E326 1415 YC, question paper for practice PDF

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Lean Manufacturing & Six Sigma, 6p and question paper has been provided for students to better prepare themselves for exams....

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School of Engineering

E326 : LEAN MANUFACTURING & SIX SIGMA UNDERSTANDING TEST 3 Monday, 24 February 2015 Duration : 90 minutes Full Name : _____________________________ Student ID : _____________________________ Class :

_____________________________

INSTRUCTIONS 1) Do not begin until you are told to do so by your invigilator.

For Official Use Question

Mark

Total

2) Ensure that there is a total of 15 PAGES (including cover page).

1

27

3) There are 5 QUESTIONS in this test. Answer ALL the questions.

2

17

4) Write all your explanations and calculations workings in the space provided online.

3

20

4

18

5

18

Total Mark

100

5) This is an open book test. Students may refer to any notes stored in their notebook computers. 6) Any form of written notes and printouts is not allowed to be on the desks by students during the test, unless otherwise specified. 7) All answers should be rounded up to two decimal places. 8) The use of calculators is allowed during the test, but the use of any other electronic devices and hand-phones for communication purposes is not allowed. 9) Any form of direct or electronic communication between the students is not allowed during the test, unless authorised and monitored by your invigilator. Penalties will be imposed, as deemed fit by the School, on students found violating this rule.

Page 1

School of Engineering Question 1 [27 marks] A process engineer is trying to improve the life of a mechanical cutting tool. He has run a 23 experiment using cutting speed (A), metal hardness (B), and cutting angle (C) as the factors. a) Table 1 below describes the experimental run order which follows Yates order. Complete the table with treatment combinations for Run 1, 3, 5 and 7. State either + or -. (4 marks) Table 1: DOE Experimental run

Run Order 1 2 3 4 5 6 7 8

Cutting Speed (A) (i)_____ + + + +

Metal hardness (B) (ii)_____ + + +

Cutting angle (C) (iii)_____ + (iv)_____ +

b) Explain what you understand by coding of factor levels. Why are coded units typically used in experimental planning? (2 marks) -

c) In DOE experiments, there are noise factors that cannot be controlled. State TWO techniques that can be used to manage the noises in the experiment. (2 marks)

-

d) State THREE areas which DOE can be applied to. If the process engineer intends to perform real-time process monitoring, which area does it fall under? (4 marks)

-

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School of Engineering e) In the DOE study, is it a good idea to run replicates consecutively? Explain why.

(2 marks)

-

f) The process engineer runs a full factorial experiment and Figure 1 shows the Pareto effect diagram he obtained from Minitab. Identify the 3 most significant terms. (3 marks)

Pareto Chart of the Standardized Effects (response is Tool Life, α = 0.05) Term

2.306 Factor A B C

AC B

Name A B C

C ABC BC A AB 0

1

2

3

4

5

Standardized Effect

Figure 1: Minitab Pareto chart

Page 3

School of Engineering g) Figure 2 shows the interaction plot from the full factorial experiment. State whether the interactions are WEAK or STRONG among the factors: cutting speed (A), metal hardness (B), and cutting angle (C). Explain your answers. (6 marks)

Interaction Plot for Tool Life Fitted Means A* B

B -1 1

500

Mean of Tool Life

450 400 350 300

A* C

B*C

C -1 1

500 450 400 350 300 -1

1

A

-1

1

B

Figure 2: Minitab Interaction Plot

Page 4

School of Engineering h) Figure 3 shows the cube plot from the full factorial experiment. State the setting for all three factors if a target tool life of 512 days is desired. Explain why. (4 marks)

Cube Plot (data means) for Tool Life 552.5

405.5

351.0

512.0

1

B

446.5

391.5 1 C

266.0

380.0

-1

1

-1

-1 A

Figure 3: Minitab Cube Plot

Page 5

School of Engineering Question 2 [17 marks] Show your workings clearly and state any assumptions made a) Zero Defect Quality (ZDQ) is a quality concept aims at zero defects and prevent passing of defects to downstream processes. Explain how Poka-Yoke functions as (i) “error prevention” and (ii) “defect detection” to achieve ZDQ. (2 marks)

b) Figure 4a shows that a car drum brake requires one long bolt and three short bolts for correct assembly. Defective drum brake will be assembled when bolts of different lengths were not installed as specified, shown in Figure 4b.

