What is Broaching? The Process, Uses, and Products
Broaching is a machining process that uses a specific tool called a broach. The broach is a custom tool with teeth that removes material to shape a part.
Broaching has been used since the 1850s, but it became more precise around 100 years ago which increased the capabilities. This is a unique type of machining because each broach is made to cut a uniquely shaped part. In the broaching process, the cuts are made in a single pass of the broach tool which makes this machining process efficient for high volumes of identical parts.
In this post, we’ll explain how broaching works and what it’s used for today.
Overview of the broaching process
The process starts by creating a broach. This is like a saw or key shaped tool that can be used to make cuts into a piece of raw material. A broach usually has 3 distinct sections:
- The roughing teeth which remove most of the material
- The semi finishing teeth provide a surface finish
- The finishing teeth provide the final finish
Broaches can be expensive, costing up to $30,000. This makes broaching a better choice for large quantities of parts. One broach can be used to machine thousands of parts. The exact number depends on many factors— the materials, the quality of the broach, and the part design. Then the tool can be resharpened and reused for more of the same parts.
The broaching process is simple because the machine only needs to move the broach in a linear direction to form the part. During the process, the broach is moved against the stationary part to remove material, or the part is moved against the broach. In both cases, the part goes from raw material to finished part in a single movement.
Here’s an example of what a broaching tool might look like:
What is broaching used for?
When broaching was first used, it was to machine internal keyways. Later on, broaching was used to add rifling to the inside of gun barrels. Today, broaching is used for many more types of metal parts. It is less precise compared to CNC machining and milling, but precise broaching can achieve a tolerance of ±0.0005 inches. CNC machining usually has a tolerance of 0.0002 inches.
Due to the high costs of broaches, they’re best used for large quantities of parts. Some common parts that are machines on broaches are precision gears, sprockets, and other transmission parts. The broach is useful because it can cut all of the gear teeth quickly, and is precise enough for the automotive and aerospace industries. Broaching is also used to make internal slots or holes.
Here are some examples of parts that could be machined with a broach.
Broaching works best when a part is parallel to the broach tool. When there are multiple surfaces, angles, or curves on the part, the broach can’t perform cuts in a single pass, and usually isn’t the best machining option.
Broaching can be used for any type of metal or plastic, but softer metals like brass and aluminum are usually ideal. Hard stainless steel, Titanium, and superalloys like Monel or Hastelloy can be broached, but the broach wears out quickly so it’s less efficient.
Different types of broaching
Internal Broaching: This creates a hole, slot, or gear teeth on the inside of a part. All internal broaching requires a starter hole in the part. A round hole can also be changed to a different, larger shape using a square shaped broach.
Surface Broaching: This removes material from the surface of a part. This can be used to cut a precise angle, form gears, splines, and slots, and much more.
Pull Broaching: This pulls the broaching tool across the surface of the raw material to form the part. The broach is usually longer compared to push broaching. This is used for larger parts and when more material needs to be removed.
Push Broaching: The push broaching tool is compressed as it’s pushed across the workpiece. The cutting teeth on the push broach are usually smaller because they break more easily.
If you have more questions about broaching machining, don’t hesitate to reach out to our team. We have worked on thousands of custom projects in a range of industries. We are happy to help you pick the best machining process for your next project.
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