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2 Integration of Heat Treatment CAD／CAE for Die and Mould
It can be seen from Fig.2 that the process design and simulation of heat treatment are the core of integration frame. After information input via product design module and heat treatment process generated via heat treatment CAD and heat treatment CAE module will automatically pide the mesh for parts drawing, simulation temperature field microstructure analysis after heat—treatment and the defect of possible emerging (such as overheat, over burning), and then the heat treatment process is judged if the optimization is made according to the result reappeared by stereoscopic vision technology. Moreover tool and clamping apparatus CAD and CAM are integrated into this system.
The concurrent engineering based integration frame can share information with other branch. That makes for optimizing the heat treatment process and ensuring the process sound.
2.1 3-D model and stereoscopic vision technology for heat treatment
The problems about materials, structure and size for die and mould can be discovered as soon as possible by 3-D model for heat treatment based on the shape of die and mould. Modeling heating condition and phase transformation condition for die and mould during heat treatment are workable, because it has been broken through for the calculation of phase transformation thermodynamics, phase transformation kinetics, phase stress, thermal stress, heat transfer, hydrokinetics etc. For example,3-D heat—conducting algorithm models for local heating complicated impression and asymmetric die and mould, and M ARC software models for microstructure transformation was used. Computer can present the informations of temperature,microstructure and stress at arbitrary time and display the entire transformation procedure in the form of 3-D by coupling temperature field,microstructure field and stress field. If the property can be coupled, various partial properties can be predicted by computer.
2.2 Heat treatment process design
Due to the special requests for strength,hardness, surface roughness and distortion during heat treatment for die and mould, the parameters including quenching medium type, quenching temperature and tempering temperature and time, must be properly selected, and whether using surface quenching or chemical heat treatment the parameters must be rightly determined.It is difficult to determine the parameters by computer fully. Since computer technology develops quickly in recent decades, the difficulty with large—scale calculation has been overcome. By simulating and weighing the property, the cost and the required period after heat treatment. it is not difficult to optimize the heat treatment process.
2.3 Data base for heat treatment
A heat treatment database is described in Fig.3. The database is the foundation of making out heat treatment process. Generally, heat treatment database is pided into materials database and process database. It is an inexorable trend to predict the property by materials and process. Although it is difficult to establish a property database, it is necessary to establish the database by a series of tests, The materials database includes steel grades, chemical compositions, properties and home and abroad grades parallel tables. The process database includes heat treatment criterions, classes, heat preservation time and cooling velocity. Based on the database, heat treatment process can be created by inferring from rules.
2.4 Tool and equipment for heat treatment
After heat treatment process is determined, tool and equipment CAD／CAE system transfers the information about design and manufacture to the numerical control device. Through rapid tooling prototype, the reliability of tool and the clamping apparatus can be judged. The whole procedure is transferred by network, in which there is no man—made interference.
3 Key Technique
3.1 Coupling of temperature, microstructure, stress and property
Heat treatment procedure is a procedure of temperature-microstructure—stress interaction, The three factors can all influence the property (see Fig.4). During heating and cooling, hot stress and transformation will come into being when microstructure changes. Transformation temperature-microstructure and temperature—microstructure—and stress-property interact on each other. Research on the interaction of the four factors has been greatly developed, but the universal mathematic model has not been built. Many models fit the test nicely, but they cannot be put into practice, Difficulties with most of models are solved in analytic solution, and numerical method is employed so that the inaccuracy of calculation exists.