# 6.8.2 Exercise: The Effect of Cellular Manufacturing on Lead Time Reduction

### Intended learning outcomes: Present the routing sheet for production of shafts. Explore the effect of cellular manufacturing on lead-time reduction.

Figure 6.8.2.1 shows a possible routing sheet for production of shafts. The batch size is 10.

Fig. 6.8.2.1        Routing sheet for production of shafts.

a. Calculate the lead time in traditional job shop production. Hint: For job shop production, lead time has to be calculated assuming a sequence of operations. Therefore, you can use the formula in Figure 6.2.2.3.

Solution: 14.22.

b. Calculate the maximum lead time for the case of cellular manufacturing, that is, using the formula in Figure 6.2.2.4. (Hint: First determine the cell drive

Solution: 10.98 (the cell driver is the operation “millcut nut” with an operation time of 7.60; setup time plus run time of all the other operations is 3.38).

c. For the given routing sheet shown in Figure 6.8.2.1, and for cellular production, find a temporal order of operations that yields minimum lead time.

Solution: Minimum total lead time is 7.88. The setup and the first unit of the batch of operations “millcut” and “lathe” can be fully executed during the setup of the cell driver, as well as the setup of the operations “pregrinding” and “final grinding”. Each unit of the batch can be run directly after its run on the cell driver operation. Thus, the run times for one unit for “pre-grinding” and “final grinding” have to be added to the cell driver operation time, or 0.12 + 0.16 + 7.6, making 7.88.

d. For the given routing sheet shown in Figure 6.8.2.1, and for cellular production, find a temporal order of operations that yields minimal load (or minimum allocated time for the operation, that is, operation time plus wait time between the units of the batch) at the workstations.

Solution: Lead time with minimum load is 8.24. Again, the setup and the first unit of the batch of operations “millcut” and “lathe” can be fully executed during the setup of the cell driver. For “pregrinding,” to be ready to execute the last unit of the batch just after the completion of the cell driver operation, the 9 units of “pregrinding” must have been just completed at point 7.6 in the time axis. Thus, the latest start date of “pregrinding” must be 7.6 – 9 * 0.12 – 1.2 = 5.32. For “final grinding,” the first unit of the batch can be executed directly after the first unit of “pregrinding” has been executed, that is, at 5.32

You can view the animated solution here:

By modifying setup and run times of the operations, change the cell driver. Try to find a combination where the variant “minimum total lead time” tends toward the “maximum lead time” value of the lead time formula for cell manufacturing.

## Course section 6.8: Subsections and their intended learning outcomes

• ##### 6.8.1 Exercise: Operation Time versus Operation Cost, or the Effect of Varying Setup Time and Batch Size

Intended learning outcomes: Explain the need to find a balance between short lead time, and low cost, for any operation. These two factors are determined by setup time and batch size.

• ##### 6.8.2 Exercise: The Effect of Cellular Manufacturing on Lead Time Reduction

Intended learning outcomes: Present the routing sheet for production of shafts. Explore the effect of cellular manufacturing on lead-time reduction.

• ##### 6.8.3 Scenario: Line Balancing — Harmonizing the Content of Work

Intended learning outcomes: Present the routing sheets for parts production out of sheet metal of three products. Explain possible ways for line balancing through harmonizing the content of work.

• ##### 6.8.4 Exercise: Calculating the Number of Kanban Cards

Intended learning outcomes: Present data on three products for calculation of the number of Kanban cards. Calculate the required number of Kanban cards before and after the process improvement.

• ##### 6.8 Scenarios and Exercises

Intended learning outcomes: Operation time versus operation cost: disclose the effect of varying setup time and batch size. Calculate the effect of cellular manufacturing on lead-time reduction. Perform line balancing through harmonizing the content of work. Determine the number of Kanban cards.