Dipten Misra

Application of artificial neural network for predicting weld quality in laser transmission welding of thermoplastics

The present work establishes a correlation between the laser transmission welding parameters and output variables though a nonlinear model, developed by applying artificial neural network (ANN). The process parameters of the model include laser power, welding speed, stand-off distance and clamping pressure; whereas, the output parameters of the model include lap-shear strength and weld-seam width. Experimental data is used to train and test the network. The present neural network model is used to predict the experimental outcome as a function of input parameters within a specified range. Linear regression analyses are performed to compute the correlation coefficients, to measure the relationship between the actual and predicted output values, for checking the adequacy of the ANN model. Further, a sensitivity analysis is performed to determine the parametric influence on the model outputs. Finally, a comparison is made between the ANN and multiple regression models for predicting laser transmission weld quality. The same data set, which are used to develop the ANN model, are also used to develop the multiple regression models. The simulation data obtained from the neural network confirms the feasibility of this model in terms of applicability and shows better agreement with the experimental data, compared to those from the regression models.

Selection of Process Parameters for Optimizing the Weld Strength in Laser Transmission Welding of Acrylics

In this paper, an experimental investigation into laser transmission welding of acrylics is carried out. The Taguchi method of parameter design is used as a statistical design of experiment technique to set the optimal process parameters. Experiments are designed and conducted by using Taguchis L16 orthogonal array. Maximization of weld strength is selected as the quality target. The signal-to-noise ratio and the analysis of variance are used to find the optimum levels within the window of parameters selected and to identify the order of importance of the process parameters. With the frame of this work the effects of process parameters on weld strength is also discussed. Finally, a confirmation test is conducted, which verifies that optimal laser transmission welding parameters can be determined effectively so as to improve weld strength through the Taguchi method.

ANALYSIS OF LAMINAR NATURAL CONVECTION FROM A DISCRETE ISOTHERMAL FLUSH HEATER MOUNTED ON THE SIDE WALL OF A PARTIALLY OPEN RECTANGULAR ENCLOSURE

A numerical study is performed for natural confection cooling of a discrete isothermal heater located on one vertical wall of a partially open two-dimensional enclosure. The governing equations are solved using the SIMPLER algorithm. Studies are performed for 103 <Ra <106 with air as the cooling medium for different heater locations and barrier heights. The primary circulation is stronger for higher Ra and lower heater positions. The barrier strongly affects the size and the strength of the recirculation formed near the barrier, although its effect on the bulk circulation and heat transfer is negligible. Correlations of average Nusselt number are developed for different heater locations and barrier heights.

Optimal process design for laser transmission welding of acrylics using desirability function analysis and overlay contour plots

In this paper, an attempt is made to set the optimal laser transmission welding parameters to attain a desired weld seam with maximum joint strength. The earlier developed mathematical models are used to optimise the welding process. Design-expert software is used to optimise the process parameters, taking into account two proposed optimisation criteria. Numerical and graphical optimisation techniques are applied. The result of numerical optimisation predicts two pareto-optimal solution sets according to the planned optimisation criteria; whereas, graphical optimisation result produces overlay contour plots, which allow quick visual inspection of the area of desirable response values.

Finite element simulation of laser transmission thermoplastic welding of circular contour using a moving heat source

In the present research, a three-dimensional transient numerical model is developed to simulate the laser transmission welding of circular contours. Polycarbonate, a thermoplastic material, is considered as work material for developing and validating the model. The welding simulation is performed, to compute the temperature distribution and shape and size of the molten pool, using the commercial finite element software ANSYS®. The results numerical analysis is further used for investigating the parametric effect on temperature field and weld bead profile. The results obtained revealthat laser power has a positive effect on all the responses investigated; whereas, welding speed has a negative effect. For constant line energy, higher temperature is obtained at a combination of high power with high welding speed.

Bend angle prediction and parameter optimisation for laser bending of stainless steel using FEM and RSM

Finite element simulation (FEM) and response surface methodology (RSM) are used to predict the bend angle and optimise the process parameters for laser bending of stainless steel. A three-dimensional sequentially coupled thermo-mechanical elasto-plastic finite element model, capable of simulating laser bending process, is developed and subsequently response surface methodology (RSM) is used to develop an empirical relation to predict the bend angle based on process parameters. The effects of laser power (125 to 375 W), scan velocity (10 to 30 mm/s), spot diameter (1.5 to 3 mm) and thickness (0.75 to 2.25 mm) on the bend angle are investigated. A quadratic polynomial equation for predicting the bend angle is developed. Optimum values of parameters are identified that would increase the productivity and reduce the total operating cost and the heat affected zone.

