JPH0757389B2 - Press molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a press forming method for drawing a plate material,
Particularly, the present invention relates to a press molding method in which wrinkles are not generated and cracks are not generated even when the punch pushing stroke is increased.

[Background technology and matters to be solved]

In a press forming method in which a blank with a wrinkle holding plate is pressed against a die having a forming cavity and the blank is pushed into the cavity with a punch, the pressing force applied to the wrinkle holding plate (blank pressing force) is generally Is constant and does not change during molding.

In such a general drawing process, if the wrinkle holding force is improper, the product will be wrinkled or wrinkled, and it is impossible to perform deep drawing. For this reason, the maximum drawing depth that can be formed without wrinkles, which is caused by various blank pressing forces (wrinkle pressing force), has been investigated.

FIG. 11 shows a diagram of the maximum drawing depth (punch stroke h) when such blank pressing force is applied. As shown by forming lines d ₁ to d ₅ in the figure, when forming with a constant blank pressing force, the limit line L _B and wrinkle that are obtained by connecting the limit points where cracks are generated in the blank are generated. It is shown by the limit line L _W obtained by connecting the limit points. As shown by the forming lines d ₁ and d ₂ , when the blank pressing force H is large, cracks are generated in the blank to limit the maximum depth of drawing, and conversely, when the blank pressing force H is small, the forming line d is small. Wrinkles occur in the blank as indicated by ₄ and d ₅ , which also limits the maximum depth of drawing.

When the blanking force H _C corresponding to the intersection of the wrinkle occurrence limit line L _B and the wrinkle occurrence limit line L _W is used for drawing, the punch stroke h becomes maximum (b _C ).

Here, when the drawing depth required for the molded product is h ₁ , the blank pressing force condition that can be molded can be adopted from H _L to H _M above and below H _C. However, when the required drawing depth is larger than h _C , molding is impossible.

In order to further improve this drawing depth, it is necessary to modify the mold and change the blank shape, dimensions, and materials, which necessitates modification of the mold and modification of the blank shape, and a press-formed product of the desired shape is obtained. It can be difficult.

Also, as a method of changing the blank pressing force during molding,
A device has been proposed in which a plurality of blank pressing parts are arranged, the amount of blanks drawn at the positions corresponding to the blank pressing parts is detected, and the pressing force of the blank pressing parts is changed so that the blanking amount becomes the same as that of a good product ( JP-A-59-159228).

However, this device is for stable forming and does not positively expand or improve the drawing limit depth. If a larger forming depth is required, the mold modification and Pilot press work is required to change the blank.

In addition, as a method of changing the blank pressing force during molding, the blank pressing force of the wrinkle holding plate at the start of molding is calculated from the pressing force corresponding to the intersection point between the wrinkle occurrence limit line and the wrinkle occurrence limit line when the blank pressing force is constant. A method has been proposed in which the pressing force is increased during the molding process, the pressing force is decreased with the increase of the punch pressing amount without crossing the crack generation limit line, and the pressing force is lower than the corresponding pressing point at the end of the molding process ( According to Japanese Patent Application No. 60-105596), the drawing depth can be increased by this method compared with the case where the blank pressing force is constant, but when the shape of the molding cavity becomes complicated, the different parts affect each other. Since it matches, it is difficult to obtain a large drawing depth.

It is an object of the present invention to obtain a press molding method that enables a deep drawing depth that cannot be obtained by the above conventional method.

[Outline and Action of Invention]

In the press forming method according to the present invention, a blank is pressed by a wrinkle holding plate to a die having a forming cavity, and the blank is pressed into the cavity by a punch, and the blank is pressed. The force (blank pressing force) is divided into a straight side part and a curved side part according to the shape of the cavity opening, and the blank pressing force at the straight side part is With the increase of the punch pressing amount from the area higher than the pressing force to the area lower than the pressing force corresponding to the intersection of the wrinkle limit line and the wrinkle limit line when the blank force is constant, It is characterized in that the blank pressing force is increased as the punch pressing amount is increased so as to intersect with the fluctuation line of the pressing force on the straight side portion.

The blank pressing force in the present invention refers to a value obtained by dividing the blank pressing force by the blank pressing area at the initial stage of molding.

There are the following three methods to classify the blank pressing force.

(1) One or both of the blank pressing portion of the wrinkle holding plate or the die is divided so that the blank pressing force can be applied respectively. (2) The wrinkle holding plate or the blank pressing portion of the die has a flexible structure, and pressing force is applied according to the divided areas.

(3) Part of the blank pressing portion of the wrinkle holding plate or die is divided and a pressing force is applied to each.

