Solved Anna University Question Papers (Reg 2013 / Dec 2017)

B.E./B.TECH. DEGREE EXAMINATION - NOVEMBER/DECEMBER 2017

Third Semester

Mechanical Engineering

ME 6302-MANUFACTURING TECHNOLOGY-I

(Common to Industrial Engineering and Industrial Engineering and Management) and Mechanical and Automation Engineering)

Time: Three hours      Maximum: 100 Marks

(Regulation 2013)

Answer ALL questions

Part A - (10 × 2 = 20 Marks)

1. What is natural moulding sand? Give its constituents.

Natural moulding sand is available from natural deposits. It needs only 5 to 8% water. These sands are available at riverbeds and it contains 80 to 90% of silica, 5 to 10% Alumina or clay and small percentage of lime and magnesia.

Natural sand is also prepared by crushing and milling the soft yellow sand stone. This sand has less refractoriness as compared to synthetic sand. This sand is generally used for making light castings in ferrous and non-ferrous metals.

2. What are hot spots and hot tears?

Some spots on the surface become hard called hot spots. These are generally developed on iron castings rich in silicon content due to local chilling of those spots by moulding sand. Due to this chilling effect, while cast iron is formed at these places, it renders them hard,

Hot tear is the crack in the casting caused by high residual stresses.

3. How does penetration vary for DCSP and DCRP welding?

In DCSP, the electrode is connected with the negative terminal of the power source and base metals are connected with the positive terminal but in DCRP, base metals are connected with the negative terminal of the power source and electrode is connected with the positive terminal. Although penetration depends on a number of factors, DCSP tends to enhance the achievable penetration. Electrons liberated from the electrode are accelerated towards base metal due to potential difference between them and finally strike the base metal surface at a very high velocity. Due to striking, the kinetic energy of electrons is converted into thermal energy. Therefore, high heat is generated at the base metal surface. So, it can be stated that DCSP provides maximum penetration and DCRP provides minimum penetration.

4. Define the terms 'weld decay' and 'dilution'. 

Weld decay is a form of intergranular corrosion usually of stainless steels or certain nickel-base alloys which occurs in the heat-affected zone during the welding operation due to sensitization.

Weld dilution is defined as the weight of the base metal melted divided by the total weight of the weld metal. For example, for dilution of 0.40, the fraction of the weld metal obtained from the consumable electrode is 0.60.

5. Differentiate flat rolling and shape rolling.

6. What is precision forging?

Precision forging normally means the close-to-final form or close-tolerance forging. It is not a special technology and a refinement of existing techniques to a point where the forged part can be used with little or no subsequent machining. Precision forging is an alternative process to replace the traditional forging of complex parts. As the precision forging is done without flash, it does not only save the time to cut the flash but also saves the material of forgings flash.

7. What is springback in sheet metal bending?

The tendency of the metal that tries to resume its original position causing a decrease in bend angle is known as springback. The springback varies from 0.5° to 5o for steel. Greater springback is caused by a larger bend radius.

Springback can be avoided by

(i) over stretching using V-type form blocks, and

(ii) coining the metal slightly at the corners of the blank to remove elastic stresses called corner setting.

8. Distinguish redrawing and reverse drawing.

9. What are commonly used fillers?

Fillers are used to economize the quantity of polymer required and to vary the properties to some extent. The fillers are used to improve the strength and stability of the plastics. The type of fillers used in plastics is mica and cloth fiber. The mica and asbestos are used to improve the heat resistance capacity of the plastics.

10. Define 'potting' and 'encapsulation'.

Potting is the process of sealing or embedding components and assemblies in a liquid resin surrounded by a plastic shell. It prevents the corrosion of metals, shortages and reduces damage caused by vibration and mechanical stress. Polyurethane, epoxy, acrylic, silicone and UV cure are the materials used for potting process.

Encapsulation is similar to a potting process. It is the process of shielding components to avoid chemical reactions or to facilitate the regulated discharge of core bioactive ingredient from the shell (capsule and coating) with efficient mass transport behavior. The materials used for encapsulation are polyurethane, epoxy and silicones which are processed at room temperature or slightly elevated.

Part B - (5 × 13 = 65 Marks)

11. (a) Draw the cupola furnace and indicate the various zones in it. Describe its operations and various zones present.

Refer chapter 1.13.2 in Page 1.64. 

Or

(b) Name any 2 casting defects and its remedies of the following categories

(i) Metallic projection (ii) Cavities (iii) Defective surfaces.

