After weeks of mold design, steel cutting, CNC machining, EDM, polishing, and assembly, your injection mold is finally ready. But before it enters mass production, it must go through a structured sampling and trial process to verify that the tool produces dimensionally accurate, visually defect-free parts at the required cycle time. This process — typically divided into T0, T1, and T2 trials — is the most critical quality gate in the entire mold-making project.
Far too many product developers underestimate the importance of mold sampling. They treat T0 as a formality and expect perfect parts immediately. In reality, the first trial almost always reveals issues that require mold adjustments: dimensional deviations, sink marks, flash, warpage, short shots, or surface defects. The T0–T2 process is designed to catch and fix these issues systematically before the mold is approved for production.
This guide explains what happens at each stage of the injection mold sampling process, what deliverables you should expect, how to evaluate sample parts, common problems and their fixes, and best practices for working with your mold maker to achieve a smooth mold qualification.
1. Overview of the Mold Trial Process
The injection mold sampling process consists of progressive trial stages, each with specific goals:
| Stage | Name | Goal | Typical Output |
|---|---|---|---|
| T0 | First Shot / Pre-Trial | Verify mold functions, fills completely | As-molded samples, initial visual assessment |
| T1 | Engineering Trial | Dimensional verification, process optimization | Dimensional report (FAI/ISIR), optimized process parameters |
| T2 | Final Approval / Golden Sample | Confirm corrections, lock process, approve production | Approved golden samples, signed-off process parameters, PPAP-ready documentation |
In some organizations, additional trials (T3, T4) may be needed if the part is complex or if significant design changes occur. For most consumer products, industrial components, and automotive parts, three trial rounds are standard.
Why Not Skip Trials?
Skipping or combining trials to save time is a common mistake. Each trial serves a distinct purpose:
- T0 catches major mold functionality issues (flow problems, ejection failures, cooling leaks) before investing time in dimensional checks.
- T1 provides the data needed to make informed steel adjustments — without it, you are guessing at corrections.
- T2 verifies that corrections worked and establishes the locked process window for production.
Rushing through this process often results in production delays later, when fixing a mold that is already in mass production is far more expensive and disruptive.
2. T0: First Shot Trial (Pre-Trial)
What Is T0?
T0 is the very first time molten plastic is injected into the completed mold. The primary goal is not to produce perfect parts — it is to verify that the mold functions correctly: the plastic fills the cavity, the part ejects cleanly, the cooling system works, and there are no mechanical issues with the tool.
Objectives of T0
- Verify mold filling: Does the plastic completely fill all cavities? Are there short shots, flow lines, or gas traps?
- Check ejection: Do ejector pins push the part out without sticking, cracking, or deforming?
- Validate cooling: Is the cooling system functioning? Are water lines flowing correctly without leaks?
- Identify obvious defects: Flash, sink marks, burn marks, warpage, or surface blemishes visible to the naked eye.
- Establish preliminary process parameters: Injection pressure, melt temperature, mold temperature, cycle time baseline.
What Happens During T0?
The mold maker mounts the mold on an appropriately sized injection molding machine — ideally one that matches the production machine specifications (clamp force, shot size, screw diameter). The process engineer sets initial parameters based on the material data sheet and mold flow analysis (if available), then runs a series of short shots to progressively verify fill:
- Mold installation: Mount mold, connect cooling lines, set core/cavity temperature controllers.
- Material drying: If the material is hygroscopic (nylon, PC, PET, etc.), dry it per the manufacturer's recommendation before trial.
- Purge and stabilize: Purge the barrel, bring melt and mold temperatures to target, stabilize for 5–10 shots.
- Progressive fill study: Start with a partial fill (20–30% of cavity), gradually increase shot size until full. This technique reveals flow patterns and air entrapment locations.
- Full shot evaluation: Once the cavity fills completely, evaluate the part visually and by touch for obvious defects.
- Ejection test: Verify the part ejects cleanly in the intended cycle. Adjust ejection speed, stroke, and count as needed.
T0 Deliverables
After T0, the mold maker should provide:
- 10–30 sample parts (as-molded, no post-processing)
- Trial report documenting: machine used, material grade, melt temperature, mold temperature, injection pressure, cycle time, and observations
- Photographs of parts showing any defects
- Preliminary assessment of what needs correction (steel changes, gate adjustments, cooling modifications, venting additions)
Common T0 Problems and Solutions
| Problem | Likely Cause | Solution |
|---|---|---|
| Short shot (incomplete fill) | Inadequate venting, low injection pressure, wrong gate location | Add/update vents, increase pressure, consider adding flow leader |
| Flash at parting line | Insufficient clamp force, mold deflection, low viscosity | Increase clamp force, check mold flatness, reduce injection pressure |
| Burn marks (diesel effect) | Trapped air igniting at end of fill | Add or enlarge vents at burn locations |
| Sink marks | Thick sections cooling slower than thin sections | Reduce wall thickness, add cooling near thick areas, increase packing pressure |
| Part sticks in mold | Insufficient draft, polish direction wrong, undercut | Add draft, repolish in draw direction, check for unwanted undercuts |
| Warpage | Uneven wall thickness, differential cooling | Balance cooling channels, adjust packing profile, consider material change |
3. T1: Engineering Trial (Dimensional Verification)
What Is T1?
