橡楚编辑部 52 min read
Xiangchu (Hubei) Rubber Co., Ltd. has been deeply engaged in the field of liquid silicone rubber (LSR) overmolding customization for many years, with mature material formula system, precision molding process and strict quality control process. It can provide one-stop LSR overmolding solutions from material selection, mold development to mass production for customers in high-end manufacturing fields such as medical, automotive and consumer electronics, effectively improving product sealing performance, weather resistance and biocompatibility, helping downstream enterprises break through product performance bottlenecks and upgrade core competitiveness.
Against the backdrop of global advanced manufacturing transformation, liquid silicone rubber (LSR) has emerged as a core functional material for high-end sectors including medical devices, new energy vehicles, consumer electronics, and food processing equipment, thanks to its exceptional biocompatibility, extreme temperature resistance (-60°C to 220°C), dielectric stability, and long-term aging resistance. However, LSR’s inherent low surface energy and poor adhesion to dissimilar substrates (engineering plastics, metals, glass) have long been a bottleneck limiting its application in multi-material integrated components.
Xiangchu (Hubei) Rubber Co., Ltd., a national high-tech enterprise specializing in LSR overmolding customization, has addressed this pain point through 12 years of accumulated material formulation, process optimization, and precision mold design capabilities. The company provides end-to-end overmolding solutions for over 300 downstream customers in high-end manufacturing segments, with a 99.2% product qualification rate and 98% customer retention rate as of 2024. This article analyzes Xiangchu’s core technical system, industry-specific application practices, and its role in driving high-end manufacturing upgrading, providing a reference for the expansion of LSR overmolding technology in advanced industrial scenarios.
LSR overmolding is a cross-disciplinary technology integrating material science, mold engineering, and precision process control. Unlike single-material LSR injection molding, overmolding requires stable bonding strength between LSR and the substrate, no residual stress at the bonding interface, and consistency of geometric tolerance across mass production runs. Xiangchu has built a four-dimensional technical system covering material modification, precision mold design, closed-loop process control, and full-cycle quality testing, breaking the technical monopoly of European and American enterprises in high-precision LSR overmolding fields.
The primary challenge of LSR overmolding lies in achieving non-destructive, high-strength bonding with different substrates, which requires targeted adjustment of LSR’s functional groups and rheological properties to match the substrate’s surface energy and thermal expansion coefficient. Xiangchu’s R&D center has developed 17 proprietary LSR formulation systems for common overmolding substrates, with bonding strength exceeding industry standards by 35% on average, as shown in Table 1.
Xiangchu’s formulation modification adopts a two-pronged approach: first, introducing silane coupling agents with epoxy groups and amino groups into the LSR base material to form covalent bonds with polar groups on the substrate surface during the curing process, eliminating the need for pre-coating of adhesive on the substrate surface for most scenarios, reducing production costs by 22% and shortening the production cycle by 30%. Second, adjusting the LSR’s crosslinking density and shrinkage rate according to the substrate’s thermal expansion coefficient, controlling the difference in shrinkage rate between the two materials after molding to within 0.1%, avoiding interface cracking or warping caused by uneven stress during post-processing or temperature cycle testing. For special scenarios requiring food contact or medical implantation, the formulation system meets FDA 21 CFR Part 177.2600, ISO 10993-5, and USP Class VI biocompatibility standards, with no precipitates after 72 hours of immersion in simulated body fluids.
Mold precision is the core guarantee for achieving consistent mass production of LSR overmolded parts, especially for micro-miniature components with tolerance requirements of ±0.01mm. Xiangchu has built a 5-axis CNC machining center and a mirror EDM workshop with a mold manufacturing accuracy of up to ±0.005mm, and has developed a modular mold design system suitable for different overmolding processes.
For insert overmolding processes where the substrate is pre-placed in the mold cavity, Xiangchu adopts a positioning design combining a conical positioning pin and a vacuum adsorption hole, controlling the position offset of the insert during LSR injection to within 0.008mm, which solves the common problem of substrate displacement caused by LSR’s high flow rate during injection. For two-shot overmolding processes where the substrate is molded in the first shot and then transferred to the second cavity for LSR coating, the company uses a rotary core exchange structure with a positioning repeatability of ±0.003mm, achieving a production efficiency of 30s per cycle for two-shot overmolded parts, 40% higher than the industry average. In addition, for LSR’s low viscosity characteristics, the mold adopts a self-sealing gating system and a precision exhaust groove design with a depth of 0.003mm, avoiding burrs and air trap defects at the bonding interface, reducing the post-processing rate of products to less than 1%.
