Machining “Bones”

The potential of rapid manufacturing was recently demonstrated by Seco Tools Inc. (www.secotools.com), a provider of various types of cutting tools for metal removal operations.  Working with Capture 3D (www.capture3d.com), Tebis (www.tebis.com), and GF Agie Charmilles (www.gfac.com), Seco engineered a process to produce a miniature-scale human skeleton from 6 x 12-in. aluminum billets.  Including the roughing, semifinishing, and finishing of the model—and realize that they’re removing about 80% of the total volume of material to get to what they affectionately call “Bones”—it requires about seven hours.

To begin the process, they used the Capture 3D white-light scanning system to obtain information about the original model.  Given the size of the object scanned, the tolerance was on the order of 0.001 in.  That scanned information, in turn, was used to generate an STL model.  The STL model was then converted into a solid model, and tool paths were generated with a Tebis computer-aided manufacturing (CAM) software system.  This data was used to drive the Agie Charmilles Mikron UCP 600 Vario machining center.  The machining center features a rotary tilting table so it is possible to get the workpiece located so that the spindle can readily machine the tibia and fibula and whatnot of Bones.  (Actually, it would actually be able to make full-sized bones, given that the work envelope is 23.62 x 17.72 x 17.72 in.)  The machine is fast.  It comes standard with a 20-hp, 12,000-rpm spindle; it is offered with an optional 40-hp spindle that operates at up to 20,000 rpm.  The X, Y, Z axes rapid moves are up to 22 m/min; the maximum acceleration is 0.6-m2.

In all, there are 10 Seco tools involved in actually machining the model.  Of the 10, nine are Jabro endmills that are specifically engineered for high-speed machining of materials including aluminum.  The smallest tool has a diameter of just 0.008 in.

Because the model has some rather thin bones (as thin as 0.002 in.), and because fixturing the part is tricky, it was determined that machining would be performed starting at the skull and working its way down to the phalanges.

While this is a compelling demonstration of micro-orthopedic machining, presumably it is an indication that there’s potential for quickly producing precise metal replacements for organic elements (a.k.a., bones).