How subtractive and additive manufacturing create the ideal equation for metal manufacturing
Designing metal parts? By incorporating both CNC machining and metal 3D printing into your manufacturing toolbox, you not only enjoy far greater flexibility in part design, but also gain the ability to procure them in less time and more cost-effectively than ever before. In order to take advantage of this, however, you must understand the shared strengths and inherent differences of each process, and how to best use them to your benefit.
Embracing the Yin and Yang of Metal Manufacturing
Nowhere is this relationship more significant than the bond that exists between CNC machining and direct metal laser sintering (DMLS), the leading technology for 3D printing complex metal parts. The latter can produce virtually any part shape using nothing more than a laser beam and a pile of metal powder, but it can be a slow process. Machining on the other hand is more limited in terms of geometry, but offers far faster production speeds. The choice, then, of which to use is primarily a question of A) can the part or parts be machined, and B) how many parts need to be made?
In many cases, the two manufacturing processes can work together. Examples? Oftentimes metal-based additive manufacturing relies on its subtractive alter ego to finish the job. Holes must be bored or reamed, threads tapped or thread-milled, critical surfaces milled, turned, or ground to size. At the very least, 3D-printed parts need some manual TLC in the form of cleaning, blasting, and support removal, pretty much guaranteeing a visit to the machine shop.
What does all this mean to you or anyone looking for the most effective way to manufacture functional prototypes and lower quantities of end-use metal parts? Plenty. By adopting a strategy where metal 3D printing and machining can be different steps in the same manufacturing process, you can leverage the best of both worlds, eliminating surprises, reducing costs, and improving part design. Here’s a handful of design considerations to think about before diving into your next metal part design project.
Building vs. Cutting Metal Parts
As mentioned at the beginning of this design tip, it’s important to have a solid grip on the processes used to make them. We know this may be common knowledge to many engineers, so bear with us for a few paragraphs.
Of the five additive manufacturing technologies used at Protolabs (which account for the lion’s share of all 3D printing processes everywhere), DMLS is the only one that prints metal. Similar to any powder bed printing process, it uses a laser (or lasers) to fuse flour-sized grains of metal powder within the machine’s build chamber. Starting from the bottom up, the machine fuses one paper-thin workpiece layer at a time, with a recoater blade dragging fresh powder across the top after each pass until the part is complete.
By comparison, machining uses super-hard cutting tools to remove metal, either by rotating said tool against and around a fixed workpiece (milling), or by moving a stationary cutting tool against and around a rotating workpiece (turning).