Laser Transmission Welding Research Articles

State-of-art review of laser irradiation strategies applied to laser transmission welding of polymers

Laser transmission welding (LTW) offers superior weld quality and mechanical performance over conventional polymer welding processes. The ever-increasing applications in a wide range of industrial products prove its competitive process advantages and cost-efficiency. The process capability and performance depend on material properties, process parameters, and laser irradiation and application strategies. A wide range of laser irradiation and application strategies have been developed and implemented in laser transmission welding. They vary in laser scanning methods, cycle time, process flexibility, etc. and their specific selection varies depending on the welding profile, work materials, part size, variety and volume of production, etc. A comprehensive survey of these approaches is carried out to evaluate their operating concepts, key features, process specifications, and implementations. Focusing on these objectives, this paper presents a state-of-the-art review of laser irradiation and application strategies applied to laser transmission welding of polymers.

Characterization of polypropylene pulsating heat stripes: Effects of orientation, heat transfer fluid, and loop geometry

A parametric analysis of the thermal performance of flat polypropylene pulsating heat pipes (PHPs) is presented. In particular, the thermal performance was characterized for pulsating heat pipes with different number of turns of the serpentine channel, different orientations with respect to gravity, and containing different heat transfer fluids. The dependence of polymeric PHPs performance on design parameters is poorly understood to date. The development of polymeric PHPs characterized by high mechanical flexibility will have significant impact on thermal management of smartphones, portable electronics, and deployable systems such as cube satellites. Several prototype PHPs with different number of turns of the serpentine channel were fabricated bonding together three polypropylene sheets by selective transmission laser welding, after cutting out a serpentine channel in the central sheet. The thermal performance of the devices was characterized by supplying an ascending/descending stepped thermal power ramp to the evaporator, and measuring the corresponding equivalent thermal resistance between the evaporator and the condenser.

Laser transmission welding of polymers – A review on process fundamentals, material attributes, weldability, and welding techniques

Laser technology often offers solutions where existing technologies have struggled or require improvements. Over the last two decades, laser transmission welding (LTW) has become a viable fabrication method for industries that engaged in polymer welding. This paper presents a comprehensive review on several aspects of LTW process. In specific, this review focuses on four major aspects of the LTW: (a) process fundamentals, including operating principles and process requirements; (b) compositions and pre-welding conditions of polymers and their effects; (c) laser weldability of polymers, considering compatibility and non-compatibility issues; and (d) welding techniques and application strategies, including technological variants and the transformation of application strategies from absorber-based to absorber-free laser welding of polymers. The conclusion of the review and the prospects for further research work are eventually addressed.

Modelling and thermal simulation of absorber-free quasi-simultaneous laser welding of transparent plastics

The growing demands on the quality of plastic components and the trend towards miniaturisation are posing a great challenge on plastics processing technology. As many complex components can no longer be manufactured in a single step, joining processes such as laser transmission welding are gaining in importance. In classic laser transmission welding, the joining partners have different optical properties. The upper joining partner is transparent in the laser wavelength range, whilst the lower partner is absorbent due to the addition of absorber materials. In medical and biotechnological applications, the addition of absorber materials is often undesirable due to strict biocompatibility requirements. If, on the other hand, radiation sources are used which emit radiation in the area of the natural absorption of the plastic (λ = 1600–2000 nm), untreated transparent plastics can also be welded. In this work, a theoretical model will be presented to calculate the temperature distribution and progression during quasi-simultaneous welding using a thulium fibre laser (λ = 1940 nm). A sensitivity analysis is carried out to investigate the influence of different parameters on the heat affected zone (HAZ). The simulated HAZ is then compared with the HAZ from the experimental work.

