Laser beam is generated in this component to heat up the welding parts. The design of upper fixture often varies from laser sources and heating modes. For example, when a YAG laser or a diode laser is used as the heat source, optical fibers are often employed to provide mobility. However, the welding part cannot move. There are three types of interactions that can occur between laser radiation and plastics: reflection, absorption and transmission. The extent of individual interaction is dependent upon materials properties, laser wavelength, laser intensity and beam speed.
Transmission of laser energy through certain polymers allows for processes such as through transmission welding.
- Laser welding of polymers?
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When the laser beam travel through the interfaces between different medium, the laser beam is refracted unless the path is perpendicular to the surface. This effect needs to be considered when laser travels through multi-layer to reach the joint region. Internal scattering occur when laser pass through the thickness in semicrystalline plastics, where crystalline and amorphous phase have different index of refraction.
Scattering can also occur in crystalline and amorphous plastics with reinforcement like glass fiber and certain colorants and additives. Laser absorption can occur at the surface of plastics or during transmission through thickness. The amount of laser energy absorbed by a polymer is a function of the laser wavelength, polymer absorptivity, polymer crystallinity, and additives i. Pyrolytic process occurs at long wavelength radiation larger than 0.
Such process is involved with heat generations, which can be used for welding and cutting purposes. The heat distribution within a laser welded polymer is dictated by the Bouger-Lambert law of absorption.
Polymers often have secondary elements added to them for various reasons i. These elements can have a profound effect on the laser interaction with the polymer component. Some common additives and their effect on laser welding are described below. Various fibers are added to polymeric materials to create higher strength composites. Some typical fiber materials include: glass , carbon fiber , wood, etc. When the laser beam interacts with these materials it can get scattered or absorbed, changing the optical properties from that of the base polymer.
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In laser transmission welding, a transparent material with reinforcement may absorb or dilute the energy beam more, effecting the quality of the weld. Colorants pigments are added to polymers for various reasons including aesthetics and functional requirements such as optics. Certain color additives, such as titanium dioxide , can have a negative impact on the laser weldability of a polymer. The titanium dioxide provides a white coloring to polymers but also scatters laser energy making it difficult to weld.
Another color additive, carbon black , is a very effective energy absorber and is often added to create welds. By controlling the concentration of carbon black with the absorbing polymer it is possible to control the effective area of the laser weld.
The laser beam energy can be delivered to the required areas through a variety of configurations. The four most common approaches include: contour heating, simultaneous heating, quasi-simultaneous heating, and masked heating. In the contour heating laser scanning or laser moving technique, a laser beam of fixed dimension passes through the desired area to create a continuous weld seam.
In the simultaneous heating approach, a beam spot of appropriate size is used to irradiate the entire weld area without the need for relative movement between the work piece and the laser source. For creating a weld with a large area, multiple laser sources can be combined to melt the selected region simultaneously.
This approach can be adopted to substitute ultrasonic welding in the case of welding components sensitive to vibration. Key processing parameters for this approach include: laser wavelength, laser power, heating time, clamp pressure, cooling time, and polymer properties. In the quasi-simultaneous heating, a work area is irradiated by the use of scanning mirrors. The mirrors raster the laser beam over the entire work area rapidly, creating a simultaneously melted region.
Some of the important parameters for this technique include: laser wavelength, laser power, heating time, cooling time, polymer properties. Masked heating is a process of laser line scanning through a region with a mask, which ensures that only the selected areas can be heated when the laser pass through. This approach is capable of creating micro-scale welds on components with complex geometries. Depending on different interactions between laser and thermoplastics, four different laser welding techniques have been developed for plastic joining. CO 2 lasers have good surface absorption for most thermoplastics, hence they are applied for direct laser welding and laser surface heating.
Through transmission laser welding and intermediate film welding require the deep penetration of laser beam, so YAG lasers and diode lasers are the most common sources for these techniques. Similar to laser welding of metals, in direct laser welding the surface of the polymer is heated to create a melt zone that joins two components together.
This approach can be used to create butt joints and lap joints with complete penetration. Laser wavelengths between 2 and Laser surface heating is similar to non-contact hot plate welding in that mirrors are placed between components to create a molten surface layer. The exposure duration is usually between s. Process parameters for laser surface heating include the laser output, wavelength, heating time, change-over time, and forging pressure and time.
Through transmission laser welding of polymers is a method to create a joint at the interface between two polymer components with different transparencies to laser wavelengths. The upper component is transparent to the laser wavelength between 0. A typical colorant is carbon black that absorb most of the electromagnetic wavelength. The two components are held by the lower fixture to control alignment and a small clamping force is added to the upper part to form intimate contact.remicalvorcta.ml
Laser Welding - A Practical Guide (Electronic book text)
A melt layer is then created at the interface between the two components, composed of a mixture of two plastic materials. There are four different modes of transmission laser welding: scanning mode, simultaneous, quasi-simultaneous, and mask heating. Many benefits can be obtained by transmission laser welding such as fast welding velocity, flexibility, good cosmetic properties and low residual stresses.
From processing perspectives, laser welding can be performed in the pre-assembled conditions, reducing the necessity for complex fixtures; however, this method is not suitable for plastics with high crystallinity due to refraction and geometric limitations. Enables the reader both to understand and to use, in a practical manner, laser welding. The author explains the principles of laser welding and provides examples of industrial applications, examines many aspects of laser welding and devotes a complete chapter to safety.
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Laser Welding Guide
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