Now – a – days, we are using many such things in our daily lives, which are made from metal sheets such as boxes, tanks, trays, etc. It is one of the fundamental forms used in metalworking and it can be cut and bent into different shapes. Sheet metal work can be done with metal such as iron, steel, aluminum, copper, brass, tin plates, etc provided that they can be easily rolled into thin sheets.
Sheet metal is generally considered to be a plate with a thickness of less than about 5 mm. It is used as automobile bodies, utensils, almirah, electronic or electrical components, refrigeration and air-conditioning parts, etc. The wire gauge is used to measure the thickness of sheets.Â
Sheet metal work is generally regarded as the working of metal from 10 gauge down to 30 gauge with hand tools and simple machines to shape and join. In this chapter, we will study different types of sheet metals, their tools, and all related aspects.
Types of Sheet Metals
The thickness of sheet metal is measured and represented by the number of Standard Wire Gauge (SWG). The relation between the SWG and the thickness of the sheet is that they are inversely proportional to each other i.e., if the number of SWG is less then the thickness of the sheet is more, and if the SWG value is more than the thickness of the sheet is less. Many types of sheets are used in sheet metal shops, which are as follows.
1. Iron Sheet
In sheet metal shops, mostly iron sheets are used because the iron sheet has various properties such as malleable, ductile, toughness, hardness, etc. These are available in different types as follows.
(i) Black Iron Sheet
It is an uncoated iron sheet, which corrodes rapidly and is made up of either mild steel or wrought iron. Due to the effect of the atmosphere, it becomes rusty. It is generally soft, ductile, and malleable, so it will be printed after making your job. It is used to make pipes, tanks, etc.
(ii) Galvanised Iron SheetÂ
To obtain galvanized iron sheets, first of all, available sheets are washed and then dipped into the tank, which is filled with molten zinc. The layer of zinc coats on iron sheet. These sheets are called galvanized iron sheets. These are free from rust. It is used to make articles such as pans, buckets, tanks, boxes, etc.
(iii) Tin Coated Sheet
Tin-coated sheets are those iron sheets, which are coated with tin. These sheets are free from rust and have a better appearance. The process of coating with tin is called tinning. It is used for making household utensils, pans, etc.
2. Copper Sheet
These sheets are more soft and ductile as compared to the iron sheets. Due to this, any type of designing or carving is done easily. It has more flexibility so that it can be easy to bend in any shape. It is a good conductor of heat and electricity. It is used to make home utensils, pipes, and electric materials.
3. Brass Sheet
These sheets are mainly made up of an alloy of copper and zinc. These sheets are tough as compared to the normal copper sheets. It has no effect on the atmosphere. It is used to make utensils.
4. Aluminium Sheet
These sheets are soft, ductile, anti-corrosive, and cheaper. It is used to make household utensils and also used in airplanes. It is a good conductor of heat and electricity.
5. Stainless Steel Sheet
Stainless steel is an alloy of iron and chromium. It has good corrosion resistance and is used in dairy food processing, doctor’s apparatus household utensils, etc. It has no effect on acid, alkaline rust, etc.
6. Lead Sheet
These sheets are very flexible in their physical structure. These have no acidity, these are used in the internal lining of the iron-made tanks.
In the sheet metal shop, during operations such as marking layout, hammering, bending, forming, punching, for molding the metal into sheets, we need some tools that help in performing an operation in the sheet metal shop, these are discussed here.
Tools of Sheet Metal Shop
In sheet metal shop, the following types of tools and types of equipment are used as below.
1. Measuring Tool
A device used to inspect, measure, or examine parts in order to determine compliance with required specifications is known as a measuring tools. Measuring tools are divided into different types, which are used in metal shops.
(i) Steel Rule
It is made up of stainless steel and available in different lengths such as 6″, 12″, or 24″ (150 mm, 300 mm or 600 mm). It can measure a minimum length of up to 0.5 mm or 164 an inch.
(ii) Steel Tape
It is used to measure long lengths of sheets. It is available up to three meters in length.
(iii) Wire Gauge
Wire gauge is used to measure the thickness of wires or metal sheets in millimeters or the number of standard wire gauges, wire gauge value is from 0 (zero) to 40. Here, 0(zero) means maximum and 40 means the minimum number of standards.
The thickness of the wire or sheet is indirectly proportional to gauge numbers.
