|
Written by Steven Ouellette
|
"My company is instituting Lean systems. What is SPC's role, if any, in the world of Lean Manufacturing? Is SPC 'lean'?"
Excellent question!
“Lean Production” (a.k.a. the Toyota Production System) has become popular over the last decade or so. As usually implemented in the US, it involves a toolbox of techniques to improve operational efficiency. As usual, the first adopters were in manufacturing, but recently we have seen more interest in non-manufacturing areas as well. SPC works well in both implementing and maintaining your effort to run lean.
There is a lot of good stuff in the TPS (if you want to learn more about Lean, I recommend Jeffrey Liker’s “The Toyota Way”), but let’s focus on the areas where SPC can actually help your Lean efforts succeed.
Liker distills the TPS into 14 principles, and we can use these as some talking points. 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)
- unneeded transport (e.g. inefficient material movement)
- overprocessing (e.g. deviation from planned processing time or rework)
- inventory (e.g. raw materials, work in progress)
- wasted motion (e.g. poor work area layout)
- defects (e.g. scrap)
Interestingly, 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 either stable (in control) or out of control on the low side (for example if you found a way to reduce waiting and are now stable at a lower level than before). Here is an example where being “out of control” is a good thing! Real-time computer-linked SPC can track some of these “behind the scenes” and provide essential improvement information to your lean implementation team.
If you are trying to achieve continuous flow and one-piece operation, you need for all the processing steps to move together like clockwork. 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. We know there is variation everywhere, so a control chart on takt time can help you monitor variation in takt time, identify special causes, and eliminate them in order to smooth out the process flow.
The objective of continuous flow is to allow your company to react rapidly to your customer demand, and so another way SPC can assist you is in tracking your time from customer order to customer acceptance. As you improve your process, this too should show out-of-control signals on the low side and alert you to process changes that need to be captured.
There are a number of other ways where SPC can help you during your effort to establish and maintain Lean systems, but you will have to wait until next month to get the rest! |
Ask the Expert 
