The faster I go, the behinder I get

Packaging lines bring out the speed drivers in all of us. Eons ago, back when I was a project engineer at Kraft Foods (as it was known then), our objective for every packaging line was to increase output. And the obvious way to do that was to run the line faster. Unfortunately, at some point, as you increase operating speed, production actually decreases, because you lose more product to problems than you gain from the increased speed.

I had a project to install 10-lane vertical form/fill/seal machines to produce small pouches of condiments. Complicating the operation, we ran up to eight different items. Each of these required dedicated machines settings, and there were no sophisticated HMIs with onboard memory. Each change required that all of the setting be changed manually. It took months to get the machines running at their rated speeds.

Inevitably, as sales increased, management decided that the least expensive way to meet requirements was to run the machines faster. After a lot of anguish and some machine modifications, we were able to increase production to some extent. And, when everything was perfect on all 10 lanes—packaging material, sealing temperatures, sealing times, web tension and alignment and much more—we could run the machines maybe 20 percent faster On some days, we could even maintain this speed for an entire eight-hour shift. Unfortunately, weekly output at this higher speed was almost always lower than the output at the slower sustainable speed.

A similar problem arises when you buy a new component for an existing line. It is only human nature to buy a faster machine than the one you had before. It’s the first step in upgrading the entire line. Unfortunately, the natural inclination is to run the line at the speed of the new machine. However, if the new filler you bought can run 300 bottles/min, but the labeler can only consistently run 280, you will encounter problems.

A number of years ago, I sat through a presentation that talked about packaging line optimization. The presenters defined this as maximizing the output of a packaging line given the constraints placed upon it, and presented a procedure to determine the optimum packaging line speed. Note that this was specifically aimed at a situation where you think you have increased the speed of your line beyond its capability, and does not apply to machine malfunctions or other mechanical problems.

This was before all of the sophisticated control and analysis systems that we have now, but I think it is still an interesting concept. For what it’s worth, here it is:
•    Slow the line incrementally until your long-term (daily? weekly?)  throughput peaks and begins to decrease.

•    Continue to slow the line for a short period to make sure that you have really maximized throughput and that the throughput is stabilized across all shifts.

•    Slowly increase speed until output starts to fall off. Then, go back to the sustainable speed.