Last updated: 2026-09-02 · 5 min read

What Happens at a Mold Trial (T1) — and How Should You Prepare for It?

The T1 trial is the first time the completed mold runs in the injection machine — and its purpose is not to produce perfect parts on the first shot, but to establish the process window, identify corrections needed and generate the data that determines whether the mold is ready for production or needs another correction loop. A well-prepared T1 produces dimensional data, process parameters and visual samples within one day; a poorly prepared T1 wastes material, machine time and weeks of schedule.

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. See also related guide.

Key Facts

  • T1 is not a production run — it is a data-gathering event: process parameters, dimensional results, visual quality and process stability (shot-to-shot consistency) are the deliverables, not a quantity of parts.
  • The trial requires the correct resin grade (production-intent material, not a substitute), dried to the supplier’s specification, and the machine sized to the mold’s clamp and shot weight requirements.
  • The trial report includes: process parameter sheet, shot weight log (20+ consecutive shots), dimensional report on critical dimensions, trial video and photos of any defects found.

    • 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.

    The T1 Trial Sequence

    Step Activity Deliverable
    1. Mold installation Mount mold, connect cooling, set clamp force Mold installation checklist signed
    2. Material preparation Dry resin to spec, load hopper Moisture reading logged
    3. Short shots Fill study at increasing pressures to find 95% fill Fill pattern documented; gate balance confirmed
    4. Process setup Set pack pressure, hold time, cooling time Process parameter sheet recorded
    5. Stability run 20+ consecutive shots, weigh each Shot weight log; Cpk calculation if required

    What the Trial Report Must Include

  • Process parameter sheet: melt temperature, mold temperature, injection speed, pack pressure, hold time, cooling time, clamp force — every parameter the machine recorded during the stable run.
  • Shot weight log: 20+ consecutive shots weighed individually; the standard deviation shows process stability — if the variation exceeds ±1%, the process is not stable.
  • Dimensional report: critical dimensions measured on the first 5 shots and the last 5 shots — the comparison shows whether dimensions drift as the mold heats up.
  • Trial video: the mold running with visible mold number, date and shot counter — this is the evidence that the trial actually happened, not a report generated from a different tool.
  • Defect log: photos of any short shots, flash, burn marks, sink or warp found during the trial — with the process condition that produced each defect.

    • What This Means for Your Quotation

    The mold quotation should specify what the T1 trial delivers: process parameters, shot weight log, dimensional report, trial video and defect photos — all included in the tooling cost, not as add-on charges. When the trial deliverables are part of the contract, the buyer receives the data needed to approve or reject the tool; when they are not specified, the mold maker may deliver samples without the supporting data, and the buyer cannot make an informed acceptance decision.

    Frequently Asked Questions

    How many T1 trials are normal before acceptance?

    One to two T1 trials are normal for a well-designed mold with a thorough DFM review. Three or more trials indicate a design or manufacturing issue that should trigger a design review rather than another trial. The quotation should specify how many trials are included and what happens if corrections are needed beyond the included count.

    Should the buyer attend the T1 trial?

    If travel is feasible, attending provides information no report captures — seeing the mold run, watching the ejection, and holding the first shots. If remote, the trial video and dimensional report are the minimum evidence. The buyer should review the report within 3–5 business days and respond with acceptance or a correction list.

    What if the T1 samples are out of tolerance?

    The mold stays at the maker’s facility for correction. The correction scope is determined by comparing the T1 dimensions to the drawing — the maker identifies which mold features need adjustment and the timeline for re-trial. The quotation should specify who pays for re-trial material and how many correction loops are included.

    Key Takeaways

    1. T1 is a data-gathering event, not a production run — the deliverables are process parameters, shot weight log, dimensional report, trial video and defect photos.
    2. Shot weight consistency (±1% variation) and dimensional comparison between first and last shots are the stability indicators that determine whether the process is ready for production.
    3. The quotation should specify the T1 deliverables and the number of included trials — so the buyer receives the data needed for acceptance, not just samples without context.

    Send aCatMould the part drawing, and the quotation specifies the T1 trial deliverables — process parameters, dimensional report, shot weight log, trial video and defect photos — included in the tooling cost, so the trial is a documented acceptance event, not a box of samples without data.

    Sources
    MoldMaking Technology — mold trial best practices
    Plastics Technology — mold trial procedures and documentation
    SPE — mold trial and process validation guidance

    Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet