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Case Study: The CPT leads the way in improving machine tool accuracy Leading engineering companies are improving the accuracy of their key machine tools with the help of a revolutionary new software product developed in Huddersfield. One such producer is Micrometalsmiths Ltd, specialists in high precision components for the microwave electronics industry, a highly competitive field in which the need to keep abreast of the latest technology is paramount. When considering how best to meet the ever higher standards demanded by their customers Micrometalsmiths were not convinced that replacing their plant would automatically give them the edge on the competition. At around £250k per unit, new machine centres would come with a specified accuracy only marginally better than those currently in use. It is apparent that, even with the rapid development of recent years, surprisingly little has been done by the makers to combat the most basic threats to component accuracy inherent in every machine tool. These are geometric alignment errors and thermal distortion of the machine structure. However, upgrade they must, so Micrometalsmiths embarked upon a collaborative project with the Centre for Precision Technologies at the University of Huddersfield. With the aim of increasing output of good components in the most cost-effective way a team of experts were given the task of enhancing the company’s existing machine tools to a higher standard than ever before, even exceeding their specification when new. This ambitious plan was made possible by Volumetric Compensation Software (VCS), a ground-breaking new technology designed to correct errors in the path of the cutting tools before they occur and thereby improve the overall accuracy of the machined product. First the performance criteria of the selected machines was measured and catalogued in minute detail. There then followed a complete mechanical and electrical refurbishment including an upgrade to the Osai series10, a controller capable of running VCS without the need for additional hardware. There then took place a second examination by the metrology experts of the CPT, this time to determine the calibration data that was to be stored for use by VCS. Finally, the fully corrected machines were subjected to a series of exhaustive trials with remarkable results. Volumetric error was typically reduced from 78 to 16 microns, an improved accuracy of 80%. Consequently cycle times fell by 15% and the proportion of scrap components by 30%. In subsequent production trials it was found that the machines can be run faster and for longer periods of time without losing accuracy. All-night unattended runs are now a reality and measurement cycles are executed at 3 times the speed previously possible. Senior Applications Engineer Allan Kennedy said “I’ve seen the most skilled engineers spend weeks trying to achieve this level of precision and then the machine might literally change with the weather! Not so with VCS adjusting automatically in response to temperatures measured at critical points. This is certainly the way forward for machine tool makers to meet the ever rising standards demanded by hi-tech industry.” Graph showing typical reductions in volumetric or (in the case of a 2 axis machine) planar errors when VCS is applied. PLEASE NOTE that it does NOT take into account the improvements made by THERMAL error compensation which may be of a far higher order.
NB. Three Axis VCS is now available for the Osai series10 and for the Siemens 840D. A version for five axis machines is currently under development Ref: |
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