Two-shot injection molding is a revolutionary technology that allows designers to combine multiple components and materials into a single product. This process streamlines manufacturing, ensures proper bonding of parts, and results in stronger, longer-lasting products. It also enables the creation of ergonomically designed products by incorporating soft materials that make them better suited for human use.
Know Your Materials
Two-shot injection molding allows for the integration of various plastic materials and colors into a single product. This eliminates the need for multiple assembly and manufacturing steps, saving time, labor, and costs. Whether you need a part with load-bearing structural components and a soft finish or a hard plastic component with a flexible grip, this technique can help. Products created using this method maintain the required mechanical characteristics and offer a high-end look, with a seamless bond between different materials.
To ensure successful results, carefully select plastic resins with comparable chemistry to ensure solid molecular adhesion between the compounds. When this is not the case, design fixes like undercuts, grooves, and shoulders can be added to improve adhesion and lock the compound together. Choose a full-service injection molding partner with extensive experience and expertise in two-shot injection molding. These partners will have excellent supplier quality scorecards and established processes for mitigating potential issues like flash, flow lines, and short-shots.
Know Your Design
The two-shot injection molding process allows manufacturers to produce multiple colors and materials in a single mold. This process saves time, engineering, and production costs while enabling engineers to create more complex geometrically designed products that may not be feasible through other means of production.
The process begins with the injection of the first layer of material (the substrate) into a standard injection mold. Then, a second injection of the overmold material is injected into, through, or around specific areas of the substrate part. This forms a powerful molecular link between the substrate and overmold materials, locking them together. For the best results, use chemically compatible compounds and conduct a thorough analysis of their adhesion qualities before starting production. In cases where adhesive quality is unknown, structural improvements such as undercuts, shoulders, and grooves can be added to the design to improve mechanical bonding.
Know Your Tool
Two-shot injection molding allows you to mold different types of plastics or a rigid component and a soft, pliable overmolding layer together in the same tool in a single step. This can save tens of thousands in development, prototyping, and assembly costs.
To master the process, it’s critical to understand how the two materials interact. Adhesion combinations require careful analysis and design consideration. For example, you may need to add undercuts or shoulders to support the second-shot material when the intrinsic bonding capacity of the first material is insufficient. It is also important to know how much the materials shrink and to choose the correct sequence in which they are injected. The first injection should be the more rigid of the two, forming a substrate for the overmold material that can be molded subsequently without warping or deforming. Additionally, consider the method of transfer between stages, such as using a rotary platen or robotic arm, to reduce production time and labor costs and eliminate the need for secondary operations like welding or assembly.
Know Your Process
Two-shot injection molding enables manufacturers to combine multiple components in a single process, allowing them to create products with complex designs that are difficult or impossible to produce through traditional methods. It also helps them take advantage of the unique properties of different materials.
One of the most important factors to consider when using two-shot injection molding is the chemistry of the materials. Some polymers bind imperfectly with each other, while others work well together and form powerful molecular adhesion. Conducting an adhesion test is critical before beginning production to ensure that the two compounds will bind well. If the bond isn’t strong enough, design elements such as undercuts, grooves, and shoulders can be incorporated into the design to improve adhesion. The right supplier can help you navigate these challenges and achieve success with your project by offering a wealth of knowledge and experience about the process and identifying potential issues before they become problems.
Know Your Supplier
Two-shot injection molding requires specialized machinery and comes with higher tooling costs compared to other injection molding methods, which can lead to budgetary challenges. To ensure a successful project, work with an experienced supplier who has excellent supplier quality scorecards, defined processes to mitigate issues like flash, flow lines, and short shots, and contingency plans to expand capacity as your production volume grows.
It’s crucial to know the chemical properties of the materials you plan on using for two-shot molding, as some materials do not bond well with each other and can cause problems during the injection molding process. Additionally, determine the sequence of the two shots, with the first shot being injected before the second to avoid deforming the substrate and preventing the second shot from adhering to it properly.
Know Your Parts
Two-shot injection molding allows you to integrate both hard and soft plastic into one product in a single machine cycle, resulting in fewer components and fewer parts that need to be joined after the manufacturing process is complete. This cuts down on development, engineering, assembly, and quality control costs.
This overmolding process is ideal for a wide range of products and parts, from vehicle interior parts to medical equipment and tools. Manufacturers can combine a multitude of components and colors to create durable, reliable, and visually appealing products. Due to its unique design, the 2 shot injection moulding process (can also be spelled molding! We also linked an additional great resource for this topic) requires a different level of expertise and precision from a supplier than other injection processes. Choosing an experienced, well-vetted partner ensures that your project is carried out with the highest standards of quality and attention to detail.
Know Your Materials (Again)
In two-shot injection molding, the first shot of plastic is molded, and then the mold is rotated or moved to another station where the second shot of a different color or material is injected into a specific area of the first-shot product. This technique allows manufacturers to combine a variety of materials that might have otherwise been impossible through other injection molding processes. In many cases, the hard, structural characteristics of one material can be bonded with the soft, flexible, or appealing qualities of another.
When working with this process, it is essential that the two materials used in the final part are compatible and have similar melt temperatures to ensure a strong bond. This is especially important for medical devices that may come into contact with bodily fluids. Conducting an adhesion test before starting the process can help ensure compatibility. It’s also important to consider how the design will work with these two materials, and a good injection molding partner will be able to help you optimize your designs for this particular process.
By following these seven steps and working with an experienced injection molding partner, you can successfully master the two-shot injection molding process and create high-quality, durable, and visually appealing products that meet your specific needs and requirements.
