Key Engineering Materials Vol. 890

Abstract: During the last 15 years, the friction stir welding process (FSW) and the techniques developed based on the FSW principle have been a main research direction within ISIM Timisoara. The paper summarizes activities and results obtained by the FSW research team within the institute. The paper presents a synthesis that aims a briefly presentation of its own achievements and contributions from recent years regarding the development of the FSW process, especially on the following directions:- Friction stir welding on couples of similar and dissimilar materials;- Use of FSW-TIG (friction stir welding – tungsten inert gas assisted) and FSW-US hybrid processes friction stir welding - ultrasonic assisted);- Friction stir welding in protective gas environment;- Friction stir welding equipment and tools;- Systems for monitoring of the welding process. Results obtained at friction stir butt welding or by overlapping of some couples of materials that are difficult or impossible to be joined using conventional welding procedures, were presented. The results obtained during these years, as well as their scientific and technical level, have allowed the proposal for implementation of solutions that involve FSW welding for specific industrial applications (especially for the automotive field).

Abstract: Friction stir processing (FSP), with tilted parent metal is a new process, which consists in the use of an inclined base plate with an angle α = 1 - 3 º related to the table of the FSP processing machine, by mounting a calibrated part under one end of the base plate. Two clamping plates are fixed with screws on the base plate, and a sheet (parent metal, PM) or a workpiece is placed between the base plate and the clamping plates. The processing tool has the same tilt angle with respect to the sheet to be processed. Said parts are components of the jig for the process described. The processing tool performs a movement with the speed v(x), correlated with a simultaneous movement with the speed v(z) = v(x) tg α. The correlation is achieved by means of a program developed for the processing machine. Due to the tilt, during the FSP process, the leading edge of the rotating tool shoulder progressively enters the PM, continuously, at the point where the shoulder penetration depth in the PM is minimal. On the multifunctional friction processing machine, MMPF type, the processing by the described process of an aluminium alloy sheet, with the sizes 300 mm x 200 mm x 4 mm was performed. A hardened C45 steel tool was used, having the following technical characteristics: shoulder diameter 14 mm, smooth frusto-conical pin with a large diameter of 2.5 mm, a small diameter of 2.0 mm, and a height of 1.5 mm. The parameters had the following values: tilt angle α = 2° 6'; pin penetration depth h = 1.60 - 1.85 mm; tool speed n = 1500 - 2000 rpm; speed v(x) = 1 - 2 mm / s; speed (software correlated) v(z) = 0.03672181 * (1 - 2) mm / s; the temperature of the sheet behind the tool t = 240 - 420 °C. The appearance of the processed sheet is appropriate. No imperfections are observed. The results are appropriate. The tilted PM brings the following advantages of the process: the mechanical stress to produce burrs and / or chips on the surface of the PM decreases; the way the FSP process is carried out is improved, by reducing gap moving and vibrations; the appearance and mechanical characteristics of the processed areas are improved; the quality level of the executed products rises; wear of processing tools is reduced; energy efficiency increases; the electricity consumption of the machine decreases; productivity increases.

Abstract: Friction stir welding is a relatively new technique, developed in 1991, which, due to its advantages, has been continuously developed and applied to industrial applications. This process of joining materials in solid state is an extremely complex one because of the physical phenomena that occur during the process, which makes the research still in full development. The paper presents an analysis of recent scientific work on the use of the FSW process for the joining of steel structures. Thus, the types of steels and merged structures, the processes used and the technological parameters used are analyzed. On the basis of this analysis, the main conclusions of the studied works are summarized and the main development directions for research on the FSW process of steel structures are identified.

Abstract: The FSW process has proven to be a promising process for joining steels and improving their characteristics. However, the use of wrongs technological parameters leads to the appearance of defects. In this study, the macro and microstructural characteristics of steel joints and their mechanical properties are analyzed, and the main types of defects of the butt steel joints are presented. The main conclusions of the works studied are summarized and the main development directions for research on the characterization of steel structures joined by the FSW process are identified.

Abstract: The scientific paper presents an extensive research on modeling and optimizing the technological parameters of the process for processing by processing electric discharges with massive electrode with and without magnetic activation. Scientific research is based on real data collected from the process of electrical discharges performed on various samples extracted from areas of welded joints of metal components made of high alloy steel. The processing of experimental data was performed both classically and actively, especially the method of the central factorial experiment composed of orthogonal and rotary. The process parameters that were initially modeled and subsequently optimized were based on a series of independent variables characteristic of dimensional processing by copying the shape of the electrical discharge processing. Subsequent research conclusions and directions, as well as original contributions, are an experimentally validated point of view and worthy of consideration. All these fundamental ideas highlighted above find their explanations and the corresponding explicit treatment in the content of this scientific paper that addresses both managers at all levels and researchers.

