Abstract
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.
Highlights
The wear of cutting tool blades in the usage process entails the necessity of their periodic regeneration
Taking the above into consideration and bearing in mind the fact that in the above-described research various methods of coolant delivery were used as the variable parameter, it may be concluded that similar microhardness values obtained during grinding with GR provided with the wet” machining (WET) method and using the minimum quantity lubrication (MQL)-cooled compressed air (CCA) method are indicative of the proper removal of heat from the grinding zone and of temperature decrease in the workpiece
On basis of the obtained results, it was concluded that the lowest Rz parameter values (Fig. 12a) were measured on the face surface grinding with the delivery of Emulgol ES-12 emulsion with the WET method
Summary
The wear of cutting tool blades in the usage process entails the necessity of their periodic regeneration. Despite the MQL method’s advantages related to its good lubricating properties, its apparent disadvantage is a lack of sufficient cooling properties in a wide range of changes of grinding process parameters as compared with the traditional WET method [5] This results mainly from the relatively low heat storage capacity of the oil and air and from the small amount of the coolant delivered into the grinding zone. Sanchez et al [27] presented a concept based on the application of the method of hybrid coolant delivery with MQL with CO2 low-temperature gas during the grinding of X153 CrMoV12-1 (AISI D2) tool steel with the use of an alumina grinding wheel In this method, known by the acronym minimum coolant grinding (MCG), both the oil mist and CO2 streams are not directed directly into the grinding zone but are sprayed onto the grinding wheel active surface. Tests on the previously ground hob cutters’ service wear were conducted by periodically measuring the wear of the cutter’s teeth flank face expressed with parameter VB
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