TC4钛合金铣削刀具C形刃几何参数优化实验研究

通过对TC4钛合金进行侧铣加工,采用正交设计方法研究了硬质合金立铣刀侧刃几何参数对切削力和表面粗糙度的影响,用极差法分析了刀具几何参数对铣削力的影响;并以最小表面粗糙度为目标,采用田口法对刀具几何参数进行了优选。结果表明:螺旋角对铣削力的影响最大,对F_x、F_z,C形刃宽度影响次之,C形刃角度的影响最小;对于F_y,C形刃角度次之,C形刃宽度的影响最小;当螺旋角为25°、C形刃宽度为0.2mm、角度为-25°时可获得最小表面粗糙度。     

A study on the cutting force and chip shrinkage coefficient in high-speed milling of A6061 aluminum alloy

In this paper, finite element (FE) simulation for high-speed milling of aluminum alloy was performed using a ductile fracture model with Mohr–Coulomb criterion proposed by Bai and Wierzbicki (BW). To verify the model, predicted cutting forces were compared to experimental results in the same cutting conditions. Then, further simulations were performed to estimate the cutting forces and chip shrinkage coefficients subjected to different cutting parameters such as cutting speeds, cutting depths, and clearance angles of a cutting tool. The obtained results were also used to determine optimal cutting parameters using the Taguchi method. The analysis of variance (ANOVA) was employed to investigate the influence percentage of each cutting parameter on cutting force and chip shrinkage coefficient. The simulation results showed that inclusion of strain rate in numerical model significantly improved the accuracy of estimated cutting force in comparison to experiment. The optimum values obtained for high-milling process were cutting speed 1000 m/min, cutting depth 1 mm, clearance angle 15°, and rake angle 4°.     

Simulation-based solid carbide end mill design and geometry optimization

Designing a high-performance solid carbide end mill is difficult due to the complex relationship between end mill geometry and numerous or conflicting design goals. Earlier approaches of computer-aided solid end mill design are limited to only a few design aspects. This article presents a three-dimensional finite element method of milling process for solid carbide end mill design and optimization. The software was secondarily developed based on UG platform, integrating the parametric design with the development of the two-dimension drawing of solid carbide end mill. The three-dimension finite element simulation for milling Ti-6Al-4V alloy was performed and the geometrical parameters were optimized based on the objective of low cutting force and cutting temperature. As a result, a simulation-based design and optimization of geometrical parameters of tool structure and cutting edge is possible. The optimized results, for the geometrical parameters of tool structure and cutting edge when milling titanium alloy using a 20-mm diameter solid carbide end mill, is a 12-mm diameter of inner circle, four flutes, a 45 ° helix angle, and a 9 ° rake angle of the side cutting edge.     

球头铣刀高速铣削斜面的三维数值模拟研究

用球头铣刀高速铣削斜面是在三轴加工中心上加工模具时的一种走刀方式。根据球头铣刀高速铣削斜面的特点,建立了在垂直向上和向下、水平向上和向下四种走刀方式下高速铣削45°斜面,以及在垂直向下走刀方式下高速铣削30°、60°、75°斜面的三维有限元模型,以分析不同走刀方式下铣削斜面以及铣削不同角度斜面时切削力和切削温度的变化规律。模拟结果表明,在铣削45°斜面时,采用向上走刀方式较向下走刀方式的切削力幅值小、波动大,且切削温度高;采用垂直向下走刀方式铣削大角度斜面时也出现类似情况。对切削力的实测结果验证了该模型的可靠性。     

Investigation on ball end milling of P20 die steel with cutter orientation

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.     

MOLECULAR DYNAMICS SIMULATION OF NANOMETRIC CUTTING

Molecular Dynamics (MD) simulations of nanometric cutting of single-crystal copper were conducted to predict cutting forces and investigate the mechanism of chip formation at the nano-level. The MD simulations were conducted at a conventional cutting speed of 5 m/s and different depths of cut (0.724–2.172 nm), and cutting forces and shear angle were predicted. The effect of tool rake angles and depths of cut on the mechanism of chip formation was investigated. Tools with different rake angles, namely 0°, 5°, 10°, 15°, 30°, and 45°, were used. It was found that the cutting force, thrust force, and the ratio of the thrust force to cutting force decrease with increasing rake angle. However, the ratio of the thrust force to the cutting force is found to be independent of the depth of cut. In addition, the chip thickness was found to decrease with an increase in rake angle. As a consequence, the cutting ratio and the shear angle increase as the rake angle increases. The dislocation and subsurface deformation in the workpiece material were observed in the cutting region near the tool rake face. The adhesion of copper atoms to the diamond tool was clearly seen. The same approach can be used to simulate micromachining by significantly increasing the number of atoms in the MD model to represent cutting depths in the order of microns.     

