Q.1.What is advantage of Cold and Hot working ?

Advantage OF HOT WORKING:

1. As the material is above the recrystallisation temperature, any amount of working can be imparted since there is no strain hardening taking place.
2. At a high temperature, the material would have higher amount of ductility and therefore there is no limit on the amount of hot working that can be done on a material. Even brittle materials can be hot worked.
3. In hot working process, the grain structure of the metal is refined and thus mechanical properties improved.
4. Porosity of the metal is considerably minimized.
5. If process is properly carried out, hot work does not affect tensile strength, hardness, corrosion resistance, etc.
6. Since the shear stress gets reduced at higher temperatures, this process requires much less force to achieve the necessary deformation.
7. It is possible to continuously reform the grains in metal working and if the temperature and rate of working are properly controlled, a very favorable grain size could be achieved giving rise to better mechanical properties.
8. Larger deformation can be accomplished more rapidly as the metal is in plastic state.
9. No residual stresses are introduced in the metal due to hot working.
10. Concentrated impurities, if any in the metal are disintegrated and distributed throughout the metal.
11. Mechanical properties, especially elongation, reduction of area and izod values are improved, but fibre and directional properties are produced.
12. Hot work promotes uniformity of material by facilitating diffusion of alloy constituents and breaks up brittle films of hard constituents or impurity namely cementite in steel.

Disadvantage OF HOT WORKING:

1. Due to high temperature in hot working, rapid oxidation or scale formation and surface de-carburization take place on the metal surface leading to poor surface finish and loss of metal.
2. On account of the loss of carbon from the surface of the steel piece being worked the surface layer loses its strength. This is a major disadvantage when the part is put to service.
3. The weakening of the surface layer may give rise to a fatigue crack which may ultimately result in fatigue failure of the component.
4. Some metals cannot be hot worked because of their brittleness at high temperatures.
5. Because of the thermal expansion of metals, the dimensional accuracy in hot working is difficult to achieve.
6. The process involves excessive expenditure on account of high cost of tooling. This however is compensated by the high production rate and better quality of components.
7. Handling and maintaining of hot working setups is difficult and troublesome.

Q.2.What is advantage and disadvantage of COLD WORKING?

ADVANTAGES OF COLD WORKING:

1. In cold working processes, smooth surface finish can be easily produced.
2. Accurate dimensions of parts can be maintained.
3. Strength and hardness of the metal are increased but ductility decreased.
4. Since the working is done in cold state, no oxide would form on the surface and consequently good surface finish is obtained.
5. Cold working increases the strength and hardness of the material due to the strain hardening which would be beneficial in some situations.
6. There is no possibility of decarburization of the surface
7. Better dimensional accuracy is achieved.
8. It is far easier to handle cold parts and it is also economical for smaller sizes.

DISADVANTAGES OF COLD WORKING:

1. Some materials, which are brittle, cannot be cold worked easily.
2. Since the material has higher yield strength at lower temperatures, the amount of deformation that can be given to is limited by the capability of the presses or hammers used.
3. A distortion of the grain structure is created.
4. Since the material gets strain hardened, the maximum amount of deformation that can be given is limited. Any further deformation can be given after annealing.
5. Internal stresses are set up which remain in the metal unless they are removed by proper heat-treatment.

Q.3.What is advantage of Welding ?

Advantages OF WELDING:

1. Welding is more economical and is much faster process as compared to other processes (riveting, bolting, casting etc.).
2. Welding, if properly controlled results permanent joints having strength equal or sometimes more than base metal.
3. Large number of metals and alloys both similar and dissimilar can be joined by welding.
4. General welding equipment is not very costly.
5. Portable welding equipments can be easily made available.
6. Welding permits considerable freedom in design.
7. Welding can join welding jobs through spots, as continuous pressure tight seams, end-to-end and in a number of other configurations.
8. Welding can also be mechanized.

Disadvantages:

1. It results in residual stresses and distortion of the workpieces.
2. Welded joint needs stress relieving and heat treatment.
3. Welding gives out harmful radiations (light), fumes and spatter.
4. Jigs, and fixtures may also be needed to hold and position the parts to be welded.
5. Edges preparation of the welding jobs are required before welding.
6. Skilled welder is required for production of good welding.
7. Heat during welding produces metallurgical changes as the structure of the welded joint is not same as that of the parent metal.

Q.4.What is advantage and disadvantage of Resistance upset butt welding & Resistance flash butt welding ?

