Tuesday, October 9, 2012

Quality Assurance for Laser Polymer Welding Processes

Transmission laser welding of polymers is a well-established industrial joining method,China Composite Resin - Structural Adhesive for Carbon/ Glass Fiber Fabrics Manufacturers its reliability makes it particularly suitable for applications where very high weld seam quality is specified. A number of quality assurance methods are available when using this technology to safeguard the specifications demanded for the quality.China Composite Resin - Structural Epoxy Paste Adhesive Manufacturers These quality assurance methods are suitable for implementing a zero-error strategy, under very economically attractive conditions. This three-part series of articles discusses the different approaches.
In this form of laser welding, the laser beam passes almost completely unhindered through the upper welding partner until it hits the welding zone where it is absorbed by the lower welding partner. China Composite Resin - Two Component Expanding Epoxy ManufacturersThe pressure of the clamp tooling enhances thermal conduction into the transparent joining partner, which then also causes local plasticization of the polymer to create a secure adhesive bond.
When the laser beam passes through a polymer, the beam can be scattered by the presence of crystalline zones and glass fibers. Moreover, coloring agents, pigments and other additives can partially absorb some of the energy. Each of these effects reduces the intensity of the beam at the joining horizon. This means that the nature and quantity of the crystallites or the pigments, fillers and other additives within the components, can indirectly influence the laser welding process.
Compounding is used to determine the material constituents. This also involves the main definition of the optical properties of the material. Fluctuations in the level of dosing do not usually influence laser plastic welding in practice.China Composite Resin - Construction Structural Adhesive for Carbon/ Glass Fiber Plates Manufacturers However, for functional reasons, the optical properties should be tested prior to any modification being made to the material compositions.
In practice, a more relevant source of errors along the process chain is the injection molding stage. This has a significant influence on the geometrical and optical properties of the joining components because of the process parameters and shape of the molds, particularly in the case of filled, reinforced or highly-crystalline polymers. In the case of fiber-reinforced polymer components, it is possible for fiber agglomerates to accumulate in parts of the injection tool.China Carbon Plate 120g/㎡, T300 1K, Plain Weave Manufacturers If the injection point is close to the welding zone, there is a risk that this may be affected by strongly fluctuating transmission conditions. The transmission values can also be significantly influenced by unsuitable cooling down speeds when processing partially-crystalline polymers.
In addition to optical properties, the dimensional stability and surface quality of the components can also have an influence on laser welding. The properties of the surface of the transmissive joining partner influence the reflection of the laser beam when it enters the polymer component as well as when the beam exits the base of the transmissive component. There could be a rise in the reflections at the ejector pin marks. The dimensional stability of the component is a critical factor for the thermal contact of the joining partner. If no gapless join can be established between the welding partners when the parts are held by the clamping tool, this will hinder thermal conduction at these points as well as having the potential to cause thermal damage to the polymer at these positions.
A similar effect arises when there are notches in one of the joining partners. Damage of this kind can be caused e.g. by improper handling during the transport and assembly processes which take place upstream of the welding process. The effects range from local heat accumulation, and the overheating of the lower joining partner, all the way to the improper sealing of the joint line.
Contamination of the components on the beam input side of the overlying transmissive part can absorb some of the laser beam energy and lead to surface burning of the plastic. Although this rarely leads to a reduction in the quality of the weld seam, residues of this kind on the surface of the component are usually unacceptable for aesthetic as well as functional reasons.

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