Broaching machines are relatively simple as they only have to move the broach in a linear motion at a predetermined speed and provide a means for handling the broach automatically. Most machines are hydraulic, but a few specialty machines are mechanically driven. The machines are distinguished by whether their motion is horizontal or vertical. The choice of machine is primarily dictated by the stroke required. Vertical broaching machines rarely have a stroke longer than 60 in (1.5 m).
· Vertical broaching machines can be designed for push broaching, pull-down broaching, pull-up broaching, or surface broaching. Push broaching machines are similar to an arbor press with a guided ram; typical capacities are 5 to 50 tons. The two ram pull-down machine is the most common type of broaching machine. This style machine has the rams under the table. Pull-up machines have the ram above the table; they usually have more than one ram. Most surface broaching is done on a vertical machine.
· Horizontal broaching machines are designed for pull broaching, surface broaching, continuous broaching, and rotary broaching. Pull style machines are basically vertical machines laid on the side with a longer stroke. Surface style machines hold the broach stationary while the workpieces are clamped into fixtures that are mounted on a conveyor system. Continuous style machines are similar to the surface style machines except adapted for internal broaching.
· Horizontal machines used to be much more common than vertical machines, however today they represent just 10% of all broaching machines purchased. Vertical machines are more popular because they take up less space.
Push Type Broaching Machine
Vertical internal push-down: Vertical push-down machines are often nothing more than general-purpose hydraulic presses with special fixtures. They are available with capacities of 2 to 25 tons, strokes up to 36" and speeds as high as 40 FPM. In some cases, universal machines have been designed which combine as many as three different broaching operations, such as push, pull, and surface, simply through the addition of special fixtures.
Pull Type Broaching Machine
Vertical internal pull-up: The pull-up type, in which the workpiece is placed below the
worktable, was the first to be introduced. Its principal use is in broaching round and irregular
shaped holes. Pull-up machines are now furnished with pulling capacities of 6 to 50 tons,
strokes up to 72", and broaching speeds of 30 FPM. Larger machines are available; some
have electro-mechanical drives for greater broaching speed and higher productivity.
Vertical internal pull-down: The more sophisticated pull-down machines, in which the work
is placed on top of the table, were developed later than the pull-up type. These pull-down
machines are capable of holding internal shapes to closer tolerances by means of locating
fixtures on top of the worktable. Machines come with pulling capacities of 2 to 75 tons, 30"
to 110" strokes, and speeds of up to 80 FPM.