Encoders upgrade vertical machining centre

After fitting linear encoders to a VMC, an equivalent machining test confirmed that the 3 micron inaccuracy previously experienced when machining beryllium had reduced to zero in the X-axis.

General Optics Taunton said that the while beryllium can be machined, it fractures easily and sharp corners contribute to crack propagation.

Tapping can be particularly difficult because of the high surface stresses involved and the material's lack of ductility.

So every aspect of the machining process is carefully monitored and controlled.

Although General Optics' vertical machining centre (VMC) had been performing well on general machining work, the exacting requirements for machining beryllium could not be met.

In an attempt to eliminate the problem of inaccuracies resulting from thermal growth, General Optics had new ballscrews fitted to the VMC, but was unsuccessful.

As the machine was fitted with a Heidenhain 426M CNC, the company approached Gary Blanch of Bournemouth-based Engineering Equipment Centre, an authorised Heidenhain distributor and retrofitter since 1986.

Blanch suggested the fitting of linear incremental encoders - an option that the VMC manufacturer had previously dismissed as impractical.

To fit the Heidenhain LS 486C encoders to the VMC, Blanch had to comply with the strict provisions of the European Integrated Pollution Prevention and Control Regulations (as airborne beryllium particles are toxic) by donning full body protective clothing with a filtering system supplying air to a breathing hood.

He was also limited to a maximum of 2.5h exposure per visit.

Also when he left the machine shop, he had to take a full body shower, while still wearing the protective clothing, to remove any traces of beryllium dust.

After the Heidenhain encoders had been fitted to the VMC, an equivalent machining test confirmed that the 3 micron inaccuracy previously experienced had reduced to zero in the X-axis and 0.5 micron in the Y-axis.

Production engineer with General Optics Taunton, Jeremy Dugdale, said: "Without these scales we would have been 'dead in the water' as far as machining tight tolerance, high value components is concerned.

Beryllium is extremely expensive to buy and, typically, most of the material is machined away, so mistakes become progressively more costly".

From this it can be argued that the typical jobbing sub-contractor has neither the means nor the expertise to machine beryllium successfully and safely.

Although milling and turning operations at General Optics Taunton are undertaken on relatively commonplace machining centres and CNC mills and lathes, clearly it is the acquired knowledge in terms of the methods employed - component design, tooling and fixturing - that is the differentiating factor, said Heidenhain.

* Berylium machining requirements - "The key machining requirements are a sharp, keen edge on the cutting tool, a well-maintained machine tool and adherence to the correct manufacturing processes," said Dugdale.

"This is the only way to avoid surface stresses and the resultant cracking that could lead to component failure".

* About General Optics Taunton - General Optics Taunton, now part of the GSI Group, has been manufacturing beryllium and aluminium beryllium composite products for more than a decade, producing high precision components for various industry sectors such as defence and aerospace, semiconductor, metrology, medical and nuclear.

Machining takes place in a dedicated 3400ft2 sealed negative pressure environment within the 8500ft2 single-source Lisieux Way, Taunton, UK facility, which in its entirety represents an investment of some GBP 3.5 million.

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