Silicone Rubber Processing Case Study: Precision LSR Injection Molding Optimization for Automotive Sealing Components

Abstract: Silicone rubber, especially Liquid Silicone Rubber (LSR), is widely applied in automotive, medical, and electronic industries due to its excellent high-temperature resistance, chemical stability, flexibility, and biocompatibility. However, precision processing of thin-walled, complex silicone rubber components always faces challenges including dimensional deviation, surface defects, unstable bonding performance, and low production efficiency. This case study focuses on the mass production optimization of automotive waterproof and dustproof LSR sealing gaskets. It systematically analyzes the core problems in traditional injection molding processing, optimizes material formula, mold structure, and molding process parameters, and formulates standardized processing and quality control procedures. After comprehensive optimization, the product qualification rate, production efficiency and service performance of silicone rubber components are significantly improved, providing a reliable practical reference for high-precision and high-volume silicone rubber processing manufacturing.

1. Introduction

With the rapid upgrading of automotive lightweighting and intelligent manufacturing, the performance requirements for auxiliary sealing components are increasingly stringent. Automotive sealing gaskets need to maintain stable physical properties in extreme environments such as high-temperature engine cabins, low-temperature cold starts, and long-term alternating humidity and heat, and must have excellent waterproof, dustproof, shock absorption and anti-aging capabilities. LSR has become the preferred material for automotive sealing components because of its superior elasticity, weather resistance, compression resistance and easy molding of complex structures compared with traditional solid silicone rubber.

The cooperative customer of this case is a professional automotive parts manufacturer, which is committed to mass-producing customized thin-walled LSR sealing gaskets for new energy vehicle motor shells. The product features irregular curved surfaces, thin wall thickness (0.8–1.2mm), and high requirements for dimensional tolerance (±0.05mm) and surface smoothness. In the initial trial production stage, the traditional LSR injection molding process exposed many defects, including bubble holes, shrinkage depressions, flash burrs, unstable dimensional accuracy, and poor compression resilience after long-term use. The product qualification rate was only 78%, which seriously restricted mass production and failed to meet the customer’s batch delivery and quality standards. Therefore, the project team carried out comprehensive processing optimization from material pretreatment, mold design, injection molding process to post-processing and quality detection.

2. Initial Processing Problems and Root Cause Analysis

In the early trial production process using conventional LSR two-component injection molding technology, the project team summarized four major defective problems through statistical analysis of 500 trial-produced samples, and conducted root cause analysis one by one.

2.1 Main Product Defects

First, surface and internal quality defects. About 12% of the products had tiny bubble holes and shrinkage depressions on the surface and inside. Bubbles were mainly distributed at the curved transition of the gasket, which reduced the compactness of the silicone rubber material and easily caused water seepage and air leakage in the sealing process. Second, dimensional accuracy deviation. Nearly 10% of the products had wall thickness tolerance exceeding the standard, and local thinning or thickening occurred in the molding process, resulting in poor assembly matching with the motor shell.

Third, flash burrs and poor edge flatness. The thin-walled structure led to easy overflow of molten LSR during high-pressure injection, forming tiny burrs on the edge of the product. Manual trimming not only increased labor costs but also easily caused edge damage, reducing product consistency. Fourth, unstable mechanical properties. The compression set of partial products exceeded 8% after aging test, and the elasticity attenuation was fast after long-term compression, which could not meet the 10-year service life standard of automotive components.

2.2 Root Cause Analysis

In terms of materials, the conventional LSR formula had single filler composition, lack of high-temperature resistant reinforcing fillers, resulting in insufficient thermal stability of the finished product. In addition, the material defoaming pretreatment process before feeding was incomplete, and trace air remained in the colloid, forming bubble defects after high-temperature curing.

In terms of mold structure, the original single-cavity mold had a simple cooling channel design, uneven mold temperature distribution, and inconsistent curing speed of thick and thin parts of the product, leading to shrinkage and dimensional deviation. Meanwhile, the mold parting surface precision was insufficient, and the gap was too large, causing molten silicone rubber to overflow and form flash burrs during injection.