(iv) Steel Square
It is made up of hard steel strips in L-shape. Both sides are at the right angle to each other. It has one side greater than the other, the long side is known as the blade, and the short side is called the tongue. Steel square is normally 90°, but squares are also available in 60°, 45° and 30° in different sizes. Steel square has marks on both sides in mm and inch.
2. Marking Tool
To make various designs of metal sheets, we need different types of tools for marking the accurate size of the job.
(i) Divider
It is used to draw a 200 mm radius of a circle or arc on the metal sheets and also used to divide a line in equal division. These are made up of high carbon steel or mild steel with hard and temper points.
It is used for marking dimensions accurately. It consists of a joint pair of legs, such with a sharp point.
(ii) Wing Compass
It is used for marking on metal sheets, which is like a divider, in which at a certain distance, a wing is attached to a compass. The nut is provided in the wing for fixing the compass legs at a certain distance.
(iii) Trammel
It is used to make a large circle or an arc having a large e-radius. A good trammel has a scale in inches and millimeters. Some trammel is attached with an extra fine adjusting carrier for fine adjustment. These are available from 15 to 50 cm.
(iv) Scriber
It is a tool that is used in marking lines on metal sheets. To draw the shape (as we draw lines on paper with the help of a pencil or pen) is called a scriber. It is normally made up of carbon or steel of thick wire. Both edges are sharp and on temper. One edge of it bends at 90°, its both points are ground to 15° to 20° (angle) as shown in the figure. They are available in different shapes.
To draw a shape, first hold firmly the job and then incline the scriber in the direction of the stroke and draw towards you.
(v) Scratch Awl
It is used as a scriber for marking the metal sheets as shown in the figure. Its one edge is sharp. Its handle is made up of wood and fixed at another end.
3. Striking Tool
All those tools, that are used to perform operations such as bending, expansion straightening riveting, etc, then job are called striking tools. These are mainly of three types as given below.
(i) Hammer
(ii) Mallet
(iii) Power Hammer
(i) Hammer
Sheet metal can be shaped by hand with the help of a hammer i.e., the hammer is used to strike metal for high expansion, bending and riveting, etc. The following types of hammers are generally used in sheet metal shops.
(a) Ball Peen Hammer
It is a peening hammer, that has two ends. One end is shaped such as an ordinary hammerhead while the other is ball-shaped. Its handle is made up of wood. It is used to spread metal in all directions.
(b) Cross Peen Hammer
A hammer with a blade-like peen at the right angle to the handle. It has a wedge shape at one end. It is used for forging. It is used to spread metal only in one direction and makes grooves in the sheet or bend the sheet at an angle.
(c) Straight Peen Hammer
A hammer with a blade-like peen is parallel to half. One end of the head is round and has a flat face. The other end is wedge-shaped. It is also used to spread metal in one direction but it is at the right angle to the line striking.
(ii) Mallet
It is also called a soft hammer and is generally made up of wood, hard rubber nylon, Teflon lead, or rawhide. It is used to fold or straighten ten thin metal sheets. A mallet strikes a blow with the minimum, damage to the surface. In sheet metal work, mostly, wooden mallets are used several types of mallets are used such as below.
(a) Standard Mallet
A standard mallet is used for general work like bending and making sheets straight. Its both faces are flat from both sides.
(b) Bossing Mallet
Both faces are in round shape and used for hollowing, panel beating, etc.
(c) End Faked Mallet
It is similar to the cross-peen hammer as shown in the figure. It is used for hammering, stretching, and carving the sheet metal. hammering, stretch
(iii) Power Hammer
Power hammers are mechanical forging hammers that use a non-muscular power source to raise the hammer preparatory to striking and accelerating it auto the work being hammered. It is also called open-die power forging hammer. A typical power hammer consists of a frame, an anvil, and a reciprocating ram holding a hammerhead or die. The workpiece is placed on the lower anvil (die) and the head (upper die) strikes the workpiece.
The power hammer stores potential energy in an arrangement of mechanical linkages and springs in compressed air or steam. It accelerates the ram on the downward stroke, which provides more force than simply allowing the weight to fall.
Power hammers are rated by the weight of moving parts that act directly on the workpiece. Power hammers are generally categorized into the following categories.
(a) Steam Hammer
Steam hammers use steam to drive the hammer. These tend to be the largest models as the great energy of steam was needed to operate them.
(b) Mechanical Hammer
This hammer tends to be smaller and was operated by a single man. These mechanical linkage machines were powered by line shaft flat belt systems or by electric motors that rotate a crank on the machine which has the ram.
