| The thin-walled conical cabin sections has become an urgent need for lightweight components in the development of high-end aerospace equipment.As the lightest metal structural material currently used,magnesium alloy has become the best lightweight material.In this paper,the thin-walled conical cabin with front and rear frames is taken as the research object.In view of the problems of low utilization rate of materials in the traditional preparation process,and the performance of small strain is difficult to meet the service conditions,a thinwalled shell shrink forming process is proposed to realize the conical shape.The shape structured and the integral forming of the end frame parts to avoid a lot of cutting and improve the bearing capacity.According to the strengthening and toughening requirements of the service environment for the components,the process design of the whole process from the initial blank modification to the overall forming of the components is carried out.The research can not only enrich the theory of deformation strengthening and toughening of magnesium alloy materials,but also have certain scientific value.It can also provide guidance and theoretical support for the actual production of thin-walled special-shaped cabins,which has good engineering application valued.The main research conclusions are as follows :1.The wall thickness variation formula is determined by analyzing the metal flow characteristics during the shrinking process,and the target extrusion part size of the blankmaking die is determined.After analyzing the structural characteristics of the traditional reverse extrusion die and the hollow blank reverse extrusion die and the stress and strain state during the metal deformation process,the extrusion ratio of the hollow blank extrusion process and the extrusion area of the punch and the blank are changed to make the extrusion process.The load force in the pressing process is greatly reduced.In order to ensure that the bottom of the cup-shaped piece obtained by reverse extrusion is fully filled,a hollow punch with a flowpromoting angle is proposed.The angle of the flow promoting angle is an important factor affecting the flow state of the metal at the bottom of the cup.In order to increase the average value of equivalent strain,reduce the equivalent strain S.D,and reduce the peak load,the optimal mold structure of a mandrel diameter of 460 mm and a flow-promoting angle of 80°was obtained.The process parameters such as punch feed speed and friction coefficient were also optimized,and finally the optimal process plan of according to punch feeds speed of1mm/s and friction coefficient of 0.3 was obtained.According to the above data,the mold was designed and the forming experiment was carried out,and finally the blank required for the neck mold was prepared.2.Based on the principal stress method,the maximum shrinking force of the necking die whose busbar is an arc curve is obtained.The results show that the shrinkage force is proportional to the radius of the arc busbar and inversely proportional to the necking coefficient.The simulation found that compared with the linear dies,the arc busbar dies can greatly reduce the forming force.And the influence of the shrinkage coefficient on the forming force is greater than that of the busbar radius.The shrinkage force formula is checked by simulation,and the error is within the acceptable range.Using the results of theoretical calculation and actual simulation,the optimal die structure parameters are obtained.At the same time,structural optimizations such as adding annular grooves on the inner wall of the die to improve the friction environment and reduce friction,and adding guide sleeves to maintain the temperature field difference in the necking process are proposed.According to the above results,a set of neck die was designed,and the physical trial production experiment was successfully completed.3.Sampling and characterizing each part of the final extruded part.The wall part of the final formed part is unevenly distributed among the height direction of the grain structure.The closer to the structure of the upper and lower ends,the larger the grain size.The structure of the end frame is the whole The smallest grain size.And the grain size is not only related to the accumulated strain,but also to the specific distribution of the strain amount of the two-pass deformation process.Regarding the issue of texture evolution,the grain structure near the small end may form a new texture direction due to the excessive deformation in the neck stage,but this will not happen to the structure near the big end,and the small end structure is due to During the shrinking process,a certain deformation rate is maintained,and the recrystallized structure formed in the first two passes can be retained.4.The mechanical properties of the three states were measured.Due to the occurrence of recrystallization,the anisotropy problem was greatly improved on the extruded state compared with the initial state.At the same time,the elongation at break also increased,which was caused by grain refinement and texture weakening.After aging,the tensile strength and yield strength in the circumferential and axial directions reached 356.13 MPa,350.20 MPa and248.11 MPa and 240.16 MPa,respectively.The increase in strength was due to the aging strengthening effect caused by the precipitation of the strengthening phase during the aging process. |
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