JP4612564B2 - Mold for hydroforming - Google Patents

Description

  The present invention relates to a mold used for hydroforming that forms a tube body (hereinafter referred to as a material tube) as a material into a predetermined shape using fluid pressure.

In recent years, hydroforming has attracted attention in the field of manufacturing exhaust system parts and suspension system parts for automobiles as one means for reducing the number of parts and reducing weight.
In this hydroforming process, as shown in FIG. 9a, the material pipe 11 is set in the upper and lower molds 12 divided, and after the mold is clamped, the liquid is injected into the material pipe and the internal pressure P is applied to the material pipe. In addition to loading, the axial pressure δ in the tube axis direction is applied to the tube to extend in the tube circumferential direction while suppressing the expansion in the tube axis direction, and the material tube is formed into a predetermined shape. For δ, for example, a load path as shown in FIG. 9b is used.

  Such hydroforming is a technology that has long been used for processing pipe joints under the name of bulge processing, but needs to be mass-produced in a short time due to the need for weight reduction as described above. The application to automobile parts is a relatively new technology, and the molding conditions may be complicated, and various technical problems remain.

  For example, the material pipe may buckle during processing, and certain parts of the material pipe may not smoothly protrude into the mold space. Trial and error must be repeated in order to find an appropriate combination of internal pressure and axial force and their load path, such as reducing the applied axial force or increasing the internal pressure. Even in that case, if the force applied to the material pipe is reduced, buckling is less likely to occur, but there are problems such as not being able to obtain a sufficient amount of deformation and a decrease in productivity. Many. Moreover, once the processing conditions are determined, appropriate processing conditions change as the material changes.

As described above, hydroform processing depends on what combination of internal pressure and axial push is used or what load path is taken, and the result after processing depends on buckling, etc. In order to prevent molding defects, a technology has been developed in which a processing state is detected by a sensor during processing to control internal pressure or shaft pressing.

  For example, in Patent Document 1, the height of the material pipe projecting into the mold space, the height of the peripheral edge of the space, and the height of the center of the space are detected by sensors, respectively. It is shown that the internal pressure or the pushing force applied to the material pipe is controlled so that the change in the value approaches the change obtained in advance by FEM (finite element analysis method) or the like.

  Further, in Patent Document 2, a sensor for detecting the amount of movement in at least one point in the pipe expansion direction in the outer surface of the raw material pipe being formed is provided so as to protrude into the mold cavity, and the outer surface of the raw material pipe and the sensor are It is shown that the amount of movement is measured from the contact, and the load path is adjusted based on the relationship between the measured amount of movement and the internal pressure. Further, Patent Documents 3 and 4 disclose the same technique as Patent Document 2. It is shown.

However, by arranging the sensors as in Patent Documents 1 to 4 above, the overhanging state during the forming of the material pipe is detected, and the load path and the like are adjusted according to the difference in the material and dimensional characteristics of each material pipe. can be carried out, it is impossible to obtain the necessary information to determine the combination and the load path of the pressing pressure and axis affects the success of hydroforming the optimum in advance.

Furthermore, in hydroforming, tensile stress is generated at the corner of the inner wall that forms the mold cavity by hydraulic pressure, and cracks occur in the inner wall of the mold near the corner. May occur and the mold may be damaged. In this case, when a crack occurs, the mold is slightly deformed due to the influence, and as a result of the deformation, a predetermined product shape cannot be obtained, and a product requiring high dimensional accuracy may lead to the occurrence of a defective product. there were.
For this reason, it was necessary to detect the crack in advance at an early stage, but such a technique has not been known.
JP 2003-39121 A JP 2003-311433 A JP 2004-322165 A JP 2000-084624 A

  In view of the circumstances as described above, the present invention provides a mold for hydroforming that can obtain both a material pipe and a state quantity relating to a mold during hydroforming, and is thus optimal for hydroforming. An object of the present invention is to make it possible to easily obtain information on a material pipe useful for determining a load path and information on occurrence of cracks in a mold.

In order to solve the above problems, the present invention is characterized in that a hydroforming die is configured as follows.
The invention of the hydroforming die according to claim 1 comprises a die divided so as to be openable and closable, and the inside of the die body close to at least one corner of the corner of the cavity inner wall of the die. Further, the measuring means for measuring strain or stress in the mold during processing is arranged in the horizontal direction and the vertical direction.
According to a second aspect of the invention of the mold for hydroforming, in the first aspect of the invention, the measuring means is disposed inside the mold main body adjacent to all corners of the inner wall of the cavity. .

