The various types of chips in metal cutting are :-

• Continuous chips
• Discontinuous chips &
• Continuous chips with built-up edge (or BUE chips)

Continuous Chips -

• If the metal chips formed during machining is without segments i.e. without breakage, then it is called as continuous types of chips.
• Continuous chips are formed when the ductile material is machined with high cutting speed and minimum friction between the chip and tool face.

The conditions which are responsible for the formation of continuous types of chips are -

• Factors responsible for formation of continuous chips:-
• Material of Workpiece: When ductile material is used as the workpiece.
• Cutting Speed: Cutting speed is high.
• Chip thickness: Thickness of chip is less.
• Rake Angle: Rake angle is large.
• Depth of cut: Depth of cut should be small.
• Lubricants and Coolants: Lubricants and coolants should be used efficiently.
• Coefficient of friction: Coefficient of material of tool should be low.

Advantages -

The formation of continuous chips during machining process has the following advantages -

• Better surface finish to the ductile material.
• Less heat generation due to minimum friction between the tool face and chip.
• Low power consumption.
• Long tool life due to less wear and tear.

Discontinuous chips :-

• If the chips formed during machining process is not continuous i.e. formed with breakage is called discontinuous chips.

• Discontinuous types of chips are formed when hard and brittle metals like brass, bronze and cast iron is machined.

Discontinuous chips are formed in the following conditions:-

• Material of workpiece: When the workpiece is made of brittle material such as cast iron and bronze.
• Bevels: Small bevels of cut tools.
• Cutting Speed: Cutting speed is low.
• Feed: When the feed is large and chip is thick.
• Rake Angle: Small rake angle.
• Friction:High friction forces at the chip tool interface.
• Depth of cut: Large value of depth of cut.

Advantages -

The formation of discontinuous types of chips in brittle materials provides good surface finish, increases the tool life and reduces the consumption of power.

Disadvantages -

When discontinuous chips are formed in the ductile materials, the workpiece result in poor surface finish and excessive wear and tear of the tool takes place.

Continuous Chips with Built Up Edge :-

• Continuous chips with built up edge is formed by machining ductile material with high friction at the chip-tool interface.

• It is similar to the continuous types of chips but it is of less smoothness due to the built up edge.

Formation of Built Up Edge:

Built Up Edges are formed mainly due to friction between the tool and interface of chip. Because of friction between the tool and the chip, very intense heat is genrated near the nose of the tool. The compressed metal near the nose of the tool get welded due to high temperature near the nose. This compressed metal near welded to the nose is called built up edge. The chip flows through this built up edge and gets broken and get carried away by the chip and are called as built up edge chip. Rest of the built up edge stick to the surface of the workpiece and make it rough. As built up edge is formed nearr nose of tool, rake angle of the tool changes and so the cutting force also changes.

Bulit Up Edge are formed in the following conditions:-

• Wokpiece Material: Metal used as workpiece is ductile.
• Friction: High friction exists near the face of the tool.
• Coolant: Insufficient coolant and lubricant.
• Temperature: High temperature near the tool face while cutting.
• Feed Rate: High value of feed rate.
• Cutting Speed: Low cutting speed.
• Rake Angle: Very small rake angle.

Advantages -

The making of the BUE has one advantage i.e. it protects the tool from getting damaged from high friction and temperature generated during the machining process and hence the tool life increases.

Disadvantages -

The formation of these types of chips results in rough surface finish, change in the rake angle and cutting forces.