Sheet Metalworking

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Sheet Metalworking
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Cutting Operations

• Shearing by two sharp cutting edges.
• Plastic deformation penetration fracture

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Shearing, Blanking and Punching

• Shearing - Cutting on sheet-metal with straight
  edges.
• Blanking - Cutting sheet-metal with a closed
  contour.
• Punching - Making holes on sheet-metal.

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Sheet-metal Cutting

• c at
• c clearance
• a allowance
• t thickness
• Blanking
• Blanking punch dia. Db- 2c
• Blanking die dia. Db
• Punch
• Hole punch dia. Db
• Hole die dia. Db 2c

0.25? to 1.5?
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Sheet-metal Cutting

• Small clearance

Cutting force StL S Shear strength of
sheet-metal t Sheet-metal thickness L Length
of cutting edge or, Cutting force 0.7TtL T
Ultimate tensile strength of sheet-metal
Large clearance
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Sheet-metal Cutting Operations

• Cut-off
• Parting

Slotting Perforating Notching /
Seminotching
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Sheet-metal Cutting Operations

• Fine blanking -
• close tolerances and smooth edges in one step.

Trimming - Cutting operation to remove excess
metal Shaving - Shearing with very small
clearance to obtain accurate dimensions.,
secondary or finishing operation.
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Bending

• V- bending Edge - bending

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Bending Analysis

• BA 2 ? A( R Kbat ) / 360
• where BA bending allowance, A bend angle, R
  bend radius, t stock thickness, Kba stretch
  factor.
• For Rlt 2t, Kba 0.33 for R? 2t, Kba 0.5.
• Spring back,
• where A include angle of sheet-metal part
• Ab include angle of bending tool
• w width of sheet-metal
• Bending force D die opening
  dimension
• Kbf 1.33 V-bending
• Kbf 0.33 edge bending

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Bending Analysis

• Spring back
• Die-opening
• dimension

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Bending Operations

• Straight flanging Stretch flanging Shrink
  flanging

Hemming Seaming Curling
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Bending Operations

• Channel bending U-bending air-bending

Offset-bending Corrugating Tube
forming
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Drawing

• c Clearance
• Db blank diameter
• Dp Punch diameter
• Rd die corner radius
• Rp Punch corner
• radius
• F drawing force
• Fh holding force

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Deep Drawing
Initial step bending of edge
straightening of side wall
Thinning and drawing final cup shape
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Drawing Analysis

• Drawing ratio, ? 2.0
• where Db blank diameter
• Dp punch diameter
• t thickness of the starting blank
• Reduction, ? 0.5
• Thickness to diameter ratio, ? 1
• Drawing force, ,
  max. at 1/3 stroke.
• Holding force,
• Holding pressure may be set at 0.015 of the yield
  strength
• T Tensile strength, Y Yield strength, Rd
  die corner radius

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Drawing Analysis

• Blank diameter can be calculated from the
  conservation of volume based on the final volume
  of the part.
• If the limits on the drawing ratio, reduction and
  thickness-to-diameter ratio are exceeded, the
  blank must be drawn in steps or having annealing
  between the steps.
• Process optimization
• Punch and die corner radii
• friction
• depth of draw (per step)
• material characteristics

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Drawing Defects

• a) Wrinkling in flange - small holding force
• b) Wrinkling in the wall - insufficient holding
  force, wrinkling initially occurring on the
  flange.
• c) Tearing - high stress, sharp die radius
• d) Earing - anisotropy of the material
• e) Surface scratches - Die or punch not having a
  smooth surface, insufficient lubrication

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Other Sheet-metal Operations

• Ironing - squeezing and drawing in conjunction
• Corning Embossing - to produce surface details
• Lancing - combination of cutting and forming

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Other Sheet-metal Operations

• Rubber forming processes
• Guerin process - low cost, small volume, pressure
  up 10 MPa.
• Hydroforming - Higher pressure, up to 100 MPa.

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Dies

• Components of a punch and die for blanking
  operation

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Dies

• Progressive dies and final part

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Press
crankshaft
Knuckle joint
eccentric

• Press are driven mechanically or hydraulically.

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Stretch Forming

• Stretching and forming with a die at the same
  time.

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Roll Forming

• Similar to the the rolling process but working on
  sheet-metal or tubes.

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Spinning

• Conventional
• spinning

Shear spinning - thinning and bending occur at
the same time.
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Spinning

• Tube spinning - similar to shear spinning but
  working on a tube.

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High Energy Forming

• Explosive forming
• Electrohydraulic forming
• Electromagnetic forming

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Tube Bending

• Stretch bending
• Drawing bending
• Compression bending
• R/D ? 3.0 with mandrel
• R/D ? 1.5 without mandrel