Ballbar for Medical Machine Tools

Its wireless operation facilitates use in small machining envelopes and allows fast checks with minimal interruption. Its volumetric accuracy testing adds a new dimension. That’s why this new ballbar technology is “just what the doctor ordered” for medical machine tools.

Ballbar analysis is a proven method for determining machine tool capability and is the most practical, convenient and comprehensive tool for assessing the contouring accuracy of CNC machines. Ballbars have been commonplace at precision machining operations for more than 20 years, but a Midwest-based medical device manufacturer is showing how the latest wireless ballbar technology makes a big difference in doing fast capability checks on small machines, as well as establishing a benchmark on machines’ volumetric accuracy.

Nemcomed, Inc. (Fort Wayne, IN), a division of Avalign Technologies, is a full-service supplier of implants, instruments, cutting tools, specialty instruments, cases and trays for medical device OEMs. Avalign’s strategy is to be a “one stop shop” for OEM providers to the orthopedic, spine and trauma sectors – aiming to supply everything a physician needs to perform implant procedures.

Ensuring that machine tools and processes are capable of producing parts to spec is a goal shared by customers and the company’s 450+ employees, as well as federal regulatory agencies. “Obviously, we have to meet FDA and ISO requirements,” states Eric Arnold, a manufacturing engineer at Nemcomed. “But we also have special customer requirements, as well a personal interest and pride, knowing that our products may end up in someone’s body. As potential patients ourselves someday, we want to make the highest quality parts possible.”

As a manufacturer of medical devices, Nemcomed must comply with both the FDA 21 CFR Part 820 Quality System Regulation and the SO 13485 Medical Device Standard. To qualify machines, the shop had been using a traditional wired QC10 ballbar from Renishaw. “We test the X-Y, Y-Z and X-Z planes and the QC10 required a setup for each, so our setup time was about 1.5 hours,” explains Arnold.

The company acquired a new QC20-W wireless ballbar from Renishaw Inc. (Hoffman Estates, IL) in 2010, which immediately had positive impact on part quality and the company’s bottom line. The new ballbar retains the principle of using a CNC circular program and powerful software to quickly diagnose and quantify machine positioning errors including servo mismatch, stick-slip errors, backlash, repeatability, scale mismatch and machine geometry as well as providing an overall circularity error value.

It also adds new capabilities. “The wireless ballbar requires just one setup – less than 15 minutes – for testing in all three planes,” notes Arnold. “More important, it doesn’t disturb our production setup, so we don’t have to reset the machine when we go back to production mode. We remove the ballbar, insert a tool and get back to making parts in minutes.”

Wireless operation is also ideal for Nemcomed’s small machines. “Machine tool makers understand how much lean operations value floor space, so the new machine tools are designed with smaller footprints,” says Arnold. “This results in less interior space to maneuver a wired ballbar, so wireless data transmission is a big advantage. Safety is also improved by the ability to fully close the doors on the machine during the tests.”