Search

Owing to the growing applications in medical equipment, the marine sector and automotive industries, laser transmission welding (LTW) is gaining increasing importance. LTW of two transparent acrylic thermoplastic materials, each of 4 mm thickness, was demonstrated using a diode laserpumped solid-state Nd:YVO4 pulsed laser. The effect of process parameters such as laser power, pulse frequency and scanning speed have been investigated and a multi-objective optimization based on desirability function technique was used for the betterment of the results. A validation test has been performed which shows that the predicted results are compatible with actual value. Scanning speed was found to be the process parameter that mostly affects the weld strength. A scanning electron microscope (SEM) was used to study the morphology of the weld zone. It was observed from SEM micrographs that the heating zone in the weld area often generates bubbles and ablation which enhance the joining strength. [ABSTRACT FROM AUTHOR]

In the present day situation higher efficiency, better beam quality, reliability and ease of beam delivery through optical fiber have given diode pump fiber laser a potential to perform in a better way than the traditionally used CO2 or Nd:YAG laser in sheet metal cutting operation. Change in focal distance in the downward direction from the top surface in a controlled manner, eliminates the problem of proper focusability which leads to the formation of uniform melt pool throughout the machining period and results in formation of kerf with high aspect ratio. Investigation of the influence of cutting angle and constant z-height movement with other process parameters like cutting speed, pulse frequency, duty cycle and average power related to the kerf deviation and surface roughness of the 1 mm thick 316L stainless steel sheet has been done. Evaluation of the parametric dependent factors of the cut quality has been made by the implementation of response surface methodology (RSM) with the help of design of experiments (DOE). The optimum parametric settings relating to different machining conditions have also been evaluated. [ABSTRACT FROM AUTHOR]

Laser beam cutting of Inconel 625 superalloy with a Nd:YAG laser in a submerged condition has been studied here. The effect of the underwater laser beam cutting parameters such as lamp current, pulse frequency, pulse width, cutting speed, height of water column on Kerf width and depth of cut are investigated using response surface methodology (RSM). The developed mathematical models are tested by analysis of variance (ANOVA) method to check their adequacy. The central composite design (CCD) technique based on RSM is employed here to carry out the experiments to achieve optimum responses with a reduced number of experiments. From the ANOVA analysis it is found that pulse frequency is the most dominant factor. Height of water column has great impact on quality characteristics of the cut zone. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an experimental investigation on diode laser transmission welding of dissimilar thermoplastics between PMMA (polymethyl methacrylate) and ABS (acrylonitrile butadiene styrene) has been carried out. The effect of the laser welding parameters such as laser power, welding speed, stand-off distance and clamp pressure on weld strength and weld width is investigated using response surface methodology (RSM). Planned experiments and subsequent analyses are carried out to develop the mathematical models to establish the correlation between the process parameters and the responses. The adequacy of the developed models is tested using the sequential F-test, lack-of-fit test and the analysis-of-variance (ANOVA) technique. A numerical multi-objective simultaneous optimization technique, in which the RSM is incorporated, is used to find the optimum solutions, according to the desired optimization criteria. In addition to that, a graphical optimization technique is, also implemented which allow identifying a region in the graphic where optimal conditions lay on. [Copyright &y& Elsevier]

Abstract: In this research, a systematic investigation on laser transmission contour welding process is carried out using finite element analysis (FEA) and design of experiments (DoE) techniques. First of all, a three-dimensional thermal model is developed to simulate the laser transmission contour welding process with a moving heat source. The commercial finite element code ANSYS® multi-physics is used to obtain the numerical results by implementing a volumetric Gaussian heat source, and combined convection–radiation boundary conditions. Design of experiments together with regression analysis is then employed to plan the experiments and to develop mathematical models based on simulation results. Four key process parameters, namely power, welding speed, beam diameter, and carbon black content in absorbing polymer, are considered as independent variables, while maximum temperature at weld interface, weld width, and weld depths in transparent and absorbing polymers are considered as dependent variables. Sensitivity analysis is performed to determine how different values of an independent variable affect a particular dependent variable. [Copyright &y& Elsevier]

Abstract: In this paper, simultaneous laser transmission welding process is systematically investigated via process modeling, using an FEM and RSM combined approach. The objective of the present research is to study the effects of process parameters on the temperature field and weld bead dimensions. The thermal field is simulated by solving a three dimensional transient heat diffusion equation with temperature dependent material properties using the ANSYS® multi-physics. Response surface methodology is then applied for developing mathematical models based on simulation results. The second order equations developed by RSM can predict the values of the responses with significant accuracy. The effect of parameters and their interactions on the responses are studied using the developed response surface models. The mathematical models are further used in search of the optimal process window for obtaining an acceptable weld. The graphical optimization results into a couple of overlay contours plots, which allow quick visual inspection of the area of feasible response values in the factor space to choose the favorable welding parameter combination. [Copyright &y& Elsevier]

