MetalicaRap:Tool head processes discussion

From RepRap
Revision as of 16:17, 26 May 2013 by Rapatan (talk | contribs) (Quote " Their are many ways to belief ")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

This page has been flagged as containing duplicate material. An editor has suggested merging this page or section into Materials/Appropriate Machines. (Discuss)

Discussion of Advantages and Disadvantages of different Tool head processes.

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. Lasers are clearly more sexy than old TV tube technology though early comparison may not turn out to be the best guide Never the less here we go!

In general for building a large part ( low 10's of cm's long)(approximate),

                                                                                           MIG welding,                                                          Laser,                                                  Electron beam on powder

Min spot size,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2 to 10mm,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 10µ to 300µ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 60µ to 1000µ for power densities (listed below)

Beam power density W/mm2 ,,,,,,,,,,,,,,,200W/mm2 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,100,000W/mm2 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,200W/mm2

Beam to metal energy efficiency,,,,,,,,,,,,, 75%,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1 to 10 % (excluding steal 98%) ,,,,,,,,80%

Beam defection rate 1m3 build,,,,,,,,,,,,,,, 0.1 m/s mechanical ,,,,,,,,,,,,,,,,,,,,,200m/s mechanical mirror ,,,,,,,,,,,,,,,,,30,000m/s magnetic deflection

Metal Mass deposition rate 40µ edge resolution,,,,,,,,,,,,,,,,,,,,,, Not high res. ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0.2Kg/hr ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0.2Kg/ hr

Home Building duration

ie single phase supply of 20cm x 20xm x 2cm part 40µ resolution

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Not high resolution ,,,,,,,,,,,,,,,,,,,,,,,,over a month duration,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2 hrs duration

In summary

man disadvantage,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Low resolution (XY Mechanical ),,,,,,,,, Cost of laser 100K$ 3 phase supply ,,,,,,,,Vacuum chamber

main advantage,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, cheap /Gas ,,,,,,, ,,,,,,,,,,,,,,,,,,,Argon tent not vacuum chamber speed ,,,,,,,,,,, Control, single phase supply

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, No large non self manufacturable bought in item

NB If your happy machining after printing then MIG welder on low resolution Cartesian XY frame is cheap and fast due to wire (3Kg a minuite) which is a good commercial option, but no use in the home setting where other machines and skills to operate them are unavailable. Remember Nasa went vacuum & wire for EBF3 due to Space environments making large/ rough structures (Later ebf3 is also interested in making final / net shape parts with a wire feed process with the addition of one light machining process /e.g. drimmel for smoothing with electron beam subtractive processes ).

(Metal Mass deposition rate low resolution 3KG /hr low resolution wire 3KG /hr low resolution wire 3KG /hr low resolution wire all needing mm's of finishing machining )

Ref. [3] [4]

N:B: "sticky particle" SLS creates weak parts suitable for metal sculptures stc.. and "Fully melted" SLS has the possibility to create full strength metal parts. The term sintering refers to a generic label for all these processes of converting powder in to metal parts, whether the powder grains are just made sticky against each other, so parts are weak and only good for sculptures, or the powder is fully melted so you can have the possibility of creating a full strength part . Confusion around this means that machines are called sinteres which actually fully melt the powder thus demanding a laser above 150W while other cheaper machines also called sinteres with smaller lasers only make weak porous parts suitable for metal sculptures are mistakenly assumed to be the same as the high powered expensive machines with large lasers..[5] 35Secs in they explain this.


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. High power laser SLS can be a "fully melt" process or be a "sticky grain" weak part production process. They are both low force not needing the built part to be specially secured in the machine and therefore low skill.

