MetalicaRap
Release status: Experimental
| Description | An Electron beam melting 3D metal powder printer with scanning electron microscope vision (SEM) & EBM/vaporizing Z axis correction in a vacuum.(Design stage).
|
| License | |
| Author | |
| Contributors | |
| Based-on | |
| Categories | |
| CAD Models | |
| External Link |
Contents
MetalicaRap . . .Open Design and Innovation
Essential PreRead; .. Self Replication Engineering Options See section 2. [1]...Factory at home,See [2]
Hi
We are now 3 months in to the development of a printer capable of printing in all common metals, which can largely print itself. Critically it can largely print the most expensive bits including the electron gun ( Equivalent to printing a 600W fiber laser in a Selective Laser Sintering machine).
This gun will point in to a vacuum chamber above a build platform covered in metal powder.
For now the self replication will not include the vacuum chamber as it will be welded from stainless steel plate, the power supply is under construction from bought in parts and the pumps will initially be purchased.
If you would like to help out with general research ; for example currently we need help with;
Could you help us get hold of the dos program EGN2 so we can check our design? (For details see here:[3]need minimum spot size Vs cathode voltage at min vaporising current eg 1mA),
Researching the sourcing of components suppliers for our mechanical or high voltage challenges?
Use your network to help us find more technical specialists, the technical specialists we currently have are very busy people already and needed in electron gun design area.
Follow the links on our website and try out our Design questions !
Help us research the scanning electron microscope signal processing and image processing.
Self study the material science to help us with its development free at [http://www.matter.org.uk/universities.htm ]'
None of the processes in them selves are new , they have all been done in other contexts, what is new is that we have combined them to bring error correction to metal powder 3D printing, enabling low porosity finished dimensional parts production.
For those space buffs, Nasa is also making there own machine but with wire not powder, to use EBM's excellent metal grain control ability to achieve "aeroelastic and acoustic tailoring into aircraft structures" For details see here [4]
kind regards
MetalicaRap team
Philosophy
"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. " [5] Adrian Bowyer
As you can see from the above quote 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 beam source ie laser, Yet an alternative beam source exists the electron beam (EBM), that may offer self manufacture, due to it largely consisting of 3 simple elements; a cathode metal ring, an anode metal tube and a hot tungsten wire.
To manufacture metal parts that can directly "fit" to produce working mechanics is another advantage, in EBM the X and Y axis accuracy is dependent on electrical control rather than mechanical sturdiness giving rise to a inherently stable self reproducibility, On the other hand the challenges of Z axis powder management brings the need for a vision system (SEM) and z axis correction method EBM/vaporization (which is currently in development stage /state of the art on commercial machines.)
Advantages
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)
Self measurement of part tolerances
May offer automatic self correction.
Disadvantages
Vacuum chamber needs on going maintenance.
Quantity and quality of metal/materials used in vacuum chamber construction, Limited outgasing required [6]
Difficultly in managing metal powders, including issues of; flatness of layers, metal powder trapped in work piece( e.g. designed internal closed cavities, designed internal porous structures,) indicated by the need to have layer error correction.
Quality Control - surface quality/polishing methodology , on the fly heat treatment process development (to overcome residual stress left in work piece).
Chamber approx 1m cube rather than desktop size
Main elements
Beyond power supplies, computing power and sensors, MetalicaRap has 5 elements; electron gun, high Vacuum chamber, roughing pump, oil diffusion pump or turbo pump and metal powder dispenser/build platform.
Design Discussion
6KW 100 KV hot cathode gun
High vacuum chamber (initially welded)
Stainless steel High vacuum 10-5 Tor / (mm mercury) NiCr Alloy (10-16) Hexagonalx40 halfhexagonalx16 endpiecesx16 384 bolts copper wire, future ; airlock so print while repump, main door Viton O ring (Euro ).
Vane pump ( initially purchased)
Oil diffusion pump or turbo pump
using existing EBS build design or Turbo pump initially purchased.
metal powder dispenser / build platform
options include ; screw/ trough design; Wiper deposit ; Metal Vapor protection Gun protection disc SEM pickup,& wiper protection
Power Supply Power Supply with Arc sense arc quench arc count.
Back ground Information on Electron beam processes; electron beam welding / vaporization EBM(1), EBM 3D printing(2),
Scanning electron microscope SEM background(3)(4).
