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II/IV B. Tech (Regular) DEGREE EXAMINATIONApril’2018

Mechanical Engineering

Casting, Forming and Welding Technology (14 ME 405)

Detailed Scheme of Evaluation

Max. Marks: 60

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1. Answer all the questions. (2x6=12)

(a) Mention any two disadvantages of die casting

Answer: 1) All metals and alloys cannot be cast.

2) The cost of machines, dies and other equipment used is high.

3) Not economical for small quantity production.

4) Heavy casting cannot be cast.

5) Special precautions are necessary for evacuation of air from die cavity, otherwise

cause porosity.

(b) What are the materials that are generally used for preparing patterns?

Answer: Patterns may be constructed from the following materials. Each material has its

own advantages, limitations, and field of application. Some materials used for making

patterns are: wood, metals and alloys, plastic, plaster of Paris, plastic and rubbers, wax, and

resins

(c) Define the casting yield.

Answer: The efficiency, or yield, of a casting is defined as the weight of the casting divided

by the weight of the total amount of metal poured

(d) What is the most commonly used type of gate? Answer: Horizontal Gating System is used most widely.

(e) Specify the advantages of the precision investment casting process.

Answer: -Excellent surface finish -High dimensional accuracy -Extremely intricate parts are castable -Almost any metal can be cast -No flash or parting lines

(f) How is a semi-permanent mould different from a permanent mould?

Answer: In a permanent mold casting there are two molds used and these molds are joined

together in which metals are molted when poured in these molds. Aluminum, lead, tin and

zinc are the normal metals that are made for permanent mold casting. The molded materials

are separated once the hot metals are cool.

The Semi-Permanent Mold Casting process uses the same general procedures as Permanent

Mold Casting but in this process expendable cores of sand or other materials are added to

the molding process to create a desired shape or an internal passage. In many cases, the

practicality of having a solid casting does not exist

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(g) What is the purpose of flux?

Answer: In high-temperature metal joining processes (welding, brazing and soldering), flux is

a substance which is nearly inert at room temperature, but which becomes strongly

reducing at elevated temperatures, preventing oxidation of the base and filler materials.

The role of a flux is typically dual: dissolving the oxides already present on the metal surface,

which facilitates wetting by molten metal, and acting as an oxygen barrier by coating the hot

surface, preventing its oxidation.

(h) What is Brazing?

Answer: It is the process of uniting two or more metals of similar or dissimilar type with the

help of an alloy in the form of spelter and flux, like borax, ash etc. these are used in tanks,

radiators, carbide tips on tool holder etc.

(i) Name the various methods of resistance welding.

Resistance Spot Welding.

Resistance Projection Welding.

Resistance Seam Welding. Resistance Butt Welding

(j) Define blanking.

Blanking is a process in which the punch operation removes a final product from a

larger piece of sheet metal.

(k) Define drawing operation.

Deep drawing is a sheet metal forming process in which a sheet metal blank is

radially drawn into a forming die by the mechanical action of a punch. It is thus a shape

transformation process with material retention. The process is considered "deep" drawing

when the depth of the drawn part exceeds its diameter.

(l) How are seamless tubes produced?

Typical methods for manufacturing seamless stainless steel tubing are by extruding,

gun drilling or piercing. However, the extrusion process provides the most uniform OD

(outside diameter) and ultimately the most concentric ID (inside diameter).

UNIT-I

2. (a) Describe the working of cupola with a neat sketch? (6M)

Answer: For many years, the cupola was the primary method of melting used in iron foundries. The cupola furnace has several unique characteristics which are responsible for its widespread use as a melting unit for cast iron. Cupola furnace is employed for melting scrap metal or pig iron for production of various cast irons. It is also used for production of nodular and malleable cast iron. It is available in good varying sizes. The main considerations in selection of cupolas are melting capacity, diameter of shell without lining or with lining, spark arrester. Shape A typical cupola melting furnace consists of a water-cooled vertical cylinder which is lined with refractory material. Construction

The construction of a conventional cupola consists of a vertical steel shell which is lined with a refractory brick.