In terms of process parameters, the initial injection pressure and speed were unreasonable. Excessively fast injection speed led to turbulent flow of colloid and entrainment of air, while insufficient pressure holding time caused shrinkage depression after material cooling. Moreover, the curing temperature gradient was not matched with the product wall thickness, resulting in incomplete local curing and poor structural stability of the finished product.

3. Comprehensive Optimization Scheme for Silicone Rubber Processing

Aiming at the above problems, the project team optimized the whole processing chain from material formula and pretreatment, mold structure upgrading, injection molding process parameter calibration to post-processing technology, forming a set of standardized high-precision LSR processing scheme.

3.1 Material Formula and Pretreatment Optimization

On the basis of the original two-component medical and automotive grade LSR raw materials, high-purity silica and ceramic micro-particle fillers were added in a targeted proportion to enhance the thermal stability and compression resistance of the material, effectively reducing the compression set after long-term high-temperature use. At the same time, the material mixing process was standardized: the A and B components of LSR were mixed in a 1:1 strict proportion, and a vacuum defoaming process was added before feeding. The vacuum degree was controlled at -0.095MPa, and the defoaming time was 8 minutes, which completely eliminated the residual air in the colloid and fundamentally solved the bubble defect problem.

In addition, the raw material storage environment was standardized to avoid moisture absorption of silicone rubber. The constant temperature and humidity storage room with temperature 22–25℃ and humidity 40%–50% was adopted to prevent the material from absorbing moisture and reacting during storage, ensuring the stability of raw material performance in batch production.

3.2 Mold Structure Upgrading and Optimization

In view of the uneven cooling and easy flash of the original mold, the project team redesigned the mold structure. First, the single-cavity mold was upgraded to a 4-cavity balanced layout mold, which not only improved production efficiency but also ensured consistent filling pressure and speed of each cavity product, reducing batch dimensional difference.

Second, the conventional straight cooling channel was replaced with an innovative waterfall circulating cooling channel. This structure optimized the cooling uniformity of the mold surface, reduced the mold temperature difference between different areas within ±2℃, realized synchronous curing of thin-walled and thick parts of the gasket, and effectively improved product dimensional stability. The optimized cooling system shortened the mold cooling cycle by 19.2%, greatly improving production efficiency.

Third, the mold parting surface was precisely polished and matched, and the gap was controlled within 0.01mm. A flash overflow groove was designed at the edge of the cavity to collect excess colloid during injection, which avoided the formation of tiny burrs and realized one-time molding without obvious flash, reducing the pressure of post-trimming processing.

3.3 Injection Molding Process Parameter Calibration

Through orthogonal experiment and repeated trial production debugging, the project team calibrated the optimal injection molding process parameters for thin-walled LSR gaskets. The mold temperature was set at 115–120℃, which ensured rapid and uniform curing of the silicone rubber material while avoiding thermal aging of the material caused by excessive temperature. The injection speed was adjusted to medium and low grade, with the initial filling speed of 35mm/s, which avoided turbulent air entrainment. The injection pressure was stably controlled at 85–90bar, with the pressure holding time extended to 12s, which fully compensated the volume shrinkage of the material during cooling and eliminated shrinkage depression defects.

In addition, the vulcanization curing time was adjusted according to the product wall thickness. The total molding cycle was controlled at 45s, which balanced the two indicators of product curing completeness and production efficiency. For the residual internal stress of molded products, a low-temperature tempering post-curing process was added. The products were placed in a constant temperature oven at 80℃ for 2h after demolding, which eliminated internal stress, improved the structural compactness of silicone rubber, and further enhanced anti-aging and compression resistance.

3.4 Post-Processing and Quality Control Standardization

In terms of post-processing, the traditional manual trimming was replaced with precise cryogenic deburring technology. Utilizing the low-temperature brittle characteristics of silicone rubber, the tiny burrs on the edge of the product were removed efficiently and completely, which avoided product damage caused by manual operation and improved the consistency of product appearance and size. At the same time, a full inspection sampling system was established for batch products.

