Our Insight video series will help you master digital manufacturing.
Every Friday we’ll post a new video – each one giving you a deeper Insight into how to design better parts. We’ll cover specific topics such as choosing the right 3D printing material, optimising your design for CNC machining, surface finishes for moulded parts, and much more besides.
So join us and don’t miss out.
Hi and welcome to another one of our insight videos.
Today we’re going to be talking about one of the most exciting, more flexible and – if I’m being honest – downright coolest production processes out there - direct metal laser sintering, or DMLS.
It may not sound too exciting from the name alone, but DMLS is a technique that allows us to turn one of the basic rules of manufacturing – namely, that as part complexity increases, so do machining and assembly costs – on its head.
Very simply, DMLS is a process for 3D printing metals, and one that helps us to produce tough, metallic parts without having to go through the traditional milling, turning, and grinding processes. It’s capable of producing fully functional metal prototypes and end-use parts, can simplify assembly by reducing component counts, and offers virtually unlimited part complexity with no additional cost.
And if that doesn’t sound exciting enough on its own, it works by blasting bits of metal with a high-powered laser beam.
Come on, that’s very, very cool.
Okay, I should probably go into a bit more detail than “high-powered laser beam,” shouldn’t I?
Well, at a fundamental level, DMLS works by slicing your part models into paper-thin layers and then “drawing” them into a bed of powdered aluminium, Inconel, titanium, stainless steel, cobalt chrome, and other metals using the aforementioned laser. Each powdered particle is melted and fused to its neighbours, one layer at a time until the part is complete.
The result is a fully dense metal product with mechanical strength and fatigue characteristics little different than – and in some cases exceeding – one machined from comparable wrought, forged, or cast material, but produced with minimal tooling costs, significantly reduced setup times, and little waste.
If this is all sounding too good to be true, well, there are a few limitations to the process.
Although the technology produces fully dense parts from high strength, corrosion resistant metals, certain part features are prone to warping and curl if not supported properly during the build process. The design of build supports isn’t something you as a product designer or engineer necessarily need to be concerned with, but you do need to know that some shapes are exceptionally difficult to build, and by altering your part design to avoid them you may find that costs may come down while product quality goes up.
Crossbars and overhangs, for example, can be problematic. Let’s say you wanted to 3D print a capital T out of metal, for some reason or another. You’re going to need some supports for that overhanging top section or it’s going to curl up like a goalpost, and that means adding bits to the build that need to be machined away after. Not impossible, of course, but a little less elegant than we’d like.
Continuing down our letter-printing idea, we also run into problems with capital B, D, R and everything else that has a gap in the middle. Unless you make these pretty tiny – say, with holes the size of a drinking straw – you’re probably going to need supports to keep things ship-shape, and removing them from the inside of a finished part is particularly tricky.
Of course, this is all assuming that we’d print them vertically, like we’d see the letters printed on a page. You could make things much easier for yourself by fiddling with the orientation and laying them all on their backs. This way, all of the letters’ walls would be vertical, with the only support being a series of interconnected vertical braces between the bottom of each letter and the DMLS build plate - picture the scaffolding used to support workers during a building renovation. These are easy to remove once the build is complete, and avoids direct contact with large, flat part surfaces that can warp or damage the build plate.
Another potential limitation is the wall thickness. Anything below about 1mm needs to maintain a height-to-thickness ratio of less than 40:1 or the structure may tumble. On the other end of the spectrum, very thick walls are wasteful and take a long time to build – it’s much better to hollow them out with a honeycomb or lattice structure, reducing material costs and processing time while preserving strength.
Indeed, lattice structures are one of the best tricks up our sleeves. They’re virtually impossible to produce via conventional machining methods but are fairly simple with DMLS, as are treelike structures, gentle twisting seashell curves, and other organic shapes, all of which are cost-effective to produce with 3D printing—all that’s required is a little imagination and the right CAD software.
Right, well I hope you’re all suitably impressed because that’s it for today. We’ll have another video up next week, so I look forward to seeing you all then.
With special thanks to Natalie Constable.