Riveting

Riveting

Riveting is a popular method of fastening and joining because of its simplicity, dependability and low cost.
Dissimilar metals and assemblies having a number of parts with non-uniform thickness can readily be fastened.
These joints are made in location where they either do not increase weight of the work at all
(over the weight of an integral work) or increase it negligibly. Structures in which riveted joints are used
may be grouped as: (a) where strength and rigidity are chief requirements, eg, coal bunkers, low pressure
liquid containers, ship hulls; (b) where strength, rigidity, as well as security against leakage should be
considered, eg, boiler drains, pressure vessels, high pressure liquid containers and gas tanks; and
(c) where the joint must resist given outside loads and have sufficient rigidity, eg, bridges, buildings, cranes,
and machine frames. Compared with screwed or bolted joints, riveting requires no additional work or
supplementary parts, such as, lock washers, and supplementary nuts. Compared with welded joints,
riveting makes possible consistently uniform results without resort to X-ray or other methods of inspection.
There are several types of rivets, and some may be solid or hollow; blind rivets are inserted from one side only.
Installing a rivet basically consists of placing the rivet in the hole and deforming the end of its shank by upsetting.
The operation may be performed by hands or by mechanical means, including the use of robots. Riveting may be
done either in room temperature or hot, using special tools, or by using explosives in the cavity of the rivet.

A riveted joint may fail during its service life by tearing, shearing or crushing. On a structure/machine element
a failure of a joint is reported as a failure symptom or mode. This means how the failure is observed. The
causes or cause events that singly, or in combination, may lead to these failure modes, or a general failure
mode, include design related, process related, operation/use related and maintenance related cause events.
The design related cause events include problem of strength analysis, improper selection of the type of joint,
improper material selection, improper size of rivets (shank diameter and length), improper size of rivet holes/
clearance, improper layout of rivet holes and improper size of cover plates/straps. The process related cause
events are improper riveting process, improper riveting environment and defective material (rivet and cover plates);
while operation related cause event is improper loading; and maintenance related cause events include problems of
riveting technicians and improper maintenance of material (including riveting equipment).

Upsetting Process

Upsetting Process: An Overview

Upset Forging or Upsetting is defined as 'free forming', by which a billet or a portion of a workpiece is reduced in height between usually plane, parallel plates [ASM Handbook 1988]. Upsetting is a basic deformation process which can be varied in many ways. Upsetting of metals is a deformation process in which a (usually round) billet is compressed between two dies in a press or a hammer. This operation reduces the height of a part while increasing its diameter. The process is mostly used as an intermediate step in multiple step forging operations. The billet may be cold, warm or hot forged. A large segment of industry primarily depends on the upsetting process for producing parts ranging in complexity from simple bolts, screws, nuts, rivets or flanged shafts to wrench sockets that require simultaneous upsetting and piercing. Hot upsetting is also occasionally used as a finishing operation following hammer or press forging, such as in making crankshafts. A sketch of the upsetting process is shown in the below figure.

Figure 1: Upsetting process


In upsetting a rigid tool is pushed onto a block of material (billet). The material is free to move at the right hand side. Successful upsetting mainly depends on two process limitations:
1.Upset strain, : that affects the forming limit or forgeability of the workpiece material

          h₀
ε = ln  —
          h₁

2. Upset Ratio (Ru): that affects the buckling of the workpiece

          h₀
R_u  =      
          d₀


Figure 2: Upset Forging of a Cylinder


Figure 3: Metal flow in non-steady state upset forging processes
In upsetting a ratio of Ru≤2.3 can be achieved in one hit if the deformation occurs over a portion of the workpiece. Larger values require several deformation stages. In upsetting the parameters that are significant are dimensions of the workpiece, its strength, its formability, the required upset ratio, the desired accuracy and the surface quality. When forming in several stages, the design of the heading preforms affects the fiber structure of the final shape. Heading preforms are to be shaped such that the workpiece is guided correctly to avoid buckling and folding. In metal forming, the flow of metal is caused by the pressure transmitted from the dies to the deforming workpiece. Therefore, the frictional conditions at the die/workpiece interface greatly influence metal flow, formation of surface and internal defects, stresses acting on the dies, and load and energy requirements
In metal forming, the flow of metal is caused by the pressure transmitted from the dies to the deforming workpiece. Therefore, the frictional conditions at the die/workpiece interface greatly influence metal flow, formation of surface and internal defects, stresses acting on the dies, and load and energy requirements. Figure above illustrates this phenomenon as it applies to the upsetting of a cylindrical workpiece. The figure(a) shows, under frictionless conditions, the workpiece deforms uniformly and the resulting normal stress is constant across the diameter. However, figure (b) shows that under actual conditions, where some level of frictional stress is present, the deformation of the workpiece is not uniform (i.e. barreling). As a result, the normal stress increases from the outer diameter to the center of the workpiece and the total upsetting force is greater than for the frictionless conditions.

