Question & Answer

A 20-in-long sheet-metal workpiece is stretched in a stretch forming operation to the dimensions shown in Figure P20.31. The thickness of the beginning stock is 3/16 in and the width is 8.5 in. The metal has a flow curve defined by a strength coefficient of 75,000 lb/in2 and a strain hardening exponent of 0.20. The yield strength of the material is 30,000 lb/in2 . (a) Find the stretching force F required near the beginning of the operation when yielding first occurs. Determine (b) true strain experienced by the metal, (c) stretching force F, and (d) die force Fdie at the very end when the part is formed as indicated in Figure P20.31(b).

A cup-shaped part is to be drawn without a blankholder from sheet metal whose thickness = 0.25 in. The inside diameter of the cup = 2.5 in, its height = 1.5 in, and the corner radius at the base = 0.375 in. (a) What is the minimum starting blank diameter that can be used, according to Eq. (20.14)? (b) Does this blank diameter provide sufficient material to complete the cup?

The foreman in the drawing section of the shop brings to you several samples of parts that have been drawn in the shop. The samples have various defects. One has ears, another has wrinkles, and still a third has torn sections at its base. What are the causes of each of these defects and what remedies would you propose?

Solve Problem 20.27 except that the corner radius on the punch = 10 mm.

Solve Problem 20.26 except that the height = 60 mm

A drawing operation is performed on 3.0 mm stock. The part is a cylindrical cup with height = 50 mm and inside diameter = 70 mm. Assume the corner radius on the punch is zero. (a) Find the required starting blank size Db. (b) Is the drawing operation feasible?

Solve Problem 20.24 except use a punch radius = 0.375 in

A deep drawing operation is to be performed on a sheet-metal blank that is 1/8 in thick. The height (inside dimension) of the cup = 3.8 in and the diameter (inside dimension) = 5.0 in. Assuming the punch radius = 0, compute the starting diameter of the blank to complete the operation with no material left in the flange. Is the operation feasible (ignoring the fact that the punch radius is too small)?

A cup-drawing operation is performed in which the inside diameter = 80 mm and the height = 50 mm. The stock thickness = 3.0 mm, and the starting blank diameter = 150 mm. Punch and die radii = 4 mm. Tensile strength = 400 MPa and yield strength = 180 MPa for this sheet metal. Determine (a) drawing ratio, (b) reduction, (c) drawing force, and (d) blankholder force.

Solve Problem 20.21 except that the stock thickness t = 1/8 in.

A deep drawing operation is performed in which the inside of the cylindrical cup has a diameter of 4.25 in and a height = 2.65 in. The stock thickness = 3/16 in, and the starting blank diameter = 7.7 in. Punch and die radii = 5/32 in. The metal has a tensile strength = 65,000 lb/in2 , a yield strength = 32,000 lb/in2 , and a shear strength of 40,000 lb/in2 . Determine (a) drawing ratio, (b) reduction, (c) drawing force, and (d) blankholder force

Solve Problem 20.19 except that the starting blank size diameter = 175 mm

A cup is to be drawn in a deep drawing operation. The height of the cup is 75 mm and its inside diameter = 100 mm. The sheet-metal thickness = 2 mm. If the blank diameter = 225 mm, determine (a) drawing ratio, (b) reduction, and (c) thickness-to-diameter ratio. (d) Does the operation seem feasible?

Derive an expression for the reduction r in drawing as a function of drawing ratio DR.

A sheet-metal part 3.0 mm thick and 20.0 mm long is bent to an included angle = 60° and a bend radius = 7.5 mm in a V-die. The metal has a yield strength = 220 MPa and a tensile strength = 340 MPa. Compute the required force to bend the part, given that the die opening dimension = 15 mm.

Solve Problem 20.15 except that the operation is performed using a wiping die with die opening dimension = 0.75 in.

Determine the bending force required in Problem 20.11 if the bend is to be performed in a V-die with a die opening width dimension = 1.25 in. The material has a tensile strength = 70,000 lb/in² .

Solve Problem 20.13 except that the operation is performed using a wiping die with die opening dimension = 28 mm.

Determine the bending force required in Problem 20.9 if the bend is to be performed in a V-die with a die opening dimension of 40 mm. The material has a tensile strength of 600 MPa and a shear strength of 430 MPa

A bending operation is to be performed on 4.0 mm thick cold-rolled steel sheet that is 25 mm wide and 100 mm long. The sheet is bent along the 25 mm direction, so that the bend is 25 mm long. The resulting sheet metal part has an acute angle of 30° and a bend radius of 6 mm. Determine (a) the bend allowance and (b) the length of the neutral axis of the part after the bend. (Hint: the length of the neutral axis before the bend = 100.0 mm).

An L-shaped part is to be bent in a V-bending operation on a press brake from a flat blank 4.0 in by 1.5 in that is 5/32 in thick. The bend of 90° is to be made in the middle of the 4-in length. (a) Determine the dimensions of the two equal sides that will result after the bend, if the bend radius = 3/16 in. For convenience, these sides should be measured to the beginning of the bend radius. (b) Also, determine the length of the part's neutral axis after the bend. (c) Where should the machine operator set the stop on the press brake relative to the starting length of the part?

Solve Problem 20.9 except that the bend radius R = 11.35 mm

A bending operation is to be performed on 5.00 mm thick cold-rolled steel. The part drawing is given in Figure P20.9. Determine the blank size required.

The foreman in the pressworking section comes to you with the problem of a blanking operation that is producing parts with excessive burrs. (a) What are the possible reasons for the burrs, and (b) what can be done to correct the condition?

Determine the tonnage requirement for the blanking operation in Problem 20.4, given that the stainless steel has a yield strength = 500 MPa, a shear strength = 600 MPa, and a tensile strength = 700 MPa