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UNIVERSITY OF MALTA

FACULTY OF ENGINEERING

B. ENG (HONS.) YEAR IV

MAY/JUNE 2015 SESSION OF EXAMINATIONS

MFE4210 Introduction to Tool Design and Manufacture 30th

May 2015

Time: 11:3013:35hours

Reading time: 11:30 11:35am

Duration of examination: 11:35am 13:35hours

This paper contains fourquestions. You are to answer any three.

Use of calculators is allowed.

1. a) Explain briefly the definition of a 2-plate mould, 3-plate mould and stack mould.

b) With regard to cold runner system:

i. What are the fourdesign criteria for runner system?

ii.

In which case is there always imbalance? Explain the reason why imbalance

occurs.

c) What is the difference between 2.5D and 3D simulation for injection moulding?

d) Which twoimportant properties of tool steel are affected by the content of chromium in

opposite ways?

e) Which permissible stress is used to calculate the minimum total ejection area for

amorphous and semi-crystalline polymer? Give reasons for your answer.

f) Explain the use of Reynolds number to design cooling channels.

(33 marks)

2. A cold runner, 2-cavity injection mould is to be designed for manufacturing square

covers with snap fits as shown in Figure 1.

a)Would you change the design of the cover before you start with the mould design? Give

reasons for your answer. If you would change the design, explain and sketch the

change. (6 marks)

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b)With regard to mould design:

i.

Explain and determine the suitable position of parting line.

ii. If the moulded covers have to be automatically degated (direct separation from the

runner), sketch and explain briefly threedifferent ways for an automatic degating.

Different mould types may be used.

iii. Select and explain the most suitable ejector type.

iv. Sketch the mould with the all necessary components. It is sufficient to sketch one

mould half only (from the symmetry plane dividing the two cavities).

(23 marks)

c)

Explain what type of polymer material is suitable for such covers with snap fits?

(4 marks)

3.

iMolding Ltdis an injection moulding company that always subcontracts the works related

to the mould design and manufacture to mould making companies. It received the first

design draft from a mould maker that is shown in Figure 2.

a)Name the type of the mould, two functions of component no 1 and explain how this

component works to fulfil both functions. (7 marks)

b)At the same time period, iMolding Ltdwishes to invest in hot manifolds and to change

from cold runner to hot runner system and from 2-cavity to 4-cavity mould:

i. Explain the major advantages and disadvantages of cold runner system.

ii. Sketch the cavity layout for the hot runner system using only twonozzles.

iii. Sketch the cavity layout for the hot runner system using fournozzles.

iv. Explain the main advantages and disadvantages of hot runner system sketched in

bii) and biii) with regardto the melt flowand material usage.v. Are the cavity layout from bii) and biii) a balanced layout? Give reasons for your

answer.

vi. Does one of the cavity layouts need venting? Give reasons for your answer.

(26 marks)

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4. Hooks with a mounting hole and a thickness of 2 mm, as shown in Figure 3, are to be

manufactured using Polystyrene (PS) and a 2-plate mould with 2 cavities.

a) Explain:

i.

Mould type,

ii. Gate type,

iii. Position of the gate, and

iv. Position of the parting line you would choose for such parts.

(12 marks)

b)

According to your choices in a), sketch the mould only in the cavity region including

some portion of the cavity plates, runner, gate, and ejection component(s).

(6 marks)

c)

Calculate the ejection force using this known data:

-

Youngs modulus of PS= 3000 N/mm

- Coefficient of friction between PS and tool steel = 0.4

-

Coefficient of linear expansion of PS = 7 x 10-4/C

- Softening temperature of PS = 80C

- Mould temperature = 20C

- Poisson's ratio of PS = 0.35

(11 marks)

d)The outer surface of the hook is cooled using cooling circuits that can be connected in

series or parallel. Explain the advantages and disadvantages of both types of circuit

connections.

(4 marks)

Figure 1: Drawing of a square cover with snap fits

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Figure 2a: A cross-sectional view of an injection mould

Figure 3: Drawing of a hook