DTEL 1 UNIT v LECTURE 33 Press working

DTEL 2 DEDICATED DIES AND PRESS WORKING LECTURE 33 Introduction to press working

DTEL 3 DEDICATED DIES AND PRESS WORKING - blanking die parts do not have two straight parallel edges. Blank can be almost any closed contour. Increase in mfg scrap. Edges of part must be separated from edges of strip by nearly twice sheet metal thickness to minimize edge distortion. LECTURE 34 Classification,types of presses,press terminology

DTEL 4 Press Working Terminology: LECTURE 34

DTEL die opening profile a) gives the highest quality work piece, the most expensive. blanking parts having complex contours with greater accuracy. b) making small parts with low accuracy. c) the simplest, making relatively large parts. d) to punch small-diame ter (d < 5 mm) holes. LECTURE 35 Force analysis in press working

DTEL 6 2. Die blocks 2.3 sectioned die workpiece- large, die opening - complicated, contours - difficult to machine Die cutting operation,types of dies LECTURE 36

DTEL 7 Cutting Operations Shearing by two sharp cutting edges. Plastic deformation penetration fracture LECTURE 36 Cutting Operations

DTEL 8 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. LECTURE 36

DTEL 9 Sheet-metal Cutting c = at c = clearance a = allowance t = thickness Blanking: Blanking punch dia. = D b - 2c Blanking die dia. = D b Punch Hole punch dia. = D b Hole die dia. = D b + 2c 0.25  to 1.5  LECTURE 36

DTEL 10 Sheet-metal Cutting Operations Cut-off Parting Slotting Perforating Notching / Seminotching LECTURE 37

DTEL 11 Progressive Dies a different operation is performed at the same station with each stroke of a series of punches Characteristics and Type of Shearing Dies Compound Dies  Operations on the same sheet may be performed in one stroke with a compound die  Limited to simple shapes due to: 1.Process is slow 2.Complex dies is more expensive LECTURE 38

DTEL 12 Shearing: Miscellaneous Methods of Cutting Sheet Metal  Other methods of cutting sheets 1.Laser-beam cutting 2.Water-jet cutting 3.Cutting with a band saw 4.Friction sawing 5.Flame cutting LECTURE 38

DTEL 13  Clearance control determine quality of its sheared edges which influence formability of the sheared part  Appropriate clearance depends on: 1. Type of material and temper 2. Thickness and size of the blank 3. Proximity to the edges of other sheared edges  When sheared edge is rough it can be subjected to a process called shaving Shearing Clearance LECTURE 38

DTEL 14 Shearing: Characteristics and Type of Shearing Dies Punch and Die Shape Punch force increases rapidly during shearing Location of sheared regions can be controlled by beveling the punch and die surfaces

DTEL 15 Bending Sheets, Plates, and Tubes Compensation for Springback Springback is compensated for by overbending the part One method is stretch bending where the part is subjected to tension while being bent Bending Force Excluding friction, the maximum bending force, P, is For a V-die, it is modified to Bending,forming and drawing LECTURE 39

DTEL 16 Also called contour-roll forming or cold-roll forming Used for forming continuous lengths of sheet metal and for large production runs Dimensional tolerances, springback, tearing and buckling of the strip have to be considered Roll Forming:- LECTURE 39

DTEL 17 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 then punch pushes metal into opening  Products: beverage cans, ammunition shells, automobile body panels  Also known as deep drawing (to distinguish it from wire and bar drawing) LECTURE 39

DTEL 18 Deep Drawing  Material beneath punch remains unaffected and becomes cup bottom  Cup wall is formed by pulling the remainder of disk inward the radius of die - Hoop stress tends to cause buckling or wrinkling - Pressure ring is used to suppress wrinkle LECTURE 39