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Ti-6Al-4V titanium alloy is known as one of the most difficult metallic materials to machine, and the machined surface residual stress distribution significantly affects properties such as static strength, fatigue strength, corrosion resistance, etc. This study utilized finite element software Abaqus 2020 to simulate the two-step cutting process of titanium alloy, incorporating stages of cooling, unloading, and de-constraining of the workpiece. The chip morphology and cutting force obtained from orthogonal cutting tests were used to validate the finite element model. Results from the orthogonal cutting simulations revealed that with increasing cutting speed and the tool rake angle, the residual stress undergoes a transition from compressive to tensile stress. To achieve greater residual compressive stress during machining, it is advisable to opt for a negative rake angle coupled with a lower cutting speed. Additionally, in two-step machining of titanium alloy, the initial cutting step exerts a profound influence on the subsequent cutting step, thereby shortening the evolution time of the Mises stress, equivalent plastic strain, and stiffness damage equivalent in the subsequent cutting step. These results contribute to optimizing titanium alloy machining processes by providing insights into controlling residual stress, ultimately enhancing product quality and performance of structural part of titanium alloy. [ABSTRACT FROM AUTHOR]

Fatigue performance is largely dependent on the machined surface integrity of engineering parts. In this paper, effect of cutting steps and directions on machined surface integrity of aluminum–silicon alloy is investigated. Machining induced surface quality under the forward and reverse finish cutting as well as the step-by-step feed cutting method is contrastively analyzed. The results indicate that the final machined surface integrity can be controlled through adjusting the finish cutting steps, and governing finish cutting directions can also be effective when the finish cutting step is fixed. High-machined surface integrity can be obtained when it adopts reverse finishing in first-step while it employs forward finishing in second-step, where there are little micro-defects on the machined surface, relatively low degree of surface hardening and surface residual stress, along with smaller surface roughness, respectively. Moreover, step-by-step feed cutting method can effectively break chips, avoid surface scratching, chips softening, and forming the built-up edge. It can also reduce the degree of elastic–plastic recovery and thermal expansion on the machined surface, improve surface hardness, and obtain surface compressive residual stress. There are many micro-defects on machined surface by single-step feed cutting. However, when the step-by-step feed cutting method is adopted, the forward finishing surface emerges almost no micro-defects, but that of reverse finishing exhibits severe grain breakage. The proposed adjusting method in cutting steps and forward-reverse cutting directions may be of interest to the engineering practice, and will help improving the machined surface quality and fatigue life of aluminum–silicon alloy engineering parts. [ABSTRACT FROM AUTHOR]

In the two-step cutting process, due to the combined effects of mechanical and thermal deformation, the microstructure and residual stress of the workpiece are changed with the change of roughing parameters, which affects the machined surface quality. In this paper, the two-step milling (roughing and then finishing) experiments of Ti-6Al-4V titanium alloy were designed to analyze the effect of different roughing parameters on the cutting force of roughing and finishing, the residual stress of finishing surface, and the microstructure. The microstructural characteristics in terms of residual stress, XRD patterns, phase composition and content, and nano-scale crystallite size of machined surface layer were characterized to reveal the machined surface layer quality adjustment and controlling mechanism from the prospective of the microscopic scale. The experimental results showed that the cutting force and compressive residual stress were larger at low roughing cutting speed than that at high roughing cutting speed because of the combined effects of mechanical and thermal deformations. In the two-step machining process, with the increase of roughing cutting speed, the β phase on the finishing surface firstly increased and then decreased. Meanwhile, the high roughing cutting speed weakened the microcrystal refinement of the finishing surface because of the work hardening effect. Therefore, the appropriate roughing machining parameters will contribute to the improvement of finishing machined surface quality in the terms of lower cutting force, higher compressive residual stress, and better grain refinement, phase content, and preferred crystallite orientation, thus increasing the microscopic mechanical properties of machined surface layer. This provides a reference for optimizing the cutting parameters to adjust and control the quality and integrity of the machined surface layer in two-step milling of Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

The machined surface integrity has significance on fatigue life. The step-by-step feed cutting is put forward and adopted to machine ZL109 aluminum-silicon piston alloy. In addition, the forward and reverse finish cutting is also proposed to improve the machined quality and fatigue life. The result indicates that the step-by-step feed cutting can effectively avoid scratching and decrease surface roughness, bring about the compressive residual stress, and improve machined quality. Moreover, there is smaller elastic-plastic recovery and thermal expansion on the machined surface, when the step-by-step feed cutting is adopted, so that the machining dimension accuracy can be ensured perfectly. The forward and reverse finish cutting can effectively decrease the surface roughness and the tensile residual stress due to the thermal stress. So the larger the cutting thickness is, the smaller surface residual stress is, when the cutting depth is 0.15–0.30 mm in the forward and reverse finish cutting. It can improve the machined quality of ZL109 aluminum-silicon piston alloy and the fatigue life when the reasonable cutting parameter is adopted. Those results have an important practical significance. [ABSTRACT FROM AUTHOR]

The residual stress on the machined surface has a significant impact on the service life and fatigue strength of machined parts. In the former studies, it has been confirmed that both pre-stress cutting process and multi-step cutting process can significantly affect the residual stress distribution of the finishing machined surface, which gives expression to the increasing trend of compressive residual stress. In this paper, a finite element software Abaqus was used to establish a two-dimensional finite element simulation model for titanium alloy cutting. The finite element model was validated by the chip shape characteristics and cutting forces obtained by orthogonal cutting experiments. Based on the validated model, the simulations of single-step cutting, multi-step cutting, pre-stress single-step cutting, and pre-stress multi-step cutting processes were conducted. The chip shape characteristics, cutting forces, and residual stress distribution of the machined surface under four machining processing conditions were comparably investigated. The influence mechanism and coupling effect of multi-step machining and pre-stress machining on residual stress distribution on machined surface was explained. Investigation results indicate that both multi-step cutting and pre-stress cutting processes can increase the compressive residual stress, while multi-step cutting will change the position of minimum residual stress along the depth direction and increase the chip segmentation degree. Among the four cutting processing conditions, the pre-stress multi-step cutting will effectively increase compressive residual stress value to the utmost extent, which should be attributed to the coupled effect of pre-stress cutting and multi-step cutting processes. [ABSTRACT FROM AUTHOR]

