Does the mold work mechanically?
Look at: mold function, water lines, cavity fill. Not part dimensions.
What problems does the design still have?
Look at: samples, trial report, dimensional report.
Did the fixes work? Is the process stable?
Look at: closed-out issue list, stability over consecutive shots, process window.
After T2 passes, projects typically move to a final cosmetic adjustment (T3), final acceptance, and production.
If you have ordered an injection mold, you have probably seen an email that says “T1 samples will ship Friday” or “we need another round of T2.” Many buyers nod along without being sure what each label means or what they should be checking.
That is a costly gap. Trial stages are where mold problems are found and fixed, and each stage answers a different question. Knowing the difference helps you review samples properly, ask for the right documents, and avoid surprises later.
Check the numbering before you compare quotes
Not every factory counts the same way, and this causes real confusion.
- Many overseas mold shops call the first time the mold runs on the press “T1.”
- Many shops in Asia call that first internal run “T0,” and reserve “T1” for the first official trial shared with the customer.
So “T1” from one supplier can be a full trial round ahead of “T1” from another. When you compare schedules or agree on milestones, ask: what exactly is included in your T1, and what comes before it?
At RpProto
T1 is the first trial shot, with samples sent to you for approval. The mechanical checks some shops label “T0” are done in-house before that, as part of mold testing prior to delivery.
T0: the mold’s health check
T0 checks the mold, not the part. It is the first time the tool goes onto an injection press, and it is normally an internal step. The questions are basic but essential:
- Does the mold move correctly? Opening and closing, ejection, slides, and lifters should run smoothly and in the right order.
- Are the cooling channels sound? No leaks, no blockages.
- Does the plastic fill the cavity? Look for short shots or missing areas.
Do not measure T0 parts against your drawing. Dimensions and wall thickness are often left intentionally on the heavy side at this stage, so the mold can be fine-tuned later. A rough-looking T0 sample is normal. Its job is to expose problems as early as possible, when they are cheapest to fix.
T1: where most problems show up
T1 is usually the first time you hold real parts from your tool. It is the key milestone of mold development, and where most issues surface: sink marks, flash, weld lines, warpage, and dimensional deviations.
The goal of T1 is not to pass. It is to find every problem in one round. A T1 that reveals a long, honest issue list is more useful than one that looks fine because nobody measured carefully.
Ask for the “three-piece set”
Trial report
Material, key process settings, observations, and known issues.
Samples
Physical parts for fit, function, and cosmetic review.
Dimensional report
Critical features measured against your drawing.
Samples without a report are close to wasted. You cannot tell which settings were used, what the supplier noticed, or whether a measurement is a one-off or a trend. Without that, the next round of modifications is guesswork.
At RpProto, T1 samples are inspected against the approved drawing, checked visually for sink marks, flash, and weld lines, photographed, and sent to you for sign-off.
Why mold modifications are cautious
After T1, the mold often needs adjustment. One principle governs most of the work: mold steel can be removed easily, but adding it back is difficult.
Milling away another 0.1 mm takes minutes. Putting steel back means welding, annealing, and re-machining, which takes much longer and can compromise the surface. This is why experienced mold makers modify in small, controlled steps, and why good mold design leaves extra steel on critical features that are likely to need tuning.
T2: proving the fixes, and proving stability
T2 verifies that the changes made after T1 actually worked, and that the process is ready for production. Useful benchmarks for sign-off:
- Every T1 issue is closed out, not just mentioned.
- Dimensions stay stable over a continuous run, typically 50 to 100 consecutive shots.
- The process window is wide enough to tolerate normal variation. As a common target, parts should still pass with mold temperature varying by about ±10 °C and holding pressure by about ±10%.
Why “great samples, failed production” happens
If the process was tuned until it just barely worked, perfect samples can be produced on trial day. Then a new resin batch arrives, or cooling water temperature drifts, and defects appear across the whole lot. A good T2 proves the mold can make good parts consistently, under normal factory variation.
How many rounds are normal?
As a rule of thumb, around two to three modification rounds is common across the industry. If a project is still changing the structure of the mold after four or more rounds, the problem is usually no longer fine-tuning. It is a design problem, and it is worth stopping to re-examine the part and the mold concept.
The best way to reduce rounds is to catch issues before steel is cut. That is why we put effort upstream:
- Free DFM review on every project: wall thickness, draft, undercuts, gate location, parting line, ejector placement. See our DFM guide for injection molding.
- Mold flow analysis for complex or tight-tolerance parts, to predict weld lines, air traps, warpage, and cooling balance before the tool exists.
- Customer design approval of the full 3D mold design before steel procurement starts.
A modification found on screen costs a few hours. The same one found at T2 costs days, and at production it costs much more.
A checklist for your next mold project
- Ask what each trial label means at your supplier, and what is included before T1.
- Don’t judge T0 parts on dimensions.
- Require the three-piece set at every T1: report, samples, and dimensional report.
- Review T1 for completeness of the issue list, not just pass or fail.
- At T2, ask for stability data across a continuous run, not only a few good parts.
- If modification rounds pass four and the changes are structural, review the design.
- Confirm in advance who owns the tooling and where it will be stored.
How RpProto runs the trial stage
As an in-house mold maker in Xiamen, China, we handle design, machining, EDM, assembly, polishing, and trial under one roof, so trial findings go straight back to the engineers and toolmakers who built the mold.
- Mold trial and T1 shot
Run on our own presses. - Inspection
Samples checked against your drawing, with photos and a dimensional report. - T1 samples shipped
Sent to you for approval. - Modifications (T2, T3) if required
With your approval before production begins. - Production
With SPC or AQL sampling.
Planning a mold project?
Whether you need bridge tooling for a market launch or a hardened-steel production mold, we can help you choose the route and plan the trial stages from the start.
- Quotes in 24 hours
- Expert engineering support
- Free DFM analysis
Not ready for tooling yet? We can also support early-stage parts with CNC machining or urethane vacuum casting.
