Machining of Nomex® honeycomb materials is the biggest challenge in industry because of the complex forms and geometry of the honeycomb structure. The latter is characterized by a low density with ...orthotropic mechanical behavior. The thin walls of the composite structure make the shaping of this material very difficult. Studying interactions between the cutting tool and material, cutting forces, and chip formation allow to understand the machining process of Nomex® honeycomb. This paper presents 3D numerical modeling of machining Nomex® honeycomb using different orthotropic approaches and failure criteria: (i) monolayer isotropic approach, (ii) monolayer orthotropic approach with Tsai-Wu failure criteria, and (iii) monolayer orthotropic approach with Hashin failure criteria. A comparison between experiments and numerical cutting forces was performed to validate the proposed model. The interaction between the tool and the honeycomb walls, which make it possible to observe the different stages of the chip formation process, was carefully modeled.
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The current research work aims at developing an analytical modelling of the gear finish hobbing process when the uncut chip thickness may be very small. Numerical models and particularly finite ...element simulations of this complex material removal process are often limited to one tooth because of the high required computational time. To analyze the performance characteristics of this process, a predictive approach for finish gear hobbing based on an analytical model of orthogonal cutting operation is proposed. To reduce the computational time, a new calculation strategy has been developed. This allows to examine the local parameters which change significantly for each tooth. During the finishing hobbing process of large gears (6 m < diameter < 16 m), the industrial conditions require low cutting speeds (less than 1 m/s) with lubrication. Therefore, in order to consider the effect of lubrication, cutting speed and uncut thickness on the friction coefficient, an appropriate friction law was identified from orthogonal cutting tests. The cutting model has been experimentally validated for different cutting conditions. Finally, the effects of hobbing process on the cutting forces and the tool-chip contact parameters (contact length, pressure, frictional stress and temperature) have been investigated and deeply analyzed using the developed model. The distributions of these local parameters, at each tooth rake face, may be used as a process signature for the resulting condition of the machined surface and subsurface layers.
In this paper, machining aeronautical aluminum alloy AA2024-T351 in dry conditions was investigated. Cutting forces, chip segmentation, and built-up edge formation were analyzed. Machining tests ...revealed that the chip formation process depends on cutting conditions and tool geometry. So continuous and segmented chips are generated. Under some cutting conditions, built-up edge formation occurs. A predictive machining theory, based on a finite elements method (FEM), was applied to reproduce and explain these phenomena. Thermomechanical behaviors of the work material and the tool-work material interface were considered. Results of the proposed modelling were compared to experimental data for a wide range of cutting speed. It was shown that the feed force is well reproduced by the ALE-FE (arbitrary lagrangian-eulerian finite element) formulation and highly underestimated by the lagrangian finite element (LAG-FE) one. While, the periodic localized shear band, leading to a chip segmentation, is well reproduced with the Lagrangian FE formulation. It was found that the chip segmentation can be correlated to the cutting force evolution using the defined chip segmentation intensity parameter. For the built-up edge (BUE) phenomenon, it was shown that it depends on the contact/friction at the tool-chip interface, and this is possible to simulate by making the friction coefficient time-dependent.
In order to simulate micromachining of Ti-Nb medical devices produced in situ by selective laser melting, it is necessary to use constitutive models that allow one to reproduce accurately the ...material behavior under extreme loading conditions. The identification of these models is often performed using experimental tension or compression data. In this work, compression tests are conducted to investigate the impact of the loading conditions and the laser-based powder bed fusion (LB-PBF) building directions on the mechanical behavior of β-Ti42Nb alloy. Compression tests are performed under two strain rates (1 s-1 and 10 s-1) and four temperatures (298 K, 673 K, 873 K and 1073 K). Two LB-PBF building directions are used for manufacturing the compression specimens. Therefore, different metallographic analyses (i.e., optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), electron backscatter diffraction (EBSD) and X-ray diffraction) have been carried out on the deformed specimens to gain insight into the impact of the loading conditions on microstucture alterations. According to the results, whatever the loading conditions are, specimens manufactured with a building direction of 45∘ exhibit higher flow stress than those produced with a building direction of 90∘, highlighting the anisotropy of the as-LB-PBFed alloy. Additionally, the deformed alloy exhibits at room temperature a yielding strength of 1180 ± 40 MPa and a micro-hardness of 310 ± 7 HV0.1. Experimental observations demonstrated two strain localization modes: a highly deformed region corresponding to the localization of the plastic deformation in the central region of specimens and perpendicular to the compression direction and an adiabatic shear band oriented with an angle of ±45 with respect to same direction.
This work presents an analysis of relationships between the non-linear vibrations in machining and the machined surface quality from an analytical model based on a predictive machining theory. In ...order to examine the influences of tool oscillations, several non-linear mechanisms were considered. Additionally, to solve the non-linear problem, a new computational strategy was developed. The resolution algorithm significantly reduces the computational times and makes the iterative approach more stable. In the present approach, the coupling between the tool oscillations and (i) the regenerative effect due to the variation of the uncut chip thickness between two successive passes and/or when the tool leaves the work (i.e., the tool disengagement from the cut), (ii) the friction conditions at the tool–chip interface, and (iii) the tool rake angle was considered. A parametric study was presented. The correlation between the surface quality, the cutting speed, the tool rake angle, and the friction coefficient was analyzed. The results show that, during tool vibrations, the arithmetic mean deviation of the waviness profile is highly non-linear with respect to the cutting conditions, and the model can be useful for selecting optimal cutting conditions.
