Moulding is measured in shots, and shots are not parts.
One shot produces as many components as the tool has cavities — and cavity count changes with the tool, several times a week. Why that must never be a machine-level setting.
Injection moulding is measured in shots, not cycles, and one shot produces as many components as the tool has cavities. That single distinction invalidates cycle-based counting entirely: a machine running a sixteen-cavity tool produces sixteen parts per shot, and a system counting shots will understate output by a factor of sixteen.
Cavity count also changes with the tool, several times a week on a job-shop moulding floor, which means it cannot be a machine-level setting.
| Concept | What it means | How it must be handled |
|---|---|---|
| Shot | One injection cycle of the machine | Detected from the machine or its PLC; the base event |
| Cavities | Components produced per shot | A property of the tool, not the machine. Set per tool, never per machine. |
| Good parts | Cavities that produced acceptable components | Short shots and blocked cavities mean shots × cavities is an upper bound, not a count |
| Cycle time | Seconds per shot | Tight and repeatable. Drift is meaningful and shows quickly. |
| Tool change | Changeover to a different mould | A major, planned event — measured separately from breakdown |
A moulding machine that runs a four-cavity tool on Monday and a sixteen-cavity tool on Wednesday has two completely different output rates for identical shot counts. If cavity count is configured against the machine, every tool change silently corrupts output, yield and cost-per-part until somebody notices — and on a job-shop floor that can be weeks.
The correct arrangement ties cavity count to the tool and requires the tool to be identified when it is loaded, by selection or scan at the machine. That one input makes shot counts meaningful, and it is the single most important configuration decision on a moulding floor.
It also enables the thing plants find most useful afterwards: blocked-cavity detection. Where actual good parts are counted downstream and compared against shots multiplied by cavities, a persistent shortfall points at a cavity that has stopped producing — which is otherwise discovered at packing, or by the customer.
Tool changes
Long, planned and frequent on job-shop work. The dominant availability loss on most moulding floors.
Material and colour changes
Purging, drying and changeover between materials. Legitimate, and worth measuring as its own category.
Startup scrap and stabilisation
The shots after a change that are not saleable. Real cost, rarely attributed to the change that caused it.
Short cycle-time drift
A machine gradually running two seconds slower per shot is invisible per shot and substantial per month.
Two moulding machines on a live dashboard this week.
Bring a machine that changes tools often. Getting cavity count tied to the tool rather than the machine is the whole exercise, and it changes every downstream number.
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