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During mass production of silicone parts for new energy connectors, medical devices and precision electronics, most R&D and procurement teams only focus on material hardness and dimensional specifications while ignoring molding process compatibility. This often results in heavy losses such as out-of-tolerance dimensions, seal leakage, insert delamination, surging manual deflashing expenses and full batch returns.
This paper fully elaborates the complete production procedures of LSR injection molding and HCR compression molding, and conducts a quantitative comparison of core process parameters. It proposes targeted solutions based on three typical mass production failure cases, and sets standardized selection criteria for new energy, medical, precision electronics and home appliance sectors. Complimentary factory DFM process reviews are available to eliminate production risks at the design stage, cut manufacturing costs and sustain consistent product yields.
I.Full Process Breakdown of the Two Major Silicone Molding Technologies
1.LSR Injection Molding | Automatic Closed-loop Dust-free Production
This process adopts fully enclosed automated production with zero manual contact with raw materials, delivering outstanding process consistency. It is ideal for high-precision, dust-free and high-volume production of premium silicone components.
（1）Constant-temperature raw material storage: Dual-component A/B platinum-cured liquid silicone is stored separately in sealed low-temperature warehouses with a constant temperature ≤25℃ to prevent premature vulcanization and material deterioration.
（2）Precision batching and mixing: Dedicated injection molding machine gear pumps deliver materials at a strict 1:1 ratio, followed by automatic sealed mixing via a static mixer, realizing dust-free and pollution-free production throughout the process.
（3）Cold runner mold injection: Adopting cold-hot separated mold structure, silicone material is conveyed in low-temperature runners while cured in high-temperature cavities. No sprue waste is generated to greatly reduce raw material consumption.
（4）In-mold high-speed vulcanization: Complete additive vulcanization at 170-210℃ with stable chemical reaction and no small molecule precipitation, complying with automotive low VOC requirements and medical biocompatibility standards.
（5）Robotic automatic demolding: Automatic part picking by manipulators produces smooth products without flash on parting lines, eliminating secondary manual deflashing.
（6）Inspection and warehousing: Full inspection on product dimensions and appearance, with qualified products directly packaged and put into storage.
2.HCR Solid Silicone Compression Molding | Semi-manual Hot Press Forming
This process relies heavily on manual operations with complicated working procedures, which is suitable for low-cost conventional sealing parts with simple structures and small production batches.
（1）Raw material pretreatment: Solid silicone rubber undergoes secondary mixing for reinforcement, followed by manual weighing and cutting into standard rubber blanks.
（2）Manual feeding and mold closing: Operators manually place rubber blanks as well as metal and plastic inserts, then close molds manually.
（3）Long-time high-temperature and high-pressure compression vulcanization: Materials are cross-linked and shaped under sealed high temperature and pressure, featuring a long vulcanization cycle.
（4）Manual cooling and part picking: Operators take out semi-finished products after mold cooling, and large flashes will be formed on product parting lines.
（5）Manual post-processing: Workers manually trim flashes and polish burrs. Qualified products after re-inspection will be packaged and put into storage.
II.Core Parameter Comparison: LSR Injection Molding VS HCR Compression Molding
Comparison Item | LSR Injection Molding | HCR Compression Molding
|
Raw Material Form
| Two-component flowable liquid platinum silicone, automated hermetic feeding | Solid silicone rubber sheets, requiring manual cutting and weighing preprocessing. |
Molding Dimensional Accuracy
| Tolerance: ±0.01~0.03 mm, minimum wall thickness 0.2 mm, suitable for precision sealing parts. | Tolerance: ±0.1 mm, minimum wall thickness ≥1 mm; thin-wall parts are prone to material shortage and deformation. |
Single Cavity Molding Cycle
| 20–60 seconds per cycle, fully automatic continuous mass production, no gate waste. | 3–8 minutes per cycle; manual loading and unloading takes extensive time with high scrap rate. |
Insert Overmolding Capacity
| Synchronous integrated overmolding process delivers high bonding strength with no delamination after high-low temperature cycling. | Uneven pressure distribution results in weak adhesion between rubber compound and inserts, leading to cracking and peeling under long-term service. |
Post-processing Cost
| Parts are flash-free, eliminating manual deflashing processes and additional secondary processing costs. | Large-area flash requires manual trimming, with labor costs accounting for over 20% of total production expenses. |
Mold Investment Cost
| Precision mold with dedicated cold runner temperature control, featuring high upfront mold development cost. | Conventional simple compression mold with straightforward structure and low mold manufacturing cost. |
Applicable Order Volume
| Annual order quantity ≥ 50,000 pcs; recommended for orders of 30,000–50,000 pcs requiring precision waterproofing or overmolding. | Annual order quantity ＜ 30,000 pcs; preferred for ordinary gaskets without precision requirements with order volumes of 30,000–50,000 pcs. |
Cleanliness & Compliance
| Fully enclosed dust-free production, free of small molecule precipitation, compliant with low VOC standards for medical and automotive applications. | Open manual operation tends to accumulate hair and dust, failing to meet medical cleanroom specifications. |
Maximum Waterproof Performance
| Consistently achieves IP67 to IP69K waterproof rating with scratch-free sealing surfaces. | Only reaches IP67 rating; trimming scratches easily damage sealing surfaces, leading to unstable waterproof yield rate. |
Sample lead time | 7-10 days (simple cold runner molds included) | 3-5 days fast sampling for structure validation. |
(I) Inherent Limitations of LSR Liquid Silicone Injection Molding
1. High upfront investment in equipment and workshop: Specialized LSR injection molding machines, sealed feeding systems and Class 10,000 cleanrooms are mandatory, resulting in substantial one-time capital expenditure on fixed assets.
