Boxtrees Precision Engineering use Renishaw probe systems on a Mazak Integrex in a clever fully-integrated 'intelligent' system that has achieved reduced unit costs, zero manual set-up times, unmanned machining, and consistent accuracy and cycle times. "Unit cost for a one-off component is the same as a batch of a thousand" says Steve Randerson, production manager at Boxtrees Precision Engineering Ltd, Halifax, UK. The company has employed a Renishaw OMP400 high accuracy touch probe and NC4 non-contact laser tool setting system on a Mazak Integrex 200-IV ST to radically reduce non-productive setting. Improvements have also been seen in component accuracy and the consistency of cycle times, with a direct effect on production scheduling, plus the vast majority of post-machining inspection has been eliminated. Boxtrees make all the machined parts for a large range of educational machine tools supplied by sister company Boxford, along with other sub-contract work. Mr. Randerson explains "Five years ago I did a detailed analysis of our machining operations and found that 40% of machine time was used setting jobs. This had to change, and what better figure to aim for than 0%? That is where we are now. Many companies have moved production out of the UK to reduce costs, we have chosen to cut costs by improving our operation here. We make what we need when we need it, there are no components that have cost us money to produce sat on the shelf not earning us money. The majority of work now is in very small batches, including single parts, but crucially that makes no difference to the productivity." The Mazak Integrex, originally fitted with the Renishaw systems when supplied, has been installed at Boxtrees for 11 months, one of three CNC machine tools in active use in a very large machine shop now containing increasingly inactive manual machines. In that time Mr. Randerson has created machining programs for over 200 different components, which can be machined in many different materials, usually mild steel, cast iron or aluminium. Every one of these programs relies on Renishaw part setting and tool breakage detection macro routines to control the process, making the most of the flexibility offered by the Mazak multi-axis mill-turn machine. Tool life is more important than cutting time "Everyone talks about reducing the time taken to cut the part," says Mr. Randerson "I'm more interested in minimising tool wear to keep tooling costs down, so we don't cut as fast as we used to, and now get 20% more tool life. I'm also keen to identify that occasional scrap part and make sure it doesn't make its way through to final assembly. If an out-of-tolerance part is assembled into a Boxford machine it can mean a 4-hour strip-down to change it. So the programs use the optimum speeds and feeds for long tool life, cut out any wasteful machine movement, and employ a lot of logic that allows the machine to make 'intelligent' decisions according to the feedback from the probe systems." Part setting and component inspection for process control The Mazak Integrex is used for twin-spindle billet work during the day when the operator is present, with many different shapes and sizes of billets, whilst overnight it runs un-manned, with material supplied by a bar feed. In both cases final part inspection is performed by the touch probe on the machine, with measured values recorded in a text file. This is fed back to the production scheduling system as a permanent record of the critical dimensions of the component and whether any feature was out of tolerance i.e. a scrap part. The OMP400 is an ultra compact probe, ideally suited to multi-axis machines thanks to innovative RENGAGE technology, which brings unrivalled 3D measurement performance.
Billet work during the day The dimensions of each individual raw billet vary considerabl
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