Designing metal parts? By absorbing both CNC machining and metal 3D printing into your manufacturing toolbox, you not only enjoy far greater flexibility partially design but also gain the power to gather them in less time and more cost-effectively than ever before. So as to require advantage of this, however, you want to understand the shared strengths and inherent differences of every process, and the way to best use them to your benefit.
Embracing the Yin and Yang of Metal Manufacturing
Nowhere is that this bonding more important than the bond that exists between CNC machining and direct metal laser sintering (DMLS), the leading technology for 3D printing complicated metal parts. The latter can produce virtually any part shape using nothing quite a beam and a pile of metal powder, but it is often a slow process. Machining, on the opposite hand, is more limited in terms of geometry but offers far faster production speeds. The selection, then, of which to use is primarily an issue of A) can the part or parts are machined, and B) what percentage parts got to be made?
“Machining and metal 3D printing are deep, complex technologies and it only by understanding how each will affect your design project that success is going to be achieved”
In many cases, the 2 manufacturing processes can work together. Examples? Oftentimes metal-based additive manufacturing relies on its subtractive friend to end the work. Holes must be renamed or bored, threads tapped or thread-milled, critical surfaces milled, turned, or ground to size. At the very least, 3D-printed parts need some manual TLC within the sort of cleaning, blasting, and support removal, just about guaranteeing a visit to the workshop.
Building vs. Cutting Metal Parts
As mentioned at the start of this design tip, it’s important to possess a solid grip on the processes wont to make them. We all know this might be public knowledge to several engineers, so bear with us for a couple of 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 that the just one that prints metal. Almost like any powder bed printing, it uses a laser (or lasers) to fuse flour-sized grains of metal powder within the machine’s build chamber. Ranging from rock bottom-up, the machine fuses one paper-thin workpiece layer at a time, with a recloser blade dragging fresh powder across the highest after each pass until the part is complete.
By comparison, machining uses super-hard cutting tools to get rid of metal, either by rotating said tool against and around a hard and fast workpiece (milling) or by moving a stationary cutter against and around a rotating workpiece (turning). There’s much more to the machining process than this micro-explanation, but what’s important to understand immediately is that machining picks up where DMLS leaves off. In other words, DMLS attaches material in single layers. Machining removes material, sometimes in large chunks, but sometimes very lightly so as to achieve fine surface finishes.
Accuracy Considerations for Metal Parts
Although DMLS can create extremely complex shapes that may rather be un-manufacturable, it’s not without its limitations. For starters, significant heating and cooling of the metal happen because the laser does its work, creating internal stresses that have got to be removed via post-build heat-treating. this suggests little to the people designing the part, except that stress relief equates to some amount of part movement and thus some loss of accuracy. this is often one reason—though not the sole one—why even a well-designed DMLS-produced part requires machining of any part feature where tolerances tighter than ±0.003 in. (0.076mm) is required, plus ±0.001 in./in. (0.001mm/mm) for every additional inch of build height.
Finishing Where DMLS Leaves Off
Another reason for combining DMLS and machining is surface finish. On a vertical or level, DMLS produces part roughness about adequate to a sand casting. All other surfaces will see some amount of stair-stepping, an impact that’s largely hooked into how the part is situated within the build chamber. If your part design requires a smooth finish, it'll get to be blasted, sanded, or quite possibly machined. This last part is not any big deal unless your part design involves a fine finish on a surface that the top mill, drill, or turning tool can’t reach. regardless of the case, make certain to call out such critical features on your CAD model when submitting to your manufacture, therefore the features needing secondary processing, including machining, are often identified.
Removing DMLS supports
Support structures should even be considered when designing metal parts in additive manufacturing. DMLS may be a little like building a metal sandcastle—without some seashells and twigs to carry the thing together, the ramparts will fall, and the architraves crumble. With DMLS, scaffold-like supports are needed to stay the semi-molten metal from drooping, curling, or otherwise misbehaving. Oftentimes, these supports are often removed with a Dremel tool, but machining could also be the well-liked method where larger part volumes are involved, or when the workpiece is headed to the workshop anyway for one among the drilling, milling, or turning operations mentioned previously.
Fixturing Printed Parts
Unlike DMLS, which needs nothing quite an easy “build plate” to hold the workpiece through to completion, machined parts must be clamped, bolted, or otherwise securely fixtured to the machine to stop cutting tool-induced movement. If your 3D-printed workpiece consists entirely of curved, organic shapes (which is one among 3D printing’s greatest appeals), how will the machinist hang on thereto for turning or milling? ask an application engineer, but you would possibly get to design during a pair of parallel surfaces or some mounting holes by which to clamp the 3D-printed workpiece for machining.
Mulling Over Machinability
Lastly, there’s the metal to believe. The lasers employed by DMLS don’t really “care” how hard or tough metal is, but cutting tools sure do. DMLS is understood for its ability to 3D print aerospace- and medical-grade metals like titanium, Inconel, cobalt chrome, et al. , and albeit different laser parameters and build speeds could also be involved, it does so with relative impunity. Machining those self-same metals, on the opposite hand, requires lighter depths of cut, slower speeds, and feeds (a little machining-speak here), and can consume more cutting tools and machining time. to ascertain a board range of metal options for machining and 3D printing, head over to Protolabs’ material comparison guide.
Combining Complex Metal Manufacturing Processes
The overall point is this: you'll actually leverage the simplest of both worlds—3D printing and machining—together for metal parts, but carefully considers the planning options covered during this design tip. Machining and metal 3D printing are deep, complex technologies, and its only by understanding how each will affect your design project that success is going to be achieved. Ask questions, embrace each process, and understand that both are close-knit partners in manufacturing.