Essential External links follow these first
1. http://www.twi.co.uk/content/spasaug2006.html
2. http://www.arcam.com/technology/ebm-process.aspx
More technical sites
3. http://www.matter.org.uk/tem/sitemap.htm , 4. http://www.uga.edu/caur/semindex.htm
General background Videos EBW see here [7]
Design criteria ; Design a Metal 3D Printer , that produces dimensionally finished parts +- 20 µ m over 20mm, metallurgy equivalent to wrought iron milled metal parts, largely self reproducing, electrical supply limited to single phase ( ie not 3 Phase,), minimum consumables beyond metal powder ( avoiding need for e.g.argon gas ... etc,),cost for parts less than a small car, build-rate can be slow i.e. .2KG per hour, no bigger than a wardrobe.
Due to lack of control in metal powder deposition & molten metal forming droplet/distortions in conventional ebeam 3D printing (e.g arcam 3d) a tolerance of 300µ in the Z axis is a typical with 10µ powder,( Lower power sizes 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 round a Vision system using 4-sector, independent channel axial Back Scatter electron detectors (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 measurement. Z axis dimensional mistakes in any particular layer can be found and corrected by removal of high points through Electron beam machining / ebeam vaporization of the metal. This brings the XYZ axis to 20µ error over 20mm (IT grade 7 See IT grade table[8] 1.). Future stage in development might include Ion beam etching gun to take dimensions to sub µ level(1µ over 20mmIT grade 0). external links 1.http://www.engineersedge.com/international_tol.htm
Self replication
Self-replication of a vacuum chamber runs into the "how to make a match box inside a match box problem". Some say the "lots of small rigid parts joined together" approach -- illustrated on the right -- has "too many joins" for a vacuum chamber. Would a relatively soft material in the gaps between parts -- like the Pb lead between parts of a stained-glass window -- compress enough to make it air-tight? Normally use copper wire to make up "CF flange".[9]
As the main consideration is avoiding non MetalicaRap conventional machining, can you make the copper wire pinch/seal of a CF flange out of the edge of a purchased plain rectangular plate? Is there a better approach?
NB. It can also weld finished parts together placed in the chamber, the chamber is twice as wide XY as build area approximately, as it needs space for removable metal powder hoppers!, can you use this extra space?,
Chamber 1.3m high, 1m wide, 0.6m depth powder build chamber is 0.3m High 0.3m Bredth 0.3m wide
Door size is up to you, could be a full side eg 1.3m by 1m.
Research Corner Welcomes Your Contribution
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 Questions;
A. Range of achievable spot sizes at target of a Pierce Electron gun running between 100W to 6KW 150KV ? ( given cathode is 1.6m from target max deflection 7 degrees ) ( spot size vs Cathode voltage, ideal guns , for max 60KV and max 150 KV guns)
B. Possible pit falls of running an SEM at 100W in four-source photometric stereo Ruderford back scatter mode ?
(Depth of field of measurements layer errors over 200µ height, typical SEM power is 0.1W. Future development issues, SEM measuring absolute distances over a 300mm depth of field in FIB mode )
C. Target metal surface temperature measurement would be a big advantage, Do you know of a electron bombardment based remote temperature measurement approach?.
Design question feed back / discussion. Add your ideas here!
For tracking the process we need help with the following Computer Simulation model's ;
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 ( energy input). Considering the following 4 situations conduction rates ; 1. Metal powder & solid metal volumes experiencing direct electron energy deposition (i.e. heat around electron penetrated regions, the depth of these volumes increases with Cathode Gun Voltage KV & vary with metal type ) see electron penetration model [10], 2. solid metal thermal conduction volumes ( the completed elements of final metal part under construction) , 3. metal powder conduction volumes ( the surrounding powder) , 4. 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 to be raised by 1 degree K (the metals specific heat capacity) from a distant energy source, 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, (this is called the thermal conductivity). 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. [11] [12],
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 resolution ( lens adjustment can alleviate. See lens simulation [13]), yet also the higher cathode voltage the faster the electrons go, so the deeper the electron energy deposition/giving rise to deeper vaporisation holes giving less vertical Z resolution, (used during Z axis error correction mode ). Also surface tension is correlated with temperature working in opposition to wetting effect flattening the metal blobs. See cathode simulation models [14] or[15]
MetalicaRap Construction; Physics Principles/Disscussion. .Metallurgy Disscussion. .High Voltage Disscussion
Metal Powder Printing; Powder issues
Current status
Based in Copenhagen Denmark Electron gun test repstrap vacuum chamber including pumps and gauges under electrical maintenance.
