Broaching is a machining process that uses a cutting tool called a broach to cut shapes in materials like metals and plastics. The most common shape produced by broaching is an internal keyway in a pulley or gear. Broaching machines and processes have remained mostly the same since the industrial revolution. Broaches can be custom made or readily available in numerous shapes and sizes. Proper alignment and lubrication are necessary for successful broaching operations.
Broaching is the machining process of cutting a shape by moving a broaching cutting tool, usually called simply a broach, across material such as metals or plastics. The broach’s rows of teeth, or chisels, progressively increase in size. Each tooth gradually removes excess material and the desired shape is only complete after the last tooth in the broach has passed through the material.
The shape found in an internal keyway in a pulley or gear is the most common shape produced by broaching as broaching is the simplest method of cutting internal shapes known as splines on gears, sprockets and hubs. Polygons such as squares are also commonly and easily produced from a broach, especially when a round hole is to be enlarged into a square or other non-circular shape. Sometimes, broaches are also used to cut external shapes such as slots.
Interestingly, due to the effectiveness of their original concept and design, today’s broaching machines and processes have remained mostly the same since the beginning of the industrial revolution. No job is too big or too small for a broach. Numerous materials such as ferrous and non-ferrous metals and many types of plastics are suitable for broaching.
Broaching tools fall under the classification of multi-pronged cutting tools as they have at least two cutting edges. Broaches can be custom made from blueprints, but stock broaches are often readily available in numerous lengths and sizes. Common broach shapes include square, round, oval, keyway, serrated, D-shaped, fluted, and bowl broaches. Typically, broaches are made of high quality tool steel such as PM-M4.
In addition to the broach cutting tool itself, broach holding devices are also required in broaching operations. For example, in keyway broaching, a device called a broach horn holds the broach in a shared circular hole.
All broaching operations require proper alignment of the broach and its supporting tools. Incorrect alignment will result in cuts that are not perfectly straight. Misalignment can also cause the broach to break. Lubrication is often used in broaching to reduce friction, either by applying cutting oil to the material being cut, or by lubricating the back of the cutting broaches, depending on the types of broaches and materials used for broaching.
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