Sheet Metal Process

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Sheet Metal ProcessWorking of sheet metal from 16 gauge down to 19 gauge with the help of hand tools and simple machines into various forms by cutting, forming into different shapes and joining is called sheet metal process.

Knowledge of three things are important for sheet metal work1.Geometry

2.Mensuration (he branch of geometry that deals with the measurement of length, area, or volume)

3.Properties of Metals

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Applications of sheet metal work

1.Production of hoppers and funnels

2.Production of guards, covers and hoods

3.Production of pipes and bends

4.Production of boxes.

5.Used in automobile industries.

6.Used in household equipment.

7.Used in building works.

8.Used in ship building, aircrafts, etc.

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Metals used for sheet metal work

Black iron • It a bluish-black in appearance and it is uncoated Sheet which corrodes

rapidly. • The use of this metal is limited to articles that are to be painted or

enameled such as tanks, pans, stove pipes, etc.

Galvanised iron • It is a soft steel coated with molten zinc to resist rust and to improve its

appearance. • This metal can be soldered easily. • It is used for products such as buckets, pans, furnaces, heating ducts,

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Metals used for sheet metal work

Copper• It is reddish coloured metal which is ductile and malleable.

• This metal does not deteriorate rapidly by the atmosphere,

• This metal can be used in electric field, water pipe, roofing, gutters, etc.

Aluminium : • It is silvery white in colour with a high strength to weight ratio and good

corrosive resistant qualities.

• It can be easily fabricated.

• It can be used for refrigerator trays, windows, duct work, construction of airplanes.

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Metals used for sheet metal workStainless steel

• It is an alloy of steel possessing the ability to resist corrosion without any surface coating.

• It can be used for buildings, food handling equipments, kitchenwares, etc.

Tin plate • It is a steel sheet coated with pure tin. • It is having a bright silvery appearance and used for making containers, cans and pans.

Terne plate • It is a thin steel coated with a mixture of molten tin and lead. • It is having dull appearance and is used for roofing and tanks

Lead • It is very soft and heavy metal.• It is used in highly corrosive acid tanks.

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Desirable properties of sheet metal work

1.Good corrosive resistance.

2.High formability.

3.Good weldability.

4.Highly weather and chemical resistant.

5.Sheets should have high strength.

6.Should have enough ductility.

7.Possess good surface finish.

8.Good machinability.

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Sheet Metal Gauges Standard Gauge Numbers (SWG)

• Use of gauge is to designate the thickness of sheet metal.

• Gauge is defined differently for ferrous (iron-based) and nonferrous metals (e.g., aluminum and brass).

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(SWG)

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Sheet Metal Operations

1. Shearing

1. Cutting off 2. Parting 3. Blanking 4. Punching5. Notching 6. Slitting 7. Lancing

2. Bending3. Drawing4. Squeezing.

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Sheet Metal Operations - Shearing

Shearing is a general sheet metal cutting operation and involves three basic steps

• Plastic deformation takes place first

• Fracture takes place as the tool moves further

• Shear takes place finally

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Sheet Metal Operations

Cutting off : It is the process of severing a piece from a strip with a cut along a single line.

Parting: It is the process of removing the scrap between the two pieces to Part them

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Sheet Metal Operations

Blanking: It is the process of cutting a whole piece from sheet metal such the at the piece removed is the useful part required

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Sheet Metal Operations

Punching: It is the process of producing circular holes in a sheet metal with a punch or die.

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Sheet Metal Operations

Notching : It is the process of removing the metal of desired shape from the side or edge of a sheet or strip.

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Sheet Metal Operations

Slitting : When shearing is conducted using rotary blades, the process is referred to as slitting. It cuts the sheet metal length-wise

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Sheet Metal Operations

• Lancing : It is the process of making a cut part way across a strip.

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Bending

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Bending

Bending is a process by which a straight length is transformed into a curved length to a desired angle. When the metal bends, the metal is stressed beyond the elastic limit in tension on the outer side and in compression on the inside of the bend. There is only one line, the neutral line which retains its original length.

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Drawing

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Bending

• Drawing is the process of producing thin-walled hollow or vessel shaped parts from sheet metal.

• The drawing process can be divided into two types, deep drawingand shallow drawing

• Deep drawing the length of the object to be drawn is deeper than its width. E.g: Tubes

• In shallow drawing or box drawing : The length of the object to be drawn is less than the width. For ex : seamless pots, tubs, cans and covers, automobile panels, tops and hoods etc.

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Squeezing

• Squeezing is a quick and widely used way of forming ductile metals.

• Common squeezing operations• Sizing• coining• hobbing• ironing • riveting

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Sizing

• Here the metal is deformed to a particular size by applying force

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Coining

• The coining process involves the production of impression and raising of images or characters from a punch and die into the metal. The metal is made to flow, and design opposite to the one on the die is formed on the coined piece.

