If someone were to ask you, “What is broaching?” would you be able to answer intelligently? Many people have not heard the term before, or at best are a little foggy about what’s involved, and for everyone else who isn’t quite sure, the following article will describe what broaching is all about, and where it fits in with the zillions of other applications available in the business world these days.
What Exactly Is a Broach?
You may actually have seen a broach without knowing it, because it’s a tool with metal teeth on all sides, and one of the most important characteristics of this kind of tool is how much material those teeth can remove in a single pass. The teeth themselves are grouped into sections on the body of the tool, with each one of three sections allocated to roughing, semi-finishing, and final finishing.
There are two main types of broaches, those being surface broaches and internal broaches. Surface broaches include many different designs, which are termed as follows: pot, straddle, contour, slot, and slab. Internal broaches, by contrast, come in styles that are termed solid, concentricity, keyway, shell, and modular.
No matter what the style type of a particular brooch, internal or surface models are generally made from either high-speed steel or alloy steel. High-speed steel types generally have their bits coated with tin, but manufacturers are careful not to use coatings which will be unable to stand up to the wear and tear of normal broach usage.
The Broaching Process
The process itself changes according to whether you’re using internal broaching or surface broaching. In surface broaching, you’ll have the most direct and straightforward operation, because the two surfaces involved act on each other. As an example, either the broaching tool stays in one place and the workpiece is moved or manipulated in contact with it, or the workpiece remains in one place while the broach is moved in some way against it.
Normally, a broach consists of many rows of teeth which do roughing work, which are followed by a few rows of teeth that accomplish semi-finishing, and then a few more rows of teeth which provide the finish for the surface being operated on. The total amount of material that is removed by a broach will be the sum of each tooth’s depth of cut, and when the final pass has been made it can leave a very smooth finished surface.
The tool design will be based on the shape which is being cut, as well as the properties of the workpiece which is being operated on. Internal and external surfaces can be broached to just about any shape you can imagine, including everything from simple slots to turbine blade hubs for advanced aircraft engines.
The broaching process is often used to make for making precise cuts which clear out diameters or to generate holes which are not round but are instead shaped like a hexagon, square, or a double D. The broaching process is also used to cut gear teeth, splines, and some other shapes. The whole point of broaching is to produce either simple or complex forms in a very short period, most often in a single pass, and with accuracy that can be repeated very reliably.
As a broach moves past the workpiece, each tooth on the brooch takes out a shallow cut along the entire length of the workpiece. It carries that chip which is cut to the end of the part and removes it. In most cases, one pass of a broach can accomplish the entire machining of a surface. When multiple passes are necessary, it’s usually because of the geometry of the part, in addition to the amount of stock that has to be removed.
As an industrial process, broaching is frequently preferred to other processes such as milling, boring, reaming, or shaping, even though it is generally more expensive to do than any of those other processes. The factor which makes it so appealing is that it is much better to use during high production runs than other processes, and that will very often totally offset the extra cost of the process itself.
Practical Uses of Broaching
You might be surprised to learn that there is a whole slew of practical uses for the broaching process. You may even have seen the results of some kinds of broaching in hand tools, automotive design, farming equipment, plumbing, automotive design, or appliances. The chief application for broaching, however, is in producing high-volume parts which require complex cuts, or cuts which are either accurate, repetitive, or both.
While broaching is an essential process for many broader applications, it is always most successful when materials are used which have a hardness rating between 26 and 28 Rockwell C. Several production companies have also enjoyed success in making broaching tools when they have used materials rated at a hardness of 32 Rockwell C.
Taking Care of your Broaches
Most brand-new brooches are capable of performing at a minimum of 8,000 cuts. However, if you’re meticulous about caring for your broach and sharpening it regularly, it is possible to get as many as 60,000 cuts out of your tool before it begins to degrade. Some people go to great lengths to do everything possible to preserve their broaches because they are fairly expensive, and that makes them a bit more difficult to replace.
Most companies cannot afford to replace broaching tools frequently, which means they have to go to great lengths to preserve them and to handle them with care, so they can last as long as possible. For this reason, some companies will send out their broaches to be sharpened and reconditioned after approximately 3,000 cuts. When you begin to notice that more force is required to cut your parts, that is a strong indication that it may be time to sharpen your broach, so that it can be more effective in its daily work.