EBM has some advantages over SLS

  • Wall socket to beam power efficiency for EBM is 85%, for higher power lasers they require up to 10 times more electricity for the same heat in the metal , C02 lasers and ND YAG lasers 10%-30% wall socket to beam efficiency, for fibre lasers and Diode lasers similar to EBM 85%.
  • Beam to heat in metal efficiency is 85% for common metals with EBM but all metals except steel reflect much more of the laser beams energy, eg. 7% laser absorption in aluminum 3% laser absorption in brass, except steal that absorbs 90%.
  • EBM may be able to reach finished parts IT grade 07 ,SLS cannot produce finished parts unless very expensive laser pointing systems are employed. So SLS lacking these highly expensive pointing devices always need further machining, so the 3D printer is not a replacement at all, as you still need all the normal machines ie cnc grinding milling..
  • electron beam melting produces parts that are void-free, and therefore fully dense and full strength, In a SLS machine a laser of over 150 W is needed to produce "Fully melted" SLS , ie full strength parts.
  • EBM does not have the limit of the one expensive bought in item ie "fully melt" SLS ( ie the laser 100K euro Yag 400W)
  • The parts that generate an electron beam are simpler/possible to replicate than the parts to generate a gas based laser beam, (Solid state lasers are extremely difficult) ( Adrian Bowyer" we may never reprap a laser").

  • Electron beam machines do not need any permit from Darpa or its European equivalent, SLS machines which produce full strength parts through fully melting the powder need powerful lasers over 150W which need a permit form Darpa or its European equivalent.
  • ... other advantages ...

(See Below for advantages of SLS over EBM). ( both ebm and "full melting" SLS can vaporize metal subtractively or fully melt powder for additive manufacture.)

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). Also 1mm lead or equivalent metal shielding will be required around the whole machine for xrays produced as the electrons strike the surface.

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[6]. Wikipedia: electron beam welding#In-air welding

A: a couple of mm's

SLS has some advantages over EBM.

  • SLS does not require a high vacuum. It works at normal air pressure , everyone uses argon barrier so get a protective enviroment or otherwise leaves the metal unprotected so metallurgy suffers leading to weak parts suitable for sculptures e.t.c
  • Most plastics, ceramics and lignin can be sintered open-air. very very locally high temp means oxygen react with material. (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. ). In commercial polymer welding single mode diode lasers 8 W are sometimes used.
  • "Sticky powder" SLS demands less development than EBM as lower power laser can be on cartesian axis, the process requires less heat and only makes the powder stick against each other (using lasers less than 150 W where no permit is required).
  • SLS that has a protective environment for metal, and fully melts powder grains together has the potential to produce full strength metal parts, this melting process requires more powerful lasers above 150W up normally 400 Wto 600W, ( Having a externally heated build chamber, which is preheated to 50 degrees below melting point, ( Fiber laser at 100 Watts ). degrees below melt which also require a permit in Europe and USA from Darpa or the Local equivalent agency. This "fully melting" SLS process is characterized by bringing all the metal powder up to 50 degrees below melting point and then apply a powerful laser to finish the melting ( above 150W typically 200W to 400W) .
  • Laser process does not produce X-rays like an electron beam process, The amount of Xray produced is proportional to the voltage applied to the apparatus, So for your your old TV it was at 30KV but as long as you keep the electrons in a box that was no problem. But If you do like those crazy people in hospitals fire them all round the place precautions need to be taken, for a 60KV xray machine 1mm of lead (or equivalent 3mm of stainless steal ) is suggested screening for some one who works with it every day. The Vacuum chamber in a electron beam machine has to be over 8mm thick stainless steal to resist the pressure .

... other advantages ...


(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/residual stresses internal compressive or internal tensile forces from localized heating and thermal expansion in the heat-affected zone of the process, loss of alloy additions giving change in alloy constituent quantities/proportions due to out-gassing, stress/strain/fracture characteristics and hardness.

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.Roughness R<math>q</math> (units nm) is a route mean square of many absolute height measurements, measured in nm, For example a polish surface R<math>q</math> of 3 nm is typical A typical powder printed finish R<math>q</math> of 25 nm

6. porosity

7. limitation on size of manufacturable parts

8. other


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. [7]

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. [8]

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. [9]

On-Line Design Tool: Laser 808 Build Speed Calculator