Die milling avoids time consuming spark erosion

For making rubber weather seals that fit around car doors, Cooper-Standard Automotive produces its own multi-part extrusion dies at its factory in Maesteg, Mid Glamorgan.

For making rubber weather seals that fit around car doors, Cooper-Standard Automotive produces its own multi-part extrusion dies at its factory in Maesteg, Mid Glamorgan.

Until recently, all features on the reverse of one part of the die known as the distribution plate had to be wire-eroded.

Now significant time savings are being achieved by milling a majority of the features using solid carbide ball-nose cutters held in BIG Daishowa toolholders supplied through NCMT, UK agent for the Japanese manufacturer.

Called New Baby Chucks, the collet-type toolholders have a compact profile to allow machining at up to 20,000 rpm in awkward areas where access is restricted.

They are also accurate, having sub-micron run-out at the nose.

Cooper-Standard Automotive's die development engineer, Nigel Francisco, uses a set of eight 40-taper shank chucks containing cutters ranging in diameter from 1 mm to 8 mm.

They are held in the 24-station tool magazine of a DMU 60T four-axis, vertical machining centre from DMG.

Said Mr Francisco, "While it is no problem to mill the front of the distribution plate, it was impossible to mill the deep 3D shape on the back within tolerance using our conventional toolholders fitted with an extension bar to gain access.

This was because the cutter stuck out so far from the body of the tool that we were loosing rigidity and accuracy.

"So we had to resort to wire EDM, which used to take between four and five hours to erode the shape at angles up to 30 degrees.

Using the New Baby Chucks, the same is completed by milling in one hour or less, despite the plate being of tool steel hardened to 55 HRc." Other jobs have also benefitted from the toolholding system.

For example, gapping guides used further down the extrusion line are milled at steep angles out of aluminium and PTFE using the New Baby Chucks.

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