The charge is introduced into the furnace body by means of an opening approximately half way up the vertical shaft.

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The charge consists of alternate layers of the metal to be melted, coke fuel and limestone flux.

The fuel is burnt in air which is introduced through tuyeres positioned above the hearth. The hot gases generated in the lower part of the shaft ascend and preheat the descending charge.

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Various Zones of Cupola Furnace Various numbers of chemical reactions take place in different zones of cupola. The construction and different zones of cupola are: 1. Well The space between the bottom of the tuyeres and the sand bed inside the cylindrical shell of the cupola is called as well of the cupola. As the melting occurs, the molten metal is get collected in this portion before tapping out. 2. Combustion zone The combustion zone of Cupola is also called as oxidizing zone. It is located between the upper of the tuyeres and a theoretical level above it. The total height of this zone is normally from 15 cm. to 30 cm. The combustion actually takes place in this zone by consuming the free oxygen completely from the air blast and generating tremendous heat. The heat generated in this zone is sufficient enough to meet the requirements of other zones of cupola. The heat is further evolved also due to oxidation of silicon and manganese. A temperature of about 1540°C to 1870°C is achieved in this zone. Few exothermic reactions takes place in this zone these are represented as: C + O2 → CO2 + Heat Si + O2 → SiO2 + Heat 2Mn + O2 → 2MnO + Heat 3. Reducing zone Reducing zone of Cupola is also known as the protective zone which is located between the upper level of the combustion zone and the upper level of the coke bed. In this zone, CO2 is changed to CO through an endothermic reaction, as a result of which the temperature falls from combustion zone temperature to about 1200°C at the top of this zone. The important chemical reaction takes place in this zone which is given as under. CO2 + C (coke) → 2CO + Heat Nitrogen does not participate in the chemical reaction occurring in his zone as it is also the other main constituent of the upward moving hot gases. Because of the reducing atmosphere in this zone, the charge is protected against oxidation. 4. Melting zone The lower layer of metal charge above the lower layer of coke bed is termed as melting zone of Cupola. The metal charge starts melting in this zone and trickles down through coke bed and gets collected in the well. Sufficient carbon content picked by the molten metal in this zone is represented by the chemical reaction given as under. 3Fe + 2CO → Fe3C + CO2 5. Preheating zone Preheating zone starts from the upper end of the melting zone and continues up to the bottom level of the charging door. This zone contains a number of alternate layers of coke bed, flux and metal charge. The main objective of this zone is to preheat the charges from roomtemperature to about 1090°C before entering the metal charge to the melting zone. The preheating takes place in this zone due to the upward movement of hot gases. During the preheating process, the metal charge in solid form picks up some sulphur content in this zone. 6. Stack Zone The empty portion of cupola above the preheating zone is called as stack. It provides the passage to

hot gases to go to atmosphere from the cupola furnace.

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(b) Explain about different types of Patterns? (6M)

Answer:In casting, a pattern is a replica of the object to be cast, used to prepare the cavity

into which molten material will be poured during the casting process.

Different types of patterns: The common types of patterns are:

1) Single piece pattern

2) Split piece pattern

3) Loose piece pattern

4) Gated pattern

5) Match pattern

6) Sweep pattern

7) Cope and drag pattern

8) Skeleton pattern

9) Shell pattern

10) Follow board pattern

Figure (s):Single piece, Split, Match-plate, Cope and Drag Pattern

Single piece pattern: This is the simplest type of pattern, exactly like the desired casting. For making a mould, the pattern is accommodated either in cope or drag. Used for producing a few large castings, for example, stuffing box of steam engine.

Split pattern: These patterns are split along the parting plane (which may be flat or irregular surface) to facilitate the extraction of the patternout of the mould before the pouring operation. For a more complex casting, the pattern may be split in more than two parts.

Loose piece pattern: When a one piece solid pattern has projections or back drafts which lie above or below the parting plane, it is impossible to with drawit from the mould. With such patterns, the projections are made with the help of loose pieces. One drawback of loose feces is that their shifting is possible during ramming.

