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为保证机构的可靠性,历史上一直在用锻钢合金批量生产高转矩变速器零件,诸如变速器齿轮、高性能链轮、单向离合器座圈及滚珠轴承座圈。虽然用粉末冶金工艺生产的零件成本低廉,但常规粉末冶金钢的静态、疲劳及耐磨性能的局限性,使粉末冶金零件不能应用于上述领域。为解决这些缺欠,近年来,一直在研发用选择性表面致密化(SSD)改进粉末冶金钢性能的各种生产工艺。特别是,PMG集团开发出了一种拥有专利权的表面致密化工艺——DensiForm。利用这种工艺可使零件表面关键部分形成深度达1mm的完全致密化表面层,而零件心部仍然是多孔性的。这种结合与粉末冶金材料合金化的灵活性,使生产的烧结钢零件的使用性能可与在高应力下使用的锻钢性能相比拟。本文将介绍2个例子,即变速器中应用的表面致密化螺旋齿轮和直齿链条的驱动链轮。本文说明了螺旋齿轮和驱动链轮的生产工艺与显微组织,介绍了轿车变速器用螺旋齿轮的性能(其中包括在三轴总成的成对试验台架上得到的滚动接触疲劳的数据)和表面致密化链轮的材料性能与使用性能。
To ensure the reliability of the organization, high-torque transmission parts such as transmission gears, high-performance sprockets, one-way clutch races and ball bearing races have historically been mass-produced from forged steel alloys. Although parts produced by the powder metallurgy process are inexpensive, the limitations of static, fatigue and wear resistance of conventional powder metallurgy steel make powder metallurgy parts unsuitable for use in these fields. In order to solve these deficiencies, various production processes for improving the properties of powder metallurgy steel by selective surface densification (SSD) have been developed in recent years. In particular, the PMG Group has developed a patented surface densification process called DensiForm. With this process, a fully densified surface layer of up to 1 mm in depth can be formed at key parts of the part surface, while the core of the part is still porous. The flexibility of this combination with alloying of powder metallurgy materials allows the performance of the sintered steel parts produced to be comparable to that of forged steels under high stress. This article describes two examples of surface-densified helical gears and sprocket driven sprockets for transmissions. This paper describes the production technology and microstructure of helical gears and drive sprockets, describes the performance of helical gears for passenger car transmissions, including the rolling contact fatigue data obtained on paired test stands of triaxial assemblies, and Surface densification sprocket material properties and performance.