Cork Institute of Technology

Bachelor of Engineering (Honours) in Mechanical Engineering – Stage 3

(Bachelor of Engineering in Mechanical Engineering – Stage 3) (NFQ – Level 8)

Autumn 2005 Manufacturing Engineering

(Time: 3 Hours) Instructions Answer FIVE questions. Answer TWO from each of Sections A and B and ONE from Section C. Use a separate answer book for each section.

Examiners: Mr. M. P. O’Mahony Dr. M. Woods Mr. D. Fallon

Prof. J. Monaghan Mr. J. E. Hegarty

Section A

Q1. (a) List FIVE advantages and/or disadvantages of thread rolling. (5 Marks)

(b) Briefly describe ONE method of Thread grinding. (5 Marks)

(c) A special fine thread has a nominal outside diameter of 4 inches. The pitch is 0.25in and

the threads are of Whitworth Form. The thread is acceptable if the effective diameter is

between nominal size and minus 0.008 in. When checked with wires of diameter 0.15in the

dimensions over wires was 4.070 in. If the flank angle and pitch are correct, calculate the

effective diameter and hence state whether the thread is acceptable.

(Note Height of fundamental triangle for Whitworth H= 0.9605P) (8 Marks)

(d) When measuring the effective diameter of a thread, explain what is meant by the term

“Best Wire”? (2 Marks)

Q2. (a) An approximation to the work done in deforming a metal can be made, subject to two

important assumptions. What are these assumptions? (4 Marks)

(b) A billet of aluminum 25mm dia x 38mm long is compressed between flat parallel steel

anvils to a length of 19mm. The initial yield stress is 65.4N/mm2 and after 50% reduction

the yield stress is 82.7N/mm2. Find the frictionless work done in deforming the material

and the mean force which would produce this amount of work.

If µ = 0.14 find the maximum load to be exerted. (6 Marks)

(c) List Three ways of countering the effects of Springback in a bending operation. (3 Marks)

(d) Fig Q2 (below)shows the dimensions of a bracket required to be bent from a flat strip of

mild steel of 450N/mm2 yield stress. If the work is drawn to a depth of 18mm below the

top surface of the die, find the punch load required for:

(i) Bending (1 Mark)

(ii) Overcoming friction, assuming the sides of the component are very slightly ironed,

take µ=0.15 (2 Marks)

(iii) Planishing at the end of the stroke (2 Marks)

(e) List TWO rules that should be followed in the design of piercing and blanking dies.

(2 Marks)

Figure 2 Q3. (a) In the context of Casting describe the purpose and use of the following:

Chaplet

Chill

Riser (6 Marks)

(b) Using diagrams, describe FOUR casting defects. 8 Marks)

(c) A cylindrical riser must be designed for a sand casting mold. The casting itself is a steel

rectangular plate with dimensions 3.0”x5.0”x1.0”. The ts for this casting is 1.6min. The

cylinder for the riser will have a D/h ratio = 1.0. Determine the dimension of the riser so

that it’s ts is 25% more than the casting. Take n=2. (6 Marks)

Section B

Q4. (a) (i) Describe the fast fracture micro-mechanism for metals. What difference is there in the

micro-mechanism between hard and soft metals? Use diagrams to illustrate your

answer.

(ii) Compare the difference in the appearance under a microscope of a material failing by

fast fracture by the ductile tearing process with that of the cleavage process.

(6 marks)

(b) A pin is inserted into partially inflated and fully inflated balloons. Explain why the

partially inflated balloon does not burst, whereas the fully inflated balloon bursts by fast

fracture. State the energetic conditions for a tear to propagate when a balloon bursts.

(4 marks)

(c) State the fast fracture condition. Define each of the parameters in the equation.

An aluminium, alloy component has a fracture toughness Kc = 23 MN m-3/2.

What is the maximum crack size that can be tolerated at the surface before fast fracture

occurs when a stress of 125 MN m-2 is applied? (6 marks)

(d) Describe the mechanism for fatigue in a metal. (4 marks)

Q5. (a) What is diffusion? Describe how substitutional [vacancy] diffusion occurs for in metals.

What are the effects of temperature and activation energy on diffusion? (8 marks)

(b) (i) State the solution to Fick’s Second Law. What does this law describe?

(ii) A carburising process is performed on 0.15% steel by introducing 1.1% C to the

surface at 1000oC. Calculate the carbon content at a depth of 0.5 mm after 1 hour.

The diffusivity of C in steel D = 5.0 x 10-11m2 s-1.

(Error function tables are provided) (8 marks)

(c) Describe the sintering process. (4 marks)

Q6. (a) Explain the origins of friction between metal surfaces. Explain how the use of a lubricant

oil reduces friction. (5 marks)

(b) (i) Describe the process of adhesive wear for two different materials (A and B) in

contact for the case of A and B having equal hardness and also differing hardness.

What happens if one of the materials has a case-hardened surface?

(ii) Describe abrasive wear of materials. Give ONE example of an application where

abrasive wear is desirable.

(iii) Explain how wear may be reduced. (10 marks)

(c) Sketch the creep curve for a material under constant load at constant temperature.

Briefly describe the temperature requirement and the creep mechanism for power law

creep in region 2 of the curve. (5 marks)

Section C: Quality Engineering Q7. (a) “A process which is in control is not necessarily capable!” Discuss whether or not this

statement is true. (6 Marks)

(b) The data shown below are the sample mean and ranges of deviations from nominal

diameter for holes drilled in a carbon fiber composite material used in aerospace

manufacturing. The values reported are deviations in ten thousandths of an inch and the

sample size is five.

(i) Using the blank control charts and tables of constants provided, set up X and R

charts on the process. Is the process in statistical control? (8 Marks)

(ii) Estimate the process standard deviation using the range method. (2 Marks)

(c) If specifications are at nominal ± 100, what can you say about the capability of the

process? Calculate Cp and Cpk indices for the process. (4

Marks)

Table 8.1

Sample 1 2 3 4 5 6 7 8 9 10

X +8 0 +6 +8 +12 +4 -2 +12 +2 +24

R 80 110 80 70 90 80 40 100 40 40

Sample 11 12 13 14 15 16 17 18 19 20

X +14 +26 +4 +6 +18 +4 +18 +14 +20 +18

R 40 30 60 60 60 40 50 70 60 50

Q8.(a) Discuss briefly whether or not improving Quality is expensive. (4 Marks)

(b) One of Deming’s 14 points urges that organisations “cease dependence on inspection to achieve

quality. Eliminate the need for mass inspection…”.

Discuss this assertion in detail in the context of quality in manufacturing. (10 Marks)

(c) Discuss what is meant by the “Quality Function” within an organization, discussing who is

responsible for the Quality of products and how that responsibility is met. (6 Marks)