15 Jun 2018

Rex Plastics is known for quality plastic injection molding. It has been part of our business since we started in 1971. Very few understand how the process works when they approach us, and likewise don’t know the advantages offered by all our other in-house services. We’d like to set the record straight. 

Is Injection Molding the Right Choice?

This should always be the first question, even before the first prototype or CAD drawing. We’re fans of injection molding (for obvious reasons), but we also know that it may not be the right manufacturing process for some jobs. Processes like spin casting, thermoforming, extrusion, or blow molding may be more appropriate depending on the design of a product and its application.

Rex Plastics will consult on your project in detail to ensure that we are, in fact, the right choice. mold injection machine

The Tooling Process

Our injection mold making process starts well before building the mold itself; it begins when you first bring your concept to us. That concept could be anything from a glimmer of an idea to a finished product design.

  • We start with a free evaluation of your design. Part of this process is visualizing what we know your tooling will look like based on your product design.
  • From there, we move on to design recommendations. This may involve a “design for manufacturing” consultation at no cost (if your product needs minor fine-tuning), or a quote for more extensive design and revision work. The goal here is to explore ways to save you time and money.
  • Next, we perform CAD design and/or create prototypes (on payment terms) to flesh out and validate product form and function. Your satisfaction and trust are of paramount importance to us, so we work hard to ensure the best results.
  • If you enlist Rex Plastics having gone through these steps, we’ll discount up to $500 worth of CAD and prototyping costs from the cost of mold-building.

Let’s look at these steps in a bit more detail.


There are a few different ways to prototype an injection molded product. These include machining, cast polyurethane, and of course 3D printing. We’ve found that 3D printing has the best combination of cost, lead time, and quality for plastic prototyping. It may not use the same plastic as the finished product, but the results that 3D printing delivers will be more precise than the alternatives.


Not all plastic parts will have perfect geometric shapes and uniform thicknesses throughout. In fact, most don’t. That creates challenges, since there are a few things we aim to avoid during the molding process.

  • Uneven injection: Each part should have proper and uniform flow so that there are fewer defects.
  • Uneven cooling: If parts don’t cool evenly, this can lead to warping, poor fit and finish, and structural defects.
  • Material waste: If the mold is inefficiently laid out, this leads to wasted plastic and cost overruns. Precision matters!

Your business’s reputation rides on the quality of your product. That’s why quality control starts well before the mold is tooled.


There’s another consideration that makes 3D printing a better option. Your first attempt(s) will often have errors, necessitating anything from minor tweaks to a major redesign. Both the hardware and software involved in 3D printing play a big role in expediting that process.

Mold Making

Now that you’ve designed, prototyped, and refined, you’re ready for the tooling of your mold. Our molds use steel construction. This ensures that the mold works within the highest tolerances, and that it’s capable of holding up over a long production life. There’s a great deal of time and money invested in a properly built mold, so it’s in our best interest as well as yours to get it right the first time.

Why Rex Plastics?

From our beginnings in 1971, Rex Plastics has stood stubbornly by a few key principles. Quality is a must. We make our products in the USA. We handle as much as possible in-house, relying on local toolmakers under exceptional circumstances so we have full visibility of, and control over, the quality of their work. Perhaps most importantly, we back our work to the hilt because our molds are built to last.

Ready to undertake the next big step in bringing your product to life, or getting it before the public? Contact Rex Plastics for a free consultation today!


  1. thanks says:

    Thanks for sharing this helpful article

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