Sheet Metal Work

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Metal Work

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<ul><li><p>UNIT 4 SHEET METAL WORK Structure </p><p>4.1 Introduction 4.2 Sheet Metal Materials 4.3 Sheet Metal Tools 4.4 HEMS 4.5 SEAMS 4.6 Sheet Metal Operations 4.7 Development Procedure 4.8 Experiment No. 1 4.9 Experiment No. 2 </p><p>-- </p><p>4.1 INTRODUCTION </p><p>Sheet metal work is generally regarded as the working of metal from 16 gauges down to 30 gauges, with hand tools and simple machines into various forms by cutting, forming into shape and joining. - - </p><p>4.2 SHEET METAL MATERIALS .- </p><p>Black Iron It is also known as uncoated sheet since it carries no artificial coating on its surfaces. However, it is probably the cheapest of all types of sheets used in sheet metal work. Being uncoated, it is prone to corrosion. Consequently, its use is confined mostly to the manufacture of such items which are to be painted before shipment, e.g. block iron is used in tanks, pans, trunks, stove pipes, etc. </p><p>Galvanized Iron Zinc coated iron is called 'Galvanized iron'. This soft steel sheet is popularly known as GI sheet. The zinc coating resist rust, improves the appearance of the metal and permits it to be soldered with greater ease; but welding is not so easy as zinc gives toxic fumes and residues. Because of zinc it can with stand contact with water and exposure to weather, e.g. articles like cabinets, trunks, buckers, pans, etc. are made of galvanized iron sheets </p><p>Copper Sheets These sheets are relatively costlier but having specific advantages in being good corrosion resistant and good in appearance. They are reddish in colour and their cold rolled variety, which is vastly used in sheet metal work, is highly ductile and malleable and therefore can be easily worked. Some representative examples of automobiles, various applications in chemical plants, domestic heating appliance, etc. </p><p>.4luminum Sheets On account of it's inherit weakness it is not used in its pure form. The useful variety of aluminium alloy. Which is rolled into sheet form, carries additions of suitable amount of silicon, manganese copper and iron. It is whitish in colour and light in weight. It offers very high resistance to corrosion and abrasion. Its coinmon applications are aeroplane bodies, kitchen ware, etc. </p></li><li><p>Workshop Technology Tin Plates Laboratory </p><p>The nomenclature tin plates are used for those iron sheets which are coated with pure tin. As a result, these sheets which are coated with pure tin. As a result, these sheets provide a bright silvery appearance. They offer good resistance to corrosion and rusting and are mainly used for making packed food containers, cans, etc. </p><p>Stainless Steel </p><p>It is highly corrosion resistant alloy steel, which exhibits a bright surface without any coating. Though it is a little tougher than galvanized iron, in sheet form it can be shaped and span. It is widely used for making kitchen ware, food handling equipment, etc. </p><p>Brass </p><p>It is basically an alloy of copper and zinc and is available in many shades and colours. In sheet and strip forms it is used in many cold working processes, such as deep drawing, pressing, stamping, spinning, etc. Earlier it used to be the principal metal for making kitchen ware and utensils. But, now it is largely replaced by stainless steel and aluminum. </p><p>I I Lead I </p><p>It is a very soft, weak, low melting point, malleable and heavy metal and possesses high resistance to acid corrosion. Due to low mechanical strength it is normally used in foil form to provide lining for containers and other articles made from some stronger material. It finds its application in sheet form in radiation shielding and an inner lining for acid tanks. </p><p>Zinc </p><p>It is bluish white metal and is quite ductile. In sheet form it is widely used for roofing work. But, in many other forms, it has its applications in coating, die casting, etc. </p><p>SHEET METAL TOOLS </p><p>Measuring Tools </p><p>Steel Rule </p><p>It is useful in measuring and laying out small work. It can be measure with accuracy of 0.5 mm. </p><p>Folding Rule </p><p>This is very useful in measuring and laying out larger work, the accuracy being 0.5 mm. </p><p>Steel Circumference Rule This is used to find out directly the circumference of a cylinder. </p><p>Swing Blade Protractor </p><p>This is used for marking and measuring angles. </p><p>Venzier Calliper </p><p>This is used for measuring dimensions up to 0.02 mm. </p><p>Micrometer Caliper </p><p>This is used to measure the thickness of metal sheets accurately up to 0.01 mm. </p><p>58 </p></li><li><p>Thickness Gauge Sheet Metal Work </p><p>This is also called slip gauge and is used to measure the clearance between the parts during assembly. </p><p>Sheet Metal Gauge This is used to measure the thickness of sheets. </p><p>Figure 4.1 : Different Parts of External Micrometer </p><p>Straight Edge and Steel Square I Straight Edge i </p><p>This is a flat graduated bar of steel with one longitudinal edge beveled. This bar comes in variety of lengths ranging from 1 to 3 meters. It is useful for scribing long straight lines. </p><p>Steel Square It is a T-shaped piece of hardened steel with marks graduated on the edges for measuring. The narrow