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Direct Metal Laser Sintering (DMLS) - How it works
CRDM currently run two Direct Metal Laser Sintering (DMLS) EOS systems, the EOSINT M 270 and the EOSINT M 250 Xtended. Both systems rely on the rigidity of a steel plate (of various thicknesses ranging from 13mm upto 45mm) to anchor the part/insert to whilst building. The first layer of metal powder is fused or bonded to the build plate, using a 200w Yb-fibre laser, in the case of the 270, or a 250watt CO² laser on the 250. Due to the heat generated during this process, dense tooling inserts built without a base plate would be prone to distortion due to differentiating rates of contraction. On building DMLS parts the software allows for a support structure to be built between the model and the plate to allow for removal, similar to SLA modelling.
In operation, the pneumatic ram of the delivery chamber rises to allow a chosen layer thickness of powder, ranging from an adjustable 20-60 micron range, to be evenly spread across the plate by the paddle. The laser beam, guided by a computer driven optic, then fuses this layer to the previous layer. As the process is repeated the sintered tool or component gradually lowers layer by layer in to the build chamber until it is completed. Finally, the excess powder is brushed away to reveal the finished sintered part.
Please see data sheets for the Nickel-Bronze, Stainless Steel and Cobalt Chrome materials currently available.
DMLS parts made from any of these materials can be welded, machined, micro shot-peened, polished and coated if required. Unexposed powder can be reused without restriction or refreshing.
Stainless Steel 17-4
EOS Stainless Steel 17-4 is a pre-alloyed stainless steel in fine powder form. Its composition corresponds to US classification 17-4 PH and European 1.4542 and fulfils the requirements of AMS 5643 for Mn, Mo, Ni, Si, C, Cr and Cu. This kind of steel is characterized by having very good corrosion resistance and mechanical properties, especially excellent ductility in laser processed state, and is widely used in a variety of engineering applications.
Cobalt Chrome MP1
The chemistry of EOS Cobalt Chrome MP1 conforms to the composition UNS R31538 of high carbon CoCrMo alloy. It is nickel-free (< 0.1 % nickel content), sterilisable and suitable for biomedical applications. The laser-sintered parts are characterized by a fine, uniform crystal grain structure. They fully meet the requirements of ISO 5832-4 and ASTM F75 for cast CoCrMo implant alloys, as well as the requirements of ISO 5832-12 and ASTM F1537 for wrought CoCrMo implants alloys except remaining elongation. The remaining elongation can be increased to fulfill even this standard by hot isostatic pressing (HIP).
DirectMetal 20 (DM20) Nickel-Bronze
DirectMetal 20 is a very fine grained bronze-based metal powder. The resulting parts offer good mechanical properties combined with excellent detail resolution and surface quality. The surfaces can be easily post processed by shot-peening and can be polished with very little effort. The specially developed DMLS powder mixture contains different components which expand during the laser-sintering process, partially compensating for the natural sintering shrinkage and thereby enabling a very high accuracy to be achieved.
This material is ideal for most prototype injection moulding tooling applications and for many functional metal prototype applications (DirectPart). It offers the highest building speed so is particularly suitable larger tools and parts. It also offers a very broad window of useable process parameters, e.g. a wide range of achievable mechanical properties and build speeds. Standard parameters use 20 micron layer thickness for the skin a 60 micron layers for the core, but for faster building the entire part can be built in 40 micron layers for the skin and 80 micron for the core, or even 60 micron layers for the skin and core. Using standard skin parameters the mechanical properties are fairly uniform in all directions, which is especially beneficial for many DirectPart applications. Parts built from DirectMetal 20 also have good corrosion resistance. Typical applications for DM20 would therefore be injection mould tooling for moulding up to a few tens of thousands of parts in all standard thermoplastics using standard injection parameters. And also the direct manufacture of functional metal prototypes. |
