Tool Wear and Failure MCQ Quiz in मल्याळम - Objective Question with Answer for Tool Wear and Failure - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Explanation:

Rake angle:

• The angle between the face of the tool and a plane parallel to its base.
• If this inclination is towards the shank, it is known as a back rake angle and if measured along with side is known as side rake angle.

Lip angle:

• The angle between the face and flank of the tool.
• As the lip angle increases, the cutting edge will go stronger.

Relief angle:

• The angle formed between the flank of the tool and a perpendicular line drawn from the cutting point to the base of the tool.

Concept:

Taylor's tool life equation is:

\({V_1}T_1^n = C\)

Calculation:

Given:

V2 = 2V1, T₂ = T₁/8

\({V_1}T_1^n = C\)

\({V_1}T_1^n = {V_2}T_2^n \)

\({V_1}T_1^n = {2V_1}\left(\frac{T_1}{8}\right)^n \)

\(T_1^n = {2}\left(\frac{T_1^n}{2^{3n}}\right)\)

2³ⁿ = 2

3n = 1

∴ n = 1/3

Explanation:

The surface finish in the machining operation depends on

1. Type of chip formation
2. Tool profile and geometry
3. Cutting speed

For a tool of finite nose radius r, the peak–to–valley roughness can be evaluated as

\(h = \frac{{{f^2}}}{{8r}}\)

Also \(h = f\tan {\gamma _e} + \frac{r}{2}{\tan ^2}{\gamma _e} - \sqrt {\left( {2fr{{\tan }^3}{\gamma _e}} \right)} \)

From the above equation nose radius, cutting–edge angles, and feed rate have an influence on the surface finish.

• Cutting speed is the most important factor in tool life and not in surface finish.

Concept:

In the machining process, the wearing action takes place on those surfaces along which there is relative sliding with other surfaces. On the rake surface, the wear takes place because of the movement of the chip over the tool, and over the flank surface, the wear takes place because of rubbing action between the tool and the workpiece.

The wear overrake surface is known as crater wear and over flank, the surface is known as flank wear.

Crater wear occurs on the rake face. For the crater wear, the temperature is the main culprit and tool diffuses into the chip material and the tool temperature is maximum at some distance from the tooltip. So crater wear starts at some distance from the tooltip.

Concept:

Cold chisels are used for cutting metal. They are made from high - carbon steel, hardened and tempered at the cutting end. The opposite end, which is struck by the hammer, is not hardened but is left to withstand the hammer blows without chipping.

The cross-section of chisels is usually hexagonal or octagonal.

• Annealing relieves the internal strains of the metal, which develops during the forging operation and thus makes a chisel tough and strong.
• The hardening of the metal makes it possible for a chisel to maintain a sharp cutting edge.
• Tempering reduces the brittleness of the metal so that the cutting edge of the chisel is less liable to be fractured.

A hot chisel can be made from medium carbon steel as it does not need much hardening of its cutting edge as it has to cut metal in the plastic state. It also does not require tempering.

Explanation:

Taylor’s Tool Life Equation based on Flank Wear:

VTn = C

where 

V = cutting speed (m/min)

T = time (min) (time taken to develop certain flank wear)

n = an exponent that largely depends on tool material

C = constant based on tool and work material and cutting condition.

Values of Exponent ‘n’

Concept:

Tool life criteria in production

1. The complete failure of cutting edge
2. Poor surface finish
3. Increase in cutting force
4. Chatter
5. Overheating and fuming due to excessive friction
6. Chips become ribbony, stingy, and difficult to dispose of

Concept:

Rake angle is an important parameter for the surface finish of the product. Rake angle decides the cutting forces and power needed for cutting a soft and a hard material.

A positive rake angle is used for cutting soft and ductile material.

A negative rake angle is used for cutting a very hard or a brittle material.

A zero rake angle is used for machining brass material.

At low positive rake angle a higher cutting force is required but with the increase of positive rake angle the lesser amount of cutting forces and power is required which gives better surface finish. But the tool becomes thin and weak.

Cutting tools may be classified according to the number of major cutting edges (points) involved as follows:

• Single point Tools (One dominant cutting edge): e.g., turning tools, shaping, cutoff/parting tool, planning and slotting tools and boring tools
• Multiple Cutting Edge Tools (More than one cutting edge): e.g., Drill, milling cutters, broaching tools, hobs, gear shaping cutters etc. 

Parting or cutoff is the operation of cutting a piece off by slicing a groove all the way through it with a special parting tool or cut off tool.

Reamer is a cutting tool used to finish and enlarge a hole and It is a multi-point cutting tool.

A drill is a multipoint cutting tool used for making the cylindrical holes of definite diameters.

Milling is a process of producing flat and complex shapes with the use of multi-point (or multi-tooth) cutting tool.

Explanation:

Crater wear occurs on the rake face. For the crater wear, the temperature is the main culprit and tool diffuse into the chip material and tool temperature is maximum at some distance from the tooltip. So crater wear starts at some distance from the tooltip.