JP2009262984A - Bottomed case and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive steel-made bottomed case which is used for a square battery case or the like, has a high dimensional accuracy of a body part and has a high reliability in welding of the body part to a bottom plate. <P>SOLUTION: A manufacturing method of the case includes the steps of: inserting a cut cylindrical steel pipe 3 having a predetermined length into forming dies 1a, 1b, 1c and 1d each having a molding surface corresponding to each corner of a desired tubular body and four molding parts movable in the direction toward each corner; moving four molding parts of the forming dies to the outside to expand the steel pipe from the inside to the outside; thereby forming the lateral cross section into a rectangular shape while stretching the circumference of the steel pipe (Fig.(c)) to manufacture a tubular body 3 having the frozen rectangular shape (Fig.(c')); and welding the steel-made bottom plate having a lateral cross-section the same as that of the tubular body or the body part to one end of the body part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bottomed case having a shape in which a cross-sectional shape is composed of a plurality of corner portions and straight portions connecting between the corner portions, and a method for manufacturing the same, which are used for manufacturing rectangular storage batteries, capacitors, and the like. .

  Currently, cases of storage batteries such as lithium batteries and cases of capacitors and the like are often made of aluminum or an alloy thereof as described in Patent Document 1. In addition, for the purpose of increasing the strength, a battery case is manufactured using a steel material, and nickel-plated steel or stainless steel is used in order to increase corrosion resistance. Furthermore, in order to reduce the weight of the storage battery and the capacitor, it is necessary to manufacture the case with a thin steel material.

  For example, various types of storage batteries are known, but a relatively large storage battery having a shape composed of a plurality of corner portions and straight portions connecting the corner portions is used. . In order to manufacture such a storage battery, a bottomed case molded into that shape is required. As a method for manufacturing a bottomed case using an aluminum material, deep drawing by press working is generally used. This method of deep drawing is a very efficient method when a bottomed case is manufactured using an aluminum material because a case having a desired shape can be manufactured by a single process.

However, it is difficult to apply this method to steel materials immediately. In other words, steel is thinner and less stretched due to weight reduction compared to aluminum, so if you try to deep-draw by a single press process, the steel will break, so as shown in FIG. The press work must be performed in several steps, and finally the flange part must be cut. This reduces productivity and increases costs.
Furthermore, deep drawing of a stainless steel plate has a problem that inclusions appear on the surface and the corrosion resistance is lowered.If a plated steel plate is used, post-processing annealing cannot be performed, so that the shape of the battery case is eventually obtained. There is also a problem that it cannot be processed.

For this reason, as a method of manufacturing a bottomed case with a steel material, a method is adopted in which a body section having a square cross section is formed and a bottom plate is welded to one end of the body section. As a method of forming the square body section, a method has been developed in which a square body section is formed by bending or roll forming a steel plate.
However, as shown in FIG. 2, in the method by bending, the steel plates bent into squares must be welded one by one, resulting in low productivity. Moreover, as shown in FIG. 3, in the method by roll forming, when processing a thin steel plate, the edge portion is stretched, so that welding is difficult. If the number of roll forming steps is increased, edge growth can be suppressed, but the equipment cost increases and the case manufacturing cost increases.

In addition, a method has been attempted in which a cylindrical steel pipe is used as a raw material and is formed into a square shape by rolling from the outside into a square shape, but as shown in FIG. In the case of molding, there is a problem in that only those having a low flatness can be produced due to contact with the roll during molding, and the bottom plate cannot be welded due to poor shape.
Furthermore, Patent Document 1 describes a method in which four rods or split molds are inserted inside a cylindrical pipe to form a square body cross section, which is made of an aluminum material. Even when trying to make a cylindrical steel pipe that deforms a pipe and is difficult to plastically deform into a square cross section by this method, only those with low flatness can be produced by springback, and those that can withstand welding of the bottom plate It could not be manufactured.
JP 2006-320918 A

In bottomed cases that require weight reduction, increased strength, and high corrosion resistance, it is difficult to manufacture a bottomed case that uses high-strength steel compared to conventional aluminum materials. Therefore, it has been desired to provide a bottomed case made of high-strength steel having sufficient dimensional accuracy and high welding reliability at a low cost.
The present invention has been devised in order to solve such problems. As a bottomed case made of steel, a bottomed case having a high dimensional accuracy of the body portion and high welding reliability with the bottom plate is inexpensive. It is intended to be provided to.

