If you are looking for a way to reduce assembly steps and improve products sealing performance with lower long-term costs, the silicone multi-shot injection molding is your best choice. Not only does this technology combine hard plastic with liquid silicone rubber, but also shows unparalleled strengths.
4 Types of Multi-Shot Molding
2-Shot(2K) Molding
2-shot molding, also called two-component injection molding, is the most common craftsmanship you will encounter. It should be equipped with a special injection molding machine of two independent injection units. Through the rotation of a turntable within the mold or the positioning of a robotic arm, the base material and liquid silicone rubber are injected into the molding machine sequentially.
Overmolding
If your project is concerned with different materials such as stainless or aluminum alloy, you might prefer this type. It is a step-by-step manufacturing process, commonly referred to as two-step molding. Firstly, the base material is produced on the conventional injection molding machine. After that, these preforms are inserted as inserts into a separate silicone mold for secondary injection molding.
Compared with 2-shot molding, it imposes lower requirements on injection molding machines and enables the bonding of silicone with dissimilar materials such as stainless steel or aluminum alloy.
Co-Injection Molding
In this type, two materials are injected into the same mold cavity sequentially or simultaneously through a specialized composite nozzle. The first material is injected into the mold walls, which can form into the layer of the product’s outer shell. The second one is subsequently injected to fill the interior. It is an ideal choice if you want a product with high-quality surface but a different core material for structural support.
Multi-Component Molding
As the highest level of molding technology, multi-component molding usually involves the composite molding of three or more materials. It requires complex mold structure design, utilizing multi-stage turntables or intricate slider mechanisms to integrate materials of different colors, hardness and transparencies within a single operation.
Process of the Technology
As a high-intensity working procedure, the silicone multi-shot injection molding is meant to improve your product consistency by reducing the process of manufacture.
The first step is to inject the base material into the mold cavity. This material is usually a grid thermoplastic plastic, requiring exact time for cooling to keep its shape stable after injection. Immediately following, the second material would be injected into the base material or around that in the same injection cycle, which can form into the strong bond at the interface between them by precisely controlling the pressure and mold temperature.
The key advantage of the molding process lies in its execution within a single mold, ensuring the extremely tight tolerance between the components, avoiding many common errors in the traditional multi-step manufacturing.
Six Core Benefits
High Productivity
Instead of adopting a multi-step process, the silicone multi-shot injection molding merges independent manufacturing processes into a single production cycle, making multiple materials complete processing in the same molding opening and closing. It can not only cut significantly the turnaround time, but also increases the output per unit of the production line.
Material Compatity
Due to the strict insolation condition every material keeps before injection, this craftsmanship avoids the prior interference between materials. With the best combination of precise temperature control during the molding process, multi-shot injection molding can effectively solve the conflicts between dissimilar materials, ensuring the stability in material integration.
Consistency in Appearance and Color
You can achieve a perfect look without secondary painting or coating. This process directly uses the master color in production molding, which reduces the risk of coating peeling and ensures the color consistency in every batch you produce during the high-volume production.
Excellent Lifespan
This integrated molding creates strong physical or chemical bonds at the material interfaces. Compared with traditional adhesive bonding or mechanical fastening with rivets, multi-shot molding integrates different materials directly during production and can reduce secondary assembly steps.
Physical Strengths
By combining the strength of base material and flexibility of liquid silicone rubber, the product gains multiple performance enhancements. What’s more, the layer of silicone rubber can provide your products with excellent sealing properties, resistance to temperature as well as biocompatibility meeting medical standards.
Cost-effective
The technology eliminates your need for manual assembly by achieving integrated molding of components. It not only reduces the labor costs but also minimizes your investment in assembly fixtures and reduces secondary defect rates caused by manual operations.
Typical Applications
Electronic Industry
In the competitive electronics market , you can create products that are both durable and aesthetically pleasing by using the seamless bond between the soft rubber and the rigid frame. Whether you are designing for manufacturing smartphone cases with IP68 waterproof ratings, skin-friendly straps for wearable devices or sealed connectors with high-precision, this process can ensure your components are robust for daily use.
Medical Industry
Due to biocompatibility of liquid silicone rubber, multi-shit injection is widely applied in productions such as handles for surgical instruments, soft sealing edges for respiratory masks and check valves for liquid delivery systems, meeting stringent requirements for clean production and function integration. It is ideal if you need to combine multiple materials into a single sterilized component with no microscopic gaps for bacterial growth, ultimately enhancing the safety and reliability of your medical devices.
