Changeover Time

Changeover time is the metric that separates shops that can run small batches from shops that have to run large ones. A shop with a four hour changeover will batch up two weeks of demand to amortize the setup. A shop with a 30 minute changeover can run a customer's order this afternoon. The first shop carries a stockroom full of finished goods. The second shop ships when the order comes in. The difference in working capital, lead time, and customer responsiveness is enormous, and it all turns on this single number.

"The shop that changes over in 20 minutes can say yes to orders the shop with the four hour changeover has to refuse."

How changeover time works

The clock for changeover time starts at the last good part out of the previous run and stops at the first good part out of the next run. Inside that window, the elapsed time breaks into rough phases: teardown of the previous setup, cleaning, fixture and tooling swap, material load, machine setup including any programming or parameter changes, trial parts, and inspection. The trial and inspection phase is where most shops lose time they did not plan for. If the first three parts off the new run are dimensionally off, the changeover is not done; the operator has to adjust, run again, and re inspect.

The methodology for reducing changeover time is quick changeover, best known through single minute exchange of die. The core move is separating internal steps (must happen with the machine stopped) from external steps (can happen while the machine still runs the previous batch) and then converting as many internal steps to external as possible. Preparing the next fixture on a cart while the current run finishes is external. Walking to the tool crib to find a missing wrench mid changeover is internal time that should have been external.

A shop that systematically reduces changeover time tends to follow the same path: measure honestly first, separate internal and external second, eliminate or convert internal steps third, then streamline what remains.

Where changeover time fits on the shop floor

Picture a 20 person plastics injection molding shop with five presses. The shop runs about 40 different parts for a handful of customers, and changeovers average two hours per press, mostly burning two operators each. Because changeover is so expensive, the shop runs each part in batches of four to six weeks of demand. Working capital tied up in finished goods is around $250,000, and customer complaints about lead time have started getting louder.

A changeover reduction project on one press would track ten changeovers honestly, identify the longest steps (usually mold preheat, hose hookup, and trial part adjustment), and rework them. Preheating the next mold offline on a cart turns 25 minutes of internal time into zero. Pre staging quick disconnect hoses turns another 15 minutes into five. Capturing the trial part settings in a written setup sheet shortens adjustment from 20 minutes to five. Changeover comes down from two hours to 50 minutes inside three months. The shop can then halve the batch size, free up roughly half the finished goods cash, and shorten lead time for the customer.

Common mistakes with changeover time

• Stopping the clock at the first part, not the first good part. Trial runs and adjustment are changeover time. Count them.
• Timing only the best changeovers. Average across shifts and operators. The number you want to improve is the typical changeover, not the best case.
• Measuring total time without step breakdown. Without step data you cannot pick a target. Five to eight steps per changeover is the right resolution.
• Confusing fast with safe. A changeover that gets fast by skipping safety checks or inspection will eventually produce a defective batch. Keep the inspection step.
• Reducing changeover and not reducing batch size. The whole point of shorter changeovers is smaller batches. If the shop keeps running the same batch sizes after the reduction, the benefit stays trapped.

Changeover time and related Lean tools

Changeover time is the metric that quick changeover and single minute exchange of die exist to reduce. Long changeovers count as planned downtime and feed directly into the availability factor of equipment effectiveness. Once changeover time is low enough, the shop can level its production schedule using heijunka, running mixed products in a repeating pattern instead of large batches.