THEORY OF METAL CUTTING
1. Define Metal Cutting .
Metal cutting or machining is the process of by removing unwanted material from a block of metal in the form of chips.
2. What are the important characteristics of materials used for cutting tools?
High red hardness High wear resistance
Low frictional co- efficient
High thermal conductivity.
3. How do you define tool life?
The time period between two consecutive resharpening, with which the cuts the material effectively is called as tool life.
4. What is tool signature?
The various angles of tools are mentioned in a numerical number in particular order. That is known as tool signature.
5. What is the effect of back rack angle and mention the types?
Back rake angle of tool is increases the strength of cutting tool and cutting action. It can be classified in to two types.
1. Negative Rake angle.
2. Positive rake angle.
6. Explain the nose radius?
Joining of side and end cutting edges by means of small radius in order to increase the tool life and better surface finish on the work piece.
7. What are all conditions for using positive rake angle?
1. To machine the work hardened materials.
2. To machine low strength ferrous and non-ferrous metals.
3. To machine long shaft of small diameters.
4. To machine the metal blow recommended cutting speeds.
5. Using small machine tools with low horsepower.
8. Define the orthogonal and oblique cutting.
Orthogonal cutting: The cutting edge of tool is perpendicular to the work piece axis. Oblique cutting: The cutting edge is inclined at an acute angle with normal to the cutting velocity vector is called oblique cutting process.
9. What are the favorable factors for discontinuous chip formation?
Maching of brittle materials. Small rake angle
Higher depth of cut Low cutting speeds
Excess cutting fluid.
Cutting ductile materials with low speed and small rake angle of the tool.
10. What are the favorable factors for continuous chip formation?
Small rake angle Low cutting speed
Strong adhesion between chip and tool face. Coarse feed
Insufficient cutting fluid. Large uncut thickness.
11. Define machineability of metal.
Machine ability is defined as the ease with which a material can be satisfactorily machined.
Life of the tool before tool failure or resharpening.
12. What is shear plane?
The material of work piece is stressed beyond its yield point under the compressive force. This causes the material to deform plastically and shear off. The plastic floe takes place in a localized region is called shear plane.
13. What is chip and mention its different types?
The sheared material begins to along the cutting tool face in the form of small pieces is called chip. The chips are mainly classified into three types.
a. Continuous chip.
b. Discontinuous chip.
c. Continuous chip with built up edge.
14. Write the factors affecting the tool life or Write the Taylor’s tool life equation.
Taylor’s equation VT n = C
i. Cutting speed
ii. Feed and Depth of cut. iii.Tool Geometry
v. Type of Cutting Fluid
vii.Rigidity of the Machine tool.
15. Define “Side relief” and “End relief” angle.
Side relief angle: It is the angle between the portion of the side flank immediately below the side cutting edge and a line perpendicular to the base of the tool, and measured at right angle to the side flank.
End relief angle: It is the angle between the portion of the end flank immediately below the end cutting edge and a line perpendicular to the base of the tool, and measured at right angle to the angle.
16. What are the importance of Nose Radius?
Nose radius is favorable to long tool life and good surface finish. A sharp point on the end of a tool is highly stressed, Short lived and leaves a groove in the path of cut. There is an improvement in surface finish and permissible cutting speed as nose radius is increased from zero value.
17. What are the differences between orthogonal cutting and oblique cutting?
Cutting edge of the tool is perpendicular to the direction of tool travel
The direction of chip flow is perpendicular to the cutting edge
The chip coils in a tight flat spiral
Produces sharp corners.
Cutting edge of the tool is inclined to the direction of tool travel
The direction of chip flow is angled to the cutting edge
The chip flows sideways in a long.
Produces chamfer at the end of cut.