Broaching is performed using a multiple-teeth cutting tool by moving the device linearly about the work in the direction of the tool axis, as in Figure 1. The machine tool is called a broaching machine and the cutting tool is called a broach.
In some jobs for which broaching can be used, it is a highly productive method of the machining process. Advantages of the broaching process include good surface finish, close tolerances, and various work shapes. Due to the broach’s complicated and often custom-shaped geometry, tooling is expensive.
Figure 1: Broaching operation
There are two principal types of broaching:
- External (surface broaching) and
- internal.
External broaching is performed on the outside surface of the workpiece to create a particular cross-sectional shape on the surface. Figure 2.1 shows some possible cross-sections that can be formed by external broaching.
Internal broaching is accomplished on the internal surface of a hole in the part. A starting hole must be present in part to insert the broach at the beginning of the broaching stroke. Figure 2.2 indicates some of the possible shapes produced by internal broaching.
Figure 2: Work shapes that can be cut by (2.1) external broaching and (2.2) internal broaching.
Cross-hatching in the above figures 2.1 and 2.2 indicates the surfaces broached.
The primary function of a broaching machine is to provide a precise linear motion of the tool past a stationary work position, but there are various ways in which this can be done. Most broaching machines can be classified as an either vertical or horizontal machines.
Most broaching machines can be classified as an either vertical or horizontal machines. The vertical broaching machine is designed to move the broach along a vertical path, while the horizontal broaching machine has a horizontal tool trajectory.
Most broaching machines pull the broach past the work. However, there are exceptions to this pull action. One exception is a relatively simple type called a broaching press, used only for internal broaching, that pushes the tool through the work part. Another exception is the continuous broaching machine, in which the work parts are fixtured to an endless belt loop and moved past a stationary broach. Because of its continuous operation, this machine can be used only for surface broaching.
