This article presents the results of experiments concerning a computational fluid dynamics (CFD)/numerical analysis of the flow of air in the grinding zone during the sharpening of the face surface of hob cutters while using the MQL method. The carrying out of a simulation allows one to determine the influence of various settings of the angle of the spray nozzle on the amount of air directly reaching the zone of contact of the grinding wheel with the workpiece, as well as the grinding wheel active surface (GWAS). In the numerical analysis, the ‘SST k-ω’ model available in the Ansys CFX program was used, and to which the Kato and Lander’s modification was applied. With the aim of verifying the results obtained from the basis of the numerical simulations, experimental testing was conducted. As a verification parameter, the percentage rate of grinding wheel clogging was used. The measurement of clogging was conducted by the optical method taking microscopic images of the grinding wheel active surface (GWAS) and then analysing it which the use of digital processing and image analysis. As a result of the numerical simulations, it was confirmed that the greatest effectiveness in delivering air to the contact zone of the grinding wheel with the workpiece being machined was achieved by setting the nozzle at the lowest of the angles tested (90°). At the same time, the greatest efficiency in delivering air to the grinding wheel active surface was achieved by setting the nozzle at the largest of the angles tested (90°). The experimental tests allowed one to state that the change in the inclination of the spray nozzle does not significantly influence the effectiveness of chip removal from the surface of the inter-granular spaces of the grinding wheel. By setting the nozzle at a 90° angle, wall shear stresses τw have a decisive influence on cleaning the GWAS, while at an angle of 30° the cleaning function is taken on by air being delivered directly into the contact zone of the grinding wheel with the face surface of the hob cutter being sharpened. A comparison of the percentage rates of grinding wheel clogging obtained from using the flood method (WET), as well as the MQL method, indicates the insufficient cleaning ability of the MQL method. A solution to this problem may be the application of additional cleaning nozzles employing streams of compressed air (CA) or cold compressed air (CCA).
Low pressure carburizing followed by high pressure gas quenching is often applied to steel elements in order to increase their strength and durability, but undesirable distortions are also formed due to this process. In order to minimize these distortions, the Vacuum UCM furnace manufactured by SECO/WARWICK conducted by single piece flow method is proposed. A refined simulation that describes the quenching phenomena with enough accuracy can reduce the project and optimization costs as it replaces the trial and error method. The goal of this study was to create a computer model that can predict the behaviour of the phase transformations that occurs at 4D quenching chamber after low pressure carburizing in single piece flow technology. First, an investigation about the simulations that has been developed in this area was done. Based on physical phenomena involved in this process, a numerical scheme was created; The numerical scheme was applied to the real steel element that was submitted to the single piece flow technology process; The numerical simulation was compared with the experimental data. As a result, a numerical model able to simulate phase transformation after complex chemical-heat treatment in the single peace flow technology was obtained.
The quenching process is related to the internal-stress phenomena, resulting in geometric changes (distortions). In this paper, the impact of hardening temperature on the quenching distortions occurring during low-pressure carburizing with gas quenching using the individual quenching method was analyzed. The reference elements were subjected to carburizing at 980°C, followed by gas quenching at temperatures of 860°C, 920°C and 980°C. The geometrical measurements of the elements were made before and after the chemical treatment and the size of the quenching distortions of their geometrical parameters was determined: external and internal diameters as well as ring thickness. The study examined whether there is a statistically significant difference between the geometrical dimensions of the elements before and after the thermo-chemical treatment for the elements in three temperature groups. It was shown that for the ring thickness parameter there are no significant differences between the groups of elements before and after heat treatment for the temperature 980°C, while for the temperature 860°C and 920°C these changes are significant. However, for external diameter bottom, there is always a difference regardless of temperature. For the single piece-flow vacuum carburizing with gas quenching using the individual quenching method, it is advisable to use the highest possible quenching temperatures to reduce quenching distortions.
