Broaching is a process in which a toothed tool is used to remove material from the workpiece and cutting a predetermined shape. This toothed tool is known as Broach.
Broaching process is used to clean any pre-existing hole or increase its diameter. It can also be used to cut a slot, keyway cutting, etc.
Most commonly circular shapes are obtained by broaching. This circular shape can be internal or external.
The price per piece of broaching is very low because of its high production and low cycles. The quality of the final product in broaching is often better than other combined cutting process.
The broaching process is best for removing materials from high volume workpieces. The complete cycle of broaching is nearly of 20 seconds with high productivity and great quality.
Broaching process is divided into two processes mainly:-
i) Linear Broaching.
ii) Rotary Broaching.
i) Linear Broaching:
In this type of broaching, the broach is run linearly against the surface of the workpiece to effect the cut. Linear broaches are used in a broaching machine.
ii) Rotary Broaching:
In this type of broaching, the broach is rotated and pressed into the workpiece to cut an axisymmetric shape.
A rotary broach is commonly is used in a lathe or screw machine.
In both linear and rotary broaching process, the cut is performed in only one pass which makes it very much efficient.
Broaching can also be divided based on cutting location on the workpiece. Based on cutting location broaching are divided into two types:-
i) Internal Broaching.
ii) External Broaching.
i) Internal Broaching:-
In internal broaching, the material is removed from the internal surface of the workpiece. It is also known as hole broaching.
For broaching internally a metal, a pre-existing hole must be made first.
It is mainly used to enlarge a hole or resize it. Internal broaching also provides good finishing.
In internal broaching, the broaching tool has teeth that become larger successively.
Internal broaching machines are automated, often CNC operated and are able to quickly and efficiently produces a hole in metal parts and products.
Two types of broach tool can be used in Internal Broaching:-
a) Pull Type Broach Tool.
Pull type broach tool is commonly long in length because it is pulled and tension is created in it while pulling. It has a longer life than Push Type Broaching.
It has a large number of teeth and it provides a longer cut.
Parts of Pull-Type Broach Tool:-
1) Pull End:-
It is the handle of the pull broach tool which is used while pulling the broach tool.
The neck connects the pull end to the root diameter.
The part from the pull end to root diameter is a shank that is hold and pulled inside the machine. The length of the tool from pull end to root diameter is known as shank length.
Teeth are placed in the pull-type broach tool after the shank. The size of the teeth increases progressively from start to end.
The teeth are divided into three portions in pull type broach tool. These are:-
a) Cutting Teeth
The portion of teeth near the shank is called cutting teeth. These teeth are also known as roughing teeth.
The size of two consecutive teeth varies largely. The difference between their sizes are large.
Cutting teeth will provide the maximum cut in the workpiece and remove maximum material from the workpiece as compared to other portions of teeth.
b) Semi finishing teeth
After cutting teeth, there are semi-finishing teeth. The difference between sizes of two teeth in semi finsihing teeth is large but less than cutting teeth.
Semi finshing teeth are used for semi finishing . These teeth remove very less material from the workpiece as compared to semi finishing teeth.
c) Finishing Teeth
The last portion of teeth after the semi finishing teeth are known as finishing teeth.
These finishing teeth do not have variation in their sizes i.e all the finishing teeth are of nearly the same sizes.
Finishing teeth will provide finishing to the cut produced by the cutting and semi finishing teeth. So these teeth are known as finishing teeth.
5) Rear Pilot
After the finishing teeth, rear pilot is present in the pull type broach tool. It is used to balance the broach tool and keep it in alignment.
6) Follower End and Retriever:
They are present at end of the pull type broach tool. They both are supporting elements of the tool and supports the tool.
b)Push Type Broach Tool.
Push type broach tool is short in length than pull type broaching tool because it experiences compressive forces while it is pushed.
It has fewer teeth than pull-type broach tool because chances of bending and getting broken is high as compressive forces are applied to it.
It provides a shorter cut than pull type broach.
The parts of the push type broach tool are the same as parts of pull type broach tool but the size of teeth and other parts of the broach tool is smaller than the tool of pull type broach.
ii) External Broaching:-
In external broaching, material is removed from the external surface of the workpiece. It is also called surface broaching.
It is used to remove material from the surface of the tool, keyway cutting and creating a slot.
The teeth of the external broach tool also increases progressively.
Nomenclature of External Broach:-
Land is present in the bottom of the teeth and it provides support to the cutting edge.
Rake is provided in each tooth of the external broaching tool. The chip from the workpiece after the cutting process flow through this rake.
# Clearance Angle
Clearance Angle is the angle of the land or bottom part of the tool with the horizontal axis. It prevents friction between the teeth and workpiece and only the cutting edge of teeth is in contact with the workpiece while the cutting process.
The height of each of the teeth is known as depth.
The distance between the cutting edges of any two teeth is known as pitch.
This radial space is present between two teeth through which the chip flow and go outside after getting curled.