arm of the square is called tongue and the wider part is known as the body. It is used for marking in the perpendicular direction to any base line. </p><p>Figure 4.2 : Vernier Caliper </p><p>Scriber, Divider and Trammel Points Scriber </p><p>This is sometimes called the metal workers pencil. It is a long wire of steel I with its one end sharply pointed and hardened to scratch lines on sheet metal </p><p>I in laying out patterns. i Dividers Dividers are used for drawing circles or arcs on sheet metal. They are also used to mark a desired distance between points and to divide lines into equal </p></li><li><p>Workshop Technology Trammel Points Laboratory </p><p>The trammel points consist pf a bar with two movable heads. It is used to draw large circles or arcs that are beyond the limits of the divider. </p><p>Punches A Punch is used in sheet metal work for marking out work, locating centers, etc. in a more permanent manner. Two types of punches are generally used : Prink Punch </p><p>It is used to make small marks on layout lines in order to mark the prick punch marks longer. </p><p>Center Punch It is used on1 y to make the prick punch marks larger at the centers of holes that are to be drilled. Solid and hollow punches are very similar the other two puncher the inner and outer faces of the punch meeting at an angle of 400.These are used for making small holes from 2.5 mm to 10 mm. </p><p>A hand level punch is sometimes used for making holes with a punch and die incorporated in the tool when a large number of holes are to be punched. </p><p>Chisel and Hammers Chisels </p><p>They are generally used in sheet metal work for cutting sheets, rivets, bolts and chipping operations. A good number of cold chisels are used. The flat chisel and round nose chisel are most widely used in sheet metal work. </p><p>Hammers They are used for forming shapes by hallo\;ling, raising, stretching or throwing off. These are many types of hammers but the most commonly used hammers are : Riveting Hammer </p><p>Uscd for riveting. Setting Hammer </p><p>Useful for setting down the edge, when making a double seam. Raising Hammer </p><p>Used for forming of a flat sheet of metal into a curved or hallow shape such as a square, bowl, tray, etc. </p><p>' Mallet These are soft hammers and made of saw hide, hard rubber, copper brass, lead or mostly of wood, used to strike a soft and light blow on the metal. </p><p>- </p><p>Rivet~ng Hammers </p><p>Figure 4.4 : Hammers for Sheet Metal Work </p></li><li><p>Figure 4.5 : Mallet </p><p>Sheet Metal Work </p><p>Snips of Shears A snip, also called a hand shear is used like a pair of scissors to cut thin, soft metal. It should be used only to cut 20 gauge or thinner metal. There are several types of snips available for making straight or circular cuts, the most common being straight snip have straight blade for straight line cutting while curved or bent snips have curved blades for making circular cuts. Both these snips are very light and can be easily handled by one hand. These are also double cutting shear, squaring shear, ring shear and circular shear used for particular requirements as the name indicates. The heavier classes are known as bench shears and block shears where one handle may be held in vice bench plate while the other handle is moved up and down to do the cutting. </p><p>Cut Only 20 Gauge of Thinner Metal </p><p>A Hand Shears w </p><p>Bent Shears </p><p>Straight Shears </p><p>Figure 4.6 : Snips and Shears I Stakes </p><p>Stakes are the sheet metal workers evils used for bending, seaming or forming, using a hammer or mallet. They actually work as supporting tools as well as forming tools. They also help in bending operation. They are made in different shape and sizes to suit the requirements of the work. </p><p>1 Double Seaming Stake i Use to make double seam I i Beak-hum Stake </p><p>Used for riveting, fonning around and square surfaces, bending straight edges and making corners. </p><p>Bevel Edge Square Stake I Used to form comer and edges. 1 Hatchet Stake </p><p>Used to make straight, sharp bends and for folding and bending edges. Needle Case Stake </p><p>I Small tubes and pipes are performed on it. </p></li><li><p>Workshop Technology Elow Horn Stake Laboratorv </p><p>Cone shaped articles are formed on it. Hallow mandrel Stake </p><p>Used for riveting, seaming and forming. </p><p>Needle case stake </p><p>Blowhorn stake Hatchet stake </p><p>Wlow mandrel stake </p><p>Figure 4.7 : Common Forms of Stakes </p><p>Groovlng with a hand groover </p><p>A Rivet set </p><p>Pliers Figure 4.8 </p><p>Common forms of soldering iron </p><p>Pliers are used for holding, cutting and bending work Flat Nose Pliers </p><p>IJsed for forming and holding work. Round Nose Pliers </p><p>Used for holding and forming various shape and patterns. Groover's and Rivet Sets </p><p>Hand Groover This is used for groove and flattern a seam. It is available in many shapes. </p><p>Rivet Set This is hardened steel tool with hollow in one end. It is used to shape the end of a rivet into round, smooth head. </p></li><li><p>Soldering Iron Sheet Metal Work </p><p>They are used for soldering work and consis1 of a forged piece of copper joined to an iron with a wooden handle. These are also called soldering coppers. They are made in various shapes and sizes. </p><p>Half moan Blck lron Funnel stake Convex </p><p>Horse head </p><p>Figure 4.9 : Soldering Iron Other General Tools </p><p>Brick Iron Used in forming long tapered cylindrical items. </p><p>Funnel Stake Used for conical works. </p><p>Side Stake Similar to brick iron but smaller in size. </p><p>HalfMoon Stake For working the edges on discs. </p><p>Pipe Stake Used for forming tubes. </p><p>Creasing Stake Used for forming beads. </p><p>Convex Stake For spherical work. </p><p>Horse Bead Used for bending and general work for supporting and holding other stakes. </p><p>Bumping Hammer Curved shapers are raised in sheet metal with the help of this tool. </p><p>- - - </p><p>4.4 HEMS </p><p>A Hem is an edge or border made by folding. It stiffens the sheet of metal and does away with the sharp edge. Three common types of hems are : Single Hem </p><p>It is made by folding the edges of the sheet metal over the make it smooth and stiff. </p><p>Double Hem It is mad- by folding the edges over twice to make it stiff and smooth. </p><p>Wired Edge </p></li><li><p>Workshop Technology 4.5 SEAMS Laboratory </p><p>A Seam is a joint made by fastening two edges together. Most common types of seams are : </p><p>Lap Seam It is the simplest type of seam and can be prepared as lap joint by means of soldering. </p><p>Grooved Seam It is made by hooking two single hems together and then locking them by a groover. </p><p>Single Seam It is used to join a bottom to vertical bodies of various shapes. </p><p>Double Seam It is similar to single seam with the difference that its formed edge is bent upward against the body. </p><p>Dovetail Seam It is similar to dovetail joint in carpentry and is used to join flat plate to a cylindrical piece. </p><p>Burred Bottom Seam It is also called Flanged Seam. It is used to join the bottom of a container to its body. The flange on cylindrical jobs is often referred to as a burr and the process of making a narrow edge is known as burring. </p><p>Step 1 Step 2 Step 3 Open Fold Making Wired Edge </p><p>a Wired Edge </p><p>Step 1 </p><p>Step 1 Step 2 Step 3 Setting Making Double Down a Double Seam Seam </p><p>A o r n e r Fold </p><p>Step 1 Step 2 Figure 4.10 : Pattern Making a Corner Fold </p></li><li><p>4.6 SHEET METAL OPERATIONS </p><p>4.6.1 Measuring and Marking The standard market sizes of metal sheets are quite large. But the required sheet size for making component may be much smaller. So, a standard size sheet may have to he cut into several smaller pieces, each piece being sufficient for making one such component. These smaller sizes are first decided and then these sizes are marketed on the larger sheet to cut the latter into small pieces along the masked lines. A little allowance for cutting is always added to the required overall sizes so that the cut pieces are not undersize. Overall dimensions, length and breadth of the required smaller pieces are marked on the large sheet with the help of marking tools, including a steel rule, a straight edge, a steel square etc and a scriber. The sheet surface may have to be coated with a colouring medium, such as cellulose lacquer, so that the scribed lines are clearly visible. If circular pieces are needed a divider or trammel may have to be used to mark the circles. Their sharp points (tips of legs) work as scriber. Similarly, in mass production of identical small items the blank can be marked using a template and a scriber. </p><p>4.6.2 Cleaning Many a times the blank surfaces need proper cleaning before being processed. This requirement is more prominent in case of non-ferrous metal sheets, like those of copper, brass and silver. For cleaning the surfaces of these blanks pickling process is used. It involves immersing the blank in a pickle both, consisting of one part of dil. &amp;So4 and twenty parts water. This bath is heated and the blanks immersed in the hot bath. After allowing sufficient time for pickling the blanks are thoroughly washed in a stream of water and then allowed to dry. Cold pickling is also sometimes used in such cases where cleaning operation is not required very frequently, but in such cases either the pickling personal is to be increased or a smaller acid to water ratio of the pickle has to be used so as to ensure an effective cleaning of the surface. </p><p>4.6.3 Laying Out It means the operation of scribing the development of the surface of the component on the sheetlsheet blank, together with the added allowances for overlapping, bending, hammering, etc. which when cut out of the blank and folded and joined will give the required component. Such a layout when made on the sheet is called a pattern and the process as pattern layout. If, however, the job to be made are small and in large number it is better to use a template for repetitive marking of the development and then cutting it along the marked contours. The template size will, obviously, include the required allowances. </p><p>Shearing Down Cutting Off Parting </p><p>Blanking Punching or Piercing </p><p>Lancing Nibbing </p><p>/ / , / / I f / / / / / / Llne of Cut </p><p>Notching Slitting </p><p>Drawn Pan </p><p>Figure 4.11 </p><p>Sheet Metal Work </p></li><li><p>Workshoe Technology 4.6.4 Cutting and Shearing Laboratory </p><p>The word cutting is used when the sheet metals is cut by means of a chisel a hammer manual....</p></li></ul>

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