Morphology evolution and micro-mechanism of chip formation during high-speed machining

In this paper, the morphology and micro-mechanism of chip formation during high-speed machining aluminum alloy 7050-T7451 is investigated based on the combination of dislocation theory and plastic deformation theory. Experiments of quick stop stoppage for turning and special method (Buda) for milling process were carried out in order to obtain shear angle in different cutting speeds. The results show that effective flow stress and temperature in front edge zone is higher and more concentrated than that in other deformation zones. The shear front-lamellar structure was observed and analyzed in the front edge zone which influences the chip formation directly. The influence of cutting speed on chip formation was analyzed by simulation and experiments. Cutting speed is an important factor affecting the morphology evolution and chip formation. When the cutting speed is below 1500 m/min, the concentration of shear stress and the shear front-lamella structure of cutting deformation are more remarkable and easier for forming continuous ribbon chips. With the cutting speed increase, the ribbon chip transforms into serrated chip when a critical cutting speed (2500 m/min) is reached. Finally, microscopic mechanism of chip formation has been revealed and critical condition of the shear front—the layer structure formation—has been determined.     

硬质合金立铣刀螺旋角对切削性能的影响

利用单因素试验法,在高温合金(GH4169)的铣削加工中,分析了硬质合金立铣刀螺旋角对切削力、已加工表面粗糙度、刀具寿命和失效形式的影响。掌握了立铣刀螺旋角对切削性能的影响,优选出在高温合金精铣加工中较为合理的刀具螺旋角。     

An analytical approach to cutting force prediction in milling of carbon fiber reinforced polymer laminates

ABSTRACT

A prediction model of cutting force for milling multidirectional laminate of carbon fiber reinforced polymer (CFRP) composites was developed in this article by using an analytical approach. In the predictive model, an equivalent uniform chip thickness was used in the case of orthogonal plane cutting, and the average specific cutting energy was taken as an empirical function of equivalent chip thickness and fiber orientation angle. The parameters in the model were determined by the experimental data. Then, the analytical model of cutting force prediction was validated by the experimental data of multidirectional CFRP laminates, which shows the good reliability of the model established. Furthermore, the cutting force component of flank contact force was correlated with the surface roughness of workpiece and the flank wear of tool in milling UD-CFRP composites. It was found that surface quality as well as flank wear has a co-incident varying trend with the flank contact force, as confirmed by the observations of the machined surfaces and tool wear at different fiber orientations. So, it can be known that low flank contact force be required to reduce surface damage and flank wear.     

Experimental investigation on chip morphologies in high-speed dry milling of titanium alloy Ti-6Al-4V

An experimental investigation of chip morphologies in high-speed dry milling of Ti-6Al-4V alloy was conducted over a variety of different cutting conditions. Observation on the multi-view characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using an optical microscope and a scanning electron microscope (SEM). The microstructural analysis indicated that the chip morphology when dry milling Ti-6Al-4V alloy in high-speed range exhibited a serrated shape for a wide range of cutting conditions. The degree of chip serration is more pronounced and evident with the increase in cutting speed, feed, and depth of cut. A significant variation in the microstructure of the chip including the thickness of the shear bands and the serrated tooth structure for different cutting speeds has been identified. The higher chip serration ratio (CSR) in high cutting speed range may facilitate appropriate machining condition for the occurrence of well-broken chips. Moreover, chip formation takes place by the mechanism of catastrophic thermoplastic shear from the observation of the shear bands using metallurgical analysis techniques. X-ray diffraction results indicated that no evidence of phase transformation was found in the shear localized chips. The variation in chip serration and metallurgical microstructure inside the shear bands and the tool/chip contact zone should be attributed to the reinforcement of coupled thermo-mechanical behavior in the cutting process with the increase in machining parameters.     

INVESTIGATION OF THE TOOL WEAR AND SURFACE FINISH IN LOW-SPEED MILLING OF STAINLESS STEEL UNDER FLOOD AND MIST LUBRICATION

This paper examines the performance of AlN/TiN coated carbide tool during milling of STAVAX® (modified AISI 420 stainless steel) at a low speed of 50 m/min under conventional flood and mist lubrication. Abrasion, chipping, fracture resulting in the formation of crater and catastrophic failure are the wear mechanisms encountered during machining under flood lubrication. The flank wear, and the likeliness of the cutting tool to fracture, chip and fail prematurely increased with an increase in the hardness of the workpiece and a reduction in the helix angle of the tool. Small quantity of mineral oil sprayed in mist form was effective in reducing the flank wear and severity of abrasion wear, and preventing the formation of crater and the occurrence of catastrophic failure. In milling 35 and 55 HRC-STAVAX® using a feed rate of 0.4 mm/tooth and a depth of cut of 0.2 mm under mist lubrication, the cutting edge of the 25° and 40° helix angle tools only suffered small-scale edge chipping and abrasive wear throughout the entire duration of testing. The influence of the ductility of the workpiece on the surface finish and the effectiveness of mist lubricant in improving the surface finish are also discussed.     

