Ballbar for Medical Machine Tools

Nemcomed manufactures approximately 1000 different parts, either implants or the tools used during implant procedures, and it supplies parts to the top orthopedic OEMs. The company makes implants for knees, hips, shoulders, wrists, elbows, fingers and the spine; tools include pliers, cutters and wire cutters. The implants are “family-sized,” with five to six sizes of each part and typical lot sizes are 30 to 40 pieces. Many of the implants have complex features, such as curved or spherical components.

The company also makes proprietary products, developed through internal R&D, and licenses them to customers. Its Flex-Shaft and Self-Retaining technologies, for example, are patented and used in a variety of applications, including spinal procedures and hip, shoulder and knee arthroplasties. The Flex-Shaft is applicable to surgical screwdrivers, taps and drills.

Parts are generally made of stainless steel, titanium or cobalt chrome, and start as bar stock or forgings (implants). Raw materials are processed through a cut-off cell, then move on to a mill or turning center, depending on complexity. “Shortly after receiving the new ballbar, we had a machine go out of spec so we tested it, as well as having the laser interferometer folks come in and test it,” explains Arnold. “Our results were identical, so we learned then the ballbar would allow us to test our CNC machines quickly and with an extraordinary level of confidence.”

This ability to test quickly and accurately led to the acquisition of a large, quality-focused customer that required verification of machine calibration. “The expense of bringing in the laser interferometer for every machine would have made it cost-prohibitive to supply this customer with parts,” states Arnold. “We showed the customer the results of the ballbar and interferometer tests, and they agreed that ballbar testing would meet their verification requirements. Basically, the QC20-W paid for itself after testing just two machines.”

The new ballbar design brings the unique advantage of testing in three orthogonal planes through a single reference point, with a single setup, which allows the accompanying software to produce a representative measurement of volumetric positioning accuracy by correlating all three. Arnold explains that this benchmark of volumetric accuracy is valuable to Nemcomed because positioning errors can be compounded by simultaneous multi-axis motion during contouring. (Note: Volumetric accuracy is also important with large machining volumes and parts, where tool path deviation is amplified across longer machine travels.)

In August 2010 Nemcomed completed a 10,000 sq ft addition to its Fort Wayne plant to consolidate another plant’s operations and add space for five new Citizen Swiss machines and a 5-axis Fanuc Robodrill to complement its lineup of Mori-Seiki and Mazak 5-axis mills, Fadal 3-axis mills, Brother and Fanuc wire EDMs, and a Samsung 3-axis lathe. The plant uses the ballbar on 20 machines, including all of its CNC mills and wire EDM machines. Maintenance engineers monitor results in a predictive maintenance program, tracking a 3-month timeframe for early detection of errors for optimum efficiency in scheduling maintenance and repairs.

The ballbar comes with a system case with spaces for the most popular accessories making it easy to transport. “We can take it to any of our four global manufacturing facilities, set it up quickly and get the machine qualifications we need,” states Arnold. “Knowing the machine’s capability before it cuts parts allows us to minimize scrap and machine downtime. That gives us high part-quality and productivity while keeping manufacturing cost down. It’s what lean manufacturing is all about: greater customer value.” The company completed another 14,000 sq ft expansion in November and as it continues to grow, Arnold said the use of the ballbar will grow with it.

Nemcomed, Inc., 8727 Clinton Park Drive, Fort Wayne, IN 46825, 260-484-1500, www.nemcomed.net.

Renishaw Inc., 5277 Trillium Boulevard, Hoffman Estates, IL 60192, 847-286-9953, Fax: 847-286-9974, www.renishaw.com.