Q.11 What do you mean by sheet metal forming (or press work)?
Ans. Sheet metal forming process is used to produce file cabinets, car bodies, utensils etc. Sheet metal parts are lighter than cast and forged parts. Versatile shapes can be achieved through sheet metal working. Low carbon steel is very suitable for sheet metal jobs. Aluminium and its alloys are used for aircraft applications.
Sheet metal is produced by rolling process. It is generally coiled after rolling if the sheet is thin; if thick, it is available as flat sheets or plates.
The basic mechanisms of sheet metal working are bending, stretching, thinning, compression, etc.
The major factors that influence the overall operation are : elongation, yeild point elongation, grain size, residual, stresses, springback, and wrinkling.
Sheet metal work requires adequate knowledge of geometry, mensuration and mechanical and physical properties of the metal because the patterns used in sheet metal operations are obtained from the development of the surfaces of a number of geometrical models, e.g. cylinder, cone, pyramid, prism, etc.
In sheet metal working, the metal used may be black iron, galvanized iron, aluminium, tin, brass, copper, stainless steel, lead, etc. Metal sheets are specified by standard gauge numbers.
Q.12 Define Coining, Embossing and Metal Spinning process with neat sketches.
Ans. Sheet metal forming process is used to produce file cabinets, car bodies, utensils etc. Sheet metal parts are lighter than cast and forged parts. Versatile shapes can be achieved through sheet metal working. Low carbon steel is very suitable for sheet metal jobs. Aluminium and its alloys are used for aircraft applications.
Sheet metal is produced by rolling process. It is generally coiled after rolling if the sheet is thin; if thick, it is available as flat sheets or plates.
The basic mechanisms of sheet metal working are bending, stretching, thinning, compression, etc.
The major factors that influence the overall operation are : elongation, yeild point elongation, grain size, residual, stresses, springback, and wrinkling.
Sheet metal work requires adequate knowledge of geometry, mensuration and mechanical and physical properties of the metal because the patterns used in sheet metal operations are obtained from the development of the surfaces of a number of geometrical models, e.g. cylinder, cone, pyramid, prism, etc.
In sheet metal working, the metal used may be black iron, galvanized iron, aluminium, tin, brass, copper, stainless steel, lead, etc. Metal sheets are specified by standard gauge numbers.
Q.12 Define Coining, Embossing and Metal Spinning process with neat sketches.
(AKTU - 2008-09)
Ans. Coining: -
Coining is the operation of producing coins, medals, etc. Coining involves cold squeezing of metal while all of the surfaces are confined within a set of dies. The metal is coined in a completely closed die cavity.
Embossing: -
Embossing is the operation of producing raised or depressed impression of letters, design figures on sheet metal parts. It is commonly used in producing name plates, number plates, identification tags on thin sheet metal or foils.
Coining is the operation of producing coins, medals, etc. Coining involves cold squeezing of metal while all of the surfaces are confined within a set of dies. The metal is coined in a completely closed die cavity.
Embossing: -
Embossing is the operation of producing raised or depressed impression of letters, design figures on sheet metal parts. It is commonly used in producing name plates, number plates, identification tags on thin sheet metal or foils.
Metal Spinning Process: -
Metal spinning is the process of shaping thin sheet metal by pressing it against a form or pattern while it is rotating. Spinning can be performed on lathe machine. The shape to be produced on the sheet metal part is made of wood or metal and is known as former.
Q.13 Give a brief account of die and punch assembly.
Ans. Die and Punch Assembly: -
For a specific operation or job on a press special tooling is designed. The tooling consist of a die and punch assembly or simply a press tool die. The various components of a die and punch assembly are shown in Fig. A simple description of each part is also given :
(1) Punch: -
It is the male member of the unit and is usually small, having sufficient strength and rigidity. The punch is made of hard and wear resistant metal.
(2) Punch Holder: -
It is anchored to the lower end of press ram with the help of a shank. It provides a wide flat surface and is made of cast steel.
(3) Die Block : It is the female working member which contains a die cavity.
(4) Die Holder : It is mounted on the bolster plate of the press. Both the guide post and die block are mounted on the die holder.
(5) Guide Posts and Bushings : These are used to hold the punch and die members in proper alignment during an operation.
(6) Bolster Plate : It is a thick plate secured to the press bed and is used for locating and supporting the die assembly. It is usually 5 to 12.5 cm thick.
(7) Stripper Plate : It is used to free the punch from scrap strip during the returning motion of the punch.
(8) Pilots : These are used in progressive dies to bring the stock into the correct position for the successive blanking and piercing operations.
Q.14. What is difference between punching and blanking? (AKTU - 2012 - 13)
Ans. Punching: -
Punching is a metal forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing. The punch often passes through the work into a die. A scrap slug from the hole is deposited into the die in the process. Depending on the material being punched this slug may be recycled and reused or discarded. Punching is often the cheapest method for creating holes in sheet metal in medium to high production volumes. In forging applications the work is often punched while hot, and this is called hot punching.
