TransCanada Corp. is in the business of manufacturing toys using assembly lines.

Question

TransCanada Corp. is in the business of manufacturing toys using assembly lines. The time to perform each task and the tasks that must immediately precede each task are:

Task                       Precedence       Duration (minutes)

A                                 ---                    .30

B                                 ---                    .50

C                                 A, B                 .20

D                                 B                     .10

E                                 C, D                .20

F                                  D                     .60

G                                 F                      .40

Demand per week is 2800 units. The company works 5-day weeks and one 8-hour shift each day. Each shift/day has 2 snack breaks of 20 minutes (each). In addition, every hour there is a 6-minute rest break.

a. Balance the line (determine the workstation assignments) using the Longest Task Time first rule and calculate the Takt time.

b. Compute efficiency of the line in (a).

c. Can we improve the efficiency of the line (by using a different heuristic (rule))? Why or why not?

d. Suppose the demand is expected to increase to 3500 per week. Can we use longest operation time heuristic to rebalance the line? Why or Why not?

Explanation / Answer

Total time available = 5days per week, daily 8 hour shift, each shift/day has 2 snack breaks of 20 minutes and 6 minutes rest break every hour = 5*(8*60-(20+20+6*8) =5*392=1960 minutes per week

Demand per week is 2800 units, therefore cycle time = 2800/1960 = 1.43 minutes

Minimum number of workstations = Total tasks time/ cycle time = 2.3(.3+.5+.2+.1+.2+.6+.4)/1.43 = 2 (rounded to next integer)

To begin with tasks A and B are eligible for the first workstation (cycle time 1.43 minutes), both are assigned and time left is .63 minutes. Next eligible candidates areC and D, these are also assigned to first workstation and the time left reduces to .33. Next eligible candidates are E & F. Although F is preferred as per longest time but it takes .60 minutes time more than available so E is next assigned to first workstation.

Therefore first workststation has A, B, C, D and E tasks with idle time of .03 minutes.

For Second workstation, first F is considered and assigned and then G is assigned having total tasks time as 1 minutes (.6+.4), hence idle time of .43 minutes.

In all we have two workstations with cycle time of 1.43 minutes each, thus total time spend is 2.86 minutes as against the total tasks time of 2.3 minutes, therefore Efficiency of the line = 2.3/2.86 5 = 80.42 % approximately

c. As the actual number of workstations is equal to the theoritical minimum number of workstations, hence efficiency can not be improved with the existing data and information.However, efficiency can be improved if we reduce the cycle time by cutting down the snack breaks and rest breaks. In case the cycle time is reduced to say 1.20 minutes, we will require the same number (2) of workstations but efficiency will be ( 2.3/2.4) 95.83%

d. In case demand is 3500 per week then cycle time will be 3500/1960 = 1.79 minutes approximately then we can assign F (based on longest operation time) to first workstation after assigning A, B, C, D and before E.Then second workstation will have E and G

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