Sheet metal is generally sheets less than 6 mm thick that are produced through rolling. Sheet metal is widely used for industrial and non-industrial applications like aircraft wings, automotive body panels, and construction roofing. Some common sheet metal materials include aluminum-zinc alloy, galvanized steel, and cold rolled steel. Sheet metal parts offer advantages like good strength, dimensional accuracy, surface finish, and low cost. Common sheet metal manufacturing processes include cutting operations like punching, blanking, and piercing as well as bending, drawing, and squeezing.

1. Sheet Metal
Raviteja Gangisetty

2. What is Sheet Metal?
Sheet metal are generally sheets less than 6 mm. Sheet metal is produced by
reducing the thickness of a long work piece by compressive forces applied through
a set of rolls. This process is known as rolling.
Introduction

3. In today’s practical and cost conscious world, Sheet metal parts have already
replaced many expensive Cast, forged and machined products. The reason is
obviously the relative cheapness of stamped, mass produced parts as well as
greater control of their technical and aesthetic parameters.
Example 1:
Designing a sheet metal part as a replacement for a spot welded assembly.
(1) (2)
The figure 1 shows a conventional product having parts attached to it by spot
welding while figure 2 shows a modification of the product through sheet
metal operations.
Introduction

4. Example 2:
Designing a sheet metal part as a replacement for a machined part.
(1)
(2)
• The figure 1 shows a machined parts while figure 2 shows sheet metal parts
replaced functionally.
• Two-part clamping hub with 6 counter bores for carrier bars with threaded
stems.
Introduction

5. Sheet metal is widely used for numerous industrial and
non-industrial applications including:
Aircraft:
Wings, body panels, trim parts, etc.
Automotive :
Automotive body panels, bumpers, doors,
chassis, trim parts, brackets etc.
Construction:
Sheet metal is used for roofing, home building
and structural applications.
Other applications:
Sheet metal is used
for manufacturing appliances, food and beverage
containers, boilers, ships, kitchen equipment and office
equipment etc.
Applications

6. Advantage of Sheet Metal Parts:
• Good strength
• Good Dimensional accuracy
• Good surface finish
• Relatively low cost
• Low weight
Advantage

7. Suitability of Materials
Most of the ductile wrought metals are suitable for sheet metal working.
Formability ratings of materials:
Aluminum, copper and their alloys: Excellent
Mild steel and stainless steel: Fair to excellent
Nickel and magnesium: Fair to good
Aluminum alloys
Brass, low leaded Hot rolled steel Low carbon steel
Austenitic Stainless
steel
Cold rolled steel
High strength-low
alloy steel
Titanium and
Titanium alloys
Beryllium copper
Cold rolled aluminum-
killed steel
Low alloy steel Zinc alloys
Some of the material suitable for sheet metal working are:
Materials

8. •Aluminum-Zinc Alloy
•Aluminum-Zinc Coated Steel
•Cold Rolled Steel
•Galvanized Steel
Types Raw Sheet metal
Material

9. Aluminum-Zinc Coated Steel (Galfan) :
Galfan is a zinc alloy coating that consists of 95% zinc and 5 %
aluminum. This alloy coating provides superior corrosion protection,
extraordinary formability and draw-ability, excellent paint-ability and
good weld-ability.
Cold Rolled Steel:
Hot-rolled coils decaled by pickling are put on the cold rolling mill
where they are rolled to a specified thickness. After being rolled on a
cold strip mill, coil-rolled coils undergo a finishing process to meet
proper hardness and to prevent stretcher strains.
Galvanized Steel:
The base coil is pickled and cold-rolled then processed through
continuous galvanizing lines. The finished product has a smooth finish
with uniform zinc coating, excellent durability and workability.
Material

10. Advantages
Good Corrosion Resistance
Excellent Paintability
Easy Weldability
High Temperature Use
High ductility and strength
Excellent high and low temperature
properties
Non-magnetic
Easy to handle & Install
Aesthetic surface finish
Life-cycle costing benefits
Disadvantages
Spring back may be significant.
Non-uniform thickness may happen.
Wrinkling, earing, tearing.
GALVANISED
STEEL
Material

