Laser Transmission Welding Process Research Articles

Laser transmission welding of Polyphenylsulfone resin using Sn film absorbent: Weld formation control and mechanical properties enhancement

Polyphenylsulfone resin (PPSU), holding significance across various domains, was successfully welded by the laser transmission welding (LTW). In order to optimize the morphology and mechanical properties of the weld seam, the Sn film was chosen as an intermediate layer and the mechanism governing the formation control and mechanical performance was unveiled. Without the addition of Sn film, weld formation was subpar, marked by defects such as bubbles occurring in the weld seam, particularly under moderate power conditions. After introducing Sn film as a metal absorbent, the molten pool pores were stabilized and the temperature distribution was optimized during LTW process, which promoted the welding process stability and facilitated the mixing and agitation of the molten pool. The Energy-dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) were conducted on cross-sections of the weld seam. Analysis revealed the formation of newly forged metallic bonds (SnC) between the metal and the PPSU, which were instrumental in bolstering the shear strength of the weld seam. After using the Sn as intermediate layer, the shear strength of welding joints increased from 23.21 MPa to 29.14 MPa. At optimal intermediate-layer thickness, the shear fracture exhibited predominantly a plastic tearing micro-pit morphology instead of brittle fracture rock pattern.

Modeling and optimization of conflicting responses in the laser transmission welding process using RSM, PSO, and TLBO algorithm

Laser transmission welding (LTW) is a widely used polymer welding technology in industries today. The performance of LTW is governed by a number of process parameters, and fine-tuning those parameters is critical for the process to achieve the intended results. Optimization of process parameters for enhancing LTW performance, like weld strength and weld width, is always tricky since they are inherently contradictory. Therefore, in this research, an effort is made to optimize the LTW parameters utilizing the three best-known optimization approaches, and the performance of those optimization approaches in LTW process optimization is compared. First, the response surface method (RSM) is employed to build empirical equations that establish an empirical correlation between process variables and desired performance features. These empirical equations are then employed as objective functions for process optimization utilizing the RSM-based desirability function approach (DFA), particle swarm optimization (PSO), and teaching learning-based optimization (TLBO) algorithms. The performance of the chosen optimization approaches is compared with reference to optimum results, accuracy, convergence rate, and computing time. PSO and TLBO algorithms outperform the DFA approach for single and multi-objective optimizations. TLBO is found to have faster convergence, whereas PSO takes less time for computation.

Multi-response optimization for laser transmission welding of PMMA to ABS using Taguchi-based TOPSIS method

Recently, the usage of laser transmission welding (LTW) technology in the automotive industry has been rising for joining thermoplastic parts regarding its superior properties in comparison to other welding technologies. However, specifying the process parameters is a crucial step to obtain satisfactory welding quality for the vehicle parts. In this context, this paper addresses the LTW process of Polimetil metakrilat (PMMA) to Akrilonitril bütadien stiren (ABS) materials for the production of taillights in an automotive company and proposes a new multi-response Taguchi-Based TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) method to optimize machining parameters in the laser welding process. In the proposed solution methodology, the main effects of the parameters on different outputs are identified by using the [Formula: see text] orthogonal array of the Taguchi method. Regarding the best parameter set for each output, the best parameter set for multi-response is identified by using the TOPSIS method, in which alternatives are evaluated through the interrelated quality measures. To optimize welding process in taillight production, PMMA and ABS samples with the dimensions of [Formula: see text] in width, [Formula: see text] in length, and [Formula: see text] in thickness are used in the experiments. The samples are welded by using LPKF Twinweld 3D 6000® laser welding machine. For the welding process, laser power, welding speed, and pressure force are taken into account as the input parameters to optimize three responses: weld strength, breaking strain, and weld width. To identify the best process parameter values, the Taguchi Method is initially employed to calculate the main effects of LTW parameters for each output. Then, the TOPSIS method is carried out to evaluate a number of alternative parameter sets generated through the Taguchi results. As a consequence of the TOPSIS ranking scores, the best parameter set that jointly optimizes three outputs of the LTW process is identified for the taillight production as [Formula: see text] power, [Formula: see text] speed, and [Formula: see text] pressure force. Based on the conducted experiments, this parameter setting achieves the highest weld strength, breaking strain level, and above-average weld width. The results of the experiments show that the proposed methodology is capable of optimizing LTW parameters for a multi-response with fewer experiments in the joining of plastic vehicle parts.

An integrated methodology for estimating the interface temperature and effects of powder diameters in laser transmission welding process

The powder diameter affects the heat generation and further influences the quality of weldments when the MZA powder is used as laser-absorbents to carry out laser transmission welding (LTW). It is difficult to measure the temperature due to its extremely short duration. A mathematical model considering the multiple reflections of metal powder is established to predict heat generation. The mathematical model is verified and then used to describe the influence of line energy density and powder diameter on the temperature profile of the LTW process. The results demonstrate that the temperature from experiments and simulation are consistent. Therefore, the established model is suitable to predict the heat generation of metal powder laser-absorbents in the LTW process.

