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.



Injection Mold Types: Hot runner molds



Hot runner molds is a generally effective method of mold making that has less scrap (sometimes the process has no scrap) due to keeping the plastic is kept above the melting temperature. Because it is more effective, it tends to be a bit more expensive than other types of molds, particularly cold runner molds. The overall savings makes up for the cost if you have large quantities to produce or if you need quick production.


Components and Process

All hot runner mold systems include two plates to complete the process quickly. It is composed of the manifold and drops. The purpose of the manifold is to convey the plastic to an area above the cavity.

Running perpendicular to the manifold are the drops, which move the plastic from the manifold to the part. Systems have some variations based on the method of heating the plastic.


Things to Consider

In addition to reducing the waste, hot runner molds have a quicker cycle time. Robotics are common in many molding processes, but you will not need as many for a hot running system. Large parts are typically best when made with hot runner molds because these molds can better accommodate the size.

However, if you have a more limited budget or fewer parts, you can save on the cost by using a cold runner system. If color is important and you are likely to need to change it frequently, hot runner systems will not be able to make the change easily.



Injection Mold Types: Collapsible core molds

The purpose of collapsible core molds is to work with various types of threads so that the parts can be easily ejected. They also come in a variety of types, such as dovetails and spring-loaded designs. As these molds have undercuts, it does take time to get the optimal design. However, when done right, collapsible core molds offer more capabilities to work with undercut molding and to hold parts together.


Overview of the Process

Unlike most other molds, when producing collapsible core molds, the mold is made to collapse radially inward, reducing the amount of time required to produce it. It is estimated that this method reduces the production time by 30% as it does not require secondary operations or additional coring once completed.


Unique Challenges

With its special design and use, this particular type of mold offers challenges not encountered with other mold types. Because it is meant to be used without requiring lubrication, wear and tear can occur faster, which means you will have to determine how often they need to be replaced. The technology is changing quickly, so you will also want to consider regular reviews to redesign your molds to keep them as efficient as possible.


Dovetail Design

There are several design types, but the newest is the dovetail. It is the easiest and quickest type of core to produce and has the largest range of uses. Their durability and strength have made them a popular choice to lock parts together.