Abstract: The main objective of this article is to familiarize readers with the first outputs from PhD research by David Bricín, especially with the metallographic analysis, which was carried out on the first series of printed samples. The PhD thesis deals with the processing of powder mixtures based on WC-Co using selective laser melting (SLM) and other technologies. This article specifically deals with the use of SLM for the processing of a WC-Co powder mix. The grains of this powder mixture are not granular, but separate grains of carbides and binders. This powder blend was processed on a 3D SLM printer using various printing parameters. Variable parameters included laser power and scanning speed. Other print parameters were kept constant. The properties of the powder mixture and the printed samples were evaluated by metallographic analysis using light and scanning electron microscopy. These analyses were further supplemented by X-ray diffraction phase analysis, chemical analysis by EDX, and analysis of mechanical properties by compression strength testing. The evaluation of the analyses determined how the printing parameters and the type of powder used affect the development and distribution of the structure in the printed samples and how the mechanical properties of the print are then affected. For example, it has been found that increasing the scanning speed results in a more pronounced mixing between the carbide grains and the binder, which then has a positive influence on the mechanical properties of the print. In addition, the experiments found the energy at which the porosity in the printed samples was significantly reduced, and the direction in which further experiments are to take.
Abstract: The paper summarizes the conclusions of the study prepared in cooperation with Janka engineering s.r.o. in production of pipe-tube joints. The parent materials (PM) were unalloyed steel P265GH and high-alloy steel X10CrNiTi 18-9. The GTAW method with filler material (FM) OK Autrod 309LSi was used. Welding parameters were optimized and their influence on the change of structure and mechanical properties of the weld joint was determined. The influence of diffusion transition zones with a marked increase of hardness was found. It was confirmed that when using low heat input, despite the formation of diffusion zones, the quality of welded joints is satisfactory.
Abstract: The present contribution focuses on finishing operations in machining. Finishing operations belong to the most time-consuming and surface quality-critical machining tasks. High-quality tools are available nowadays for choosing optimal tool paths for finishing. Yet, the finishing options for general shaped surfaces are still severely limited. Although CAM systems can efficiently generate tool paths, none of them offers the combination of finishing tool paths, modern productive methods and adaptive tool paths. Increasing the productivity while maintaining dimensional accuracy and the quality of finished surfaces is the key point in finishing. One of the ways to improving productivity is the use of constant cutting speed. The aim of this article is to present experimental verification of these assumptions and demonstrate the impact on the quality of the finished surface
Abstract: The presented paper deals with the problems associated with laser machining of metal materials. Specifically, it solves the question of structural changes that occur as a result of the transfer of heat to the material. Experimental machining of selected technical materials was carried out, and on the basis of the hardness measurement near the cutting point, the heat-affected zone was evaluated after passing the laser beam. To confirm the detection of the affected zone width the models of transient temperature field were arranged, to represent the distribution of temperature in the vicinity of the cutting edge.
Abstract: In the present study austempered ductile irons (ADI) with an upper and lower bainitic structure with nanosized particles of cubic boron nitride cBN (50nm) are studied. The austempering modes include austenization at 900оС during an hour and isothermal retention at 280оС from 0.5 to 6 hours and at 380oС from 0.5 to 6 hours. The samples microstructure is investigated by means of an optical metallography, scanning electron microscopy and X-ray analysis. Tests for hardness, impact toughness and wear are performed. The influence of nanosized additives on the kinetic of the bainitic transformation and on the morphology of the obtained bainitic structure is studied. It is established that the changes of the bainitic cast irons microstructure under influence of the nanoparticles of cBN lead to the cast irons impact toughness and wear resistance increase. The research is aimed at expanding the scope for new ADI applications in the industry.
Abstract: This paper deals with experimental determination of toughness, hardness and impact properties of AISI H13 (DIN 1.2344) tool steel which was manufactured using Selective Laser Melting (SLM) technology. The H13 is a chromium-based tool steel which is primarily used for hot working applications such as pressure casting moulds for automotive industry. Evaluation of toughness and impact properties are vital for reliable use of SLM-processed material, especially in the case of highly loaded structures. Mechanical tests were carried out on printed specimens, subjected to thermal treatment and proper data were evaluated. For better understanding of differences between conventionally produced and SLM-processed material, same mechanical tests were done even for hot-rolled H13 tool steel. SLM-printed material shows more brittle behaviour than conventionally made material. This is most probably caused by combination of H13 thermal properties and fast melting and solidification due to SLM processing.
Abstract: Electroless nickel (Ni) and composite nickel coatings (Ni+TiN) are investigated in this study. EFFTOM -Nickel Method for electroless nickel plating is applied. Nanosized TiN particles (50nm) are used as a strengthening material. The coatings are plated on ductile cast iron samples. The wear tests of the coatings by the classic model TABER ABRASER “disc to disc” are carried out. The observation of the samples microstructure by means of an optical metallographic microscope GX41 OLIMPUS and the microhardness measurements by Knoop Method are performed. The wear resistance, the thickness and microhardness of the samples before and after thermal processing at 290°C, 6 h are defined.
Abstract: Face teeth grinding of special tools, as hobing worm milling cutters are, is the shape and cinematically complex operation with the respect to achieving the necessary accuracy and resultant shape geometry. The grinding wheel shape, it ́s size and the control helix angle of hobing worm are the primary factors which are compelling the ground groove accuracy during the face teeth sharpening process. Inappropriately selected combination of these parameters causes undercut of this surface and the negative impact on required accuracy. The main aim of the solution is to find a variable and to create a parametric mathematical model to calculate appropriate grinding wheel shape according to the input factors – hobing worm and grinding wheel parameters which affects this issue. This system will be used to create the initial grinding wheel surface and a helix groove undercut calculation program. The graphical part of this programme will be the next benefit.
Abstract: Resistance spot welding is the dominant method for joining the materials in the car body production. Progressive materials are being developed to improve the car’s fuel consumption and the safety of passengers as well. Advanced high strength dual-phase steels are such materials. Despite of the dominancy of resistance spot welding in car body production, innovative methods are being developed to reduce the joining time, process costs and improve the load-bearing capacity of a particular joint. Mechanical clinching is such process. The research focused on the evaluation of the possibility of clinching as an alternative method to the resistance spot welding. Experimental samples were prepared from dual-phase steel sheets DP600. The samples were tested by uniaxial tensile test, microhardness test and metallographic observations. Both joining methods have advantages and disadvantages which could destine them for specific utilization. Clinching joining is a progressive, fast and low-cost technique, but the joint’s load-bearing capacity is lower when compared to resistance spot weld.