Broaching

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Various broaching methods are performed in broaching job shops to cut internal splines, gears and sprockets, as well as keyways, slots and serrations on the surface of a work-piece. These products are fabricated in high volumes, a process called production broaching, which takes place in a facility that specializes in broached parts. While broaching machines are specialized and have somewhat limited ranges of abilities, there are many different kinds that do different kinds of broaching, including spline cutting, keyway broaching using a keyseater machine and gear hobbing. Broaching machines work on the outside of a work-piece or create holes by internal broaching, which reaches all the way through the material. They are either horizontal or vertical machines, depending on the size of the work-piece and the involvement of the manual worker. Vertical broaching is used for higher volumes of products. The holes and grooves that are made with a spline shaft, which contains a series of successively larger teeth that are strong enough to cut through metals, may reach all the way through the work-piece, forming a hole, or make shallow indents that blind broaching produces. Rotary broaching is a popular method that spins the broach tool at high rotations and pushes or pulls it through the work-piece. Pot broaching inverses the machinery movements-the broach tool stays stationary while the work-piece moves through the broaching machine.

The broaching process produces many different parts and products, mostly for use within the industrial sector, and usually made of softer metals like aluminum, brass and copper, although harder metals like steel grades and other materials including plastic and wood are also able to be broached. The most common broached products are gears. A broaching process called gear hobbing forms their shape by externally broaching the grooves on the gear's external surface. Sprockets, pulleys, the heads and threading on fasteners like screws, nuts and bolts, smaller wheels, gun components, industrial machinery parts, tools like wrenches and bushings all get their shape from the broaching process, which doesn't generate or require any heat and therefore is less prone to error. During the broaching process, machines such as automatic lathes, CNC Swiss lathes and rotary transfer machines are used to push or pull a broaching tool with cutting teeth through or over a work-piece. The only limit to the process is the length and width of the part that is being machined.

The most common form of broaching services is done using hydraulic driven machines, since they require a large amount of power in order to operate continuously. There are three main methods to forming the holes and indents in the work-piece, including pull broaching, push broaching and pot broaching. When the broach cutting tool is pulled through the part in a single pass, this process is called pull broaching. The second most common type of broaching services used is push broaching. Broaching job shops most often utilize this service on short run jobs using a hydraulic press, or more commonly, a hand operated arbor press. Pot broaching, on the other hand, moves inversely-while the broaching tool remains stationary, the work-piece is pushed through it inside a hollow casing shaped like a pot. Broaching job shops can also perform broaching on a lathe, which spins at a high rotation. During rotary broaching, the tool must be held at a 1° angle to the work-piece. The cutting face of the broach should be positioned as close to the centerline of the work-piece as possible. The tool and part are stationary while the broach holder spins on a spindle. As the broach tool and the part come into contact, the tool moves in a "wobble" motion; thus, another name for this process is wobble broaching.

The entire broaching process takes a matter of seconds, and is fully automated. High production runs are possible, making broaching cost efficient, economical and fast. Broaching has many advantages, including high productivity, economical operation, accurate cuts over large runs, close tolerances, versatility and smooth finishes. Chips tend to accumulate in the broaching hole. Therefore they must be cleared periodically so that they do not cause damage to the broach tool. Also, the hole must be drilled as deep as possible to allow room for the chips to accumulate. Sometimes a pressure relief vent on the broach tool is necessary when broaching a tight hole if air, oil and coolant cannot escape. If enough hydraulic pressure is generated, the broach will be pushed back and could cause damage to the machine. A ventilation hole on the tool prevents this occurrence.

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Broaching Types

• Blind broaching is another term for external broaching, the broaching process that is surface level.
• Broaching Job Shops are facilities devoted to providing broaching services.
• Gear hobbing is the process of using a broaching machine to cut gear teeth.
• Internal broaching involves using a broach tool to make precise cuts to a preexisting hole on the inside of a workpiece.
  
• Keyseaters are machines that make the keyway holes inside locking mechanisms.
• Keyway broaching uses keyseater machines to make keyholes in a variety of materials.
• Pot broaching is one external broaching method specifically sued to form gears.
• Production broaching when a machine is used to make mass amounts of a single product.
• Rotary broaching, also known as wobble broaching, is a popular broaching method that has been used for years on automatic lathes, and is now gaining popularity on rotary transfer machines and CNC Swiss lathes.
  
• Spline cutting is a broaching process that cuts grooves into the length of a spline shaft.
• Spline shafts have grooves created by broaching machines.
• Surface broaching involves using a broach tool to precisely cut the surface of a workpiece.
  
• Vertical broaches are cutting tools with successively larger teeth.

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Broaching Terms

Broach - A metal cutting tool with a series of cutting teeth.

Chip Space - The space between the teeth on a broach that accumulates chips during the cutting operation.

External Broach - A broach that cuts along the external surface of a workpiece.

Face Angle - The angle of the cutting edge of a broach tooth.

Finishing Teeth - Teeth for finishing a surface that are arranged at a constant size at the end of a broach.

Gullet - Another name for "chip space."

Hook Angle - Another name for a tooth's "face angle."

Internal Broach - A broach that is pulled or pushed through a hole in the workpiece in order to bring the hole to a desired size and shape.

Overall Length - The length of a broach tool.

Pitch - The measurement from the cutting edge of one tooth to the same point on the next.

Pull Broach - A type of broach that is pulled through or over the surface of the workpiece during an operation.

Push Broach - A type of broach that is pushed through or over the surface of the workpiece during an operation.

Roughing Teeth - The teeth that cut first in a broaching operation, with heavier cuts than semi-finishing teeth.

Round Broach - A broach with a circular section.

Shear Angle - On surface broaches, the angle between the cutting edge of a shear tool and the line perpendicular to the broach axis or line of travel.

Shear Cutting Tooth - A type of tooth used on surface and external broaches, positioned so that it does not make a right angle with the direction of broach motion.

Surface Broach - An external broach that is used to cut a flat or contoured surface.

Tooth Depth - From the root to the cutting edge, the height of the tooth or broach gullet.

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