Stage 1: Identify Internal and External Steps
An internal step is a step that must be performed while the machine or operation is stopped; internal setup time is downtime. An external step is a step that can be performed while it is running. Referring to the types of steps listed earlier, most Type 1 steps are external, while most Type 2, 3, and 4 are internal.
The primary focus in setup time reduction is not on total setup time (Internal + External) nor on setup labor time, but on internal time alone. While reducing total setup time and labor hours is desirable, it is only of secondary importance.
Learning the setup steps and classifying them requires an actual study of each setup procedure. The study is performed by detailed observation of the procedure and may involve stopwatch analysis of the steps, worker interviews, and video recording the operation. During the analysis certain steps might be identified as obsolete or no longer practical for the current application. Such steps are classified as unnecessary and eliminated from the procedure. The results of the study are recorded on a worksheet like the one shown in Figure 6.1.
In the average factory, no distinction is made between internal and external steps; everything is treated as if it must be internal. For example, although material, jigs, and tools for the next job could be brought to a machine while the current job is running, those things are not done until after the current
job is completed and the machine stopped. The machine then sits idly while the operator or setup person fetches the tools and fixtures to do the setup. This is illustrated in Figure 6.2 for the seven setup steps listed in Figure 6.1.
Figure 6.1 Setup worksheet.
In Figure 6.2, note that every step, whether potentially classified as internal (solid lines) or external (dashed lines), is done after the machine is stopped. Notice that except for step 5, the operator is not involved and is idle during the setup procedure (zs).
Stage 2: Convert Internal Steps to External
The initial principal objective of setup improvement is to reduce internal setup time. The more setup steps, decisions, adjustments, whatever, that can be done on external time, the better. To that end, wherever possible, setup steps formerly done while the operation was stopped (on internal time) are now done while the operation is running (on external time). This usually results in a dramatic reduction in internal setup time, frequently as much as 50%.
Figure 6.2 Setup procedure: no distinction between internal and external setup steps (times from Figure 6.1).
Figure 6.3 shows the setup time for the procedure in Figure 6.1 when the operator does the external steps, some while the machine is running. (Assumed here is that the operator can leave the machine to do steps 1 and 2.) In this case, two of the external steps, 4 and 5, are done while the machine is stopped, but that is because the operator would otherwise be idle and because doing them while the machine is stopped does not affect the elapsed setup time anyway. Elapsed setup time is affected only by the internal setup time, 42 minutes.
Figure 6.3 Setup procedure: internal and external steps performed separately.
All internal setup steps should be reexamined closely to determine if any of them could be reclassified as external. For example, in producing metal castings, the casting mold must first be raised to a certain temperature, otherwise the castings are defective. The usual way to raise temperature is to attach the mold to the machine, then inject it with molten metal. This raises the temperature of the mold, though until the temperature gets high enough the castings produced are defective and must be melted and remolded. Heating up the mold can be converted into an external step by using gas or electricity to preheat the mold before attaching it to the machine. The mold would then produce good castings immediately. One company found that preheating the molds using the same oven that melts the metal saved 30 minutes of internal setup time. The only cost to the company was the expense of building a special rack to hold the hot molds.5
Stage 3: Improve All Aspects of the Setup Operation
Converting internal steps to external steps reduces setup time, although usually not enough to be in the single-minute range (less than 10 minutes). It also does not reduce the labor or material cost of the setup. (In the previous example of preheating molds there was a cost savings since melting and remolding of parts was eliminated; ordinarily however, simply converting an internal step to an external step alters the elapsed setup time but not the cost.) As long as the average total internal and external setup time exceeds the average run time, the setup time constrains the number of lots (and the minimum size of lots). Setup-reduction efforts must then focus on both internal and external steps, or on whichever most constrains the minimum lot size for a particular operation.
The emphasis in the setup in Figure 6.1 should be on decreasing internal task time, because as it stands that setup reduces by 42 minutes the time available at the operation for processing. With the operator doing the external tasks, a minimum of 13 minutes is needed for tasks 1 and 2 while the machine is running. If the machine run time is less than 13 minutes, then the time to perform tasks 1 and 2 must also be reduced to less than 13 minutes.
Reducing setup time focuses on simplifying and standardizing procedures on existing equipment. Although procuring new equipment that requires little or no setup is an option, it is often less costly and more effective to improve the setup on the existing equipment.
Setup reduction should reduce setup time to the point where setup is no longer an issue in lot-size determination, that is, to the point where the cost associated with setup is minuscule compared to inventory carrying costs. To minimize lot sizes, setup times must be small enough such that virtually any small lot size—whatever is necessary to meet demand, smooth the production flow, or meet other requirements—is practical to produce. For that to happen, the rule of thumb is that a setup should take less than 10 minutes and involve no more than a single-touch procedure. Shingo has dubbed the latter part of this goal OTED for one-touch exchange of dies.
The setup procedure should be simplified enough so that eventually machine operators can do it themselves. This deskilling of setup procedures takes setup out of the hands of a few skilled specialists and enables changeovers to be performed as needed, without schedules. As discussed in later chapters, this is one requirement for pull production.
Stage 4: Abolish Setup
Beyond OTED comes the ultimate setup improvement: complete abolishment of the setup. Here are some ways to eliminate setups:
1. Reduce or eliminate differences between parts. Fewer or no differences in parts means fewer or no changeovers to manufacture the parts. This is a product-design approach to eliminating setups. For each new product the designer raises the question “Are we currently producing parts for other products that could be used in this product?” or “How can I design this product to minimize the number of new parts (without sacrificing product functionality and customer appeal)?” For existing products, the designer asks, “What existing different parts can be standardized and used on all or many of our products?” Answers for such questions are addressed in a design methodology called
design for manufacture.
2. Make multiple kinds of parts in one production step; for example, form two kinds of parts from the single stroke of a press (rather than forming the two parts sequentially, with a setup in between). 3. Dedicate machines to making just one item. If only one item is ever made on a machine, then the
machine never needs changeover. Obviously, this approach is practical only when machines are relatively inexpensive compared to the costs of setups or when the number of different kinds of items produced is small.
It should be noted that to abolish a setup, it is not necessary to have gone through the other three steps. The alternatives for abolishing setups are very doable and it might be possible to do them right away.
The goal of setup reduction is to maximize the transfer of setup responsibility to operators, to minimize machine downtime, and to abolish setup; it is not to eliminate the jobs of setup specialists. Specialists are still needed but to do different things such as to standardize setup procedures; to modify procedures, machines, tools, and fixtures to improve setups; and to perform difficult, first-of-a-kind or one-and-only setups.