Press Scheduling

Scheduling Presses on Demonstrated Parts Per Hour

Schedules built on theoretical parts per hour miss shipments. How to establish demonstrated rates, manage blocked cavities, and run an hourly count cadence.

Every scheduling promise your plant makes rests on one number: parts per hour by tool. Overstate it 10 percent and a 6,000 hour schedule quietly contains 600 phantom hours, which surface in August as expedites and weekend overtime at 1.5 times labor. A press hour costs $45 to $120 fully burdened, so scheduling against a rate the floor cannot hit burns money twice: once in the missed plan and again in the recovery. The fix is not better software. It is a demonstrated rate standard for every tool and the discipline to schedule against it.

The gross math is cycle time and cavitation. At a 25 second cycle with 4 cavities, the tool delivers 3,600 divided by 25 times 4, which is 576 parts per hour. The Mold Parts Per Hour calculator gives you that ceiling instantly. But nobody ships gross. Apply 90 percent operational efficiency for micro-stoppages, restarts, and slow cycles, then 98 percent yield, and the net rate is 508 parts per hour. That 12 percent gap between gross and net is the difference between a schedule and a wish, and it varies tool by tool from 5 to 25 percent.

Schedule on demonstrated rate, not theoretical. Pull the trailing 4 weeks of production counts and run hours by tool and compute what each tool actually did. Where demonstrated sits within 5 percent of standard, trust the standard. Where the gap exceeds 10 percent, either fix the process or fix the standard, but do not schedule the fiction. In most plants the top 10 tools carry 60 to 70 percent of volume, so auditing ten standards a month covers most of the risk. A standard nobody has verified in a year is a rumor with a decimal point.

Cycle time is the lever with the most travel, and cooling is 60 to 70 percent of cycle. Every added millimeter of wall thickness raises required cooling time steeply, since cooling scales with thickness squared, so design reviews matter more than press tweaks. On the press, get cooling water turbulent: Reynolds number above 4,000, typically 4 to 8 liters per minute per circuit. Trim mold open, close, and ejection: a 3 second robot pick on a 25 second cycle is 12 percent of capacity, and shaving it to 1.5 seconds buys 6 percent more parts per hour without touching the process.

Blocked cavities are silent capacity theft. Running 3 of 4 cavities cuts the rate 25 percent, but half the shops I have walked still show the tool at full rate in the scheduling system. Make it a rule: blocking a cavity requires a rate change in the system the same shift, a repair work order with a date, and an escalation if it runs blocked more than 2 weeks. A 4 cavity tool blocked to 3 for a quarter on a 500 part per hour standard forfeits about 135,000 parts, enough to turn a comfortable schedule into a customer escalation.

Common failures: quoting and scheduling gross rate when net is what ships. Averaging rates across a family of tools so the fast tool subsidizes the slow one on paper. Ignoring startup scrap, which typically eats 30 to 60 minutes of good production per changeover; at 10 changeovers a week that is 5 to 10 hours of phantom capacity. And letting standards decay upward after improvements: the team cuts cycle from 28 to 24 seconds, the standard stays at 28, and the 14 percent gain disappears into slack instead of into the schedule.

Run the cadence tight. Hourly, operators log counts against standard at the press; a miss of 5 percent or more triggers a supervisor response within the hour, not at shift end. Every shift handoff reviews rate misses with a reason code. Weekly, planning audits demonstrated versus standard on the top 10 tools. Monthly, standards are formally updated and the quote model inherits the changes, so sales prices what the floor proves. That loop, hour to month, is the entire management system, and it costs nothing but discipline.

World class is boring and specific: schedule adherence at 95 percent or better, demonstrated rates within 5 percent of standard on the top 80 percent of volume, blocked cavities visible in the system within a shift, and changeover startup scrap under 20 minutes. Plants at that level quote lead times a week shorter than competitors and hit them, because their parts per hour is a measured fact, not a negotiation between sales optimism and floor reality.

Published 2026-07-02.