Download - Sheetmetal Working
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SHEET METALWORKING
Cutting Operations Bending Operations
Drawing
Other Sheet Metal Forming Operations es an resses or ee e a rocesses
Sheet Metal Operations Not Performed on Presses
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Sheet Metalworking Defined
Cutting and forming operations performed on relativelythin sheets of metal
c ness o s ee me a = . mm n o mm
(1/4 in)
>
Operations usually performed as cold working
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Sheet and Plate Metal Products
Sheet and plate metal parts for consumer andindustrial products such as
. u omo es an ruc s
2. Airplanes
.
4. Farm and construction equipment
5. Small and lar e a liances
6. Office furniture
7. Computers and office equipment
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Advantages of Sheet Metal Parts
High strength Good dimensional accuracy
Good surface finish
Relatively low cost or arge quan es, econom ca mass pro uc on
operations are available
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Sheet Metalworking Terminology
1. Punch-and-die Tooling to perform cutting, bending, and drawing
2. Stamping press
Machine tool that performs most sheet metal
3. Stampings
Sheet metal roducts
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Sheet Metal Processes
1. Cutting Shearing to separate large sheets; or cut part
per me ers or ma e o es n s ee s
2. Bending
3. Drawing
Formin of sheet into convex or concave sha es
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Cutting: Shearing between two sharp cutting edges
(1) just before the
punch contacts work
punc eg ns to pus nto wor ,causing plastic deformation
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3 unch com resses and
penetrates into work causing a
smooth cut surface
opposing cutting edges which
separates the sheet
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Shearing, Blanking, and Punching
Three principal operations in pressworking that cutsheet metal:
ear ng
Blanking
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Shearing - sheet metal cutting operation along a
s ra g ne e ween wo cu ng e ges
subsequent operations
Blanking - sheet metal cutting to separate piece from
surrounding stock
Cut piece is the desired part, called a blank
Punching - sheet metal cutting similar to blanking
except cut piece is scrap, called a slug
Remaining stock is the desired part
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ear ng operat ona) side view of the shearing operation
b) front view of power shears equipped with inclined upper cuttingblade symbol v indicates motion
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(a) Blanking and (b) punching
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Clearance in Sheet Metal Cutting
Typical values range between 4% and 8% of stock
thickness
- If too small, fracture lines pass each other, causing doubleburnishing and larger force
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excessive burr results
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Cutting Forces
Important for determining press size (tonnage)
F = S t L or F= 0.7 t L
where S = shear strength of metal (MPa) = tensile strength (MPa)
t = stock thickness (mm), and
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Deep Drawing
Sheet metal forming to make cup-shaped, box-shaped,or other complex-curved, hollow-shaped parts
Sheet metal blank is positioned over die cavity and
Products: beverage cans, ammunition shells,
automobile body panels
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Stages in Deformation of the Workpiece during Deep Drawing
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-shaped part:
(1) start of operation
contacts work(2) near end of
(b) Correspondingworkpart:
(1) starting blank
2 drawn art
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Clearance in Drawing
Sides of punch and die separated by a clearance cgiven by:
c = .
where t = stock thickness
,
stock thickness
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Drawing Ratio DR
Most easily defined for cylindrical shape:
b
D
DR
= = p
Indicates severity of a given drawing operation
- Upper limit = 2.0
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Reduction r
,
b
pb
Dr
Value of rshould be less than 0.50
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Thickness-to-Diameter Ratio
Thickness of starting blank divided by blank diameterThickness-to-diameter ratio = t/Db
Desirable for t/Db ratio to be greater than 1%
As t/Db decreases, tendency for wrinkling increases
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Blank Size Determination
For final dimensions of drawn shape to be correct,starting blank diameter Db must be right
o ve or b y se ng s ar ng s ee me a an
volume = final product volume
part wall
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Other drawing operations:
Redrawing Reverse Drawing
1 start
(2) finish
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Shapes other than Cylindrical Cups
Square or rectangular boxes (as in sinks), Stepped cups,
Cones,
Cups with spherical rather than flat bases, rregu ar curve orms as n au omo e o y pane s
technical problems in drawing
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Common defects in drawn parts
a wr n ng n ange
b) wrinkling in walls
c) tearing
d) earinge) surface scratches
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Other Sheet Metal Forming on Presses
Other sheet metal forming operations performed onconventional presses
pera ons per orme w me a oo ng
Operations performed with flexible rubber tooling
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Dies for Sheet Metal Processes
Most pressworking operations performed withconventional punch and die tooling
us om es gne or par cu ar par
The term stamping die sometimes used for high
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Components of a punch and die for a blanking operation