The process of two-shot molding is outlined as follows, highlighting the intricate steps involved in creating a composite component within a single molding cycle:

Meanwhile, with SLS technology, the most commonly used material is Nylon (PA 11 or PA 12). Since this technique uses a high-powered laser to sinter powder together into a 3D model, both the material and print quality is superior to FDM. Plastic prototypes created via SLS 3D printing are generally more functional, have a higher resolution, and can be more flexible and durable than FDM prints.

Instead of using filament, SLA 3D printing utilize plastic resin materials to create plastic prototypes. The process features a high-powered laser that solidifies the model from a vat of resin. This process is widely used for various prototyping purposes, especially within the medical, dental, and consumer goods space.

Although injection molding and rapid tooling is sometimes used for mass production, it also offers a fast and affordable way to produce plastic prototypes. After creating a metal die, plastic resin is sent into a heated barrel, mixed, and injected with force into a metal die. This plastic is rapidly cooled into a solid part, making a plastic prototype that has a high quality surface finish and better mechanical properties than 3D printing, for example.

Two-shot molding necessitates the use of a specialized two-shot injection molding machine and precisely designed molds. The design of the mold must take into account the flow, cooling, and solidification characteristics of both materials to ensure they combine correctly within the mold. The steps are as follows:

Let’s take a look at how to create a plastic prototype with 3D printing, CNC machining, injection molding and vacuum casting. While each provides its own benefits, knowing the inner workings of the technology, compatible materials and common applications will help you decide which rapid manufacturing technique is best suited for your plastic prototype.

But on the industrial stage, most other 3D printing materials tend to offer more functionality than PLA. For instance, ABS is an ancient material used to create plastic prototypes, and is ideal for functional prototypes that will undergo a fair amount of impact, wear or high temperatures. This material is widely used in the automotive and aerospace industries, and is also well-suited for electronics, consumer goods and more.

Two-shot injection molding, also known as dual-shot or double injection molding, is an efficient injection molding technology that creates composite components made of two different colors or types of plastic materials within a single molding cycle.

Nylon is a material that can be used with both FDM and SLS 3D printing, and is known to be tough and flexible. It’s perfect for functional prototypes, as well as gears and tooling. When you need a plastic prototype that has rubber-like flexibility, TPE and TPU are great 3D printing materials to utilize.  The rubber-like characteristics of this material are beneficial when producing plastic prototypes for protective gear, phone cases, and various industrial components.

Additive manufacturing–more commonly known as 3D printing— is actually a blanket term that encompasses a handful of different manufacturing technologies. The three most popular options for producing plastic prototypes is Fused Deposition Modeling (FDM), Stereolithography (SLA) and Selective Laser Sintering (SLS).

Well, the best time to use 3D printing for your prototyping needs is when you have a small volume that you need produced as quickly as possible. Additive manufacturing helps designers and engineers to cut down on product development time, as they can rapidly iterate their plastic prototype and test or modify the design. However, if you need to produce a large batch of plastic prototypes, or require superior mechanical properties to what 3D printing can offer, there’s likely a more preferable rapid manufacturing technique for you.

Vacuum casting is another manufacturing tool that can be utilized to produce plastic prototypes. This distinct technique is performed in a three-step process, starting with the production of your CAD design into a master model, which can be done with 3D printing or CNC machining. Once the master mold is complete, silicone-based casting molds are developed and filled with casting resins into the cavity of the mold. As for materials, vacuum casting is compatible with an array of materials that range from opaque to transparent, as well as many colors.

Enhanced Product Quality: Two-shot molding can produce more durable, structurally stable products. The integration of two materials can improve overall performance, such as impact resistance and sealing properties.

In nearly every single instance of product development, no matter what industry it’s for, prototyping is a necessary stage that will ultimately determine whether your production efforts will be successful or not. The rise of rapid prototyping has made it both easy and affordable to quickly iterate a plastic prototype. However, there are a range of manufacturing technologies that are capable of producing a plastic prototype, and knowing which one you should use will optimize the entire product development process.

This video shows the trial process of 2-shot molding. Because the product is small and has an undercut feature, it can’t be automatically removed from the mold. It might get stuck on the mold’s lifter, so it needs to be taken out manually.

Mold design is also critical in ensuring a good combination of the two materials. The mold must precisely control the flow path of each material, ensuring that the second material forms a stable and uniform coverage over the first material’s surface.

The mold design and review process must be highly meticulous. Given the high cost of two-shot molds, any flaws in the design could lead to modifications in both sets of molds, thereby incurring additional costs. Therefore, the design stage of the molds must carefully consider various elements, including the design of gates and runners, the arrangement of sliders, and the layout of the cooling system. These aspects require thorough verification and validation to ensure no oversight.

