A Simple Guide to the LSR Product Manufacturing Process

Table of Contents

Introduction of LSR Product Manufacturing Process

The LSR product manufacturing process involves a specialized two-component liquid silicone rubber utilized in the production of elastic items through the injection molding method.

Raw Materials

LSR is supplied to the manufacturer in two distinct containers, containing an “A” compound and a “B” catalyst. These components are mixed in a 1:1 ratio, and pigment is added to initiate the curing process.

Curing Process

The curing of LSR products within the mold occurs rapidly, taking only seconds. This swift curing process enables efficient cycling and the production of large quantities in a short timeframe.

Machine Settings

To accommodate LSR and meet specific job requirements, the molder adjusts various settings on the injection molding machine. These adjustments include selecting the shot size of LSR as well as configuring temperature, pressure, cycle time, and injection rate.

a guide to the lsr product manufacturing process

LSR Injection Molding

The LSR injection molding machine heats the mold and applies force to the clamp. Subsequently, the LSR is delivered into the mold’s cavities. The liquid silicone rubber undergoes curing until it solidifies, after which the molded part is ejected from the mold.

LSR Product Manufacturing Process Finishing Steps

The finalization of the LSR product involves several steps, including curing, inspection, deflashing, and packaging. These steps ensure the production of high-quality and finished elastic items.

Multi-Component LSR Technology

In addition to the standard LSR manufacturing process, multi-component LSR technology involves the simultaneous injection of LSR in combination with engineered plastics and potentially other substrates. Commonly known as 2K, 2shot, 2C LSR, or co-injection, this method is employed to create innovative solutions by combining two or more materials into a single fully bonded component. The combinations may include hard-soft and soft-soft variations, providing versatility and unique properties to the final product.

Jiaze Silicone’s LSR Product Manufacturing Process

Communication Process

Initial Contact

When you submit your requests for liquid silicone rubber-molded products to Jiaze Silicone, our dedicated communication process begins.

Assigned Project Engineer or Sales Representative

A project engineer or sales representative is assigned to your account. They become your primary point of contact, working with you from initial inquiry through full qualification, validation, and approval.

Ongoing Collaboration

Throughout regular production, your purchasing team coordinates with a customer service representative. This representative monitors your product orders and ensures timely delivery.

Design Changes and Next-Generation Products

When modifications or new designs are required, the assigned engineer continues to collaborate closely with you to ensure successful product modifications or launches.

Engineering and Design Support

Comprehensive Assistance

Jiaze Silicone offers support in engineering, tooling, manufacturing, quality assurance, assembly, and packaging. This comprehensive assistance helps keep costs low, aligning with our commitment to cost-effectiveness.

Early Partnership Benefits

Partnering with Jiaze Silicone early in your project can save time and money as your product progresses from conception to full production.

Continuous Improvement

Our engineers assist with modifications, next-generation enhancements, and evaluating the manufacturing process for optimization, including lean cell manufacturing and advanced processing.

Technical Analysis

Various technical analyses are conducted, including NDA (Non-Disclosure Agreement), DFMEA (Design Failure Mode and Effect Analysis), PFMEA (Process Failure Mode and Effect Analysis), Mold Flow Analysis, Statistical Analysis, and Color Matching.

a simple guide to the lsr product manufacturing injection molding process

Material Considerations

LSR Grade and Manufacturer Impact

The choice of LSR grade and manufacturer significantly influences the final product design.

Durometer Consideration

For silicone products, durometer (hardness) is a crucial consideration, ranging from 20 to 80 shore A.

Decision-Making Process

Once the material is selected, decisions regarding product shape, gating, material usage, and cost are carefully considered. A series of questions is employed to determine the most effective approach.

Jiaze Silicone’s meticulous attention to communication, engineering support, and material considerations ensures a streamlined and efficient LSR injection-molded product manufacturing process.

Molding Considerations in LSR Product Manufacturing Process

Product Molding

Molding Types and Automation

Product geometries play a pivotal role in deciding the molding type—be it horizontal LSR molding or vertical machine molding—guiding the overall manufacturing process. Automation is efficient for horizontal LSR molding, while the manual operation of vertical machine molding is suitable for specific cases. The complexity of the geometry dictates the mold size and, consequently, the size of the molding machine.