In terms of quality detection, dimensional tolerance detection, surface defect detection, compression set test, high and low temperature aging test and waterproof sealing performance test were carried out in batches. All detection data were recorded electronically to realize traceability of production quality, which effectively avoided unqualified products flowing into the market.

4. Processing Effect and Performance Verification

After the full-process optimization of material, mold, process and detection, the project carried out batch trial production of 2000 samples, and comprehensively verified the processing effect and product performance.

4.1 Production Efficiency and Qualification Rate Improvement

The optimized 4-cavity mold and efficient cooling system increased the daily output from 800 pieces to 2800 pieces, and the production efficiency was increased by 250%. The product surface bubble, shrinkage and flash defects were basically eliminated, the dimensional tolerance qualification rate reached 99.2%, and the overall product qualification rate was increased from 78% to 98.5%, which greatly reduced the production cost of defective products and rework labor cost, realizing high-efficiency and low-consumption batch production.

4.2 Product Physical and Sealing Performance Upgrade

Performance test results show that the optimized LSR gasket has more stable mechanical properties. The compression set is reduced to less than 5% after 1000h high-temperature aging test at 120℃, which is far better than the industry standard of 8%. The product maintains excellent elasticity and structural stability in the temperature range of -40℃ to 150℃, without deformation, cracking or aging failure. In the waterproof and dustproof sealing test, the product passes the IP67 protection grade test, and no water seepage or dust leakage occurs after long-term alternating vibration and high and low temperature cycle tests, fully meeting the service requirements of new energy vehicle motor components.

4.3 Batch Stability Verification

After one month of continuous batch production tracking, the dimensional deviation of mass-produced products is stable within ±0.03mm, the batch performance difference is less than 1%, and the product consistency is significantly improved. The standardized processing procedure effectively avoids the quality fluctuation caused by manual operation differences, realizing stable and sustainable mass production.

5. Processing Experience and Industry Enlightenment

This LSR precision injection molding processing case fully verifies that the processing quality of silicone rubber products is affected by the coupling of materials, molds, processes and post-processing. For high-precision thin-walled silicone rubber components used in automobiles, electronics and medical industries, single process optimization cannot solve comprehensive quality problems, and whole-chain systematic optimization is required.

First, material pretreatment and formula optimization are the foundation of stable product performance. Vacuum defoaming and constant temperature and humidity storage can effectively eliminate inherent defects of raw materials, and targeted filler modification can significantly improve the environmental adaptability of silicone rubber. Second, mold structural optimization is the key to improve dimensional accuracy and production efficiency. Balanced multi-cavity layout and efficient circulating cooling system can solve the problems of uneven curing and large batch dimensional difference of complex thin-walled products.

Third, precise calibration of process parameters is the core to eliminate molding defects. Reasonable matching of injection speed, pressure, temperature and holding time can avoid bubbles, shrinkage and flash problems fundamentally. In addition, standardized post-processing and perfect quality detection system are important guarantees for batch stable delivery of high-quality products.

6. Conclusion

Aiming at the quality defects and low production efficiency of automotive LSR sealing gaskets in traditional processing, this study completes the systematic optimization of silicone rubber processing technology from material formula, mold structure, injection process to post-processing and quality control. After optimization, the product qualification rate and production efficiency are greatly improved, and the mechanical properties, aging resistance and sealing performance of the products are significantly enhanced, which fully meet the stringent application standards of new energy automotive components.

This case summarizes a set of mature and replicable precision processing technology for thin-walled complex silicone rubber parts, which solves the common pain points of bubble defects, dimensional instability and poor batch consistency in silicone rubber injection molding production. It provides valuable practical experience and technical reference for the mass production and high-precision processing of silicone rubber functional components in automotive, electronic and medical industries, and has strong practical application and industrial promotion value.