The automobile torsion bar spring is a critical component that utilizes the torsional elastic deformation of a rod to function as a spring. Two essential processes in its manufacturing are quenching and pre-twisting. Traditionally, manufacturers have relied on conventional quenching and cold pre-twisting at room temperature. However, these methods come with several drawbacks, such as torsion bar bending, uneven hardness, poor fatigue resistance, and significant slack deformation. To address these issues, this paper introduces an innovative approach using rolling quenching and hot pre-twisting.
Currently, torsion bar springs are commonly categorized into solid and hollow types, with round cross-sections being the most common. Compared to coil and leaf springs, torsion bars offer advantages like a simpler structure, no friction during operation, stable performance, and high energy storage per unit volume. They are widely used in vehicles, trains, tanks, and armored vehicles due to their compact size and lightweight design.
The traditional manufacturing process includes cutting, upsetting, annealing, end processing, conventional quenching, tempering, cold pre-twisting, shot peening, inspection, and rust prevention. However, the conventional quenching and cold pre-twisting steps often lead to problems like uneven hardness, deformation, and low fatigue resistance. For example, vertical quenching can cause "S"-shaped bending, while horizontal quenching may result in distortion. Cold pre-twisting also requires multiple cycles, increasing production time and resource consumption.
To overcome these challenges, a new manufacturing technology has been developed. It replaces conventional quenching with rolling quenching and cold pre-twisting with hot pre-twisting, while keeping other steps unchanged. Rolling quenching involves a specialized device with components such as speed control, straightening mechanisms, a bed, quenching nozzles, and levers. This system ensures even cooling, reduces bending, and improves surface hardness.
Hot pre-twisting, performed at elevated temperatures, reduces the number of required pre-twisting operations and enhances fatigue resistance. The process involves tempering the spring at 450–480°C, followed by hot pre-twisting using industrial robots or personnel wearing heat-resistant gloves. Afterward, a final cold pre-twisting is applied to ensure optimal stress distribution.
Testing results show that the new process significantly improves straightness, hardness uniformity, and reduces relaxation and fatigue deformation. For instance, the second group, which used the new method, achieved a straightness of 0.3 mm compared to 2.4 mm in the original process. The hardness was more consistent, and the relaxation deformation was reduced from 1.8° to 0.3° after 240 hours of load testing. Fatigue resistance also improved, with hysteresis deformation dropping from 2.5° to 0.6° after 50,000 cycles.
In conclusion, the new manufacturing process using rolling quenching and hot pre-twisting offers substantial improvements over traditional methods. It enhances product quality, reduces defects, and shortens the production cycle, making it a promising advancement in torsion bar spring manufacturing.
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