Chip Formation

Every Machining operation involves the formation of chips. The nature of which differs from operation to operation, properties of work piece material and the cutting condition. Chips are formed due to cutting tool, which is harder and more wearer-resistant than the work piece and the force and power to overcome the resistance of work material. The chip is formed by the deformation of the metal lying ahead of the cutting edge by a process of shear. Four main categories of chips are:

1.       Discontinuous Chips

2.       Continuous or Ribbon Type Chips

3.       Continuous Chip Built-up-Edge (BUE)

4.       Serrated Chips

 Types of Chips

Discontinuous Chips: These chips are small segments, which adhere loosely to each other. They are formed when the amount of deformation to which chips undergo is limited by repeated fracturing. Hard and brittle materials like bronze, brass and cast iron will produce such chips.
Continuous or Ribbon Type Chips: In continuous chip formation, the pressure of the work piece builds until the material fails by slip along the plane. The inside on the chip displays steps produced by the intermittent slip, but the outside is very smooth. It has its elements bonded together in the form of long coils and is formed by the continuous plastic
deformation of material without fracture ahead of the cutting edge of the tool and is followed by the smooth flow of chip up the tool face.
Continuous Chip Built Up Edge: This type of chip is very similar to that of continuous type, with the difference that it is not as smooth as the previous one. This type of chip is associated with poor surface finish, but protects the cutting edge from wear due to movement of chips and the action of heat causing the increase in tool life.
Serrated Chips: These chips are semicontinuous in the sense that they possess a saw-tooth appearance that is produced by a cyclical chip formation of alternating high shear strain followed by low shear strain. This chip is most closely associated with certain difficult-to-machine metals such as titanium alloys,
nickel-base super alloys, and austenitic stainless steels when they are machined at higher cutting speeds. However, the phenomenon is also found with more common work metals (e.g., steels), when they are cut at high speeds. Some of the conditions favorable for continuous chip formation can be summarized as: Ductile work piece material. Small chip thickness. Fine feeds. Sharp cutting edge of the cutting tool. A large rake angle on the cutting tool. High cutting speeds. Using coolant. Causes of discontinuous chips formation Cutting conditions are the main causes for discontinuous chips such as, ·         Very low or very high cutting speed ·         Large depth of cut ·         Low rake angle ·         Lack of cutting fluid ·         Vibration on the machine tool