2. High amortized mold costs: High-precision mold steel and independent temperature control structures are required for liquid material molding, making molds far more costly than conventional
compression molds. For annual orders below 30,000 pieces, the per-unit mold amortization expense becomes prohibitively high, undermining economic viability.
3. Relatively high sampling costs: LSR mold commissioning poses high technical barriers and demands highly experienced operators, leading to elevated trial production expenses. This process is only suitable for projects with long-term mass production plans.
(II)Inherent Drawbacks of HCR Solid Silicone Compression Molding
1. Poor dimensional stability: Manual material preparation causes inconsistent weight of rubber blanks, resulting in large dimensional deviations within the same batch of products, which easily leads to water leakage of sealing parts and assembly jamming.
2. Flash cannot be completely removed, impairing sealing performance: Burrs tend to form on parting lines; manual deflashing may scratch sealing surfaces and drastically reduce waterproof yield rate.
3. Weak bonding strength of overmolded inserts: Uneven stress distribution during compression molding creates micro-gaps at the interface between silicone and metal terminals, causing delamination and debonding after alternating high and low temperature cycles.
4. Insufficient production cleanliness: Open manual operations are prone to contamination by dust and hair, failing to meet the cleanroom control standards for medical and high-end automotive applications.
IV.Review of Three Real Mass Production Pitfall Cases & Practical Solutions
Case 1: Sealing Rings for New Energy High-Voltage Connectors – Full Batch Rejection Caused by Improper Use of HCR Compression Molding
Project Overview
Waterproof sealing rings for automotive high-voltage terminals, with requirements including IP68 waterproof rating, precision tolerance of ±0.05 mm, and resistance to temperature cycling ranging from -40°C to 150°C. Annual order volume stands at 400,000 pieces.
Process Pitfalls
The customer opted for HCR compression molding to cut mold development costs, yet three fatal defects emerged during mass production:
1. Scratches formed on sealing surfaces during manual deflashing, dragging the waterproof yield down to merely 72%;
2. Severe dimensional variation across batches caused terminal assembly jamming, pushing the reject rate beyond the acceptable limit;
3. Extensive delamination and debonding occurred between silicone and metal terminals after high-low temperature alternating cycles.
Consequences & Losses
All finished products were fully rejected by the vehicle manufacturer, incurring substantial costs for rework, logistics and compensation claims.
Rectification Solution
Switch to LSR cold runner injection molding:
One-piece molding eliminates flash completely; Automated production achieves tight control over dimensional tolerances;Integrated overmolding of inserts boosts bonding strength by 60%. The waterproof test pass rate reaches 100%, enabling stable mass delivery.
Case 2: General Silicone Gaskets for Small Home Appliances – Project Losses from Blind Adoption of LSR
Project Overview
Standard flat sealing gaskets for household appliances without high precision tolerance or advanced waterproof requirements, with an annual order volume of only 8,000 pieces.
Identified Pitfalls
The customer blindly adopted the new process and customized an LSR cold runner mold. The small-batch order failed to amortize the high mold development cost, driving the unit cost 45% higher than compression molding and resulting in project losses.
Solution
Switch to HCR solid silicone compression molding. This process meets basic sealing performance requirements while slashing unit costs. It is suitable for small-batch sampling and mass production to sustain stable supply.
Case 3: Silicone Masks for Medical Ventilators – Manual Compression Molding Failed Cleanliness Inspection
Project Overview
Medical breathing masks with a wall thickness of 0.3 mm. The products must be dust-free and impurity-free, compliant with biocompatibility standards, with an annual order volume of 120,000 pieces.
Identified Pitfalls
HCR compression molding was adopted in the initial stage. The open manual production process was prone to contamination by dust and lint. Manual deflashing scratched the sealing contact surfaces, leading to failure in both cleanliness and sealing performance tests, making the products undeliverable.
