K.Y. Benyounis

Optimization of different welding processes using statistical and numerical approaches - A reference guide

Welding input parameters play a very significant role in determining the quality of a weld joint. The joint quality can be defined in terms of properties such as weld-bead geometry, mechanical properties, and distortion. Generally, all welding processes are used with the aim of obtaining a welded joint with the desired weld-bead parameters, excellent mechanical properties with minimum distortion. Nowadays, application of design of experiment (DoE), evolutionary algorithms and computational network are widely used to develop a mathematical relationship between the welding process input parameters and the output variables of the weld joint in order to determine the welding input parameters that lead to the desired weld quality. A comprehensive literature review of the application of these methods in the area of welding has been introduced herein. This review was classified according to the output features of the weld, i.e. bead geometry and mechanical properties of the welds.

AN ANN AND TAGUCHI ALGORITHMS INTEGRATED APPROACH TO THE OPTIMIZATION OF CO2 LASER WELDING

Abstract Nowadays several numerical methods are widely used for either modelling or optimizing the performance of the manufacturing technologies. That has been advanced due to the large diffusion of the personal computer and the numerical algorithms. The knowledge of those methods and the ability in integrating their functions can make both the manufacturing engineer and the researcher ace their duties. In this paper, two of those methods have been employed, the backpropagation artificial neural network and the Taguchi approach to the design of the experiment. They were applied to find out the optimum levels of the welding speed, the laser power and the focal position for CO2 keyhole laser welding of medium carbon steel butt weld. The optimal solution is valid in the ranges of the welding parameters that were used for training the neural networks. Extrapolation over those limits would restrict the applicability of the found solution. The proposed approach would be extendable to other keyhole laser welding processes for different materials and joint geometries.

Employment of finite element analysis and Response Surface Methodology to investigate the geometrical factors in T-type bi-layered tube hydroforming

Bi-layered tubing which consists of two different metallic layers is recommended to use in complex working environments as it offers combined properties that single layer structure does not have. However, in this wok, producing of T-shape bi-layered components using the tube hydroforming process is investigated. In this regard, the bulge height and the wall thickness reduction of the bi-layered hydroformed parts (responses) are modelled as functions of the geometrical factors using the combination of the finite element modelling (FEM) and Response Surface Methodology (RSM) for design of experiments (DOE). The geometrical factors effects and their interactions on the responses were determined and discussed. Based on the resultant models, a multi-response optimization study was conducted. Furthermore, for the optimum solutions, a significant agreement was indicated between the predicted and numerical values.

Finite element comparison of single and bi-layered tube hydroforming processes

Abstract In this paper, single and bi-layered tube hydroforming processes were numerically simulated using the finite element method. It was found that the final bulges heights resulted from the models were in good agreement with the experimental results. Both types of modeling have been kept with the same geometry, tube material, and process parameters to compare between the obtained hydroformed products (branch height, thickness reduction, and wrinkling) using different loading path types. Results were discussed.

Residual Stresses Prediction for CO2 Laser Butt-Welding of 304-Stainless Steel

Residual stresses are an integral part of the total stress acting on any component in service. It is important to determine and/or predict the magnitude, nature and direction of the residual stress to estimate the life of important engineering parts, particularly welded components. This work aims to introduce experimental models to predict residual stresses in the heat-affected zone (HAZ). These models specify the effect of laser welding input parameters on maximum residual stress and its direction. The process input variables considered in this study are laser power (1.03 - 1.368 kW), travel speed (26.48 – 68.52 cm/min) and focal point position (- 1 to 0 mm). Laser butt-welding of 304 stainless steel plates of 3 mm thick were investigated using a 1.5 kW CW CO2 Rofin laser as a welding source. Hole-drilling method was employed to measure the magnitude, and direction of the maximum principal stress in and around the HAZ, using a CEA-06- 062UM-120 strain gauge rosette, which allows measurement of the residual stresses close to the weld bead. The experiment was designed based on Response Surface Methodology (RSM). Fifteen different welding conditions plus 5 repeat tests were carried out based on the design matrix. Maximum principal residual stresses and their directions were calculated for the twenty samples. The stepwise regression method was selected using Design-expert software to fit the experimental responses to a second order polynomial. Sequential F test and other adequacy measures were then used to check the models adequacy. The experimental results indicate that the proposed mathematical models could adequately describe the residual stress within the limits of the factors being studied. Using the models developed, the main and interaction effect of the process input variables on the two responses were determined quantitatively and presented graphically. It is observed that the travel speed and laser power are the main factors affecting the behavior of the residual stress. It is recommended to use the models to find the optimal combination of welding conditions that lead to minimum distortion.

