Control charts are useful tools that have been used for decades by operators and engineers to understand their processes better and know when it is time to adjust them. If appropriate statistical rules are in place and an ever-watching computer is monitoring those rules, do operators really need to spend a lot of time reviewing control charts? 

Control charts are “action charts” that help an operator answer the critical question, “Should I adjust my process, or should I leave it?” Likely, they just need to be alerted to exceptions so they can stay focused on their jobs. Putting control charts in front of operators at all times is unnecessary.

control chart

 Control Charts and SPC

Statistical process control (SPC) is all about the data you collect. In SPC, there are rules to govern exceptions. If a data point falls a certain distance from your mean (or its fellow data points), then something unexpected probably happened during your process. And if your process starts exhibiting a trend, that’s when it’s time to pay attention.

Control charts were created to provide a visual representation of trends and abnormal patterns to let you, the operator, know when something has changed from your normal expectations. 

They were designed to be easy to plot on paper. Measurements are taken, a mean and standard deviation are calculated, and those two statistics are then plotted as points on charts. As you look at the charts, ask yourself key questions such as:

  • “Did the plot points in question fall too far away from the expected mean?” If yes, then something definitely happened, and you’ll need to take action on the process.
  • “Did two out of three of the last points fall between two and three standard deviations from the expected mean?” If yes, take action on the process.

You’ll find many more such questions, but these should help you get started. 


Paper and Pencil

Using control charts is like reading a story of your process. It tells you where you’ve been, where things are trending, where things might be going. As an operator, you make necessary adjustments along the way. 

While we love good stories, we also love what’s familiar. Most people don’t like change, and that includes daily processes and tools like control charts. Paper control charts were all manufacturers had for a long time. They served their purpose, and the information they provided was valuable. When control charts were on paper, it was easy to pin them to the wall and take notes in the margins. However, manual control charts mean calculating means and standard deviations—a tedious and error-prone task. 

Most operators liked the transition to using computers for control charts because they no longer had to deal with manual calculations and plotting. However, we kept the traditions of printing out control charts and pinning them to the wall. 

Eventually, perhaps we stopped printing and displayed them on a monitor.  We embraced the technology to generate control charts and we held onto the tradition of continually looking at control charts. That made sense when our software was installed on local computers and used a file-based system that wasn’t shared across the site. The rallying point was still the printed paper or the monitor.

But what about now, when we have cloud-based systems that not only allow you to share control charts across the site, but across all the sites? Should operators still be printing out control charts? Do they really need to look at that monitor all day? 

Let’s ask that differently: There was a time when printing emails was convenient, but now that virtually anyone can access email from a computer, tablet, and smartphone, does it need to be printed out? No. It’s much easier to look at email when it is convenient. The same is true for your control charts.


Not Always the Best Solution

Still not convinced? Here are the two biggest challenges when you rely on users to analyze control charts:

  1. Wrong decision. Having to review too many charts is frustrating and a waste of time. What happens if you don’t pick up that trend? You might skip over a control chart that needs attention because you’re trying to slog your way through a slew of them. We hear this a lot from companies because it’s all too easy to create MANY control charts after switching to computers.
  2. Trying to help can make the process worse. We all want to fix things (especially us Dads). For example, your shift just took over, and you spot five ascending dots in a row. As an SPC rule reminder, you’ve set the rule that six in a row ascending/descending means there’s an issue, and you should intervene; so, you want to fix it. That’s tampering with the process, and tampering makes your variation worse. It sounds harsh, but that’s what it’s really called—you’re not supposed to touch anything until you hit that magic number “6.”

Why talk about the “negatives” with control charts? As an operator, is it really your job to be an SPC chart interpretation expert? Or is it your job to run the equipment and make the product?


Moving On…

In the past, operators were asked to look at control charts because that was the only way they could get an immediate Yes/No answer to the question, “Do I do something or not?”

If you are responsible for adjusting a machine when something goes wrong or when something is out of control, you need that story—you need that control chart.

At InfinityQS, we’re not saying we should take control charts out of people’s hands; you do not want to lose the benefits of that time-honored tool. Instead, we’re saying, “You don’t need to worry about control charts until you need to worry about them.” We are here to offer you something new and different.


