---
title: "Measure the loss from mold and material changeovers"
description: "Mold and material changes cost every minute from last good shot to first good shot, purge included. Log them apart, price a week two ways, then pick a target."
category: "Machines and connectivity"
author: "Applications Engineering Team"
published: "2026-10-15"
updated: "2026-11-02"
source_url: "https://www.iotflows.com/blog/mold-and-material-changeovers/"
---
> Question: How much downtime do our mold and material changes cost?

## Key takeaways

- A mold change swaps the mold and its settings, while a material or color change keeps the mold and purges the barrel.
- Time both kinds from the last good shot of the old run to the first good shot of the new one.
- Purge resin and trial shots belong to the changeover, even though a machine monitor reads them as running time.
- Price a week of changeovers two ways, by type and from the logs, and expect the two totals to agree.
- Attack the change type with the largest weekly total first, unless the schedule can remove changes altogether.

Mold and material changes cost every minute from the last good shot of one run to the first good shot of the next, purge and trial shots included, multiplied by how often each kind happens. A single stopwatch reading can’t price that. Log mold changes and material changes as separate reasons for two to four weeks, then total each type’s stopped minutes and run-up.

This guide is for plant managers running a molding fleet. It works one hypothetical week on a 250-ton press and ends with which change to attack first. The counting side of a mold change, re-entering the shot time and cavities, is in [monitoring injection molding machines](/blog/monitor-injection-molding-machines/#changeovers).

## Mold change or material change?

A mold change replaces the tool and its settings, while a material change keeps the tool and replaces what flows through it. Both stop the press, but different people do the work and different things make it slow.

> **Definition.** **Mold change** is a changeover that pulls one mold out of an injection molding machine and hangs another, with its water lines and heater connections, so the shot time and the cavity count change with it.

> **Definition.** **Material change** is a changeover that keeps the mold in the press and swaps the resin or the colorant, purging the old material out of the barrel and screw before the new one makes a good shot.

Both are changeovers in the [glossary sense](/docs/get-started/glossary/#changeover): the clock runs to the first good part. What fills that time differs.

| Trait | Mold change | Material or color change |
|---|---|---|
| What changes | Mold, shot time, cavities | Resin or colorant only |
| Stopped work | Unhook, swap, hook up, heat | Empty the hopper, clean, purge |
| Run-up | Trial shots to a good part | Purge and shots until clean |
| Lead work outside the stop | Stage and preheat the mold | Dry the next resin |
| Who owns it | Setup lead | Process technician |
| What makes it slow | Hookups and mold heat | Purge length and dryer timing |

Log the two as separate reasons. Averaged together, three 95-minute mold changes and six 30-minute color changes give a 51.7-minute mean that describes neither, and the fix for one does nothing for the other.

Inside material changes, record the from and the to. A purge from black to natural runs longer than natural to black, and a resin swap that needs a dryer cycle runs longer than a colorant swap on the same resin. Keep color change and material change as one reason until your log shows they last differently.

## Where does each changeover start and end?

Each changeover starts at the last good shot of the old run and ends at the first good shot of the new one. The Lean Enterprise Institute measures changeover time the same way: from the last piece of the completed run to the first good piece after the change.[1]

On a molder, name the event behind each boundary, so every crew times the same thing.

| Event | Mold change | Material or color change |
|---|---|---|
| Clock starts | Last good shot from the old mold | Last good shot in the old resin |
| Machine stops | Mold opens to come out | Production halts for the swap |
| Machine restarts | First cycle on the new mold | Purge starts on the new material |
| Clock stops | First good shot signed off | First in-spec shot signed off |
| Signed off by | Quality or the setup lead | Process technician or quality |

The restart is not the end. Between the restart and the first good shot sits the *run-up*: purge, trial shots and adjustments, with the screw and the hydraulics working and no good parts coming out.

Figure: Two changeovers on one scale. A mold change is 80 minutes stopped plus 15 minutes of run-up, 95 in all. A color change on the same mold is 20 minutes stopped plus 10 of purge and trial shots, 30 in all.

*Run-up is about a sixth of the mold change and a third of the color change. Sample data.*

> **A restart doesn’t end a color change**
>
> A machine monitor reads purge and trial shots as running time, because the screw and the pump are working. Its downtime log shows only the stopped part, so a color change with 20 stopped minutes and 10 minutes of purge reads as 20. Time the run-up from the restart to the first good shot sign-off.

