Recent Question/Assignment

You may use this document for your answers.
You may use separate, hand-written answers IF you follow the instructions on page 1
Question 1 (50 Marks)
(Question 1 has multiple parts. Please answer them all)
A Discuss the purpose, application and relevance of Design for Manufacture and
Assembly in a modern manufacturing process. Consider ‘over-the-wall’ and
‘concurrent’ engineering as alternative manufacturing design paradigms, philosophies, or attitude, as well as the effect of globalisation when making your arguments.
Write your answer in the form of a single coherent essay that has a title, an introduction, a discussion, and a conclusion. You may use the descriptions and questions in points (i) – (iv), in the order you choose, to guide you.
i. The expression ‘over-the-wall’ manufacturing is used to describe a particular design approach (i.e. a paradigm or philosophy) or an attitude, that is, ‘we design it, you make it’. This attitude is said to have serious problems. Why would this be so?
ii. ‘Over-the-wall’ manufacturing is also often shown as a process. How is this different from the ‘we design it, you make it’ attitude?
iii. ‘Concurrent’ engineering is often presented as an alternative for the failings of ‘over-the-wall’. What is it ‘fixing’ - the attitude or the process? Is it a process or an attitude? iv. How does the globalisation of production affect the design and manufacturing process?
As a guide write around 2000 words. Do not write more than 5000 words.
(30 marks)
B The image below shows an exploded view of a ballpoint pen assembly.
B1. For the three parts (refill sub-assembly, barrel, and stopper), show all six combinations of the three parts in Table B1 (overleaf). Recall that in a combination the order of selection does not matter.
Indicate in the space provided whether each combination is a valid assembly order or not, that is, can this combination be assembled? (Yes/No)
Indicate in the space provided which of the assembly order or orders would be preferred or not (Yes/No). Justify your answer by completing the sentence below the table
Part name 1
Part name 2
Part name 3
Valid Assembly order? (Yes/No)
Preferred Assembly order? (Yes/No)
Table B1
Parts are: Refill, stopper and barrel.
Combination(s) _________ is/are a preferred assembly order because _______________________________________________________
_______________________________________________________________________________________________________________ (5 marks)
B2 For one of your preferred assembly orders shown in table B1, complete the following DFA worksheet. Remember to show the total
assembly time, assembly cost, and DFA index (design efficiency): (10 marks total)
Table B2: DFA work sheet
1 2 3 4 5 6 7 8 9
Item Name/Operation ? ? ??? t s
TM CM NM (?? =100*(3*NM/TM))
Table B3: DFA work sheet (for question B3 if required)
1 2 3 4 5 6 7 8 9
Item Name/Operation ? ? ??? t s
TM CM NM (?? =100*(3*NM/TM))
B3 With regard to the design efficiency (or DFA index) and the possible handling difficulties of some of the parts, show design and or component changes to improve the design efficiency. You may use a sketch as an aide to communicate your ideas. Recalculate the design efficiency for your new design and comment on the changes. (5 marks)
Q1 Part B3 (continued)
You may use this document for your answers.
You may use separate, hand-written answers IF you follow the instructions on page 1
Provide ALL assumptions and mathematical steps, ensure you JUSTIFY every answer.
There are maximum 50 marks available in this section. However only Q 3 is worth 30 marks. Q2 and Q4 are worth 20 marks each.
Question 2: (20 Marks)
(Question 2 has three parts A, B and C)
A vibratory-bowl feeder orienting system is designed to orient a part that has four orientations on the bowl track. The first device is a step whose performance can be represented by the following matrix:
The remaining devices are designed to reject orientations b, c, and d.
Experiments showed that the four possible feeding orientations for the part, have the following % probabilities:
a: 27% b: 35% c: 35% d: 3%
A. Present the complete orientation system matrix and the initial part distribution matrix.
B. Determine the feed rate of oriented parts if the input rate to the system is 2.5/sec.
C. estimate the effect on this performance if a further identical step is added to the beginning of the system.
Question 3: (30 Marks)
(Question 3 is in three parts A, B and C)
Analysis of Vibratory Feeder. The track is considered to move bodily with simple harmonic motion along a straight path:
Maximum inertia force acting on a part in vibratory feeding when the track is at its upper limit for motion. Forward sliding is shown.
A. Assuming that the motion of the part is independent of its shape and that air resistance is negligible and that the part does not roll down the track, show that for hopping to occur during the vibration cycle:
If we use the term An/gn to express the dimensionless normal track acceleration, where An is the normal track acceleration (?? = ?? ?? = ?? ?? sin??) and gn is the normal acceleration due to gravity (??cos??), show that for hopping to occur:
B. For values of µs = 0.7, ? = 4°, and ? = 40° what must the ratio of An/gn be greater than for backward sliding? And for forward sliding?
C. Does hopping occur after forward sliding or after backward sliding? Does hopping always occur in the vibration cycle? Fully Justify your answer. Include in your answer your own diagrams, and all your working out. (10 Marks)

Question 4: (20 Marks)
(Question 4 is in two parts: A and B)
A. A fully automatic 4 station high speed assembly system operates on a cycle time of 7 seconds. It is fed with components having on average a ratio of defective components to acceptable components of 2%. Approximately 80% of the defective components will cause the machine to stop and on average it takes 30 seconds to clear a fault. The machine is required to produce 450 acceptable assemblies per hour on a production run basis. Calculate the ‘down-time’ on the system due to defective components and comment of the feasibility of achieving the target of acceptable assemblies. Justify any expression used in the analysis.
B. Considering your answer to Part A, suggest ways of reducing down-time on assembly machines caused by defective components.

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