Abstract: The influence of the carbon black on temperature distribution and weld profile, during laser transmission welding of polymers, is investigated in the present research work. A transient numerical model, based on conduction mode heat transfer, is developed to analyze the process. The heat input to the model is considered to be the volumetric Gaussian heat source. The computation of temperature field during welding is carried out for polycarbonates having different proportion of carbon black in polymer matrix. The temperature dependent material properties of polycarbonate are taken into account for modeling. The finite element code ANSYS® is employed to obtain the numerical results. The numerically computed results of weld pool dimensions are compared with the experimental results. The comparison shows a fair agreement between them, which gives confidence to use the developed model for intended investigation with acceptable accuracy. The results obtained have revealed that the carbon black has considerable influence on the temperature field distribution and the formation of the weld pool geometry. [Copyright &y& Elsevier]

Laser transmission welding (LTW) is widely recognized as an effective joining method for thermoplastic polymers. Excellent mechanical, physical and thermal properties of polypropylene makes it suitable for many application in aerospace, automotive manufacturing and laboratory accessories; however, joining of semi-crystalline and amorphous polymers is very difficult due to their poor compatibility or different crystal structure. To overcome this problem, white ink is applied at the interface of weld to increase the solubility and retain the laser heat input. As white ink is an opaque, containing copolymer resins which helps to enhance the bonding strength. Here, acrylic (amorphous) and polypropylene copolymer (PPCP) (semi-crystalline) each of 4 mm thickness have been joined by low power diode laser. Experimental analysis of the effect of process parameters such as laser power, scanning speed and pulse frequency on the weld zone has been studied. Greater weld strength is achieved at low scan speed. A novel multi objective snap drift cuckoo search (SDCS) optimization technique has been implemented for betterment of weld strength and weld width. A scanning electron microscope (SEM) has been used to observe the welded zone morphology. It is observed that weld strength is primarily dependent on mechanical interlocking between the two layers of polymers. [ABSTRACT FROM AUTHOR]

Nd:YAG lasers are widely used in metal cutting industries; however, they have not yet been fully exploited in creating micro-features on samples because of high heat affected zone (HAZ) and uncontrolled material removal. In this work a Nd:YAG laser has been utilized in creating microchannels on polymethylmethacrylate (PMMA) in submerged water condition. Taguchi methodology with L-16 orthogonal array design has been chosen for performing the experiments. Lamp current, scanning speed, pulse frequency and pulse width has been selected as input process parameters. Width and depth of the microchannels have been taken as output quality characteristics. Analysis of variance has been performed for each quality characteristics to check the compatibility of this methodology. Each quality characteristics has been optimized using Taguchi's technique. Multiple quality characteristics have been optimized using grey based Taguchi technique. Grey based Taguchi technique provides efficient and effective way to optimize the process based on grey relational grades. Underwater laser processing resulted in lowering heat affected zone (HAZ) and debris formation therefore producing clean structures than air. Experiments showed that the process can be readily used in micromachining facilities to create micro-features on materials. [ABSTRACT FROM AUTHOR]

The current research elaborates an experimental study on poly (methyl methacrylate) (PMMA), to produce microchannels using the laser transmission cutting technique, utilizing a nanosecond pulsed Nd:YAG laser system. The cutting operation was carried out in partially submerged condition. The prime objective during the machining operation was to minimize the heat affected zone (HAZ) and kerf width. Lamp current, pulse frequency, pulse width and cutting speed were the process parameters under consideration during the experimentation. The developed microchannels characteristics such as HAZ and kerf width were subsequently measured and analysed. Response surface methodology (RSM) technique was applied to develop the mathematical relationships between the input process parameters and output responses. Model adequacy was tested using the method of analysis of variance (ANOVA). The optimal combinations of process parameter settings were obtained through single and multi-objective optimizations methods. [ABSTRACT FROM AUTHOR]

• Carried out Nd:YAG laser micro-drilling operations on gamma titanium aluminide. • Observed quality characteristics of through micro-drilled holes. • Proposed a combined Fuzzy-TOPSIS and RSM technique for parametric optimization. Multi criteria decision making methods and response surface methodology based approaches are invariably utilized in improvement of quality in several manufacturing industries. This paper presents the technique to determine optimal process parameters during micro-drilling using Nd:YAG laser source on gamma titanium aluminide alloy using fuzzy-TOPSIS (fuzzy-technique for order preference by similarity to ideal solution) and RSM (response surface methodology) together. A new alloy, Gamma-titanium aluminide (Ti-44.5, Al-2, Cr-2, Nb-0.3B (at%)) has been chosen for experimentation. This material possesses desirable qualities like very high hardness, high strength temperature resistant, high yield stress and ultimate strength in tension, good creep, very low density, resistance to oxidation etc., found applications in technologically advanced industries like spacecrafts, aerospace, nuclear power plants, electronics, automobiles etc. A model has been developed which can be used for decision making in identifying the optimum laser parameters like lamp current, pulse frequency, air pressure and thickness of the workpiece, which affect several quality aspects of micro-machined job such as hole circularity at entry, hole circularity at exit and taper of drilled hole. Triangular fuzzy numbers are being utilized to calculate weighting factor of each machining criterion. Also, the combination of most desirable factor levels has been obtained using a fuzzy-TOPSIS method. [ABSTRACT FROM AUTHOR]