5-AXIS MACHINING SPEEDS DEVELOPMENT OF MEDICAL COMPONENTS

To alleviate bottlenecks in the production of prismatic parts, Professor Saeed Zahedi, Technical Director, invested in his department’s first full 5-axis machining centre at the end of 2009. Supplied by Geo Kingsbury Machine Tools, it is a Hermle C 20 U which joins an existing 3-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 remarkable, 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 set-ups on the 4-axis machine. The reduced number of set-ups has the additional advantage that fewer fixtures need to be made, saving further time.

Turnaround for prismatic components in the R&D department is on average twice as fast as previously, which is invaluable when two or three of Blatchford’s designers want their components urgently – a not unusual occurrence.

“In some instances, total machining time has been reduced from four hours to 15 minutes on the C 20 U,” Mr Woolford confirmed. “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 5-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 90 degrees to the tool.”

He 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 3- or 4-axis machining. 5-axis machining also gives Blatchford’s designers greater freedom to create lighter parts that would otherwise be problematic or unduly 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 am to 5.00 pm, rather than running two shifts from 6.00 am to 10.00 pm.

A wide variety of materials is machined using solid and indexable-insert carbide tools, mainly from ITC, in the 18,000 rpm spindle of the Hermle
C 20 U. Metals include aircraft grade aluminium, stainless steels and titanium. Tolerances are down to four microns total on dimensions and hole positions. Carbon fibre is also machined in the R&D department, but this tends to be put onto a CNC turret mill to avoid abrasive dust causing 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 knee pads or carbon fibre foot springs.

These and other more complex parts are programmed with the assistance of solid CAD models generated in SolidWorks by Blatchford’s designers. Cutter paths are created using a seat of Delcam’s PowerMill CAM software on the shop floor of the R&D department. Simpler jobs are programmed at the Heidenhain control system fitted to the Hermle.

Now in its 120th anniversary this year, Blatchford is a global supplier of prosthetic and orthotic products and services, offering lower limb prosthetic component manufacture and distribution worldwide as well as clinical supply of prostheses and orthoses in selected markets including the UK and India.

The Queen’s Award-winning company is at the heart of the development of digital electronic and intelligent interface systems. One of the most exciting products to be released this year is the Echelon self-aligning foot with variable ankle control. It is one of four shortlisted nominations this year for the prestigious MacRobert Award from the Royal Academy of Engineering. The development of increasingly complex products like these will benefit considerably from the introduction of full 5-axis CNC machining at Basingstoke.