Xiangchu also integrates a conformal cooling/heating system in the overmolding mold, adjusting the mold temperature distribution according to the thermal conductivity of the substrate: for metal substrates with high thermal conductivity, a rapid heating system is set in the area near the substrate to ensure that the LSR at the bonding interface maintains sufficient fluidity before curing; for plastic substrates with low heat resistance, a segmented cooling system is adopted to control the substrate temperature below its heat distortion temperature during the LSR curing process, avoiding substrate deformation. The average service life of Xiangchu’s overmolding molds reaches 1.2 million shots, which is 50% higher than the industry average, greatly reducing the amortization cost of molds for customers in mass production.
LSR overmolding process parameters have a significant impact on bonding strength and product consistency: small changes in injection pressure, curing temperature, or metering ratio can lead to interface debonding or unqualified dimensional accuracy. Xiangchu has built an intelligent production line integrating MES (Manufacturing Execution System) and sensor real-time monitoring, realizing full closed-loop control of the entire overmolding process.
The company’s LSR injection molding equipment is equipped with a high-precision metering system with a mixing accuracy of A/B component ratio up to ±0.1%, and the injection pressure is controlled in real time through a closed-loop feedback system with a fluctuation range of less than ±0.5 bar, ensuring consistent filling of LSR in the mold cavity for each shot. The mold temperature control system adopts a PID adjustment algorithm with a temperature control accuracy of ±0.3°C, which ensures consistent curing degree of LSR at the bonding interface, avoiding incomplete curing or over-curing caused by temperature fluctuations. For each production run, the MES system automatically collects 27 core process parameters including injection speed, holding pressure, curing time, and substrate pre-treatment temperature, and correlates them with the final product testing data, forming a process parameter optimization model through big data analysis. In 2023, Xiangchu realized a 99.2% qualification rate for mass-produced overmolded products, which is 8 percentage points higher than the industry average of 91%.
For high value-added products such as medical device components, Xiangchu also integrates a full-process traceability system: each product has a unique QR code, which records raw material batch, mold number, production date, process parameters, and testing data, supporting traceability of the entire production chain within 10 seconds, meeting the strict regulatory requirements of the medical industry.
Different high-end manufacturing sectors have differentiated requirements for LSR overmolded products: the medical industry emphasizes biocompatibility and sterility resistance, the new energy vehicle industry requires high and low temperature cycle resistance and insulation performance, and the consumer electronics industry pursues micro-miniature precision and aesthetic appearance. Xiangchu has developed targeted overmolding solutions for different sectors, helping customers break through technical bottlenecks in product performance.
LSR has become the preferred material for contact parts of medical devices due to its excellent biocompatibility and repeated sterilization resistance. However, most medical device components require a combination of LSR’s soft contact properties and the structural strength of engineering plastics or metals, which puts forward extremely high requirements for overmolding interface stability and non-toxicity.
Xiangchu’s medical overmolding solutions cover three core scenarios:
The medical device overmolding production workshop of Xiangchu has obtained ISO 13485 quality management system certification, with a 100,000-level clean production area, and the entire production process follows GMP specifications, supporting customers to complete product registration and market access quickly.
The rapid development of new energy vehicles has put forward higher requirements for the reliability of electronic and electrical components under extreme working conditions. LSR overmolded components can achieve both sealing, insulation, and structural fixation functions, and are widely used in high-voltage connectors, battery management systems, and sensor components.
Xiangchu’s new energy vehicle overmolding solutions focus on three key performance indicators:
In 2023, Xiangchu supplied over 12 million LSR overmolded high-voltage connector seals to leading new energy vehicle enterprises, with a zero failure rate in field application, helping customers reduce the comprehensive cost of connector components by 18% compared with imported solutions. The company has also obtained IATF 16949 automotive quality management system certification, supporting the customization and mass production of overmolded components for vehicle-level application scenarios.
Consumer electronics products are developing towards miniaturization, lightweight, and wear resistance, requiring LSR overmolded components with micro-size, high precision, and excellent appearance. For example, smart watch waterproof buttons, TWS earphone sound outlet sealing rings, and wireless charging coil sealing components all have size requirements below 5mm and tolerance requirements of ±0.01mm.
Xiangchu has developed a micro-precision overmolding process for consumer electronics, achieving a minimum overmolding LSR wall thickness of 0.08mm, with dimensional accuracy controlled within ±0.008mm. For TWS earphone sound outlet components, the company adopts a two-shot overmolding process of PC substrate and liquid silicone, with a bonding strength of 6.5 N/mm, passing 10,000 times of plug wear tests and IP67 waterproof tests, and the LSR surface can achieve a matte effect with a glossiness of 10±2 GU, meeting the aesthetic requirements of consumer electronics products. For smart watch heart rate sensor window components, Xiangchu’s overmolding process achieves seamless bonding between optical grade LSR and sapphire glass, with a light transmittance of 94% in the visible light band, improving the accuracy of heart rate monitoring by 12% compared with traditional assembly processes.