  In order to achieve the object, the bottomed case of the present invention is formed by pushing and expanding a cylindrical steel pipe from the inside, the circumference is longer than the circumference of the steel pipe, and the cross-sectional shape is a plurality of corner portions. A cylindrical body frozen in a shape composed of straight portions connecting the corner portions is used as a body portion, and a bottom plate made of a steel plate having the same shape as the cross-sectional shape of the body portion is welded to one end of the body portion. It is characterized by being joined by.

Further, the manufacturing method of the bottomed case of the present invention includes a step of cutting a cylindrical steel pipe into a predetermined length, inside the steel pipe cut into a predetermined length, and at each corner portion of a desired cylinder. A molding die having a corresponding molding surface and having a plurality of molding portions movable in the direction of each corner portion is disposed, and the four molding portions of the molding die are moved to the outside to move the steel pipe from the inside. Forming the body part by forming the body part into a shape composed of a plurality of corner parts and straight parts connecting the corner parts while extending the circumference of the steel pipe by expanding outwardly; And the process of joining the bottom plate which consists of a steel plate of the same shape as the cross section of this trunk | drum to the one end of the said trunk | drum by welding is provided.
At this time, it is preferable to use a molding die in which protrusions or corners are provided at both ends of the molding surfaces of the plurality of molding portions as the molding die having a plurality of molding portions.

  According to the bottomed case and the manufacturing method thereof of the present invention, for example, a cylindrical steel pipe that can be obtained at low cost is used as the material of the body of the prismatic battery case, so that it is possible to produce a large number of bodies at a low cost. It is. In addition, the cylindrical steel pipe is expanded from the inside using a molding die, and the cross-sectional shape is formed into a rectangular shape while extending the circumference of the steel pipe. It is frozen, and the trunk | drum whose cross-sectional shape with a sufficient dimensional accuracy is a rectangle is obtained. Furthermore, since the dimensional accuracy of the body portion is good, a bottomed case with high welding reliability, such as a rectangular battery case, can be produced without causing misalignment or the like during welding with the bottom plate.

The inventors of the present invention have made various studies on a method of manufacturing a high-strength, lightweight, large-bottomed case with high molding accuracy using a thin steel material as a raw material. In particular, since a large-sized storage battery is often used in a rectangular shape, various studies have been conducted to develop means for manufacturing a steel rectangular storage battery case.
Since a steel square bottomed case is difficult to manufacture by deep drawing, it is manufactured by welding a body having a rectangular cross section and a bottom plate. The inventors of the present invention have studied a manufacturing method of a body having a rectangular cross-sectional shape, and do not press and fold a steel plate, or roll and shape it into a rectangular shape. We studied to form a rectangular shape using steel pipes.

In order to make the cross-sectional shape of the cylindrical steel pipe, which is the material, rectangular, first insert a mold that expands the cylindrical steel pipe into a rectangular shape inside the cylindrical steel pipe, and then expand the mold to expand the cylinder. When deforming the steel pipe into a rectangular cross-sectional shape, by deforming the cylindrical steel pipe and extending the circumference of the steel pipe at the same time, by distorting the steel material and causing the shape to freeze, It has been found that a cylindrical body having a rectangular cross section with good dimensional accuracy can be manufactured.
Details will be described below. In the following, an example of a rectangular cross section is described. However, in addition to the rectangle, the corner portion may have three triangular shapes, or the corner portion may have many polygonal shapes. Moreover, the ellipse which consists of two corner parts with comparatively large corner R and the straight line which connects it may be sufficient.

First, a molding die shown in FIG. 5 was prepared. FIG. 5 is a top view and a front view of the molding die. As shown in FIG. 5, the molding die includes four molding parts 1 a to 1 d that can move in the direction of each corner part of a rectangular cross section, and four for moving these molding parts in the direction of each corner part. It is composed of a pyramid portion 2. This square weight portion 2 is attached to the tip of a hydraulic cylinder (not shown). The side that contacts the steel pipe of each molded part 1a to 1d is designed to have the same shape as each rectangular corner part of the cross-sectional shape of the cylinder that becomes the body part of the bottomed case. The contact side is designed to have a flat surface shape that is paired with the quadrangular pyramid portion 2. It is preferable that projecting portions 1a ′ to 1d ′ for positioning the steel pipe to be processed are provided at the end portions of the forming portions 1a to 1d on the side in contact with the steel pipe.
When the square weight part 2 is in the lowered position, the molding parts 1a to 1d are in the positions shown in FIG. 5 (a). By raising the square weight part 2 by a hydraulic cylinder, the molding parts 1a to 1d are shown in FIG. As shown in (b), it moves in the direction of each corner of the rectangular cross section.

