If you are developing a new silicone product or purchasing silicone parts in bulk, choosing the right silicone molding method is important to the success of your project. This guide will detail each silicone molding process, compare their advantages and limitations to help you determine which process is better.
The Important Role of the Molding Process in Silicone Manufacturing
The silicone molding process is a key step in the process of realizing the silicone rubber from silicone gum to silicone products in the silicone manufacturing process. Through different molding methods, silicone raw materials are detached from their original glue or solid gum state and processed into a variety of products ranging from silicone toothpicks to silicone sheets.
It determines the characteristics of the silicone product, such as precision, shape and function, so it plays an important role in the quality of your product.
Different silicone molding processes have vastly different production efficiencies and costs. Choosing the right silicone molding process will enable you to perform better when faced with temporary high-volume orders and ensure that you get timely silicone parts.
Types of Silicone Molding Processes
Compression Molding
Silicone compression molding is one of the most common silicone molding processes. After the silicone raw materials are mixed well with colors, fillers, and additives, they are cut to size and sent to the mold.
You can imagine this as the process of making a bear shape using a modeling clay mold. The silicone material is fed into a metal mold and then heated and compressed by a hydraulic press so that it will fit the mold into the desired shape.
Because compression molds are almost always simple shapes, just like playdough molds, using this process for custom silicone products can often save you a lot of money spent on molds. It’s also generally quick to go from mold design to finished product.
Its limitations are also obvious: it can make large, simple products, but it’s difficult to obtain very thin or tiny silicone products.
Like making playdough bears, someone needs to constantly put the silicone raw material into the mold, so it’s not suitable for mass production of silicone products.
Liquid Silicone Rubber Injection Molding(LIM)
Liquid Silicone Rubber Injection Molding (LIM) is a molding process dedicated to the production of Liquid Silicone Rubber (LSR) products, and is currently the mainstream silicone molding technology.
In the injection molding process, mixed liquid silicone rubber raw materials are injected into molds under high pressure and then cured at high temperatures to become silicone products that meet different needs. Because it offers these advantages, it has become the first choice for manufacturing silicone products ranging from medical devices to aerospace parts.
- High precision:Due to the low viscosity of liquid silicone rubber, it can easily fill every detail within a mold. Therefore, you can easily customize complex products with LSR injection molding. Complex surface textures, delicate brush tip ends, or extremely thin pacemaker components can all be manufactured using LSR injection molding.
- Flexibility:LSR injection molding can also produce highly intricate components. Since silicone is soft, even shapes like chamfers can be manufactured and demolded. This flexibility extends to being able to use two silicone types simultaneously (two-color injection molding) or directly encapsulating LSR around other materials for secure bonding (overmolding).
- Automation capability:Unlike compression molding, LSR injection molding enables fully automated production after mold creation, requiring no additional manual intervention.
- High material utilization: Since curing occurs directly within the mold, and material loss during system transfer is minimal, resulting in exceptionally high material utilization rates for LSR injection molding.
- Stable quality: LSR injection molding’s fully sealed process enables the production of high-purity silicone rubber with outstanding performance in transparency, weather resistance, and other properties.
- High production efficiency: LSR’s rapid curing speed allows for the mass production of products within a short time.
Despite its many advantages, LSR injection molding also has its limitations:
- Not suitable for small-batch production: Custom molds for LSR injection molding and developing new LSR formulations require significant investment. If you only need a small quantity of customized silicone products, LSR injection molding offers poor cost-effectiveness.
- Customization process takes considerable time: Molds used in LSR injection molding require cold runner systems, and combined with precision requirements, producing the necessary custom molds will take longer.
Transfer Molding
If you are finding a silicone molding process for producing electronic component encapsulations, transfer molding is an excellent choice.
It works by placing the silicone raw material into a transfer chamber, where a piston pushes it into the mold cavity. The material is then heated and cured within the mold.
