The principle of high-frequency welding and how to achieve uniform heating at the molecular level

High-frequency welding utilizes a high-frequency electromagnetic field to generate heat through molecular polarization friction within materials, enabling non-contact fusion. Its core challenge lies in achieving molecular-level uniform heating via technical design to eliminate localized overheating or incomplete melting. Below is an explanation of its principles and key uniform heating mechanisms:

I. Basic Principles of High-Frequency Welding

1. Energy Conversion

   • High-frequency equipment generates an electromagnetic field (e.g., 27.12 MHz or 40.68 MHz).
   • Polar materials (e.g., PVC, TPU) placed in this field undergo rapid dipole realignment, causing intense intermolecular friction and heat generation.
   • Electrical energy is directly converted into thermal energy, raising the material to its melting point.

2. Fusion Process

   • Molten material flows under applied pressure and solidifies upon cooling, forming seamless bonds without external heat sources.

II. Mechanisms for Achieving Uniform Molecular Heating

1. Uniform Electromagnetic Field Distribution

• Coaxial Electrodes: Vertical penetration of the electromagnetic field across the welding area prevents edge field scattering and localized hotspots.
• Electromagnetic Shielding: Absorbs excess field energy to ensure uniform surface field intensity, enabling synchronized heating.

2. Frequency-Material Compatibility

• Dielectric loss properties (a material’s ability to absorb field energy) vary by type.
• Equipment selects optimal frequencies (e.g., 27.12 MHz for PVC; 40.68 MHz for TPU) to concentrate energy in target layers, minimizing heat transfer to non-welded regions.

3. Dynamic Power and Pressure Control

• Real-Time Monitoring: Sensors track material temperature and feed data to control algorithms.
  • Example: Power to overheated zones is reduced; insufficiently heated zones receive increased energy.
• Precision Pressure: High-precision molds distribute force evenly to prevent thickness variations.

4. Surface Pretreatment

• Plasma Cleaning/Coating Modification: Removes oils, oxides, and enhances surface energy to improve field-material coupling efficiency.
• Ensures energy focuses on the weld layer, minimizing losses and enhancing uniformity.

Technical Advantages

• Zero Contact: Eliminates tool wear and contamination.
• Energy Efficiency: Direct energy conversion reduces waste.
• Consistency: Submicron-scale uniformity ensures weld integrity for critical applications (e.g., medical devices, automotive seals).