Piston

Pistons are vital component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders etc. It is the reciprocating component which moves inside the cylinder and converts the reciprocating motion into rotary motion or vice versa.

Figure 4: Piston
Forged Piston Vs Casted Piston: The majority of original equipment and aftermarket pistons are manufactured through casting. The technical description is 'gravity die casting'. However for the sake of simplicity, a cast piston is manufactured by pouring molten aluminium /silicon alloy into a mold. Forged pistons differ fundamentally in manufacturing and inherent character. As opposed to casting, the forging process basically takes a lump of billet alloy and stamps the shape of the piston from a die.
Casting and forging results in two different types of piston. A die for forged piston must be designed so it can easily be removed and, as a result, the forged blank (or unfinished piston) has a relative simple shape. Casting can achieve a more complex blank and, therefore, facilitate lightweight construction. Also, due to relative manufacturing procedures, forged pistons tend to be more expensive than cast items. A cast pistons is more likely to shatter and damage the engine, as a whole, more than a forged piston where as a big advantage with forged pistons is they generally result in a more ductile material, with the effect being the piston can take a higher level of detonation before failing. In extremely high rpm/high horsepower applications, the great strength of the forged piston can add reliability.

Manufacturing Forged Piston: During Manufacturing of Piston the billet of Aluminium alloy is taken and hot forging operation is performed over it. The billet is preheated to a temperature of about 427 C before placing it onto the lower die and performing forging operation over it.. This leads to the upsetting operation taking place in the billet. The change in microstructure tends to increase the strength of piston. Dies used for the process consists of impression of the piston on lower die as well as the upper die as shown in the following figures:

          
Figure 5: Lower Die               Figure 6: Upper Die
The manufacturing process used in the process is shown in the following figure:


Figure 7: Manufacturing process
Alloy Whee: Alloy wheels are automobile (car, motorcycle and truck) wheels which are made from an alloy of aluminum or magnesium. They are typically lighter for the same strength and provide better heat conduction and improved cosmetic appearance. There are quality standards to govern the production of wheels. A wheel is comprised of a hub, spokes and rim. Sometimes these components will be one piece, sometimes two or three. The hub is the centre portion of the wheel and is what attaches the wheel to the suspension. The spokes radiate out from the hub and attach to the rim. Most alloy wheels are manufactured using casting, but some are forged. Forged wheels are usually lighter, stronger, but much more expensive than cast wheels. There are basically three processes when it comes to manufacturing alloy wheel which are one piece in construction: cast alloy, forged alloy wheels, and billet alloy wheels. Each one of these will produce a highest quality alloy wheels however there are some distinct difference in the strength of the finished product worth nothing.

A CAST ALLOY WHEEL - is a manufacturing process whereby molten aluminium is pored into an alloy wheel mould and once it is cooled, the result is a wheel. There are three types of cast wheel production: Gravity fed, low- pressure fed, spun-rim.

A FORGED ALLOY WHEEL - is a manufacturing process in which intense heat and pressure is used to force a chunk of aluminium (often called a slug or stock) into the alloy wheel shape desired. This process will create an alloy wheel which is up to 300% stronger than a cast alloy wheel and is lighter as well.

A BILLET ALLOY WHEEL - is a manufacturing process here by a chunk of aluminium is machined into the alloy wheel design. This involves a very expensive machine called CNC (computer numeric control) which reads specific instructions then drives the machine tool to complete the task.
Magnesium alloy wheels, or "mag wheels", are sometimes used on racing cars, in place of heavier steel or aluminium wheels, for better performance. Magnesium wheels can be produced through various methods.

FORGING: Forging can be done by a one or multi-step process forging from various magnesium alloys, most commonly AZ80, ZK60 (MA14 in Russia). Wheels produced by this method are usually of higher toughness and ductility than aluminium wheels, although the costs are much higher.

