Tales from the Trenches
is an ongoing series of blogs and videos
designed to help manufacturing quality professionals deal with the issues that arise on the plant floor...no matter what industry you are in.
In the first three blogs of this series, we discussed reducing customer complaints
, using assignable cause and corrective action codes
, and data entry errors
For today’s article, I’m going to take a close look at overfill, its impacts, and how you can use InfinityQS software to reduce it. Product giveaway, or overfill, happens whenever you fill your packages with more than the declared quantity printed on the packaging, and while it seems like an innocuous, delightful little bonus to your consumers, it brings with it a host of complications and risks. And giveaway can really a manufacturer’s bottom line and exposure to regulatory risk.
We’re going to look at some of those risks and complications, at what causes them, and at what you can do to resolve them.
Automatic Filling and SPC
I will share with you what I’ve done to limit overfill, and in the process, what I’ve done to keep my company’s product costs low, keeping us competitive in the marketplace.
In manufacturing today, it’s almost unheard of to have a manual filling operation. Whether it’s beverages of all kinds, chocolate candies, sheet metal screws, or medication, almost everything is filled using automated equipment. This equipment is fast and accurate. But it’s not infallible and it still relies on operator input to function efficiently. And, because of this reliance, operators possess the most direct control over how much product giveaway is happening on your plant floor.
By giving them statistical process control (SPC
) software that focuses on reducing overfill, we can harness the skills of operators to help us limit overfill, thus optimizing fill weights—reducing costs and reducing the risk of violating net content regulations.
In Spec vs. To Target
In a previous article, I discussed the difference between running within specifications, or in spec,
and running to target
and how running to target increases process capability, lowers product costs, and improves customer satisfaction. The same principles apply to overfill.
A process that is run in spec, not necessarily to target, tends to have results scattered throughout the specification range. Instead of a smooth trend line, it’s a jittery mix of high, low, and on-target results, without any predictive ability to know where the next result will land.
Because of this, and because of net content
regulations, filling operations become constrained by the lowest likely fill weight and manufacturers must overcompensate to ensure that even the least-filled packages contain the minimum amount required by law.
As a result, reduction of overfill takes a back seat to reduction of underfill
What is needed is a way to address the root cause of the fill weight variation, so we can eliminate both underfill and overfill
Eliminating Underfill and Overfill
Anytime a product is overfilled, the cost must be accounted for somewhere. Either the company pays (losing money), or the customer pays (raised cost of the product) to account for the consistent overage.
One instance that stands out to me is a situation in which operator practices had unintended consequences that led to a decrease in process capability, limiting our ability to lower fill weights and reduce overfill.
In the case of a popcorn filling operation, popcorn travels via conveyor into weigh hoppers that empty into the finished product containers. A typical setup involves anywhere from 12 to 16 weigh hoppers, each one a specialized scale that opens and closes to allow product to gravity fill (or fall) into a container below.
To fill a container, the filling system is programmed with logic that uses the best combination of 8 to 10 weigh hoppers to achieve the target weight while minimizing overfill.
When running a product such as caramel corn, the weigh hoppers get sticky and become less accurate. Frequent cleaning is required to keep fill weights consistent.
Operators also have the ability to take individual weigh hoppers offline, either to clean them or to prevent a troublesome hopper from dumping. The unintended consequence of taking hoppers offline is that the filling logic now has fewer potential combinations it can use to fill containers. As a result, fill weights start to vary and process capability decreases.
In the absence of a structured SPC program, my fill weights were all over the place, unpredictably consuming my entire spec range, and cutting into my ability to consistently meet regulatory net content requirements.
Governments typically regulate the quantities of products sold to consumers. In the U.S., the Federal Trade Commission and Food and Drug Administration are responsible for assuring that companies fill their packages with quantities that match their label claims.
For food products, a value known as the Maximum Allowable Variance, or MAV, is established to provide for minor inconsistencies in filling processes. Typically, the MAV for a product represents approximately 10% of the declared weight, allowing for products to be filled with 90% of their declared weight and still be compliant. However, the underfill must represent only a small fraction of a product lot and cannot be compensated for by overfilling other packages from the same lot.
It is important to note that the FTC and FDA guidelines and the MAV only apply to the lower end of fill-weight variation.
Naturally, there is no enforcement of overfill.
Process capability is a measure of the likelihood that a process will remain within specifications.
Consider two machines performing the same process with a specification range of 50–100.
Both have an average of 75, but when you look at the control charts, you see that process A has a nice tight range of values, with almost all of them centered between 70 and 80. Process B, on the other hand, has values across the entire specification, with concentrations of values near both 50 and 100, caused by operators making adjustments just before the process goes out of spec.
While both are running in spec, only Process A has a high process capability index (Cpk)
If this process is a filling operation, and the MAV is 45, only Process A can confidently be adjusted to reduce fill weights. Any adjustment to Process B will shift all results down, causing a significant quantity to be in violation of net content regulations.
Quality Intelligence in Real Time
tracks process capability in real time, allowing management to implement SPC rules to optimize processes. We were using ProFicient™
One of the most fundamental values of an SPC program is the idea that data that is monitored is acted upon, not ignored (the squeaky wheel gets the grease). By monitoring control charts in ProFicient—and not just relying on 12- and 24-hour averages—it becomes easy to know if a process is using the full specification range or if it’s tightly centered around target.
Selecting the right combination of SPC alarm rules is critical when attempting to control process capability.
Rules such as 2 of 3 in Zone A or Beyond, 4 of 5 in Zone B or Beyond, and even 8-in-a-row Avoiding Zone C, can quickly identify special cause variation that is driving poor process capability; there’s no need to wait for customer complaints, failed product inspections, or process upsets.
Processes are not “one-size-fits-all,” and SPC rules shouldn’t be either. InfinityQS quality management software allows for endless combinations of rules to be enabled so that emphasis can be placed on detecting special causes that are unique to your products, processes, and customer requirements.
By implementing a unique set of SPC rules, problems like overfill and risk of underfill become a thing of the past.
In the case of my popcorn fill-weight struggles, selecting the right set of SPC rules was the foundation of my successful process improvement project. For me, a combination of 2 of 3 in Zone A or Beyond and 7 Consecutive Points in Lower Zone C worked the best.
One nice feature of the ProFicient software is that you can individually enable and disable the upper and lower versions of an SPC Rule. While my goal was improving process capability and addressing both underfill risk and overfill, I found that an asymmetrical set of rules was the most effective. While the 2-of-3 rule helped me drive to target from both the upper and lower specification limits, the 7-in-a-row rule was only there to help meet my regulatory net contents requirements.
Operators were happy, too. Not only were the SPC rules helping to reduce rework, improve capability, and increase profits, it was serving as a notification system alerting them to weigh-hopper issues in real time before a failure or downtime event.
The Benefits of Using SPC
Every three months I evaluated my fill weight data and process capability, and after each analysis I was able to lower my fill targets, saving money without increasing my risk of net contents violations. In my opinion, reducing overfill is one of the most rewarding ways to utilize SPC and continuous improvement.
With InfinityQS software driving net content control, you are taking the same amount of product and spreading it out across more consumers during each production run. Sounds like a plan, doesn’t it?
To see details of the ProFicient software in action, please check out the Tales from the Trenches
video series here
Feel free to check out the other blogs in this series:
Take advantage of the technology at your fingertips today: contact one of our account managers (1.800.772.7978 or via our website
) for more information.