1. Materials: Good materials are half the battle. Stretching cannot be ignored. Cold rolled steel plate is mainly composed of 08Al.08.08F.10.15.20 steel, of which 08 steel is the most widely used, divided into boiling steel and killed steel. The price of boiling steel is low and the surface quality is good, but the segregation is serious and there is a tendency to adapt to aging. Not suitable for parts with high stamping performance and strict appearance requirements.
2. Determination of blank size: The blank diameter of a simple rotating body drawing part does not become thinner during the drawing process. Although the thickness of the material has changed, it is basically very close to the original thickness. It can be calculated according to the principle of the area of the blank and the area of the drawn part (if there is trimming, the trimming allowance must be increased. However, the shape and process of the deep-drawn part are often complicated, sometimes thinning and stretching. Although there are many three-dimensional The software can calculate the material, but its accuracy is less than 100%.
The solution: material testing. A product part should go through multiple processes, the first of which is usually the process of material transportation.
First perform material calculations to have a rough idea of the shape and size of the blank to determine the overall dimensions of the material delivery die. After the mold design is completed, do not deal with the convex and concave die dimensions of the material conveying die. First use wire cutting and machine the blanks (when the blanks are large, they can be milled with a milling machine and then repaired). After trial and error in the subsequent stretching process, half the size of the feed conveyor die was finally determined.
3. The drawing coefficient m is one of the main process parameters in the calculation of the drawing process, and is often used to determine the drawing sequence and drawing times. There are many factors that affect the elongation coefficient m, including the properties of the material. The relative thickness of the material. Drawing method (with or without a blank holder). number of stretches. stretching speed. Punch and concave die fillet radius. The calculation and selection principle of the tensile factor m is the focus of introduction in various stamping manuals, including calculation. View the form. calculation and many other methods.
The relative thickness of the material. Drawing method (with or without a blank holder). In the process of mold repair, the number of stretches is not easy to adjust, so be careful! When you choose the stretch factor m, it is better to find another colleague. Grease the concave die or place a film bag on the sheet.
4. When stretching and cracking, apply lubricating oil on the die (do not apply it on the punch), and cover the plastic film of 0.013-0.018 mm with the die.
5. During the stretching process, due to the cold plastic deformation, the parts are cold hardened, the plasticity is reduced, the deformation resistance and hardness are increased, the mold design is unreasonable, and intermediate annealing is required to soften the metal and restore the plasticity. Note: annealing is not necessary in the general process. After all, in order to increase the cost, choose to increase the process and increase the amount of annealing, and use it with caution! Annealing generally adopts low temperature annealing, that is, crystallization annealing.
Two points should be noted during the annealing process: carbon and oxidation. It’s mostly about oxidation. Oxidized skin has two hazards: thinning the effective thickness of the workpiece and increasing die wear. When the company’s conditions are not met, ordinary annealing is generally used. To reduce the production of oxidized skin, the furnace should be filled as much as possible during the annealing process. I also used the soil method: 1. The workpiece can be mixed with other workpieces (premise: the annealing process parameters should be basically the same) 2. The workpiece is put into the iron box for welding, and then the electric furnace is installed. To eliminate scale, the furnace should be filled as much as possible during the annealing process.
When the company conditions are met, nitrogen furnace annealing, that is, bright annealing, can be used. Don’t look closely, it’s almost the same color as it was before annealing. Add the intermediate annealing process when there is no other way to deal with cracks in cold-hardened metal or die tests.
The above is about the mold processing of the drawn parts. When judging the cause of cracks in the processing of tensile parts, it can be referred to: the cracks caused by poor material quality are mostly serrated or irregular in shape, and the cracks generated by the process mold are generally neat. To ensure wear resistance and prevent tensile scratches, punches and dies and blank holders must be hardened and, if necessary, plated with hard chrome. Hope the above content can be helpful to readers.Read More →