What are Machining Chips?
Machining chips are excess material that gets removed during a machining process.
There are 3 types of chips that are formed during a machining operation.
- Continuous chips
- Continuous chips with built-up edge
- Discontinuous chips or segmental chips
Well, this was just a simple overview. But there are more things that you should know about machining chips.
Let’s dive right into it!
How are Machining Chips formed?
Basically the machining process comprises of four elements;
- Cutting fluid
When the relative motion occurs between the workpiece and cutting tool, the material removal process takes place.
The relative motion between the workpiece and cutting tool is provided either by keeping the workpiece stationary and moving the tool or by keeping the tool stationary and moving the workpiece.
During the machining operation, the edge of a single point cutting tool is set perpendicular to the relative motion of the workpiece.
When the edge of the tool comes in contact with the workpiece, it exerts a pressure on it.
Because of this, the workpiece metal gets highly compressed which results in high temperature shear stresses and this shear stress is maximum along the narrow zone called primary deformation zone (or shear plane).
As the tool advances, the stress in the workpiece reaches a value that is more than the ultimate strength of the workpiece material.
Because of this, the metal particles start to deform plastically along the shear plane as shown in the above diagram.
At this stage, a chip starts to form which moves up along the face of the tool.
As the tool proceeds, the cycle of compression, plastic flow and shearing away is repeated which continuously produces the chips from metal.
The further deformation of a chip may occur due to friction between the tool face and underside of the metal chip.
This deformation of chip during a machining process is called secondary deformation (shown in diagram as secondary shear zone).
Methods of Chip Control (How to control chips during metal cutting?)
There are 2 methods for controlling chips during machining operation.
- Self chip breaking (Without using a separate attachment)
- Using a chip breaker (Using cheap breaking attachment)
When you turn ductile metals, long hot continuous chips are produced which gets curled around the rotating metal piece or the cutting tool.
Because of this, it becomes difficult to handle the metal cutting processes.
It is also hazardous for the machine operator while operating the machine.
Also the cutting edge of the tool gets spoiled due to crater formation.
Ultimately this leads to poor surface finish on the workpiece.
Because of all these reasons, it becomes necessary to control the chips (or to deform the chips).
Methods of Chip control are necessary to;
- To improve the surface finish of workpiece
- To prevent any hazardous accident with the machine operator
- To prevent the damage of workpiece
- To easily collect and dispose the chips
Chip control during machining also reduces the cutting force and crater wear of cutting tool, as well as it improves the machinability as the chip-tool contact area is reduced.
Let’s discuss each method of chip control.
#1) Self chip breaking
There are 3 types of in-built chip breakers.
- Step type
- Groove type
- Secondary rake type
Groove type chip breaker has a grinding groove on the tool face. This groove is slightly behind the tool tip and it leaves a small land near the tip.
Step type chip breaker has a grinding step on the tool face which is adjacent to the cutting edge.
Secondary rake type chip breaker consists of a rake that helps in breaking the metal chips (see the above diagram).
#2) Using a chip breaker
Chip breakers (also known as clamped type chip breakers) are exactly similar to the step type chip breakers. They have special attachment which help in varying the width of the step as shown in the diagram.
Clamped type chip breakers are generally used with carbide tipped cutting tools.