The blank pressure area is divided according to the shape of the die cavity opening, and is divided into a straight side portion and a curved side portion of the above shape.

For example, in the case of the opening of the cavity 10 having the shape as shown in FIGS. 4 and 5 (a regular square cylinder with curved corners),
The blank pressing portion of the wrinkle holding plate 16 or the die 12 has four straight sides 165,166,167,168 and four curved sides 161,162,163,
It is classified into 164.

The boundary between the straight side and the curved side of the shape of the opening of the die cavity is a position to be divided, and this position is the boundary between the straight side and the curved side depending on the shape of the entire die cavity and the blank shape. It is also possible to set it at a position more offset than that. The blank pressing force applied to the divided area may be uniform over the entire divided area, or may be concentrated on a part of the area or have a pressure distribution.

In addition, it is judged whether the straight side portion is the curved side portion by comparing each portion of the shape of the molding cavity with each other, and the portion relatively close to the straight line is set as the straight side portion, and relative to this. The part that is considered to be close to the arc curve may be the curved side part.

The blank pressing force at the straight side corresponds to the intersection of the crack generation limit line and the wrinkle generation limit line when the blank pressing force is constant and the punch pressing amount is reduced in the punch stroke where the crack is not generated when the blank pressing force is constant. A region higher than the pressing force is reduced to a region lower than the pressing force.

As a method for reducing the blank pressing force on the straight side portion during the forming, the blanking pressure is linearly reduced with a constant slope as shown by the forming line d ₆ in FIG. 1 or the decreasing rate is shown as the forming line d _7. or a polygonal line shape is changed in the middle, or is changed to a continuous curved as shown in the forming line d _8, it can be reduced by combining these straight lines appropriately.

In this way, the blank pressing force (crease pressing force) at the initial stage of molding
When the blank pressing force is increased as the punch stroke progresses, wrinkles do not occur even when the wrinkling limit is reached when molding is performed under the condition of constant blank pressing force during molding. As shown by forming lines C _{1 to} C ₄ in FIG. 2, it was found that the wrinkle limit line L _W moves to L _W1 when the blank pressing force H is reduced as the drawing process progresses. It depends on what was done. On the other hand, the crack generation limit line L _B does not move to the high punch stroke side unlike L _W , despite the change in the blank pressing force.

Therefore, since otherwise the molding limit line is blank pressing force H _F wrinkle generation area when a predetermined blank pressing force of the forming initial in the molding end As is clear from Figure 1 does not move, the blank pressing force H _F is H _C There is no effect unless it is below. On the other hand, since the blank pressing force H _S at the initial stage of molding can be expected to be effective by decreasing the blank pressing force from the initial stage of molding to the final stage of molding, H _S must be larger than H _C. .

In the process of reducing the blank pressing force during forming, as the forming lines C _{1 to} C _{3 in} Fig. 2 show, wrinkles are generated as the blank pressing force near the wrinkle limit line L _{W is} constant when the blank pressing force is constant. The depth that can be molded without
The blank pressing force is preferably large enough to prevent cracking.

Even when the blanking force is reduced and drawing is performed, wrinkling will occur if the forming line that the punch stroke moves to intersects the wrinkle generation limit line L _W1 that has moved to some extent. The rate of pressure decrease is shown in the molding line in Fig. 2.
By changing to C ₆ , that is, by continuing the drawing without reducing or decreasing the blank pressing force reduction rate, the drawing depth can be further increased.

The pressing force on the straight side portion can be kept low in the narrow punch stroke range in the initial stage of molding in order to prevent the occurrence of cracks. That is, as shown by the curve L ₁ in FIG. 8, the pressing force on the straight side portion may be increased from a low region in the initial stage of molding and then decreased. In addition, in order to prevent the generation of wrinkles, the pressing force corresponding to the intersection may be made lower and then increased in the latter stage of molding.

On the other hand, the blank pressing force at the curved side portion is increased with an increase in the punch pressing amount so as to intersect with the fluctuation line diagram of the pressing force at the straight side portion within the punch stroke in which no crack occurs when the blank pressing force is constant.

As a method of increasing the blank pressing force at the curved side during forming, the blank pressing force is increased linearly at a constant gradient, the increasing rate is changed midway to form a polygonal line, or the curve is changed continuously. These straight lines and curves can be increased in any suitable combination.

