Components manufactured using a combination of materials or substrates has become an attractive option and is being used by a variety of industries for applications ranging from sealed connectors in automotive, spray formers in shower heads, and pump housings in medical devices. Multi-material components offer the unique benefit of exhibiting the characteristics of the individual materials, as well as their advantages. In addition to producing a multi-functional component, the process of combining various materials/substrates in a single molding process also offers the OEM benefits such as reduced assembly costs, and superior sealing for improved quality. Design capabilities are also enhanced allowing for complex part geometries and the use of non-plastic substrates.
At its most basic, to produce a multi-material component using the injection molding process, two or more materials, or a material and a substrate are molded together or on top of one another. If properly executed, the result is a strong bond, eliminating the need for primers and adhesives.
Liquid Silicone Rubber (LSR) has increasingly become the preferred material for overmolding or two-shot injection molding with thermoplastics. LSR’s offer numerous advantageous properties, including environmental resistance, electrical insulation and biocompatibility. It can be used for waterproof airtight seals, resistance to shock and vibrations, and comfort for body contact applications.
The three primary injection molding processes used to produce multi-material LSR components are as follows. Each has its own advantages and is the best choice depending on the desired performance characteristics and environmental surroundings of the component:
These processes are explained in further detail below.
What Is LSR Overmolding?
Basic LSR Overmolding incorporates LSR with other substrates, these substrates include plastic components or metal masses. The LSR portion of the multi-material component is molded in or around the completed plastic part or metal substrate during the molding process.
The injection overmolding process works as follows:
- Mold creation: The overmolding process begins with a mold designed and built to produce the LSR component in overmolding. A mold is built for production of the LSR molded part that will surround the metal substrate or completed component. The mold is integral to the process and typically requires the largest capital investment, and accounts for the most time in the total injection molding process.
- Component: During the LSR molding process, the completed plastic part or metal substrate that is to be overmolded with LSR, is positioned within the LSR mold during the molding process.
- LSR injection: Once in place, the mold closes, the LSR is injected into the mold, and the LSR is molded directly onto the part.
Once injected, the LSR bonds to the component, acting as a seal, membrane or dampener.
When Is Overmolding the Right Choice?
Overmolding is the best manufacturing process choice in the following situations:
- Non-plastic substrates: Overmolding is the best choice for any application where LSR needs to be applied to a base component that isn’t made of plastic. In fact, overmolding is the only way to cover non-plastic materials/substrates with an injection-molded material. For example, overmolding is used on metal parts to create ergonomic grips for tools or for a seal.
- Un-matching size/weight: Overmolding is also the best choice for any application where the base component is significantly dissimilar in size and/or weight compared to the LSR component. This is because the base part is placed inside the LSR mold, minimizing spatial limitations.
Benefits of Overmolding
LSR overmolding is a highly versatile process used across various industries and applications. If you’re interested in pursuing an overmolding project, you can look forward to the following potential benefits:
- Functional Integration: Overmolding LSR allows the combining of the mechanical properties of a rigid substrate with the sealing, cushioning, or biocompatibility properties of LSR.
- Improved Sealing: Overmolding allows for bonding to the metal/plastic for better sealing and secures seals in place preventing seal displacement or seal roll-over quality issues downstream.
- Cost Savings: Reduced overall manufacturing time, improved quality and performance all contribute to improved cost efficiency and product performance. OEMs can increase output and efficiency, with reduced material and less waste, and reduce the opportunities for errors and quality problems later on.
For these reasons, many manufacturers across a range of industries and applications use overmolding. From overmolded handles on tools to sealing membranes, overmolding has a range of potential uses.
Two Shot Molding
What Is Two-Shot LSR Injection Molding?
Another molding technology utilized to produce multi-material components is two-shot molding. Also called twin shot or 2k injection molding, this process involves molding two materials in the same machine at the same time. For true two-shot LSR molding, an injection molding machine equipped with two injection units is required allowing two materials to be injected into the molds during the same molding cycle. Usually, these materials are an LSR and a thermoplastic, or two LSRs that are different grades, durometers or colors.
The process works as follows:
- Mold creation: In two-shot injection molding, a mold is designed and built for each of the materials and run in the same machine in the same process.
- Material injection: The first material is injected into the appropriate mold cavities and the molded part is robotically rotated or transferred to the LSR mold cavities.
- Secondary material injection: Once the first material component is molded and precisely placed, the second material is injected into the mold and encapsulates the mating part.
The result is a multi-substrate, multi-functional component with an exceptionally strong bond.
When Is True, Two-Shot the Best Choice?
LSR two-shot injection molding is suited for components comprised of LSRs and injection moldable plastics (usually engineered plastics), and when the individual parts are similar in weight/volume and relative size. The following are other guidelines to look for to determine if true two-shot molding is the best choice:
- Compatible materials: Two-shot injection molding is the best option when the two materials in the product are compatible from a processing standpoint and adhesion/bonding perspective. For example, a combination of different LSR grades, or an LSR with a plastic material that has a heat deflection > 150°C, and that is not inherently resistant to adhesion.
- High precision applications: When precise, accurate placement of the LSR on the other substrate is critical, two-shot injection molding is ideal and preferred.
