(SEM V) THEORY EXAMINATION 2019-20 MANUFACTURING SCIENCE & TECHNOLOGY-II

MANUFACTURING SCIENCE & TECHNOLOGY – II (RME-503)

B.Tech (SEM-V) – AKTU

SECTION A

(Attempt all questions – 2 × 7 = 14 marks)

Q1 (a) During metal cutting operation with coefficient of friction μ = 0.3 and rake angle α = 12°, calculate shear plane angle using Lee and Shaffer theory.

According to Lee and Shaffer theory, the shear plane angle is given by
ϕ = 45° + α − β

Where friction angle β = tan⁻¹(μ)
β = tan⁻¹(0.3) ≈ 16.7°

Substituting values,
ϕ = 45° + 12° − 16.7°
ϕ ≈ 40.3°

Q1 (b) Differentiate between up milling and down milling.

In up milling, the cutter rotates opposite to feed direction and chip thickness increases gradually. In down milling, cutter rotates in the same direction as feed and chip thickness decreases. Up milling causes more tool wear, while down milling gives better surface finish.

Q1 (c) Differentiate between polishing and buffing operation.

Polishing is used to remove scratches and improve surface finish using abrasive particles. Buffing is a finishing process that gives mirror-like shine using soft wheels and fine abrasives.

Q1 (d) Define tolerance sink.

Tolerance sink is the reduction in permissible dimensional tolerance due to accumulation of errors during machining and assembly, affecting product quality.

Q1 (e) Define deposition rate, reinforcement, weld bead and throat related to welding process.

Deposition rate is the amount of weld metal deposited per unit time.
Reinforcement is excess weld metal above parent surface.
Weld bead is the deposited molten metal during welding.
Throat is the minimum distance from root to face of weld.

Q1 (f) Define the term duty cycle.

Duty cycle is the ratio of welding time to total cycle time. It indicates how long a welding machine can operate safely without overheating.

Q1 (g) Differentiate between chemical machining and electrochemical machining.

Chemical machining removes material using chemical etchants, while electrochemical machining removes material by anodic dissolution using electric current. ECM offers higher precision and no tool wear.

SECTION B

(Attempt any three – 7 × 3 = 21 marks)

Q2 (a) Show that during orthogonal cutting with zero rake angle, the ratio of shear strength to specific cutting energy is constant.

In orthogonal cutting with zero rake angle, cutting energy depends on shear strength of material and shear plane area. By deriving expressions for cutting force and specific cutting energy, it is shown that their ratio remains constant for a given material, validating the machining theory.

Q2 (b) Explain the principle and working of resistance spot welding.

Resistance spot welding joins sheets by applying pressure and passing high current through contact points. Heat is generated due to resistance, forming a weld nugget. It is widely used in automobile industries due to speed and automation.

Q2 (c) Explain the working principle of electrochemical grinding (ECG).

ECG combines electrochemical machining and grinding. Material removal occurs mainly by electrochemical dissolution with grinding wheel providing shape and accuracy. It is suitable for hard and brittle materials.

SECTION C

(Attempt any one part from each question – 7 × 2 = 14 marks)

Q3 (a) Calculate optimum cutting speed for minimum total cost using Taylor’s tool life equation.

Given:
Job cost = Rs. 18C/V
Tool cost = Rs. 270C/Tv
VT⁰·²⁵ = 150

Using Taylor’s tool life equation and cost minimization condition, the optimum cutting speed is calculated by differentiating total cost equation with respect to speed. The result gives optimum cutting speed for minimum total cost.

Q4 (b) Show that maximum chip thickness in slab milling is given by

tₘₐₓ = (2f / NZD) √(D − d)**

Using milling geometry, chip thickness depends on feed, cutter diameter, depth of cut and number of teeth. By resolving chip formation at entry point, the expression for maximum chip thickness is derived.

Q5 (a) Discuss material removal mechanism of chip formation in grinding process.

In grinding, material is removed by micro-cutting, ploughing, and rubbing actions of abrasive grains. Chips formed are very small due to high cutting speed. Grinding provides high accuracy and surface finish.