Mechanism of Tool Wear MCQ Quiz in मराठी - Objective Question with Answer for Mechanism of Tool Wear - मोफत PDF डाउनलोड करा

Concept:

Nose radius is the radius at the tip of the tool between the major and minor cutting edges.

It is provided to obtain a better surface finish and strength of the cutting tip of the tool.

The surface finish (R) can be calculated from the following relation,

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

where f - feed rate; r - nose radius; h = surface roughness

Calculation:

Given:

R = 2 mm, h = 4 μ 

\(4\times10^{-3} = \frac{{{f^2}}}{{8 \times 2}}\)

f = 0.252 mm/rev

Concept:

• In the machining process, the wearing action takes place on those surfaces along which there is relative sliding with other surfaces.
• The wear over rake surface is known as crater wear and over flank surface is known as flank wear.

Flank wear occurs mainly on: 

• The flank or the relief face of the tool
• The nose part of the cutting tool

Flank wear occurs due to: 

• Abrasion by hard particles and inclusions in the work piece.
• Shearing off the micro welds between tool and work material.
• Abrasion by fragments of built‐up‐edge ploughing against the clearance face of the tool.
• At low speed flank wear predominates.
• If MRR increased flank wear increased.

• 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.

\(\begin{array}{l} {\rm{Flank\;wear}} \propto {\rm{\;cot\;\alpha }}\\ \therefore \;{\rm{Tool\;life}} \propto {\rm{\;tan\;\alpha }}\; \end{array}\)

T = k tan α

\(\begin{array}{l} \% \;change = \left( {\frac{{{T_2} - {T_1}}}{{{T_1}}}} \right) \times 100 = \left( {\frac{{k\tan {\alpha _2} - k\tan {\alpha _1}}}{{k\tan {\alpha _1}}}} \right) \times 100\\ = \left( {\frac{{k\tan {\alpha _2}}}{{k\tan {\alpha _1}}} - 1} \right) \times 100 = \left( {\frac{{\tan 7^\circ }}{{tan10}} - 1} \right) \times 100 = - 30.3\% \;decrease \end{array}\)

Friction at the tool-chip interface can be reduced by increasing the cutting speed.

With the increase in speed

• the cutting force decreases
• continuous chip without BUE forms
• High temperature generation
• Surface roughness is low i.e. better surface finishing
• Friction at the chip-tool interface decreases due to less cutting force and softening of the material at high temperature.

Decrease in rake angle as well as increase in depth of cut will lead to increase in cutting force as well as a chip with built up edge will form, thus friction increases at the chip-tool interface.