Through the methods and mechanisms described above, two-shot molding can achieve a tight bond between the substrate and the overmolding layer, producing composite material products that are both aesthetically pleasing and high-performing. This technology is widely applied in various fields such as electronic devices, automotive parts, and medical instruments, offering more possibilities for product design and functionality.

Environmental Concerns: Utilizing two distinct materials complicates recycling efforts, as effectively separating these materials can be challenging. The complexity of recycling and the inability to reuse production rejects pose significant challenges for two-shot molding.

In some cases, the substrate’s surface may undergo special treatments such as sandblasting, chemical etching, or surface activation to increase its roughness and chemical reactivity, thereby enhancing the bond strength with the overmolding layer.

Second Injection: After the first part has solidified and been moved to the second position, the second material is injected into the mold through another injection unit, bonding with the first part to form the final product. This step requires precise control to ensure good adhesion between the two materials.

Just as we described with 3D printing, ABS material is great for plastic prototypes that require impact resistance, toughness, and heat resistance. Injection molded PC is completely unique from most other thermoplastics, as it is able to undergo deformation without cracking or breaking, and is best suited for products like eyewear lenses, medical devices and automotive components.

In conclusion, while both two-shot molding and overmolding serve to create composite materials through multiple injection processes, they each offer unique benefits suited to different manufacturing needs.

Each mold can produce around 25 prototypes, and the turnaround time is an average of two weeks. All in all, it’s a quick way to actualize your design into a plastic prototype, pushing the development process closer to mass production.

All in all, finding the right manufacturing technology and material is critically important to the success of your plastic prototype. Our team at 3ERP is more than happy to help you find the right process for you, so contact us today to learn more about our rapid manufacturing services.

This process requires a specialized two-shot injection molding machine equipped with two separate sets of screws and barrels. This technology is capable of producing components with both aesthetic appeal and functional strength, finding widespread applications in the automotive, consumer electronics, and medical equipment industries.

For plastic prototype production, vacuum casting is generally used for small production runs, especially for objects such as casings or housings. This technique is also utilized for visual models or prototypes that don’t serve much of a mechanical purpose. At 3ERP, we offer a wide range of plastic materials for vacuum casting.

If you want to create a colorful prototype that will not serve much of a mechanical purpose, PLA (Polylactic Acid) is an exceptionally diverse and affordable material. It can even be fused with wood and metal composites to conjure up exoctic filaments, and also spliced with mechanically superior materials like carbon fiber to enhance functionality.

Mold Opening and Ejection: After cooling and solidification, the mold is opened, and the finished two-color product is ejected.

Considering the emphasis on production efficiency in two-shot molding, mold designs should aim for automatic degating whenever possible. This means that at the end of the injection molding process, excess material from the injection ports can be automatically removed from the product without manual intervention. This reduces labor costs and enhances production efficiency.

At the interface of the two materials in their molten state, molecular diffusion occurs, meaning molecules from one material penetrate into the other. This helps form stronger chemical bonds and physical entanglements, enhancing the adhesion between the two materials

Cooling and Solidification: Following the injection of the second material, the entire component cools and solidifies within the mold. This stage is critical for the quality of the product, necessitating precise control over cooling speed and time.

The precision of mold alignment is crucial. Two-shot molding employs molds that include two sets of lower molds (moveable) and two sets of upper molds (stationary), which need to rotate or shift during the molding process to align interchangeably. It is essential to ensure that both sets of molds are completely consistent in terms of outer dimensions, internal cavities, and height.

FDM 3D printing uses an extrusion process to deposit plastic material in a layer-by-layer fashion until an object is created. This is the most widely used form of 3D printing, and almost exclusively employed by the maker community and consumers. Industrial-grade FDM 3D printers can be used to manufacture plastic prototypes in high resolution and strength, depending on the material used.

The parameters during the injection molding process, such as temperature, pressure, and cooling time, need careful adjustment to suit the characteristics of both materials. Proper temperature and pressure can promote good material bonding, while the right cooling time ensures that the materials solidify without internal stress, affecting the bond strength.

Increased Production Hourly Rates: Specialized two-shot molding machines are more expensive than standard injection molding machines. Additionally, operating these machines requires specialized skills, contributing to higher hourly rates.

