Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

6.2.3 Line Balancing — Harmonizing the Content of Work

Intended learning outcomes: Identify how tasks of the same duration at each production structure level result in a rhythmic flow of goods. Explain why the various operations at a workstation (for all the products) as well as the various operations for a single product should be of the same approximate duration. Produce an overview on measures for changing lead time of operations.


Line balancing balances the assignment of the tasks to workstations in a manner that minimizes the number of workstations and the total amount of idle time at all stations for a given output level (cf. [APIC16]).

Line balancing is particularly important for line manufacturing, that is, repetitive manu­facturing performed by specialized equipment in a fixed sequence (i.e., an assembly line). Line balancing is an important tool for reducing “mura” and can be realized by harmonizing the content of work.

Harmonizing the content of work means to design the following so that they require the same length of time: (1) the various production structure levels, and (2) the times required for individual operations within a production structure level.

This concept can — by the way — also be very useful in a job shop production environment.

With regard to (1), production structure levels must be designed or redefined in such a way that lead times at the individual levels are either identical or multiples of each other. Harmonization thus demands close cooperation bet­ween design and product engineering (simultaneous engineering). Product and process must be designed together from the start. Figure 6.2.3.1 illustrates this principle at the levels of assembly, preassembly, and parts production. The lead time for parts production is half as long as that for the levels of preassembly and assembly. In the example, the batch size at the part production structure level comprises half the usage quantity for a batch in preassembly or assembly.

Fig. 6.2.3.1        Harmonizing the content of work: tasks of the same duration at each production structure level result in the rhythmic flow of goods.

With regard to (2), the following should be of the same approximate dura­tion: the various operations at a workstation for all the products, and all the operations for a single product. Figure 6.2.3.2 illustrates this principle.

Fig. 6.2.3.2 Harmonizing the content of work: The various operations at a workstation (for all the products) as well as the various operations for a single product should be of the same approximate duration.

There will be little variation of the operation time, and this results in turn in a reduction of lead time. Queue time, except for its dependency on capacity utilization and average operation time, is, namely, a function of the variation coefficients of operation times.[note 611] In job shop production, queue times at the work­stations to a large extent determine inter­operation times, which themselves have a significant effect on lead time.[note 612]

Such harmonization of the content of work within a production structure level and through­out all levels of production results in a rhythmic flow of goods. Batch size reduction alone cannot achieve this. Workstations and the content of the individual operations must be newly defined. This is a very difficult task that can only be surmounted when product engineering cooperates with development and design. New technologies may be used for certain operations in order to change lead time at the very location where harmoni­zation is required.

To complete the task, product engineering in cooperation with design must repeat the following two steps until sufficient results are achieved:

1. Determine the duration of one unit of harmonized content of work, that is, the operation time of the harmonized content of work inclu­ding necessary inter­operation times before and after the (internal or external) operation. To start, experienced personnel in product engineering determine this time unit empirically. For further itera­tions, the new time unit will result from correction of a previously unsatisfactory result. The shorter the harmonized con­tent of work is, the more flexibly processes can be put together.

2. Perform measures to change lead times of operations, chosen from the various possible measures in Figure 6.2.3.3.

Fig. 6.2.3.3        Measures for changing lead time of operations.

Because of measures connected with suppliers, harmonizing work contents leads to closer cooperation with other companies. Because control must no longer observe priority rules, the advantage resulting from all these measures to harmonize the content of work is very simple management of queues. Such detailed and comprehensive measures to harmonize the content of work are comparable to the design of a railway timetable of departures at regular intervals: Investiture in new lines takes place as a function of postulated rhythms in the regular interval departure plan. As a result, processes in the railway net can be automated, and there is maximum throughput through the net.

The strategic considerations underlying these measures are long term in nature and can be put into practice only if a company’s financial policies are in agreement with them. Investiture in capital assets will not accord well with savings. Whenever possible reduction of delivery lead time is projected, the response of the customer to the improvement becomes the important factor. Estimating possible effects of this kind is a matter for decision making at the company level. It is for this reason that traditional profitability calculations generally fail here. However, the calculations are often not necessary at all. A company attempting to stay in competition will be forced to make the investment.


Quiz Harmonizing the content of work - not yet available

[kml_flashembed movie="https://opess.ethz.ch/wp-content/uploads/2016/09/Q_623.swf" height="75%" width="100%" /]

Course section 6.2: Subsections and their intended learning outcomes

Print Top Down Previous Next