During the forming process of metal stamping parts, uneven plastic deformation of the material results in significant residual stress. If this residual stress is not effectively eliminated, it can lead to deformation, cracking, and even affect the fatigue life and corrosion resistance of the parts during use. Various methods can be used to effectively eliminate residual stress, which will be analyzed below from the perspectives of process optimization, mechanical treatment, heat treatment, and emerging technologies.
Mechanical vibration aging is a method that uses periodic external forces to induce resonance in the part, releasing residual stress through grain slip and twinning deformation. This method applies alternating stress to the part using specialized equipment, causing plastic deformation of its internal microstructure, thereby reducing stress peaks and improving stress distribution. Its advantages include high processing efficiency, low cost, and no need for heating or complex clamping of the part, making it particularly suitable for mass-produced stamped parts. However, it should be noted that vibration aging cannot completely eliminate residual stress and usually needs to be used in conjunction with other methods.
Heat treatment aging is a traditional method for eliminating residual stress. By controlling the heating, holding, and cooling processes, the material undergoes recrystallization or phase transformation, thereby releasing internal stress. In practice, parts are slowly heated to a specific temperature (usually below the phase transition point), held at that temperature for a period of time, and then slowly cooled. During this process, dislocations within the material rearrange, lattice distortion decreases, and residual stress is relaxed. Heat treatment aging is highly effective, but the processing cycle is long, and the parts may deform due to differences in thermal expansion, requiring strict control of process parameters.
Mechanical stretching induces uniform plastic deformation in the parts through preloading, thereby offsetting the original residual stress. For example, applying a reverse tensile force to a bent stamped part can redistribute its internal stress to achieve equilibrium. This method is suitable for regularly shaped, high-strength parts, but the amount of stretching must be precisely controlled to avoid excessive deformation leading to dimensional deviations. Additionally, mechanical hammering can also reduce stress peaks through localized plastic deformation, but it easily introduces new defects on the surface and should be used with caution.
Surface strengthening treatment introduces residual compressive stress on the surface of the part, which can partially offset internal tensile stress, thereby improving the overall stress state. Common methods include shot peening and rolling: shot peening uses high-speed projectiles to impact the surface, forming a hardened layer and a compressive stress zone; rolling, on the other hand, uses rollers to compress the surface metal, causing plastic flow and forming a smooth compressive stress layer. These methods not only eliminate residual stress but also improve the surface hardness and fatigue strength of parts, but appropriate process parameters must be selected based on material properties.
Pulse magnetic treatment is an emerging non-contact stress relief technology. It uses an alternating magnetic field to induce magnetic domain reconstruction and dislocation movement within the metal, promoting the return of atoms to their equilibrium positions. This method requires no heating or mechanical contact, avoiding surface damage and thermal deformation that can occur with traditional methods, making it particularly suitable for high-precision parts. Studies have shown that pulse magnetic treatment can significantly reduce residual stress while improving the magnetic and mechanical properties of materials; however, the equipment cost is high, and it is not yet widely adopted.
Natural aging is the simplest method for eliminating residual stress, allowing the internal stress of the part to release naturally through prolonged static placement. This method requires no additional equipment, but the processing cycle can be as long as months or even years, making it only suitable for high-value parts with no strict delivery deadlines. In actual production, natural aging is often combined with artificial aging to balance efficiency and effectiveness. The elimination of residual stress in metal stamping parts requires comprehensive consideration of part shape, material properties, and production requirements. Mechanical vibration aging and heat treatment aging are currently the most widely used methods; the former is suitable for mass production, while the latter is more thorough. Surface strengthening treatment and pulsed magnetic treatment improve part performance by improving stress distribution or introducing compressive stress. Natural aging, while simple, is inefficient and is usually used as an auxiliary method. In the future, with the development of materials science and intelligent manufacturing technology, the active control of residual stress will become possible, providing more solutions for optimizing the performance of stamped parts.
