Plastic Materials Compatible With CO₂ Laser Welding Technology

The following is a comprehensive analysis of plastic materials compatible with CO₂ laser welding technology and their key characteristics, combining multiple research papers and industrial application cases:

I. Classification and characteristics of applicable materials**

1. Thermoplastic polymer matrix

- Polypropylene (PP)

Penetration welding can be achieved by CO₂ laser, and the melting depth can be accurately controlled to about 1mm in overlapping PP sheets by wavelength fine-tuning (such as using a tunable CO₂ laser), without thermal damage or melting on the surface. Its semi-crystalline structure shows good controllability in laser energy absorption and melting behavior.

- Polycarbonate (PC)

It has high transparency, impact resistance and thermal stability. As a matrix material, its composite materials (such as glass fiber reinforced PC) can achieve high-strength bonding by laser welding, especially for applications requiring optical transparency.

- Polyamide (PA6/PA12)
Carbon fiber reinforced polyamide composites (such as PA6-CF) show high energy absorption rate in CO₂ laser welding and are suitable for fast processing. Its high melting point and low hygroscopicity help reduce porosity defects during welding.

2. Engineering plastics and composites
- Polyphenylene sulfide (PPS)
Semi-crystalline thermoplastic, high temperature resistant (Tg about 90°C) and low hygroscopicity. Resistance welding studies have shown that its joints composited with carbon fiber still retain 61% of the original strength at high temperatures (150°C), indirectly verifying its adaptability to laser heat input.
- **Polyetheretherketone (PEEK)**
High melting point (343°C) and excellent thermal stability make it suitable for high-power laser welding, but the heat input needs to be precisely controlled to avoid thermal degradation. Studies have shown that its composite materials can optimize the microstructure through cyclic heat input in laser additive manufacturing.

 

  Second, key technical parameters for material selection
1. Optical absorption characteristics
- The energy of CO₂ laser (wavelength 10.6μm) is mainly absorbed by polymers containing polar groups (such as PA, PPS), while low-polarity materials (such as PP) need to enhance absorption efficiency through additives (carbon black, graphene) or interface design (such as transparent heat sink).
- Two-dimensional mesoporous polymer/graphene heterostructures (such as mPDG) optimize laser energy transfer through high specific surface area and conductivity, and are suitable for high-precision welding of micro devices.

2. Thermal behavior and crystallinity
- The melting-recrystallization behavior of semi-crystalline materials (such as PP, PPS) needs to match the laser parameters to avoid excessive heat input leading to interface embrittlement. For example, wavelength selection in PP welding can adjust the melting depth and reduce the heat-affected zone.
- Amorphous materials (such as PC) have no clear melting point, so the welding window needs to be controlled by the glass transition temperature (Tg) to prevent material degradation.

3. Influence of reinforcing fibers
- Laser welding of carbon fiber reinforced composites (CFRP) requires a balance between fiber orientation and matrix melting behavior. For example, carbon fiber/PA6 composites exhibit high strength and interlayer bonding in screw extrusion additive manufacturing, and their laser welding needs to consider the interference of fiber distribution on energy absorption.

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  III. Process optimization strategy
1. Laser parameter control
- Wavelength tuning (such as tunable CO₂ laser) can optimize energy absorption for different materials, such as precise control of melting depth by wavelength fine-tuning in PP welding.
- Power density and scanning speed need to match the thermal diffusivity of the material to prevent overheating (such as PEEK) or insufficient fusion (such as PA6).

2. **Interface design and auxiliary technology
- The use of transparent heat sinks (such as quartz glass) can accelerate the cooling of the welding zone and reduce thermal damage, which is suitable for welding thin layers of materials.
- Preheating or post-treatment (such as infrared heating) can improve interlayer bonding strength, especially for high fiber content composites.

 

  IV. Application Cases and Challenges
1. Successful Cases
- Automotive Lightweight Components: Laser-welded PA6-CF composites are used for door brackets, with a 30% increase in strength over conventional injection molded parts.
- Flexible Electronics: Polyester-spandex fabrics achieve high conductivity (4Ω/cm) through laser direct metallization, suitable for smart textile sensors.

2. Technical Bottlenecks
- Highly reflective materials (such as aluminum powder-filled polymers) require the development of anti-reflective coating technology.
- The difference in thermal expansion coefficients of dissimilar polymers in multi-material welding can easily lead to interfacial stress concentration.

 

  Summary
The selection of materials for CO₂ laser welding technology needs to comprehensively consider the effects of optical absorption, thermal behavior and reinforcement phase. Future research can focus on: ① Developing new absorbents to expand the scope of material application; ② Optimizing welding parameters in combination with machine learning; ③ Exploring the potential for in-situ regulation of material microstructure by cyclic heat input.