(c) Air Power Hammer
Air power hammers use pneumatics to drive the hammer. It is a small hand-held or free-standing hammer used in fabrication work, forging, driving nails, etc.
4. Cutting Tool
These tools are used for cutting metal sheets as per requirement. Therefore, the selection of cutting tools always depends on the thickness of the sheet. Thus, cutting tools are classified as follows.
(i) Snip
It is also called a hand shear and similar to the scissors. It is made up of high-carbon steel and its cutting edges are hard and tempered. It is used to cut metal sheets up to 1.2 to 11.29 mm thickness. Its cutting blades are ground at an angle of 80°.
According to its construction, there are two types of snip as given below.
(a) Straight Snip
It is used to cut a big circular curve or straight line. It has a straight blade.
(b) Bent Snip
 It has curved blades for marking circular cuts. It is also used for cutting sheets in cylindrical or conical shapes.
(ii) ShearÂ
It is used to cut metal sheets which are not possible or very difficult to cut by snip but can easily cut by shear.
Its blades are grinded at 87°. As per work, these are classified into three types.
(a) Stock Shear
(b) Block Shear
(c) Bench Shear
Mostly, stock shear and block shear are used to cut thick stocks and trips. Due to certain disadvantages, these shears are rarely used in sheet metal shops.
Bench shear is used to cut metal sheets. It is fixed on the table with the help of nuts and blots. The long handles are used with bench shear to make it easy to cut. The long handle is also called the shear lever. If we down the shear lever, then the blade moves downward with rotates on the pivot.
(iii) Shearing Machine
The shearing machine is made up of straight blades that act stock without making a formation of chips or making use of burning or melting. Shearing machines are commonly used to produce sheet metal or plates.
However, rods can also be sheared. The process covered by the shearing machine includes blanking, piercing, roll slitting, and trimming. The shearing machine is of two types as given below.
(i) Hand-operated shearing machine
(ii) Mechanical shearing machine.
(i) Hand Operated Shearing Machine
Hand-operated shearing machines are used for cutting small sheets up to 0.8 mm in thickness. Its one end is fixed while the other is movable.
A hand-operated machine may be fitted on the table.
(ii) Mechanical Shearing Machine
Mechanical shearing machines are used for cutting sheets up to 6 mm thick. It also has one fixed and one movable blade. Generally, these machines are robust in construction and granted on the floor.
5. Piercing Tool
Those tools, which are used to make holes in solid metals or sheet metals are called piercing tools, which are as follows.
(i) Solid Punch
It is used to make holes in metal sheets. For making holes, a thick wooden piece is placed at the bottom of the sheet for support, then a solid punch is placed at that point and struck by the hammer, so by this process.
(ii) Hollow Punch
It is a hollow punch and is used to make holes in thin metal sheets. e.g., Aluminium, copper, leather, rubber, plastic flat belt, etc. When you use a hollow punch, must be used to a thick wooden piece at the bottom of the sheet for support.
(iii) Pin Punch
It is used to remove pins or rivets from the metal sheets and pipes. It is available in different diameters, one set has 3, 4, 5, 6, and 8 mm diameter pin punches.
6. Stake
When we are bending a metal sheet in different shapes. It needs special support and this support is called stake. Therefore, stakes actually work as supporting tools as well as forming tools. It consists of a shank and a head or horn. According to the work, there are different types of stakes, which are as follows.
(i) Round Bottom Stake
The round bottom stake is used to bend the sheet in a round shape. Its upper part is circular and flat. It is used in the case of hard work.
(ii) Beak Iron Stake
It is used for forming, riveting, and seaming articles made up of sheet metal parts. It is in the shape of an anvil. It has one side conical-shaped horn and a second side flat base.
The conical shape horn is used to add the substance of a funnel shape or perform in another work and a flat base is used for holding and adding rivets on the sheet or cutting the sheet in a straight line.
(iii) Hatchet Stake
It is used for making sharp bends, bending edges, and forming boxes and pans of sheet metal by hand. e.g., Tray and boxes. Its upper part is like a knife.
(iv) Half Moon Stake
It is designed with a semi-circular shape at the top and used for flanging utensils and bending sheets half-round.
(v) Funnel Stake
It is used for planishing tapered work and hand-forming funnels and similar conical shapes of sheet metal. Its one end is semi-circular and its sharp second end, is shaped like a funnel, so it is called a funnel stake.