The invention for a hydroforming die according to claim 3 comprises a die which is divided so as to be openable and closable, the tip of the die from the bottom and side surfaces of the die toward the corner of the die cavity. It is characterized in that a pore positioned close to the part is provided, and a measuring device for measuring strain or stress of the mold being processed is arranged at the tip of the pore.
According to a fourth aspect of the invention for a hydroforming die according to the third aspect, one end is connected to the pore and the other end reaches the side surface of the die. A wiring lead-out groove is provided.

According to the invention of claim 1, it is possible to provide a mold for hydroforming that can obtain both the material pipe and the state quantity relating to the mold during the hydroforming process. Information about material pipes useful for determining the optimal load path can be obtained in advance, and information on the deformation state of material pipes during hydroforming and information on the occurrence of cracks in the mold can be easily obtained. Can get to.
According to invention of Claim 2, the state quantity regarding the raw material pipe | tube and metal mold | die in the said hydroforming process can be obtained still more accurately.
According to the invention of claim 3, even if it is an existing mold, the present invention can be applied by a simple modification, so that the effect of the invention of claim 1 can be obtained even with an existing mold. it can.
According to the fourth aspect of the present invention, when the present invention is implemented, the wiring can be easily routed with respect to the measuring means.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.
The present inventors paid attention to the stress that the mold receives during hydrofoaming, which has not been noticed as a state quantity that changes during hydrofoaming. And if we can know the stress applied to the mold during hydroforming or the change in strain generated in the mold in relation to the internal pressure, both the state quantity related to the material pipe and the state quantity related to the mold can be obtained. Therefore, the stress applied to the mold or the change in strain generated in the mold was examined in relation to the internal pressure.

1 to 4 show a hydroforming die used for examining the above relationship.
Reference numeral 1 denotes a lower die of a hydroforming die that is divided into upper and lower portions, and a die cavity 3 is provided at a central portion of the dividing surface 2. The mold cavity 3 has semicircular recesses 3a and 3b corresponding to the outer diameter of the material tube and a rectangular recess corresponding to the central portion of the material tube in order to bulge the center portion of the material tube having a circular cross section. 3c, a recess 3d for smoothly connecting the recesses 3a and 3c, and a recess 3e similar to the recess 3d.
The upper mold corresponding to the lower mold is also configured in the same shape as the lower mold.
Reference numeral 9 denotes a positioning pin for positioning the upper and lower molds at the time of mold clamping, and a positioning hole into which the positioning pin is inserted is formed in the upper mold.

In this mold, four corners 4 in total are formed on the inner wall forming the mold cavity 3 at the upper and lower molds in the axial section, and close to all the upper and lower corners. In each mold body, a quartz crystal piezoelectric sensor was installed as a sensor for measuring strain in the mold during molding or stress received by the mold.
As shown in more detail in FIG. 2, the sensor is provided with pores 7 whose tips are located close to the corners from the bottom surface 5 and the side surface 6 of the mold toward the corners of the inner wall of the cavity. The sensor was placed at the tip of the pore. The bottom surface 5 of the mold is provided with a groove 8 having one end connected to the pore 7 and the other end reaching the side surface 6 of the mold, and the sensor wiring can be drawn out of the mold by the groove. I did it.
The sensor is arranged at three locations per corner, and a total of 12 upper and lower molds.

Next, the knowledge obtained by measuring strain or stress in the mold during hydroforming using this mold will be described.
(1) Detection of contact of the outer surface of the material pipe to the inner wall of the mold cavity A material steel pipe having a tensile strength of 440 MPa and a wall thickness of 2.3 mm is set in the above mold, and after clamping with a mold clamping force of 15000 kN, the internal pressure is reduced. The pressure was increased to 0 to 250 MPa. The axial push was 50 mm on each side. At that time, the value detected by the sensor during the processing was recorded together with the change in the internal pressure, and the deformation process of the material steel pipe was observed.

FIG. 5 shows an example of changes in the internal pressure and the stress value detected by the sensor at this time. Moreover, the shaping | molding state of the raw material steel pipe in each point shown by (1)-(3) of FIG. 5 is shown to FIG.
As shown in FIG. 5, there were some differences in the sensor detection values between the measurement position on the right side of the lower mold and the measurement position on the right side of the upper mold, but the manner of change was almost the same.
In addition, since there was almost no difference in the detected stress of the sensor at the left and right measurement positions for the upper mold and the lower mold, those values are not shown in FIG.

