Brazing Carbide

January 26, 2017

Silver brazing shims have proved the best way to secure carbide to tools.  Shims require no additional space and can be replaced or salvaged by melting off and re-brazing.

Torch and induction brazing are the most adaptable processes for joining carbide tips:  torch brazing for occasional work or in cases of varying size, and induction brazing for a production environment.  While furnace brazing is possible, it is not recommended due to problems positioning and holding the carbide during heating.  However, a furnace and assembly fixturing may be economical in the case of large production requirements.

As tungsten carbide is difficult to wet, a brazing alloy containing nickel should be used. BrazeIt A50N is the most commonly used alloy when brazing carbide, whether it be in solid or plymetal form.  For applications where carbide and heat treatment of steel is done in one operation, BrazeIt A40N2 is the recommended alloy.  Coupled with black flux, run out of alloy is better controlled at longer and higher brazing temperatures.

Tungsten carbide has a thermal expansion rate of 1/2 that of steel. During cooling, the contraction of carbide will be 1/2 the contraction of the steel shank.  The brazement, being proportional to the size of the carbide, is placed under internal shear stress, which when combined with service stress during use, can lead to joint failure on large inserts and cracking or breaking on thin carbide blanks.  To prevent failure, use plymetal on carbide exceeding 3/8 or 3/4 in maximum dimension.