When the cylindrical steel pipe 3 is attached to the molding die thus designed and the quadrangular pyramid portion 2 is raised by the hydraulic cylinder, the molding portions 1a to 1d are moved outward as shown in FIG. The steel pipe to be processed can be formed into a rectangular cross section. FIG. 6 (a) shows the relationship between the forming parts 1a to 1d and the steel pipe 3 to be processed when the steel pipe 3 to be processed is attached to the forming die in the state of FIG. 5 (a). FIG. 5B and FIG. 5C show the relationship between the forming parts 1a to 1d moved in the direction of the corners of the rectangular cross section in the state of FIG. A case formed into a rectangular cross section shown in FIGS. 6 (b ′) and 6 (c ′) by lowering the square weight part 2 after forming and returning the formed parts 1a to 1d to remove the steel pipe 3 to be processed. A torso is obtained.
In addition, as the steel pipe 3 to be processed, a long cylindrical steel pipe cut into a length corresponding to the length of the bottomed case is used.

  By the way, as shown in FIG.6 (b), when the cylindrical steel pipe of the same circumference as the circumference of the cross-sectional shape of the trunk | drum of a desired bottomed case is used as a to-be-processed steel pipe, When the steel pipe to be processed is removed from the mold, a spring back is generated, and only a cylindrical body with poor shape accuracy can be obtained as shown in FIG. Therefore, as shown in FIG. 6 (c), using a steel pipe having a circumference shorter than the circumference of the cross-sectional shape of the barrel portion of the desired bottomed case, the circumference of the steel pipe to be processed can be set at the time of molding by a mold. When it was formed into a rectangular cross section while being stretched, there was little adverse effect of the shape change due to the spring back, and a cylindrical body with high flatness and good dimensional accuracy was obtained as shown in FIG.

This is considered to be due to the fact that the steel pipe material is distorted and the shape is frozen by extending the circumference of the steel pipe to be processed during molding into a rectangular cross section by a mold. In order to cause the shape freezing, it is necessary to process the steel pipe to be processed by extending it by several percent.
Although it depends on the wall thickness of the steel pipe to be processed, in the case of a stainless steel pipe, an elongation of about 1% is necessary, and in the case of a plated steel pipe, an elongation of about 1% is necessary.
In addition, as a plated steel pipe, the thing which gave aluminum plating other than what gave nickel plating is used.

However, even when the material is processed by being stretched by several percent, if the corner portion of the target bottomed case has a large curvature portion, the target shape may not be obtained due to the springback of the steel pipe. In that case, as shown to Fig.7 (a) (b), a spring back can be reduced by providing few protrusions and a corner | angular_corn on the both ends of the shaping | molding surface which contact | connects the steel pipe of shaping | molding part 1a-1d. FIG. 7 (a) shows slight protrusions provided at both ends of the molding surface, and FIG. 7 (b) shows that the corners are left without chamfering at both ends of the molding surface. is there.
By providing the protrusions and corners, a greater stress is concentrated on the bent portion than in normal processing, the stress is uniformized, and the spring back is reduced.
That is, forming accuracy can be improved by providing slight protrusions and corners at both ends of the forming surface in contact with the steel pipe of the forming portion.

On the other hand, if the target bottomed case is long, the mold to be spread out will be long, but if the mold is long, the shape of both ends of the spread steel pipe will be shown due to the clearance between the molded part and the quadrangular pyramid part. A slight variation as shown in FIG. When the target bottomed case is long, for example, as shown in FIG. 8 (b), the quadrangular pyramid portion 2 attached to the tip of the hydraulic cylinder and the surface where the molded portions 1a to 1d that spread the steel pipe are in sliding contact with each other, It is preferable to provide grooves and protrusions that mesh with each other to prevent each molded portion from spreading unstablely.
By using the above method, the material steel pipe is expanded and frozen, and the rectangular shape of the cross section can be made uniform and accurate, and a cheap and stable body for a square battery case can be produced. It becomes. Further, the butt shift at the time of welding is eliminated, and it is possible to prevent the occurrence of a bottomed case with poor welding or poor shape, and for example, it is possible to manufacture a cheap and stable prismatic battery case.

  Moreover, when welding the steel plate which becomes the bottom of a bottomed case, since the four sides are welded, the bottom can be attached by four times of welding, but when the curved portion is provided at the corner portion, each side is Separately, the curvature must be welded. However, when laser welding is adopted as the welding method, the depth of focus is deep, so it is possible to weld the curvature part if the radius is constant with the side welding, and omit the welding of the curvature part separately from each side. can do. Therefore, it is preferable to perform the welding used for attaching the bottom portion by racer welding. FIG. 9 shows a joining procedure by laser welding of the body portion and the bottom plate 4 in the case where a curved portion is provided at the corner portion. As shown in FIG. 9A, the body portion and the bottom plate 4 are chucked with a vice or the like, and laser welding is performed four times in the order shown in FIG. 9B. In addition, about the attachment method of a baseplate, arbitrary methods are applicable, without being limited to said means.

