FLOW STRESS MODELING FOR AERONAUTICAL ALUMINUM ALLOY 7050-T7451 IN HIGH-SPEED CUTTING

The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.

CUTTING TEMPERATURE MEASUREMENT IN HIGH-SPEED END MILLING

A computer aided measurement system is used to measure the cutting temperature directly in high-speed machining by natural thermocouples and standard thermocouples. In this system the tool/workpiece interface temperature is measured by the tool/workpiece natural thermocouple, while the temperature distribution on the workpiece surface and that of interior are measured by some standard thermocouples prearranged at proper positions. The system can be used to measure cutting temperature in the machining with the rotary cutting tools, such as vertical drill and end milling cutter. It is practically used for the research on high-speed milling with hardened steel.

CUTTING FORCES FOR HIGH-SPEED DRILLING OF COMPOSITES

The thrust and the torque of various carbide drills are studied for the high-speed drilling of fiber reinforced epoxy composites. The orthogonal experiment is carried out with different feed speeds at high rotation speed. Experimental results show that the spindle rotation speed is the most influential factor. The thrust andthe torque decrease under the condition of high rotation rate. With the decrease of the feed speed, the thrust and the torque decrease. But the effect of the feed speed is less than that of the spindle rotation rate. Moreover, the effect of drill materials on the thrust and the torque is more notable than that of the drill geometries and the feed speed. The thrust is greatly affected by the feed speed while the torque is obviously affected by drill geometries.

Crosswind stability of high-speed trains in special cuts

Analysis of the aerodynamic performance of high-speed trains in special cuts would provide references for the critical overturning velocity and complement the operation safety management under strong winds.This work was conducted to investigate the flow structure around trains under different cut depths,slope angles using computational fluid dynamics(CFD).The high-speed train was considered with bogies and inter-carriage gaps.And the accuracy of the numerical method was validated by combining with the experimental data of wind tunnel tests.Then,the variations of aerodynamic forces and surface pressure distribution of the train were mainly analyzed.The results show that the surroundings of cuts along the railway line have a great effect on the crosswind stability of trains.With the slope angle and depth of the cut increasing,the coefficients of aerodynamic forces tend to reduce.An angle of 75°is chosen as the optimum one for the follow-up research.Under different depth conditions,the reasonable cut depth for high-speed trains to run safely is 3 m lower than that of the conventional cut whose slope ratio is 1:1.5.Furthermore,the windward slope angle is more important than the leeward one for the train aerodynamic performance.Due to the shield of appropriate cuts,the train body is in a minor positive pressure environment.Thus,designing a suitable cut can contribute to improving the operation safety of high-speed trains.

基于HSC的数控铣削系统装备及编程的研究

分析高速切削(HSC)的数控铣削系统装备及编程要点。提出高速数控铣削机床结构,刀具系统及基于CAM的高速数控铣削编程的策略,实践证明,效果良好。

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties.Specifically,thin-walled titanium(Ti)cylinders have received increasing attention for their applications as rocket engine casings,aircraft landing gear,and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio.However,the conventional cutting(CC)process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity,high strength,and low stiffness.Instead,high-speed ultrasonic vibration cutting(HUVC)assisted processing has recently proved highly effective for Ti-alloy machining.In this study,HUVC technology is employed to perform external turning of a thinwalled Ti cylinder,which represents a new application of HUVC.First,the kinematics,tool path,and dynamic cutting thickness of HUVC are evaluated.Second,the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model.HUVC can increase the critical cutting thickness and effectively reduce the average cutting force,thus reducing the energy intake of the system.Finally,comparison experiments are conducted between HUVC and CC processes.The results indicate that the diameter error rate is 10%or less for HUVC and 51%for the CC method due to a 40%reduction in the cutting force.In addition,higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.

Research on cutting characteristics of fiber bundle with high-speed photography

Cutting is an essential and complicated process in many fields.Efficient and low-consumption cutting operations are of great significance for environmental protection and energy conservation.The development of high performance cutting parts relies on a deep understanding of the cutting process and cutting mechanism.In this research,a new type of cutting test bench with high-speed photography was developed,and the cutting tests were conducted on the jute fiber bundle from quasi-static cutting at 10 mm/s to dynamic cutting in the speed range of 0.6-2.4 m/s.The cutting process was captured by a high-speed camera.Analysis shows that compression exists before quasi-static cutting,and the compression force curve with respect to the compression ratio follows an exponential function.The cutting speed has a significant effect on cutting energy.The cutting energy consumption is not a monotonous function of cutting speed owing to the combined effect of elastic deformation and friction of fibers.The cutting energy increases with increasing cutting speed in the range of 0.6-1.2 m/s due to the increase of the friction within fibers and the friction between the blade and fibers.The cutting energy decreases with increasing cutting speed in the range of 1.2-1.8 m/s,and tends to be a fixed value when the cutting speed exceeds 1.8 m/s due to the stabilized elastic deformation and friction coefficient.From the perspective of energy saving,it is meaningless to increase the blade speed excessively when cutting fiber bundles.

