Deciding the best way of making a motor cover

To find a way of manufacturing an electric motor cover economically a subcontractor produces both parts of the end assembly in multiple operations using different machining techniques.

To find a way of manufacturing an electric motor cover economically for one of its customers, Abingdon-based Holifields has decided to produce both parts of the end assembly in multiple operations using different machining techniques.

First they cut out the blanks on a high-pressure water jet profiler, then they mill and drill them on one or two machining centres.

The approach won the business for the contract machinist, whereas prismatically machining these end flanges from the solid would have been too time consuming and expensive, and in any case could not have been completed in one hit.

Two different types of flange are involved, the larger being the more complex.

In the latter case, the process starts with cutting a 2.5m x 1.25m x 25mm thick 6082T6 aluminium plate into two halves and profiling an array of nested semi circular rings from each plate simultaneously on a twin-head Flow machine.

Feed is set at 90 mm/min to achieve a good quality, square edge as specified by the customer.

The part is then put up on a 12-station, turret-type Miyano TSV-35 machining centre where the inside radius is skimmed and one millimetre is milled off the thickness.

A boss on one side is finish machined to a depth of 10 mm and an 11mm hole is drilled through it.

The process is completed on a 4-axis vertical machining centre, normally either a Hitachi Seiki VS40 or a Daewoo ACE V50.

After clamping the part vertically on an indexing head, two holes are drilled and rigid tapped at 90 degrees in the flange ends.

After indexing through 22.5 degrees, a third M6 hole is drilled and tapped at an intermediate angle on the outside of the semi circular profile.

Virtually any machining centre on Holifields' shop floor could carry out the first prismatic operations, including the machines that perform the second drill / tap cycle, so considerable flexibility exists for allocation of resources according to work flow at any given time.

The cylindrical rolled steel case of the motor cover is bought in pre-painted.

It remains for Holifields to secure the above flange and another, smaller aluminium flange on the top, then secure the assembly on one side with a complicated steel hinge that is CNC turned at the Abingdon premises.

This is an example of Holifields' consignment stocking service, whereby individual components, kits of parts or assemblies such as this are manufactured and held in the stores until the customer calls them off, at which time they are delivered on a just-in-time basis and only then does the customer pay.

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