Another fast-paced and viable option for creating functional plastic prototypes is with CNC milling. This technology uses a variety of different sized tools to carve out a 3D model from a solid block of material. Compared to 3D printing, CNC machining offers more potential for threads and undercuts, tight tolerances, reduced size limitations and more surface finishes. Depending on the complexity of the plastic prototype model and the manufacturing service used, CNC milling can also provide extremely quick turnaround times. Learn more about plastic machining prototypes.

In summary, two-shot molding is an advanced injection molding technique that efficiently combines two different materials or colors in a single cycle, offering significant advantages in terms of design flexibility, product quality, and production efficiency. Despite its higher initial investment in mold design and machinery, the technology presents a compelling case for applications requiring complex, multi-material components with high precision and strength.

In two-shot molding, the bonding between the substrate and the overmolding layer is achieved through chemical and physical processes, involving material selection, mold design, and processing conditions. This bonding process ensures that two different materials tightly integrate in the final product, forming a structurally intact and functionally robust composite. Here are several key factors in this bonding process:

Higher Mold Costs: The complex requirements for two-shot molds result in higher costs. Designing and manufacturing these molds demand extensive experience and precision, significantly increasing initial investments compared to traditional molding techniques.

Reduced Production Steps and Costs: This method consolidates the injection of multiple materials into one cycle, eliminating subsequent processes and lowering both production costs and time.

Injection molding remains the most popular method for full-scale production and prototyping, and is widely used across many industries, including consumer electronics, home appliances, medical devices, automotive and aerospace.

Mold Rotation or Shifting: For some two-shot molding processes, the semi-finished product from the first injection needs to be transferred within the mold to a second injection position. This can be achieved by rotating or shifting the mold, depending on the design of the two-shot molding machine used.

Two-shot molding has the distinct advantage of producing complex, high-quality products with diverse appearances in a single molding cycle. It can reduce post-processing steps, enhance production efficiency, and lower costs. However, this technology demands high requirements for mold design and manufacturing, leading to relatively high initial investments.

With injection molding, Nylon is used to produce plastic prototypes that promote stability and resistance to environmental factors like abrasion and chemicals. On the flip side, polyethylene, which comes in the form of HDPE or LDPE, offers a wide range of distinct mechanical properties, including high levels of ductility, tensile strength and resistance to impact and moisture absorption.

This detailed process showcases the technical complexity and precision required in two-shot molding, allowing for the production of high-quality, multifunctional components used across various industries.

Two-shot molding, a sophisticated injection molding technique that simultaneously uses two different materials or colors in the same molding process, demands highly precise molds. Ensuring the success of this process involves strict control over several aspects.

Choosing compatible materials is crucial for a successful bond. The substrate and overmolding materials must be compatible in their molten states without adverse chemical reactions. Material suppliers often provide guidance on which material pairings achieve the best adhesion.

There are a handful of advantages that CNC machining holds over 3D printing technology, one of which is the mechanical quality and available range of thermoplastic materials. Parts that are CNC machined also bestow improved structural integrity upon plastic parts, which is essential when creating functional prototypes. Typically, this production method is used to create plastic prototypes that will be tested under the same conditions as injection molded parts.

Design Flexibility: It allows designers to combine different colors or types of plastics in one component, offering unique visual and tactile qualities.

Other FDM materials include PETG, a thermoplastic that is most commonly used to create water bottles; and Polycarbonate (PC), which is an industrial-grade material that is used to produce plastic prototypes that will be used for engineering applications and face harsh environments.

Typically, a CMM (Coordinate Measuring Machine, a three-dimensional measuring equipment) is used in production to check the precision of the molds, preventing injection molding defects such as flash due to misalignment.

First Injection: The process begins with the injection of the first material into one of the injection units of the molding machine, forming part of the product. Once this step is completed, the partially formed component remains fixed within the mold or is moved to another position through rotation or shifting of the mold.

Some of the most popular plastics used for injection molding are also utilized in 3D printing and CNC machining. These include ABS, PC, Nylon, HIPS, PP, as well as Polyethylene.

While producing injection molding tooling for a small volume of plastic prototypes is generally too expensive, CNC machining allows you to test the form, fit and function of injection molded parts without having to produce injection mold tooling. There are a wide range of plastics that 3ERP offers through our CNC machining service, including ABS, PC, PP, POM, PMMA (Acrylic), HDPE, Teflon, PEEK and many others. To find out which type of material is ideal for your plastic prototype, you can contact our team of experts for more information.

Specialize in CNC machining, 3D printing, urethane casting, rapid tooling, injection molding, metal casting, sheet metal and extrusion

When discussing two-shot molding technology, it’s common to compare it with overmolding. Though these two techniques seem similar in many aspects, involving multiple (two or more) injection molding processes, there are key differences between them.