Xiangchu Hubei Rubber: LSR Overmolding Customization for High-end Manufacturing Upgrade

Introduction

Liquid Silicone Rubber (LSR) overmolding, a precision manufacturing process that bonds LSR to rigid substrates (including engineering plastics, metals, and glass), has become an indispensable enabling technology for high-end manufacturing sectors ranging from medical devices to new energy vehicles and consumer electronics. Unlike conventional adhesive bonding or mechanical fastening, LSR overmolding delivers seamless, hermetically sealed assemblies with combined properties of substrate rigidity and LSR’s inherent biocompatibility, temperature resistance, and elasticity, eliminating assembly gaps, reducing part count, and extending product service life by 30–50% in typical use cases. However, the process poses steep technical barriers: precise control of material surface energy, injection temperature uniformity, and cure kinetics is required to avoid delamination, flash, or residual stress, all of which can lead to product failure in high-stakes applications.

Xiangchu (Hubei) Rubber Co., Ltd. is a specialized LSR overmolding solution provider that has built a 12-year track record of addressing these exact challenges for global high-end manufacturing clients. The company operates a 25,000 m² production facility equipped with 42 all-electric LSR injection molding machines with clamping forces ranging from 55 to 650 tons, supported by a Class 100,000 cleanroom for medical-grade production and an in-house material R&D center staffed by 18 material scientists and process engineers. Unlike general-purpose rubber processors, Xiangchu focuses exclusively on custom LSR overmolding, with 92% of its output serving the medical, new energy, and smart wearable sectors, and has obtained ISO 13485, IATF 16949, and FDA 21 CFR Part 177.2600 certifications to meet the strict regulatory requirements of these industries. This article delves into Xiangchu’s core technical capabilities, end-to-end customization workflow, and real-world impact on high-end manufacturing upgrading.

Core Technical Competencies of Xiangchu’s LSR Overmolding

The reliability of LSR overmolding hinges on three interconnected technical pillars: material formulation compatibility, precision process control, and non-destructive quality validation. Xiangchu has invested over RMB 28 million in R&D over the past five years to build proprietary capabilities in each of these areas, setting it apart from low-cost, commodity LSR molders that rely on off-the-shelf materials and generic process parameters.

Proprietary Material Formulation and Substrate Bonding Technology

One of the most common failure modes in LSR overmolding is interlayer delamination, which occurs when the interfacial bond strength between LSR and the substrate falls below the application’s minimum stress threshold. For example, in medical implantable devices, delamination can cause fluid ingress and device failure, while in new energy battery seals, it can lead to thermal runaway risks. Xiangchu addresses this challenge with a two-tiered material system: custom LSR formulations tailored to specific substrates, and in-situ surface modification processes that eliminate the need for external adhesives.

Xiangchu’s R&D center has developed 14 patented LSR formulations with adjustable Shore hardness (from 10 A to 80 D), elongation at break (up to 850%), and functional additives (antimicrobial agents, thermal conductive fillers, UV stabilizers) that match the thermal expansion coefficient (CTE) of the target substrate, minimizing residual stress during curing. Table 1 outlines the bond strength of Xiangchu’s custom LSR formulations to common substrates, compared to industry-standard generic LSR:

All Xiangchu overmolded assemblies achieve cohesive failure (the LSR itself breaks before the bond interface), which is the gold standard for overmolding reliability, as opposed to the adhesive failure (interface separation) common with generic materials. For substrates with inherently low surface energy, such as PTFE and PP, Xiangchu uses a patented atmospheric plasma surface treatment process that raises substrate surface energy to >72 dynes/cm before overmolding, eliminating the need for solvent-based primers that can leave toxic residues in medical applications.

Precision Closed-Loop Process Control System

LSR is a two-part thermoset material that cures irreversibly when exposed to heat, making process consistency far more critical than for thermoplastic injection molding. Even a 2°C variation in mold temperature or 0.1 s variation in injection speed can lead to incomplete curing, flash, or bond failure in high-tolerance parts. Xiangchu’s production lines are equipped with a proprietary closed-loop process control system that monitors and adjusts 12 critical process parameters in real time, with a tolerance of ±0.5% for all key variables.

