MetalicaRap:Tool head processes discussion

List of future tool head concepts FutureToolIdeas

External links for Processes comparison

Introduction to non conventional machining processes: J.P. Kaushish. "Manufacturing Processes". 2010. [1]

Introduction to machining and EBM 19 page: J. A. McGeough. "Advanced methods of machining". 1988. [2]

Quote " Their are many ways to belief "

Many routes need to be followed and researched, they all have their own value. Early comparison may not turn out to be the best guide. Never the less here we go!

SLS vs EBM

SLS and EBM have some similarities: both put down layers of powder, and both scan a beam over each layer of powder to get the powder to stick together in the right places.

EBM has some advantages over SLS

• EBM may be able to reach finished parts IT grade 07 ,SLS cannot produce finished parts unless very expensive laser pointing systems are employed.
• electron beam melting produces parts that are void-free, and therefore full density and full strength.
• The parts that generate an electron beam seem simpler/possible to replicate than the parts to generate a laser beam ( Adrian Bowyer" we may never reprap a laser").
• An EBM machine can do both additive machining -- melting new powder grains onto a part -- and also subtractive milling -- vaporizing outer layers of a part.( 600 W ND Yag Q lasers can also vaporize but expensive 100,000 euro)
• in principle, it seems possible to EBM materials that are completely transparent to laser beams, (reflectivity of aluminum for example means a laser cannot touch it, but steel has 98% of laser energy entry, so is fine) .
• ... other advantages ...

(See Below for advantages of SLS over EBM).

Discussion questions:

Q: The EBM machines I've seen photographs of generate the electron beam at the top, then focus and steer the beam to strike the appropriate spot on the powder at the bottom. That requires high vacuum -- otherwise the electron beam is completely absorbed by the air or other gas. is it possible to generate the electron beam on a moving toolhead a short distance above the appropriate spot on the powder?

A: Yes but beam spreads out and looses power, but the main problem is your metallurgy suffers so they are no longer equivalent to wrought iron milled parts, which is only possible in a vacuum 10-3Torr or better. Welding is traditionally a poor metallurgical join so weakness is allowed for in the join design, but this weakness through out a part often makes the part too inferior compared with milled parts. see (Bureau of Mines 1993) below).

Q: How short does the distance traveled by the electrons through air need to be, in order that at least half the energy of the beam makes it all the way through to melt the powder, rather than heating the air/nitrogen/argon atmosphere? See the artist's conception of a potential "Cartesian robot gantry" for non-vacuum electron beam welding[3]. Wikipedia: electron beam welding#In-air welding

A: ?

SLS has some advantages over EBM.

SLS does not require a high vacuum. It works at normal air pressure.

Most plastics, ceramics and lignin can be sintered open-air. (Most metals require an inert Argon or Nitrogen atmosphere, which is still an advantage over high vacuum in simplicity but not metallurgy eg.see (Tisza 2001) below Hydrogen metal cracking. ).

SLS appears to have lower cost and less research time before we get the first RepRap prototype working.

It is impossible to accidentally generate X-rays from a laser beam. Your normal TV tube produces X-rays which is not a problem as long as you keep them in a box/tube. The problem comes when you fire them around the room, like those wild people in hospitals do. (Generally a 50KV breast scanner Xray machine operator is recommended to use 1mm lead shielding or equivalent to reduce dose to a "harmless" level).

... other advantages ...

EDM vs SLS

(Electric discharge machining Selective laser sintering)

EDM has sub micron tolerance

SLS requires very expensive pointing method to achieve micron level tolerance.

other Advantages Disadvantages....

General guidance on comparison with the production of metal parts.

For Metal parts the main issues when comparing alternative processes with conventionally machined parts need to include; 1. Metallurgy; including; Resultant grain structure from cooling profile and metal alloy type (ingredients) , heat damage/distortion of process, 2. IT grade dimensional tolerance achievable , 3 Difficulty/special requirement of securing part in machine/skill required , 4 Metal - gas chemical reactions at temperature. 5. other

Info

Free 60 page summary of the important metal processes, ( beyond the well know milling grinding etc ) chapter 5-3 to 5-31. Bureau of Mines. "New Materials Society, Challenges and Opportunities: New Materials Science and Technology". 1993. [4]

As a Metal alloy cools at different rates, the different metal types ( eg Nickel & Chromium) form different types of crystals, some hard , some ductile, etc.. . This defines the metals quality/usefulness, in any manufacturing process the rates of change of temperature at any particular part of the product are therefore critical, these diagrams allow you to predict the metal products final qualities. Phase Diagrams are explained in this book: Miklós Tisza. "Physical metallurgy for engineers". 2001. [5]

Existing self replicating finished parts IT grade 7 or better machines

List your successful; largely self replicating/ finished parts producing machines!

Combined CNC and EDM machine have produced finished parts IT grade 0 , Self replicating, Amazing Yes!! unfortunately many years (15 yrs) experience is needed to operate it.

Further reading

S. Narayanan. "CAD/CAM Robotics and Factories of the Future: 22nd International Conference". 2007. [6]