HIGH PRESSURE DIE CASTING (HPDC): This process uses a die arranged in a large machine that has high closing force to clamp the die closed. The molten magnesium is poured into a filler tube called a shot sleeve. A piston pushes the metal into the die with high speed and pressure, the magnesium solidifies and the die is opened and the wheel is released. Wheels produced by this method can offer reductions in price and improvements in corrosion resistance but they are less ductile and of lower strength due to the nature of HPDC.

LOW PRESSURE CASTING (LPDC): This process usually employs a steel die; it is arranged above the crucible filled with molten magnesium. Most commonly the crucible is sealed against the die and pressurized air/cover gas mix is used to force the molten metal up a straw like filler tube into the die. When processed using best practice methods LPDC wheels can offer improvements in ductility over HPDC magnesium wheels and any cast aluminium wheels, they remain less ductile than forged magnesium.

GRAVITY CASTING (PERMANENT MOLD AND SAND CASTING): Gravity cast magnesium wheels have been in production since the early 1920's. This method offers wheels with good ductility, and relative properties above what can be made with aluminium casting. Tooling costs for gravity cast wheels are among the cheapest of any process. This has allowed small batch production, flexibility in design and short development time.

Swaging

Swaging

Swaging is a process that is used to reduce or increase the diameter of tubes. A swagged piece created by placing the tube inside a die that applies compressive force by hammering radially.
The term swage can apply to the process of swaging (verb), or to a die or tool used for swaging (noun).

Manufacturing Processes: As a general manufacturing process swaging may be broken up into two categories. The first category of swaging involves the workpiece being forced through a confining die to reduce its diameter, similar to the process of drawing wire. This may also be referred to as "tube swaging." The second category involves two or more dies used to hammer a round workpiece into a smaller diameter. This process is usually called "rotary swaging" or "radial forging". Tubes may be tagged (reduced in diameter to enable the tube to be initially fed through the die to then be pulled from the other side) using a rotary swagger, which allows them to be drawn on a draw bench. Swaging is normally the method of choice for precious metals since there is no loss of material in the process.
Swaging can be further expanded by placing a mandrel inside the tube and applying radial compressive forces on the outer diameter. Thus, through the swage process, the inner tube diameter can be a different shape, for example a hexagon, and the outer is still circular.

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Tube Swaging
Rotary swaging: Rotary swaging process is usually a cold working process, used to reduce the diameter, produce a taper, or add point to a round workpiece. It can also impart internal shapes in hollow workpieces through the use of a mandrel (the shape must have a constant cross-section). Swaging a bearing into a housing means flaring its groove's lips onto the chamber of the housing. A swaging machine works by using two or four split dies which separate and close up to 2000 times a minute. This action is achieved by mounting the dies into the machine's spindle which is rotated by a motor. The spindle is mounted inside a cage containing rollers (looks like a roller bearing). The rollers are larger than the cage so as the spindle spins the dies are pushed out to ride on the cage by centrifugal force, as the dies cross over the rollers they push the dies together because of their larger size. On a four-die machine, the number of rollers cause all dies to close at a time; if the number of rollers do not cause all pairs of dies to close at the same time then the machine is called a rotary forging machine, even though it is still a swaging process.

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Rotary Swaging
A variation of the rotary swagger is the creeping spindle swaging machine where both the spindle and cage revolve in opposite directions, this prevents the production of fins between the dies where the material being swagged grows up the gap between the dies. There are two basic types of rotary swaging machine, the standard (also known as a tagging machine), and the butt swaging machine. A butt swaging machine works by having sets of wedges that close the dies onto the workpiece by inserting them between the annular rollers and the dies, normally by the use of a foot pedal. A butt swaging machine can allow a workpiece to be inserted without the dies closing on it, for example a three foot workpiece can be inserted 12 inches and then the dies closed, drawn through until 12 inches remain and the dies are then released, the finished workpiece would then, for example, be four feet long but still of its initial diameter for a foot at each end.

Applications

Electronics: In Printed Circuit Boards assembly individual connector pins are sometimes pressed/swagged into place using an arbor press. Some pins have a hollow end that is pressed over by the arbor's tool to form a mushroom shaped retaining head. Typical pin diameter range from 0.017 to 0.093 inches or larger. The swaging is an alternative or supplement to soldering.

