SHEET METAL WORKS Sheet Metal Works Involves the Development of Surface Or Layout of the Sheet for Many Important Engineering Ar

SHEET METAL WORKS

Sheet metal works involves the development of surface or layout of the sheet for many important engineering article for applications in houses, agriculture machine, decorative articles etc. it involves manufacturing articles from sheet metal or thin sheets. Sheet metal is generally considered to be a plate with thickness less than about 5 mm. As compared to casting and forging, sheet-metal parts offer advantages of lightweight, less expensive and versatile in shapes. There is also no need for further machining as required for casting and forging works.

Types of Sheet Metals Metals used in sheet metal work are black iron, galvanized iron, stainless steel, copper, brass, zinc, aluminum, tin plate and lead. Black Iron Sheet It is probably the cheapest of all the metal used for sheet metal work. It is bluish black in appearance and is used generally in form of uncoated sheet. It can be easily rolled into the desired thickness. Since it is uncoated it corrodes rapidly. Hence to increase its life it can be painted or enameled. This metal is generally used in the making or roofs, food containers, stove pipes, furnace fittings, dairy equipment, tanks, cans and pans, etc. Galvanized Iron (G.I.) It is popularly known as G.I. sheets. It is soft steel coated with molten zinc. This coating resists rust formation on surface and improves appearance and water resistance. Articles such as pans, furnaces, buckets, cabinets etc. are made from GI sheets. Copper sheet It is commonly used for making radiators of automobile engine, heating appliances, equipment for chemical plant. These sheets are costly and have better resistance to corrosion. Brass sheet They are used in making varieties of articles through cold working process like pressing, drawing, etc. It is often used for making kitchen wares and utensils. Tin sheet They are tin coated and have silvery appearance. They offer good resistance to rusting and atmospheric corrosion. They are used in containers for edible oils, dairy products etc. Aluminum sheet They are extensively used in industries for dairy or milk products. They are normally used for roofing, doors, window frame, kitchen cabinets, kitchen wares, containers etc. Stainless Steel It is an alloy of steel with nickel, chromium and small percentages of other metals. It has good corrosion resistance. It is costlier but tougher than GI sheets. 1t is used in kitchenware, food processing equipment, food

1 handling articles, tools and instruments for surgery work in hospitals and components of chemical plants etc.

Tools used in sheet metal work The following tools are commonly used for sheet-metal work: (i) Measuring and marking tools These tools are used to mark the sheets according to the required dimension. The most commonly used are Steel rule T-square Scriber Divider Trammel Punches Circumference rule Vernier caliper Micrometer Thickness gauge

(i) Cutting tools Commonly used cutting tools involve types of files, chisels, hollow punch, snips, scraper and hacksaws.  Files: These are flat, square, round, triangular, knife, pillar, needle and mill types.  Chisels: The flat chisel and round nose chisel are most widely used in sheet metal work for cutting sheets, rivets and bolts.  Scrapers: These are flat, hook; triangular, half round types.  Hollow punch: used when circular holes are to be cut in thin sheet.

Hallow punch  Hacksaws: Hacksaw may be hand hacksaw or power hacksaw.  Straight snip: Blades are straight and it is used for cutting along straight lines.

Straight snip

 Bent snip: Blades are curved back from the cutting edge which allows the metals to slid over top blades.

Bent snip (ii) Striking tools Hammers The uses of different kind of hammers are given as under: (a) Smoothing hammer: used for leveling and smoothing a sheet metal joint. (b) Stretching hammer: used for stretching sheet. (c) Creasing hammer: used to close down joint edges of sheets metal part. (d) Hollowing hammer: used for hollowing sheet metal part. It is used for generating sharp radii also. (e) Riveting hammer: used for forming riveted heads. (f) Planishing hammer: used for removing small marks or indentations from the sheet metal job surface and to true the shape of the work. It smoothens off the finished sheet metal work.

Soft hammer or Mallets Mallets are used when working with soft metal sheets and light force is required. They may be of wood, rubber or raw hide. A mallet strikes a blow with the minimum damage to the surface. It is used for smoothening of sheet. In sheet metal work, the commonly used mallets are bossing mallet, tinman’s mallet and rawhide mallet.

Bossing mallet Tinman’s mallet Rawhide mallet

(iii) Supporting tools Stakes Stakes are used to form the metal sheets into various shapes. It is a sort of anvil, which supports the sheet for sheet metal work. It consists of a shank and a head or horn. The shank of stake is designed to fit into a tapered bench socket. The head or horn of stake is available in a number of varieties of sizes and shapes. Their working faces of stakes are machined or ground to needed shape. With the help of a hammer, operations such as bending, seaming or forming can be easily performed on these stakes. Some stakes are made of forged mild steel faced with cast steel whereas the better class stakes are made either of cast iron or cast steel. Types of stakes a) Beak horn stake. It is basically used for forming, riveting and seaming articles made of sheet metal part. It is not much suitable like blow horn stake. It has a thick tapered horn at one end and a rectangular shaped horn at the other. b) Funnel stake. Funnel stake is commonly used for planishing tapered work and hand forming of funnels and similar conical shapes of sheet metal. c) Half-moon stake. It is basically used for throwing up edges of curved sheet metal work and for preliminary stages of wiring curved edges. d) Round bottom stake. It is commonly used for squaring up edges and setting up the bottom of cylindrical jobs made up of sheets. e) Bick iron. It is mainly used for forming taper handles, spouts and tubular work in general. The narrow flat anvil end of bick iron is very useful on rectangular work. f) Hatchet stake. Hatchet stake is generally used for making sharp bends, bending edges and forming boxes and pans of sheet metal by hand. This stake has a sharp straight edge beveled along one side. g) Creasing with horn stake. Creasing horn stake has a round horn used for forming conical shaped pieces in sheets. The other end has a tapering square horn with grooved slots for wiring and beading. h) Needle case stake. It is generally used for bending of sheets. It has a round slender horn for forming wire rings and tubes.

i) Candle mold stake. It has two horns for different tapers when forming, seaming and riveting long flaring articles made up of sheet metal. j) Blow horn stake. Blow horn stake is generally used in forming, riveting and seaming tapered articles such as funnels. k) Conductor stake. It has two cylindrical horns of different diameters. It is used for forming, riveting, and seaming small sized pipes and tubes. l) Double seaming stake. Double seaming stake consists of two cylindrical horns of different diameters and it is commonly used for riveting forming, and seaming tubes and small pipes.

