Broaching is a cutting process using a broach as the cutting tool. As the broach moves linearly relative to the workpiece, the machining allowance is sequentially removed by the progressively larger teeth on the broach. Typically, a single stroke is sufficient to complete the machining process, making it a highly efficient finishing method. However, due to the complex structure and high manufacturing cost of broaches, and their specialized nature, broaching is primarily used for mass production. Based on the characteristics of the machined surface, broaching is divided into internal broaching and external broaching.
① Internal Broaching: Used to machine through holes and internal slots of various cross-sectional shapes, such as round holes, square holes, polygonal holes, spline holes, keyway holes, internal gears, etc. A pre-machined hole is required before broaching to allow the broach to be inserted. The diameter range for broaching holes is 8–125 mm, and the hole depth does not exceed 5 times the diameter. In special cases, the diameter range can be as small as 3 mm and as large as 400 mm, with a hole depth reaching 10 meters.
② External broaching: Used for machining non-closed surfaces, such as planes, shaped surfaces, grooves, tenons, blade tenons, and external gears. It is particularly suitable for machining large planes and complex surfaces in mass production, such as cylinder blocks, bearing seats, and connecting rods in automobiles and tractors. The dimensional accuracy of broached surfaces can reach IT8-5, and the surface roughness is Ra2.5-0.04 micrometers. The accuracy of broached gears can reach grade 6-8 (JB179-83).
During broaching, the sequence and method of removing machining allowance from the workpiece include forming, incremental, rotary, and combined rotary methods.
① Forming: High machining accuracy and low surface roughness, but lower efficiency; the broach length is relatively long, mainly used for machining small to medium-sized round holes and shaped surfaces with high precision requirements.
② Incremental: Suitable for rough broaching of complex surfaces, such as square holes, polygonal holes, and spline holes. The broaches used in this method are easier to manufacture, but the surface quality is poorer.
③ Wheel cutting has high efficiency and can reduce broach length, but the surface finish is poor. It is mainly used for machining round holes with large dimensions, large machining allowances, and low precision requirements.
④ Combined wheel cutting uses wheel cutting for rough broaching and forming method for fine broaching, combining the advantages of both. It is widely used for round hole broaching.
