“Lean Manufacturing” (a.k.a. the Toyota Production System) is a toolbox of techniques to improve operational efficiency and eliminate waste.
There are many sources about TPS (if you want to learn more about Lean Manufacturing, I recommend Jeffrey Liker’s “The Toyota Way”).
Liker distills the TPS into 14 principles which we can use as talking points for this article. Principle 2 is “Create continuous process flow to bring problems to the surface.” This principle will force you to drive non-value-added waste activities out of your process.
SPC can be used to monitor the level of:
- Excess production (e.g. “just-in-case” finished inventory)
- Waiting (e.g. downtime)
- Unnecessary transport (e.g. inefficient material movement)
- Overprocessing (e.g. deviation from planned processing time or rework)
- Defects (e.g. scrap)
Since your purpose is to reduce or eliminate these, what you would like to see in a process that is continuously improving is that all these are stable (in control) and moving towards zero. Real-time SPC can track these and provide essential improvement information to your Lean implementation team.
Another Lean Manufacturing term is “Takt time”. Takt time is the “heartbeat” of the process and is the amount of time every step of the process needs to produce a part. (Liker, p. 94) If one operation is producing faster or slower than the takt time, that operation is either creating work-in-progress piles or starving subsequent operations.
If you are trying to achieve continuous flow and one-piece operation, you need all the processing steps to move together like clockwork. We know there is variation everywhere, so a control chart on Takt time can help you monitor variation in your production, identify special causes, and eliminate them in order to smooth out the process flow.
The objective of continuous flow is to link processes and people together so that problems surface right away. SPC is a tool that can assist you in improving your processes and alerting you of special causes before they impact your bottom line.
There are a number of other ways where SPC can help you during your effort to establish and maintain Lean systems. Next month I will address some of those additional ways.
Steven Wachs, Principal Statistician
Integral Concepts, Inc.
Integral Concepts provides consulting services and training in the application of quantitative methods to understand, predict, and optimize product designs, manufacturing operations, and product reliability. www.integral-concepts.com