Enabling laser transmission welding of additively manufactured thermoplastic parts using an expert system based on neural networks

In order to use laser transmission welding (LTW) for additively manufactured parts such as prototypes, small series, or one-off products, an enhanced process knowledge is needed to overcome the difficulties in the part composition resulting from the additive manufacturing process itself. In comparison to an injection molding process for thermoplastic parts, the additive manufacturing process fused deposition modeling leads to an inhomogeneous structure with trapped air inside the volume. In this paper, a neural network-based expert system is presented that provides the user with process knowledge in order to improve the weld seam quality of laser welded additively manufactured parts. Both additive manufacturing and LTW process are assisted by the expert system. First, the designed expert system supports the user in setting up the additive manufacturing process to increase the transmissivity. During welding, the additive manufacturing and LTW process parameters are used to predict the weld seam strength. To create the database for the expert system, specimens of transparent and black polylactide are additively manufactured. In order to change the transmissivity at an emission wavelength of 940 nm of the diode laser used, the manufacturing parameters for the transparent parts are varied. The transmissivity of the parts is measured with a spectroscope. The transparent samples are welded to the black samples with laser powers between 8 and 14 W in the overlap configuration and shear tensile tests are performed. In this work, the predictions of the transmissivity and the shear tensile force are demonstrated with an accuracy of more than 88.1% of the neural networks used for the expert system.

Modeling and experiments of the thermal degradation behavior of PMMA during laser transmission welding process

Reducing thermal degradation of plastics during laser transmission welding (LTW) process is the key to obtain high-quality weld seam. In this study, a thermal degradation prediction model is proposed. First, using polymethyl methacrylate (PMMA) as an exemplary material, the weld seams are prepared at different process parameters, including the laser power, welding velocity and carbon black (CB) content. Full characterization of the prepared weld seams was performed through shear tests, scanning electronic images, and ultra-depth-of-field microscope. The results reveal that thermal degradation occurs with bubbles at the interface and decreases the shear strength of the weld seam. Second, the thermal history model during LTW is simulated through a 3-D transient heat transfer finite element method (FEM), where the highest temperature is extracted to aid in comprehension of thermal degradation mechanism. Third, a thermal degradation prediction model is proposed based on the thermal history model and thermal degradation kinetic model which is solved by the thermogravimetric analysis (TGA). The results from the proposed prediction model is consistent with the occurrence of the initial thermal degradation and the trend of shear strength of the weld seam. Therefore, this study might present a potential way to optimize the processing window by effectively suppressing the appearance of thermal degradation.

Expert system-supported optimization of laser welding of additively manufactured thermoplastic components

Laser transmission welding (LTW) is a known technique to join conventionally produced thermoplastic parts, e.g. injected molded parts. When using LTW for additively manufactured parts (usually prototypes, small series), this technique has to be evolved to overcome the difficulties in the part composition resulted in the additive manufacturing process itself.In this paper, a method is presented to enhance the weld seam quality of laser welded additively manufactured parts assisted by a neural network-based expert system. To validate the expert system, specimens are additively manufactured from polylactide. The parameters of the additive manufacturing process, the transmissivity, and the LTW process parameters are used to predict the shear tensile force with the neural network. The transparent samples are welded to black absorbent samples in overlap configuration and shear tensile tests are performed. In this work, the prediction of the shear tensile force with an accuracy of 88.1% of the neuronal network based expert system is demonstrated.

Laser Transmission Welding is a promising joining technology technique – A Recent Review

Laser transmission welding (LTW) is one of the latest evolutions in joining technology. Simply, it involves joining two similar or dissimilar materials by melting and fusing two parts at their interface using laser radiation. The upper material is transparent in order to allow the laser radiation to pass and heat the second material which is in this case an absorbent material. This technique is also known with other names such as Laser Plastic Welding, Through-Transmission Welding and Laser Assisted Metal to Polymer Joining. The developments occurred in this field have also enabled LTW to approach different Lasers like Diode Laser, CO2 Laser, Nd: YAG Laser and Fiber Laser. This review aims to explain LTW process, working procedures, effect of Laser types and process parameters on this approach. It especially clarifies using LTW to weld thermoplastics materials together or with metals. It also attempts to help scholars to have an overview on LTW technique and achieve their answers related to this topic.