In this way, when the blank pressing force at the curved side at the initial stage of forming is reduced and the blank pressing force is increased as the punch stroke progresses, when the blank pressing force during forming is constant, or when the straight side is pressed. Similar to the blank pressing force of No. 1, it is more effective than when it is decreased during forming, and the depth that can be formed without wrinkling increases. This is because the following results as shown in FIG. 3 were obtained. As shown by forming line D ₁ , the blank pressing force on the straight side is reduced as the drawing process progresses, and the blank pressing force on the curved side is set to the initial blank pressing force on the straight side as shown by forming line D _2. In the same manner, if it is made constant during molding, cracks will occur earlier than the maximum forming depth h _C when the blank pressing force at the straight side and the curved side are made constant and made constant during forming. As shown by forming line D ₄ , the blank pressing force on the curved side is made smaller than the initial blank pressing force on the straight side, and if it is kept constant during molding, the blank pressing force on the straight side and the curved side becomes the same. Wrinkles occur at a later time compared to the maximum forming depth h _c when it is kept constant during forming, but wrinkles occur. As shown by forming line D ₅ , the initial blank pressing force on the curved side is made smaller than the initial blank pressing force on the straight side,
As the punch stroke progresses, the D ₂ and
As compared with the case of the D _4, cracks to a large draw depth can be molded without generating wrinkles. In addition, the drawing depth obtained with D ₅ is
It becomes larger than the drawing depth obtained when the blank pressing force at the straight side and the curved side indicated by the combination of D ₁ and D ₃ is made the same and the blank pressing force is reduced during forming.

Therefore, it is necessary to make the initial blank pressing force on the curved side portion smaller than the initial blank pressing force on the straight side portion and increase it as the punch stroke progresses. In addition, since the initial blank pressing force on the straight side is set to be larger than the blank pressing force H _C when the maximum forming depth is shown during constant forming, the initial blank pressing force on the curved side has a greater effect. to issue, it is desirable that the following H _C. Also, if the pressing force on the curved side continues to increase in the latter half of the punch stroke,
When cracks occur early, they can be kept constant or reduced without increasing after crossing the fluctuation lines of the pressing force on the straight side.

(Embodiment of the Invention) Embodiment 1. A blank 14 is mounted on a die 12 provided with a molding cavity 10 as shown in FIGS. 4 and 5, and the periphery of the blank 14 is pressed by a wrinkle holding plate 16. Then, the blank 14 is pressed with the punch 18. As a result, the punch 18 draws the central portion of the blank 14 into the molding cavity 10.

Punch 18 is a square 150mm x 150mm, corner radius 18mm,
Shoulder radius 12 mm, molding cavity 10 is a regular square tube drawing type of 152 mm × 152 mm, corner radius 20 mm, shoulder radius 7 mm, and the wrinkle holding plate is divided (8 divisions) at the boundary between the straight side and the curved side, The structure is such that each blank pressing force can be given arbitrarily. The blank 14 was cut out from a mild steel plate having a plate thickness of 0.7 mm and used for press forming.

The blank 14 is a 340 mm x 340 mm square plate. For lubrication with the mold, cleaning rust preventive oil is applied to the surface of the blank 14 to form a die 12
Placed on top, the punch 18 was hydraulically driven. The split wrinkle retainer plates were individually driven by hydraulic pressure.

Molding was performed under the conditions of constant blank pressing force during molding under various blank pressing forces, and the crack generation limit line L _B and wrinkle generation limit line L _W were determined. Blank pressure at the intersection
H _C was 8.0 kgf · cm ⁻² . Next, the initial blank pressing force H _S was set to 22.7 kgf · cm ^-2 so that the blank pressing force during molding on the straight side decreased while crossing this H _C , and the initial blank pressing force on the curved side was higher than H _C. With a small size of 3.4 kgf · cm ⁻² , the punch 14 pushed the blank 14 into the molding cavity 10. Here, the blank pressing forces H _C and H _S are values obtained by dividing the force applied to the blank by the wrinkle holding plate by the initial blank pressing area.

The punch speed was set to 43 mm / min, and the blank pressing force on the straight side portion was kept constant until the punch stroke was 10 mm along with the pushing of the punch 18, and then it was curvilinearly reduced (Fig. 6, forming line E ₁
reference). On the other hand, on the curved side, the blank pressing force was kept constant until the punch stroke was 20 mm, and then it was increased in a curve (see Fig. 6, forming line E ₂ ). Cracks occurred when the punch stroke exceeded 43.5 mm, but it was possible to mold up to 43.5 mm without cracks or wrinkles.

