JP2006192443A - Method for drawing square tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drawing a square-tube by which the generation of wrinkles and break in the round part of a corner die are suppressed by quantitatively adjusting the contact of a die by using bearing-pressure difference between a straight side part and a corner part. <P>SOLUTION: When a tube-shaped body having a tetragon-shaped cross section is drown in the middle part of a blank in the state where the peripheral part of the blank composed of a tetragonal sheet is held with a blank holder, the bearing pressures between the blank holder in the straight side part and the corner part of the tubular body having the tetragon-shaped cross section and the die are measured from the variation in a tone of a pressure sensitive paper to which the pressure is added when performing a trial drawing using the pressure sensitive paper and a die the contact of which is adjusted so that the bearing pressure in the straight side part is higher than the bearing pressure in the corner part is used. It is preferable that the adjustment of the bearing-pressure difference is performed by adjusting the thickness of shim plates which are inserted between the blank holder and a back-up plate with which the blank holder is pressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rectangular tube drawing method that suppresses generation of wrinkles and breakage of a corner die R portion when a rectangular tube container is manufactured by drawing a rectangular thin metal plate, particularly a stainless steel plate.

  Since the cylindrical drawing process causes shrinkage flange deformation, the processed flange portion gradually increases in thickness from the die R to the flange tip. Furthermore, since the wrinkle pressing force is applied to the thickest outer periphery of the flange, a gap is formed on the wrinkle pressing surface near the die R, and this makes it easy for flange wrinkles to occur near the die R. . In particular, when a stainless steel plate that is easily work hardened is used as a raw material, it is difficult to remove the wrinkle, so that the mold adjustment is strictly performed so that the wrinkle does not occur. In general, in order to draw the outer periphery of the wrinkle holding surface and draw it, the contact of the mold is adjusted by inserting a shim plate on the back side of the die or blank holder.

In the rectangular tube drawing process, the deformation mode differs as a whole due to the bending process at the right side and the drawing deformation at the corner part. In addition, since the corner portion increases in thickness due to shrinkage deformation, the corner portion has a greater resistance to deformation of the flange than the corner portion.
Therefore, in general, in order to facilitate the material inflow of the corner portion, it is considered that the drawing process is preferably performed by weakening the contact of the corner portion with respect to the mold rather than the straight side portion.

In order to weaken the contact between the corner and the mold than the straight side, the thickness of the shim plate to be inserted into the back side of the die or blank holder is made thinner than the straight side. Non-Patent Document 1 proposes this.
For the same purpose, Non-Patent Document 2 proposes polishing the corner portion of the blank holder with a grindstone.
Masao Fukuoka, et al. 2, “Press Technology”, Vol. 10 No. 4 (1972), 103 Satoshi Ota, “Press Technology”, Vol. 35, No. 5 (1997), 95

By the way, the adjustment per die at the manufacturing site is based on the transfer status of the light aluminium applied to the die surface to the wrinkle holding surface and the discoloration state of the pressure-sensitive paper interposed between the die surface and the wrinkle holding surface. It is done by knowing.
Such a tapping operation can be easily performed with a small number of adjustments by a skilled worker having abundant press working experience. However, if it is a normal worker, adjustment by trial and error is often performed, and adjustment per die takes time and productivity is deteriorated.

Furthermore, since there is no quantitative evaluation standard for judging the condition of Kokaridan and the discoloration state of the pressure-sensitive paper obtained by trial strikes after mold adjustment, we always rely on feeling and experience. For this reason, the adjustment work per die in the rectangular tube drawing process must be handled by qualitative judgment, and there is a personal difference.
The present invention has been devised to solve such a problem, and by making use of the difference in surface pressure between the straight side portion and the corner portion to perform quantitative adjustment per die, wrinkles are generated and the corner die R portion. An object of the present invention is to provide a rectangular tube drawing method that suppresses breakage of the steel sheet.

In order to achieve the object, the square tube drawing method of the present invention draws a cylindrical body having a rectangular cross section at the center of the blank in a state where the peripheral portion of the blank made of a rectangular thin plate is held by a blank holder. At the time, when the test paper is made using pressure-sensitive paper, the surface pressure between the blank holder and the die at the straight side portion and the corner portion of the rectangular cross-section cylindrical body from the density change of the pressure-sensitive paper to which the pressure is applied. And using a mold that is adjusted so that the surface pressure of the straight side portion is higher than the surface pressure of the corner portion.
The adjustment of the surface pressure difference is preferably performed by adjusting the thickness of the shim plate inserted between the blank holder and the backup plate that presses the blank holder.

