JP2001314924A - High tensile steel pipe for hydroform process and hydroform processed product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high tensile steel pipe for hydroform process and a hydroform processed product capable of obtaining a HF component which highly strengthens a desired region without fear of wall thickness reduction through HF process, and which can be produced at a low cost. SOLUTION: A high strength steel pipe for hydroform process which has an aperture 5 piercing preferably in the length direction, in a part of the total length and a resin filling section 2, and by forming this resin filling section in a large pipe expansion predetermined section at the time of HF process, deterioration in stiffness owing to a thinner wall thickness of the pipe 3 can be compensated. And, since this is the hydroform processed product having the resin filling section in the part of the total length, this resin filling section is formed in the thin wall thickness section after HF process, resulting in securing stiffness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a high-strength steel pipe for hydroforming and a hydroformed part. Hydroform (hereinafter referred to as HF as appropriate)
This is a technology for manufacturing hollow closed-section structural parts by integrally forming a steel pipe by applying axial force and internal pressure. Specifically, a steel pipe is mounted in a mold, a liquid is charged into the pipe, the pipe is extended in the circumferential direction, and the pipe is expanded into a predetermined shape. This technology is mainly used for the production of automobile parts.

[0002]

2. Description of the Related Art Hydroform processing materials include:
Usually, an electric resistance welded steel pipe formed by electric resistance welding of a low carbon steel sheet is provided. A normal HF processed part manufactured by hydroforming the normal material can be applied to an independent member such as an engine cradle without any problem. However, structural members such as front side members and center pillars have both a low-strength part that absorbs impact energy by collapsing and a high-strength part that does not collapse to maintain space for occupant safety. However, it is difficult for ordinary HF parts to satisfy this requirement. In order to satisfy this requirement, it is considered effective to partially increase the expansion rate and increase the strength by work hardening, but it is unavoidable to reduce the thickness of the part where the expansion rate is increased, This is because there is naturally an upper limit to the possible expansion rate, and sufficient strength cannot be obtained.

[0003] For this reason, at present, automobile manufacturers and component manufacturers adopt tailored blanks or tailored tubes in which members having a plurality of strengths are joined as structural members such as front side members and center pillars. I have. However, in the tailored blank method (method of processing a tailored blank into parts),
After press-working a material (ie, a tailored blank) obtained by joining two or more types of steel plates, two or more parts are welded to form a closed cross-sectional structure. For this reason, the material requires a flange portion as a weld seam, and waste of material occurs as compared with HF processing. Further, in a flat portion where the tip of the punch hits at the time of press working, the deformation amount is small and an increase in strength due to work hardening cannot be expected. If the work hardening is increased by increasing the amount of processing as much as possible, the degree of non-uniformity of strain throughout the part is increased, and the thickness of the portion where the strain is large is excessively reduced, which may result in weakening.

In the tailored tube method (method of processing a tailored tube into a part), a plurality of thick or steel tubes are connected to each other by butt welding to form a tailored tube, which is processed by HF to form a part. Here, waste like the flange portion does not occur. However, there is a concern that the manufacturing cost is increased because the accuracy of the part where two or more kinds of tubes are butt-welded is severe.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention makes it possible to obtain an HF-processed part in which a desired portion is strengthened without fear of weakening due to a decrease in wall thickness in HF processing. Another object of the present invention is to provide a high-strength steel pipe for hydroforming and a hydroformed part that can be manufactured at low cost.

[0006]

SUMMARY OF THE INVENTION The present invention is a high-strength steel pipe for hydroforming, which has a resin-filled portion in a part of the entire length. It is preferable that the resin filling portion has a hole penetrating in the length direction. The resin filling portion is preferably formed by injection molding. Further, the present invention is a hydroformed part having a resin-filled part in a part of the entire length. The part may be one obtained by hydroforming a steel pipe having a resin-filled portion in a part of its entire length, or one obtained by hydroforming a steel pipe and then filling the inside thereof with a resin.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When manufacturing a structural member by subjecting a pipe to HF processing, a process of prebend (bending the pipe) → prepress (pressing the bent pipe so as to enter a mold) → HF forming. Is taken.

