JP2008105053A - Hydroform process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydroform process having high safety which is hardly affected by the variance of a material. <P>SOLUTION: In the hydroform process, the internal volume Vz during the process of a product which can be calculated by formula Vz =((V0+Vi0)×(R-P)/R)-Vip is controlled as the shaft pressing is advanced, where V0 denotes the volume inside a metallic pipe before starting the hydroforming; Vi0 denotes the total value of the volume inside a booster machine and the volume inside a high-pressure pipe before starting the hydroforming; Vip denotes the total value of the volume inside the booster machine and the volume inside the high-pressure pipe during the hydroforming; R denotes the volume elasticity of a hydroforming liquid, and P denotes the internal pressure during the hydroforming. By controlling the internal volume Vz of the product which is the pipe expansion value of the product as the shaft pressing is advanced, the high internal pressure is naturally loaded to a material having high strength and large thickness, and the low internal pressure is loaded to a material having low strength and small thickness, and any defect caused by the variance of the material can be suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention attaches the metal tube into the mold, fills the metal tube with the molding liquid, and then increases the internal pressure while applying the axial pushing force through the punch to allow the material to flow into the mold. The present invention relates to a hydroform molding method in which a metal tube is expanded and molded in close contact with a mold.

In hydroforming, a metal tube 1 is mounted in a mold 2 as shown in FIG. 1 and the metal tube is filled with a molding solution. Thereafter, an appropriate internal pressure that does not cause wrinkles or cracks. While applying a load, an axial pushing force is applied through the punch 3 to allow the material to flow into the mold 2 and to expand the metal tube 1 to be in close contact with the mold 2 to obtain a desired part shape. At this time, in the conventional hydroform molding, for example, as disclosed in Patent Document 1, a good molded product free from cracks and wrinkles can be obtained by trial and error using a test material before mass production is started. The optimum load path represented by the internal pressure and the shaft push amount as shown in Fig. 2 is obtained, and production is performed by controlling the internal pressure and the shaft push amount using the load path as a molding condition during mass production. However, in practice, there are variations in the strength and plate thickness of the metal tube before hydroforming due to variations that occur in the manufacturing process and pre-working process of the metal tube 1. Therefore, when the strength varies compared to the test material used when formulating the optimum load path or when the plate thickness is thicker, the internal pressure is too low in the load path that has been formulated in advance, so wrinkles occur. On the other hand, if the strength is low or the plate thickness is thin, the internal pressure is too high in the previously determined impossibility route and cracking occurs. As described above, when the production is carried out by controlling the internal pressure as the shaft is pushed, there is a problem that a molding defect occurs due to variations in the thickness and strength of the material. The cause of molding failure due to such variations is due to the fact that current hydroforming molding is generally performed with the internal pressure, which is a force parameter, being controlled.
JP2000-42646

In conventional hydroform molding, molding is performed by performing control to load an appropriate internal pressure as the amount of axial push increases. For this reason, when the material strength and the plate thickness vary, there is a problem that cracks and wrinkles occur and the defect rate increases.
An object of the present invention is to provide a hydroform molding method that is not easily affected by material variations and has high stability.

In order to solve the problem, the gist of the present invention is as follows.
(1) The metal tube 1 is mounted in the mold 2, the metal tube 1 is filled with a molding liquid, and then the material is put into the mold 2 by applying axial force through the punch while increasing the internal pressure. In the hydroform molding method in which the metal tube 1 is expanded and brought into close contact with the mold 2 while being infused, the volume V0 inside the metal tube before molding, the volume inside the pressure booster before molding and inside the high-pressure pipe In the middle of molding a molded product that can be calculated as shown in Equation (1) where the total value Vi0, the total volume Vip inside the intensifier during molding and the inside of the high-pressure pipe, volume elastic modulus R of molding fluid, and internal pressure P during molding A hydroform molding method characterized by controlling the internal volume Vz of the steel as the axial push proceeds.
Vz = ((V0 + Vi0) × (RP) / R) −Vip (1)

  According to the present invention, it is possible to provide a highly stable hydrofoam molding method that is not easily affected by material variations.

  3A is a plan view, FIG. 3B is a front view, and FIG. 3C is a side view, which is an example of a hydroform component in which a central portion of a pipe is expanded into a rectangular cross section. Details will be described.

