International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In several metal forming processes, relation between stress and effective strain of the material must be known for obtaining important forming parameters such as forces and work, required for metal forming processes. Dependence of the flow stress on the effective strain is called the flow curve and is influenced by strain rate and temperature. In order to reach high quality and full functionality of the product, the characteristics of formed material must be determined as precisely as possible and flow stress is one of the main characteristic of the metal materials. In general, flow curves are determined by experiments such as tensile test, upsetting test and torsion test. The proper choice of testing method depends on the metal forming process to be simulated.
In this paper we present the experimental measurements of flow stress for stainless steel at elevated temperatures by using torsion test. In the experimental work a torque, temperature and number of twists of test pieces were measured. Also, the influence of forming parameters such as strain, strain rate and temperature on flow stress was analysed. Experimental results are presented in form of tables and diagrams. Finally, from experimental data the regression model was obtained for successful prediction of flow stress of stainless steel at elevated temperatures. The method of regression analysis allows with relatively small number of experiments the accurate information about the influence to mathematical model of the process.

Plasma arc cutting is a non-conventional manufacturing process that has potential for modern day metal cutting demands with good dimensional accuracy and high-quality surfaces without any extra operation. In this experimental study, AISI 304, AISI 430 and EN S235JR sheet materials having 5 mm. thicknesses, has cut with plasma arc cutting. Each material has cut with 6 different variations. Current, cutting speed, arc voltage, gas pressure and gas flow rate have been changed as process parameters. The quality of the cut has been monitored by measuring the edge roughness, the hardness of the heat-affected zone (HAZ) and the results has compared.

This paper considers the process electron beam welding of stainless steel type 1H18NT in vacuum. Based on experimental data, the influence of the variations of the following process parameters: electron beam power, welding velocity, the distances from the magnetic lens of the electron gun to the beam focus and to the surface of the treated sample is investigated.

Neural and regression models for the geometry characteristics of the welded joints: surface of the weld cross-sections, weld depths and mean weld widths of the samples are estimated, as well as models for defining the areas of the process parameters, where the appearance of defects is or is not expected. The obtained models are used for developing the graphical user interface aiming investigation and prediction of the electron beam welding characteristics and process parameter optimization. This software can be implemented for supporting the operator’s choice of appropriate work regimes, obtaining the required welds quality standards, for education and investigations.

This article discusses a modelling approach for the welded seam form obtained by electron beam welding based on experimental data and types of mathematical functions. The process of electron beam welding is carried out by dividing the electron beam into two parts, resulting in the formation of two liquid baths. The samples that are welded are made of stainless steel with a change in process parameters: the distance between the two electron beam parts and the ratio of the power distribution between the two beam parts, the frequency of the deflection signal, the beam current, and the welding speed. Focusing current is of constant value. The weld cross sections shown in different process parameters are used to evaluate their shape using standard mathematical function – Gaussian functions.

This investigation was performed on the request of the Company for production of the solar systems collectors. Subject of the investigation is the segment of the solar stainless steel collector for the heating water in the swimming pool. The system was installed in the private property and was in use until August 2015 (about one month after installation) when it was disconnected for a period of about one month. After that system was restarted again and it was noticed that many cracks appeared in vertical tubes φ8 mm of collector manufactured of S304 stainless steel. In the horizontal pipes made of S316 steel cracks were not detected. This investigation should give the answer what is the reason for appearing of cracks in stainless steel pipes for pretty short period of exploitation.

The investigation of the interface connection area of the three-layer tube "steel / vanadium alloy / steel" after different deformation-heat treatments was performed. Furthermore, a qualitative and quantitative analysis of the structure of the three-layer material were conducted, including analysis of the contact area of the steel and the vanadium alloy and the diffusion layer between them was obtained. The analysis of the microstructure and mechanical properties (microhardness, ultimate tensile strength, yield strength and elongation) of three-layered material has been carried out.

AISI 316Ti stainless steel is prone to local corrosion in aggressive chloride environments. Its resistance to pitting in the absence and presence of molybdate inhibitor was tested by two independent tests with different mechanisms of corrosion process: by exposure (24 hours immersion test) and electrochemically (potentiodynamic polarisation test). Both tests were carried out in 1 M chloride acidic solution without inhibitor and with two different amounts of added inhibitor (concentration ratio inhibitive/aggressive anions was 1:10 and 1:20 respectively), at room temperature. Results of immersion tests were evaluated on the bases of corrosion rates calculated from corrosion losses during immersion and by morphology of pitting. Results of potentiodynamic polarisation tests were evaluated by pitting potentials.

The EA Signal tests registered during the static stretching of the X6CrNiTi18-10 steel (according to EN 10088) have been o included in the work. The tests were done in the room temperature and in the high temperature of – 400 C on the universal strength (tensile) machine ZDM-5 with the range of 0-50 kN equipped with the digital registration of the strength and stretching. The analysis of the EA signal intensity has been conducted, depending on the deformation of the sample and test temperature. On the basis of the EA signal there have been the own characteristic oscillation frequencies of the samples designated, being the effect of the degradation of the structure as a result of the increased load.

Since diffusion bonded joint is formed from atomic migration across an interface without a liquid phase, the interface is homogeneous microstructure and hence mechanical properties are not different from those of the matrix metal. However, it is not easy to control process variables at high temperature. This paper presents diffusion bonding process and a machinery with tool material selection to develop diffusion bonding press machine for joining complex contoured metals using hot forming and diffusion bonding technology.