Problem 1

A screw thread is cold rolled on a 1015 low-carbon steel bolt of 6.25 mm diameter. Observation shows that the length of the contact zone between die and screw blank is L = 1.25 mm. The average strain hardening during rolling corresponds to a strain of

? = 0.4.

Calculate:

(a) the applicable flow stress, and

(b) the average interface pressure in the contact zone.

Determine:

(c) if there is any danger of internal fracture (make a sketch to illustrate the point).

Problem 2

Circular blanks (slugs) of 1100Al, diameter d = 25 mm and thickness h = 3 mm, are to be mass-produced as the starting material for toothpaste-tube extrusion. The available presses are of 500 N capacity and can take a maximum 220 mm wide strip. Economy of material utilization increases with increasing number of rows cut from one strip width.

(a) Calculate the torque required for blanking a single slug.

(b) Estimate the number of slugs that can be blanked simultaneously with the available press.

(c) Suggest the optimum layout for the slugs if the web (remaining material between cuts at edges) is approximately h, but seldom less than 1 mm.