Figure: Loose piece pattern Gated pattern:A gated pattern is simply one or more loose patterns having attached gates and runners. Because of their higher cost, these patterns are used for producing small castings in mass production systems and on molding machines.

Figure: Gated pattern

Match plate pattern: A match plate pattern is a split pattern having the cope and drags portions mounted on opposite sides of a plate (usually metallic), called the "match plate" that conforms to the contour of the parting surface. The gates and runners are also mounted on the match plate, so that very little hand work is

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required. This results in higher productivity. This type of pattern is used for a large number of castings. Piston rings of I.C. engines are produced by this process.

Sweep pattern: A sweep is a section or board (wooden) of proper contour that is rotated about one edge to shape mould cavities having shapes of rotational symmetry. This type of pattern is used when a casting of large size is to be produced in a short time. Large kettles of C.I. are made by sweep patterns.

Figure: Sweep pattern

Cope and drag pattern: A cope and drag pattern is a split pattern having thecope and drag portions each mounted on separate match plates. These patterns are used when in the production of large castings; the complete mouldsare too heavy and unwieldy to be handled by a single worker.

Skeleton pattern: For large castings having simple geometrical shapes, skeleton patterns are used. Just like sweep patterns, these are simple wooden frames that outline the shape of the part to be cast and are also used as guides by the molder in the hand shaping of the mould. This type of pattern is also used in pit or floor molding process.

Figure: Skeleton pattern

Follow board pattern: A follow board is not a pattern but is a device (wooden board) used for various purposes.

Figure: Follow board pattern

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(OR)

3. (a) Explain in brief about various moulding techniques. (6M)

Answer: Molding processes can be classified in a number of ways. Broadly they are classified either on the basis of the method used or on the basis of the mold material used. (i) Classification based on the mold material used: (a) Sand molding:

1. Green sand mold 2. Dry sand mold, Skin dried mold. 3. Cement bonded sand mold 4. Carbon-dioxide mold. 5. Shell mold.

(b) Plaster molding, (c) Metallic molding. (ii) Classification based on the method used (a) Bench molding. (b) Floor molding, (c) Pit molding. (d) Machine molding. a) Bench Molding This type of molding is preferred for small jobs. The whole molding operation is carried out on a bench of convenient height. In this process, a minimum of two flasks, namely cope and drag molding flasks are necessary. But in certain cases, the number of flasks may increase depending upon the number of parting surfaces required. b) Floor Molding This type of molding is preferred for medium and large size jobs. In this method, only drag portion of molding flask is used to make the mold and the floor itself is utilized as drag and it is usually performed with dry sand. c) Pit Molding Usually large castings are made in pits instead of drag flasks because of their huge size. In pit molding, the sand under the pattern is rammed by bedding-in process. The walls and the bottom of the pit are usually reinforced with concrete and a layer of coke is laid on the bottom of the pit to enable easy escape of gas. The coke bed is connected to atmosphere through vent pipes which provide an outlet to the gases. One box is generally required to complete the mold, runner, sprue, pouring basin and gates are cut in it. d) Machine Molding For mass production of the casting, the general hand molding technique proves uneconomical and inefficient. The main advantage of machine molding, besides the saving of labor and working time, is the accuracy and uniformity of the castings which can otherwise be only obtained with much time and labor. Or even the cost of machining on the casting can be reduced drastically because it is possible to maintain the tolerances within narrow limits on casting using machine molding method. Molding machines thus prepare the molds at a faster rate and also eliminate the need of employing skilled molders. The main operations performed by molding machines are ramming of the molding sand, roll over the mold, form gate, rapping the pattern and its withdrawal. Most of the molds making operations are performed using molding machines.

(b) Explain the procedure of core making? (6M) Answer: Cores are compact mass of core sand (special kind of molding sand) prepared separately that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy space for solidification in that portion and hence help to produce hollowness in the casting. The environment in which the core is placed is much different from that of the mold. In fact the core has to withstand the severe action of hot metal which completely surrounds it. They may be of the type of green sand core and dry sand core. Core Making: Core making basically is carried out in four stages namely core sand preparation, core making, core baking and core finishing. Each stage is explained as under.