(vi) Planishing Anvil
Planishing anvil has a flat upper plane. It is used to dress the flange portion of a job or make a hole in that job.
(vii) Creasing Iron Stake
The creasing iron stake has one side plane and the other side is straight grooves. This stakehead has grooves of different sizes. These grooves are used to bend sheets of round shapes.
(viii) Hoarse Stake
It has holes on both ends, which have shapes like a square or rectangular.
Many of the tools used in the workshop and in sheet metal works of rivets are mainly used. Those tools are specially used by a fitter so in order to have a proper knowledge of those tools, it is essential to know how to make them first. So in this way, rivets play are important role.
Rivet
To join sheets or plates together, the metal round rod is used having a head on one side and a tail on the second side of the rod, which is called a rivet.
A rivet is a permanent mechanical fastener. During installation, the rivet is placed in a punched or drilled hole, and the tail is deformed to weld the rivet in place. The original head of the rivet is called the factory head and the deformed end is called the shop head or bucktail.
The dimensions of the length and diameter of the rivet can be found as follows.
Diameter of rivet (d) = 1.2 t
Lenth of Revet (L) = t + 1.5 d
Where,Â
             T = Thickness of Plate
             D = Diameter of rivet
For countersunk rivet, the following formula is used to find out its length and diameter.
            Lc = t + 0.6 d
      d = 1.2 t
According to the shape and uses, the rivets are classified into the following types.
(i) Snap Head Rivet
It has a snap head on both sides of the metal, one is vice to support the head of the rivet, and the second to shape the tail after it has been expanding with the hammer.
(ii) Pan Head Rivet
A rivet having a head whose shape is that of a truncated cone is called a pan head rivet. It is less frequently used and difficult to form.
(iii) Mushroom Head Rivet
A rivet has a large circular head shape. It is commonly used for aluminum boat manufacturing. It has a corrosion resistance property.
(iv) Flat Head Rivet
It is made up of mild steel, stainless steel, copper, brass, and aluminum and its alloys. It is widely used in metal roof finishing.
(v) Flat Countersunk 90° Rivet
It has a round part hex and fluted body shapes. It is flat, countersunk, and flush head styles at open and closed ends. It is made up of stainless steel.
(vi) Oval Countersunk 60°
Rivet Its tapper sunk is 60′. It is made up of mild steel. It has flush head styles and open and closed ends. It is also known as a rounded countersunk rivet.
(vii) Tubular Rivet
It is a special type of rivet which is used at a place where no space is available to make the head of rivet. These types of rivets are generally used in aircraft.Â
It is of two types as follows.
(a) Pop Rivet
It is a pipe-shaped hollow rivet, whose stem is like a nail. It is fitted by using a special type of device i.e., a riveting gun.
(b) Hank Rivet
It is bush-shaped. It is fitted in the threaded hole of the sheet. The stem of the rivet is made flat after riveting with the help of the hammer.
Tinman rivet
Tinman rivet consists simply of a shaft and head, which are deformed with a hammer or rivet gun. The use of a rivet compression or crimping tool can also be used to deform this type of rivet. This tool is mainly used on rivets close to the edge of the fastened material since the tool is limited by the depth of its frame.
Riveting Joints
When metal sheets are joined with each other by rivets, this type of joint is called the riveting joint.Â
There are two types of riveting join which are as follows.
(i) Lap Joint
It is very frequently used in metalwork. When the edges of the two plates are to be connected and overlap each other all rivets pass through both plates, then a lap joint is formed.
These are of two types as given below.
(a) Single riveted lap joint
(b) Double riveted lap joint
(ii) Butt Joint
In these types of joints, two metal plates are placed in such a way that their ends face each other and a metal strip is placed over them, then riveted. Strip is used on either one side or both sides of the plate.
Butt joints are of the following types.
(a) Single riveted single cover butt jointÂ
(b) Single riveted double cover butt Joint
(c) Double riveted double cover chain butt Joint
(d) Double riveted double cover zig-zag butt joint
Riveting Tools
The tools which are used to fit the rivets in the sheets are known as riveting tools. They are of many types and are distinguished from one another according to their uses.
(i) Rivet Set
It is like a hollow punch so that the rivet stem enters into the rivet set hole. It is used to bring two sheets close to each other.
(ii) Dolly
It is used to give support to the rivet head. Its face has a cavity in which the rivet head is fitted so that it protects the rivet head from any type of damage.
