Do you worry about a part exploding when you are machining it? Probably not if you are working with parts that are casted or forged. But in DMLS processes where metal powders are being handled, it is difficult to avoid the danger of explosions, especially during postprocessing.
Even after removing the part from the build chamber and cleaning it, trace amounts of powder feedstock is still expected to be present. Many people overlooked that support structures of metal parts are often hollow, which traps metal powder inside.
Submerged-wire EDM is often used because the trapped powder is released into the atmosphere when support structures are removed from the build plate. Although this subjects the machine to higher wear and tear, it releases much less powder into the air.
Other cleaning operations to remove the trapped powder trapped may be used instead. It might seem simple to vacuum the metal powder, but it’s not easy with loose, unsintered particles (and partly sintered material after stress-relief treatment) that are sticking to the inside walls of the supports. In many cases, after vacuuming, more loose powder can still be removed by tapping, shaking, or vibrating the part. This is not a reliable way to clean the part, and more research is needed to find out if blasting, peening, or chemical polishing is more effective.
Meanwhile it is very important to use generous amount of lubricant during machining, so that loose powder is washed away and the risk of sparking minimized. You may also wish to install filters that can capture these particles, which are much finer than the swarfs from a machining processes.
Removing Metal Supports from DMLS Parts
After completely removing metal particles from DMLS-built parts, what is the best method to remove the metal support structures? Since these support structures are made up of the same material as the part itself, you might machine the support structures away from the part in the same way as you would machine another part made from the same material, be it a nickel alloy such as IN625 or a titanium alloy such as Ti6Al4V. But this may not be the best method for two reasons.
First, objects are constructed in traditional manufacturing by successively cutting material away from a solid block of material. In additive manufacturing, however, objects are constructed by successively depositing material in layers until it becomes shape you want. Consequently, both parts will be different, even after heat treatment, aging, and solution-annealing for the desired properties. In a nutshell, you don’t know exactly what material you are working on when post-machining the part.
Second, support structures are usually hollow. When machining one, you will first cut through a thin wall; next, air; and finally, a thin wall again. So, it is easy to crush the supports instead of removing them. Or perhaps tear the supports away instead of making a clean cut.
In conclusion, machining away metallic supports remains a challenge for DMLS manufacturing. The post-processing work not only has an explosion risk but can also leave marks on the surface, or even damage the area where it was in contact with the support. Support removal may even break the part if its features are small and intricate. It is necessary to spend time studying how to remove support structures effectively.
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