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1. Core Sand Preparation Preparation of satisfactory and homogenous mixture of core sand is not possible by manual means. Therefore for getting better and uniform core sand properties using proper sand constituents and additives, the core sands are generally mixed with the help of any of the following mechanical means namely roller mills and core sand mixer using vertical revolving arm type and horizontal paddle type mechanisms. In the case of roller mills, the rolling action of the mulling machine along with the turning over action caused by the ploughs gives a uniform and homogeneous mixing. Roller mills are suitable for core sands containing cereal binders, whereas the core sand mixer is suitable for all types of core binders. These machines perform the mixing of core sand constituents most thoroughly. 2. Core Moulding: Cores can be prepared by ramming core sands in the core boxes by machines based on the principles of squeezing, jolting and slinging. Out of these three machines, jolting and slinging are more common for core making. 3. Core baking Once the cores are prepared, they will be baked in a baking ovens or furnaces. The main purpose of baking is to drive away the moisture and hard en the binder, thereby giving strength to the core. The core drying equipments are usually of two kinds namely core ovens and dielectric bakers. The core ovens are may be further of two type’s namely continuous type oven and batch type oven. 4. Core Finishing: The cores are finally finished after baking and before they are finally set in the mould. The fins, bumps or other sand projections are removed from the surface of the cores by rubbing or filing. The dimensional inspection of the cores is very necessary to achieve sound casting. Cores are also coated with refractory or protective materials using brushing dipping and spraying means to improve their refractoriness and surface finish. The coating on core prevents the molten metal from entering in to the core.

UNIT-II

4. (a) Draw labelled diagram of a mould box showing pattern, gates, runner and riser. What do

you understand by directional solidification of casting? (6M)

Answer: The main elements needed for the gating system are as follows: Pouring basin or bush. Sprue or downspure. Sprue Well Runner Ingate Ladle Slag trap or filter.

The characteristics of each element are mentioned below:

Pouring basin: This is otherwise called as bush or cup. It is circular or rectangular in shape. It collects the molten metal, which is poured, from the ladle.

Sprue: It is circular in cross section. It leads the molten metal from the pouring basin to the sprue well.

Sprue Well: It changes the direction of flow of the molten metal to right angle and passes it to the runner.

Runner: The runner takes the molten metal from sprue to the casting. Ingate: This is the final stage where the molten metal moves from the runner to the mold

cavity. Slag trap: It filters the slag when the molten metal moves from the runner and ingate. It is

also placed in the runner.

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Directional solidification (DS) and progressive solidification are types of solidification within

castings. Directional solidification is solidification that occurs from farthest end of the casting and

works its way towards the sprue. Progressive solidification, also known as parallel solidification, is

solidification that starts at the walls of the casting and

progresses perpendicularly from that surface.

(b) What do you understand by die casting? Write advantages of die casting. (6M) Answer: Die casting is a type of die casting that uses alloys with low melting temperatures (i.e. Zinc, some Magnesium alloys). Using alloys with high melting temperatures would result in damage to the gooseneck, nozzle and other components. In a hot chamber die casting machine, the fixed die half is called a cover die, which is mounted to a stationary platen (large plate to which each die half is mounted) and aligns with the nozzle of the gooseneck. The movable die half is the ejector die and is mounted to a movable platen, which slides along tie bars.

The metal is contained in an open holding pot, which is placed in the furnace and melted to the needed temperature. When the plunger is in the “up” position, the molten metal flows into the shot chamber. As the plunger moves down, it forces the molten metal through a gooseneck and into the die at injection pressures ranging from 1,000 – 5,000 psi.

The machine pushes the moving platen towards the cover die and holds it closed with great pressure until the molten metal is injected. The plunger remains in the “down” position to hold the pressure while the casting “cools off.” After solidification, the plunger is retracted and the cast part is either ejected, manually removed from the machine or pushed off the cover die. This ejection system, which includes an ejector die and ejector pins, allows the casting to be pushed out while releasing the die halves.

Advantages of the die casting process: 1. High production rate. 2. High accuracy in part dimensions. 3. Smooth surface finish for minimum mechanical finishing. 4. Ability to make many intricate parts such as hole opening slot trademark number etc. 5. Much thinner wall sections can be produced which can’t be produced by other casting methods.

