ME 6302 Mechanical Engineering Third Semester UNIT-3 · 1. (i) Explain hot working and cold working with their advantages and limitations. (8) [A/M 15] Hot working refers to processes

ME 6302 – MANUFACTURING TECHNOLOGY - 1 Mechanical Engineering

Third Semester UNIT-3 Part A

1. What are the various forming processes? [A/M 15] Forming processes are particular manufacturing processes which make use of suitable stresses (like compression, tension, shear or combined stresses) which cause plastic deformation of the materials to produce required shapes. During forming processes no material is removed, i.e. they are deformed and displaced. 2. Name various defects in parts produced by drawing. [A/M 15] benefits aside, one main disadvantage to the deep drawing process is that it isn’t valued as effective in small quantities. The cost of press setup is remarkably high and requires significant experience and expertise, rendering deep drawing more expensive for short runs. Generally, for deep drawn production to be cost effective, the minimum order quantity should be in the hundreds. 3. Why is the surface finish of a rolled product better in cold rolling than in hot rolling? [M/J 16] Cold working processes allow desirable metal qualities that cannot be obtained by hot working, such as

eliminating errors attending shrinkage. As such, a much more compact and higher dimensional accuracy metal

can be obtained with cold working. Furthermore, the final products have a smoother surface (better surface

finish) than those of hot working and the strength, hardness as well as the elastic limit are increased. However,

the ductility of the metal decreases due to strain hardening thus making the metal more brittle. As such, the

metal must be heated from time to time (annealed) during the rolling operation to remove the undesirable effects

of cold working and to increase the workability of the metal.

4. What is strain rate sensitivity? [M/J 16]

Strain rate is the change in strain (deformation) of a material with respect to time.

The strain rate at some point within the material measures the rate at which the distances of adjacent parcels of the material change with time in the neighborhood of that point. It comprises both the rate at which the material is expanding or shrinking (expansion rate), and also the rate at which it is being deformed by progressive shearing without changing its volume (shear rate). It is zero if these distances do not change, as happens when all particles in some region are moving with the same velocity (same speed and direction) and/or rotating with the same angular velocity, as if that part of the medium were a rigid body.

5. Why isdrop forgingca l led so? [N/D 14] Drop forging is a forging process where a hammer is raised and then "dropped" onto the workpiece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and closed-die drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the workpiece, while the latter does.

6. What does angle of biteinrolling m e a n ? [N/D 14]

An obtainable angle which is its maximum and is between the first contact of metal and the radius of

the roll, it joins the opposing rolls and the centres of them, when metal is rolled. ANGLE OF BITE: "Angle of bite is seen in rolled metal."

7. Whatdoyoumeant byLateral E x t r u s i o n ? [N/D 15] Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms parts with an excellent surface finish.

8. Whatdoyoumeant byangleofbite? [N/D 15] The bite angle is a geometric parameter used to classify chelating ligands in coordination chemistry, including organometallic complexes. Although the parameter can be applied generally to any chelating ligand, it is commonly applied to describe diphosphine ligands, which can adopt a wide range of chelate ring sizes 9. Why is it necessary to condition the metal before hot rolling? [N/D 16]

The removal of surface defects (seams, laps, pits, etc.) from steel; usually done when the steel is in semifinished condition (bloom, billet, slab). It may be accomplished after an inspection by chipping, scarfing, grinding, or machining.

10. Give a few examples of hot forged products. [N/D 16]

Forging of steel

Forging of aluminium These ,aluminium forged parts are mainly used in aerospace, automotive industry and many other fields of engineering especially in those fields, where highest safety standards against failure by abuse, by shock or vibratory

Part B

1. (i) Explain hot working and cold working with their advantages and limitations. (8) [A/M 15] Hot working refers to processes where metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high.[1] This contrasts with cold working. Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot metal. Temperature

The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 60% its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece.[1] The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C).[2]

Lower limit hot working temperature for various metals[1]

Metal Temperature

Tin Room temperature

Steel 2,000 °F (1,090 °C)

Tungsten 4,000 °F (2,200 °C)

Advantages & disadvantages

The advantages are:

Decrease in yield strength, therefore it is easier to work and uses less energy or force Increase in ductility Elevated temperatures increase diffusion which can remove or reduce chemical inhomogeneities Cold Working a change in the structures—and correspondingly the properties—of metals and alloys caused by plastic deformation of aworkpiece at a temperature below its recrystallization temperature. The industrial process of producing a strengthened stateof materials by cold plastic deformation of the surface is also called cold working. The phenomenon of cold working may be explained by the accumulation within the metal of part of the energy of deformationthat is expended on distortion of the crystal lattice, formation of predominantly oriented crystals (structures), changes in thedislocational structure, and an increase of the specific volume of the metal in the layer. Cold working may also be the resultof action of external deformation forces (deformation cold working) or, less frequently, of phase transformation (phase coldworking). Cold working is accompanied by an increase in strength and hardness and a decrease in plasticity. Cold working is used for surface hardening of parts. In addition, it generates a favorable system of residual strains in thesurface layer of the metal; the effect of such strains is mainly responsible for the large strengthening effect of surface plasticdeformation, which is reflected in increased fatigue strength and sometimes in increased wear resistance. Cold working is performed by special methods, using special equipment. For example, cold rolling of cylindrical surfaces isperformed by rollers, gear teeth are hardened by rollers or toothed rollers, shaped articles are hardened by shot peening,and other articles are hardened by impact tools. (ii) Explain various forging operations. (8) [A/M 15] Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it is performed: cold forging (a type of cold working), warm forging, or hot forging (a type of hot working). For the latter two, the metal is heated, usually in a forge. Forged parts can range in weight from less than a kilogram to hundreds of metric tons.[1][2]Forging has been done by smiths for millennia; the traditional products were kitchenware, hardware, hand tools, edged weapons, cymbals, and jewellery. Since the Industrial Revolution, forged parts are widely used in mechanisms and machineswherever a component requires high strength; such forgings usually require further processing (such as machining) to achieve a finished part. Today, forging is a major worldwide industry Advantages and disadvantages

Forging can produce a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.[4] Additionally, forgings can target a lower total cost when compared to a casting or fabrication. When you consider all the costs that are involved in a product’s lifecycle from procurement to lead time to rework, then factor in the costs of scrap, downtime and further quality issues, the long-term benefits of forgings can outweigh the short-term cost-savings that castings or fabrications might offer. [5] Some metals may be forged cold, but iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forging, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are

generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high-temperature furnace (sometimes referred to as the forge) is required to heat ingots or billets. Owing to the size of the massive forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations use metal-forming dies, which must be precisely machined and carefully heat-treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved.

