Eugen Cicala

Experimental design approach to optimize selective laser melting of martensitic 17‐4 PH powder: part I – single laser tracks and first layer

Purpose – The purpose of this paper is to investigate the effect of main process parameters of selective laser melting (SLM) technology on single lines and single layers manufactured from 17‐4 PH martensitic powder using the experimental design approach.Design/methodology/approach – A fractional factorial approach has been applied to vary and to identify the optimal set of process parameters using three different powder particle size distributions for 17‐4 PH steel. This paper assesses the impact of influence factors such as process and material parameters on objective factors such as dimension of single lines and single layers, as well as surface roughness.Findings – The influence of process parameters and materials properties on single line and single layer manufacture is shown and proved statistically. The effect of each process parameter and their interactions on single layer and single line stability and quality has been investigated, and a complex objective function analyzing geometrical stability o...

Diode laser welding of ABS: Experiments and process modeling

The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is determined by combining both experimental and theoretical aspects. In modeling the process, an optical model is used to determine how the laser beam is attenuated by the first material and to obtain the laser beam profile at the interface. Using this information as the input data to a thermal model, the evolution of the temperature field within the two components can be estimated. The thermal model is based on the first principles of heat transfer and utilizes the temperature variation laws of material properties. Corroborating the numerical results with the experimental results, some important insights concerning the fundamental phenomena that govern the process could be extracted. This approach proved to be an efficient tool in determining the weldability of polimeric materials and assures a significant reduction of time and costs with the experimental exploration.

MoSi2 laser cladding—elaboration, characterisation and addition of non-stabilized ZrO2 powder particles

Abstract The cladding process using laser beam radiation comprises different operational regimes, depending on the involved lasers (usually CO 2 or Nd:YAG) and materials. A series of experiments has been carried out to investigate Nd:YAG laser cladding using MoSi 2 powder. Procedures and operating parameters for producing clad layers has been developed and their properties evaluated. The feasibility of the laser cladding technique, using a high power Nd:YAG laser, by projecting MoSi 2 powder on steel substrate was demonstrated. The results indicate a low density of cracks, elevated powder catchment efficiency (between 65 and 90%) and hardness values around 1200–1300 HV. Our goal consists in crack reduction (ideally elimination) and to reach that we have considered the addition of components that can create opposing stresses during solidification, like non-stabilized Zirconia powder particles. The results of these experiments are also widely presented in the paper.

Dissimilar steels laser welding: Experimental and numerical assessment of weld mixing

Upcoming strict CO2 regulations lead car manufacturers to look for mass saving solutions. The use of advanced high strength steel (AHSS) solutions enable optimizing both crash performances and mass saving. Particularly, the use of laser welded blanks made of dissimilar high strength steels is an efficient weight optimization solution. To support the joining of AHSS in car body design, a 3D model of heat transfer, turbulent flow and transport of species in the laser weld pool has been developed. It aims at providing a better understanding of diffusive-convective mixing in the weld and its influence on the weld mechanical properties. The presented model allows predicting the weld geometry and the element distribution. To validate the model, experimental tests were carried out. Welding of two dissimilar steels with different laser beam offset from the joint line was performed. Numerical and experimental investigations of dissimilar butt laser welding between high Mn and dual phase steels were carried out. The cross sections of the welds were characterized by scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) elemental analysis. Quantitative mappings of Mn distribution in the melted zone offer an overview of mixing intensity. The results of the simulation have been found in good agreement with the experimental data. To go further and to assess the effect of weld mixing on mechanical performances, tensile tests were done. It was found that tensile behavior of the welds is determined by level of Mn and C dilutions. For attaining maximal joint performances, it is necessary to comprehend the elements distribution in the melted zone and to be able to control it through an accurate choice of operational parameters.Upcoming strict CO2 regulations lead car manufacturers to look for mass saving solutions. The use of advanced high strength steel (AHSS) solutions enable optimizing both crash performances and mass saving. Particularly, the use of laser welded blanks made of dissimilar high strength steels is an efficient weight optimization solution. To support the joining of AHSS in car body design, a 3D model of heat transfer, turbulent flow and transport of species in the laser weld pool has been developed. It aims at providing a better understanding of diffusive-convective mixing in the weld and its influence on the weld mechanical properties. The presented model allows predicting the weld geometry and the element distribution. To validate the model, experimental tests were carried out. Welding of two dissimilar steels with different laser beam offset from the joint line was performed. Numerical and experimental investigations of dissimilar butt laser welding between high Mn and dual phase steels were carried out. Th...