Laser transmission welding of polymers – A review on welding parameters, quality attributes, process monitoring, and applications

• A comprehensive review on several aspects of the laser transmission welding process is presented. • Laser transmission welding parameters and their effects on the performance of the welds are discussed. • Laser transmission weld quality attributes used to assess the quality of the welded joints are reviewed. • Process monitoring techniques for the laser transmission welding process are discussed. • Several applications of laser transmission welding in different industrial sectors have been identified. Laser transmission welding (LTW) is nowadays a well-received polymer joining process. New applications are emerging more and more due to the unique advantages of LTW over conventional joining processes. This paper provides a comprehensive review on various aspects of LTW techniques through a detailed survey of several scholarly publications, industrial studies, scientific reports, etc. This review focuses primarily on five major aspects of LTW, which are (a) welding parameters and their effects, (b) weld quality attributes, (c) process monitoring techniques, (d) material combinations, and (e) industrial applications. After an introduction to the process, the welding parameters, and how they influence the LTW process are described first. This is followed by a description of the quality attributes of LTW, including weld strength, weld pool dimensions, part gap-bridging ability, meltdown, and weld morphology. Several process monitoring techniques applied to LTW are then discussed for pre-, post-, and real-time monitoring of the process. Subsequently, material combinations that are successfully welded using LTW are described, including welding of polymer to polymer, metal, ceramic, glass, wood, etc. Finally, several applications of LTW in different industrial sectors are identified, and the results of the review are concluded.

Laser transmission welding of dissimilar plastics: 3-D FE modeling and experimental validation

This paper presents a three-dimensional finite element model (FEM) of laser transmission welding of dissimilar plastics. Welding of polycarbonate to ABS (acrylonitrile butadiene styrene) with a moving volumetric heat source is modeled using ANSYS® Parametric Design Language. In model development, consideration is given to all major thermal phenomena associated with the laser transmission welding process, such as heat conduction, convection, and thermal radiation. The model also incorporates the effects of dilution on temperature cycles. Welding experiments are conducted to validate the numerical model. The model predicted simulation results are in good agreement with the measurements. The results predicted by the model can further be used for the optimization of the process.

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.

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.

Optimization of Laser Transmission Welding Process Parameters Using Single Objective and Multi Objective Optimization Technique

Optimization of Laser Transmission Welding Process Parameters Using Single Objective and Multi Objective Optimization Technique

Fabrication of bi-layer PMMA and aluminum 6061-T6 laminates by laser transmission welding: Performance prediction and optimization

Laser transmission welding can be effectively used in fabrication of laminated parts. In the present work an attempt was made to fabricate a polymeric laminate structure made of polymathic methacrylate (PMMA) and aluminum 6061-T6 by laser transmission welding process. A series of laser welding experiment has been carried out to analyze effect of laser power, welding speed, focal position and axial pressure on lap shear force and weld seam width. Response surface methodology including regression analysis, analysis of variances and desirability approach function has been utilized here to analyze the processing data. It is found from the results that focal position has greatest influence on both the lap shear force and weld bead width. Optimization is also carried out in two different criteria for achieving desired welding performance. The optimization results obtained by this approach are consistent well with the results measured through confirmatory experiments.

3-D FE heat transfer simulation of quasi-simultaneous laser transmission welding of thermoplastics

Laser transmission welding of thermoplastics is a non-contact welding process for producing aesthetically and qualitatively high-grade joints with low thermal and mechanical stresses. In this research work, a three-dimensional heat transfer model is developed to simulate the quasi-simultaneous variant of laser transmission welding of thermoplastics. The thermal analysis is implemented to acquire the temperature history in this multi-pass welding process. The transient temperature field is computed using ANSYS® finite element code. The multi-pass movement of laser beam is realized by implementing a subroutine in ANSYS® Parametric Design Language (APDL). The effect of process variables namely laser power, welding speed, number of welding passes and line energy on temperature field during welding is investigated. The predicted outcomes of the temperature profiles, weld pool and time–temperature history are useful for optimizing the process parameters in the quasi-simultaneous laser transmission welding process.

3D modeling of thermoplastic composites laser welding process – A ray tracing method coupled with finite element method

Laser Transmission Welding process (LTW) is a well know technic for polymer welding. This technic can also be applied to thermoplastic glass fiber composite (polymer + continuous glass fibers). But in this case two phenomenon occur and are able to make the welding in a poor quality: light absorption and light scattering. The two phenomenon occurring into the semi-transparent substrate of reinforced fiber thermoplastic, during the LTW, are numerically examined. A 3D transient thermal model of LTW is achieved with the FEM software COMSOL. A ray tracing software is developed to compute the heat source term used in the FEM simulation. First, the energy distribution coming from the laser irradiation is assessed. Ray tracing techniques allowed us to deal with both absorption and a strong light-scattering caused by the heterogeneity of composite: polymer matrix and glass fibers. Then, the energy balance equation was solved in order to study the heating stage. The present paper proposes an investigation on the influence of the absorption on the heat affected zone. The interest to consider absorption was shown for process optimization purposes and for the use of reinforced composites colored or filled with additives.

