Laser Welding Solutions for Metallic Materials and Composites-ShangHai RunQia Electronics Technology Co.,Ltd.

Laser Welding Solutions for Metallic Materials and Composites

In automobile manufacturing, the joining of components is an indispensable process. Especially driven by the demand for automotive lightweighting, the application of fiber-reinforced composite materials is gradually increasing. The joining of metal and composite materials has become a critical problem that material suppliers and vehicle manufacturers must solve.

Unlike adhesive bonding, laser welding requires no additional adhesives. It also avoids structural damage to components caused by mechanical fastening. As a result, it has become a popular dissimilar material joining process in recent years. Currently, laser welding is one of the most promising scalable production technologies for metal-to-composite joining.

Fabrication of Roof Reinforcement Ribs

Reinforcement ribs are fabricated by hot pressing continuous glass fiber reinforced PA6. The semi-finished continuous glass fiber reinforced composite is first heated to the processing temperature by infrared heaters, then compression molded and trimmed. Afterwards, metal brackets need to be mounted on the reinforcement ribs for assembly with the vehicle roof. The metal brackets are stamped from steel sheets.

(1) Principle of Laser Welding Technology

The metal bracket is pre-treated by laser to modify its surface structure. The laser then heats the metal bracket, melting the composite material in contact with the metal surface. A firm joint is subsequently formed under applied pressure.

To guarantee joining quality, the research team adopted thermal imaging technology for non-destructive defect detection of welded joints. During welding, laser irradiation induces ablation on the metal surface to form cavity structures. Meanwhile, the adjacent composite material melts and forms molten beads along the processing direction. Repeating this process creates a special geometric structure on the bonding interface, establishing a positive mechanical interlock between the polymer and the metal.

Therefore, the strength of the hybrid structure is affected by the welding layout. Welding points can be arranged in a targeted manner to better match practical application requirements.

To realize on-line process control, a microstructure tracking and processing system was developed, capable of rapidly processing 2.5D geometric features. A high-speed infrared camera for process monitoring was also developed, enabling real-time on-line control and verification of the welding process.

Induction heating is widely applied in composite joining. It usually heats the composite itself for composite-to-composite bonding; for hybrid metal–composite joining, however, it generally targets the metal component. In this project, researchers adopted continuous induction heating technology.

When high-frequency alternating current passes through an inductor, an alternating electromagnetic field is generated. Heat is produced inside the metal via resistive loss and hysteresis loss. The metal is induction-heated to a temperature above the polymer melting point but below its thermal degradation temperature. At the contact interface, the composite material melts and fills the cavities on the metal surface under pressure.

(2) Laser Welding Process

When welding composite reinforcement ribs to metal brackets, laser radiation is emitted by diode stacks and focused onto the workpiece through optimized optical components. The metal absorbs the laser energy and converts it into heat.

There are two mainstream laser joining processes:

1) Laser Transmission JoiningBy selecting a specific laser wavelength, the laser beam transmits through the transparent polymer and irradiates the metal surface. Thermal conduction raises the polymer temperature and causes melting at the contact interface. However, the glass fiber reinforced composite used in this project has low optical transparency, making laser transmission joining unsuitable.

2) Laser Heat Conduction JoiningAs an alternative to transmission joining, laser radiation acts directly on the metal surface, and heat is conducted to the bonding zone through the metal substrate.

3) Energy input is determined by laser power, irradiation duration, and laser absorptivity of the metal surface. The project adopted adjustable optical elements to optimize beam geometry and path, achieving uniform energy input. In addition, clamping devices apply consolidation pressure to ensure complete wetting of the metal surface by the molten polymer and reliable bonding performance.

(3) Thermal Imaging Quality Inspection

For industrial mass production, thermal imaging technology was introduced to ensure stable product quality. Using halogen lamps and other optical heat sources, the detection depth can be adjusted by modulating frequency, enabling efficient quality inspection of finished components.