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![Theory of saw-tooth chip formation mechanism. a Adiabatic shear band [14, 17] and b cyclic crack [22, 24]](publication/337743799/figure/fig1/AS:832614135001116@1575522087652/Theory-of-saw-tooth-chip-formation-mechanism-a-Adiabatic-shear-band-14-17-and-b.png)
Theory of saw-tooth chip formation mechanism. a Adiabatic shear band [14, 17] and b cyclic crack [22, 24]
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Vibration-assisted drilling (VAD) of Ti6Al4V is typically used in the aerospace industry to enhance the performance of the machining process. A mix of continuous and saw-tooth chip formation is associated with VAD of Ti6Al4V. In this paper, a comprehensive experimental study is developed to examine the effect of process parameters on the dominant c...
Citations
... To understand the observed differences among all the tested workpieces, the theory of plastic deformation during machining should be clarified. It has been reported by Hussein et al. [42] that a chip segment is first formed ahead of the drilling bit and starts to increase the shear stress. With the progress of machining, the shear stress continues to increase until reaching the critical stage (critical shear stress), where the thermal softening rate is higher than the strain hardening rate. ...
In the current study, Ti-6Al-4V (Ti64) and Ti-6Al-7Nb (Ti67) alloys were prepared by vacuum arc melting. The produced samples were then subjected to different heat treatment regimes. The evolved microstructures and their corresponding hardness were investigated. Computerized drilling tests using TiAlN-coated high-speed steel bits were performed to assess the machinability of the prepared specimen regarding cutting force, tool wear, and thickness of the deformed layer. It was observed that Ti64 specimens that were water quenched from either α/β or β range contained martensitic phase. In Ti67, samples showed martensite only when water quenched from the β-phase range (1070 • C). Formation of martensite resulted in higher hardness and hence led to higher cutting forces and increased tool wear during the drilling process. Machined samples with higher hardness formed a thicker subsurface deformation area (white layer) and increased burr heights. Surface roughness in Ti64 workpieces was generally higher compared to Ti67 specimens. The coat of the drilling bit was partially attacked in the as-cast specimens, which was evident by elemental N on the machining chips. The machining tool deteriorated further by increasing the workpiece hardness through martensitic formation, where elements such as Cr, V, Fe, etc. that came from the tool steel were detected.
... Bleicher et al. (2019) demonstrated that chip breaking is effective, even in small-diameter drilling, and that the chip removal rate is increased by reducing the frequency and increasing the amplitude. In particular, this method was adopted for aerospace materials such as CFRP/Ti6Al4V, CFRP/aluminum, and Ti-6Al-4V titanium alloy (Hussein et al., 2019;Seeholzer et al., 2019;Yang et al., 2019;Hussein et al., 2020;Paulsen et al., 2020). ...
Low-frequency vibration cutting is a machining technology in which chips are broken by applying periodic vibrations along a specific axis. Periodic vibration deteriorates the surface roughness and roundness of the workpiece when compared to without vibration cutting. In this study, the properties of a machined surface under low-frequency vibration were simulated. Based on the simulation results, a tool was designed to reduce the effects of periodic vibration on the surface properties. Actual machining experiments were conducted using the proposed tool to clarify the relationship between tool shape, surface roughness, and roundness under low-frequency vibration. Using the proposed tool on low-frequency vibration cutting, the surface roughness was reduced (from 5.74 µm to .94 µm in Ra and 23.09 µm–6.66 µm in Rz), average roundness improved (from 4.73 µm to 2.95 µm), and maximum roundness decreased (from 15.34 µm to 3.61 µm) compared with those of the conventional tool.
... Furthermore, rotational speed is a decisive variable, as this can trigger a resonance of the machine tool, which can cause bending vibrations. In contrast, torsional vibrations are primarily influenced by the feed rate and the workpiece material [17]. Therefore, high strength materials effect chatter vibrations. ...
Deep hole drilling processes for high-alloyed materials are characterised by worn guide pads and chatter vibrations. In order to increase feed rates, process stability and bore quality in STS deep hole drilling, various investigations were carried out with adjustments to the tool. First, a new process chain for the production of tribologically optimised guide pads and their effects on the guide pad shape is described in detail. The results of these studies show that the shape change in the area of the axial run-in chamfer through a micro finishing process leads to a better bore hole quality. Furthermore, the influence of guide pad coating and cooling lubricant on the deep hole drilling process was investigated. In addition, the machining of the austenitic steel AISI 304 is analysed by using a conventional steel boring bar and an innovative carbon fibre reinforced plastic (CFRP)-boring bar. While the conventional drill tube oscillates with different eigenfrequencies, the CFRP-boring bar damps chatter vibrations of the drill head and stabilises the process. Even at higher feed rates up to f = 0.3 mm, it is possible to machine austenitic, difficult-to-cut-materials with significantly reduced vibrations.
... Pęknięcia cykliczne, w których wzdłuż pasma ścinania zlokalizowane są duże pęknięcia i mikropęknięcia, są dominującym mechanizmem powstawania wiórów zębatych przy wierceniu Ti6Al4V z LF-VAD. Tworzenie się tych pęknięć wykazało znaczącą zależność od amplitudy drgań [19]. Wyniki świadczyły o zmniejszeniu współczynnika grubości wióra oraz wzroście stopnia segmentacji przy zwiększaniu amplitudy drgańrys. ...
