Cooling usually accounts for the largest share of the moulding cycle. When the cycle won't come down, the first reaction is often to blame the machine or the material — but cooling capacity is essentially fixed at the mould-design stage. Trial moulding can only fine-tune it; it cannot change the layout.
Take a common case: a multi-cavity housing mould looks fine on a single T0 part, but after continuous running, some cavities start to warp and the overall cycle stretches. Investigation shows it was neither a material change nor an unstable machine — the cooling lines sat at uneven distances from the cavity surface, and the moving/fixed halves had no zoned temperature control. The temperature difference only surfaced once heat accumulated. (Scenario is a generic illustration, not referencing any specific project.)
Heat travels from the cavity to the cooling water along a path already machined into the steel: cooling-line position, circuit length, series/parallel arrangement, and the relationship to the cavity surface — all fixed in one go when the mould is built. A mould temperature control unit (TCU) can only adjust setpoints and flow, optimizing along an already-built path. If the path itself is unreasonable, tuning usually just moves the temperature difference from one spot to another — suppressed this round, back again after a batch change.
Cooling lines are not a case of "as long as they exist." The 4 variables below decide whether heat can be carried away evenly.
# | Variable | What it affects | What to confirm at DFM stage | What happens if ignored |
① | Cooling-line layout vs. cavity | Heat-removal uniformity, warpage, local hot spots | Cooling-line layout drawing, relationship to cavity surface, presence of dead zones | Single part passes; warpage after continuous running |
② | Zoned temperature control & circuits | Moving/fixed half temperature difference, local over- or under-cooling | Number of zones, series/parallel arrangement, TCU matching | Uneven shrinkage between two sides, dimensional error |
③ | Temperature measurement & records | Whether the design intent was actually realised | Thermocouple placement, measured mould-temperature records | No evidence when problems arise; tuning by feel only |
④ | Maintainability | Cooling efficiency decay after scaling | Cleaning ports, cooling-line test records, maintenance intervals | Cycle lengthens month by month under the same parameters, with no traceable cause |
(General process practice, not a national standard and not mandatory; specific layout, dimensions and temperatures are subject to material-supplier data, specified equipment parameters and the bilateral technical agreement. The table contains no numerical values.)
Measuring-point no. & location / moving- and fixed-half readings / readings after stable running / corresponding batch, machine & environment / recorder & time.
Special note: problems only show up after heat accumulation. Recording only the first shot after start-up amounts to not measuring at all — that is not the mould's temperature in production state.
A local hot spot is not just "a bit slower" — it is a chain: slow local heat removal → cooling time forced to the slowest point → longer cycle; temperature difference between front and rear halves → uneven shrinkage on both sides → warpage and dimensional error; for thermoset materials, local differences in the degree of cure may also appear. Further downstream, scaling in the cooling lines reduces heat-removal capacity month by month under the same set of parameters — parameters unchanged, yet the cycle slowly lengthens. More insidiously, most of these phenomena only appear after continuous running reaches thermal steady state, and are nearly invisible in single-part trials. Releasing a mould on the strength of a few conforming T0 parts tends to leave the risk for mass production.
The cycle lengthens under the same parameters, with no change in material or machine to be found;
Temperature difference or dimensional variation between cavities of the same mould grows;
Cooling-line flow drops and TCU load rises.
If any of these appears, check cooling-line scaling and flow first — don't rush to change injection parameters.
The same cooling solution does not carry the same risks across products. Before the review, determine which category the part falls into — don't apply one cooling-line layout to every part.
Product type | Main cooling risk | What to check at review |
Thin-wall / fast-cycle parts | Cooling takes a high share of the cycle; uneven heat removal easily causes warpage | Cooling-line layout vs. cavity surface, basis of cycle-time estimation |
Multi-cavity parts | Inter-cavity temperature difference causes dimensional scatter and inconsistent yield | Cooling-line symmetry across cavities, whether zones can be controlled independently |
Thermoset-material parts | Local mould-temperature differences affect consistency of the degree of cure | Mould-temperature uniformity, thermocouple placement |
High-gloss / appearance parts | Mould-temperature fluctuation affects surface replication and gloss consistency | Moving/fixed half temperature difference, steady-state mould-temperature records |
(General process experience, not a national standard; specifics subject to material-supplier data, specified equipment parameters and the bilateral technical agreement. The table contains no numerical values.)
How to use this table: at the mould design review, first tick the product type, treat the corresponding row as a mandatory check item and the rest as general items; if a project falls into two categories at once (e.g. multi-cavity + high-gloss appearance), check both rows. This turns the cooling review from "check whether cooling lines exist" into "check whether the key risks are covered."
One line: Cooling is decided at the design stage; trial moulding can only fine-tune it. To change the cycle, look at the cooling-line drawing first, then talk about the machine and the material. Any "mould temperature is fine" unsupported by measured records is only a setpoint, not the actual temperature.
Jingmu delivers cooling solutions and cooling-line records based on product type, retains measured steady-state mould-temperature data at the agreed measuring points, and supports the corresponding reviews and verifications.
The above is general process practice and empirical classification, not a national standard or mandatory requirement; specific layout, dimensions and temperatures are subject to material-supplier data, specified equipment parameters and the bilateral technical agreement.
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