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Cork Institute of Technology
Bachelor of Engineering (Honours) in Mechanical Engineering- Stage 3
(NFQ Level 8)
Summer 2007
Manufacturing Engineering
(Time: 3 Hours)
Instructions: Answer FIVE questions Answer TWO from each of Sections A and B and ONE from section C Use a separate answer book for each section
Examiners: Mr. M. P. O’Mahony Dr. M. Woods Mr. D. Fallon Mr. P. Clarke Prof. M. Gilchrist
Section A
Q1. (a) List FIVE advantages and/or disadvantages of thread rolling. ( 5 Marks ) (b) Briefly describe ONE method of Thread grinding. ( 5 Marks ) (c) A special fine thread has a nominal outside diameter of 4 inches. The pitch is 0.25in and the threads are of Whitworth Form. The thread is acceptable if the effective diameter is between nominal size and minus 0.008 in. When checked with wires of diameter 0.15in the dimensions over wires was 4.070 in. If the flank angle and pitch are correct, calculate the effective diameter and hence state whether the thread is acceptable. (Note Height of fundamental triangle for Whitworth H= 0.9605P) (8 Marks) (d) When measuring the effective diameter of a thread, explain what is meant by the term “Best Wire”. (2 Marks)
Q2. (a) Compare Die-Casting to Sand Casting; costs, materials, methods, volume, applications, examples. (10 Marks) (b) In the context of Casting describe the purpose and use of the following: Chaplet Chill (4 Marks) (c) Using diagrams, describe THREE casting defects. (6 Marks)
Q3. (a) The shape as illustrated in Fig Q3 is to be punched in steel plate 4mm thick. The material is a cold rolled 0.4% carbon steel for which the ultimate shear stress is 550N/mm^2. With 10% clearance on the tool, cutting is complete at 40% penetration of the punch. Give suitable dimensions for the Punch & Die. If shear is put on the punch along the XX axis equal to the thickness of the material, estimate the minimum Press size in tonnes required. (9 Marks) (b) Using the manufacture of a simple flat washer from a continuous strip as an example, explain the difference between “Progressive Die” and “Compound Die” construction for a blanking operation. (4 Marks) (c) List FOUR rules that should be followed in the design of piercing and blanking dies. (4 Marks) (d) List Three ways of countering the effects of Springback in a bending operation. (3 Marks)
Fig Q
Q6. (a) (i) Briefly describe the physical conditions required for fast fracture occur in a component. (ii) State the (^) equation for the energy requirements for fast fracture when a load performs work δW. (iii) Define the toughness (Gc ) for a material. Comment on the relative values of Gc for ductile metals and ceramics. (6 marks) (b) State the fast fracture condition equation. Define each of the parameters in the equation. A titanium alloy aircraft component has a fracture toughness Kc = 65 MN m-3/2^. What is the maximum crack size that can be tolerated at the surface before fast fracture occurs when a stress of 250 MN m-2^ is applied? (6 marks) (c) (i) At what temperatures does creep become significant for a metal of melting point Tm? (ii) Explain the role of dislocations and diffusion for Power Law Creep. How does temperature and stress affect these roles? (iii) Describe ONE example of the effects of Power Law Creep for a turbine for either constant load or constant displacement. (8 marks)
Section C: Quality Engineering
Q7. (a) A company can choose to use the following techniques to ensure high quality, i. 100% Inspection ii. Acceptance Sampling iii. Use of Control Charts Briefly define each technique and state a major advantage and disadvantage associated with each. (9 marks) (b) Which attribute control chart would you use if you were investigating the following: i. Cracked ‘Polo Mints’ found by customers ii. Scratches on a dashboard Explain the reason for your choice. (4 marks) (c) Calculate the centre line and control limits for a np-chart with the following data.
Table Q1 - Data for np-chart Lot Number Sample Size No. Defective 1 100 9 2 100 6 3 100 7 4 100 3 5 100 4 6 100 6 7 100 3 8 100 3 9 100 3 10 100 4 11 100 4 12 100 6 13 100 4 14 100 5 15 100 2 16 100 3 17 100 2 18 100 8 19 100 4 20 100 3 21 100 2 22 100 3 23 100 4 24 100 8 25 100 6 Σ= 112 (7 marks)
Q8. (a) Explain how the Taguchi loss function deals with the concept of variability and how this differs from a more traditional approach using tolerances_. (8 Marks)_
(b) Control charts for (^) X and R are maintained for an important quality characteristic. The sample size is six. X (Sample Mean) and R (Sample Range) are computed for each sample. After 25 samples we have found that
4550
25 1
∑^ =
i =
Xi and 560
25 1
∑^ =
i =
Ri
(i) If the quality characteristic is normally distributed and if the specifications are 190 ± 20, calculate the Cp and the Cpk indices. Make a comment on the process capability. (^) (8 Marks) (ii) Suppose the finished part sells for €250 and an average of 10,000 parts are made each year; Calculate the loss to society using the Taguchi loss function and make a comment on your answer. (4 Marks)