Refer chapter 1.18 in Page 1.93.

12. (a) With suitable diagram, discuss the principle and variables of operation in TIG welding. What are the functions and names of shielding gases used in TIG and MIG? 

Refer chapter 2.6 in Page 2.21 for operation of TIG welding and Page 2.26 for MIG welding gases.

Or

(b) What is explosive welding? Describe its principle, process parameters and applications.

Explosive welding (EXW) is a solid state (solid-phase) welding process that uses a controlled application of large pressure generated by the detonation of applied explosives. In explosive welding, welded parts (plates) are metallurgically bonded as a result of oblique impact pressure exerted on them by a controlled detonation of an explosive charge.

The following terms are frequently used in the explosive welding.

(i) Cladding metal or cladder is the thinner plate that is either in direct 'contact with the explosive or it is shielded by a flyer plate from the explosive.

(ii)  Flyer plate is a sacrificial plate placed between cladder and explosive to protect 9100 to the cladder metal.

(iii) Interlayer is a thin metal layer which is sometimes placed between cladder and hoqeac) base plate to enhance joining.

(iv) Base plate or backer is the plate that the cladder is being joined.

(v) Anvil is the surface on which backer rests during the joining operation.

(vi) Standoff is the distance between cladder and base plate prior to the joining operation.

(vii) Bond window is the range of process variables such as velocity, dynamic bend and standoff distance that result in a successful weld.

(viii) Bonding operation is the detonation of the explosive which results in the weld. 

Before welding, the surface to be welded must be cleaned. To carry out the welding process, one of the parts to be welded is kept as stationary and the other one is made as movable. The movable part is called flayer plate. The base plate kept as stationary is rested on an anvil and the flyer plate is located above the base plate with O an angled or constant interface clearance as shown in Figure Q1(a). On top of the flyer plate, the rubber spacer is placed to avoid the rapid effect of burnt explosives. Explosives are placed on this rubber spacer with a detonator. Detonation starts at an edge of the plate and propagates at high velocity along the plate. The flyer plate moves towards the base plate at very high velocity (4 to 5 km/s) due to the impact of kinetic energy in the form compressive stress during detonation of explosives to bus collide with a stationary part to be joined. The maximum detonation velocity is about 120% of the material sonic velocity. The compressive stress is in the order of thousands of MPa. The material at the intersection points behaves similar to a viscous fluid, after explosion. The slags (oxides, nitrides and other surface contaminants) are expelled by the metallic jet created just ahead of the bonding front as shown in Figure Q1 (b). It also creates wavy surface as shown in Figure Q2. no to nongove telo During bonding, normal inter-atomic and intermolecular force takes place between these two surfaces. During the process, the surrounding material is work hardened by the shockwave and there is no metallurgical changes occur.

Figure Q3 illustrates the explosive welding process of tube details during three stages such as before welding, during welding and after welding.

The welds made are sound and allow higher operating pressure and temperature than with fusion welding. The explosive used for welding is Trimonite. It must have a low detonation velocity, below the velocity of sound in the material and there is no limit to the joint area.

For the tube plate welds, several charges can be simultaneously fired and the explosive is being in cartridge form. The explosive should be of pre-fabricated shape and cheap. The charge is electrically fired from a fuse head on the inner end of the charge and it initiates the explosion to the detonation front and then it is passing progressively through the charge.

The size of the charge depends upon the following variables.

(i) Surface finish

(ii) Angle of inclination of tube and plate

(iii) Yield strength

(iv) Melting point of the materials

(v) Tube thickness, and

(vi) Diameter.

Most of the commercial metals and alloys may be bonded (welded) by explosive welding. The following combination of dissimilar metals may be joined by explosive welding:

• Copper to steel

• Nickel to steel

• Aluminum to steel

• Tungsten to steel

• Titanium to steel

• Copper to aluminum.

Advantages, limitations and applications of explosive welding:

Advantages:

1. It ensures high quality bonding such as high strength, no distortions, no porosity and no change of the metal microstructure.

2. There is no heat-affected zone (HAZ) other than weld surface.

3. There is no diffusion.

4. Only, minor melting occurs.

5. Differences in material melting temperatures and coefficients of thermal expansion do not affect the final product.

6. Combination of dissimilar metals, copper to stainless steel, aluminium to steel or titanium to steel can be easily welded.

