I’ve been posting on 8020, Lean, & Kaizen thus far. I want to shift to quality for this discussion.
I don’t know about you, but my eyes start to get glassy when the conversation gets into details related to quality practices. The list of acronyms and supporting math has grown exponentially. I’ll cover some basic approaches that will help you resolve most of what you may experience. As always, I’ll try to keep it sensible. Tall order for this topic!
I have often reminded folks to make sure they use a cure that’s suitable for the problem. If a light bulb burns out, just replace it. You don’t need a 6-sigma project to take care of it. If it burns out in a fraction of the time other bulbs do, then use more sophisticated tools. For the record, I championed several 6-sigma projects, so I am a fan. Let the problem seek an appropriate level of solution. Be sensible!
Measurements — Regardless of company size or complexity, everyone wants to leap to solutions. It gets even more interesting when it involves multiple levels in the supply chain. I’ll use a measurement example for this discussion. Do not skip this step! Make sure everyone is using the same tools to measure; make sure they know how to use the tools; and make sure the tool is suitable for the tolerance.
For example, if your team is measuring a machined part with a +/- 0.0001 tolerance, it would be better to use calipers than pi tapes. We’ll discuss how to evaluate your alternatives objectively in a minute.
This may seem obvious to you, but I have witnessed this one first hand. The supplier was using a basic pi tape for their final inspection, while the customer was using a caliper for incoming inspection. As you might imagine, the supplier was not accepting the customer’s non-conformance. The debate went on for the better part of a month. At a minimum, make sure everyone uses the same tool! If the tolerances are tight, they should measure at the same room temperatures.
To find out if you are using the right tool, you need to make sure the tool’s measurement variation isn’t excessive. To be ridiculous about it, imagine giving 5 people a yardstick to measure the diameter of this part to 4 decimal places. Clearly, you would have 5 very different results and they would vary well beyond a +/- 0.0001 tolerance. The best way to find out if a tool is suitable is to conduct a gage R&R evaluation.
The first “R” is repeatability — How much variation exists when the same operator measures a part multiple times with the same tool in the same location. The second “R” is reproducibility – How much variation occurs among operators. There is good software available to calculate the statistics and provide you with the result. What’s important is that you know the tool in use is capable.
Let’s argue that you have confirmed that all parties are using the same tool and the tool is suitable. And, you still have a problem. Before we get into a discussion on process capability, we need to visit product design for a moment. Are tolerances on drawings sensible? Has anyone looked at them recently? Before you consider more expensive tooling or process designs, make sure you ask the 5-Why’s! Assuming you agree with the tolerances, it’s time to discuss process capability and control.
Process Capability – Recall my earlier comment about leaping to solutions? It will happen again at this stage. There are 2 basic indices related to Process Capability – Cp and Cpk. There is a significant difference between the 2 metrics. It is equally important that you focus on them in the right order. Cp is focused on how much variation exists versus the spec without regard for position to target. Cpk includes position to the mean or the target.
Let’s use a sport analogy to explain Cp. Picture a struggling field goal kicker, who is spraying the ball from sideline to sideline. In this case, there would be a very low Cp reflecting almost no control. Ask yourself if it matters all that much which way you pointed him. A leap to using Cpk is futile until you achieve acceptable control. To keep this posting brief, I’ve skipped over tools to get to root cause and corrective actions. Your quality and operations folks are probably familiar with many of these. Use them as needed to get your Cp to a minimum value of 1.75 to 2.0. The higher, the better!
Until you achieve numbers in this range, I would avoid looking at Cpk. Again, with no little or no process control, you’re probably not going to reach a sustainable gain. If you get to a 1.75 to 2.0 Cp that looks like this, it’s time to work adjustments to target Cpk. Pivoting the kicker will now have an impact.
Make your adjustments to achieve a minimum Cpk 0f 1.33. Some clients may require a minimum Cpk of 1.6.
Let’s say that despite everything you’ve tried, you can’t seem to get a Cp to break 1.0. This is where it may be appropriate to consider a 6-sigma project.
6-Sigma – This is a powerful approach to solving problems that have defied all prior attempts. This is because certain processes are not controlled by a single variable. In another words, you can’t simply turn 1 dial to bring it back into control. Simply stated, to me, 6-sigma is a decoder ring that helps you discover the 2 or 3 variables interacting together to impact a process. Once you know this information, you can set up a set of controls to manage these variables.
I championed a 6-sigma project focused on extruded blank weights for high-dollar fluorocarbon compounds used to mold automotive parts. Since a low blank weight would result in unfills and scrap product, operators would simply produce heavier blanks. Remember our field goal kicker? Well, in this case, we told him that we would give him points for anything to the right of the left post…
This would remove the scrap because of unfills but result in excessive flash that you paid to landfill. In rough numbers, we were throwing away about $100K in compound every year due to this practice.
The fishbone diagram the team assembled for this project showed there were dozens of variables impacting extruded blank sizes and weights. They discovered there were only 2 that were significant. They developed and set up autonomous controls to manage these variables and saved the $100K. Cp and Cpk values were on target and the products were in spec.
In sum, I go to 6-sigma level tools when the basics haven’t produced acceptable results. If you are experiencing a condition along these lines, you should consider using this problem as an opportunity to certify one of your folks.
Summary — To wrap it up:
- Use Common Sense!
- Make sure everyone involved – from suppliers to customers – are using the same measurement tools.
- Ensure the tools being used can do the measurement on a reliable basis.
- Confirm that the tolerances are sensible.
- First establish control of the process.
- Once in control, adjust to target.
- Elevate to 6-Sigma if your traditional approaches haven’t solved the issue.
As you explore some of these ideas in your own facilities, I hope to hear from you. If you have questions, feel free to reach out to me by email or through the Contact Me button or page. Please post your own success stories in response so other readers will benefit from your experiences.
Thanks & Good Wishes for a successful 2018!
Mike