  In the present invention, the hitting adjustment of the mold is adjusted by the measurement value of the surface pressure by using a general-purpose pressure sensitive paper and the density change of the pressure-sensitive paper by using a general-purpose measuring instrument. Therefore, since the contact adjustment of the mold is performed based on the quantitative surface pressure measurement value, not only the influence of individual differences is reduced, but the adjustment time is shortened, and the overall shape accuracy is excellent. This makes it possible to produce a rectangular cylinder drawn product with high productivity.

By the way, the drawing die usually received from the die manufacturer is not adjusted per die because the press machine used at the processing destination cannot be specified. The die contact is adjusted according to the press machine and work material at each processing destination. Depending on the shape and type of steel, there are products that can be drawn without adjustment per die, but especially when drawing austenitic stainless steel sheets that increase work hardening and flange thickness increase, adjustment per die is required. Is mandatory.
If the die contact is the entire surface or the outer contact, the inflow resistance of the flange increases, so that processing cracks are likely to occur. In order to reduce the inflow resistance of the flange, it is necessary to perform a drawing process at the inner end. For this purpose, a shim plate is inserted between the blank holder and a backup plate that presses the blank holder.

In the rectangular tube drawing process, the deformation mode differs as a whole due to the bending process at the right side and the drawing deformation at the corner part. As described above, since the corner portion increases in thickness due to shrinkage deformation, the deformation resistance of the flange portion is not only greater at the corner portion than at the straight side portion, but also the inflow resistance of the material at the corner portion is increased. Become. In order to promote the material inflow of the corner portion, it is necessary to make the material easier to enter than the right side portion.
Although depending on the initial state of the mold (the per-die state), when the shim plate is inserted in the right side of the mold when the entire surface is in uniform contact, a gap is generated at the corner. By forming this gap, the flange material of the corner portion is easily pulled in, and processing cracks can be prevented. However, if the gap is too large, wrinkles are likely to occur.

As described above, the die contact at the rectangular tube diaphragm can be adjusted by inserting the shim plate. However, since the initial state of each mold is different, it is difficult to quantify the arrangement and thickness of the shim plate to be inserted.
Therefore, the present invention quantifies the contact between the straight side and the corner of the shim plate by adjusting the thickness of the shim plate as the surface pressure difference when drawing the square tube, regardless of the initial state of the mold, and the influence of individual differences. It is intended to manufacture a rectangular tube drawing product excellent in shape accuracy with low productivity and high productivity.
Hereinafter, the present invention will be described in more detail.

In the rectangular tube drawing method, an apparatus having a die composed of an upper die and a lower die attached to a press as shown in FIG. 1 is usually used. The mold includes an upper holder 1 mounted on a slide of a press machine, an upper mold 5 in which a plate 2, a die 3 and a knockout mechanism 4 are incorporated, a lower holder 7 fixed to a bolster 6 of the press machine, a punch 8 and It consists of a lower mold 12 in which a blank holder 9, a backup plate 10, and a cushion pin 11 are combined.
Basically, the above-described square tube drawing apparatus as described above is also used in the method of the present invention.

A method for adjusting the die contact using the mold apparatus shown in FIG. 1 will be described.
For adjustment per die, for example, a hard material of a stainless steel thin plate whose thickness is adjusted to 50 μm is used as the shim plate S. The shim plate S is inserted between the die 3 and the plate 2 of the upper mold 5 or between the blank holder 9 and the backup plate 10 of the lower mold 12. Considering the premise, it is preferable that the lower mold 12 is inserted between the blank holder 9 and the backup plate 10.

  As described in the above description of the prior art, due to the shrinkage deformation in the drawing process, an increase in the thickness of the flange portion adds a wrinkle holding force to the outer periphery of the flange and creates a gap in the vicinity of the die R. As a result, the flange Wrinkles are likely to occur near the die R. Therefore, in order to suppress the formation of the gap, it is preferable that a shim plate having a width slightly larger than the die R is disposed close to the punch.

After inserting the shim plate, a commercially available pressure sensitive paper cut out in the shape of a blank is placed on a blank holder, and a test strike is performed by pressing.
After performing the test punching by press working, the pressure sensitive paper on the blank holder is taken out. The surface pressure of the portion where the color of the pressure sensitive paper is changed is measured using a commercially available surface pressure measuring tool in a flat place. Specifically, the surface pressure difference between the straight side and the corner where the shim plate is arranged is measured, and the difference in surface pressure between the two, and then the occurrence of wrinkles and cracks in the square tube drawing body when it is actually drawn. Contrast with. And the thickness of a shim board is changed variously and it sets as an appropriate range of a surface pressure difference when a wrinkle and a crack do not generate | occur | produce in a square tube drawing molded object.

