Applied Mechanics and Materials Vol. 657

Abstract: Research evolution timely tendencies, in the nonconventional technologies field, are: manufacture conditions optimization and complex equipments design. The increasing of ultrasonic machining use, in various technologies is due to the expanding need of a wide range materials and high quality manufacture standards in many activity fields. This paper present a experimental study made in order to analyze the welded zone material structure and welding quality. The effects of aluminium ultrasonic welding parameters such as relative energy, machining time, amplitude and working force were compared through traction tests values and microstructural analysis. Microhardness tests were, also, made in five different points, two in the base material and three in the welded zone, on each welded aluminium sample. The aluminum welding experiments were made at the National Research and Development Institute for Welding and Material Testing (ISIM) Timişoara. The ultrasonic welding temperature is lower than the aluminium melting temperature, that's so our experiments reveal that the aluminium ultrasonic welding process doesn't determine the appearance of moulding structure. In the joint we have only crystalline grains deformation, phase transformation and aluminium diffusion.

Abstract: Currently there is a continuous extension of application areas of titanium aluminides but their processing encounters a number of difficulties such as the precision of machining and modifying the properties of the surface layer. In the specialist literature [1, 2, 4, 7] different authors address the processing of these materials by conventional methods. In this context, this paper aims at finding the optimal regimes for the electrical discharge machining (EDM) of titanium aluminides Ti-40Al-5NB-3V and provides the analysis of the process parameters effect on cutting through wire EDM technological characteristics. In the case of wire EDM a relatively good output has been obtained as well as very good roughness of the processed surfaces. On the contrary, when considering the die sinking edm, due to very small output, several experimental measurements were performed on three machines – Sodick, ONA and ELER. Based on the experimental data, it has been established that the best output is to be obtained by reverse polarity machining.

Abstract:

Nonconventional machining methods are based on the transfer of the energy to the work zone in ways distinct from those applied in the case of the so-called classical machining methods. A group of nonconventional machining methods achieve material removal from workpiece by using the motion of the electrical charged particles in a liquid. Practically, some machining techniques included in the larger groups of electrical discharge machining and in electrochemical machining are based on the motion of electrical charged particles in fluid. The problem addressed in this paper is to identify the zones where differences between the two groups of machining methods appear. A theoretical analysis was developed in order to identify the common aspects and respectively the differences between the electrical discharge machining and electrochemical machining, if the machining liquid is considered. Some experimental tests were developed to highlight aspects specific to the above mentioned machining techniques. The research facilitated obtaining a more complete image of some common and distinct characteristics of electrical discharge machining and electrochemical machining. The significance of the electroconductive or insulating properties of the work liquid was highlighted.

Abstract: The current work investigates the electro-discharge machining (EDM) of plain woven carbon reinforced polymer composites with pulse durations of 100 μs, 200 μs, 300 μs, currents 1 A, 3 A and 5 A, and a voltage of 100 V. An x-ray computed tomography (CT) is employed to examine the delaminations, while a delamination factor model utilizing the equivalent delamination diameter provides the measuring quantity for assessment. Finite element simulations compute the stress concentrations around the holes by taking into account the delamination equivalent diameters of the open-holes, as monitored from the x-ray CT. The Whitney-Nuismer point stress criterion is utilised in order to predict the failure strength of the machined open-hole laminates and it is compared with the experimentally derived mechanical strength values. The results reveal that EDM is a feasible method for open-hole machining of composites, however proper selection of the operational parameters is needed. By accurately measuring the peripheral delamination areas of the machined holes, it is shown that the analysis of the mechanical behaviour of the plain woven laminates by the means of finite element method and the Whitney-Nuismer criterion can accurately predict the response of such composites when subjected to tensile loads.

