The present invention relates to metal pipes, part of which is made thicker than the other part, and a method and a device for processing the metal pipes.
For example, metal pipes have been used in part of exhaust systems of internal combustion engines mounted in automobiles. The metal pipe repeatedly receives heat of exhaust gas, and stress is concentrated on a junction between the metal pipe and the other component due to vibrations of the internal combustion engine and a vehicle body. Thus, the metal pipe, particularly the junction, is likely to break. To prevent the break, the metal pipe may be thickened, or may be made of a material having higher strength.
When the pipe is thickened, part of the pipe on which the stress is not concentrated, i.e., part of the pipe which is less likely to break, is also thickened. This unnecessarily increases weight of the metal pipe. Even when the material is changed, the weight of the metal pipe hardly changes.
As disclosed by Patent Document 1, for example, reduction of the weight of the metal pipe has been attempted while preventing the break by making part of the metal pipe on which the stress tends to concentrate thicker than the other part. According to Patent Document 1, a metal pipe of a uniform thickness is heated to a high temperature of about 1200° C. to reduce deformation resistance, and then the metal pipe is pressed in an axial direction thereof using a die and a mandrel to form a thick portion in the metal pipe.
According to Patent Document 1, the metal pipe needs to be heated to high temperature. The heating takes time, and reduces production efficiency. Further, the processing consumes much energy.
When the metal pipe processed at high temperature is cooled to room temperature, thermal contraction does not always occur uniformly. This reduces dimensional accuracy of the metal pipe.
In view of the foregoing, the present invention has been achieved. The present invention is concerned with providing a metal pipe having a thick portion with high production efficiency, high precision, and reduced energy consumption.
In view of the above concern, a first aspect of the invention is directed to a method for processing the metal pipe by providing a stress concentration portion in an axial center of the metal pipe, applying an axial pressure to the metal pipe to concentrate stress on the stress concentration portion to deform the stress concentration portion, and forming a thick portion from the deformed portion as a starting point.
The first aspect of the invention provides a method for processing a metal pipe to make part of the metal pipe in an axial direction thereof into a thick portion thicker than a different portion, the method includes: forming a stress concentration portion in an axial center of the metal pipe to concentrate a stress on the stress concentration portion when an axial pressure is applied to the metal pipe; setting the metal pipe in an outer die for holding an outer peripheral surface of the metal pipe; and forming the thick portion by inserting an inner die in the metal pipe to provide space for forming the thick portion between the inner die and the outer die, and applying the axial pressure to the metal pipe to concentrate the stress on the stress concentration portion to deform the stress concentration portion after the forming of the stress concentration portion and the setting of the metal pipe, thereby forming the thick portion from the deformed stress concentration portion as a starting point.
With this configuration, the stress is concentrated on the stress concentration portion of the metal pipe when the pressure is applied to the metal pipe. Thus, unlike the conventional example, deformation of the metal pipe starts without reducing the deformation pressure by heating the pipe. The deformation of the metal pipe occurs in the space between the outer die and the inner die from the first deformed portion as the starting point. Thus, the thick portion is formed in the metal pipe between the outer die and the inner die.
According to a second aspect of the invention related to the first aspect of the invention, a shoulder is formed in the metal pipe in the forming of the stress concentration portion to use the shoulder as the stress concentration portion.
With this configuration, stress concentration can reliably be caused when the axial pressure is applied to the metal pipe by forming the shoulder.
According to a third aspect of the invention related to the second aspect of the invention, the shoulder is formed by expanding the metal pipe in the forming of the stress concentration portion.
This configuration allows easy provision of the shoulder by the expansion.
A fourth aspect of the invention is directed to a device for processing a metal pipe, wherein a stress concentration portion is formed in an axial center of the metal pipe using a stress concentration portion formation device, and an inner die is pressed in the axial direction of the metal pipe by a drive to apply an axial pressure to an end of the metal pipe.
The fourth aspect of the invention provides the device for processing the metal pipe to make part of the metal pipe in an axial direction thereof into a thick portion thicker than a different portion, the device including: a stress concentration portion formation device for forming a stress concentration portion in an axial center of the metal pipe to concentrate a stress on the stress concentration portion when an axial pressure is applied to the metal pipe; an outer die for holding an outer peripheral surface of the metal pipe; an inner die which is inserted in the metal pipe to provide space for forming the thick portion between the outer die and the inner die, and comes into contact with an end of the metal pipe; and a drive which presses the inner die in the axial direction of the metal pipe to apply an axial pressure to the end of the metal pipe.
