JP2009090318A - Method of deep-drawing square tube made of metal plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of deep-drawing a square tube made of a metal plate improving productivity by fastening forming speed while taking the conditions of a die, etc. into consideration when applying the deep drawing of the square tube near the limit drawing ratio to a blank. <P>SOLUTION: When performing the deep drawing of the square tube by forcing a punch into the metal plate to be worked fixed with a die and a blank holder, the blank the corner parts of which are cut is used. Under a condition that there is no bead having inflow inhibitory action of a flange material of straight side parts in the straight side parts between the die and the blank holder, punch forcing speed is fastened in the early stage of the working and the punch forcing speed is decreased compared with the speed in the early stage of the working at the point of time before the forcing position of the punch reaches the position of 2/3×forming height. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a square tube deep drawing method for a metal plate in which the forming speed after the middle stage of processing during drawing is slowed to improve deep drawing formability.

As a method of manufacturing a seamless bottomed container such as a cylinder, square tube, or hemisphere from a thin metal plate material, a method of deep drawing using a punch, a die, or an alternative tool is often used. Has been.
In the deep drawing method, a pressing device is used, and the blank is punched by fixing the thin plate blank to be processed on the die of the press machine with a blank holder and lowering and raising the punch while applying a pressing force to the blank holder. It is transformed into a shape.
And as a press system of a press machine, conventionally, two systems of a hydraulic press and a mechanical press are adopted.

The hydraulic press is suitable for deep drawing because it can be molded at low speed, but its productivity is low. On the other hand, the mechanical press has an advantage of excellent productivity because of its high processing speed. On the other hand, if the processing speed is high, there is a drawback that the material to be processed tends to crack. For this reason, in order to improve deep drawing workability with respect to the mechanical press, a link motion press is also used in which a link mechanism is provided to reduce the processing speed during drawing (for example, see Non-Patent Document 1).
Furthermore, recently, as can be seen in, for example, Patent Document 1, a servo press capable of arbitrarily setting a slide motion using an AC servo motor as a drive source is also used.
Nakada Hiroyasu, “Theory and Practice of Press”, Corona Co., Ltd., February 20, 1973, p.171 JP 2002-263742 A

  By the way, there is a crank motion press using a crank mechanism as a typical mechanical press. The forming speed in the crank motion press, that is, the moving speed of the slide to which the die or punch is detachably attached, commonly called the sliding speed, is the fastest in the middle of the moving length of the slide on the mechanism. And it becomes slow as it approaches the bottom dead center, and the speed becomes zero at the bottom dead center. Therefore, when deep drawing is to be performed, deep drawing is started from a position higher than the bottom dead center, so that the slide speed at the initial stage of processing is increased and processing cracks are likely to occur.

A link mechanism is a mechanism that can achieve an ideal speed within a specific mechanical range with respect to the crank mechanism. There is a link motion press that uses this link mechanism to smoothly change the slide speed from high speed to low speed, perform processing at the speed suitable for processing, and increase it after processing.
The link motion press can improve the drawability or the formability by utilizing the speed dependency of the press work. However, characteristics such as slide displacement and speed change of the link motion press are usually determined by the structure and size ratio of the link. For this reason, the normal slide motion has only one pattern, and there is a limit to cope with all the drawing processes of various depths.

Up to now, it is said that it is better to have a lower slide speed during drawing, and even with link motion etc., the slide speed is slow until the bottom dead center, that is, until the drawing process is completed, and slides after the bottom dead center is passed. It was a motion that speeded up.
Servo presses that have recently been used more frequently than mechanical presses use AC servo motors as the drive source, so they can arbitrarily perform forward rotation, reverse rotation, stop, speed switching, etc. . In addition, by reducing the processing speed at the time of punching, reduction of noise and improvement of mold life can be expected.

In the servo press, the slide motion can be set arbitrarily. However, which slide position actually affects the drawing processability, that is, at which slide position when performing the drawing process with high productivity. Since it was not possible to grasp whether it was effective to increase the molding speed, the characteristics of the servo press could not be fully utilized for drawing.
The present invention has been devised to solve such a problem. When performing rectangular tube deep drawing at a blank size near the limit drawing ratio in the rectangular tube, molding is performed while taking into account the mold conditions and the like. An object of the present invention is to provide a method of deep drawing a rectangular tube of a metal plate that has increased productivity by increasing the speed.