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(OR)

5. (a) What are the requirements of a good gating system used in casting process? (6M)

Answer:Thefollowing points are the requirements of a good gating system.

The mould should be completely filled in the smallest time possible

The metal should flow smoothly into the mould without any turbulence.

Unwanted material such as slag, dross and other material should not enter into the mould

cavity.

The metal entry into the mould should be properly controlled in such a way that aspiration

of atmospheric air is prevented.

A proper thermal gradient is maintained so that the casting is cooled without any shrinkage

cavities or Distortions.

Metal flow should be maintained in such a way that no gating or mould erosion takes place.

Gating system must be economical

The gating system should ensure that enough molten metal reaches the cavity

Ultimately, the casting yield must be maximized.

(b) Explain the use of chills with an example. (6M)

Answer: A chill is an object used to promote solidification in a specific portion of a metal casting mold. Normally the metal in the mold cools at a certain rate relative to thickness of the casting. When the geometry of the molding cavity prevents directional solidification from occurring naturally, a chill can be strategically placed to help promote it.

There are two types of chills: internal and external chills.

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UNIT-III

6. (a) Explain the TIG and MIG systems of arc-welding. Give the applications of each. (6M)

Answer: Though similar in the name, TIG and MIG welding have quite a few differences. Deciding which one is suitable for your company depends on the precision of weld required, time allocated for setup, utilization and initial cost. There are several benefits and fallbacks to using TIG and MIG welding, depending on your facility's needs.

MIG Welding, or Metal Inert Gas welding, combines two pieces of metal together with a consumable wire connected to an electrode current. A wire passes through the welding gun at the same time as the inert gas. The inert gas protects the electrode from contaminants.

TIG welding, also known as Tungsten Inert Gas welding, uses nonconsumable tungsten, along with

an inert gas, to weld two work pieces together. The tungsten electrode provides the electricity, but

not the filler, for the welding process. While it can use filler, it sometimes creates a weld where one

part melts into another

MIG WELDING TIG WELDING

1. This welding is known as metal inert gas welding.

1. This is known as tungsten inert gas welding.

2. Metal rod is used as electrode and work piece used as another electrode.

2. Tungsten rod is used as electrode.

3. It is gas shielded metal arc welding. 3. It is gas shielded tungsten arc welding.

4. Continuous feed electrode wire is used which are fast feeding.

4. Welding rods are used which are slow feeding.

5. The welding area is flooded with a gas which will not combine with the metal.

5. Gas is used to protect the welded area form atmosphere.

6. MIG can weld materials such as mild steel, stainless steel and aluminum. A range of material thicknesses can be welded from thin gauge sheet metal right up to heavier structural plates.

6. TIG weld things like kitchen sinks and tool boxes. Pipe welding and other heavier tasks can also be performed, you just need to have a unit that is capable of putting out the amount of power that you need.

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7. MIG requires consumable metallic electrode. 7. It used non consumable tungsten electrode

8. Electrode is feeded continuously from a wire reel.

8. It does not require electrode feed.

9. DC with reverse polarity is used. 9. It can use both A.C and D.C.

10. Filler metal is compulsory used. 10. Filler metal may or may not be used.

11. It can weld up to 40 mm thick metal sheet. 11. Metal thickness is limited about 5 mm.

12. MIG is comparatively faster than TIG. 12. TIG is a slow welding process.

(b) What are the defects that are generally found in welding? Describe their cause and

remedies. (6M)

Answer:Welding defects are very common problem but need to solve it because it leads to failure to

the material. So, understanding common defects, their causes and remedies is very important.

