{"id":4062,"date":"2021-11-24T20:57:00","date_gmt":"2021-11-25T02:57:00","guid":{"rendered":"https:\/\/sybridge.com\/?p=4062"},"modified":"2023-11-20T11:50:27","modified_gmt":"2023-11-20T17:50:27","slug":"material-compatibility-multi-material-injection-molding","status":"publish","type":"post","link":"https:\/\/sybridge.com\/material-compatibility-multi-material-injection-molding\/","title":{"rendered":"What You Need To Know About Material Compatibility For Multi-Material Injection Molding"},"content":{"rendered":"\n

Originally published on fastradius.com on November 24, 2021<\/em><\/p>\n\n\n\n

Multi-material injection molding is an umbrella term referring to any injection molding<\/a> process in which two or more different materials are bonded to form a single plastic part. The most common types of multi-material injection molding are overmolding<\/a> and two-shot injection molding.<\/p>\n\n\n\n

Overmolding is a process that forms a unified product from two or more different thermoplastics<\/a>. During this process, an engineer molds a substrate out of the rigid overmold material and then places the substrate in an overmold cavity in a separate tool. Then, the molten overmold material is ejected into, onto, or around the substrate. As the thermoplastics cool, the materials become either chemically or mechanically bonded \u2014 which gives the end product a high degree of strength and durability. While this drives up the overhead cost of a tool, it can save you a fortune down the line by eliminating the need for an assembly process, thus cutting labor and resource costs.<\/p>\n\n\n\n

You can achieve many of the same properties using two-shot injection molding, also known as double-shot injection molding. The difference between overmolding and two-shot molding is that the former is done using two tools while the latter is done using one tool. During two-shot injection molding, the first material is injected into a mold to create the substrate, which is then transferred into the other chamber of the mold by an end of arm tool after it solidifies and cools. After that, the mold opens and the side with the substrate rotates 180\u00b0 to meet the other mold chamber. Once the substrate is in place, the injection molding nozzle injects the second material into the cavity, bonding it with the substrate.<\/p>\n\n\n\n

From an overhead perspective, two-shot injection molding is more expensive to design and build, but it\u2019s faster and better-suited for high-volume production runs than overmolding. Overmolding requires manual labor since someone has to physically remove the first part of the mold and place it in the second mold, which is only economical for smaller production sizes.<\/p>\n\n\n\n

Since the materials involved in overmolding and two-shot injection molding must be bonded together, the plastics must be compatible with one another. Material compatibility, which has its roots in chemical compatibility, is a measure of how stable a material is when it comes into contact with another material. If two materials come in contact with one another and cause a chemical reaction, they\u2019re incompatible and cannot be used together in multi-material injection molding.<\/p>\n\n\n\n

For materials that are not chemically compatible, a positive fastening feature or mechanical bond is typically recommended. This joins the two materials together without a chemical bond.<\/p>\n\n\n\n

\"joins\"<\/figure>\n\n\n\n

Here\u2019s what you need to know about choosing injection molding thermoset<\/a> materials based on material compatibility, and negotiating other factors like friction, wear, and adhesion:<\/p>\n\n\n\n

Key considerations for injection mold material selection<\/h2>\n\n\n\n

When it comes to multi-material injection molding, accidentally mixing two incompatible materials can be catastrophic. At best, you might notice an awful smell permeating the production room floor. At worst, your injection molding machine barrel might explode into pieces. To avoid adverse outcomes, engineers and product teams must choose resins carefully and ensure there are no contraindications.<\/p>\n\n\n\n

As a general rule, the following common injection molding materials should never be used together:<\/p>\n\n\n\n