Example 1
A cylindrical steel pipe made of SUS430 having an outer diameter of 58 mm and a plate thickness of 0.4 mm is used as a material. The inner diameter is 50 mm × 50 mm, the corner is a curved portion of a quarter circle with an inner radius of 10 mm, and a straight portion of each side. A bottomed case having a cross section of 30 mm in length and a height of 200 mm was manufactured.
First, the steel pipe was cut into a length of 200 mm in accordance with the length of the desired bottomed case. Inside the cut steel pipe, a molding die composed of four molding parts movable in the direction of each corner part and a quadrangular pyramid part pressed by a hydraulic cylinder was arranged. Grooves and protrusions that engage with the grooves were provided on the sliding contact surfaces of the molded portions and the square weight portions. In addition, the four molded parts that spread the steel pipe part have a radius of curvature of the tip convex part of 10 mm, are in contact with only the corner part of the case, and are not in contact with the straight part, and the boundary part is chamfered. The corners were left without giving. (See Fig. 7 (b))

By pushing up the quadrangular pyramid portion with a hydraulic cylinder, the four molded portions were moved outward, and a cylindrical body having a rectangular cross-sectional shape having an inner diameter of 50 mm × 50 mm and a curved portion with an inner radius of 10 mm at the corner portion was molded.
The cylindrical body has a peripheral length of 184 mm. Since a cylindrical steel pipe having an outer diameter of 58 mm, which is smaller than the cylindrical steel pipe corresponding to the peripheral length, is used as the work tube, the peripheral length is 1 at the time of molding. A cylindrical body having a high flatness and a high dimensional accuracy obtained by stretching by 7% was obtained.

Next, the obtained cylindrical body was used as a body part, and a bottom plate was attached to one end of the body part by welding.
The bottom plate was manufactured by cutting a steel plate having a plate thickness of 0.4 mm with SUS430 in the same shape as the cross-sectional shape of the torso as with the torso. The body part was placed sideways, the bottom steel plate was aligned with the bottom part, and the butt part that became the joint was welded.
At this time, because of the square shape, the welded portion has four sides. Welding of the curved part of the corner is performed simultaneously with the welding of the straight part, but in order to surely weld the corner part and the straight part, the body part and the bottom plate are joined using a laser welding method with a deep focal depth.
The manufactured bottomed case had high flatness of the straight portion of the body portion, good dimensional accuracy, and high welding reliability.

The figure explaining the manufacturing method of the case which interposed the annealing process The figure explaining the case manufacturing method which combined the bending method and the welding method The figure explaining the case manufacturing method which combined the roll forming method and the welding method The figure explaining the method of forming a cylindrical steel pipe into a square shape by the roll forming method The figure explaining the method of shape | molding a cylindrical steel pipe into a rectangle using a shaping die The figure explaining the shape freezing action at the time of shape | molding into a rectangle using a shaping die The figure explaining the processus | protrusion and angle | corner which are provided in the molding part of a shaping die The figure explaining the relationship between the groove | channel and protrusion provided in the shaping | molding part and square pyramid part of a shaping die The figure explaining the aspect which welds and joins a baseplate to the edge part of a rectangular trunk | drum

Claims (3)

  Formed by expanding a cylindrical steel pipe from the inside, the circumference is longer than the circumference of the steel pipe, and the cross-sectional shape is composed of a plurality of corner portions and straight portions connecting the corner portions A bottomed case characterized in that a cylindrical body whose shape is frozen is used as a body portion, and a bottom plate made of a steel plate having the same shape as the cross-sectional shape of the body portion is joined to one end of the body portion by welding.   A step of cutting a cylindrical steel pipe into a predetermined length, having a forming surface corresponding to each corner portion of a desired cylindrical body inside the steel pipe cut into a predetermined length, and in the direction of each corner portion By disposing a molding die having a plurality of movable molding parts, moving the plurality of molding parts of the molding die to the outside and expanding the steel pipe from the inside to the outside, the circumference of the steel pipe is increased. Forming a body part by forming a cross-sectional shape into a shape composed of a plurality of corner parts and straight parts connecting between the corner parts while stretching, and crossing the body part at one end of the body part A method for manufacturing a bottomed case, comprising a step of joining a bottom plate made of a steel plate having the same shape as a surface by welding.   3. The bottomed case according to claim 2, wherein a molding die having protrusions or corners provided at both ends of molding surfaces of the plurality of molding portions is used as the molding die having the plurality of molding portions. Production method.

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