Demolding Process

Importance of Design for Demolding

Designing for ease of demolding is crucial. Silicone’s high green tear strength allows for large undercuts in product design. Parts can be stretched over these undercuts during demolding without permanent deformation. However, challenges arise with silicone’s tendency to adhere to mold steel, especially in thick-walled and highly undercut parts. Careful consideration of undercuts and wall thickness during the design phase is essential.

Material Feeding to Cavities

Runner System Considerations

The method of feeding material to cavities significantly impacts waste generation. Traditional runner systems result in substantial material waste that cannot be reused. In contrast, a cold-runner system offers a more sustainable approach, allowing for direct gating with no material waste.

Cold Runner System

Cold runner systems, featuring water-cooled nozzles within the mold, feed material directly to each cavity. This design minimizes waste and prevents curing of the material within the cold nozzles. Analogous to a hot runner system in thermoplastic molding, the cold runner system optimizes material usage and contributes to a more efficient manufacturing process.

Mold Design and Process Considerations in LSR Molding

Gate Selection

Types of Gates

After choosing the runner system, various gate types are available, including pin, submarine, automatic degating, edge, fan, and ring. The selection depends on the chosen runner system and specific molding requirements.

Flexibility in Gating Styles

LSR, similar to thermoplastics, offers flexibility in gating styles. The choice of gate type can impact efficiency and waste generation during the molding process.

Gate Location

Cavity Filling Considerations

Similar to thermoplastic injection molding, achieving cavity filling from the thickest areas of the part is crucial. Gate location, especially in parts of an assembly, should not interfere with the final product’s assembly or function.

Tooling Design

Collaboration of Product and Tooling Design

Product and tooling design in LSR molding go hand in hand. Tool designers consider customer requirements, cavity geometry, and the limited space within an injection molding tool.

Key Questions for Mold Design

  • Wall and Rib Thicknesses
  • Mass Reduction and Uniform Wall Thickness
  • Parting Lines
  • Undercuts
  • Part Ejection
  • Draft
  • Gating and Venting
  • Expected Tolerances

Linear Shrinkage

Shrinkage Considerations

LSR products experience overall shrinkage after cooling, typically ranging from 2–3%. Geometric variations and processes, like overmolding, can influence shrinkage. For uncertain geometries, prototype tooling proves valuable, simulating full production to address any uncertainties in the manufacturing process.

Mold Heating

Consistent Mold Heating

Maintaining consistent heating of LSR molds is vital for proper part geometry. Heating methods include resistance or induction, either placed inside the mold plates or in a universal base that heats the entire mold from the outside.

Precise Control

Placing heaters directly in the mold plates enhances control, allowing more effective changes in the heater on/off timing. The choice of heating type depends on budget constraints and geometric considerations.


Importance of Venting

Venting is critical for proper LSR molding due to its low viscosity and high injection speeds, leading to potential issues like dieling and flashing.

Venting Depth

LSR requires shallower vents (near 0.005 mm) compared to thermoplastics (0.025 mm) to prevent scorching and minimize flash formation.

Vacuum Evacuation

Vacuum evacuation is common for LSRs to swiftly remove trapped air from the cavity, reducing the risk of gas trapping.

Surface Finish

Demolding Considerations

Surface finish, often dictated by customer requirements or product design, plays a vital role in demolding.

Preferred Finish

Prefer non-polished finishes, like SPI mold finishes of B1 or lower, as LSR has a tendency to adhere to polished surfaces, posing challenges during demolding.

Maintenance Planning

Importance of Maintenance

Properly maintained molds are crucial for LSR molding to ensure tight tolerances and prevent flashing and dimensional issues.

Considerations for Maintenance

  • Easy replacement of wear items (bushings, side locks)
  • Accessibility for regular cleaning of cavities and cores
  • Design considerations for cold runner disassembly and assembly

LSR Molding Process

Transforming High-Consistency Silicone

High-consistency silicone often requires labor to transform it into a moldable size and shape before the molding process.

Material Preparation

Pump LSR A + B components into a static mixer, inject them into the mold, and control pigment streams seamlessly during the process.

Injection and Curing

Inject the material into the mold, clamp it for curing, and efficiently remove the cured product by an operator or robot, completing the cycle in just 30 seconds.

Efficiency of LSR Molding

Compared to organic materials or high-consistency silicone, LSR molding offers significant cost savings in labor with a much shorter average cycle time.