The current challenge for industrial companies, involved in improving CNC—computer numerical control—mechanical manufacturing machines, consists in integrating production decision aid adapted to the ...constraints associated with dry machining processes. This tool provides the best choice of appropriate production parameters for dry machining, which has a direct impact on productivity, system degradation and the quality of the final product. The proposed study develops an integrated production-maintenance policy which considers simultaneously several parameters related to production process and manufacturing system environment. In fact, our goal consists in determining an economical integrated production maintenance strategy that minimize the total cost including raw materials, production, recycling, and maintenance. Considering two types of raw materials (steel and aluminum) and requesting to a random demand over a finite horizon dissociated to subperiods, the economical integrated maintenance-production, which is obtained by minimizing the total cost, is illustrated by the processing time of each type of raw materials for each subperiod and the optimal preventive maintenance time. The impact of the type of raw material with regard to some parameters like cutting speed, recycle cost, and the degradation system is taken into account in the determination of the economic plan. An analytical model expressing the objective function, the total cost, according to the variable decisions is developed. A numerical solving procedure, a numerical example and a sensitivity study are proposed in order to prove the developed analytical model.
The selection of the suitable production parameters for dry machining remains a challenging task which impacts the productivity, the system degradation and the quality of the output product. This ...study proposes an integrated production-maintenance policy allowing the simultaneous consideration of the production parameters, mainly the cutting speed, the production time and cost, the preventive maintenance period and the quality levels and the selling prices of the output product. A special feature of this strategy, defined on a finite time span, is to allow a change of the cutting speed at a certain instant to be determined in an optimal way concurrently with the preventive maintenance period, such as to maximise the total expected profit per time unit. A mathematical model is developed to express the average profit per time unit as a function of the decision variables. A solving procedure is also proposed. A numerical example and a sensitivity analysis are presented in order to show the impact of some major input parameters on the optimal policy.
In this work, experimental and numerical investigations are conducted to investigate the precision cutting cutting of Ti42Nb titanium alloy produced by laser-based powder bed fusion. Experimental ...precision cutting tests are carried out using precision turning lathe. Trials are performed with two cutting velocities of 60 m/min and 90 m/min and different feed rates, varying from 5 to 40
μ
m/rev. For the numerical study, a porous crystal plasticity-based model is proposed to address the impact of anisotropy and microstructure heterogeneities of the polycrystalline material. The crystal plasticity-based model is identified using strain–stress curves obtained from compression tests performed under two strain rates and a wide range of temperatures. Numerical precision cutting simulations are performed in order to gain insight into the impact of crystallographic orientation and grain size on the machinability of the alloy. According to the results, the effect of the strain rates and the temperature on the thermomechanical behavior of the Ti42Nb alloy produced by laser-based powder bed fusion is correctly depicted. The model captured the strain localization on adiabatic shear band. According to the precision cutting simulations, the local variables such as temperature, damage and plastic deformation are strongly impacted by the crystallographic orientation and the grain size. Depending on the crystallographic orientations, the chip morphology changes form continues, slightly segmented to largely segmented.
The BUE can affect the tool wear and surface integrity when machining ductile metals. The main goal of the present work is to investigate the close link between the BUE formation and the tribological ...behaviour at the tool–workmaterial interface when machining ductile metals. Machining AA2024-T351 aluminium alloy with cemented carbide tool WC–Co is considered as a case study. A new method based on the contact conditions variation (i.e. introduction of a time-dependent friction coefficient) at the tool–workmaterial interface is proposed to predict the BUE formation in the frame of a finite element (FE) modelling. A 2D ALE-FE model of orthogonal cutting has been developed for this purpose. Two cases have been considered, which correspond respectively to an abrupt change and a gradual evolution of the friction at the tool–workmaterial interface. Results are discussed based on the effects of the friction change on predicted thermomechanical fields at the cutting zone.
•The Built-Up Edge (BUE) formation in machining ductile metals is analysed.•A close link between the BUE and the tribological behaviour is established.•2D ALE-FE modelling of the cutting process to predict the BUE is developed.•Two cases are considered: an abrupt change and a gradual evolution of the friction.•Friction change effect on thermomechanical fields at the cutting zone is discussed.
•A simple analytical model allows predicting temperature rise during bone drilling, as a function of spindle speed.•The lateral friction during bone drilling plays a significant role in the duration ...of the temperature increase inside bone.•It is unsuitable to consider bone as an infinite medium inside thermal models, to reproduce temperature rise during drilling..
Predicting the bone thermal response in a surgical operation remains a major challenge. In the previous works, metal machining theory has frequently been used to predict bone temperature in drilling process. However, several experimental studies demonstrate that the chip formation process is very complex compared to metal cutting. In the present study, a simplified analytical model based on the moving heat source approach combined with the method of image sources is developed. The heat source due to the drill-bit tip was supposed to be proportional to the cutting energy. The friction at the tool-hole contact was also considered. An experimental study was performed on fresh femur pig bone for cutting speeds from 2 to 20 m/min. Temperature rise, drilling forces and bone volume fraction were measured. The experimental validation showed that the model reproduces satisfactorily the increase in temperature up to the maximum value while it overestimates the temperature during the cooling stage. A parametric study (thermal boundary conditions, lateral friction) was also performed. From the predicted results, it appears that the model can be improved by considering the effects of the bone volume fraction which can present a significant variation in the bone sample.
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