Last week’s AMUG conference was a great meeting to see lots of the current technology on metal 3D printing. With machines ranging from the methods where parts are made directly by melting the metal particles with a laser, ballistic particle methods where metal particles are blown into the path of a laser or melted then thrown onto a build platform, metal powders with binders that are formed by use of a laser then the bonder burned off and any voids replaced with other materials, and more. The types of machines, the metal suppliers and the technology was new and yet the same as in years past.
Back in 1996, Barbara Arnold-Feret worked with a firm called Plynetics Express exploring the PHAST (Prototype Hard and Soft Tooling) concept where metal particles coated with a plastics binder were sintered with a laser to form green parts. The green parts where carefully removed from the powder bed, cleaned and then the binder burned out by placing the green part into a hydrogen furnace, cycling, then adding a second metal to the graphite crucible to be sucked up into the void created by the burnout of the binder. The development was eventually passed to P & G, who then donated for further research to the Milwaukee School of Engineering. The end goal of the project to develop and commercialize a metal matrix production tool with conformal cooling built into the inserts. The inserts were then used in a MUD base for injection molding. About the same time, development of the 3D Systems KelTool was being evaluated.
KelTool was first brought to market by 3M, and after the purchase by 3D systems, KelTool was an early prototype tooling method. KelTool relied on making a master pattern from which a RTV rubber mold was cast around for both halves of the inserts. After the pattern was removed, the resulting RTV cavities were filled with thoroughly mixed “slurry” of 70% A6 tool steel powder, tungsten carbide powder, and 30% epoxy binder which is used to bring the two powders together.
Once this slurry was cured in the mold, the resulting “green part” was removed and lightly finished to ready the green part for sintering. The green parts are placed into a graphite furnace boat, which is then loaded into a hydrogen-reduction furnace. During sintering the binder material burned off yielding a “brown part” that was including a 30% air space from the burned off binder. The final step filled the open spaces in the brown (sintered) part with copper by the brown part absorbing molten copper which had been placed as copper blanks into the graphite boat adjacent to the brown part. The result was a part comprised of 70% A6 tool steel and tungsten carbide, and 30% copper.
Challenges with both methods included “mass compensations errors.” Simply put, thick walls drew up more copper into the voids than thinner walls, which made predicting tolerance difficult from area to area of the tool. Adjacent features, such as ribs and bosses would also cause nearby walls to sink in towards the boss or rib due to material being shifted away from the thin section to the thicker and more “demanding” area that required more infiltration.
However, with the newer and more straightforward methods of producing metal parts, many of the problems with older methods of building metal tools or parts seem to be lessening. New equipment for building metal pieces is meant to produce prototype metal parts without the expensive and time consuming hydrogen oven. However they all require a gas generator to eliminate the safety hazard of putting a laser into a powder vat. But all in all, the processes are still evolving and “not yet” on the timeline for mass adoption as production technology.
So what were users looking for last week? They were evaluating the ROI, the cost of ownership, the potentials and finally the comparisons of dollars spent on proven existing tech versus unproven and still evolving processes.