ENGMP214-23A

2023 A TRIMESTER EXAMINATIONS

SECTION A

(Answer All TWENTY-FIVE questions from this section on the multi-choice answer sheet provided. Each question is worth 1 mark)

1 Which one of the following temperatures would you choose as the best sintering

temperature for a powder compact consisting of only Ti powder (the melting point of Ti powder is about 1668°C)?

A 800°C B 1350°C C 1250°C D 700°C

2 In surface roughness measurement, the direction of the predominant surface pattern produced during processing is called:

A Surface roughness B Waviness

C Lay D Flaw

3 Which of the following design features would be difficult or impossible to achieve by conventional pressing and sintering?

(i)      outside rounded corners

(ii)     side holes

(iii)   threaded holes

(iv)    vertical stepped holes

(v)     vertical wall thickness of 1/8 inch (3 mm)

A (ii), (iii), and (iv) B (i), (ii), and (v)

C (i), (ii), and (iii) D (iii), (iv), and (v)

4 Which feeding mechanism requires the highest pressure?

A Liquid feeding B Mass feeding

C Interdendritic feeding D Solid feeding

5 In snap GO/NO-GO gages, which one of the following best describes the function of the GO gage:

A Check limit of maximum tolerance B Check maximum size

C Check minimum size D None of All

6 Which of the following is NOT the purpose of powder compacting?

A To achieve the shape of the final product

B To make the distribution of the green density of the compact more uniform.

C To establish contacts between particles which are needed for sintering

D To establish a metallurgical bonding between powder particles

7 In designing a casting pattern, which of the following is NOT a consideration:

A Shrinkage allowance must be given

B Position of parting line must allow removal of the pattern after moulding

C Draft allowance (1-2o) is needed to assist removal of pattern

D An appropriate material needs to be selected

8 Which one of the following powder metallurgy processes does NOT involve the powder compacting step?

A Vacuum sintering B Powder compact forging

C Laser sintering D Sinter-HIP

9 Total solidification time is defined as which one of the following:

A Time between pouring and complete solidification

B Time between pouring and cooling to room temperature

C Time between solidification and cooling to room temperature

D Time to give up the heat of fusion

10 Which of the following are advantages and characteristics of hot working relative to cold working:

(i)        fracture of workpart is less likely

(ii)       friction is reduced

(iii)     increased strength properties

(iv)      isotropic mechanical properties

(v)       less overall energy is required

(vi)      lower deformation forces is required

(vii)    more significant shape changes are possible

(viii)    strain-rate sensitivity is reduced

A (i), (ii), (iv), and (vii) B (iii), (iv), (v), and (viii)

C (i), (iv), (vi), and (vii) D (ii), (iv), (v), and (vii)

11 During solidification of an alloy when a mixture of solid and liquid metals is

present, the solid-liquid mixture is referred to as which one of the following:

A Eutectic composition B Liquidus

C Pasty Zone D Solidus

12 Which one of the following arc-welding processes uses a non-consumable electrode?

A Gas Melt Arc Welding B Gas Tungsten Arc Welding

C Shield Metal Arc Welding D Submerged Arc Welding

13 Which of the following rolling mill types are associated with relatively small diameter rolls in contact with the workpiece:

(i)      cluster mill

(ii)     four-high mill

(iii)   continuous rolling mill

(iv)    reversing mill

(v)     three-high configuration

A (i) and (ii) B (i) and (iii)

C (ii) and (iv) D (iv) and (v)

14 Which of the following statements is NOT correct:

A The weldability of steel is determined by the extent of transformation to unwanted microstructure in the fusion zone and HAZ during cooling

B The weldability of steel is related to the steel’s hardenability

C Carbon Equivalent (CE) is a measure of the ease of transformation to martensite in the fusion zone and HAZ during cooling

D If the Carbon Equivalent (CE) of a steel is higher than 0.45, the weldability is high

15 Turbulence during pouring of molten metal is undesirable for which of the following reasons:

A It causes discoloration of the mould surfaces

B It dissolves the binder used to hold together the sand mould

C It increases erosion of the mould surfaces

D It increases the mould filling time

16 Which of the following solid-state welding processes applies heat from an external source:

A Diffusion Welding B Friction Welding

C Ultrasonic Welding D Cold Welding

17 Which of the following descriptions regarding mechanical forming is NOT correct:

A The material must allow a sufficient amount of plastic deformation without fracturing

B The force applied must be sufficient to cause the required amount of plastic deformation of the workpiece

C The majority of materials shaped by mechanical forming are metallic materials

D Both bending and wire drawing are bulk deformation processes

18 Which of following descriptions are correct:

(i)      Extrusion is a process in which metal is compressed and forced through the shaped die opening

(ii)    During the extrusion, the metal in the centre of the billet experiences little shear

(iii)   During the extrusion, the metal in the centre of the billet experiences large shear

(iv)    During the extrusion, the metal near the edge of the billet experiences a large amount of shear

(v)     During the extrusion, the metal near the edge of the billet experiences a little amount of shear

(vi)    During the extrusion, the billet experiences a uniform. deformation

A (i) and (vi) B (i), (iii), and (v)

C (iii) and (v) D (ii) and (iv)

