Materials

Insert produced by selective laser melting (SLM).	Test part formed by ProMetal process, based on Three-dimensional Printing.	Steel test part formed by electron beam melting process.
(Courtesy, MCP-HEK Tooling GmbH, Germany)	(Courtesy, ProMetal Div. of ExOne Co.)	(Courtesy, Arcam AB, Sweden)

Selective laser sintering (SLS) offers two basic choices, which can be rudely described as soft and hard. The particular materials used are exclusive to each of the two competing SLS manufacturers in the market, EOS GmbH (Germany) and 3D Systems. Soft material is represented by a bronze alloy system from EOS. The hard materials are steels from both 3D Systems and EOS.

Both EOS's bronze alloy and steel materials can be used without secondary thermal burnout cycles, although they require finishing operations. The bronze alloy is a complex material that is designed to limit dimensional changes, shrinkage and internal stresses, but a porous part is produced and it may have to be infiltrated with an epoxy or another metal before it can be used. Hundreds to low thousands of plastic parts can be produced from such molds.

3D Systems uses metal powder particles that are coated with a thin polymer layer in their process. The polymer is used to form temporary bonds between particles by the use of a relatively low power laser resulting in a "green" part. This green part then undergoes a thermal burnout cycle to sinter it and infiltrate it with bronze to make it fully dense. EOS sinters their steel material directly in the rapid prototyping machine using a higher power laser resulting in a part that is 95% dense without added thermal cycles. In both cases, substantial secondary finishing is likely to be required. Hundreds of thousands of parts can be produced from these steel molds.

Titanium engine valves fabricated with laser engineered net shaping (LENS ®).	An injection mold fabricated with laser engineered net shaping (LENS ®).
(Courtesy, Optomec Design Co.)

LENS ® (Reg. trademark of Sandia National Labs. and Sandia Corp.) and other laser powder forming processes offer the direct fabrication of fully-dense steel parts. AeroMet's Laser Additive Manufacturing (LAM) process was mainly aimed at producing large parts from reactive materials such as titanium, but the company has become inactive. Final machining is necessary before parts can be used.

Three dimensional printing (3DP) is also being used to make steel parts. Extrude Hone's ProMetal process requires similar thermal cycles to selective laser sintering (SLS) to consolidate and infiltrate the parts to final density. Finish machining is also required.

Arcam AB (Sweden) is introducing the Electron Beam Melting (EBM) process. It's a powder-based process having a lot in common with selective laser sintering (SLS), but replaces the laser with a scanned electron beam and produces fully-dense parts. Two types of steel are available at present. As with other processes, the parts require some final-machining after fabrication.

Complex, metal injector component fabricated by EFAB technology, and original CAD representation.
(Courtesy, Microfabrica Inc.)

Microfabrica Inc. (formerly MEMGen) offers a process that can produce very small metal parts in large volumes. The initial material offered is nickel, but in the future the technology may be able to offer any material that can be plated. The process was introduced commercially in 2002 and is based on EFAB technology developed at the University of Southern California.