  The square tube deep drawing method of the metal plate of the present invention achieves the purpose, and when the square tube is deep drawn by pressing a punch into the metal plate to be processed fixed by a die and a blank holder, Using a cut blank, with no bead in the blank straight side between the die and the blank holder, at the initial stage of machining, the punch pushing speed is high and before the punch pushing position reaches the 2/3 x forming height position. At this point, the punch pressing speed is made slower than the initial machining speed.

In the method of the present invention, the processing speed is increased in an area where there is no risk of wall cracking, and the processing speed is decreased in an area where wall cracking is likely to occur, thereby improving the formability without causing a decrease in productivity.
According to the method of the present invention, it is possible to perform processing at a productivity higher than that of a mechanical press by using a servo press as much as a hydraulic press, resulting in a reduction in work cost.

The inventors of the present invention have studied a pressing method that can increase productivity when a rectangular tube is deep-drawn into a blank.
In general, when square tube deep drawing is applied to a square blank, a plate with a cut corner may be used as a blank to prevent cracking at the punch shoulder, but the corner cut amount is large. In this case, the inflow difference between the flange material at the corner portion and the right side portion becomes large, and wall cracking is likely to occur. Therefore, in order to reduce the inflow difference between the flange material at the corner portion and the right side portion, there is a case where a bead is provided at the right side portion to suppress the material inflow at the right side portion. However, when a bead is provided, the bead portion must be cut later before making a product, which contributes to an increase in material cost. For this reason, when processing is performed without providing beads to avoid an increase in material costs, the inflow of the flange material at the corners and straight sides is managed by finely controlling the amount of corner cut to prevent wall cracking. The actual situation is adjusting the balance.

In general, when the forming speed at the time of drawing is increased, the deformation progresses before the strain propagates to the surroundings, and therefore, the strain is concentrated locally and often leads to a crack. Simply reducing the molding speed during drawing will reduce the productivity as with a hydraulic press.
Therefore, since the corner cut amount of the square blank is not appropriate, the inflow difference between the corner portion and the flange portion of the flange is large, and wall cracking is likely to occur. Under the condition that the bead having the inflow suppressing action of the straight side flange material is not provided on the side portion, the forming speed is reduced only in the region having a large influence on the drawability, and in the region not related to the drawability. We studied to increase the molding speed of the steel.
As a result of the examination, under the square tube deep drawing conditions where wall cracks are likely to occur because there is no bead in the square blank with the corner cut, the initial processing speed is increased and the final processing speed is increased. It was found that by slowing down the generation of wall cracks was suppressed and productivity could be secured.
The details will be described below.

In general, as shown in FIG. 1, a rectangular tube deep drawing is performed by using a die 1 having a predetermined length and width, a predetermined corner radius and a shoulder radius, and a punch 2 having a predetermined length and width, a predetermined corner radius and a shoulder radius. In this state, the punch 2 is pressed into the die 1 while the blank 3 having a thickness t is pressed against the die 1 with the plate presser 4.
By the way, a typical crack at the time of deep drawing is a crack at the punch shoulder. Usually, whether or not a crack occurs is determined by the magnitude relationship between the breaking strength of the punch shoulder and the drawing resistance of the contraction flange. In general, if the punch shoulder has a breaking strength greater than the shrinkage flange portion, it can be processed without cracking, and if the shrinking flange portion has a drawing resistance greater than the punch shoulder strength, the punch shoulder Cracks occur at the part.
When a square blank is deep drawn by a rectangular tube, cracks are likely to occur in the punch shoulder as the blank is drawn deeper using a blank having a size larger than that of the punch as in the case of the cylindrical drawing.