A change can swap both the mold and the resin. Log it as one mold change, since the mold swap sets its length, and note the new resin. If the hung, heated mold then waits on resin still in the dryer, [split the stop](/docs/monitoring/classify-downtime/#split) at the moment the press was ready and give the wait its own reason, such as Waiting on material. The minutes still count in the week’s changeover loss; the split sends the fix to whoever runs the dryers.

Crew handovers are a different loss with different fixes, so keep them out of this log. [Shift changeover losses](/blog/shift-changeover-losses/) covers them.

## Does purge scrap count as changeover loss?

Yes. Purged resin and the trial shots made before the first good shot fall inside the changeover, so they are changeover loss, in minutes and in material. The stopped part costs availability; the run-up costs both run time and resin.

Record three numbers for every change:

- run-up minutes, from the restart to the first good shot sign-off;
- purge weight in kilograms, weighed off the floor or the purge bin;
- trial shots × cavities, logged as scrap with a changeover reason.

Log trial-shot parts under their own [scrap reason](/docs/production/log-scrap/#reason), such as Purge or Startup, rather than a general reject code. Scrap from a changeover and scrap from a drifting process need different fixes.

On a hot-runner mold, purge in two steps: the injection unit first, then the hot runner, so contaminants in the barrel don’t carry into the manifold.[4] Time the two steps as separate elements, so a long run-up shows which step to work on.

A material change also has lead work that never touches the press. Many resins must be dried before they reach the hopper. Covestro lists 2 to 3 hours at 120 °C in a dry-air dryer for one polycarbonate grade, with moisture no higher than 0.02%.[2] A 20% glass-fiber grade of the same resin needs 4 to 6 hours.[3]

Start the dryer at least the drying time before the change. Start it when the press stops, and the press waits hours for resin, a wait no faster purge can recover.

## Work one week on a 250-ton press

Price a week of changeovers two ways: by type, from counts and means, and from the logs, from stopped minutes plus run-up. The two totals must agree. When they don’t, a change is missing a timestamp.

#### Worked example: One week on a 250-ton press, for example

- Schedule: 2 shifts × 5 days × 8 hours = 80 hours. One 4-cavity mold on a 30-second shot makes 120 shots, or 480 parts, an hour.
- Mold changes: 3, stopped 70, 80 and 90 minutes, each with 15 minutes of run-up.
- Color changes on the same mold: 6, stopped 15, 18, 20, 20, 22 and 25 minutes, each with 10 minutes of purge and trial shots.

**By type.** Mold changes take 3 × (80 + 15) = 285 minutes, using their mean of 240 ÷ 3 = 80 stopped minutes. Color changes take 6 × (20 + 10) = 180 minutes, using their mean of 120 ÷ 6 = 20. The total is 285 + 180 = 465 minutes, or 7.75 hours.

**From the logs.** The downtime log holds 240 + 120 = 360 stopped minutes under the two changeover reasons, or 6.0 hours. The run-up gaps between restart and sign-off add 3 × 15 + 6 × 10 = 105 minutes, or 1.75 hours. The total is 6.0 + 1.75 = 7.75 hours.

**Result:** Changeovers take 7.75 h a week, 9.7% of 80 scheduled hours

The downtime log alone shows 6.0 hours. It misses 1.75 ÷ 7.75 = 22.6% of the loss, and color changes hide the larger share of it: 60 of the 105 run-up minutes.

Figure: Two bars of 7.75 hours. By type, mold changes take 4.75 hours and color changes 3.0. From the logs, changeover downtime is 6.0 hours and run-up adds 1.75, which is 22.6% of the loss.

*Both methods give 7.75 hours; the downtime log alone gives 6.0. Sample data.*

Put the hours in the units your plant reviews. At 480 parts an hour, 7.75 hours is 7.75 × 480 = 3,720 parts the press didn’t make. At a hypothetical rate of $90 per machine hour, it’s 7.75 × 90 = $697.50 a week, before the purged resin.

Marking these changes as planned doesn’t take them out of the total. A scheduled changeover still lowers availability under the common OEE convention, as [planned vs unplanned downtime](/blog/planned-vs-unplanned-downtime/#changeovers) explains.

## Which change should you attack first?

Attack the change type with the largest weekly total, run-up included, unless the schedule can remove changes for less effort. In the example week, mold changes lead with 4.75 hours against 3.0, even though there are half as many.

