What to Expect on the First Mold Run

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There’s a certain satisfaction we get as mold builders when a mold comes together on the bench the first time. You think about all the design, programming, fitting, polishing, and craftsmanship that went into it. But then you realize your about to clamp it closed with several tons of pressure and blast high-pressure molten plastic into it. Okay, I’m over-dramatizing this, but it’s something we do every day as injection molders and tool builders. So what should you expect on the first run of a new mold?

Well, hopefully, it’s the part you ordered, but the first run isn’t just about the part. The first run is just as much about testing the mold, checking tolerances at temperature, allowing it cycle, and getting an initial molding process setup.

The first run may the first time that all surfaces of the molding area have come together under clamp force. When we are building a mold, it may not be possible to fit all the components together until the mold is completely built. Once the mold is together, the parting line is tested as a sum of its parts rather than individual components. For more complicated molds, we may quickly check the surfaces for fit by opening and closing the mold a few times with a special compound to check for proper shut-off. 

Since some plastics require high mold temperatures, the first run may be the first time all moving components of the mold have been cycled together at high temperature. When building molds and components, we pressure test all the water circuits at more extreme settings than in the production environment. However, at high temperatures, these components expand and tolerances change (usually are reduced). We plan for this, but it’s usually the first time these components are tested completely assembled. 

The first run will also be the first time sensors, switches, and hydraulics will be functioning together. We are confirming that they are functioning properly and that the signals are being relayed properly to the molding machine. For more complicated molds requiring crash prevention measures, we will test that functionality carefully to confirm safe operation. Once all this is tested, we can begin setting up initial processing parameters for molding the first part. 

We will start processing with some modest processing parameters ensuring that we fill the mold without over-packing and flashing the parting lines. During this first process, we’re watching the molding machine parameters to confirm correct runner and gate sizing, and if utilized, testing the functionality of the hot runner system

If all goes well, we will run several hundred cycles of the mold to produce sample parts and continue testing the mold. Even if we are not manufacturing parts in a production environment. we will further refine the processing parameters. In the end. we want to have a solid process that our customers can reproduce at their facility.

At this point, we are also checking dimensions and planning any adjustments that may be required. For more complicated molds with critical tolerances, we may have designed in “steel safe” conditions. This is where we leave extra steel in specific locations, check the dimensions after molding, and make final adjustments to the tooling. In many cases, it’s better to plan for this than risk more invasive measures for tooling adjustments.

When we are building a mold for another injection molding company, we realize that a majority of the life of the mold will be at another facility. Therefore, we need to watch the mold for as long as possible, checking for machine parameter changes. We will also set monitoring conditions in the molding machine to alert us if any pressures or temperatures are changing.

This is where the experience of being a mold builder and an injection molder meet. Our team knows both sides of the business, and we work together to make a complete solution for our customers. When we build a mold, sampling and testing are included. We want to ship a mold that has been proven in a production environment.

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