Résumé: To investigate the effect of the slide diamond burnishing process on the mechanical properties of GCR15 steel, an experimental study was carried out. For this purpose, burnished and unburnished specimens have been prepared and compared in fatigue performance, surface roughness, microhardness, and SEM analysis. The burnishing process was carried out at a speed of 560 rpm, a burnishing force of 10 Kgf, a feed rate of 0.074 mm/rev and several passes of 3. Rotary bending fatigue tests were performed on the burnished and unburnished specimens, S–N curves were plotted from a maximum load representing 66% of tensile strength. The findings indicate that the fatigue strength was increased by up to 36% because of slide diamond burnishing compared to the non-burnished case. At lower stress levels, the improvement in fatigue strength is clearly observed. The fatigue curves reveal a slight reduction in the fatigue strength results compared to those reported in the literature, which can be attributed to the specimen’s small shoulder fillet value

Résumé: The present work is a contribution in order to highlight the contradictory efect of machining conditions on wear evolution in the main cutting zone of twist high-speed steel (HSS) grade drill bits. Wear tests have been conducted on annealed and hardened C22 steel according to the planning experience methodology (L8). The input parameters are cutting speed, feed rate, and drill diameter; meanwhile, the output parameters are values of lank and chisel wears related to the tool life. Results show that the tool life of a twist drill depends on both lank wear and chisel wear. Meanwhile, the two wears can be competitive as a function of cutting conditions. For instance, within the three cutting parameters, feed rate is most inluencing, then the cutting speed, and the tool diameter efect is nonsigniicant. In the annealed condition, when feed rate and cutting speed increase, lank wear (VB) and chisel wear (VCH) are faster. That is good agreement with literature review on machinability of steels. The higher the cutting speed and feed rate, the lower the tool life. In the hardened condition, chisel wear becomes increasingly competitive with lank wear and even faster under certain cutting parameters. However, increasing the cutting speed results in lower wear evolution and, consequently, a better tool life. This contradictory efect of cutting speed is unique to drilling operations with HSS steel drill bits. Finally, chisel wear models have been presented to make evidence of their importance for industrial application where drilling hardened steel is required.

Résumé: The present work is a contribution in understanding the effect of quenching and tempering of C22 steel on the tool life of twist high speed steel (HSS) grade drill bits. Experimental investigation has been conducted on annealed and tempered steel according to the planning methodology (L8). The input parameters are cutting regime elements (cutting speed, feed rate and drill diameter) and the output parameter is the tool wear related to tool life. Beyond, the common behavior that suggests that when the feed rate on tool life increases the tool life increases, the most interesting phenomenon is the controversial effect of the cutting speed when drilling the steel in tempered condition. The objective of this contribution then to in make in evidence the benefit effect of quench hardening on drill tool life through exploratory chip microstructure observations.

Résumé: – This work aims to understand the influence of cutting parameters on the twist highspeed steel (HSS) drill bits wear when drilling C35 steel before and after quenching. An experimental investigation has been conducted using the planning experience methodology (L8) on C35 steel in the annealed and hardened states. The input parameters are cutting regime elements, cutting speed (Vc), feed rate (f), and drill diameter (D), while the output parameters are the tool wear related to its tool life. The most interesting phenomenon is the controversial effect of cutting speed when drilling C35 steel in hardened conditions. The drilling life increases with increasing cutting speed for different cutting regimes (1 to 8). In addition, the 20 mm diameter drill related to the high value of the depth of cut (f) has given better life before and after hardening, contrary to the literature on cutting tool life. The analysis of variance (ANOVA) has showed that the feed rate (f) is the most significant factor in the annealed state while it is the depth of cut (ap) in the hardened state. The correlation coefficients R2 determined by the ANOVA before, and after quenching, are very satisfactory, and testify the good adequacy of the proposed model. Copyright © 2021 Praise Worthy Prize S.r.l. - All rights reserved

Résumé: The present work is a contribution in understanding the machinability of hardened C22 steel under drilling operations using twist high-speed steel (HSS) grade drill bits. Experimental investigation has been conducted on annealed and hardened C22 steel according to the planning experience methodology (L8). The input parameters are cutting regime elements, cutting speed, feed rate, and drill diameter; meanwhile, the output parameter is the tool wear related to tool life. Apart from the common observation that tool life decreases when the cutting speed increases, the most interesting phenomenon is the controversial effect of the cutting speed when drilling the steel in hardened condition. The latter has been assessed through exploratory chip microstructure observations

Résumé: Dans ce travail sont exposés les résultats d’une investigation expérimentale sur le comportement à l’usure des forets hélicoïdaux en acier rapide lors du perçage de l’acier C18. Les essais de perçage ont été effectués avec des forets de différentes longueurs et de différents diamètres. La longueur du perçage est d'environ 80 mm en présence d'une lubrification abondante et d'un cycle de débourrage adopté. La méthodologie entreprise pour la réalisation des essais est celle de planification des expériences. Le paramètre de sortie étudié est l'usure (durée de vie du foret). Les paramètres d’entrée investigués sont la vitesse de coupe, l’avance et le diamètre du foret. Le critère retenu de l'usure admissible est VB=0,5 mm suivant la surface en dépouille principale. Les résultats montrent que l'acier C18 se caractérise par une bonne usinabilité (la durée de vie T varie de 19 à 495 min) et ceci pour toutes les combinaisons du plan d’expérience étudié.

