Broaching process refers to the sequence and method by which the broaching allowance is cut from the workpiece. It determines the cross-sectional shape of the cutting layer cut by each tooth, hence the term broaching pattern. The appropriateness of the chosen broaching process directly affects the load distribution on the teeth, the length of the broach, the magnitude of the broaching force, the wear and durability of the broach, the surface quality of the workpiece, productivity, and manufacturing costs. Different broaching processes require different broaching design methods, making it a crucial step to determine in broaching design. Broaching processes can be categorized into three types: layered, segmented, and combined.
Layered Broaching: Layered broaching involves the broach teeth sequentially cutting off the broaching allowance layer by layer, with each tooth removing one layer based on its tooth rise. Layered broaching results in a smaller cutting thickness, leading to a smoother broaching process and higher surface quality. However, it requires a larger unit cutting force, more cutting teeth, and a longer broach. This results in higher tool costs and lower productivity. Depending on the surface formation process, layered broaching can be further divided into contour-based and incremental broaching.
Segmented Type: Broaches designed with segmented broaching patterns have cutting sections composed of several tooth groups. Each tooth group has 2-3 teeth of the same diameter, working together to cut off a layer of metal from the machining allowance. Each tooth only cuts a portion of a layer. The most common type is the rotary broaching type. The cross-section and broaching pattern of a rotary broaching type are as follows: the first and second teeth have the same diameter, but their cutting edges are staggered, each removing a few segments of material from the same layer of metal on the workpiece. The remaining metal is removed by the third cutting edge of the same group. This tooth does not have a circular chip flute. To avoid friction between the cutting edge and the workpiece surface cut by the first two cutting edges and to prevent the cutting of a complete circle of chips, its diameter should be 0.02-0.04 mm smaller than the blind diameter of the other two teeth in the same group.
Integrated broaching combines the advantages of layered broaching and segmented broaching. The roughing and transition teeth are designed with a rotary cutting structure, while the finishing teeth employ a layered structure. This shortens the broach length, maintains high productivity, and achieves better workpiece surface quality.