Abstract:

Welding is an assembly process used in different industries. The residual stresses influences fatigue behavior, fracture strength, corrosion resistance and for these reasons knowing their values are important. During time, many destructive as well as nondestructive methods to evaluate residual stresses were developed. Stress is evaluated by inducing a sound wave with the frequency of several megahertz into the sample and measuring velocity related parameters. Besides stress which affects sound velocity there are many others characteristics of metals with same influence and for this reason sorting from different influences made the estimation difficult. On another hand ultrasonic technology has many wave modes to investigate materials including bulk wave (longitudinal and shear wave), surface wave (Rayleigh) every mode offering unique parameters for extracting information. Of the several characteristics that may be used to measure stress the most exploited seems to be sound velocity dependence on the elastic modulus. Our research to estimate residual stress into steel welded parts is based on dependence between sound velocity and elastic modulus using longitudinal sound wave. To conduct the experiments was designed sample as a frame. The sample was loaded using adapted equipment and the results were used for FEA tools (SolidWorks SimulationXpress) to obtain the distribution of stresses and displacements. This approach allowed the location of points of interest to the investigation with ultrasound. The ultrasound investigation was made and presented in comparative tables. It is found that the variation of the velocity of sound for the two charge states of the piece is, on average, 5.8 per thousand. Particular values of residual stress values are observed for the points corresponding with weld or fusion zone and heat-affected zone. The ultrasonic investigation permits the evaluation of bulk stress state of welded components with acceptable accuracy.

Abstract: Ultrasonic processing proves particularly effective in leading branches of technology, such as: precision mechanics, optics, electrical engineering, nuclear technology etc. High-strength joints, short machining time and low energy consumption are only three of the main ultrasonic welding advantages that determined research intensification in this field. This paper presents experimental data that illustrates the interdependence between some process parameters and their influence on the joint resistance of the copper sheet ultrasonically welded. Due to the surface friction energy, which is generated in the ultrasonic welding process, some intermolecular connections are broken and other are new are created. In order to demonstrate the quality of the ultrasonically welded copper, there were made macro and microstructural analysis that are proving an excellent metallurgical bonding. The results of microhardness tests, that were made in five different points, on each welded copper sample, revealed the ultrasonic welding process quality showing that the welded material hardness doesn't change. The copper welding experiments were made at the National Research and Development Institute for Welding and Material Testing (ISIM) Timişoara.

Abstract: Electrochemical discharge machining (ECDM) is based on synergetic action of anodic dissolution with erosive effect of electrical discharges in material removal process. Drilling by ECDM can be applied for hard to be cut materials, when no drilling by cutting or no EDM machine is available.

Abstract: Various research on the influence of different process parameters on quality characteristics of metallic structures assembled by welding have been accomplished [1 - 8, etc.]. The deformations of metallic structure components assembled by welding depend on the characteristics of the components, welded gap, welding speed, scheme and time of components fixing, etc. The paper presents the data and main results of an experimental research on the influence of two process parameters - the welding gap and the fixing time of the components - on the geometric deformations of certain metallic structure components in industrial conditions. Complex experiment and set-up including industrial welding robot and advanced measurement system have been designed and used. The geometric deformations of the welded metallic structure components are caused by forces and phenomenon heating - cooling, i.e. dilatation - contraction, respectively, acting during the periods of fixing - welding, fixing - cooling, cooling without fixing. Relevant dependences between the geometric deformation of welded structure and the considered influencing process parameters have been evidenced.

Abstract: The optimization of complex, electrical and electrochemical erosion processing focuses on improving quality and reducing energy consumption while processing, considering the actual growing of the energy crisis. The technological process is considered to be a system and its components are considered to be subsystems. This paper contains an analysis of the optimization methods that can be applied to dimensional processing using complex, electrical and electrochemical erosion and states the optimization directions and methods that can be used in order to increase the performance of some of the components of the technological process (the subsystems) or of the whole process (the system).

Abstract: This paper presents a methodology for the simulation and optimization in a virtual environment of a manual assembly process. For validation of the methodology the authors chose an assembly process that is already used in the manufacturing industry. In the first step of the proposed methodology the existing process is simulated and then based on the simulation the activities and equipment involved are being analyzed and in the next step the assembly process is to be optimized using simulation and a series of modification vectors such as: layout, devices, tools and movement sequences. The case study presented in the paper aims to optimize the assembly process of a pneumatic actuator of a butterfly type valve.