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Written by Steven Ouellette
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"My company is instituting Lean systems. What is SPC's role, if any, in the world of Lean Manufacturing? Is SPC 'lean'?" (continued)
Last month we had begun to answer this question and I promised you some more ways in which SPC can be used to make your efforts to achieve Lean processes more successful.
The third of Liker’s TPS principles (as in “The Toyota Way”) is to “use ‘pull’ systems to avoid overproduction.” This is a system that provides what your downstream internal or external customer needs when they need it. This minimizes inventory from raw materials to work in progress to finished goods and allows a company to respond quickly to changes in customer demand. SPC can be applied by tracking the various inventory levels, looking for stability in some areas and identifying the effect of establishing pull system efforts in others. Since your vendors are part of the pull system, tracking the inventory levels and usage rates for supplies and raw materials can help you and your external vendors predict what minimum levels of these supplies need to be in order to meet your customer needs.
The ultimate goal of this principle is to eliminate inventory, both raw materials and work in progress by creating a system that makes only what the customer wants when they want it. However, Liker’s next principle is “level out the workload” and since customers don’t order smoothly, there is a dynamic tension between load leveling and pull systems. The goal of eliminating all inventory generally remains a spur to creatively look for ways of decreasing inventory while still meeting customer demands. SPC can show you how much variation is present in your production flow rate. As you make improvements in your load leveling, you should see reduced variation around the target level.
Liker’s fifth principle is to “build a culture of stopping to fix problems.” Up to this point, SPC has been a tool that you can use to baseline, monitor, and track improvements as you institute Lean, but ultimately success in using SPC to achieve these principles will mean you can eliminate some of these charts. The fifth principle is when SPC becomes part of your ongoing process. If you are monitoring product characteristics, SPC will act as an early warning system for when your product output differs significantly from historical levels. As you learn more about your process, you can move to real-time SPC charts on the process variables that control those outputs. Once you have an SPC chart on the critical process variables controlling the product output, you can catch a problem in the process before it is reflected in your product. By collecting the sources of these problems when they happen, you can generate a Pareto chart of the causes and prioritize activities to eliminate those causes.
Principle seven is to “use visual controls so no problems are hidden.” Real-time SPC is the best way to display visually what is going on in a process and whether that process is being affected by unexpected sources of variability. When it is, your operators are visually signaled to record and react, insuring a quick response time and accurate data collection for improvement efforts.
The eighth principle is to “use only reliable, thoroughly tested technology.” Using SPC and other statistical techniques during the start-up and optimization of new process lines will avoid problems many businesses experience. During a functional start-up, you might test the first ten units that come off of a newly installed line, find nothing out of spec, and conclude that the line meets your specified criteria. Upon running the line, however, you might find an unacceptably high rate of nonconformance in production. By calculating an appropriate sample size and performing a capability analysis, you can statistically estimate the proportion of nonconformance over the long term, determine if further process optimization is needed, and prove out the line’s ability to meet your conformance objectives on the first day of production.
These are some ways in which SPC can help as you implement Lean in your company. As I hope I have shown you, SPC is integral in running any process, and gives you some special abilities to turn a microscope on your process looking for opportunities for Lean improvements. |
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