7. Explosive welding is much suited to cladding application.

8. Process is simple and rapid. It also gives close thickness tolerance.

9. Low melting point and low impact resistance materials cannot be effectively welded.

10. Large surfaces may be welded.

11. It is less costly.

12. Surface preparation is not required.

13. Large areas can be bonded quickly and the weld itself is very clean due to surface material of both metals.

14. Minimum fixturing/jigs are needed.

15. There is no effect on parent material properties.

16. Small quantity of explosive is used.

Limitations:

1. Brittle materials cannot be processed.

2. Only, simple shape parts may be bonded.

3. Thickness of flyer plate is limited.

4. Safety and security aspects of storage and using explosives are difficult.

5. Metals must have high enough impact resistance and ductility.

6. The geometrics welded must be simple in the shape of flat, cylindrical and conical shapes.

7. The cladding plate cannot be too large.

8. Noise and blast can require worker protection, vacuum chambers and buried in sand/water.

9. The use of explosives in industrial areas will be restricted by the noise and ground vibrations caused by the explosion.

10. Area should be cleaned and sound grounded for explosion.

11. Licenses are necessary to hold and use explosives.

Applications:

1. This process is applied to welding of tubes and tube plates in heat exchangers, feedwater heaters and boiler tubes to clad tube plates.

2. The tubes may be of steel, stainless steel or copper, aluminium brass and bronze tubes in naval brass tube plates are welded.

3. It is used for manufacturing clad tubes and pipes, pressure vessels, aerospace structures, heat exchangers, bi-metal sliding bearings, ship structures and weld transitions.

4. It is used to clad thick plates with corrosion resistant layers where other techniques (e.g. roll bonding) are not practical.

5. It is used in tube plugging.

6. It is used in remote joining in hazardous environments.

7. It is used in fixing cooling fins.

8. It is also used in cryogenic industries.

13. (a) Name the different types of rolling mills. Explain any types with a meat sketch.

Refer chapter 3.11 in Page 3.41.

Or

(b) (i) Explain the process of making seamless tube.

Refer chapter 3.13.3 in Page 3.60.

(ii) Discuss how the tubes for shaving creams/tooth paste is produced.

Refer chapter 3.19.2 in Page 3.78.

14. (a) (i) What is stretch forming? Explain how it is useful for forming large sheet metal parts.

Refer chapter 4.11 in Page 4.33.

(ii) Discuss any one method of testing the formability of sheet metal.

Refer chapter 4.13.1 in Page 4.37.

Or

(b) What is high energy rate forming? List the different types and explain any 2 in detail,

Refer chapter 4.14.5 in Page 4.49 for explosive forming and refer Electro-hydraulic forming process in Page 4.44.

15. (a) Describe the process of extrusion of plastics. Name some products made by this process.

Refer chapter 5.3.9 in Page 5.26.

Or

(b) Name and explain the suitable process for producing the barrel and plunger of a syringe.

Injection moulding process is suggested to manufacture the barrel and plunger of a syringe. Refer chapter 5.4.1 in Page 5.10 for explanation of injection moulding process.

Part C - (1 × 15 = 15 Marks)

16. (a) Name and describe any one of the methods of joining dissimilar materials having different coefficient of thermal expansion.

Laser beam welding is suggested to join dissimilar materials having different coefficient of thermal expansion. Refer chapter 2.14 in Page 2.57 for laser beam welding.

Or

(b) Suggest and explain suitable process for forming hearing-aids. Also, highlight its capabilities.

High precision micro injection moulding process of plastics is suggested for forming hearing-aids. It is similar to screw type injection moulding process. Refer chapter 5.3.1.2 in Page 5.12.

Micro-components are often smaller than a single grain of granulate. A homogeneous preparation of the melt, short dwell times of the plastics and operation according to the first-in, first-out principle are the key quality of the parts.

A micro injection unit combines an 8-mm injection screw with a second screw for melting the material. Greater flexibility is offered by micro injection module which operates according to the same principle of screw type injection moulding process.

Capabilities of high precision micro injection moulding machines:

1. High precision mass-manufacturing of highly functional 3D multi-material 

2. Optimal micro part quality

3. Effective product and process control

4. Micro manufacturing on a mass production scale

5. One-component and multi-material micro components bowl

6. High accuracy with tolerances in the micrometer range

7. High quality production level according to ISO 13485

8. Wide range of options: screws with a diameter of 15 or 12 mm and a special micro injection unit and micro injection module with an 8-mm screw

9. High level of repeat accuracy during moulding even with short travel distances