Probably the main weakness of thin-film diamond-coated inserts is lack of toughness. CVD diamond films are brittle when deposited on low cobalt substrates. These inserts are not always robust enough to endure high mechanical shock. They are not always the best choice for heavy metal removal and interrupted cutting.
As with most coated inserts, thin-film diamond-coated inserts are "throwaways." They cannot be reground.
Predicting the performance of CVD diamond inserts is still somewhat uncertain. Vagaries in cobalt distribution in the tungsten carbide substrate makes wear difficult to predict. Nevertheless, compared to non-diamond inserts, a tool-life increase of 10 to 50 times is common--depending, of course, on machining conditions and material.
At this time, diamond tools are limited to cutting only non-ferrous materials. However, experiments involving super-cold gases blown into the interface between a steel workpiece and a diamond tool are being conducted with encouraging results. It may be practical to cut ferrous materials with diamond in the near future.
By Chris Koepfer
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