Rank by the weekly total, not by the longest single change. A 95-minute mold change looks like the obvious target, but six short color changes a week can outweigh it on another press.

| Signal in the log | What it means | First move |
|---|---|---|
| One type leads the weekly total | Largest pool of hours | Start with that type |
| Long stopped time on mold changes | Work done with the press down | Stage and preheat the mold |
| Run-up over a third of a change | Purge is the slow part | Write a purge procedure |
| Waits right after material changes | Resin not dried in time | Start the dryer earlier |
| Same colors repeat in one week | Sequence adds changes | Group colors, light to dark |
| Wide spread for one from-to pair | No standard method | Standardize before cutting |

> **Mold changes or material changes first?**
>
> Choose mold changes first when their weekly total leads and most of the stopped time is fetching, hooking up and heating, which [moving work outside the stop](/blog/measure-changeover-time/#elements) shortens. Choose material changes first when they are frequent, when run-up is a third or more of each one, or when the press waits on the dryer. Those fixes are a purge procedure, a dryer schedule and a color sequence, with no tooling to buy.

You don’t need a faster color change if the planner can drop it. Running two black jobs back to back instead of black, natural, black removes one change and its purge, and costs nothing on the floor.

## Track molding changeovers automatically

IoTFlows puts a SenseAi on each molding machine, which detects every stop from vibration with no PLC connection. Create Mold Change and Material Change categories, as the [molding setup guide](/docs/production/injection-molding/#changeovers) describes, and operators classify each stop in a tap, with the from and the to in the note.

The Downtimes report ranks the two reasons by hours and trends them week by week. Its CSV export carries one row per stop, with category and note, for the per-type math above. [Injection molding machine monitoring](/solutions/injection-molding-machine-monitoring/) shows what each press reports.

Datwyler runs more than 20 injection molding machines in Ontario, California. Its results list “30% less material-changeover downtime, from targeting the material types that needed the longest setups”, within six months, as [Datwyler’s story](/customers/datwyler/) describes.

## Start the log on one press

1. **Create the reasons.** Add Mold change, Material change and Waiting on material. Add Color change as its own reason only once your log shows it runs differently from a resin swap.
2. **Post the boundaries at the press.** Write down the last good shot and the first good shot as the start and stop, and name who signs off the first good shot for each type.
3. **Note the from and the to.** On every material change, record the outgoing and incoming resin or color, so you can rank the pairs later.
4. **Time the run-up and weigh the purge.** Record the minutes from restart to sign-off, the purge weight, and the trial-shot parts as scrap with a changeover reason.
5. **Split mixed stops.** Split any change that ran into a fault or a wait for dried resin, so each part keeps its own reason.
6. **Total the week two ways.** After two to four weeks, compute each type’s weekly total by count × mean and from the logs. Chase any gap between the two before you trust either.
7. **Pick the first target.** Use the signal table to choose the type and the first move, then compare the next four weeks with the same rules.

## Questions

### Should a color change and a material change share one reason?

Share one only when they last about the same and the same person fixes them. Split them when a resin swap needs a dryer cycle and a longer purge than a colorant swap on the same resin, because averaging the two hides which one is slow. Record the from and the to in the note either way.

### How do I log a change that swaps both the mold and the resin?

Log it as one mold change, since the mold swap sets its length, and record the new resin in the note. If the hung and heated mold then waits on resin still in the dryer, split that wait off under a waiting-on-material reason, so a late dryer is not blamed on the setup crew.

### Do purge shots count as scrap?

Yes. Purged resin and the trial shots made before the first good shot are material lost to the changeover. Weigh the purge, count the trial shots and log both with a reason tied to the change, so the material loss sits beside the stopped minutes in the same weekly review.

### Is a scheduled color change planned downtime?

It is planned, because you chose it, but under the common OEE convention it still lowers availability, since the press was scheduled to run. Log the scheduled minutes under a planned reason and any overrun under an unplanned one, so the review shows whether the plan or the change went wrong.

## Sources

1. [Changeover](https://www.lean.org/lexicon-terms/changeover/), Lean Enterprise Institute, accessed Oct 30, 2026
2. [Makrolon 2407](https://solutions.covestro.com/en/products/makrolon/makrolon-2407_000000000086286874), Covestro, accessed Oct 30, 2026
3. [Makrolon MD4821](https://solutions.covestro.com/en/products/makrolon/makrolon-md4821_86175029-05125427), Covestro, accessed Oct 30, 2026
4. [A Planned Purging Program Can Boost Your Hot-Runner Efficiency](https://www.ptonline.com/articles/a-planned-purging-program-can-boost-your-hot-runner-efficiency), Plastics Technology, accessed Oct 30, 2026