LSR & Liquid Silicone Overmolding is an injection & transfer compression molding process which molded silicone rubber onto a substrate material like plastic & thermoplastics, metal, (magnet, steel, aluminum or brass), wire, electronic parts (PCB circuit board), glass with the assistance of bonding adhesive or glue to complete the final part.
LSR Overmolding | Insert Molding
LSR Overmolding & Liquid Silicone Insert Molding is an injection & transfer compression molding process which molded & cover silicone rubber onto a substrate material like plastic & thermoplastics, metal, (magnet, steel, aluminum or brass), wire, electronic parts (PCB circuit board), glass with the assistance of bonding adhesive or glue to complete the final part. LSR Overmolding, also called two-shot Molding, Liquid Silicone Rubber Overmolding or LSR Insert Molding.
LSR Overmolding are generally made by two-shot molding & insert moulding process. To fix the substrates on the mold first, and then inject the liquid silicone(LSR) material in on the substrates at the appropriate temperature, and finally to achieve the finished products.
Liquid silicone rubber (LSR materials) is lower temperature silicone as it is cured by platinum vulcanization agent, its curing temperature is about 120-150℃. Compared with HCR silicone compression overmolding, LSR insert & overmolding are more choice of substrate material, like medical plastic & thermoplastics (PC, PBT, PA+GF PPS, PPSU), metal, (magnet, steel, aluminum or brass), wire, electronic parts (PCB circuit board), glass etc.
The other wide application substrate material is metal, like aluminium,steel or brass.
What's LSR Overmolding & Insert Molding Manufacturing Process
First step, substrate treatment. Before the liquid silicone (LSR) material is wrapped on the substrates, the surface of the substrate must be treated well. It is mainly to ensure that the substrate surface is smooth and without defects, so as not to crack when the force is applied. And the substrate surface must be clean and without oil.
Secondly, prime coating: without prime, liquid silicone(LSR) can not bonded with other material (metal,thermoplastics) . So when process lsr overmolding to metal/plastic,we need to coat prime on the substrates.
Different substrate materials, different prime coating.
**Note:After apply prime coating on the metal and plastic substrate material, remember to dry them.
-Lastly, liquid silicone rubber injection molding. Inject the liquid silicone（LSR）material into mold cavity by liquid silicone rubber injection molding machine to wrap & cover the substrates.
Here shows the LSR overmolding breathing mask manufacturing procss.
LSR overmolding injection temperature is different from the substrates.
Therefore, when design LSR overmolding structure, we should take into account the suitability of the substrate and liquid silicone(LSR).
Not all plastic material can be used as substrate in LSR overmolding process. The most important point is the heat resistance.
|Overmold Material Compatibility Chart|
|Low Pressure||ASTM D 648||High Pressure||ASTM D 648|
|Plastic Types||℃||Plastic Types||℃|
Look at bonding, materials, and general moldability principles when creating overmolded parts.
LSR overmolding has been used extensively in various fields, we has learned several tips to help ensure a good bond between the silicone & LSR and substrates.
Tip1.Keep the surface of the substrate clean and dry
Cleaning is essential for bonding LSR with substrates, so must keep the substrate clean and dry.Contaminants such as oils and mold release agents can thwart both the chemical and mechanical bonding of the liquid silicone rubber (LSR) to the substrates. Some contaminants can even hinder the curing of the silicone. While, if LSR 2-shot & overmolding,no need to consider this problem.
Tip2. Heat the substrates
The bonding of LSR to substrates is a chemical reaction that requires a combination of time, temperature and pressure. The substrate must be hot, this is very important, in general, the hotter the better.
For LSR, typical mold temperatures range from 120 to 150 ° C. This temperature must be reached inside the LSR for it to cure adequately. The hotter it is, the faster it solidifies, and the shorter the curing period can be obtained.
Tip3.Good design structure into the substrate for mechanical bonding.
Loops and other such features in the substrate allow the silicone to flow into the substrate and mechanically lock into it. This is especially true if Liquid Silicone Rubber (LSR) is used to overmold.
Tip4.When necessary, treat the substrate’s surface with primers.
Sometimes the silicone and substrate are incompatible when it comes to chemical bonding. Care should be taken with using primers for medical devices, since the primer can impact the
biocompatibility of the finished device. That’s why plasma surface treatment is preferred, as that process doesn’t introduce new substances.
To minimize the number of processing steps, LSR manufacturer are introducing new "uncoated" or "self-adhesive" grades.
They themselves have good b with thermoplastics.Even so, the above specifications need to be followed in order to achieve good results.
Production Problems During LSR Overmolding Process.
The substrate is dislocated and deformed.
-Too large machine pressure, uneven material and bad temperature control.
-Deisign the locating struture. Reduce the molding temperature; Choose heat resistance substrates.
There are flash & burr on the metal substrate.The silicone rubber material or LSR material overflow to the substrates.
-Increase the clamping force; Reduce injection pressure.
Separation of silicone rubber & liquid silicone(LSR) and substrates due to poor adhesion or external force.
-Change the prime glue, and check if the substrates are cleaned.
Why choose LSR overmolding process?
The main reasons for LSR overmolding are quality and performance, such as simplifying assembly and improving sealing quality between metal/plastic substrates and silicone rubber or LSR material. The reasons may vary from application to application, but most important is lower assembly costs and the realization of device functions such as electronic sealing.
Silicone rubber, Liquid silicone(LSR) acts as a protective layer against dust, water, shock, heat and electrical shock.
LSR overmolding/Silicone overmolding is widely applied on the following fields.
-Medical Electronic Sealing
-Electrical and thermal insulation
-Food & Beverage
Xiamen Better Silicone Rubber Co.,ltd is specialized in design and producing LSR overmolding, silicone plastic overmolding, rubber metal overmolding. We provide you manufacturability and moldability analysis according to your design drawing. As a professional silicone overmolding company, we provide the following production solutions for your products:
· Liquid Silicone Rubber to Plastics
· Liquid Silicone Rubber to Metals
· Elastomers to Thermoplastics
· Two-Shot Over Molding
· Insert Molding
· Silicone Rubber Compression Molding
· Overmolded Silicone Diaphragm & Membrane
· Rubber overmolded handle
· LSR Overmolding Baby Products
· Medical LSR Silicone Overmolding Devices
· Electronics Silicone Overmolding
LSR Overmolding Rubber to Metal Bonding-Electronics Overmolding Parts
LSR Overmolding Silicone To Plastic Diaphragm & Membrane Process