In a previous article we introduced the various types of Additive Manufacturing (AM) that are being used in industry. One of these technologies, Direct Metal Laser Sintering (DMLS) or more colloquially, “powder bed processes” will be looked at a bit more closely today.
The DMLS process uses a powder bed machine to melt metal alloy powder in layers that typically range from 20 to 100 microns thick. These layers are applied in the shape of the “slice” that is the design for that specific layer of the prospective build. If one was watching this process, one would see the build platform lower before each layer of powder is applied, and see the machine repeat this process hundreds to a few thousand times with different “slices” on every layer until the build is complete.
But, how do you know if DMLS machine is right for your manufacturing process? Let’s explore 6 key considerations you need to thrive with this technology:
1. Create Custom Parts with Excellent Small Details
The only major limitation in DMLS part construction is the build space, so fine details that would take a regular machinist weeks to create in a subtractive process can be built in a fraction of the time. Those small details in design can be made as long as they fit the width of the laser, because of this, it should be no surprise that jewelry and dental implant makers use powder bed machines. Turnaround is quick and multiple customized builds can be made on one platform as long as they fit.
That means that the smarter your design and layout is formed in DMLS the quicker the build is completed as one of the biggest time sinks with this method is the actual powder applicator moving across the build surface for each layer. The actual act of melting the powder is done in a flash.
2. Safety Considerations
It is important to note that there are numerous safety practices that must be followed in order to keep powder bed equipment, material, and personnel safe. The metal powder used in DMLS is a fine particulate that necessitates a respirator any time the powder is exposed to open air. Besides preventing the inhalation of airborne powder, the material also presents a fire risk as powders are flammable, potentially explosive and anti-static and anti-fire precautions must be implemented. An enclosed space in your facility must be dedicated solely to this process to ensure these precautions are met.
3. Quality Surface Finish Allows for Minimal Post Processing
Parts made from this process are roughly the same strength as cast materials. While parts made from DMLS aren’t as strong as those made in subtractive processes, their design benefits generally outweigh those weaknesses. The same can be true for the outside of the material too. Creation of a quality surface finish is where powder bed processes excel over other additive methods. Depending on the use case for the part you intend to build, minimal post processing needs to be done to have a presentable part.
4. Extensive Support Removal
After the DMLS build process is completed, you must extract the build from the remaining metal alloy powder that wasn’t melted. One must first clear the powder away from the build like an archaeologist removes dust from an artifact at a dig – very delicately. Then the build plate must be removed from the machine followed by the removal of the supports from the part. The process is a necessary evil because without supports the part would be fused to the build plate and some overhangs in the geometry would not be possible. Nevertheless, these supports must be machined away or removed by hand depending on the setup. Safety gear may also be necessary to protect the user removing the supports.
5. Creating Unique and Complex Geometry
As we mentioned earlier, DMLS presents the benefit of small details and customization. However, the powder bed process is not just for cosmetics. General Electric famously uses DMLS for their airplane fuel nozzles at a large scale. Since powder beds make parts layer-by-layer, (instead of removing material away from a block of metal), the process allows for internal geometries that would not be feasible in a large industrial setting. This benefit is the backbone of the powder bed process. The only alternative to creating parts of this complexity is a more traditional process that requires an enormous amount of machining time with complex and specialized tools to try and machine the internal pathways. With this in mind, it is easy to see why this technology is the preferred method for complex alloy parts.
6. The Risks of Misapplication
Some of the drawbacks of DMLS include the risks of the misapplication of the powder. An interruption or uneven application can cause incomplete builds. For simple builds this usually isn’t a problem, however, when there is more solid surface area that the applicator must brush over, any imperfection in the build tends to compound and increase the risk of an incomplete build.
This can generally be mitigated by increasing the amount of powder applied, but refinement of the process for each specific build sometimes needs to happen to get the build process just right. It’s rather heartbreaking to be 8 hours in a 12 hour build only to notice a chunk of your part is missing – so you will need to watch this process closely when you start out to increase your chances for success.
When all the risk factors are controlled, DMLS presents many appealing benefits. Powder bed machines can rapidly create prototypes with fine details and unique designs that customized builds require. While the only key limitation of the design is the dimensions of the build space, the safety and process constraints mentioned earlier must be addressed for consistent success. Surely safety and space are always at the forefront, but properly moderated DMLS machines and workflow allows a production process to both decrease production time and increase part complexity, meaning the benefits may make the process and safety constraints worth dealing with in the long run to meet your unique needs.
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Tech Tuesday is a weekly series by TechSolve designed to help manufacturers keep up with emerging technologies and identify ways to translate them into their own manufacturing environments.