  (1) in FIG. 5 shows the position where the raw steel pipe bulges and the outer surface of the pipe first starts contact with the upper and lower inner walls of the mold cavity closer to the distance (state shown in FIG. 6a). The position where contact has begun on the left and right inner walls (state shown in FIG. 6b) and (3) are the positions where contact is made except for the corner R portion of the inner wall of the mold (state shown in FIG. 6c). Yes. Further, (4) shows a position where the mold inner wall is almost completely contacted.

The change in the stress value in the mold as shown in FIG. 5 as the internal pressure increases can be explained as follows.
Since the mold is not subjected to stress from the internal pressure of the raw steel pipe at the start of molding, it receives a certain stress corresponding to the clamping force. Thereafter, as the internal pressure increases, the material pipe starts to bulge, and first, at the point (1), the central outer surface of the pipe comes into contact with the upper and lower inner walls of the mold cavity closer. The tube continues to bulge and contacts the left and right inner walls at point (2). After that, it deforms to a shape that closely follows the fine shape of the mold corners, and requires a large internal pressure to reach almost the entire inner wall of the mold, so the detected stress increases as the internal pressure increases. To do.

As shown in FIGS. 5 and 6, the position (2) at which the outer surface of the steel pipe is in contact with the upper, lower, left and right inner walls of the mold is clear as the point where the stress in the mold, which is measured as the internal pressure increases, starts to increase. Can be detected.
The appropriate processing load path for hydroforming varies depending on the product, but generally, as shown in FIG. 7, only the internal pressure is increased, and the axial pressing is performed at a level necessary to seal the pipe end (step 1). ) Next, the shaft is pushed with the internal pressure kept constant, or both the shaft push and the internal pressure are changed (Step 2). The final pressure, especially the corner R portion, Although it is configured by the stage of forming (step 3), it is necessary to appropriately set the internal pressure when shifting from step 1 to step 2.

  If the internal pressure set as shown in (a) is higher than the appropriate internal pressure as shown in (b) of FIG. 7, there is a risk of cracking of the product in step 3, and it is set as shown in (c). If the internal pressure is low, the product will wrinkle. And as an appropriate internal pressure of FIG.7 (b), the internal pressure when the outer surface of a raw material pipe | tube contacts the metal mold | die inner wall of the upper and lower sides and right and left is appropriate.

  Therefore, in order to prevent defective molding, if the above-described test is performed using a material tube to be molded in advance, and the relationship between stress and internal pressure is obtained in advance as shown in FIG. By knowing the timing at which the contact with the inner surface of the mold, it is possible to determine the value of the internal pressure when starting the axial push in the second step.

  In addition, by detecting the internal pressure at the point where the detected stress begins to rise every time hydroforming is performed, variations in material and dimensional characteristics of each material pipe can be detected from the fluctuations in the internal pressure, and the load path from step 2 to step 3 Can be modified according to the material and dimensional characteristics of the material pipe.

(2) Detection of Crack Generation Next, a change in stress when a crack occurs in the inner wall of the mold cavity will be described.
In order to investigate the change in stress when cracks occur in the mold, a mold in which a fine cut is formed at the base of the R portion at the left corner of the lower mold shown in FIGS. Hydroform processing was performed using the same material tube and processing conditions as when 5 was created.

FIG. 8 shows an example of the relationship between the detected stress and the internal pressure obtained. As shown in FIG. 8, the value of the detected stress of the sensor arranged at the left position of the lower mold near the position where the fine notch is formed is larger than the value of the sensor arranged at the right position of the lower mold. Get higher.
From this, if the detected value of the stress at the end of processing is recorded, the occurrence of cracks in the inner wall of the mold cavity can be detected in advance from the change in stress, such as when a high stress value is continuously detected. It becomes possible.

(3) Fluctuation detection of material tensile strength In hydroforming, it is known that the deformation state of a material pipe is affected by variations in material properties such as the tensile strength of the material pipe used and internal stress. Even in the techniques disclosed in Patent Documents 1 to 4, it can be said that a difference in deformation state due to variations in material characteristics of individual material pipes is detected and controlled by a sensor.
Therefore, in order to investigate how the variation in the material properties of the material pipe affects the detected stress, a plurality of material steel pipes having the same wall thickness of 2.3 mm but different tensile strengths are used. Prepared and hydroformed under the same conditions as when FIG. 5 was created, and the sensor detected stress at a predetermined internal pressure was measured.

An example of the results is shown in Table 1.
From Table 1, it was found that the detected stress values differed depending on the tensile stress of the material pipe even when the internal pressure was the same. From this, even if the steel pipe manufactured from the same material has a variation in tensile strength, there will be a difference in the stress applied to the mold. If you record the manufacturing history of steel pipes (for example, which part of the coil was made as a raw material) and store it in advance, if you know the manufacturing history of the new steel pipe to be hydroformed, It is possible to grasp the hydroforming conditions that are optimal for the material characteristics.