Résumé: In this work, the results of an experimental investigation are presented to put into evidence the wear evolution of chisel and main cutting edges of high speed steel helical drills (HSS) during the machining of hardened and unhardened C22 steel. To do so, a series of tests was carried out according to the experimental design methodology. The investigated output parameter is the tool wear (lifetime) whereas, the input parameters are the cutting regime elements (cutting speed, feed rate and drill diameter). Machining was performed in the presence of an abundant lubrication. Unlike ISO standard (3685: 1993), stating that the criterion of permissible wear (VBmax = 0.5mm) to determine the tool lifetime is that of the major flank face (main cutting edge), it is found that for some experimental design regimes the increase in speed of the wear of the chisel cutting edge is higher than that of the main cutting edge; i. e., a more intense wear grows earlier on another cutting edge of the active part of the drill than the standardized one. Thus, the permissible wear criterion has to be taken into account when determining the lifetime of cutting tool. The analysis of the obtained results also reveals that the wear of the chisel cutting edge is more intense for the regimes working with low feeds and low cutting speeds. Meanwhile, we note that machining with higher cutting speeds and low feed rates contributes to reduce wear on the chisel cutting edge. 

Résumé: Drilling is a complex machining operation. The latter comes from the fact that the various points of the cutting edge of the drill work under very varied cutting conditions. Indeed, the cutting speed at the center of the drill bit is almost equal to zero, where the removal of the material (chip) is mainly by extrusion. Then, as one moves away from the center (along the cutting edge), the cutting speed increases gradually to its maximum value at the periphery of the drill bit. On the cutting edges material removal occurs by shear in the same manner as for turning and milling tools, with the cutting speed and rake angle varying with distance from the drill center. Furthermore, the cutting takes place in a confined environment inside the part, which makes it impossible to observe the chip flow process. Chip evacuation from the cutting zone is also confronted with countless difficulties (excessive friction with the machined surface of the hole, intense heat release, blocking and braking, forces and cutting moments, etc.). Access of the lubricating and cooling liquid in the cutting zone is hampered by accumulation and reverse flow of the chips. All this leads to the generation of stresses of thermal and mechanical solicitations on the active part of the drill bit, which considerably influences its wear resistance behaviour .

Résumé: The study of the helical drill wear phenomenon assumes the knowledge of the various factors that are required to cause their damage. Among these factors, we mention those of the cutting regime such as speed (Vc), advance (f) and depth of pass (ap). For our case it is the diameter of the drill (d), the geometry of the tool (r, α, β, γ, x, ε ...) and the characteristics of the material used (HB, Rr,% C ,% S, ...), as well as the working conditions (machine, lubrication ...), All these factors constitute the input parameters of the machining system. The holding, the precision, the efforts etc ... present the parameters of exit The objective of this study is statistical modeling of the life of HSS drills. Two series of long-term tests were performed on unalloyed steel C22 and HV22. The length of the hole is approximately 80 mm and 10 to 20 mm in diameter, in the presence of an abundant lubrication of 2.5 l / min and an adopted cleaning cycle. The methodology undertaken for the realization of the tests is that of the planning of the experiments. The factor studied is the wear (lifetime of the drill) on the different cutting zones. The criterion of acceptable wear retained is 0.5 mm depending on the undercut surface. Statistical analysis (ANOVA) allowed the detection of the predictive model of the service life (T) according to the main effects and their interactions. The results show that the service life of the tool for different machining conditions varies between 19 and 495 min.

Résumé: The purpose of this work is to study the quenching effect on C18 steel machinability in drilling. For this reason, a comparative experimental study was conducted on a non-hardened and tempered workpiece. Cutting tools used are drills of high speed steel (HSS) grade. The tests are performed according to the planning methodology (L8). Machining was carried out in the presence of an abundant lubrication. The input parameters are cutting regime elements (cutting speed, feed rate and drill diameter). The output parameter is the tool wear (tool life). The results show that when drilling tempered C18 steel, drill wear decreases with the increase of cutting speed. This latter improves machinability. This is in stark contrast with the results obtained during the drilling of the same non-hardened C18 steel (annealing). It should also be noted that this phenomenon is observed especially for high cutting speeds. A deep analysis was carried out to explain the physical phenomenon occurring in the cutting zone.