Research On Open-die Warm Extrusion Forming Process Of Spur Gear

Gear transmission is the most widely used transmission mechanism in mechanical transmission system.As the most typical gear part in gear transmission mechanism,spur gears are manufactured by traditional machining methods which have the disadvantages of low material utilization,high energy consumption and low production efficiency.Especially,the exertion of metal material performance is limited,as a result of metal fibers been cut off.That is not conducive to the improvement of comprehensive mechanical properties of gear parts and structure lightweight.China's gear industry scale has ranked the first throughout the world,however the development level remains large but not strong.With the increasing aggravation of energy crisis and environment issue,the demand for sustainable development have become increasingly prominent in gear manufacturing industry.A green manufacturing technology with more economical,environmentally friendly and efficient is urgently desired to be sought for spur gear manufacturing.The development of precision plastic forming technology of gear parts is not only the development demand of gear industry,but also throughout the development of metal material precision plastic forming technology.Especially,the precision plastic forming technology of spur gear is a hotspot and difficult issue of applied research in the field of metal plastic forming.The development course and research status of spur gear precision plastic forming technology are firstly summarized in this thesis.The applications of closed-die forging,open-die extrusion and rolling in spur gear manufacturing field and the characteristics of each forming process are expounded.Open-die warm extrusion forming technology of spur gear is systematically researched on the basis of the existing research results of spur gear extrusion forming technology,in order to develop a spur gear precision plastic forming technology which is economic,environmental,efficient and well feasible.20Cr₂Ni₄A alloy steel is selected as the experimental material in this study.The warm deformation behavior of 20Cr₂Ni₄A alloy steel is explored through isothermal compression tests.The Arrhenius-type constitutive models of 20Cr₂Ni₄A alloy steel are derived by using apparent constants and physically-based constants respectively.It provides the material science basis for this study,and plays the positive guide role in the establishment of process plan and the optimization of process parameter for the open-die warm extrusion forming of spur gear.In addition,the dynamic recrystallization model of 20Cr₂Ni₄A alloy steel is constructed to enrich the research of material characteristics of 20Cr₂Ni₄A alloy steel.According to the structural feature of spur gear,the structures of punch,die and blank are designed for the open-die warm extrusion forming process.The process principle of the open-die warm extrusion forming of spur gear is analyzed.Based on the commercial finite element simulation software DEFORM-3D,the simulation model of the open-die warm extrusion forming of spur gear is established.By using the design method of orthogonal experiment combining with single factor cycle experiment,the influences of lubricating condition,die entrance angle,blank size,extrusion speed and forming temperature on the open-die warm extrusion forming of spur gear are thoroughly studied.It is found that the forming process of spur gear open-die warm extrusion consists of three stages,including gear tooth indexing,gear tooth forming and truing stripping.The lubricating condition,die entrance angle and blank size are determined as three crucial factors affecting the forming quality.The experimental system which including forming equipment,heating equipment and experimental mold is designed according to the requirements of spur gear open-die warm extrusion forming process.In order to meet the requirement of the warm extrusion forming for extrusion speed,the forming equipment is transformed from a general 315 T hydraulic machine.In the condition of requested forming load for the open-die warm extrusion forming of spur gear,the operating speed of hydraulic machine slide can achieve the experimental requirement after transformation.It is learnt from the preliminary experiments that the ideal lubricating condition is extremely difficult to achieve,due to the lack of suitable lubricant for warm extrusion forming and the restrict of spur gear complex structure and open-die extrusion forming process characteristic.Therefore how to manufacture spur gear by warm extrusion forming in a poor lubricating condition becomes an important issue.Through the defect cause analysis,it is certain that the root reason causing the insufficient section of formed gear by open-die warm extrusion is the unbalanced velocity field during the extrusion forming process,lubricating condition and die structure are two decisive factors.To reach the required lubricating condition for open-die warm extrusion forming of spur gear is difficult and high cost in actual production.In order to realize warm extrusion forming of spur gear in a poor lubricating condition,the die structure is optimized by using Response Surface Methodology.The response surface function models of insufficient section height and gear tooth filling are respectively established by using the complete second-order function model.The quantitative analysis of insufficient section height and gear tooth filling can be realized.The aims to control the insufficient section height and improve the gear tooth filling are achieved.On the basis of in-depth research on spur gear open-die warm extrusion forming process,in order to reduce the machining allowance of warm extrusion formed gear,variable contour two-step warm extrusion forming process of spur gear is proposed.This process includes two procedures which are pre-extrusion forming and finish-extrusion sizing.Contour variation as the key process parameter is quantitatively analyzed through the numerical simulation,and it is verified by physical experiment.At last the die suitable for continuous production is designed.