Ex 1. A small electrical appliance is to be produced on a single model assembly line. The work content and precedence is listed in Table . Thc estimated annual demand is 100,000 units/yr. The line will operate 50wk/yr, 5 shifts/wk, 7.5hrs/shift. Previous experience suggests that the uptime efficiency of the line will be 96% and repositioning time lost per cycle will be 0.08min.
(i) Draw the precedence diagram
(ii) Required hourly production rate
(iii) The cycle time per station
(iv) Use the Rank Positional Weight method, obtain a suitable allocation of work elements to work stations in the assembly line.
(v) Calculate the balance delay and balance loss
(vi) Suggest a means of improvements
|
Step
|
Time (min)
|
Description
|
Steps that must precede
|
|
1
|
0.2 /
|
Place frame in work holder and clamp
|
---
|
|
2
|
0.4 /
|
Assemble plug, grommet to power cord
|
---
|
|
3
|
0.7 ,/
|
Assemble bracket to frame
|
1
|
|
4
|
0.1 /
|
Wire power cord to motor
|
1,2
|
|
5
|
0.3 v.
|
Wire power cord to switch
|
2
|
|
6
|
0.11 z.
|
Assemble mechanism plate to bracket
|
3
|
|
7
|
0.32 '
|
Assemble blade to bracket
|
3
|
|
8
|
0.6 ,/
|
Assemble motor to brackets
|
3,4
|
|
9
|
0.27,
|
Align blade and attach to motor
|
6,7,8
|
|
10
|
0.38 ,
|
Assemble switch to motor bracket
|
5,8
|
|
11
|
0.5 ,
|
Attach cover, inspect & test
|
9,10
|
|
12
|
0.12
|
Place in tote pan for packaging
|
11
|
EX 2. A Mode1.1 Wagon is to be assembled on a conveyor belt. 500 wagons are required per day. Production time per day is 435 minutes. The assembly steps and times for the wagon are given in the Table. Uptime for the line is expected to be 98% and repositioning loss of 1.2 seconds is to be allowed for.
(a) Use the Rank Positional Weight method, obtain a suitable allocation of work elements to work stations in the assembly line.
(b) Calculate the balance delay and balance loss
(c) By considering a re-distribution of work elements, show how an improvement on the solution obtained in (a) above can be realized.
|
Step
|
Time (seconds)
|
Description
|
Steps that must precede
|
|
A
|
44
|
Position rear axle support and hand fasten
four screws to nuts
|
---
|
|
B
|
II
|
Insert rear axle
|
A
|
|
C
|
9
|
Tighten rear axle assembly and hand
fasten with four screws to nuts
|
B
|
|
D
|
46
|
Position front axle assembly and hand
fasten with four screws to nuts
|
---
|
|
E
|
15
|
Tighten front axle assembly screws
|
D
|
|
F
|
12
|
Position rear wheel #1 and fasten hubcap
|
C
|
|
G
|
12
|
Position rear wheel #2 and fasten hubcap
|
C
|
|
H
|
12
|
Position front wheel #1 and fasten hubcap
|
E
|
|
I
|
12
|
Position front wheel #2 and fasten hubcap
|
E
|
|
J
|
8
|
Position wagon handle shaft on
front axle assembly and hand
fasten bolt and nut
|
F,G,H,I
|
|
K
|
9
|
Tighten bolt and nut
|
J
|
Ex3
The operations for a product are shown in the table. Thc line works an eight hour day during which the target output is 48 units. Design a balanced layout for the process, using RPW method. Suggest improvements
|
Operation
|
Time (Min)
|
Operations must
Follow
|
|
A
|
5
|
-
|
|
B
|
10
|
A
|
|
C
|
4
|
B
|
|
D
|
6
|
B
|
|
E
|
4
|
C,D
|
|
F
|
2
|
E
|
|
G
|
4
|
F
|
|
H
|
5
|
G
|
|
I
|
3
|
H
|
|
J
|
2
|
G
|
|
K
|
5
|
J
|
|
L
|
8
|
G
|
|
M
|
4
|
L
|
|
N
|
2
|
I,K,M
|
|
0
|
6
|
N
|
|
P
|
1
|
0
|
|
Q
|
5
|
P
|
|
Total time
|
76
|
|