Solution
Switch to fully automatic LSR injection molding in a Class 10,000 cleanroom. The one-piece forming process eliminates the need for deflashing and prevents low-molecular-weight substance precipitation. All products pass medical cleanliness and biocompatibility tests, with the product yield increased by 28%.
V.Standardized Precise Material & Process Selection Guide by Industry
（I）Application Scenarios Prioritizing LSR Liquid Silicone Injection Molding
I.Industry & Product Categories
New Energy Vehicles: Sealing rings for high-voltage connectors, waterproof silicone components for battery packs, charging gun seals, overmolded inserts for automotive sensors
Medical Devices: Minimally invasive instrument parts, ventilator masks, medical sealing valves, auxiliary implant silicone components (cleanroom-grade and biocompatible required)
Precision Electronics: Ultra-thin miniature waterproof parts, integrated overmolding for precision terminals, high-precision sensor seals
II.Order Criteria
1. Annual order volume ≥ 50,000 pieces;
2. Annual orders ranging from 30,000 to 50,000 pieces with at least one of the following requirements: IP68 waterproof rating, ultra-thin wall thickness, metal insert overmolding, or cleanroom standards for medical/automotive applications;
3. High-end export industrial orders requiring flash-free molding without manual deflashing, high yield rate and consistent batch performance.
（II）Cost-Effective Application Scenarios of HCR Solid Silicone Compression Molding
I. Products by Industry
Household appliances and general industrial equipment: Simple-structured sealing gaskets, non-cosmetic parts, and general miscellaneous components without high precision or high waterproof performance requirements.
Large-size thick-walled products: Thick silicone parts with no complex undercuts and no demand for precision insert overmolding.
II. Order & Product Requirements
1.New product sampling and small-batch trial production
Annual order volume below 30,000 pieces, with controlled mold development costs solely for structural verification.
2.Low-value non-core accessories
Products without critical sealing surfaces, acceptable minor flash, and eligible for manual deflashing post-treatment.
VI.One-stop Process & Technical Solutions for R&D Selection Challenges
The full-process supporting technical support covers four core services:
1.Drawing Process Evaluation We accept 3D drawings in STEP, EASM and other formats. Combined with tolerances, service environment, order volume and budget, we customize the most suitable molding process for your project.
2.Pre-inspection of Mass Production Risks Predict potential defects in advance such as thin-wall short shot, insert delamination, flash and incomplete vulcanization, and optimize product structure to reduce scrap rates.
3.Delivery of Complete Mass Production Solutions Provide accurate mold quotation, production lead time, yield estimation, as well as full sets of reliability test schemes including high-low temperature cycling, waterproof performance and peel strength tests.
4. Small-Batch Trial Production Verification Conduct pre-sampling and small-lot trials to verify process stability. Mass production will only be launched after full confirmation to avoid batch scrap losses and customer complaints.
VII.Common FAQ
Q1: Annual order volume ranges from 30,000 to 50,000 pieces. Should we choose LSR or HCR?
A: The selection depends on product requirements. Opt for LSR if IP68 waterproof rating, ultra-thin walls, metal insert overmolding, or cleanroom standards for medical/automotive applications are required. Choose HCR for ordinary gaskets without precision performance demands to cut upfront investment.
Q2: Can LSR cold runner molds be modified to produce multiple products?
A: Yes. Cavity inserts can be replaced to accommodate iterative mass production of various specifications within the same product line, amortizing mold costs over the long term.
Q3: Can HCR compression molded parts meet medical production standards?
A: Hardly. The open manufacturing process is prone to impurity contamination. Extra dust removal and deflashing procedures would be mandatory for medical-grade products, driving up overall costs significantly. LSR is a more cost-effective alternative.
Q4: Is there a difference in service life between parts made by the two processes?
A: LSR achieves complete vulcanization with no low-molecular-weight precipitation and firm insert adhesion, delivering superior resistance to high-low temperature cycles. HCR parts suffer from uneven compression and deflashing damage, so sealing components are more likely to leak water and delaminate after long-term service.
Q5: How much higher is the sampling cost of LSR compared with HCR? Is LSR suitable solely for structural verification?
A: Sampling costs for simple LSR cold runner molds are substantially higher than HCR. If only structural verification is needed with no long-term mass production plan, HCR is recommended to save expenses.
Q6: Is a cleanroom mandatory for LSR production? Can manufacturing be carried out in ordinary workshops?
A: Class 10,000 cleanrooms are required for medical, infant care, and low-VOC automotive products. While general consumer goods can be produced in regular workshops, cleanliness and extractables levels will fail to satisfy high-end clients’ specifications.
（PS: If you require a free DFM process analysis for your silicone connector seals, simply send us your 3D drawings. Our engineering team will deliver a professional process evaluation report within 24 hours.）
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