Pipes and Cables: The most common use of swaging is to attach fittings to pipes or cables (also called wire ropes); the parts loosely fit together, and a mechanical or hydraulic tool compresses and deforms the fitting, creating a permanent joint. Pipe flaring machines are another example. Flared pieces of pipe are sometimes known as "swage nipples," "pipe swages," "swaged nipples," or "reducing nipples." In furniture, legs made from metal tubing (particularly in commercial furniture) are often swaged to improve strength where they come in contact with the ground, or casters.

Saw blade teeth: In sawmills, a swage is used to flare large bandsaw or circle saw teeth, which increases the width of the cut, called the kerf. A clamp attaches a mandrel and die to the tooth and the eccentric die is rotated, swaging the tip. A much earlier version of the same operation used a hardened, shaped swage die and a hand held hammer. Saw teeth formed in this way are sometimes referred to as being "set." A finishing operation, shaping, cold works the points on the tooth sides to flats. It might be considered as a side swage. This slightly reduces the tooth width but increases the operating time between "fittings." Swaging is a major advance over filing as the operation is faster, more precise and greatly extends the working life of a saw.

Firearms and ammunition: In internal ballistics, swaging describes the process of the bullet entering the barrel and being squeezed to conform to the rifling. Most firearm bullets are made slightly larger than the inside diameter of the barrel, so that they are swaged to engage the rifling and form a tight seal upon firing. In ammunition manufacture, swaged bullets are bullets manufactured by swaging room temperature metals into a die to form it into the shape of a bullet. In contrast, swaged bullets, since they are formed at the temperature at which they will be used, can be formed in molds of the exact desired size. This means that swaged bullets are generally more precise than cast bullets. The swaging process also leads to fewer imperfections, since voids commonly found in casting would be pressed out in the swaging process. The swaging process in reference to cold flow of metals into bullets is the process not of squeezing the metals into smaller forms but rather pressing smaller thinner items to form into shorter and slightly wider shapes. Swaging is used to form unjacketed bullets, usually made of a mix of lead and some antimony to improve working properties (lead alone is usually too soft). Many reloading equipment manufacturers started by marketing both reloading and bullet swaging dies and equipment.

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Forging Defects

Forging Defects

Though forging process give generally prior quality product as compared to the other manufacturing processes. There are some defects that are lightly to come a proper care is not taken in forging process design.
Forging Defects can be categorized into two broad categories:

1. Geometrical Defects
2. Non Geometrical Defects

Geometrical Defects: The main types of geometrical defects are

1. Laps and folds
2. Underfills
3. Overfills

There are a number of other different geometrical defects that can occur during forging. These include:

• Piping
• Forging shape does not match design
• Die deflection, yielding or wear
• Eccentricity or buckling

A) Unfilled Section: In this some section of the die cavity are not completely filled by the flowing metal. The causes of this defects are improper design of the forging die or using forging techniques.

B) Cold Shut: This appears as a small cracks at the corners of the forging. This is caused mainly by the improper design of die. Where in the corner and the fillet radii are small as a result of which metal does not flow properly into the corner and the ends up as a cold shut.

C) Laps and Folds: This is caused by the improper die design, making the laps created onto the final part which is very much undesirable as they distort the surface finish and also tend to weaken the product due to internal or external cracks.
Less-than-optimum process and preform design is the principal cause of most geometrical defects. By understanding the process issues, the forge is better able to design its processes to minimize the occurrence of such defects.
When the press or hammer dies close, the work piece will move in a path of least resistance. It is imperative that the die and pre-form design create this least resistant path so that the net result is a sound forging. On occasion, the die design may create a situation in which the path of least resistance is the one that results in a defect during forging. By examining the various types of geometrical defects, the fundamental cause can be understood and the die designer can produce a die that creates a sound, defect-free product

Non Geometrical Defects: The main type of Non geometrical defects are:

A) Flakes: These are basically internal ruptures caused by the improper cooling of the large forging. Rapid cooling causes the exterior to cool quickly causing internal fractures. This can be remedied by following proper cooling practices.

B) Scale Pits: This is seen as irregular deputations on the surface of the forging. This is primarily caused because of improper cleaning of the stock used for forging. The oxide and scale gets embedded into the finish forging surface. When the forging is cleaned by pickling, these are seen as deputations on the forging surface.

Sheet Metal Working

1. Introduction

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material. Thicknesses can vary significantly, although extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate.