... Cyclic cracks, where gross and micro cracks are located along the shear band, are the prevailing mechanism for saw-tooth chips in LF-VAD of Ti6Al4V. The formation of these cracks showed a significant dependency on the vibrational amplitude [55]. The results showed a reduction in the chip thickness ratio and an increase in the segmentation degree when increasing the vibration amplitude (Fig. 29). ...
... Fig. 29. Geometric characterization for LF-VAD chips cross section for hmax, hmin and segmentation degree [55] During LF-VAD operation for Ti6Al4V, discrete chips are produced only at certain amplitude-frequency conditions, which have been represented in the form of a characteristic U-curve, which can serve as a ready reference to select the suitable modulation conditions for interrupted chip generation [56] (see Fig. 30). Fig. 30. ...
The paper presents an update of the recent literature on advances in machining of difficult to machine materials such as nickel and titanium-based alloys, and composites used in aeroengine and aerostructure applications. The review covers the following issues: advances in high-performance cooling techniques as cryogenic machining, minimum quantity lubrication, the combination of MQL and cryogenic cooling, and high-pressure lubricoolant supply and hybrid cutting processes – vibration assisted machining (both low and high frequency), laser, plasma and EDM assisted machining. Examples of applications in industrial processes are also given
... Barani et al. (2014) indicated that the short chip length of VAD processing was the main reason for friction reduction, which decreased the tool wear and surface roughness. Hussein et al. (2019) proposed that vibration amplitude was closely related to the thickness and length of the chips. Sanda et al. (2016) used the VAD technology to conduct drilling experiments of composite materials and titanium alloys. ...
Vibration-assisted machining (VAM) is implemented in titanium alloy processing to solve some challenges, such as difficulty in chip breaking, large cutting forces, and high cutting temperatures. Based on the multi-region dynamic angles and the double-side wedge angle deformation mechanism, this study improves the vibration-assisted drilling (VAD) cutting forces and chip breaking model. The dynamic kinematics angles, the behavior of parameter influence, and the cutting strain effect of intermittent VAM are analyzed. VAD and conventional drilling (CD) experiments are carried out for model validation and mechanism analysis. The experiments show that the maximum deviation of the drilling forces simulation value and the experimental value is 9.13 %. Compared with the CD, the cutting force of the VAD is decreased by 10.1 %-46.2 %. The dynamic feed angle causes multiple cutting angles fluctuations, which affects cutting performance. The adjustment of the VAD cutting parameter value could reduce the chip length by 26.6 %-43.9 %. Material cutting strain presents multi-region characteristic, which influences the chip morphology. This study provides a reference for VAM parameter optimization.
Le procédé de perçage consiste en une opération complexe générant d’importants efforts, couples et températures au sein d’une zone très localisée et confinée. Ce chargement thermomécanique peut conduire à l’usure prématurée des outils et à l’altération des surfaces générées, notamment lors du perçage du Ti6Al4V, matériau difficilement usinable. L’objectif de ces travaux de thèse est de fournir les clés pour une meilleure compréhension des phénomènes en jeu et une évaluation fiable et pertinente de ce chargement induit par le passage de l’outil sur la paroi du trou percé. Expérimentalement, du fait des vitesses élevées et de la zone de coupe difficile d’accès, obtenir des informations fiables et de qualité constitue un réel défi. Le volet expérimental de cette thèse a donc porté sur la mise en place et la réalisation d’essais pour la mesure de champs thermomécaniques à différentes échelles d’étude. Cette approche multi-échelle a permis d'identifier les phénomènes mis en jeu à différents niveaux, mais aussi de confronter les études aux différentes échelles afin de les valider et de permettre le changement d'échelle. En complément, une étude numérique est menée. Face aux difficultés expérimentales, la modélisation numérique apparaît comme une alternative pertinente pour l’évaluation des données souhaitées. La démarche adoptée ici est de la coupler à la stratégie expérimentale en vue d'élaborer une modélisation multi-échelle du perçage du Ti6Al4V qui se veut robuste. Cette modélisation est basée sur des lois de comportement et d'endommagement présentant un couplage explicite des phénomènes thermiques et mécaniques, ainsi que sur une détermination fine des lois de frottement et des coefficients de partage. Finalement, une confrontation des résultats numériques et expérimentaux est réalisée à chaque échelle d’étude et a permis de statuer sur la pertinence du modèle numérique proposé.
The present paper investigates the thermo-mechanical loading involved in hole drilling of Ti-6Al-4V. Indeed, the heat and strains developed in a very restricted area at the tool vicinity are responsible for various undesired side effects among which: tool damage, residual stresses, poor surface roughness, and metallurgical alterations. The confined nature of the drilling process prevents from any experimental access to some governing physical data such as local strain fields and local energies. Therefore a mixed numerical-experimental approach is herein proposed in order to provide local in-sight to essential tool-related thermal and mechanical sources. It relies on strain and temperature measurements at various locations of the cutting edge that are used to validate a multi-scale numerical model. This latter is then used to assess the energy budget involved in the material removal. The presented results prove the ability of such technique in obtaining valuable information on the in-process generated heat and the way it spreads within the workpiece and beyond. Results also show the spatial heterogeneity of the cutting phenomenon along the cutting edge and highlight the complexity of defining optimal cutting parameters and optimal tool design.
