TYPES OF CHIPS
There are three types of chips:
1. CONTINUOUS CHIP
During the cutting of ductile materials, a continuous chip is produced due to the presence of tool cutting edge in compression and shear. These types of chips are in the form of long coils and have the same thickness throughout the length.
This type of chip is required, since it gives a good surface finish, improving the tool life and less power consumption. However, chip disposal is not easy and the surface finish of the finished work gets affected.
The following condition favors the formation of continuous chips.
1. Smaller depth of cut.
2. High cutting speed.
3. Large rake angle.
4. Proper cutting fluid.
5. Low friction between the tool face and the chips.
2. DISCONTINUOUS CHIP OR SEGMENTAL CHIP
Discontinuous chips as shown in the figure are produced while machining brittle materials such as grey cast iron, bronze, and high carbon steel at low cutting speed without fluids when friction exists between the tool and chip.
During machining, the brittle materials lack the density which is necessary for plastic chip formation. But, it should be less. This will result in the formation of the discontinuous chip. In continuous chip formation, the shearing occurs at the head of the cutting tool continuously without fracture whereas in discontinuous chip formation, intermittently rupture occurs which will produce a segment of chips.
Handling of these chips is easier and they can be easily disposed of off since they are having a small length. Also, it will not spoil the finished workpiece surface as they do not interfere.
The following condition favors the formation of discontinuous chips.
2. Small rake angle.
3. Higher depth of cut.
4. Low cutting speed.
5. Excess cutting fluid.
6. Cutting ductile material at very low feeds with a small rake angle of the tool.
3. CONTINUOUS CHIP WITH BUILT-UP EDGE
During the cutting process, the interface temperature and pressure are quite high and between the tool-chip interface, the friction is also high. It causes the chip material to weld itself to the tool face near the nose as shown in the figure. These are called “built-up edges”.
The formation of built-up edges in the continuous chips is a transient and not steady phenomenon. The collected built-up chip material will then break away, part adhering to the undesired of the chip and part to the workpiece. Thus, the process will result in a poor surface finish on the machined surface and accelerated wear on the tool face.
However, this type of chip has some advantages, one important favor of it is that from the wears the rake face of the tool is protected due to moving chip and the action of heat. It may result in an increase in tool life.
The following condition favors the formation of the continuous chips with built-up edges.
1. Low cutting speed.
2. Small rake angle.
3. Coarse feed.
4. Large uncut thickness.
5. Insufficient cutting fluid.
Chip formation is the result of material being removed from a workpiece. Chips are small pieces of material that have been cut off the surface of a larger piece. There are two types of chips: primary and secondary. Primary chips are created when the cutting tool first contacts the workpiece. Secondary chips are created after the initial contact between the cutting tool and the workpiece. The type of chip formed depends on the type of material being cut and the speed at which the tool is moving relative to the workpiece.
Causes of Chip Formation
The causes of chip formation are many and varied. A few of these causes include:
• Tool wear
• Workpiece hardness
• Cutting speed
• Feed rate
• Feed direction
• Angle of attack
• Surface finish
• Tool geometry
The impact of chip type in machining
There are three basic types of chips: rough, smooth, and burr. Rough chips are created when the tool is not sharp enough to remove the entire amount of material from the workpiece. These chips are often referred to as “oversized” chips. Smooth chips are created when the material being cut is soft enough to allow the cutting tool to completely penetrate the workpiece. Burrs are created when the cutting edge of the tool becomes dull. When the cutting edge is dull, the tool does not fully penetrate the workpiece, causing the material to stick to the side of the tool.