As of 2024, Xiangchu has provided micro-precision overmolding solutions for 7 top 10 global consumer electronics brands, with a monthly production capacity of 35 million micro overmolded parts, meeting the demand for large-scale delivery of consumer electronics products.
High-end manufacturing upgrading is essentially a process of continuously improving product performance, reducing production costs, and shortening the research and development cycle. Xiangchu’s end-to-end LSR overmolding customization service provides core support for downstream customers to achieve these goals, and its value is mainly reflected in three dimensions: performance improvement, cost optimization, and R&D efficiency improvement.
Traditional multi-material component assembly processes (adhesive bonding, ultrasonic welding, mechanical fastening) have inherent performance bottlenecks: adhesive bonding has poor long-term aging resistance, ultrasonic welding easily causes damage to fragile substrates, and mechanical fastening increases product weight and size. LSR overmolding realizes molecular-level bonding between LSR and substrates, greatly improving the comprehensive performance of components.
Taking medical surgical instrument handles as an example, the traditional process uses adhesive to bond LSR sleeves and PEEK handles, with a peel strength of only 2.3 N/mm, and interface delamination occurs after 200 autoclave cycles. Xiangchu’s overmolding process increases the peel strength to 7.8 N/mm, with no delamination after 1000 autoclave cycles, extending the service life of the instrument by 4 times. For new energy vehicle high-voltage connectors, the traditional assembly process uses a separate LSR sealing ring, with a sealing failure rate of 0.3% after temperature cycle testing. Xiangchu’s integrated overmolding process eliminates the assembly gap, reducing the sealing failure rate to 0.001%, greatly improving the safety of the vehicle high-voltage system.
In addition, the overmolding process can realize complex structural designs that cannot be achieved by traditional assembly processes, such as three-dimensional curved surface sealing, micro-channel integrated molding, and flexible hinge structure design, providing more space for downstream customers’ product innovation.
Xiangchu’s LSR overmolding customization service helps customers reduce the whole life cycle cost of products from three links: production, use, and maintenance. In the production link, the integrated overmolding process eliminates the pre-treatment, adhesive coating, and assembly steps required by traditional processes, reducing the production labor cost by 45% and shortening the production cycle by 30%. For example, for a household food processor blade sealing component, the traditional process requires 7 production steps including metal blade stamping, LSR sealing ring molding, adhesive coating, assembly, and testing, with a unit cost of 1.2 yuan. Xiangchu’s insert overmolding process integrates the production into 2 steps, reducing the unit cost to 0.7 yuan, with a cost reduction of 41.7%.
In the use link, the high reliability of overmolded components reduces the product failure rate, thus reducing the after-sales maintenance cost. According to customer feedback data, after adopting Xiangchu’s LSR overmolded high-voltage connector seals, the after-sales maintenance cost of new energy vehicle enterprises caused by connector sealing failure decreased by 92% year-on-year. In the product development link, Xiangchu provides DFM (Design for Manufacturing) services in the early stage of customer product design, optimizing the product structure and process plan in advance, reducing the risk of mold modification and process adjustment in the later stage, and shortening the product development cycle by an average of 40%.
High-end manufacturing sectors such as medical devices and new energy vehicles have a large number of small-batch customized component needs in the product development stage: the order quantity is usually between 50 and 5000 pieces, and the requirements for product performance and delivery cycle are extremely high. Traditional LSR processing enterprises are often unwilling to undertake such orders due to high mold costs and long adjustment cycles.
Xiangchu has built a rapid response R&D and production system for small-batch customization: the modular mold design system can realize rapid mold manufacturing within 7 days for small-batch trial production, and the flexible production line can adjust process parameters within 2 hours to switch between different products. For medical device customers’ new product trial production needs, the company can provide qualified overmolded prototype samples within 10 days, which is 50% faster than the industry average delivery cycle. In addition, Xiangchu’s R&D team provides 1-on-1 technical support for each customized project, participating in the customer’s product design process, putting forward material selection and structural optimization suggestions based on overmolding process characteristics, helping customers avoid design defects in the early stage, and improving the success rate of product development. In 2023, Xiangchu undertook 217 small-batch customized R&D projects, with a project success rate of 96.3%,