11. Theoretical sheet metal thickness gauges:
Non ferrous gauges (Aluminum) are not the same as ferrous gauges (Steel & stainless)
It is common practice to specify the aluminum simply in the decimal thickness.
For example, “MATERIAL : 0.100 5052-H32 ALUMINUM”.
Steel and Stainless steel are frequently specified by gauge and decimal thickness.
For example, “MATERIAL: 16 GA (.059) COLD ROLL STEEL”.
There are other gauges than those listed in this table, but these are the ones that are commonly available.
Gauges

12. BEND RADIUS GUIDE LINES ARE AS FOLLOWS:
For most materials, the minimum inner radius should be at least 1 material
thickness.
Bending using tight radiuses often results in burrs and fractures on the outside of
the bends. These can be eliminated by using larger bend radiuses and by
providing relief notches at the edges on the bend line.
Bend relief notches should be 2 times the thickness in width (min 1.5mm/0.060
in) and radius + thickness in length.
Bend radius should be kept same for all radiuses to minimize the set up
changes.
Bend relief eliminates tearing
W= 2 X thickness
L= Bend Radius + Thickness
No Bend relief
causes tearing
Bend
Radius
Design

13. Distance between two cuts or punches & Distance between
part edge and cut or punch:
For Hole
Dia <10T
For Hole
Dia <5T
1.5T
2T
For
L <10T
For
L >10T
2T
4T
Guidelines for Hole and slot spacing according to size.
Design

14. The minimum flange width should be at least 4 times the stock thickness plus the
bending radius. Violating this rule could cause distortions in the part or damage to
tooling or operator due to slippage.
On bends, the short leg (inside length) should be a minimum of 2.5 x stock
thickness + radius.
Flange width:
Bend height of walls:
Design

15. Distance between bend and cut or punch:
When a bend is made too close to a hole, the hole may become deformed. Figure A
shows a hole that has become teardrop shaped because of this problem. To save the
cost of punching or drilling in a secondary operation the following formulas can be used
to calculate the minimum distance required.
For a hole Dia <1, minimum distance =2T+Bend radius
For a slot width or Hole Dia >1, minimum distance =2.5T+Bend radius
Design

16. SHEET METAL MANUFACTURING ARE CLASSIFIED INTO TWO GROUPS:
CUTTING NON CUTTING
CUTTING:
PUNCHING
BLANKING
PIERCING
PARTING OFF
NOTCHING
SLITTING
LANCING
BENDING:
ANGLE BENDING
CURLING
PLUNGING
DRAWING:
BULGING
SQUEEZING:
COINING
EMBOSSING
FLATTENING OR
PLANISHING
Manufacturing

17. DIE :-
The word DIE has several definitions.
a. A complete production tool, the purpose of which is to produce the piece parts
consistently to required specifications.
b. The female part of a complete die.
A punch is a male member of a press tool. It is usually the upper member
and is clamped to the top bolster (but it is depends on the requirement.)
Punches are used for Piercing, Blanking, Bending, Embossing, forming, etc..
PUNCH :-
SHEARING PROCESS
Manufacturing

18. Shearing action between two sharp edges
• Punch: upper cutting edge
• Die: lower cutting edge
Shearing Process-Steps
• Plastic deformation
• Penetration
• Fracture
A cut edge has Roll-over (about 5% of the thickness), Shear (about 30% of the
thickness, Break (the remaining % of the thickness) and Burr, potentially up to
10% of material.
Manufacturing

19. Plastic Deformation
- Punch engages the sheet metal
- Pulls the material downward
- Slightly drawing the material into the clearance
- Creates a Rollover
Penetration
- Punch continues to travel
- Shear the upper portion of the material
- Material becomes locked between the punch and the die
- Creates a burnished area
Fracture
- Punch travel further
- Material is fractured or separated completely
- Creates Burr
Manufacturing

20. Rollover
• Rounded corner
Burnish
• Smooth surface
Fractured Zone
• Rough surface
Burr
• Sharp corner
Sheared
Edges
A cut edge has Roll-over (about 5% of the thickness), Shear (about 30% of the
thickness, Break (the remaining % of the thickness) and Burr, potentially up to 10% of
material.
Manufacturing

