1. A company proposes to manufacture barbecue spits by locally flattening 5 mm diameter mild steel wire. The process is to be done cold with a lubricant which gives a friction coefficient between the die and the workpiece of 0.1. The flattened portions are 50 mm long and 2 mm thick. For steel: K = 620 MPa and n = 0.18.

a) Sketch the feature after manufacture

b) Identify the strain category, with justification.

c) Estimate the force required (use chart supplied).

(plane strain, 448 kN).

2. a) Why is oxygen used with acetylene for gas welding of steel rather than air with acetylene?

b) Why may polymers be filled with an inert material?

c) What is an elastomer and explain briefly how its properties are varied.

3. Why is the clearance between the punch and die important in sheet metal blanking / punching operations. Briefly describe some of the disadvantages and problems that may occur if working with non-optimum clearance. Use simple sketches if appropriate.

4. Describe briefly the wear and failure mechanisms that cutting tools / tips used on a lathe may suffer. Use simple sketches where appropriate.
Summarise the key developments in cutting tool technology that have helped to reduce these wear mechanisms and increase tool life.

5. What are the advantages and limitations of using cutting tools for a lathe or milling machine made from the following materials:

a) High speed steel (HSS)

b) Tungsten carbide

c) Tools coated with diamond.

6. A cylindrical copper billet 50 mm in diameter and 100 mm high is to be upset at 900^oC to a 15 mm thick disc. The speed of the press is 2.4 m/minute and a lubricant reduces the coefficient of friction between the tools and workpiece to 0.2. Sketch the process, calculate the average die pressure and the force needed to achieve this operation (C = 41 MPa, m = 0.2).
What would you expect to happen if no lubricant was used? (89.8 MPa, 1.18 MN).

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David J Grieve, 21st November 2002.