LSR Overmolding Process: From Substrate Pretreatment to Final Inspection

LSR overmolding is a key technology that injects LSR onto pre-placed substrates for chemical bonding and mechanical interlocking. This article details the complete process from substrate pretreatment to final inspection.

1. Overview of LSR Overmolding

1.1 What is LSR Overmolding

LSR overmolding refers to injecting a layer of liquid silicone rubber onto a pre-formed substrate (metal, plastic, etc.), achieving firm bonding through chemical bonding and mechanical interlocking.

1.2 Advantages

• Soft-hard combination with functional zoning
• One-shot molding, reduced assembly
• Enhanced feel and aesthetics
• Added sealing and protection functions

2. Substrate Pretreatment

2.1 Metal Substrate Pretreatment

1. Degreasing (solvent/ultrasonic)
2. Sandblasting (increased surface roughness)
3. Plasma treatment (increased surface energy)
4. Primer application

2.2 Plastic Substrate Pretreatment

1. Clean off release agents
2. Flame/plasma treatment
3. Primer application

2.3 Primer Selection Principles

• Chemical compatibility with substrate
• Matching LSR cross-linking reaction
• Environmental aging resistance
• Compliance with product regulations

3. Overmolding Injection Process

3.1 Insert Placement Methods

• Manual placement: for small batches
• Robotic placement: for high volumes
• Visual positioning: for accuracy

3.2 Injection Parameters

• Injection pressure: 40-100 MPa
• Injection speed: Medium (prevent insert displacement)
• Mold temperature: 160-190 degrees
• Cure time: 40-90 seconds

3.3 Key Control Points

• Insert positioning stability
• Primer drying degree
• Injection speed profile
• Curing temperature uniformity

4. Common Quality Issues

4.1 Poor Bonding

Causes: Wrong primer selection, unclean substrate surface, insufficient curing temperature

Solutions: Change primer, improve cleaning, increase mold temperature

4.2 Short Shots

Causes: Insufficient injection volume, unbalanced runner, poor venting

Solutions: Increase shot volume, optimize runner, improve venting

4.3 Insert Displacement

Causes: Excessive injection pressure, insecure insert fixing

Solutions: Reduce injection speed, improve positioning structure

5. Final Inspection

5.1 Visual Inspection

• Overmold completeness
• Surface defect-free
• Uniform color

5.2 Bond Strength Testing

• Pull test
• Torsion test
• Peel test

5.3 Environmental Reliability Testing

• Temperature-humidity test
• Thermal cycling
• Salt spray test

Conclusion

LSR overmolding is a comprehensive technology. Mastering substrate pretreatment, primer selection, and injection process control are the three key elements for ensuring overmolded product quality.