Tag Archives: cold runner molds

Hot-to-Cold Injection Mold Making Experts



Most injection molders and injection mold makers are well familiar with the standard mold base, consisting of two halves, referred to as the A and B side of an injection mold.  The standard mold base will have two sides, and gates where the plastic will flow into the mold, through a ‘channel’ to get to the cavity or multiple cavities where the parts will mold.   This standard mold base is also called a cold runner mold.  


When the polymer resin hardens in the cavity to form the part, it hardens in the channel as well, which is also called the runner or the sprue.  In most cases, the runner is scrap, and will either be ground up and kept in raw material inventory as regrind to possibly be used in future jobs that will allow it, or it will simply be thrown away.  


Some injection molders grind up runners and keep the regrind material, but it can pile up and become an eyesore as most injection molding jobs require the use of 100% virgin material.  Even if it can be reused, it’s value is greatly diminished if it is stored in inventory.  Some molders feel it’s not worth the space on the floor to keep regrind material.  


If this runner is large, it can be a huge expense built into the part production, as the cost of the material is one of the biggest, if not the biggest expense of producing the part.   In some cases, especially for extremely small parts, the runner is larger than the part being produced.  In cases such as this it may be advisable to construct a hot runner mold.


A hot runner mold has a nozzle at each cavity supplying plastic directly into the cavity, rather than flowing through a ‘channel’, creating a runner.  This is a big saver if you can avoid creating a large runner for a high-volume production job.  


Hot to Cold Injection Mold


A hot runner mold may be worth the investment in cases of excess waste with high volume, although it is typically quite a bit more expensive than a cold runner mold.  Another option is called a hot-to-cold mold which is a hybrid of the two.  


Rather than have a nozzle at each cavity, there is a nozzle supplying a shortened runner system, supplying material to more than one cavity, thus greatly reducing your material cost.  A benefit of a hot-to-cold mold as opposed to a hot runner mold is the cost, it is generally less expensive as there are not as many nozzles and inner workings.  


A hot-to-cold mold is often the most economical option, providing significant cost savings with a reduced runner size, while not imposing the added cost burden of a full hot runner mold.  

Michiana Global Mold is experienced at constructing cold runner, hot runner, and hot-to-cold runner molds.  We have been in business for over 50 years, providing high performance tools with complex, precision designs.  Contact us today for a FREE design consultation and to learn more about how Michiana Global Mold can reduce your purchased injection mold costs.  



Injection Mold Types: Cold runner molds


Cold runner molds are often used for different plastic injection mold processes. Heated plastic is cooled before it passes from the nozzle to the cavity. Once it is through this part of the process, both the part and the material are  ejected from the system. Compared with the  hot runner mold process, cold runner molds area  considerably cheaper and simpler alternative for smaller projects.


Components and Process

The average cold runner system can have either two or three plate molds. In two plate systems, there is a parting line that divides the mold in two.

Systems that have three plates have two of these lines so that the mold splits into three different sections once the part is ejected. Though more difficult, three plates offer more flexibility, as well as having more gates when directed  by the final requirements.


Things to Consider

When you begin with cold runner molds, here are some additional things to consider:

  • Thicker dimensions than the starting component will allow the heated plastics to be added during the cooling process.
  • Round runner is the most common cold runner system design. It is a two-plate system with each plate containing exactly half of the runner’s diameter.
  • Round trapezoid is another design; it allows for the milling of the cavity (or core side) of the tool.
  • Gates are important to the process as a primary reason for choosing this particular system. They are removed from the part once the mold opens or once the part ejects from it.