Sheet Metalworking

Cutting Operations Shearing by two sharp cutting edges. Plastic deformation penetration fracture

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.

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

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

Sheet-metal Cutting Operations Cut-off Parting Slotting Perforating Notching / Seminotching

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.

Bending V- bending Edge - bending

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 R< 2t, Kba= 0.33 ; for R 2t, Kba= 0.5. Spring back, where A’ = include angle of sheet-metal part A’b = 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

Bending Analysis Spring back Die-opening dimension

Bending Operations Straight flanging Stretch flanging Shrink flanging Hemming Seaming Curling

Bending Operations Channel bending U-bending air-bending Offset-bending Corrugating Tube forming

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

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

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

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 Operations Redrawing Reverse drawing r, 40%-45% first draw r, 30% second draw r, 16% third draw Drawing without blank holder,

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

Other Sheet-metal Operations Ironing - squeezing and drawing in conjunction Corning & Embossing - to produce surface details Lancing - combination of cutting and forming

Other Sheet-metal Operations Rubber forming processes: Guerin process - low cost, small volume, pressure up 10 MPa. Hydroforming - Higher pressure, up to 100 MPa.

Components of a punch and die for blanking operation Dies Components of a punch and die for blanking operation

Dies Progressive dies and final part

Press Press are driven mechanically or hydraulically. crankshaft Knuckle joint eccentric Press are driven mechanically or hydraulically.

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 Conventional spinning 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 forming Electrohydraulic forming Electromagnetic forming

Tube Bending Stretch bending Drawing bending Compression bending R/D  3.0 with mandrel R/D  1.5 without mandrel