Laserwelding of biopolymers

Due to the scarcity of the resource oil but also to increasing environmental awareness the market of biopolymers show a continuous growth. Biopolymers have different properties compared to conventional polymers which could lead to different processing requirements for the laser transmission welding process. In order to investigate the suitability of the process and to elaborate the differences between conventional polymers and biopolymers, three biopolymers [PLA, Bio-PE, and Bio-PET] are selected and on these laser welding tests are performed. An adapted diode-laser-beam source is used for the welding process. The created samples are analyzed and evaluated by thin sections and tensile tests.

Modeling of the heating process during the laser transmission welding of thermoplastics and calculation of the resulting stress distribution

At present, various welding techniques are used in many different process chains and steps. Moreover, when joining metallic materials, welding processes are used to create integrated material bonds of organic as well as inorganic materials. One of the methods used to join thermoplastics is laser transmission welding. In addition to the low heat introduced into the welded parts, high welding speed is one of the reasons why this process is used in industry. Highly accurate simulation of the heating process would improve understanding of the process, facilitate and reduce the time required for process installation in the long run, and provide a significant contribution for computer-aided component design. The quality of the weld line in laser transmission welded plastic parts is affected by material properties, machine parameters, and their interactions with each other. For these reasons, a thermal simulation model was developed as part of a research project due to support the operator of the laser transmission welding process in setting up the process faster and more reliably. First, the presented model considers the various interferences of the welding process by the material, the thermal, and optical properties which are often not known exactly enough. Second, interaction between the laser beam and the material was determined and implemented. The developed calculation model allows for highly reliable determination of the size of the heat affection zone. The exact process window can be identified and predicted. Furthermore, the heating and cooling process can be reproduced using the spatial temperature distribution, which allows cycle time to be optimized on the basis of these results. In addition to the impact on weld quality, residual stresses can be found in welded thermoplastic parts as a result of local thermal expansion and shrinkage. Especially, tensile stresses are undesired effects of the welding process because they can have an unfavorable impact on the local mechanical properties of the welded components. Mainly, in laser transmission welded parts, these tensile residual stresses occur in the weld seam. These tensile stresses can overlap with permitted operating stresses, and this may result in early failure of the component. This can take place, in particular, when the structural part is exposed to oscillating and/or highly corrosive stresses. These are the reasons why it is important to know the residual stresses introduced into the component, in order to minimize the distribution of these stresses by means of suitable process management. To calculate the mechanical behavior in the structural simulation of a welded part, precisely mapping the temperature field is of fundamental importance. Residual stresses and warping are directly based on the temperature field. Based on thermal calculations, the paper presents thermo-mechanical simulations for the determination of residual stress distribution in the weld seam, depending on the welding parameters.

An approach to select the optimal process parameters of laser transmission welding using firefly algorithm

In the present work, laser transmission welding process is investigated and optimised using firefly algorithm, a population-based metaheuristic and bio-inspired algorithm. Laser power, welding speed, stand-off distance and clamp pressure are the laser transmission welding process parameters which control the output qualities like lap-shear strength and weld-seam width of the welded part. To select the optimal setting of process parameters, single-objective and multi-objective optimisations are performed using firefly algorithm, in which the objective functions are developed using response surface method. Results obtained by using firefly algorithm are found to be superior to those obtained using conventional optimisation technique. Firefly algorithm also found to be superior to particle swarm optimisation algorithm, differential evolutionary algorithm, and shuffled frog leaping algorithm in terms of convergence rate. It is found that firefly algorithm is an excellent optimisation tool with respect to fast convergence and locating global optima. It is also very efficient in predicting trends of multi-dependent responses.

Simulation and experimental study of laser transmission welding considering the influence of interfacial contact status

The traditional finite element model (FEM) of laser transmission welding (LTW) is generally assumed that the interface of transparent and opaque materials is ideal. This assumption ignores the influence of real interfacial contact status on welding results. For this problem, the volumetric heat source model is constructed based on the Lambert–Beer law in this paper. And thermal contact model of LTW is constructed in the mode of volumetric absorption. Then the numerical simulation of temperature contours during LTW process is taken into thermal contact model. Under the condition of no interface gap (S=0), the weld temperature contours and weld profile of transparent and opaque PA66 are obtained by numerical simulation and experiment. Furthermore, under the condition of interface gap (S=20), the weld temperature contours and weld profile of thermal contact model are analyzed and predicted. The results show that thermal contact model is more consistent with real model when compared with traditional model. And thermal contact model can reasonably predict the changes of weld temperature contours and weld profile. Therefore, thermal contact model can be used to characterize the influence of interfacial contact status on welding results and improve the accuracy of numerical simulation in the process of LTW.