Many people are deterred from drawing dies because not only do many factors need to be considered when designing drawing dies, but more importantly, they often cannot be formed in one go during the die trial, and they have to go through multiple die repairs to achieve the desired result. Therefore, it is of great benefit to the design of drawing dies to accumulate experience in practice. 1. Material: SPCC-SD deep stamping steel Good materials are half of the success, and they must not be ignored for drawing. The cold-rolled thin steel plates for drawing mainly include 08Al, 08, 08F, 10, 15, and 20 steels. Among them, the largest amount is 08 steel, which is divided into boiling steel and killed steel. Boiling steel has a low price and good surface quality, but it has serious segregation and a tendency to "strain aging". It is not suitable for parts with high requirements for stamping performance and strict appearance requirements. Killed steel is better, with uniform performance but higher price. The representative grade is aluminum killed steel 08Al. Foreign steel has used Japanese SPCC-SD deep stamping steel, and its tensile performance is better than 08Al. Mold experts scan and add my WeChat Experience 1: When the customer's requirements for materials are not very strict and repeated mold trials cannot meet the requirements, you can try another material. 2. Determination of blank size: Confirmation of blank size
The blank diameter of a simple rotating body stretching part changes in the non-thinning stretching, but it is basically very close to the original thickness. It can be calculated based on the principle that the blank area is equal to the stretching part area (if trimming is required, trimming allowance must be added). However, the shape and process of the stretching part are often more complicated, and sometimes it is necessary to thin and stretch. Although there are many 3D software available for unfolding calculation, its accuracy cannot meet the requirements 100%. Solution: Test material. A product has to go through multiple processes, and the first process is generally the blanking process. First, the unfolding material calculation should be carried out to have a general understanding of the shape and size of the blank in order to determine the overall size of the blanking die. Do not process the convex and concave die sizes of the blanking die after the mold design is completed. First, use wire cutting to process the blank (if the blank is large, it can be milled by a milling machine and then clamped), and after repeated experiments in the subsequent stretching process, the size of the blank is finally determined, and then the convex and concave dies of the blanking die are processed. Experience 2: Invert the process, try the stretching die first, and then process the blank's blanking edge size, which will get twice the result with half the effort. 3. Stretching coefficient m. Stretching coefficient of hardware die stretching die
The stretching coefficient is one of the main process parameters in the stretching process calculation, and it is usually used to determine the order and number of stretching. There are many factors that affect the stretching coefficient m, including material properties, relative thickness of the material, stretching method (referring to whether there is a blank holder), number of stretching times, stretching speed, convex and concave die corner radius, lubrication, etc. The calculation and selection principles of the stretching coefficient m are the key points introduced in various stamping manuals. There are many methods such as extrapolation, table lookup, and calculation. I also selected according to the book, and there is nothing new. Please read the book. Experience 3: The relative thickness of the material, the stretching method (referring to whether there is a blank holder ring), and the number of stretching times are not easy to adjust when repairing the mold. Be careful!! It is best to ask a colleague to calibrate it when selecting the stretch coefficient m. Mold experts scan and add my WeChat
4. Apply lubricating oil on the die, or put a film bag on the thin plate. Experience 4: When encountering stretch cracking, apply lubricating oil on the die (do not apply it on the punch), and cover the workpiece with a 0.013-0.018mm plastic film on the side of the die. 5. Workpiece heat treatment heat treatment workshop
During the stretching process, the workpiece undergoes cold plastic deformation, resulting in cold work hardening, which reduces its plasticity, increases its deformation resistance and hardness, and coupled with unreasonable mold design, intermediate annealing is required to soften the metal and restore plasticity. Note: In general processes, intermediate annealing is not necessary. After all, it will increase costs. You have to choose between adding processes and adding annealing. Use with caution! Annealing generally uses low-temperature annealing, that is, recrystallization annealing. There are two things to pay attention to during annealing: decarburization and oxidation. Here we mainly talk about oxidation. After the workpiece is oxidized, there will be oxide scale, which has two harms: it makes the effective thickness of the workpiece thinner and increases the wear of the mold. When the company's conditions are not met, ordinary annealing is generally used. In order to reduce the generation of oxide scale, the furnace should be filled as much as possible during annealing. There are also some other methods: 1. When there are few workpieces, they can be mixed with other workpieces (prerequisite: the annealing process parameters should be basically the same) 2. The workpiece is placed in an iron box and welded before loading the furnace. In order to eliminate the oxide scale, pickling treatment should be carried out according to the situation after annealing. When the company's conditions are met, nitrogen furnace annealing, that is, bright annealing, can be used. If you don't look closely, the color is almost the same as before annealing. Experience 5: For metals with strong cold work hardening or when cracks occur in the test mold and there is no other way, add an intermediate annealing process. 6. A few additional points: 1. The dimensions on the product drawing should be marked on one side as much as possible to make it clear whether it is the external dimension or the inner cavity dimension. The internal and external dimensions cannot be marked at the same time. If there are such problems in the drawings provided by others, you should communicate with them. If they can be unified, then unify them. If they cannot be unified, you must know the assembly relationship between the workpiece and other parts. 2. For the last process, the workpiece size is outside, mainly based on the die, and the gap is obtained by reducing the punch size; the workpiece size is inside, mainly based on the punch, and the gap is obtained by increasing the die size; 3. When designing the radius of the corners of the punch and die, use the smallest allowable value possible to facilitate subsequent mold repair. 4. When judging the cause of the workpiece cracking, you can refer to: the cracks caused by poor material quality are mostly jagged or irregular in shape, and the cracks caused by the process and mold are generally neater. 5. "More wrinkles, less cracks", according to this principle, adjust the flow conditions of the material. Methods include adjusting the pressure of the blank holder, increasing the drawing ribs, trimming the corner radius of the punch and die, and cutting the process opening on the workpiece. 6. In order to ensure wear resistance and prevent stretching scratches, the punch and die and the blank holder must be quenched, and hard chrome plated if necessary. What do you think of this? Leave a message below and let everyone comment together
