---
title: "How to monitor injection molding machines"
description: "Count shots, multiply by working cavities and keep mold-open pauses out of downtime. Learn why a molder's count reads double or half, and how to check it."
category: "Machines and connectivity"
author: "Applications Engineering Team"
published: "2024-06-14"
updated: "2026-10-20"
source_url: "https://www.iotflows.com/blog/monitor-injection-molding-machines/"
---
> Question: How do I count shots, cavities and stops on a molding fleet, and why does a count read double or half?

## Key takeaways

- A molder's part count is its shot count multiplied by the number of working cavities in the mold.
- Mold open, eject and close happen inside every shot, so a filter window keeps those pauses out of downtime.
- A count that reads exactly double, half or a quarter is a cavity setting, not a sensor fault.
- Every mold change needs its own shot time and cavity count, while a material change keeps both and needs a reason.
- Validate each new setup against a hand count and the machine's shot counter before anyone acts on the number.

To count shots, cavities and stops on a molding fleet, you count each machine's shots, multiply every shot by the working cavities in its mold, and filter the few seconds of mold open and eject so they never read as stops. A count that reads exactly double or half is a cavity setting, not a sensor fault: fix the multiplier, then check the count against a hand count.

This guide is for plant managers and process engineers running a fleet of molding machines. It follows one hypothetical 4-cavity mold on a 24-second shot, from the vibration trace to a validated part count.

## What to monitor on a molding machine

> **Definition.** **Shot** is one complete cycle of an injection molding machine: the mold closes, the screw injects and packs the melt, the part cools, and the mold opens and ejects. One shot makes one part per working cavity.

A molder's output follows from three numbers: how many shots it ran, how many cavities each shot filled and how many of those parts were good. Its losses are the stops between runs of shots, and shots that ran slower than the mold's set cycle.

> **Definition.** **Quantity per cycle** is the number of parts one machine cycle produces. On an injection molding machine it equals the number of working cavities in the mold, so a 4-cavity mold makes 4 parts per shot, and 3 with one cavity blocked off.

The glossary entry for [quantity per cycle](/docs/get-started/glossary/#quantity-per-cycle) uses the same meaning. Multiply it by the shot count and you have the part count.

**Parts** = Shots × working cavities

| Number | What it tells you | Where it comes from |
|---|---|---|
| Shot count | How many cycles the machine ran | Sensor or machine controller |
| Shot time | How long each cycle took | Sensor or machine controller |
| Working cavities | Parts per shot | The mold, set once per mold |
| Stops | When and how long it stood | Sensor or machine controller |
| Stop reason | Why it stood | The operator |
| Scrap | Parts made but not good | The operator or inspection |

Count *working* cavities, not the number on the mold drawing. For example, a 4-cavity mold running with one cavity blocked for a damaged insert makes 3 parts a shot. Left at 4, every shot from that moment overcounts by one part in three.

The count is gross output. Startup shots after a mold change, purge shots and rejects are all shots, so log scrap separately and compare good parts with good parts.

## How a molding cycle looks to a sensor

A shot has four phases: fill, pack and hold, cooling, then mold open, eject and close. In one published example, fill took 0.26 seconds, pack and hold 8.0 seconds and cooling 10.0 seconds, inside a 21.43-second cycle.[1] That leaves about 3.2 seconds for everything else, including opening the mold, ejecting the parts and closing it again.

A vibration sensor on the injection unit or near the hydraulic power unit feels the clamp, the screw and the pump through every phase. The trace stays above the *running threshold*, the vibration level calibrated to separate running from idle, for most of the shot. It dips for a few seconds as the mold opens and ejects, then climbs again.

Figure: A vibration trace over 3 minutes on a 4-cavity mold with a 24 s shot: four shots, each with a 3 s mold-open dip below the threshold, then a 60 s stop that runs past a 48 s filter window, then a fifth shot.

*Mold-open dips fall inside the filter window and count as running; the 60-second stop does not. Sample data.*

That shape decides how you count. The dips last only a few seconds and the machine never rests between shots, so a detector that looks for one burst per shot can miss or merge shots.

Divide running time by the measured shot time instead. At a 24-second shot, 1 hour of running is 3,600 ÷ 24 = 150 shots, or 600 parts from 4 cavities.