However, if the shoulder radius of the die is relatively small compared to the thickness of the metal plate to be processed, and the shoulder radius of the punch is sufficiently large compared to the shoulder radius of the die, if you try to squeeze deeply, the deep drawing middle to late In some cases, cracks may occur in the wall, not the punch shoulder. When the shoulder radius of the punch is sufficiently large, strain concentration at the punch shoulder is unlikely to occur, so that it is presumed that cracks at the punch shoulder at the initial stage of machining are unlikely to occur.
On the other hand, the material of the corner portion flows into the die cavity while undergoing shrinkage flange deformation, and is subjected to tensile deformation close to plane strain after entering the wall.

  When the shoulder radius of the die is sufficiently smaller than the shoulder radius of the punch and is relatively small compared to the thickness of the metal plate to be processed, and when the blank size is large, the flange portion shrinks at the corner or the die shoulder Since the bending and unbending deformation increases, the flange flows into the die cavity after the middle stage of processing, the material of the portion that becomes the vertical wall portion of the corner portion is greatly damaged, and the breaking strength is reduced. That is, when deep drawing is performed in a state in which the shoulder radius of the die is sufficiently smaller than the thickness of the metal plate to be processed, cracks are likely to occur in the drawn vertical wall portion at the corner from the middle stage to the latter stage.

As described above, when a rectangular blank having a corner cut is deep-drawn into a square tube, the inflow difference between the corner portion and the flange material at the right side portion is increased, and wall cracking is likely to occur.
Therefore, as a preliminary experiment, as shown in FIG. 2, square tube deep drawing without a bead on a regular square blank using a regular square punch, a steel plate having a thickness of 0.8 mm as a test material, a blank size and I tried changing the amount of corner cut. The punch size was 100 × 100 mm and the corner R10 mm. Then, a wrinkle pressing force of 140 kN was applied, and processing was performed at a slide speed of 200 mm / second, which is a relatively high speed.
As a result, a result as shown in FIG. 3 was obtained. In FIG. 3, OK indicates that molding is possible, α indicates punch shoulder fracture, and WB indicates wall cracking.

When the blank size is 200 × 200 mm, a wall crack occurs when the corner cut amount exceeds 50 mm and is less than 80 mm. In the range where the corner cut amount exceeds 50 mm and is less than 80 mm, it is presumed that the wall crack occurred due to the inflow of the flange at the corner portion being delayed as compared with the right side portion. If the corner cut amount is 50 mm or less or 80 mm or more, square tube deep drawing can be performed without causing wall cracks. When the blank size is 200 × 200 mm, if the corner is cut so as to be 80 mm or more, the material is insufficient at the corner portion, and the molding is finished before the wall crack occurs, so that a desired molding height cannot be obtained.
Moreover, when the blank size is 250 × 250 mm, when the corner cut amount exceeds 25 mm, a wall crack occurs. In addition, when the blank size exceeds 250 × 250 mm, a crack occurs at the punch shoulder.

Here, the relationship between the corner cut and the amount thereof and the occurrence of wall cracking will be considered.
The flange on the straight side moves toward the die cavity while sliding between the die and the crease presser during processing. On the other hand, the flange of the corner portion shrinks and deforms when the flange is moved toward the die cavity between the die and the presser foot during processing. This shrinkage flange deformation generates a large deformation resistance, and prevents the corner flange material from flowing into the die cavity.
When there is no corner cut, there is an effect of pulling in the flange material at the corner portion at the same time as the flange material in the immediate vicinity of the corner flows in. Cracks are less likely to occur. On the other hand, when the corner is cut, there is no material in the immediate vicinity of the corner, and the effect of pulling in the flange material in the corner when the flange material in the direct side flows in cannot be obtained. As a result, when the amount of corner cut exceeds a predetermined amount, the difference in flange inflow between the straight side and the corner increases, and a large shearing force is generated in the vertical wall of the corner, causing wall cracks. it is conceivable that.

The square blank is not provided with a bead that suppresses the inflow of flange material and the corner cut amount is not appropriate. If the speed is high, the deformation progresses before the strain propagates to the surroundings, so the strain is concentrated locally and cracking is likely to occur. In addition, the heat generated by the deformation increases due to the deformation, and the breaking strength of the material to be processed is further reduced, and wall cracking is likely to occur.
Such wall cracks can be suppressed by slowing the processing speed. That is, by slowing the processing speed, local concentration of strain is avoided and processing heat generation is suppressed. As a result, a decrease in fracture strength of the material to be processed is suppressed, and the occurrence of wall cracks is suppressed.

