Research On The Process And Key Equipment For Precision Forming Of Spur Gears

Gears have widely used in auto, vessel and all classes of machine in the form of principal part of movement and power driven. They are the basic components of unitized mechanized equipment in the 21st century. The design and manufacture of gears have direct effect on performance and quality of engineering goods, so gears play a very important role in the development of mechanical industry, known as a kind of symbol of industrialization.Our gear manufacture began early, but compared with industry developed countries, we still have a long way to go, whether the development of advanced manufacture equipment or technological level of advanced manufacturing process. In the 21st century, competition in the gear market is becoming fiercer and low-level products are far from meeting the needs of market development. The competition will be concentrated on technological innovation. Conventional machining and plastic working of billets no longer meet the growing demands of gear production. Hence, to quicken technological innovation and concentrate strength on developing advanced manufacturing process and equipment, it is of great practical significance for raising our gears'competitiveness in the international market. It becomes a trend for gear manufacturing to make great efforts to develop advanced manufacturing technology (AMT) of gears. For a kind of AMT, precision forming of gears is an important process between production of raw materials and manufacture of final products.Finite element method (FEM) on the basis of sure assumption and boundary condition remains to be perfected in predicting defective technology and accurately calculating such as loads, stresses and so on when it is used in the field of bulk forming. The results draw by FEM need to be verified by experiment. Physical simulation method has the advantages including easy method and intuitive experimental results, which can not be substituted by FEM. In recent years, it becomes a developing direction in the field of metal plastic forming to solve the main issue of the practical production by FEM and physical simulation method. These methods should be used comprehensively, which can make it easy to acquire deformation rule and can provide technique literatures and guides of theory. Hence, it is of great practical significance to combine FEM with physical simulation method in the process of precision forging of gears. Only by comprehensively applying these advanced technologies can precision forging of gears be promoted to make technological progress.Spur gears are difficult to shape for their precision forging, because the geometric shape of spur gear is complex and there is much influencing factor. The research on their deformation rule lags behind and can not meet the need of practical production. Hence, domestic and overseas scholars'focus will be concentrated on precision forging of spur gears and simulation of forming process. There is much research on precision forging of spur gears and the method of research is different, but most research has always focused on experimental study for certain reasons. Only few countries can produce spur gears by precision forging, only for small modulus & diameter spur gears. With the rapid development of gear industry, we badly need to develop a new process in order to solve the fundamental problems of precision forging of spur gears and make it apply to a large-scale industrial production.The main technological programs of precision forging of spur gears are stated in the paper. Such problems as incomplete filling at the addendum position, heavy load, short die life and microcracks at the dedendum position during the plastic forming of spur gears are analyzed. During traditional upsetting forming of spur gears, because the shaping force is normal to the flow direction of metal in the toothed mould cavity of cavity die, its component force is zero in the flow direction of metal theoretically. Hence, according to the constant volume condition during the plastic forming, metal is forced to flow into the toothed mould cavity when height of the billet reduces under the pressure. However the mould cavity is difficult to be filled with metal at the addendum position and microcracks are easy to appear at the dedendum position at the same time. Furthermore, the upsetting shaping force is very large and the die life is very short, especially for large diameter & modulus spur gears. These are the major challenges during the precision forging of spur gears. In order to sole these problems the new process and key equipment are presented in the paper, starting with both process and equipment. The systematic research is conducted into the precision forging of spur gears by the combination of FEM and physical simulation method. The research content and approach in the paper have certain innovation. The fundamental research involving new process and equipment are very important to the subsequent trial production of precision forming of gears. Under the new forms of greatly encouraging to establish innovation-typed nation, it can effectively improve the quality of domestic gears and accelerate our step into the powerful nation of gear manufacturing to conduct research into the new process and equipment of precision forging of gears which have proprietary intellectual property rights.In the paper the combination forming of upsetting and extruding of spur gears is presented according to its deformation features and mechanical principle. The technological flow of precision forging of spur gears is designed according to a nitrogen-protected system designed to prevent oxygen during thermo-plastic precision forming. The combination forming of upsetting and extruding is a process to combine extruding with upsetting. According to this forming principle, not only is the toothed mould cavity completely filled with metal, but also extruding force works during the whole process. So the manufacturing procedure includes advantages of preventing microcracks at the dedendum position from appearing, considerably reducing shaping force, improving stressed state of the die and extending its service life. The process can shape larger modulus spur gears by precision forging.The fulfillment of new technique needs new equipment, again the presence of new equipment subsequently develops new technique, which is the main development path of manufacturing industry. The typical double-acting hydraulic