> **Divide run time or count bursts?**
>
> Divide running time by the shot time when the machine cycles on its own and the shot repeats to the second. Count each burst as a shot when the machine waits between cycles, for example when an operator loads inserts by hand or takes parts off before the next cycle starts. That molder behaves like a machining center, which [counts cycles one by one](/blog/how-to-monitor-cnc-machines/#count).

Dividing by the shot time makes that number the accuracy of the count. Once the machine is at temperature, time 10 consecutive shots with a stopwatch, from shot start to shot start, and average them. Never copy the shot time off the setup sheet, and never time a part instead of a shot.

## Keep mold-open pauses out of downtime

Every mold-open dip is a fall below the threshold. Without a filter, a monitoring system records each one as a stop, so a 24-second shot produces 150 three-second "stops" an hour. The downtime list fills with pauses nobody on the floor would call a stop.

The count suffers too. Those 150 dips take 450 seconds of running time out of every hour, so a count built from running time reads 3,150 ÷ 24 = 131 shots instead of 150, about 12.5% low.

> **Definition.** **Downtime filter** is a window, set as a percentage of the cycle time, inside which a stop is counted as running time instead of downtime, so the brief pauses inside every cycle of a continuously cycling machine never reach the downtime record.

Read the percentage as a length of time. At a 24-second shot, 200% is a 48-second window and 50% is a 12-second window. Because the window scales with the shot, re-timing the shot moves the window with it.

| Filter | Window at a 24 s shot | Counted as running | Kept as downtime |
|---|---|---|---|
| 0% | None | Nothing | Every mold-open dip |
| 50% | 12 s | Mold-open dips | A 20 s robot fault and longer |
| 200% | 48 s | Dips and a 40 s material hiccup | A 60 s stop and longer |

The wider the window, the fewer stops anyone has to explain, and the more short problems disappear into running time. For example, a dryer alarm that holds the screw for 40 seconds reads as production at 200% and as a stop at 50%.

> **A wide window inflates the count**
>
> When running time drives the count, every stop the filter absorbs is credited with shots. Three absorbed 40-second stops an hour add 120 ÷ 24 = 5 phantom shots, which is 20 phantom parts on a 4-cavity mold. Start wide, then narrow the window once you see which short stops recur.

Stops longer than a mold-open dip but shorter than the window are micro-stops: they cost shots without ever reaching the downtime list. The [guide to micro-stops](/blog/micro-stops/) covers how to find them.

## Why a count reads double or half

Divide the monitored count by a hand count over the same shots, and read the ratio rather than the difference. A clean ratio is a multiplier: exactly 2, 4, 0.5 or 0.25 means each shot is credited with the wrong number of parts. No change to the sensor or the counting method fixes a multiplier.

An uneven ratio, such as 0.93 or 1.08, is a timing problem. The shot time is off, or the filter window is too narrow or too wide.

Figure: A ratio scale of monitored count divided by hand count. Clean ratios of 0.25 and 0.5 mean the cavity count is set too low, 2 and 4 mean it is set too high, and a ratio within 5% of 1 needs no change.

*A clean multiple of the hand count points at the cavity setting first; an uneven ratio points at timing.*

| Ratio | Likely cause | Fix |
|---|---|---|
| Exactly 0.25 or 0.5 | Cavities left at 1 | Set the working cavities |
| Exactly 2, 3 or 4 | Cavities set above the working count | Set the working cavities |
| A multiple, cavities correct | Per-part time entered as shot time | Enter the full shot time |
| Wrong since a mold change | The old mold's settings still apply | Apply the new mold's settings |
| Uneven, below 1 | Shot time too long, or dips as stops | Re-time, or widen the window |
| Uneven, above 1 | Shot time too short, or stops absorbed | Re-time, or narrow the window |

The per-part row catches a common timing mistake. A 2-cavity mold on a 22-second shot makes a part every 11 seconds, and entering 11 seconds as the shot time doubles every count. The [part-count troubleshooting guide](/docs/production/troubleshoot-part-counts/#half) works through the same checks for every counting method.