Increasing the surface pressure difference by mold adjustment tends to reduce the frequency of occurrence of defective molding in the moldable region. If the surface pressure difference is small, the frequency of occurrence of processing cracks is high, and if the surface pressure difference becomes too large, wrinkles are likely to occur. Since there is a surface pressure difference suitable for processing depending on the steel type and the shape of the molded product, it is necessary to obtain an appropriate surface pressure difference in advance for each.
In the case of using SUS304, which is austenitic stainless steel, as a raw material, and obtaining an angular drawing molded product of corner R40 with a long side of 190 mm, a short side of 90 mm, and a depth of 90 mm, a surface pressure difference of 5 to 7 MPa is preferable.

A description will be given of an example in which a rectangular tube drawn product is actually manufactured using austenitic stainless steel (SUS304) having a thickness of 0.7 mm.
A blank obtained by corner-cutting a cut plate of 310 mm × 295 mm into a polygon was used.
The shape of the rectangular tube diaphragm was an oval having a long side of 190 mm, a short side of 90 mm, and a corner R of 40R. The mold apparatus used was the same as that shown in FIG. 1, and the mold punch R was 15 mm and the die R was 10 mm. The press machine was an 80-ton hydraulic press, water-based lubricant was used, the wrinkle holding force was changed within a range of up to 50 tons, and the product height after drawing was 90 mm.

In the mold apparatus shown in FIG. 1, the surface pressure distribution of the straight side portion and the corner portion when the thickness of the shim plate S inserted between the blank holder 9 and the backup plate 10 is variously changed between 10 and 100 μm. In addition to the measurement, the appearance of the rectangular tube drawn product when drawn under the conditions was observed.
The surface pressure distribution was performed using “Prescale” (registered trademark) manufactured by Fuji Photo Film Co., Ltd. as the pressure-sensitive paper, and using a prescale dedicated densitometer manufactured by Fuji Photo Film Co., Ltd. as the surface pressure measurement tool. In addition, the appearance of the rectangular tube drawn product was visually observed.

FIG. 2 shows the relationship between the thickness of the shim plate and the surface pressure distribution at the straight side portion and the corner portion, and FIG. 3 shows the relationship between the thickness of the shim plate and the appearance of the rectangular tube drawn product.
From the results shown in FIG. 1, the surface pressure difference between the straight side and the corner is 5 to 7 MPa when the thickness of the shim plate is 10 to 20 μm, whereas when the thickness is within the range of 50 to 100 μm It can be seen that there is almost no difference in surface pressure at the corner.
Further, from the results shown in FIG. 2, a rectangular tube drawing molded product can be obtained without generating wrinkles with a wide range of wrinkle pressing force when the thickness of the shim plate is in the range of 10 to 20 μm. On the other hand, when the thickness of the shim plate is in the range of 50 to 100 μm, wrinkles are easily generated or cracks are easily generated.

The result shown in FIG. 3 is also to indicate a moldable range that is a measure of stable mass production at the actual production level. In other words, the wider the moldable region, the smaller the occurrence of defects such as wrinkles and cracks, and the better the drawing workability, even if the material variation or the press conditions change.
2 and 3, when the thickness of the shim plate is 10 to 20 [mu] m, the surface pressure difference is 5 to 7 MPa, and the conditionable range is widened to facilitate drawing.
In other words, it can be said that when a square tube drawing is performed using a die whose contact is adjusted so as to have an appropriate surface pressure difference by using a shim plate, a drawn product free from wrinkles and cracks can be easily obtained. .

Schematic showing the mold equipment The figure which shows the relationship between the thickness of a shim board, and the surface pressure distribution of a straight side part and a corner part The figure which shows the relationship between the thickness of shim board and the appearance state of the square tube drawing molding product

Explanation of symbols

1: Upper holder 2: Plate 3: Die 4: Knockout mechanism 5: Upper mold
6: Bolster 7: Lower holder 8: Punch 9: Blank holder
10: Backup plate 11: Cushion pin 12: Lower mold S: Shim plate

Claims (2)

  When the peripheral part of a blank made of a rectangular thin plate is held by a blank holder and drawn into a cylindrical body having a rectangular cross section at the center of the blank, the pressure is applied when a test is performed using pressure-sensitive paper. The surface pressure between the blank holder and the die at the straight side and corner of the rectangular cross-section cylindrical body is measured from the density change of the added pressure-sensitive paper, and the surface pressure at the straight side is determined from the surface pressure at the corner. A rectangular tube drawing method characterized by using a die adjusted so as to be higher.   The square tube drawing method according to claim 1, wherein the adjustment of the surface pressure difference is performed by adjusting the thickness of a shim plate inserted between the blank holder and a backup plate that presses the blank holder.

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