When producing complex multi-material products, 2 shot injection molding is one of the commonly used and efficient processes.
This technology injects two different colored plastics into the same mold, resulting in a final product that combines the unique properties of both materials.
But how is this process carried out? What are its distinctive technical features? And in which industries is it typically applied?
Let’s explore the secrets of 2 shot injection molding together.
What Is 2 Shot Injection Molding?
2 Shot injection molding (also known as 2k injection molding) involves injecting two different materials, typically plastics of different colors, into the same mold in sequence.
This process creates a multifunctional plastic product with an integrated structure in a single injection molding cycle.
The 2K injection molding technology originated in 1961 when the German company Arburg developed the first two-shot injection molding machine.
However, due to the high cost of early 2 shot machines and the complexity of designing two shot molds, many manufacturers initially used a secondary injection process to achieve dual-material molding.
In the 1990s, Taiwan introduced and applied the two-shot molding process, driving the development and production of two-shot injection molding machines.
Today, 2K injection molding technology is widely used in various industries, including electronics, medical devices, home appliances, and toys, becoming a key process for creating innovative products across many sectors.
How Dose Two Shot Injection Molding Works?
In 2K injection molding, two injection molding machines of the same specifications are typically used alternately to inject molten material.
Through the action of program-controlled valves, two different colored molten materials are injected into the same mold through the nozzle.
To facilitate this process, a rotating core rod is often added to the nozzle, allowing both injection units to simultaneously, with the same amount, pressure, and speed, inject the two different molten materials into the mold, thus creating various unique patterns on the molded product.
Additionally, the molding mold can rotate 180 degrees around a central axis.
This means that after the first injection is completed, the mold rotates 180 degrees before the second injection is performed, resulting in a two color molded product.
For the dual-pattern injection molding process, two barrels are generally used, with a gear mechanism driving the rotating shaft.
This allows different colored molten materials to alternate into the mold cavity, creating a plastic product with radiating patterns of different colors from the center outward.
In the dual color mixing injection molding process, two barrels are also used, each with its own channel connected to the nozzle.
The opening and closing of the valve controls the order and proportion of the molten material entering the nozzle, resulting in various mixed color effects for the molded plastic products.
Features Of Two Shot Injection Molding Process
The main process characteristics of 2 shot injection molding include the following aspects:
Structure of the 2 shot Injection Molding Machine
The 2K injection molding machine consists of two identical plasticizing injection units.
The nozzle design needs to have a special structure according to the production requirements, or be equipped with rotating molds.
During plasticization and injection, the process parameters such as the melt temperature, injection pressure, and melt amount in both units should be consistent, minimizing fluctuations in the process parameters.
Material Selection
Materials with good thermal stability and low melt viscosity are typically chosen to avoid decomposition due to high melt temperatures and prolonged residence time in the flow channel.
Commonly used plastics include polyolefin resins, polystyrene, and ABS.
Process Parameters
In 2 shot injection molding, higher values for melt temperature and injection pressure are required, primarily because the flow channels of 2 shot molds are longer and more complex, resulting in higher flow resistance.
To ensure that the two different colored melts fuse well in the mold and to ensure the quality of the molded product, higher melt temperatures, mold temperatures, injection pressures, and injection speeds must be used.
Mold Design
2 shot injection molding requires a special mold design, which includes a core mold and two cavity molds.
Although two color injection molding is a one shot process, it involves two injections.
The first injection is carried out in the core mold and the first cavity mold.
After the first molding, the part is directly transferred to the second cavity mold for the second injection.
Pros of 2 Shot Molding
Compared to traditional injection molding, two shot injection molding offers several advantages:
Enhanced Aesthetics and Value
It allows for vibrant, contrasting colors, improving the visual appeal and added value of products like electronics, toys, and toothbrushes.
Improved Functionality and Durability
Different plastic materials can enhance product features, such as soft-hard combinations for better user experience, and functions like waterproofing, dustproofing, and anti-slip.
Cost Savings and Efficiency
With two independent injection units, it reduces mold changes and secondary processing time, increasing production efficiency and lowering costs by reducing waste and defects.
