Traditionally, case hardening is based on carburizing in atmospheres and oil quenching; this is carried out in sealed quench furnaces and in continuous lines (pusher, roller or rotary furnaces). They are technologies and devices developed more than 50 years ago and, over the course of time, they have exhausted their development potential. At present, they hardly meet the incoming requirements of the modern industry regarding quality and replicability, integration and organization of production, and environment protection. A solution for weak points of traditional case hardening is the use of vacuum technologies and equipment. Vacuum carburizing increases the resulting precision and replicability, and the variety of vacuum equipment for heat treatment allows the adaptation to modern industry requirements. Two applications are described in the article. The first one – evolutionary – is based on the triple- chamber vacuum furnace for semi-continuous production as a wide alternative for traditional devices. The second system – innovative – is based on the true single-piece flow method. Both solutions have specific and characteristic properties that predispose them for different applications depending on quality requirements and organization of production.

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 τ_w 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).

This article presents the results of research on the influence of the condition of surface layers obtained after grinding a hob cutter tool face using the hybrid combined minimum quantity lubrication (MQL) and compressed cold air (CCA) (MQL-CCA) method of delivering the coolant, on its wear. In the MQL-CCA method, the minimum quantity of the lubricating (MQL) and the cooling agents, in the form of cooled compressed (CCA), were introduced into the grinding zone, simultaneously. For comparison, the tests were also conducted by separately applying the coolant with the WET method with MQL, as well as CCA. In the scope of the described grinding conditions, applying the MQL-CCA method does not cause considerable microhardness of the surface layer as compared to “wet” machining (WET). In addition, the surface roughness obtained through the application of the MQL-CCA method and expressed with 2D and 3D parameters is comparable to that obtained in grinding with the WET method. SEM images for the MQL-CCA and WET methods did not reveal any typical defects in the form of burrs or chippings, occurring on the edges of the ground surfaces. The wear curves corresponding to hobs ground with the application of the coolant using the WET method and using the MQL-CCA method show similar courses, which is indicative of a lack of influence of the surface layer condition resulting from providing coolant during grinding onto intensity of the tool wear process in tangential hobbing. This conclusion is also confirmed by the similar number of teeth affected by measurable wear signs. Therefore, using the hybrid MQL-CCA method, which decreases the amount of coolant provided during the grinding of hob cutters, may constitute, in the described scope of the grinding conditions, an alternative to grinding processes carried out most often with the WET method which entails considerable expenditures for purchasing, maintaining, and utilization of the coolant.

This paper describes the research on abrasive machining conditions and their influence on microhardness and residual stresses distribution in the technological surface layer of 20MnCr5 steel. The roughness of ground samples was also measured. Samples underwent a vacuum carburizing process (LPC) followed by high-pressure gas quenching (HPGQ) in a 4D quenching chamber. Processes were realized with a single-piece flow method. Then, the flat surfaces of samples were ground with a Vortex type IPA60EH20VTX alumina grinding wheel using a flat-surface grinder. The samples were ground to three depths of grinding (a_e = 0.01; 0.02; 0.03 mm) with grinding fluid supply using either flood method (WET) or minimum quantity lubrication (MQL) method. The condition of the technological surface layer was described using microhardness and residual stresses, as well as some selected parameters of surface roughness. The results obtained revealed that changes in microhardness as compared to microhardness of the material before grinding were lower in samples ground with grinding fluid supplied with MQL method. At the same time, the values of residual stresses were also better for samples ground using MQL method. Furthermore, the use of grinding fluid fed with MQL method produced lower values of surface roughness compared to the parameters obtained with WET method. It was concluded that for the tested scope of machining conditions, the MQL method can be a favourable alternative to the flood method of supplying grinding fluid into the grinding zone.