Key parameters controlled by the system include:

1. Metering ratio of LSR A/B components: Maintained at 1:1 ±0.2% via Coriolis mass flow meters, preventing under-curing or over-curing caused by off-ratio mixing
2. Barrel and mold temperature: Regulated via 16 independent thermocouples per mold, with temperature uniformity across the cavity of ±1°C
3. Injection pressure and speed: Adjusted dynamically based on cavity pressure sensor feedback, ensuring consistent filling of complex micro-features as small as 0.02 mm
4. Cure time and post-cure temperature: Optimized for each material combination to achieve 98% crosslink density without warping the substrate

This level of control allows Xiangchu to hold dimensional tolerances of ±0.01 mm for overmolded parts, a 75% improvement over the industry average of ±0.04 mm. The system also logs all process data for every part produced, creating a full traceability record that meets the requirements of medical device regulators and automotive quality management systems.

Multi-Modal Non-Destructive Quality Validation

For high-end applications where part failure can have catastrophic consequences, destructive testing (such as pull tests and cross-section analysis) is not sufficient, as it only validates a small sample of production runs. Xiangchu has integrated a three-stage non-destructive testing (NDT) workflow into every production line, ensuring 100% of overmolded parts meet performance requirements before shipment.

The NDT workflow includes:

1. High-resolution machine vision inspection: 12-megapixel cameras with backlighting detect flash, surface defects, and misalignment between the substrate and LSR layer, with a detection accuracy of 0.01 mm
2. Ultrasonic thickness and bond testing: 20 MHz ultrasonic transducers measure LSR layer thickness and detect voids or delamination at the bond interface with a resolution of 0.05 mm, without damaging the part
3. Functional performance testing: Customized for each application, including hermeticity testing (up to IP68/10 bar pressure), thermal cycling (-40°C to 200°C), and biocompatibility screening for medical parts

Xiangchu’s quality control system has achieved a <200 ppm defect rate for medical and automotive overmolded parts, a 60% reduction from the industry average of 500 ppm, with zero field failures reported for parts used in Class II medical devices and new energy battery systems over the past three years.

End-to-End Custom LSR Overmolding Workflow

Xiangchu’s value proposition extends beyond manufacturing: the company works with clients from the earliest product design stages to optimize part geometry, material selection, and manufacturability, reducing product development cycles by 30–40% and lowering total production costs by an average of 22% compared to clients that use separate design and manufacturing partners.

Collaborative Design for Manufacturability (DFM) Support

Many high-end product teams design overmolded parts based on ideal performance requirements, without accounting for the inherent constraints of the LSR overmolding process, leading to costly design revisions and delayed production launches. Xiangchu assigns a dedicated engineering team to each client project, starting with a DFM analysis within 48 hours of receiving a part design.

The DFM analysis covers three core areas:

• Part geometry optimization: Identifying undercuts, sharp corners, and non-uniform LSR wall thicknesses that can cause filling defects or residual stress. For example, Xiangchu’s engineers recommend a minimum LSR wall thickness of 0.2 mm and a maximum draft angle of 3° for rigid substrates to ensure proper bonding and easy demolding.
• **Material pairing recommendation: Selecting the optimal LSR formulation and substrate combination to balance performance, cost, and regulatory compliance. For instance, for a wearable glucose monitor part that requires skin contact biocompatibility and resistance to sweat and UV exposure, Xiangchu may recommend a medical-grade LSR with antimicrobial additives overmolded to a PC substrate, rather than the more expensive PEEK that the client initially proposed.
• Mold design validation: Using Moldflow simulation software to model LSR filling, curing, and shrinkage before mold fabrication, identifying potential air traps and weld lines that can lead to part failure. Xiangchu’s mold design team includes 12 tooling engineers with an average of 10 years of experience in LSR overmolding, and all molds are built with hardened S136 stainless steel to withstand the high temperatures and abrasive fillers used in custom LSR formulations, with a typical mold life of 1 million+ cycles.