With this configuration, the metal pipe provided with the stress concentration portion can be held by the outer die, the inner die can be inserted in the metal pipe, and the axial pressure can be applied to the end of the metal pipe by the drive. Thus, the stress is concentrated on the stress concentration portion of the metal pipe to deform the stress concentration portion, and the thick portion is formed between the outer die and the inner die from the deformed stress concentration portion as a starting point.
According to a fifth aspect of the invention related to the fourth aspect of the invention, the inner die includes a first die which is inserted in part of the metal pipe except for part of the metal pipe for forming the thick portion, and a second die which is separated from the first die, and is inserted in the part of the metal pipe for forming the thick portion, and the second die is driven by the drive.
With this configuration, the pressure is applied to the metal pipe with the first die being inserted in the part of the metal pipe except for the part of the metal pipe for forming the thick portion, and the second die separated from the first die being inserted in the part of the metal pipe for forming the thick portion. Thus, the first die inserted in the part of the metal pipe except for the part of the metal pipe for forming the thick portion can be kept stationary, and the first die does not axially rub an inner peripheral surface of the part of the metal pipe except for the part for forming the thick portion. This can prevent the inner peripheral surface of the metal pipe from damage or deformation due to the rubbing of the inner die in the axial direction.
A sixth aspect of the invention is directed to a metal pipe which is processed by the method according to any one of the first to third aspects of the invention.
According to the first aspect of the invention, the stress concentration portion is formed in the axial center of the metal pipe, and the metal pipe is set to the outer die. Then, the inner die is inserted in the metal pipe, and the axial pressure is applied to the metal pipe to concentrate the stress on the stress concentration portion and deform the stress concentration portion. The thick portion is formed from the deformed stress concentration portion as the starting point. Thus, there is no need to heat the metal pipe to high temperature to reduce the deformation resistance. This can increase production efficiency and dimensional accuracy of the metal pipe, and can reduce energy consumption. Thus, the metal pipe which is lightweight, and has a required strength in a required portion can be obtained with high precision at low cost.
According to the second aspect of the invention, the shoulder is formed in the metal pipe, and the shoulder is used as the stress concentration portion. Thus, stress concentration can reliably be caused when the pressure is applied, and the thick portion can be formed as desired.
According to the third aspect of the invention, the shoulder is formed by expanding the metal pipe. Thus, the shoulder can easily be obtained, and the metal pipe can be obtained at lower cost.
According to the fourth aspect of the invention, like the first aspect of the invention, the metal pipe can be provided with the thick portion without heating the metal pipe to high temperature to reduce the deformation resistance. This can increase production efficiency and dimensional accuracy, and can reduce energy consumption. Thus, the metal pipe which is lightweight, and has a required strength in a required portion can be obtained with high precision at low cost.
According to the fifth aspect of the invention, the first die is inserted in the part of the metal pipe except for the part of the metal pipe for forming the thick portion, the second die is inserted in the part of the metal pipe for forming the thick portion, and the second die is driven by the drive. This can prevent the inner peripheral surface of the metal pipe from damage or deformation in thickening the metal pipe.
An embodiment of the present invention will be described in detail below with reference to the drawings. The embodiment will be set forth merely for the purposes of preferred examples in nature, and is not intended to limit the scope, applications, and use of the invention.
In the description of the present embodiment, an upstream part of the metal pipe 1 in a direction of an exhaust stream will be simply referred to as an “upstream part”, and a downstream part of the metal pipe 1 in the direction of the exhaust stream will be simply referred to as a “downstream part” for the sake of easy description.
As shown in
The metal pipe 1 is made of a steel pipe. As shown in
As shown in
An outer diameter of part of the metal pipe 1 corresponding to the thick portion 10 is larger than an outer diameter of the other part. Thus, the thick portion 10 is thickened to bulge outward from the metal pipe 1. As shown in
A surface 10b, which is part of the outer peripheral surface of the metal pipe 1 upstream of the diameter-increasing portion 10a, extends substantially parallel to an axis of the pipe. An axial dimension of the diameter-increasing portion 10a is sufficiently smaller than an axial dimension of the surface 10b.