Figure 4a:

Figure 4b:



X

Figure 4: Requirement in car drum brake assembly i) State TWO possible types of human errors which can happen in the above assembly process. (2 marks)

errors in identification and forgetfulness

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School of Engineering ii) In the current production of the drum brake shown in Figure 4 above, a random check is performed at the final process on the assembly line, but defect detection would sometimes be overlooked. Propose TWO suitable Poka Yoke devices/methods to eliminate this checking error and explain how the mistake-proofing functions are applied. (4 marks) contact method as functions by detecting whether a sensing device make contact with a part o object in the process and motion sequence method/limit switch can be installed to confirm the correct depth

iii) Suggest ONE type of inspection at the drum brake to attain Zero Defect Quality in the drum brake assembly. (2 marks) point of origin . as the mistake can be corrected before it becomes a defec

c) Figure 5 shows a plastic cup lid that changes color when the contents are hot. This feature allows the user to know whether the drink is hot or not. It also allows the user to judge the proper temperature visually by looking at how red the lid is. This is an example of Poka-yoke concept being applied.

Figure 5: Lid color of cold and hot contents i) Explain TWO reasons if this is ‘Control’ or ‘Warning’ approach. (3 marks) warning - It only provides visual que of hot contents but It does not stop scalding from happening

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School of Engineering ii) Explain TWO reasons if the mistake – proofing category for the plastic cup lid is ‘Error Prevention’ or ‘Defect Detection’ approach. (3 marks)

Error prevention It helps prevent users from being scald but it does not detect after users are being scalded

ii) What is the Poka-yoke setting function applied in the plastic lid? (1 mark) warning

ANS: _____________________________________________

Page 8

School of Engineering Question 3 [20 marks] A wheel rim manufacturing company has a normally distributed manufacturing process that is stable over time. The process in control has an estimated standard deviation of 2 mm. The product produced by this process has specification limits of 120 ±8 mm and a target value of 120 mm. The current process mean is 118 mm. a) Answer the following questions: i) Calculate the process capability Cp. (3 marks) ii) Explain what Cp is and its limitations. (2 marks)

b) Calculate the process capability CpL. (3 marks)

c) Calculate the process capability CpU. (3 marks)

d) A wire bonding process wishes to obtain the process’s Cpk. Calculate the process capability Cpk if CpL is given to be 1.333 and CpU is given to be 1.776. (3 marks)

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School of Engineering

e) Suggest at least TWO ways to improve the process capability of each of the following three processes shown in Figure 6 below. (6 marks)

Figure 6: Process 1 – 3 Process distribution

Page 10

School of Engineering Question 4 [18 marks] Company Beta is performing an Overall Equipment Effectiveness (OEE) study on one of the machines from the production line. The Manufacturing Engineer in-charge has collected the data which has been tabulated in the following Table 2: Table 2: Data collected on 1 machine Activities Daily working hours Tea Breaks (Morning and Afternoon) Lunch break Down Time Ideal Run Rate Total Pieces produced Reject Pieces out of total pieces produced

Time Taken / Performance 8 hours 15 minutes each 30 minutes 50 minutes 60 pieces per minute 20000 pieces 500 pieces

For all the questions below, show your workings clearly and state any assumptions and formulae used. State your answers rounded to 2 decimal places. a) Calculate planned production time. (2 marks) 8*60 = 480 minutes planned production time = 480-15*2-30 =420minuts

b) Calculate the operating time. (2 marks) operating time = 420 -50 =370 minutes

c) Determine the “Availability” of this OEE study. (2 marks) availability = 370/420 * 100 = 88.10% (2dp)