21. Clearance (C)
Distance (Gap) between punch and die
4%-8% of sheet thickness
Small Clearance
double burnishing
large cutting force
Large Clearance
Sheet becomes pinched
excessive burr
Manufacturing

22. Manufacturing

23. Cutting Forces (F)
• F = S * t * L
– S - shear strength
– t - thickness
– L - length of cutting edge
• F = 0.7TS * t *L
– TS - Ultimate tensile strength
• Max F is used to determine press for
operation
Manufacturing

24. BLANKING
The actual cutting or the blank of component is done by the cutting edge or the die
opening. There fore die opening determines the die of the blank of component
OR
-Cutting along an outline in a single step and produce required part
Is called PIECE PART. Cutting of flat metal sheet or strip stock into the
required size and shape
Blanking is sub divided into two groups
1. Conventional blanking.
2. Fine blanking.
Manufacturing

25. Process Characteristics
Shears the work piece from the
parent stock as the punch enters
the die.
Produces burnished and sheared
section on the cut edge
Produces burred edges
Quality is controlled by the punch
and die clearance
CONVENTIONAL
BLANKING
Conventional blanking is a shearing
process in which a work piece is
separated from the parent material
when the punch enters the die.
Manufacturing

26. Process Characteristics
Die clearance is approximately 1% of stock
thickness.
Produces clean, smooth edges.
Hole sizes and spacing can equal stock
thickness.
Material thicknesses of 0.0006 in. to 0.60
in. for steel, brass, aluminum, etc.
Produces minimal surface distortion
Punch does not enter die Uses a V-ring
that is embedded in the stock to control
fracture
FINE BLANKING
Fine blanking is a controlled shearing
process in which a tightly clamped work
piece is forced through a fixed die opening to
produce accurate work pieces with a fine
finish and straight edges. A V-shaped ring
around the perimeter of the work piece
presses into the stock to control material
flow.
Manufacturing

27. PUNCHING
The actual cutting or the opening in stock material is does by the punch.
There fore size or the punched opening determined by the punch. Cutting
openings such as holes and slots in sheet stock, strip material, or a
part
Or
-This operation is Same as blanking but produces SCRAP (SLUG) PART
REQUIRED BLANK
SCRAP
Manufacturing

28. Process Characteristics
Is the most economical method of
making holes in sheet or strip metal
for medium to high production
Can produce various shaped holes
Punches and dies are normally made
of conventional tool steel or carbides
Produces a burnished area, roll-over,
and die break on the sidewall of the
resulting hole
PUNCHING
Punching is a shearing process in
which a scrap or slug is separated
from the work piece when the
punch enter the die. The sidewall
of the resulting hole displays a
burnished area, rollover, and die
break.
Manufacturing

29. PARTING OFF
The parting is the operation of cutting a sheet metal in two parts. Unlike cutting
of potation, some quality of scrap is removed to make the work piece in two
parts.
Manufacturing

30. Process Characteristics
Removes metal from the edges of the
work piece
Can produce different angled notches
by adjusting the position of the work
piece
Directly produces re-entrant cuts not
possible by shearing
Can facilitate bending or drawing to
achieve final geometry
NOTCHING
Notching is a shearing operation by which
metal scrap is removed from the outside
edge of a work piece by multiple shear
blades set at right angles to each
other. Notching can be used to provide
relief from wrinkling before drawing or
forging. It is a manually operated, low
production process.
Manufacturing

31. Process Characteristics
Is limited to relatively thin materials
(0.001 to 0.125 in.)
Burrs are normally present to
some extent on slit edges
May be used on ferrous and
nonferrous metals, plastics, and
paper
Is a high production, width-control
process
SLITTING
Slitting is a shearing process
used to cut wide coils of material
into several coils of narrower
width as the material passes
lengthwise through circular
blades.
Manufacturing

32. Process Characteristics
Cuts a portion of the periphery of the
hole, and the remainder is bent to
the desired shape
Removes no metal from the work
piece
Can use a single cut to facilitate the
making of special features
LANCING
Lancing is a combined shearing and
bending operation where a portion of
the periphery of a hole is cut into the
work piece and the remainder is bent to
the desired shape. No material is
removed from the work piece by this
process.
Manufacturing

