Product category:
Miscellaneous machine tool equipment (fixtures, rotary tables etc.)
News Release from: Renishaw | Subject: QC10 Ballbar
Edited by the Manufacturingtalk Editorial
Team on 28 June 2005
Machine tools often checked to hold
tolerances
Medical implant maker determines machine tool capabilities through simple and accurate ballbar diagnosis for consistently producing tight-tolerance work in widely variable production.
Replacement hips, knees and shoulders from Smith and Nephew Orthopaedics return flexibility and range-of-motion to thousands annually One of the world's largest makers of medical implants, the Memphis, USA, company finds that all 325 machines tools which create those implants must be just as flexible, while being capable of producing precision parts to Six Sigma
This article was originally published on Manufacturingtalk on 7 Mar 2001 at 8.00am (UK)
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Implants are produced from titanium, stainless steel and other exotic metals in a great range of sizes to provide best fit across all physical types.
To keep its machines capable of producing tight-tolerance work in such variable production, Smith and Nephew regularly tests machine performance with the Renishaw QC10 ballbar system.
* Six Sigma salvation - when Richard Grimes, calibration specialist, was put in charge of the company's CNC testing, repair and validation program in February, 1998, the performance of the plant's most critical machine categories was unacceptable.
Further reading
Ballbar test gets powerful diagnosis software
Significantly enhanced Ballbar 5 HPS software adds a historic review function, machine performance acceptance limits, part program generator and ballbar plot simulator.
Regular ballbar 'medicals' keeps machines in trim
Monitoring machine capability with a ballbar test has proved crucial to a successful machining sub-contractor that specialises in the pharmaceutical and aerospace industries.
Getting the most out of a machine tool
A machine tool may be designed to maintain a particular tolerance, but wear and temperature changes will affect its capability to maintain factory specifications unless checked regularly.
Using the Six Sigma measurement system, thread whirling machines were rated at only 3.0 Sigma.
That meant that 7% of the time those machines failed to perform their tasks within a specified tolerance.
Vertical millers operated at 2.25 Sigma (greater than 20% failure rate) and horizontal millers operated at less than 1.0 Sigma (failure rate 69% of the time).
This caused much rework and scrap, as well hitting the company in the pocketbook.
Since Grimes implemented ballbar diagnosis with Renishaw's QC10 Ballbar, 325 of the plant's CNC machines are now operating at true 6 Sigma, or 0.0003% failure rate.
"Cost savings have not been figured, but the result on our bottom line can be imagined," says Grimes.
"We now make better products and have less down time since we can catch problems before they happen." Grimes notes that ballbar tests typically take about 15 minutes.
The ballbar attaches magnetically between the machining center's spindle and table, and tracks machine movement to +/-0.5 micron (0.000020in).
A simple CNC circular program is run which allows the ballbar software to calculate machine circularity error, servo gain mismatch, vibration, stick-slip errors, backlash, repeatability and scale mismatch, as well as machine geometry.
In all, Grimes uses the ballbar to check 13 performance parameters.
The company's quality department determined that those 13 items combined must not be off by more than +/-0.003in.
"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 or exceeds our established spec." While the ballbar's 100mm length makes it suitable for most of the company's machine tools, Grimes uses Renishaw's 50mm small ballbar attachment for very small machines.
He has also implemented Renishaw's new Windows-based Ballbar 5 software, which provides a user-friendly interface, comprehensive online help and three convenient user modes for high accuracy calibration checks in minimal time.
"The Windows environment is much easier to use and makes tests much quicker to set up," notes Grimes.
The QC10 ballbar measures multi-axis errors that are only apparent when the machine is in motion.
It plugs directly into the RS232 port of any IBM-compatible computer, including notebook models for portability on the shop floor.
Renishaw's diagnostic software calculates machine errors, weighs those errors based upon the measured values, and converts the ballbar data into a polar plot of the machine's true movement.
Early error detection with the ballbar permits optimum efficiency in scheduling maintenance and repairs.
Ballbar inspection can also be used to grade machines according to their accuracy, per ASME B5.54 and ISO 230.
The plant is ISO 14001-certified and Grimes manages and retains all paperwork involved with the calibration and validation program.
Besides ISO compliance, the orthopedic products maker is under watchful the eye of the Food and Drug Administration, which has its own special requirements for compliance management and environmental control.
Grimes must keep machine records for a three-year period per FDA regulations, but actually keeps records longer for historical and maintenance purposes.
This regimen of periodic ballbar checkups and record keeping allows Grimes to keep his huge army of 325 CNC machines tools fit and flexible.
Smith and Nephew's commitment to strict compliance and thorough machine evaluation assures that implants fit precisely and function flawlessly to return people to active enjoyment of life. Request a free brochure from Renishaw ...
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