Audi

Machining cast iron cylinder bores at Audi

The V8 TDI engine was developed by Audi for its A8 TDI range about three years ago. Among its many new features were for the first time pearlitic cast iron cylinder liners which were finished machined with tungsten carbide tools.
However, the company was looking for improvements in tool life and machining time, so decided to carry out trials using a single-edged polycrystalline diamond (PCD) boring tool.

The tool (pictured above) was fitted with an indexable insert with an average diamond grain size of 25µm. In these trials the same depth of cut (0.15 mm) and the same feed (0.20 mm) was used as with the carbide tools, but the cutting speed was 50% higher. The results of the trials showed that the use of PCD tools at moderate cutting speeds achieved a tool life of 3,000 bores - almost seven times that obtained with carbide. Also, not only was the specified life of 1,500 bores greatly exceeded, but because of the greater cutting speed there was no problem in meeting the specified cycle time.

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