JP4628217B2 - Bulge forming method and its mold - Google Patents

Description

  The present invention relates to a bulge forming method for performing a pipe expanding process for expanding a pipe by circulating a pressure fluid through a tubular member, and a mold thereof.

  As a technique for producing a hollow molded body that is long and has a different cross-sectional shape / dimension in a direction orthogonal to the longitudinal direction depending on the part, bulge molding is employed. The bulge forming process using a straight pipe as a raw material will be described in detail. First, the straight pipe is sandwiched and accommodated in a mold, and in this state, pressure fluid (generally, high-pressure water) is placed inside the straight pipe. To be supplied.

  For this reason, the inner peripheral wall of the straight pipe is pressed by the pressure fluid, whereby the straight pipe expands outward in the diameter direction. Since the straight pipe is accommodated in the mold, the expanded portion is finally blocked by the mold, and for this purpose, the straight pipe is molded into a shape corresponding to the cavity. This process is also called a pipe expansion process.

  Next, the expanded straight pipe is transferred to another mold, and the straight pipe is pressed under the action of a compression mechanism to be preformed into a predetermined shape. Furthermore, a finish molding process is performed with another mold, and thereby a final molded product is obtained.

  By the way, in the preforming, a part of the expanded straight pipe is crushed. At this time, for example, a deformed portion that is depressed more than necessary may be formed in the crushed portion of the straight pipe. When a deformation occurs, it is not easy to remove it by a finish molding process, and therefore, a final molded product in which the deformation remains is produced.

  Therefore, Patent Document 1 proposes performing crushing while applying pressure from the inside of the hollow member in order to avoid the occurrence of deformation. That is, the hollow member is expanded to the same peripheral length as the final molded product in the molding die, and then the same die is used to press with a pad that moves up and down while supplying pressure fluid to the inside of the hollow member.

JP 11-47842 A

  In the technique described in Patent Document 1, a high pressure of 100 to 200 atmospheres (approximately 10 to 20 MPa) is applied to the hollow member. In order to raise the pressure fluid to such a high pressure, a large-scale facility is required. In other words, capital investment increases.

  Eventually, the technique described in Patent Document 1 has a problem that deformation cannot be avoided unless equipment that can supply the pressurized fluid at a high pressure is provided.

  The present invention has been made to solve the above-described problems, and provides a bulge forming method and a mold thereof that do not require a high pressure to be applied to a tubular member, and that do not cause an increase in capital investment. With the goal.

In order to achieve the above-mentioned object, the present invention has a tube expanding step for expanding a tube by circulating a pressure fluid through the tubular member, and a forming step for pressing a part of the expanded tubular member to perform a forming process. A bulge forming method,
Among the portions pressed in the molding step, a flat portion is provided in the tube expansion step at a position where the length ratio defined by the following formula (1) is 0.2% or more and less than 1.0%. And

  That is, in the present invention, a flat portion is provided at a position where the length ratio falls within a predetermined range. For this reason, a deformation | transformation does not arise by sagging of excess meat. Further, since the length ratio is less than 1% at the maximum, the final dimension of the portion where the flat portion is provided does not become significantly short of the target dimension of the final molded product.

Further, the present invention is a bulge forming mold for performing a tube expanding process for expanding a tube by circulating a pressure fluid through a tubular member,
The cavity has a flat part molding part in which a flat part in which the length ratio defined by the following formula (1) is 0.2% or more and less than 1.0% is provided in the tubular member,
The flat part forming part is characterized by forming a portion to be pressed to be pressed in the next step in the tubular member as a flat part.

  By setting it as such a structure, the pipe expansion molded object which has a flat part with this metal mold | die is produced. Since the dimension of the flat portion molding portion is set so as to be within the range of the length ratio described above, it is avoided that deformation occurs even when the flat portion is crushed in the subsequent molding step. Further, since the length ratio is less than 1% at the maximum, the thickness of the flat portion is not significantly different from other portions.

  In addition, according to the present invention, even if the deform is formed, the degree thereof is remarkably small. Therefore, the deform is restored and removed by supplying a relatively low pressure fluid to the inside of the tubular member. Accordingly, there is no need to provide special equipment, so that capital investment will not increase. That is, it is possible to avoid the deformation remaining in the final molded product at a low cost.

  According to the present invention, in the tube expansion process, the flat portion is provided at a position where the length ratio of the arc and the string is within a predetermined range. For this reason, even if the flat portion is crushed in the next step, the occurrence of deformation at the crushed portion is suppressed. In addition, since the upper limit of the length ratio is less than 1%, the final dimension of the flattened flat part is significantly insufficient for the target dimension of the final molded product, and the thickness of the flat part is smaller than other parts. Significant differences are avoided.

  That is, according to the present invention, it is possible to obtain a bulge-formed product that is prevented from being deformed and has good dimensional accuracy at a low cost without providing special equipment.