#### Worked example: A 4-cavity mold that reads a quarter

- Mold: 4 working cavities. Shot time: 24 seconds, averaged over 10 timed shots.
- The machine runs a full hour with no stops, so it makes 3,600 ÷ 24 = 150 shots and 150 × 4 = 600 parts.
- The monitoring system shows 150 parts for the hour. Counting the parts from 10 shots at the press gives 40.

The ratio is 150 ÷ 600 = 0.25, a clean quarter: quantity per cycle is still 1. Set it to 4.

Over the next hour, the monitored count reads 600. The shot counter on the machine's own screen moves from 18,240 to 18,388, which is 148 shots or 592 parts.

**Result:** Accuracy = 600 ÷ 592 = 101.4%, inside the 95 to 105% band

## Handle mold and material changes

A mold change and a material change look alike on the downtime list: the machine stands for a while. They are not alike for the count.

A mold change replaces the shot time and the cavity count, so the settings must change with the mold. Skip that, and every shot of the new mold is counted with the old one's numbers. For example, swapping a 4-cavity clip mold on a 24-second shot for a 2-cavity housing mold on a 30-second shot, without changing the settings, reads (30 ÷ 24) × (4 ÷ 2) = 2.5 times the real output.

Set up one entry per mold, not one per part number. The same clip run in a 2-cavity and a 4-cavity mold needs two entries, because the cavity count differs.

A material or color change keeps the mold, the shot time and the cavities, so nothing in the count changes. The stop is the number worth tracking, so give it its own reason and [time it by one rule](/blog/measure-changeover-time/#start-stop).

| Reason | What it covers | Who acts on it |
|---|---|---|
| Mold change | Pulling and hanging a mold, hookups | Setup lead |
| Material change | Resin swap and purge | Process technician |
| Color change | Colorant swap and purge | Process technician |
| Startup | First shots until parts pass | Quality |
| Waiting on material | Empty hopper or dryer not ready | Materials |
| Auxiliary equipment | Robot, conveyor or chiller fault | Maintenance |
| Mold problem | Stuck part, flash or blocked cavity | Tooling |
| Shift change | Handover between crews | Supervisor |

A starting list. Split a reason only when it grows large enough to hide two different causes.

Keep the list short enough that an operator picks a reason in one tap. The [starter list of reason codes](/blog/downtime-reason-codes/) holds the reasons operators pick to 8 to 12.

## Read the controller or use a sensor?

Many molding machines can report their own shots. EUROMAP 63, the older interface between molding machines and central computers, works by transferring text files. EUROMAP 77 is the OPC UA interface written to replace it.[2] Its first version was released on 4 May 2018, and release 1.01 is identical to OPC 40077.[3]

The OPC UA model gives a molder's data names. Each running job reports `JobCycleCounter`, the number of finished cycles in the job, and `LastCycleTime`, the duration of the most recent cycle, beside counters for good, bad and test-sample parts.[4] The job information can carry `NumCavities`, the number of cavities in the mold used for production. That property is optional, so check that your machine fills it in before you trust a part count built on it.[5]

The interface is more than a feed of numbers. The OPC Foundation says EUROMAP 77 provides no direct control functions or functions needed for safe operation,[2] but its use cases include sending jobs from the MES to the machine and releasing production.[6] A connection to the controller is a security concern for many plants, and IT usually reviews it first.

Choose the controller connection when:

- the machines support EUROMAP 77 and IT has approved the connection;
- you need process values, such as temperatures and pressures, beside the shot count;
- you want the machine's own good and bad part counters per job.

Choose a sensor on the outside of the machine when the fleet mixes builders and decades, when some machines have no interface, or when you need shots and stops this month rather than after an IT review. The [protocol guide](/blog/machine-communication-protocols/) explains OPC UA alongside MTConnect and Modbus. The [sensor-based versus PLC comparison](/compare/sensor-based-vs-plc-machine-monitoring/) sets out what each approach sees.

## Monitor molders with IoTFlows

IoTFlows puts a magnetic SenseAi on the injection unit or near the hydraulic power unit of each molder, with no PLC connection. Each mold is its own operation on Continuous Analysis, which divides running time by the shot time you timed. QTY/OP holds the cavity count, and a Downtime Filter of 0 to 200% keeps mold-open pauses out of the downtime record, as the [downtime filter settings](/docs/production/cycle-times-and-filters/#filter) describe.