Details of setting the timing for reducing the processing speed will be given in the description of the embodiment. However, in the present invention, as shown in FIG. 4, as shown in FIG. To do.
The molding speed at the initial stage of processing is preferably about 200 mm / second. Moreover, it is preferable that the shaping | molding speed at the time of making a processing speed slow shall be about 10 mm / sec. By increasing the molding speed at the initial stage of processing to about 200 mm / second, the entire processing time for one stroke becomes the same level as that of the mechanical press method, and inferior productivity can be secured.

Example 1;
As a test material, a SUS304 annealed steel sheet having a thickness of 0.8 mm was used.
A die having a punch size of 100 × 100 mm, a die size of 102.5 × 102.5 mm, and a corner R of 10 mm was used. The punch and die shoulders R were 10 mm and 5 mm, respectively.
Then, a 200-270 mm square blank is appropriately cut in corners, and a 140 kN wrinkle pressing force is applied to form a rectangular tube deep drawing up to a molding height of 65 mm. The slide speeds are 200 mm / second and 10 mm / second. It was done in a mode that was changed in the middle.
Of these, the variable motion A is the one in which the first half of the machining is fast and the latter half of the machining is delayed, and the variable motion B is the one in which the first half of the machining is delayed and the second half of the machining is accelerated. The time of change was 43 mm, which corresponds to 2/3 height of the molding height of 65 mm.

The state of occurrence of cracks during each deep drawing was observed, and the relationship between the blank size and the amount of corner cut and the occurrence of cracks was investigated and organized as Tables 1 and 2.
In Tables 1 and 2, those that can be molded without any problem are indicated by ◯, those that break in the punch shoulder are indicated by α, and those that are cracked in the wall are indicated by W.
As can be seen from the results shown in Tables 1 and 2, variable motion B, that is, when the first half of machining is slow and the latter half of the machining is accelerated, wall cracking is likely to occur, and variable motion A, that is, the first half of machining is fast and the second half of machining is delayed. In some cases, wall cracking is less likely to occur.

Example 2;
Using the same test material and mold as in Example 1, a 200-270 mm square blank is appropriately cut in corners and given a crease pressing force of 140 kN to give a square tube deep drawing up to a molding height of 65 mm. The slide speed was changed in the middle between 200 mm / sec and 10 mm / sec.
Of these, the variable motion C is the first half of the processing that is faster and the second half of the processing is delayed, and the time of switching is the half height of the molding height of 65 mm. The variable motion D is the first half of the processing that is faster than the second half of the processing. At the time of switching, the molding height was set to 3/4 height of 65 mm.
And the same evaluation as Example 1 was performed. The results are shown in Tables 3 and 4.

As can be seen from the results shown in Tables 3 and 4, the variable motion D, i.e., the time of switching is 3/4 height of the molding height 65 mm, and the variable motion C, i.e., the time of switching is the molding height. Wall cracking is less likely to occur when the height is ½ of 65 mm.
When the results of Examples 1 and 2 are combined, the punch pressing position Hc is formed as shown in FIG. 4 at a switching timing in which the punch pressing speed is high in the initial stage of processing and slower than the initial processing speed in the late stage of processing. It can be understood that it is necessary to set a point in time before reaching the height position of 2/3 of the height Hp.

Diagram showing the mold used for deep drawing Diagram showing the relationship between the blank shape and punch shape used in the preliminary test Diagram showing the relationship between blank size and corner cut amount and formability Diagram showing the forming process of deep drawing

Claims (1)

  When a punch is pushed into a metal plate fixed by a die and a blank holder and a square tube is deep drawn, a blank with a cut corner is used, and there is no bead at the blank side between the die and the blank holder. According to the conditions, the punch indentation speed is high at the initial stage of machining, and the punch indentation speed is made slower than the initial stage of machining before the punch indentation position reaches the position of 2/3 × forming height. Square tube deep drawing method for metal plates.

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