Why it works

Mechanism	A mold needs a set clamping force, the force that holds it shut, and more force adds nothing. So the smallest press that can hold it shut makes the same part. Once each mold's record names that press, its jobs go there first, and the large presses are kept for the molds only they can run. A smaller press also has a smaller motor and heaters, so the same job uses less electricity.
Math	A freed press hour earns about $55 when an order fills it, and we assume orders fill 70 percent. So 300 freed large-press hours per year are worth about $11,600. In a smaller press the same hours use 3,000 kWh less, about $300. The scheduler's weekly check, 1.5 hours per week for 50 weeks at $40 per hour, costs about $3,000. That leaves about $8,900 per year. Recording each mold's smallest press costs about $930 once, a payback of about five weeks.
Industry evidence	Resin suppliers' guides size a press at 2 to 5 tons of clamping force per square inch of the part, plus about 10 percent. The mold must also fit between the four steel bars the press closes along. And the press must melt the right amount of plastic for each shot. We found no measured case of how many hours this frees, so the hours are our estimate.
Limitations	A freed press hour earns nothing until an order fills it. About one order in seven shipped late, so orders do wait, but the records do not show for which presses. A job can move only when a smaller press is idle, and one visit cannot show how often that is. A mold in a press too small for it makes bad parts, so each mold's smallest press is one it has already run in.

Illustrative sample. The plant, the walk and the footage are synthetic. Figures from our analysis are estimates made with AI, not guarantees.