In this article we will discuss about the classification of broaching machines used in industries.
(1) Pull-Broaching:
In this case, tool moves past the work and the work is stationary.
(2) Push-Broaching:
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In this case job is held stationary and the broaching tool is pushed through the job. Push broach is commonly used on a breaching press but it may also employ pull-broaches, if fitted with pull down adaptor.
The required length of the broach in comparison to its diameter decides whether push or pull broaching is to be adopted. It must be remembered that a broach is stronger in tension than in compression. Accordingly a push broach must be strong enough to withstand the broaching pressure without undue bending.
(3) Surface-Broaching:
In this case, the job and the broaching tool move across each other and this is the most commonly used process in machining flat surfaces.
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(4) Continuous-Broaching:
The work is moved continuously against stationary broaching tools. The path of movement may be either straight or circular. For smoother operation, most of broaching machines are hydraulically operated.
Another classification of broaching machines is based on the construction. In general they are classified as vertical or horizontal machines. Vertical machines are well adapted for surface broaching with the tool supported on a suitable slide, although both pull and push type internal broaching machines are made in this design.
Horizontal machines pull the broach and are often used for internal broaching of small, medium size and heavy work. They too have many surface broaching applications. Horizontal machines have good facility of handling and as such internal broaching of heavy or bulky parts is best suited on it.
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Sometimes broaching machines are also classified as single ram or double ram type. Dual ram machines provide more output than two single ram machines since the operator can load one ram while the other is cutting. It also avoids additional handling of the part between machines.
Horizontal Pull-Type Broaching Machine:
There are two important types of horizontal machines. One has a bed much like a lathe, with the broach moving like a tail-stock on ways. This type mostly does internal work. The second type has a broach and sliding surfaces mounted in vertical plane in fount of the machine.
This type is more commonly used for surface broaching, such as automobile connecting rods, bearing caps and similar jobs. This type of machine is very convenient to work at and very fast in loading etc.
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In manual operated machines, the broach-front pilot is passed manually through the work and connected to the ram through the puller for each cutting stroke. Automatic machines handle the broach automatically. The machine can also be arranged to handle more than one broach at each cycle.
In the case of long broaches, the machine is fitted with an outer support carriage to return the broach to starting point.
On many machines doing external work, the operator has to pass the front pilot of the broach through the work manually and connect it to the ram before the cutting stroke starts. When this type of job is performed, the front end of pilot may be stepped so that area is smaller than that of the remainder of the pilot (or the work).
The result is that on the first few mm of the broach travel the broach rides up a slight ramp to bring full engagement of the remainder of the pilot with the starting of hole in the work. This arrangement makes it easy to load the work and start the stroke.
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When surface broaching is done, the broaches are always permanently connected to the draw head. Often more than one broach is used for surface work, which consists of more than one short broach mounted in random so that the desired result can be obtained.
Vertical Broaching Machine:
This type of machine is more easily adapted to multiple operations and multiple broaches than the horizontal type. As many as four sets of broaches may be mounted on one ram on such jobs as involving cutting of multiple slots on the surface of a workpiece. Besides the single ram type, a dual-ram machine may be used to machine two pieces alike at the same time.
Single-ram machines have a return stroke which operates at twice the speed of the cutting stroke. Dual-ram machines operate at the same speed in each direction, because the broach on one ram removes material in forward stroke while the broach on other ram is effective in return stroke.
It is also possible for the operator to load one fixture while the other is cutting. Vertical machines require an operator plate form but are more economical as regards floor space than the horizontal type.
Because of horizontal table, a variety of fixture setups can easily be arranged. Vertical machines are more adaptable to multiple operations, since it is convenient to pass work from one machine to another. Of the three models available, pull up, pull down and push down, the pull up type is most popular.
If it is desired to produce special splines, the machine can be equipped with a special head and spiral lead bars to guide the tool in a spiral path. In this case, it is more convenient to hold the work stationary and rotate the tool.
Continuous Broaching Machine:
This type of broaching machine is confined to surface broaching operations. One type consists of continuous chain travelling in a horizontal plane over sprockets at each end of the machine. Fixtures are mounted at intervals on the chain and travel in a continuous path with the chain. The broaches are fixed horizontally above the chain. This type is limited to small parts which can be loaded in these small fixtures.
Another type is a vertical continuous broaching machine. This machine mounts a series of plates on a continuous chain. Broach sections are then mounted on broach holders in the usual manner and moved continuously past the work, which is held in the usual manner on a horizontal table. This arrangement allows continuous broaching on a complete part with the equivalent of one long stroke or several strokes.