What is Chip formation?
Chip formation is part of the process of cutting materials by mechanical means, using tools such as saws, lathes, and milling cutters. An understanding of the theory and engineering of this formation is an important part of the development of such machines and their cutting tools.
The formal study of chip formation was encouraged around World War II and shortly afterward, with increases in the use of faster and more powerful cutting machines, particularly for metal cutting with the new high-speed steel cutters.
Chip formation is usually described according to a three-way model developed by Franz. This model is best known within the field of machine tool design, although it is also used when an application area, such as woodworking, requires a vocabulary to describe chip formation in more detail than is usually attempted.
Types of Chips
1. Continuous Chips
In the machining process, continuous chips are formed during the machining of ductile material with high speed and minimum friction between the tool and material. Due to continuous plastic deformation by applying the tool, this type of chip is produced.
Mild steel and copper is ductile material. The thickness of the chip is equal to entire the length. It commonly provides a good surface finish. The main drawback of this type of chip is difficult to handle and dispose of. The conditions which are responsible for the formation of continuous types of chips are
- Ductile material like mild steel is used.
- The bigger rake angle of the tool.
- High cutting speed.
- Minimum friction between the chip and tool interface.
- Small depth of cut.
The formation of continuous chips during the 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.
2. Discontinuous Chips
If the chips during the machining process are not continuous i.e., formed with breakage are called discontinuous chips.
Discontinuous chips are formed when brittle or hard metals like brass, bronze, and cast iron are used as workpieces in the machining process.
Discontinuous chips are also formed in ductile material when the friction between tool and workpiece is high. Discontinuous chips are not a good sign for machining of ductile material as it gives poor surface finish and machining process becomes slow.
Conditions that are responsible for the formation of discontinuous chips are:
- Low feed rate.
- Small rake angle of the tool.
- High cutting speed.
- High friction forces at the chip tool interface.
- Too much depth of cut.
The formation of discontinuous types of chips in brittle materials provides a good surface finish, increases the tool life, and reduces the consumption of power.
When discontinuous chips are formed in the ductile materials, the workpiece results in poor surface finish, and excessive wear and tear of the tool takes place.
3. Continuous Chips with Built-Up Edges
In the machining process of ductile material, continuous chips are made with built-up edges when the temperature and pressure in the cutting and friction of the chip and tool face are high.
It is almost similar to the continuous chips but it is rough due to the built-up edge. This function may cause the material to stick or weld to the edge of the tool.
You may wonder how it produces?
It is created, When the chip flows upward and friction between the interface of the chip and tool is high. The heat is generated at the nose of the tool is very high, due to the high friction between the chip and the tool.
Hence, compressed metal fit to the tool nose is welded therefore it is known as built-up edges. If the chip flows through this built-up edge, it breaks and is sent away from the chip and is termed as built-up edge chips. The rest of the built-up edge adheres to the surface of the workpiece and does it thicker.
Why do Continuous Chips with BUE occur when your machine?
- By using the ductile material while machining.
- Due to the smaller rake angle of the tool.
- The cutting speed of the tool is slow.
- Lack of coolant and may cause increases in friction between chip-tool faces.
- The thickness of the chip is high.
- Due to the high temperature between workpiece and tool.
- High rate of feed of the tool.
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.
The formation of these types of chips results in a rough surface finish, change in the rake angle, and cutting forces.