The Research On The Coupled Thermal-Mechanical Numerical Analysis And The Structure Optimal Design To Aluminum Hot Extrusion Dies

Aluminum extrudates have been widely used in the fields of aeronautics andastronautics, transportation, architectural upholster, etc. because of their characteris-tics such as low weight, high strength as well as beautiful shape, etc. The hotextrusion die is the most important component in the aluminum hot extrusion, whichnot only determines the geometrical shape, dimension precision, surface quality ofextrudates but also affects extrusion power and performance of extrudates. The hotextrusion die works under the condition of high temperature, high pressure, highfriction as well as local stress concentration, which makes the stress distribution in thebody of the die not uniform, and very apt to experience various forms of failure suchas bridge crack, die core offset, local deformation, etc., making the service life of thehot extrusion die very short. This has become an obstacle to improve the quality ofextrudates and the production efficiency. China produces large amounts of aluminumextrudates and more than 300 thousands of dies are used every year, but huge direct orindirect economic loss has been caused by low service life of dies.It's indicated through theoretical research and practical experience that thefailure of the die is related to the working temperature and its distribution, the frictionbetween the aluminum alloy and the surface of the die as well as the structure of thedie. The traditional structure design and strength check method has left manyproblems to be researched ulteriorly about the influence of such factors as thetemperature of the die during extrusion, local structural size of the die, the frictionbetween the billet and the die, etc. on the stress distribution and stress concentration inthe body of the die, which results in low service life. With the development of theoriesin the fields of heat conduction, elasticity and plasticity mechanics, thermal elasticityand plasticity mechanics and finite element method, optimal design technology, etc., acoupled thermal-mechanical model of the hot extrusion die under actual workingconditions can be built up, and the accurate calculation and analysis can be made withthe help of numerical calculation methods, resulting in the actual distribution of stressand strain in the body of the die, which supplies true and reliable dates used for thestrength calculation and analysis, thereby the strength check method is expanded andthe foundation of structural optimal design of the die is enhanced, the distribution ofstress and strain can be obviously improved and the maximum value of stress can alsobe reduced, resulting in improvement of the carrying capacity and service life of the die to a large extent.In this paper, the typical hot extrusion dies are used as research object, theimprovement of dies' service life as research objective, the temperature field, thermalstress field, thermal elasticity and plasticity coupled thermal-mechanical stress field asresearch contents, 5 scientific research items such as "the research on the strengthanalysis and optimal design of hot extrusion dies" (Project supported by HunanProvincial Natural Science Foundation of China), etc. as research supports, themethod, which combines theoretical analysis and numerical simulation, is used tomake a coupled thermal-mechanical numerical analysis and structural parametersoptimal design on the hot extrusion die, resulting in some research results as follows.1. Based on the theories in the fields of heat conduction, elasticity and plasticitymechanics, thermal elasticity and plasticity mechanics, mathematical models abouttemperature fields and thermal stress fields of hot extrusion dies are built up andboundary conditions under actual physical working environments are determined, thefinite element method is used to calculate the temperature fields and thermal stressfields of the hot extrusion die, which establishes the basis for the research of stressdistribution under different temperature conditions.2. The research is done onthe three-dimensional (3D) solid modeling technologyfor hot extrusion dies. Using ANSYS as a platform, APDL (ANSYS ParametricDesign Language) included in ANSYS as developing tools, a 3D parametric solidmodeling system for porthole compound dies is built up.3. The strength calculation and analysis of aluminum square profile hot extrusionporthole compound die is done quantitatively and therefore the values of Von. Misesstress and strain in the die body as well as their distribution can be acquired. Theresults indicate that there exists a stress concentration at the junctions between the diecore and the porthole bridge at which the fatigue crack often occurs. This agrees quitewell with the actual conditions. The research is done on the effects of structuralparameters of the hot extrusion die on the maximal Von. Mises stress and the curve ofmaximal Von. Mises stress vs. structural parameter is obtained.4. The optimal design system, which contains the functions of strength analysisof the die, structural parameters optimal design and in company with solid modelingof hot extrusion dies under the coupled loads of temperature, friction between thebillet and surfaces of the die and extrusion power. The system is used to optimize thestructure parameters of aluminum square profile hot extrusion porthole compound die such as die height, radii of porthole, die bridge cone angle, etc. Compared with theoriginal structure of the die, the maximum value of stress of the die with optimalstructural parameters is descended by 32.2 %, and at the same time, the distribution ofstress and therefore the carrying capacity and service life of the die is improved to alarge extent.5. The optimal design system developed in the paper is also used to optimize themajor structural parameters of aluminum double-hole and polygonal profile hotextrusion porthole compound die. Compared with the original structure, the maximumvalue of stress and strain of the die with optimal structural parameters is descended by36.4% and 32.0% respectively. The research results are applied to an aluminumextrudates manufacturing factory in the south which is in good coincidence with thecomputing results.The research results in the paper can be used to do accurate strength analysis andstructure parameters optimal design of hot extrusion dies under actual physicalconditions, which is helpful to get rid of the traditional "trial and error" design modelof aluminum profile hot extrusion dies and establishes the basis of integration ofcomputer-aided design/engineering/optimization of aluminum profile hot extrusiondies.