Silicone Rubber Overmolding
Silicone Rubber Overmolding, also known as Medical Silicone Overmolding, Rubber Metal Bonding & Plastic Insert Molding, LSR overmolding & liquid silicone overmolding. Silicone Rubber Overmolding is a process to overmold silicone rubber onto a wide variety of thermoplastics, metals, glass, electronics and other substrates to complete the final parts. With silicone overmolding, look, functionality, and bond strength of final products can be improved while saving production time and reduce production cost.
Silicone Overmolding Types:
Liquid Silicone Rubber Overmolding to Plastics
Liquid Silicone Rubber Overmolding to Metals
Elastomers Overmolding to Thermoplastics
Insert Overmoding & Rubber Metal Bonding
Liquid Silicone Rubber Overmolding Design Guide & Tips
Select materials properly
The typical silicone curing temperature is from 170℃ to 220℃. At a first pass, the over-molded part must be able to withstand the silicone curing temperature.
Thermoplastics–Plastic components are common as a base substrate. It should be noted that many plastic substrates have low softening and melting temperatures, which are not rigid enough to overmold silicone using standard processes. It is best to select a substrate material with a softening temperature above 170℃. Such as PBT, PPS.
We have developed processes for specialty liquid silicone overmolding at low temperatures in order to support temperature sensitive substrate projects. We have successfully bonded to a number of thermoplastics including Polyetherimide, Nylon, Polycarbonate, and others.
Keep the surface of the substrate clean and dry.
Contaminants such as oils and mold release agents can thwart both the chemical and mechanical bonding of the silicone to the base metal or plastic. Some contaminants can even hinder the curing of the silicone.
Keep the substrates warm
It’s vital for substrate parts to be hot because the bonding of LSR to the thermoplastic is a chemical reaction; it needs a combination of time, temperature and pressure. The hotter the temperature, the shorter the cure cycle. Temperature is less of an issue if the substrates are molded in a two-shot mold, because the residual heat left in the substrate from the first shot helps cure the LSR. If the substrate is molded separately in a transfer overmolding process, it’s a good idea to preheat it in a conveyor oven or on a hot plate.
One of the important aspects of silicone overmolding is to achieve the desired adhesion between the silicone and the plastic or metal substrate. This can be done is several ways, through mechanical interlocking, primers or self adhesive silicone.
Mechanical interlocking: if you have the design freedom to adjust the insert or substrate design, add a few undercutting features which will lock and hold the silicone rubber in place.
Primers: If you do not have the option to modify the insert design, the next best option is to use a primer to treat the surface. Once applied, the primer dries off anywhere between 30 mins to 2hrs, depending on the primer used. Once ready we overmold the insert with silicone rubber and this process produces a good bond.
Surface Treatments: Plasma, Corona, Particulate Blasting are common techniques. Corona discharge is commonly used for plastics inserts. These surface treatment techniques increase the surface area and change the surface chemistry to enhance the bonding between the two materials.
Self Adhesive Materials: There are several self adhesive liquid silicone rubber (LSR) materials which bond to plastics without the use of primers and surface treatments. These silicone elastomers bond well with Polycarbonate (PC), PolyEthylene Terepthalate (PET), PolyButylene Terepthalate (PBT), PolyPhenylene Sulfide (PPS),PolyEther Ether Ketone (PEEK) and Nylons (PA).
Silicone Rubber Overmolding Manufacturing Process
LSR Overmolding & Liquid Silicone Plastic Overmolding Manufacturing Process
Silicone Rubber Transfer Overmolding Manufacturing Process
Rubber Metal Bonding & Insert Overmolding Manufacturing Process
Advantages of Silicone Rubber Overmolding
Improve products quality and performance. Such as simplifying assembly and improving sealing quality between components. Silicone rubber overmolding produces parts that are waterproof, airtight, and more resistant to shock and vibrations. And silicone overmolding adds value to product designs
Cost-effective and time savings. By molding silicone directly onto a metal or plastic substrate, you’ll save the expense and time required to assemble a complex part manually. This can dramatically reduce your manufacturing costs and turnaround time, allowing you to get your product to market more economically.
These advantages leads them to use in a wide range of silicone overmolding applications.