Last updated: 2026-09-05 · 5 min read

T1 is the first time real plastic meets the new mold — the trial that converts a steel promise into physical samples. What it proves: the mold fills, parts come out, and the process behaves largely as designed. What it does not prove: that the mold is finished, because T1 exists precisely to find what the DFM and simulation could not see. The trial is a diagnostic event, not a verdict — and the buyers who treat it that way, arriving with drawings and acceptance criteria rather than hope, turn T1 from a suspense moment into the quality gate it is meant to be.

Key facts

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  • T1 = first trial shots of a new or newly modified mold; the numbering (T0/T1/T2) conventionally counts the trial rounds.
  • A disciplined trial runs short shots first, then fill, then pack — each phase answers a different question about the mold.
  • T1 samples are judged against the drawing and the DFM agreements, not against memory or mood.
  • The trial’s output is a written report: settings, findings, and the correction list with owners and dates.
  • Defects found at T1 are the system working — corrections before shipment are measured in days, the same defects found after are measured in programs.

    • Parting line — The line where the two mold halves (A-side and B-side) meet. Parting line location affects: gate placement, ejector pin marks, witness lines, and cosmetic appearance. A well-designed parting line minimizes visible witness marks. The related guide covers adjacent topics.

    What T1 actually is

    The naming convention is loose across the industry but the meaning is stable: T0 (where used) is the first short-shot or smoke trial proving the mold mechanically cycles; T1 is the first trial producing complete parts; T2 and onward repeat after corrections. Whichever convention a factory uses, the first full-samples event is the milestone buyers plan around — the moment the program stops being documents and becomes parts.

    T1 trial — the first full-sample molding trial of a new mold, run under documented process settings, producing samples for dimensional and cosmetic judgment against the drawing. Its purpose is discovery: confirming what the design got right and exposing what remains to correct, before the tool ships or production begins.

    The trial, step by step

    1. Mount and set up. The mold is fitted to the press, cooling and connections verified, ejection and slides exercised. Mechanical problems — a binding lifter, a leaking circuit — are found here, before plastic adds variables on top.
    2. Prepare the material. The agreed resin, dried and conditioned to spec. A trial run on wet resin produces a mold’s defects without the mold’s involvement, which is why material state is documented in the report.
    3. Short shots. Injection fills a fraction of the cavity: the flow front is observed, filling balance across cavities checked, weld and vent behavior read. This phase diagnoses the filling story the mold was designed around.
    4. Fill to full. Injection advances to complete filling at controlled speed, revealing pressure behavior, gate performance and any hesitation or burn signatures in the actual geometry.
    5. Pack and hold. Packing pressure and time are set to compensate shrinkage — where sink risk, gate freeze and dimension stability prove themselves. The sink prediction made in the DFM faces its first physical verdict here.
    6. Stabilize and sample. Once the process reaches a repeatable window, consecutive shots are pulled as samples: dimensions measured, cosmetics examined, candidates photographed for the record.
    7. Report and list. The trial ends with a written summary — settings used, findings, samples shipped — and a correction list with owners and a date for the next trial if one is needed.

    What T1 can and cannot prove

  • Can prove: the mold fills and cycles; the flow, gate and ejection concepts work as designed; the process window is reachable on the intended press class; and the dimensional trend against the drawing.
  • Can prove: cosmetic feasibility — how seams, gate vestige and finish actually read in plastic, against the agreed zones and limits.
  • Cannot prove: long-term stability. T1 runs minutes to hours; production runs months. Wear, cooling drift and material lot variation belong to later verification, not to the first trial.
  • Cannot prove: that every dimension will hold forever. T1 dimensions are the first data point of a distribution, not the last word — the tolerance conversation spans the whole capability question.
  • Cannot prove: the parts are approved. Approval is a separate act — the buyer reviews samples against criteria and signs. Trials produce evidence; acceptance is a decision.

    • The buyer’s job at T1

    A trial rewards preparation more than attendance. The buyer’s contribution, in order of leverage: arrive with the drawing and the DFM agreed limits — the reference documents every judgment runs against; review the physical samples against those criteria rather than against memory of the 3D render; separate the findings into acceptance-blocking corrections and cosmetic preferences, because the two travel differently through engineering; and require the report — settings, findings, corrections — in writing, because the trial that produces no document cannot be referenced when the memory disputes begin. Buyers who run this discipline report the same effect: the trial becomes a checklist being worked, not a drama being watched, and the correction list that leaves the room is shorter for it.

    After T1: corrections, re-trials and approval

    Almost no T1 ends with nothing to correct, and that is by design — the trial’s job is to surface what remains. The corrections typically divide into three classes: dimensional corrections requiring steel or process changes, cosmetic corrections to surfaces and seams, and process-only adjustments that need no steel at all. Each goes onto the list with an owner and a date, and the mold returns for the next trial — T2, T3 — repeating until the samples meet the agreed criteria. Only then does the acceptance conversation close: samples approved against the criteria, the dimensional report produced, and the mold either shipped or released to production. The number of trials is not a quality verdict by itself; a first trial that finds nothing usually means the trial was not deep enough, while two disciplined trials finding and closing a short list is the system working exactly as built. What separates programs is not whether corrections exist but whether they are written, owned and dated — the same evidence discipline the RFQ stage set up and the DFM review carried forward.

