When a packing line cannot keep up with order volume, the instinct is to upgrade the equipment that appears slowest. That instinct is often wrong. The constraint that limits throughput is not always the machine that looks busy. It is the step that the rest of the line waits for, and identifying that step correctly determines whether an equipment investment actually improves throughput or simply shifts the waiting to a different part of the process.
The first step in identifying the bottleneck is to observe the line rather than the equipment. Where do partially packed orders accumulate? Where do operators wait? Where does work-in-progress stack up? The step immediately after the accumulation point is usually the constraint. If cartons pile up before the sealing station, the sealing station is the constraint, not the packing station that appears busy.
The second step is to measure the time each step takes. A packing step that takes ninety seconds per order and a cushioning step that takes twenty seconds per order are not equally likely to be the constraint. But time per order is not the only measure. The constraint is the step whose total capacity is closest to the total demand. A step that takes thirty seconds but runs continuously may be a tighter constraint than a step that takes ninety seconds but only operates for part of the shift.
The third step is to consider variability. Some steps have consistent cycle times and some do not. A cushioning step that depends on an operator pulling material by hand has variable cycle times, because the amount of material needed varies and the operator's speed varies. A cushioning step that uses a machine producing a set length has consistent cycle times. Consistent steps are easier to plan around, and variable steps tend to become the constraint even when their average time is lower.
The fourth step is to evaluate the cost of the constraint. If the constraint is the packing step, upgrading the cushioning system will not improve throughput. If the constraint is the cushioning step, upgrading the packing station will not help either. The investment should target the step that is actually limiting output.
Aircosan manufactures paper bubble machines at its own facility in Foshan, Guangdong, and builds units up to 80cm wide. The machines produce cushioning at a set length, which converts a variable step into a consistent one. For operations where hand-wrapping with plastic void fill creates variability that limits throughput, the machine addresses the constraint directly by removing the estimation and cutting time from the packing cycle.
There is a fifth step that is often overlooked. The constraint may not be a single step but the handoff between steps. If the cushioning is stored in a separate area and the operator has to walk to retrieve it, the walking time becomes part of the cycle and may be the real constraint. Positioning the machine at the packing station eliminates that walking time, which is one of the reasons placement matters as much as equipment capability.
For operations managers, the discipline of identifying the real bottleneck before investing in equipment prevents the common mistake of buying capacity that does not improve output. The machine is only valuable if it addresses the step that is actually limiting the line.