3. What is sheet metal ?
Sheet metal is metal formed by an industrial process into
thin, flat pieces.
It is one of the fundamental forms used in metalworking
and it can be cut and bent into a variety of shapes.
Countless everyday objects are fabricated from sheet
metal.
Thicknesses can vary significantly; extremely thin sheets
are considered foil or leaf, and pieces thicker than 6 mm
(0.25 in) are considered plate.
4. Foil
A foil is a very thin sheet of metal, usually made by
hammering or rolling.
Foils are most easily made with malleable metals, such as
aluminium, copper, tin, and gold.
Foils usually bend under their own weight and can be
torn easily.
For example, aluminium foil is usually about 1/1000 inch
(0.03 mm), whereas gold can be made into foil only a few
atoms thick, called gold leaf.
5. Plate
When sheet metal pieces thicker than 6 mm (0.25 in)
are considered plate.
It is thicker than foil. So you can have more strength
then foil and used for industrial purpose, where
strength are needed.
6. Sheet metal thickness in mm and
gauge
In most of the world, sheet metal thickness is
consistently specified in millimeters.
In the US, the thickness of sheet metal is commonly
specified by a traditional, non-linear measure:-
GAUGE
The larger the gauge number, the thinner the metal.
Commonly used steel sheet metal ranges from 30
gauge to about 7 gauge.
Gauge differs between ferrous metals and nonferrous
metals such as aluminum or copper.
8. Application of Sheet metal
Aluminum is also a popular metal used in sheet metal
due to its flexibility, wide range of options, cost
effectiveness, and other properties.
The four most common aluminium grades available as
sheet metal are 1100-H14, 3003-H14, 5052-H32, and 6061-
T6.
Grade 1100-H14 is commercially pure aluminium, highly
chemical and weather resistant. It is ductile enough for
deep drawing and weldable, but has low strength. It is
commonly used in chemical processing equipment, light
reflectors, and jewelry.
9. Application of Aluminium
Grade 3003-H14 is stronger than 1100. It is often used
in stampings, spun and drawn parts, mail boxes,
cabinets, tanks, and fan blades.
Grade 5052-H32 is much stronger than 3003. Common
applications include electronic chassis, tanks, and
pressure vessels.
Grade 6061-T6 is a common heat-treated structural
aluminium alloy. It is weldable, corrosion resistant,
and stronger than 5052. It is used in modern aircraft
structures.
10. List of process of sheet metal
working for non-ferrous metal and
alloy
Bending
Curling
Decambering
Deep drawing
Expanding
Hydro-forming
Perforating
Punching
Roll forming
Rolling
Spinning
Stamping
Water jet cutting
Wheeling
11. Commonly used processess are:
Bending
Curling
Deep drawing
Punching
Roll forming
Rolling
12.
13. Bending
Bending is a manufacturing process that produces a V-
shape, U-shape, or channel shape along a straight axis
in ductile materials, most commonly sheet metal.
Typical products that are made like this are boxes such
as electrical enclosures and rectangular ductwork.
14. Bending Process
In press brake forming, a work piece is positioned over
the die block and the die block presses the sheet to
form a shape.
When bending is done, the residual stresses cause the
material to spring back towards its original position,
so the sheet must be over-bent to achieve the proper
bend angle.
The amount of spring back is dependent on the
material, and the type of forming.
15. Bending Process
When sheet metal is bent, it stretches in length.
The bend deduction is the amount the sheet metal will
stretch when bent as measured from the outside edges
of the bend.
The bend radius refers to the inside radius.
The formed bend radius is dependent upon the dies
used, the material properties, and the material
thickness.
16. Types of Bending
Air bending
Bottoming
Coining
Three-point bending
Folding
Wiping
Rotary bending
Roll bending
Elastomer bending
Joggling
17. Calculations for Bending
Lf = flat length of the sheet
BA = bend allowance
BD = bend deduction
R = inside bend radius
K = K-Factor, which is t / T
T = material thickness
t = distance from inside face to the neutral line[6]
A = bend angle in degrees (the angle through which
the material is bent)
21. Advnatage of Bending
Bending is a cost effective process when used for low to
medium quantities.
22.
