Broaching Basics
A toothed tool is called a broach and the machining process that is used is called broaching, which is used to remove material. There are two types of broaching: rotary and linear. Rotary has the broach rotating and pressing into the work piece to cut a symmetric shape with an axis. It is used in a screw or lathe machine. A broaching machine is used for linear and linear broaching is the most common process of the two. The tool is used linearly against the surface of the work piece, which affects the cut. The cut is efficiently performed in one pass of the tool using either process of the broaching.
Broaching is great to use for odd shaped pieces of material and when precision machining is required. The most common machined surfaces are non-circular and circular holes, flat surfaces, keyways, and splines. Work pieces include sizes up to medium range like forgings, castings, stampings, and machine parts. When high quantity production is needed, broaching is usually chosen over other methods.
There are three sections of the broach: roughing, semi finishing, and finishing. The feed is already built into the tool, which makes it a unique machining process. The machined surface will always be the inverse of the broach’s profile. The RPT or rise per tooth, also known as feed or step, will determine the size of the chip and the amount of material needing to be removed.
There are two types of broaching process, internal and surface. Internal is more complicated. The work piece has to be held down to something like a chuck, fixture, or work holder. Then, it is mounted into the broach machine. The elevator or part that moves the broach tool above the work piece will lower the tool through the work piece. The machine’s puller or hook will grab it when it goes through. It is grabbed at the pilot of the broach and the elevator will release the top and the puller will pull the broach through the work piece. The broach can be rotated to create gun barrel rifling or a spiral spline.
A simple process is called Surface broaching. The work piece is held stationery and the broach is moved against it, or the work piece is moved against a stationary surface broach.
There is no skilled labor or complex motions needed as the features are already built into the broach. The broach basically is just a collection of cutting tools that are single point that are arranged in sequence and cuts one after another. The cuts are analogous a shaper and its multiple passes.