Engineer reviewing injection mold diagrams

What to Expect When You Order a Mold: The Pilot Run and Mold Modification Process

By Ichiplas Tooling Team · Oct 2025 · Updated Nov 2026 · Reviewed by the Ichiplas engineering team

You've signed the quote and paid the deposit for your new injection mold. Congratulations—you've officially started the transition from design to physical production.

This final stage is an exciting one, but it's important to understand the process, especially when it comes to reviewing your first sample parts and making any necessary adjustments.

This is the last, best chance to get everything perfect before committing to a full production run. A little diligence here can save you from major headaches down the road.

The First Shots (T1 Samples)

After several weeks of mold design and fabrication, we will conduct the first trial run. The initial parts from this run are called “T1 samples.” This is your first opportunity to hold a real part produced from your production tool.

When you receive your T1 samples, your job is to perform a thorough review. At this stage, you should focus on:

Fit and Form: Does the part have the correct dimensions?
Assembly: Does it assemble correctly with its mating parts?
Function: Do the snap-fits engage properly? Do the moving parts work as intended?

Don't worry about color or surface texture at this stage. T1s are typically run in a natural, uncolored resin, and the final texture is often not applied to the mold until after the part geometry is fully approved.

Making Mold Modifications: The “Steel Safe” Rule

What if something isn't quite right? A snap is too loose, or a clearance is too tight. This is when we discuss mold modifications. When making changes, we are always guided by one simple but critical rule: it is easy to remove steel from a mold, but it is very difficult and expensive to add it back.

This gives rise to the term “steel safe.”

A “steel safe” change is one where you want to add plastic to your part. To do this, we simply machine away more steel from the mold cavity. This is a relatively straightforward and low-cost modification.
A non-“steel safe” change is one where you want to remove plastic from your part. This requires us to add steel to the mold, which involves precision micro-welding and then re-machining the surface. This process is complex, costly, and not always possible.

Because of this, it's always best practice to design features like press-fits or tight clearances to be “steel safe”—meaning, design them a little tight, with the expectation that we can easily open up the tolerance by removing a tiny amount of steel if needed.

From First Shots to Production: The Trial Stages

Typical stages from mold trial to production approval
Stage	Purpose	What you typically receive
T0 (internal trial)	Toolmaker checks the mold runs and fills	Usually nothing; internal only
T1 samples	First review of fit, form and function	Sample parts and an initial dimensional report
Mold modifications	Correct dimensions, fit or cosmetic issues	A list of changes and the agreed steel-safe adjustments
T2 / T3 samples	Confirm the modifications worked	Revised samples and an updated dimensional report
Texture and final finish	Apply texture once geometry is approved	Textured samples in the production color
First article inspection (FAI)	Full dimensional sign-off against the drawing	FAI report on a stable, production-process sample
Pilot run	Prove the process at production rate	A small production lot and process settings
Production release	Start serial production	Approved samples kept as the quality reference

Most molds reach approval in two to three trial loops. Complex parts, tight tolerances or design changes after T1 can add more.

Frequently Asked Questions

What are T1 samples in injection molding?

T1 samples are the first parts shot from a new production mold, used to check dimensions, fit, assembly and function. They are often molded in natural or uncolored resin, before final texture is applied, so the focus should be on geometry rather than appearance.

How many mold trials are normal?

Two to three trials (T1 to T3) is typical for a new mold before the part is approved. A well-reviewed, simple part may be approved at T1 or T2; complex parts, tight tolerances or design changes requested after T1 usually add further loops.

What does steel safe mean?

A steel safe design is one where any likely adjustment can be made by removing steel from the mold, which adds plastic to the part and is quick and cheap. Changes that require adding steel — removing plastic from the part — need welding and re-machining, which is slower, costlier and not always possible. Critical fits are therefore deliberately cut tight at first.

Who pays for mold modifications after T1?

Common industry practice is that the molder corrects anything that doesn't match the approved drawing at its own cost, while changes the customer requests to the design itself are quoted separately. The split should be agreed in the tooling quotation before the mold is built.

What is a first article inspection (FAI)?

A first article inspection is a full, documented measurement of every dimension and requirement on the drawing, taken from parts made with the final mold and production process. It is the formal evidence that the process can make conforming parts before serial production begins.

Your Partner in Production

From initial design review to final part approval, our job is to be your expert partner. We help you navigate these final steps to ensure the part you designed is the part you receive, every single time.

This concludes our introductory series on designing for injection molding. If you're ready to put these principles into practice, our team in Johor Bahru is here to help turn your design into a world-class product. Contact us today to start the conversation.

Getting your design ready for production can feel complex. Our team in Johor Bahru lives and breathes this process every day. If you want to ensure your design is optimized for manufacturing from the start, reach out to us. We're here to help.