Secondary Steps

Employ post-bake and deflashing processes to reduce volatility, enhance compression set, and eliminate unwanted flashing.

Cleaning and Packaging

The final step involves cleaning the product to remove foreign material, ensuring quality, and packaging it for shipment.

a specific guide to the lsr product manufacturing process

Key Components of the Two-Part LSR Product Manufacturing Process

1. Supply Drums

Plungers or containers for liquid silicone supply connect to the pumping system. The inclusion of a third container for pigment offers flexibility in color customization.

2. Metering Units

The metering device pumps two liquid materials in predetermined ratios, ensuring a consistent release at a steady ratio. This precise control is crucial for achieving the desired material properties.

3. Mixers

After passing through the metering unit, a static mixer combines the liquid-forming materials. Pressurize and direct this homogenous blend into the mold, guaranteeing uniformity in the molded product.

4. Injectors

Responsible for moving the LSR-forming material into the pumping mechanism under pressurized force. Operators have the capability to adjust pressure and injection rates, providing flexibility for different project specifications.

5. Nozzles

The liquid compound flows into the mold through a nozzle equipped with an automatic shut-off valve. This feature prevents leaks and ensures precise control over the injection process, preventing overfilling of the mold.

6. LSR Molding Cycle

A well-defined molding cycle includes key steps such as curing, material injection, mold opening and closing, and the initiation of the next cycle.

Ideal LSR Product Manufacturing Process Environment

  • Lean and Compact Machines: In an ideal production environment, the basic liquid injection molding machine should be lean and compact. This ensures efficiency and minimizes the footprint of the molding setup.
  • Configurable Secondary Devices: Secondary devices should be configured based on the specific requirements of a particular project. This adaptability enhances the versatility of the production setup.

Molding Parameters

  • Low Back Pressures and Screw Speeds: LSRs, unlike thermoplastics, require low back pressures and screw speeds. This minimizes stress on the material during the injection process.
  • 99% Cavity Filling Rule: The shot size is determined by the rule of thumb that 99% of the cavity should be filled. The remaining filling is done by material expansion during the curing process.
  • Optimized Injection Speeds: Injection speeds are set to optimize pressure during filling. Due to the low viscosity of LSR, flashing is a concern, making low-pressure molding essential.
  • Temperature Considerations: Mold temperatures should be set within the suggested range of the material supplier. Hotter molds facilitate faster curing but should not compromise material flow during injection.

Mold Preparation

  • Cleaning with Solvents: Mold tools must be carefully prepared before production. Cleaning with isopropyl alcohol or other solvents removes residues from previous runs or during long production cycles.
  • Mold Release Agents: After cleaning, mold release agents are applied to cavities and runners. These agents facilitate easy demolding and contribute to the overall efficiency of the molding process.

Material Changes

  • Constant Pressure Requirement: LSR materials require constant pressure during pumping. Changing material containers while the pumping unit is operating may necessitate stopping the injection molding machine.
  • Second Pumping Unit: To avoid machine stoppage during material changes, a second pumping unit, switchable by valve, can be employed. While effective, this solution involves a substantial capital investment.

Potential Innovations by Jiaze Silicone

1. Two-Shot Molding

Recent advancements in self-bonding LSRs have reduced the need for priming agents in LSR overmolding. This innovation unlocks the door to two-shot molding, enabling the processing of thermoplastics and LSRs on a single machine with a single mold.This process not only lowers manufacturing costs but also provides increased design freedom.

2. Improved Cold Runner Technology

Cold runner technologies are gaining importance. Jiaze Silicone highlights the introduction of off-the-shelf cold runner systems, similar to hot runner systems for thermoplastic molding. Standardization in cold runner systems may lead to more efficient and cost-effective solutions.

LSR Product Manufacturing Process Conclusion by Jiaze Silicone

Jiaze Silicone emphasizes its rich experience in producing custom-molded LSR products and silicone products with FDA or LFGB-approved standards. They possess the FDA register list number 3011147430, showcasing compliance with regulatory requirements.

For those seeking custom molded silicone products or molded silicone projects with technical support, Jiaze Silicone invites inquiries through their website. This conclusion reflects their commitment to quality, compliance, and providing assistance to clients in their molding endeavors.