Sebastião Carlos da Costa

Weighted Multivariate Mean Square Error for processes optimization: A case study on flux-cored arc welding for stainless steel claddings

A mathematical programming technique developed recently that optimizes multiple correlated characteristics is the Multivariate Mean Square Error (MMSE). The MMSE approach has obtained noteworthy results, by avoiding the production of inappropriate optimal points that can occur when a method fails to take into account a correlation structure. Where the MMSE approach is deficient, however, is in cases where the multiple correlated characteristics need to be optimized with varying degrees of importance. The MMSE approach, in treating all responses as having the same importance, is unable to attribute the desired weights. This paper thus introduces a strategy that weights the responses in the MMSE approach. The method, called the Weighted Multivariate Mean Square Error (WMMSE), utilizes a weighting procedure that integrates Principal Component Analysis (PCA) and Response Surface Methodology (RSM). In doing so, WMMSE obtains uncorrelated weighted objective functions from the original responses. After being mathematically programmed, these functions are optimized by employing optimization algorithms. We applied WMMSE to optimize a stainless steel cladding application executed via the flux-cored arc welding (FCAW) process. Four input parameters and eight response variables were considered. Stainless steel cladding, which carries potential benefits for a variety of industries, takes low cost materials and deposits over their surfaces materials having anti-corrosive properties. Optimal results were confirmed, which ensured the deposition of claddings with defect-free beads exhibiting the desired geometry and demonstrating good productivity indexes.

Mathematical Modeling of Weld Bead Geometry, Quality, and Productivity for Stainless Steel Claddings Deposited by FCAW

In recent years, industrial settings are seeing a rise in the use of stainless steel claddings. The anti-corrosive surfaces are made from low cost materials such as carbon steel or low alloy steels. To ensure the final quality of claddings, however, it is important to know how the welding parameters affect the process’s outcome. Beads should be defect free and deposited with the desired geometry, with efficiency, and with a minimal waste of material. The objective of this study then is to analyze how the flux-cored arc welding (FCAW) parameters influence geometry, productivity, and the surface quality of the stainless steel claddings. It examines AISI 1020 carbon steel cladded with 316L stainless steel. Geometry was analyzed in terms of bead width, penetration, reinforcement, and dilution. Productivity was analyzed according to deposition rate and process yield, and surface quality according to surface appearance and slag formation. The FCAW parameters chosen included the wire feed rate, voltage, welding speed, and contact-tip-workpiece distance. To analyze the parameters’ influences, mathematical models were developed based on response surface methodology. The results show that all parameters were significant. The degrees of importance among them varied according to the responses of interest. What also proved to be significant was the interaction between parameters. It was found that the combined effect of two parameters significantly affected a response; even when taken individually, the two might produce little effect. Finally, the development of Pareto frontiers confirmed the existence of conflicts of interest in this process, suggesting the application of multi-objective optimization techniques to the sequence of this study.

Otimização do processo de soldagem FCAW usando o erro quadrático médio multivariado

The optimization of welding processes is not a trivial task, mainly due to the great number of exigible and desirable characteristics that must be analyzed. Moreover, the optimization of a welding process with multiple characteristics without to consider the variance-covariance structure, may lead to inadequate optimum. To help in this task, a method of multiobjective optimization based in the Multivariate Mean Square Error applied in the study of multiple correlated characteristics of a FCAW (Flux Cored Arc Welding) welding process will be presented. This method characterized by a combined approach based in the Response Surface Methodology, Design of Experiments and Principal Components Analysis consisted in an attempt to achieve the nearest values to specific targets, for each studied characteristic (penetration, deposition rate, deposition efficiency, convexity index of the weld bead and dilution) considering the welding variables expressed in function of welding voltage (V), wire feed speed (Va) and the contact tip to workpiece distance (d). The results point out a good adequacy of the proposed method.

Modeling and Optimization of Multiple Characteristics in the AISI 52100 Hardened Steel Turning

This work aimed to develop a multiple response optimization procedure for the AISI 52100 hardened steel turning process. Optimizing this turning operation is important so that multiple quality characteristics are achieved simultaneously. The considered responses are: total cost, cutting time, total turning cycle time, tool life, material removal rate, and surface roughness. The adjusted process parameters were cutting speed, feed rate and depth of cut. A multi-objective optimization technique based on the Global Criterion Method and Genetic Algorithm were employed to identify the optimal settings for parameters with objective functions built through Response Surface Methodology. This two-fold approach lead up to optimized responses settled near the desired values were obtained with cutting speed = 214 m/min, feed rate = 0.088 mm/rev and depth of cut = 0.33 mm.

Optimization of the FCAW process by weld bead geometry analysis

The flux cored arc welding process has grown in use in recent times as a function of its characteristics of high rate of deposition, associated with suitable mechanical properties in the welded joint. However, many aspects still remain obscure in regard to greater utilization of this process. As a result, the intention of this work is the analysis and optimization of the voltage, wire feed speed and contact tip part distance welding parameters, in a process using tubular wire with shielding gas, on the penetration and convex index of the weld. By means of statistical techniques, a mathematical model was developed with subsequent optimization of the responses. Based on the results obtained, the strong influence of the wire feed speed on the process was seen, followed by the voltage and, with less intensity, the contact tip to workpiece distance (CTWD). Statistical analyses indicated that the best condition for the parameters analysed was obtained with voltage values between 32 and 34 V, associated with a wire feed speed of 12 m/min and a CTWD of 20 mm. On the other hand, tensions at around 36 V caused surface defects that prejudiced the quality of the weld. Later tests showed an acceptable forecast of the results of the mathematical models when compared to the actual results.

