Last updated: 2026-09-05 · 5 min read

T2 Mold Trial Acceptance — What Must Be Verified Before the Mold Is Approved for Production?

T2 is the correction-verification trial: every issue flagged at T1 must show a documented fix with before-and-after data. The full CMM report covers all critical dimensions — not just the corrected ones — because mold modifications shift adjacent features. Cycle time must be within 5% of the quoted value, surface finish must match the SPI grade, and 50–200 samples from multiple cavities must demonstrate process stability across 5+ consecutive shots per cavity.

Key Facts

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  • T1 identifies issues; T2 proves they are fixed. The T2 report must include a side-by-side comparison: T1 measurement vs. T2 measurement for every dimension that was out of tolerance. If the T2 report only shows “pass/fail” without the actual numbers, you cannot verify that the correction was effective.
  • Dimensional drift is the hidden risk: correcting one feature can shift its neighbor. A modification that reduces flash at one parting line may change the cooling pattern and shift an adjacent bore by 0.03mm. The T2 CMM report must cover all critical dimensions — not just the ones that were corrected — to catch drift.
  • Process window verification: T2 samples must be molded at the nominal parameter set and at ±10% injection speed / ±5°C mold temperature. If good parts only form at one narrow setting, production will drift out of spec when ambient conditions change or the mold wears after 50K shots.

    • Ejector pin — A steel pin that pushes the molded part out of the cavity after cooling. Typical diameter: 2–10mm. Pin marks are visible on the part surface — position at non-cosmetic areas. Pin count and placement affect ejection force and part warpage. The related guide covers adjacent topics.

    What Does the T2 CMM Report Need to Show?

    Report Element What to Check
    Dimension list All critical dimensions from the drawing — not just the T1 out-of-tolerance items. A complete list catches dimensional drift from mold modifications.
    T1 vs. T2 comparison Each corrected dimension must show the T1 measured value and the T2 measured value side by side. “Pass/fail” alone is insufficient — you need the actual numbers to confirm the correction moved the dimension toward nominal.
    GD&T callouts True position, flatness, profile and perpendicularity must be reported in the same datum reference frame as the drawing. CMM software must use the drawing’s datum scheme, not the mold maker’s preferred alignment.
    Cavity-by-cavity data Each cavity’s dimensions reported separately — not averaged across cavities. Averaging hides cavity-to-cavity imbalance that causes assembly problems downstream.
    Measurement uncertainty CMM accuracy specification stated (typically ±0.003mm). If the tolerance is ±0.05mm and the CMM uncertainty is ±0.01mm, the measurement system is adequate (10:1 ratio).

    If the T2 CMM report does not include all five elements above, request a revised report before approving the mold. A report that only shows corrected dimensions and averaged cavity data is not a T2 acceptance document — it is a summary that hides the information you need to make the approval decision.

    What Three Failures Most Commonly Cause T2 Rejection?

    1. Partial corrections. The mold maker fixed the obvious T1 issues but missed secondary issues — flash on one parting line resolved, but sink mark on a thick section ignored. Cross-reference every T1 issue against the T2 report.
      If the correction list had 8 items and only 6 are verified, the T2 is incomplete and should not be approved.
    2. Dimensional drift from modifications. Correcting one dimension shifts adjacent features — adding material to reduce a short shot changes the cooling pattern and moves a nearby bore. The T2 CMM report must cover all critical dimensions, not just the corrected ones.
      Compare the full T2 report against the drawing tolerance, not against the T1 report.
    3. Narrow process window. T2 samples molded at one parameter set only — no verification that the process works at ±10% injection speed or ±5°C mold temperature. If the process only works at one narrow setting, production will drift out of spec when ambient conditions shift.
      Require a process window study as part of the T2 deliverable.

    Process parameter — A controllable variable in the injection molding process: melt temperature, injection speed, holding pressure, cooling time, mold temperature. Each parameter affects part quality — deviations cause defects. Parameters are set during T1 and locked for production.
    The related guide covers adjacent topics.

    T2 CMM report must include: all critical dimensions (not just corrected ones), T1 vs. T2 side-by-side comparison, GD&T in drawing datum frame, cavity-by-cavity data (not averaged), and measurement uncertainty stated. 50–200 samples, 5+ shots per cavity. Process window at ±10% speed / ±5°C temperature. If the report hides any of these, it is not an acceptance document.

  • Key parameter identified — critical variable confirmed against spec.
  • Tolerance within achievable range — commercial ±0.15mm or tighter as needed.
  • Material matched to application — resin grade selected for end-use environment.
  • Process window validated at T1 — parameters locked after first trial.
  • Inspection method defined — CMM, visual, or functional test specified.

    • Frequently Asked Questions

    What happens if T2 still shows out-of-tolerance dimensions?

    The mold maker must make corrections and submit T3 samples. The purchase order should specify who pays — typically, the mold maker pays for corrections from machining errors; the buyer pays for changes from drawing revisions after T1.

    If the same issue persists at T3, the root cause was not correctly identified. The mold maker should re-evaluate the correction strategy rather than repeat the same fix. A third attempt at the same correction is a sign of fundamental process or design incompetence.

    How many trials are typical before approval?

    For a well-designed mold, T2 is the approval trial — T1 identifies issues, T2 verifies corrections. For complex molds (multi-cavity, hot runner, tight tolerance), T3 or T4 may be needed.

    If the mold requires more than T4, the mold maker’s capability should be questioned. A competent mold maker should not need more than 3–4 trials for a standard production mold. More than four trials indicates the design or machining process has fundamental issues.

    Should the buyer attend the T2 trial in person?

    For critical programs, yes — attending allows you to see the mold running, verify process parameters and inspect samples immediately. For less critical programs, the T2 samples and dimensional report can be shipped for review.

    If attending is not possible, request a live video walkthrough of the trial with real-time process parameter display visible. The cost of travel ($2,000–5,000) is often less than the cost of a miscommunication that delays the program by weeks.

    Key Takeaways

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  • T2 proves T1 corrections worked. Report must show T1 vs. T2 numbers, not just pass/fail.
  • Full CMM report: all critical dims, GD&T in drawing datum, cavity-by-cavity, measurement uncertainty.
  • Three failures: partial corrections, dimensional drift, narrow process window.
  • 50–200 samples, 5+ shots/cavity, process window at ±10% speed / ±5°C temperature.

    • Send the part drawing and T1 correction list — the T2 trial follows a documented acceptance checklist so the mold approval is based on verified measurement data, not subjective judgment.

    Sources: MoldMaking Technology — Mold Trial Acceptance Criteria and T2 Verification · Plastics Technology — CMM Reporting Standards for Mold Trials · Society of Plastics Engineers (SPE) — Mold Trial Guidelines and Sample Approval Procedures · Hexagon — CMM Measurement Uncertainty and GD&T Reporting · Kistler — Process Window Verification During Mold Trials

    — Arthur, Tooling Engineer at aCatMould