The plastic injection molding technology has developed significantly since its beginning. It has grown significantly in terms of productivity and cost-effectiveness, as well as new and creative approaches to product manufacturing. Two-shot injection molding is one of these creative processes. Multi-material, two-material, two-color, 2k or double-shot injection molding are some other names for this process. It can be adaptable to produce complex design out of a variety of materials. Two-shot injection molding is a cutting-edge plastic manufacturing technique to achieve high quality of products.
A description of the two-shot injection molding process
As the name implies, two injection shots are used in this process rather of simply one as in conventional injection molding. This process makes use of a unique mold that meets the needs of these two shots. The mold and the supporting system that are made to perform two shots without discharging the first molded part from the mold in between steps.
Just like regular injection molding, the process begins with the mold sealing to create the first cavity. In this initial configuration, the secondary step’s runner is sealed off while the runner for the first cavity is aligned with the base material’s sprue. The first melt plastic is then injected and filled the first cavity. Following the first step, the mold opens and the core half holding the first molded part rotates 180 degrees on a horizontal axis to line up with the sprue for second injection. Under this stage the first cavity is isolated from any injection, and the second shot now starts molding the remaining portion of the product, as the sprue of the second material is now in line with the runner for the second cavity.
In two shots injection molding, two separate materials are injected into the same mold to create the product. These materials are injected in succession rather than simultaneously. The first molded part is not discharged from the mold in between the two shots, but it is over-molded in the second step. The second shot covers the first shot that has solidified. The substrate is created by the first shot, while the over-molding is created by the second shot. Typically, a new material is shot in the second shot over the first shot of the filled mold. For example, the substrate material of first shot is thermoplastic, and then the over-molding can be thermoplastic or thermoset elastomer.
Two-Shot Injection Molding is used to create complicated molded parts from two different materials. With highly specialized and automated process, we control the injection of two different resins, out of multiple hard and soft materials, into a single or multi-cavity mold. Two-shot molding has somewhat high initial costs because the transfer between molds is frequently carried out by a rotary platen, robotic arm, slide, or some other type of specialist equipment. However, the procedure is mainly automated once set up, which makes two-shot molding particularly economical for the manufacturing of large volume of parts.
The many applications of two-shot injection molding
- Power Tools
Two shot injection molding works well for Power Tool Handle and Housing due to the desirable properties of plastic in an acoustic or vibration dampening environment. Hard-wearing base areas can be combined with softer seal surfaces.
- Personal Care Products
Items such as electric tooth-brush, face cleaner and shaver can be perfectly molded with two-shot molding. A rigid base plastic can be combined with a softer rubber second shot for better grip and coloration.
- Consumer products
Plastic consumer products with LED incorporated into the design can be effectively produced with two-shot molding. A translucent insert can be molded into the design to spread or colour the LED light.
- Medical equipment
Medical equipment such as bone saws can be manufactured using two-shot molding. Rubber grips are very important in the function of this equipment. Two-shot molded items also improve hygiene as there are fewer crevices where sub-parts interface, as compared to conventionally assembled items.
- Containers and Bottles
Plastic storage containers and Bottles can be manufactured with this process. Different colours can be added, along with silicone rubber edges to seal lids, or soft container surfaces to protect contents.
- Toys
Plastic toys lead themselves especially well to this process, rigid parts with soft grips, flexible hinges or movable segments. Multiple colors and textures can be molded into the fun playing items.
The benefits of two-shot injection molding
1.Lower unit cost
Two shot injection molding excels in this situation. A production line can now produce more complicated goods with fewer steps than ever before thanks to two-shot molding. Think about the conventional injection molding process that two different materials would have needed to be molded separately in two different molds, followed by a manual assembly phase, if a certain product was to be made of those materials. With two-shot injection molding, these two components are fused together as well as formed in a single mold setup, doing away with the need for any assembly. Also reduces cost and waste associated with assembly defects.
2. Improved mechanical bond
Two shot injection molded products have excellent mechanical characteristics. Assuming good materials are applied, different levels of the product form a molecular bond in the molding process. It is often that this bond is more durable than conventional molding and assembly, and also stronger than other advanced injection techniques like over-molding and insert molding.
3. Multi-material efficiency
The best utilization of multiple materials can be realized through the application of two shot molding. Engineering plastics may have a wide range of beneficial yet quite distinctive properties. To accomplish the desirable outcomes, the designer can combine the good structural qualities of a hard plastic with the soft and appealing nature of a different material.
4. Higher quality plastic part fabrication
Two-shot molding offers exceptionally precision manufacturing compared to conventional molding and assembly. There is no possibility of material misalignment because the semi-finished product does not need to be removed from the mold between steps. The finished product can be just as accurate as the mold itself if thermal impacts are appropriately managed through proper product design.
5. Reduced production time
The reduction in production time is a crucial advantage of two shot injection molding. There is frequently no need to perform secondary assembly of the item because multiple levels of a product can be added during this operation. All that conventional injection molding would require a secondary step in manufacturing can now be done in one combined molding process.
6. Aesthetics
Products made by a two-shot molding can have good-looking while maintaining the necessary structural characteristics. The load-bearing structural component can be molded in the first step of this process, and the finishing touches can be applied in the second step using a more appealing material.
7. Ergonomics
Two-shot injection molding is a process that is ideal for producing goods that are ergonomically designed. It is simple to cover or add to structural plastic with materials that are more suited for human interface, especially silicone rubber material offers a greater grip and a gentler and softer touch.
General considerations for two-shot injection molding
Both two-shot injection molding and over-molding, when done correctly, benefit from the chemical bonds that develop between the materials as the part cools. For these bonds to form, the two materials need to compatible with each other. However, two-shot molding material compatibility refers to how stable the two materials are when they come in contact. If contact results in a chemical reaction, no matter how small, such two materials cannot be used together.
The molding sequence of the two shots is another critical factor that should be taken into account. The more rigid of the two materials should typically be injected first, so as to create the substrate for the second material. In other words, the second shot runs the risk of deforming the entire part if the material with the higher melting temperature is not injected first. For the same reason, transparent materials should be injected first when a component contains both opaque and transparent parts. Additionally, the shrinkage rate for each material must be considered, because uneven shrinkage might result in flash or wrapping defects during the production and cooling process.
An improved step over the conventional injection molding process is the two-shot injection molding. No surprise that some products can be made successfully without two-shot injection molding. The following factors can be thought about to help determine whether two-shot molding is the best option.
- Is there more than one part to the product?
- Can the product’s components be formed in a single mold?
- Does the product require the use of multiple materials?
- Can the product be injection molded using both materials?
- Will the components remain combination after molding?
- Is the softening temperature of the substrate higher than that of the overmolding?
Conclusion
Two-shot injection molding does not require several manufacturing steps, so it gives designers more freedom. It offers molding manufacturers a number of benefits, including reduced manufacturing costs, improved ergonomics and aesthetics, superior mechanical bonding, and quicker production times. This process can be used to produce a wide range of products, including power tools, personal care products, medical equipments, containers & bottles, and toys and etc.
Collaborating with a professional plastic molding team with the technical knowledge and expertise to master the two-shot injection molding process, such as GEMS Manufacturing Ltd, can be a game-changer for clients in all industries. If you are looking for a trusted, experienced plastic injection molder to handle your products, reach out to GEMS today, or visit our website for a full view of GEMS-MFG Capabilities.