Experimental and numerical study of the laser transmission welding between PA6/sepiolite nanocomposites and PLA

PA6/sepiolite nanocomposites have been manufactured at different wt% sepiolite loading and a fixed minimum load of a IR absorber additive (CAA). Nanocomposites were characterised and welded with PLA specimens through transmission laser welding technology (TLWT). Resulting welded specimens were also characterised. Experimental data obtained from the characterisations were introduced and processed in a Computer-Aided Engineering (CAE) software to obtain a suitable fracture model based on cohesive zone model (CZM) and capable of predicting the behaviour of the nanocomposite/PLA welds against shear forces. A correlation analysis was performed to assess the goodness of fit between the experimental and simulation data.

Research on temperature-assisted laser transmission welding of copper foil and polyethylene terephthalate

Abstract Copper foil is widely used in printed circuit board because of its good conductivity, especially in flexible printed circuit board. A traditional two-layer flexible copper clad laminate avoids introduction of an additional adhesive, its application range is improved, but its peel strength is low. Laser, as an efficient and clean energy, has great potential application value in this field. Based on the research of parameters of laser transmission welding copper foil and polyethylene terephthalate (PET), to prepare a two-layer flexible copper clad plate and improve the bonding strength of welding joints in laser welding, this study proposes to change the surface roughness of the copper foil and preheat the weldment in the welding process. The bonding properties of the welded joint were tested by a micro-tensile test bench. Through the study of laser parameters, a welding speed of 300 mm/min was used to explore the surface roughness of the copper foil, it was found that the overall welding effect was best when the surface roughness of the copper foil was 400 nm. The effect of the preheating temperature on the bonding properties of weldments was studied by preheating samples at different temperatures. A high-speed camera was used to record the instantaneous tensile state of the welding sample, the surface roughness of the debonding sample under different conditions was measured by atomic force microscope. The interface morphology of the sample was characterized by optical microscope, X-ray photoelectron spectrometer, and high-resolution field emission scanning electron microscope. The bonding mechanism was revealed, and the reason for the strength improvement of the welding joint was discussed. In view of the research results of the PET/copper foil high-strength bonding in this paper, it shows that the laser welding technology has an important application prospect in the production of a two-layer flexible copper clad laminate.

Effect of Different Laser Welding Parameter on Welding Strength in Polymer Transmission Welding Using Semiconductor

In this work, the diode laser (810μm wavelength) was used for laser transmission welding application on PMMA (polymethylmethacrylate). The welding was done between opaqueness and transparent with thickness 2 mm and 2.57 mm, respectively. The effects of different process parameters, laser speed, spot size and force with different values (5, 15, 20 mm/min), (2, 2.5, 3mm) and (2, 6, 10 N) respectively were used to study their effect on weld width and strength. L9 Taguchi orthogonal array has been used to design the experiments and optimize the result. The result of the signal to noise ratio shows that, the width of welding decrease with increasing both the welding speed and the spot size while it was increased with increasing the force on the sample. The narrower width observed at speed (20mm/min), spot size (3mm), and force (2N). Also, the best strength was found at speed (15 mm/min), spot size (2.5mm), and force (10N).

Laser transmission welding of absorber-free semi-crystalline polypropylene by using a quasi-simultaneous irradiation strategy

Unlike other joining techniques, laser transmission welding offers unique advantages such as selective and contactless energy deposition. This enables the fabrication of flexible seam geometries at low mechanical and thermal stresses. However, the use of absorbing additives for the lower joining partner such as carbon black is crucial as most polymers are transparent in the spectral range of typical beam sources (800–1100 nm). A novel approach is the application of beam sources emitting radiation within the polymeric intrinsic absorption bands between 1500 and 2000 nm. This enables absorber-free laser welding of transparent polymers for medical or microfluidic applications such as Lab-on-a-Chip devices. The main drawback on the other hand is the large heat affected zone (HAZ) due to the volume absorption which is extending over the entire cross section. A possible way to overcome this disadvantage is a quasi-simultaneous irradiation strategy. It could be proved in the past that the HAZ of polycarbonate (PC) can be reduced in the vertical direction by up to 30% compared with contour welding. Since the effects of light scattering on the absorber-free quasi-simultaneous irradiation strategy are still unknown, the beam propagation was simulated in polypropylene (PP). Based on the results, a thermal simulation of the welding process was carried out using the finite element method (FEM). The simulation model was then evaluated by comparing the results with experimental trials.