2. Sheet metal processing

The raw material for sheet metal manufacturing processes is the output of the rolling process. Typically, sheets of metal are sold as flat, rectangular sheets of standard size. If the sheets are thin and very long, they may be in the form of rolls. Therefore the first step in any sheet metal process is to cut the correct shape and sized �blank� from larger sheet.

3. Sheet metal forming processes

Sheet metal processes can be broken down into two major classifications and one minor classification

 Shearing processes: processes which apply shearing forces to cut, fracture, or separate the material.

 Forming processes: processes which cause the metal to undergo desired shape changes without failure, excessive thinning, or cracking. This includes bending and stretching.
Finishing processes: processes which are used to improve the final surface characteristics.

3.1 Shearing Process

1. Punching: Punching is a metal forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing. The punch often passes through the work into a die. A scrap slug from the hole is deposited into the die in the process. Depending on the material being punched this slug may be recycled and reused or discarded. Punching is often the cheapest method for creating holes in sheet metal in medium to high production volumes. When a specially shaped punch is used to create multiple usable parts from a sheet of material the process is known as blanking. In forging applications the work is often punched while hot, and this is called hot punching. Production rate of this process is very high so it is good for the industrial purpose. In given figure industrial punching machine is shown. A die is located on the opposite side of the workpiece and supports the material around the perimeter of the hole and helps to localize the shearing forces for a cleaner edge. There is a small amount of clearance between the punch( upper die) and the lower die to prevent the punch from sticking in the die and so less force is needed to make the hole. The amount of clearance needed depends on the thickness, with thicker materials requiring more clearance, but the clearance is always less than the thickness of the workpiece. The clearance is also dependent on the hardness of the workpiece. The punch press forces the punch through a workpiece, producing a hole that has a diameter equivalent to the punch, or slightly smaller after the punch is removed. we also used a pressure pad to provide proper pressure on working sheet.

Figure: Initial Work Sheet


Figure: Punching Operation

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Figure: Work Sheet after Punching Operation

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Figure: Final Sheet 2. Blanking: shearing process using a die and punch where the exterior portion of the shearing operation is to be discarded.

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Figure: Shearing Operations - Punching and Blanking
3. Perforating: punching a number of holes in a sheet.
4. Parting: shearing the sheet into two or more pieces.
5. Notching: removing pieces from the edges.
6. Lancing: leaving a tab without removing any material.

3.2 Forming Processes

3.2.1 Sheet Metal Bending

Introduction: Bending is a manufacturing process by which metal can be deformed by plastically deforming the material and changing its shape. The material is stressed beyond its yield strength but below its ultimate tensile strength. There is little change to the materials surface area. Bending generally refers to deformation about one axis only.
Bending along a straight line is the most common of all sheet forming processes; it can be done in various ways such as forming along the complete bend in a die, or by wiping, folding or flanging in special machines, or sliding the sheet over a radius in a die.
Bending is done using Press Brakes. Press Brakes can normally accommodate stock from 1m to 4.5m (3 feet to 15 feet).Thickness can vary significantly, although extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate. The thickness of the sheet metal is called its gauge.

Bend Allowances: When sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched. Somewhere within the thickness of the metal lies its Neutral Axis, which is a line in the metal that is neither compressed nor stretched.

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Figure: Tension and Compression in the bend area of the sheet In practical terms is that if we want a work piece with a 90 degree bend in which one leg measures A, and the other measures B, then the total length of the flat piece is NOT A + B as one might first assume.

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Bending Allowance Formula (when bending is at some particular angle)

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Figure: Bending allowance atttributes
where A_b = bend allowance, a = bend angle, R= bend radius, t = stock thickness,
K_ba is factor to estimate stretching. If R < 2t, K_ba = 0.33
If R = 2t, K_ba = 0.50
Spring Back: Because all materials have a finite modulus of elasticity, plastic deformation is followed by elastic recovery upon removal of the load; in bending, this recovery is known as spring back. The amount of spring back depends on the material, thickness, grain and temper. The spring back will usually range from 5 to 10 degrees.
As shown in Figure below, the final bend angle after spring back is smaller and the final bend radius is larger than before. This phenomenon can easily be observed by bending a piece of wire or a short strip metal.

Approximate formula to estimate spring back :

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Figure: Spring Back after Banding
where Ri and Rf are the initial and final bend radii, respectively.
Y - Yield strength of the material.
E - Modulus of elasticity of the material.
T - Thickness of the material.

