Injection Mold Trial: Why Repeated T1–T3 Failures Occur and How to Prevent Cost Overruns
Injection mold trials are the critical stage for validating design intent and machining quality. However, if underlying risks are overlooked, projects can stall, and costs can escalate rapidly. In one real project, three consecutive trial failures occurred: the first T1 sample showed a dimensional deviation of 0.3 mm and could not be assembled (in this case, the allowable assembly clearance was ≤0.2 mm, so the 0.3 mm deviation caused functional failure); the second sample presented severe sink marks; and the third sample suffered a gate breakage, resulting in immediate scrap. Due to insufficient supplier capability, repeated blame-shifting, and a contract lacking clear responsibility allocation, the trial cost eventually spiraled out of control. This article summarizes insights from our customer consultations on injection mold development projects.
Core Failure Mechanisms: From Dimensional Out-of-Tolerance to Surface Sink Marks
Behind a failed mold trial are often deeper engineering defects. In practical mold development, we have seen similar issues. After T1, the assembly failed due to latch misalignment and a measured dimensional deviation of 0.3 mm (assembly was impossible because the product required ≤0.2 mm clearance). The T2 sample exhibited irregular sink marks, and during T3, the gate fractured directly. All these symptoms point toward insufficient cavity machining accuracy.
The cavity acts as the “template” for product formation—its accuracy directly affects dimensional stability, surface flatness, and molding stress. Poor cavity precision results in uneven melt flow and inadequate packing pressure, leading to out-of-tolerance dimensions and sink marks. Gate breakage is often associated with poor runner machining accuracy, which creates localized stress concentrations.
Supplier Risks: Technical Insufficiency and Responsibility Evasion
The technical competence and accountability of the supplier are the hidden thresholds in injection mold projects. In one cooperation case, after repeated trial failures, the supplier insisted that “the mold is fine; the molding machine parameters weren’t set correctly,” and refused to open the mold for cavity inspection. Only after we dispatched engineers for on-site measurement did we discover a 0.15 mm machining deviation at a key cavity location. This combination of “technical inadequacy + refusal to take responsibility” easily traps projects in endless trial loops.
When selecting suppliers, two evaluation dimensions are essential: first, technical capability—whether the shop is equipped with CMM inspection, and whether their process documents include cavity precision control standards; second, accountability—which can be assessed via peer feedback regarding problem-response speed (such as whether corrective action plans are provided within 24 hours).
Contract Clauses That Prevent Cost Overruns: Responsibility, Trial Limits, and Delivery Protection
Vague contract terms are one of the main drivers behind uncontrolled trial costs. In one real case, the buyer only specified “supplier guarantees conforming quality” and did not define the maximum number of free mold trials. As a result, the supplier attempted eight trials, yet the mold still failed to meet requirements, exceeding the expected budget by 60%.
To avoid such situations, three critical clauses must be clearly defined:
- Responsibility Allocation: for example, “If mold machining accuracy issues cause trial failure, all rework costs shall be borne by the supplier.”
- Trial Limit: such as “A maximum of 3 free mold trials; additional trials will be charged at 5% of mold cost per trial.”
- Delivery Guarantee: add penalty clauses such as “0.5% deduction per delayed day, up to a maximum of 10%.” This compels the supplier to improve the efficiency of corrective actions.
Conclusion
The lessons from repeated mold trial failures show that supplier selection and contract detail reinforcement are the two most effective measures for risk mitigation. Companies must screen suppliers using hard indicators such as cavity machining accuracy and process-control documentation, while using contractual clauses—responsibility assignment, trial limits, and delivery penalties—to lock down risks and avoid the vicious cycle of “trial → failure → blame → retrial.”
Practical Recommendations
- Request cavity machining accuracy inspection reports from the supplier’s most recent three projects.
- Define responsibility for rework and set a clear limit for free mold trials in the contract.
- Include tiered penalty clauses for delivery delays, such as “0.5% deduction per delayed day, up to 10%.”
