broaching

a process of working metals by cutting on broaching machines using a tool with multiple blades called a broach. In light of the complexity and high cost of manufacturing broaches, the use of broaching is worthwhile for working large batches of parts, as in production of large lots or in mass production.

Types of broaching are distinguished on the basis of the order in which the final layer of stock is cut to size. In one method of cutting, all the broach’s cutting teeth remove the final layer, but they do not participate in the final shaping of the surface; this is done only by the last tooth. In a second method, each cutting tooth, in cutting the final layer of stock to size, simultaneously participates in forming the surface. A third method involves removing relatively large amounts of stock. In this method, all the teeth, which are arranged in groups of two or three, remove a layer of metal in sections rather than all at once across the entire width.

There are both free and coordinated methods of broaching. In the free method, the broach produces only the desired size and shape of the surface; in the coordinated method, the broach also produces the worked surface in the exact desired location relative to the reference surface.

In broaching, from 2 to 6 mm of stock is removed when working holes in forgings and castings. In holes produced by drilling, countersinking, countersink reaming, or boring, 0.2-0.5 mm of stock is left to be removed by broaching. The cutting speed in broaching is relatively low (2–15 m/min); efficiency is high, however, because the total length of the simultaneously cutting edges is great. Broaching produces a precision of class 3-2; the surface roughness of the worked surface varies from class 7 to class 9. A characteristic feature of broaching is the constant accumulation of chips in the depressions in front of each tooth. The teeth are often provided with grooves to break up the chips, thus improving the process of chip removal and preventing the broach from jamming.