Two manufacturers,common goal

After machining, the femoral knee component is hand-polished to a mirror-like surface finish so fine that the part can only be handled with gloves.

Brown Precision Inc. (BPI) in Huntsville, AL, wanted to expand into the medical market the“right” way. Fortunately, information the firm had learned in machiningfive-axis aerospace parts served it well in cutting complex medicalparts from forged stainless steel and titanium.

Onejob involved making a plate from 316 forged stainless steel to holdtogether broken bones. Some of the plate holes were 90° from eachother. The plate had many free-flowing surfaces, curves, varying anglesof holes, and threading inside holes. Making matters worse, surfacefinishes inside the holes had to be free of tool marks.

Usingan older machine, it had taken BPI several setups to get the bone plateright. So the company purchased a Makino a61 horizontal machiningcenter, which can do the part in one setup. The five-axis capabilitiesmade it easy to get into tight spots at tough angles on the precisionparts. As a result, the shop gained a 40% improvement in cycle time.

The femoral knee component’s smooth, sweeping geometries provide greater flexibility in the body, but make it difficult to machine the part.

Another manufacturer, FPD in McMurray, PA, needed capabilities to produce a femoral component fora well-known artificial-knee system. The part, made of cobaltchromium-molybdenum alloy, includes difficult geometries, especially inthe deep patella groove. It must be precisely machined to reducecontact stresses against the tibial insert.

FPDworked closely with Makino's Engineering Services with the goal ofidentifying a manufacturing process that accurately machined the entireoutside surface of the knee component in one operation. The finish hadto be 16 Ra and the cycle time less than 40 min/part. The solutioncombined an a61 machine tool, carbide endmills, shrink-fit holders, anda Parlec tombstone vice.

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