SHEET METAL PROCESS
- 1. SHEET METAL PROCESSES Sheet metal characteristics - Typical shearing operations, bending and drawing operations – Stretch forming operations –– Formability of sheet metal – Test methods – Working principle and application of special forming processes - Hydro forming – Rubber pad forming – Metal spinning – Introduction to Explosive forming, Magnetic pulse forming, Peen forming, Super plastic forming.
- 2. Introduction The working of metal thickness from 3mm to 5mm with hand tools and simple machines into various forms is known as sheet metal work. Sheet metals Black iron Galvanized iron Stainless steel Brass Copper Zinc , Aluminium, tin plate and lead.
- 3. Sheet metal hand tools: 1. Measuring tools 2. Straight edge 3. Steel square 4. Scriber 5. Divider 6. Trammel points 7. Punches 7. Chisel 9. Hammers 10. Snips or shears 11. Pliers 12. Stakes 13. Groovers 14. Rivet set and 15.Soldering iron. Measuring tools are steel rule, folding rule, circumference rule, vernier caliper, micrometer, thickness gauge and sheet metal gauge.
- 4. Shearing process: The process which applies shearing force to cut, fracture or separate the material is called shearing. The following shearing processes are commonly carried out: Punching Blanking Perforating Parting Notching Lancing
- 5. Forming process: The process which causes the metal to undergo shape changes without failure, excessive thinning or cracking is called forming. Various forming processes used in sheet metal work as follows: Bending Stretching Drawing Roll forming.
- 6. Finishing process: The process which improves the final surface characteristics is called finishing.
- 7. CHARACTERISTICS OR PROPERTIES OF SHEET METALS Strength: The strength of a sheet metal is the property of resistance to external loads or stresses while not causing the structural damage. Tensile strength: Tensile strength is the ability of a metal to resist being pulled apart by opposing forces acting in a straight line. Compressive strength: Compressive strength is the ability of a material to withstand pressures acting on a given plane. Shear strength: Shear strength is the ability of a materials to resist being fractured by opposing forces acting in a straight line but not in the same plane.
- 8. Elasticity: Elasticity is the ability of material to return to its original size, shape and dimensions after being deformed. Also, the property of regaining the original dimensions upon removal of the external load is known as elasticity. Ductility: Ductility is capacity of a material to be drawn or stretched in to wire under tension loading and permanently deformed without rupture or fracture. Plasticity: Plasticity is the ability of a metal to be deformed extensively without rupture.
- 9. Toughness: Toughness is a combination of high strength and medium ductility. Toughness is the ability of a material or metal to resist the fracture after the damage has begun. Hardness: Hardness is the ability of a material to resist penetration and wear by another material. Brittleness: Brittleness is the property of breaking the material without visible permanent deformation. It is the reverse of toughness.
- 10. Corrosive resistance: Corrosive resistance is the resistance to eating away or wearing by the atmosphere moisture or other agents such as acid. Springback: The tendency of the metal that tries to resume its original position causing a decrease in bend angle is known as springback. The spring back varies from 0.50 to 50 for steel. Greater spring back is caused by a larger bend radius. Elongation: It is the capability of the sheet metal to stretch without necking and failure.
- 11. SHEARING PROCESS Shearing is a metal fabricating process used to cut straight lines on flat metal stock. During the shearing process, an upper blade and a lower blade are forced past each other with the space between them determined by a required offset. Normally, one of the blades remains stationary. This action has three important basic stages. Plastic deformation Shear and Fracture.
- 12. stages of the shearing process
- 13. SHEET METAL OPERATIONS Sheet metal operations are under the following two categories: Shearing or cutting operations Forming operations.
- 14. Shearing or Cutting Operations Shearing operations, the workpiece is stressed beyond its ultimate strength and cut-off into two pieces. The common shearing operations are described below. Blanking: Blanking is the operation of cutting a flat shape from the sheet metal as shown in Figure 4.2. The metal that is punched out is called ‘blank’ and the metal left out is called ‘scrap’.
