A Star Micronics GB system for turning, thread cutting, milling and gun-drilling titanium alloy tips and transducers for ultrasonic aspirators has proved successful for Integra Neuro Sciences.

A Star Micronics GB system for turning, thread cutting, milling and gun-drilling titanium alloy tips and transducers for ultrasonic aspirators has proved successful for the Andover factory of US-owned Integra Neuro Sciences. The tips, used in the treatment of brain tumours, are now produced 26 per cent faster, despite requiring a fine, 80:1 length-to-diameter hole drilled down the centre. The machine package is based on a Star SV-20 sliding-headstock, multi-axis, mill-turning centre fitted with a JBS guide bush that is able to compensate for variability in the diameter of the bar, which is fed by an FMB Turbo magazine.

Star Micronics GB, as well as being a subsidiary of its similarly named lathe manufacturing parent company in Japan, is also sole UK agent for the German suppliers, FMB and JBS.

Also fitted to the machine are a high-pressure (2,000psi) through-tool, neat oil coolant delivery system, automatic fire suppression and a range of tooling that best suits the various cutting operations.

Ceratizit inserts are used for profile turning and threading, Iscar Multi-Master tooling with modified chamfers have been chosen for milling hexagon flats, whilst solid carbide Botek gun drills are sourced through Mollart.

Completing the total manufacturing system supplied by Star were a suite of programs for machining tips and transducers to be used in Integra's new aspirator range, operator training and service back-up, including telephone help desk support from the supplier's Melbourne headquarters.

Commented Rob Sellwood, machine shop manager at the Inegra Andover factory: 'We used to produce 800 to 1,000 disposable titanium tips per month in a one-hit cycle averaging 15 minutes on an old and somewhat unreliable sliding-headstock lathe from another manufacturer.

The average cycle time has been reduced to 11 minutes on the Star lathe, representing a 26 per cent saving.' Key to achieving such a significant productivity increase is the capability of the sub spindle on the Star, which has led to the cutting cycles being balanced accurately between the two spindles.

Gun-drilling of Integra's component families is exacting, as exemplified by the two parts on which Star was asked to carry out time studies during three days of capability trials under production conditions at Melbourne.

The 120mm long tip was machined from 12.7mm diameter, 2TA11 titanium alloy bar and required a 1.5mm diameter gun-drilled through-hole down the centre, representing a length to diameter ratio of 80 to one.

In the case of the 144mm long transducer, a 2.7mm hole was needed down the 16mm diameter bar, equating to a length to diameter ratio of the 53 to one.

A very accurate result is achieved.

For example, drawing tolerance for concentricity at the tip end is 0.1mm, whereas less than 10microns is routinely held.

A tolerance of 0.3mm for concentricity is required at the back end, where the tip screws on to the transducer, yet half that figure is held.

Turned profile tolerance is +/- 50microns on the drawing, while +/- 10microns to 20microns is the norm in practice.

Moreover, they are achieved from a cold start in the morning through to the end of the single, eight-hour shift.

Integra does not rotate the gun drill on the Star, relying instead on a rotating component (bar) and a static drill.

The need for a guide bush is avoided by first drilling a pilot hole to a depth of three times diameter in to the bar end using a carbide twist drill.

The gun drill is programmed to advance in to this hole prior to the high-pressure coolant being switched on, as otherwise the tip would deflect during the delicate manoeuvre.

Gun-drilling to 13.6 metres is achieved between regrinds, substantially better than the 10 metres quoted by the supplier said Star.

According to Star, the JBS compensating guide bush has brought significant benefits to Integra.

Using the company's original sliding-headstock lathe, it was necessary when titanium bars were delivered, to measure the diameter of each along its length and segregate them in to different batches, such is the dimensional variability of the centreless-ground stock.

Even so, from five per cent to 10 per cent of components machined by Integra had to be scrapped, wasting machine time and expensive stock.

Now, with the JBS system, pneumatically operated grippers move in and out, compensating continuously for variations in bar diameter as it is fed through the guide bush, resulting in zero scrap.

Other systems on the market are adjustable, but once set, the bush is fixed and cannot self-adjust to suit the varying bar diameter.