A cross-section of a forged connecting rod that has been etched to show the grain flow There are many different kinds of forging processes available; however, they can be grouped into three main classes:[1] Drawn out: length increases, cross-section decreases Upset: length decreases, cross-section increases Squeezed in closed compression dies: produces multidirectional flow Common forging processes include: roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging and upsetting.[1] Temperature Main articles: Hot working and Cold working All of the following forging processes can be performed at various temperatures; however, they are generally classified by whether the metal temperature is above or below the recrystallization temperature. If the temperature is above the material's recrystallization temperature it is deemed hot forging; if the temperature is below the material's recrystallization temperature but above 30% of the recrystallization temperature (on an absolute scale) it is deemed warm forging; if below 30% of the recrystallization temperature (usually room temperature) then it is deemed cold forging. The main advantage of hot forging is that it can be done more quickly and precisely, and as the metal is deformed work hardening effects are negated by the recrystallization process. Cold forging typically results in work hardening of the piece.[6][7] Drop forging

Boat nail production in Hainan, China Drop forging is a forging process where a hammer is raised and then "dropped" onto the workpiece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and closed-die drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the workpiece, while the latter does. Open-die drop forging

Open-die drop forging (with two dies) of an ingot to be further processed into a wheel Open-die forging is also known as smith forging.[8] In open-die forging, a hammer strikes and deforms the workpiece, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the surfaces that are in contact with the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. The operator therefore needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For example, a die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool.[9] Open-die forgings can be worked into shapes which include discs, hubs, blocks, shafts (including step shafts or with flanges), sleeves, cylinders, flats, hexes, rounds, plate, and some custom shapes.[10] Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. In some cases, open-die forging may be employed to rough-shape ingots to prepare them for subsequent operations. Open-die forging may also orient the grain to increase strength in the required direction. 2. (i)Describe the ring rolling and thread rolling process. (8) [A/M 15]

"Rolling mill" redirects here. For mills that use rollers to crush grain or stone, see roller mill.

Rolling schematic view

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 workingprocesses.[1][2] 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.

Thread Rolling

Thread rolling is the preferred method for producing strong, smooth, precise, and uniform external thread forms. Thread rolling is different from other types of threading processes like cutting, grinding, and chasing.

Thread rolling is a cold forging process that can be performed on any ductile metal. The forming process can be used to produce other special forms, such as knurls. For the best quality threads, the process is performed on precision centerless ground blanks. The blank diameter of a rolled thread is at the pitch diameter, a theoretical point between the major diameter and minor diameter.

Thread Rolling Inc. produces rolled threads on a wide variety of parts. Often, rolled threads are required by design because of their superior tensile, shear, and fatigue strength. Other processes remove material to produce the thread form, but thread rolling displaces the material with hardened steel dies. These dies typically have a hardness between a range of Rc58-Rc63 and

there is a specific set of dies for each thread size and each thread form. The dies have the reverse for of the finished thread.

The result of moving the material grains (molecules) into the shape of the thread rather than weakening it by removing material, is that the grains become denser at the critical parts of the thread, especially in the root and on the flank below the pitch diameter. This effect improves the quality of the thread form. Additionally, the burnishing action of the steel dies produces an excellent (better than Ra32) micro-finish. The superior finish improves assembly between external and internal threads and reduces wear between mating components, thereby extending their life. A smooth finish is another advantage that roll threaded components have over other threaded components.

Roll Threading

Process: In-feed Roll Threading Thread types: 60º thread form/machine screw type threads/pipe threads Forms: UNR, UNF, UNC, UNJ, UNJF, UNJC (classes 1A, 2A, 3A, 5A) Metric forms: ISO and DIN (classes 6g and 4g6g) Minimum size: .078 inch (2mm) Maximum diameter: 2.500 inch (63mm) Pitches: Coarse, Fine, Extra Fine Material Hardness: Cold rolling to Rc45 depending on material type and size Notes: Flight Safety Threads, System 22/23, QSLM, right and left hand Volume: 1 piece to 100,000 pieces (ii) Explain the forward and backward extrusion process. (8) [A/M 15] Direct extrusion

Plot of forces required by various extrusion processes.

Direct extrusion, also known as forward extrusion, is the most common extrusion process. It works by placing the billet in a heavy walled container. The billet is pushed through the die by a ram or screw. There is a reusable dummy block between the ram and the billet to keep them separated. The major disadvantage of this process is that the force required to extrude the billet is greater than that needed in the indirect extrusion process because of the frictional forces introduced by the need for the billet to travel the entire length of the container. Because of this the greatest force required is at the beginning of process and slowly decreases as the billet is used up. At the end of the billet the force greatly increases because the billet is thin and the material must flow radially to exit the die. The end of the billet (called the butt end) is not used for this reason.[9]

Indirect extrusion

In indirect extrusion, also known as backwards extrusion, the billet and container move together while the die is stationary. The die is held in place by a "stem" which has to be longer than the container length. The maximum length of the extrusion is ultimately dictated by the column strength of the stem. Because the billet moves with the container the frictional forces are eliminated. This leads to the following advantages:[10]

A 25 to 30% reduction of friction, which allows for extruding larger billets, increasing speed, and an increased ability to extrude smaller cross-sections

There is less of a tendency for extrusions to crack because there is no heat formed from friction

The container liner will last longer due to less wear

The billet is used more uniformly so extrusion defects and coarse grained peripherals zones are less likely.

The disadvantages are:

Impurities and defects on the surface of the billet affect the surface of the extrusion. These defects ruin the piece if it needs to be anodized or the aesthetics are important. In order to get around this the billets may be wire brushed, machined or chemically cleaned before being used.

This process isn't as versatile as direct extrusions because the cross-sectional area is limited by the maximum size of the stem.

Hydrostatic extrusion

In the hydrostatic extrusion process the billet is completely surrounded by a pressurized liquid, except where the billet contacts the die. This process can be done hot, warm, or cold, however the temperature is limited by the stability of the fluid used. The process must be carried out in a sealed cylinder to contain the hydrostatic medium. The fluid can be pressurized two ways:

1. Constant-rate extrusion: A ram or plunger is used to pressurize the fluid inside the container.

2. Constant-pressure extrusion: A pump is used, possibly with a pressure intensifier, to pressurize the fluid, which is then pumped to the container.

The advantages of this process include:

No friction between the container and the billet reduces force requirements. This ultimately allows for faster speeds, higher reduction ratios, and lower billet temperatures.

Usually the ductility of the material increases when high pressures are applied.

An even flow of material.

Large billets and large cross-sections can be extruded.

No billet residue is left on the container walls.

The disadvantages are:

The billets must be prepared by tapering one end to match the die entry angle. This is needed to form a seal at the beginning of the cycle. Usually the entire billet needs to be machined to remove any surface defects.

Containing the fluid under high pressures can be difficult.

A billet remnant or a plug of a tougher material must be left at the end of the extrusion to prevent a sudden release of the extrusion fluid.

Drives

Most modern direct or indirect extrusion presses are hydraulically driven, but there are some small mechanical presses still used. Of the hydraulic presses there are two types: direct-drive oil presses and accumulator water drives.

Direct-drive oil presses are the most common because they are reliable and robust. They can deliver over 35 MPa (5000 psi). They supply a constant pressure throughout the whole billet. The disadvantage is that they are slow, between 50 and 200 mm/s (2–8 ips).

Accumulator water drives are more expensive and larger than direct-drive oil presses, and they lose about 10% of their pressure over the stroke, but they are much faster, up to 380 mm/s (15 ips). Because of this they are used when extruding steel. They are also used on materials that must be heated to very hot temperatures for safety reasons.[11]

Hydrostatic extrusion presses usually use castor oil at pressure up to 1400 MPa (200 ksi). Castor oil is used because it has good lubricity and high pressure properties.