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Ironing

• Ironing is the operation in which a hard punch is pressed over a sheet metal cup placed over the stationary die to reduce its thickness

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Hobbing

• Hobbing is the process of deforming the metal to a specific surface shape using the die of required shape and applying required force

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Riveting

• Riveting operation is carried out to join two metal strips

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Press work

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Press work

• Press working may be defined as the chipless manufacturing process by which various components are made from sheet metal.

• This process is also known as cold stamping.

• The press is a metal forming machine tool designed to shape or cut metal by applying mechanical force or pressure.

• The presses are exclusively used for mass production work and they represent the fastest and most efficient way to form a sheet metal into finished.

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Types of presses

A. According to the source of power

1. Hand press / ball press / fly press

2. Power Press (Mechanical / Hydraulic / Pneumatic)

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Types of presses

A. According to the Design of frame

1. Gap

2. Inclinable

3. Adjustable

4. Horn

5. Straight side

6. Pillar

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Types of presses

A. According to Actions

1. Single Action

2. Double Action

3. Triple Action

B. According to Mechanism

1. Crank type

2. Eccentric type

3. Cam type

4. Toggle joint

5. Rack and Pinion

6. Gear

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Press operation

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Working of Press work

• Power press ram can be driven by hand or it can be driven by power

• The power press may be operated mechanically (by and electric motor) or by hydraulic or pneumatic power where compressed fluid gives the necessary power

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Mechanical power press

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Mechanical power press operation• A simple working of mechanical power press driven by crank and connecting rod

mechanism as shown in figure

• The punch is fitted to the ram end and the die is fitted on the bolster plate.

• The fly wheel is mounted at the end of the crank shaft. When the power is switched on, the motor rotates the flywheel fixed on the crank shaft and this rotary motion is converted into reciprocating motion by means of crank shaft and ram with punch moves downward to press the sheet metal between the punch and die.

• The flywheel is used to store the energy for maintaining a constant downward speed of the ram when the sheet metal is pressed between the punch and the die.

• In this press the motor runs continuously and stores energy in the flywheel. When the operator presses a foot pedal or actuates a button, the clutch gets engaged, the punch moves towards the die and sheet kept between the punch and die is deformed

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Hydraulic power press operation

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Hydraulic power press operation

• The operating principle of hydraulic power press is shown in fig. It essentially consists of double acting cylinder, ram directly attached to the piston in a cylinder, upper die and lower die.

• Fluid under presser forces the piston downwards which causes the ram and upper die to move downwards and press against the lower die.

• For return stroke, the fluid enters from the lower side and pushes the piston up.

• These press require greater maintenance than mechanical press.

• The piston movement is quite slow thus the squeezing action is completely carried to the Centre of the workpiece being pressed.

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Ball or Fly press

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Ball or fly press

• It consists of a C-shaped rigid casting machine frame to withstand the repeated heavy thrust exerted by a ram as shown in figure

• The front face of the frame is open to facilitate the feeding of the sheet metal below the ram from side of the machine.

• The screw of the press operates in a nut by means of handle at the top end of the frame.

• The two heavy iron balls are mounted at the two ends of the arm, which is bolted to the screw so that when the handle is turned, it causes the screw to rotate within the nut to move the ram up and down in the guides

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Ball or fly press• The ram is attached to the lower end of the nut and the punch is

attached to the lower end of the ram. The punch and die constitute the press tool.

• The die is fixed over the press table known as bolster.

• The ram is taken up slowly to the sufficient height and then the sheet metal to be formed is placed between the punch and die. Now the handle is rotated to store the kinetic energy in the two heavy balls, which forces the ram to move downward with high pressure.

• The pressing of sheet by the ram against the die with high pressure causes the sheet to form a desired shape. Abdul Khader AA

05 Marks Questions :

1. State the uses of sheet metal in engineering. May 2017)

2. Explain properties and gauges of sheet metal. (Dec. 2016)

3. Name different metals used for sheet metal work. (May 2016)

4. Explain shearing and bending operation of sheet metals.

5. Explain briefly with sketch drawing operation of sheet metal.

6. Explain briefly squeezing and blanking operation of sheet metal (Nov. 2015, Dec. 2016)

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10 Marks Questions

1. Explain with necessary sketches of different shearing operations in sheet metals. 10

2. Explain with sketch the following sheet metal operations :a) Bending b) Drawing. 10

3. a) State any Four applications of sheet metals. (Nov. 2015) 04

b) Explain following shearing operation in sheet metal a) Cutting off b) Blanking. 06

4. a) State any three applications of presses. 03

b) Explain Power press with a neat sketch. (Dec. 2016) 07

5) a) State any three applications of presses. (May 2016) 03

b) Explain Ball or fly press with a neat sketch. 07

6. Briefly explain lancing (May 2017)

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