ME3162/ME3162E
NATIONAL UNIVERSITY OF SINGAPORE
ME3162/ME3162E – MANUFACTURING MANUFACTURING PROCESSES
(Semester I : AY2010/2011)
Time Allowed : 2 Hours
INSTRUCTIONS TO CANDIDATES:
1.
This examination paper contains EIGHT (8) questions and comprises SEVEN (7) printed pages.
2.
Answer ALL questions.
3.
This is an OPEN-BOOK EXAMINATION.
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ME3162/ME3162E
QUESTION 1
Figure 1
Which of the four options below is the correct order for making M8 bolts by the thread forming methods shown in Figure 1 to maximize their strength and dimensional accuracy? (a)
Extrude a bar, progressively cold tensile draw down to diameter 8 mm, cut to length, cold upset forge the bolt head, heat treat (heat and quench in oil), cold thread form (ie. cold roll the threads)
(b)
Extrude a bar, progressively cold tensile draw down to diameter 8 mm, cut to length, heat treat (heat and quench in oil), cold upset forge the bolt head, cold thread form (ie. cold roll the threads)
(c)
Extrude a bar, progressively cold tensile draw down to diameter 8 mm, cut to length, cold upset forge the bolt head, cold thread form (ie. cold roll the threads), heat treat (heat and quench in oil),
(d)
Extrude a bar, progressively cold tensile draw down to diameter 8 mm, cut to length, hot upset forge the bolt head, hot thread form (ie. hot roll the threads), heat treat (heat and quench in oil), (4 marks)
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ME3162/ME3162E
QUESTION 2
The fast internet system is possible because of the fibre optic technology in submarine (underwater) communications cables. The fibres are made of glass. Such cables consist of concentric components as shown in Figure 2.
Figure 2
The various components are as follows: Item Material
Purpose
1
High density polyethylene (10 mm outer dia)
Protection against wear and sea creatures
2
Mylar 0.1 mm tape (PET sheet)
Protection against sea-water corrosion
3
Steel wires 1 mm diameter
For strength
4
Aluminium (outer diameter 5 mm)
Water barrier
5
Polycarbonate
Shock absorber
6
Copper tube
Water barrier
7
Petroleum jelly
To fill up space between optical fibres
8
Optical fibres
To transmit signals at the speed of light
Explain how you would manufacture items 1, 2, 3 and 4. (8 marks)
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ME3162/ME3162E
QUESTION 3
Figure 3 shows a portion of a staircase railing. It is made of stainless steel. The top bar is fabricated from a 2 mm thick hollow tube of external diameter 50 mm. The rest are 4 mm thick 40 mm wide plates/slabs. (a)
Starting from the molten stainless steel, trace the entire production process until the final product (ie. the complete railing) (10 marks)
(b)
Describe how will the production process be different from part (a) if the whole railing was made of mild steel (3 marks)
(c)
Describe how will the production process be different from part (a) if the whole railing was made of aluminium (3 marks)
(d)
Describe how will the production process be different from part (a) if the whole railing was made of acrylic (a transparent thermoplastic) (5 marks)
Figure 3
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ME3162/ME3162E
QUESTION 4
Your company is weighing the merits and demerits of the following methods of producing 1 million aluminium disk drive covers, as shown in Figure 4. Draw a table to rank (using the numbers 1,2,3,4,5,6,7) the dimensional accuracy and strength of each of the seven methods of production. (1 = best dimensional accuracy, highest strength, 7 = worst dimensional accuracy, lowest strength)
Figure 4
Dimensional accuracy
Strength
Sand cast Die cast Investment cast Forge, followed by die sinking EDM Shallow draw from cold rolled 2 mm sheet, followed by conventional milling of details and piercing the holes with automatic punch and die Hot roll 5 mm plate, followed by hollowing out using conventional milling and conventionally drilling the holes Powder metallurgy (14 marks)
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ME3162/ME3162E
QUESTION 5
(a)
Figure 5 shows a CD cover. List the reasons why it is made of polystyrene (a thermoplastic) and not mild steel. (6 marks)
Figure 5
(b)
For the CD case (all made of polystyrene) to open easily, the front cover is hinged to the back cover at the left-hand seam. This hinge requires the back cover to have two holes of 3 mm diameter which are included in the injection mold design. Give two main reasons why EDM (Electro-discharge machining) is not a feasible method to drill these holes. (4 marks)
QUESTION 6
Your company is planning to produce four types of steel pipes/tubes as follows: (a)
1 m outer diameter, 10 mm wall thickness, for irrigation of farms
(b)
25 mm outer diameter, 1 mm wall thickness, for water pipes in houses
(c)
25 mm outer diameter, 1 mm wall thickness, for high internal pressure
(d)
1 mm outer diameter, 0.1 mm wall thickness, for hypodermic needles
Match the four methods of production below to each of the above requirements: (i) (ii) (iii) (iv)
roll bending a mild steel plate and joining by submerged arc welding hollow hot extrusion, followed by progressively cold drawing through a die with a central mandrel electrical induction welding of a continuous metal strip passing through rollers method (ii) above, followed by further cold drawing through a die without a central mandrel (8 marks)
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ME3162/ME3162E
QUESTION 7
200 mm diameter steel bar stocks of 320 mm length are to be turned to make 300 mm long shafts of 180 mm diameter using a lathe of 40 KW motor running at an efficiency of 80%. The machining time for both roughing and finishing operations should be completed in 15 min. The specific cutting energy ps, for the work material is 2.75 GJ/m3, and the time taken to load and unload a workpiece is 2 min. Select proper cutting speeds, feed rates, depth of cut, tool materials and type of rake angles for both roughing and finishing operations. (15 marks)
QUESTION 8
Jobs are to be performed using a CNC lathe which costs $100,000.00. The tool holder used on this machine costs $30.00, the tool-holder life is 2000 inserts, cost of each insert is $2 and positive rake angle tools are used. The number of cutting edges of the insert used is 4. As a general practice, the job shop works 8 hours/day, 5 days/week, 40 weeks/year and its amortization period is 10 years. The operator's wage including his overheads is $10/hour. The machine overheads are 80%. The loading/unloading time is 2 min and the tool changing time is 1 min. According to the results of experimental study carried out in the job shop, the Taylor’s tool life equation was found to be VT0.25 = 160 [where V is the cutting speed (m/sec) and T is the tool life (sec)]. 180 mm diameter mild steel shafts are to be machined using this lathe. If the depth of cut used is 2 mm, feed rate is 0.1.5 mm/rev, length of cut on the shaft is 350 mm, calculate (a)
Minimum production cost.
(b)
Minimum production time. (20 marks)
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