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Chas A Blatchford and Sons, a medical component manufacturer specialising in lower-limb prosthetics and orthotics, has invested in a full five-axis machining centre from Geo Kingsbury Machine Tools.

To alleviate bottlenecks in the production of prismatic parts, Prof Saeed Zahedi, technical director of the company’s research and development department, made the decision to invested in the Hermle C 20 U at the end of 2009.

This latest investment joins an existing three-axis model from a different supplier fitted with a fourth-axis indexing unit.

The increase in production efficiency using five CNC axes instead of four is significant, according to Bill Woolford, senior technician at Blatchford.

He said that, in 75 per cent of cases, the Hermle can produce parts in one hit that previously needed two or three setups on the four-axis machine.

The reduced number of setups has the additional advantage that fewer fixtures need to be made, saving further time.

The turnaround for prismatic components in the research and development department is, on average, twice as fast as previously, which is useful when two or three of Blatchford’s designers want their components urgently.

Woolford said: ‘In some instances, total machining time has been reduced from four hours to 15 minutes on the C 20 U.

‘This is the case even though at present we are machining in 3+2 mode, with two axes clamped.

‘When we progress in the near future to fully interpolated five-axis cycles, we expect even greater savings on some jobs.

‘For example, components with tapers or angled faces that we currently scan with a ball-nose cutter will be milled much faster by continuously keeping the surface at 90deg to the tool,’ he added.

Woolford cited a general improvement in the accuracy of parts produced on the Hermle, as it is sometimes difficult to hold tolerance when resetting parts repeatedly for three- or four-axis machining.

Five-axis machining also gives Blatchford’s designers greater freedom to create lighter parts that would otherwise be problematic or time consuming to produce – weight reduction being especially important for modern prostheses.

A further benefit to Blatchford since the arrival of the Hermle has been a return to single-shift working, 8:30 to 17:00, rather than running two shifts from 6:00 until 22:00.

A variety of materials are machined using solid- and indexable-insert carbide tools, mainly from ITC, in the 18,000rev/min spindle of the Hermle C 20 U.

Metals include aircraft-grade aluminium, stainless steels and titanium.

Tolerances are down to four microns in total on dimensions and hole positions.

Carbon fibre is also machined in the research and development department, but this tends to be put onto a CNC turret mill to avoid abrasive dust causing the deterioration of the machining centre slideways.

In addition to manufacturing prototype parts for testing, the C 20 U is used for machining moulds for producing, for example, rubber kneepads or carbon-fibre foot springs.

These and other more complex parts are programmed with the assistance of solid computer-aided-design (CAD) models generated in Solidworks by Blatchford’s designers.

Cutter paths are created using a seat of Delcam’s Powermill computer-aided-manufacturing (CAM) software on the shop floor of the research and development department.

Simpler jobs are programmed at the Heidenhain control system fitted to the Hermle.

Geo Kingsbury Machine Tools

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