Theoretical model for subsurface microstructure prediction in micro-machining Ti-6Al-4V alloy – Experimental validation

Self Cite

The surface integrity and machining accuracy of thin-walled micro parts are significantly affected by micro-milling parameters mostly because of their weak stiffness. Furthermore, there is still a lack of studies focusing on parameters optimization for the fabrication of thin-walled microscale parts. In this paper, an innovative approach is proposed for the optimization of machining parameters with the objectives of surface quality and dimension accuracy, which integrates the Taguchi method, principal component analysis method (PCA) and the Non-dominated sorting genetic algorithm (NSGA-II). In the study, surface arithmetic average height Sa, surface root mean square height Sq, and 3-D fractal dimension Ds are selected to evaluate surface quality. Then micro-milling experiments are conducted based on the Taguchi method. According to the experimental results, the significance of machining parameters can be determined by range analysis. Besides, regression models for the responses are developed comparatively, and the PCA method is employed for dimension reduction of the optimization objective space. Finally, two combinations of machining parameters with the highest satisfaction are obtained through NSGA-II, and verification experiments are carried out. The results show that the surface quality and dimension accuracy of the thin-walled microscale parts can be simultaneously improved by using the proposed approach.

Section: Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Optimization of the process parameters for micro-milling thin-walled micro-parts using advanced algorithms

Wang

Bai

Cheng

et al. 2022

Self Cite

“…During the process of high-speed cutting, the plastic deformation of the machined surface is serious, the grains are elongated and broken, the original morphology is changed, and the surface lattice distortion and dislocation movement are also intensified. This causes the machined surface grains to become refined, internal stress is generated between the grains and microcrystals, and, finally [23], the diffraction peak width increases. The XRD spectra of 7050 aluminum alloy at different cutting depths…”

Section: Xrd Analysis Of the Machined Surface Layer At Different Cutt...mentioning

confidence: 99%

Study on the surface integrity of 7050 aluminum alloy with different crystal orientations during high-speed machining

Zong

et al. 2022

This paper investigates the effect of crystal orientations and machining parameters on the surface integrity of 7050 aluminum alloy in high-speed machining. Three groups of pre-compression deformations (10%, 15%, and 20%) are performed on the aluminum alloy to fabricate specimens with different crystal orientations. A single-factor dry cutting experiment was designed, and the surface roughness, surface morphology and defects, work hardening, and X-ray diffraction (XRD) were tested. The results show that the 15% pre-deformed 7050 aluminum alloy specimen had lower surface roughness and the best surface quality under the same cutting parameters. The surface roughness of 7050 aluminum alloy with different crystal orientations tended to first increase and then decrease with the increase of the cutting speed, and the surface roughness was positively correlated with the cutting depth and feed rate. Under different cutting parameters, the machined surfaces of 7050 aluminum alloy specimens with different crystal orientations exhibited different degrees of plowings, apophysis, sticky chips and pits. Moreover, the degree of work hardening of the 15% pre-deformed 7050 aluminum alloy specimen was small, while that of the 20% predeformed specimen was more serious. XRD analysis demonstrated that the diffraction peak width of the 10% pre-deformed 7050 aluminum alloy specimen slightly increased with the increase of the cutting depth. Moreover, the (111) and ( 200) diffraction peak intensities of the 15% pre-deformed 7050 aluminum alloy specimen increased with the increase of the cutting speed, and there was no obvious Al 2CuMg phase on the machined surface of the 20% pre-deformed specimen.

“…Ginting et al [9] reported the dependence of the surface integrity properties, including roughness, defects, microhardness, and microstructure on machining parameters in dry milling titanium alloy. Bai et al [10] studied the dislocation distribution at subsurface damage layer in micro-milling Ti-6Al-4V, and pointed out that the work hardening effect might attribute to the dislocations piling-up zone and persistent slip band observed at the machined subsurface. However, it is recognized that the fundamental research on the microstructural evolution processes in high-performance cutting requires many experimental matrices and cumbersome procedures of nano-characterization tests.…”

Section: Introductionmentioning

confidence: 99%

A novel multiscale material plasticity simulation model for high-performance cutting AISI 4140 steel

Bai

Tong

2021

Self Cite

The achievable machined surface quality relies significantly on the material behavior during the high-performance cutting process. In this paper, a multiscale material plasticity simulation framework is developed to predict the deformation behaviors of AISI 4140 steel under various high-performance cutting conditions. The framework was built by coupling a three-dimensional discrete dislocation dynamic (3D-DDD) model with a finite element method (FEM) through the optimization of a dislocation density-based (DDB) constitutive equation (compiled as a user-defined subroutine in ABAQUS). The movement of edge and screw dislocations such as generation, propagation, siding, and their interactions, was performed by 3D-DDD, and the statistical features of dislocations were used to optimize the critical constants of the DDB constitutive equation. For validation, a classic FEM cutting model (Johnson-Cook constitutive equation) was employed as a reference. The simulation results indicated that the proposed multiscale model not only can precisely predict the stress, strain, cutting force, and temperature as those predicted by the classic FEM simulations, but also capture the microstructure characteristics such as grain size and dislocation density distributions under the tested cutting conditions. Severe dynamic recrystallization phenomena were found at the core shear zones. The recrystallization process reached a dynamic equilibrium at the machined surfaces when the cutting speed is larger than 280 m/min or the external-assisted temperature is between 200 and 350°, indicating an optimal range of machining parameters for improved surface integrity.