3. With neat diagram explain the process of forwardextrusion. Explain also how hollow sections can be produced in this process. (16) [M/J 16]

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms parts with an excellent surface finish.[1] Drawing is a similar process, which uses the tensile strength of the material to pull it through the die. This limits the amount of change which can be performed in one step, so it is limited to simpler shapes, and multiple stages are usually needed. Drawing is the main way to produce wire. Metal bars and tubes are also often drawn. Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold. Commonly extruded materials include metals, polymers, ceramics, concrete, modelling clay, and foodstuffs. The products of extrusion are generally called "extrudates". Hollow cavities within extruded material cannot be produced using a simple flat extrusion die, because there would be no way to support the centre barrier of the die. Instead, the die assumes the shape of a block with depth, beginning first with a shape profile that supports the center section. The die shape then internally changes along its length into the final shape, with the suspended center pieces supported from the back of the die. The material flows around the supports and fuses together to create the desired closed shape. The extrusion process in metals may also increase the strength of the material. Direct extrusion

Plot of forces required by various extrusion processes. Direct extrusion, also known as forward extrusion, is the most common extrusion process. It works by placing the billet in a heavy walled container. The billet is pushed through the die by a ram or screw. There is a reusable dummy block between the ram and the billet to keep them separated. The major disadvantage of this process is that the force required to extrude the billet is greater than that needed in the indirect extrusion process because of the frictional forces introduced by the need for the billet to travel the entire length of the container. Because of this the greatest force required is at the beginning of process and slowly decreases as the billet is used up. At the end of the billet the force greatly increases because the billet is thin and the material must flow radially to exit the die. The end of the billet (called the butt end) is not used for this reason. 5. (i) With suitablesketches describe indirectand direct extrusion (8)[N/D 14]

Forming internal cavities

Two-piece aluminum extrusion die set (parts shown separated.) The male part (at right) is for forming

the internal cavity in the resulting round tube extrusion.

There are several methods for forming internal cavities in extrusions. One way is to use a hollow billet and then use a fixed or floating mandrel. A fixed mandrel, also known as a German type, means it is integrated into the dummy block and stem. A floating mandrel, also known as a French type, floats in slots in the dummy block and aligns itself in the die when extruding. If a solid billet is used as the feed material then it must first be pierced by the mandrel before extruding through the die. A special press is used in order to control the mandrel independently from the ram.The solid billet could also be used with a spider die, porthole die or bridge die. All of these types of dies incorporate the mandrel in the die and have "legs" that hold the mandrel in place. During extrusion the metal divides, flows around the legs, then merges, leaving weld lines in the final product.

Direct extrusion

Plot of forces required by various extrusion processes.

Direct extrusion, also known as forward extrusion, is the most common extrusion process. It works by placing the billet in a heavy walled container. The billet is pushed through the die by a ram or screw. There is a reusable dummy block between the ram and the billet to keep them separated. The major disadvantage of this process is that the force required to extrude the billet is greater than that needed in the indirect extrusion process because of the frictional forces introduced by the need for the billet to travel the entire length of the container. Because of this the greatest force required is at the beginning of process and slowly decreases as the billet is used up. At the end of the billet the force greatly increases because the billet is thin and the material must flow radially to exit the die. The end of the billet (called the butt end) is not used for this reason.

Indirect extrusion

In indirect extrusion, also known as backwards extrusion, the billet and container move together while the die is stationary. The die is held in place by a "stem" which has to be longer than the container length. The maximum length of the extrusion is ultimately dictated by the column strength of the stem. Because the billet moves with the container the frictional forces are eliminated. This leads to the following advantages:

A 25 to 30% reduction of friction, which allows for extruding larger billets, increasing speed, and an increased ability to extrude smaller cross-sections

There is less of a tendency for extrusions to crack because there is no heat formed from friction

The container liner will last longer due to less wear

The billet is used more uniformly so extrusion defects and coarse grained peripherals zones are less likely.

The disadvantages are:

Impurities and defects on the surface of the billet affect the surface of the extrusion. These defects ruin the piece if it needs to be anodized or the aesthetics are important. In order to get around this the billets may be wire brushed, machined or chemically cleaned before being used.

This process isn't as versatile as direct extrusions because the cross-sectional area is limited by the maximum size of the stem.

(ii) Draw a simplesketch showing rolling process and make ashort noteondeformation o fgrains inrolling. (8) [N/D 14]

"Rolling mill" redirects here. For mills that use rollers to crush grain or stone, see roller mill.

Rolling schematic view

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 workingprocesses.[1][2] 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.

METALWORKING PROCESSES are commonly classified as either hot working or cold working operations. Primary metalworking processes, such as the bulk deformation processes used to conduct the initial breakdown of cast ingots, are always conducted hot. The term bulk deformation implies large amounts of material movement, such as in hot rolling or forging. Secondary processes, which are used to produce the final product shape, are also conducted either hot or cold. Some secondary processes, such as sheet forming, do not involve large amounts of deformation. Hot working processes are conducted at temperatures above the recrystallization temperature, which is approximately 0.5 Tm. Cold working processes are conducted at or near room temperature, while warm working processes are conducted at intermediate temperatures. Hot working produces a recrystallized grain structure, while the grain structure due to cold working is unrecrystallized and retains the effects of the working operation. Bulk deformation changes the shape of a workpiece by plastic deformation through the application of compressive forces, as for the typical bulk deformation processes in Fig. 16.1. In addition to shaping the metal, bulk deformation is used to refine the structure that results from solidification. To refine the Workpiece F F v Roll Roll Rolling F Workpiece Die Die v Forging F v Ram Workpiece Die Extrusion F v Workpiece Die Wire Drawing Fig. 16.1 Bulk deformation processes. Source: Ref 1 Name ///sr-nova/Dclabs_wip/Metallurgy/5224_279-302.pdf/Chap_16/ 3/6/2008 10:15AM Plate # 0 pg 279 Elements of Metallurgy and Engineering Alloys F.C. Campbell, editor, p 279-302 DOI: 10.1361/emea2008p279 Copyright © 2008 ASM International® All rights reserved. www.asminternational.org inhomogeneous structure resulting from solidi- fication, cast ingots and continuously cast slabs and blooms are typically hot worked into intermediate product forms, such as plates, bars, and sheet. Large plastic deformation in combination with heat is very effective in refining the microstructure, breaking up macrosegregations, collapsing and sealing porosity, and refining the grain size. This product may be suitable for its intended application, but in many cases, it provides the starting material for secondary deformation processes such as drawing, hot or cold forging, and sheet metalworking. Because most processes involve sliding contact between the workpiece and a tool or die, friction affects material flow, die pressures, and the force and energy requirements. In many instances, lubricants are used to minimize friction. Lubricants also reduce die wear, help in providing temperature control, and minimize high-temperature oxidation. 16.1 Hot

Working Hot working normally takes place at approximately 70 to 80% of the absolute melting temperature. During hot working, the strainhardened and distorted grain structure produced by deformation is rapidly eliminated by the formation of new strain-free grains as a result of recrystallization. Dynamic recrystallization occurs during deformation, while static recrystallization occurs after deformation is complete but while the workpiece is still hot. For processes such as hot rolling, hot extrusion, and hot forging, the time within the deformation zone is usually short, and grain refinement is usually accomplished by static recrystallization after hot working. A high level of hot deformation followed by holding the workpiece at an elevated temperature causes static recovery and recrystallization, resulting in a fine grain size. This may occur during hot rolling where there is time between roll passes, or after hot forging, where the workpiece slowly cools to room temperature. Very large deformations are possible in hot working, and since recovery processes keep pace with the deformation, hot working occurs at essentially a constant flow stress (the shear stress required to cause plastic deformation of the metal). Since the flow stress decreases with increasing temperature, metals become more malleable, and less energy is needed to produce a given amount of deformation. However, as the temperature increases, the strength also decreases. Therefore, hot working processes usually involve the use of compressive forces to prevent cracking or failure. Because recovery processes take time, flow stress, sf, is a function 6.(i)Explain hot working and cold working with their advantages and limitations.(8)[N/D 14] Hot working refers to processes where metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high.[1] This contrasts with cold working. Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot metal. Temperature

The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 60% its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece. The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C).

