Thursday, 31 March 2016

Types of Chips in Metal Cutting

Today I will tell you about types of chips in metal cutting form during machining process. The machining of material is highly dependable on chips. Before discussing on this topic, first you should know about machining process. Machining is a process of cutting metal work piece by means of a tool to convert it into desire shape. It is a finishing or semi finishing process by removal of excess material from work piece. The excess material removes from work piece in form of chips. 

The chips types are depend on

* Nature of work piece
* Nature of tool
* Dimension of tool
* Feed rate
* Cutting speed
* Friction between tool and work piece
* Cutting environment like temperature, friction etc.

The knowledge of chips types is essential for every machinist because it gives prediction about condition of machining. Today we will learn about it.

Types of chips in Metal Cutting:

Chips formation is part of machining process. It is form during cut the work piece by some of mechanical means. The chips depend on the material of work piece and tool and cutting condition. There are mainly three chips types.

1. Continuous chips:

According to its name, continuous chips have a continuous segment. This chip is form during cutting of ductile material like aluminum, mild steal, cooper etc. with a high cutting speed. The friction between tool and material is minimum during this process. This is form due to continuous plastic deformation of the material by application of tool. These chips have equal thickness throughout the length. It generally gives good surface finish. 


continuous chips

The most favorable conditions of forming continuous chips are

1. Work piece should have ductile in nature.
2. The rack angle should be large.
3. Friction between work piece and tool should minimum.
4. Cutting speed should high.
5. Deft of cut should be small.
6. Proper use of coolant and lubricant.
7. Tool should have low coefficient of friction.

Continuous chips are the most preferable type of chip due to following benefits.

1. It gives high surface finish of machining ductile material.
2. Continuous chips form when low friction which minimize friction loss.
3. Due to low friction, tool life is high
4. Power consumption is low.

2. Discontinuous chips or segmental chips:

According to its name, this chips form in segment. It is form when machining of brittle material like cast iron, brass etc. with slow cutting speed. Chips cut into small segment during cutting. This is formed during slow cutting speed with small rack angle. This chips form in ductile material when the friction between tool and work piece is high. Discontinuous chips in ductile material give poor surface finish and slow machine. It is suitable form of chips of machining brittle material. 
discontinuous chips

The favorable conditions of forming this type of chip are

1. The work piece should have brittle in nature.
2. Slow speed of cutting
3. Small rack angle of tool
4. Depth of cut should large

3. Continuous Chips with built up edge:

This type of chip is same as the continuous chips except a built edge is form at the face of tool. It is form during machining of ductile metal with excessive friction between tool and work piece. This chip is not smooth as continuous chips. The built up edge form due to high temperature between tool and work piece. This high temperature is due to high friction force between tool and work piece. 
continuous chips with built up edge

The common factors promoting built up edge are

1. Cutting of ductile metal.
2. High friction force at the face of tool.
3. High temperature between tool and work piece.
4. Lack of coolant and lubricant

Comparison of Continuous chips, Discontinuous chips and Continuous chips with built edge:


S. No.

Material type


Rack angle

Depth of cut 

Cutting speed

Continuous Chips


Ductile

High

Small

Large/medium

Discontinuous Chips



Brittle, Ductile but hard


Medium


High


Low

Continuous chips with built edge



Ductile


Low/Medium


Medium


Medium


Today we have learnt about types of chips in metal cutting. If you have any query regarding this article, ask by commenting. 

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