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Departments: Quality Applications
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Implant Manufacturer Maintains Quality with Renishaw System

 

 

Implant Manufacturer Maintains Quality with Renishaw System
Renishaw’s QC10 ballbar system

The human body is an intricate association of complex mechanisms and synergistic collaboration. When a joint fails--especially if it’s a knee or hip--quality and precision are paramount to manufacturing a replacement. Smith & Nephew Orthopaedics in Memphis,

Tennessee, has always emphasized accuracy and quality in its products, so change was imminent when the company found itself mired in a quality control bog in early 1998. The quality crackdown commenced when Richard Grimes was placed in charge of the company’s CNC testing, repair and validation program. Grimes, a calibration specialist, was faced with the task of calibrating and maintaining the 325 machines that create Smith & Nephew implants--a daunting task considering the implants are produced from titanium, stainless steel and other metals in myriad shapes and sizes.

Smith & Nephew had been creating medical devices, lubricants and implants since 1931. Although advancing technology has brought unparalleled progress, it has also increased the opportunity for error. By February 1998, performance of the plant’s most critical machines had reached unacceptable levels. Based on the Six Sigma scale, thread whirling machines were operating at only 3 sigma. That meant that 7 percent of the time, those machines failed to perform their tasks within a specified tolerance. Vertical mills operated at 2.25 sigma (greater than a 20-percent failure rate) and horizontals operated at less than 1 sigma (a 69-percent failure rate). Instead of smooth, efficient production, Smith & Nephew was becoming increasingly involved in rework and scrap--to the detriment of the company’s bottom line. That was before Grimes implemented ballbar diagnosis with Renishaw’s QC10 ballbar.

The QC10 ballbar system reduces scrap and unexpected machine downtime by checking machine performance before component manufacture. This concept--recognizing problems before they adversely affect production--is a benchmark of the Six Sigma strategy. The QC10 ballbar calculates machine circularity error, servo gain mismatch, vibration, stick slip errors, backlash, machine geometry, and repeatability and scale mismatch. All data are analyzed to ISO 230-4, ANSI B5.54 or B5.57 performance standards, and machine errors are ranked according to their significance to overall machine accuracy. The wide range of machines at Smith & Nephew would usually pose a problem for a system like the QC10, but adaptors are available, allowing the QC10 to be used on different machines.

The QC10 ballbar measures multi-axis errors that are apparent only when the machine is in motion. The QC10 is portable and plugs directly into the RS-232 port of any Windows-based personal computer, including notebook models. Renishaw’s diagnostic software calculates machine errors, weighs the feedback based upon the measured values, and converts the ballbar data into a polar plot of the machine’s true movement.

Grimes uses the ballbar to check 13 performance parameters. The company’s quality department determined that those 13 items combined must be within ±0.003 in. “When new equipment comes in, I first test the machine with the ballbar,” explains Grimes. “If a machine is moved, crashes or loses a spindle, I run a ballbar test. Regardless, each machine gets an annual test and will not run until it meets our established specification.”

Grimes notes that the ballbar tests typically take about 15 minutes. The standard 100 mm ballbar attaches magnetically between the machining center’s spindle and table, tracking machine movement with a sensor accuracy of ±0.5 µm (0.000020 in.). Grimes uses the 50 mm ballbar attachment for small machines and has implemented Renishaw’s Windows-based Ballbar 5 software. “The Windows environment is much easier to use and makes tests much quicker to set up,” notes Grimes. The latest release includes a “history” feature with an NC part program generator and integrated simulator. The latter allows maintenance personnel to carry out “what if?” scenarios on test data without actually adjusting the machine.

Smith & Nephew has experienced a quality revival since Grimes implemented the QC10 ballbar. The plant’s 325 CNC machines are currently operating at Six Sigma. “Cost savings haven’t been figured, but the result on our bottom line can be imagined,” says Grimes. “We now make better products and have less downtime because we can catch problems before they happen.” Smith & Nephew’s commitment to strict compliance and thorough machine evaluation ensures that implants fit precisely and function flawlessly. This dedication to quality appeals to not only business professionals but also to implant recipients eager to reclaim their active lifestyles.

Renishaw’s QC10 ballbar system

Benefits:

  • Portable device provides rapid assessment of machine accuracy and performance.
  • Analysis in accordance with ISO 230-4, ANSI B5.54, B5.57 and JIS B6194
  • Ballbar5 HPS software maintains detailed history of machine performance over time.

www.renishaw.com