Rapid progress

One of the world's largest producers of implants and instruments for spinal surgery, DePuy Spine of Raynham, Massachusetts, is dramatically reducing lead times for making new and customised equipment for minimally invasive surgery (MIS). It follows the adoption of additive layer manufacturing by laser-sintering powdered metal, a technique developed by German company EOS. MIS is one of the fastest-growing areas in treatment of the spine, leading orthopaedic surgeons to demand increasingly sophisticated surgical instruments. They must exhibit improved access and control through smaller incisions, have sufficient strength to cut through cartilage and bone, and be made from materials that are biocompatible. The traditional process of prototyping, design revisions, materials selection, cadaver testing and manufacturing normally results in a lead time of many months. This has been considerably reduced by using an EOSINT M 270 Direct Metal Laser Sintering (DMLS) machine that fuses successive layers of stainless steel to produce the instrument directly from a CAD model. DePuy Spine makes more than 70 products with tens of thousands of product codes that are distributed globally from the US, UK and Switzerland. In the first year of using its M 270 DMLS machine, DePuy processed 2,000 prototype parts, including benders, extractors, surgical screws, clamps and reduction devices. Staff team leader Peter Ostiguy says delivery times for surgical tool prototypes have shrunk from months to less than a week, in some cases. He states: "Laser-sintering is very well suited to our environment, because we need to produce our products quickly. We've really impressed surgeons with our ability to turn around what they're looking for in a short amount of time." Those surgeons' opinions are important, as some of them are active consultants to DePuy throughout the product development process. "We work with the thought-leaders in the industry, many of whom tour our rapid prototyping lab every year, as do other surgeons not on the project teams," continues Mr Ostiguy. "What has cut development time so dramatically is the capability of the M 270 to build multiple iterations of an instrument prototype in a matter of days." The DePuy development team starts with a basic design idea, often making a plastic prototype first on a different machine, and shows it to the surgeons for feedback. After taking on board the comments, DePuy turns to the M 270 to create a metal prototype, if the application is appropriate. The result of introducing laser-sintering into DePuy's development centre has been a paradigm shift in the thought process for designing tools, according to Mr Ostiguy. He says that they are not designing for manufacturability any more, but for functionality. Previously, during the design process they were constantly thinking about how they were going to make the part within process limits. With laser-sintering, that no longer matters. DePuy recently purchased another M 270 for manufacturing parts; this will be dedicated to a single, heat-treatable material, EOS Stainless Steel PH1 (precipitation hardening stainless steel). This material is characterised by high hardness, strength and corrosion resistance, and can be machined, spark-eroded, welded, micro shot-peened, polished and coated, if required. The new M 270 can buld in layers of either 20 or 40 microns (a thicker layer cuts down on run time, a thinner one provides finer detail) and can process multiple materials as well. Although his group is concentrating on laser-sintering PH1 material for now, Mr Ostiguy says that the possibilities are endless for future product development. Article first published in Machinery, April 2009