Study On Local Flow-controlled And Mold Temperaturecontrolled Die Forging Technology For Shape/property Controlled Of Large Aerospace Components

The production technology of large-scale aeronautical components is one of the important indicators of the level of science and technology in a country.With the vigorous development of the international aviation field,the demand and the types for aeronautical components are increasing,and the performance requirements are also higher.Landing gear is one of the important parts on the aircraft.It is a typical large-scale aeronautical component.The horizontal projection area of this forging is very large,the longitudinal bulge is high and narrow,the longitudinal section area changes drastically,and there are many high requirements on shapes and performances.At present,the integral die forging is the core technology for the manufacture of such forgings.However,at present stage,when such products are formed by integral die forging technology,defects such as insufficient filling and coarse grain size are easily caused.Therefore,how to obtain the forgings with satisfactory shape and performance on the basis of improving material utilization rate and reducing forming load is an urgent research topic.Based on this,this paper proposed the local flow-controlled method and the mold temperature-controlled method to control the shape and performance of the final forging,and combined the BP neural network and genetic algorithm to optimize the parameters.It provided a guiding role for realizing the forming of the B787 front landing gear outer tube forging successfully.Firstly,the structural characteristics of the B787 front landing gear outer tube forgings were analyzed.The shape of the pre-forging and the billet were designed according to its shape and structure.The die forging technology of the landing gear outer tube forging was designed: cutting ?heating ?upsetting ?drawing out ? heating ? flattening ? heating ? pre-forging ? heating ? final forging.The final forging flash size was designed according to the conventional flash design method.Then the finite element simulation software DEFORM-3D was used to simulate the whole process of the die forging of the B787 landing gear outer tube forging.The simulation results showed that the bulge of the final forging process was not complete full,it needs to be improved.Secondly,in order to solve the not being fully filled problem of the head of the B787 front landing gear outer tube forging,the method of adjusting the local flash thickness to control the metal flow was proposed.The model of solving the flash size was established and the local flash thickness of the final forging was obtained based on the slab method and the stress balance condition of the split surface.Then,according to the original technology project of the landing gear outer tube forging,the finite element numerical simulation software DEFORM-3D was used to simulate the whole hot die forging process of the forging,and the metal flow and strain distribution of the whole forming process as well as grain size distribution of the final forging are analyzed.The results showed that the local flowcontrolled method obtains the shape-qualified,faultless final forging.At the same time,the local flow-controlled experiment was carried out according to the technology.The forging obtained was completely filled,the flash was uniform,and there were no forming defects.The simulation results and the experiment verified the correctness of the local flow-controlled method simultaneously.However,both the simulation and the experiment found the grain size of some area of the final forging is coarse.Then,in order to solve the problem of coarse grain size appearing in the final forging forming process,a project for adjusting the mold temperature to improve the grain size was proposed.On the basis of ensuring the local-controlled flow,16 sets of orthogonal experiments were designed by selecting the upper mold temperature,the lower mold temperature,the mold moving speed,the flash thickness of the bulge as elements and the maximum forming load of the final forging and the maximum grain size as objective functions to build the BP neural network model,then genetic algorithm was combined with to conduct parameter optimization to obtain the optimal combination of parameters,and DEFORM-3D finite element simulation software was used to verify it.The simulation results showed that the forging with qualified shape and grain size was obtained by controlling the mold temperature.Finally,the forming experiment of simple bulge workpiece was carried out.The grain size of four different area of a certain section of the obtained forging was compared with the grain size simulated under the same conditions,and the error was found to be less than 5%.It can be proved that the grain size obtained by the DEFORM-3D simulation coupled with the microstructure evolution model is accurate,which further proved that the mold temperature-controlled method can refine the grain size.