Jack Mans, a 45 year packaging industry veteran and contributor to Packaging Digest, wrote a piece laying out the case for slowing packaging lines down to increase output on a consistent basis.
The Faster I Go the Behinder I Get – 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 agree that this case exists and when a line performing very poorly, slowing things down to get control of the situation is the first and easiest thing you can do. There is, however, a reason management wants to increase production: It’s incredibly profitable to do so and worth the time (and money) to figure out how. Slowing down is not the only way to increase throughput on a consistent basis.
if the new filler you bought can run 300 bottles/min, but the labeler can only consistently run 280, you will encounter problems.
Jack’s slowdown approach would have us run the filler at a consistent rate of 280/min to match the labeler. Let’s assume that “running consistently” equates to an efficiency of 98% and this can be achieved at both the filler and the labeler. At a line speed of 280/min, the overall throughput of our simple line is 0.98 * 0.98 * 280 = 268.9 products per minute (ppm).
Higher efficiency doesn't always mean more throughput
If you raise the line to the rated filler speed (300/min) and raise the labeler to 320/min, you’re going to take a hit in efficiency on the labeler, right? If we add a buffer with a capacity of 900 products between the filler and labeler, we can withstand efficiencies on the labeler as low as 84% before dropping the line speed below 268.9ppm. For reference ow how bad 84% is, that is equal to one hour, sixteen minutes, and forty-eight seconds of downtime in an eight hour shift. If we can consistently hold an efficiency of 92% (38 minutes of downtime per shift) at the higher speed, our line will run at 294ppm. This is a 9.3% increase over slowing the line down.
Slow Down:
0.98 * 0.98 * 280 = 268.9ppm
Buffered:
0.98 * 300 = 294ppm
0.92 * 320 = 294.4ppm
294 – 268.9 = 25.1
25.1/268.9 = 0.093 = 9.3%
Jack ends with three steps:
• 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.
In many cases this may work to improve results, but it will not maximize throughput or get management off your back. If the line described above runs two eight hour shifts per day, five days per week, fifty weeks out of the year, and has a profit margin of $0.50 per product, a 9.3% improvement translates to $3,012,000 in yearly positive cash flow.
To maximize throughput:
• Identify the constraint
• Protect the constraint from all interruptions
• Increase the speed of the constraint if possible
More examples and formulas:
Packaging Throughput Example
How Big Should my Buffer Be?
Non-linear line analysis
Accumulation in a Puck Line