On the other hand, for comparison, the maximum forming depth h _C when forming with a constant blank pressing force during forming was 35.5 mm, and therefore, in this embodiment, a deeper drawing by 8.0 mm was possible. . In addition, the maximum forming depth h _C ′ is 26.5 mm when the blank presser plate is integrally formed without dividing as in the conventional method and the blank pressing force during forming is constant. Also, a deep aperture of 17 mm is possible. Further, in the case where the blank pressing force at the straight side portion and the curved side portion are made to be the same by the wrinkle holding plate used in the present embodiment and the blank pressing force is reduced as the punch stroke progresses (see FIG. 6, forming lines E ₁ and F ₂₎ . The maximum forming depth of () is 39.5 mm, and therefore, in this embodiment, it is possible to draw deeper by 4 mm.

(Example 2) Using the same mold, blank, lubrication and punch speed as in Example 1, the initial blank pressing force H _{S on} the straight side and the reduction rate of the blank pressing force H were also the same, and the initial blank on the curved side was used. The pressing force was the same and the drawing was performed by changing the way of changing the curved side during forming.

The punching stroke was 25 mm and the initial blank pressing force was kept as it was, and thereafter, the punching rate was increased at the same rate as in Example 1 (No. 6).
(Refer to the forming line G _{2 in the} figure.) However, it was reduced to 46 mm, wrinkles did not occur, and it was possible to reduce by 10.5 mm more than when the blank pressure was constant.

(Example 3) The same mold, blank, lubrication and punch speed as in Example 1 were used. The initial blank pressure on the straight side and the rate of change thereafter, and the initial blank pressure on the curved side are the same,
The method of changing the blank pressing force on the curved side in the latter half of molding was changed. If the initial blank pressing force is kept constant up to the punch stroke of 20 mm, and the rate of increase thereafter is smaller than that in Example 1 (see FIG. 6, forming line I ₂ ), the punch stroke is 42 mm, wrinkles do not occur, and the blank pressing force is constant. It has become possible to stop by 6.5mm more than in the case of.

(Example 4) The same mold, blank, lubrication and punch speed as in Example 1 were used. The initial blank pressing force on the straight side was also made the same and decreased as the punch stroke progressed. This reduction rate is the same as in Example 1 (see FIG. 7, forming line J ₁ ). When the initial blank pressing force on the curved side is also the same as that in the first embodiment, the punch stroke is kept constant up to 10 mm, and then increased at the same rate as in the first embodiment (see FIG. 7, forming line J ₂ ).
Since wrinkles do not occur up to mm, wrinkles do not occur, and a deeper drawing of 5.5 mm is possible compared with the case where the blank pressing force is constant.

(Example 5) The same mold, blank, lubrication and punch speed as in Example 1 were used. The blank pressing force on the straight side is the same as that of the first embodiment (see FIG. 7, forming line K ₁ ), and the blank pressing force on the curved side is the same as that of the fourth embodiment up to the punch stroke of 17.5 mm. when the blank pressing force constant (see Fig. 7 molding line K _2), cracks up to 40 mm, it was possible only deeper aperture 4.5mm compared to the case wrinkle causes blank pressing force constant without generating.

(Example 6) The same mold, blank, lubrication and punch speed as in Example 1 were used. The initial blank pressing force on the straight side is 11.5 kg
f ・ cm ^-2 , 1.13kgf ・ cm ^-2 as the punch stroke progresses
It increases to 22.7 kgfcm ^-2 at a rate of / mm, and then decreases at the same rate as in Example 1 (see FIG. 8, forming line L ₁ ). When the blank pressing force of Kyokuhen portion is the same as in Example 3 We up (8 see FIG molding line L ₂₎ 45 mm, wrinkles do not occur, 9.5 mm by deep diaphragm as compared with the case of a constant blank pressing force Became possible.

(Example 7) The same mold, blank, lubrication and punch speed as in Example 1 were used. The blank pressing force on the straight side is 30 in the punch stroke.
The same as in Example 6 up to mm, and then 0.23 kgf · cm ⁻² / mm
(Refer to the molding line M _{1 in} FIG. 8), the blank pressing force at the curved side is the same as in Example 6 up to the punch stroke of 20 mm, and then increases at a rate of 0.23 kgf · cm ⁻² / mm. (Eighth
(Refer to the figure forming line M ₂ ) Wrinkles and wrinkles did not occur up to 42 mm, and a deep drawing of 6.5 mm was possible compared with the case where the blank pressing force was constant.

(Comparative Example 1) The same mold, blank, lubrication and punch speed as in Example 1 were used. The initial blank pressing force Hs on the straight side is 3.4 kgf
-Cm ^-2 , the punch stroke is kept constant up to 10 mm, and then increases as the punch stroke progresses. The rate of increase is the same as the rate of increase in the curved side portion of Example 4 (FIG. 9 molding). See line N ₁ ). The curved side has an initial blank pressing force.
Punch stroke is 22.7 kgf · cm ^−2, and the punch stroke is kept constant up to 10 mm, and then decreases. However, if the small proportion is made the same as the reduction proportion of the straight side of Example 1 (see FIG. 9, forming line N ₂ ), up to 25 mm. Although it was possible to form without wrinkles and wrinkles, good results were not obtained compared to when the blank pressing force was constant.

