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P23993 Design for Quality Assignment Answers

Academic Year 2020/21

P23993 – Design for Quality

Question 1

Consider a tolerance chain given in Figure Q1 with dimensions shown in Table Q1.

P23993 Design for Quality img1

Figure Q1

Table Q1

     

Last digit of the student number upxxxxxX

   

1

2

3

4

5

6

7

8

9

0

A1

138

136

134

151

152

149

147

143

128

119

A2

2

4

4

3

3

2

3

2

3

2

A3

5-0.12

5-0.12

6-0.12

4.5-0.12

5-0.12

4-0.12

5-0.12

5-0.12

4-0.12

4-0.12

A4

151

151

151

164

166

160

161

156

140

130

A5

5-0.12

5-0.12

6-0.12

4.5-0.12

5-0.12

4-0.12

5-0.12

5-0.12

4-0.12

4-0.12

AΔ

   

1+0.7

   

1. Allocate tolerances using Worst Case – Average Tolerance Grade Method [20 marks]

2. Allocate tolerances using RSS method [13 marks]

Question 2 – Selective Assembly

A company intending to produce components for a fit with guaranteed clearance / interference as given in Table Q2 (Jmin, Jmax or Smin, Smax respectively). It has been experiencing problems when machining both holes and shafts caused by lack of process capability, see Manufacturing Methods in Table Q2. Maintaining fit characteristics transform the tolerances to suit company's capability implementing selective assembly method.

Table Q2

Second from the

last digit of

the student number upxxxxXx

Nominal size, mm

Manufacturing method

Fit requirements

System

Hole

Shaft

Clearance

Interference

Jmin

Jmax

Smin

Smax

0

Ø26

Drilling (IT13)

Rough

Turning

(IT12)

70

260

42

272

Hole

1

Ø15

Reaming

(IT8)

Precision

Turning (IT7)

30

48

37

53

Shaft

2

Ø40

Rough

Broaching

(IT10)

Rough

Turning

(IT11)

90

190

24

136

Hole

3

Ø8

Honing

(IT5)

Lapping (IT6)

2

7

3

9

Shaft

4

Ø30

Boring (IT9)

Turning (IT8)

30

73

34

74

Hole

5

Ø64

Milling (IT10)

Precision

Turning (IT7)

55

135

72

147

Shaft

6

Ø12

Diamond

Boring

(IT6)

Precision

Turning (IT7)

58

72

48

59

Hole

7

Ø10

Broaching

(IT8)

Turning (IT9)

42

69

54

77

Shaft

8

Ø25

Honing

(IT8)

Polishing (IT7)

35

59

33

54

Hole

9

Ø20

Drilling (IT11)

Rough

Turning

(IT10)

3

83

47

147

Shaft

  1. Determine tolerances of the mating parts based on the manufacturing methods [4 marks]
  2. Calculate the number of groups [4 marks]
  3. Calculate upper and lower limit deviations for the hole and the shaft [8 marks]
  4. Draft the tolerances, indicating the groups [8 marks]
  5. Calculate maximum and minimum interference / clearance for each group [10 marks] Question 3 – Quality control

You are employed as a quality engineer and you have been asked to help in designing a limit gauge for quality control of machined shafts. Your company quality policy requires prevention of acceptance of any defective parts.

a. Using the appropriate approach allocate the tolerances for ‘GO’ and ‘NOT-GO’ ends of a snap gauge for controlling diameter of a shaft ØAB . Support your answer with all relevant tolerance diagrams.

Table Q3

Third from the last digit of the

student number upxxxXxx

Shaft diameter ØA,

mm

Tolerance B

1

10

h10

2

20

h9

3

30

h8

4

40

h7

5

50

h6

6

60

h10

7

70

h9

8

80

h8

9

90

h7

0

100

h6

[20 marks]

b. Using the diagram from part (a) showing the allocation of Limit Gauge tolerances, give an example of a situation where a shaft with a particular actual dimension is made in the tolerance, but when inspected by this Limit Gauge (worn, but still within the gauge tolerance), might be misjudged as bad. Plot it on the tolerance diagram. [13 marks]

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