Mumbai University > Mechanical Engineering > Sem 4 > Production Process II

Marks: 5M

Year: May 2014, May 2015

Cemented Carbides: They are so named because they are composed principally of carbon mixed with other elements. The basic ingredient of most cemented carbides is tungsten carbide which is extremely hard. Pure tungsten is mixed with lamp black in the ratio of 94% and 6% by weight at about 1500 degree. The new compound tungsten carbide is then mixed with cobalt until the mass is entirely homogenous. This is made into blocks at very high pressure and then heated in hydrogen. The amount of cobalt used will regulate the toughness of the tool.

After the cutting edge wears out the tool has to be removed and then reground which is a time consuming process. The need for a more efficient method led to the development of inserts, which are individual cutting tools with a number of cutting edges and in various shapes. Thus a square insert has eight cutting edges and a triangle insert has 6 edges. They are available with a variety of chip breaker features for controlling chip flow and reducing vibration and the heat generated. They are usually clamped on the tool shank with various locking mechanisms. Less frequently inserts are brazed to the tool shank however due to different thermal expansion of the shank and the insert brazing must be done carefully to avoid cracking or warping. Clamping is preferred method because after one cutting edge is worn out, it is indexed (rotated in its holder) so that another edge can be used. Also a wide range of other tool holders are now available for specific applications, including tool holders with quick insert insertion and removal features for more efficient operation. The diagram shows the types of insert and mounting method using thread less lock pins.