Plastic syringes, bone saws, and rubber grips are among many products that use the two-shot injection molding process for accuracy and precision. This also helps reduce production time and costs by eliminating multiple molding and assembly operations.

Choosing the right materials is crucial to ensure that they can effectively bond with each other when injected sequentially. It is necessary to have a high-level chemical bond as well as a mechanical one.

High Design Range

Two-shot injection molding allows designers and manufacturers to create more complex products that incorporate multiple materials and integrated features. The process also provides a more attractive and classic look for products that are made with the method. Additionally, it allows for soft-touch layers over rigid components to add comfort and aesthetic qualities. This is especially important for plastic electronics such as LED’s and medical equipment that require rubber grips, for example.

The two-shot process utilizes a substrate base and an overmold that is formed with a pliable material such as thermoplastic elastomer (TPE) or liquid silicone rubber (LSR). During the first shot, the raw materials are injected into the tool to form a substrate base. After solidifying, the substrate is transferred either manually, robotically or via a rotary plane to a second cavity in the same tool to allow another resin to be injected to overmold it.

Both shots of the product must be molded with high precision to ensure that the second shot adheres properly to the substrate and that there are no gaps or crevices where one of the shots is not firmly attached to the other. This requires proper draft angles, precise injection timing and sequencing, and good cooling of both the injected materials and the mold.

Additionally, the chemistry of the materials must be taken into consideration. While some materials will establish a compelling molecular bond, others may not. This is why it’s crucial to choose the right materials for two-shot injection molding.

High Precision

With the help of two-shot injection molding, manufacturers can easily incorporate both soft and hard plastic polymers into one product design. This allows them to add more texture, color and comfort to products such as toothbrush handles, buttons, switches and caps/closures and hand and power tools. In addition, the use of multiple materials can improve the ergonomics of these products by reducing (or eliminating) gaps and crevices where sub-parts interface with each other.

The 2 shot injection process can be accomplished with either a rotating platen, or two separate injection units that integrate into the same machine. In either case, the different injection processes are synchronized to a specific sequence. In most cases, the first injection is of the more rigid of the two materials. In other cases, the more transparent material is injected first. Regardless of which option is used, the molding process must be designed to ensure that both shots are produced without damage and that the injected materials are compatible with each other.

The key to ensuring compatibility is that the injection unit for the first step must be able to rotate. Additionally, the runner for the second injection must be in line with the runner for the first cavity. This prevents the product from being removed or shifted during the process, eliminating post-process defects caused by irregular cooling. In addition, it’s essential that the mold be sized to ensure accurate and thorough flow of the second injection. For this reason, it’s important to run a flow simulation before building the mold. This will provide valuable information such as injection rates, pressures and temperatures to ensure the desired result. This will also help identify any areas where the adhesion between the two materials may be compromised due to factors such as temperature, chemical interaction and injection speed.

High Durability

With tighter tolerances and a high level of accuracy and repeatability, 2 shot plastic injection molding offers greater functionality. It also eliminates the need for secondary processes like sonic welding or assembly, which saves you time and money. In fact, using this process can save you tens of thousands in development, engineering, prototyping and production costs – with this 2 shot injection molding guide being great for additional reference as well.

It also allows for complex mold designs that integrate multiple materials to achieve functionality that cannot be achieved through older molding processes. For example, molded graphics enhance product aesthetics, and soft-touch layers over rigid components can add comfort while improving functionality. This is commonly seen in power tools and electric toothbrush handles for instance, as well as medical equipment.

A key factor to consider when incorporating two-shot injection molding into your project is the chemical compatibility of your two compounding materials. The chemistry of your materials should complement one another, establishing powerful molecular adhesion. This allows for the use of two different colors and plastic resins, or hard and soft components, as part of a single product design.

Two-shot injection molding is also ideal for applications requiring a more durable substrate base with a softer overmold layer. This is commonly seen in power tools and electrical appliances, or in medical devices such as syringes and bone saws. The overmold layer may be made from a softer thermoplastic elastomer or liquid silicone rubber, which is injected into the first cavity of the mold, with the tougher substrate base molded at a separate station in the same tool. For optimal results, your supplier should use an indexing system with primary and secondary injection stations to control the temperature of the first shot.

High Functionality

Two-shot injection molding is a process that allows for multiple different materials to be used in the same part. This can be useful for a wide range of applications, from consumer goods to industrial products and automotive parts. It enables the creation of many innovative and highly functional products, including handles that combine hard plastic with soft grips, flexible hinges, and movable segments. It can also be utilized to create a variety of aesthetic features, including different colors, textures, and designs.

To achieve this, a two-shot injection mold has to be carefully engineered. The first step is to inject a base material in the shape of a substrate part. This can be done using a thermoplastic, a thermoset plastic, or liquid silicone rubber (LSR). The next step is to overmold this with the second material. This can be done using a robot or by rotating the part 180 degrees and then inserting it into a different cavity of the injection mold.

The key is to ensure that both shots are injected in the correct sequence and that each shot’s injection time is synchronized with the other. The timing is important to avoid overlapping the two shots and potentially deforming the finished product. The substrate and overmold materials should be matched in terms of their shrinkage rates as well.

It is important to work with a supplier that understands the complexity of this process and has a solid track record in manufacturing complex multi-resin components. They should have supplier quality scorecards and defined processes to mitigate against flash lines, short shots, and other defects. In addition, they should be able to offer contingency plans to expand capacity as your production needs grow.

Low Cost

Two-shot injection molding is a cost-effective option for many manufacturing and industrial applications. It allows for greater design flexibility, as well as the ability to produce complex parts that can’t be molded using other methods. This can help companies reduce their overall production costs by eliminating the need for secondary processes such as sonic welding or assembly.

In addition, the use of the two-shot process can help manufacturers create innovative products that utilize multiple different materials and colors. This can be an effective solution for a variety of industries and product types, including medical equipment, consumer electronics, and hand or power tools. For example, a toothbrush handle can be molded from both hard plastic and soft rubber, providing a more comfortable grip and ensuring that the product is safe for children.

The process is also relatively easy to set up and operate. It typically involves a rotating platen, robot arm, or slide that moves the molded substrate between two separate molds. The second mold then injects a secondary resin or color into, through, around, or on the substrate to form a chemical bond and complete the final molded part. The resulting multi-resin product is then cooled and ejected from the mold.

When considering a two-shot molding project, it’s important to work with an experienced and vetted supplier that understands the nuances of the process. This will ensure that the specialized material combinations are compatible and can be produced successfully without any potential problems such as short shots, flash, or inconsistent color distribution. It’s also vital to choose a partner that has defined quality standards and processes to mitigate issues like these before they can affect production.

In conclusion, two-shot injection molding is a versatile and cost-effective process that offers numerous benefits for product designers and manufacturers. By allowing for the integration of multiple materials and colors into a single part, it enables the creation of highly functional and aesthetically pleasing products. With careful engineering and the right supplier partnership, two-shot injection molding can help companies reduce costs, improve product performance, and stand out in a competitive marketplace.