Lower limit hot working temperature for various metals[1]

Metal Temperature

Tin Room temperature

Steel 2,000 °F (1,090 °C)

Tungsten 4,000 °F (2,200 °C)

Advantages & disadvantages

The advantages are:[1]

Decrease in yield strength, therefore it is easier to work and uses less energy or force Increase in ductility Elevated temperatures increase diffusion which can remove or reduce chemical inhomogeneities Pores may reduce in size or close completely during deformation In steel, the weak, ductile, face-centered-cubic austenite microstructure is deformed instead of the

strong body-centered-cubic ferrite microstructure found at lower temperatures Usually the initial workpiece that is hot worked was originally cast. The microstructure of cast items does not optimize the engineering properties, from a microstructure standpoint. Hot working improves the engineering properties of the workpiece because it replaces the microstructure with one that has fine spherical shaped grains. These grains increase the strength, ductility, and toughness of the material.[2] The engineering properties can also be improved by reorienting the inclusions (impurities). In the cast state the inclusions are randomly oriented, which, when intersecting the surface, can be a propagation point for cracks. When the material is hot worked the inclusions tend to flow with the contour of the surface, creating stringers. As a whole the strings create a flow structure, where the properties are anisotropic (different based on direction). With the stringers oriented parallel to the surface it strengthens the workpiece, especially with respect to fracturing. The stringers act as "crack-arrestors" because the crack will want to propagate through the stringer and not along it The disadvantages are Undesirable reactions between the metal and the surrounding atmosphere (scaling or rapid

oxidation of the workpiece) Less precise tolerances due to thermal contraction and warping from uneven cooling Grain structure may vary throughout the metal for various reasons Requires a heating unit of some kind such as a gas or diesel furnace or an induction heater, which

can be very expensive Cold working processes allow desirable metal qualities that cannot be obtained by hot working, such as eliminating errors attending shrinkage. As such, a much more compact and higher dimensional accuracy metal can be obtained with cold working. Furthermore, the final products have a smoother surface (better surface finish) than those of hot working and the strength, hardness as well as the elastic limit are increased. However, the ductility of the metal decreases due to strain hardening thus making the metal more brittle. As such, the metal must be heated from time to time (annealed) during the rolling operation to remove the undesirable effects of cold working and to increase the workability of the metal.

(ii)Explainindetail about wired r awing. (8) [N/D 14] Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die(s). There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels, and stringed musical instruments. Although similar in process, drawing is different from extrusion, because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed at room temperature, thus classified as a cold workingprocess, but it may be performed at elevated temperatures for large wires to reduce forces.[1] Process

Wire drawing concept The wire drawing process is quite simple in concept. The wire is prepared by shrinking the beginning of it, by hammering, filing, rolling or swaging, so that it will fit through the die; the wire is then pulled through the die. As the wire is pulled through the die, its volume remains the same, so as the diameter decreases, the length increases. Usually the wire will require more than one draw, through successively smaller dies, to reach the desired size. The American wire gauge scale is based on this. This can be done on a small scale with a draw plate, or on a large commercial scale using automated machinery.[1][2] The process of wire drawing changes material properties due to cold working. The area reduction in small wires is generally 15–25% and in larger wires is 20–45%.[1] The exact die sequence for a particular job is a function of area reduction, input wire size and output wire size. As the area reduction changes, so does the die sequence.[3] Very fine wires are usually drawn in bundles. In a bundle, the wires are separated by a metal with similar properties, but with lower chemical resistance so that it can be removed after drawing If the reduction in area is greater than 50%, the process may require an intermediate step of annealing before it can be redrawn. Commercial wire drawing usually starts with a coil of hot rolled 9 mm (0.35 in) diameter wire. The surface is first treated to remove scales. It is then fed into a wire drawing machine which may have one or more blocks in series. Single block wire drawing machines include means for holding the dies accurately in position and for drawing the wire steadily through the holes. The usual design consists of a cast-iron bench or table having a bracket standing up to hold the die, and a vertical drum which rotates and by coiling the wire around its surface pulls it through the die, the coil of wire being stored upon another drum or "swift" which lies behind the die and reels off the wire as fast as required. The wire drum or "block" is provided with means for rapidly coupling or uncoupling it to its vertical shaft, so that the motion of the wire may be stopped or started instantly. The block is also tapered, so that the coil of wire may be easily slipped off upwards when finished. Before the wire can be attached to the block, a sufficient length of it must be pulled through the die; this is effected by a pair of gripping pincers on the end of a chain which is wound around a revolving drum, so drawing the wire until enough can be coiled two or three times on the block, where the end is secured by a small screw clamp or vice. When the wire is on the block, it is set in motion and the wire is drawn steadily through the die; it is very important that the block rotates evenly and that it runs true and pulls the wire at a constant velocity, otherwise "snatching" occurs which will weaken or even break the wire. The speeds at which wire is drawn vary greatly, according to the material and the amount of reduction. Machines with continuous blocks differ from single block machines by having a series of dies through which the wire is drawn in a continuous fashion. Due to the elongation and slips, the speed of the wire changes after each successive redraw. This increased speed is accommodated by having a different rotation speed for each block. One of these machines may contain 3 to 12 dies. [2] The operation of threading the wire through all the dies and around the blocks is termed "stringing-up". The arrangements for lubrication include a pump which floods the dies, and in many cases also the bottom portions of the blocks run in lubricant.[4] Often intermediate anneals are required to counter the effects of cold working, and to allow more further drawing. A final anneal may also be used on the finished product to maximize ductility and electrical conductivity.

An example of product produced in a continuous wire drawing machine is telephone wire. It is drawn 20 to 30 times from hot rolled rod stock While round cross-sections dominate most drawing processes, non-circular cross-sections are drawn. They are usually drawn when the cross-section is small and quantities are too low to justify rolling. In these processes, a block or Turk's-head machine are used Lubrication Lubrication in the drawing process is essential for maintaining good surface finish and long die life. The following are different methods of lubrication Wet drawing: the dies and wire or rod are completely immersed in lubricants Dry drawing: the wire or rod passes through a container of lubricant which coats the surface of the

wire or rod Metal coating: the wire or rod is coated with a soft metal which acts as a solid lubricant Ultrasonic vibration: the dies and mandrels are vibrated, which helps to reduce forces and allow

larger reductions per pass Roller die Drawing (also referred as Roll drawing): roller dies are used instead of fixed dies to

convert shear friction to rolling friction with dramatic reduction in the drawing forces as reported by Lambiase.[7][8][9] When roller dies are adopted, the drawing stages are composed by 2-4 idle rolls and the wire is pulled within the rolls clearance. This type of solution can be easily adopted also to produce flat or profiled drawn wires.

Various lubricants, such as oil, are employed. Another lubrication method is to immerse the wire in a copper(II) sulfate solution, such that a film of copper is deposited which forms a kind of lubricant. In some classes of wire the copper is left after the final drawing to serve as a preventive of rust or to allow easy soldering.[citation needed]The best example of copper coated wire is in MIG wire used in welding 7. (i) Explain with neat sketch various types of rolling stand arrangement. (8) [N/D 15] Types of Rolling mills

Rolling mills may be classified according to the number and arrangement of the rolls.

(a): Two high rolling mills

(b): Three high rolling mills

(c): Four high rolling mills

(d): Tandem rolling mills

(e): Cluster rolling mills

1: Two high rolling mills

Two high rolling mills may further classified as

· Reversing mill

· Non reversing mill

A two high rolling mill has two rolls only.