Types of stakes

Stake Holder It is a rectangular cast iron plate that has conveniently arranged tapered holes so that the various stakes may fit in and may be used in different positions for tackling the sheet metal job for a particular work.

Stake holder

(iv) Hand shears or snips They resemble a pair of scissors and are used to cut thin soft metal sheets of 20 gauge or thinner. They can make straight or circular cuts. Different types of hand shears are: Straight hand shear: It is used for general purpose cutting, making straight cuts and trimming away extra metal. Universal shear: Its blades are designed for universal cutting straight line or internal and external cutting of contours. It may be of right hand or left hand type, easily identifiable, as the top blade is either on the right of on the left. Curved hand shear: It is used for cutting circular or irregular curved shapes ranging from 20 to 35 cm.

Types of hand shear or snips

Sheet Metal Joints Joints used in sheet metal works are commonly used to fasten bottoms to cylinders, square or rectangular containers. Some of the commonly used such joints are Lap joint: It is very frequently used in sheet metal work and can be prepared by means of soldering or riveting. It is the most common type for general use. Seam joint: This joint is commonly used in sheet metal work. It is locked, so as to ensure a positive grip and also to make the joint flush with the surface. Locked seam joint: This joint is used for locking seam joints in sheet metal work. Hem (single and double), wired edge, cup and angular joints: These enable the edges of sheet metal part to join to the pieces along them. Flanged joint: It is commonly used in making pipe connections. Flush joint: Used where one face of the article is required to be level or flush. Cap joint: It provides another useful form of locked seam joint on sheet metal component with good appearance and strength. It is generally used for assembling cross seam of ducts made up of in sheet metal part.

Various types of sheet metal joints

Operations in sheet metal working A variety of shapes can be made with the help of various operations of sheet metal which are described below 1. Measuring and marking: to produce an article first of all, sheet is measured with the required dimension and then it is marked with the help of marking tools like scriber, try square, trammel etc. 2. Laying out and cutting blanks: a blank is an appropriate profile of shape and size or the article. The blank has the required amount of allowance included in its dimension as bending and lapping margins in making joints during the formation of shape of article. Blanks are cut from the sheet with the help of hand snips or shears or sometimes with a chisel and hammer. Layiong out is basically scribing the development of surface on the sheet. 3. Hand forming (Hollowing and raising): forming of metal to various shapes involves the bending of sheet metal in three dimension through stretching or shrinking the metal in all direction. Hollowing involves the stretching of sheet metal by beating it into a hollow indentation. Raising is to shrink or to reduce the circumference of blank to the desired form. 4. Nibbling: it is the process of continuous cutting along a contour which may be straight line or irregular profile, with the help of a nibbler. 5. Circle cutting: it is an operation of cutting circular blank or curved contour. It is a continuous cutting operation 6. Shearing: it involves cutting of sheet metal with the help of shear machine or snips.

7. Piercing and blanking: piercing is punching a hole while blanking is an operation of cutting a blank for further process to convert into a useful product. 8. Joint marking: sheet metal components are joined together in several ways like joining by riveting, welding, brazing, soldering, folding and adhesive joining. Edge forming and wiring: edge forming or folding of ends or edges of the sheet metal is done to provide stiffness and strength to the sheet metal product and also to ensure safety against cutting of hands during handling the sheet or the product under formation. The edges on part need to be folded to eliminate the sharp edges of sheet metal component. Sometimes the edges are reinforced further by inserting a metal wire or rod in the curled edge of the sheet. The common types of folded edges are: a) Single hem. It is made by folding the edge over. To layout such a hem, a line is drawn at a distance equal to the desired hem width. b) Double hem. It is a single hem with its end bent under. To layout such a hem, draw two parallel lines each equal to the width of the hem. c) Wired edge. It consists of an edge, which has been wrapped around a piece of wire. This edge is used where more strength is needed. To layout wired edge the diameter of wire is to be determined. The steel metal will be needed to roll around the wire.

Types of edges (i) single hem (ii) double hem (iii) wired edge 9. Flanging: it is the process of hammering the edges of a disc or cylinder in such a way that a flange of a given width is formed.

Flanging operation. (i) The complete flange (ii) Bending of flange

10. Flattening: it is the process of making a sheet flat by beating it on its face, thereby removing wrinkles and making the sheet flat.

Flattening operation: (a) sheet with wrinkles (b) flattened sheet 11. Bending: it is carried out by hammering sheet over suitable stakes, blocks of wood, angle iron, channels, etc. Sheet metal is required to be bent to different angles and curvatures by stretching the metal on outer surface and compressing it on the inner surface along the neural line during the process of making an article. 12. Drawing: it is the production of thin walled hollow shapes from the sheet metal using die and punch. In shallow drawing, the drawn length of the article is less than its diameter whereas in deep drawing, the drawn length is more than the diameter or width.