Blanking deformation process and cross-section analysis
The blanking deformation process and cross-sectional analysis are crucial components of blanking process research. By delineating the stages of the deformation process and analyzing cross-sectional characteristics in detail, they provide a theoretical basis for mold design, process parameter optimization, and quality control of blanked parts. The three stages of the blanking deformation process—elastic deformation, plastic deformation, and fracture separation—leave distinct characteristic traces on the cross-sectional surface of the blanked part. These traces reflect the material’s behavior at different stages of deformation and are crucial for determining the rationality of the blanking process. In-depth analysis of the relationship between the blanking deformation process and cross-sectional characteristics can help resolve quality issues in blanking production and improve the precision and consistency of stamped parts.
During the elastic deformation stage, the sheet metal deforms primarily through elastic compression and bending. While the cross-section of the blanked part has yet to develop distinct features, the deformation during this stage can influence the subsequent plastic deformation and fracture separation processes. If the gap between the punch and die is too large, the sheet metal will experience significant bending deformation during the elastic deformation stage, causing the stress concentration areas at the punch and die edges to deviate from the center plane of the sheet metal, resulting in uneven subsequent plastic shear deformation. This uneven elastic deformation can leave indirect traces on the cross-section, such as increased inclination or localized depressions. Conversely, if the gap is too small, the sheet metal undergoes less elastic bending deformation, concentrating the stress concentration areas near the cutting edges. This promotes uniform plastic deformation and lays the foundation for a smooth cross-section. Therefore, while the elastic deformation stage does not directly shape cross-sectional features, its influence persists throughout the entire blanking deformation process and is essential for ensuring cross-sectional quality.
During the plastic deformation stage, a bright band is formed on the cross section of the blank. This is the best quality part of the blank section and is characterized by flatness and smoothness. The formation of the bright band is due to the fact that during the plastic shear deformation process of the sheet metal, the material is squeezed by the punch and die, resulting in violent plastic flow, which causes the shear surface to be squeezed flat, forming a smooth area perpendicular to the sheet metal surface. The width of the bright band is related to the plasticity of the material, the gap between the punch and die, and the stamping speed. Materials with good plasticity can produce greater plastic deformation and a larger bright band width; a reasonable gap can make the plastic deformation uniform and the bright band distribution symmetrical; while a higher stamping speed will shorten the plastic deformation time and slightly reduce the width of the bright band. In actual production, the width and uniformity of the bright band are important indicators for evaluating the quality of blanking parts. It is usually hoped that the width of the bright band is as large as possible and evenly distributed to ensure the dimensional accuracy and surface quality of the blanking parts.
During the separation stage, fracture bands and burrs form on the cross-section of the blanked part. The fracture bands are located below (for blanked parts) or above (for punched parts) the bright band and exhibit a rough, slanted appearance. This is due to the irregular crack propagation path during the separation process. The roughness of the fracture band is related to the stability of crack propagation. If the upper and lower cracks meet smoothly, the fracture band is relatively smooth. If the crack deviates during propagation, the band will show noticeable tearing and unevenness. Burrs are another important cross-sectional feature during the separation stage. They form at the edges of the sheet metal due to incomplete crack propagation and partial stretching of the material. The size of the burr is related to the gap between the punch and die, the sharpness of the cutting edge, and the material properties. Excessive or insufficient gaps will increase the size of the burr, while edge wear will make the burr more pronounced. Materials with high plasticity are more prone to burrs. The presence of fracture bands and burrs can affect the assembly performance and safety of the blanked part, so optimizing process parameters is necessary to minimize their impact.
The cross-section of a blanked part also includes a fillet band, located at the outermost layer of the cross-section. This band is formed by bending and stretching the sheet metal edge during the elastic and plastic deformation stages. The size of the fillet band is related to the thickness and plasticity of the sheet metal. The thicker the sheet metal and the greater its plasticity, the larger the fillet band. While the presence of the fillet band has little impact on part precision, it is necessary to control the size of the fillet band in some applications where edge shape is critical, such as in the blanking of bearing rings. Overall, the cross-section of a blanked part consists of four components: the fillet band, the bright band, the fracture band, and the burr. The proportions and characteristics of each component reflect the rationality of the blanking deformation process. By adjusting process parameters such as the punch-die gap, the sharpness of the cutting edge, and the punching speed, the proportions of these components can be altered, thereby improving cross-section quality. For example, maintaining an appropriate gap (generally 5%-10% of the sheet metal thickness) can increase the width of the bright band and reduce the fracture band and burrs. Maintaining a sharp cutting edge can reduce burrs. Properly increasing the punching speed can inhibit crack propagation and improve the quality of the fracture band.
The analysis of the blanking deformation process and cross-section not only helps optimize existing processes, but also provides guidance for the development of blanking processes for new materials and new structural parts. For example, when blanking high-strength steel plates, due to their low plasticity and poor fracture toughness, the plastic deformation stage in the blanking deformation process is short and the fracture separation stage is early, which easily produces large burrs and rough fracture zones. Through cross-section analysis, the die gap and cutting edge angle can be adjusted in a targeted manner, and processes such as heated blanking or stepped blanking can be used to extend the plastic deformation stage and improve the cross-section quality. Therefore, the analysis of the blanking deformation process and cross-section is an important means of studying the stamping process and is of great significance to improving the quality and efficiency of stamping production.