Bending Force Formula: The equation for estimating the maximum bending force is
where k is a factor, T is the ultimate tensile strength of the metal. L and t are Length and thickness of sheet metal respectively.

Types of Bending processes: There are three basic types of bending on a press brake, each is defined by the relationship of the end tool position to the thickness of the material. These three are:

I. AIR BENDING: Air Bending is a bending process in which the punch touches the work piece and the work piece does not bottom in the lower cavity. As the punch is released, the work piece springs back a little and ends up with less bend than that on the punch.
In air bending, there is no need to change any equipment or dies to obtain different bending angles because the bend angles are determined by the punch stroke. The forces required to form the parts are relatively small, but accurate control of the punch stroke is necessary to obtain the desired bend angle.

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Figure: Air Bending II. BOTTOMING: In bottoming, the sheet is forced against the V opening in the bottom tool. U-shaped openings cannot be used. Space is left between the sheet and the bottom of the V opening. Bottoming is a bending process where the punch and the work piece bottom on the die. This makes for a controlled angle with very little spring back. The tonnage required on this type of press is more than in air bending. The inner radius of the work piece should be a minimum of 1 material thickness.

III. COINING: Coining is a cold working process which is similar to forging which takes place at an elevated temperature. It uses a great force to deform a workpiece plastically. More concisely, it is the squeezing of metal while it is confined in a closed set of dies.
For a particular operation, the dies are shown below:

Figure: Upper Die

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Figure: Lower Die The billet used is a machined thin cylindrical metal as shown below. The billet used for this purpose is of 100 mm diameter and 10 mm height.

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Figure: Billet A work piece is placed a confined (lower) die as shown below . A movable punch is located within the die. The action of this punch cold works the material and can form intricate features.

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Figure: Coining Process Coining is a form of precision stamping in which a workpiece is subjected to a high stress such that a plastic flow is developed on its surface. After the process the billet looks like:

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Figure: Billet after Process Generally, a high tonnage pressure is required in coining than in stamping because the work piece is not cut but deformed plastically. Hence, coining is used where high tonnage is required.

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Figure: Final Coin The coining process can be done by using hydraulic press, gear driven press or, mechanical press.

The beneficial features provided by coining are:

1. In some metals, it reduces surface grain size
2. It results in hardening of surface
3. Material retains its toughness while it is deep in the part
It is used in manufacturing parts when there is requirement of high relief or very fine features. For example: It is used to produce coins, medals, buttons and batches etc.

IV. Bead Forming: Bending is one of the most common forming operations. A large amount of parts and components are shaped by bending. It is used not only to form flanges, seams and corrugations but also to impart stiffness to the part.
There are many types of bending operations. Beading is one of the common bending operations which are used to form beads at the end of the sheets. In beading, the periphery of the sheet metal is bent into the cavity of the die as shown in following figure. A bead or a round corner is formed at the end of the sheet. The bead imparts the stiffness to the part by increasing the moment of inertia of the section. Also, it improves the appearance of the part and eliminates exposed sharp edges. Some of the beading operations are shown in the following figure.

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Figure: Beading Operation In over simulations we have to type of billets. One is rod and other is a chip, bead is to be formed at the end of these two billets. The first video is of beading of rod. In beading of the rod a groove has to be cut in the upper die for the movement of the rod without bending in the other direction. Symmetric planes are taken to prevent bending of the rod. The initial billet and final product of the process are shown in figure (i).

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Figure (i)                                   Figure (ii)
Arrangement of dies in Beading Process The second video is of beading operation of the sheet. In this video a bead is formed at the end of the sheet by beading process. All the planes of symmetry are considered to prevent the bending of the sheet. The initial and final form of the sheet is shown in following figure.

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Figure: initial and final form of the sheet
V. OTHER COMMON TYPES OF BENDING

a) V Bending: In V-bending, the clearance between punch and die is constant (equal to the thickness of sheet blank). It is used widely. The thickness of the sheet ranges from approximately 0.5 mm to 25 mm.

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b) U Die Bending: U-die bending is performed when two parallel bending axes are produced in the same operation. A backing pad is used to force the sheet contacting with the punch bottom. It requires about 30% of the bending force for the pad to press the sheet contacting the punch.

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Figure: U Bending c) Wiping Die Bending: Wiping die bending is also known as flanging. One edge of the sheet is bent to 90 while the other end is restrained by the material itself and by the force of blank-holder and pad. The flange length can be easily changed and the bend angle can be controlled by the stroke position of the punch.

