Wrinkling during the stamping process of stainless steel stamping parts not only affects the appearance quality of the product but may also reduce structural strength and dimensional accuracy, even leading to part scrap. The essence of wrinkling is that during plastic deformation, localized areas of the material become unstable due to compressive stress, forming wavy wrinkles. To reduce this phenomenon, comprehensive optimization from multiple dimensions is needed, including material properties, process parameters, mold design, lubrication conditions, and operating procedures.
Material selection is fundamental to controlling wrinkling. The elongation, yield strength, and anisotropy coefficient of stainless steel directly affect its stamping performance. Materials with lower elongation are more prone to wrinkling due to insufficient stretching during deformation. Therefore, stainless steel grades with higher elongation, such as austenitic stainless steels like 304 and 316, should be prioritized, as their elongation is generally superior to martensitic or ferritic stainless steels. Furthermore, the uniformity of material thickness is also crucial; excessive thickness deviation can lead to localized stress concentration, exacerbating the risk of wrinkling. If the material itself has internal stress or surface defects (such as scratches or oxide scale), it can also cause stress concentration during stamping. Therefore, strict inspection of raw materials is necessary, and pretreatment (such as stress relief annealing and surface polishing) is required when necessary.
Proper setting of process parameters is key to reducing wrinkling. Stamping speed, blank holder force, and drawbead design are the three core parameters. Excessive stamping speed can lead to uneven material flow, excessively high local deformation rates, and instability; too slow a speed may cause material accumulation due to increased friction. Therefore, the optimal stamping speed range must be determined experimentally based on material properties and part shape. Blank holder force is the core parameter for controlling material flow. Insufficient blank holder force allows material to flow freely into the die cavity, leading to wrinkling; excessive blank holder force increases frictional resistance and may even tear the material. In actual production, elastic blank holder devices or segmented blank holder structures can be used to dynamically adjust the blank holder force according to the different needs of the deformation area. Draw beads, by altering the material flow path and resistance, can effectively balance the degree of deformation and reduce wrinkling tendency. Their position, quantity, and height need to be optimized using simulation software based on the part shape.
Die design plays a decisive role in wrinkling control. The punch-die clearance, fillet radius, and structural rigidity of the die directly affect the material deformation state. Too small a clearance increases frictional resistance, leading to difficulty in material flow; too large a clearance may cause wrinkling due to free material flow. Generally, the clearance value should be slightly larger than the material thickness, with the specific value determined experimentally. Too small a fillet radius can cause excessive stretching of the material at the bend, increasing the risk of wrinkling; too large a radius may lead to material accumulation due to insufficient deformation. Therefore, the punch fillet radius is generally 8-10 times the material thickness, and the die fillet radius is 10-12 times. Furthermore, insufficient die rigidity can cause elastic deformation during stamping, altering the clearance distribution and thus causing wrinkling. Therefore, it is necessary to ensure the structural strength of the die, using high-strength die steel or adding reinforcing ribs when necessary.
Lubrication is an auxiliary means of reducing wrinkling. Good lubrication reduces the coefficient of friction between the material and the die, decreases frictional resistance, and makes material flow more uniform. Lubricants must possess extreme pressure anti-wear properties, cooling properties, and adhesion to withstand the high-pressure, high-speed stamping environment. In actual production, lubricating oil, grease, or solid lubricants (such as graphite or molybdenum disulfide) can be used; the specific choice depends on the material characteristics and process requirements. The application method of the lubricant also needs attention. Over-coating may result in an excessively thick oil film on the material surface, affecting dimensional accuracy; uneven coating may cause wrinkling due to excessive local friction. Therefore, it is recommended to use an automatic spraying device to ensure that the lubricant evenly covers the material surface.
Operating procedures and process monitoring are crucial for ensuring stamping quality. Operators must strictly adhere to process specifications to avoid wrinkling caused by improper operation (such as incorrect adjustment of blank holder force or sudden changes in stamping speed). Furthermore, real-time monitoring of the stamping process is necessary. Sensors should collect parameters such as pressure and displacement, and a visual inspection system should be used to observe the material flow state, promptly identifying wrinkling tendencies and adjusting process parameters. For complex-shaped stainless steel stamping parts, step-by-step stamping or multiple drawing processes can be used to break down large deformations into multiple smaller deformations, reducing the degree of deformation in a single step and thus reducing the risk of wrinkling.
Reducing wrinkling during the stamping process of stainless steel stamping parts requires coordinated optimization of materials, processes, dies, lubrication, and operations. By selecting materials with high elongation, setting appropriate process parameters, optimizing die design, improving lubrication conditions, and strictly adhering to operating procedures, stamping quality can be significantly improved, wrinkling defect rates reduced, and the high precision and high quality requirements of high-end manufacturing for stainless steel stamping parts met.
