(SEM V) THEORY EXAMINATION 2018-19 MANUFACTURING SCIENCE &TECHNOLOGY-II

MANUFACTURING SCIENCE & TECHNOLOGY – II (RME-503)

B.Tech (SEM-V) – AKTU
                                                                                                   Time: 3 Hours  Max Marks: 70

SECTION A

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

Q1 (a) What is metal cutting?

Metal cutting is a manufacturing process in which unwanted material is removed from a workpiece in the form of chips using a cutting tool to obtain the desired shape, size, and surface finish. It is commonly carried out on machines like lathes, milling machines, and grinding machines.

Q1 (b) Define shear plane angle.

Shear plane angle is the angle between the shear plane and the direction of cutting velocity during metal cutting. It plays an important role in determining chip thickness, cutting force, and energy consumption.

Q1 (c) What is tool life?

Tool life is the time period during which a cutting tool performs satisfactorily before it fails due to wear. It is generally expressed in minutes and is influenced by cutting speed, feed, depth of cut, and tool material.

Q1 (d) What is up milling?

Up milling is a milling operation in which the cutter rotates opposite to the direction of feed. In this process, chip thickness starts from zero and increases gradually, resulting in higher cutting forces and poorer surface finish.

Q1 (e) Define tolerance.

Tolerance is the permissible variation in a dimension of a manufactured part. It ensures proper fit, interchangeability, and economical production.

Q1 (f) What is electrochemical machining (ECM)?

Electrochemical machining is a non-traditional machining process in which material is removed by anodic dissolution using electrical energy and an electrolyte, without direct contact between tool and workpiece.

Q1 (g) Define welding.

Welding is a permanent joining process in which two or more metal parts are joined by heating them to a suitable temperature, with or without pressure and filler material.

SECTION B

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

Q2 (a) Explain the mechanism of chip formation in metal cutting.

During metal cutting, a wedge-shaped cutting tool penetrates the workpiece. Due to compressive stress, plastic deformation occurs along a narrow zone called the shear plane. The material shears and flows in the form of a chip. Depending on material properties and cutting conditions, chips may be continuous, discontinuous, or built-up edge type.

Q2 (b) Explain resistance spot welding with neat sketch.

Resistance spot welding joins metal sheets by applying pressure and passing high electric current through the contact surfaces. Heat generated due to electrical resistance melts the metal locally, forming a weld nugget. It is widely used in automobile and sheet-metal industries.

Q2 (c) What is indexing? Explain different methods of indexing.

Indexing is a machining operation used on milling machines to divide a workpiece into equal parts.
Methods of indexing include simple indexing, compound indexing, differential indexing, and direct indexing. These methods allow accurate cutting of gears, splines, and slots.

Q2 (d) Explain electrochemical grinding (ECG).

Electrochemical grinding is a hybrid machining process combining electrochemical machining and conventional grinding. Material removal occurs mainly by electrochemical action, while the grinding wheel removes the oxide layer and provides accuracy. It is suitable for hard and brittle materials.

SECTION C

(Attempt any two – 7 × 2 = 14 marks)

Q3 (b) A batch of 1500 steel parts each 120 mm in diameter and 400 mm in length is to be rough-turned using a feed of 0.7 mm/rev.

Cost of grinding tool = ₹75
Tool resetting time = 2 min
Machining cost = ₹300/hr
Loading & unloading time = 2 min
Initial setup time = 3 hrs
Taylor’s equation: V T⁰·²⁵ = 650**

(i) Optimum cutting speed and tool life for minimum cost

Using minimum cost criterion:

Topt=1−nn×TcCmT_{opt} = \frac{1-n}{n} \times \frac{T_c}{C_m}Topt​=n1−n​×Cm​Tc​​

Substituting values, optimum tool life is calculated.
Using Taylor’s equation, corresponding optimum cutting speed is obtained.

(ii) Total production time and cost

Total production time includes:

Setup time

Machining time

Tool changing time

Loading & unloading time

Total cost is calculated by multiplying total time with machining cost rate and adding tool cost.

(iii) Calculation using maximum production rate criterion

For maximum production rate:

Topt=1−nn×TcT_{opt} = \frac{1-n}{n} \times T_cTopt​=n1−n​×Tc​

Using this tool life, cutting speed, total time, and cost are recalculated.
Maximum production rate results in higher speed but lower tool life.

**Q4 (a) What do you understand by indexing? Explain compound indexing.

Cut 72 teeth on a blank of 40 mm diameter using compound indexing.**

Compound indexing is used when simple indexing is not possible. It uses simultaneous movement of index plate and crank.

For 72 teeth:

Crank movement=4072=59\text{Crank movement} = \frac{40}{72} = \frac{5}{9}Crank movement=7240​=95​

This is achieved by suitable combination of two index plates.
Thus, compound indexing enables accurate cutting of teeth not possible by simple indexing.