Modeling And Experimental Investigation On Workpiece Temperature Field For Turn-milling Of High Strength Steel

As a national strategic industry, aviation industry can drive the development of national economy and strengthen the national defense construction. High requirements for high-quality aeronautical components are growing due to their special service occasions. Therefore, high surface quality is regarded as a criterion in aviation industry. A large proportion of aeronautical materials are difficult-to-cut materials. The cutting force and workpiece temperature during the cutting process, especially the finish machining stage, have direct impacts on the surface quality of workpiece. The processing performance of difficult-to-cut materials is poor. In addition, cutting force and thermal loads seriously influence the surface quality. In light of this, accurate predictions of cutting force and workpiece temperature have a profound significance for guaranteeing the machining quality and service performance of key aviation parts.The airplane landing gear is one of key aeronautical components. Its material,300M steel, has the typical characteristics of the difficult-to-cut materials in aviation industry, such as high strength, high hardness, and poor thermal conductivity, which can lead to rapid tool wear. End milling and orthogonal turn-milling are two representative processing techniques in landing gear manufacturing. It is necessary to study cutting force and heat conduction of these two operations deeply. However, the academic achievements in the modeling of complicated three-dimension cutting temperature field are limited. The study about the finite element simulation and surface integrity of300M steel is also fare. Therefore, the relevant fundamental researches of manufacturing300M steel for the two processing techniques are carried out in the thesis.The cutting force models of end milling and orthogonal turn-milling considering the flank rubbing effect have been developed. After the cutting zone was discretized, the geometry, kinematics and mechanics have been analyzed based on the mechanistic cutting force model. The whole cutting forces and flank frictional forces have been solved. Based on analysis of elemental forces on normal plane, an approach to calculate the shear force from the three orthogonal cutting force components obtained by mechanistic cutting force model has been proposed, satisfying the requirements of the investigation on temperatures of shear force and shear friction.Based on the conception of cutting heat source discretization and time discretization, the instantaneous elemental heat source is regarded as the instantaneous rectangle heat source. In this way, workpiece temperature model considering shear plane heat source and flank wear-land heat source has been proposed. The heat flux and heat proportion on shear plane and flank wear-land have been analyzed. Direct and reverse integration algorithms have been presented, which can describe the workpiece temperature field history and reveal the periodic variation of temperature field with the movement of cutting tool respectively. Through constructing a periodic temperature rise function series, an available solution has been provided for reverse integration algorithm. The convergence proof of the proposed algorithm has been deduced. The thermal model not only can achieve accurate workpiece temperature simulations similar with those obtained by the finite element software but also shorten the computing time dramatically, serving as an alternative method for the cutting temperature field studies.In order to obtain the important input parameters in the forecasting model, the geometry of cutter has been measured by reverse engineering. Additionally, thermal parameters of cutter and workpiece have been detected by material thermal analysis. Under the different conditions of spindle speed, feed per tooth, workpiece radius, rotation speed ratio and tool flank wear width, the end milling and orthogonal turn-milling experiments have been carried out. In the experiments, the cutting forces and workpiece temperatures have been measured to verify the accuracy of mechanical and thermal models. In the meantime, the significant test about impacts of different cutting conditions on cutting force and temperature in orthogonal turn-milling has been accomplished by variance analysis and range analysis.The finite element model of300M steel for end milling has been established. Material constitutive equation has been determined by a series of material mechanics properties measurement experiments. The finite element model has been validated by the comparison of the finite element simulation results and experimental measuring cutting forces and workpiece temperatures. The influences of different cutting velocities on workpiece temperatures have been observed. The data without experimental detecting and the data hard to be measured have been obtained by the finite element technology.Utilizing the prediction results and experimental measurements, the influences of spindle speed, feed per tooth and tool wear on workpiece surface roughness, surface residual stress and hardening depth have been analyzed. Microhardness distribution regularities of workpiece have also been discussed.The model proposed in this thesis can be also extended to studies of other difficult-to-machine materials and predictions about the cutting forces and temperatures of other complicate machining operations. Moreover, some research achievements can provide references for machining parameters optimization and products quality control during the production.