Advantages of Diamond Coated Inserts

The metalcutting advantages of diamond are well known. It's not only the hardest substance on earth, but it also has a very low coefficient of friction (less than Teflon) and exhibits thermal conductivity several times better than copper.

Until the CVD diamond process became practical, shops had one type of diamond tool available: polycrystalline diamond (PCD). PCD has been used in metalworking for several years. It consists of diamond crystals in a cobalt binder. Segments of the PCD are brazed on the cutting edge of a carbide insert. Usually only one cutting edge receives a diamond segment, which is precisely shaped by a wire electrical discharge machine to fit a recess in the insert.

The cutting edge geometries of PCD are limited, leading the industry to explore CVD thin-film technology as a complement or even replacement.

Flexibility in insert design is a big advantage of thin-film diamond-coated inserts. As with other coated inserts, chipbreakers and rake geometries are molded into the insert when it is pressed. PCD tools, on the other hand, are limited to very basic geometries with few chipbreaker designs available.

The CVD process "grows" diamond over the entire substrate surface. Depth of cut is not limited by the size of the diamond segment as in PCD tools. Complete surface coverage with CVD thin-film diamond also helps chip flow. Because diamond has a low coefficient of friction, chips move across the various faces of the insert smoothly. When cutting gummy materials, this slippery coating discourages material build up on the cutting edge and insert body.

A diamond insert has multiple cutting edges. Because all edges are coated, the inserts are truly indexable--a triangle has three usable edges, a square has four, and so on.

Performance characteristics of CVD diamond inserts are comparable to PCD. In many applications, CVD diamond inserts can be a direct replacement for PCD. In some cases, the use of chipbreaker geometry allows the machine tool feeds, speeds and depth of cut to be increased over PCD tools without such geometry.

CVD diamond inserts tend to wear evenly. As cutting erodes the diamond film to the point where carbide is exposed, the substrate tends to continue cutting although much less efficiently. This gradual wear-through permits in-process tool monitoring when machines are running lightly tended.

REF: Diamond-Coated Carbide Inserts-Ready, Set, Go By Chris Koepfer