Comparison of LSR Overmolding and Compression Overmolding
Author : yejia silicone | Published On : 23 Apr 2026
Silicone overmolding is a critical manufacturing process used to combine silicone rubber with substrates such as plastic or metal, creating durable, multi-functional components. Among the most widely used techniques are LSR (Liquid Silicone Rubber) overmolding and compression overmolding.
While both processes achieve similar goals, they differ significantly in materials, processing methods, cost, precision, and applications. This detailed guide explores these differences to help you make the right choice.
Overview of the Two Processes
LSR Overmolding (Injection-Based)
LSR overmolding involves injecting liquid silicone rubber into a mold cavity where it flows over a pre-placed substrate. The material is then cured (vulcanized) under heat to form a मजबूत, integrated part.
- Uses liquid, two-part platinum-cured silicone
- Injection molding process
- High automation and repeatability
Compression Overmolding
Compression overmolding uses pre-measured solid silicone (HCR – High Consistency Rubber) placed into a heated mold. The mold is closed, and heat and pressure shape the material around the substrate.
- Uses solid silicone rubber
- Heat + pressure forming process
- Manual or semi-automatic operation
2. Process Workflow Comparison
LSR Overmolding Steps
1. Substrate placement in mold
2. Injection of liquid silicone under pressure
3. Rapid curing (120–150°C typical)
4. Cooling and ejection
LSR flows easily and fills intricate mold features, ensuring precise results.
Compression Overmolding Steps
- Preform silicone placed in heated mold
- Mold closed to apply pressure
- Material flows and bonds to substrate
- Curing (longer cycle time)
- Ejection and trimming
This process relies more on mechanical pressure than fluid injection.
3. Key Differences in Detail
A. Material Type and Behavior
- LSR Overmolding:
- Low-viscosity liquid silicone
- Flows easily into complex geometries
- Platinum-cured (clean, fast curing)
- Compression Overmolding:
- High-viscosity solid silicone (HCR)
- Limited flow capability
- Often peroxide or heat cured
👉 LSR is ideal for intricate designs, while compression suits thicker, simpler parts.
B. Precision and Tolerance
- LSR: Ultra-high precision (±0.05 mm), excellent for micro-features
- Compression: Moderate precision (±0.2 mm), suitable for larger parts
👉 LSR dominates in applications requiring tight tolerances and fine details.
C. Cycle Time and Production Speed
- LSR: Fast cycles (30–90 seconds), highly automated
- Compression: Slow cycles (5–15 minutes), labor-intensive
👉 LSR is best for high-volume manufacturing, while compression fits small batches.
D. Tooling and Cost Structure
- LSR Overmolding:
- High initial tooling cost
- Lower cost per unit at scale
- Compression Overmolding:
- Lower tooling investment
- Higher per-part labor cost
👉 Compression is cost-effective for prototypes; LSR becomes economical in mass production.
E. Bonding Strength
- LSR: Strong chemical bonding with substrates due to injection and curing process
- Compression: Strong mechanical bonding via heat and pressure
👉 Both provide reliable bonding, but LSR offers more consistent adhesion.
F. Surface Finish and Quality
- LSR:
- Smooth surface
- Minimal flash or burrs
- Excellent aesthetic quality
- Compression:
- More flash and trimming required
- Surface finish depends on mold quality
👉 LSR provides superior cosmetic and functional finish.
G. Material Compatibility
- LSR: Compatible with a wide range of plastics (PC, PA, PPS, etc.)
- Compression: Requires heat-resistant substrates due to higher curing temperatures
👉 LSR offers greater flexibility in material combinations.
H. Design Flexibility
- LSR:
- Supports thin walls, undercuts, micro-features
- Ideal for complex geometries
- Compression:
- Better for simple, thick designs
- Limited ability for intricate features
I. Material Waste
· LSR: Minimal waste due to precise injection control
· Compression: Higher waste due to excess material (flash)
4. Advantages and Disadvantages
Advantages:
- High precision and repeatability
- Fast production cycles
- Excellent surface quality
- Biocompatibility and safety (medical-grade applications)
- Strong, consistent bonding
Disadvantages:
- High tooling cost
- Complex mold design
- Requires specialized equipment
Compression Overmolding
Advantages:
- Lower tooling and setup cost
- Suitable for low-volume production
- Flexible material options
- Good for large, simple parts
Disadvantages:
- Slower production speed
- Lower precision
- More post-processing required
5. Applications Comparison
LSR Overmolding Applications
· Medical devices (catheters, seals)
· Consumer electronics (keypads, waterproof seals)
· Automotive components
· Wearables and smart devices
Compression Overmolding Applications
· Industrial gaskets and seals
· Large silicone covers
· Low-volume custom parts
· Prototyping and testing
6. When to Choose Each Process
Choose LSR Overmolding if:
· You need high precision and complex geometry
· Production volume is high
· Product requires biocompatibility or premium quality
Choose Compression Overmolding if:
· You need low-cost tooling
· Production volume is low to medium
· Design is simple and less detailed
Conclusion
Both LSR overmolding and compression overmolding are essential technologies in silicone manufacturing.
· LSR overmolding excels in precision, automation, and scalability, making it the preferred choice for high-end and mass-produced products.
· Compression overmolding remains a practical, cost-effective solution for simpler designs and smaller production runs.
Understanding these differences allows manufacturers and designers to select the most efficient process—ensuring optimal performance, cost control, and product quality in their applications.
