High Cpk for lathe with 3 tool carriers

Geo Kingsbury Machine Tools has supplied an Index ABC lathe with three tool carriers to an automotive component maker, achieving a process capability of Cpk 2.0 on tolerances as tight as 22 microns.

A very high process capability of Cpk 2.0 on tolerances as tight as 22 microns is being achieved around the clock in the production of turbocharger bushes at a major automotive component manufacturer in the Midlands.

To achieve this level of accuracy, operational tolerances on the machine must be one half of those stipulated, ie down to 11 microns total.

Underpinning the final external grinding operation is a turning cycle on an Index ABC lathe with three tool carriers, built in Germany and supplied through UK agent, Geo Kingsbury Machine Tools, Gosport.

The CNC machine faces, chamfers and bores the sintered metal alloy component to within 30 microns tightest TIR (total indicated run-out), and down to 22 microns on bore diameter.

Four sizes of bush from 10 to 38 mm long and between 10 and 18 mm in diameter are turned in cycle times ranging from 10 to 15 seconds.

Sintered blanks from a vibratory bowl are fed down an inclined chute into the machining area, where a loading device mounted in the upper turret collects the part and transfers it into the main spindle.

So that machining time is not lost during loading, tools in the lower turret are simultaneously facing and chamfering the first end of the previously loaded bush, and machining the bore.

A synchro spindle in the upper turret then comes in to hold the part and present it to cutters in a third tool carrier which face and chamfer the reverse end.

Front-end turning of the next blank takes place in the main spindle at the same time.

Clamping pressure of the synchro spindle is light, ensuring that the delicate sintered component is not deformed during the final turning operations.

Ejection of the fully machined bush overlaps with loading of the next blank.

The lathe is reset approximately every two days to machine a different size of bush.

To speed this process, Geo Kingsbury designed and built the feeding mechanism with six quick-release bolts, enabling changeover in under one hour.

The automotive component manufacturer considered an all-grinding solution for machining the bushes, but an internal grinder would have been needed at double the cost of the Index lathe, which is more than capable of achieving the required bore tolerances.

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