Blanking: -
Blanking is the operation of cutting a desired shape from a metal strip. The metal punched out from the strip is known as blank. The metal punched out (blank) is the required product in blanking which is used for further operations. The remaining metal strip is scrap. Blanking is a basic die-cutting operation. A blanking die must have clearance, otherwise the blank would not fall freely, it might retain struck in the die block.
[I] Choose Correct Answers
1. Which of the following operation is used to produce sheet & plates :
(a) Extrusion (b) Spinning (c) Rolling (d)deep drawing
2. Forging of metal is a (AKTU - 2008-09)
(a) Machining process (b) Welding process
(c) Joining process (d) Metal forming process.
(a) Machining process (b) Welding process
(c) Joining process (d) Metal forming process.
3. Metal forming is the process in which (AKTU - 2008-09)
(a) Removal of metal takes place
(b) Shaping of metal by forces applied through various dies and tools.
(c) Some additional materials are joined to the raw material.
(d) Material addition, through melting and pouring.
4. At large scale seamless tubes can be produced by :
(a) Embossing (b) Coining (c) Rolling (d) Extrusion
5. Hot working process take place at temperature, which is
(a) higher the recrystallization temperature
(b) Lower the recrystallization temperature
(c) equal the recrystallization temperature
(d) none of above
(a) higher the recrystallization temperature
(b) Lower the recrystallization temperature
(c) equal the recrystallization temperature
(d) none of above
6. The process which takes place below recrystallization temperature is known as
(a) Hot working process (b) casting process
(c) cold working process (d) none of above
(a) Hot working process (b) casting process
(c) cold working process (d) none of above
7. Nuts and bolts are manufactured by
(a) Hot piercing (b) extrusion (c) cold peening (d) embossing
(a) Hot piercing (b) extrusion (c) cold peening (d) embossing
8. Recrystallization temperature of steel is
(a) 10000C (b) 5000C (c) 4000C (d) 8000C
(a) 10000C (b) 5000C (c) 4000C (d) 8000C
9. Cold or hot working of metal increases
(a) hardness (b) yield strength
(c) tensile strength (d) all of above
(a) hardness (b) yield strength
(c) tensile strength (d) all of above
10. Process of shaping thin metal sheets by processing then against a form is known as
(a) Upsetting (b) Spinning (c) Rolling (d) Extrusion
(a) Upsetting (b) Spinning (c) Rolling (d) Extrusion
11. In drawing operation the metal flow due to
(a) Plasticity (b) Malleability (c) Brittleness (d) Shearing
(a) Plasticity (b) Malleability (c) Brittleness (d) Shearing
12. Cold or hot rolling does not produce
(a) Channel section (b) T section
(c) l section (d) a hollow circular section
(a) Channel section (b) T section
(c) l section (d) a hollow circular section
13. Suitable material for extrusion is
(a) Stainless steel (b) low carbon annealed steel
(a) Stainless steel (b) low carbon annealed steel
(c) low carbon work hardened steel (d) Cemented carbide
14. Which one is correct about result of cold working
(a) it increases strength, hardness and elasticity
(b) handling of parts is quite easy
(c) dimension tolerances and finish are relatively high
(d) all the above
(a) it increases strength, hardness and elasticity
(b) handling of parts is quite easy
(c) dimension tolerances and finish are relatively high
(d) all the above
15. Work hardening is the cold working process in which
(a) hardening increases (b) hardness decreases
(c) increase in corrosion resistant (d) none of them.
(a) hardening increases (b) hardness decreases
(c) increase in corrosion resistant (d) none of them.
16. The process by which strong components can be produced
(a) Casting (b) Forging (c) Moulding (d)Cold rolling
(a) Casting (b) Forging (c) Moulding (d)Cold rolling
17. Coining process is a
(a) hot forging process (b) cold forging process
(c) hot rolling process (d) extrusion process
(a) hot forging process (b) cold forging process
(c) hot rolling process (d) extrusion process
18. In which process the reducing diameter of round bars and tube rotating die which open and close rapidly on the work.
(a) Hot rolling (b) Coining
(c) Rotary swaging (d) Mounding
(a) Hot rolling (b) Coining
(c) Rotary swaging (d) Mounding
19. Press working of metal is a (AKTU - 2008-09)
(a) Machining process (b) Welding process
(c) Joining process (d) Metal forming process.
[II] True or False Statements
(a) Machining process (b) Welding process
(c) Joining process (d) Metal forming process.
[II] True or False Statements
20. Hot working is carried out below the recrystallization temperature. (AKTU - 2008-09)
1. (c) 2. (d) 3. (b) 4. (d) 5. (a)
6. (c) 7. (a) 8. (d) 9. (d) 10. (b)
11. (a) 12. (d) 13. (b) 14. (d) 15. (a)
16. (b) 17. (b) 18. (c) 19. (d) 20. (F)