Modeling high-speed cutting of SiC_(p)/Al composites using a semi-phenomenologically based damage model

In this paper,we attempts to investigate cutting mechanisms in high-speed cutting of Al6061/Si C_(p)/15p composites using a semi-phenomenologically based damage model in the equivalent homogeneous material(EHM)framework.By combining macroscale EHM modeling and underlying microscale physical mechanisms,a feasible semi-phenomenological plastic model is proposed for prediction of cutting forces and chip morphology during high-speed turning Al6061/Si C_(p)/15p composites.This model incorporates the modified Weibull weakest-link effect to represent the strain-based damage evolution in large deformations.This proposed semi-phenomenological constitutive model is implemented by compiling material subroutines into cutting finite element(FE)codes.The effects of the critical shear stresses on chip formation that depend on the toolchip frictional coefficient are accounted for in the cutting FE model.The chip formation mechanism affecting material removal behaviors during high-speed turning is further investigated.The capabilities of the proposed constitutive model are evaluated by comparing cutting forces and chip morphologies between experiments and simulations at different cutting speeds associated with strain rates.The EHM-based and microstructure-based models are further compared in both computational efficiency and accuracy.The simulation results show that the developed semiphenomenological constitutive formalism and cutting model are promising and efficient tools for further investigation of dynamic mechanical and cutting behaviors of particle-reinforced composites with different volume fraction and particle size.

Chip morphology and cutting temperature of ADC12 aluminum alloy during high-speed milling

The ADC12 aluminum alloy is prone to severe tool wear and high cutting heat during high-speed milling because of its high hardness.This study analyzes the highspeed milling process from the perspective of different chip morphologies.The influence of cutting temperature on chip morphology was expounded.A two-dimensional orthogonal cutting model was established for finite element analysis(FEA)of high-speed milling of ADC12 aluminum alloy.A theoretical analysis model of cutting force and cutting temperature was proposed based on metal cutting theory.The variations in chip shape,cutting force,and cutting temperature with cutting speed increasing were analyzed via FEA.The results show that,with the increase in cutting speed,the chip morphology changes from continuous to serrated,and then back to continuous.The serrated chip is weakened and the cutting temperature is lowered when the speed is lower than 600 m·min^(-1)or higher than 1800 m·min^(-1).This study provides a reference for reducing cutting temperature,controlling chip morphology and improving cutting tool life.

Solution and Analysis of Chatter Stability for End Milling in the Time-domain

In this paper, the instantaneous undeformed chip thickness is modeled to include the dynamic modulation caused by the tool vibration while the dynamic regenerative effects are taken into account. The numerical method is used to solve the differential equations goveming the dynamics of the milling system. Several chatter detection criteria are applied synthetically to the simulated signals and the stability diagram is obtained in time-domain. The simulation results in time-domain show a good agreement with the analytical prediction, which is validated by the cutting experiments. By simulating the chatter stability lobes in the time-domain and analyzing the influences of different spindle speeds on the vibration amplitudes of the tool under a Fixed chip-load condition, conclusions could be drawn as follows： In rough milling, higher machining efficiency can be achieved by selecting a spindle speed corresponding to the axial depth of cut in accordance with the simulated chatter stability lobes, and in Fmish milling, lower surface roughness can be achieved by selecting a spindle speed well beyond the resonant frequency of machining system.

超高速切削技术及其新进展

阐述了超高速切削的概念、特点和发展这项技术的重要性 ,分析了超高速切削的技术体系、技术现状和发展趋势 。

高速切削温度场的三维有限元建模与动态仿真

根据温度场控制方程及其边界条件,建立高速切削的三维有限元分析模型,将切削过程的温度分布和变化情况以及切削速度、进给量和切屑厚度等对切削温度的影响进行仿真分析,与相同切削条件下的二维仿真结果和实际测试结果进行对比,可以得出结论:三维建模仿真得到的高速切削温度变化趋势与相关文献结果基本一致,但三维仿真获得的温度值比二维仿真要高些,并且三维仿真的温度值更接近于实际测量值。

CMIT 2001切削技术发展及刀具展品述评

对第七届中国国际机床展览会 (CMIT2 0 0 1)上展出的先进切削技术和刀具产品进行了综合评述 ,分析了世界工具工业的最新发展趋势及特点 ,对我国工具行业的发展方向及策略提出了建议。

高速切削热分配的有限元模拟

基于有限元法建立了典型的正交切削模型,结合切削热分配的解析法,研究了高速切削中切削热在切屑、工件和刀具部分的量化分配规律,并通过实验验证了模拟数据准确性,为高速切削热的相关研究提供了一种新的方法。

基于高速切削刀具与刀具系统的研究

根据高速切削高效率、高质量的加工目的,分析高速切削的特点,提出高速切削加工对刀具系统的要求,并提出刀具的选择要点,以及提高工艺系统刚性与安全性的要求,以提高切削效率和加工质量。

高速切削加工技术在模具制造中的应用

介绍了作为"第三代制模技术"的高速切削加工技术在模具制造中的应用优势,以及高速切削加工模具的关键技术(包括机床、刀具和加工策略等)。以便携式电脑电池盖注射模主型腔的制造为例,给出了工艺方案和高速切削加工参数。

高速加工刀具工艺参数的优化

以几种典型模具材料的高速加工为例 。

高速切削自滚切刀具

介绍了自滚切刀具的基本原理与基本概念 ,说明了其适宜于高速切削的原因 ,并对自滚切刀具的优、缺点进行了评价。

VARIABLE MODEL FOR BUILDING CASE BASE AND ITS APPLICATION

The case variable model is put forward by analyzing the system model and the IDEFO model. The component variables of the machining system are classified into four types, I. E uncontrolled variables, process variables, controlled variables and output variables. The process of building the case base is given. The high-speedcutting data base system is developed based on the presented variable model.

模具高速切削及其合理运用

通过将高速切削与传统加工进行比较,阐述了模具高速切削的优越性,分析了模具的高速切削对机床的要求,介绍了应用高速切削加工模具应注意的几个问题。