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Broaching is the process of removing metalwith a tool which has teeth arranged in arow. Each tooth is successively higher than the

previous tooth and removes more material. Inbroaching, one stroke or cycle of the machineproduces a finished part.

Broaching is used to produce both internal and

external features. Production rates are highand tolerances of +/- .0005 are possible.

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Chip Formation Chip formation involves three basic requirements:

The cutting tool must be harder than the partmaterial

There must be interference between the tool and thepart as designated by the feed rate and cut per tooth

There must be a relative motion or cutting velocitybetween the tool and workpiece with sufficient

force to overcome the resistance of the partmaterial.

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Tool Feed DirectionGullet

Workpiece

Depth of

cut per tooth

Tool

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How and Where Heat is Generated The force or energy that is put into the tool creates

movement in a group of metal atoms in the workpiece. Thisgroup is a finite number of atoms which are forced tochange their positions in relationship to each other.

As the atoms in the metal ahead of the tool are disturbed,the friction involved in their sliding over one another isthought to be responsible for 60% or more of the total heatgenerated.

This internal friction, and the heat it generates, can becompared to the friction and heat caused by bending apaper clip back and forth until it breaks.

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How and Where Heat is Generated As the tool continues to push through the work piece, a chip

eventually slides up the cutting face of the tool. This slidingcreates an external friction which again releases heat. Thisexternal friction accounts for about 30% of the total heatgenerated.

The third area of heat generation is on the land or flank of thetool. This area accounts for about 10% of the heat generated.

This is assuming that the tools are sharp and made correctly asfar as clearance angles and face angles are concerned. As thetool wears, the above percentages will vary, especially whenthere is excess wear on the land, or if the clearance angle isinsufficient for the material or the part configuration. Thiscontact zone will actually increase as the part continues toclose in after the cut resulting in extremely high pressures onthe land area of the tool.

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Advantages

Rough to finish in one pass

Production rates are high

Cutting time is quick

Rapid load and unload of parts

External and internal features

Any form that can be produced on a broaching tool canbe produced

Production tolerances are excellent

Surface finishes are equal to milling

Operator skill is low

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Pull broaching - broach is pulled through or acrossstationary work

Push broaching - broach is pushed through or acrosswork

Surface broaching - either the work or the broachmoves across the other

Continuous broaching - the work is movedcontinuously against stationary broaches. The pathof the movement may be straight or circular.

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Vertical single and double slide - Table moves partinto position for broaching, part is broached and thetable retracts for unloading.

Vertical push broaching - Used for internal features

such as holes, rounds, or slots.

Vertical pull down

Tool is suspended above work

Lowered into pull mechanism in the base of the machine

Advantages Part positioning is easy

Large parts are handled efficiently

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Vertical single and double slide

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Horizontal

Versatile machine capable of producing internal andexternal features

key-ways

gear teeth

riffling

High cutting speeds in the range of 10-40ft/min withreturn speeds of 110 ft/min

MRR of in per stroke is possible

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Horizontal

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Rotary

Parts are mounted to a rotating table and are moved todifferent stations for different operations

Primarily used on small parts

Typical operations include:

Slotting

Holes

Key-ways

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Considerations

Material to be broached

Size and shape of cut

Quality of surface finish Part tolerance

Productions rates

Type of machine

Workholding method

Strength of the workpiece

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