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Design of working part of drawing die

Convex and female mold structure design

The structure of the drawing punch and the die depends on the shape and size of the workpiece, the drawing method, the number of drawing processes, and other process requirements. Different structure forms have an influence on the drawing deformation, the degree of deformation, and the quality of the product. Different influences. The structure of common convex and concave molds is as follows.

Structure form of drawing die without pressing material

Figure 1-2 shows the convex and concave die structure used in one-time deep drawing without a blank holder. The arc-shaped die shown in Figure 1-2(a) has a simple structure and convenient processing, which is commonly used. The structure of the deep drawing concave die. The tapered die and involute die shown in Figure 1-2 (b) and Figure (c) is advantageous in resisting instability and wrinkling, but the processing is complicated, and they are mainly used for drawing parts with a small drawing coefficient. Figure 1-2(d) shows the isometric structure.

Structure form of drawing die with pressing material

Figure 1-3 shows the structure of the male and female molds with blank holders. The male and female molds shown in Figure 1-3 (a) have rounded corners and are used for drawing with a diameter d≤100mm. Pieces. The convex and concave molds shown in Figure 1-3(b) have a taper angle structure and are used to draw deep-drawn parts with a diameter d≥100mm. The use of such a punch and die with a taper angle not only improves the flow of the metal, reduces the deformation resistance, the material is not easy to thin, and other general tapered die features, but also can reduce the degree of repeated bending deformation of the blank and improve the part side The quality of the wall makes it easy to locate the blank in the next process.

Regardless of the structure used, attention should be paid to the coordination of the shape and size of the punching dies in the two previous processes, so that the shape of the semi-finished product obtained in the previous process is conducive to the forming of the subsequent process. For example, the shape and size of the blank holder should be the same as the corresponding part of the punch in the previous process, and the taper angle α of the deep drawing die should also be consistent with the taper angle of the punch in the previous process.

In order to make the bottom of the part flat after the last drawing, if it is a punch with a rounded structure, the center of the corner radius of the last drawing punch should be located on the same line as the center of the second penultimate drawing punch’s corner radius. Centerline. If it is an oblique die structure, the oblique line at the bottom of the punch of the penultimate process should be tangent to the fillet radius of the last punch.

Regardless of whether the drawing die adopts a pressing device, in order to facilitate the removal of the workpiece, the drawing punch should be drilled with air holes, the dimensions of which are shown in the table below.

Drawing die gap

The drawing die gap refers to the double-sided gap between the convex and concave dies. The size of the gap has a great influence on the drawing force, the quality of the drawn part, and the life of the die. When the clearance is small, the deep-drawn part has a small spring back, the sidewall is straight and smooth, the quality is better, and the precision is higher.

If the gap value is too small, the drawing force will increase, resulting in serious thinning of the workpiece, or even cracking, severe friction and wear between the mold surfaces, and reduced mold life. When the gap is too large, the drawing force is reduced and the life of the die is increased, but the blank is prone to wrinkles, the taper of the drawn part is large, and the precision is poor.

Therefore, the gap value of the drawing die should be reasonable, and the blank holder condition, the number of drawing times, and the accuracy of the workpiece should be considered when determining. The principle is to consider not only the tolerance of the sheet material itself but also the thickening phenomenon of the sheet material. The value of the gap is generally slightly larger than the thickness of the blank.

Deep drawing without pressing device

For drawing dies without pressing the device, the gap between the convex and concave dies can be calculated by the following formula.

Z/2=(1~1.1)t_max

In the formula, Z/2—Drawing convex and concave die unilateral clearance;

t_max—-The maximum limit size of the thickness of the sheet;

1~1.1—-For the first and middle drawing or the deep drawing parts that do not require high dimensional accuracy, take the larger value; for the last drawing or the drawing parts that require high dimensional accuracy, take the formula The smaller value.

Deep drawing with pressing device

For drawing die with pressing device, the gap between convex and concave die is shown in Table 1-2.

• When the external dimensions and tolerances of the parts are required, as shown in Figure 1-4 (a), based on the die, according to the law of wear, the basic dimensions of the die are:

D _concave = (D-0.75Δ) 0^+δ concave

The basic dimensions of the punch are:

D _convex = (D-0.75Δ-Z) 0_-δ convex

D _convex = (d+0.4Δ) 0_{-δ convex}

• When the internal dimensions and tolerances of the parts are required, as shown in Figure 1-4 (b), based on the punch, according to the law of wear, the basic dimensions of the die are

D _concave=(d+0.4Δ+Z) 0^+δ _concave

Where D—The maximum limit size of the outer diameter of the part, mm;

d—-The minimum limit size of the inner diameter of the part, mm;

Δ—-Tolerance of parts;

Z—Double-sided gap of drawing die, mm;

δ _convex, δ _concave—-the manufacturing tolerances of convex and concave molds are selected according to the tolerance of the workpiece. When the workpiece tolerance is above IT13, δ _convex and δ _concave can be taken according to IT6~8; when the workpiece tolerance is below IT14, δ _convex and δ _concave can be taken according to IT10.