23. Curling
Curling is a sheet metal forming process used to form
the edges into a hollow ring.
Curling can be performed to eliminate sharp edges and
increase the moment of inertia near the curled end.
Other parts are curled to perform their primary
function, such as door hinges.
24. Curling Operations
In the curling operation, the flare, or burr, should
always be turned away from the die.
This will help prolong the life of the die by avoiding
unnecessary damage due to scratching.
The stroke of the die must be as long as the curl.
Curling is often performed as part of a high
production, multiple operation progressive forming.
25. Tools used for Curling
The curling die is designed to curl a material of
specific thickness.
Dies are generally made of hardened tool steel because
of the amount of wear caused by the operation.
Their smooth, rounded cavities are often lapped and
polished to help curl the material uniformly.
26.
27. Deep drawing
Deep drawing is a sheet metal forming process in
which a sheet metal blank is radially drawn into a
forming die by the mechanical action of a punch.
It is thus a shape transformation process with material
retention.
The process is considered "deep" drawing when the
depth of the drawn part exceeds its diameter. This is
achieved by redrawing the part through a series of
dies.
28. Deep drawing process
The total drawing load consists of the ideal forming load and an
additional component to compensate for friction in the contacting
areas of the flange region and bending forces as well as unbending
forces at the die radius.
The forming load is transferred from the punch radius through the
drawn part wall into the deformation region (sheet metal flange). In
the drawn part wall, which is in contact with the punch, the hoop
strain is zero whereby the plane strain condition is reached.
In reality, mostly the strain condition is only approximately plane.
Due to tensile forces acting in the part wall, wall thinning is
prominent and results in an uneven part wall thickness, such that
the part wall thickness is lowest at the point where the part wall
loses contact with the punch, i.e., at the punch radius.
29. Deep drawing process
The thinnest part thickness determines the maximum stress that
can be transferred to the deformation zone. Due to material volume
constancy, the flange thickens and results in blank holder contact at
the outer boundary rather than on the entire surface.
The maximum stress that can be safely transferred from the punch
to the blank sets a limit on the maximum blank size (initial blank
diameter in the case of rotationally symmetrical blanks).
An indicator of material formability is the limiting drawing ratio
(LDR), defined as the ratio of the maximum blank diameter that
can be safely drawn into a cup without flange to the punch
diameter. Determination of the LDR for complex components is
difficult and hence the part is inspected for critical areas for which
an approximation is possible. During severe deep drawing the
material work hardens and it may be necessary to anneal the parts
in controlled atmosphere ovens to restore the original elasticity of
the material.
30. Deep drawing force requirement
Softer materials are much easier to deform and
therefore require less force to draw. The following is a
table demonstrating the draw force to percent
reduction of commonly used materials.
31. Tools used for Deep drawing
Punches and dies are typically made of tool steel,
however cheaper (but softer) carbon steel is
sometimes used in less severe applications.
It is also common to see cemented carbides used
where high wear and abrasive resistance is present.
Alloy steels are normally used for the ejector system to
kick the part out and in durable and heat resistant
blankholders.
32.
33. 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.
When a specially shaped punch is used to create multiple usable parts
from a sheet of material the process is known as blanking. In forging
applications the work is often punched while hot, and this is called hot
punching.
Slugging- It is the operation of punching in which punch is stopped as
soon as the metal fracture is complete and metal is not removed but
held in hole.
34. Punching Process
Punch tooling (punch and die) is often made of hardened
steel or tungsten carbide. A die is located on the opposite side
of the workpiece and supports the material around the
perimeter of the hole and helps to localize the shearing forces
for a cleaner edge. There is a small amount of clearance
between the punch and the die to prevent the punch from
sticking in the die and so less force is needed to make the
hole.
The amount of clearance needed depends on the thickness,
with thicker materials requiring more clearance, but the
clearance is always less than the thickness of the workpiece.
The clearance is also dependent on the hardness of the
workpiece. The punch press forces the punch through a
workpiece, producing a hole that has a diameter equivalent to
the punch, or slightly smaller after the punch is removed.