Analysis of the interaction process during laser transmission welding of multilayer polymer films with adapted laser wavelength by numerical simulation and thermography

The field of application of multilayer polymer films ranges from the packaging of food and other goods to medical technology and the encapsulation of organic electronics. The layer structure of the polymer films is adapted to the respective areas of application. Usually, polymer film systems contain several individual layers. A trend toward more flexible production and batch sizes down to one can be identified in all the above-mentioned areas of application. This requires new production processes. Laser transmission welding with adapted laser beam sources represents a promising approach for this. It is characterized by a contactless and a locally limited energy position. A very high degree of format flexibility is also possible, thanks to a purely numerical adjustment of the welding contour. In many applications, it is desired to keep the polymer film as it is available on the market. If two multilayer polymer films should be welded with laser radiation in an overlapping arrangement, sufficient absorption of the laser radiation in the material is required. Each individual polymer layer has wavelength-dependent material-specific optical properties. Due to the vibrations of polymer chains, polymers have absorption peaks in the near infrared range. If a suitable laser beam source is now used for the welding process, the energy can be deposited directly in the material without modifying it beforehand. The energy input should be the highest at the point of contact or in the sealing layers of the two polymer films so that it is locally heated and melted. The surrounding film layers are also thermally influenced by heat conduction processes. In addition, the optical properties of the other layers influence the propagation of the laser radiation through the multilayer polymer film. For a comprehensive understanding of the process, it is imperative to examine these processes in detail. Therefore, the interaction process is considered in depth and, especially, the propagation of the temperature field within the material, which is not directly accessible for real measurements, is analyzed exactly. For this purpose, on the one hand, a numerical temperature model is set up, which depicts the real experimental setup and takes into account the optical properties and heat conduction variables of the individual layers. The numerical model allows the temporal resolution of interaction processes within the multilayer polymer film to be viewed from different angles. On the other hand, thermographic images of the real samples are taken during the welding process. For this purpose, the emitted heat radiation of the polymer films is measured off-axis. The data obtained are evaluated and compared with each other. For the final discussion of the results, additional analyses of the weld specimens microscopy and thin sections are used.

Modeling three-dimensional rough surface and simulation of temperature and flow field in laser transmission welding

• A numerical model for rough surface is established by applying the anisotropic 3D surface reconstruction method. • A 3D FEM model considering rough surface is developed to simulate and analyze the temperature field, molten pool geometry and flow fields in the LTW process. • The temperature of the contact surface between the transparent and absorbent layer is discontinuous, which is consistent with the incomplete contact under real welding conditions. The traditional Laser Transmission Welding (LTW) simulation method assumes that the welding contact interface is smooth. However, the actual welding interfaces exhibit a large number of rough surfaces. The mismatch may decrease the accuracy of the traditional finite element model (FEM). Thus, this work aims to establish a three-dimensional (3D) FEM model considering the rough surface. Numerical model for 3D rough surface of welding specimen is established. The distribution of molten pool area, temperature and flow field coupling are discussed. Then, a series of experiments were set up to obtain the weld width to verify the model. The results show that the temperature of the contact surface between the transparent part and the absorbent layer is discontinuous, which is consistent with the incomplete contact of the contact surface under real welding conditions. The error of weld width values between the simulated and experiment is smaller, which also confirm that the established model is more precise.

Laser Welding of Transmitting High-Performance Engineering Thermoplastics.

Laser processing is a rapidly growing key technology driven by several advantages such as cost and performance. Laser welding presents numerous advantages in comparison with other welding technologies, providing high reliability and cost-effective solutions. Significant interest in this technology, combined with the increasing demand for high-strength lightweight structures has led to an increasing interest in joining high-performance engineering thermoplastics by employing laser technologies. Laser transmission welding is the base method usually employed to successfully join two polymers, a transmitting one through which the laser penetrates, and another one responsible for absorbing the laser radiation, resulting in heat and melting of the two components. In this work, the weldability of solely transmitting high-performance engineering thermoplastic is analyzed. ERTALON® 6 SA, in its white version, is welded by a pulsed Nd:YAG laser. Tensile tests were performed in order to evaluate the quality of each joint by assessing its strength. A numerical model of the joint is also developed to support the theoretical approaches employed to justify the experimental observations.