Datwyler runs more than 20 injection molding machines in Ontario, California. With SenseAi on every machine and a reason on every stop, it cut shift-changeover downtime by 50% and material-changeover downtime by 30% within six months, as [Datwyler's story](/customers/datwyler/) tells. [Injection molding machine monitoring](/solutions/injection-molding-machine-monitoring/) shows what each machine reports.

## Roll it out across the fleet

1. **Start with one machine of each kind.** Pick one fully automatic molder and one an operator tends. They count differently, so each needs its own check.
2. **Time ten shots at temperature.** Average 10 consecutive shots from shot start to shot start. Write the result next to the mold's cavity count.
3. **Set up one entry per mold.** Enter the shot time and the working cavities for each mold, not for each part number.
4. **Start the filter wide.** Begin at a window of about twice the shot time, run a shift, then narrow it if short stops worth seeing disappear into running time.
5. **Check the ratio against a hand count.** Count the parts from 10 shots to catch a multiplier, then compare an hour against the machine's shot counter to catch timing. The [accuracy bands](/docs/production/choose-an-algorithm/#validate) set the line: 95 to 105% is a working setup.
6. **Recheck after every mold change.** Confirm the new mold's shot time and cavities are in place before the first good part, and count one more set of 10 shots.
7. **Set goals from each machine's baseline.** After a week, set each machine's uptime goal at its own baseline plus 5 to 10%. The [molding uptime ranges](/docs/production/injection-molding/#expectations) show where tended, automatic and lights-out machines land.

Once the first two machines read correctly, copy their setup to the rest of the fleet. More machine-by-machine guides are under [machines and connectivity](/blog/topics/machines-and-connectivity/).

## Questions

### What is the difference between a shot and a part?

A shot is one complete cycle of the molding machine: the mold closes, fills, cools, opens and ejects once. A part is one molded piece. A shot makes as many parts as the mold has working cavities, so a 4-cavity mold makes 4 parts a shot, or 3 with one cavity blocked off.

### Should mold-open time count as downtime?

No. Opening the mold, ejecting the parts and closing it again happen in every shot and last a few seconds. Count them as running time, and treat only stops longer than a set window, such as twice the shot time, as downtime. Check the window against your real stops so a short material problem is not hidden.

### What uptime should an injection molding machine reach?

It depends on how much of the cycle a person carries. As a guide, a machine where an operator loads inserts or takes parts off runs 60 to 75% of the time, a fully automatic one 75 to 85% and a lights-out cell 85 to 90%. Set each goal from that machine's own baseline plus 5 to 10%.

### Can I read shot counts from the molding machine's controller?

Often, yes. Machines with EUROMAP 77 report a job cycle counter and the last cycle time over OPC UA, and can also report the number of cavities in the mold. Older machines may use EUROMAP 63, which exchanges text files. A connection to the controller is a security concern for many plants, so IT usually reviews it before it goes live.

## Sources

1. [Injection Molding Cooling Time: A Breakdown](https://www.designworldonline.com/injection-molding-cooling-time-a-breakdown/), Design World, accessed Oct 16, 2026
2. [Plastics and Rubber Machinery (EUROMAP 63 and EUROMAP 77)](https://opcfoundation.org/markets-collaboration/plastics-and-rubber-machinery/), OPC Foundation, accessed Oct 16, 2026
3. [EUROMAP 77: Data exchange between injection moulding machines and MES](https://www.euromap.org/euromap77), EUROMAP, accessed Oct 16, 2026
4. [OPC 40083, OPC UA for Plastics and Rubber Machinery, General Type Definitions: 18.4.7 ActiveCyclicJobValuesType](https://reference.opcfoundation.org/specs/OPC-40083/18.4.7), OPC Foundation, accessed Oct 16, 2026
5. [OPC 40083, OPC UA for Plastics and Rubber Machinery, General Type Definitions: 18.2.11 CyclicJobInformationType](https://reference.opcfoundation.org/specs/OPC-40083/18.2.11), OPC Foundation, accessed Oct 16, 2026
6. [OPC 40077, Data exchange between injection moulding machines and MES: 5 Use cases](https://reference.opcfoundation.org/specs/OPC-40077/5), OPC Foundation, accessed Oct 16, 2026