Silicone Overmolding | LSR Overmolding
Silicone Overmolding known as rubber overmoulding and Liquid Silicone Overmolding & LSR Overmolding, which is the process of molded & bonded plastic, metal (Aluminum, Steel, Brass), glass or electronic parts (PCB circuit board) to silicone rubber or liquid silicone （LSR） with the assistance of bonding adhesive or glue through overmolding into a finished part. Bonded plastic or metal substrates act as the first parts that are put into additional silicone molded chamber for a second-shot overmolded with silicone rubber or liquid silicone. Silicone Rubber & LSR material then cover or wrap on the plastic or metal, which should be high temperature resistant materials, generally above 120oC. More high-temperature plastic material information, please click the link: silicone plastic overmolding
Liquid Silicone Overmolding Design Guide
In liquid silicone to plastic & metal overmolding, plastic & metal pieces should be coated with primer (glue / bonding agent) first before overmolding, for a stronger bonding between substrates with rubber elastomer.
Without glue on metal or plastic substrates, liquid silicone rubber can not be overmolded with substrates tightly. Metal and plastic parts will be easily taken apart from the elastomer.
1) Before coating primer (glue), remember to clean metal & plastic parts to remove dirts, grease or other contaminations.
2) After applying glue to metal & plastic substrates, drying them in room temperature.
For products with high quality requirements, we need to post cure them in oven under specific temperature.
In liquid silicone injection overmolding to plastic, we need pay attention to plastic substrates geometry design, for a good sealing but without burrs (flash).
For example, when we overmold a plastic buckle to silicone band, this plastic buckle should be carefully designed, in order to create a sealing surface to stop silicone flowing to other area, and prevent flash around the joint lines between plastic parts and silicone elastomer.
We add steps to the two buckles. The steps create a sealing boundary to stop silicone flowing here, and prevent flashing (burrs) arond the round steps.
Before silicone overmolding, plastic buckles are covered with silicone caps, just like below picture. The silicone caps help plastic buckles firmly fix into mold cavities, and avoid movement during overmolding.
Plastic heat resistance should also be considered in rubber to plastic overmolding. LSR injection molding curing temperature is at least 120 °C, and compression molding lowest temperature for low-temperature-curing silicone is 135 °C.
Thus, plastic substrates heat resistance should be higher than overmolding curing temperature, otherwise plastic parts will deform in overmolding process.
Liquid Silicone Overmolding Manafacturing Process
LSR Overmolding & Liquid Silicone Rubber Injection Overmolding Manufacturing Process
Silicone Transfer Overmolding Manufacturing Process
Silicone Rubber Compression Overmolding Manufacturing Process
Rubber Injection Overmolding Process
Liquid Silicone Overmolding
include PC, PPSU, PA+GF, and PBT etc, all of which are high-temperature resistant thermoplastic material. And common subsequent materials is silicone (High-temperature silicone or low-temperature silicone ) or liquid silicone rubber (LSR). Compared with assembled or adhesive rubber to plastic parts, overmolded rubber plastic parts are more robust.
Steel, brass, aluminum, or plastic
also known as rubber overmolding or two-shot injection moulding, in-mold assembly, LSR Overmolding, Liquid Silicone Overmolding, Rubber Overmolding, Overmolding Silicone Onto Silicone, which is an injection molding process that molds silicone over, under, or through a substrate material (silicone, plastic, metal, glass and so on), and which combines the best of two materials to complete the final part. LSR Overmolding is widely used in healthcare, infant care, high precision sealing gasket, automotive and medical industries.
There are two ways to achieve Silicone overmolding: multi-shot molding or insert molding. With double-shot molding, the first material shot is the substrate and the second is the overmold. A press with multiple barrels shoots two different resins into the same injection molding tool. The entire operation uses one machine in a continuous process, but double-shot molding is better-suited for larger volumes since the molds and machinery are more expensive.
What is Insert molding? Usually will place the substrate (metal, plastic, glass and so on) into the mold and then overmolding some or all of the part. In order to achieve optimum bond strength, we will preheat the insert part to make its surface temperature closer to the melt temperature of the overmold. And we will also add a coating on the surface of the insert part to make sure silicone will overmold well. Across lower volumes, insert molding is more cost-effective than double-shot molding; however, insert molding requires a tool for the substrate and a different core and cavity to create the volume for the overmolded material.
Liquid Silicone Overmolding's Advantages:
Saving tiem and cost—By silicone overmolding, silicone directly onto a metal or plastic substrate, we can save the manually assemble cost and time. Silicone Rubber Overmolding can dramatically reduce your manufacturing costs and turnaround time, allowing you to get your product to market more economically.
Suitable for Complicated Design Structure——Liquid Silicone/thermoplastic injection molding can meeet the complex design requirements of the automotive and medical industries. Silicone rubber overmolding produces parts that are waterproof, airtight, and more resistant to shock and vibrations.
Good Quality control——LSR/plastic injection overmolding process can meet high tolerance and pass strict quality control, making it suitable for use in any application where precision is required.