MAPAL optimises precision and tool life for Doncasters

At that time, as now, one of Doncasters’ major products was impellers for use in turbochargers, when in operation they rotate at speeds of up to 250,000 rpm. This means that exceptionally accurate machining is essential. For example, the permissible tolerance on the finished bore used to connect the impeller on the turbocharger shaft is just 6 microns.

Machining the blade profile presents a special challenge as it involves and intermittent cut on blades that are often less than a millimetre thick and are thus very easily distorted.

When it first set up its machining operations, Doncasters approached MAPAL to supply tooling, as it knew of the company’s expertise and experience in providing efficient and effective tooling for unusual and demanding applications. While the tooling supplied by MAPAL at that time offered excellent performance, Doncasters – like all manufacturing companies – was always looking for ways to reduce production costs.

When approached by another tool supplier with tools that apparently offered a lower cost per part, it agreed to use them. It quickly became apparent, however, that the results were less than satisfactory. While the new tools were, on occasion, capable of delivering results of the required standard, it was not possible to achieve these results consistently.

At this point, Doncasters decided to reinstate MAPAL as a key tooling supplier and the companies have been working together ever since.

In order to address the need for continual improvement, MAPAL has recently been collaborating with and part funding Rattanachai Rattanakit, an MSc student from Birmingham University who is sponsored by Doncasters and who is investigating ways in which PCD tooling can be used to cut production costs.

To date, this collaborative effort has allowed the introduction of PCD tooling for the turning operations, and this is delivering decisive benefits. These include reduced cutting pressure, which minimises the risk of distorting the delicate impeller blades, improved surface finish and extended tool life.

Work is currently ongoing to finalise the design of PCD tools that will bring similar benefits to the bore machining operations, a task that is made more complicated by the very small diameter of the bore, which in most cases is 6 mm or less.

Good progress is being made and the most recent prototype PCD drills and reamers delivered by MAPAL already have the potential to outperform their carbide equivalents and to return a very attractive cost per part.

“Almost every supplier claims that they approach and treat their customers as partners,” said Brendan Haffner, Technical Manager of Doncasters’ Coventry Operations, “so it’s not surprising that such claims are often taken with a pinch of salt. Our experience shows, however, that in the case of MAPAL, the claim to be a partner really is justified.”