Characteristics of thinning and deep drawing
Thinning drawing is a special drawing process that is mainly used to reduce the wall thickness of a hollow blank while increasing its height to obtain thin-walled parts with specific dimensions and mechanical properties. Compared with ordinary deep drawing, the notable feature of thinning deep drawing is that during the drawing process, the wall thickness of the blank is significantly reduced, while the diameter changes little or even remains basically unchanged. This process is usually used to produce thin-walled parts with uniform wall thickness and high precision requirements, such as shell casings, cans, high-pressure gas cylinders, etc. It can effectively improve the utilization rate of materials and the strength of parts, and meet the lightweight and high performance requirements of products.
The deformation characteristics of ironing and deep drawing are significantly different from those of ordinary deep drawing. In ordinary deep drawing, the deformation of the material is mainly radial stretching and tangential compression, resulting in a decrease in the diameter of the blank, an increase in the height, and a small change in the wall thickness; in ironing and deep drawing, the deformation of the material is mainly axial stretching and radial compression. The blank is forced through the die under the action of the punch. The working part of the die squeezes the wall thickness of the blank, thinning the wall thickness. At the same time, the material extends axially, causing the height of the part to increase. During the deformation process, the flow direction of the material is mainly axial, and radial flow is strictly restricted. Therefore, the diameter accuracy of the part is high and it can maintain good dimensional stability. In addition, the degree of deformation in ironing and deep drawing is large, and a single deep drawing can achieve a large amount of wall thickness thinning, so the number of deep drawing times can be reduced and production efficiency can be improved.
Ironing and deep drawing place high demands on the die. The precision and surface quality of the die directly affect the quality of the part and the service life of the die. Due to the strong friction and extrusion between the material and the die during the ironing and deep drawing process, the working part of the die needs to have high hardness and wear resistance. It is usually made of high-strength alloy tool steel and undergoes appropriate heat treatment to increase its service life. At the same time, the taper angle and working band length of the die are key parameters in the design of ironing and deep drawing dies. The size of the taper angle affects the flow resistance and deformation uniformity of the material, while the working band length directly affects the amount of wall thickness reduction and the dimensional accuracy of the part, and needs to be accurately calculated and designed according to the requirements of the part. In addition, the guiding accuracy of the die is also very important to ensure the concentricity of the punch and die to avoid uneven wall thickness or cracks in the part due to eccentricity.
During the ironing and drawing process, the stress state of the material is relatively complex. Under the tensile force of the punch, the blank is subjected to axial tensile stress. At the same time, under the extrusion of the die, it is subjected to radial compressive stress and tangential stress. This stress state puts the material in a three-dimensional stress state, which is conducive to improving the plasticity of the material and reducing the occurrence of cracks. However, excessive stress may also cause defects such as wrinkling and cracking in the parts. Therefore, it is necessary to reasonably control the drawing force and the extrusion degree of the die. In actual production, the wall thickness is usually gradually reduced through multiple ironing and drawing. The thinning amount of each drawing should not be too large to avoid excessive deformation and failure of the material. At the same time, annealing treatment is required between each drawing to eliminate the work hardening of the material, restore its plasticity, and ensure the smooth progress of the subsequent drawing process.
Ironing and deep drawing have high production efficiency and material utilization, and can produce thin-walled parts that are difficult to process by ordinary deep drawing. Therefore, it has been widely used in aerospace, automobile manufacturing, weapons industry and other fields. However, this process also has some limitations. For example, it has high requirements for the plasticity of the material. It is usually suitable for metal materials with good plasticity, such as aluminum, copper, and low-carbon steel. For high-strength, low-plasticity materials, ironing and deep drawing are more difficult and special process measures need to be adopted. In addition, the equipment investment for ironing and deep drawing is large, and special drawing equipment and high-precision molds are required. Therefore, the application cost in small-batch production is relatively high. With the continuous development of manufacturing technology, the ironing and deep drawing process is also constantly being optimized. For example, computer simulation technology is used to optimize mold parameters and process parameters, improve the quality and production efficiency of parts, and expand its scope of application.
