JPH0366421A - Squeezing method for high-strength tube - Google Patents

Abstract

PURPOSE:To obtain a prescribed shape without cracking by performing squeezing work by use of a projecting indenting punch which is provided with two- stepped bottom on the cross section in the lateral direction when a part of the high-strength tube of a specified tensile strength is squeezing worked in the longitudinal direction. CONSTITUTION:A part of the high-strength tube of the tensile strength >=35 kg f/mm<2> is concavely performed by squeezing in the longitudinal direction. Indenting depth H is restricted by the indenting punch with the two-stepped bottom and a prescribed squeezing depth B is obtained. When the middle part (c) of the part to be worked is squeezed with the middle bottom part 3 of the punch, also the bottom part 4 on both sides starts to squeeze the squeezed top part (f) of tube and, since that, the increase of indenting depth H is equal to the increase of squeezing depth B. From that point of time, the relative position of the (b), (d) part of the starting part of contact with the punch and the squeezed top part (f) is kept constant and the working degree of (b), (d) is hardly increased. By this way, the crack that is generated on the (b), (d)-part of the starting part of contact with the indenting punch can be prevented.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to crushing of high-strength tubes.

(Prior art) In the pipe structures of automobile seat frames, furniture, etc.
A pipe is used in which a part of the pipe is crushed using a press depending on the purpose.

The situation of the crushing process will be explained below.

Figure 2 shows the indentation punch and the state of the tube after crushing.

3(a) is a longitudinal cross-sectional view, and FIG. 2(b) is a cross-sectional view taken along the line ■■■ in (a). In the figure, 11 indicates the indentation punch, 12 indicates the tube after crushing, a and e indicate the end of the deformation of the tube by crushing, b and d the start of contact with the indentation punch, and C indicates the processed part. The central part is shown, D is the outside diameter of the tube before processing, and H is the outside diameter of the tube before processing.
indicates the indentation depth, and B indicates the crushing depth.

As shown in the figure, the push punch 11 is pushed into the tube by a press (not shown), and the tube is longitudinally divided into a, b,
, c, d, and e, and in the cross-sectional direction, are crushed into the shape shown in the cross-sectional view taken along the line ■-■.

In such a crushing method, in order to obtain a predetermined crushing depth B, the indentation depth H must be made larger than necessary, which causes cracks to occur in the crushed part. In order to prevent this cracking, it is necessary to lengthen the distance between the end portions a and e of the pipe deformed by the crushing process shown in FIG. 2, and to make the crushing depth B small. However, since the structure is usually designed to be compact, the distance between a and e is short and the crushing depth B is large.

(Problems to be Solved by the Invention) As described above, in the conventional method, the indentation depth becomes large in order to obtain a predetermined crushing depth. Therefore, the tensile strength is 35
Although it is possible to crush soft steel pipes with a weight of less than "kgf/am" using conventional methods, crushing is possible with high-strength pipes that have low elongation, and pipes that have undergone shrinkage processing where elongation is further reduced, as shown in Figure 2 (a). There was a problem in that the degree of processing at the start of contact with the indentation punch (S, d) was significantly increased, and cracks were generated in this area, resulting in breakage.

(Means for Solving the Problems) The present invention was completed as a result of intensive research and repeated consideration by the present inventors in view of the problems of the conventional pipe crushing method explained above. The first invention uses a convex push punch with a double bottom in the cross section in the width direction when crushing a part of a high strength pipe with a tensile strength of 35 kgf/mm" or more into a concave shape in the longitudinal direction. A second invention provides a method for crushing a high-strength tube using a convex push punch having two bottoms in the cross section in the width direction. This is a method for crushing high-strength pipes, in which crushing is performed using a force punch that satisfies the following (2).

A(攬ll)≦H,-B・・・・・・・・−・
・・・・・・・・・－・・■ However, Hll-73-13, 31nT S H8: Limit pushing depth (mm) B: Crushing depth (m+w) TS: Tensile strength of pipe (kgf/mm” ) (Function) Hereinafter, the function of the present invention will be explained.

FIG. 3 shows the state of the indentation punch provided with the two-stage bottom according to the present invention and the tube after crushing. Figure (a) is a longitudinal cross-sectional view;
(b) is a sectional view taken along the line ■-■ of (a). In the figure, 1 is the push punch, 2 is the tube after crushing, 3 is the center bottom,
4 indicates the bottom portions on both sides. a and e indicate the end of the deformation of the tube by crushing, b and d the start of contact with the indentation punch, C the center of the processed portion, and r the top of the crushing process. D indicates the outer diameter of the tube before processing, H indicates the indentation depth, and B indicates the crushing depth.

The indentation punch 1 shown in the figure has a two-stage bottom and is intended to limit the indentation depth H shown in FIG. 2 and obtain a predetermined crushing depth B. That is, in FIG. 3, when the central bottom part 3 of the punch has crushed the central part C of the processed part of the pipe to a certain stage, the bottom parts 4 on both sides also start to crush the crushed top part f of the pipe. The increase in depth H and the increase in crushing depth B are equal. From this point on, the relative positions of the contact start portions S and d with the third (2) indentation punch and the crushing top portion r become constant, and the degree of machining of portions b and d hardly increases. Therefore, the point of contact with the indentation punch is
The crack that occurred in the d section is prevented.

