Analysis Of Influencing Factors Of Bending Strength Of POM Gear And Its Strength Test

Polyoxymethylene(POM)is one of the five major general engineering plastics,known as "Saigang".POM gears are light in weight,low in noise,and good in machinability,and are widely used in various precision transmission systems.However,the high crystallinity of POM causes the gear to easily shrink and deform.In addition,poor thermal conductivity and low strength are also problems to be solved urgently for POM gears.In this paper,experimental research and theoretical analysis are carried out with the goal of improving the bending strength of tooth roots,a new method of gear bending strength testing is proposed,a special fixture for testing is designed and processed,the process parameters are optimized through orthogonal experiments,and the optimized design results are verified by experiments.The microscopic mechanism affecting the bending strength of POM gears is analyzed.The main tasks of this paper are as follows:(1)In view of the particularity of the gear structure,the self-developed tooth profile design software and UG software are used to design a special fixture for gear strength testing,which improves the accuracy of the strength test and simplifies the testing process.Aiming at the failure mode of POM gear tooth root fracture,the tooth root bending strength is used as the mechanical performance index,and the method for determining the position of the tooth root fracture section is optimized based on the "30° tangent method",and the accurate tooth thickness and moment at the fracture position are obtained,Improve the accuracy of the calculation of tooth root bending strength.(2)Aiming at the bending strength of the POM gear tooth root,the gear technology experiment and strength test were designed and carried out.The orthogonal test analysis showed that the degree of influence was mold temperature,melt temperature,holding pressure,injection speed,cooling Time,holding pressure speed.According to the results of range and variance analysis of bending strength,a set of optimal process parameters are obtained by applying the principle of orthogonal experiment.Experiments show that the tooth root bending strength formed by the combination of this parameter is the highest.(3)The crystallinity test,the crystal structure and the cross-sectional morphology of the gear samples of the orthogonal test process were carried out at the fracture position.The experimental results showed that the greater the crystallinity of the polyoxymethylene gear,the higher the bending strength of the tooth root;the higher the crystallinity The thickness of the core layer of the polyoxymethylene gear of high degree is larger,and there are fully grown spherulites in the core layer.These larger spherulites will increase the strength of the gear;between the spherulites,micron-level micropores will be formed.It plays a role in dispersing the stress when subjected to force,and also improves the bending strength of the tooth root of the gear.