Tech Talk

What are "Dressing and Crushing Techniques"?

Efficient use of diamond and CBN profile grinding wheels in automatic processes can be achieved if suitable conditioning and dressing processes are available. In this regard, the creation of chip spaces and the efficient removal of chip, abrasive and bond residues from these chip spaces are of great importance along with the actual profiling of the grinding wheel.

Basically, with dressing a distinction can be made between stationary and rotary dressing techniques. Diamond and CBN grinding wheels are dressed predominantly using driven rotary dressing tools.

Profiling techniques may be subdivided into four different types of process - with and without relative motion, and with line contact or point contact.

Compared with the use of a diamond profile roller, profiling using a diamond form dresser offers and considerably greater degree of flexibility, since the grinding wheel profile is generated by controlling the path of the tool as the rotating form dresser is moved in a radial and an axial direction. This technique is used for, amongst other things, the profiling of CBN grinding wheels.

Diamond grinding wheels are generally profiled using the crushing technique. In this case, steel or carbide profile rollers are used, with the large contact areas resulting in high forces combined with expansion of the system and consequently resulting in shape defects. Crushing must be carried out away from the grinding machine. In addition, each different profile requires a separate crushing roller. When this method is adopted, the profiling tools used for this process are subject to relatively high degrees of wear.

Point crushing is a new technique. For the most part, with this method there is no relative speed between the dresser and the grinding wheel, i.e. the form dresser rolls on the wheel.

The grinding wheel profile is produced by the path followed by the form dresser. The aim of the point crushing operation is to break up the bond bridges on the grinding wheel surface. Vitrified bond grinding wheels specially developed for this process may be used for this purpose.

The crushing roller is fed in until contact is made. The well-known touch dressing techniquea are suitable for this. The dressing or crushing infeed of a few microns generates a normal force capable of breaking up the bond bridges in a controlled fashion.

Because of these characteristic features, point crushing offers considerable advantages over the full-width crushing technique, since point contact means that lower forces are generated, and these can be precisely adjusted, by means of the crusher infeed, to suit the behaviour of the grinding wheel. Also, point crushing can be employed at higher speeds, which enables this technique to be integrated into existing grinding machines.

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