There are 3 types of machining chips.
Let’s discuss each of these types of machining chips one by one.
#1) Continuous chips
Continuous chips are the long coil type chips of single piece havisame thickness.
During the machining process, the continuous chips generally remain as a single piece unless they are broken manually.
The main factors that are responsible for the formation of continuous chips are;
- Ductile material (like mild steel, copper, etc)
- High court speed
- Sharp cutting edge
- Large rake angle
- Low friction between the cutting tool and workpiece
Continuous chips provide stable cutting with low power consumption which results in a good surface finish on the workpiece.
Thus continuous chips are the most desirable type of machining chips.
But longer chips are hazardous to the machine operator as well as it disturbs the machining process.
Longer continuous chips may wrap around the workpiece or the cutting tool and interrupt the machining operation.
#2) Continuous chips with built-up edge
Continuous chips with built-up edges are similar to continuous chips but they are not as smooth as continuous chips.
If there is a very high friction between the tool and workpiece, then some particles of the chip weld near the tool tip.
This lump of welded particles acts as a cutting edge in place of the actual cutting edge of the tool.
These edges formed on the metal chips are called built-up edges.
Because of the built-up edges, the surface finish obtained on the workpiece will be poor as well as fluctuations in cutting forces, which may result in vibrations in the cutting tool.
But one benefit of a built-up edge is that the tool life increases as the built-up edge protects the cutting edge of the tool.
The main factors that are responsible for the formation of built-up edges are;
- Machining of ductile material
- Lower cutting speed
- Smaller rake angle
- Dull cutting edge
- Very high tool feed
- Insufficient cutting fluid
- High friction between tool tip and workpiece
How can built-up edges be avoided?
There are few methods by which built up edges can be avoided during a machining operation.
- By reducing the friction between tool tip and workpiece by supplying sufficient cutting fluid.
- By keeping larger rake angles.
- By maintaining high cutting speed and low feeds.
#3) Discontinuous chips or segmental chips
Discontinuous chips (also known as segmental chips) are produced in the form of small segments that may loosely adhere to each other.
The main factors that are responsible for the formation of discontinuous chips are;
- Machining a brittle material (like cast iron, brass, etc)
- Machining at lower cutting speed
- Machining with a cutting tool having smaller rake angle
Discontinuous chips are very easy to handle and they are easily disposable.
Because of the discontinuous chips, the chips do not interfere with the workpiece or tool, plus it requires less power consumption and so the tool life increases. Also because of these reasons, better surface finish is obtained on the workpiece.
Machining of ductile metals with small rake angle and lower cutting speed also gives discontinuous chips, but this leads to poor surface finish and tool wear.