Injection molding is a standard process in the world of plastic manufacturing. It is the integral process to create plastic products by injecting molten plastic material into a mold. Plastic injection molding can be performed with the help of other materials as hosts, most commonly metals, to any types of injection molds. These hosts are also melted in a heated barrel and is then forced into the mold cavity along with the raw plastic material.
We have already discussed the process of plastic injection molding in past wiki articles. In this one, we will focus on the different types of injection molds including the advantages and disadvantages for each type and how runners function for specific molding designs.
There are generally two different types of injection molds known as the cold runner and the hot runner. The runner is a fundamental part within the mold which allows the plastic material to travel from the barrel of the injection molding machine on to its target location. As the name suggests, both different types of plastic molding uses opposite temperatures to create plastic parts and each cycle uses a single runner for each plastic part produced.
It has to be taken care that the machines are set up well in any case. Studies find that the reason for defects is most commonly caused by wrong machine settings for both cold and hot runner molds.
In a cold runner mold, the molding process uses cold temperature to cool the runner and so it will be ejected along with the plastic part. Each cycle, a runner and the plastic part is ejected out of the mold. The biggest con to this injection mold design is the amount of wastes generated out of each cycle and that very delicate shapes are not possible sometimes. If the mold is too thin, the plastic material might simply cool off before getting there.
Most of the time, the runners are simply disposed unless the plastic molding company finds a way to reground or reprocess the runner with the plastic material. But then again, the entire manufacturing process becomes much lengthier as another process is added on to it. The regrinding process will also alter the physical properties of the plastic part produce which could end up as a different variation from its original design.
For most electronics products cases and other simply products that involve ABS, PP or similar, this method is usually chosen due to its affordability. Types of Cold Runner Molds:
The two plate cold runner is the most basic type of custom plastic molding. It named as such because the mold splits into two halves out of a single parting plane. The runner is placed on the parting plane which means the plastic part is only gated around its perimeter.
The three plate cold runner has an additional parting plane which means the mold splits into three thirds once the plastic part is ejected out of the mold. The runner can be placed on either parting plane with the plastic part on the opposite parting plane. Plastic molding companies love to use the three plate cold runner because it can be gated anywhere on its surface giving them flexibility in gating options.
In a hot runner mold, the molding process uses a temperature beyond the plastic material’s melting point to heat the mold with the runner placed within molding setup. This injection mold design reduces and sometimes completely eliminates possible wastes generated out of each cycle. Furthermore, it allows for more complex and fine shapes than cold runner molds.
The biggest disadvantage to this type of injection mold is the cost involved for the setup. A hot runner mold requires expensive maintenance and needs skill specialization in order to supervise such custom injection molding process. Dealing with color changes is also a problem with hot runner molds since you cannot remove all of the molten plastic with the runner stuck inside the mold.
On the other hand, hot runners have a lot of pros for the injection molding company. Aside from eliminating plastic wastes or by keeping them at a minimum, there are no runners to deal with post-molding process since the runners are placed inside the molds. Once the plastic part is ejected, the runner is already blended within the part and there would be no need for regrinding or reprocessing.
Among these types of injection molds, the cold runner mold is most popular in high volume plastic manufacturing companies due to its affordability and efficiency. Some established plastic injection molding companies prefer to use hot runner injection molds to cater for their clients’ high demand and strict guidelines. They can easily afford the maintenance costs for this molding design and they are most likely staffed with professionals who are equipped with the right skills to handle hot runner molds.
Cold runner mold is a type of injection mold popular among small up to mid-sized injection molding companies. The usual reason for choosing this plastic part design is due to its cost-effective methods which usually fit their budget and cold runners are perfectly suitable for most simple designs. Find some more general information on plastic production and recycling here.