    What to measure before the press cools

    Samples are worth the most in the hours they are made. Measurements that wait a week compete with memory; measurements taken at the press compete only with the drawing. The set worth demanding covers:

  • Dimensions on the controlled features. The drawing’s tight-tolerance callouts measured on fresh samples — not every dimension, the ones the drawing and DFM flagged, read on calibrated equipment and listed against nominal.
  • Part weight, consecutive shots. Three to five parts weighed in sequence: stable weight says the process is repeating; a drifting trend says packing or check-ring behavior needs attention before any dimensional verdict is trusted.
  • Cycle time as actually run. The clock that produced the samples, recorded per segment — fill, pack, cooling, ejection. This is the baseline every later improvement argues against, and it belongs in the report, not in recollection.
  • Cosmetic zones against agreed limits. Gate vestige, seam witness and ejector marks read inside the zones the DFM defined, under the same light distance and angle both parties will use later.
  • The sample set itself. Labeled, dated and tied to the shot number — the physical evidence every later conversation references when opinions drift.

    • None of this requires the buyer’s presence; it requires the requirement. Written into the trial plan in advance, the measurement list costs minutes; demanded after shipment, it costs arguments. The molds that ship with clean trial records tend to be the ones whose buyers asked for the record before the press was ever scheduled — the same evidence-first instinct that separates a document-driven program from an optimistic one.

    Common T1 findings and what they really mean

  • Flash at seams. The parting surfaces meeting under real clamp for the first time; usually a fit-and-process pass, occasionally an early warning about edge wear — the mechanics are in the parting line guide.
  • Short shots or hesitation. The filling concept meeting real resin; resolved by process, gate or vent corrections that the trial data now points to precisely.
  • Sink over bosses and ribs. Packing answering the geometry — expected where predicted, actionable where new, and priced by the correction class it falls into.
  • Drag marks and ejection witness. Release and ejection behavior under real shrinkage grip; typically a draft or ejection-timing refinement with a named owner.
  • Weld and vent signatures. Air and fronts meeting where the flow map predicted or did not; vent additions are the routine response and a planned part of trial corrections.

    • The trials I worry about are not the ones with findings — they are the ones with no findings and no report. A first trial that finds nothing has usually tested nothing; a trial without a written record cannot protect anyone when the discussion moves three weeks downstream. The trials that make programs succeed are boring in the best way: settings documented, samples measured against the drawing, corrections listed with names and dates. Nothing about that is luck — it is just the design conversation continuing, now with plastic in the loop.

    — Arthur, Tooling Engineer at aCatMould

    Frequently asked questions

    How many trials does a new mold usually need?

    Commonly one to three for a well-reviewed design: T1 to find what remains, a correction round, and a confirmation trial. More trials are not automatically a red flag — a documented list that shrinks each round is health, whether it takes one pass or three.

    Should I attend the T1 trial in person?

    Attendance helps judgment-heavy decisions — cosmetic sign-offs, trade-off calls — but the leverage is in preparation: drawings, agreed limits and criteria. Remote buyers do well by demanding the full report, measured samples and photographs rather than relying on presence.

    Who pays for corrections found at T1?

    It follows the fault the correction belongs to: geometry agreed in the DFM and built wrong is the factory’s; design changes the buyer requests after seeing parts are the buyer’s; ambiguity that neither document resolved is the reason documents exist. This is precisely what a written DFM exists to keep unambiguous.

    What should a T1 report contain?

    Machine and material identification, the process settings used, filling observations, sample photographs, dimensional results against the drawing, findings, and the correction list with owners and dates. A trial without this document has not finished yet.

    Can T1 samples be used for real assembly trials?

    Yes, with clear labeling: they are genuine parts from the genuine tool, useful for fit checks and early feedback. They are not production parts — the process is young — so treat them as engineering samples, not as the approval basis by themselves.

    Is a video of the trial worth requesting?

    Yes — a short, timestamped video of the mold cycling and parts ejecting is inexpensive evidence of mechanical behavior that photos cannot carry. It documents the moment the tool first ran, which later disputes tend to revisit.

    Key takeaways

    1. T1 is the first full-sample trial of the mold — a diagnostic event that converts design promises into physical evidence.
    2. The disciplined sequence runs setup, material, short shots, fill, pack, stabilize, then samples and a written report.
    3. T1 proves filling, cosmetics and dimension trends; it cannot prove long-term stability or substitute for the approval decision.
    4. The buyer’s leverage is preparation: drawing, agreed limits, criteria-based review, and a report required in writing.
    5. Corrections found at T1 are the system working — written, owned and dated lists are what separate programs, not trial counts.

    If you have a mold approaching its first trial, send us the drawing set and the agreed limits. You will get a trial plan with the sequence, the acceptance criteria and the report structure spelled out in advance — from a named engineer, so the first plastic finds every question already written down.

    Sources
    Autodesk Moldflow — injection molding simulation ahead of mold trials
    ISO 20457:2018 — Plastics moulded parts: Tolerances and acceptance conditions
    Plastics Industry Association — SPI mold standards and surface finish sets

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