Two high reversing mill:

In two high reversing rolling mills the rolls rotate ist in one direction and then in the other, so that rolled

metal may pass back and forth through the rolls several times. This type is used in pluming and

slabing mills and for roughing work in plate , rail , structural and other mills.

These are more expensive compared to the non reversing rolling mills. Because of the reversible drive

needed.

Two high non reversing mill:

In two high non reversing mills as two rolls which revolve continuously in same direction therefore

smaller and less costly motive power can be used. However every time material is to be carried back

over the top of the mill for again passing in through the rolls. Such an arrangement is used in mills

through which the bar passes once and in open train plate mill.

2: Three high rolling mill:

It consists of a roll stand with three parallel rolls one above the other. Adjacent rolls rotates in opposite

direction. So that the material may be passed between the top and the middle roll in one direction and

the bottom and middle rolls in opposite one.

In three high rolling mills the work piece is rolled on both the forward and return passes. First of all the

work piece passes through the bottom and middle rolls and the returning between the middle and the

top rolls.

So that thickness is reduced at each pass. Mechanically operated lifted tables are used which move

vertically or either side of the stand. So that the work piece fed automatically into the roll gap.

Since the rolls run in one direction only a much less powerful motor and transmission system is

required. The rolls of a three high rolling mills may be either plain or grooved to produce plate or

sections respectively.

3: Four high rolling mill:

It has a roll stand with four parallel rolls one above the other. The top and the bottom rolls rotate in

opposite direction as do the two middle rolls. The two middle are smaller in size than the top and

bottom rolls which are called backup rolls for providing the necessary rigidity to the smaller rolls.

A four high rolling mill is used for the hot rolling of armor and other plates as well as cold rolling of

plates, sheets and strips.

4: Tandem rolling mills:

It is a set of two or three stands of roll set in parallel alignment. So that a continuous pass may be

made through each one successively with change the direction of material.

5: Cluster rolling mills:

It is a special type of four high rolling mill in which each of the two working rolls is backup by two or

more of the larger backup rolls for rolling hard in materials. It may be necessary to employ work rolls

of a very small diameter but of considerable length. In such cases adequate of the working rolls can

be obtained by using a cluster mill.

(ii) Explain with a neat sketch the process of wire drawing. (8) [N/D 15] Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die(s). There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels, and stringed musical instruments. Although similar in process, drawing is different from extrusion, because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed at room temperature, thus classified as a cold workingprocess, but it may be performed at elevated temperatures for large wires to reduce forces.[1] Process

Wire drawing concept The wire drawing process is quite simple in concept. The wire is prepared by shrinking the beginning of it, by hammering, filing, rolling or swaging, so that it will fit through the die; the wire is then pulled through the die. As the wire is pulled through the die, its volume remains the same, so as the diameter decreases, the length increases. Usually the wire will require more than one draw, through successively smaller dies, to reach the desired size. The American wire gauge scale is based on this. This can be done on a small scale with a draw plate, or on a large commercial scale using automated machinery.[1][2] The process of wire drawing changes material properties due to cold working. The area reduction in small wires is generally 15–25% and in larger wires is 20–45%.[1] The exact die sequence for a particular job is a function of area reduction, input wire size and output wire size. As the area reduction changes, so does the die sequence.[3]

Very fine wires are usually drawn in bundles. In a bundle, the wires are separated by a metal with similar properties, but with lower chemical resistance so that it can be removed after drawing If the reduction in area is greater than 50%, the process may require an intermediate step of annealing before it can be redrawn. Commercial wire drawing usually starts with a coil of hot rolled 9 mm (0.35 in) diameter wire. The surface is first treated to remove scales. It is then fed into a wire drawing machine which may have one or more blocks in series. Single block wire drawing machines include means for holding the dies accurately in position and for drawing the wire steadily through the holes. The usual design consists of a cast-iron bench or table having a bracket standing up to hold the die, and a vertical drum which rotates and by coiling the wire around its surface pulls it through the die, the coil of wire being stored upon another drum or "swift" which lies behind the die and reels off the wire as fast as required. The wire drum or "block" is provided with means for rapidly coupling or uncoupling it to its vertical shaft, so that the motion of the wire may be stopped or started instantly. The block is also tapered, so that the coil of wire may be easily slipped off upwards when finished. Before the wire can be attached to the block, a sufficient length of it must be pulled through the die; this is effected by a pair of gripping pincers on the end of a chain which is wound around a revolving drum, so drawing the wire until enough can be coiled two or three times on the block, where the end is secured by a small screw clamp or vice. When the wire is on the block, it is set in motion and the wire is drawn steadily through the die; it is very important that the block rotates evenly and that it runs true and pulls the wire at a constant velocity, otherwise "snatching" occurs which will weaken or even break the wire. The speeds at which wire is drawn vary greatly, according to the material and the amount of reduction. Machines with continuous blocks differ from single block machines by having a series of dies through which the wire is drawn in a continuous fashion. Due to the elongation and slips, the speed of the wire changes after each successive redraw. This increased speed is accommodated by having a different rotation speed for each block. One of these machines may contain 3 to 12 dies. [2] The operation of threading the wire through all the dies and around the blocks is termed "stringing-up". The arrangements for lubrication include a pump which floods the dies, and in many cases also the bottom portions of the blocks run in lubricant.[4] Often intermediate anneals are required to counter the effects of cold working, and to allow more further drawing. A final anneal may also be used on the finished product to maximize ductility and electrical conductivity. An example of product produced in a continuous wire drawing machine is telephone wire. It is drawn 20 to 30 times from hot rolled rod stock While round cross-sections dominate most drawing processes, non-circular cross-sections are drawn. They are usually drawn when the cross-section is small and quantities are too low to justify rolling. In these processes, a block or Turk's-head machine are used Lubrication Lubrication in the drawing process is essential for maintaining good surface finish and long die life. The following are different methods of lubrication Wet drawing: the dies and wire or rod are completely immersed in lubricants Dry drawing: the wire or rod passes through a container of lubricant which coats the surface of the

wire or rod Metal coating: the wire or rod is coated with a soft metal which acts as a solid lubricant Ultrasonic vibration: the dies and mandrels are vibrated, which helps to reduce forces and allow

larger reductions per pass Roller die Drawing (also referred as Roll drawing): roller dies are used instead of fixed dies to

convert shear friction to rolling friction with dramatic reduction in the drawing forces as reported by Lambiase.[7][8][9] When roller dies are adopted, the drawing stages are composed by 2-4 idle rolls and the wire is pulled within the rolls clearance. This type of solution can be easily adopted also to produce flat or profiled drawn wires.

Various lubricants, such as oil, are employed. Another lubrication method is to immerse the wire in a copper(II) sulfate solution, such that a film of copper is deposited which forms a kind of lubricant. In

some classes of wire the copper is left after the final drawing to serve as a preventive of rust or to allow easy soldering.[citation needed]The best example of copper coated wire is in MIG wire used in welding 8. (i) Discuss the advantages and limitations of hot working and cold working. (8) [N/D 15] Advantages of hot working process (i)Due to refinements of grains, mechanical properties such as toughness, ductility, elongation and reduction in area are improved. (ii) Great latitude in shape and size of farm is possible to reduction of elastic limit. (iii) The power required to finish the part from ingot is less. (iv) Directional property resulting from a fiber structure is obtained. (v) The strength and hardness decreases at elevated temperature. Disadvantages of hot working process (i) The life of the tools used is less. (ii) Tooling and handling costs are high. (iii) Close tolerances cannot be maintained, oxide films are surface characteristics. Advantages of cold working process (i) Surface finish is improved and close tolerance can be maintained. (ii) Distortion or fragmentations of the grain structure is created. (iii) Accurate dimensions of parts can be maintained. (iv) Strength and hardness of the metal are increased but ductility is decreased. (v) Resistance to corrosion is decreased while ultimate tensile strength, yield point and hardness are increased. (vi) Loss of metal due to oxidation is prevented. Disadvantages of cold working process (i) The grain structure is not refined and residual stress have harmful effects on certain properties of metals. (ii) Tooling costs are high and as such it is used when large quantities of similar components are required. (iii) Only small size components can be easily cold worked as greater forces are required for large section. Extrusion process : The process of extrusion consists of compression a metal inside a chamber to force it out through a small opening called die. The extrusion process can be classified as : (i) Direct or Indirect extrusion (ii) Forward or backward extrusion (ii) Explain the steps involved in drop forging with neat sketches. (8) [N/D 15] Drop forging process General closed die drop forging process includes dies making,billetcutting,billetheating,dropforging,trimming,heattreatment,shotblasting,machining,surface treatment and inspection.Below we would like to introduce the drop forging process in detail. Step 1.Dies design&making Making dies is the first step for starting drop forging process.We will first design and produce dies according to the die drawing.Such dies normally include forging dies,trimming dies and flat die.Among

these dies,flat die is not necessary,as it is just used to used to flaten the products to ensure geometric tolerances. Step 2.Billet cutting&heating Normally,we will prepare commonly used material specifications(like 20#,35#,45#,20Cr,40Cr,20CrMnTi,20CrMo, 30CrMo,35CrMo,42CrMo,Q235,Q345,A105,ect) in stock,and cutting the billet to the estimated size.Then using the medium frequency furnace to heat the billets to a certain temperature,after that deliver the heated bars to a metal frame and wait for forging. Step 3.Drop forging Before forging,forging upper and lower dies will be attached to the anvil of forging press.Then workers will pick up a billet and place between forging dies so that the billet will be pressed at a high speed for several times to desired shapes. Step 4.Trimming After forging,we will see the redundant flash around the drop forging blanks.Soremoving flash is also a necessary step.Workers will first assemble the trimming dies under the punching machine,and then press the forging blanks at a time so that flash will be removed.We call this process "trimming". Step 5.Heat treatment Heat treatment will help to reach the required mechanical properties and hardness.Such heat treatment processes are normalization,quenching,annealing,tempering and hardening,solutionteratment,ect. Step 6.Shot blasting By shot blasting,the drop forgings will look more smooth and clear.You will see a better surface finish.Normally,the surface finish of drop forging products will reach Ra6.3,whose surface is much better than that of lost wax casting. Step 7.Machining For some parts,drop forging process is not enough to get the required tolerance,then machining will be workable,we will do machining with different machining facilities,such as milling machine,boringmachine,drillingmachine,grindingmachine,cnc,ect. Step 8.Surface treatment In most cases,we will just do water/oil anti-rust on the surface of drop forgings if there is no special requirement.But we could also follow other surface treatment demands,likepainting,powdercoating,galvalization,electropainting,ect according to the requirement of our customers. Step 9.Final inspection To ensure superior quality,we must do dimension inspection.Sometimes we also need to do inspection for mechanical properties and chemical composition. Step 10.Package&delivery

Usually,we will pack the forgings with ploybag,and put in a strong wooden case.Such package could also be customized to meet customer's demand.Located in Ningbo,both Ningbo seaport and airport are very convenient for us to deliver products to our customers' destination port. 9.(i) Briefly explain the various operations performed in forging process. (7) [N/D 16] Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it is performed: cold forging (a type of cold working), warm forging, or hot forging (a type of hot working). For the latter two, the metal is heated, usually in a forge. Forged parts can range in weight from less than a kilogram to hundreds of metric tons.[1][2]Forging has been done by smiths for millennia; the traditional products were kitchenware, hardware, hand tools, edged weapons, cymbals, and jewellery. Since the Industrial Revolution, forged parts are widely used in mechanisms and machineswherever a component requires high strength; such forgings usually require further processing (such as machining) to achieve a finished part. Today, forging is a major worldwide industry Advantages and disadvantages

Forging can produce a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.[4] Additionally, forgings can target a lower total cost when compared to a casting or fabrication. When you consider all the costs that are involved in a product’s lifecycle from procurement to lead time to rework, then factor in the costs of scrap, downtime and further quality issues, the long-term benefits of forgings can outweigh the short-term cost-savings that castings or fabrications might offer. [5] Some metals may be forged cold, but iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forging, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high-temperature furnace (sometimes referred to as the forge) is required to heat ingots or billets. Owing to the size of the massive forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations use metal-forming dies, which must be precisely machined and carefully heat-treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved.

A cross-section of a forged connecting rod that has been etched to show the grain flow There are many different kinds of forging processes available; however, they can be grouped into three main classes:[1] Drawn out: length increases, cross-section decreases Upset: length decreases, cross-section increases Squeezed in closed compression dies: produces multidirectional flow Common forging processes include: roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging and upsetting.[1] Temperature

Main articles: Hot working and Cold working All of the following forging processes can be performed at various temperatures; however, they are generally classified by whether the metal temperature is above or below the recrystallization temperature. If the temperature is above the material's recrystallization temperature it is deemed hot forging; if the temperature is below the material's recrystallization temperature but above 30% of the recrystallization temperature (on an absolute scale) it is deemed warm forging; if below 30% of the recrystallization temperature (usually room temperature) then it is deemed cold forging. The main advantage of hot forging is that it can be done more quickly and precisely, and as the metal is deformed work hardening effects are negated by the recrystallization process. Cold forging typically results in work hardening of the piece.[6][7] Drop forging

Boat nail production in Hainan, China Drop forging is a forging process where a hammer is raised and then "dropped" onto the workpiece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and closed-die drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the workpiece, while the latter does. Open-die drop forging

Open-die drop forging (with two dies) of an ingot to be further processed into a wheel Open-die forging is also known as smith forging.[8] In open-die forging, a hammer strikes and deforms the workpiece, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the surfaces that are in contact with the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. The operator therefore needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For example, a die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool.[9] Open-die forgings can be worked into shapes which include discs, hubs, blocks, shafts (including step shafts or with flanges), sleeves, cylinders, flats, hexes, rounds, plate, and some custom shapes.[10] Open-die forging lends itself to short runs