Typical structure of drawing die

The structure of the drawing die is one of the most basic contents in the design of the drawing die. The drawing dies can be divided into first drawing dies and subsequent drawing dies according to the process sequence; according to the equipment used, they can be further divided into drawing dies for single-action presses, drawing dies for double-action presses and three-action presses Drawing dies for presses; according to the combination of processes, it can be divided into single-process drawing dies, composite dies and continuous drawing dies;

In addition, it can also be divided into drawing dies with and without a crimping device according to the presence or absence of the crimping device. Here are some typical drawing die structures.

First drawing die

Figure 1-5 shows the first drawing die without a blank holder. The semi-finished workpiece is positioned by the positioning plate 5, and the drawing punch 2 runs downwards until the drawing punch presses the sheet into the drawing die 3 to form a workpiece, and the drawing ends. The drawing punch 2 runs upward, and the deep drawing is pulled off by the unloading ring 4 at the lower part of the drawing die. Because the drawing punch 2 has to go deep below the drawing female die 3, the die is only suitable for shallow drawing. In order to prevent the workpiece from sticking to the punch and difficult to remove after drawing, drawing punch 2 is provided with vent holes.

This type of mold has a simple structure and is often used for deep drawing when the sheet metal has good plasticity and relatively large thickness.

Figure 1-6 shows the first drawing die with the edge holding device on it. Before deep drawing, the semi-finished workpiece is positioned by the positioning plate 6. When drawing, the punch 10 moves downwards, and the semi-finished workpiece is firstly pressed flatly on the surface of the drawing die 7 by the press ring 5 due to the action of the compressed spring 4, the punch 10 continues to move downwards, and the spring 4 continues to be compressed. , Until the workpiece is formed by deep-drawing.

At the end of the drawing, the punch moves upwards, and the blank holder returns under the action of the spring to scrape off the workpiece wrapped on the drawing punch. This kind of first drawing die with an elastic blanking device is the most widely used first drawing die structure, and the blank holding force is generated by the compression of elastic elements. The punch of this kind of mold structure is relatively long, which is only suitable for workpieces with a small drawing depth. At the same time, due to the limited space position of the upper die, it is impossible to use a large spring or rubber, so the upper pressing device has a small pressing force, and this device is mainly used in occasions where the pressing edge is not large.

Each subsequent drawing die

Due to the limited drawing coefficient of the first deep drawing, many parts cannot meet the requirements in size and height after the first deep drawing. They also need to go through the second, third, or even more times of deep drawing, which are collectively referred to as the subsequent times of drawing. deep. The blanks used for each subsequent drawing are semi-finished cylindrical parts or tapered parts that have been drawn for the first time, instead of flat blanks. Therefore, the positioning device and the blanking device are completely different from the first drawing die.

There are three commonly used methods for positioning the drawing dies in each process in the future: the first is to use a specific positioning plate; the second is to process a cavity on the die for the positioning of the semi-finished product, as shown in Figure 1-2; The third type is to use the inner hole of the semi-finished product to locate by the shape of the punch or the shape of the blank holder. The edge holding device used at this time is no longer a flat structure, but a cylindrical or conical structure.

As shown in Figure 1-7, the blank is a semi-finished cylindrical part with a certain size after being drawn through the previous process. After being placed on the concave mold 13 of the mold, the drawing punch 11 descends to contact the blank for deep drawing until it is drawn out. For the workpiece, after the drawing is finished, the drawing punch moves upward, and the deep part is pulled off by the step (discharge neck) at the lower part of the die 13.

Blanking and deep drawing compound die

As shown in Figure 1-8, it is a blanking and deep drawing compound die. The mold generally uses strips as blanks, so a guide mechanism is required on the mold. The top surface of the drawing punch 19 should be lower than the top surface of the blanking die 4 so that when the mold is working, the material is first blanked and then drawn.

At the same time, the amount of sharpening of the cutting edge of the die needs to be reserved. During drawing, the press air cushion is used to hold the edge through the ejector pin 2 and the blank holder 3. After the drawing is completed, the workpiece is ejected by it, leaving the workpiece in the convex and concave mold 17, and finally, by the punching rod 15, the pusher block 18 is pushed out, and the fallen waste is discharged by the rigid discharge plate 20.