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School of Engineering d) Determine the “Performance” of this OEE study. (3 marks)

performance = (20,000/370) / 60 * 100 = 90.09% (2dp)

e) Determine the “Quality” factor of this OEE study. (3 marks)

good piece = 20,000-500 =19,500 quanlity = 19,500 / 20,000 *100 = 97.50% (2dp)

f) Determine the overall OEE (rounding your answer to 2 decimal places), clearly stating the Performance, Availability and Quality value used. Does it meet the world class OEE standard? Justify your answer by comparing individual OEE factors with the world class level. (6 marks)

OEE = 88.10% * 90.09% * 97.50% * 100 = 77.39 % no , it does not meet whole class standard Availability (88.10% vs 90%) = not meeting performance (99.10% vs 95%) = not meeting Quality (97.50% vs 99.9%) = not meeting

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School of Engineering Question 5 [18 marks] Answer the following short questions. a) Explain with ONE reason if you agree with the following statement: (2 marks) “A control plan is a document that identifies critical input or output variables and associated activities to maintain control of the variations. The control plan will not be maintained or updated once it has been developed and endorsed.”

no . it need essential for maintaining process control over the long run

b) A project team in Company Alpha has just completed a Lean Six Sigma improvement project for the main production line. The project team developed a control plan for ensuring the ongoing success of the improved process. i) Explain with ONE reason which team is going to be responsible for sustaining the improvements: “the project team” or “the production team”. (2 marks) ii) Explain with ONE reason if the control plan will be affected when the leader of the production team resigned from the company. (2 marks)

i) Production team Production team will sustain improvements as the project team has completed the Lean project and wi hand over control of the control plan to the production team. ii) yes . a person change/turnover is one of the triggers for updating control plans

c) Explain with ONE reason if you agree with the following statement: (2 marks) “The application of DMAIC in Six Sigma is limited to improving existing processes; it does little to address the design of new product or processes. Therefore, all the available tools in DMAIC cannot be used for designing new product or processes.”

no. Available tools can be used for designing new product or processes

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School of Engineering d) Explain with ONE reason if you agree with the following statement: (2 marks) “Design for Six Sigma (DFSS) is a systematic methodology using tools, trainings and measurements to enable the design of product, services and processes to meet customer expectations at Six Sigma quality levels; therefore, gradual process improvement is the objective of the DFSS.”

no . utilized to re-engineer or design new processes when existing process is not capable

e) Customers are not always very good at identifying exactly what they want or need in measurable terms. The data from a restaurant outlet of ABC Food Group was collected and analyzed. Translate the following feedback received to the “Customer requirement” AND “Measurement variable” for each question below. i) Feedback 1 (2 marks) “Every time it takes me at least 30 minutes to complete the whole ordering process. Which is very slow and unacceptable.”

requirements : fast ordering measurement : amount of time customer waiting for the orde

ii) Feedback 2 (2 marks) “Very often long waiting is needed before my reservation phone calls were attended. I will look for other restaurants after a few unanswered calls.

requirement : shorter waiting time for reservation phone ca measurement : faster time answering the calls

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School of Engineering

f) For each of the following scenarios, state whether “Kaizen approach” or “Innovation approach” is more suitable, or being adopted, to make improvements for the company. (5 marks) i.The management team is very unhappy about the production scraps and demands for immediate improvements. kaizen

ANS: _____________________________________________ ii.The management team wants everyone in the production line to be involved in the fight to reduce the production defects level. kaizen ANS: _____________________________________________

iii.The management team has approved the proposal to buy a new machine with the latest technology to improve the yield of the production line. innovation

ANS: _____________________________________________ iv.The company is growing slowly and steadily and wants to make improvements in their factory operations. kaizen ANS: _____________________________________________

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