Environmental Sustainability
Using recycled materials reduces reliance on virgin plastics, lowers waste, and extends the life of plastics.
Design Flexibility
It provides more creative freedom for product design, allowing customization to meet consumer preferences.
Cons of 2 Shot Molding
Although 2K injection molding technology offers significant advantages in enhancing product aesthetics, functionality, and durability, its high equipment costs and technical challenges are factors that businesses need to carefully consider:
High Equipment Costs
The advanced equipment and technical requirements of 2K injection molding result in high procurement costs, increasing the initial investment burden for manufacturers.
Technical Complexity
This technology demands rigorous mold design and skilled operation. Operators must undergo professional training to achieve proficiency.
Limited Material Options
While recycled and low-viscosity materials can be used, the selection of certain specialized materials may be restricted, potentially impacting specific product performance.
Common Applications Of 2 Shot Injection Moulding
The applications of 2 shot injection molding are incredibly versatile, spanning multiple industries and product categories:
- Electronics: Keyboard keys, phone cases, power switches
- Home Appliances: Refrigerator interior components, washing machine knobs, remote control casings
- Medical Devices: Surgical instrument handles, medical device housings
- Toys: Building blocks, children’s toy cars
- Power Tools: Handles, tool casings
- Automotive Components: Steering wheels and control buttons, interior trims
- Daily Goods: Toothbrushes
What Is The Difference Between Two Shot And Overmolding?
Two-shot injection molding and overmolding are both multi-material injection molding processes, but they differ in terms of process flow, mold requirements, applications, and costs.
Two shot injection molding uses two injection machines or a specialized 2 shot injection molding machine to inject two different materials into the same mold, typically with different colors or functional plastics, to form a structurally integrated, multi-functional product.
This process requires high-end equipment and mold designs and is suitable for products that require different functions or aesthetic designs, such as handles with hard and soft combinations, buttons, and more.
Overmolding, on the other hand, typically uses a single injection machine to first inject a base material (such as hard plastic or metal) and then cover it with a second material (such as soft rubber or plastic).
This process does not require a special two-shot injection machine and has a simpler mold design.
It is suitable for products that only need a soft material added over a hard substrate to enhance comfort or functionality, such as tool handles or waterproof seals for electronic products.
Overall, two-shot injection molding is ideal for applications that require a tight bond between two different materials in the same product, while overmolding focuses more on applying a second material as a cover layer, usually with lower costs and simpler processes.
Development Trend Of 2 Shot Injection Molding
As consumers’ demands for product appearance and personalization continue to rise, the market demand for 2 shot injection molding technology is also steadily increasing, driving the innovation and development of this technology.
In addition to 2 shot molding, the technology has gradually expanded towards multi-color injection molding, with applications now extending to three-color and even four-color injection molding.
Multi color injection molding machines can meet the needs of complex products, achieving high precision molding through multi task rotary tables.
Furthermore, with the advancement of multi functionality, modern multi color injection molding machines can fulfill the production requirements of various products.
For example, in the automotive industry, by optimizing the configuration of injection units, a single multi color injection molding machine can simultaneously produce both front and rear automotive lights.
At the same time, the rapid development of smart manufacturing and digital technologies will promote the close integration of two shot molding with other advanced technologies, such as in-mold labeling (IML) and in-mold assembly (IMA), which will further enhance production efficiency and product value.
In the future, two-shot molding technology will place greater emphasis on environmental sustainability, focusing on reducing the use of chemical agents and energy consumption, thus driving green manufacturing to meet the market’s growing demand for eco-friendly products.
Conclusion
In summary, 2 shot injection molding technology has a promising future in plastic product manufacturing.
It not only enhances product aesthetics and functionality but also meets consumers’ demands for personalized products.
With technological advancements and market expansion, two shot injection molding will play an even greater role in the future.
If you are looking for a reliable two-shot injection molding manufacturer, FOWMOULD is your best choice.
We offer custom two-shot mold design and product manufacturing services.
Contact FOWMOULD today to start your journey into 2 shot injection molding!