Materials Science Forum Vols. 836-837

Abstract: Laser assisted machining (LAM) is one important solution for machining difficult-to-machine materials. The heat transfer model of quasi steady state in laser assisted micro machining is built, and the simulation software for temperature distribution measurement is developed based on MATLAB. The simulated temperature distribution of the ZrO₂ ceramic heated by pulse laser shows a good agreement of tendency with the corresponding experimental results through the infrared temperature measurement method, while the simulated temperature is consistently overestimated. This difference maybe results from the neglect of the heat loss caused by the heat radiation and the heat convection in the model. The proposed model in this paper could provide reference for the selection of optimal process parameters and improve the machining quality, which are closely related to the temperature distribution.

Abstract: Machining deformation has been a bottle-neck issue in aeronautical manufacturing field. Due to the large amount of material removal and other issues, machining deformation is predicted more difficultly during the process of 2026-T3511 aluminum alloy rim. Hence a simple full-size model of margin monolithic was built to study the deformation under the influence of residual stress releasing. The process of the structural parts was simulated and the deformation law of overall structure considering residual stress releasing only was revealed. Through the comparative study of different machining processing, control strategy reducing the final part machining deformation and optimum machining allowance range were proposed.

Abstract: Finite element simulation of high speed machining of Ti6Al4V alloy was carried out based on the software of Abaqus. The Johnson-Cook constitutive model was chosen for the material of Ti6Al4V, the parameters of the model were obtained through the SHPB (Split Hopkinson Pressure Bar) experiment. The similarity of the chips obtained from the simulation and that obtained from the experiment indicated that the parameters of the Johnson-Cook constitutive model for Ti6Al4V alloy were reliable. Different cutting parameters and different tool geometric parameters were used in the simulations to find out their effects to the simulation results. Also a comparison was made between the results got form the simulations results and the experimental results, a good agreement between them indicated that the finite element simulation of high speed machining of Ti6Al4V is reliable, so it can be concluded that the finite element simulations of high speed machining can be widely used in practice to study the more about the machining process and reduce the experimental expenses.

Abstract: This paper briefly describes the principle of the ultrasonic single point incremental forming of the sheet metal. In which we established the finite element model and finished the finite simulation with ABAQUS. According to the simulation result, we analyzed the influence law of vibration frequency of the axis on the distribution of the stress and strain of the sheet metal, the thickness, and the axial force in the process of ultrasonic single point incremental forming of the sheet metal. The result shows that the influence on the stress and thickness of the sheet metal is minimal, and the influence on the strain follows the law of cosines in which the strain is minimum when the vibration frequency is equal to 15kHZ.The influence on the axial force is that when the frequency is f=0kHz～40kHz the axial force decreases with the increase of the frequency. However, the axial force increased dramatically with the increase of the frequency when the frequency is above 40kHz.

Abstract: A systematic and parametric study of the effect of grain size and volume fraction of secondary phase on crack propagation behavior of Al₂O₃ based ceramic tool materials was carried out. Two-dimensional centroid V toughness oronoi tessellations were generated with random grain orientations. Cohesive Zone Method (CZM) was utilized to simulate crack propagation behavior. Zero-thickness cohesive elements were embedded on grain boundaries and inside grains. Crack initiation and propagation in ceramic tool materials microstructure were simulated without predefined crack. Simulation results revealed that crack initiated at the maximum stress position and propagated along the direction perpendicular to external load. Decreasing the grain size or increasing the volume fraction of secondary phase can improve the fracture stress of Al₂O₃ ceramic tool materials.

Abstract: When milling the complex surface with the ball-end milling cutter, the cutting thickness always changes in ball-end milling process. At present, many milling models are actually simplified with unchanged cutting thickness, which ignores the ball-end milling cutting with complex tool-work piece relationship. According to the characteristics of the ball-end milling, orthogonal variable thickness cutting model is established based on the study of three-dimensional contact relationship of tool-work piece. The simulation of the stress field and the temperature field in hardened steel Cr12MoV orthogonal variable thickness cutting process is conducted, and comparative analysis of stress and temperature field distribution of high-speed milling and conventional milling is made. The cutting model of orthogonal variable thickness cutting can reflect the characteristics of surface milling accurately, which can be further used in the study of changing characteristics of physical fields and the optimization of cutting and tool parameters to improve the machining efficiency and quality.

Abstract: Low Pressure Heater is one of important equipment in nuclear power industry; within the manufacturing of plate of heater, the deep-hole drill technology is a key point, and BTA (Boring and Trepanning Association) is applied. It is difficult to keep the high-quality hole of BTA due to the poor cutting condition, chip breaking, heat dissipation, and low rigid of the machining system. Therefore, this proposes a high precision to drilling tools, especially the design of the blade is of great importance. Based on the analysis of drill structure, this dissertation uses the method of parametric design which is suitable for NX. Combining the Visual Studio and Microsoft Access platform develops the fast digital modeling software design. The parameterization design can not only realize the rapid modeling of BTA deep-hole drill, but also shorten the design cycle and improve the efficiency of the drill which benefited from the convenient design of the blade, which has a significantly practical application value.

Abstract: 300M ultrahigh strength steel has good mechanical properties. It has been widely used in the force bearing components of aircraft. In this paper, By using Gleeble1-500D thermal simulator, we studied the change regularity of stress-strain curve of 300M steel using hot compression deformation when temperature is from 800°C to1100°C, strain rate is from 0.001 S^-1to 1 S^-1 and the strain is 0.7.The experimental results showed that when the strain rate is constant, the flow stress and the peak stress decrease with the increase of deformation temperature. When the deformation temperature is constant, the flow stress and peak stress increase with the increase of strain rate. From the test, we got the true stress-strain curve, calculated the thermal deformation constants such as the deformation activation energy of 300M ultrahigh strength steel. Eventually, we built the thermal deformation constitutive model in hyperbolic sine form of 300M steel.

Abstract: The dislocation theory is applied to study plastic deformation in high-speed cutting to show the formation characteristics of the micro scale deformation zone in high-speed cutting. Through the quick stoppage experiment of aluminum alloy 7050-T7451 in high-speed cutting and the further research of inclined cutting chip formation mechanism and deformation of shear zone in plastic mechanics and dislocation theory respect .The stress, the strain state and microstructure near the front edge of the rake face edge is analyzed. Effective flow stress, effective strain distribution and variation in shear deformation zone is simulated. According to the experimental and simulation results and from the microscopic respect, the traditional cutting deformation zone is reclassified, the deformation zone of the front edge and dislocations compression zone is increased to achieve a more accurate description of the deformation zone and provide a theoretical basis for the study of high-speed cutting deformation mechanism.

Abstract: This paper deals with singular configurations of a 5-axis machine tool in high speed milling which may lead to the appearance of large incoherent movements of rotary axes near singularity points. These movements generate slowdowns of the actual feedrate during the execution of the tool path, which affect quality and productivity. Thus, this paper proposes a method to detect these behaviors during machining simulation and correct the tool path. Unlike the literature methods, this correction consists in modifying the tool axis orientation by going through the singularity point while respecting maximum velocity, acceleration and jerk of the rotary axis. For that purpose, the initial articular positions of the rotary axis near the singularity point are fitted with B-spline curves, modified and finally discretized for linear interpolation. Experimental investigations on a test part are carried out to show the efficiency of the method.