Quality Intelligence to the Rescue

Before we dive into quality intelligence, let’s think about what we’ve talked about so far: operators look at control charts to see whether something is trending in the wrong direction and answer that magical Yes/No question about whether they need to do anything about it.

Because that is the main reason for using control charts, we know that we can help you put them away. InfinityQS Quality Intelligence solutions monitor your data streams using your control chart rules, but this happens in the background. That way, you can focus on the myriad other tasks you’ve been assigned and stop worrying about control charts every few minutes (like we know many of you do).

Quality Intelligence is the information gained when raw data values are converted into information. InfinityQS software products are designed to do just that: Convert data into actionable information. Using our software, you can review any quality data and uncover information about every step in your manufacturing operations.

Our Quality Intelligence solutions can help you in many ways:

  1. Alert you when you need to do something; when the answer is “Yes.” When you receive a notification of a statistical rule violation, then you can turn your attention to the control chart and determine what action to take. The notification includes a link to the control chart so you can get there immediately.
  2. Prioritize your control charts. When you have a stack of charts to review, you want to first address violations and, when time permits, turn your attention to the others.
  3. Find your control charts. In your industry, if you take dozens of measurements on each part, it is helpful to find the right chart when you need it, for example:
    • All the control charts for OD – Loc A that have statistical violations, or
    • All the control charts from Lathe 167 for Part 123 and Part 124 for OD – Loc A, OD – Loc B, and OC – Loc C

The software allows you to browse your data and look for improvement opportunities more proactively rather than waiting for statistical violations. It’s like being able to shuffle that stack of charts to get the exact ones you want to see.

Enact®, the InfinityQS Quality Intelligence platform, features a Stream Summary dashboard tile to help you accomplish these things. Enact gives you all the power of control chart analysis without constantly looking at chart after doggoned chart.

summary filtered

Charting a Course

We mentioned how control charts tell a story. However, they aren’t the only way to tell stories. You should consider tools that continually monitor your data and automate control chart analysis so that you can focus on things like exceptions and summaries. 

Some great tools include:

  • Process Event Paretos summarize events to allow users to see where problems are happening and slice and dice information by different criteria (e.g., site, feature, part, shift). Questions like, “Which production line is having the most specification limit violations for net weight?” are a snap to answer.
pareto
  • Box-and-Whisker Charts are another tool for comparing data in various ways that a control chart just can’t accomplish. Trying to line up and compare many control charts at once is not feasible, but Box-and-Whisker charts are designed to do this kind of analysis.
box and whisker charts
  • Stream Grading in Enact can simplify how you look at process performance. You can easily zoom from a site level view to an individual data stream view to understand where process improvements can have the most impact on product yield. While control charts are great decision charts, especially for immediate decisions, that same data is valuable for making bigger, longer-term decisions as well.
stream grading

 None of these visualizations are designed to replace a control chart. But using the right tool for the right circumstance can give you even more insight into your operations. You can now look beyond individual data streams (like on a control chart) and start looking at the more significant patterns and trends of your manufacturing processes.

Final Thoughts on Control Charts

Let’s return to the pencil and paper. Imagine you’re creating control charts by hand and you’ve been tasked with making 100 of them. 

Now, imagine you’ve got a new “helper” who says they will: 

  • Find and tell you each time one of those charts has a violation 
  • AND divide those 100 control charts into a sorted pile of charts with violations, so those with most violations are at the top of the stack
  • AND make a different pile for charts without violations 
  • AND instantly reshuffle and reorganize all the charts based on your specified criteria

Would you welcome that kind of help?

That’s precisely what we offer with our Quality Intelligence platform, Enact. Control charts are useful tools; however, operators and engineers don’t need to have their eyes on them all the time. They just need to be alerted to exceptions so they can stay focused on their jobs and keep pumping out a great product.

Are you tired of staring at control charts all day? We invite you to try Enact free for 3 months. Simplify your processes, adapt quickly to production line issues, and improve your efficiency. Try Enact Free for 3 Months