Introduction to Five Methods of Laser Plastic Welding

Introduction to Five Methods of Laser Plastic Welding

In recent years, with continuous technological advancements, the trend of laser plastic welding has shown gradual growth. In the past, some laser technologies had not yet achieved breakthroughs, and the high cost of laser equipment meant that the initial investment was significantly higher compared to traditional welding methods, making it difficult to yield quick returns. However, the economic advantages of laser technology have now become evident. Laser plastic welding reduces the design complexity for engineers.

Currently, many industries—including automotive semiconductors, medical and food sectors—have extremely high requirements for processing precision and aesthetic appeal. This has made laser welding an essential process in the production of such products, further driving the development of laser welding technology.

The closer the compatibility, fusion temperature, and matching properties of the plastic materials are in laser welding, the better the results. The application methods of laser plastic welding differ somewhat from metal welding, including contour welding, quasi-simultaneous welding, simultaneous welding, and mask welding.

1. Contour Welding

The laser moves along the contour line of the plastic welding layer, melting it and gradually bonding the plastic layers together. Alternatively, the clamped layers can be moved along a fixed laser beam to achieve welding.

Illustration of Laser Contour Welding

In practical applications, contour welding imposes high requirements on the quality of injection-molded parts, especially for components with complex weld lines, such as oil-gas separators. During the laser plastic welding process, contour welding can achieve a certain depth of fusion along the weld line. However, this depth is minimal and uncontrollable, necessitating minimal deformation in the injection-molded parts.

2. Simultaneous Welding

The laser beams from multiple diode lasers are shaped using optical components and directed simultaneously along the contour of the welding layer. This generates heat across the entire weld seam at once, causing the full contour line to melt and bond in a single step.

Illustration of Laser Simultaneous Welding

Simultaneous welding is primarily used in automotive lighting and medical industries. This method employs multiple beams that are optically shaped to form a welding pattern, with the key advantage of reducing internal stress. Due to its high precision requirements and relatively higher cost, it finds extensive application in the medical field.

3. Scan Welding (Quasi-Simultaneous Welding)

Scan welding, also known as quasi-simultaneous welding, combines the principles of contour welding and simultaneous welding. This technique employs high-speed mirrors to direct a laser beam at speeds up to 10 m/s along the welding path, causing the entire joint area to heat up progressively and fuse together.

Illustration of Laser Scan Welding

Quasi-simultaneous welding is the most widely used method, particularly in automotive parts manufacturing. It utilizes high-frequency XY galvanometer scanners, with its core advantage being precise control over material collapse during plastic welding. Unlike contour welding—which generates significant internal stress that can compromise sealing performance—quasi-simultaneous welding's rapid scanning motion, combined with advanced control systems, effectively minimizes internal stress.

4. Roll Welding

Roll welding is an innovative laser plastic welding process with various forms. There are two main types of roll welding: 

Illustration of Laser Roll Welding

The first is Globo ball welding. The laser lens tip is equipped with an air-cushioned glass ball, which serves both to focus the laser and clamp the plastic parts. During the welding process, the Globo lens is driven by a motion platform to roll along the welding line, completing the weld. The entire process is as simple as writing with a ballpoint pen. Globo welding does not require complex upper fixtures—only a bottom mold to support the product. A variant of the Globo ball welding process is the Roller drum welding process, which replaces the glass ball at the lens tip with a cylindrical glass barrel to achieve a wider laser line segment. Roller drum welding is suitable for wider welds.

The second is the TwinWeld welding process. This laser plastic welding technique features a metal pressure wheel attached to the lens tip. During welding, the pressure wheel presses against the edge of the welding line to perform the weld. The advantage of this process is that the metal pressure wheel does not wear out, making it suitable for large-scale production. However, the pressure applied by the wheel to the edge of the welding line can easily generate torque, leading to various welding defects. Additionally, the relatively complex structure of the lens poses some challenges for welding programming.

5. Mask Welding

The laser beam is positioned through a template to melt and bond the plastic. The template only exposes a very small, precise welding area on the underlying plastic layer, allowing the laser beam to heat only the parts of the product not covered by the mask. This technology enables high-precision welding with resolutions as fine as 10 micrometers.

Illustration of Laser Mask Welding

The mask welding principle allows for precise and stable welding of microfluidic components. The channel geometry remains intact, preventing molten material from flowing into narrow channels as small as 200 µm.

Key Advantages of Songsheng Optoelectronics Laser Plastic Welding System: 

Illustration of Songsheng Optoelectronics Laser Plastic Welding System

1. Utilizes high-energy-density laser heat sources to optimize the temperature at plastic joining interfaces, ensuring both high speed and precision in the laser welding process.

2. By  adjusting the laser beam's shape and size, the heat-affected zone and joint area can be minimized. The welded surface shows no visible traces or damage from the welding process.

3. Components can be pre-assembled before welding, making the process highly straightforward.

4. No restrictions on component shape or size, significantly enhancing design flexibility.

5. Vibration-free operation, making it ideal for vibration-sensitive components such as electronic devices and medical instruments.

6. Non-contact processing (no physical interaction between the components and heat source), ensuring compliance with hygiene and safety standards for medical and food equipment.

7. High flexibility in laser beam delivery, enabling easy automation integration.

8. No toxic fumes generated, ensuring a safe and reliable welding environment.