Jacek Sawicki

THE INFLUENCE OF GRINDING CONDITIONS ON THE DISTRIBUTION OF RESIDUAL STRESS IN THE SURFACE LAYER OF 17crni6-6 STEEL AFTER CARBURIZING

This paper presents the results of a study aimed at determining the residual stress which results from developing the surface layer by low-pressure and conventional carburizing and grinding of 17CrNi6-6 steel. A synergistic effect of thermochemical and abrasive treatment was examined on ring samples used to study residual stress by Davidenkov’s method. Samples were subjected to vacuum carburizing and conventional carburizing, which was followed by grinding with a 38A60K8V aloxite grinding wheel and a CBN grinding wheel RNB80/63B75V. The following cutting fluids were used during the grinding process: oil emulsion 5%, supply rate ca. 20 l/min, Micro5000 oil supplied at the minimum quantity lubrication (MQL) of ca. 25 ml/h, dry machining. The study determined the effect of the type of grinding wheel and the cooling and lubricating agent on the distribution of residual stress in the surface layer. The best effects of grinding with respect to the residual stress were achieved with flood cooling with oil emulsion and grinding with a CBN grinding wheel.

EXPANDED PERLITE, EXPANDED VERMICULITE AND MICROSPHERES AS FILLERS IN NEW GENERATION PAPER PULP MIXTURES USED FOR CONTACT WITH LIQUID METAL

Liquid metal when filling sand casting mould while pouring it out from ladle at the first moment comes across the sprue/gate system of the mould the purpose of which is to transfer liquid metal and feed the mould recess. The materials presently used for the elements of the sprue/gate systems are based on ceramics or the mixtures based on paper pulp. In this study the use of alternative mineral additions such as expanded perlite, expanded vermiculite, and microspheres as the fillers to paper pulp acquired from waste-paper for the use for the elements of mould sprue/gate systems or also other applications for the contact with liquid metal are presented. Experimental mould tube shapes made on the basis of the paper pulp based mixture patented by the authors were poured over with liquid metal. For the comparison, ceramic shapes and commercially available cellulose shapes were investigated in the same way. In order to compare the crystallization processes, a measurement of the cooling off liquid metal was carried out for all the analysed tube samples. From the so obtained metal samples metallographic microsections were made to compare cast iron microstructures. The results obtained from the investigations carried out have shown that the patented paper pulp based mixture may well be applied as an alternative material used for the elements of the sprue/gate systems for disposable sand moulds.

Gas Evolution Qualitative Analyses From Modified Cellulose Mixtures During Thermal Degradation in Air and Argon

This paper presents the application of mineral additives, such as expanded perlite, expanded vermiculite and microspheres in items used in founding. Mixed with paper pulp and aluminosilicate resin as a binder, these additives are the base of a mixture patented by the authors, which can be used in the production of pipe shapes and connectors with a circular cross-section in casting systems in the founding industry. These mixtures were subjected to TG thermal degradation during which a quantitative analysis of the emitted fumes was carried out. The analysis did not detect any other compounds than those formed by the combustion of cellulose materials, which indicated that no chemical reaction took place between the applied additives and cellulose at high temperatures.

HARDENING-RELATED DEFORMATIONS OF GEAR WHEELS AFTER VACUUM CARBURISING AND QUENCHING IN GAS

The purpose of modern surface hardening technology is obtaining reproducible, precisely planned parameters of the carburized layer, minimizing the negative phenomena that result in dimensional changes after hardening and making it possible to determine the nature and magnitude of these changes. This concerns mainly the concept of singlepiece flow in heat treatment applied for the purposes of mass production, employing a special autonomous 4D Quenching chamber for high pressure gas quenching (HPGQ). The main components of the 4D Quenching chamber include a system of cooling nozzles surrounding the processed item and providing a uniform inflow of cooling gas from all directions (3D) and a table rotating together with the item processed, contributing to uniform cooling (4D). Within the framework of this paper there was studied the impact of gear wheel quenching in a 4D Quenching chamber using nitrogen at pressure of 6 and 10 bar on changes in geometry. Geometric measurements of facewidth of gear, hole diameter and outside diameter were performed before and after carburization and quenching. The results obtained allowed us to determine the impact of quenching pressure inside a 4D Quenching chamber on dimensional changes in gear wheels analyzed. The thermo-chemical treatment resulted in a decrease in outside diameters and hole diameters measured and an increase in facewidth of gears.

