Broaching is a machining process that uses a toothed tool to remove material in a consistent and accurate way. There are two types of broaching services, linear and rotary, which are used to produce different kinds of machining finishes, but in either case, production broaching is typically only used for precision applications and high-quantity production.
Broaching was pioneered during the mid-1800s when it was used to create pulleys and gears. During the early 1900s, it was used to create barrels for firearms. Today, broaching is used to create everything from small fasteners to automotive transmission gears, airplane components and more.
The Cutting Tools
The cutting tool used in broaching is called a “broach.” This cutting tool resembles a saw in profile, but width and tooth configuration can vary significantly. Broach teeth are precisely designed so that each tooth stands slightly higher than the last. As the broach passes along the workpiece, each tooth makes a small cut in the surface and carries a chip away from the workpiece. The difference in height between the first tooth and the last tooth is called the “rise,” and represents the maximum amount of material a broach can remove.
Broaches are often designed for specific jobs, and they can take on many shapes and sizes. There are several broach categories that relate to the work being performed and the broaching machine used to supply the force.
A push broach is a tool designed to be pushed by the broaching machine, while a pull broach is a tool designed to be pulled by the broaching machine.
A stationary broach is a tool designed to remain stationary while a machine moves the workpiece
The simplest broaches, designed to cut a single surface, may be rectangular in cross section with a single set of cutting teeth. Because broaches often cut internal characteristics, their cross sections vary extensively depending on the work being performed.
Simple broaching can be performed with an arbor press, but more complex operations require dedicated broaching machines. Several characteristics of broaches depend on the machine that will be used to move them across the workpiece. As mentioned above, some broaching machines pull the cutting tool while others push it. Traditional broaching machines are oriented vertically, moving the broach in an upward or downward direction. Others are oriented horizontally, and because they often hold the cutting tools in braces they can accommodate longer lengths without significant bending.
Advantages of Broaching
Broaching can be an ideal process for many CNC machining applications. One key advantage to broaching is that machine operators can perform broaching operations with little training. Because the complexity is built into the tool itself, very few parameters require adjusting during production. Perhaps most importantly, broaching can save time because the cutting process itself is rapid and easily repeatable.
Compared to sawing and grinding, however, broaching often acts on workpieces with greater force. Machining professionals must ensure that the workpiece material is strong enough to withstand the forces involved in broaching. Furthermore, if internal broaching is required, a hole must be made in the workpiece by casting or drilling before broaching is possible.