Laser Transmisson Welding (LTW)
Laser Transmission Welding of Plastics
Laser transmission welding is a well-established process for joining plastic components with high precision and reliability. It is based on the principle of transmitting laser energy through a transparent joining partner and selectively absorbing it in the underlying material, generating localized heat and creating a strong, clean weld.
The process is particularly suitable for applications requiring high optical quality, tight seams, and minimal thermal impact. It enables particle-free, non-contact joining and is widely used in industries such as automotive, medical, and consumer products.
Depending on component geometry, material combination, and production requirements, different process variants can be applied. These include mask welding, contour welding, radial welding, quasi-simultaneous welding, advanced quasi-simultaneous welding, and simultaneous welding.
Each method offers specific advantages in terms of cycle time, flexibility, and weld quality. This allows manufacturers to select the optimal process for their application, ensuring efficient production and consistent, reproducible results.
Process Variants
In contour welding, a focused laser beam follows the weld seam once or several times along the defined joining contour. The plastic is melted only at the point of direct laser impact and solidifies again immediately after the beam has passed. This results in a clean, precise weld without visible melt expulsion, which makes the process particularly suitable for components with aesthetic or functional surface requirements. Contour welding is also highly flexible, as the welding path can be adapted to different component geometries. It can be used for both small and large plastic parts, including components with complex contours or larger dimensions.
Typical applications include automotive lighting, large housings, display components, and plastic tanks or reservoirs.
Radial welding is a special form of contour welding designed for round or rotationally symmetrical components. Typical applications include pipes, connectors, reservoirs, ring-shaped housings, and fluid-carrying plastic assemblies. Unlike other process variants, the joining pressure can often be generated by the component geometry itself, for example through an interference fit. This can reduce the need for external clamping technology in direct contact with the part. Depending on the setup, either the component rotates, the laser moves around the component, or the beam is guided by mirrors. The result is an economical and reproducible process for circular weld seams.
Typical applications include cooling pipes, fluid connectors, cylindrical filter housings, and ring-shaped sensor or actuator components.
In mask welding, the weld geometry is defined by a physical mask placed between the laser source and the component. Only the areas exposed by the mask are irradiated and welded, while the surrounding material remains protected. This enables very fine, sharply defined weld structures and is especially useful for small parts or applications with delicate geometries. Typical fields include microfluidic components, diagnostic cartridges, and precise channel or membrane structures. Mask welding is less flexible than scanner-based processes when geometries change, but it offers excellent accuracy and clean seam definition where very small or complex weld patterns are required.
Typical applications include lab-on-chip cartridges, microfluidic channel plates, diagnostic consumables, and fine membrane or filter structures.
In quasi-simultaneous welding, a scanner guides the focused laser beam along the weld contour several times at very high speed. Because the laser passes over the entire contour repeatedly, all areas of the seam are heated and melted almost simultaneously. Under clamping force, both joining partners move toward each other and the molten material is displaced laterally at the weld seam. This joining path can compensate for component tolerances and can also be used for process monitoring.
Quasi-simultaneous welding is especially suitable for housings, sensors, electronic components, and flat assemblies that require tight, reliable, and economical welds.
Advanced Quasi-Simultaneous Welding is a patented EVOSYS process that extends the possibilities of conventional quasi-simultaneous laser plastic welding. The process combines two laser sources with different wavelengths in one processing head. Depending on the material and application, the two lasers can irradiate the joining area simultaneously or alternately at a defined frequency. This allows both joining partners to be heated more directly and more selectively. As a result, the welding process can become faster, the process window can be expanded, and new material combinations can become possible. AQW is particularly valuable for demanding applications where strength, process stability, short cycle times, or clear-clear welding concepts are important.
Typical applications include transparent plastic assemblies, high-strength housings, challenging material combinations, and components with demanding tightness or cycle-time requirements.
In simultaneous welding, the entire weld seam is heated and melted at the same time by one or more laser sources or by specially shaped optics. The energy distribution must be designed so that the line energy is as uniform as possible across the complete weld contour. Similar to quasi-simultaneous welding, the joining partners move toward each other under clamping force, and the joining path can be used to compensate for tolerances and monitor the process. Simultaneous welding offers very short cycle times and high repeatability, making it especially suitable for high-volume production, recurring geometries, spot welds, ring welds, and applications with high visual quality requirements.
Typical applications include ring-shaped welds, high-volume sensor housings, medical consumables, and visually demanding plastic assemblies.
Frequently asked questions
This depends from material, design and function and requirements of your product. Manufacturing tolerances of single parts also should be considered.
Sounds complex, but our team can easily define the best variant when knowing your requirements with a short quick review.
The Advanced Quasi-Simultaneous welding method enables you to weld material combinations which are not easily weldable with other methods and it increases stability and robustness of welding results in serial production.
For lab machines, the AQW welding head additionall provides maximum flexibility as you can do almost all other LTW process variants like contour and quasi-simultaneous welding or use the higher wavelength for EvoClear welding.
Actually, there is no standard welding method but all variants are useable depending on your parts, material and requirements.
Most commonly used for flat parts is Quasi-Simultaneous Welding with the integrated collapse control to ensure highest quality of produced parts and best cycle times. For specific materials or other requirements, other methods or combinations of different methods may be preferred.
Would you like a personalized consultation?