35. Punching process
All ductile materials stretch to some extent during
punching which often causes the punch to stick in the
workpiece. In this case, the punch must be physically
pulled back out of the hole while the work is
supported from the punch side, and this process is
known as stripping. The hole walls will show
burnished area, rollover, and die break and must often
be further processed. The slug from the hole falls
through the die into some sort of container to either
dispose of the slug or recycle it.
36. Punching characteristics
Punching is the most cost effective process of making
holes in strip or sheet metal for average to high
fabrication.
It is able to create multiple shaped holes
Punches and dies are usually fabricated from
conventional tool steel or carbides.
Creates a burnished region roll-over, and die break on
sidewall of the resulting hole.
It's quick.
37. Geometry for Punching
The workpiece is often in the form of a sheet or roll. Materials for
the workpiece can vary, commonly being metals and plastics.
The punch and die themselves can have a variety of shapes to
create an array of different shaped holes in the workpiece.
Multiple punches may be used together to create a part in one
step.
Extruded holes with the punch and die used to create them. No
pilot hole was used on the left.
Usually, the punch and die are close to the same dimensions,
creating a sheared edge when they meet. A punch that is
significantly smaller than the die can be used to produce an
extruded hole where the punch displaces the punched material
to the sides, forming a tube perpendicular to the punched sheet.
38. Equipment used in punching Most punch presses are mechanically operated, but
simple punches are often hand-powered. Major
components of this mechanical press are the frame,
motor, ram, die posts, bolster, and bed.
The punch is mounted into the ram, and the die is
mounted to the bolster plate. The scrap material drops
through as the workpiece is advanced for the next hole.
A large computer-controlled punch press is called a CNC
turret punch. It houses punches and their corresponding
dies in a revolving indexed turret. These machines use
hydraulic as well as pneumatic power to press the shape
with enough force to shear the metal.
39. Calculation in punching process
The punch force required to punch a piece of sheet metal can be estimated
from the following equation:[
Where t is the sheet metal thickness, L is the total length sheared
(perimeter of the shape), and UTS is the ultimate tensile strength of the
material.
Die and punch shapes affect the force during the punching process. The
punch force increases during the process as the entire thickness of the
material is sheared at once. A beveled punch helps in the shearing of
thicker materials by reducing the force at the beginning of the stroke.
However, beveling a punch will disort the shape because of lateral forces
that develop. Compound dies allow multiple shaping to occur. Using
compound dies will generally slow down the process and are typically more
expensive than other dies. Progressive dies may be used in high production
operations. Different punching operations and dies may be used at
different stages of the operation on the same machine.
40. Related processs
Other processes such as stamping, blanking,
perforating, parting, drawing, notching, lancing and
bending operations are all related to punching.
41.
42. Roll forming
Roll forming, also spelled rollforming, is a type of rolling
involving the continuous bending of a long strip of sheet
metal (typically coiled steel) into a desired cross-section.
The strip passed through sets of rolls mounted on
consecutive stands, each set performing only an
incremental part of the bend, until the desired cross-
section (profile) is obtained.
Roll forming is ideal for producing constant-profile parts
with long lengths and in large quantities.
43. Roll forming process
A variety of cross-section profiles can be produced, but each profile
requires a carefully crafted set of roll tools. Design of the rolls starts
with a flower pattern, which is the sequence of profile cross-sections,
one profile for each stand of rolls. The roll contours are then derived
from the flower pattern profiles. Because of the high cost of the roll
sets, computer simulation is often used to develop or validate the roll
designs and optimize the forming process to minimize the number of
stands and material stresses in the final product.
Roll-formed sections may have advantages over extrusions of a similar
shapes. Roll formed parts may be much lighter, with thinner walls
possible than in the extrusion process, and stronger, having been work
hardened in a cold state. Parts can be made having a finish or already
painted. In addition, the roll forming process is more rapid and takes
less energy than extrusion.[
44. Process of Roll forming
Roll forming is, among the manufacturing processes, one of
the simplest. It typically begins with a large coil of sheet
metal, between 1 inch (2.5 cm) and 20 inches (51 cm). in
width, and 0.004 inches (0.10 mm) and 0.125 inches (3.2 mm)
thick, supported on an uncoiler.
