Selective laser melting (SLM) for metals is a process that I find to be very exciting. It is a direct manufacturing method that I hope could someday become a very common means of parts creation. For now it remains a developing form of rapid prototyping.
Like all modern rapid prototyping processes, a 3D CAD model is sliced into hundreds or even thousands of 2D layers from the bottom up.
In SLM, a bed of metallic powder has it’s top surface melted by a laser beam that is projected from above as it solidifies each 2D layer. The powder-bed then drops down by a measure of one cross-section layer thickness. It is followed by an automated rake that smooths a new layer of powder over the top of the previous layer. The laser then melts a new cross-section and the process repeats. The finished product is a solid metal part (comprised of hundreds or possibly thousands of thin layers) with excellent densities sometimes even superior to parts produced by traditional methods.
In my opinion the greatest benefits of SLM are:
- Finished parts are nearly 100% dense and have strengths comparable to original raw materials.
- Almost zero material is wasted. (In traditional machining a significant portion of raw material must be carved away to produce the finished part.) In SLM, whatever powder that wasn’t solidified remains in the bed for reuse.
- Shapes that cannot be produced by any conventional methods can be produced via SLM. (For example a one-piece steel mold with a looped internal cooling channel.)
- Test alloys can be utilized directly within the prototyping equipment. The powder-bed technology utilized by SLM allows for quick and cheap powder metallurgy. The alloy can be easily and inexpensively adjusted by changing the ratio of elemental powders located in the powder-bed. In traditional metallurgy, an custom alloy must be melted, cooled, and shaped via a variety of processes to produce usable test material. This method requires a significant amount of time and comes at a high cost.
In my opinion, the current drawbacks of SLM are:
- SLM is a little known process, more attention will increase demand and help to improve the methods.
- SLM parts have a coarse to grainy surface finish. Secondary machining or polishing processes are often necessary to produce usable parts. I believe an SLM machine should be developed that contains a high-speed integrated CNC vertical milling head. This would enable beautiful and high-precision parts to be printed directly in solid metal!
- SLM takes too long to compete with mass production methods. This is the number one area that I feel has room for improvement. If this technology could be developed so that large, complex, precise parts could be quickly and efficiently produced directly from CAD models, all other processes would be redundant!! I am a traditional manufacturing professional who would love to be able to simply design a 3D CAD model, send it to my equipment, and walk away.