Manufacturing Processes

Metal Forming ProcessesLecture#8 (Sheet Metal Working)

Cutting OperationsShearing by two sharp cutting edges.Plastic deformation penetration fracture

Shearing, Blanking and PunchingShearing - Cutting on sheet-metal with

straight edges.Blanking - Cutting sheet-metal with a closed

contour.Punching - Making holes on sheet-metal.

Sheet-metal Cuttingc = atc = clearancea = allowancet = thickness

Blanking:Blanking punch dia. = Db- 2cBlanking die dia. = Db

PunchHole punch dia. = Db

Hole die dia. = Db+ 2c0.25° to 1.5°

Sheet-metal Cutting

Small clearance

Large clearance

Cutting force = StLS = Shear strength of sheet-metalt = Sheet-metal thicknessL = Length of cutting edgeor, Cutting force = 0.7TtLT = Ultimate tensile strength of sheet-metal

Sheet-metal Cutting OperationsCut-off

Parting

Slotting Perforating Notching / Seminotching

Sheet-metal Cutting OperationsFine 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.

Bending

V- bending Edge - bending

Bending Analysis

Spring back

Die-openingdimension

Bending Operations

Straight flanging Stretch flanging Shrink flanging

Hemming Seaming Curling

Bending Operations

Channel bending U-bending air-bending

Offset-bending Corrugating Tube forming

Drawingc = ClearanceDb = blank diameterDp = Punch diameter

Rd = die corner radius

Rp = Punch cornerradius

F = drawing forceFh = holding force

Deep Drawing

Initial step bending of edge straightening of side wall

Thinning and drawing final cup shape

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

Other Drawing OperationsRedrawingReverse drawing

– r, 40%-45% first draw– r, 30% second draw– r, 16% third draw

Drawing without blank holder, tDD pb 5 <−

Drawing Defects

a) Wrinkling in flange - small holding forceb) Wrinkling in the wall - insufficient holding force,

wrinkling initially occurring on the flange.c) Tearing - high stress, sharp die radiusd) Earing - anisotropy of the materiale) Surface scratches - Die or punch not having a smooth

surface, insufficient lubrication

Other Sheet-metal OperationsIroning - squeezing and

drawing in conjunctionCorning & Embossing - to

produce surface detailsLancing - combination of

cutting and forming

Other Sheet-metal OperationsRubber forming processes:Guerin process - low cost,

small volume, pressure up 10 MPa.

Hydroforming - Higher pressure, up to 100 MPa.

Dies

Components of a punch and die for blanking operation

Dies

Progressive dies and final part

Press

Press are driven mechanically or hydraulically.

Knuckle jointcrankshaft

eccentric

Stretch Forming

Stretching and forming with a die at the same time.

Roll Forming

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

Spinning

Conventionalspinning

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

Spinning

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

High Energy Forming

Explosive formingElectrohydraulic formingElectromagnetic forming

Tube Bending

Stretch bending

Drawing bending

Compression bending

R/D ≤ 3.0 with mandrelR/D ≤ 1.5 without mandrel