Furthermore, in order to ensure prevention of cracking, the concept of limit indentation depth was introduced for the purpose of determining the indentation depth H in accordance with the pipe strength. The critical indentation depth indicates the indentation depth at which cracks do not occur depending on the strength of the pipe, and is determined by the following formula.

H* -7313,31nT S However, H3: Limit indentation depth (mm) TS: Tube tensile strength (kgf/mm") The limit indentation depth HR determined by the above formula indicates the limit of indentation depth H. Therefore, the value obtained by subtracting the crushing depth B from the limit pressing depth He corresponds to the step difference A between the center bottom and both side bottoms of a convex pressing punch with a two-step bottom.

This is the formula for finding this person.

A (open)≦H* B However, HR=73 13.31nT S HR: Limit pushing depth (question) B: Crushing depth (mm) TS: Tensile strength of pipe (kgf/mm”) Determined by the formula The push punch has a step A between the center bottom and both side bottoms.
When a tube having the strength used to obtain A is crushed, no cracks occur.

As described above, the convex indentation punch provided with the two-step bottom can disperse the degree of machining in the crushing process of the tube and perform the crushing process without causing cracks.

(Example) Although the configuration of the present invention is as described above, an example will be described below.

The test tube was an ERW steel pipe with an outer diameter of 25 mm and a wall thickness of 1 mm.
Crushing was performed according to the crushing conditions shown in the table.

The results are also listed in Table 1.

Table 1 shows the punch shape, crushing conditions, tensile strength of the pipe,
The presence or absence of cracks and the limit indentation depth are shown respectively.

(Left below) Table 1 - Comparison method: A < I+,
- B is Ho ×; fracture * O: end fracture * l, , 3-1331nTS (Hereafter the margin) In all of the crushing processes shown in Table 1, the crushing depth is constant as ham, and in order to obtain this crushing depth. Measure the indentation depth of
Furthermore, the presence or absence of cracks in the crushed portion was observed.

Steel pipe 1.2 in Table 1 was crushed using the conventional method, but since steel pipe 1 has a low tensile strength of 30 kgf/ms, it can be crushed using the conventional method without cracking.

However, since the steel pipe 2 has a high tensile strength of 50 kgf/am, the indentation depth exceeds the limit indentation depth in order to obtain the crushing depth of 9. As a result, cracks occur in the crushed part. It has occurred.

Steel pipe 3.4 was crushed using the method of the present invention, and has a tm
Pipe 3 has a tensile strength of 50 kgf/mm” or more, 1lt4
Despite having a high tensile strength of 70 kgf/am'' or more, it is possible to crush the processed parts without cracking.

Steel pipe 5 is a comparative method and uses a punch with a two-step bottom, but since the step A of the two-step bottom is outside the appropriate conditions,
The indentation depth has increased and exceeds the maximum indentation depth for this tube. Therefore, although the steel pipe 5 has the same tensile strength as the steel pipe 4, cracks have occurred in the crushed portion.

An example of the push punch according to the present invention is shown in FIG.
Figure (a) shows the basic shape, (b) shows the punch with a curvature at the bottom, and (c) shows the punch with steps on both sides.
(d) shows a shortened central bottom. In any of these shapes or a combination of these shapes,
The indentation punch according to the present invention does not cause cracks during crushing.

As is clear from the above examples, the method for crushing a high-strength tube according to the present invention can crush a high-strength tube without causing cracks in the crushed portion.

(Effects of the Invention) As explained above, the method for crushing high-strength tubes according to the present invention has the above-mentioned configuration, so that even when crushing high-strength tubes with low elongation or tubes processed into $1 tubes, the tubes can be crushed. This has an excellent effect in that a predetermined shape can be obtained without any trouble.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a push punch according to the present invention. The figure (a) shows the basic shape, (b) shows the punch with a curvature at the bottom, (c) shows the punch with steps on both sides, and (d) shows the punch with a shortened center bottom. It is a diagram. FIG. 2 is a diagram showing a conventional push punch and the state of the tube after crushing. The same figure (a) is a longitudinal cross-sectional view, (b) is (a)
It is a figure which shows the sectional view on the ■-n line of. FIG. 3 is a diagram showing the condition of the push punch provided with the two-stage bottom according to the present invention and the tube after crushing. FIG. It is a diagram showing a sectional view taken along the line -■. 1.--Push punch 2-.Pipe 3 after crushing...Central bottom 4.Bottoms on both sides 11.Press punch 12.Pipe a, e after crushing.-- End part of pipe deformation due to crushing bSd・
・-Contact start point c with the indentation punch - Center part f of the processed part... Crushing top part A... Step difference between the center bottom and the bottoms on both sides B - Crushing depth D... Pipe before processing Outer diameter H...Pushing depth Fig. 1

Claims (2)

[Claims] (1) When crushing a part of a high-strength pipe with a tensile strength of 35 kgf/mm^2 or more into a concave shape in the longitudinal direction, a convex push punch with a two-step bottom in the cross section in the width direction is used. A method for crushing a high-strength pipe, which is characterized by performing crushing. (2) In a convex push punch with two bottoms in the cross section in the width direction, the step A between the center bottom and both side bottoms is as follows [1
] A method for crushing a high-strength pipe, characterized in that crushing is performed using an indentation punch that satisfies the formula. A (mm)≦H_R-B...[1] However, H_R=73-13.31nTS H_R: Limit pushing depth (mm) B: Crushing depth (mm) TS: Tensile strength of pipe (kgf/mm ^2)