The Johnson-Cook (JC) constitutive model was utilized to simulate the processing of Al-Si piston alloy ZL109 to obtain the optimal finishing parameters in polycrystalline diamond (PCD) tool, and studied the machining quality of ordinary-turning under the optimized cutting parameters. PCD is brittle, so it is difficult to manufacture orthogonal blades and is easy to break and high cost. We have adopted ordinary-turning quality to verify simulation results. Effect of cutting parameters on residual stress, cutting force and temperature was investigated through simulation, meanwhile, effect of cutting parameters on surface roughness and residual stress was analyzed by experiments. It indicates the verification method is practicable, and residual stress, cutting force and temperature are the smallest in simulation, and the experimental values of surface roughness and residual stress are also the smallest under the optimal cutting parameters, which can guide the cutting parameters selection to obtain higher machining quality. [ABSTRACT FROM AUTHOR]

It is well known that the multi-axis machining technology has been developed into a key technique applied in the manufacturing field. The machined surface integrity is one of the most important factors influencing the performance of the produced components. Hence, this research concentrated on the machined surface integrity induced by the multi-axis milling operation with different inclination angle combinations. In this research work, the cutting conditions of the conventional or up-milling process with tool orientations were divided into eight different types, and the machining characteristics corresponding to different cutting strategies were discussed. The varying conditions of surface topography, texture and other machining features induced in machining process which corresponds to different inclination angle combinations were analyzed by geometrical analysis, and the surface roughness and linear profile along specific directions on the machined surface were also investigated. There is a special corresponding relationship between the rotation angle and tool tilt and lead angles. Better surface roughness could be achieved when rotation angles are 0° (positive lead), 60° (combination of positive tilt and positive lead), 90° (positive tilt) and 330° (combination of negative tilt and positive lead). Then, the samples used for study of the metamorphic layer were produced by lapping and polishing process, and the macro hardness (HL) and micro-hardness (HV) of the top machined surface were investigated. According to the measured results of both Leeb hardness and micro-hardness, higher surface hardness could be obtained under rotation angles of 60° (combination of positive tilt and positive lead), 120° (combination of positive tilt and negative lead) and 210° (negative tilt and negative lead). Moreover, the variations of the micro-hardness along the depth direction of the samples were studied. Finally, discussions on the machined surface residual stresses in both feed and cross-feed direction were carried out. Compressive surface residual stress in both feed and cross-feed direction could be generated when rotation angles are 210° (combination of negative tilt angle with smaller value and negative lead angle with larger value) and 330° (combination of negative tilt angle with smaller value and positive lead angle with larger value). Generally, the evaluation indicators of surface integrity are not all very satisfying under one special cutting condition with a certain inclination angle combination, and the optimal cutting parameters should be selected based on the specific application requirements. Finally, the optimal tool orientations and related cutting parameters were recommended, and further studies of the related topics were also presented. [ABSTRACT FROM PUBLISHER]

The cutting performance, failure types, and mechanisms of the graded nano-composite ceramic tools were investigated during dry face milling of Inconel 718. In these tests, round ceramic inserts were used at cutting speeds ranging from 500 to 1,100 m/min. The structures of the chips, cutting forces, and surface roughness were also examined. Failure surfaces of the tools were characterized by scanning electron microscopy. The results showed that the graded tool possessed a self-sharpening characteristic and exhibited higher cutting performance compared with the homogeneous ones, as a result of its enhanced mechanical properties, higher abrasive wear, and fracture resistance. The failure mechanisms of the tools involved chipping, flaking, notch wear, abrasive wear, and adhesive wear. The mechanisms responsible for the higher cutting performance of the graded tools were inferred to be the formation of compressive residual stress in the surface layer induced by the graded compositional structure. [ABSTRACT FROM AUTHOR]

The generation mechanism of machining-induced residual stresses is a complex nonlinear and thermal-mechanical coupling problem. The cutting forces and cutting temperature produced in machining process must be considered simultaneously. The influence of cutter orientation and feed per tooth on the cutting speed, cutting forces, cutting temperature, and residual stresses is discussed in the present study. Effective cutting speed in accordance with the inclination angle in feed direction is analyzed. The cutting forces are gained by milling experiment, and the cutting temperature is obtained by finite element method. Moreover, the influence of the effective cutting speed on the cutting forces and cutting temperature is stated, and the relationship among the cutting forces, cutting temperature, and residual stresses is discussed. The experimental and numerical methods are both adopted in this study to give a better understanding of the milling process. After analysis of the phenomenon, several conclusions are made. The inclination angle in feed direction affects the effective cutting speed, and then the cutting forces, cutting temperature, and residual stresses are affected. Priority selection of inclination angle in feed direction is suggested from 5° to 30° in order to reduce the cutting forces. The overall trend of the workpiece temperature presents the parabolic shape, while the chip temperature increases with the increasing inclination angle in feed direction. Residual stress in feed direction almost increases with the increasing feed per tooth, which is not obvious in the general scope of the feed rate. The inclination angle of 5° and 15° is the priority in order to produce residual compressive stresses in cross feed direction. [ABSTRACT FROM AUTHOR]