We are particularly looking out for Metallurgists/Material Scientists, High Voltage Engineers and electron gun designers/support (Electron beam welding/accelerator) .
Get involved! the current team donate there free time, Current tech team; 2 software developers, 1 Ultra high vacuum metal deposition specialist, 1 material scientist , 2 High voltage system designer and 1 mechanical Design Engineer.
Do get in touch
Related Projects
Specialist Parts Chamber CF flange Electrical connectors, 1x 140KV 2KW , 2x140kV low current, 8x 30A 200V? coils , 8x SEM pickups low current low voltage,
2 windows
3x 12mm Motor shaft Vaccum chamber motion feed through. 10-5 Tor
Future Development .....Green Tech..... Focus on products that serve the environment
A solar cell production plant design that MetalicaRap will be able to print, that will then utilize MetalicaRap's vacuum chamber and beam for solar cell manufacturing processes of spluttering / pulsed beam deposition, and so produce solar cells at under 11 cents per Watt peak. We have had some interest already!
So Solar cells cost for a family 3 Bed house; Average Electricity usage 4200KW per year, 4200KW/1800= 2.3KW peak solar cell panel required, at 11cents per Watt peak the solar cell's would cost only 253 dollars, though cost of inverter and installation would be an additional to this.
(1KWatt peak solar panel system under 4.9 hours peak sunshine per day gives approx 1800KWh per year )
Focused ion beam / Ion beam etching gun to take dimensions to sub µ level(1µ over 20mmIT0).
Ion Pump to remove waste vaporized metal.
Polishing Plasma through the addition of argon and a defocused beam, polishing out roughness from a typical powder printed finish Rq of 25 nm to a polished surface Rq of 4 nm is possible , there are other low tech polishing methods that may be easier eg. Tumble finishing. EBeam Polishing [16]
Files and Parts
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 depoosition assembled tested. MetalicarapVacuumChamber parts Electron beam sintered by our system. MetalicarapVacuumchamber assembled tested. 5 Elements assembled and tested.
Downloads
Photos and Drawings
More Examples
Practical manufacturing walk through
Given Electricity is 2kwh per hour .5Euro/hr
Part A Stainless size 300x300x200mm 15Kg
10µ Stainless powder (40Euro/kg) melt print 100µ Z layer thickness
1 minute per Z 100µ each layer heated melting-point – 20 0C then printed by beam
3.4 minute per Every 10th layer Z axis correction ; SEM ( part assumed to occupy 1/9 of whole print area; 1/9* 300*300=10 000mm2 measurement at every 10µ, SEM picture 500x500 pixel so 5mmx5mm, So for 10,000mm2 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 ( Risk of underestimate factor x100 ) 1.4min
Remove metal by Vaporization 1ms per 70µ diameter spot area 4000x10-6 mm2 ( 850µs duration & 150µs beam movement) 1/10 of part high(Risk of underestimate factor x2) ( 1/10*10 000mm2/ 4000x10-6 mm2= 1x105 spots 1x105 spots*1ms= 100Sec 2min Time so far 200* Z correction layers 3.4 Min each + 1800 printed layer 1min each = 2480 min ( 1.7 days)
To add a 40mmx4mm = 160mm2 bearing surface by removing up to 40µ to achieve 0.1µ specification Ion beam abrasion 20min per 1mm2 160*20min =3200min
Time total so far 200* Z correction layers 3.4 Min each 1800Min + 1800 printed layer 1min each 1800 = 2480 Min + ion beam bearing surface 3200= 5680( 4 days)
Cost 665 Euro materials 600Euro Electricity 65
Part B Aluminum size 300x300x20mm 1.5Kg
Aluminum 15Euro 10µ powder, melt print 100µ Z layer thickness
Time 20* Z correction layers 3.4 Min each + 180 printed layer 1min each = 248 Min 4 hours No ion beam abraison Cost 25 Euro materials 22 Euro Electricity 3 Euro
Powder
injection molding powder
Aluminum powder 15 Euro/Kg 10µ
Carbon chromium 40Euro a kg. 74µ
Stainless powder 40Euro/kg 10µ
Useful links
EBM introduction [17]
Images EBM / EBW [18]
General background Videos EBW see here [19] EBM technical background lecture See here [20]
Discussion of Advantages and Disadvantages of different Tool head processes.
