【作者】 金俊松；

【导师】 夏巨谌；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 博士

【摘要】 齿轮作为汽车的一个重要传动零件,近年来,随着汽车工业的迅速发展,对其生产技术的要求愈来愈高。冷精锻齿轮与传统加工方法生产的齿轮相比,具有节约材料、机械性能好、生产效率高等优点,是当今齿轮特别是轿车齿轮生产的发展趋势。本文围绕轿车齿轮闭式冷精锻近/净成形技术做了系统的研究。以避免端啮,减少震动和噪声,提高轿车直锥齿轮啮合传动平稳性为目的,研究了其修形理论和方法,给出齿向的修形量计算公式和“鼓形”修形中心位置的确定方法,同时根据啮合过程中齿轮基节的变化特点,提出确定齿顶修形量的计算方法。闭式冷精锻是轿车齿轮类零件的主要近/净成形技术,它既适合于传统的直锥齿轮近/净成形,也是修形的直锥齿轮近/净成形的一种理想加工工艺,因为目前尚无经济合理的精密切削加工工艺实现修形直锥齿轮的加工。采用刚粘塑性有限元法,模拟了直锥齿轮闭式冷精锻近/净成形过程,得到了金属流动和工件内部损伤值的分布规律,并预测了成形力,为近/净成形工艺优化奠定了理论基础。其成形过程显示材料首先向凹模底部流动,然后在沿径向流动的同时作反向流动,直至整个型腔充满。锻件从小端至大端其损伤值总体均呈上升趋势,而且越靠近大端,损伤值增长速度越快,而在齿顶中间部位,由于挤压过程中材料的汇聚导致损伤值分布曲线上出现较小的波峰。锻件成形过程中,从开始到凹模型腔基本充满,其载荷逐渐上升,至完全充满型腔后,载荷急剧上升,因在凹模型腔上设置了多余金属的分流腔,从而有效抑制了载荷的急剧增大。发明了一种闭式冷精锻专用液压模架,阐明了其基本结构和工作运动原理。设计了曲面分模和平面分模两种模具结构,并根据分流锻造原理提出了分流腔的设计原则和方法。分析了曲面分模模具的齿顶断裂和平面分模结构中凹模底部开裂原因。根据分析结果,提出了非均匀过盈预应力组合凹模新结构,并采用传统厚壁圆筒理论、Matlab编程计算和有限元相结合的方法实现了三层组合凹模进行优化设计,有效提高了模具寿命。提出直锥齿轮精锻模具的数字化设计与制造技术:同时,采用基体钢代替高速钢并适当降低凹模淬火硬度,使其适合于硬质合金刀具高速精密加工,成功实现了采用高速数控铣代替传统的电火花加工方法加工直齿锥齿轮精锻凹模,显著地提高模具精度和生产效率。在分析了螺旋圆柱齿轮结构特点的基础上,采用经典塑性成形理论和有限元数值模拟相结合的方法,对多个螺旋圆柱齿轮闭式冷精锻近/净成形方案进行了探讨,最后得出单向挤压,底部外侧分流为最佳工艺方案,以此为基础,提出了带旋转顶出机构的闭式冷精锻模具方案,为进一步研究和应用打下了理论基础。针对上述研究内容和结论(螺旋圆柱齿轮近/净成形除外),采用Y28-400/400数控双动液压机,对轿车直锥齿轮闭式冷精锻近/净成形工艺,精锻齿形凹模的数字化建模与制造技术,非均匀过盈预应力组合凹模及专用液压模架等,进行了详细的实验研究,充分验证这些结论的正确性。应用这些成果,在东风汽车精工齿轮厂建立了生产线,实现了轿车直锥齿轮闭式冷精锻近/净成形的批量生产,所生产的直锥齿轮超过国标GB11365-89的7级精度,齿面粗糙度Ra=0.8～0.4μm,其齿形部分不需任何机械加工就达到了直接装车使用的要求,并已创造出显著的技术经济效益。更多还原

【Abstract】 Gears are widely used as an important part in power transmission device in car. In recent years, with the rapid development of automobile, the demand on gear’s manufacturing becomes much strict. For the cold precision gear forging has a lot of advantages when compared to conventional gear shaping, such as material saving, better mechanical properties and higher productivity etc, cold precision forging has become an alternative method to conventional method in gears manufacturing. This paper studied the closed precision die forging process systematically.To avoid edge contact, reduce vibration and noise, increase the stability during power transmission, the gear modification theory and method were studied. The method of calculating modification quantity in teeth length direction and the method to establish the center of crown teeth face were given. Based on the character of base pitch variation during the gears working, the calculation method of modification quantity in teeth tips was obtained.Closed die forging is a main near/net shaped forming method for gear parts; it is the best process for producing modified bevel gears until now. Rigid-plastic Finite element method (FEA) was employed to analyze the bevel gear forging process, damage distribution was obtained and the forming load was predicted, that laid the foundation of optimizing process for bevel gear forging. FEA results show that the material flows to the bottom of the teeth cavity die first, and then it flows into the teeth cavity in radial direction until the die cavity is full filled, meanwhile, it flows backward. The damage became higher from the small end to the big end of the bevel gear. Because of the confluence of material, a small peak appears in the middle of the damage distribution curve along the teeth tip. The load keeps rising during forging, when the cavity is full filled, the load rise sharply, since the material can flows into the process compensation space, the load increase can be effectively inhibited.A die set for bevel gear forging was invented; its structure and principle of work were described. A curved parting-face die and a plane parting face die were designed. Based on the divided flow forging theory, principle and method for designing process compensation space was given. The fracture of the teeth tip in a curved parting.face die and the crack at the bottom corner in a plane parting face die were analyzed. According to the analysis results, a non-uniform assembled die structure was proposed. A three-layer assembled die was optimized by a combined method of classic thick-wall cylinder theory, Matlab programming and FEA, and its life was obviously increased.Digitized design and manufacturing technique was proposed. A matrix steel was used as die material instead of high-speed steel and the heat treatment hardness was decreased to fit the milling requirement. It is successful to use milling as an alternative method to electro-spark machining to manufacture bevel gear cavity die, which greatly increased the accuracy of the die and the manufacture efficiency.Based on the characters of helical gear, a number of near/net shaped forging processes were analyzed by classic plastic theory and FEA method. According to the analyse results, the single punch forging with a process compensation space at the big radii-side of the die cavity bottom were decided as the best forging case. Based on the forging characters and selected forging case a die set with a rotational reject device was designed, that laid a foundation for a further study.Based on the results above (except for helical gear), experiments for near/net forging of bevel gears were carried on Y28-400/400 double action press. It verified the forging process, digitized die modeling and manufacturing technique, non-uniform assembled structure die. A product line has been built in Dongfeng finished gear plant in Shiyan, the products has a better accuracy than the seventh grade of Chinese standard GB11365-89 and has a teethsurface roughness of Ra=0.4～0.8μm, the teeth can be used in car without any furthermachining, that means the cold forging technology of bevel gears is producing remarkable technical and economic benefit.更多还原