Q. Short note on: Types of chip.

1. The form and dimension of a chip in metal machining indicate the nature and quality of a particular machining process, but the type of chip formed is greatly influenced by the properties of the material cut and various cutting condition.

2. General Types of Chips are as follows:

   (i) The discontinuous or segmental form.

   (ii) The continuous or ribbon type.

   (iii) The continuous with built up edge.

(i) Discontinuous or segmental chips:

1] It consists of elements fractured into fairly small pieces ahead of the cutting tool.

2] This type of chip is obtained in machining most bottle materials, such as cast iron and bronze. These materials rupture during deformation and form chips as separate small pieces.

3] As these chips are produced, the cutting edge small over the irregularities and a fairly good finish is obtained.

4] Tool life is reasonably good, and the power consumption low.

5] Discontinuous chips can also be formed on some ductile metals only under certain conditions particularly at very low speeds and if the co-efficient of friction is low.

6] with ductile metals, however the surface finish is bad and the tool life is short.

7] Conditions tending to promote discontinuous chip formation includes:

A. Brittle metal.

B. Greater depth of cut.

C. Low cutting speed.

D. Small rake angle.

(ii) Continuous chips:

1] It consists of elements bonded firmly together without being fractured.

2] The upper side of a continuous chip has small notches while the lower side, which slides over the tool face, is smooth and shiny.

3] The continuous form is considered most desirable for low friction at the tool chip interface, lower power consumption, long tool life and goof surface finish.

4] Factor favorable to its formation are:

A. Ductile metal [MS, Copper, etc.]

B. Fine feed

C. High cutting speed

D. Large rake angle

E. Smooth tool face and an efficient lubrication system.

Continuous chips with built up edge:

1] The term built up edge implies the building up of a ridge of metal on the top surface and above the cutting edge.

2] It appeals that, when the cut is started in metals, a pie of compressed and highly stressed metal forms at the extreme edge of the tool. Owing to the high heat and pressure generated there, this pied up metal is welded to the cutting tip and forms a “false”. Cutting edge to the tool. This is usually referred to as the “built up edge”.

3] The weaker chip metal tears away from the weld as the chip moves along the tool face.

4] The built up becoming unstable, breaks down and some fragments leave with the chip as it passes off and the rest adheres to the work surface producing the characteristics rough surface.

5] The built up edge appears to be a rather permanent structure as long as the cut is continuous at relatives high speeds and has the effect of slightly altering the rake angle.

6] At very high speeds, the built up edge is very small or non-existent, and a smooth machined surface result.

7] Conditions tending to formation of built up edges include:

A. Low cutting speed.

B. Low rake angle.

C. High feed.

D. Lack of cutting fluid and

E. Large depth of cut.