  Hereinafter, preferred embodiments of the bulge forming method according to the present invention will be described in detail in relation to a mold for carrying out the method, and will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic overall perspective view of a straight pipe 10 to be subjected to bulge forming, and FIG. 2 is a longitudinal sectional view of a main part of a pipe expansion mold 14 along the longitudinal direction of the pipe expansion molded body 12. That is, in the present embodiment, the straight pipe 10 shown in FIG. 1 is subjected to pipe expansion processing by the pipe expansion processing mold 14 shown in FIG. In FIG. 2, a part of the pipe expansion molded body 12 and the pipe expansion processing mold 14 are shown.

  The straight pipe 10 shown in FIG. 1 is clamped so as to be pressed from both ends by a clamping mechanism (not shown), and in this state, is conveyed to the tube expansion mold 14 shown in FIG. The pipe expansion mold 14 includes a lower mold 16 and an upper mold 18, and a cavity 20 is formed by clamping and the straight pipe 10 is accommodated in the cavity 20.

  An insert 24 provided with a substantially flat flat portion forming portion 22 is detachably installed on the forming surface of the upper mold 18. As will be described later, the flat portion 26 is formed on the tube expansion molded body 12 by the flat portion forming portion 22.

  Compressed gas or the like is supplied to the straight pipe 10 accommodated in the cavity 20 through the clamping mechanism. As a result, the internal pressure of the straight pipe 10 increases, and as a result, the straight pipe 10 expands toward the molding surfaces of the lower mold 16 and the upper mold 18.

  Finally, the outer peripheral wall of the straight pipe 10 is blocked by the molding surfaces of the lower mold 16 and the upper mold 18, thereby forming the pipe expansion molded body 12 shown in FIG. 2.

  As can be understood from FIG. 2, the tube expansion molded body 12 is manufactured by providing the flat portion 26 at the tube expansion portion 28. As will be described later, the flat portion 26 is pressed in the next step.

  Here, FIG. 3 shows a longitudinal side view of the tube expansion molded body 30 that is manufactured without subjecting the straight tube 10 to tube expansion processing and without providing the flat portion 26. When the arc portion 33 of the tube expansion portion 32 in the tube expansion molded body 30 is pressed by T in the next step to provide the string 34, in reality, as shown in FIG. Will be formed.

  This is because the arc portion 33 is longer than the string 34 when the arc portion 33 of the expanded portion 32 is crushed to provide the string 34. That is, as the arc portion 33 is crushed, surplus meat flows to the center, and as a result, the deform is formed by the sagging of the meat.

  In order to avoid the occurrence of the deformation 36, it is recalled that the string 34 is provided in the tube expansion process. However, in this case, since the straight pipe 10 is not expanded uniformly, there is a problem that the wall thickness of the expanded portion 28 in the expanded molded body 12 is not uniform.

  Therefore, in the present embodiment, in the tube expansion process, the flat portion 26 is provided to such an extent that the deform 36 is not generated in the next preforming process and a significant difference in the wall thickness does not occur. Specifically, as shown in FIG. 5, a line L2 parallel to the axis L1 is drawn to the tube expansion portion 28, and a chord CH and an arc AR are provided by a contact point between the virtual circle C1 of the tube expansion portion 28 and the line L2. The lengths of the chord CH and the arc AR are obtained, and the length ratio defined by the following equation (1) is calculated.

  The flat portion 26 is provided so as to be at the position of the string CH where the length ratio is 0.2% or more and less than 1.0%. For example, FIG. 6 shows the relationship between the length of the arc AR and the chord CH and the length ratio when the diameter of the virtual circle C1 is 113.6 mm.

  Note that when the length ratio is less than 0.2%, the arc AR and the chord CH substantially coincide. For this reason, the string CH is formed at a substantially flat portion of the arc AR. On the other hand, if it is 1.0% or more, as shown in FIG. A more preferable range of the length ratio is 0.3 to 0.6%, and a more preferable range is 0.35 to 0.5%. Note that “◯” in FIG. 6 means that the deform 36 was not formed, and the final dimension of the portion where the flat portion 26 was present was within the allowable range as the target dimension of the final molded product. To do.

  In this manner, the flat portion 26 having a length ratio with the arc AR within a predetermined range is formed by the flat portion forming portion 22 of the nest 24 that constitutes the tube expansion mold 14 shown in FIG. Of course, the size of the insert 24 is set so that the flat portion 26 is provided at a position where the length ratio of the arc AR and the chord CH is 0.2% or more and less than 1.0%.

  The length ratio can be changed by installing the insert 24 having a different dimension such as the flat portion molding portion 22 in the upper mold 18.

  The pipe expansion molded body 12 produced by subjecting the straight pipe 10 to the pipe expansion process is conveyed to a pre-forming station, where the pre-forming is performed. That is, the tube expansion portion 28 of the tube expansion molded body 12 is crushed by pressing, and the flat portion 26 is also crushed accordingly.