Determination of an empirical law of aluminium and magnesium alloys absorption coefficient during Nd?:?YAG laser interaction

Welding laser modelling requires knowledge about relative changes of many thermo-physical parameters involved in the interaction. The absorptivity of the material is one of the most important. In this study, experimental measurements of absorptivity with an integrating sphere on two alloys (aluminium and magnesium) were made. These results were compared with an analytical calculation that takes into account the trapping of the beam by multiple reflections inside the keyhole. Based on a statistical method, an empirical law is proposed connecting absorptivity with the peak power of the laser and the duration of interaction. During the interaction, two distinct phenomenologies are brought to light. A threshold is then defined after which the physical process becomes stable. Below this threshold, the measurement of absorptivity is problematic, and the values are widely dispersed.

Off-line multiresponse optimization of gas-jet-assisted CO2 laser cutting of polymettacrylate

From the phenomenological point of view, laser cutting processes are complex, weakly organized and diffuse systems. Off line optimization of such processes demands relative simple, but accurate enough models, which could be obtained by experimental way. The article presents the results of a large factorial designed experiment, having three main objectives: to identify which factors are statistically important, to build a quantitative model relating the important factors to the response functions, to optimize these response functions and particularly the material removal rate, the kerf walls parallelism deviation and the specific energy consumption. The obtained results allow the choice of laser cutting optimal parameters.

Characterization of Fusion Lines Obtained with Laser Welding on Ductile Iron Plates

This paper studies the ductile iron (DI) weldability using laser welding. For performing an Yb:YAG continuous laser was used, with a maximum power of 6 kW. The parametrical window power (P) - welding speed (S) was explored by carrying out the fusion lines on ductile iron plates without preheating, to determinate areas of weldability (complete penetration, correct geometry) to allow further characterization. The criteria for selection of focus areas were the geometry of the fusion lines and the absence of the welding defects. The unsatisfactory domains were characterized by: collapse of the melted metal, incomplete penetration, low fusion lines quality (geometry, compactness). In present study, several values of power and welding speed have been tested to identify their influence on geometry, compactness of the joints and mechanical properties. As result, the power-welding speed diagram for feasible domains of laser welding was generated.

The numerical simulation of heat transfer during a hybrid laser-MIG welding of duplex steel

The present study is dedicated to the numerical simulation of an industrial case of hybrid laser-MIG welding of high thickness duplex steel UR2507Cu with Y-shaped gap geometry. It consists on stimulating the heat transfer during the welding by COMSOL Multiphysics software using heat equivalent source approach. A numerical exploratory designs method is used to identify and to optimize the heat sources parameters in order to obtain a small relative error between the numerical results and the experiment.

Lasers for material processing

The selection of the best laser for a given application is a common problem of laser users. However, a direct relationship between laser intrinsic characteristics and a potential application, risks to make the laser source selection process unilateral and partially mistaken. In fact, the best processing technology for a given application must be chosen. Therefore, the present paper proposes an indirect, more realistic selection process. This process starts from a general laser application definition. Then, it passes through the analysis of the needed laser beam--workpiece material interaction and of the necessary laser technological system. Finally, the selection process ends with the laser processing technology definition, where the choice of the most suitable laser source becomes in fact possible.

Establishing the regression polynomials for the objective function that defines dimensional accuracy in the case of laser drilling

The aim of the paper is to optimize the microholes machining, in the case of laser drilling. The laser used for experiments was a Neodim-15 laser. The material used for drilling was 41MoCr11 austenitic stainless steel with a 1,5 mm thickness. As parameters of the laser drilling process were considered: diaphragm diameter, focal point position, focal length of the lens and laser pulse power. The objective functions were the diameter of the microhole in the area of the laser beam entrance of material (Di), the diameter of the microhole in the area where the laser beam exit the material (De), respective their tolerances (Ti and Te). It was used on complete factorial experiment 24. The established mathematical models are useful in finding the optimum values of the parameters in various combinations, such as the hole diameter to be closer to the required diameter.