SHEET METAL PROCESS

Introduction about sheet

1. SHEET METAL PROCESSES
Sheetmetalcharacteristics-Typicalshearingoperations,bendingand
drawingoperations–Stretchformingoperations––Formabilityofsheet
metal–Testmethods–Workingprincipleandapplicationofspecial
formingprocesses-Hydroforming–Rubberpadforming–Metal
spinning–IntroductiontoExplosiveforming,Magneticpulseforming,
Peenforming,Superplasticforming.

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 0.5
0
to 5
0
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 workpieceis 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

32. Inclinable Presss

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. SHEARINGOPERATION-BENDING
TYPESOFBENDINGOPERATION
-AngleBending

39. -AngleBending
-RollBending

40. -RollForming
Iftheedgesareformedtoadesiredshapeintheformofbendis
madeonthesheetmetal
-Seaming
Theprocessofprovidinglockbetweenthetwoedgesofthe
differentworkmetal.
SHEARINGOPERATION-DRAWING
-DeepDrawing
Lengthofthepartdrawnisdeeperthenwidth.
-BoxDrawing
Lengthofthepartdrawnislesserthenwidth

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. STRETCHFORMINGOPERATION
Stretchingistheprocessofstressingtheworkblankbeyonditselasticlimit
bymovingaformblocktowardstheblank.
FORMBLOCKMETHOD

48. FORMBLOCKMETHOD
MATINGDIEMETHOD

49. SPECIALFORMINGPROCESSES
1.0HYDROFORMING
1.HydroForming
2.RubberPadForming
3.MetalSpinning
4.Explosiveforming
5.Magneticpulseforming
6.Peenforming
7.Superplasticforming
a)HydroMechanicalforming
b)ElectroHydraulicForming

50. 1)HydromechanicalForming

51. b) Electro Hydraulic Forming

52. 2.0RUBBERPADFORMING

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.

55. RUBBERHYDROFORMING PROCESS

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. 3.0METALSPINNING
a)ManualSpinning
b)PowerSpinning
Applications:Ashtrays,flowerpots,lampshades,missileandradarunits

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).EXPLOSIVEFORMINGPROCESSES
-Standoffoperations
Theexplosivechargeislocatedatsomedistanceawayfromtheblank
andenergyistransmittedthroughsomefluidmediumsuchaswater.
-ContactOperations
Theexplosivechargeisdirectlylocatedovertheblank.
AEROSPACECOMPONENTS

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. 5.0MAGNETICPULSEFORMINGPROCESS

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. 6.0PEENFORMINGPROCESS

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. 7.0SUPERPLASTICFORMINGPROCESS
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. BASICSHEARINGOPERATION
1.0Cuttingoperations
(a)Blanking

70. BASICSHEARINGOPERATION
1.0Cuttingoperations

71. BASICSHEARINGOPERATION
1.0Cuttingoperations

72. BASICSHEARINGOPERATION
2.0Formingoperations
(a)Bending
(b)Drawing
(c)Sequeezing
(d)Embossing
(e)Nibbling
Itisanoperationofcuttinganyshapefromsheetmetal
withoutspecialtools.Itisdoneonanibblingmachine.

73. FORMABILITYOFSHEETMETAL
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. FORMABILITYTESTMETHOD
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. FORMABILITYTESTMETHOD
3) Full scale forming test