After T0 corrections are completed (steel changes, venting additions, gate modifications), the mold goes through T1 — the engineering trial. T1 is where the parts are measured against the 3D CAD model and drawing tolerances. This is the dimensional verification stage.
Objectives of T1
- Full dimensional inspection: Measure every critical dimension on the part drawing and compare to tolerance.
- Process window exploration: Vary processing parameters systematically to understand how they affect dimensions and defects.
- Validate T0 corrections: Confirm that steel changes resolved the issues identified during T0.
- Optimize surface finish: Check for polish quality, texture depth, gate vestige, and ejector pin marks.
- Generate First Article Inspection (FAI) report: Document all measured dimensions with pass/fail status.
First Article Inspection (FAI / ISIR)
The FAI report — also called ISIR (Initial Sample Inspection Report) in European automotive standards — is the core deliverable of T1. It is a comprehensive measurement document that includes:
- Every dimensional feature on the part drawing: linear dimensions, diameters, angles, radii, flatness, parallelism, position
- Nominal value (from CAD), tolerance range (from drawing), measured value (from CMM or hand gauges), and deviation
- Pass / Fail / Conditional status for each dimension
- GD&T callouts if applicable (true position, profile of a surface, cylindricity)
- Measurement method used (CMM, optical scanner, caliper, gauge)
For multi-cavity molds, the FAI should include measurements from every cavity to verify cavity-to-cavity consistency. Typically, 3–5 parts per cavity are measured to assess variation.
Measurement Methods Used in T1
| Method | Accuracy | Typical Use |
|---|---|---|
| CMM (Coordinate Measuring Machine) | ±0.005 mm | Tight-tolerance dimensions, GD&T features, datum references |
| Optical 3D Scanner (GOM/ATOS) | ±0.02 mm | Full-field comparison to CAD, overall part geometry, warpage analysis |
| Calipers / Micrometers | ±0.01–0.05 mm | Quick checks, non-critical dimensions |
| Height Gauge / Surface Plate | ±0.02 mm | Flatness, parallelism, overall length |
| Bore Gauge / Pin Gauge | ±0.005 mm | Internal diameters, hole sizes |
| Thread Gauges (Go/No-Go) | Class 6H/6g | Internal and external threads |
Process Optimization During T1
Beyond dimensional checks, T1 is when the process engineer dials in the optimal processing window. Key parameters explored include:
- Melt temperature: Typically varied ±10°C from the material data sheet baseline to assess flow and surface finish impact.
- Mold temperature: Varied ±5°C per zone to find the setting that minimizes warpage and sink while maintaining cycle efficiency.
- Injection speed: A speed sweep identifies the point where surface quality is best without causing shear burn or flash.
- Packing pressure and time: Critical for dimensional stability and sink mark elimination. Gate freeze time is determined by weighing parts at different packing times until weight stabilizes.
- Cooling time: Reduced progressively until parts remain stable upon ejection (no distortion, acceptable temperature for handling).
- Cycle time baseline: Establish the production cycle time target for cost calculation.
T1 Deliverables
- 30–50 sample parts from optimized process parameters
- Complete FAI/ISIR report with all dimensions, tolerances, and measurement data
- 3D scan color map (if applicable) showing deviation from CAD
- Process parameter sheet documenting the recommended production settings
- List of required corrections for T2 — any dimensions still out of tolerance, defects that need steel fixes
4. Steel Corrections Between Trials
Between T0 and T1, and between T1 and T2, the mold maker performs steel corrections based on the trial findings. These corrections fall into several categories:
Dimensional Corrections
When a measured dimension is consistently out of tolerance, the mold steel must be adjusted. The correction approach depends on the direction of error:
- Part too large (cavity side): Remove steel from the cavity — CNC, EDM, or hand grinding.
- Part too small (cavity side): Add steel to the cavity — this requires welding (TIG or laser) and re-machining, or inserting a replaceable steel insert.
- Part too large (core side): Remove steel from the core.
- Part too small (core side): Add steel to the core via welding or insert replacement.
Surface and Cosmetic Corrections
- Gate vestige reduction: Modify gate geometry (size, angle, land length) to achieve cleaner break.
- Ejector pin marks: Adjust pin height flush with part surface, or move pins to non-cosmetic areas.
