Silicone injection molding presents an excellent means of manufacturing elastic, temperature- and impact-resistant parts in bulk. The process facilitates production of numerous useful silicone parts for a number of industries.
Principle Of Silicone Injection Molding
Basically, the process entails using an injection molding machine to create a blend of two silicone components together with a catalyst. The equipment will then push the blend into a mold cavity in which it will cure and take the mold shape.
Typical silicone injection molding machines feature 6 vital parts:
Injectors
Injectors are useful in pushing the liquid silicone material into the metering components under pressure. You can adjust the rate of pumping and pressure to the ideal settings for the silicone part you are molding.
Metering Units
This is where the injection molding machine pumps the silicone components in carefully regulated portions. It delivers the silicone resins concurrently at a steady ratio.
Supply Drums
These are the drums that hold the silicone resins. Normally, you will need another drum for the pigment.
Mixers
It is in the mechanical mixer unit where the system blends the components.
Nozzle
After mixing, the injection molding equipment pushes the liquid silicone into the mold via the nozzle. Automated shut-off valves fitted on the nozzles help in hindering material leaking or over-filling.
Mold Clamp
The system triggers the mold clamp in coordination with supply units, pump and injector. It fastens the mold in position and opens it after product curing.
Steps for Silicone Injection Molding Process
Injection molding is one of the most affordable and largely applied process for production of silicone parts. The process commonly uses high consistency silicone rubber, liquid silicone rubber, fluoro-liquid silicone rubber, and fluorosilicone rubber.
Here are the major steps for silicone injection molding process:
Step 1: Silicone Material Preparation
The injection molding operation begins with you preparing the silicone rubber material in two drums. It entails blending the two materials before molding. One drum carries the catalyst that promotes curing whilst the other contains base forming material.
The silicone part A comprises a supplemental platinum catalyzer, with part B having a cross-linking constituent. Usually, reinforcement fillers like quartz or silicic acid are also included in both components. These silicone components come in 200-liter or 20-liter metal drums.
Step 2: Silicone Material Injection
First, connect the supply drums with the metering system. Replace the drums covered by disk pistons of material loading units and electric or hydraulic feed devices.
When the disk pistons move, they exert pressure on the silicone materials in the drum. As a result, the system feeds both materials into the static mixer via tube connections. The feeding of the two components happens concurrently and in equivalent amounts.
Step 3: Liquid Silicone Mixing
The process of blending initiates the cross-linking reaction of additives. You can also mix colorants and supplementary additives into the liquid silicone rubber material.
After mixing, the injection molding machine conveys the activated silicone material mixture under pressure to the feed area of the LSR drum. Liquid circuit zones cool the drum to around 20 – 25 degrees Celsius to decelerate the process of cross-linking.
Step 4: Silicone Injection into the Mold
Upon dosing a set amount of the liquid silicone mixture, the equipment injects it into a heated mold. Normally, the mold gets heated to about 170 – 220 degrees Celsius using electrical heaters or through heated water flowing within the mold.
Moreover, you can integrate a cold runner mechanism to hinder premature flowing silicone curing within the runners or around them.
Step 5: Silicone Rubber Curing
After filling the mold cavity with silicone, you increase its temperature to fasten the cross-linking process. This leads to the silicone rubber changing its state from liquid to solid, a procedure commonly referred to as curing.
The duration of curing phase is distinct for a specific silicone type and product. Heating accelerates the LSR cross-linking, making it take a few seconds to complete.
Step 6: Silicone Part Demolding
Eventually, let the silicone product cool in the mold before you demold the part. Subsequently, allow the demolded silicone part to cool in ambient environment then use them as production parts or prototypes.
Silicone Injection Molding Advantages
The process blends two sets of advantages: the elastomeric material features of silicone and high-volume, high-quality manufacturing abilities of injection molding.
Here are the main benefits of silicone parts manufacturing using injection molding process:
Efficiency
Silicone injection molding is an exceedingly efficient process, allowing for quick manufacturing of big orders.
Detail
Because of high pressure during injection, the liquid silicone rubber fills every section of the mold before it cures. This makes it more effective in comparison to melted thermoplastic.
Enhanced Design Freedom
Uniform cooling is not necessary when molding silicone parts. Moreover, removing the parts from the mold is an easy process, which permits increased design freedom.
Material Properties
Silicone rubber products have excellent electrical, thermal and chemical resistance, in addition to reduced compression set.
Affordability
Rapid and efficient manufacturing guarantees low cost for each part. Silicone material works specifically well with affordable aluminum molds, which further decreases costs.
High-volume Production
Using injection molding facilitates high-volume manufacturing of silicone products.
However, some of the disadvantages of Silicone Injection Molding are non-recyclability and non-reformability of the parts. The high initial tooling cost that can lead to increased cost for each part when involved in small scale production. The other limitations are additional time required to blend the 2 silicone components and certain design limitations.
Applications Of Silicone Injection Molding Process
Silicone injection molding commonly find use in the following industries:
Automotive Industry
Injection molded silicone parts have many applications in the automotive sector. This is mainly because of its exceptional high temperature resistance that allows it to work near engines and other sources of heat.
Popular auto parts and components manufactured using silicone include A/C vent cushions, connectors, electronic covers, assemblies, flange, single-wire and radial seals.
A more conspicuous silicone injection molding applications is in soft boundaries of windshield wiper blade. The material is the perfect choice since does not scrape the surface of the windshield. Silicone blades are also long-lasting compared to conventional rubber because exposure to sun rays does not degrade them.
Medical Industry
Silicone injection molding is very instrumental in the producing medical products. This is as a result of its outstanding biocompatibility. Silicone is safe for prolonged use on human skin in addition to its elasticity and softness.
Injection molded silicone parts for medical use may include fluid management systems, drug delivery systems, and biotechnology components. They can also find use in casings for electronic medical gadgets, lenses, respiratory masks, catheters, and seals.
Industrial Applications
The appropriateness of silicone injection molding for products such as gaskets and seals add to its prevalence in industrial sector. Other popular silicone rubber products for industrial use comprise of grommets and strain relief devices. These injection molded parts are long-lasting, and give superior temperature, chemical and UV resistance.
Consumer Products
You can employ silicone injection molding process to manufacture consumer products such as baby bottles, pacifiers, toys, wearable technology, and kitchenware.
Conclusion
Contact us today if you have any silicone molding project. We provide full-service silicone manufacturing solutions, including product development, silicone prototyping, and cleanroom silicone injection molding.
More Resources:
What is Silicone Made of – Source: LegenDay
Silicone Material – Source: LegenDay
Silicone Overmolding – Source: LegenDay
Liquid Silicone Injection Molding Process – Source: LegenDay