Numerical simulation of melting and solidification in laser welding of mild steel

Melting and solidification which is mainly responsible for weld pool geometry in a laser welding process is analysed following two different transient models: (1) without fluid flow, that is, pure conduction and (2) with surface tension driven flow considering various beam power, beam diameter and scanning speed. Based on these models, numerical simulations for laser welding of mild steel has been carried out using commercial software, Fluent. By solving the conservation equations of energy, momentum and mass, the temperature distribution, liquid fraction and flow fields has been predicted and the fusion zone and Heat Affected Zone (HAZ) were obtained. Using predicted results, this present study investigates the effects of laser beam power, beam diameter and scanning speed on heat transfer and the weld pool geometry. Analysis shows that the effect of consideration of fluid motion has pronounced effects on the thermal field and weld pool geometry. [Received 20 January 2007; Accepted 14 September 2007]

Integrating Taguchi Method with Desirability Function Analysis to Optimize the Laser Transmission Welding Process

This paper presents a hybrid approach based on Taguchi method and desirability function analysis to optimize the laser transmission welding process. The Taguchi L25 orthogonal array, for a four factor five level design, is used for the study. The welding parameters, namely: laser power, welding speed, stand‐off distance and clamp pressure are optimized with considerations of multiple quality characteristics including weld strength and weld width. The multiple quality characteristics are then combined into a dimensionless measure of performance called composite desirability function to simplify the optimization procedure. Subsequently, analysis of variance (ANOVA) is performed to determine the significance of parameters and to identify the optimum levels of parameters based on the composite desirability function. The confirmation experiment at the optimal levels shows that the targeted multiple quality characteristics can be significantly improved to achieve more desirable levels.

3D laser forming through circle line heating

Metal forming by a moving heat source is a proven method for forming a sheet metal into desired shape. Line heating in straight line path is sufficient to form shapes with single curvature. However, to form spatially curved or doubly curved surfaces, it is more convenient to apply circle line heating. A single pass of circle line heating at a stretch for full circle over the plate generates waviness in the circumferential and radial directions. The present study investigates a strategy for laser scanning so as to minimize this waviness to a tolerable limit for generation of a bowl shape from a circular sheet. For the analysis, a coupled thermo-mechanical finite element model is formulated and solved to predict the final deformation by laser scanning over discrete circular sectors with appropriate beam diameter, power and scanning speed. The present work reports the angular bending and the waviness as a function of the number of passes and the sequence of heating for a specific laser beam parameter combination for AH36 steel. The present work can be further extended for generation of complex shapes by combining circular sector heating with straight line heating.Metal forming by a moving heat source is a proven method for forming a sheet metal into desired shape. Line heating in straight line path is sufficient to form shapes with single curvature. However, to form spatially curved or doubly curved surfaces, it is more convenient to apply circle line heating. A single pass of circle line heating at a stretch for full circle over the plate generates waviness in the circumferential and radial directions. The present study investigates a strategy for laser scanning so as to minimize this waviness to a tolerable limit for generation of a bowl shape from a circular sheet. For the analysis, a coupled thermo-mechanical finite element model is formulated and solved to predict the final deformation by laser scanning over discrete circular sectors with appropriate beam diameter, power and scanning speed. The present work reports the angular bending and the waviness as a function of the number of passes and the sequence of heating for a specific laser beam parameter combina...

Study of Laser Transmission Welding Process Using a Volumetric Heat Source Model and Experimental Analysis

In this paper, the laser transmission welding of polycarbonate is studied via numerical modeling and experimental investigation. A 3-dimensional transient heat transfer model is developed and experimentally validated. The developed model is able to predict the transient temperature field and weld pool size. It is found from the sensitivity analysis of boundary conditions that the effect of heat conduction is predominant on temperature field distribution during laser transmission welding. Temperature results from the numerical model and the experimentally measured of weld strength results are used as responses for parametric analysis. It is seen that the peak temperature reaches when the laser power is maximum and welding speed and beam diameter are at minimum values. However, the maximum welding strength is obtained when the laser power and beam diameter are at maximum values and welding speed is minimum. It is further noticed that, the maximum value of welding strength corresponds to the peak temperature of 595 °C, which is just above the decomposition temperature of the parent material.