To accomplish internal broaching, it is necessary to create a pre-existing hole in the material being worked on. The internal broach being used would then alter the shape and size of that starter hole into a hole that has a keyway, a spline, and some type of custom design profile, which might be square or hexagonal in shape.
The broaching tool itself will have successively larger teeth, and these will penetrate through the pre-existing whole, either by pulling or pushing their way through the part of the workpiece which is metal. Nowadays, internal broaching machines are entirely automated, and they can produce holes in metal parts and products very quickly and very efficiently.
The broaching process itself is always more effective on soft metals such as bronze, graphite, aluminum, or brass, and the broaching process is capable of producing many different machinery parts and tools. Some of these might include gears, screw heads, keyholes, pulleys, and a variety of other hardware. All these tools and parts which are produced by broaching are in great demand in a wide variety of industries.
That calls for the broaching service itself to be offered by several job shops around the country, which have extensive facilities and equipment for providing these kinds of broaching services. Another big advantage of having your broaching process done by the professionals is that a high degree of repeatability is achievable, as well as reliable machining. When it is necessary to produce products with virtually no variance or error, that calls for tremendous precision on the part of your broaching service.
Types of Internal Broaching
There are basically two types of internal broaching, and these are referred to as rotary and vertical broaching, each of which has its own specific method for forming a wider hole in a metal workpiece. When the pre-existing starter hole has been produced, this is referred to as blank prepping, and the workpiece is then ready for internal broaching, either of the rotary broaching type or the vertical type.
Vertical broaching can consist of either push broaching or pull-down broaching, and push broaching is accomplished using vertical machines in the broaching tool itself, which would be pushed up or down throughout the metal workpiece. Short broaches are most commonly used so as to prevent any kind of buckling, although this does limit the amount of metal which can be moved in a single pass.
Push broaching is ideal for relatively light work and shorter runs, with the machinery necessary being far less expensive than what’s required for pull-down broaching. In pull-down broaching, it is only possible to push the pool tool down vertically on the machine, and it ensures that the tool is kept in tension with no buckling being possible. This kind of broaching calls for thin, long broaches that are capable of making exceptionally deep holes. Both types of vertical broaching make use of machinery that is very space-efficient, and which provide a range of cut lengths which can be customized to specifications.
Rotary broaching makes use of a rotating broach tool in order to produce a specific design and is often used when you need to create an asymmetrical whole that must be produced in a single pass. Sometimes a screw machine or lathe will be used for this purpose, depending on the indicated design. Rotary broaching is most often used when a component is comprised of hard material, and when a lathe will be used rather than a traditional broaching machine.
No matter which type of broaching is used, they all have the same objective, which is to minimize the time spent in producing components that are highly specific and require extraordinary precision. These parts must meet exacting standards of quality while also being produced quickly and efficiently. While many parts can be produced in a single pass, some complex parts require multiple broaching machines and multiple passes.
Types of Internal Brooches
There are six main types of internal broaches, with solid broaches being the most common of all. As you might expect from the name, this type of broach is made from a single solid piece of material. Similar to a solid broach is another internal tool called a shell broach, but the distinctive characteristic of a shell broach is that it creates a hole that passes through its center where it can be mounted on an arbor.
While shell broaches might cost more money in the beginning, you would eventually save money with a shell broach because when replacement is necessary, the pilots are already situated on the mandrel, which means you don’t have to reproduce them each time there is a replacement required. Modular broaches are generally used on extremely large internal broaching applications and are similar to shell broaches in that they have a construction which is multi-piece in nature.
Both these types of broaches are constructed that way because it’s much cheaper to build and to sharpen them than it would be to build and sharpen a broach which is of solid design. Another common type of brooch is the keyway broach, and this one uses a special fixture which is termed a horn, to support it and accurately position the workpiece part concerning the broach itself.
A concentricity broach is a unique kind of spline-cutting broach that is capable of cutting both the spline and the minor diameter to ensure precision in concentricity. One last type of internal broach is the cut-and-recut broach, and the primary usage for this type of tool is in cutting workpieces that have thin walls.
Thin-walled workpieces tend to expand significantly while being cut, and then afterward they shrink back down. The cut-and-recut broach overcomes this issue by broaching the part with standard roughing teeth, which is then followed by a relief section as the workpiece undergoes shrinkage. Following the relief section, you would then have the normal roughing, semi-finishing, and finishing teeth, which would impart the final finish to the work surface.