Rapid Prototyping and Low-Volume Pilot Production

High-end manufacturing clients often require 50–5000 functional prototypes for performance testing and regulatory submission before full-scale production, a need that most large-scale LSR molders cannot meet efficiently due to long lead times and high minimum order quantities (MOQs). Xiangchu operates a dedicated prototyping center with 8 small-tonnage LSR injection molding machines and in-house 3D printing capability for rapid tooling, delivering functional overmolded prototypes in 3–7 days, compared to the industry average lead time of 14–21 days.

Xiangchu offers two prototyping options to meet different client needs:

1. Rapid soft tooling: Aluminum molds with a lifespan of 500–1000 parts, ideal for initial design validation and low-volume clinical trials, with costs 60% lower than hardened steel production molds
2. Pre-production hard tooling: Hardened S136 steel molds identical to full-scale production tooling, suitable for regulatory testing and pilot production runs of 10,000–50,000 parts, with a lead time of 10–15 days

After prototyping is complete, Xiangchu runs a 24-hour pilot production run to validate process stability and part consistency, providing clients with a full process capability index (CpK) report before moving to full-scale production. This approach reduces the risk of costly production delays, with 94% of Xiangchu’s client projects moving from prototype to full production without additional design revisions.

Scalable High-Volume Production and Supply Chain Integration

For clients moving to mass production, Xiangchu’s 42 injection molding lines can support production volumes from 10,000 to 10 million parts per year, with flexible production scheduling that allows for 20% volume adjustments within 72 hours to accommodate fluctuations in client demand. The company also offers value-added post-processing services, including pad printing, plasma coating, and assembly of sub-components, allowing clients to source fully finished overmolded assemblies from a single supplier, reducing logistics and quality management costs.

Xiangchu’s supply chain integration capabilities are particularly valuable for global high-end manufacturing clients:

• The company maintains a 3-month safety stock of 28 common LSR and substrate materials, eliminating supply chain disruptions caused by material shortages
• It operates two distribution centers in Shanghai and Los Angeles, with ocean and air freight partnerships that deliver parts to clients in North America, Europe, and Asia within 7–14 days
• It provides full regulatory documentation for all parts, including FDA master access files (MAFs) for medical materials and IATF 16949 compliance reports for automotive parts, reducing the time clients spend on regulatory approval by an average of 2 months

Application Cases of Xiangchu’s LSR Overmolding in High-end Manufacturing

Xiangchu’s custom LSR overmolding solutions have been adopted by over 120 high-end manufacturing clients globally, delivering measurable improvements in product performance, reliability, and manufacturing efficiency across three key sectors.

Medical Device Implantable and Wearable Components

The medical device sector has the strictest requirements for LSR overmolding, with biocompatibility, hermeticity, and sterilization resistance being non-negotiable performance criteria. Xiangchu has worked with 37 medical device clients to develop overmolded components for Class I, II, and III devices, including implantable pacemaker leads, wearable insulin pumps, and surgical instrument handles.

A notable example is a collaboration with a leading global wearable continuous glucose monitor (CGM) manufacturer to develop an overmolded sensor housing. The client’s original design used a two-part assembly with an adhesive bond between the PEEK sensor substrate and LSR skin contact layer, which had a 1.2% failure rate during autoclave sterilization and caused skin irritation in 3.5% of users due to adhesive residue. Xiangchu’s solution:

• A custom medical-grade LSR formulation with silver ion antimicrobial additives that reduce skin irritation risk to <0.1%
• Plasma surface treatment of the PEEK substrate that eliminates the need for adhesive, delivering a hermetic seal that withstands 100+ autoclave cycles at 134°C
• Precision overmolding that reduces part weight by 18% and lowers total production cost by 27%

The resulting CGM sensor has obtained FDA 510(k) clearance, and Xiangchu now produces 4.2 million of these overmolded housings annually, with a defect rate of <120 ppm.

