Technical Principle of CO₂ Laser Welding for Thermoplastic Carbon Fiber Reinforced Thermoplastics (CFRTP)

Technical Principle of CO₂ Laser Welding for Thermoplastic Carbon Fiber Reinforced Thermoplastics (CFRTP)CO₂ laser welding of carbon fiber reinforced thermoplastics (CFRTP) is an efficient, non-contact advanced joining technology. It utilizes laser energy at a specific wavelength to realize melting and molecular chain diffusion at the material interface, thereby forming high-strength welded joints.

Aiming at the process configuration of 1500W laser power and 200kg (approximately 2000N) pressure, the core technical principles and key points are as follows:1. Core Technical PrincipleCO₂ laser welding follows the physical process of Energy Absorption → Heat Conduction → Melting and Compaction.Energy Absorption MechanismThe wavelength of CO₂ laser is typically 10.6 μm. Thermoplastic resins (such as PEEK, PPS, and PA) and carbon fibers exhibit an extremely high absorption rate for this wavelength.

Function of carbon fiber: As an efficient heat absorber, carbon fibers heat up rapidly after receiving laser energy.

Resin melting: The heat absorbed by carbon fibers is transferred to the surrounding thermoplastic resin matrix through heat conduction, raising the temperature above the melting point (Tm) or glass transition temperature (Tg), and converting the resin into a high-viscosity molten state.Molecular Chain Diffusion and EntanglementIn the molten state, the thermoplastic molecular chains at the welding interface acquire sufficient kinetic energy and diffuse across the interface mutually.Tight Bonding under PressureThe pressure of 200 kg is critical to ensuring welding quality. The pressure forces the molten resin to fill microscopic interfacial gaps and discharge bubbles, and promotes strong physical entanglement of molecular chains between the two layers under compression.2. Analysis of Key Technical Points1. Laser Power Control (1500W)1500W belongs to the medium-to-high power range. For CFRTP welding, power density determines the size of the Heat Affected Zone (HAZ).2. Pressure Compensation (200kg)The static or dynamic pressure of 200 kg serves three functions during welding:

· Resisting springback: Carbon fibers possess elasticity; pressure ensures the materials remain in close contact without separation during thermal expansion.

· Densification: Reduces the void content in the welded area and improves the shear strength of joints.

· Auxiliary heat conduction: Close contact improves interlayer heat conduction efficiency and achieves uniform molten layer thickness.3. Spot Quality and Path OptimizationCO₂ laser generally has a relatively large spot size, which is favorable for CFRTP welding. A wider spot provides a gentle temperature gradient and reduces the risk of direct carbon fiber burnout.3. Process Flow and Precautions· Interface effect: Carbon fibers feature thermal conductivity anisotropy — heat conducts faster along the fiber direction and slower in the vertical direction. The welding path should be arranged according to the fiber layup direction.

· Preheating and cooling: At 1500W laser power, the temperature of the welding zone rises extremely fast. Pressure should be maintained for a certain holding time after welding until the temperature drops below the solidification point, to prevent warpage or debonding.

· Shielding gas: Nitrogen or argon is recommended as shielding gas to prevent oxidative degradation of resin at high temperatures.4. ConclusionUnder the synergistic effect of 1500W laser power and 200kg pressure, CO₂ laser welding enables rapid and automated joining of CFRTP.

· 1500W provides sufficient energy reserve for deep penetration melting;

· 200kg pressure guarantees the structural quality at the physical level.

This process combination is especially suitable for the manufacturing of thick-section components and high interlaminar strength structural parts in aerospace and automotive industries.