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Determining and Maintaining Optimum Screen-Inventory Levels

(November 2006) posted on Mon Dec 18, 2006

Learn how to use mesh and frame management to streamline changeovers and ensure that screens are always ready when needed.

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By Mark A. Coudray

You'll have a slice of a typical week at the conclusion of your analysis. Keep in mind the run lengths of the work you do during the test period. Make sure they were typical, neither too many big jobs, nor too many small jobs. The longer you track this, the more accurate your daily forecast will be.

Cycle requirement

The cycle requirement is where we pull it all together. Highly efficient companies expose screens just before they need them, sometimes only minutes or hours before going to press. The goal is to be comfortably close to press time—just in time—but never miss a press schedule to wait on frames. I try to have screens ready no more than four hours ahead of press time.

In the beginning, you may want to expose screens up to one day ahead until you become confident that your system works. The times will drop as you get better and better and control the flow of information within the company.

For the cycle to work well, the screen department must know well in advance when the job is due on press and what size frames and mesh will be required for each color in the image. This can be daunting. These decisions need to be made upstream of the screen department. In other words, I don't want the screenmakers choosing mesh on the day the screens are due.

The frame size, image positioning, and mesh count should all come to the screenmaking department along with the scheduled on-press time. The screenmaker can use this information to quickly determine how many frames must be prepped and imaged for the schedule in hand. Ideally, the screen department should have the schedule one day ahead of the press time. In reality, this is often not the case.

Last-minute changes and late art delivery often impact the schedule, and the screen department ends up with the job just a few minutes or hours before it is due on press. This is where your screen-usage trends come into play. You can forecast the inventory levels needed on a daily basis as determined by the recorded daily and weekly trends you've been studying. The job becomes easier and easier as you work toward reducing mesh counts and standardizing frame sizes.

My goal is to have screens in inventory for no more than 24 hours. Over the years, I've found that I get the best results when the screens are imaged within 24 hours of being coated. This is especially true for halftone work, which is the majority of what I do. My inventory requirement is for three days of production: Day one is reclaim, retension, degrease, and coat; day two is image and press prep; day three is print and breakdown. If the shop images 50 screens per day, the minimum requirement is 150 screens—a very tight inventory that I cannot recommend to any shop that isn't very experienced and controlled.

A particular screen-related variable can challenge the practice of managing inventory this way. That variable is how many screens (as a percentage of inventory) will break on press, or be torn in handling. The finer meshes are more susceptible to damage, and in tracking mesh failure, we know they have a definite life cycle. But the cycle is different for every company. This variable will add one to two days to your anticipated inventory level. In the beginning, you will run with more inventory, heading toward the five-day level. With time, you will trend toward three days, or slightly longer. I have yet to visit a high-volume shop where the inventory runs fewer than three days.

Finally, there is forecasting for growth. This could be the subject of an entirely different column, but it is something you must consider now. Any material change to the work day—adding a half shift or a full shift, or adding machines—will definitely impact your inventory levels. Be aware that the change is not linear. In other words, adding a second or third press will not double or triple your inventory requirement. This is a rate-related problem. As your proficiency increases, the need for more days of inventory decreases. But adding capacity changes the proficiency level (new operators and screen makers), and you will find the inventory requirement moving up initially before dropping again.

How long does it take to get a good handle on your situation? That's difficult to say. The more turnover you have in the screenmaking and press departments, the longer it will be. With a stable group of workers and good reporting, you should have the cycle requirement well established within three to six months.


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