On the five longest-running jobs, shorten the cooling timer one second at a time and check each part.
Cost
$2,100 of technician time
Payback
About 1 month
Limitation
It saves nothing on a job whose timer is already right. A part whose process a customer approved waits for the customer's sign-off.
What changes
A process technician, who sets up the presses, takes the five longest-running jobs one at a time.
The cooling timer comes down one second at a time.
After each step the parts are left to go cold, then checked for size and shape.
When a part fails, the timer goes back one second, and that time goes on the job's settings sheet.
What it costs and could save
The trials take about 40 hours of the technician's time, about $2,100, and nothing is bought.
If the timers hold spare time, this could save about $23,100 per year, a payback of about 1 month.
Why it works
Mechanism
A part can leave the mold once its thickest wall is stiff enough to hold its shape.
Every second the mold stays shut after that makes nothing.
A shorter timer ends each cycle sooner, so the same job takes fewer press hours.
Trimmed one second at a time, a timer ends on a 0 or a 5 about one time in five, and all seven we read did.
Math
The five longest-running jobs ran about 18,000 press hours in twelve months, at an average cycle of 30 seconds.
Taking one second off each cycle frees about 600 of those hours.
A freed press hour is worth $55 once an order fills it, and we count 70 percent of freed hours as filled.
That is 420 hours, about $23,100 per year.
The trials cost about $2,100 once: five jobs at about 8 hours each, at $52 per hour of a process technician.
That is a payback of about 1 month.
Industry evidence
In published cases of shorter molding cycles, cooling is often 60 to 80 percent of the cycle.
The standard cooling formula in molding handbooks ties the time a part needs to the square of its thickest wall, so a timer can be checked against its part.
We found no published figure for the spare time in the timers of a plant like this one, so the seconds we count are our estimate.
Limitations
A freed press hour is money only when an order fills it.
With no order waiting, the press stands idle longer and nothing is saved.
A round number is a sign, not a proof, so some timers may already be right.
A timer cut too far lets a part warp or shrink after it leaves the press, which is why each step is checked on cold parts.
On a part whose process a customer approved, a shorter cycle generally waits for the customer's sign-off, which can take four to twelve weeks.
Cooling may also not set the pace: if the press needs that time to melt the plastic for the next shot, the cycle stays as it is.