Manufacturing Processes - Tutorial 1

1. Sketch Mohrs Circle to represent the state of stress in the following:

• uniaxial tension
• uniaxial compression
• plane stress
• plane stress - special case - pure shear
• plane strain
• hydrostatic compression
• triaxial tension

2. What are the approximate temperature ranges where hot and cold working are carried out? What are the relative merits of these 2 types of processing?

3. Why do the yield strength and UTS of metals increase with increasing amounts of cold work? How can the effects of cold work be removed?

4. What defects may occur in an extrusion process?

5. Explain, with the aid of Mohrs Circle diagrams why applying back tension can be beneficial in rolling and wire drawing.

6. Show that during a cold tension test the maximum load occurs at the point when n (the strain hardening exponent) is approximately equal the true strain, epsilon.

7. A Ti6Al4V titanium billet, 1.5 m long x 100 mm diameter is being forged at 900^oC and reduced to a rectangular slab with a thickness of 30 mm.
Sketch the process.
Can this process be described as plane strain and if so why, or if not, why not?
Determine the press force required, assume the press has a constant speed of 0.05 m/s and the coefficient of friction is 0.2
Briefly state why it is important to complete the operation in the minimum time.
Solution

8. A steel strip 2 mm thick is cold rolled through a 4 stand tandem mill. A reduction of 40% is taken at each pass. The strip speed into the first pass is 3 m /s. Calculate the strip thickness and strip speed after each stand.
1.2, 0.72, 0.432, 0.26; 5, 8.33, 13.9, 23.15 m/s.
Solution

9. A stainless steel billet 80 mm diameter and 160 mm high is upset at 1000^oC to a 20 mm high 'pancake'. The press speed is 3 m/minute and a graphite lubricant reduces the friction coefficient to 0.2. Sketch the process and calculate the average die pressure and total force. For the material, C = 170 MPa and m = 0.1 (see chart from appropriate text).
17.2 MN
Solution

10. Determine the maximum theoretical reduction possible in wire drawing, without back tension, neglecting friction and assuming no work hardening.
(d_o / d₁) = 1.65
Solution

11. The initial stage in the manufacture of a knife blade made from grade 410 stainless steel involves forging a 90 mm length of 8mm dia. bar at 1000^oC in a press with a speed of 0.005 m/s. You may assume that the frictional shear factor is 0.2.
Sketch the process, determine the maximum mean platen pressure and the force required to carry out the operation.
Soln: P_p = 214.3 MPa, force = 323000N. click here

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