Assessment and Optimization of CO2 Laser Cutting Process of PMMA

The width of kerfs and quality of the cut edges, are affected by laser process parameters. In addition to the work‐piece material thickness, laser power, cutting speed, compressed air pressure, and focal point position are the main factors affecting the process output. In this paper CO2 laser cutting of four thicknesses of Polymethyl‐methacrylate (PMMA) were investigated by implementing Box‐Behnken design to develop the experiment. The aim of this work is to relate the cutting edge quality parameters namely: upper kerf (UK), lower kerf (LK) and the ratio between upper to lower kerfs to the process parameters mentioned above. Then, an optimization routine was applied in line to define the optimal cutting conditions. Mathematical models were developed to determine the relationship between the process parameters and the process output. The optimal laser cutting conditions were found.

Assessment and Minimization of the Residual Stress in Dissimilar Laser Welding

Establishing the relationship between process parameters and the magnitude of residual stresses is essential to determine the life of welded components. It is the aim of this paper to develop mathematical models to assess residual stresses in the heat-affected zone of dissimilar butt jointed welds of AISI304 and AISI1016. These models determine the effect of process parameters on maximum residual stress. Laser power, travel speed and focal position are the process input parameters. Plates of 3 mm thick of both materials were laser welded using a 1.5 kW CW CO2 Rofin laser as a welding source. Hole-drilling method was used to compute the maximum principal stress in and around the HAZ of both sides of the joint. The experiment was designed based on a three factors five levels full central composite design (CCD). Twenty different welding runs were performed in a random order, 6 of them were centre point replicates and the maximum residual stresses were calculated for each sample. Design-expert software was used to fit the experiential data to a second order polynomial. Sequential F test and other adequacy measures were used to check the model’s performance. The results show that the developed models explain the residual stress successfully. Using the developed models, the main and interaction effect of the process input variables on the residual stresses at either side of the weld were investigated. It is found that all the investigated laser parameters are affecting the performance of the residual stress significantly.

High Power CO 2 Laser Cutting for Advanced Materials – Review

Laser beams of light can be focused to very small spot sizes and are therefore, capable of delivering high energy-densities to small areas of a material. This localized high energy can be used to melt or vaporize the material to perform a cut. There are many types of laser systems that are currently in use for materials processing. CO 2 laser is among these types, which offers the highest average power for materials processing. Compared with other lasers, the higher power capability of the CO 2 type allows their use in processing different materials in mass production in many industrial applications. Consequently, they are often selected for automotive and other steel parts fabrication.

Multi‐response Optimization of Geometrical Factors in Bi‐layered Tube Hydroforming

In the last years many researchers were concentrating to develop and design new unconventional metal forming processes. Among such new technologies, tube hydroforming was proved as one of the most promising. Geometries of the tube and die were found to have significant effects on the hydroformed part. Based on the mathematical models, which describe the effect of the geometrical factors on bi‐layered tube hydroforming, a multi‐response optimization study was proposed in this paper with the aim to achieve different quality objectives for two different criteria. The optimal geometrical factors of bi‐layered tube hydroforming combinations were tabulated and discussed.

Review of Microstructures, Mechanical Properties, and Residual Stresses of Ferritic and Martensitic Stainless-Steel Welded Joints

Welding is a metal joining process widely used in industry. In this process, homogeneous microstructures, residual stresses, and variations in mechanical properties greatly affect the quality of welded joints. However, defects can occur due to intense concentration of heat in the welded region. These defects vary depending on the type of the welded material, welding process, and cooling rate of the welded parts. Over the years, different standard tests have been performed by researchers to measure and to quantify welded joints. Hardness and impact testing have been widely used to evaluate microstructures and variations in mechanical properties of welded joints. Hole drilling and x-ray diffraction have been developed to evaluate the residual stress. Tensile tests are performed to obtain the tensile and yield strengths of welded components. This chapter aims to show and compare the variations of hardness, microstructure, tensile properties, residual stresses, and impact strength for the most important welding processes in welded joints. The work focuses solely on ferritic and martensitic stainless-steel materials, for similar and dissimilar materials.