3D Metal Printing is the process by which powdered metals are selectively superheated or "sintered" until they melt and resolidify into a solid, three dimensional shape. A variety of methods for 3d metal printing exist, but the two most commonly seen types are deposition and direct metal laser sintering (DMLS). Deposition or "spray" type printing involves spraying powder into the path of a laser, which can be mounted as a 5 axis head. While this method is relatively faster, the movement of the powder produces parts which are more porous and less accurate, limiting the application of this process primarily to repair work and welding. DMLS printing, on the other hand, is slightly more time consuming, but producing parts with significantly greater accuracy and material properties nearly identical to traditional stock materials, such as 420, 316, and 630 stainless steels, among others. While the material properties my be the same as traditional materials, the process and application of 3d metal printing is quite different from traditional processes, with its own advantages and challenges.
3D Printing, by nature of growing parts from the inside out, is capable of producing complex, internal shapes that are impossible to recreate using traditional methods. That is because traditional, subtractive manufacturing must reach from the outside in, meaning that external structures can impede the tool's access to inner shapes. For this reason, many of today's 3D printing applications involve the production of components that would otherwise be impossible to make, such as 3D conformal cooling channels for plastic injection molds.
The other advantage of 3D metal printing is the consolidation of complex pieces which previously have been made as separate parts. In one instance, a Sodick subsidiary was able to consolidate a 52 part mold into a 3 part mold: a one part cavity and a two part core. The result is a process the significantly reduces the man hours used to design multiple components and set up each process, 52 times.
Just as important as knowing when to use 3D printing is knowing when not to use 3D printing. In general, a good rule of thumb is that if you can easily make something through traditional methods, then there is no reason to move that process to additive manufacturing methods. However, there are some specific things to keep in mind.
Manufacturers considering a switch to additive should be aware of the process's limitations. In addition to the slower process speeds as compared to traditional machining methods, additive manufacturing requires a shift in design considerations. By nature of the process, best results are yielded when overhangs are supported, requiring either added support structures or native design capable of self-support. Whereas a sharp, flat overhang may be more difficult to process, designs implementing a 20-50° angle yield significantly improved overhang processing. In cases where external supports are added to the build, be advised that the best method for support removal is wire EDM. For this reason, it is best to arrange supports in such a way that they are easily accessible to a wire machine for quick removal. Finally, surface finish is an important consideration for 3d metal printing, as the particles of metal powder leave a gritty finish on the surfaces of the completed product. Until recently, parts made in a 3d printer would almost universally require significant post-processing, usually Sinker EDM. However, at IMTS 2016 Sodick released an integrated solution to this problem, the OPM250L.
Sodick's OPM250L solves the problem of surface finish by introducing a 45,000 RPM mill during the sintering process, within the same machine. By combining DMLS printing with milling, Sodick's One Process Machining center produces a finished part without subsequent EDM finishing. The process works by interspersing layers of DMLS printing with HSM finishing. The OPM's 500W fiber laser melts 50µm layers, and after 10 layers or 500µm, the 45,000 RPM spindle will finish the surfaces of these layers, before resuming the next round of DMLS printing. Once begun, the process runs unattended using the tool paths generated via the machine's proprietary OS-FLASH software. Unlike first generation printers, which rely on EDM finishing, the OPM250L is actually capable of finishing internal structures that are unreachable from outside the finished part. That is because the HSM spindle is capable of reaching these structures as they are printed, before they become fully enclosed. With the potential to print and finish complex interior structures, the OPM opens the door to possibilities never available on any machine - until now.