In a tool room while machining process is performed in a work piece. The material removal takes place. This material removes in the form of chips. These material chips could be of many types. The type of chips determines the nature and properties of material. As this topic is related to machining process so one should understand what is machining process or metal cutting process.

Machining or Metal Cutting is a process under which a specimen is shaped in a desired product by removing the material from the specimen. For machining process a machine tool with a cutting tool is necessary. This material will be removed in the form of chips. Machining is a finishing or a semi finishing process while removing the material. Other finishing process can be implemented after machining if better surface finish is required.

The chips formed after machining can be classified into following types.

  • 1. Discontinuous or segmental Chips
  • 2. Continuous Chips
  • 3. Continuous chips with built-up edge

1) What are Discontinuous Or Segmental Chips ?

These types of chips forms while machining the brittle material. The Chips are collected in the form of segments or pieces. A series of rupture occurs to form these segments. The rupture in the material generally takes place perpendicular to the face of the tool. Good surface finish can be achieved in this type of chips with preserving the tool life for longer. Continuous breaking of chips causes the reduction in friction between tool and chips. The discontinuous or segmental chips are easy to handle, transport and dispose or recycle. 

Segmental chips forms when one or more condition given below satisfies

1. Material is brittle
2. Cutting speed is low
3. Large chip thickness
4. Large depth of cut
5. Small Rack angle in the tool

2) What are Continuous Chips ?

This types of chips generates in the form of continuous segment that is why it is called continuous chips. Due to machining in the ductile material like low carbon steel, copper aluminium etc. this types of chips forms. In a high cutting speed machine this type of chips forms. There would be the continuous plastic deformation in the material to form continuous chips by applying the tool. The friction between the job and tool is less during the process. Chips formed continuously would have uniform thickness throughout the length of the chip. 

The continuous chips forms when one or more condition given below satisfies

1. Material is of ductile nature
2. High cutting speed
3. Large rack angle
4. Depth of cut is small
5. Friction between tool and job work-piece is less
6. Using coolant according to type of material.

3) Continuous Chips with Built up Edge

These types of chips are quite similar to the continuous chips. The difference in this type of chips is that it has a built up edge adjacent to the face of the tool. These chips are not as smooth as continuous chips. Ductility of the material is required same as in continuous chips but the high surrounding temperature, high pressure for cutting and high friction between tool and work-piece will cause the chips to stick on the tool edge. Resulting this phenomenon successive layers will be added and a built up edge is formed. When this series of layers become larger the edge will breaks up in parts. The size of built up edge changes during cutting operation. During cutting first the edge increases, then it decreases and again increases. 

The conditions of formation of built up edge is given below-

1. Machining in ductile material
2. High friction at the face of cutting tool.
3. Proper coolant is not used.
4. High pressure and temperature between specimen and tool.

*Non Homogeneous Chips In Machining*

When the hardness of the material to be machined is very high such as titanium and hard alloys, these types of chips generates. Due to high hardness, yield strength of material decreases and temperature between interface increases.

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