Broaches are long, multi-toothed cutting tools equipped with progressively deeper cuts. The process of broaching involves machining both internal and external surfaces such as keyways and various types of gears. Each of the teeth on a broach will remove a pre-set quantity of material from a given location, and the total amount of material that is removed will be comprised of the depth of the cuts from each tooth on the broach part.
The process of broaching is valuable because it can produce parts with a superior surface finish and which also has tremendous dimensional accuracy. As opposed to other processes such which might be used, broaching can be a very good alternative, and even though broaches tend to be expensive themselves, they can be used in high-production runs to mitigate the cost. Here is an overview of the various types of broaches that are most commonly used in various industries today.
Push and Pull Broaches
It’s necessary for a push broach to be fairly short since it would tend to buckle and break if it had to support a load that was too heavy. Push broaches are most often used in uncomplicated arbor presses when the volume of work will be relatively low. In medium-to-high volume runs, a push broach would be used in conjunction with a broaching machine.
Pull broaches are pulled by a machine in a horizontal direction, or downward across a workpiece. Flat broaches can be rigidly mounted, so that a workpiece can easily be guided over the broaching teeth, especially in cases involving automobile cylinder blocks, which are often faced in this manner. Internal broaches can be either pushed or pulled through a beginning hole, and the machine used can either be fully automated or it can have multi-station verticals to accomplish simple presses.
Keyway broaches are almost always used to cut the keyways in machine tools and parts because they consist of slender, flat bars that have been fitted out with cutting teeth that are spaced along a single surface. Internal and external keyways can be cut using broaches of this type. Internal keyways generally require a slotted bushing or a horn which can fit the hole, so that a keyway broach can be pulled right through the horn and can be guided by the slot. When you are machining a number of parts with the same diameter and keyway size, it will be possible to use an internal keyway broach which has been designed to fit the hole.
Shell broaches are often used for the semi-finishing, roughing, and finishing sections associated with any broach tool. The main advantage of using a shell broach is that any sections which are worn can be removed, and either replaced or re-sharpened much more cheaply than a conventional uni-piece tool. When shell broaches are used for the finishing teeth, it will be possible to grind the shell teeth to much greater accuracy than those used in a long, conventional broach tool.
Those broaches which are used to remove material from an external surface are considered to be surface broaches. These broaches are generally pulled over a workpiece surface to accomplish the work, although alternatively, the workpiece can be passed over the tool on a vertical, horizontal, or chain machine, so as to produce contoured surfaces or flat surfaces.
Although some types of surface broaches do have solid construction, most of them actually have a built-up design which includes inserts, sections, or tool bits which are assembled, and which are secured in some kind of broach holder. This holder will fit on a machine slide and will provide a good deal of support and rigid alignment.
Vertical Broaching Machines
The majority of all broaching machines currently in existence are vertical broaching machines, and of these, the numbers are equally divided between vertical internals and vertical surface machines. Vertical broaching machines are nearly always driven by hydraulic systems, and they’re used in all major facets of metalworking. Vertical internal broaching machines can be of several types, those being pull-up, pull-down, push-down, or table-up, depending on how the machine was designed to operate.
Horizontal Broaching Machines
The original screw-driven machines were constructed so as to be horizontal units, but gradually these types of vertical machines evolved when it became obvious that floor space could be used much more effectively by having vertical units installed. Now horizontal machines, which are either mechanically-driven or hydraulically-driven, are becoming more popular among users because they have extremely long strokes, and they are not limited by ceiling height in the same way that vertical machines are.
Something like 40% of the broaching machines in existence now are horizontal broaching machines, and they are used exclusively for tasks such as finishing automotive engine blocks. The greatest amount of horizontal internal broaching is accomplished on machines which are of the hydraulic-pull type, and whose configurations have become standardized.
The majority of horizontal broaching machines today are horizontal internal machines, and of all these machines, about 25% are more than 20 years old. They are used most commonly in the production of general industrial equipment, but in truth, they are also found in practically every kind of industry in the world.
Chain Broaching Machines
This type of machine is most popular when used for surface broaching in high-volume production runs. In order to make this kind of machine productive, it will be necessary to eliminate the return stroke by mounting any tools or workpieces on a continuous broaching chain. Most commonly, the tools will remain stationary and mounted in a kind of tunnel on the machine’s top section, allowing the chain-mounted workpieces to pass below them.
Turn Broaching Machines
These types of machines are used for circular, linear, and spiral operations, and the peripheral type cutter assemblies are generally assembled in segments. Any turn-broaching system will generally use its standardized components for finishing and roughing, and the machine type determines the design of the tool, whether that be linear, spiral, or circular.
The roughing inserts and the number of segments the tool has will depend on requirements relative to the stock removal rate. Finishing segments are equipped with inserts in adjustable cartridges which can be established at very tight tolerances. It is possible to achieve a very long tool life with such broaching machines because of the relatively brief engagement of individual cutting edges.