- 15. (a) Punching or Piercing: Punching operation is producing the hole on the workpiece by a punch. In punching, the removed metal is called scrap and the left out metal is called workpiece.
- 16. Shearing: It is the operation through which a metal is cut along a single line, usually a straight line as shown in Figure
- 17. Notching: Notching is the operation through which the metal pieces are cut from the edge of a sheet, strip or blank as shown in figure
- 18. Perforating: Perforating is multiple holes which are very small and close together are cut in flat work material as shown in Figure Slitting: In this operation of making an unfinished cut through a limited length and projecting slightly as shown in Figure .
- 19. Lancing: Lancing consists of cutting the sheet metal through a small length and bending this small cut portion downwards Figure
- 20. Forming Operations Bending: Bending is the operation of forming the metal between a suitably shaped punch and forming block. Drawing: Drawing is the operation of a punch which forces a sheet metal blank to flow plastically into the clearance available punch and die surfaces so as to acquire the required shape.
- 21. Squeezing: In squeezing operation, the metal is caused to flow to all portions of a die cavity under the action of compressive force.
- 22. Coining:
- 23. Embossing:
- 24. Curling:
- 25. Nibbling: Nibbling is a process of punching series of small overlapping slits or holes along a path to cut-out a larger contoured shape. This operation is used to cut any shape from the sheet metal without special tools. The time taken to cut the required shape is less compared to other cutting processes .It is done on a nibbling machine.
- 26. SELECTION OF PRESS: The following factor should be considered while selecting a press for a given workpiece Force required to cut the metal Die space Size and type of die Stroke length Method of feeding and size of sheet blank Shut height Type of operation Speed of operation
- 27. Advantages of press working: Material economy Reduction of weight and considerable cost reduction of fabricated parts High productivity Use of unskilled labour High degree of precision Uniformity of parts Predictable strength characteristics Use of less labour Possibility of automation
- 28. TYPES OF PRESSES; 1. According to the source of power a. Manually operated- Hand, ball of fly presses b. Power presses – Mechanical, hydraulic 2. According to the type and design of frame: a. Inclinable, b. straight side c. Gap frame d. Horning e. Adjustable bed, f. Open end 3. According to the position of frame A. Inclinable b. Vertical C Horizontal d. Inclined 4. According to the action A. Single action b. Double action c. Triple action.
- 29. PRESSES
- 30. Mechanically Operated Power Press or OBI Press(open back inclinable)
- 31. Inclined Press
- 33. Arch press: These type of presses are suited for blanking, bending & trimming used in paint cans forming shovels & kitchenware. Straight side Press: This frame are used both mechanical and hydraulic presses. These presses are high capacity presses with increased strength and rigidity of the frame. Horn press: Mainly used for cylindrical objects performing seaming, flanging, punching, embossing and riveting operations. Crank driven press: The ram or slide moves up and down within the guide when the crank rotates. Rack and gear driven press: The pinion gear rotates, the ram connected with rack slides up and down. To raise the ram quickly, a quick return motion mechanism will be incorporated.
- 34. Types of Cutting Dies 1.Progressive Dies
- 35. Compound Dies
- 36. Blanking
- 37. Piercing
- 38. SHEARING OPERATION - BENDING TYPES OF BENDING OPERATION - Angle Bending
- 39. - Angle Bending - Roll Bending
- 40. - Roll Forming If the edges are formed to a desired shape in the form of bend is made on the sheet metal - Seaming The process of providing lock between the two edges of the different work metal. SHEARING OPERATION - DRAWING - Deep Drawing Length of the part drawn is deeper then width. - Box Drawing Length of the part drawn is lesser then width
- 41. DRAWING PROCESS Drawing is the operation of producing cylindrical or shell shaped components by applying the required force using a die set.
