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Integral Logistics Management: Operations and Supply Chain Management Within and Across Companies,

Paul Schönsleben, Steven R. Schmid, Bo O. Jacobson

Chapter 5

The Lean / Just-in-Time Concept and Repetitive Manufacturing - all with Video Answers

Educators

Chapter Questions

Problem 1

Operation Time versus Operation Cost, or the Effect of Varying Setup Time and Batch Size

This exercise will help to illustrate the need to find a balance between (1) short lead time, and (2) low cost, for any operation. These two factors are determined by setup time and batch size. You will find the effect of setup time and batch size on
a. The operation time, which is a measure of the lead time of the order.
b. The operation time per unit (that is, operation time divided by batch size), which is a measure of the cost of the operation and therefore of the cost of the production or procurement order.

Solve the following tasks:
(0) First, suppose a setup time of 200 , a run time per unit of 100 , and a batch size of 4 . Calculate the operation time and the operation time per unit.
(1) If batch size is increased to 20 , what are the effects on operation time and operation time per unit? In your opinion, what effects are positive or negative?
(2) Suppose that because of the hard work of the process engineers (e.g., by applying SMED measures), setup time could be reduced to 100 . What is the effect of this, if the batch size is maintained at 20 ?
(3) To what extent can the batch size be reduced after the reduction of setup time to 100 , so that the operation time does not exceed the original operation time of 600 ? What will the operation time per unit be?
(4) To what extent can the batch size be reduced after the reduction of setup time to 100 , so that the operation time per unit does not exceed the original time per unit of 150 ? What will the operation time be?

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Problem 2

The Effect of Cellular Manufacturing on Lead Time Reduction

Figure 5.8.2.1 shows a possible routing sheet for production of shafts. The batch size is 10 .
$$
\begin{array}{|l|c|c|}
\hline \text { Operation } & \text { Setup time } & \begin{array}{c}
\text { Run time per } \\
\text { unit }
\end{array} \\
\hline \text { Millcut } & 0.02 & 0.02 \\
\hline \text { Lathe } & 0.6 & 0.06 \\
\hline \text { Millcut nut } & 1.6 & 0.6 \\
\hline \text { Pregrinding } & 1.2 & 0.12 \\
\hline \text { Final grinding } & 1.2 & 0.16 \\
\hline
\end{array}
$$
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 5.2 .2 .3 .
b. Calculate the maximum lead time for the case of cellular manufacturing, that is, using the formula in Figure 5.2.2.4. (Hint: First determine the cell driver).
c. For the given routing sheet shown in Figure 5.8.2.1, and for cellular production, find a temporal order of operations that yields minimum lead time.
d. For the given routing sheet shown in Figure 5.8.2.1, 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.

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11:52

Problem 3

Line Balancing - Harmonizing the Content of Work

Figure 5.8.3.1 shows a possible routing sheet for parts production out of sheet metal. Three different products are produced: items 1,2, and 3. All have a similar routing sheet. For the different operations, the number in the table is the operation time, and the number in parentheses is the setup time.

In accordance with the discussion in Section 5.2.3, assume a duration of one unit of harmonized content of work of 12 time units. The task is to perform measures to change lead times of operations, chosen from the various possible measures to line balance or harmonize the content of work listed according to Figure 5.2.3.3.
(COLUMN CANT COPY)
a. Suppose that the first two operations can be combined into one (why is this a feasible assumption?). Item 3 seems - at first glance - to fit quite well into three units of harmonized content of work. Therefore, according to the first one of the measures listed in Figure 5.2.3.3, try to change lot sizes of items 1 and 2 (use the empty columns in Figure 5.8.3.1), to obtain for each of them a total operation time on the order of 36 units of time.
b. Is it possible, in practice, to combine the last two operations into one, fitting them into one unit of harmonized content of work?
c. For item 1, the third and the fourth operations do not fit into unit of harmonized content of work, despite significant changes to the batch size. What other possible measures listed in Figure 5.2.3.3 could be implemented?
d. After implementing all these measures, are there still problems?

Jacquelyn Trost
Jacquelyn Trost
Numerade Educator

Problem 4

Calculating the Number of Kanban Cards

An automotive company has implemented a JIT program using kanbans to signal the movement and production of product. The average inventory levels have been reduced to where they are roughly proportional to the number of kanbans in use. Figure 5.8.4.1 shows the data for three of the products.
$$
\begin{array}{|c|c|c|c|c|c|c|}
\hline \text { Item ID. } & \text { Lead time } & \begin{array}{c}
\text { Length of } \\
\text { the } \\
\text { statistical } \\
\text { period }
\end{array} & \begin{array}{c}
\text { Usage } \\
\text { during } \\
\text { statistical } \\
\text { period }
\end{array} & \begin{array}{c}
\text { Number of } \\
\text { parts } \\
\text { (units) per } \\
\text { container }
\end{array} & \begin{array}{c}
\text { Safety } \\
\text { factor }(\%)
\end{array} & \begin{array}{c}
\text { Number of } \\
\text { containers } \\
\text { per } \\
\text { transport } \\
\text { batch }
\end{array} \\
\hline 1 & 36 & 20 & 600 & 200 & 0 & 1 \\
\hline 2 & 36 & 20 & 100 & 25 & 0 & 1 \\
\hline 3 & 36 & 20 & 50 & 10 & 0 & 1 \\
\hline
\end{array}
$$
Fig. 5.8.4.1 Data on three products for calculation of the number of kanban cards.
a. The process engineers have been hard at work improving the manufacturing process. They have initiated a new project to reduce lead time from 36 days to 21 days. What would the percentage change in average inventory be for each item?
b. Calculate the number of kanban cards using other data values. Try to answer the following questions:
- What is the minimum number of kanban cards required in any case?
- How do the safety factor and the number of containers per transport batch influence the number of kanban cards required?

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