and is appropriate for art smithing and custom work. In some cases, open-die forging may be employed to rough-shape ingots to prepare them for subsequent operations. Open-die forging may also orient the grain to increase strength in the required direction. (ii) With suitable sketches, explain the stages involved in shape rolling of structural sections. (6) [N/D 16] The purpose of this project is to learn the manufacturing process of structural steel (channels, angels, flats, column, round bars, etc…) which are manufactured in hot rolling mills and hot re-rolling mills. These structures form the basic pillars for construction and it is a very huge business market. Through this project we shall be able to know how to manufacture, materials used, why they are used and much more. All the results and details obtained will be revealed and discussed. Fig. Structural elements INTRODUCTION OF STRUCTURAL SHAPE ROLLING:- Raw Materials: In this rolling mainly uses three types of raw materials, such as 1. Billets 2.Blooms 3. Ingots Internati Billets: The ingots and billets are almost similar but billets have better finish and there is less chance of blow holes being present inside within and fulfils the customer requirement. The final product obtained by using billets have better finish when compared to the ingots. Billets are more refined raw material which has less chance of blow holes and smooth surface finish. Bloom: Bloom is of rough surface finished, whereas ingot is of rough surface as well as tapered cross-se2ction. Some initial preparation is needed for bloom and ingot, whereas billets can be used directly. That is the reason the plant mainly uses billets. Ingot: The ingots have a structure similar to a trapezoid. It is like a cuboids structure but with A little taper included at the sides. This makes the area of one side of ingot bigger than the other end. These ingots are manufactured by casting process with either iron ore or iron scrap at a furnace plant.. The Billet The Blooms The Ingots Inspection of Raw materials: The incoming material is inspected visually at the initial stage before it unloaded. The QA person tags yellow ribbon to the material which indicates the material is for inspection. After inspection based on the C% the respected Ribbon colors will be issued. The stacked is done based on the color Code. The ingots are identified by lot number, color Code is issued based on the C%.Billets don’t have any standard color coding but they are tested and coding is done bythe company itself. There is a heat number mentioned on Billets which is evidenced to the chemical composition in Supplier TC. Before feeding there is a procedure of inspection where there is a series of chemical tests done which determines the percentage of Carbon, Sulphur, Phosphorous and Manganese. 1. The presence of carbon affects the strength where 0.23% is the maximum. 2. The presence of Sulphur and phosphorous gives more strength where the maximum allowable level is 0.045% STRUCTURAL SHAPE ROLLING: Structural shape rolling, also known as shape rolling and profile rolling, is a metal forming process where structural shapes are passed through rollers to bend or deform the work piece to a desired shape while maintaining a constant cross-section. Structural shapes that can be rolled include: I-beams, H-beams, T-beams, Ubeams, angle iron, channels, bar stock, and rail road rails. The most commonly rolled material is structural steel, however other include metals, plastic, paper, and glass. Common applications include: railroads, bridges, roller coasters, art, and architectural applications. It is a cost-effective way of bending this kind of material because the process requires less set-up time and uses pre-made dies that are changed out according to the shape and dimension of the work piece. ROUGHING MILL: The roughing mill has 47 inch wide rolls for rolling ‘broadside’ to make a slab wider. A 800hp motor drives 12’’ diameter work rolls through 28:1 gears to reduce the slab’s thickness by 21 /2’’. The last four roughing mills each incorporate edges for width control and roll the billet into 5 to 6’’ incrementally down to around an inch and a quarter, depending upon customer’s ordered width, gauge and steel grade. The 3rd and 5th mills each have high pressure de scaling headers operating at 1,500psi. The individual roughing mills are spaced increasingly further apart to accommodate the lengthening of transfer bars as they are rolled thinner and thinner. FINISHING MILL: SIL-IV’s Hot Roll Mill includes finishing mills, which reduces the thickness of the transfer angles down to the gauge required by the customer or the next process. The

rolling speed is set to allow the last strand to perform the final reduction at the finishing temperature, between 900oC to 950oC, specified to reach certain mechanical properties. 10. (i) Explain the working of Mannesmann process with neat sketch. (7) [N/D 16] Rotary piercing

Rotary piercing is a hot working metalworking process for forming thick-walled seamless tubing. There are two types: the Mannesmann process and Stiefel process.

Mannesmann process

A schematic of rotary piercing. Key:

1. Roller configuration

2. The process starts with the blank fed in from the left.

3. The stresses induced by the rolls causes the center of the blank to fracture.

4. Finally, the rolls push the blank over the mandrel to form a uniform inner diameter.

A heated cylindrical billet workpiece is fed between two convex-tapered rollers, which are rotating in the same direction.[1] The rollers are usually 6° askew from parallel with the billet's axis. The rollers are on opposite sides of the billet, and the surface of their largest cross sections are separated by a distance slightly smaller than the outside diameter (OD) of the original billet. The load imparted by the rollers compresses the material and the 6° skew provides both rotation and translation to the billet. The friction between the rollers and the billet is intentionally high, and is sometimes increased by using knurled rollers. This friction establishes stresses varying radially through the billet, with the highest stresses at the OD and the central axis. The stress exceeds the yield strength of the billet and causes circumferential fissures to propagate at various radii near the OD, and a central longitudinal void to form at the axis. A tapered mandrel is set inside and a short distance from the start of the central void. This mandrel forces the material outward and compresses the material against the back side of the tapered rollers. This compressive loading fuses the circumferential fissures and sets the initial internal diameter and OD values. The formed tube is then cooled and can be cold worked to refine the diameters and to achieve the desired yield strengths.

Mannesmann mills can produce tubes as large as 300 mm (12 in) in diameter.

Stiefel process

The Stiefel process is very similar to the Mannesmann process, except that the convex rollers are replaced with large conical disks. This allows for larger tubes to be formed.

(ii) How is tube drawing carried out? Explain with suitable sketch. (6) [N/D 16] Tube drawing: Tube drawing is a tube finishing process carried out on the tubes made through the

other methods like Mannesmann mill. Tube sinking is done without using a mandrel, to reduce the

diameter of the tube without affecting the thickness. Tube drawing is used to reduce thickness and

diameter using mandrels. Mandrel or plug may be cylindrical or conical in shape. Using a plug

ensures uniform thickness. The mandrel may be kept stationary or moved along with the tube.

Floating mandrel are used where the length of the tubes are long. Drawing forces involved in tube

drawing with plug are always higher. With moving mandrel, there is a forward frictional drag which

pulls the metal into the die, at the entry.

Where phosphating is used for the cold drawing of seamless tube, the requirements are somewhat

different from those applicable to welded steel tube. Until about 30 years ago, phosphate coating

weights of 20-40 g/m² were used allowing the largest possible number of successive draws. Such

coatings were formed with nitrate-accelerated systems at 90-95°C.

Over the years, in search for increased operational efficiency, the number of draws for a given

reduction of seamless tubing, has decreased. In order to maintain the dimensional tolerances and

quality of surface finish, tubes in the mid-range of available sizes are now reduced in a single or, at

most, two draws. At the same time, drawing rates have been increased. For these reasons phosphate

coating for drawing of seamless tubing are now formed with weights of 4-10 g/m². This has improved

the efficiency of the surface treatment and, at the same time, avoided the adverse effects which act in

the firs drawing stage where coarser-crystalline phosphate coating are found. The most suitable

coating is based on nitrate/nitrite accelerated zinc phosphate, formed at 40-75°C. At the upper end of

this temperature range, the option exists to use self dosing nitrate type systems. Chlorate accelerated

zinc phosphate baths are also found. In all cases, the preferred form of the phosphate for cold

drawing of tube and section is strongly adherent but soft structured.

In the drawing of welded tubing, the seam must first be ground down. In the case of smaller diameter

tubing, this is not possible inside the welding machine. In some cases, there may be a deformation to

give a particular cross-section. Since, as a rule, less severe deformations can be tolerated by welded,

as opposed to seamless tubing, the use of phosphating is widespread, coating weights being of the

order 1.5 - 5 g/m². These are mostly based on zinc phosphate baths operated between 50 and 75 °C

with additives used to promote thinner coatings.

Phosphating is also used for tubing of un-alloyed or low-alloyed steel with chromium content up to 4-

6%. Such coatings offer a number of advantages, all arising from reduced metal-to-metal contact

between tube and die. Thus, cold welding damage, leading to grooving or crack formation, is

minimised, tool and die life is extended and higher drawing rates may be used. Zinc phosphate

coating also allows a greater degree of reduction per pass and an increased number of passes

without intermediate heat-treatment.

Part – A

1. What are the types of Moulding Sand?

Green Sand, Dry sand, Loam Sand, Facing Sand, Parting sand, Core Sand. 2. What are the components of Gating system?

Poring cup, Spure, Runner, Gate, Riser. 3. What are the types of Moulding methods?

