Collet change turns productivity around by 45%

By specifying the Hainbuch collet system from Leader Chuck Systems, Hawke International has been able to raise turning productivity by around 45 per cent through taking higher depths of cut.

By specifying the Hainbuch collet system from Leader Chuck Systems, Hawke International of Ashton under Lyne has been able to raise turning productivity by around 45 per cent through higher depths of cut and increased feed rates.

Combining the collets with a new CNC single-spindle lathe has given Hawke the capability to manufacture components in a single operation as opposed to the two set-ups previously required.

As a result, set-up times have been reduced by 50 per cent.

Machining cycle time for a family of components used in a range of large-diameter cable glands has typically reduced by 40 per cent.

This has been achieved mainly because the security of clamping available with the collets has allowed rough machining to proceed with double the depth of cut and 20 per cent higher feed rate than could previously be sustained.

Moreover, these productivity improvements have been combined with improved accuracy and finish on the machined components.

Part of the McKechnie Group, Hawke International specialises in the development and manufacture of a range of electrical accessories for use in hazardous environments.

These conform to international safety standards and are produced under the aegis of a BS EN ISO 9001 accredited quality system.

Hawke's customers are mainly offshore exploration companies as well as onshore petroleum and petrochemical process plants that require intrinsically safe electrical installations.

The Hawke range of cable glands comprises precision manufactured assemblies in brass, stainless steel and other materials.

They are produced to standard and customer specification, and incorporate features designed to confine a flame front generated by an explosion or fire within an electrical enclosure, so preventing a more serious incident from developing.

Keith Wright, the production engineer involved with the Hainbuch project, explains: "We manufacture a large range of cable glands suitable for cables of virtually any size.

From a manufacturing standpoint we broadly define them by the across flats (AF) measurement of the hexagonal body components.

On this project we were aiming to improve manufacturing efficiency on the larger sized glands that we manufacture, which range from 65mm AF up to 4 inch AF." He continues: "Smaller sized gland parts are made on either multi-spindle machines or bar-fed CNC lathes, and historically we have produced the large components from sawn-off lengths of extruded hexagonal tube.

This was machined in two operations, mainly because we didn't possess a CNC lathe with a spindle tube diameter large enough to accommodate the 4 inch AF hexagonal bar.

"However, we began to have a requirement for larger diameter turned components, which justified the investment in a large capacity CNC lathe and allowed us to upgrade the machining process for large diameter components." Each gland typically comprises three external 'body' components machined from brass or stainless.

In addition, there are a number of metal and non-metal internal and external components.

All external components have a mix of internal and external threads and finely finished internal bores.

"Bore finishes are important as the assembly needs to be gas-tight," says Keith Wright.

"We also need a high standard of finish on the sealing face where the gland connects to the enclosure.

Ensuring this means that we need rigid, vibration free location of the workpiece during machining." The revised process route for body component machining allows production of the parts from lengths of thick wall tube.

These are accommodated in the spindle tube of the machine.

The sequence of operations starts with the location of the workpiece, which is fed out to full component length and gripped in the collet.

The machining cycle is then to externally turn at both ends, complete all internal boring work and finish to size, machine all internal threads, machine external threads and part-off.

Previously the two-stage operation required a hexagonal collet for the first operation and a round collet for the second operation, when the workpiece was gripped on an external thread.

This separation of front and back end machining cycles resulted in extended lead times.

"The single operation approach is much more efficient," Keith Wright reflects.

"However, it makes more demands on the collet as we are supporting a much heavier workpiece.

"Experience with a different collet system gave us some cause for concern as it was prone to blockage with fine brass swarf - and this would compromise a semi-automatic cycle of production.

Nor did it have a fully parallel clamping action and this limited machining speed if we were to maintain quality.

Our lathe supplier then recommended the Hainbuch system, and this has proved extremely effective in overcoming both shortcomings." Since the installation of the Hainbuch system, performance of the system is judged to be highly satisfactory with immense security of clamping.

It allows tolerance and finish to be maintained with relative ease, in tandem with significantly higher productivity.

"We achieve a similar level of improvement whether machining free cutting brass or 316 stainless steel," Keith Wright concludes.

"In addition, the simplicity of the collet extraction and replacement system makes changeover between different sizes very straightforward.

All in all, the Hainbuch system has proved to be a very cost-effective investment." .

(This was Manufacturingtalk's Top Story on 14 December 2001).

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