刀具几何参数对钛合金铣削力和表面完整性的影响

针对TC18钛合金铣削过程,采用正交试验研究了硬质合金刀具几何参数对铣削力和表面完整性的影响,建立了铣削力经验模型,并分析了铣削力对刀具前角、后角和螺旋角的绝对灵敏度和相对灵敏度;采用田口法分析了刀具几何参数对表面粗糙度和表面残余应力的影响。结果表明：大前角、小后角、大螺旋角的条件下铣削力较小,铣削力对刀具螺旋角的变化最敏感,对后角次之,对前角最不敏感;铣削表面均为残余压应力,刀具螺旋角对表面粗糙度的影响显著,刀具后角对表面残余应力的影响显著。     

Theoretical modelling of cutting forces in helical end milling with cutter runout

A theoretical cutting force model for helical end milling with cutter runout is developed using a predictive machining theory, which predicts cutting forces from the input data of workpiece material properties, tool geometry and cutting conditions. In the model, a helical end milling cutter is discretized into a number of slices along the cutter axis to account for the helix angle effect. The cutting action for a tooth segment in the first slice is modelled as oblique cutting with end cutting edge effect and tool nose radius effect, whereas the cutting actions of other slices are modelled as oblique cutting without end cutting edge effect and tool nose radius effect. The influence of cutter runout on chip load is considered based on the true tooth trajectories. The total cutting force is the sum of the forces at all the cutting slices of the cutter. The model is verified with experimental milling tests.     

磨粒转角对磨削的影响分析

磨粒形状比较复杂,运用DEFORM-3D软件进行棱锥状磨粒的单颗磨粒磨削仿真,分析了磨粒转角对磨屑形状、磨削温度、磨削力的影响,旋转角度分别为0°、10°、20°、30°、40°、45°,通过对比分析得出结论:转动角度为45°时,磨削中最高温度较低,可以降低磨削热;转动角度为0°时,磨削的切向力与法向力较小。不同转动角度下,磨屑的形态与温度的分布不同。     

高速铣削淬硬钢时的切屑形态试验研究

使用Ti Al N涂层整体圆柱立铣刀,以(151~942)m/min的铣削速度,对淬硬的45钢和3Cr2Mo钢进行了高速铣削试验,研究了各种切削速度下的宏观及微观切屑形态。发现在高的铣削速度下形成了带有绝热剪切带的锯齿形切屑,并分析了切屑形态的演化过程。工件材料的硬度、强度、导热性能及切削速度对切屑形态和绝热剪切带的形成有着重要的影响。工件材料越硬、强度越高、导热系数越低,切削速度越大,越容易形成带有绝热剪切带的锯齿形切屑,而且,随着切削速度的增加,切屑的形态由卷曲向平坦发展。     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

Cutting force prediction in ball-end milling with inclined feed by means of geometrical analysis

A geometrical model for the analysis of cutting forces in ball-end milling has been presented in a previous work (Tsai CL, Liao YS, J Mater Process Technol 205:24–33, 10), which can be used to analyze cutting forces in vertical or horizontal feed. In this paper, the three-dimensional geometrical analysis is depicted with different interacting relations among cutting edge, undeformed chip and shear zone along nonhorizontal cutting direction, and a general geometrical model of inclined feed in ball-end milling is presented. According to the geometrical analysis, the cutting directions of horizontal, vertical, inclined downward, and inclined upward feed are defined with a feed angle. A general force model is derived, and the three-dimensional cutting forces are predicted. Experiments are conducted to verify the geometric force model. The influences of different feed angle and helix angle on cutting forces in inclined downward and inclined upward feed are discussed and simulated.     

Prediction of cutting forces and machining error in ball end milling of curved surfaces -I theoretical analysis

This paper presents a theoretical model by which cutting forces and machining error in ball end milling of curved surfaces can be predicted. The actual trochoidal paths of the cutting edges are considered in the evaluation of the chip geometry. The cutting forces are evaluated based on the theory of oblique cutting. The machining errors resulting from force induced tool deflections are calculated at various parts of the machined surface. The influences of various cutting conditions, cutting styles and cutting modes on cutting forces and machining error are investigated. The results of this study show that in contouring, the cutting force component which influences the machining error decreases with increase in milling position angle; while in ramping, the two force components which influence machining error are hardly affected by the milling position angle. It is further seen that in contouring, down cross-feed yields higher accuracy than up cross-feed, while in ramping, right cross-feed yields higher accuracy than left cross-feed. The machining error generally decreases with increase in milling position angle.