machines mainly apply to streching process, during which the holddown slider executes holddown force and the master slider executes shaping force. There is only an ejecting cylinder at the bottom of the bench. The ejecing cylinder only can act as liftout or hydraulic die cushion, which can not offer a reverse holddown force at the same time. Namely, the hydraulic machine only can fulfill oneway double action. The process requires the equipment to provide the shaping force and movement of upsetting and extruding, such as combination forming of upsetting and extruding and so on. Obviously, it is difficult to conduct the combination forming of upsetting and extruding on the traditional double-acting hydraulic machine. Hence, the paper presents the new equipment applied to combination forming of upsetting and extruding of spur gears, namely self-adjusting hydraulic machine for combination forming of upsetting and extruding according to the mechanical principle of fulfilling the upsetting and extruding in the relative directions. The hydraulic machine is designed with the construction that the upsetting cylinders are connected with the gas-liquid accumulators. It can fulfill combination forming of complex parts and closed-loop control according to the need of the process by control system. The hydraulic transmission and control system of the machine is simpler than those of traditional double-acting or three-acting hydraulic mahcine, so the machine has high utilization rate of energy. The paper presents the water-jacketed cooling system according to the features of thermo-plastic precision forming, which can overcome the bad effect of hot environment on the hydraulic machine. The self-adjusting hydraulic machine for combination forming of upsetting and extruding can fulfill the upsetting and extruding in the relative directions. It can slove the problems of precision forming of spur gears and can apply to the mass production of key parts, such as spur gears and so on. Furthermore, the machine has the advantages of sound construction, compatible function and low manufacturing cost. It can fulfill shaping in both long direction and cross direction and is especially suitable for the combination precision forming of upsetting and extruding at warm or elevated temperatures and stretching of timber.Aiming at the problems during precision forming of spur gears, the paper presents assessment method of precision forming of spur gears and establishs FEM system for precision forming of gears. The precision forming of larger modulus spur gear is studied during upsetting, forming of relief end faces and combination forming of upsetting and extruding by FEM respectively. The research shows that there are still such problems as incomplete filling at the addendum position, heavy load and microcracks at the dedendum position during traditional upsetting of spur gears at elevated temperature. The hot metal has good fluidity, so it flows into relief direction where there is small resistance during hot forming of relief end faces founded on the relief principle and it is difficult to completely fill at the addendum position. The shaping force is still great. The metal flows in the same direction with that of the filling of toothed mould cavity during combination forming of upsetting and extruding presented in the paer, so more metal flows into the toothed mould cavity and it is easy to fill the toothed mould cavity with metal, especially for the filling at the addendum position. Because extruding force works during the whole forming process, the equivalent stress falls down at dedendum position and the machanical property is perfected effectively. Comparing with upsetting, combination forming of upsetting and extruding of spur gears has lower shaping force, so reduces elastic deformation of dies and improves the forming precision of gear teeth. The filling capability of metal is greatly improved, so spur gears can be completely shaped under lower load.The effect of typed technological parameters such as relative upsetting, radius of extruding punch, deformation velocity and temperature on the precision forming of spur gears is emphasized to study. With an increase of relative upsetting, the extruding deformation decreases and extruding stroke decreases accordingly, but the shaping force has small changes. The radius of extruding punch has considerable influence on the equivalent stress and shaping force. During the stage of upsetting the bigger is the radius of extruding punch, the smaller is the shaping force. During the stage of extruding the bigger is the radius of extruding punch, the shorter is the stroke of extruding and the greater is the shaping force. The deformation velocity has little influence on the shaping force. The final load has small changes until the end of the deformation process. The higher is the initial temperature of the billet, the smaller is the shaping force. The paper also presents process program of upsetting preforging & combination final forging of upsetting and extruding of spur gears and the forming process is studied by FEM. The research shows that the process can effectively improve stressed state at the dedendum position during the forming process of spur gears and solve the problem that microcracks are easy to appear at the dedendum position. Consequently, the machanical property of gears is improved.Finally, the paper conducts experimental study on upsetting, combination forming of upsetting and extruding and upsetting preforging & combination final forging of upsetting and extruding of spur gears by physical simulation. The testing material is made of clay plasticine and cylindric testing billets are made by stratified coloured plasticine. The research shows that stratified coloured plasticine can apply to research on the forming of complex parts such as gears, with satisfactory results. For the precision forging of spur gears, there are such problems as incomplete filling at the addendum position, heavy load and microcracks at the dedendum position during the traditional upsetting. The combination forming of upsetting and extruding can deal with these problems satisfactorily. It can shape spur gears completely filled with metal and the shaping force is reduced remarkably. The upsetting preforging & combination final forging of upsetting and extruding presented in the paper further solves the problem that microcracks are easy to appear at the dedendum position, applying to closely shape spur gears with high performance.