MMME1043-E1 Materials and Manufacturing
Materials and Manufacturing
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MMME1043-E1
Materials and Manufacturing
Time allowed TWO Hours
Candidates may complete the front cover of their answer book and sign their desk card but
must NOT write anything else until the start of the examination period is announced.
Answer ALL questions
Only silent, self-contained calculators with a Single-Line Display, or Dual-Line Display are
permitted in this examination.
Dictionaries are not allowed with one exception. Those whose first language is not English
may use a standard translation dictionary to translate between that language and English
provided that neither language is the subject of this examination. Subject specific translation
dictionaries are not permitted.
No electronic devices capable of storing and retrieving text, including electronic dictionaries,
may be used.
DO NOT turn examination paper over until instructed to do so
In this exam students are required to answer All questions
ADDITIONAL MATERIAL:
INFORMATION FOR INVIGILATOR:
Students MUST LEAVE the question paper, the answer sheets and any rough paper in the
examination room.
Please collect ALL examination papers, the answer sheets and any rough paper and return
them to the Department with the examination scripts.
1. An example of a key is shown below in Figure Q1.
Figure Q1
a) The material used for the key is an alloy steel. State one advantage of using alloy
steel over ceramic and one advantage over polymer for this application.
[2 marks]
b) The initial shape of the key (without the fine details for the locker) was made from a
large sheet of steel via deformation processes. Please describe how the initial shape
of the key is made.
[2 marks]
c) Describe how the fine details of the key for the locker are obtained.
[1 mark]
d) The final step is electro-plating a thin NiCu layer on the key. Explain why this is
helpful for the key.
[2 marks]
e) The key can also be made by die casting. With the aid of a suitable sketch, describe
the die casting process of the key.
[4 marks]
f) The fracture toughness of the alloy steel is 150 MPa m1/2. Use the following
equation,
1 = 1.1σ√
(i) assume the allowed stress is 800 MPa, calculate the maximum allowed crack
size.
(ii) assume the cracks size produced from die casting is 5 mm, calculate the
maximum allowed stress.
[4 marks]
Continued on the next page
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g) To improve the toughness of the key after die casting, quenching and tempering
process are applied. Describe the quenching and tempering process and explain how
the toughness is enhanced.
[4 marks]
h) The die casting process time to make the key is 0.5 mins. The load and unload the
machine takes 0.2 mins. The time to change and reset the tooling for 40 parts is 3
mins. Calculate the cycle time for each part in mins.
[3 marks]
i) Laser additive manufacturing can be used to make the key but it is less competitive.
List THREE reasons why laser additive manufacturing is not a good choice to make
this key.
[2 marks]
j) A company would like to identify a cheaper process for manufacturing different batch
sizes of the key. Approximate cost data are given below.
Process 1 Process 2
Material cost, Cm 5 6
Overhead rate, Ċoh ( hr-1) 110 230
Tool cost, Ct 1500 25,000
Production rate, ṅ (hr-1) 10 200
Given: The equation for the cost of a component is given as follow:
where n = batch size.
i) Identify the batch size at which Process 1 and Process 2 have the same cost.
ii) Calculate the cost at the batch size obtained from i).
iii) State which process is cheaper when the batch size is 100,000.
[6 marks]
Turn Over
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2. A lightweight material is required as a temporary bridging material for people to cross a
stream 5 m wide (L). The design is as shown in Figure Q2a. It takes the form of a solid plank
with breadth, b, and depth, h, and should be as light as possible. The breadth, b, is to be 180
mm to ensure reasonable footing for each person. It is found that the deflection, , cannot be
more than 240 mm to ensure the stability of the person crossing the bridge. The plank should
support the weight, F, of up to 1500 N.
Figure Q2a
The deflection of the panel is given by,
δ =
3
48
where I = bh3/12, E is the Young’s modulus of the material.
(a) Write an equation for the mass, m, of the plank in terms of its dimensions and
material properties.
[2 marks]
(b) To minimise the mass, m, derive the performance equation for mass with free variable
eliminated.
[4 marks]
(c) Write down an expression in terms of material properties to minimise the mass of the
plank.
[2 marks]
An aluminium-copper alloy is selected for this application. Figure Q2b is a schematic diagram
of the Al-Cu phase diagram (NOT drawn to scale). Three phases are shown, namely two solid
phases and θ, and the liquid L. You may assume that all phase boundaries are straight
lines. The dotted lines are not phase boundaries, but simply give an indication of what
compositions are being referred to.