• Top Considerations for a Hot Runner Mold

    Here are the TOP considerations when contemplating a hot runner mold over a cold runner mold, including all points for a detailed cost analysis.

Top Considerations for a Hot Runner Mold


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If you are considering a hot runner mold for your next injection molding job, you are probably weighing the benefits versus the costs.  A hot runner mold is typically more expensive to construct, but the return on investment can be well worth it.  Here are some of the most important considerations when contemplating a hot runner mold.

Elimination of Costly Runners

One of the greatest benefits realized from a hot runner mold is the elimination of costly runners.  If the design of a cold runner mold would produce a large runner that would go to waste, a hot runner tool can provide a quick return on investment.  This is especially true if the part itself is small or a micro molding job, the runner is often larger than the molded part or parts.

If your resin is a specialty raw material, it can be even more beneficial to paymore for a hot runner tool, and save considerably by not wasting expensive raw plastic resin.  If the job is projected to support a high-volume production requirement over an extended period of time, the savings in material can be tremendous, especially if you cannot reuse the runner as regrind material.   

A quick cost analysis should reveal the savings in material versus a cold runner tool.  Michiana Global Mold can assist you in determining your cost savings with a hot runner tool design.  

Improved Geometrical Tolerances

In a cold runner tool, the raw material flows through the runner system into the cavities molding the part, as opposed to the hot runner tool where material is injected directly into the cavity through a nozzle.  By injecting material directly into the cavities, the material fills and packs with more pressure thus improving filling into critical dimensions.  

The improved pressure of a hot runner mold can improve the quality of tight tolerance parts requiring critical fill areas.   Michiana Global Mold has vast experience designing hot runner molds with tight geometric tolerances, and satisfying strict customer specifications.

Improved Cycle Time

A hot runner tool will usually produce a faster cycle time due to the increased pressure in packing and filling.  Improved cycle times equate to increased profits on high volume jobs, where even a few seconds can produce thousands of dollars in annual returns with improved efficiencies.  

Most OEMs today require a continual improvement plan with cost reductions in either cycle time, or automated efficiencies.  The cost savings can be significant when evaluating cycle time on a multi-cavity, high volume production job.  

The cavitation, volume and projected life of the program are important considerations when evaluating the cost savings of an improved cycle time from a hot runner mold.  

Flexibility of Gate Location

When designing a hot runner tool, the injection mold designer will have some flexibility in determining the optimum location for gating to achieve consistent filling and packing.  Gate location is important in high visibility parts for aesthetics, as well as part functionality.

With hot runner tools, there are two different types of gating mechanisms.  A hot-tip gate is also called a thermal gate, while the other type is a valve gate.  With a hot tip gate, the material hardens at the nozzle tip, which allows the parts to disconnect from the tip for ejection. This leaves a visible gating mark, or a small vestige, protruding from the part.  This vestige can be compensated for by the addition of a gate well or dimple if any gating vestige impacts the part function.

In a valve gate design, a valve slides over in front of the tip of the nozzle prior to ejection, which assists with ejection for materials that do not completely solidify in the nozzle tip.  Typically larger gate sizes can be achieved benefiting material processing and cycle times.  Valve gates may leave a witness of the gating location, but will be free of any gate vestige.

There are many benefits to a hot runner mold, in the right environment and circumstances. Michiana Global Mold specializes in complex, tight tolerance cold and hot runner molds satisfying strict specifications of OEMs around the globe.   We can assist you in determining the most cost effective mold design for your injection molded project.

Michiana Global Mold employs skilled engineers and designers with in-depth knowledge and experience designing and manufacturing precision hot runner tools.  We are an ISO registered mold making facility, providing high quality injection molds meeting demanding customer specifications.  Contact us today for a free cost analysis of your next mold building project.