[0008] For example, the front side member for an automobile is desirably relatively low in strength at the portion near the front of the vehicle body, because it is required to be crushed during a collision and absorb impact energy. In a portion close to the passenger compartment, it is desirable to have a relatively high strength in order to secure a space where the occupant is not crushed even in the event of a collision. However, in a single tube of an electric resistance welded steel pipe which is a conventional material for HF processing, the material strength of a specific portion can be increased to some extent by increasing the expansion ratio of a specific portion during HF forming.
When the expansion ratio is increased, the wall thickness is reduced accordingly, and it is difficult to secure the strength as a structural member.

On the other hand, in the present invention, as shown in an example in FIG. 1, a resin filling portion 3 having a hole (through hole) 5 penetrating in a length direction is provided in a part of the entire length of a pipe (pipe) 3. Since the steel pipe for HF processing has a high expansion ratio with respect to the resin-filled portion 2, the deterioration in rigidity due to the thinning of the pipe 3 can be compensated by strengthening the lining of the resin 4 and the strength as a structural member Can be easily secured. Therefore, it is possible to easily manufacture a part having a high strength part and a low strength part with one steel pipe. Here, the hole 5 penetrating in the length direction
Is preferably provided to insert a liquid into the hole 5 and pressurize the resin-filled portion 2 from inside to expand the tube during HF processing.

The resin is preferably one having thermoplasticity and solidification at room temperature. Examples of the resin include polyetheretherketone, polyetherimide, polyarylate, polycarbonate, polyacetal, polyamide, modified polyphenylene ether, polybutylene terephthalate, and the like.
GF-reinforced polyethylene terephthalate, ultrahigh molecular weight polyethylene, polysulfone, polyethersulfone, polyphenylene sulfide, polyamideimide, polyimide, liquid crystalline polyester, polytetrafluoroethylene, polyaminobismaleimide, polybisamidetriazole, and the like can be preferably used.

Further, it is preferable that the resin thickness of the resin filling portion is 5 mm or more. The high-strength steel pipe for HF processing of the present invention is H
By performing the F processing, an HF processed part of the present invention having a resin-filled portion in a part of the entire length is obtained. It goes without saying that the resin-filled portion of the HF processed part can correspond to the high-strength portion, and the single-pipe portion can correspond to the low-strength portion.

However, the HF-processed part of the present invention is not limited to the one in which the resin-filled portion is formed before the HF-working. For example, as shown in FIG. Good. Even with this configuration, it is possible to reinforce the deterioration of rigidity due to the thinning of the pipe 3, and to secure the strength as a structural member. When the resin is filled after the HF processing, the resin filling portion 2 may be formed in a hollow mold having a through hole 5 (FIG. 2A), or a solid mold having no through hole. (FIG. 2B).

As the resin to be filled into the tube after the HF processing, the above-mentioned thermoplastic / room-temperature-setting resin is preferable.
From the viewpoint of weight reduction, a foamable resin is particularly preferable. The high-strength steel pipe for HF processing and the HF processed part of the present invention can be manufactured by a method of filling a predetermined length range in a pipe with a resin, and the manufacturing method includes a tailored butt welding of different (or different thickness) steel pipes. Since the accuracy can be made coarser than the tube method, the manufacturing cost can be reduced.

As a method for filling the resin into the tube, it is preferable to use injection molding. A method of filling a resin into a pipe will be described by taking a screw method generally used as a kind of injection molding as an example. FIG. 3 is a schematic view showing a resin filling method by screw-type injection molding. in this way,
As shown in FIG. 3A, the pipe 3 attached to the injection molding die 6 and clamped by the press 21 is inserted into the pipe 3 from one end side.
An injection molding chamber is formed by inserting a stopper tube 7 whose leading end forms a core 8 for forming a through hole, and the plastic resin 11 is injected into the injection molding chamber from the other end of the pipe 3 using an injection device. Molding.
In addition, an O-ring (not shown) that closes a gap with the inner surface of the pipe 3 is attached to the stopper tube 7, and a drag 22 opposing the internal pressure of the tube is applied at the time of injection.