Unlike LSR injection molding, transfer molding requires manual material loading into the transfer chamber and dedicated scrap removal, whereas LSR injection molding is fully automated.
Its current use for insert molding stems primarily from its combination of good production accuracy and significantly lower flow velocity of silicone material into the mold compared to injection molding. This effectively prevents damage to or displacement of internal metal inserts.
Since transfer molding requires a transfer chamber, the size of silicone products it can produce is constrained by the chamber dimensions, making it unsuitable for manufacturing excessively large silicone items.
Extrusion Molding
Silicone extrusion molding is a process mainly used to produce strip-shaped silicone products. Similar to piping cream through a pastry bag, changing the shape of the piping nozzle allows for the production of silicone strips in various forms. These silicone strips are then sent through a curing oven to vulcanize into usable products.
Its most significant feature is the ability to produce continuously until the silicone product reaches your desired length. The extruder continuously pushes heated silicone raw material through a mold. So silicone wires and sealing strips are typically manufactured using silicone extrusion molding.
This characteristic also results in high production efficiency and material utilization. What’s
more, the production cost of silicone “nozzle” molds is lower than that of compression molding and LSR injection molding, making it an economical method for mass production.
Silicone products manufactured this way exhibit stable shapes and dimensions. On the other hand, it can’t produce items with varying thicknesses. Its production precision is also lower and cannot match that of LSR injection molding.
Calendering
Silicone extrusion molding is used to produce strip-shaped silicone products, while silicone calendering is used to produce sheet-shaped silicone products.
The calendering production line has multiple sets of rollers, with the gap between these rollers becoming progressively narrower toward the end of the line. Simply feed the silicone compound into the rollers, which gradually roll it out like a rolling pin into a sheet of consistent thickness.
After heating and vulcanization in an oven, you will obtain smooth, uniform silicone sheets or silicone fabrics reinforced with nylon.
The calendaring process is indispensable for producing large, continuous sheets of silicone. It enables the manufacture of silicone sheets up to 1-2 meters wide, significantly expanding your product design possibilities.
Foam Molding
Foam molding is a specialized forming process used to manufacture sponge silicone. Unlike other molding techniques, foam molding involves injecting air or foaming agents into the silicone raw material, creating a dense network of tiny pores throughout its structure. This results in silicone products with significantly lower density and weight.
Foam molding significantly enhances silicone’s shock absorption, cushioning properties, and softness, making it suitable for applications like shock-absorbing pads and makeup sponges.
However, the internal pore structure makes it difficult to achieve smooth surfaces in foam-molded silicone products. What’s more, it is difficult to obtain precisely sized silicone products through foam molding.
Silicone Dip Molding
When you need very thin silicone gloves, silicone dip molding comes in handy. Instead of injecting silicone material into the mold, the process involves dipping the mold into liquid silicone material, much like coating ice cream with a chocolate shell.
After repeating this process several times, the silicone coating on the mold achieves enough thickness. After heating and curing, followed by demolding, you can own seamless silicone products. Achieving seamless results with injection molding or other methods is often difficult or involves higher costs.
Silicone dip molding offers a low-cost solution for creating molds. It can produce both simple and complex thin-film shapes as long as the molds can be submerged in the silicone material, making it highly convenient.
Due to gravity, silicone material may flow from the sides toward the bottom and pool, resulting in variations in overall thickness. The repeated dip-and-remove cycle also means lower production efficiency and automation levels.
How Do I Choose the Right Silicone Molding Method?
Select Molding Processes Based on Product Type:
- Sheet-shaped silicone products: For silicone gaskets, especially large ones, transfer molding offers the highest efficiency and supports the production of oversized gaskets.
- Strip-shaped silicone products:When selecting a process for silicone wires or tubes, extrusion molding is the superior choice. It produces exceptionally long, uniformly thick strip-shaped silicone products.
- Simple-structured silicone products:For silicone keyboards, silicone rollers, and similar items, compression molding offers a more cost-effective solution, reducing project expenses.