- Polish improvement: Refine surface finish to meet SPI specifications.
- Texture adjustment: Adjust EDM texture depth or re-etch to match texture sample.
- Weld line relocation: Adjust flow pattern (gate position, flow leaders) to move weld lines to non-visible areas.
Functional Corrections
- Cooling improvement: Add cooling lines or baffles in hot spots identified by thermal imaging.
- Venting enhancement: Add vent pins, vent grooves, or porous steel inserts at burn mark locations.
- Ejection balance: Add or reposition ejector pins to prevent distortion during ejection.
5. T2: Final Approval Trial (Golden Sample)
What Is T2?
T2 is the final mold trial. By this stage, all steel corrections from T1 have been completed, and the goal is to confirm that the mold now produces parts that meet all dimensional, cosmetic, and functional requirements. T2 establishes the "golden sample" — the reference standard for all future production runs.
Objectives of T2
- Verify all T1 corrections: Re-measure every dimension that was out of tolerance in T1.
- Confirm process stability: Run 50–100 consecutive shots to verify the process is stable and repeatable.
- Cavity-to-cavity consistency: For multi-cavity molds, verify all cavities produce equivalent parts.
- Cosmetic approval: Customer or customer's representative visually inspects and approves surface quality, color match, and texture.
- Lock process parameters: Document the final, frozen process settings for production.
- Produce golden samples: Set aside 5–10 approved parts as the reference standard.
The Golden Sample
The golden sample (also called the "approved sample" or "reference part") is a critically important deliverable. It serves as the visual and dimensional baseline for:
- Incoming quality inspection during mass production — parts are compared to the golden sample for visual approval.
- Dispute resolution — if there is disagreement between buyer and supplier about acceptable quality, the golden sample is the reference.
- Process drift detection — if production parts start deviating from the golden sample, it signals tool wear or process drift.
Golden samples should be labeled, sealed in protective packaging, and signed by both the mold maker and the customer. They should never be used for functional testing or assembly — they are reference artifacts only.
Process Capability Assessment (Optional but Recommended)
For automotive and medical applications, T2 may include a process capability study (Cpk/Ppk) where 30–50 consecutive parts are measured for key dimensions. The capability indices indicate whether the process can reliably hold tolerances:
- Cpk < 1.00: Process is not capable — significant improvements needed.
- Cpk 1.00–1.33: Marginal capability — acceptable for non-critical dimensions.
- Cpk 1.33–1.67: Good capability — acceptable for most applications.
- Cpk > 1.67: Excellent capability — suitable for critical, high-precision dimensions.
T2 Deliverables
- Updated FAI report showing all dimensions now within tolerance
- 50–100 approved production parts from the locked process
- 5–10 golden samples labeled and signed
- Final process parameter sheet — frozen settings for production
- Mold qualification sign-off — formal document acknowledging the mold is approved for production
- PPAP documentation (if automotive) or DHF/DMSR documentation (if medical)
6. Industry-Specific Sampling Requirements
Automotive (IATF 16949 / PPAP)
Automotive mold sampling follows the PPAP (Production Part Approval Process) framework, which is more rigorous than general sampling:
- Significant Production Run (SPR): A minimum of 300 consecutive parts from the production mold, at production cycle time, using production material.
- Level 3 PPAP is typically required, including: dimensional layouts, material certifications, performance test results, process flow diagrams, PFMEA, control plan, and MSA (Measurement System Analysis).
- Cpk ≥ 1.67 for special characteristics (SC/CC) is typically required for approval.
- Multiple T-trials are often extended to T3 or T4 for complex automotive parts.
Medical (ISO 13485)
Medical device molding requires IQ/OQ/PQ validation:
- IQ (Installation Qualification): Verify the mold and machine are installed correctly.
- OQ (Operational Qualification): Verify the process produces acceptable parts across the full operating window (worst-case parameters).
- PQ (Performance Qualification): Verify the process is reproducible over extended runs (typically 3 runs of 50+ parts).
Consumer Products
For general consumer products, the sampling process is typically less formal but should still follow the T0–T2 structure. Key focus areas:
- Cosmetic quality is often more important than tight dimensional tolerances.
- Color matching to Pantone or master sample requires multiple iterations.
- Assembly fit-up with mating parts is critical and may require T1.5 iterations.
7. Best Practices for Successful Mold Sampling
For Buyers and Product Developers
- Provide complete documentation: 3D CAD (STEP + native), 2D drawings with GD&T tolerance callouts, material specification, color (Pantone/RAL), surface finish spec (SPI standard), and critical-to-quality (CTQ) feature list.
- Specify acceptance criteria upfront: Define what constitutes a "pass" for each dimension and cosmetic feature before T0 begins.