An injection device supplies a raw resin (resin pellet) 10 into a header 13 having a nozzle 14 at the tip from a rear portion of the header 13 by a hopper 12, and rotates a screw 16 by a drive gear 18 through a rod 17. While moving forward, the heater 15 disposed on the outer periphery of the header 13 heats it to, for example, about 200 ° C. to form a plastic resin 11 having high fluidity, and the rod 17 urged by a hydraulic cylinder 19 from the rear. By pressing
The inside of the header 13 is pressurized so as to have a pressure of, for example, about 40 MPa, and is ejected from the ejection port at the tip of the nozzle 14. At the tip of the nozzle 14, a lid flange 20 that seals the opening of the end of the injection molding chamber other than the injection port is attached.

After the plastic resin 11 in the injection molding chamber is cooled and solidified, the injection flow is cut off by the cut plate 23, as shown in FIGS. Then, the injection mold 6 is opened, the pipe 3 is taken out, and an end chamfer 24 is performed to remove an excess portion of the resin 4. Thus, the high-strength steel pipe for HF processing of the present invention having the resin-filled portion 2 in a part of the entire length is completed. The formation position of the resin-filled portion 2 is, of course, adjusted to the position where strong processing is performed during HF processing (which can be determined from component design specifications).

After the high-strength steel pipe for HF processing is appropriately preformed (prepress-prebend), for example, FIG.
As shown in FIG. At this time, of course, the resin filling portion 2 is positioned so as to fit in the large-diameter portion (the portion having a large internal volume) of the HF mold 25. And
While closing both ends of the tubular body with push shafts 26 and 26 ', respectively, and axially pushing 27 both ends of the tubular body toward the center, liquid is injected into the tubular body through a liquid passage 28 provided on the push shaft 26 at one end 29. Apply internal pressure to increase the diameter. Thereby, the HF processed part of the present invention is completed.

When a resin is filled in the pipe after the HF processing to manufacture the HF processed part of the present invention, the pipe may be filled by injection molding as shown in FIG. It is more preferable that the foaming resin is sprayed on the inner surface of the strongly processed portion to foam and solidify the foamed resin. Also, HF
When filling after processing, it is not necessary to provide a through hole in the resin as described above.

[0019]

EXAMPLES (Example 1) ST having a yield strength of 350 MPa
A steel plate equivalent to KM13A is formed into a tube by bending and a seam (bending arc end) is welded by electric resistance welding to produce a plurality of tubes having different wall thicknesses and outer diameters. A polyetheretherketone resin having a strength of 90 MPa, an elongation of 100% or more, and a specific gravity of about 1.3 was injected into a tube by injection molding shown in FIG. 3 to form a resin-filled portion. Here, the formation range of the resin-filled portion was a range from the longitudinal center of the tube to one end.

These tubes are prepressed to make a corner bending radius of 3 mm, a cross section of 60 mm square, and a length of 300 mm.
Is inserted into a processing chamber of a mold having a processing chamber (a mold for HF), and the pipe end is fixed, and a liquid pressure is applied to the inside to form a prismatic pipe (FIG. 5).
The HF molded part of Example 1 was designated as Example 1 of the HF processed part of the present invention. When performing HF molding on a prismatic tube, the molding size is determined by trial and error, the total length: 300 mm, the low strength part 30 (single pipe part) length: 150 m
m, high-strength part 31 (resin-filled part) length: 150 mm, steel pipe wall thickness (average in circumferential direction): 1.6 mm, resin wall thickness (average in circumferential direction): 6
mm.

(Embodiment 2) The same steel plate as in Embodiment 1 is similarly subjected to electric resistance welding to produce a plurality of tubes having different thicknesses and outer diameters, and these tubes are prepressed to form the same mold as in Embodiment 1. HF was formed into a prismatic tube (FIG. 5) by using trial and error, and the molding size was adjusted to a total length of 300 mm and a steel tube thickness of 1.6 mm, and thereafter, within a range of 150 mm from one end of the prismatic tube. The same type of resin is injected by the injection molding shown in FIG. 3 to form a resin-filled portion having a resin thickness of 6 mm, and this range is made to be a high-strength portion 31. did.