19 The advantages of non-destructive testing include:

A Provide a direct and reliable measurement on how the materials respond to service conditions

B Can be performed on 100% of the components produced

C Different tests can be performed on the same component

D Both (b) and (c)

20 Which of the following processes are classified as fusion welding?

(i)      oxyful gas welding

(ii)     electron-beam welding

(iii)   explosion welding

(iv)    forge welding

(v)     laser-beam welding

(vi)    ultrasonic welding

A (i), (ii), and (iii) B (ii), (iii), and (iv)

C (iv), (v), and (vi) D (i), (ii), and (v)

21 Aluminium and titanium slabs are rolled at 400°C for making aluminium and titanium plates, which of following description regarding the working process type is correct?   (The melting point for Aluminium is about 660°C and titanium is about 1660°C):

A Hot working for both of aluminium and titanium

B Hot working for aluminium and cold working for titanium

C Cold working for aluminium and hot working for titanium

D None of above

22 The size and properties of HAZ do not depend on:

A Rate of Heat Input B Rate of Cooling

C The Temperature Reached D Filler Meal Used

23 A tolerance is which one of the followings:

A Clearance between a shaft and a mating hole

B Measurement error

C Total permissible variation from a specified dimension

D Variation in manufacturing

24 An outside caliper would be appropriate for measuring which of the followings:

A Hole depth B Hole diameter

C Part length D Surface roughness

25 In cold isostatic pressing, the mold is most typically made of which one of the followings:

A Rubber B Sheet metal C Textile D Polymer

SECTION B

(Answer All THREE questions from this section)

26         A Why is it important to ensure that the density distribution of a powder compact is as uniform as possible? What techniques are used to ensure that the density distribution of a powder compact is as uniform as possible?     (5 marks)

B Please  describe how to use the conventional powder metallurgy process to make a cylindrical Ti-6Al-4V (wt.%) alloy part from elemental powders (such as titanium powder, aluminum powder, and vanadium powder). Please also discuss the major concerns of the process.                                                                                                (6 marks)

C Describe a basic rolling process of a steel slab consisting of equiaxed grains and how the  microstructure   of  the   slab   changes   during   hot   rolling   and   cold   rolling, respectively.           (7 marks)

D Please use words and drawings to discuss how the ram force changes during the direct and in-direct extrusion.             (7 marks)

27         A A cylindrical riser must be designed for a sand-casting mould. The casting itself is a steel rectangular plate with dimensions  12.5cm×7.5cm×2cm. Previous observations have  indicated  that  the  total  solidification  time  for  this  casting  t  =  1.6min.  The cylinder for the riser will have a diameter-height ratio=1.0. Please use Chvorinov’s rule (t=Cm(V/A)2) to determine the minimum dimensions of the riser.                   (5 marks)

B Please  describe how to use the investment casting process to make a titanium part with a maximum dimensional size of 50mm and a 2mm thin-wall section (Figure 1, below).     Please     also     discuss     the      major     concerns      of     the     process. (6 marks)

Figure 1. Titanium part

C Please  refer to the Figure  2  Iron-Carbon  equilibrium phase  diagram  (on  the next page), discuss how the phase and microstructure change in the fusion zone and heat affected zone (HAZ) of a welded cold-worked low carbon steel.                          (9 marks)

Figure 2. Iron-Carbon equilibrium phase diagram

D Please discuss how the “sensitisation” phenomenon is formed in stainless steel, and

how to avoid/eliminate this phenomenon.                                                        (5 marks)

28         A Your  company  is  asked  to  manufacture  1,000,000 plastic boxes  such  as  the  one sketched in Figure 3 (below) (length = 15 cm, width = 15 cm, and height = 10 cm).

i.      Comment on which process you would use to make the boxes. Your answer is expected to include (but it is not limited to): type of polymers to be used and why, justification  of the  chosen process,  and  a  detailed  description  of the process including the discussion of relevant manufacturing aspects.

ii.      Briefly describe the process you would use if a batch of 1,000 much bigger boxes (length = 2.5 m, width = 2.5 m, and height = 2 m) were to be manufactured.              (9 marks)

Figure 3. Dimension of plastic boxes to be manufactured.

B A cylindrical stock of ∅74 mm × 200 mm mounted on the chuck (Figure 4, below) is used to machine a shaft of ∅71 mm × 55 mm using a lathe. A total length of 70 mm of the AISI 1026 cylindrical stock is turned down to ∅71 mm.

i.     List  the   operations  and  the  tools  to  obtain  a   finished  part   separated  from  the cylindrical        stock.

ii.     Calculate the spindle speed for the turning operation (Note: state your assumptions) and briefly comment on the main factors determining the cutting speed and the ones affecting the feed rate.    [5 marks]

Figure 4. Sketch of the ∅74 mm × 200 mm cylindrical stock mounted on the chuck.

Formulae:

Table 1. Cutting speed chart.

C Describe two peripheral milling operations and two face milling operations highlighting any similarities or differences between those milling operations.    (4 marks)

D Name and briefly describe the four types of chip formation mechanisms. Your

answer should include (but it is not limited to) the type of material, the cutting conditions, the relevant tool’s parameters, and the primary deformation mechanism.                                                                       (7 marks)