Sustainable Gears-Design of Gear Body Modified Powder Metal (PM) Gears

摘要

The increasing requirements for noise emission and resource efficiency of drive systems are determined based on the awareness of the surrounding noise and climate change as well as the legally increasing emission limits (Ref.11). The progressive electrification of the powertrain is, as a result of the reduction to the elimination of the masking noise of the conventional internal combustion engine, a major influencing determinant (Ref.21). In order to reduce the costs and increase the power density of the electric motor, there is a trend towards high-speed electric motors in combination with a transmission (Ref.10). The demand for high ratios of the individual cylindrical gear stages leads to an increase of the outer diameter of the gear. The increase in power density can be achieved by reducing the gear body mass. Regarding a limited load-carrying capacity, a reduction in mass can be achieved by gear body modifications in the generally oversized gear body of a cylindrical gear. Due to their locally adjustable material density, powder metallurgical (PM) gears offer additional lightweight design potential as well as increased damping properties. As a result of the near-net-shape production of the gears, gear body modifications can be manufactured without additional process steps. The manufacturing process for PM gears is characterized by special tools, which are required for the pressing and densification process. Due to the high cost of specialized tools, the PM production chain is particularly suitable for series production of gears (Ref.9). The pressing tools have a service life of several thousand components (Ref.14). The higher investment costs of the tools can be compensated due to the higher resource efficiency in terms of material and energy use (Ref.15). Frech et al. and Klocke et al. determine the potential savings in raw material used as well as the savings in energy costs for a typical PM gear in the range m_n = 2 mm compared to machining (Refs. 8, 12). The resource efficiency of the PM process chain leads to a savings potential of 5.4 percent with respect to energy and 52.2 percent with respect to the material used. In summary, these two potential savings result in a cost advantage of 21.7 percent for the PM process chain compared with the conventional process chain. Furthermore, the lower material input due to gear body modifications leads to a reduction in transport costs, which have not yet been taken into account in the savings potential. Other cost advantages include lower machine costs due to shorter process times and lower space and maintenance costs (Ref.22).