One of the major metal additive technologies is known as Powder Bed Fusion. This technology builds parts in the following manner: A layer of fine metal powder is spread across a machine bed. One or more lasers move across the bed, fusing sections of the powder to the layer beneath them in a specific pattern. The process repeats layer by layer until the entire part is built. Un-melted powder is removed to reveal the finished parts on the build plate.
Powder bed fusion is known by a number of trademarked acronyms including Direct Metal Laser Sintering (DMLS), Selective Laser Melting (SLM), Direct Metal Laser Melting (DMLM), and Laser Cusing. However, the process is essentially the same; the same lasers and the same basic melting process, the major difference is the marketing behind the name.
The process is essentially the same. There are differences in how the machines for this process are designed and operated.
For the most part, powder bed fusion machines follow the industry standard build size of a 250 mm x 250 mm platform with a build height of 250-300 mm. But larger build sizes are available. Vendors will recommend that engineers read the specs carefully to find the differences in build envelop size.
All vendors are developing methods to increase the speed of a build to produce more parts. Build time is probably the most typical reference point for comparing machines, even though a range of factors influence overall system throughput. Speed is affected by the following factors:
–How the powder is spread onto the build tray. Depending on system design, powder can be spread in both directions or only in one direction. Feeding powder in both directions can save hours of production time. A single build can contain 10,000 layers and “wasted” seconds on each layer add up quickly.
–Laser configuration. Lasers are the heart of the system, so, theoretically, the more lasers, the faster the machine can produce more parts. Several metal additive systems use at least four lasers. In some cases, each of these lasers is used to build one complex part. In other cases, each laser is building one part for a production of four parts simultaneously.
–Material feed into the build chamber. Consider whether the material is fed continuously or in a batch process. Batch fed systems can require the machine to be interrupted to refill supplies during a run, which slows down the process.
While there are more questions to consider in the purchase of a metal additive manufacturing machine, one more important factor should be considered. Can I use new or different materials?
The answer depends on your expertise with the additive system. Initially, it can be best to use materials and parameters supplied by the equipment supplier. Once you are familiar with the technology, then it’s time to discuss materials with potential suppliers. For example, if you wish to use a custom blend, will the material supplier share your experience with others? What are their business practices and how might they affect you?
Will you have access to machine operating parameters to alter them if needed? If you are going to explore new materials, you will almost certainly be developing and enhancing operating parameters. Not every manufacturer will make parameters available.
