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If anyone had said it to Mark Eldridge a decade ago that he would be inspecting components produced on presses to micron tolerances, he would not have believed them. Yet in his current position as quality manager at Wild Manufacturing Group, that is exactly what he is doing on an LK co-ordinate measuring machine (CMM) from Metris.
A case in point is the ball washer that forms part of the front suspension for a major OEM. Wild makes 33,000 per week, the bore being the most critical dimension at 17.67 mm diameter, + 0, - 0.04 mm. This level of accuracy is required after heat treatment and plating, however, both of which use up tolerance, so the washers must be accurate to within 30 microns when they come off the presses.
Wild has been making these high-alloy steel components since the late 90s. However, even in that relatively short time, quality standards have risen in the automotive industry to the point where the Birmingham pressworker's old toolroom CMM was not up to the job of supporting its statistical process control (SPC) procedures. These are necessary to enable very tight tolerances to be maintained and to achieve high process capability figures – Cpk 2.0 in the case of the ball washer.
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The importance of maintaining such close control over quality cannot be overstated, as if the washer is faulty, the bore pin can fracture, leading to suspension failure and expensive vehicle recall. This is why, in addition it to putting three washers every two hours onto the CMM to monitor the production process, every component is checked on an optical sort machine before delivery to the customer.
"The problem with our previous CMM was its poor repeatability and reproducibility (R&R), which resulted in as much as 10 microns measuring uncertainty from component to component," commented Mr Eldridge. "R&R needed to be under 10 per cent, as on the LK, so that the measuring process takes a maximum of three microns of the washer's working tolerance off the press, leaving us seven microns to play with."
The Metris LK G-90C 8.7.6 was duly installed in November 2005, complete with LK CAMIO software that allows rapid programming of inspection routines off-line, directly from the CAD model of the part. Cycle time for inspecting the ball washer is now two minutes, including component reversal and reclamping, compared with 7.5 minutes on the old CMM, so measuring productivity is higher too.
LK CAMIO provides Wild with the required functionality for SPC, with full reporting. There is a further module, called Launchpad, that uses on-screen component photographs to guide metrology staff when fixturing parts and instigating measuring programs.
The combination of Metris' accurate measuring hardware and powerful software has started to result in new contracts for Wild and is helping to expand its business into the manufacture of complex assemblies. For example, a tier-1 automotive supplier recently asked the pressworker to quote for producing the front and side panels for a complex radio housing. Tolerances were fairly open at ± 0.1 mm, but there were 400 dimensions on each side of the front panel alone that needed to be measured.
"Manufacturing the components was not a problem, but manual inspection would have been impossibly time-consuming, and our old CMM would have been too inaccurate," continued Mr Eldridge. "The Metris LK G-90C allowed us to take on this work and fully inspect a front panel in 49 minutes using a program generated in LK CAMIO from the customer's IGES file."
Other components so far inspected on the LK G-90C include a key and washer for a major OEM braking system. In addition, the machine has been used to verify the ac curacy of form tools and fixtures, which are also produced from components' CAD models.
Wild looked at different measuring technologies before deciding that a bridge-type CMM with digital scanning capability was the way to go. Mr Eldridge had been a serial user of LK equipment at three previous manufacturing companies in the automotive sector. The good service back-up he had received, combined with high machine accuracy and competitive price, clinched the sale.
In conclusion, he said, "Investment in CMM technology to guarantee quality for customers is not a luxury any more - it is essential to winning and retaining business.
"It takes SPC to the next level, allowing suppliers to exercise much closer control over their production processes to meet ever more stringent quality standards demanded in today's manufacturing environment."
Download: Wild Manufacturing uses LK CMM for inspection of precision pressings (PDF file)
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