Applied Mechanics and Materials Vol. 657

Abstract: In abrasive water jet cutting, the cut quality is of great importance. In this paper, artificial intelligence model was developed for the prediction of cut quality in abrasive water jet cutting of aluminum alloy. To this aim, artificial neural network (ANN) model was developed in terms of workpiece material thickness, traverse rate and abrasive flow rate. Three-layered feedforward ANN model having four hidden neurons trained with backpropagation algorithm with momentum was used for modeling purposes. The mathematical model showed high prediction accuracy with average absolute percentage error of about 3 %. Using the developed ANN model, 3-D graphs, showing the interaction effects of the traverse rate and abrasive flow rate for three different thicknesses, were given. It was showed that ANNs may be used as a good alternative in analyzing the effects of abrasive water jet cutting parameters on the cut quality characteristics.

Abstract: Sections: Fiber laser is a widely used “tool” for micro-machining various materials, in high accuracy condition. Still, there are not set rules and / or principles, so that to be sure of obtaining the required geometric precision for the part. This paper presents some attempts for setting procedures and parameters values domains, so that to further develop technologies for fiber laser micro-drilling of stainless steel sheets, with thickness of 0.5 mm.

Abstract: Stainless steels are one of the most important engineering materials widely used in the industry. This paper presents multi-objective optimization of CO₂ laser cutting of stainless steel considering different cut quality characteristics and material removal rate (MRR). Laser cutting experiment trials were conducted based on Taguchis L₂₇ experimental design by varying the laser power, cutting speed, assist gas pressure and focus position at three levels. Using obtained experimental data, six mathematical models for the prediction of surface roughness, kerf width, kerf taper angle, width of heat affected zone, dross height and MRR were developed using artificial neural network (ANN). The developed mathematical models were taken as objective functions for the multi-objective optimization using genetic algorithm based on Pareto concept. As a result of multi-objective optimization, five 2-D Pareto fronts were generated covering all combinations of cut quality characteristics and MRR. It was observed that the mathematical relationships in the Pareto fronts between MRR and cut quality characteristics are in some cases linear and in another nonlinear.

Abstract: Abrasive electrochemical machining (AECM) is a complex technological method used for machining hard materials. This method is based on a combination of mechanic, electric and chemical factors. Present paper presents the results of experimental researches accomplished by authors in order to determine the influence of main working parameters (such as voltage, abrasive wheel speed, longitudinal feeding rate, contact pressure) upon performances of electrochemical grinding (total amount of removed material, roughness of machined surfaces, radius of edge roundness) of high speed steel.

Abstract: The paper presents the optimization of spot welding parameters using offline simulation. The procedure of making simulation with SORPAS® is similar to the procedure of doing practical welding process, which can be divided into the following three steps:Data preparation - the materials and geometries of the workpieces and electrodes are defined, the type of welding machine is selected and the process parameters are specified.Running simulation of welding - the parts are welded in the selected welding machine with the specified process parameter settings. The simulations can be carried out in four ways: single simulations, batch simulations, automated optimizations and weld planning.Evaluation of results - the results of welding and quality of weld are evaluated thus the design and parameter settings are verified. With the optimization procedures the weld growth curve can be obtained.

Abstract: Within this article, there are presented a series of researches that are related to the field of customized medical implants made by Additive Manufacturing techniques, such as Selective Laser Melting (SLM) technology. Lattice structures are required in this case for a better osteointegration of the medical implant in the contact area of the bone. But the consequence of using such structures is important also by the mechanical resistance point of view. The shape and size of the cells that are connected within the lattice structure to be manufactured by SLM is critical in this case. There are also few limitations related to the possibilities and performances of the SLM equipment, as well. This is the reason why, several types of lattice structures were designed as having different geometric features, with the aim of analyzing by using finite element method, how the admissible stress and strain will be varied in these cases and what would be the optimum size and shape of the cells that confers the optimum mechanical behavior of lattice structures used within the SLM process of the customized medical implant manufactured from titanium-alloyed materials.

Abstract: One of the serious problems in the SLM process, using metallic powders is the thermal distortion of the model during forming. As a result of the locally concentrated energy input, the temperature gradient mechanism and the related processes lead to residual stresses and part deformations. Since the solidified part is cooled rapidly, the model tends to be deformed and cracked due to the thermal stresses. All these aspects were considered for a series of analyses that were made using the finite element method in order to determine the optimum process parameters (laser power, scanning speed, powder bed temperature) that are required in order to improve the accuracy of the metallic parts made by Stainless Steel 316L material using the Selective Laser Melting process.

Abstract: The paper deals with experimental study on unsynchronised (out of phase) ultrasonic assistance (US) of electrical discharge machining (EDM) process, considering finishing and semi-finishing operations. The main output technological parameters at classic EDM are not as good as they are expected due to instability of material removal process and long duration of gas bubble formed around plasma channel. The US longitudinal oscillations of electrode-tool produce cavitation within frontal working gap leading to collective implosion of gas bubbles. This hydraulic phenomenon can remove the workpiece material in solid or plastic state or even in liquid state. The goal of our study is to emphasize and quantify the influence of US assistance into EDM process and also to determine a correlation between EDM and US parameters, considering an unsynchronised condition. Nevertheless some optimization conditions of working parameters are needed to attain notable expected performances. From experimental data analysis, it can be noticed that significant growth in process productivity is achieved when EDM process frequency is equal with the ultrasonic assistance frequency.

Abstract: The paper presents the research work carried out in order to optimize the technology and reactive magnetron sputtering system used for the deposition of hard, multielemental, multiphase coatings. On the basis of a model of dynamic pressure developed and validated by us, regulatory structures for dynamic pressure inside the deposition chamber were designed and implemented. By using this optimization, extensive experiments involving nanostructured (Ti, Al, Si)N coatings, with a thickness of approx. 2 μm, were carried out. Using TEM microscopy, SAED and Vickers microhardness characterizations the results of deposition system optimization on the microstructure and microhardness of thin films were investigated.

Abstract: The statement from the specialty literature that with the increasing diameter of spot welded by cold pressure decreases the amount of resistance to shear force is due to reporting of the breaking by shear at the circular section of the point. Our experimental research shows that a welded cold joint in spots, correctly done, will be torn off near the weld spot by drawing the point from one of the tins. By reporting the force to the real section of breaking it resulted a constant shear resistance, no matter which the size of the welded point was. Therefore, the approximate theoretical calculation of the breaking force of a cold welded point, correctly executed, can be achieved by knowing the mechanical properties of the metal base and taking into account the real section of the breaking point given by points periphery and the thickness of the panel after deformation. The calculation is encompassing, because due to cold hardening, the real mechanical characteristics are higher.