What Is Broaching in Precision Mechanics? And How Does It Differ from Slotting?

Mechanical machining operations are numerous and we have often dealt with various operations to transform a shapeless metal block into a structure capable of performing all the necessary activities to achieve a goal. In this list of operations we can also mention broaching, less well-known than hole reaming and grinding but equally important.

Why? Because it is crucial to know the details of broaching and what the differences are with very similar activities like keyseating? In this blog we deal with exactly this: clarifying doubts to work in the world of metalworking operations.

What is Broaching, a Definition

By this term we mean a typical operation of mechanical machining with chip removal using cutting tools. The broaching activity allows the operator to obtain complex, internal or external profiles of great precision.

Another typical characteristic of broaching is the excellent surface finish, which is obtained with a single pass. This is one of the reasons why these techniques are used to create extremely precise elements for auto and motorcycle engine mechanisms.

What Equipment is Needed for Broaching?

The work in question is performed with a tool that has a particular name: the broach. It is a machine that uses a cutting tool for hard metals that removes the excess element, transforming it into chips, to obtain complex shapes with a single pass that determines extreme precision, with now microscopic tolerances.

Although this has not always been the case, since broaching began its first steps in the first half of the nineteenth century. At the beginning of the work, the levels of professionalism were not comparable with those that can be achieved with current activities.

Over the years, the spinatrice (another useful name for indicating the broaching tool) has acquired greater execution precision and today it presents itself as a machine for precision metal processing that with a combination of cutting edges can define particular shapes on holes and profiles, depending on whether one uses an internal or external spinatrice.

Advantages and Disadvantages of this Machining

Before evaluating whether or not to use a broaching operation, this table can be useful to understand the positive aspects and the criticalities of this condition. One cannot decide whether or not to use broaching without knowing the subject.

As you can well understand from this comparison table, the broaching phase is perfect for large-scale professional activities and for a good number of tools or gears. A broach (known as a slot cutter) can hardly be used for the single element. Because it is complex and absolutely expensive equipment, it cannot be used independently and for hobby activities.

In Which Activities is Broaching Used?

Certainly, it doesn't happen every day that you need to ask a broacher to work a steel block to create, for example, the profile of a keyway. Many colleagues and customers ask us: "When is broaching actually used? Who needs this?"

The answer is quite simple: broaching is the absolute protagonist in the automotive industry and in the production of transmission components. Where you find gears, teeth, irregular profiles for pulley and crankshaft inserts, there is a trace of broaching that becomes essential especially where special and unusual asymmetries are needed, especially when going beyond the classic cylindrical shape of the hole. And it's needed, for example, a toothed seat to transmit energy from an engine.

How is This Technical Operation Performed?

To describe the broaching process is possible by imagining the result itself: to realize such articulated profiles you must have a professional broach, a tool for precision metal processing that can perform the work with a unique speed. Unlike keyseating, where you use a single-blade tool that to achieve the same result must pass dozens or hundreds of times over the part.

Everything starts with a pilot hole since broaching cannot perform this first pass. The rule to follow: the diameter of the first hole must be slightly larger than the initial part of the broach. But always smaller than the final profile.

This is so that the blade can remove the excess material. The workpiece to be machined is inserted into the broaching machine and the cutting tool is passed through the pilot hole. The teeth pass one after the other and first remove the raw metal.

Then they finish the final work. Meanwhile, the nozzles spray cutting oil to reduce friction and facilitate chip evacuation. This step is fundamental - together with the choice of broach - to prevent chips from damaging the block.