The strip is fed through an entry guide to properly align the
material as it passes through the rolls of the mill, each set of
rolls forming a bend until the material reaches its desired
shape. Roll sets are typically mounted one over the other on a
pair of horizontal parallel shafts supported by a stand(s). Side
rolls and cluster rolls may also be used to provide greater
precision and flexibility and to limit stresses on the material.
The shaped strips can be cut to length ahead of a roll forming
mill, between mills, or at the end of the roll forming line.
45. Geometrical possibilities
The geometric possibilities can be very broad and even include
enclosed shapes as long as the cross-section is uniform.
Typical sheet thicknesses range from 0.004 inches (0.10 mm) to
0.125 inches (3.2 mm), but they can exceed that. Length is almost
unaffected by the rolling process. The part widths typically are not
smaller than 1 inch (2.5 cm) however they can exceed 20 inches (51
cm). The primary limitation is profile depth, which is generally
limited to less than 4 inches (10 cm) and rarely larger than 6 inches
(15 cm) due to roll-imparted stresses and surface speed differentials
that increase with depth.
Tolerances can typically be held within ±0.015 inches (0.38 mm) for
the width of the cross-sectional form, and ±0.060 inches (1.5 mm)
for its depth.[
46. Productin Rate
The production rate depends greatly on the material
thickness and the bend radius; it is however also affected
by the number of required stations or steps.
For bend radii of 50 times the material thickness of a low
carbon steel 0.7 inches (18 mm) thick can range from 85
feet per minute (26 m/min) through eight stations to 55
feet per minute (17 m/min) through 12 stations or 50 feet
per minute (15 m/min) through 22 stations.
47.
48. Rolling Process
In metalworking, rolling is a metal forming process in
which metal stock is passed through one or more pairs of
rolls to reduce the thickness and to make the thickness
uniform.
The concept is similar to the rolling of dough. Rolling is
classified according to the temperature of the metal
rolled.
If the temperature of the metal is above its
recrystallization temperature, then the process is known
as hot rolling. If the temperature of the metal is below its
recrystallization temperature, the process is known as
cold rolling.
49. Rolling
In terms of usage, hot rolling processes more tonnage
than any other manufacturing process, and cold rolling
processes the most tonnage out of all cold working
processes.
Roll stands holding pairs of rolls are grouped together
into rolling mills that can quickly process metal, typically
steel, into products such as structural steel, bar stock,
and rails. Most steel mills have rolling mill divisions that
convert the semi-finished casting products into finished
products.
50. Hot Rolling
Hot rolling is a metalworking process that occurs above the
recrystallization temperature of the material. After the grains deform
during processing, they recrystallize, which maintains an equiaxed
microstructure and prevents the metal from work hardening.
The starting material is usually large pieces of metal, like semi-finished
casting products, such as slabs, blooms, and billets. If these products came
from a continuous casting operation the products are usually fed directly
into the rolling mills at the proper temperature. In smaller operations the
material starts at room temperature and must be heated. This is done in a
gas- or oil-fired soaking pit for larger workpieces and for smaller
workpieces induction heating is used.
As the material is worked the temperature must be monitored to make
sure it remains above the recrystallization temperature. To maintain a
safety factor a finishing temperature is defined above the recrystallization
temperature; this is usually 50 to 100 °C (90 to 180 °F) above the
recrystallization temperature. If the temperature does drop below this
temperature the material must be re-heated before more hot rolling.
51. Cold Rolling
Cold rolling occurs with the metal below its recrystallization
temperature (usually at room temperature), which increases
the strength via strain hardening up to 20%.
It also improves the surface finish and holds tighter
tolerances. Commonly cold-rolled products include sheets,
strips, bars, and rods; these products are usually smaller than
the same products that are hot rolled.
Because of the smaller size of the workpieces and their greater
strength, as compared to hot rolled stock, four-high or cluster
mills are used. Cold rolling cannot reduce the thickness of a
workpiece as much as hot rolling in a single pass.
52. Types of Rolling
Roll bending
Roll forming
Flat rolling
Ring rolling
Structural shape rolling
Controlled rolling
Forge rolling
53. Defect in Rolling
Flatness and shape
Profile
Draught
Surface defect types:
Lap
Mill shearing
Rolled in scale
Scabs
Seams
Silver
54.