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3.2.2 Stretching: Forming process causes the sheet metal to undergo the desired shape change by stretching without failure. Ref fig.3

3.2.3 Deep Drawing:   Deep Drawing is a sheet metal process in which metal sheet is radial drawn into a forming die by the mechanical action of punch. It is thus shape transformation process with material retention. The process is considered 'deep' drawing when depth of drawn part is more then its diameter. The sheet metal in the die shoulder area (flanged region) experiences a radial drawing stress and tangential compressive stress due to material retention properties. Deep drawing is always accompanied by other forming technique within the press. These other forming method includes trimming, bulging, sidewall piercing, crimping, date or pattern stamping and etc. Industrial uses of deep drawing processes include automotive body, structural parts, aircraft components, utensil, etc.

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Figure: Schematic of the Drawing process 3.2.4 Roll forming: Roll forming is a process by which a metal strip is progressively bent as it passes through a series of forming rolls.

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Figure: Various Bending Operations

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Figure: Eight-roll sequence for the roll forming of a box channel
4. Dies and Punches

� Simple: Single operation with a single stroke.
� Compound: Two operations with a single stroke.
� Combination: Two operations at two stations.
� Progressive: Two or more operations at two or more stations with each press stroke, creates what is called a strip development.

Corrugated Sheet: Most of us are familiar with corrugated cardboards, used to make cartons, boxes and shipping containers. Corrugated cardboards, made of flimsy paper, are more rigid and stronger than a stack of plain paper. This is due to the wavy pattern in which the papers are arranged. The same principle applies in case of corrugated sheet metal roofing too. Corrugated metal sheet roofing uses metal sheets as roofing materials which have a wave-like pattern (with ridges and grooves). This pattern gives them extra strength, despite being lightweight. These corrugated metal roofing sheets are stronger than plain metal sheets.

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Figure: Corrugated Sheet
Corrugated sheet metal roofing is available in copper, aluminium, zinc alloy and stainless steel. All these types vary in their features like durability, appearance and cost. Among them, aluminium is most preferred for residential purposes, as it is inexpensive and extremely lightweight. It is also durable and is resistant to rust, even if there is no coating, though for better looks and a longer lifespan, they are usually coated and painted. Stainless steel corrugated sheets come with a 'tern' coating, which gives a natural matte-grey finish to the roofing. However, this type is very expensive. Corrugated metal sheet roofing is also available in copper. They are resistant to rust and corrosion, and are very easy to install, but very expensive. Metal sheet roofing can also be made of alloys, which are very strong and durable, but again, the cost of alloys are on the higher side.

Advantages of Corrugated Sheet Metal Roofing: The most popular feature of this roofing material is its durability. These roofing sheets can easily last for about 20 to 50 years. Corrugated metal roofing sheets are treated and coated with chemicals to prevent the growth of algae and mildew. They are also resistant to rot, rust and insects. Other beneficial feature include its non-combustible nature. These sheets have a Class A fire rating, which is the highest rating as far as fire-resistance is concerned. They are also lightweight, which facilitates easy installation and reduces the load on the roof structure Large sprung curves. Most metal roofing products require very little or no maintenance.

Disadvantages of Corrugated Sheet Metal Roofing: One of the common problems of corrugated metal sheet roofing is that it is prone to denting. It can be caused by any heavy object which falls on the roofing. Even hailstorms can lead to dents in your metal sheet roofing. Another drawback is the high cost of installation, but this is usually offset by the very less maintenance or repair work required by this type of roofing. Most people also complain about the noise created by rain falling on these metal sheets. This, however, can be reduced by using any insulation beneath the sheet at the time of installation. Corrugated sheet metal roofing, though long lasting, may scratch, chip, peel or fade with time. Care must be taken on large roofs to provide for thermal expansion and movement. Movement caused by differences in temperature may cause objectionable noises in some roofs; for example, curved roof surfaces. However, this is not a common occurrence. Care must be taken with all metal roof products to avoid the use of incompatible materials. Dissimilar metals can cause unexpected and rapid corrosion.

Applications:-
� Green houses
� Swimming Pool and Stadium Roofing
� Industrial Roofings
� Building and Construction

Thickness: 0.76 mmto 1.5 mm
Colours: Clear, Opal, Bronze, Grey, Green, Blue, and Customized Colours.

Junoon`s Wiki

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