The article presents results of research concerning computational fluid dynamics (CFD) of water oil emulsion in grinding zone during sharpening of hob cutter face surface. The numerical simulations made possible to determine the influence of different angular nozzle settings and nominal emulsion flow rate on the quantity of emulsion directly reaching the area of contact between the grinding wheel and the machined material. "SST k-ω" model, available in Ansys CFX program, was used in the numerical analysis; however, Kato and Launder's modifications were used in the model. Experimental tests were carried out in order to verify results obtained on basis of the numerical simulations. The percentage rate of grinding wheel clogging was used as a verifying parameter. Analysis of the clogging made it possible to indirectly evaluate results of the numerical simulation. The clogging measurements were carried out using optical method by taking microscopic images of the grinding wheel active surface (GWAS), which were later analyzed using an image analysis program. As a result of the conducted numerical simulations, it was concluded that the greatest effectiveness of emulsion provision into the grinding zone was obtained when the nozzle was set at the smallest of the examined angles (30°) and greatest of the examined nominal flow rates (7 l/min). This conclusion was confirmed with results of experimental tests, where it was also observed that increasing the nominal flow rate over 5 l/min does not have significant influence on the amount of clogging on the grinding wheel active surface.
The aim of the experiment described in the paper was to determine the effect of selected conditions of abrasive machining on the size and distribution of microhardness and residual stresses developed in the technological surface layer of flat specimens made of 20MnCr5 steel. The specimens were subjected to single-piece flow low-pressure carburizing (LPC) and high-pressure gas quenching (HPGQ) in a 4D Quenching chamber, in order to achieve the effective case depth of ECD=0.4 mm. This was followed by grinding the specimens with Quantum and Vortex alumina grinding wheels made by Norton. Cooling and lubricating liquid were supplied to the grinding zone in both cases by the flood (WET) method and by the minimum quantity lubrication (MQL) method. The measurements for each specimen were made twice - after the thermo-chemical treatment and after the grinding. Microhardness and residual stress was measured by the X-ray method sin2Ψ. The final part of the article provides an analysis of the measurement results and presents conclusions and recommendations for further studies.
Low-pressure carburizing followed by high-pressure quenching in single-piece flow technology has shown good results in avoiding distortions. For better control of specimen quality in these processes, developing numerical simulations can be beneficial. However, there is no commercial software able to simulate distortion formation during gas quenching that considers the complex fluid flow field and heat transfer coefficient as a function of space and time. For this reason, this paper proposes an algorithm scheme that aims for more refined results. Based on the physical phenomena involved, a numerical scheme was divided into five modules: diffusion module, fluid module, thermal module, phase transformation module, and mechanical module. In order to validate the simulation, the results were compared with the experimental data. The outcomes showed that the average difference between the numerical and experimental data for distortions was 1.7% for the outer diameter and 12% for the inner diameter of the steel element. Numerical simulation also showed the differences between deformations in the inner and outer diameters as they appear in the experimental data. Therefore, a numerical model capable of simulating distortions in the steel elements during high-pressure gas quenching after low-pressure carburizing using a single-piece flow technology was obtained, whereupon the complex fluid flow and variation of the heat transfer coefficient was considered.
Purpose: The purpose of this article is to discuss the method of determining the mathematical model used for calculating the amount of emulsion reaching directly the grinding zone during the hob sharpening process. Design/methodology/approach: The mathematical model, in the form of a multiple regression function, was determined based on the acceptance and rejection method. The data for the calculations was obtained by conducting numerical simulations of fluid flow in the Ansys CFX software. Findings: A mathematical model enables calculating the amount of efficient expenditure of emulsion reaching directly the zone of contact between the grinding wheel and workpiece (hob cutter rake face) at various nozzle angle settings and different nominal expenditures of emulsion. The verification of the mathematical relationship confirmed its accuracy. Research limitations/implications: Further research should focus on the other types of grinding process and other types of cooling and lubricating fluids. Practical implications: The mathematical model enables a selection and application in the workshop and industrial practice of various variants of emulsion supply during the grinding of hob cutter rake face. Analysis of the multiple regression equation created on the basis of the acceptance and rejection method also allows predicting changes in the analyzed numerical model. Originality/value: The literature review has shown that no research of this type has been conducted with regard to analyses and optimisation of the grinding process during hob cutter sharpening. The results of this research are a novelty on a worldwide scale.
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