| Monolithic components are being widely used in the field of aviation due to their lower height, higher structural efficiency and higher working reliability compared with traditional riveted parts. However, owing to the large dimension , complicated structure, and long process(ing) cycle, monolithic components deformation during machining is almost inevitable, such as bending, distortion or their combination. There are many factors that can cause the doformation of monolithic component such as material property and structure of monolithic components, initial stress, cutting force, cutting heat and clamping forces. Since theses reasons, there are no effect techniques that can completely eliminate the effects causing deformation up to day, so it is needed to correct the deformation.The flow stress equation of A17050-T7451 that can suit for machining condition was modeled based on reverse method through orthogonal cutting method. By comparison the cutting forces and cutting temperature between experiment and FEM simulation, the model was validated. By using this method, the flow stress model can reflect the real cutting conditions, such as larger strain, strain rate and temperature raising rate that the compression test and Split Hopkinson Pressure Bar Test (SHPB) can only reflect at a relatively low scale. By using this method, the expense of experiments can be decreased. The flow stress equation derived from orthoigonal cutting experiments was used in two teeth milling FEM simulation analysis to predict the cutting forces, temperature distribution along tool-chip interface that varies with tool rotation. It shows that milling force increases sharply at the beginning of the milling process, and then decreases slowly as the relative static milling process keeps up and at last goes down fast as the tooth leave the cutting area. The temperature on the chip, workpiece and milling cutter were predicated. It shows that the temperatures on the chip are much higher than that on the workpiece. The reason of this phenomenon is mainly because that the majority of cutting heat is carried off by the chip during high speed machining. The chip formation process was simulated. The simulated chip morphology is similar with that obtained from experiment by using the same parameters as FEM. The cutting forces of FEM model were well agreed with the experimental results, the largest error is no more than 15%, so the FEM model is verified. The predicted results were used as the initial conditions for the multi-stress coupling model to predict the deformation of multi-frame thin-walled monolithic component. By using this method, the effects of initial residual stress, mechanical stress, heat stress and clamping stress which is substituted with boundary conditions. Transient milling forces and heat getting from the 3D FEM milling process were added on the multi-stress coupled model as dynamic loads. The moving track of dynamic loads is the same as the real tool-path in experiment for milling the workpiece. The monolithic components deformation and stress, strain distribution were examined during cutting process. The releasing process of fixture was simulated by using 3-2-1 constrain boundary conditions so that the final deformation and distribution of stress and strain of onolithic components were achieved. To validate the multi-stress coupled model, the experimental test of frame monolithic components was designed. The predicted deformation of monolithic components by FEM was well agreed with the experimental results.The 2D thin-walled structure rolling FEM model was built according to the physical and mathematical analysis. The material flow, stress and strain distribution were investigated under different rolling force, wall thickness. And the stress superposition between rolling stress and initial stress was anslysised. It is shown by analysis that the superposition process between rolling mechanical stress and initial stress can reduce different plastic deformation and the comprehensive residual stress. When the rolling force is low, rolling process can only produce larger residual stress in subsurface, and the rolling force scale is low level. As the rolling force increasing, the rolling stress in deep material gradually surppass that in subsurface and can cause larger stresss variation in deep material, this rolling force scale is intermedia level. When rolling stress in subsurface surppass the stress in deep material, the rolling force is high level. The intermedia level rolling force can affect the stress both in subsurface and inner deep material without reducing too much plastic deformation. The largest residual stress and its exist position in depth will not change much under the same rolling force although the thickness of wall may be different, but the peak value of largest rolling stress and the average rolling stress in inner deep material will decrease. Based on this stress superposition relation, the rolling deformation of T-shaped workpiece was analyzed. And the straightening reference spectrum for bending deformation of T-shaped workpiece was raised and verified through FEM simulation.Since the stress distribution in the blank after pre-stretching process could be recognized to be in plane 2D stress condition that the stress varies along the depth condition but no shear stress between different depths, the deformation caused by initial stress redistribution during the material removal was analyzed by analytical and FEM methods. It is shown that the inistial stress state has the definitive effect: when the initial stress in in and near surface is compressive, in intermedia is tensile, the deformation of workpiece after material removal from one side will appear bending deformation with cockup at two ends and cockdown at middle; when the intial stress in and near the surface is tensile, the deformation trend is just opposite. The locally sidewall rolling straightening FEM model of two frame monolithic component for bending deformation was built, the relationship between rolling stress and initial stress, and the deformation under different rolling parameters were analyzed. The the straightening reference spectrum of two frame monolithic component was derived and used in FEM simulation for bending deformation. And this method is verified by experiment through three frame monolithic component. There may be the errors in real applications, if the deformation can not be straightened to satisfy the need, additional rolling process could be used by enquirying the reference spectrum until it satisfy the needs of design and assembly.The rolling straighten machinery is designed to be used in experiment. In order to investigate the surface integrity variation after rolling process, the thin wall part rolling experiments were designed to take the surface roughness, surface micro-hardness and wear-resistance into account. It is shown that the surface roughness decreases as the rolling force increases, the micro-hardness increases as the rolling force increases, but the rate of increasement for the rolled surface produced by high cutting speed is small. The micro-hardness after rolling could be seen as the combinination between the rolling process and the cutting process, as the rolling force increasing, the micro-hardness produced by rolling will surpass the cutting process. It could be seen through the wear resistance property experiment that, as the rolling force increases, the surface shows better performance of wear-resisting and lower friction coefficient. After rolling, although the friction coefficient is different for the surface produced by different speed, but the wear resistance of surface produced by high speed is close, this means the surface roughness has more effects on friction coefficient and the micro-hardness and its depth has more effects on wear resistance. The residual stress distribution of thin walled part was measured using X-ray diffraction test. The surface stress distribution before and after rolling was measured, and the stress distribution along the depth was also measured using electrical polishing method. According to the measurement results, it shows that, by using rolling process, the desired residual distribution could be combined in thin wall surface and beneath, if the rolling force is at relative low level, rolling process can reduce larger residual stress peak and distribution depth, this trend is consistent with the FEM simulation prediction. |
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