Micro-patterned metal current collectors for high aspect ratio flexible graphene supercapacitors

When graphene thin films are used as high aspect ratio supercapacitor electrodes, their performance can be limited due to graphene’s relatively low electrical conductivity, compared with metals. The integration of the graphene film with a metal current collector can overcome this limited conductivity. However, poor adhesion between pristine graphene and metal films adversely affects a supercapacitor’s flexibility. In this study, a metal current collector film was patterned on a flexible substrate in the form of a microgrid, via selective laser sintering of silver nanoparticles. The delamination of the graphene film was mitigated by interlocking it with the substrate using laser transmission welding. A specific capacitance of 5.8 mF/cm2 was obtained at 1.5 mA/cm2 with PVA- H3PO4 electrolyte, and the capacitance was retained at up to 94% when the electrode length was increased by six times. In addition, a thin gold (Au) layer was electrodeposited to the silver grid to improve its electrochemical stability. As a result, the capacitance change remained below 10% for 10,000 charging/discharging cycles. The electrodeposition of pseudocapacitive manganese dioxide (MnO2) nanoparticles was also performed, further increasing the capacitance to 49.1 mF/cm2 at 1 mA/cm2 with 0.5 M Na2SO4 electrolyte.

Laser transmission welding of thermoplastic with beam wobbling technique using particle swarm optimization

Laser transmission welding is growing day by day with an increase of the uses of thermoplastic materials. This article presents the effect of various process parameters on weld strength and weld seam width obtained. The transparent polycarbonate and black carbon filled PMMA, each of 2.8 mm thickness have been joined by using low power laser. Here, effect of wobble frequency and wobble width are studied along with other process parameters. It is observed that weld seam width much depends upon the wobble width and the effect of wobble frequency is minimum. It has been observed that laser beam wobbling provides the greater weld strength by enlargement of joint area. Moreover, Beam wobbling plays a significant role to achieve better weld strength and weld width. Response surface methodology has been used to model the laser welding process parameters and responses of welding through regression analysis. The results of ANOVA reveal that the models formed appropriately predict the responses within the range of process parameters. A confirmation experiment has also been conducted to validate the results. A multi objective optimization has been used to find the optimum solution by Particle swarm optimization technique.

Laser Transmission Welding of additive manufactured parts: process modifications to reduce cavities inside the weld seam

For small batches, prototypes, and customized mass production, additive manufacturing is a prominent technology in the production of complex thermoplastic parts. A frequently used process is Fused Deposition Modeling (FDM). For more and more applications, additive manufactured components have to be joined in order to form larger functional assemblies. Laser transmission welding (LTW) of thermoplastics is an industrial established technique, e.g. for joining injection molded parts in the automotive sector.Compared to injection molding, the FDM process itself results in an inhomogeneous structure with a significant amount of air inside a component. Because the part is built up layer by layer, it supports the formation of cavities inside the weld seam and thus a reduction in the weld seam strength.To optimize the weld seam quality, new strategies for the design of FDM parts for LTW are being investigated. Welded parts are being analyzed with tensile testing and cross sections.

Absorber-free laser transmission welding of transparent polymers using fixed focus optics and 3D laser scanner

Laser transmission welding is a well-known joining technology for thermoplastics, providing reliable and hermetical sealing without adhesives or particle formation. The main advantages of laser-based energy input - high precision, no additional adhesive and no particle emission - are essential for medical and optical applications. To obtain sufficient absorption in visually transparent polymers, thulium fibre lasers emitting in the polymers’ intrinsic absorption spectrum are used. Optics with high numerical aperture provide large intensity gradients inside the specimen, enabling selective fusing in the joining zone. Although the basic feasibility has already been demonstrated, the welding process lacks stability and productivity.Aim of this work is the determination of optimized settings for a fast and reliable welding process. Thus, the interplay of process parameters as well as their impact on the seam are analysed by thermal simulations. Calculated settings are verified by welding tests with COC, PA6 and PETG, using a fixed-focus optics and a 3D laser scanner with up to 200 mm/s feed rate.