55. Decambering
Decambering is the metalworking process of removing
camber, or horizontal bend, from strip shaped
materials. The material may be finite length sections
or continuous coils. Decambering resembles flattening
or levelling processes, but deforms the material edge
(left or right) instead of the face (up or down) of the
strip.
56. Expanding
Expanding is a process of cutting or stamping slits in
alternating pattern much like the stretcher bond in
brickwork and then stretching the sheet open in accordion-
like fashion.
It is used in applications where air and water flow are
desired as well as when light weight is desired at cost of a
solid flat surface.
A similar process is used in other materials such as paper to
create a low cost packing paper with better supportive
properties than flat paper alone.
57. Hemming and Seaming
Hemming and seaming are two similar metalworking
processes in which a sheet metal edge is rolled over onto
itself.
Hemming is the process in which the edge is rolled flush
to itself, while a seam joins the edges of two materials.
Hems are commonly used to reinforce an edge, hide
burrs and rough edges, and improve appearance.
Seams are commonly used in the food industry on
canned goods, on amusement park cars, and in the
automotive industry.
58. Hyrdoforming
Hydroforming is a process that is analogous to deep
drawing, in that the part is formed by stretching the blank
over a stationary die.
The force required to do so is generated by the direct
application of extremely high hydrostatic pressure to the
workpiece or to a bladder that is in contact with the
workpiece, rather than by the movable part of a die in a
mechanical or hydraulic press.
Unlike deep drawing, hydroforming usually does not
involve draw reductions.
59. Ironing
Ironing is a sheet metal forming process that
uniformly thins the workpiece in a specific area.
This is a very useful process when employed in
combination with deep drawing to produce a uniform
wall thickness part with greater height-to-diameter
ratio.
One example of ironing can be found in the
manufacture of aluminum beverage cans, which are
actually pressed from flat sheets of thicker material.
60. Laser cutting
Sheet metal can be cut in various ways, from hand
tools called tin snips up to very large powered shears.
With the advances in technology, sheet metal cutting
has turned to computers for precise cutting. Many
sheet metal cutting operations are based on computer
numerically controlled (CNC) laser cutting or multi-
tool CNC punch press.
61. Laser cutting
CNC laser involves moving a lens assembly carrying a beam
of laser light over the surface of the metal.
Oxygen, nitrogen or air is fed through the same nozzle
from which the laser beam exits. The metal is heated and
burnt by the laser beam, cutting the metal sheet. The
quality of the edge can be mirror smooth and a precision of
around 0.1 mm (0.0039 in) can be obtained. Cutting speeds
on thin 1.2 mm (0.047 in) sheet can be as high as 25 m (82
ft) per minute. Most laser cutting systems use a CO2 based
laser source with a wavelength of around 10 µm; some more
recent systems use a YAG based laser with a wavelength of
around 1 µm.
62. Photochemical perforating
Photochemical machining, also known as photo etching, is
a tightly controlled corrosion process which is used to
produce complex metal parts from sheet metal with very
fine detail.
The photo etching process involves photo sensitive polymer
being applied to a raw metal sheet.
Using CAD designed photo-tools as stencils, the metal is
exposed to UV light to leave a design pattern, which is
developed and etched from the metal sheet.
63. Spinning
Spinning is used to make tubular (axis-symmetric)
parts by fixing a piece of sheet stock to a rotating form
(mandrel).
Rollers or rigid tools press the stock against the form,
stretching it until the stock takes the shape of the
form.
Spinning is used to make rocket motor casings, missile
nose cones, satellite dishes and metal kitchen funnels.
64. Stamping
Stamping includes a variety of operations such as
punching, blanking, embossing, bending, flanging,
and coining; simple or complex shapes can be formed
at high production rates; tooling and equipment costs
can be high, but labor costs are low.
Alternatively, the related techniques repoussé and
chasing have low tooling and equipment costs, but
high labor costs.
65. Water Jet Cutting
A water jet cutter, also known as a waterjet, is a tool
capable of a controlled erosion into metal or other
materials using a jet of water at high velocity and
pressure, or a mixture of water and an abrasive
substance.