Metodologia Não Destrutiva de Parametrização da Queima do Zinco no Processo de Soldagem a Ponto por Resistência

Galvanized steel is used in large numbers, especially in the automotive, for its corrosion resistance and low cost. The welding of these materials, this industrial sector is usually performed through the spot welding process. Depending on the galvanized steel with a film of coating based on zinc is usually used in welding, a technique called burn zinc (zinc burning) to minimize the detrimental effects of zinc in the material during the welding cycle. In this context, this paper studied a non-destructive method, aiming to find an appropriate removal of this layer of zinc, for considering this, the signals generated by a sensor that records the dislodgement during stages of the spot welding, using as a basis the reading of the thermal expansion of galvanized steel sheet. Thus, physical simulation experiments were performed by varying the current and the time for the preheating phase cycle. The responses from the burn zinc generated by the sensor and visual analysis by attribute, were shown in graphs through an operating envelope. Evidence showed that the sign of displacement of the electrode, proved to be an efficient non-destructive method for determining the appropriate parameters in the burn zinc in process of spot welding for galvanized steel plates.

FCAW process optimization using the multivariate mean square error

Optimization of welding processes is not a trivial task, mainly due to the great number of required and desirable characteristics that must be analysed. Moreover, the optimization of a welding process with multiple characteristics without considering the variance–covariance structure may lead to inadequate optimum. To help with this task, a method of multi-objective optimization based on the multivariate mean square error applied in the study of multiple correlated characteristics of a flux-cored arc welding process is presented. This method characterized by a combined approach based on the response surface methodology, design of experiments, and principal components analysis consisted of an attempt to achieve the nearest values to specific targets, for each characteristic (penetration, deposition rate, deposition efficiency, convexity index of the weld bead, and dilution), considering the welding variables expressed as a result of welding voltage (V), wire feed speed (Va), and contact tip to workpiece distance (d). The results point, to a good adequacy of the proposed method.

Otimização de Múltiplos Objetivos na Soldagem de Revestimento de Chapas de Aço Carbono ABNT 1020 Utilizando Arame Tubular Inoxidável Austenítico

The stainless steel cladding process has highlighted in the industrial environment for allowing anti-corrosive surfaces are made from low cost materials. However, in order to ensure the claddings final quality, it is important that the welding procedure is well adjusted, so that the welds are deposited with the desired geometry, with productivity and flawless. The aim of this work is the multiple characteristics optimization in cladding of ABNT 1020 carbon steel plates using ABNT 316L stainless steel cored wire. The optimized features include the bead width, penetration, reinforcement and dilution, representing the weld bead geometry. Productivity has been maximized through the deposition rate and process yield. As quality responses, we considered the slag formation and surface appearance. The modeling and optimization strategy was based on a combination of Response Surface Methodology, Global Criterion Method and Genetic Algorithm. The results indicate that the response surface models developed for the process characteristics had high adjustments. The Global Criterion Method and Genetic Algorithm were implemented successfully, allowing the results optimization.

Non-destructive methodology for parameterization of Burn-Zinc in the resistance spot welding process

Abstract Galvanized steels are used in large quantities, mainly in the automotive industry, for their corrosion resistance and low cost. In this industrial sector, these materials are normally welded by the spot welding process. Because galvanized steels have a zinc-based covering layer, welding is normally carried out using a technique called the Burn-Zinc technique, to minimize the harmful effects of the zinc on this material, during the welding cycle. In this context, this work studied a non-destructive method, with the aim of finding suitable removal of this layer of zinc, on the basis of the signals generated by a sensor that records the electrode displacement during the phases of the spot welding process, taking the reading for the thermal expansion of the galvanized steel sheet as a basis. Thus, physical simulation experiments were undertaken, varying the current and the cycle time of the preheating phase. The Burn-Zinc responses generated by the sensor and the visual analyses by attribute were shown as graphs via an operating envelope. The evidence showed that the signal from electrode displacement proved to be an efficient non-destructive method for determining suitable Burn-Zinc parameters in the spot welding process for galvanized steel sheet.

Otimização dos parâmetros de pintura com múltiplas respostas: um estudo em problemas de pintura em anéis automotivos

The use of optimization assists in decision making in many industrial and business problems. The objective of this paper is to present a practical application of optimization with multiple responses to problems related to painting automotive rings, and evaluate the performance of these methods with the application of DOE (Design of Experiments). The spray painting system has showed significant advantages compared to other painting application methods. This is used as a reference for identifying the assembly of the piston rings. Considering this application system some variables were optimized: thickness of the paint, the paint strip width and the distance of the track. The parameters used included the distance of the application, the machine operating pressure and speed of application. The results showed the importance of choosing the correct method, aiming at obtaining results closer to the reality of the analyzed problem.