Comparative Example 2 The same mold, blank, lubrication and punch speed as in Example 1 were used. Initial blank pressing force H _S on the straight side is 10.3 kg
f · cm ⁻² , which decreases in a curve with the progress of the punching process (see forming line Q _{1 in} FIG. 9). The initial blank pressing force H _S of the curved side is set to 15.7 kgf · cm ^-2 , and increases linearly with the progress of the punch stroke (see Fig. 9, forming line Q ₂ ) and 3.5 m
Although wrinkles did not occur up to m, no good results were obtained compared to when the blank pressing force was constant.

Example 8 The same mold, lubrication and punch speed as in Example 1 were used. The blank is 325 mm x 325 mm from 0.8 mm thick mild steel plate
The square plate was cut out and used.

The initial blank pressing force on the straight side is set to 32.5 kgf ・ cm ^-2 , and it is reduced at a rate of 0.55 kgf ・ cm ^-2 / mm as the punching process progresses, and the initial blank pressing force on the curved side is 5 kgf ・ cm ^-2. West,
As the punching process progresses, it increases up to 0.55 kgf · cm ^-2 / mm at a rate of 0.55 kgf · cm ⁻² / mm (see pressure change line R in Fig. 10), and it can be molded without wrinkling.

The maximum drawing depth that does not cause cracks when the blank pressing force on the straight side and the curved side is made various combinations and kept constant during molding is as shown in Fig. 10. In the figure, the curve group S is an equal drawing depth line, ○ mark indicates that no wrinkle is generated at the draw depth indicated by ○ mark, and △ mark indicates the draw depth indicated by △ mark. It's what is happening. Therefore, the area on the right side of the curve T is a region in which no wrinkle is observed when a wrinkle occurs.

As shown in Fig. 10, the maximum forming depth was 34 mm (from the limit line T of the wrinkle generation area in Fig. 10 when the blank pressing force on the straight side and the curved side was combined to make it constant during forming. It can be estimated), and in the present embodiment, a diaphragm 3 mm deeper was possible.

(Effects of the Invention) As described above, in the pleating method according to the present invention, the blank pressing force is divided into the straight side portion and the curved side portion according to the shape of the cavity opening, and the blank pressing force is kept constant. In the punch stroke that does not occur, the blank pressing force on the straight side is lower than the above pressing force from the region higher than the pressing force corresponding to the intersection of the crease occurrence limit line and the crease occurrence limit line when the blank pressing force is constant. As the area decreases,
The feature is that the blank pressing force at the curved side is increased with the increase of the punch pressing amount so as to intersect with the fluctuation line of the pressing force at the straight side. It has an excellent effect that it is possible to obtain a large drawing depth which is impossible when the wrinkle holding pressure is constant or when it is reduced during molding.

[Brief description of drawings]

1, 2, and 3 are blank pressing pressure diagrams for punch strokes for explaining the present invention, FIG. 4, and FIG.
The figures are front view, cross-sectional view, FIG. 6, FIG. 7, FIG. 8 and FIG. 10 of the molding die used in the first embodiment, which show the blank pressing force for the punch stroke according to the embodiment of the present invention. FIG. 9 and FIG. 9 are diagrams showing the blank pressing force with respect to the punch stroke according to the comparative example, and FIG. 11 is a diagram of wrinkle holding force with respect to the punch stroke in the conventional press forming. 10 ... Molding cavity, 12 ... Die, 14 ... Blank, 16 ... Wrinkle retainer plate, 18 ... Punch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 60-145227 (JP, A) JP 60-190327 (JP, A) JP 51-33762 (JP, A) JP 61- 266130 (JP, A)

Claims (1)

[Claims] 1. A press molding method comprising pressing a blank into a die having a molding cavity with a wrinkle holding plate, and pressing the blank into the cavity with a punch to draw-form the blank. Depending on the shape of the part, it is divided into the straight side and the curved side, and the crack does not occur when the blank pressing force is constant.In the punch stroke, the blank pressing force at the straight side is the limit of the crack generation when the blank pressing force is constant. Line and wrinkle occurrence limit line from the region higher than the pressing force corresponding to the intersection point to the region lower than the pressing force as the punch pushing amount increases with the blank pressing force at the curved side, The press forming method is characterized in that the press force is increased with an increase in the punch pressing amount so as to intersect with the fluctuation diagram of the pressing force.