Resistance upset butt welding & Resistance flash butt welding:

Advantage:

1. It is comparatively much faster than butt welding.
2. This method utilizes less current in comparison to butt welding as the small portion of the metal is only being heated for getting a good weld.
3. Created joint by this welding is much stronger than the butt welding joint. Also the strength of the weld produced is high even more than that of the base metal. Theend of the metal pieces to be welded in this welding need not be squared as it is the basic requirement in butt-welding.
4. A high degree of accuracy can be easily achieved in terms of length alignment of weld.

Disadvantage:

1. The periodic maintenance of machine and replacement of insulation is needed as flashing particles of molten metal are thrown out during welding which may enter into the slide ways and insulation of the set up.
2. Welder has to take enough care against possible fire hazard due to flashing during welding.
3. Additional stock has to be provided for compensating loss of metal during f1ashing and upsetting. This increases to the cost of weld.
4. Cost of removal of flash weld metal by trimming, chipping, grinding, etc. will increase to the welded product.
5. Surface of the jobs where they come in contact with the gripping surfaces, should be clean otherwise they will restrict the flow of electric current.
6. The available power, opening between the jaws of the gripping clamps and upsetting pressure of the welding set limit the size and cross sectional area of the jobs to be welded.

Q.5.What is advantage and disadvantage of Shell Molding ?

Shell Molding of Advantages:

The main advantages of shell molding are:

1. High suitable for thin sections like petrol engine cylinder.
2. Excellent surface finish.
3. Good dimensional accuracy of order of 0.002 to 0.003 mm.
4. Negligible machining and cleaning cost.
5. Occupies less floor space.
6. Skill-ness required is less.
7. Moulds formed by this process can be stored until required.
8. Better quality of casting assured.
9. Mass production.
10. It allows for greater detail and less draft.
11. Unskilled labor can be employed.
12. Future of shell molding process is very bright.

Disadvantages

The main disadvantages of shell molding are:

1. Higher pattern cost.
2. Higher resin cost.
3. Not economical for small runs.
4. Dust-extraction problem.
5. Complicated jobs and jobs of various sizes cannot be easily shell molded.>
6. Specialized equipment is required.
7. Resin binder is an expensive material.
8. Limited for small size.

Q.6.What is advantage and Applications of Metalic Molding ?

Metalic Molding of Advantages:

1. Fine and dense grained structure in casting is achieved using such mold.
2. No blow holes exist in castings produced by this method.
3. The process is economical.
4. Because of rapid rate of cooling, the castings possess fine grain structure.
5. Close dimensional tolerance is possible.
6. Good surface finish and surface details are obtained.
7. Casting defects observed in sand castings are eliminated.
8. Fast rate of production can be attained.
9. The process requires less labor.

Metalic Molding of Disadvantages:

Applications:

1.This method is suitable for small and medium sized casting.
2.It is widely suitable for non-ferrous casting.

Q.7.What is advantage and disadvantage of Cold chamber die casting ?

Cold chamber die casting:

Advantages:

1. It is very quick process.
2. It is used for mass production.
3. castings produced by this process are greatly improved surface finish.
4. Thin section (0.5 mm Zn, 0.8 mm Al and 0.7 mm Mg) can be easily caste.
5. Good tolerances.
6. Well defined and distinct surface.
7. Less nos. of rejections.
8. Cost of production is less.
9. Process require less space.
10. Very economic process.
11. Life of die is long.
12. All casting has same size and shape.

Disadvantages:

 
1. Cost of die is high.
2. Only thin casting can be produced.
3. Special skill is required.
4. Unless special precautions are adopted for evaluation of air from die-cavity some airis always entrapped in castings causing porosity.
5. It is not suitable for low production.

Q.8.What is advantage and disadvantage of Cell mold costing ?

Cell mold costing:

Advantages:

The main advantages of shell molding are:

1. Very suitable for thin sections like petrol engine cylinder.
2. Excellent surface finish.
3. Good dimensional accuracy of order of 0.002 to 0.003 mm.
4. Negligible machining and cleaning cost.
5. Occupies less floor space.
6. Skill-ness required is less.
7. Molds can be stored until required.
8. Better quality of casting assured.
9. Mass production.

Disadvantages:

1. Initial cost is high.
2. Specialized equipment is required.
3. Resin binder is an expensive material.
4. Limited for small size.
5. Future of shell molding process is very bright.