As shown in FIGS. 4 and 5, in hydroforming, the metal tube 1 is axially pressed by the left and right axial push punches 3 and the piston 5 of the pressure booster 4 is pushed in, so that the molding liquid inside the pressure booster 4 is fed into the molded product. The tube is expanded by controlling the internal pressure. The internal pressure at the time of molding is measured by a pressure gauge 6 attached in a high-pressure pipe connecting the intensifier 4 and the molded product. Thus, in the conventional molding method, molding is performed by controlling the force called internal pressure. Therefore, if the material is the same material, strength, and thickness as the test material used to determine the molding conditions, molding defects will not occur, but if the material, strength, and thickness vary, the applied internal pressure Is not an appropriate value, and molding defects occur. On the other hand, in the hydroform molding method of the present invention, the internal volume Vz of the molded product, which is the amount of pipe expansion of the molded product, is controlled instead of controlling the strength of the pressure to be applied as the shaft is pushed. In this way, by controlling the shaft push amount to keep the progress of tube expansion of the molded product properly, molding is performed, and a high internal pressure is naturally applied to materials with high strength and large thickness. On the other hand, a low internal pressure is applied to a material with low strength and a small plate thickness, and defects due to material variations can be suppressed. At this time, the effect of the present invention is not lost if the actual value of the control is in the range of several percent above and below the target Vz. In addition, the volume V0 inside the metal tube before hydroforming, the total value Vi0 inside the pressure booster and the inside of the high pressure pipe before starting hydroforming, the volume modulus R of the molding fluid, and the internal pressure P during hydroforming Then, the volume of all molding liquids during molding is expressed as ((V0 + Vi0) × (RP) / R). From this, the remainder after subtracting the total value Vip of the volume inside the intensifier and the high-pressure pipe during hydroforming is the internal volume Vz of the molded product being molded. This is the formula (1) Vz = ((V0 + Vi0) x It can be expressed as (RP) / R) -Vip. The actual procedure is as follows.
(1) As with normal hydroforming, the relationship between the internal pressure and the axial push amount is adjusted by trial and error using test materials, and the internal pressure and axial push can be obtained without wrinkles and cracks. Determine the load path.
(2) When molding is performed using this load path, the values of the axial push amount D, internal pressure P, volume Vip in the intensifier 4 and high-pressure piping are measured as the molding progresses. To do. Here, Vip can be measured from the volume in the pressure booster determined from the piston position of the pressure booster 4 and the cross-sectional area of the piston, and the volume in the high pressure pipe. From these values, the relationship between the volume Vz inside the molded product and the axial push amount D in the molding in which a good molded product was obtained using the formula (1) is obtained. The relationship between the shaft pushing amount D and the volume Vz inside the molded product obtained here is the molding condition in the molding method of the present invention.
(3) Hydroform molding is performed by controlling the position of the pressure booster piston 5 with the progress of the shaft push so as to always reproduce the relationship between the volume Vz inside the molded product obtained in (2) and the shaft push amount D. .

An example of specific implementation is shown below.
Using a steel pipe with a length of 530 mm and an outer diameter of 63.5 mm, a molded product with a1 = 460 mm, a2 = 100 mm, a3 = 400 mm, b1 = 63.5 mm, b2 = 75 mm, b3 = 90 mm in FIG. Produce. First, to determine appropriate molding conditions before production, using a steel pipe with a tensile strength of 440 MPa and a plate thickness of 1.4 mm as a test material, it is possible to obtain a molded product free of cracks and wrinkles by trial and error. A load path as shown in FIG. Next, formula (1) is obtained from the data of internal pressure P, shaft push amount D, internal pressure intensifier 4 and high-pressure pipe volume Vip when a test material is molded using the load path shown in FIG. When the change in the internal volume Vz of the molded product with the progress of molding was obtained, the relationship between the axial push amount D and the internal volume Vz as shown in FIG. 7 was obtained. Molding was performed by applying a shaft push while controlling the piston position of the pressure booster 4 so that the relationship between the shaft push amount D and the internal volume Vz in FIG. 7 was satisfied. In order to confirm the stability against material strength and thickness variation, a steel pipe with a thickness of 1.4 mm and a tensile strength of 340 MPa, a steel pipe with a thickness of 1.4 mm and a tensile strength of 590 MPa, and a steel pipe with a thickness of 1.3 mm and a tensile strength of 440 MPa are used. Table 1 shows the molding results when molding is performed. As a comparative example, the result of a conventional molding method in which molding is performed so as to satisfy the relationship between the internal pressure and the shaft pressing shown in FIG. 6 is also shown.

表１に示されるように、本発明の成形法を用いることで成形条件を決定する為に用いたテスト材から強度板厚が大きくバラつく場合でも良成形品を得られることがわかった。一方、内圧を制御する従来の成形方法では、テスト材から強度・板厚がずれた場合割れやシワが発生してしまい成形不良となる事が分かる。

As shown in Table 1, it was found that a good molded product can be obtained even when the strength plate thickness varies greatly from the test material used for determining the molding conditions by using the molding method of the present invention. On the other hand, in the conventional molding method for controlling the internal pressure, it can be seen that cracks and wrinkles occur when the strength and the plate thickness deviate from the test material, resulting in molding failure.

It is sectional drawing which shows the hydroform shaping | molding method, (a) is before axial pushing load, (b) shows the state in process of shaping | molding. It is a graph which shows the molding conditions of the conventional hydroform molding method. It is a three-plane figure which shows the example of the hydroform components by which the center part of the pipe is pipe-molded by the rectangular cross section. It is sectional drawing which shows a mode that the internal volume of a molded article changes with Hyde foam shaping | molding, and shows the state before the molding liquid inflow by a load and a pressure booster piston occurs. It is sectional drawing which shows the state which the molding liquid flowed in into the molded article by the pressure booster piston, the axial pushing was loaded, and the pipe expansion advanced. It is a graph which shows the hydroform molding conditions for shape | molding the test material for shaping | molding condition formulation in an Example. It is a graph which shows the shaping | molding conditions of the hydroform shaping | molding method of this invention in an Example.

Explanation of symbols

1 Metal Pipe 2 Mold 3 Punch 4 Pressure Booster 5 Pressure Booster Piston 6 Pressure Gauge 7 Molded Product

Claims (1)

Mount the metal tube in the mold, fill the metal tube with the molding liquid, and then increase the internal pressure while applying the axial pushing force through the punch to expand the metal tube while allowing the material to flow into the mold In the hydroform molding method in which the mold is brought into close contact with the mold, the volume V0 inside the metal pipe before molding, the total value Vi0 inside the pressure booster before molding and inside the high-pressure pipe, inside the pressure booster during molding And the total volume Vip inside the high-pressure pipe, the bulk modulus R of the molding fluid, and the internal pressure P during molding, the internal volume Vz in the middle of molding of the molded product that can be calculated as shown in Equation (1) A hydrofoam molding method characterized by control.
Vz = ((V0 + Vi0) × (RP) / R) −Vip (1)

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