It was found that measuring the strain and stress in the mold during hydroforming as described above can provide useful information for setting the processing conditions for hydroforming and monitoring the mold condition. The hydroforming die according to the present invention for measuring strain and stress in the die will be described.
As described with reference to FIGS. 1 to 5, the hydroforming mold according to the present invention is in the middle of the mold body adjacent to at least one corner among the corners of the cavity. Measuring means for measuring strain or stress of the mold are arranged in the horizontal direction and the vertical direction.

  The reason for placing the sensor as a measuring means inside the mold body close to the corner of the mold cavity is to measure the stress near the cavity more accurately without affecting the molding, In the case of a mold having a right-angled corner R as shown in FIG. 2, the main stress direction of the stress value given to the mold by the metal tube contact is horizontal. This is because of the vertical direction. However, when the corner corner R of the cavity is wider or narrower than a right angle (90 degrees), the principal stress direction is different, so the orientation of the sensor must be evaluated in advance by FEM analysis, etc. The arrangement is not limited to the direction and the vertical direction.

  The sensor should be placed at least in the corner of the mold cavity close to the inner wall of the mold where the material tube first contacts, and inside the mold body close to at least one corner. However, it is desirable to install sensors in all corner R portions.

In the corners of the mold cavity, there are three places in the mold shown in FIGS. 1 to 4, but the number of corners is not limited to that, and the number of the corners may be set according to the length of the corners. .
As a sensor to be disposed, for example, a crystal pressure sensor, a strain gauge, a laser strain measuring device, etc. can be used as a device for measuring strain, and a stress gauge, a laser stress measuring device, etc. are used as devices for measuring stress. Can be used.

In particular, as shown in FIG. 2, the sensor is arranged by forming pores whose tips are located close to the corners of the mold cavity from the bottom and side surfaces of the mold toward the corners of the mold cavity. It is preferable to provide the sensor and dispose the sensor at the tip of the pore because it can be applied to an existing mold.
However, other methods for forming pores, such as a method of embedding a thin tube at the time of mold manufacture, can also be adopted. In this case, the pores can be curved.
The position of the tip of the pore is preferably 5 to 20 mm or more away from the corner. In the example of FIG. 2, L is preferably about 15 mm.
When pores are used, the location and number of sensors must be selected so as not to affect the mold strength.

  The embodiment described above is an example of the present invention, and the present invention is not limited by the embodiment, and is defined only by matters described in the claims of the claims. Other embodiments can also be implemented.

It is a top view of the metal mold | die for hydroforming of this invention. It is the AA arrow directional view and partial enlarged view of the metal mold | die for hydroforming of FIG. It is a side view of the metal mold | die for a hydroforming process of FIG. It is a bottom view of the metal mold | die for a hydroforming process of FIG. It is a figure which shows the change of the internal pressure during hydroforming, and the stress value which the sensor detected. It is a figure which shows the deformation | transformation state of the raw material pipe | tube during a hydroforming process. It is explanatory drawing of the load path | route in hydroforming. It is a figure which shows the change of the internal pressure during hydroforming and the stress value which the sensor detected when there exists a crack in a cavity inner wall. It is explanatory drawing of the conventional hydroforming processing technique.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower mold | die of the metal mold | die for hydroforming processing 2 Mold split surface 3 Mold cavity 4 Corner | angular part of mold cavity 5 Mold bottom face 6 Side face of mold 7 Pore 8 Groove for wiring 9 Positioning pin

Claims (4)

  It consists of a mold that can be opened and closed, and measures the strain or stress in the mold during processing inside the mold body close to at least one corner of the cavity inner wall of the mold. A mold for hydroforming, characterized in that measuring means to be arranged are arranged in a horizontal direction and a vertical direction.   2. The hydroforming die according to claim 1, wherein the measuring means is arranged inside a die body adjacent to all corners of the inner wall of the cavity.   It consists of a mold that can be opened and closed, and provided with a pore whose tip is located close to the corner from the bottom and side surfaces of the mold toward the corner of the cavity inner wall, and at the tip of the pore A mold for hydroforming, wherein a measuring means for measuring strain or stress in the mold during processing is arranged.   The hydroforming metal mold according to claim 3, wherein a groove for drawing out a wiring is provided on the bottom surface of the mold, one end of which is connected to the pore and the other end reaches the side surface of the mold. Type.

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