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What impact does tap coating and geometry achieve?

Tuesday, July 9, 2019

Shark Line is our assortment of material specific taps which provide high performance and process reliability. Johan Bodin, R&D and global product manager for threading at Dormer Pramet, outlines the impact various coatings and geometries of this range have on performance.

 

Our Shark Line range of taps include a PVD multi-layer ceramic coating which has been through a post smoothing process. After the TiAlN coating is deposited an additional surface treatment is applied, making the surface smoother and more resistant to built-up-edge. This makes it ideal for high cutting speeds.

 

On specific Shark taps, such as our Blue-ring, a SUPER-B coating is applied. This has the high hardness and temperature resistance of TiAlN, combined with the frictional and lubrication properties of a WC/C (mix of tungsten carbide and carbon) surface layer, to further promote smooth chip flow.

 

This is particularly advantageous when threading tough, long-chipping, heat resistant materials, such as stainless steel, as it prevents swarf sticking to the cutting tool. It is also recommended for aluminium, as the WC/C surface acts as a barrier to limit adhesion between the workpiece material and the TiAlN-coating.

 

An important element in threading applications is the cutting angle and force with which the tap enters the workpiece. This action increases temperature and stress, resulting in the deformation of the material, to the point that it breaks into chips.

 

Working with a general cutting geometry in materials that have a low resilience can have the effect that the threaded diameter becomes oversized. In materials that have a high resilience, the threads of the tap can be enclosed by the workpiece, increasing the risk of binding and tap breakage.

 

The geometry of our Shark taps has been designed to avoid this and support continuous production. Entering the work piece material with rake and relief angles specifically suited for that range of materials is essential for producing the correct threads.

 

A low rake angle provides the stability needed for working in hard materials, while a high rake angle

gives the lower cutting force for working in soft materials. A high relief angle prevents binding when working in materials with high resistance and resilience, while a low relief angle prevents oversized threads in materials with low resistance and resilience.

 

 

Johan Bodin

R&D & Global Product Manager – Threading

Dormer Pramet

 

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