What is Liquid Silicone Rubber (LSR) injection molding


                        Liquid Silicone Rubber (LSR) can be processed in a liquid injection molding (LIM) process. The liquid raw material is mixed from two separate components in a ratio of 1:1 and injected via a cold-runner-system into a hot mold. Curing of the parts in the mold takes place within seconds, therefore offering the advantage of fast cycling and production of large quantities quickly.

                        Due to the flexibility in design and tooling, LSR injection molding is ideal for the production of complex geometries and can consolidate various functional features into a single part. LIM offers significant advantages in terms of product reliability and total cost of ownership.

                        It it used in many industries such as:

                        • Automotive

                        • Medical

                        • Electronics

                        • Appliances

                        Some of the Advantages of LSR:

                        • Superior ability to compensate deviations in wall section and has almost no sink

                        • Undercuts are possible

                        • Thin sections (0.1mm) possible

                        • Flash-free parts

                        • No Ejection pins required

                        The LSR-Injection Process

                        LSR is most commonly used for injection molding. LSR is a two-component liquid raw material, which is divided into A component and B component. The most commonly used commercial packaging is 20 kg (about 5 gallon) bucket or 200 kg (about 55 gallon) drum packaging.

                        The drums are placed in a high-pressure pump equipped to push the viscous component out into the feeding tubes ( 1 ). Since some products need coloring or other additives they can be added to the dosage system ( 2 ) .

                        The composition of liquid A + liquid B, additives, colorants, etc. are fully mixed in the Mixing Block ( 3 ) and Static Mixer ( 4 ). In the mixing system that handles the two components of LSR, a cooling medium such as cooling water must be able to ensure that the mixture is maintained at a controlled cooling temperature (10º ~ 20 ° C) to prevent premature curing reactions. The LSR mixture in the cold state can be stable for a long time for several days.
                        LSR special plasticizing screw ( 5 ) has the function of homogenization and mixing at the same time, the mixture is injected into the heated mold ( 6 ), and the initial cross-linking reaction is triggered to cure the silicone material and form the final product (7).

                        Plastic vs. Silcon rubber injection

                        As mentioned on the section above the process of LSR-Injection is very similar to the process of Plastic injection, however with the major difference that for plastic injection is heated and cooled in the mold, where as silicon is injected cold and the heated mold will cause the chemical reaction that will cure the silicon.

                        Please see the table below for some more details for the differences between these two production Technologies.

                        Process

                        Plastic Injection

                        LSR Injection

                        Material

                        Single source pellets

                         Two part liquid

                        Feed hopper

                        Single feed, no mixing

                         Two part mixing chamber

                        Barrel

                        Heated barrel and compression screw to meld raw material

                        Injection Process

                        Injected under pressure

                        Mold Tool

                        Cooling lines to reduce temperature of injected material

                        Heating lines to keep tool hot which heats the injected material

                        Curing Process

                        Cooling of injected material cures the material into a final product

                        Heating of injected material cures the material into a final product

                        Our Manufacturing Partner & Capabilities

                        With our long term production partner in the south of China we are able to deliver you the best ratio in cost/quality. 

                        We can offer Products with:
                        max. size - 30cm x 20cm
                        max. weight - 200g
                        min. wall thickness: 0.1 mm

                        Typically, we follow the standard tolerance for rubber level M1(very fine) and M2(fine), according DIN ISO 3302-1.

                        Materials:

                           Standard silicone (30, 40, 50, 60, and 70 durometers)
                          Optical-grade silicone
                          Medical-grade silicone
                          Fluorosilicone (fuel and oil resistant)

                        Certification: ISO 9001, ISO 13485, ISO 10993


                        Need any help with your part design?

                        We have a team of experienced engineers to help you make your product idea happen

                        Engineering Guideline


                        Wall Thickness

                        Recommended wall thickness considerations for LSR molding:

                        • Walls as thin as 0.1 mm are possible, depending on the size of the wall and the location.

                        • The radii of (inside) fillets should be approximately equal to the wall thickness. Radii that are  larger or smaller than this may cause porosity issues

                        • Rib thickness should be from 0.5 to 1 times the connecting wall thickness.


                        Undercuts

                        LSR molding can produce parts with undercuts. Many simple undercuts can be easily removed by the operator without additional tools.

                        Draft

                        While 1 degree of draft is common in LSR parts, zero draft can also be attained for parts. The characteristics of LSR allows the rules of draft to be stretched more so than thermoplastics, if mold design permits. 


                        Radii

                        Some part corners will have a radius rather than a edge since the mold is manufactures by CNC milling which will cause radi during machining. We will point out any radii which will need to be changed due to mold constuction.