Design of compound die for punching, blanking, cutting and bending
Punching, blanking, notching and bending compound die design is an efficient integrated forming die technology, which can complete punching, blanking, notching and bending processes in one set of dies, greatly improving production efficiency. It is suitable for batch production of small and medium-sized complex parts, such as electrical components, auto parts, etc. The core of this type of die design lies in the reasonable arrangement and coordination of the processes, and it is necessary to ensure that each process is carried out in an orderly manner in one stamping stroke to avoid mutual interference. In the early stage of design, it is necessary to analyze the structural characteristics of the parts in detail, including the location and number of punching holes, the outer dimensions of blanking, the depth and distribution of the notches, and the angle and radius of the bend. For example, for a part with 3 holes of 5mm diameter, an outer dimension of 50mm×30mm, two 90° bends and 4 notches, the order of each process needs to be accurately calculated . Usually, blanking is done first to ensure the shape, then punching, then notching, and finally bending, so as to reduce the impact of material deformation on subsequent processes. At the same time, the punching force required for each process needs to be calculated based on the thickness of the material (such as 1-3mm Q235 steel plate) and mechanical properties. The total punching force is the sum of the forces of each process, and a safety factor of 10%-15% is taken into account to select the appropriate press tonnage.
The overall structure of the mold consists of two major parts: the upper mold and the lower mold, including key components such as the punch, the die, the convex and concave molds, the positioning device, the unloading device and the guide device. The convex and concave molds are the core parts of the compound mold, which have the dual functions of the blanking die and the punching die. They are usually made of Cr12MoV material, and the hardness reaches HRC58-62 after quenching to ensure sufficient strength and wear resistance. The blanking die and the punching die are installed at the corresponding positions of the upper mold and the lower mold respectively, and the gap between them needs to be strictly controlled. The blanking gap is generally 8%-12% of the material thickness, and the punching gap is 5%-8% of the material thickness to ensure the cross-sectional quality of the blanked parts. The cutting and bending mechanisms need to be set in appropriate positions, the cutting edges of the cutting punch and the die need to be sharp, and the fillet radius of the bending punch and the die needs to be determined according to the bending radius of the part, which is usually 0.1-0.2mm larger than the required radius of the part to compensate for the rebound of the material. The positioning device usually adopts a combination of a stop pin and a guide plate to ensure the accurate position of the blank in the mold and prevent part size deviation due to inaccurate positioning.
The coordination and interference avoidance of each process are the key links of the design. During the mold closing process, the blanking process is first carried out to separate the shape of the part from the blank; then the punching punch moves downward to complete the punching; then the notching punch performs the notching operation to prepare for the subsequent bending; finally, the bending punch and the die cooperate to complete the bending forming. In order to achieve this orderly process, the length difference of each punch needs to be reasonably designed. The length of the blanking punch and the die is the longest, followed by the punching punch, then the notching punch, and the shortest is the bending punch. The length difference is determined according to the stroke of each process, generally between 5-10mm. At the same time, a reliable unloading device should be set up. The upper die adopts an elastic unloading plate and the lower die adopts a rigid top device to ensure that after the stamping is completed, the part can be smoothly separated from the punch and the die to avoid jamming. For the bending process, a pressing device is also required to prevent the material from shifting and wrinkling during the bending process. The size of the pressing force should be moderate, which can be achieved by adjusting the preload of the spring.
The guiding and precision assurance system is crucial to the service life of the mold and the quality of the parts. The compound mold usually adopts a rigid guide of the guide pin and guide sleeve. The clearance between the guide pin and the guide sleeve is controlled at 0.01-0.03mm to ensure that the upper and lower molds are accurately aligned during the stamping process to avoid dimensional deviation of the parts and the phenomenon of mold gnawing. The diameter of the guide pin is selected from 20-30mm according to the size of the mold, and the length must ensure that when the mold is opened to the maximum, no less than 1/3 of the length of the guide pin remains in the guide sleeve. The mounting base of the mold needs to be precisely machined, and the flatness error is controlled within 0.05mm/m to ensure the accuracy of the mold installation on the press. In addition, the installation position accuracy of each working part (punch, die, convex and concave die, etc.) needs to be strictly controlled, and the pin positioning and bolt tightening methods are adopted to ensure that the coaxiality and verticality errors do not exceed 0.02mm.
The debugging and maintenance of the mold is an important guarantee to ensure the stability of production. In the mold trial stage, it is necessary to first run it without load to check whether the movement of each component is flexible and whether there is any jamming phenomenon; then use waste materials for trial punching to observe the forming quality of the parts, including whether the blanking shape is complete, whether the punching position is accurate, whether the incision depth meets the requirements, and whether the bending angle meets the standard. If there is a deviation in the bending angle, it can be corrected by adjusting the angle of the bending punch or die; if there are burrs in the punching, the gap between the punching punch and the die needs to be ground. In daily maintenance, the iron filings and oil stains on the surface of the mold should be cleaned regularly, and the wear of the cutting edge should be checked every 1000 times of work. When the cutting edge is cracked or the wear exceeds 0.2mm, it needs to be repaired or replaced in time. The guide device should be regularly filled with grease to ensure that it is well lubricated. The guide pin and guide sleeve should be tested for accuracy every 5000 times of work to ensure that the guide accuracy meets the requirements. When stored for a long time, anti-rust oil should be applied to the working surface of the mold, and the mold should be placed on a flat pad to avoid deformation under pressure.
