The cutters of a PDC bit are mounted on a bit body. There are two types of bit body used for PDC bits. One of these is an entirely steel body and the other is a steel shell with a Tungsten Carbide matrix surface on the body of the shell.
The cutters on a steel body bit are manufactured as studs (Figure 19). These are interference fitted into a receptacle on the bit body. Tungsten carbide button inserts can also be set into the gauge of the bit to provide gauge protection. The stud can be set with a fixed backrake and/or siderake (see below). An advantage of using a stud is that it may be removed and replaced if the cutter is damaged and the body of the bit is not damaged. The use of a stud also eliminates the need for a braze between the bit body and the cutter. Field experience with the steel body bit indicates that face erosion is a problem, but this has been overcome to some extent by application of a hardfacing compound. Steel body bits also tend to suffer from broken cutters as a result of limited impact resistance (Figure 20). This limited impact resistance is because there is no support to the stud cutter.
Matrix body bits use the cylindrical cutter (Figure 18) that is brazed into a pocket after the bit body has been furnaced by conventional diamond bit techniques. The advantage of this type of bit is that it is both erosion and abrasion resistant and the matrix pocket provides impact resistance for the cutter. Matrix body bits have an economic disadvantage because the raw materials used in their manufacture are more expensive.
Institute of Petroleum Engineering, Heriot-Watt University