New from the Fab Labs: Lightweight but Superstrong Parts

A rapid-manufacturing technique fabricates 3D-lattice structures that can replace solid metals and even encourages bone ingrowth in medical implants. By Leslie Gordon, Senior Editor How often has one of your designs been a trade-off of weight versus strength? Too heavy, and you waste material. Too light, and parts might fail. Hold on to your hat. A new technology fabricates components that are strong and lightweight. Called electron beam melting (EBM), the technique shoots electrons moving at half the speed of light onto powdered metal to melt and weld the material, one layer at a time. As with any other additive method, EBM builds parts that can fill arbitrary volumes. It suits jobs demanding costly materials where machining would leave expensive chips lying on the floor. EBM is also a great way to generate so-called “lattice structures” or arrangements of repeating patterns with engineered stiffnesses. There is often no other practical way to fabricate some of these geometries. Lattices are of interest to aerospace because they provide lightweight yet strong components. And in the medical area, lattices can replace material in implants. The resulting structures cost less as well as help facilitate bone ingrowth. In general, lattice structures can reduce weight, transfer heat, absorb impact, dampen vibration, and be engineered to a specific stiffness. Electron-beam machines (e-machines) have a build envelope around 200 200 180 mm and a build platform usually made from stainless steel. Since the melted parts have a different thermal expansion than stainless steel, they just pop off with no need for cutting or sawing. Titanium and cobalt-chromium alloy work well with EBM and there is a continuously growing list of other materials that work as well. Arcam AB in Molndal, Sweden, which invented the technology, says its versions of the alloys show no remaining layering effects or weld lines from the build process and that material microstructures still feature a normal grain structure. “Lattice structures are actually any porous geometry or what we call nonstochastic foam,” says Denis R.