Common weld seam design errors in plastic laser welding

Laser is a very effective tool for joining thin plates, films, thermoplastics and fabrics. Its greatest feature is the ability to quickly and accurately adjust the energy to the desired heating point. The laser output covers a range of wavelengths. Lasers of different wavelengths have different interactions with plastics. The laser welding process is also affected by the type, color, thickness and additives of the plastic.

Plastic laser welding is a non-contact welding method. Compared with traditional ultrasonic welding, it can protect vibration-intolerant components or complex electronic components, and there are no vibration particles. The laser welding trajectory can be freely set, and the structure and appearance design are very flexible.

For laser welding, different locations on different parts usually require different sized weld spots. The equipment needs to be able to quickly obtain the location of the smallest spot, and then move up and down to enlarge the spot to meet the welding needs. These can be done manually or automatically with standard tools.

The shape of the welding area should be designed according to the requirements of the welding task. The choice of welding process, the shape of the injection molded part, and the optical and mechanical properties of the two welded parts determine the type of welded joint. The overlapping part of the injection molded part (such as joints, slots, positioning structures, etc.) cannot be located between the laser light source and the weld joint, because it will create a shadow and hinder the laser transmission.

For laser welding, the two plastic parts need to be placed flat against each other. The laser beam must pass through the transmissive layer to reach the welding area, and the laser beam cannot be blocked, reflected, refracted or attenuated.

The welding ribs are preferably designed in the lower part and have a rectangular cross-section. In this way, the surfaces of the two parts are parallel to each other during pre-assembly. The triangular or trapezoidal cross-sections designed for ultrasonic welding ribs are not recommended.

For appearance parts, it is necessary to design a retaining groove to prevent the overflow from being visible. For example, design a corresponding groove on the upper part.

For circumferential welding, the overfit between the two cylinders must be designed because it is impossible to clamp the external tool.

Common weld design errors

Structural design

Considering the optical characteristics of the laser beam, some common design errors should be avoided.

For the above transmitter, a flat surface should be designed above the weld seam without special geometry. Ideally, the laser beam should be roughly perpendicular to the component. Or you can tilt it at a small angle (15掳). If the tilt angle is too large, the transmitted laser power will be reduced due to scattering.

During the irradiation process, the laser beam should also be considered to avoid the raised structure of the part or the fixture platen, which partially or completely blocks the laser beam.

Injection mold design

When designing the injection mold, the injection point and ejector pin should be designed at the injection point and ejector pin. These characteristics easily lead to irregular and uneven plastic welding surfaces, affecting the welding results.

Deformation of plastic parts

During the design and manufacturing stages, the possible bending and warping of the parts should be avoided. If the parts are deformed too much, the parts will not be able to be assembled or the gaps will be large.

In some cases, the parts can be pressed back to their original shape for welding. However, a large internal stress will be formed inside the parts, which may cause the weld to break again. Pay special attention to the reinforcements.