Mould Trials Explained: T0, T1 and T2 Samples Before You Approve an Injection Mould

Mould Trials Explained: T0, T1 and T2 Samples Before You Approve an Injection Mould

A mould trial is a test run of a new injection mould in a moulding machine, used to prove that the tool fills, cools and ejects good parts before it is approved. Most moulds go through two or three rounds. T0 is the toolmaker's own first shot, T1 is the first set of samples sent to the buyer, and T2 (and sometimes T3) follows after corrections. Approval should rest on measured parts, a stable process and a documented mould check, not on a handful of good-looking samples and a photo.

Key facts

• T0 checks that the mould works: it opens, closes, fills and ejects without damage. Parts from T0 are usually not for approval.

• T1 samples are the first ones worth measuring against your drawing. Expect a dimensional report, a trial video and a list of issues with the planned fixes.

• Most corrections happen between T1 and T2. A well-prepared mould is often approved at T2 or T3. Each extra round typically adds about one to two weeks.

• Critical dimensions are often cut "steel safe", leaving about 0.05 to 0.1 mm of extra steel so the tool can be adjusted by removing metal rather than welding it back.

• Texture, final polish and engraving usually come after the dimensions are approved, because changing steel after texturing ruins the finish.

• Agree the acceptance criteria in writing before T1: which dimensions are critical, which cosmetic standard applies, how many parts are measured and what process data you want.

What happens at each trial stage?

Each stage answers a different question, so it helps to know what you should and should not expect from each one.

T0: does the mould run?

• Run in-house by the toolmaker, often on the first day the mould is assembled.

• Checks the basics: alignment, slides and lifters, ejection, cooling circuits, hot runner zones and venting.

• Parts may show flash, short shots or burn marks. That is normal at this stage, and the toolmaker fixes the obvious faults before inviting the buyer to T1.

T1: first samples for review

• Moulded in the specified resin grade and colour where possible, with the process roughly stabilised.

• The buyer receives sample parts, a dimensional report, the trial process sheet and a short trial video.

• The output is a correction list: dimensions out of tolerance, cosmetic defects, fit problems with mating parts and any design changes the buyer wants.

T2 and T3: corrections and final approval

• The mould is adjusted, usually by removing steel at the steel-safe areas, improving venting or changing gate size.

• Parts are measured again. If they pass, texture and final polish are applied and a short confirmation trial follows.

• Final approval should include a stable process window, not just one good shot.

A design change requested by the buyer after T1 is not a correction. It is a modification, and it should be quoted and scheduled separately so both sides know where the extra time and cost came from.

Why do the first samples rarely match the drawing exactly?

Plastic shrinks as it cools, and it does not shrink by exactly the amount the mould designer assumed. The mould is cut oversize by an estimated shrinkage factor, and the first trial shows how the real part, in the real resin and mould, behaves.

• Typical shrinkage ranges. ABS and PC usually shrink around 0.4 to 0.7 per cent, PP around 1.5 to 2 per cent, and glass-filled nylon less in the flow direction than across it. Always use the datasheet value for the exact grade.

• Direction matters. Glass-filled and semi-crystalline resins shrink differently along and across the flow, which causes warpage that no single scale factor can correct.

• Process changes size. Packing pressure, melt temperature and mould temperature can move a dimension by several hundredths of a millimetre, so the dimension report only means something if the process is recorded with it.

• Measure at the right time. Parts keep shrinking for hours after moulding. Measure after a set conditioning time, often at least 24 hours at room temperature, and condition nylon parts for moisture if the drawing assumes it.

This is why experienced toolmakers cut tight dimensions steel safe. It is far cheaper to machine a little more steel away after T1 than to weld and recut a cavity.

What should a T1 sample package include?

Ask for these items with every trial, not just the parts. Without them, you are approving the mould on appearance alone.

• Sample parts. A set from each cavity, marked with the cavity number and shot number. Five to ten parts per cavity is a common minimum for review, more if you plan a capability study.

• Dimensional report. Every dimension on a ballooned drawing, measured on parts from each cavity, with the nominal, tolerance, actual value and pass or fail.

• Process sheet. Machine size, resin grade and lot, drying conditions, melt and mould temperatures, injection speed, pack pressure and time, cooling time and cycle time.

• Trial video. Showing the mould running several cycles in a row, with ejection and any slides or lifters visible.

• Issue list. Every defect found, the cause and the planned fix, with a date for the next trial.

• Part weight. Shot and part weight per cavity. On multi-cavity tools, a big difference in part weight between cavities is an early warning of unbalanced filling.

How do you judge whether the process is stable?

A single good shot proves very little. A mould is ready for production when it makes good parts across a reasonable range of settings, so small changes on the production floor do not turn good parts into scrap.

• Gate freeze study. Part weight is recorded at increasing pack times until it stops rising. This shows when the gate has frozen and sets a pack time that is long enough without wasting cycle time.

• Fill balance. On multi-cavity moulds, short shots at partial fill show whether all cavities fill together. Unbalanced cavities give different sizes and different defects.

• Process window. Running at the low and high ends of key settings, such as melt temperature and pack pressure, shows whether parts stay in tolerance across that range.

• Short capability run. For critical dimensions, measuring a larger sample, often 30 parts or more per cavity, lets you calculate process capability. A Cpk of at least 1.33 is a common target for critical dimensions, and many automotive programmes ask for 1.67 at initial approval. Agree the target with your supplier before the run.

