Injection molding is used to create many things, in many different materials. Resins, plastics, and metals are used to create simple to complex pieces of any size. The variety of items created by custom injection molders is nearly endless. The one thing every one of those pieces has in common is that they all started with a mold. But not all molds are the same. There are two primary types of molds: Hot and Cold or Hot Runners and Cold Runners.
Custom injection molders will be able to tell you which process is best for your application, but there are a few key differences that you should be aware of. This information can help you make a more informed decision down the line.
Hot runner molds have two plates heated with a manifold system. This system makes it possible to send melted plastic to fill the part cavities without the need for runners. The plastic can be heated either externally or internally. Internal systems provide better control of flow while external systems are better for polymers that are sensitive to thermal variation.
Hot runner systems usually have faster cycle times, produce less waste and eliminate the runners associated with cold systems. With no runners to worry about, recycling and regrinding does not affect cycle times, contributing to the speed of the process. Hot molds can accommodate larger parts and don't require robotics to remove the runners, but the molds are more expensive. Color changes are not quick or easy and there are higher maintenance costs associated with hot runner molds.
Cold runner molds have two or three plates that are held in the mold base. Plastic is injected via a sprue, or channel, and fills the runners, which fill the cavity. Once the material has cooled, the pieces are ejected into two or three separate parts, usually with the assistance of robotics.
Cold runner systems are less expensive to produce and maintain than hot runner systems and can accommodate many different types of polymers. Color changes can be made quickly, but the overall cycle times are slower than hot systems. The runners also produce more plastic waste than hot systems, especially if the polymers cannot be reground and recycled.
To determine the best solution for your specific project needs, consult custom injection molders. These professionals work with polymers and molding processes all day long and will be able to gauge what system is best for your needs. They'll look at factors such as the complexity of the piece, the materials being used, and the production needs. Consult a pro who is familiar with the many different types of molding and plastics processing to get the most thorough analysis and solid recommendation. In some cases, either system will work and your mold professional should be able to provide you with a cost-benefit analysis so you can choose the application that makes the most sense for your business needs.
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