The lightweight of nodular cast iron metro gear box requires structural optimization at first. Under the condition that the main wall thickness meets the requirements of operation mechanics, determine the reasonable wall thickness of the box. According to the material and specific structure of nodular cast iron metro gear box, design reasonable chemical composition, appropriate melting temperature and pouring temperature, select appropriate pouring system for rapid filling, mold preheating and other measures to ensure mass production of lightweight nodular cast iron metro gear box castings.

Through the optimization and simulation calculation of the structure of the original nodular cast iron metro gear box, under the condition of ensuring the safe operation of the nodular cast iron metro gear box, the main wall thickness of the casting is optimized to 6~7mm, and the weight of the casting can be reduced to 135kg. As shown in the figure, the finite element mesh model of the gear box is established, and the static strength and fatigue strength finite element analysis of the ductile iron metro gear box is carried out. The analysis results show that the maximum stress of the ductile iron metro gear box in the static strength calculation condition is 171.1MPa, which is less than the yield strength of the material 310MPa, and meets the static strength requirements; Under the fatigue strength calculation condition, according to the material fatigue limit of 98MPa, the surface nodes of the ductile iron metro gear box can fall into the Goodman fatigue limit diagram of the material, meeting the fatigue strength requirements.