(iii) Rivet Snap
It is used to give accurate shape to riveted joints. Its function is to give the correct shape and size on both sides of the rivet.
(iv) Drift
It is a cylindrical punch and is available in different diameters to correct the rivet hole by bringing in a straight line. It is made up of steel, then hardened and tempered. It is used for finishing the size of punched holes.
(v) Caulking Tool
It is used to set the plate’s ends and rivet head edges in line with the plane surface.
(vi) Fullering Tool
It is a tool that is used to make leakproof joints. Joining two plates’ edges together.
Hem
The hem is an edge or border made by folding. It stiffens the sheet of metal and avoids sharp edges. It also prevents damage and wear of the edge.
There are three types of hem as discussed below.
1. Single Hem
A single hem is made by folding the edge of the sheet metal with a single fold.
2. Double Hem
The double hem is made by folding the edges over twice to make it smooth. This is a thicker and safer hem, which has more strength.
3. Wire Edge
Wire edge is done to provide more strength to the job by bending the edge of the job and placing a mild steel wire in the bend.
Seam
After the sheet metal has been formed to the required shape, the edges must be joined to hold the shape rigidly together and in some instances to make the article waterproof and sometimes airtight. These joints are called seams.
There are the following types of seam.
1. Lap Seam
The lap seam is a basic metal seam, where the edge of one piece overlaps the other or is hooked with one another and then joined by soldering or brazing. Lap seams are often used to connect two ends to make a cylinder and are used in making boilers, auto bodies, wall panels, metal sculpture, and metal roofing.
2. Grooved Seam
It is made by hooking two folded edges of sheet metal parts together and then offsetting the seam. The seam as shown in the figure on one piece draws one line equal to half the width of the seam from one edge. Then, draw the second line at a distance equal to the width at the seam from the first line.
3. Single Seam
It is used to join the bottom of buckets or boxes, etc. The joint is also known as a paned paned-down joint make this joint, leak-proof soldering is done.
4. Double Seam
It is similar to the single seam. If a single seam joint stands straight, then it is called a double seam and it is stronger than a single seam.
5. Double Grooved Seam
In double grooved seam, the edge of the sheet is twisted and hooked with another twisted sheet as shown in the figure. These types of seams are used in roofs.
A device, which is to locks the seam formed in the sheet is known as a groover.
Notch
In the process of laying out on sheet metal part, some provision is to be made for bent sections, when they have folded edges. The openings left at corners of seams and edges of sheet metal parts are called notches.
There are different types of notches, which are as follows.
1. Straight Notch or Slit
It is prepared by making a straight cut, where the bend is to be made in sheet metal part.
2. Square Notch
It is made when forming a rectangular or square box with inaccurate measuring.
3. Slant Notch
It is used where single hems are to meet at the right angle. In this process, they should be clipped at a 45° angle on the sheet. metal part.
4. V-Notch
V-notch is made by cutting both sides at 45° to the edge of the sheet when making a job with a 90° bend.
5. Wire Notch
The main function of a wire notch is to prevent the wire edge from overlapping the seam. To make a wire notch, a cut made at a distance of 312 of wire diameter from the top at an angle of 30°
Precautions to be taken in Sheet Metal Shop
(i) Your feet must be protected by sturdy shoes. Open-toe or sandals are not permitted
(ii) Any oil spill, coolant, or other fluid spill must be removed from the floor immediately. Use paper towels, a wiping cloth, or a mop.
(iii) Long hair and loose dress or tie pose an extreme safety hazard around machine tools and therefore, must be netted for safety.
(iv) Use a brush (table brush or paint brush) to clear chips from machine tools, do not use your hands or a rag.
(v) Rags must be kept clear of the rotating parts of machinery. If for any reason a rag gets caught in a machine switch off the machine and stand clear of it until it comes to a complete stop.
(vi) All soiled rags must be stored in the covered metal containers provided.
(vii) Remove burrs/sharp edges from parts immediately after they are machined to avoid cuts on your hands in addition, parts with burrs or sharp edges will receive reduced credit when evaluated for grading.Â
(viii) Watches and rings are to be removed during lab periods. Do not leave your watch or ring on the table in the classroom or on the sink.
(ix) A shop apron or shop coat is recommended to protect your clothing Shirt sleeves are to be either short or rolled up above the elbow. Loose sweaters and jackets are to be removed.
(x) Do not remove any guards or shields from any piece of equipment.Â