The basic fabrication process for SLM and DMLS are very similar. Here is how it works:
The build chamber is first filled with inert gas (for example argon) to minimize the oxidation of the metal powder and then it is heated to the optimal build temperature.
2。A thin layer of metal powder is spread over the build platform and a high power laser scans the cross-section of the component, melting (or fusing) the metal particles together and creating the next layer. The entire area of the model is scanned, so the part is built fully solid
3. When the scanning process is complete, the build platform moves downwards by one layer thickness and the recoater spreads another thin layer of metal powder. The process is repeated until the whole part is complete.
When the build process is finished, the parts are fully encapsulated in the metal powder. Unlike polymer powder bed fusion process (such as SLS), the parts are attached to the build platform through support structures. Support in metal 3D printing is built using the same material as the part and is always required to mitigate the warping and distortion that may occur due to the high processing temperatures.
When the bin cools to room temperature, the excess powder is manually removed and the parts are typically heat treated while still attached to the build platform to relieve any residual stresses. Then the components are detached from the build plate via cutting, machining or wire EDM and are ready for use or further post-processing.
Characteristics of SLM & DMLS
In SLM and DMLS almost all process parameters are set by the machine manufacturer. The layer height used in metal 3D printing varies between 20 to 50 microns and depends on the properties of the metal powder (flowability, particle size distribution, shape etc).
The typical build size of a metal 3D printing system is 250 x 150 x 150 mm, but larger machines are also available (up to 500 x 280 x 360 mm). The dimensionally accuracy that a metal 3D printer can achieve is approximately ± 0.1 mm.
Metal printers can be used of small batch manufacturing, but the capabilities of metal 3D printing systems resemble more the batch manufacturing capabilities of FDM or SLA machines than that of SLS printers: they are restricted by the available print area (XY-direction), as the parts have to be attached to the build platform.
The metal powder in SLM and DMLS is highly recyclable: typically less than 5% is wasted. After each print, the unused powder is collected, sieved and then topped up with fresh material to the level required for the next built.
Waste in metal printing though comes in the form of support structure, which are crucial for the successful completion of a build but can increase the amount of the required material (and the cost) drastically.
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