- 42. Factors affecting Drawing Type of material Ductility Yield strength Force of friction Blank holder pressure Lubrication Radius on punch Radius on die Drawing speed Die clearance.
- 43. REDRAWING The process of deepening the cup after the first draw is known as redrawing. If the deep drawing process cannot produce a cup sufficiently deep in one operation, then redrawing operation is used. It may be obtained by any one of the following three methods: Direct redrawing Indirect redrawing Ironing.
- 44. Direct Redrawing
- 45. Indirect redrawing or reverse drawing
- 46. Ironing
- 47. STRETCH FORMING OPERATION Stretching is the process of stressing the work blank beyond its elastic limit by moving a form block towards the blank. FORM BLOCK METHOD
- 48. FORM BLOCK METHOD MATING DIE METHOD
- 49. SPECIAL FORMING PROCESSES 1.0 HYDRO FORMING 1.Hydro Forming 2. Rubber Pad Forming 3. Metal Spinning 4. Explosive forming 5.Magnetic pulse forming 6. Peen forming 7. Super plastic forming a) Hydro Mechanical forming b) Electro Hydraulic Forming
- 50. 1) Hydro mechanical Forming
- 51. b) Electro Hydraulic Forming
- 52. 2.0 RUBBER PAD FORMING
- 53. Punch is called male die and upper pattern is called female parts is just move and touch on the work. The force is applied gradually increased on the blank through rubber die. The blank holder ring is used to distribute uniform pressure thought out the blank. The required shape is formed on the sheet metal between male and female parts. The retainers are placed on both sides of the rubber pad. Function of retainers to apply hydrostatic pressure on the blank and prevents sideward motion. The rubber pad is released by moving upward. The completed shell is stripped out from the punch.
- 54. Advantages: Process is more economical Tooling cost is less Many required shapes can be formed in one rubber pad There is no need of lubricants No thinning metal blank take place Tool setting time is less Deeper shells can be drawn Limitations Rubber pads will wear out rapidly Sharp corners cannot be made accurately.
- 56. Force is applied on the blank through a pressurized liquid behind the rubber pad. The force is used to form the sheet metal into the required shape. Rubber act as a seal between pressure forming chamber And blank. Due to application of hydrostatic pressure over the blank is formed into required shape. Hydro forming presses, the hydraulic pressure energy is directly applied over the surface of the blank. Rubber pad forming press, the pressure is applied over the surface of the blank by the rubber pad which is operated by hydraulic ram.
- 57. 3.0 METAL SPINNING a) Manual Spinning b) Power Spinning Applications: Ash trays, flower pots, lamp shades, missile and radar units
- 58. Form block is mounted on the head stock of the spinning lathe. The blank is tightly held between form block and tail stock spindle. The required contour surface is made on the form block The pressure is applied by the roller type forming tool which is placed on the tool post of the spinning lathe. The required shape is gradually formed by continuous application of pressure by the roller. During spinning process, some stretching and thinning of material take place. Spinning speed varies with size, design, type of metal and thickness sheet metal. Al, copper, brass and stainless steel can be spin in the spinning process. The lubricants of grease, linseed oil and bees wax are used.
- 59. 4).EXPLOSIVE FORMING PROCESSES - Stand off operations The explosive charge is located at some distance away from the blank and energy is transmitted through some fluid medium such as water. - Contact Operations The explosive charge is directly located over the blank. AEROSPACE COMPONENTS
- 60. Explosive forming process is used for blanking, cutting expanding, coining, embossing, flanging, power compacting, drawing and sizing operations etc. Various forms such as rod, sheet granules, liquid, stick etc Contact operation: Explosive charge is directly located over the blank. This operation is mainly used for welding, hardening, compacting and cutting process. Advantages: Less capital investment Presses are not required Only one die is enough to form the sheet metal Required shapes of components are formed in one stroke Large and complex shapes can also be handled.