(Comparative Example 1) From the same steel plates as in the example, a 1.6 mm-thick plate was selected for the low-strength portion and a 2.6 mm-thick plate was selected for the high-strength portion, and both plates were butt-welded to form a tailored blank. This tailored blank is pressed and further welded, and the corner bending radius: 3 mm, cross section: 60 mm square,
Length: 300mm (Low strength part length 150mm, High strength part length 150m
m) and a prismatic tube having a flange width of 10 mm was used as Comparative Example 1 (tailored blank press welded part).

(Comparative Example 2) From the ERW tubes manufactured in the same manner as in the example, a thin tube for a low strength portion and a thick tube for a high strength portion were selected, and both tubes were butt-welded to form a tailored tube. The tailored tube is subjected to the same prepressing and HF molding as in the embodiment, and the molding dimensions are adjusted by trial and error to the thickness of the low-strength part (average in the circumferential direction): 1.6 mm, the length of the same part 150 mm, and the high-strength part Thickness (average in circumferential direction): 2.6mm,
According to the same section length: 150 mm, a prismatic tube having the appearance shown in FIG. 5 was used as Comparative Example 2 (tailored tube HF processed part).

The following impact test was performed on each of the components of the examples and comparative examples. A stopper is set so that a 10kg weight is hit directly at 50km / h (collision direction is parallel to the long axis direction of the part) at one end of the low strength part side of each part, and stops when the one end is displaced 150mm. to the load continuously measuring the load between the collision start to weight stop - displacement curve determined absorbed energy e per weight absorbed energy E _s and component units by which the integrating displacement load based on _s was calculated. Table 1 shows the results.

[0025]

[Table 1]

[0026] From Table 1, in Embodiment 1 also in Example 2, were comparable to Comparative Example 2 (tailored tubes), absorbed energy e _s of greater per part unit weight than Comparative Example 1 (tailored blanks) are obtained. Moreover, when the man-hours for manufacturing the HF processing steel pipe were compared between Example 1 and Comparative Example 2,
The man-hour for filling the resin into the single tube of Example 1 is about 90% of the man-hour for butt welding different thickness pipes of Comparative Example 2, and it is confirmed that the present invention is more advantageous in terms of manufacturing cost than the tailored tube. Was.

[0027]

As described above, according to the present invention, it is possible to obtain an HF part having a shock absorbing performance comparable to the case where the tailored tube is made of a material for HF processing, and the high strength steel pipe for HF processing of the present invention is tailored. Because it can be manufactured at a lower cost than tubes, it will be possible to supply HF processing materials that contribute to automotive structural members more economically.
It has a significant effect on industry.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a steel pipe for hydroforming according to the present invention.

FIG. 2 is a sectional view showing an example of a hydroformed part according to the present invention.

FIG. 3 is a schematic view showing a method of filling a resin into a tube by screw injection molding.

FIG. 4 is a sectional view showing an example of a method for manufacturing a hydroformed part according to the present invention.

FIG. 5 is a schematic diagram showing the external dimensions of a prismatic tube subjected to a collision test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single pipe part 2 Resin filling part 3 Pipe (pipe) 4 Resin 5 Hole (through-hole) 6 Injection molding die 7 Plug 8 Core 10 Raw resin (resin pellet) 11 Plastic resin 12 Hopper 13 Header 14 Nozzle 15 Heater 16 Screw 17 Rod 18 Drive gear 19 Hydraulic cylinder 20 Lid cylinder 21 Press 22 Drag 23 Cut plate 24 Edge chamfer 25 HF mold 26, 26 'Push shaft 27 Shaft push 28 Liquid passage 29 Liquid injection 30 Low strength Part 31 High strength part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Ito 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term (reference) 4R206 AA32 AD03 AD12 AG08 AG25 AH17 JA07 JB12

Claims (6)

[Claims] 1. A high-strength steel pipe for hydroforming, which has a resin-filled portion in a part of the entire length. 2. The steel pipe according to claim 1, wherein the resin filling portion has a hole penetrating in a length direction. 3. The steel pipe according to claim 1, wherein the resin-filled portion is formed by injection molding. 4. A hydroformed part having a resin-filled part in a part of the entire length. 5. A hydroformed part obtained by hydroforming a steel pipe having a resin-filled portion in a part of its entire length. 6. A hydroformed part formed by hydroforming a steel pipe and then filling the inside thereof with a resin.