Study On The Worm Wheel Grinding Method Of The Tooth Surface Texture Improvement

Modern gearboxes are characterized by high torque load demands, low running noise and compact design. In order to fulfill these requests, higher demands on gear properties are being proposed than in the past, especially the reduction of gear noise performance. Gear noise is primarily affected by macro- and micro- geometry of gear tooth. Marco-geometry is the shape of gear tooth while micro-geometry is tooth surface topology such as roughness, waviness, texture and so on. As the gear fine machining process determines both the final macro- and micro-geometry, it has directly influence on gear noise.At present, worm wheel grinding has already replaced forming grinding in mass production of small and medium sized gears, becoming the most wildly used fine machining method, due to its higher efficiency and quality. Although its high macro-geometry precision, the process of worm wheel grinding has a tendency to produce a microscopic regular surface texture on the gear tooth flanks, generally in the lengthwise direction, that is believed to be the cause of noise when such gears are in mesh. Therefore, this paper researched on the generating principle of regular texture of tooth surface in the process of worm wheel grinding, proposed a modified processing method with variable worm wheel feed rate, and verified the validity of the this processing method via experiment. The main contents of the paper are as follows:(1)Utilizing mesh theory of space crossed axes gears, studied the principle and motion of worm wheel grinding, set up mathematic model of worm wheel grinding process. Analyzed contact properties in grinding process, visualized tooth surface grinding area. According to abrasive particle cutting principle, analyzed grinding properties of worm wheel and gear, expressed the generating process of grinding scratch, and conducted research on geometry motion model of plane grinding to find out factors affected on morphological features of grinding scratch, conclusions were also applicable to worm wheel grinding. According to contact and grinding properties, analyzed formation principle of tooth surface texture.(2)Studied main gear noise excitations, combined the experiment conclusions, analyzed affecting mechanism of tooth surface regular texture on gear noise. Macroscopically completed the simulation of contact path through solving mesh equations of worm wheel and gear in MATLAB, while microscopically simulated cutting path of abrasive particle on tooth surface via establishing cutting velocity model of instantaneous contact points. Found out influence factors of generating regular tooth surface texture from the two aspects above. Through the discussion of affecting factors proposed a modified processing method with variable worm wheel feed rate in order to get irregular texture. Combined the technology improving tooth surface of gear honing and practical processing technology of worm wheel grinding, confirmed the final speed function.(3)On the basis of analyzing motion principle of YW7232 CNC worm wheel grinding machine and process of worm wheel grinding, proposed two methods to realize variable-speed machining at the grinding machine. Integrated variable-speed machining function to existing interface of CNC grinding machine by the secondary development of SIEMENS 840 D. On YW7232 CNC worm wheel grinding machine, finished variable-speed machining and regular machining. Analyzed tooth surface textures of the two methods by 3D microscopic system, which showed that variable-speed machining is able to produce irregular surface textures.(4)Designed mesh properties contrast experiment of mating gears finished by variable-speed machining and regular machining. Tested mesh noise and vibration data at different speed respectively. Through the analysis of the frequency spectrum, found out that compared to regular machining, the total value of noise SPL of variable-speed machining reduced about 3dB and vibration acceleration at mesh frequency was obvious less than regular machining, which verified the validity of the irregular tooth surface texture processed by variable-speed processing method to reduce gear noise and vibration.The subject comes from The National Key Technology R&D Program “The Key Technology of Gear Transmission Design and Manufacturing in Precision Machinery and Its Application on Machine Tool(SQ2014GX03D00214)”, which aims to change properties of high precision gear through the improvement of tooth surface texture.