S. No Defect Causes Remedies

1 Undercut Improper welding technique or Excessive current

Use proper technique and current

2 Incomplete Fusion

Improper manipulation of welding Electrode Weld joint design. Surface contamination which leads slag formation prevents fusion

Minimum heat input to be maintained

Avoid molten pool flooding the arc

Correct Electrode angle

3 Porosity

Improper coating on the electrode. Improper Preheating Too low and too high arc currents

Use low hydrogen welding process Use preheat Clean joint surfaces and

4 Slag Inclusions

Improper cleaning Presence of grease & dirt Incomplete slag removal from previous bead

Proper cleaning Avoid grease & dirt Complete remove slag from previous bead

5 Hot Cracking

high welding current poor joint design that does not diffuse heat Base metal contamination

Medium welding current Proper weld joint design Avoid contamination of base metal

6 Cold Cracking

high thermal severity Presence of impurities High welding speeds and low current density

Preheat as per Welding Procedure Specification Remove impurities As per requirement Use of welding speeds and current density

7 Lamellar Tearing

Poor ductility of weld metal High Sulphur content of the base metal

Use the base metal which has higher ductility Low sulphur& Low inclusions in base metal

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(OR)

7. (a) Distinguish between arc and gas-welding processes from the point of view of heat

concentration, temperature and ease of operation. (6M)

Answer:

S. No Arc Welding Gas Welding

1. In the arc welding, electricity is used to generate heat.

In gas welding, fuel gases like acetylene, hydrogen are used to generate heat.

2. This welding generates higher temperature than gas welding. The temperature is about 6000C.

This welding generates lower temperature than arc welding. The temperature is about 3600C.

3. This welding generates stronger joint compare to gas welding.

It gives weaker joint.

4. It gives poor surface finish. This welding gives good surface finish.

5. In arc welding consumable electrode is used.

In gas welding non consumable electrode is used.

6. The electrode is combined with the filler metal.

A filler rod is used separately if required.

7. It can be used in welding alone. It can be used in welding, brazing and soldering.

8. There is risk of explosion due to high voltage.

There is risk of explosion due to high pressure.

9. It is mostly used to joint similar material.

It is mostly use to join both similar and different metals.

10. The heat is concentrate in arc welding. The heat is distributing according to the flame. There is higher loss of energy.

11. It is more efficient. It is less efficient.

12. Speed of welding is high. Speed of welding is low.

13. The initial cost of arc welding is high. The setup cost of gas welding is low.

(b) Explain briefly the procedure of the manual metal-arc welding process. (6M)

Answer: Manual metal arc welding was first invented in Russia in 1888. It involved a bare metal rod with no flux coating to give a protective gas shield. The development of coated electrodes did not occur until the early 1900s when the Kjellberg process was invented in Sweden and the Quasi-arc method was introduced in the UK. It is worth noting that coated electrodes were slow to be adopted because of their high cost. However, it was inevitable that as the demand for sound welds grew, manual metal arc became synonymous with coated electrodes. When an arc is struck between the metal rod (electrode) and the workpiece, both the rod and workpiece surface melt to form a weld pool. Simultaneous melting of the flux coating on the rod will form gas and slag which protects the weld pool from the surrounding atmosphere. The slag will solidify and cool and must be chipped off the weld bead once the weld run is complete (or before the next weld pass is deposited).

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The process allows only short lengths of weld to be produced before a new electrode needs to be inserted in the holder. Weld penetration is low and the quality of the weld deposit is highly dependent on the skill of the welder.

UNIT-IV

8. (a) Explain with neat sketch, basic working principle of rolling. Describe its applications in

an industry (6M)

Answer: Rolling is a compressive deformation process, which is used

for producing semi-finished products such as bars, sheets, plates and

finished products such as angles, channels, sections.

In metalworking, rolling is a metal forming process in

which metal stock is passed through one or more pairs of rolls to

reduce the thickness and to make the thickness uniform. The concept

is similar to the rolling of dough. Rolling is classified according to the

temperature of the metal rolled. If the temperature of the metal is

above its recrystallization temperature, then the process is known

as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process

is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other

manufacturing process, and cold rolling processes the most tonnage out of all cold

working processes. Roll stands holding pairs of rolls are grouped together into rolling mills that can

quickly process metal, typically steel, into products such as structural steel (I-beams, angle stock,

channel stock, and so on), bar stock, and rails. Most steel mills have rolling mill divisions that convert

the semi-finished casting products into finished products.