33. Perforating
• punching of a pattern
Trimming, Shaving
• operations to clean up and
smooth out edges
Manufacturing

34. BENDING is usually defined as "the plastic
deformation of a sheet metal along a straight line".
Air Bending is done with the punch touching the work piece and the work
piece, not bottoming in the lower cavity. This is called air bending. As the
punch is released, the work piece ends up with less bend than that on the
punch (greater included angle). This is called SPRING BACK. The amount
of spring back depends on the material, thickness, grain and temper. The
spring back usually ranges from 5 to 10 degrees. Usually the same angle is
used in both the punch and the die to minimize setup time. The inner radius
of the bend is the same as the radius on the punch.
Manufacturing

35. Spring back:
Materials will have a finite modulus of elasticity, plastic deformation
is followed by elastic recovery upon removal of the load.
In bending, the recovery is known as spring back
Elastic recovery: SB=(A’-A’b)/(A’b)
A’b=included angle of the bending tool,
A’=included angle of the sheet metal part
Manufacturing

36. Spring back Compensating Methods
Over bending :
Punch and Die angle is less than the part angle
Die angle = Part angle + Spring back
<90
Manufacturing

37. Spring back Compensating Methods
Bottoming:
Clearance between the punch and die surface is less than the blank thickness.
As a result, the material yields slightly and reduce the spring back.
Bottom bending requires considerably more force (about 50%~60% more)
Manufacturing

38. Spring back Compensating Methods
Coining:
Compressive stress is applied to bending region to increase the amount of
plastic deformation. This reduces the amount of spring back.
Manufacturing

39. Bending
Methods
V-Bending:
Clearance between punch and die is constant
U-Bending:
Two parallel bending axes are produced in the
same operation.
Edge Bending:
One edge of the sheet is bent to 90 while the other
end is restrained
Manufacturing

40. BENDABILITY (the smallest achievable bending radius without failure) of
materials is improved by heating or application of hydrostatic
pressure. Cracking can also be eliminated by inducing compression in the
bending direction. Bendability of narrow sheet is higher than wide
sheets. Narrow sheets are observed to crack usually at the edges, while wide
sheets tend to crack at the center.
Manufacturing

41. Estimating the minimum bend radius:
Metal can only be bent to a certain angle before cracks form at the bend
and, ultimately, the work piece breaks. To predict the smallest
achievable radius that a sheet can be bent to, the following equation
can be used:
Where
t : thickness
Rmin : minimum bend radius
r : reduction in area in a tensile test for a given material (%)
Ao and Af are the original and final (fracture)
Manufacturing

42. Bending
Operations
Flanging:
Hemming:
Seaming:
Curling:
Manufacturing

43. Here are some examples of parts manufactured by bending.
Manufacturing

44. CURLING
Curling is a operation of forming the edges of a component into a roll or
a curl by bending the sheet metal in order to strengthen the edges and
to provide smoothness to its surface.
Manufacturing

45. PLUNGING
Plunging is the operation of bending a sheet metal to the desired shape
for accommodating a screw or a rod through plunged hole. The plate is
first pierced at the required position and then the plunging punch is
pressed in the hole. This causes displacement of the metal in the die
cavity and The shape of the plunged hole depends on the shape of the
punch.
Manufacturing

46. Photograph showing the
bulged shapes in the three
stages in repeated bulging of
copper tubes with interstate
annealing. From left to right,
1st stage, 2nd stage and the
3rd stage, respectively.
BULGE FORMING BY HYDRAULIC
PRESSURE
Assembly of the tooling for
bulging.
BULGING
Manufacturing

47. Drawing leads to wrinkling and puckering at the edge where the sheet metal is
clamped. This is usually removed by a separate trimming operation.
Design Considerations:
Round shapes (cylinders) are easiest to draw. Square shapes can also be
drawn If the inside and outside radiuses are at least 6 X stock thickness.
Other Shapes can be produced at the cost of complexity of tooling and part
costs.
Manufacturing

48. Making A Cup shape part
Blanks
Many shapes and sizes
Die Cavity
Shape in which the metal will take on
Punch
Pushes metal into die cavity
Blank Holder
A device to hold the blank
Manufacturing

