Research On Optimization Of Injection Molding Process For POM Gears Under Dynamic Fatigue Test

As one of the five general engineering plastic materials,polyoxymethylene has many advantages that metal materials do not have,and is widely used in precision instruments and microtransmissions.With the advancement of industrial technology,the application environment of POM gears has become more and more complicated.Its small elastic modulus and low strength limit its application range and service life.Therefore,improving the strength of POM gears is an urgent need to solve.question.In this thesis,the purpose of improving the fatigue strength of POM gears is to carry out experimental research and theoretical analysis,and to design a dynamic fatigue test method.Through the dynamic fatigue orthogonal test,the influence degree and trend of each process parameter on the fatigue strength of the POM gear were obtained,and the two parameters with the greatest influence were selected to carry out the dynamic fatigue single-factor test,and the optimized process gear was obtained and verified,and the two parameters were further analyzed from the microscopic level.Influence mechanism of process parameters on dynamic fatigue strength of polyoxymethylene gears.The main work is as follows:1 Considering the special gear structure,this thesis uses gear design software and UG modeling to design a separate gear test fixture.A new calculation method for plastic gear parameters is proposed,considering the influence of the molding process on the size of the injection-molded gear,and the displacement coefficient and root fillet radius of the molded gear under each process condition are calculated separately.And based on the 30° tangent method,the arm and tooth thickness at the fracture position of the gear teeth are accurately obtained,the same bending stress is set,and the load pressure of the gear test under different conditions is calculated,using the Shimadzu hydraulic servo dynamic fatigue testing machine,Complete the dynamic fatigue test.2.In order to discuss the influence of injection molding process parameters on the fatigue strength of POM gears,Moldflow was used to optimize the molding window,and dynamic fatigue orthogonal experiments were designed.The degree of influence of dynamic fatigue is followed by mold temperature,holding pressure,injection speed,cooling time,holding speed and melt temperature.3.Considering the complexity of gear features and the interaction of orthogonal processes,single-factor experiments were carried out on the two process parameters with the greatest influence,and the influence trend of mold temperature and holding pressure on the fatigue strength of POM gears was analyzed in detail and optimized.Combined and verified by test,the results show that the dynamic fatigue strength of the optimized gear is significantly higher than that of the single-factor test gear.4.Take the same position for the single factor experimental gear and the optimized gear to do DSC and polarization analysis,analyze the internal reasons why the strength of the optimized process gear is better than different mold temperature and pressure holding gear from the microscopic level,and discuss the parameters of mold temperature and holding pressure.Influence mechanism of micro-features of POM gears.