Automotive Industry
This technology can also be widely used in the automotive industry. If you want to produce multi-color interiors, shock-absorbing gaskets and dashboard buttons with precise tactile feedback, you can take it into consideration. It can make sure the components maintain exceptional sealing performance under extreme temperature. Also, it is beneficial to reduce the noise, vibration and harshness(NVH) during the vehicle operation.
Furthermore, with the growing adoption of smart cockpit concepts, this integrated molding technology is also being utilized to incorporate complex electronic touch interfaces, thereby enhancing the overall technological sophistication and structural durability of cockpit designs.
Consumer Goods
In the consumer goods market, it is commonly used for baby bottle components, handles of high-end kitchenware and the non-slip grips of electronic toothbrushes. This technology achieves the combination between rigid structural support and soft tactility, significantly improving the products’ handling feel and ergonomic design.
In addition, due to no gaps between silicone layer and plastic base material, the surface of the products not only resists dirt accumulation but also reduces the risk of coating peeling associated with traditional methods, which significantly improve the safety standard. If you need hygiene levels of baby products and home goods, it is a great choice.
Common Failures: What you should Watch Out For
Delamination
If you notice the separation of silicone from the substrate at the bonding interface, please check that. This typically occurs due to contamination on the substrate surface, insufficient mold temperature, or mismatched polarity between the two materials, leading to failure of the chemical bond.
Air Burns
When the gases inside the mold cavity were trapped and cannot be vented promptly, high pressure would lead to localized overheating, resulting in scorched marks on the silicone surface. It is advisable to optimize the mold venting system and adjust the injection speed.
Flash
Due to its low viscosity, it is easier for liquid silicone rubber to bleed out from molding parting lines or insert gaps. In order to resolve this issue, you must maintain precise control of clamping pressure and mold machining precision to prevent material bleeding out.
FAQs
Q: What’s the difference between 2-shot molding and overmolding?
A: The core distinction lies in the production efficiency and bonding strength. The former is completed in the same mold and cycle. By using residual heat from the substrate, it achieves molecular-level bonding, which is suitable for high-precision mass production. The overmolding is a two-step process, typically used to encapsulate silicone around metal or preformed plastic components. It offers greater flexibility but demands extremely precise molds to prevent flash.
Q: How to ensure the adhesion of silicone rubber and plastic without using primer?
A: There are two methods mainly used to achieve strong adhesion. One is to choose the self-adhesive LSR, and the other one can achieve mechanical locking by designing the physical interlocking structures such as dovetail grooves or through-holes.
Q: Does this technology comply with the biocompatibility standard of medical devices?
A: Of course. Mult-shot injection molding usually complies with ISO 10993 and medical LSR with FDA standard. Due to its fully automated process, it can efficiently decrease the risk of contamination, making it an ideal manufacturing method for surgical instrument handles and respiratory masks.
Q: Which thermoplastics are suitable for multi-material injection molding with liquid silicone rubber (LSR)?
In multi-material injection molding, polycarbonate (PC), polyamide (PA/Nylon), and polybutylene terephthalate (PBT) are the most ideal base materials. The reason is that these materials possess high heat deflection temperatures, enabling them to withstand the elevated temperatures required for LSR vulcanization, and they form excellent chemical bonds with self-adhesive silicone.
Q: How to prevent thermal deformation of the substrate in the mult-shot injection molding?
A: The key is to keep a balance between curing temperature of LSR and the softening point of substrate. Specifically, it is useful to avoid part deformation by optimizing the mold cooling system or selecting high-heat-resistant engineering plastics such as PEEK or reinforced PA.
Q: Will silicone multi-shot injection molding parts be recycled?
A: It is still a challenge because silicone is a thermosetting material which cannot be remelted once vulcanized. However, it can achieve partial recycling of the plastic substrate through the design for disassembly in the initial design phase or by physically separating the substrate from the silicone.
Final Thoughts
If you are seeking to enhance product reliability or optimize production solutions for complex parts, please contact our experts. As a manufacturer who supplies custom silicone products, Legensilico can provide professional manufacturability assessments, enabling you to transform your innovative design concepts into high-quality products.
