| Long-axis heavy forgings are widely used for transmission shaft.As the basic parts of many heavy machines and equipments, the quality requirements of long-axis heavy forgings are very strict.Due to the large size and the heavy weight,the heavy forgings is forged directly by large ingots.Howevery, the forging performance and the organization is uneven seriously after being forged.To achieve the performance requirements, it is necessary to develop a reasonable process of heat treatment that improve the organization performance and save time and energy.The research subject are financially supported by the 2009 major scientific and technological projects in Guangdong province (2009A080304004)"Research on forging reduction of heavy forgings and technology of using waste heat and its application in shipping industry".In this paper, based on the basic theory of heat transfer, the long-axis heavy forgings as the research object, and formulate the process specification of remained heat treatment, finite element method combited with experiment examination was used to simulate heat treatment process, then optimization algorithm was used to optima parameter of heat treatment process.The main research contents and conclusions of this paper are summarized as follows:(1)Based on chemical composition,thermophysical properties,TTT and latent heat, a library of 35CrMo has been developed.A mathematical model is established to calculate the temperature of the surface of forging from the temperature data of the center of forging.This algorithm of FDM (Finite Difference Method) is programmed and the curve of heat transfer coefficient is obtained.(2)The process of remained heat treatment is validated by experiment, the results show that this process is feasible.The forging made with the new process have improved surface wear-ability and inner structure of forging.Also, the new technique has advantages in shortening heat preservation, saving heating time more than 58%.(3)A FEM (Finite Element Method) model of remained heat treatment process is built based on the FEM software DEFORM-3D.The model is validated by experiments, the simulation results basically fit those measured in experiments.The results show that due to chilling effect of quenching, the temperature differences between surface and core of the forging are tremendous;During the process, the stress of the round areas of forging is maximum at 5min, which is 410Mpa, and the stress has no possibilities of plastic deformation.After quenching-tempering, the main organization of forging is temper-sorbite, with good mechanical properties.(4) A method combining SVM (Support Vector Machine) with GA (Genetic Algorithm) to optimize heat treatment process parameters of long-axis heavy forgings was put forward, taking quenching temperature,quenching holding time,tempering temperature and tempering holding time, and so on as optimizing parameters.Heating time and residual stress as optimizing objective, the final heat treatment process of long-axis heavy forgings is optimized.Firstly, through the orthogonal experiment of the technical factors in heat treatment,the mapping model of SVM was established based on data above experiment.Then, through optimizing the model by useness of GA, the optimum heat treatment process parameters have been given.The results show that compared to conventional process, this process has save heating time more than 22% and the residual stress more than 24%. |
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