(1) The designed stamping parts must meet the product use and technical performance, and can be easily assembled and repaired.
(2) The stamped parts designed must be beneficial to improve the utilization of metal materials, reduce the variety and specifications of materials, and minimize the consumption of materials. Use low-cost materials wherever possible, and make parts as free as possible and with less waste.
(3) The designed stamping parts must have a simple shape and a reasonable structure, which is beneficial to simplify the mold structure and simplify the number of processes, that is, to complete the processing of the entire part with the least and simplest stamping process, reduce the processing by other methods, and facilitate the stamping operation. It is easy to organize mechanization and automated production to improve labor productivity.
(4) Designed stamping parts, under the condition of ensuring normal use, try to make the dimensional accuracy grade and surface roughness grade requirements lower, and it is beneficial to product interchange, reduce waste and ensure product quality stability.
(5) The designed stamping parts should be used to process the existing equipment, process equipment and process as much as possible, and to facilitate the extension of the service life of the die.
1, adhesion, scratches: due to the material rubbing with the punch or die to appear on the surface of the workpiece or mold;
2, burr: mainly occurs in the shearing die and blanking die, the gap between the cutting edge or large or small will produce burrs;
3, line offset: when the part is formed, the part that first contacts the mold is squeezed and forms a line;
4, convex and concave: the unwinding line has foreign matter (iron filings, rubber, dust) mixed into the convex and concave;
5, zigzag: due to uneven stress, poor drawbead matching or poor control of the slider of the press, etc., causing tortuosity and strain of the r-angle or embossed part of the workpiece;
6, wrinkles: due to poor adjustment of the slider of the press, low precision of the press, improper adjustment of the air cushion pressure, large punch or r parts caused by wrinkles at the edge or r.
7. Other specific problems: In daily production, there will be cases where the punching size is too large or too small (may exceed the specification) and the difference from the size of the punch is large, except for the design dimensions of the forming convex and concave molds. In addition to factors such as machining accuracy and blanking clearance, it should be considered from the following aspects.
(1). When the cutting edge is worn, the tensile stress of the material increases, and the tendency of the stamping parts to turn and twist is increased. When the material is turned, the punch size will become smaller.
(2). The strong pressure on the material causes plastic deformation of the material, which will lead to a larger punching size. When the strong pressure is reduced, the punching size will become smaller.
(3). The shape of the end of the punch edge. If the end portion is chamfered or curved, the punching force is less likely to cause turning and twisting due to the slowing of the punching force, and therefore, the punching size will become larger. When the end of the punch is flat (no bevel or arc), the punch size will be relatively small.
8. Method for suppressing the turning and twisting of stamping parts
(1). Reasonable mold design. In the progressive die, the arrangement of the blanking sequence may affect the accuracy of the forming of the stamping. For the blanking of the small parts of the stamping parts, generally, a large area of punching and cutting is arranged, and then a small area of punching and cutting is arranged to reduce the influence of the punching force on the forming of the stamping parts.
(2). Squeeze the material. Overcoming the traditional mold design structure, the material gap is opened on the unloading plate (that is, when the mold is closed, the material can be compacted. The key forming part, the unloading plate must be made into an inlaid structure to facilitate the long solution. The time stamping causes the grinding (pressure) loss generated at the pressing portion of the unloading plate, and the material cannot be pressed.
(3). Add a strong pressure function. That is, the thickening size of the pressing portion of the unloading insert (normal unloading insert thickness H+0.03 mm) is used to increase the pressure on the material of the concave mold side, thereby suppressing the turning and twisting deformation of the stamping part during punching.
(4). The end of the punch edge is trimmed or curved. This is an effective way to reduce the buffering power. By reducing the cushioning force, the tensile force on the material of the die side can be alleviated, thereby suppressing the effect of turning and twisting the stamping part.
(5). In the daily mold production, attention should be paid to maintaining the sharpness of the punching and concave die edge. When the blanking edge is worn, the tensile stress of the material will increase, and the tendency of the stamping material to turn and twist will increase.
(6). Unreasonable punching gap or uneven gap is also the cause of the turning and twisting of the stamping parts, which needs to be overcome.
GB/T13914-2002 Stamping Dimensional Tolerance specifies the dimensional tolerances of stamped parts. Dimensional tolerances are specified for flat stampings and formed stampings, respectively. The dimensional tolerance values of the stamped parts are related to the dimensions of the stamped part and the thickness of the sheet, and on the other hand to the level of accuracy.
Flat stamping part dimensional tolerance: divided into 11 grades, denoted by ST1 to ST11, where ST represents the flat stamping part dimensional tolerance, and the tolerance grade code is represented by Arabic numerals. The accuracy level from ST1 to ST11 is sequentially lowered.
Forming stamping dimensional tolerances: Forming stampings are divided into 10 precision grades, denoted by FT1 to FT10, where FT is the dimensional tolerance of the formed stampings and Arabic numerals are the tolerance grades. The accuracy level from FT1 to FT10 is sequentially reduced.
Stamping part limit deviation: the hole size press deviation is 0, the upper deviation is the lower deviation plus the dimensional tolerance; the shaft size specifies the upper deviation as the basic deviation, the value is 0, and the lower deviation is the upper deviation minus the dimensional tolerance. The upper and lower deviations of the hole center distance, the hole margin, the length of the bending, the drawing, and the like are specified as half of the dimensional tolerance.