Abstract

Key Lock parts in automotive Electronic Power Steering (EPS) systems must possess mechanical properties such as fatigue resistance, high toughness, and high strength. Therefore, forging is not only suitable for meeting the performance requirements of EPS but also offers cost advantages. However, the hollowness, narrow grooves and densely packed teeth of Key Lock parts restrict material flow and cause uneven stress distribution within the parts, making forging a significant challenge. This paper uses S35C medium carbon steel as raw material and compares the following three different forging methods: cold forging, warm forging, and hot forging, through actual die-cutting to understand the impact of different forging methods and the forging deformation rate between different process passes on surface hardness. Experimental results show that, observed under an optical microscope, the grain size is coarsest after hot forging, followed by warm forging, and finest after cold forging. Hardness increases with increasing forging deformation rate; cold forging yields the highest hardness, followed by warm forging, and hot forging yields the lowest. In terms of dimensional accuracy, cold forging has the best precision, followed by warm forging. Hot forging requires additional processing to meet the dimensional requirements due to thermal expansion and contraction. These experiments provide manufacturers with insights to help them choose the appropriate process to meet their specific needs.

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