Procedure to Make Tungsten Carbide Cutting Tools Ⅷ

In last part we know that tungsten carbide cutting tools are obtained through a final machining process on carbide blanks, including grinding, cutting, drilling, milling and sawing, etc. But machining may not be the final step for some type of cutting tools, since thereafter they are usually coated with special layers of wear resistant materials for longer life and better cutting efficiency. We explain firstly CVD.

Coating

To prolong tool life under challenging cutting conditions, many types and combinations of coatings have been developed for tungsten carbide cutting tools. TiC layers were the first to be applied by CVD. Others followed like TiN, TiCN, Al₂O₃, AlON as well as combinations and permutations. They can be applied mainly in two ways: by chemical vapor deposition (CVD) or physical vapor deposition (PVD). Both types are applied in furnaces. Coated hardmetal is the dominant tool material for indexable inserts.

CVD-Chemical Vapor Deposition

For CVD, the coating is usually 5- 20 microns thick. Milling and drilling inserts usually receive 5–8 microns, as these operations require better surface finish, and they encounter more impact, so they require greater edge toughness. To apply a CVD coating, the parts are placed on trays and sealed in a furnace. The furnace is drawn down to a vacuum.

For each layer, the appropriate gases are introduced into the furnace, such as hydrogen, titanium tetrachloride, methane, nitrogen, aluminum chloride. A chemical reaction occurs, depositing the layer of coating on the inserts.

 (To be continued-This article is divided into several parts and this is part 8, for part 7 please refer to http://news.chinatungsten.com/en/tungsten-information/80277-ti-10330; for part 9 please refer to http://news.chinatungsten.com/en/tungsten-information/80279-ti-10332)

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