How to Buy a Broaching Machine

Broaching machines generate a fast and accurate machining process where metal is detached through the use of a broach, a tool with multiple teeth that pushes and pulls through prepared holes. This process of machining holes into other shapes in the part simultaneously for both internal and external or flat contours are utilized today in both large and small plants where broaching machines replicate parts that need to be manufactured swiftly and economically. Usually, the width of each surface can be machined in one pass. The flexibility of broaching enables one to keep errors at a minimum since the process does not generate a lot of heat, so mistakes due to heat are hardly seen. However, with all the benefits, broaching is not an all-purpose process and is generally not recommended for removing large amounts of stock. Machines with dual-rams are made so when one ram is on the cutting stroke, the other is on the return stroke which is executed. rapidly to gain time. Horizontal machines, generally the pull type, are used for internal broaching operations and sometimes for surface jobs with suitable work-holding fixtures. Vertical machines can be either push or pull type, however most surface broaching is done on vertical pull-types.

• Base - Heavily constructed, rigid main casting that is the mounting point for all machine components.
• Column - Stands vertically from the back of the bed and is a bearing for a ram to be attached.
• Ram - Along with the slide assembly, it carries the broach and is mounted in ways on the column's front and moves vertically. For dual-rams there are two rams next to each other both carrying a broach.
• Motor - Gives vertical reciprocating movement to the slide. Generally a hydraulic system is used, but some models are electromechanical. With hydraulic, a motor powers a pump that drives the ram by hydraulic power going through a network of pipes and valves.
• Hydraulic power unit - Contains the hydraulic oil reservoir, pumping units and valves. A pumping system that meet JIC standards.
• Slide - A heavy duty piece with guide slots for rectangular ways.
• Lubrication system - Connected to the side of the column administering cutting fluid to the cutting area.
• Work table - Can be hydraulically actuated and 45 degree tilting, otherwise it's in a fixed position.

Broaching machines are available in two models: vertical and horizontal. The horizontal model has the advantage of enabling the operator to reach any part of the machine, especially the work station, and is easily adjustable for stroke in order to meet varying broach lengths. The vertical model takes up little floor space and is usually limited to short stroke models because verticals with long strokes may have a pit or a platform in order for the operator to reach the workstation. Vertical broaches can last up to twice as long as a horizontals since the broach and workpiece is immersed in cutting fluid.

Broaching machines are classified in four categories: (1) broaching presses; (2) pull broaching; (3) surface broaching; (4) continuous broaching. Broaching presses are usually used for internal push broaching operations like hole sizing and keyway cutting. Push broaching machines, which are generally hydraulic arbor-type presses specially equipped for broaching, have the workpiece placed on the table under the vertical ram that pushes the broach through the work. Pull broaching machines which are usually used for internal broaching also have surface broaching capabilities. On a horizontal pull broaching machine, the broach's shank is run through the prepared opening in the piece and attached to the puller that pulls it upward or downward then draws it through the opening. On a vertical pull down the broaches are pulled from below the table, making them perfect for work where large and irregular sized pieces must be loaded. Cutting fluid is effective on pull-downs and vertical pull-ups have the broaches start from below the table working up against the underside where the parts are free to fall down a chute when it's done. Surface broaching machines are both horizontal and vertical, but are also available with double-ram models. The operator in single ram models has to load and unload the fixture retracted from the broach while the ram rises, whereas in double ram models where one ram carries the broach and fixture down into cutting position while the other ram returns as its fixture is unloaded and loaded in a retracted position. The time saved here can make operations partially continuous. Continuous broaching machines have their cutters held stationary while the workpieces held in fixtures are carried past the cutters. The pieces are loaded at one end and come out down a chute at the other end of the machine. Here, parts are broached as fast as they can be loaded.

The main advantage of broaching is that it's fast, it usually takes just seconds to do a job and provides the workpiece with accuracy and a good finish. However, workpieces not strong enough to withstand heavy forces or a surface cannot be broached because of an obstruction in the path of the broach travel are not recommended for broaching. One of the disadvantages of broaching is the cost of the tools since they're usually specially made for one job only. Calculating the cost of output per finished piece part made by broaching and comparing it to another method usually will be recommended over other methods. When considering broaching as a selected method, choosing a dual-ram machine is better when production runs past its capability in a single-ram machine since the operator saves time in the loading and unloading of the pieces. Also, dual-rams come in handy if the user's production calls for a number of different operations on a given part. If production requirements call for the internal broaching of bigger and heavier parts, horizontal press or pull-downs are recommended. And if push broaching is needed for your production requirements, then a broaching press would be your best answer. Here, a push broach must be strong to withstand the pressures without breaking down or bending. Broaches are more rigid in tension than in compression.

INSPECTION

NON-POWER

1. Look over the machine for rigidity and strength, check all structural support for cracks, breaks and welds.
2. Look at all ways, slides and toll mounting devices for excessive wear and damage that would make the work inaccurate.
3. Make sure there is adequate stroke adjustment so that surface distortion and lost motion are prevented.
4. The readjusting slide should be checked for excessive slop and to see if it has been pulled from the T-slots.
5. The mechanical and trip linkage should be looked at for excessive wear.

UNDER POWER

1. Run the machine through an entire cycle, look for any hesitations.
2. See if the broached surface and axis are parallel to each other as the machine repeats, there must be no obstructions here.
3. Look for any deflection since the backoff or clearance angle on the top of the cutting teeth will be ineffective since the tool will create an abnormal pyramid force in the cut.
4. If the machine is hydraulically powered, check the valves and hoses for any leaks. For mechanically driven machines, make sure there is no slop on the rams and no rattling sounds from the gears.
5. Run the machine again checking its speed and feed range, return speeds should be doubled that of cutting speeds in order to reduce idle time.
6. The tool on the return stroke should be moved away adequately to prevent any possible contact.
7. Make sure the coolant and lubrication systems are working properly in order to dissipate the heat created during the process.

This is one article in a series of    How to Buy Metalworking Equipment.   Each article showcases and explains a particular type of metalworking machine. They were originally published in the Metalworking Machinery Mailer published by the Tade Publishing Group.

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