There are many types of rolling processes, including ring rolling, roll bending, roll forming, profile rolling, and controlled rolling.

(b) Describe Blanking, Punching and Coining with neat Sketches. (6M)

Answer: Blanking and piercing are shearing processes in which a punch and die are used to modify

webs. The tooling and processes are the same between the two, only the terminology is different: in

blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap.

The process for parts manufactured simultaneously with both techniques is often termed "pierce

and blank." An alternative name of piercing is punching.

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Coining: It is a metal squeezing operation where the male and female dies are different (not matching). The flow occurs only and the top and bottom layers of the metal.

The design on the top and bottom are not the same.

(OR)

9. (a) With the help of neat sketch, describe about (i) Extrusion (ii) Brazing (6M)

Answer: (I) Extrusion: Extrusion is a compressive deformation process in which a block of metal is

squeezed through an orifice or die opening in order to obtain a reduction in diameter and increase in

length of the metal block. The resultant product will have the desired cross-section. Extrusion

involves forming of axisymmetric parts. Dies of circular on non-circular cross-section are used for

extrusion. Generally, extrusion involves greater forming forces.

Extrusion is classified as follows: 1. Based on Direction: Direct/indirect or Forward/ backward 2. Based on operating temperature: Hot and Cold

(a) Hot Extrusion: Hot extrusion can be employed for higher extrusion ratios. Inhomogeneous deformation can occur due to die wall chilling of the billet. Metal may get oxidized. The oxide layer can increase friction as well as the material flow. Glass is used as lubricant for hot extrusion. Molybdenum disulfide or graphite are the solid lubricants used in hot extrusion. Canned extrusion using thin walled cans made of copper or tin is usually used for extruding highly reactive metals and metal powders.

(ii) Brazing:It is the process of uniting two or more metals of similar or dissimilar type with the help of an alloy in the form of spelter and flux, like borax, ash etc. these are used in tanks, radiators, carbide tips on tool holder etc. Types of brazing: It is classified on the basis of actual heating as:-

Torch brazing

Electric brazing

Immersion brazing.

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Process of brazing:

The step by step procedure for brazing is as follows:

The metal parts which are to be brazed must be thoroughly cleaned.

The flux must be applied to the surface.

The parts are to be clamped in the required position.

The flux ha to be applied on the surfaces.

The job has to be heated using the blow torch or the furnace etc.

The molten spelter has to be allowed to flow by capillary action into the joint.

The job has to be allowed to cool slowly.

(b) Distinguish between spinning and cup drawing with reference to the processes and

components produced (6M)

Answer: Metal spinning, also known as spin forming or spinning or metal turning most commonly, is a metalworking process by which a disc or tube of metal is rotated at high speed and formed into an axially symmetric part.

Metal spinning does not involve removal of material, as in conventional wood or metal turning, but forming (moulding) of sheet material over an existing shape.

The spinning process is fairly simple. A formed block is mounted in the drive section of a lathe. A pre-sized metal disk is then clamped against the block by a pressure pad, which is attached to the tailstock. The block and workpiece are then rotated together at high speeds. A localized force is then applied to the workpiece to cause it to flow over the block. The force is usually applied via various levered tools. Simple workpieces are just removed from the block, but more complex shapes may require a multi-piece block. Extremely complex shapes can be spun over ice forms, which then melt away after spinning. Because the final diameter of the workpiece is always less than the starting diameter, the workpiece must thicken, elongate radially, or buckle circumferentially.

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Cup Drawing: Cup drawing or deep drawing is one of the widely used sheet metal forming operations. Cup shaped objects, utensils, pressure vessels, gas cylinders, cans, shells; kitchen sinks etc are some of the products of deep drawing. In this process, a sheet metal called blank is placed on a die cavity, held in position using a holding plate or holding ring and pressed against the die cavity using a solid punch. The sheet metal attains the shape of the die cavity with flat bottom. Both die and punch should be provided with corner radius in order to avoid shearing of the sheet.

Prepared by:

Rajasekharababu. K,

Asst. Professor,

Dept. of Mechanical Engineering

Cell: +91 8106199932

Bapatla,

18. April. 2018