Broaching is a machining process used to produce linear slots, splines, keyways and general straight features on a workpiece by dragging a toothed cutting tool called a broach through the metal. A broach is a multi-tooth cutting tool with the teeth arranged in a line, much like a hacksaw blade. The teeth successively remove layers of metal as it progresses through the workpiece, producing a smooth accurate surface. This gives broaching the ability to create intricate slots and forms with very high precision and little finishing required. The many teeth also make broaching a fast machining technique.
Types of Broaching Tools
There are two main categories of broaching tools based on the tool material and construction: solid-tooth broaches and inserts broaches. Within each category there are also sub-types based on the specific application.
Solid-tooth Broaching Tools have teeth made from a solid piece of tool steel. They are used for heavier cutting applications and can be made in a variety of profiles to machine complex internal and external shapes. The most common solid-tooth broach types are:
- Straight: Used for cutting straight slots, keyways and similar linear features. The teeth form a straight line.
- Form: Feature teeth specially contoured to cut complex contours, gear teeth and splines.
- Combination: Feature both straight and form teeth to machine complex contours with some linear sections.
Insert broaches on the other hand have multiple individually replaceable cutting inserts mounted in holes in the broach body. This makes insert broaches suitable for mass production work as the inserts can be changed out efficiently when worn. Common insert broach types are:
- Multi-tooth: Have several standard inserts arranged linearly for slotting.
- Form: Contain special contoured inserts designed for complex tooth-by-tooth profiling.
- Combination: Utilize a mix of straight and profiled inserts.
Broach Construction and Tooth Design
Regardless of whether it is a solid-tooth or insert broach, all broaching tools are constructed with carefully engineered tooth profiles, geometries and land widths to efficiently cut metal without breaking or chipping. Some key design aspects:
- Tooth profiles: Each tooth subtly varies in profile length and shape to progressively increase the cut. This staircase effect prevents snatching.
- Clearance lands: The gaps between teeth provide clearance for removed chips. Wider lands are needed for tougher cuts.
- Tooth geometries: Rake, relief and lead angles all influence cutting action and tool life.
- Shank designs: Broach bodies use tapered, straight or expandable shanks to match holder designs.
- Construction materials: Broach teeth/bodies crafted from premium tool steels like D2 or M2 for hardness and wear resistance.
Broaching holders, pullers and lubrication systems are also important components that support high precision broaching. When constructed and applied correctly broaching tools can achieve cuts accurate to within a few thousandths of an inch.
Broaching Applications
Given the precision and versatility they offer, broaching tools are used across many industries for critical applications such as:
- Gears: Broaching produces highly accurate internal and external involute gear teeth. Popular for automotive transmissions.
- Splines: Helical, straight and worm splines for shafts are broached for precise fit. Found in machinery, vehicles and more.
- Keyways: Broaching straight and tapered internal or external keyways for fasteners. Regularly broached in industry.
- Complex profiles: Broaches cut intricate internal and external contours for aerospace components, molds and dies more efficiently than milling or grinding.
- Slotting: Straight slots, undercuts and cross drilled holes are everyday broaching uses for parts in a range of industries from appliances to firearms.
- Micro broaching: Especially small broaches cut miniature features for electronics, medical devices and other precision applications under microscope.
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