- Be available for fast feedback: After each trial, review the FAI report and samples within 48 hours. Delays in feedback translate directly to project delays.
- Understand that steel corrections take time: welding, re-machining, re-polishing — allow 3–7 days between trials for corrections.
- Don't change the design mid-sampling: Design changes after T0 essentially reset the process. Freeze the design before mold steel cutting begins.
For Mold Makers
- Use the right machine: Sample on a machine that matches the production press (clamp force, shot capacity, screw diameter). Sampling on a much larger or smaller machine can produce different results.
- Dry hygroscopic materials properly: Wet nylon or PC will produce defective parts that look like mold problems but are actually material problems.
- Document everything: Machine brand/model, material lot number, all process parameters, ambient conditions, operator name. This documentation is invaluable for troubleshooting and future reference.
- Be conservative on shrinkage: It is always easier to remove steel than to add it. Apply shrinkage compensation slightly conservatively for the first cut.
- Conduct a mold flow analysis before T0: Mold flow simulation predicts flow patterns, weld line locations, air traps, and warpage — allowing preemptive corrections before steel is cut.
8. Timeline and Cost Considerations
Typical Timeline
| Phase | Duration | Notes |
|---|---|---|
| Mold design | 1–3 weeks | Depending on complexity |
| Mold manufacturing | 3–8 weeks | Steel type, complexity, number of cavities |
| T0 trial + corrections | 1–2 weeks | Including steel changes and re-polishing |
| T1 trial + corrections | 1–2 weeks | Dimensional corrections, process optimization |
| T2 trial + approval | 1 week | Final verification, golden sample, sign-off |
| Total (typical) | 7–16 weeks | From PO to approved production mold |
Cost of Additional Trials
Each trial round has associated costs:
- Machine time: $50–200/hour depending on machine size and region.
- Material: Engineering grades (PEEK, LCP) can cost $100–500/kg.
- Engineering time: Process engineer, quality inspector, mold maker for corrections.
- Steel correction cost: $200–2,000+ per correction depending on complexity.
A typical mold project budgets for 3 trials. Each additional trial beyond T2 can add $1,000–5,000 to the project cost, plus 1–2 weeks of delay. This is why thorough design review and mold flow analysis before steel cutting are so valuable — they reduce the number of trials needed.
9. Common Questions About Mold Sampling
Q: How many sample parts should I receive at each trial?
A: T0 typically yields 10–30 parts (focus is on mold function). T1 should provide 30–50 parts for dimensional measurement. T2 should produce 50–100 parts from the locked process, plus 5–10 golden samples set aside for reference.
Q: Can we use T0 parts for functional testing?
A: You can, but with caution. T0 parts may have dimensional deviations and surface defects. They are useful for checking basic fit and assembly, but not for qualifying the design. Always communicate clearly whether parts are from T0 or approved T2.
Q: What if dimensions are still out of tolerance after T2?
A: If specific dimensions remain problematic, discuss with your mold maker whether the tolerance is realistic for the material and process. In some cases, the part design may need modification (e.g., loosening tolerance, adding features to control warpage). If the tolerance is correct and achievable, additional steel corrections and a T3 trial may be needed.
Q: How long does the golden sample remain valid?
A: The golden sample remains the quality reference for the life of the mold. However, after significant mold maintenance (cavity polishing, core replacement, major repair), a new golden sample may need to be produced and approved.
Q: What is a "safe" shrinkage rate to start with?
A: Shrinkage depends on material, wall thickness, processing conditions, and part geometry. Generic data sheets provide ranges (e.g., ABS: 0.4–0.7%, PP: 1.0–2.5%, glass-filled nylon: 0.2–0.5%). Mold flow analysis provides the most accurate prediction. Always consult with your mold maker's experience with similar parts and materials.
10. Conclusion
The injection mold sampling process — T0, T1, T2 — is not just a series of technical checkpoints. It is the structured dialogue between design intent and manufacturing reality. Each trial reveals information that cannot be known in advance, even with the best simulation software. The key to success is approaching each trial with clear objectives, thorough measurement, and prompt, decisive corrections.
For product developers sourcing molded parts from China (or anywhere in the world), understanding this process is essential for managing expectations, communicating effectively with your mold maker, and avoiding the costly mistake of approving a mold that is not truly production-ready. A well-executed T0–T2 process produces a mold that runs reliably for hundreds of thousands — or millions — of cycles, with consistent quality and minimal downtime.
At Huanze Technology, we follow a rigorous T0–T2 sampling protocol for every mold we build. Our process engineers use scientific molding principles and comprehensive measurement equipment to ensure that when we ship your mold, it is ready for production. Contact us to discuss your injection molding project — we will walk you through the entire process from mold design through final approval.
Ready to start your injection molding project? Get in touch with our team for a free consultation and mold quotation.