Multi-Cavity Injection Mold Fill Balance: A Buyer's Acceptance Checklist

Why a batch average can hide the purchasing risk

Consider an illustrative mold producing several small industrial components per cycle. The supplier reports an acceptable average part weight, but does not identify the individual cavities. A consistently heavier cavity and a consistently lighter cavity can disappear into the average. This example is a review problem, not a reported GEERPOWER project or evidence of a particular defect.

The buyer needs to know which decision the supplier's chart supports. A study of how cavities fill, a report on completed-part weight and a dimensional acceptance report are related records, but they are not interchangeable. Start by asking what was measured, under which conditions and how the result is linked to each cavity.

Beaumont's Molding Genius description uses short-shot weight information to analyze filling imbalance and distinguishes different sources of variation. It supports requesting a defined study rather than relying on a visual runner layout. It does not establish a universal acceptance percentage or imply that GEERPOWER uses that software on every project.

Agree the study boundary before collecting samples

Ask the supplier's qualified process team to define the study in advance. Record the purpose, method, material grade and lot, mold revision, machine configuration and relevant process conditions. State which equipment is actually present and whether any production-intent components are substituted. The buyer should review the resulting evidence, not improvise a process change at the press.

Include a cavity map that the sampling team and receiving quality team can both interpret. Define how each sample is separated, labeled and retained, including family molds that intentionally produce different components. Comparing unequal parts by raw weight alone does not create a meaningful cavity-balance decision.

This is a procurement checklist, not operating instructions for making incomplete shots or changing process controls. Study execution, equipment suitability and safety remain with trained personnel following the equipment and material instructions and the approved trial plan.

Keep filling, packing and finished-part quality separate

A filling study is useful for comparing the distribution of material during the defined filling condition. Fully molded parts also reflect the subsequent process and the product's geometry and material behavior. Ask for the supplier's interpretation of each dataset and avoid relabeling a completed-part weight chart as a complete filling study.

RJG's discussion of cavity pressure explains why machine-side stability and part weight are not sufficient proof of every dimensional requirement. Our buyer-side recommendation is to keep the process evidence and the product acceptance evidence connected, while retaining their different meanings. Installing a sensor or producing a curve does not automatically approve a molded part.

If in-mold measurements are included, request the sensor locations, channel-to-cavity mapping, units and the conditions under which curves were collected. If those measurements are not in the contract, ask which other evidence will answer the agreed question. Do not assume a particular instrument or proprietary method is mandatory for every mold.

Require an explicit metric instead of an unexplained percentage

A statement such as balance within a certain percent is incomplete unless the supplier defines the calculation. Ask whether it refers to a range, a deviation from a target, a difference from the mean or a software-specific measure. Also ask whether the result applies to each observation or only to a cumulative dataset.

For an arithmetic illustration only, suppose four comparable observations are 9.9 g, 10.0 g, 10.0 g and 10.1 g. Their mean is 10.0 g. Under a specifically chosen weight-spread formula of maximum minus minimum, divided by mean and multiplied by 100, the result is 2%. The maximum absolute departure from the mean, divided by the mean, is 1%. These are different descriptions of the same invented numbers.

Neither value is a recommended acceptance limit, a universal filling-balance definition or an actual test result. Put the selected formula in the approved plan and preserve the underlying readings. The example shows why percentages from two offers cannot be compared until the methods match.

Do not diagnose the cause from the runner sketch alone

A geometrically tidy runner drawing is not the same as a demonstrated balance result. Ask for evidence that the proposed material, tool and process have been evaluated together. If simulation is offered, retain the input assumptions and compare the prediction with the relevant trial observations before treating the issue as closed.

When a cavity differs, record the observation first and keep the proposed cause separate from the evidence. Have the supplier investigate the applicable flow path, tooling condition, gate and vent features, thermal conditions and process repeatability within its qualified review. Do not assume every imbalance can be corrected by one adjustment or by modifying a gate.

If the supplier changes steel, a hot-runner setting or a process condition, request a change log and the affected repeat checks. The buyer should be able to see what changed between the original and revised reports. A new chart without revision traceability does not explain whether the same study was repeated.

Use a practical release and handover checklist

Before the trial, agree which characteristics are checked by cavity and how the sample plan covers the required production conditions. Let the responsible quality team set the sample quantities and limits. Do not borrow a capability threshold or a balance percentage from an unrelated mold just because it appears in another supplier's report.

At the release review, bring together the cavity map, raw observations, calculation, process record, dimensional results, agreed functional evidence and the exception list. Identify whether the decision authorizes shipment, a further trial or production use at the receiving site. Keep these milestones separate when installation and site-specific work remain.

For an export mold, include the approved process and inspection records in the handover package and identify what must be reproduced after transfer. The receiving machine, material supply or utilities may differ from the trial setup. Agree who assesses those differences and which verification is required; do not describe a factory trial as proof of a cell that has not yet been assembled.

• Trace every dataset to the same mold and revision.
• Retain all observations, including excluded data with its explanation.
• Identify accepted and unresolved cavities or requirements.
• Record the approval owner and the remaining release conditions.
• Keep the receiving-site verification responsibility explicit.

What to send for a GEERPOWER mold-acceptance review

Share the part drawings, resin grade, cavity layout, required good-part output, proposed machine configuration and the acceptance requirements already agreed with your quality team. If a study exists, send its raw cavity-level data and method as well as the summary chart. Identify which production conditions were represented and which are still assumptions.

Ask the offer to separate mold manufacture, study support, process monitoring where requested, sample inspection, corrective trials and receiving-site support. These activities affect scope and should not be inferred from a general turnkey label. A useful review makes the next technical decision clear without promising an unverified cycle time, yield or quality result.