Analysis of the Impact of Double Shot Peening on the Value of Roughness Parameter and Distribution of Stresses in the RSA 501 Alloy (Al Mg5 Mn1 Sc0.8 Zr0.4)

The bead blasting process is widespread in both the automotive and aerospace industry and is performed in order to improve the fatigue strength of various components. Bead blasting is a cold plastic forming process during which the surface of the material processed is hit by small, hard particles consisting of steel pellets, bearing balls or glass beads. It increases the hardness of the outer layer and establishes compression stresses inside it, which is why this processing is often used to improve fatigue strength. Contrary to other peening methods, bead blasting does not result in a reduction in the height of the processed surface’s unevenness in most cases. Shot peening changes the residual tensile stresses into residual compression stresses, thanks to which, the lifetime of the parts processed is extended and their carrying capacity is increased. The double shot peening process proposed by the authors consists in a two-stage bead blasting process. The first stage consists in blasting with round cast steel pellets, pellets cut from wire or cast iron pellets. During the second stage the same samples underwent glass bead blasting. The tests conducted on the RSA-501 aluminum alloy indicate that as a result of the processing medium’s impact in the form of glass beads or pellets of different diameter and shape, a permanent plastic deformation of the material surface occurs. On the basis of the obtained results it is possible to infer that the choice of parameters of both conventional shot peening and the double shot peening determine the impact thereof on the material’s mechanical properties. Thanks to the application of the double shot peening process there is a noticeable decrease in value of the Ra parameter, by about 40% on average. When analyzing the compressive stress results it is possible to state that after the first blasting process the value of stress was increasing when moving deeply into the sample from its surface, while after the glass bead blasting the value of compressive stress was significantly higher already near the surface. Double shot peening results in an increase in the value of compressive stresses by 40-50% when compared to conventional blasting.

APPLICATION OF AN EQUIVALENT TRUSS MODEL FOR DETERMINING THE STRESS STATE IN MULTI-PHASE MATERIALS WITH CELLULAR AUTOMATA METHOD

The Cellular Automata represent a universal method of modelling and simulation. They enable the performance of calculations for even the most complex processes and phenomena. They are also used successfully in mechanical and material engineering. In this paper, the concept of application of the Cellular Automata method for simulating the behaviour of material under stress is presented. The proposed numerical algorithm created performs a number of calculations of local stress states in the structure of precipitation hardened material. The principle of its operation is based on the application of the equivalent truss model, which is often used in the optimisation and design of structures. In this paper, this model was used to simulate a system embodying a section of the material containing various phases with different mechanical properties.

System of single-piece flow case hardening for high volume production

Purpose: Purpose of this paper is development of single-piece flow system to precision thermal treatment of parts of mechanical gear using a short-pulse low-pressure carburising technology (developed for a new large-chamber furnace). Design/methodology/approach: Sections of the article discuss the novel constructions of the device in which parts being carburised flow in a stream, as well as the low-pressure carburising experiment. Findings: The method has been found proper carburised layers on typical gear used in automotive industry. Research limitations/implications: The short-pulse low-pressure carburising technology needs further investigation to fully understand its all mechanisms. Practical implications: The device resulting from the experiment can be a fully robotised part of a production line which can be included in a system of automatic control of a production process. Originality/value: The device resulting from the experiment is only known solution on the world.

Method of determining the strain hardening of carburized elements in Ansys environment

The paper presents a method based on FEM analysis of determining the strain hardening of elements after the thermochemical treatment. A computational algorithm, which takes into account two factors, has been suggested. Firstly, the gradient of material properties resulting from the changes in the carbon content in the surface layer after the carburizing process. Secondly, the phase transformations occurring during the hardening of the material. The proposed flowchart did not include the flow effect, which greatly reduced the computation time by eliminating tedious CFD calculations. Thanks to an original program Converter coupled with a commercial softwares SimHard, SimCarb J Math Pro and Ansys the carburizing process followed by quenching in gases was modeled. In parallel to the numerical calculations the results were verified experimentally. The results of FEM analysis for the tube made of stainless EN 16CrMn5 subjected to three processes of thermochemical treatment have also been presented in the paper. The experimental results were compared with the numerical simulations and a satisfactory convergence has been achieved.