- Strong seals: A true two-shot injection molding process molds both materials in the same process for excellent chemical and physical bonding, resulting in superior sealing performance.
- Intricate designs: Two-shot injection molding can handle more complex geometries, making it the best choice for parts with intricate thin membranes or seals.
Benefits of True Two-Shot Molding
The two-shot molding process can have many benefits when making various components. These potential benefits include:
- Time savings: True two-shot injection molding is accomplished in one machine cycle. This makes it a very quick and easy process, even for complex parts. The multi-material component is completed in one process and eliminates the need to perform surface activation or post-mold assembly operations. Therefore, lead and running times are significantly reduced in the manufacturing process.
- Improved integrity: Two-shot injection molding creates better bonds between the mating surfaces. This means that the materials create a stronger, tighter seal without the need for adhesives, primers, gaskets or other components. As a result, two-shot injection molded components exhibit exceptional watertight seals and integrity in various environmental conditions.
- Tight tolerances: Like overmolding, two-shot injection molding is accomplished through automation, which allows for extremely tight tolerances. This makes it a good choice for applications that require precision or involve complex geometries.
- Design flexibility: Two-shot injection molding can be used in a range of applications and allows for complex part geometries. The result is a component with excellent performance and part weight optimization.
- Reduced flash: Flash is a common problem in injection molding processes. Flash is the excess material remaining around a component after molding. Usually, this is the result of space between mating mold surfaces. Two-shot injection molding results in less flash due to the defined cavity-to-cavity designation from thermoplastic to LSR.
- Improved seals: Two-shot injection molded seals are extremely high quality. Because the LSR is bonded to the plastic in a two-shot process, seal roll-over or displacement common with secondary loose-piece assembly is eliminated. True two-shot molding also can achieve intricate, very thin seals or membranes on 3D sealing surfaces.
- Material Optimization: The two-shot process allows for sealing only in targeted areas, optimizing material usage and resulting in delicate yet optimized seals.
- Reduced costs: High product quality, tight tolerances and the streamlining of production reduces qualification and inspection costs of multiple components and numerous processes. In addition, automated production and reduced running time also contributes to improved overall costs, reduced labor costs, and increased production capabilities overall.
True two-shot molding is an attractive option for any application that involves two compatible materials and can be further optimized by working with an experienced two-shot and multi-shot provider like SIMTEC Silicone Parts.
True, two-shot molding and overmolding are both good choices and best depending on the materials and application. If you have multiple mating materials and components however, multi-shot molding may be your best option.
What Is Multi-Shot Injection Molding?
Multi-shot molding is a hybrid of overmolding and two-shot molding with numerous variations. As is the case with true two-shot molding, in true multi-shot injection molding, all components are molded and integrated in the same machine, process and cycle.
The process works like this:
- Mold creation: Like the other processes, the molds need to be created first. Like two-shot molding, two molds are needed for this process.
- Component placement: The substrate or material, whether plastic or metal, is placed in the first mold.
- First material injection: Once the substrate is accurately positioned, the first material is injected into the mold.
- Secondary material injection: Immediately after the first injection, the overmolded component is transferred to the second mold. Once accurately placed, with precise cavity-to-cavity alignment, the second material is injected into the mold integrating with the first overmolded component.
For the multi-material (metal, plastic, LSR) component in the example shown at right, the plastic outer frame and center piston are overmolded around the metal mass insert. This overmolded plastic/metal component is then transferred to the LSR mold in the same molding machine for the molding of the LSR bellow – all in the same cycle.
Multi-shot injection molding is the best option when combining multiple materials, and to take advantage of the two-shot molding benefits.
Why Choose SIMTEC?
Whether it’s overmolding, true two-shot or true multi-shot injection molding, you need a supply partner with a knowledgeable team, advanced technology, and molding equipment to get it done right.
SIMTEC is a leader in LSR two-shot and multi-shot injection molding. We offer LSR injection molded solutions, relying on our knowledge and experience, advanced technology, and molding expertise.
On top of our continued dedication to our work, there are several factors that make us the best in the industry:
- Convenient location: Based in Miramar, Florida, we are conveniently located near major air, sea, rail and highway shipping routes. As a member of the European-based RICO Group, we have the added strength and resources of our sister companies, and an expanded global footprint to meet European market requirements.
- Extensive experience: SIMTEC has over nearly 20 years of experience with LSR components used in a wide range of industries and applications, allowing us to work with some of the best companies in the world in the automotive, medical, life sciences, technology and consumer goods industries.
- Advanced technology: SIMTEC has the technologically-advanced production capabilities to meet our customers’ most challenging needs. Our LSR, overmolding, two-shot and multi-shot molding technology are guided by our ISO certified practices to meet your exact specifications. Our uniquely designed smart Class 8 clean room meets the needs of our customers’ medical devices and other hygienic part requirements.
- Customer-focused team: We offer value-added services at each stage of the process. From design support, engineering and customer service, through production, packaging and delivery, our team will work with you every step of the way.
With our combined capabilities, service, experience and outstanding quality, SIMTEC is undeniably your ideal partner for your LSR projects.
To discuss your single- or multi-material LSR component requirement, contact SIMTEC today.