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

6.2.2b Cellular Manufacturing and One-Piece Flow — Lead Time Reduction Through Adaptation of the Production Infrastructure

Intended learning outcomes: Explain cellular manufacturing, one-piece flow, and the formula for lead-time calculation with cellular manufacturing.



Continuation from previous subsection (6.2.2).

A further consistent application of production or manufacturing segmentation leads to cellular manufacturing.

A cell is, according to [APIC16], a manufacturing or service unit consisting of a number of workstations, and the materials transport mechanisms and storage buffers that interconnect them.

A work cell is, according to [APIC16], a physical arrangement where dissimilar machines are grouped together into a production unit to produce a family of parts having similar routings.

The process of cellular manufacturing is closely linked with work cells.

In cellular manufacturing, or near-to-line production, workstations required for successive operations are placed one after the other in succession, usually in an L-shaped line or U-shaped line configuration. Preferably, the individual units of a batch go through the cell according to the one-piece-flow concept.

One-piece flow is a concept that processes items directly from one step to the next, one unit at the time, that is, without having to wait for the other units of the batch between any two operations.

Figure 6.2.2.2 illustrates this concept, showing the change from job shop production to cellular manufacturing.

Fig. 6.2.2.2        Changeover to cellular manufacturing.

As cellular manufacturing may require multiple machines, it is not unusual to find older machines, retrieved from the “cellar” so to speak, in these lines. While this is specialized machinery that has a dedicated capacity,[note 608] it is inexpensive enough, for generally it has already been depreciated.

Efforts to identify business processes and reorganize them (business process reengineering) can also lead to the distributing of machines in lines that correspond to the new business processes. Cellular manufacturing is, moreover, significantly easier to control than job shop-type production. And, in many cases, less area is required for the machines.

Cellular manufacturing and one-piece flow can achieve a lasting reduction of lead time, and thereby also of work-in-process and many other forms of “muda.” On the one hand, inter­operation times can be reduced to zero. On the other hand, cellular manufacturing allows overlapping operations (Section 13.4.2), as shown in the following.

Using the definition in Figure 6.2.1.1, the lead time of an order — assuming a sequence of operations and omitting inter­operation times and administration times — is the sum of all n operation times, as shown in Figure 6.2.2.3 (for details, see Section 13.3.2).

Fig. 6.2.2.3        Formula for lead time with a sequence of operations.

With cellular manufacturing, the estimate in Figure 6.2.2.4 is calculated:

Fig. 6.2.2.4        Formula for lead time with cellular manufacturing.

The following is a possible routing sheet for shaft production. Look at the difference between the lead time for job-shop production and the lead time with cellular production. Also, look at the difference between the theoretical minimum lead time in this particular case and the maximum lead time for cellular manufacturing, as well as at the difference between the actual minimum lead time and the lead time that entails the minimum load (or miminum allocated time for the operation, that is operation time plus wait time between the units of the batch) at the workplaces. By modifying setup and run times of the operations, change the cell driver. Try to find a situation where the value for minimum total lead time tends towards the theoretical maximum lead time for cellular manufacturing.

To understand this formula intuitively, consider the following: The longest operation, the so-called cell driver, provides the minimum lead time. The other operations overlap. Lead time then increases at most by setup and one run time per unit of all other operations. In concrete cases, lead time will fall at some point between the minimum and the maximum.





Course section 6.2: Subsections and their intended learning outcomes