Green Sand, Dry Sand, Loam Moulding, Bench Moulding, Floor Moulding, Pit Moulding, Sweep Moulding, Plate moulding, Machine Moulding( Jolt Machine, Sand Slinger, Top & Bottom Squeezer.

4. What is meant by Core & Core print? (NOV/DEC 2012) Core: It is used to make a hollow type casting. The core is placed in the mould and is removed after casting. Core

Print: A projection made in the pattern is called core print. It is used to form a core seat in the mould.

Part – B

11. Explain thermit welding & Diffusion welding with neat sketch. (16) TW - Thermit Welding is a welding process utilizing heat generated by exothermic chemical reaction between the components of the thermit (a mixture of a metal oxide and aluminum powder). The molten metal, produced by the reaction, acts as a filler material joining the work pieces after Solidification. Thermit Welding is mainly used for joining steel parts, therefore common thermit is composed from iron oxide (78%) and aluminum powder (22%). The proportion 78-22 is determined by the chemical reaction of combustion of aluminum: 8Al + Fe3O4 = 9Fe + 4Al2O3 The combustion reaction products (iron and aluminum oxide) heat up to 4500°F (2500°C). Liquid iron fills the sand (or ceramic) mold built around the welded parts, the slag (aluminum oxide), floating up , is then removed from the weld surface.Thermit Welding is used for repair of steel casings and forgings, for joining railroad rails, steel wires and steel pipes, for joining large cast and forged parts.

(1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold;(3) metal solidifies to produce weld joint. Advantages of Thermit Welding:

No external power source is required (heat of chemical reaction is utilized); Very large heavy section parts may be joined.

Disadvantages of Resistance Welding:

Only ferrous (steel, chromium, nickel) parts may be welded; Slow welding rate; High temperature process may cause distortions and changes in Grainstructure in the weld region.

Weld may contain gas (Hydrogen) and slag contaminations.

12. Explain Spot Welding & Electro slag welding with neat sketch. (16) In Spot welding overlapping sheets are joined by local fusion at one or more spots, by the concentration of

current flowing between two electrodes. This is the most widely used resistance welding process. It essentially consists of two electrodes, out of which one is fixed. The other electrode is fixed to a rocker arm (to provide mechanical advantage) for transmitting the mechanical force from a pneumatic cylinder. This is the simplest type of arrangement. The other possibility is that of a pneumatic or hydraulic cylinder being directly connected to the electrode without any rocker arm. For welding large assemblies such as car bodies, portable spot welding machines are used. Here the electrode holders and the pneumatic pressurizing system are present in the form of a portable assembly which is taken to the place, where the spot is to be made. The electric current, compressed air and the cooling water needed for the electrodes is supplied through cables and hoses from the main welding machine to the portable unit. In spot welding, a satisfactory weld is obtained when a proper current density is maintained.

Fig. Resistance spot welding machine setup

A resistance welding schedule is the sequence of events that normally take place in each of the welds. The events are:

1. The squeeze time is the time required for the electrodes to align and clamp the two work-pieces together under them and provide the necessary electrical contact. 2. The weld time is the time of the current flow through the work-pieces till they are heated to the melting temperature. 3. The hold time is the time when the pressure is to be maintained on the molten metal without the electric current. During this time, the pieces are expected to be forged welded. 4. The off time is time during which, the pressure on the electrode is taken off so that the plates can be positioned for the next spot.

ESW - Electroslag Welding is a welding process, in which the heat is generated by an electric current

passing between the consumable electrode (filler metal) and the work piece through a molten slag covering

the weld surface. Prior to welding the gap between the two work pieces is filled with a welding flux.

Electroslag Welding is initiated by an arc between the electrode and the work piece (or starting plate).

Heat, generated by the arc, melts the fluxing powder and forms molten slag. The slag, having low electric

conductivity, is maintained in liquid state due to heat produced by the electric current.

The slag reaches a temperature of about 3500°F (1930°C ). This temperature is sufficient for melting the

consumable electrode and work piece edges. Metal droplets fall to the weld pool and join the work pieces.

Electroslag Welding is used mainly for steels.

Advantages of Electroslag Welding:

High deposition rate - up to 45 lbs/h (20 kg/h);

Low slag consumption (about 5% of the deposited metal weight);

Low distortion; Unlimited thickness

of work piece.

Disadvantages of Electroslag welding:

Coarse grain

structure of the

weld; Low

toughness of the

weld;

Only vertical position is possible. 13. (a) Discuss about soldering & Brazing with neat sketch. (08)

SOLDERING: Soldering is a method of joining similar or dissimilar metals by heating them to a suitable temperature and by means of a filler metal, called solder, having liquidus temperuatre not Welding exceeding 450°C and below the solidus of the base material. Though soldering obtains a good joint between the two plates, the strength of the joint is limited by the strength of the filler metal used. Solders are essentially alloys of lead and tin. Basic Operations in Soldering For making soldered joints, following operations are required to be performed sequentially. 1. Shaping and fitting of metal parts together Filler metal on heating flows between the closely placed adjacent surfaces due to capillary action, thus, closer the parts the more is solder penetration. This means that the two parts should be shaped to fit closely so that the space between them is extremely small to be filled completely with solder by the capillary action. If a large gap is present, capillary action will not take place and the joint will not be strong. 2. Cleaning of surfaces This is done to remove dirt, grease or any other foreign material from the surface pieces to be soldered, in order to get a sound joint. If surfaces are not clean, strong atomic bonds will not form.

BRAZING: Like soldering, brazing is a process of joining metals without melting the base metal. Filler material

used for brazing has liquidus temperature above 450°C and below the temperature of the base metal. The filler metal is drawn into the joint by means of capillary action (entering of fluid into tightly fitted surfaces). Brazing is a much widely used joining process in various industries because of its many advantages. Due to the higher melting point of the filler material, the joint strength is more than in soldering. Almost all metals can be joined by brazing except aluminum and magnesium which cannot easily be joined by brazing.Dissimilar metals, such as stainless steel to cast iron can be joined by brazing. Because of the lower temperatures used there is less distortion in brazed joints. Methods of Brazing Torch Brazing It is the most widely used brazing method. Heat is produced, generally, by burning a mixture of oxy-acetylene gas, as in the gas welding. A carbonizing flame is suitable for this purpose as it produces sufficiently high temperature needed for brazing. Furnace Brazing It is suitable for brazing large number of small or medium parts. Usually brazing filler metal in the granular or powder form or as strips is placed at the joint, and then the assembly is placed in the furnace and heated. Large number of small parts can be accommodated in a furnace and simultaneously brazed.

Braze Welding

In welding processes where the joint of the base metal is melted and a joint is prepared havinghigher joint strength, it is likely to cause metallurgical damage by way of phase transformations and oxide formation. In this process, the base metal is not melted, but the joint is obtained by means of a filler metal.

14. Describe plasma Arc welding and give their applications. (NOV/DEC 2012) (08) PAW - Plasma Arc Welding is the welding process utilizing heat generated by a constricted arc struck between a tungsten non-consumable electrode and either the work piece (transferred arc process) or water cooled constricting nozzle (non-transferred arc process). Plasma is a gaseous mixture of positive ions, electrons and neutral gas molecules. Transferred arc process produces plasma jet of high energy density and may be used for high speed welding and cutting ofCeramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel alloys.

Non-transferred arc process produces plasma of relatively low energy density. It is used for welding of various metals and forplasma spraying (coating). Since the work piece in non- transferred plasma arc welding is not a part of electric circuit, the plasma arc torch may move from one work piece to other without extinguishing the arc.