Transmission Laser Welding of Polyamides: Effect of Process Parameter and Material Properties on the Weld Strength

Transmission laser welding (TLW) is an environmentally friendly and versatile process for assembling polymeric parts. Welding by transmission requires the upper element to be transparent to the laser wavelength whereas the inferior part is absorbent to the same wavelength. Thus, the energy of the laser beam is concentrated at the interface, allowing both polymeric parts to be melted. Upon temperature, the interdiffusion of polymeric chains takes place at the interface, creating bridges between both parts, resulting in a strong assembly. Laser welding is in principle applicable to any thermoplastic, provided that it is transparent to the laser wavelength.In the present work, carbon black filled polyamide has been assembled with two types of 2 mm and 4 mm thick partially transparent polyamide specimens. The effect of the process parameters such as energy density, speed of the laser beam and the part thickness have been correlated with the mechanical strength of welds, measured by wedge tests. The thermomechanical and optical properties of the samples have been assessed and correlated to the dimensions of the heat affected zone (HAZ). For a deeper understanding of the effect of optical and thermal properties of the materials on the quality of the welded joint, a numerical modeling is proposed. The ray tracing method is able to determine the light scattering and the absorption at the micro-scale in the polyamide semi-transparent part. The results of the ray tracing are the volume term source and the heat flux that generates temperature elevation.

Spatially-resolved crystallinity determination of polymer welding seams by Raman-microscopy

In polymer laser transmission welding (LTW) the process parameters affect the weld seam crystallinity, which impacts mechanical, optical and chemical properties of the weld seam material. However, correlations between process parameters and these material properties are still under investigation. To improve the necessary understanding, spatially resolved crystallinity measurements by Raman microscopic mapping offer valuable insights. This paper demonstrates an advanced spectroscopic evaluation method capable of resolving crystallinity distributions even within the absorbing joining partner. Besides the description of the utilized self-developed Raman microscope, the main focus is put on the mathematical spectral reconstruction by multiple Voigt functions used to calculate the crystallinity.

Correlation between weld seam morphology and mechanical properties in laser transmission welding of polypropylene

In laser welding of polymers, the morphology of weld seams is decisive for the weld strength. Usually, time consuming parameter screening with subsequent destructive tests are performed in order to find suitable process parameter sets resulting in strong weld seams. For more effective and flexible process development, non-destructive characterization methods which base on, for example, crystal structure detection in the welding zone require a deep understanding of interrelations between weld seam morphology and strength.Therefore, polypropylene samples welded overlapping are analysed regarding crystal structure in the heat-affected zones by microscope before and after tensile testing is used to quantify the weld strength. Experimental results show that there is an almost linear relationship between the increase in force and the cross-sectional area of weld seams in the absorption joining partner. Moreover, it is shown that thermal FE simulations allow the prediction of the size of the heat affected zone, which strongly influences the crystal structures inside the weld.

Scanning techniques for optimized damage tolerance in quasi-simultaneous laser transmission welding of plastics

Fiber lasers are increasingly replacing the commonly used diode lasers in laser transmission welding of plastics for challenging applications due to their superior beam quality and the ability to use long working distances and small spot sizes. At the same time, these smaller spot sizes increase the risk of thermal degradation. In this work, we investigate different scanning strategies that allow controlling the weld seam widths. These strategies are characterized regarding the demands on the performance of the scanner system, the risk of thermal degradation and the mechanical properties of the resulting welds.

聚酰胺-不锈钢激光透射焊接工艺特性

聚酰胺-不锈钢激光透射焊接工艺特性