You do not need every study on every mould. A simple single-cavity cap may only need a dimensional check, while a four-cavity medical or automotive part usually needs the full set.

What are the most common T1 problems, and how are they fixed?

Most first-trial issues fall into a few groups. Knowing the usual fix helps you judge whether the correction plan is reasonable.

Dimensional problems

• Dimension out of tolerance: adjust steel at the steel-safe area, or fine-tune pack pressure if the deviation is small.

• Warpage: balance the cooling, adjust mould temperature on each half, check the gate position and, if the design allows, add ribs or even out the walls.

• Poor fit with mating parts: check both parts against their drawings first. The fault may be in the other part or in the tolerance stack, not in the mould.

Filling and cosmetic problems

• Short shots and burn marks: add or deepen vents at the end of fill, and check gate size and injection speed.

• Flash: fit the shut-off surfaces again, check parting line contact and confirm the press has enough clamp force for the projected area.

• Sink marks: raise pack pressure or time, enlarge the gate if it freezes too early, or reduce the rib or boss thickness in the design.

• Weld lines in visible areas: move or add a gate, raise melt or mould temperature, or improve venting where the flow fronts meet.

• Splay or silver streaks: dry the resin properly. Check the dryer and the drying time against the datasheet.

Mechanical problems

• Parts sticking or ejector marks: polish the core in the draw direction, add draft or ejection area, or add air poppets on deep parts.

• Slides or lifters binding: check fit, wear plates and lubrication, and confirm the moving parts have their own cooling where needed.

What should be checked on the mould itself before it ships?

Approving the parts is only half the job. If the mould is shipping to your own moulder or another country, inspect the tool too, because problems found after delivery are slow and expensive to fix.

• Cooling circuits. Each circuit pressure tested for leaks and flow checked, with the circuits labelled IN and OUT on the mould.

• Hot runner. Every zone heated and tested, with the wiring diagram, zone numbers and the hot runner brand documented.

• Steel and hardness. Steel certificates for the cavity, core and inserts, and hardness readings where parts were heat treated.

• Mould drawings. The final 3D model and 2D drawings of the tool as built, including the changes made after T1.

• Spare parts. Agreed spares such as ejector pins, gate inserts, springs and heater elements.

• Identification. A nameplate with mould number, part number, cavity count, steel, mould weight and the date.

• Rust protection and packing. Cavities cleaned and protected, water lines blown dry, and the mould packed in a fumigated or heat-treated wooden case with desiccant for sea freight.

If you cannot attend in person, ask for a final trial video showing the mould running several cycles, plus photos of the parting line, cavity surfaces and nameplate, taken just before packing.

How long do mould trials add to the schedule?

Trials are part of the mould schedule, not an afterthought. A typical plan looks like this:

1. T0 and T1: at the end of mould building. Samples usually reach the buyer within a few days of the trial by courier.

2. Buyer review: often three to five working days to measure parts, test fit and confirm the correction list. This step is often the slowest, so plan who will review the samples before they arrive.

3. Corrections and T2: commonly one to two weeks, depending on how much steel work is needed.

4. Texture, final polish and confirmation trial: often another week or so if the part is textured.

5. Mould inspection, packing and shipping: a few days before sea or air freight.

Our injection mould page lists typical prototype and production mould lead times. Ask for any quote to show the trial rounds separately, so you can see how many are included in the price and what an extra round costs.

What should you agree before the first trial?

1. Which dimensions are critical, and what tolerance and capability target apply to each?

2. Which cosmetic standard applies, and which faces are class A visible surfaces?

3. Which resin grade and colour will be used at T1, and who supplies it?

4. How many trial rounds are included in the mould price, and how are design changes charged?

5. How many sample parts per cavity, measured how, and after what conditioning time?

6. What documents come with each trial: dimensional report, process sheet, video and issue list?

7. What will be inspected on the mould before shipment, and who signs it off?

8. Who owns the mould, the drawings and the spare parts after final payment?

Frequently asked questions

What is the difference between T0 and T1? T0 is the toolmaker's internal first shot to check that the mould runs. T1 is the first trial whose samples are sent to the buyer for measurement and review.

How many mould trials are normal? Two or three rounds are common. A simple mould may be approved at T1, while a complex multi-cavity tool or a part with design changes can need more.

Who pays for extra trials? Corrections needed to meet the agreed drawing are normally the toolmaker's responsibility. Changes to the design after T1 are usually charged to the buyer. Write this into the purchase order.

Should texture be applied before T1? Usually not. Texture is applied after the dimensions are approved, because adjusting steel after texturing damages the finish.

Can I approve a mould from photos and a video? You can, but measure real parts as well. Ask for samples from every cavity, a full dimensional report and a video of the mould running several cycles.

What is a steel-safe dimension? A dimension cut with a little extra steel left on, so that if the part comes out wrong it can be corrected by machining away metal rather than adding it back by welding.

Need a mould built and trialled properly?

HongYing Tooling manages mould making and production through a network of verified manufacturing partners in China, and we act as one engineering contact for the whole project. Send us the 3D model, the resin grade, your critical dimensions and cosmetic requirements, and your yearly volume. We will review the design before any steel is cut, agree the trial and approval plan with you up front, and send the dimensional reports, process data and trial videos at each stage. You can start on our injection mould page, see our CAD and DFM engineering page, request a quote on our instant quote page, or email jayson@hongyingtooling.com.