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ResourcesInjection MoldingHot Runner vs. Cold Running Molds: Differences and Comparison
Hot runner mold. Image Credit: Shutterstock.com/Rogue Ace Photography

Hot Runner vs. Cold Running Molds: Differences and Comparison

Learn about the differences between these mold designs and the advantages of each.

Xomety X
By Team Xometry
August 30, 2022
 7 min read
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Injection molding is a manufacturing process that produces plastic components. It is a popular method for low-volume production, pilot-run, and prototyping of designs. Injection molding has two main types of mold designs: hot runner and cold runner. A hot runner mold uses a heated runner to transfer molten thermoplastic or polymer to the mold cavity where the final product takes on its shape. A cold runner mold uses an unheated runner channel to transfer the molten material from the machine nozzle to the mold cavity. 

While these two methods both produce plastic parts, hot runner mold and cold runner mold systems differ in terms of cost, speed, and accuracy of the molded parts. Hot runner molds are more expensive to set up and maintain than their cold runner counterparts. But, hot runner molds produce parts with a higher degree of tolerance and have a shorter lead time. A cold runner mold, on the other hand, is more affordable and works with a vast array of thermoplastic materials including heat-sensitive types.

This article will compare hot runner vs. cold runner, examine their advantages and disadvantages, as well as discuss the alternatives to both.

Hot Runner Definition and Comparison to Cold Running Molds

A hot runner is an injection molding system that utilizes a manifold as the heating element. It was first manufactured and commercialized by Mold-Masters Ltd in 1963. The runner, which is made up of two plates, is heated along with the molten thermoplastic. As the molten plastic flows through the runner, the manifold ensures uniformity in the temperature of the heating cylinder and the runner. The molten plastic is fed to the nozzle, which in turn fills the mold cavity. Afterward, the molded plastic is ejected free of the runner. Compared to the cold runner mold, the hot runner mold produces more parts per unit time.

What Are the Advantages of Hot Runner Compared to Cold Running Molds?

Some advantages of hot runner vs. cold running molds are:

  1. Hot runner molds do not need the help of robotics to separate the runner from the mold, unlike the cold runner mold.
  2. The parts produced by hot runner molds are more precise in their dimensions than those from cold runner molds.
  3. Larger volumes and sizes of parts can be produced by hot runner molds.

What Are the Disadvantages of Hot Runner Compared to Cold Running Molds? 

Some of the disadvantages of hot runner vs. cold running are:

  1. Hot runner molds have higher maintenance costs compared to cold running molds.
  2. Hot runner molds do not suit some heat-sensitive thermoplastic materials compared to cold running molds.
  3. It is difficult to make color changes in hot runner molds.

Cold Running Molds Definition and Comparison to Hot Runner

Cold running molds use unheated runners to convey molten thermoplastic material from the nozzle to the mold or cavities. These are made up of two or three plates, depending on the design. When the process is complete, the runner comes out attached to the molded part. A cold running mold is sometimes preferred over a hot runner mold because of the low setup and maintenance cost.

What Are the Advantages of Cold Running Molds Compared to Hot Runners?

Some advantages of cold running molds compared to hot runner molds are:

  1. Cold running molds accommodate a variety of thermoplastics compared to hot runner molds.
  2. Cold running molds are cost-effective compared to hot runner molds.
  3. Cold running molds allow for quick changes in design or color.

What Are the Disadvantages of Cold Running Molds Compared to Hot Runners?

The disadvantages of cold running molds compared to hot runner molds are:

  1. Cold running molds produce more waste than hot runner molds.
  2. Cold running molds produce parts with lower tolerances than those of hot runner molds.
  3. The production process of cold running molds is slower than hot runner molds. Therefore a lesser number of parts can be produced via cold running molds.

Comparison Table Between Hot Runner and Cold Runner

Table 1 below highlights the attributes when comparing cold runner vs. hot runner molds:

The hot runner mold produces parts with a tighter tolerance than those of a cold running mold. However, when changes in design or color are required, a cold running mold is the best option.

Hot Runner vs. Cold Runner: Cost Comparison

Hot runner molds have a higher setup and maintenance cost. It is generally a more expensive alternative to cold runner molds. However, in some cases,  the high rate of waste production in cold runner molds counterbalances any potential cost savings. The improper management of waste can raise the overall cost of production.

Hot Runner vs. Cold Runner: Speed Comparison

A hot runner mold produces more parts per unit time than cold runner parts. This is because cold runner molds need to separate the runner from the mold and grind and recycle the runner to avoid waste. In contrast, hot runner molds are not affected by any of these factors so the lead time is shorter.

Hot Runner vs. Cold Runner: Volume Comparison

A larger volume of parts can be produced with hot runner mold than with cold runner molds, as the use of the hot runner eliminates the need to separate the runner from the part. This reduces the cycle time and allows for faster processing of materials.

Hot Runner vs. Cold Runner: Materials Comparison

When comparing hot runner vs. cold runner with regard to the types of thermoplastic materials used, it is helpful to realize how negatively hot runner molds impact thermal-sensitive resin or polymers. Materials that are particularly sensitive to heat should not be used in this system. The elimination of the heating element in cold runners makes them compatible with a large number of polymers or thermoplastics including thermal-sensitive options.

What Are the Mutual Alternatives to the Hot Runner and Cold Running Molds?

The mutual alternative of a hot runner and cold runner mold is the use of extrusion:

  • Extrusion: Extrusion is a technique that allows the transfer of molten thermoplastic or metal through a series of dies so that the desired shape is formed. Extrusion is similar to hot runner and cold runner mold systems in that they all transfer molten thermoplastics during their processes.

What Are the Similarities Between Hot Runner and Cold Running Molds?

These are some similarities that both molding systems share:

  1. Both the hot runner and cold runner mold systems transfer molten thermoplastic to the mold cavities to take the desired shape.
  2. Both systems have nozzles that control the movement of the molten thermoplastics.

What Are the Other Comparisons for Hot Runners Besides Cold Running Molds?

Another comparison to hot runner molds is:

  • Hot Runner vs. 3D Printing: 3D printing is an additive manufacturing process in which a heated thermoplastic material is placed layer by layer until the required shape is formed. It replicates the design of the digital 3D model built with CAD software.

What Are the Other Comparisons for Cold Running Molds Besides Hot Runner?

Another comparison to cold runner molds is:

  • Cold Runner vs. Thermoforming: Thermoforming is a manufacturing process that involves the heating of a thermoplastic sheet until it becomes pliable or soft. Afterward, it is stretched and manipulated in a specific way to achieve the desired shape and features before it is left to cool down.

Summary

This article provided a comparison of hot runner versus cold running injection molding techniques. To learn more about hot runner vs. cold runner molds and how they can be applied to your projects, contact a Xometry representative for assistance and expert guidance.

Xometry provides a wide range of manufacturing capabilities, including 3D printing, injection molding, and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.