  The length of the flat portion 26 does not change much before and after the crushing. That is, the flat portion 26 that has been crushed is only slightly longer than before the crushing. For this reason, surplus meat does not flow to the central portion and sagging does not occur. In other words, the occurrence of the deformation 36 is avoided.

  Further, even if the deform 36 occurs, the degree of depression is small. Therefore, if compressed gas or the like is supplied to the inside of the tube expansion body 12 so that the pressure is about 0.5 to 2.0 MPa, the deform 36 is pressed and restored by the compressed gas or the like. That is, in the present embodiment, unlike the bulge forming method according to the prior art, it is not necessary to set the pressure fluid to a very high pressure in order to restore and remove the deformed shape. For this reason, capital investment does not soar.

  Further, the flat portion 26 is provided at a position where no significant difference in thickness from other portions of the tube expansion portion 28 occurs in the final molded product. Therefore, a final molded product having a substantially uniform thickness can be easily obtained.

  The pipe expansion molded body 12 subjected to the preforming is conveyed to the next finishing molding station and finished to the dimensions of the final molded product. When the flat part 26 is provided in the pipe expansion molded body 12, the dimension of the portion where the flat part 26 was present may be insufficient for the target dimension of the final molded product, but the length ratio of the arc AR and the chord CH Since the flat portion 26 is provided at a position where the value is less than 1.0%, the shortage amount is extremely small and within the allowable range.

  In the above-described embodiment, the case where the virtual circle C1 is illustrated as a perfect circle has been described as an example. However, the flat portion 26 is provided in the gently curved curved portion 42 in the tube expansion portion 40 illustrated in FIG. The inscribed circle IC including the curved portion 42 as an arc may be illustrated to obtain an arc and a chord. Even in this case, the length ratio of the arc and the chord is set within the range of 0.2% or more and less than 1.0%.

  Moreover, you may make it perform finish shaping | molding, without performing preforming after a pipe expansion process.

It is a general | schematic whole perspective view of the straight pipe to which a bulge forming process is given. It is a principal part longitudinal cross-sectional view of the pipe expansion process metal mold | die along the longitudinal direction of a pipe expansion molded object. It is a longitudinal direction side view of the pipe expansion fabrication object produced without providing a flat part. It is side surface sectional drawing in alignment with the longitudinal direction of the pipe expansion molded object which shows the state by which the pipe expansion molded object of FIG. 3 was pressed and a deformation | transformation was formed. It is a definition explanatory drawing explaining the definition of a string and an arc in a pipe expansion part. It is a graph which shows the relationship between the length ratio of an arc and a chord, and processing precision. It is a longitudinal direction side view of a pipe expansion fabrication object concerning another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Straight pipe 14 ... Mold 18 for pipe expansion processing ... Lower mold 18 ... Upper mold 20 ... Cavity 22 ... Flat part shaping | molding part 24 ... Insert 26 ... Flat part 36 ... Deformation AR ... Arc C1 ... Virtual circle CH ... String IC ... Inscribed circle

Claims (2)

A bulge forming method applied to a tubular member,
A tubular member loaded in a bulge forming mold having a flat portion forming portion in the cavity is expanded by circulating a pressure fluid through a tubular member, thereby forming a circular arc shape in a longitudinal section of the tubular member. A tube-expanding step for forming a tube- expanded portion including an arc portion forming the flat portion and the flat portion formed by the flat portion forming portion ;
A molding step of performing a molding process to form a chord shape with respect to the arc portion by pressing the tube expansion portion including the flat portion ;
I have a,
In the tube expansion step, the flat portion is provided in the tube expansion step at a position where the length ratio defined by the following formula (1) is 0.2% or more and less than 1.0%. Bulge forming method.

A tubular member loaded in a bulge forming mold having a flat portion forming portion in the cavity is expanded by circulating a pressure fluid through a tubular member, thereby forming a circular arc shape in a longitudinal section of the tubular member. Forming a tube expansion portion including a circular arc portion forming the flat portion and the flat portion formed by the flat portion forming portion, and forming a chord shape with respect to the arc portion by pressing the tube expansion portion including the flat portion used in the expanding process in bulge forming which includes a molding step of subjecting the molding to, a bulge forming die of order to Ru is tube expansion by flowing pressurized fluid into the tubular member,
A tube expansion part forming part for forming the tube expansion part including the arc part and the flat part;
Wherein provided on the expandable tube portion forming part, and the flat part forming portion flat portion length ratio defined is less than 0.2% or more and 1.0% you molded into the tubular member by the following formula (1) ,
I have a,
The flat part forming part forms a part of the pipe expansion part as a flat part when forming the pipe expansion part in the tubular member by the pipe expansion process .

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