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Mould maker gets to grips with tool holding

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article image The tool carousel on the DMG contains 60 toolholders, 43 of which are CoroGrip.

ONE of the UK's largest installations of Sandvik Coromant's recently introduced CoroGrip tool holding solution is proving its value at the Aylesbury operations of Beaubury Precision Moulds Limited - a company specialising in the design and manufacture of blow moulds for cosmetic containers, household products and automotive parts.

Corogrip was introduced at the MACH 2000 exhibition and is a high precision hydro-mechanical power chuck with a performance claimed to be superior to any conventional system on the market.

CoroGrip provides a clamping force comparable to that of 'shrink fit' tool holders and three times higher than hydraulic chucks. Its precision matches that of shrink fit holders and the system is suitable for all applications from super finishing to heavy roughing.

Prior to investing in a new DMG 60P 5 axis machine the production team at Beaubury had experienced a number of problems with the tool holding on other machines - run out was a big issue with collet wear and cracking also being experienced. For their new investment they were anxious to ensure the toolholding solution overcame these problems.

"We had previous positive experience with Coromant Capto modular tooling and called in Graham Manning from Coromant Local Services to ascertain if this system or some other Coromant products could provide the solution for the DMG," Beaubury senior programmer Paul Matthews explained.

"This was just prior to the official launch of CoroGrip but Graham arranged for project specialist Tony Godden to undertake a demonstration and we were highly impressed. We not only saw the opportunity to overcome our immediate problems but at 20 seconds a set up with guaranteed accuracy, we could contemplate some significant time savings in tool setting."

The DMG operates at 18,000rpm, usually cutting Dural aluminium alloy at feeds of 12 metres a minute. The tool carousel features 60 toolholders in total, 43 of which are CoroGrip. Most of the work undertaken on the machine ranges from 2 ½D multi-face machining right through to full 5 axis.

The primary competitor to CoroGrip is the technique of heat shrink clamping but Beaubury had an unfavourable experience when trialing this concept and found Coromant's balanced-by-design cold clamping concept easy to use and totally predictable.

The clamping force of CoroGrip is to H tolerance 6 with a consistent accuracy of 4 micron.

"The clamping force and accuracy is exceptional and is highlighted in one area where we drill waterways in the mould using gun drills," Paul Matthews explained.

"Using CoroGrip we pre-drill with a solid carbide drill and then machine to a depth of 235mm from each side with a Coromant gun drill, achieving perfect concentricity. Previously that operation would have involved a lengthy pecking cycle."

Finally, a further testimony to the strength of grip and sustained accuracy of CoroGrip is offered by Paul Matthews.

"The DMG machine is equipped with an automatic tool setter which checks the tool after every operation. Since equipping the machine with CoroGrip tool holders we have not had a single instance of tool run-out."

The CoroGrip clamping unit is positioned adjacent to the DMG and features foot operation with a clamping force of 700bar. One unit accommodates the entire CoroGrip range (12mm-42mm) and with its guarantee of accuracy, eliminates lengthy tool setting operations.

CoroGrip chucks are manufactured with close tolerances resulting in a maximum run out at the cutting edge of only 0.002 to 0.006mm - measured at a length of three times the tool diameter. The run out is consistently maintained throughout the machining operation, enhancing tool life and workpiece quality.

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