Lower cost lathe turns IDs within +/-2 micron

A CNC lathe, costing 30% less than its predecessor, is turning the internal form of diamond wheel dresser moulds to within a +/-2 micron tolerance to meet growing deamnd.
Lower cost lathe machines mould IDs within +/-2 micron A CNC lathe, costing 30% less than its predecessor, is turning the internal form of diamond wheel dresser moulds to within +/-2 micron tolerance. A Daewoo lathe from Mills Manufacturing Technology has been installed at Tyrolit, Crawley, to turn the internal form of bespoke diamond roller dresser moulds to within +/-2 micron tolerance. Over 80 per cent of the dressers are for sharpening the profile of Viper and conventional creep-feed grinding wheels used for machining the tip and root features on aero engine hot-end turbine blades, which are produced from nickel and other exotic alloys.

Other applications include high precision roller dressers for grinding wheels used in the manufacture of land-based turbine blades, bearings including double-track types, saw blades and automotive components such as gear trains.

Around a third of production is exported, Israel and China being particularly buoyant markets at present.

Commented Norman Crown, Tyrolits Technical Manager - Roller Dresser Unit, 'We are expecting a 70 per cent increase in throughput at Crawley within the next 12 months as our parent company in Austria transfers its dresser production to the UK to make way for manufacture of a new product over there.

So we needed to increase our mould turning capacity by installing a second lathe.

The decision was made to buy a Daewoo Puma 240LC, as the cost was 30 per cent less than a new version of the Japanese turning machine we have used for the same job since we set up operations on this site in September 2003 - yet trials showed that the Korean-built machine was just as accurate'.

Accuracy is the watchword in turbine blade production.

Engine manufacturers stipulate a very tight tolerance on the critical fir tree root form, often extending this tolerance to all dimensions on the root and tip.

The form on the grinding wheel, and consequently that of the dresser, needs to be within the same tolerance.

This applies not only to the internal profile of the dresser mould but also to the concentricity of internal features with the outside diameter, which can be up to 250mm.

Profile accuracy is verified using a contour measuring machine, on which every turned mould is checked.

The measured trace is aligned on computer screen as a best fit within a tolerance band taken as DXF output from the CAD model of the dresser, or of the component that will eventually be ground.

The system shows that Tyrolit routinely holds +/-2 microns on mould profile using the Daewoo lathe, well within tolerance, eliminating the need to diamond lap the resulting dresser, which is time consuming and reduces its service life.

The CAD model is normally used to download programs to the Daewoo lathe via Pathtrace EdgeCam software and a suitable post-processor.

Sometimes if the program is simple, the X,Y co-ordinates generated by the CAD system are entered by the operator into the Fanuc control, reducing the load on the CAD/CAM department.

The 10-station turret of the Puma 240 LC lathe is large enough to house boring bars for turning the majority of moulds produced at Crawley, so the indexable carbide insert tools are accurately clamped and rarely exchanged.

The bed is extended on this lathe model to allow the long boring bars to gain access to the inside of moulds used to make the wider Tyrolit dressers.

Average diameter of the finished product is around 130 to 150mm, although it can be as low as 50mm for some Viper grinding applications; and width is normally 50 to 60mm.

Tyrolit dressers are made using the industry-standard method of reverse-plating, which results in a nickel-based matrix carrying industrial diamond grit, with natural diamonds set by hand around the periphery of the dresser where there are sharp changes in the contour.

A finished roller dresser can easily cost GBP 1,500, which is why customers normally leave ordering a new one to the last minute.

Tyrolit prides itself on turning round quotes in 24 hours and keeping lead times short six weeks for standard deliveries.

Purchase of the Daewoo lathe will mean that the Crawley facility will continue to provide this level of service when production is transferred from Austria.