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AIM Processing Small Plastic Parts Blog

Injection Molding Techniques: Hot Runner Manifolds vs. Cold Runners

[fa icon="calendar"] May 16, 2024 12:01:00 AM / by Jon Gelston


Today’s advanced injection molding techniques take an intelligent, disciplined approach to the manufacturing process that ensures both higher precision and efficiency. Making the right choice between hot runner manifold systems and conventional cold runners is just one of the many considerations we make. Nevertheless, it’s one of the most critical decisions in order to optimize our injection molding methods for your unique products and volume requirements.

At AIM Processing, we strive to remove any guesswork or uncertainty from our plastic molding services. By employing disciplined injection molding solutions, we help ensure better end products created through a more sustainable production process. On that note, let’s take a look at the crucial differences between hot runners and cold runners.

What are hot runner manifolds in plastic injection molding?

A hot runner manifold is a complex apparatus that integrates heating components into the runner system embedded in the tool. The manifold is designed to evenly distribute molten plastic from the injection unit to multiple mold cavities without the need for conventional runners. Due to the more direct injection of heated material, we are able to more precisely control both temperature and flow rates.

The major downside is that hot runner manifold systems require increased up-front tooling costs along with more complicated maintenance. Especially in the case of low-volume injection molding projects, the higher price of entry often makes cold runner systems the more economical choice.

The Advantages of Hot Runners:

  • Ideal for ensuring repeatability in high-volume injection molding services.
  • Reduced cycle times for higher throughput.
  • Minimum waste through the elimination of scrap produced by conventional runners and sprues.
  • Allow for flexibility in gate location to accommodate more complex mold designs.
  • Facilitate more precise temperature control to more effectively maintain part quality and repeatability.
  • Hot runner interface is often on the top, cosmetic surface of the part.

What are cold runners in plastic injection molding?

Cold runners are what most people picture when they think of conventional injection molds. A cold runner mold system consists of a two- or three-plate mold. The separate mold cavities are connected by a series of small channels called runners – in this case cold runners because they cool before the injection molding cycle is complete. A large central channel called a sprue feeds molten plastic into the runners, which are designed to precisely deliver the flowing material into the mold cavities.

Once the injection molded part is complete, the runner and sprue channels are thus molded onto the part as well. These excess features must be removed, adding an additional step to the production process compared to hot runner systems.

The Advantages of Cold Runners:

  • Great for low-volume injection molding projects.
  • Easier to machine, minimizing your up-front tooling costs.
  • Low maintenance and easy to clean.
  • Ideal for frequent color changes in production.

Scientific Injection Molding Solutions Since 1993

AIM Processing is the Colorado region’s leading manufacturer of high-quality injection molded plastics. Our team applies scientific molding techniques with advanced design considerations to establish the most reliable, efficient, and sustainable production process possible for every unique project.


Topics: Plastic Injection Molding Defects, Plastic Types, Quality, Texture, Choosing the right plastic injection molder

Jon Gelston

Written by Jon Gelston