49. In drawing , a blank of sheet metal is restrained at the edges, and the middle
Section is forced by a punch into a die to stretch the metal into a cup shaped drawn
Part. This drawn part can be circular, rectangular or just about any cross-section.
DRAWING
Manufacturing

50. DRAWING
Manufacturing

51. DEEP DRAWING
Part formed deeper than the diameter (DR > 2.0)
Manufacturing

52. DRAWING OPERATION FOR AUTO MOBILE PANELS
Drawing operation of the auto mobile panels is different than general drawing
operation.
In this operation component may have any complicated profile, not like as
simple Circular or as simple rectangular shapes.
Drawn component Finished
components
LH
RH
Manufacturing

53. DEFECTS IN
DRAWING
Wrinkling
Splits/Cracks
Earing
Surface Scratches
Earing Wrinkles
Manufacturing

54. Wrinkling/Splits
DEFECTS IN
DRAWING
Manufacturing

55. If the thickness of the sheet it enters to the die is more than the clearance
between die and punch the thickness has to be reduced to meet the precise
dimensions, this effect is called a ironing
Smaller clearance greater the amount of ironing
IRONING
Manufacturing

56. Manufacturing

57. DIES:-
Simple - Single operation with a single stroke
Compound - Two operations with a single stroke
Combination - Two operations at two stations
Progressive - Two or more operations at two or more stations with
each press stroke, creates what is called a strip
development
Manufacturing

58. SIMPLE DIE:-
Single operations with a single stroke
Manufacturing

59. COMPOUND DIE:-
Two operations with a single stroke
Manufacturing

60. PROGRESSIVE DIE:-
Two or more workstations
One or more operations under each
working station.
Strip moves from first to last station to
produce complete components.
Manufacturing

61. Tool pictures of some of the progressive dies used in Appliance and Auto industries
Large pierce die with multiple hand
operated gags for tractor trailer side
11 Station pierce, pilot, lance, bead
and blank out progressive die
Thirteen (13)
station large 2' X 4' Progressive
Die to produce shelf brackets
Manufacturing

62. Tool pictures of some of the progressive dies used in Appliance and Auto industries
Manufacturing

63. CHARACTERISTICS OF PROGRESSIVE DIES
Utilization of multiple cutting and/or forming operations.
Suitable for producing small parts at a rapid rate.
Necessity to invest in expensive die sets.
Ability to save time and money by combining forming
operations.
Capability to maintain close tolerances.
Manufacturing

64. Advantages of PROGRESSIVE DIES:
Shorter operation time.
Less material handling.
Higher accuracy.
Disadvantages of PROGRESSIVE DIES:
Higher degree of skill required for manufacturing.
Higher tool cost.
Serious maintenance problems.
Higher material wastage.
Manufacturing

65. PRESSES:
The presses can be categorized to two types:
Mechanical presses:- Eccentric,crankshaft,knuckle joint
Hydraulic presses:- Driven by a piston/cylinder system
Manufacturing

66. MECHANICAL PRESSES
Mechanical presses has a mechanical flywheel to store the energy, transfer it to the
punch and to the workpiece. They range in size from 20 tons up to 6000 tons.
Strokes range from 5 to 500 mm (0.2 to 20 in) and speeds from 20 to 1500 strokes
per minute. Mechanical presses are well suited for high-speed blanking, drawing and
for making precision parts.
Manufacturing

67. HYDRAULIC PRESSES:
Hydraulic Presses use hydraulics to deliver a controlled force. Tonnage can vary
from 20 tons to a 10,000 tons. Strokes can vary from 10 mm to 800 mm (0.4 to 32
in). Hydraulic presses can deliver the full power at any point in the stroke; variable
tonnage with overload protection; and adjustable stroke and speed. Hydraulic
presses are suitable for deep-drawing, compound die action as in blanking with
forming or coining, low speed high tonnage blanking, and force type of forming
rather than displacement type of forming.
Manufacturing

68. Dies and
Presses
Mechanical C-Frame
Hydraulic C-Frame
Mechanical Open Frame
Manufacturing