- 61. 5.0 MAGNETIC PULSE FORMING PROCESS
- 62. Advantages: This process is carried out with uniform rate of forming The surface finish of the process is excellent Time of operation is less as compared to conventional process Disadvantages: Non conducting materials are not processed without aid of conducting materials It is limited for sheet metal forming process not an forming bulk material. Applications: Producing bulging of tube, shrinkage of tube, attaching tube, forming a torque joint forging of structural joints, instrument gear assembly, embossing and sizing of cups
- 63. 6.0 PEEN FORMING PROCESS
- 64. Peen forming is a process of well established surface cleaning. In this process, a stream of metal shots is blasted against the surface of the blank to be made into required shape. A stream of small ball is suddenly forced with very high velocity against the surface of the blank. Used to form irregular contour surfaces of al sheet and plates. The length of contour of the blank to be formed may be larger. Advantages: Complex contour can be produced easily Does not require any die and punch
- 65. Disadvantages: It requires longer time for forming the required shape It requires additional devices for forming out metal shots Applications: Used in producing specific portions on crankshaft, connecting rods and gears. It is used for producing honeycomb panels like aircraft wings and large tubular shapes.
- 66. 7.0 SUPER PLASTIC FORMING PROCESS a) Loading b) Forming c) Forming d) Release
- 67. SPF is valuable tool for the fabrication of complex parts used in the aircraft and automobile industries. SPF of sheet metal has been used to produce very complex shapes and integrated structures and lighter and stronger than the assemblies they replace SPF process, the material is heated to the SPF temp within a sealed die. Inert gas pressure is then applied, at a controlled rate forcing the material to take the shape of the die pattern. The flow stress of the material during deformation increases rapidly with increasing strain rate Super plastic alloy can be stretched at higher temp by several times of their initial length with out breaking.
- 68. SPF process: Consists in hot forming up to 1000 celsius super plastic alloys by using an inert gas pressured up to 50 bars. Combined with diffusion bonding, this process allows honeycomb structures made of several sheets in a single operation. Loading: The blank is loaded in the form die. The hot press heats the die and the blank pressure to the material super plastic temp Forming: Once the temp is reached, it is accurately controlled, the gas pressure slowly inflates the blank. The gas keeping inflating the part to fit the die. The material at the super plastic temp can allow up to 500% elongation.
- 69. BASIC SHEARING OPERATION 1.0 Cutting operations (a) Blanking
- 70. BASIC SHEARING OPERATION 1.0 Cutting operations
- 71. BASIC SHEARING OPERATION 1.0 Cutting operations
- 72. BASIC SHEARING OPERATION 2.0 Forming operations (a) Bending (b) Drawing (c) Sequeezing (d) Embossing (e) Nibbling It is an operation of cutting any shape from sheet metal without special tools. It is done on a nibbling machine.
- 73. FORMABILITY OF SHEETMETAL Formability = f(f1, f2) F1 = Material Variables - ductility F2 = Process Variables – stress system, lubrication, die design etc Law 1 – Process of fracturing Ductility of the same material is lower if the section size is large. Law 2 –Law of geometrical Similitude 1 Blank are geometrically similar to dimension, thickness, width etc. 2 Unit strain at corresponding locations are identical 3 Forces required directly proportional to the square of the thickness . 4 Consumption of work proportional to the cube of its thickness.
- 74. FORMABILITY TEST METHOD 1 Formability tests for bulk deformation Elastic deformation and Plastic deformation 2 Formability test for elastic plastic deformation 1) Tensile test a) Stretch forming - local thinning b) Drawing operation – Lower punch by thinning under bi-axial stresses. 2) Simulative tests a)Erichsen test – Stretchability based on erichsen number b)Olsen test c) Swift test - based on blank to punch diameter- drawing ratio d) Fukui test – both assessed - based on formability index
- 75. FORMABILITY TEST METHOD 3) Full scale forming test