New Energy Vehicle Sealing and Sensor Components

The new energy vehicle (NEV) sector requires LSR overmolded components that can withstand extreme temperature fluctuations, high voltage, and corrosive fluids, while maintaining tight dimensional tolerances for 15+ years of service life. Xiangchu supplies overmolded parts to 8 leading NEV manufacturers, including battery pack seals, high-voltage connector insulators, and autonomous driving sensor housings.

One key project was the development of an overmolded cooling plate seal for a 800V NEV battery pack. The client’s original design used a separate rubber gasket bonded to an aluminum cooling plate, which had a 0.8% leak rate during thermal cycling testing between -40°C and 120°C, leading to potential battery thermal runaway risks. Xiangchu’s solution:

• A custom thermally conductive LSR formulation (thermal conductivity of 2.3 W/m·K) that improves heat transfer between the cooling plate and battery cells by 22%
• Direct overmolding of the LSR seal to the aluminum plate, eliminating the gasket assembly step and reducing part count by 50%
• A hermetic seal that withstands 10 bar of pressure and 3000+ thermal cycles, with zero leaks detected in 10,000 hours of durability testing

The overmolded cooling plate is now used in 3 of the client’s NEV models, with Xiangchu producing 1.8 million units annually, helping the client reduce battery pack assembly time by 12% and lower warranty costs related to cooling system failures by 92%.

Smart Wearable and Consumer Electronics Interface Components

The smart wearable and premium consumer electronics sectors require LSR overmolded parts that combine aesthetic appeal, tactile performance, and long-term resistance to sweat, UV exposure, and daily wear and tear. Xiangchu supplies overmolded components to 21 leading consumer electronics brands, including smart watch wristbands, wireless earbud tips, and waterproof smartphone button assemblies.

A recent collaboration with a global smart watch manufacturer focused on developing an overmolded titanium watch case with a soft LSR inner lining for improved wearer comfort. The client’s initial design had issues with LSR delamination after 6 months of use, and the high hardness of the titanium case caused skin irritation for users with sensitive skin. Xiangchu’s solution:

• A custom low-modulus LSR formulation with a Shore hardness of 25 A that conforms to the wearer’s wrist, reducing skin pressure by 35%
• A patented nano-coating treatment for the titanium substrate that increases bond strength to 3.7 N/mm, preventing delamination even after 10,000 cycles of bending and stretching
• Precision overmolding that maintains a uniform LSR lining thickness of 0.3 mm, preserving the watch’s slim design while adding impact resistance that reduces case damage from drops by 40%

The resulting smart watch has won multiple design awards, and Xiangchu now produces 2.7 million overmolded cases annually for the client, with a customer return rate related to case comfort or durability of just 0.3%, a 70% reduction from the previous model.

Conclusion

As high-end manufacturing sectors continue to demand smaller, more reliable, and more functional integrated assemblies, LSR overmolding will play an increasingly critical role in enabling product innovation. However, the technical complexity of the process means that success depends on partnering with a specialized provider that combines deep material science expertise, precision process control, and end-to-end customization capabilities. Xiangchu (Hubei) Rubber Co., Ltd. has established itself as a leader in this space, with proprietary material formulation technology, a closed-loop process control system, and a client-centric customization workflow that delivers measurable value for medical, automotive, and consumer electronics clients.

Looking ahead, Xiangchu is investing RMB 50 million in expanding its production facility and R&D capabilities, with plans to add 28 additional injection molding machines and a Class 10,000 cleanroom for Class III medical device production by 2026. The company is also developing next-generation LSR overmolding technologies, including in-mold sensing for real-time bond quality monitoring and bioresorbable LSR formulations for temporary implantable devices, to further support high-end manufacturing upgrading globally. For product teams working on high-stakes applications that require reliable,