a suction cup or similar possibly with a magnetorehological fluid that can be solidifed at will with a magnetic field to interface to the object instead of a rubber seal, thus it is conformable but also can be made rigid when desired. A scanner for dimensional feedback could help too, as can precomputation to simulate the process and compensate for the elasticity of the fixturing. 5 Axis machine tool can help with the reach problem. Machining leaders separately and then lowering them into place and epoxying them down could work too, possibly with alignment pegs machined into the leader that are subsequently removed by machining. There are other possibilities mentioned on the multimaterial page and elsewhere on this page.

Precisely forming the bottom of surfaces can be helped by depositing the metal onto a shaped area of support material so it takes the negative shape but this has accuracy limitations due to metal shrinkage etc. In some cases it may be possible to machine the part separately upside down in another area of the printer and then essentially weld it to the rest of the object with metal deposition though thermal distortion may again be a problem there perhaps no more so that in any other situation.

Again, the main hurdle here is thermally induced stress and distortion. If we can solve this to an adequate degree we will be on cloud nine.