Abstract: Modern materials cutting operations are traditionally part of the research priorities and also in the production activities of ISIM Timișoara. In the last decade, within the institute, a special emphasis was placed on the development of the abrasive water jet cutting process as well as on implementing the research results obtained into industrial activities. The paper presents own achievements and contributions of ISIM to the development of the abrasive water jet cutting process in the following directions: cutting technologies for materials with different characteristics, innovative new patentable solutions regarding the cutting process respectively important modules in the composition of the water jet cutting equipment, ways to recycle used abrasive waste, solutions to streamline the process. The proposed solutions have been verified with good results in industrial applications, or have been proposed for analysis and development together with specialists in the field from important research units.

Abstract: The application of the 3D printing processes is continuously increasing due to their large number of technical and economic advantages when produce prototypes, but in the mass fabrication as well, especially for metal printing of low dimension products. The process produces pollution as all technological processes. Noise, fume and polymer wastes are the main elements which exit from the process and they are not products. The types and the volumes of those pollution emissions depend on the process parameters. The paper presents the results of FDM process emissions analysis. It was recorded the noise for different stages of the printer functioning. It was measured the volume and the contents of the fume produced during the extrusion of the polymer, for PLA polymer and for ABS polymer filaments. Specific risks were analysed and conclusions were reported. The measurement was done for a random chosen product and the results were compared with the pollutant emissions from traditional technological processes applied to erect the same type of product. It has been concluded that the noise emitted during the FDM printing is about 82-85% of the noise produced when apply milling to create similar shapes and dimensions (it was recorded values for the sound pressure in a large range: 42-68 dB, depending on the working regime). Regarding the fume emission, the intensity of emission was up to 40% higher in the FDM process comparing to the milling process. That was explained as being a direct result of the fluid-viscous state in which the material is put during the printing process. When discuss about the risks, most of the main identified risks in the milling and/or extrusion process were almost inexistent in the FDM printing. Electrical injuries and heat injuries are the main risks to which the operator is exposed. Mechanical injuries are sensitively lower than in the traditional processes, as milling The FDM process is safer and produces lower material wastes. It can be concluded that the FDM printing process has lower impact with the environment and with the operator.

Abstract: FDM printing is based on resistance to heat of the polymer filament, which starts in a viscous state and is extruded from nozzle to the printing area. The printing area is hot around 70°C for a better adherence of the deposited polymer and for slow cooling of it. The later deposited layers will experience faster cooling and the characteristics of the polymer will suffer light changes. The paper aims to present the results of a preliminary research regarding the double source successive heating and double source hybrid heating of the extruded polymer in FDM process. There were used two distinct heat sources, the resistive source mounted in the extrusion nozzle and IR lamp heat source placed in the printing chamber. The first heating, which acts during the extrusion process, is a hybrid heating and it is developed inside the extrusion nozzle (hot-end); it is given by the resistive heat source by the IR lamp. After the extrusion, during the deposition process and after the deposition process, the heating of the polymer continues due to the IR lamp. The difference between the printing with IR heating and without IR heating was monitored. A decreasing of about 5-8% of the material stiffness was noticed when the IR lamp was introduced. The material became more viscous and the bonding of the successive layers was improved. DSC analysis has been performed in both cases: with and without IR heat source. The evolution of the elastic modulus proved a decreasing of the plasticity during the simple printing process. The decreasing was less (at least by about 25%) when used IR heat source. The elongation viscosity was analysed and its values were decreasing while the temperature was increasing that took place. The decreasing was produced by the reduction of the elasticity, when the chain branches were decreasing their length. The decreasing is more pronounced while the increasing of the temperature. A low difference (of about 2-5%) was observed to the mechanical characteristics after tensile tests.

Abstract: The paper presents the results of the research on the vibration cavitation erosion of the CuSn12-C bronze, subjected to the volumetric heat treatment of quenching to 700 °C, with water cooling, followed by tempering to 250 °C, with slow cooling in the air. The applied heat treatment shows the improvement of the behavior and the resistance to the cavitation erosion, compared to the initial state, of molded semi-finished product. The evaluation of the behavior and the resistance to the cavitation erosion is made by comparing the value of the parameters MDEmax, Rcav and Rz with those of the delivery state, as well as on the comparison of the characteristic curves MDE(t) and MDER(t) with those of the CuNiAl I-RNR bronze (used at propeller casting). The tests were conducted on the vibrating apparatus with piezoceramic crystals from the Cavitation Laboratory of the Polytechnic University of Timisoara.

Abstract: The paper presents the results of the behavior and resistance to the erosion by vibrating cavitation of the CuZn39Pb3 brass, obtained by quenching the volume heat treatment from 800^°C with water cooling, followed by the stress-relief to 250^°C, with air cooling. Comparison with both the delivery status and the naval brass (used for ship propellers), based on the characteristic parameters values, recommended by the ASTM G32 standards and used in the Cavitation Laboratory of the Polytechnic University of Timisoara, shows that the hardness increase resulted from the heat treatment led to a significant increase of resistance to vibrating cavitation.