Rapid Prototyping Provides Speed, Cost-Effective Castings.

Based in Warsaw, Indiana, Biomet, Inc., designs, manufactures and markets products used by orthopedic medical specialists in both surgical and non-surgical therapy. In these products, it uses up to 1000 castings/month. Although a majority of these are traditional investment castings, up to 60/month are implantable castings produced via rapid-prototyping using an ABS pattern built by a Stratasys FDM rapid prototyping system. These prototypes then are invested in the ceramic slurry that forms the mold in which molten metal is poured. The prototypes enable Biomet to produce a casting in less than 2 weeks.

Biomet currently uses the rapid prototypes to verify existing designs before high-scale production, but also to speed its time-to-market. Initially, the firm saw rapid prototyping as a way to facilitate quick, inexpensive castings. "The idea of going from a wax pattern to an investment casting was the basis of our cost justification of the rapid prototyping system," said John McDaniel, supervisor of engineering services at Biomet.

Biomet had previously used an outside service bureau for its rapid prototypes, but it was costing the firm $300-400/part and $180,000/year and the turnaround time was 1-2 weeks. The firm then would have to send the prototypes off to its captive foundry to produce the cast components. By deciding to purchase a rapid-prototyping system for in-house use, the firm has reduced its costs to $ 120-125/part and is saving up to $120,000/ year factoring in the overhead for the systems. In addition, it can have prototypes for making a mold and casting in days.

To build the prototype, Biomet uses a .STL file. "When I have a part I need cast, I take a sketch or an .STL file to our foundry and get their input on gate locations," McDaniel notes. "Sometimes it'll even indicate where the vents should be." Biomet then builds the gating and vents into the CAD solid model, saves it as a .STL, then imports it into another software program specific to the prototyping equipment.

Once built, the prototype's surface finish is smoothed before it is shipped for casting. At the foundry, the prototype is treated just like a normal wax pattern used for investment casting. "We use seven or eight coats of ceramic," indicates McDaniel. The ceramic shell and pattern are put in a furnace at 1900F to burn out the pattern and then the finished shell is cast with cobalt or stainless steel.

Biomet typically builds three prototype iterations of an implant prior to casting to ensure the design's accuracy. From design to casting, Biomet can complete an implant in as little as 2 weeks using FDM patterns. "If we didn't have a queue of parts on our FDM machines and at our foundry, we could get a casting even faster than 2 weeks," maintains McDaniel. "But the machines are always running, so we sometimes have to wait for the next build to get patterns made."