- Silicone parts requiring precision or complexity: For products like silicone interdental brushes and medical check valves, LSR injection molding excels at reproducing intricate details.
- Products containing small internal inserts: Transfer molding gently encapsulates inserts, preventing internal electrical components from shifting within the silicone due to impact.
- Hollow and thin products like silicone gloves and sleeves:Dip molding significantly reduces production costs while eliminating mold lines or flash.
- Silicone products for shock absorption and cushioning: Foam molding is ideal for creating lightweight, soft ear muffs and construction cushion pads.
Select the Molding Process Based on the Quantity of Products You Need:
- Large Orders:Liquid silicone rubber injection molding is highly automated, enabling rapid mass production of your silicone products once custom molds are finalized. While customization needs higher upfront costs, great demand makes it a cost-effective solution.
- Small Orders: Compression molding uses simpler molds with lower production investment, making it a more economical choice for smaller batches.
FAQ
What Molding Process Is Safest for Food-grade and Medical-grade Silicone Products?
The liquid silicone rubber injection molding process is sealed, effectively preventing external contaminants and bacteria from entering the silicone. This makes it safer for food-grade and medical-grade silicone applications.
For medical-grade silicone products with stricter hygiene requirements, liquid silicone injection molding performed in cleanrooms achieves higher purity levels to meet the demands of ISO 10993 safety standards.
Which Molding Process Minimizes Flash and Trimming?
LSR injection molds are highly precise, and raw materials have good flow properties, resulting in minimal flash and trimming on silicone products. With meticulous control, flash on silicone products manufactured from LSR injection molding can be reduced to less than 0.02mm.
Immersion molding also has no flash on products.
Compression molding presents the most severe flash and trimming problems, typically requiring post-processing to remove these obvious flashes after production.
Does the Type of Silicone Used Affect the Choice of Silicone Molding Process?
Yes. Certain silicone molding processes impose specific requirements on the hardness and viscosity of silicone raw materials. Liquid silicone rubber is typically processed by injection molding, while HCR silicone or other highly viscous silicone rubbers are manufactured using compression molding, extrusion molding, calendering, and similar techniques.
Silicone dip molding can’t use silicone raw materials with excessive fluidity, as they struggle to adhere to the mold. Therefore, RTV silicone with a certain viscosity that can cure at room temperature is selected for the silicone dip molding process.
Why Is Heating Necessary for Silicone Molding?
In addition to RTV, the molding process for most silicone rubbers requires a chemical process called vulcanization or curing, and heating is a necessary condition for this vulcanization process.
Vulcanization of LSR and HCR requires high temperatures. If the temperature is insufficient, not only will the vulcanization rate of the silicone raw materials be slow, thereby affecting production efficiency, but it will also significantly impact the physical strength of the silicone product, making it less durable.
Can Silicone Extrusion Processes Combine Two Different Silicone Rubbers?
Through co-extrusion, the silicone extrusion process enables the combination of two silicone rubbers. During co-extrusion, two distinct silicone raw materials flow through separate channels before converging to produce silicone products such as multi-layer silicone tubing or automotive window guide channels.
Why Is There Size Inaccuracy in Silicone Products after Molding?
The main reason for dimensional deviations in silicone products after molding is that the final product’s size is not completely the same as the mold cavity size. Silicone shrinks after vulcanization and cooling. Due to factors such as curing time and formulation, even different batches of silicone may exhibit varying degrees of shrinkage, making precise estimation challenging.
Selecting a silicone manufacturer with mature processes, strict control over molding conditions, and even making shrinkage testing can keep such dimensional deviations within your acceptable limits.
Final Thoughts
Legensilico is a silicone product manufacturer in China with over 20 years of experience, specializing in various molding processes, including LSR injection molding and compression molding. We deliver products with minimal size deviations and offer cost-effective customized silicone solutions. Click to learn more!