A surface 1a, which is part of the outer peripheral surface of the metal pipe 1 except for the thick portion 10, extends substantially parallel to the axis of the pipe. A curved surface 1b is formed between the surface 1a and the diameter-increasing portion 10a, and the surface 1a and the diameter-increasing portion 10a are continuously connected through the curved surface 1b. A radius of curvature of the curved surface 1b is 5 mm to 15 mm, both inclusive. The provision of the curved surface 1b reduces the occurrence of stress concentration. When the radius of curvature of the curved surface 1b is smaller than 5 mm, a stress generated near the curved surface 1b increases, thereby reducing reliability of the metal pipe 1. When the radius of curvature of the curved surface 1b is larger than 15 mm, a total length of the metal pipe 1 increases, thereby reducing ease of layout.
An angle α formed by an extension line of the surface 1a of the metal pipe 1 (a dotted line shown in
A large diameter portion lc having a larger diameter than a downstream portion is formed in an inner peripheral surface of an upstream end of the metal pipe 1. Part of the inner peripheral surface downward of the large diameter portion 1c is tapered to form a diameter-reducing portion 1d which has an inner diameter reduced toward the downstream side, and is continuous with the large diameter portion 1c. With the provision of the diameter-reducing portion 1d, the thickness of the upstream end of the metal pipe 1 is gradually reduced toward the large diameter portion 1c. Since the diameter-reducing portion 1d is formed to gradually change the thickness, stress concentration is less likely to occur. An axial dimension of the large diameter portion 1c and an axial dimension of the diameter-reducing portion 1d are significantly smaller than an axial dimension of the thick portion 10.
A method for processing the metal pipe 1 to provide the thick portion 10 will be described below.
The metal pipe 1 has a round cross-section before processing. The unprocessed metal pipe 1 has a thickness of 1.2 mm, and an outer diameter of about 40 mm. The unprocessed metal pipe 1 has a length of about 120 mm. The thickness, the outer diameter, and the length of the unprocessed metal pipe 1 described above are merely examples, and are not limited to the above examples.
As shown in
The expansion is performed using a known expansion device 15. Thus, a shoulder 100 is formed in an axial center of the metal pipe 1. The shoulder 100 is a stress concentration portion of the present invention. In this way, the stress concentration portion is formed, and the expansion device 15 is a stress concentration portion formation device.
The expanded metal pipe 1 is set in an outer die 20 as shown in
As shown in
When the metal pipe 1 is inserted in the outer die 20 with the expanded portion facing upward, the entire outer peripheral surface of the metal pipe 1 is held by the outer die 20. Thus, the pipe is set.
An inner die 25 is inserted in the metal pipe 1 after the expansion and the setting of the pipe.
Either of the expansion and the setting of the pipe may be performed first. Specifically, the expansion may be performed after the setting of the pipe.
As shown in
The first die 27 is in the shape of a vertically extending column. As shown in
As shown in
The second die 28 is also in the shape of a column. As shown in
An outer diameter of a body 28d of the second die 28 upward of the second small diameter portion 28c is substantially the same as an inner diameter of an upper part of the through hole 20a of the outer die 20. A step 28e is formed between the body 28d and the second small diameter portion 28c. The upstream end of the metal pipe 1 is fitted in the step 28e.
The second die 28 is provided with a threaded hole 28f extending along an axis thereof. The threaded hole 28f is opened in an upper end surface of the second die 28. A spring insertion hole 28g is formed in a lower part of the second die 28 in which the spring 29 is inserted. An upper end of the spring 29 abuts a bottom of the spring insertion hole 28g.
As shown in
A drive 33 is coupled to the plate 30. The drive 33 is provided to move the second die 28 in the vertical direction.
In inserting the inner die 25 in the metal pipe 1, the first die 27 is inserted in the metal pipe 1, and then the second die 28 is inserted. As the second die 28 is inserted, the spring 29 is pressed downward, thereby pressing the first die 27 downward. Thus, the lower end of the first die 27 is inserted in the through hole 23a of the base plate 23.
When the inner die 25 is inserted in the metal pipe 1, space S for forming the thick portion 10 is provided between the inner die 25 and the outer die 20 as shown in
When the second die 28 is pushed downward by the drive 33 as indicated by an outline arrow in
When the second die 28 is further moved downward by the drive 33, deformation of part of the metal pipe upward of the shoulder 100 starts from the deformed shoulder 100. The deformation occurs in the space S between the outer die 20 and the inner die 5, and the deformed part of the metal pipe 1 is molded between the inner peripheral surface of the outer die 20 and the outer peripheral surface of the inner die 25 to become the thick portion 10.
A thickness of part of the metal pipe 1 except for the expanded part is not greatly changed for the following reasons. Specifically, a small clearance is provided between the outer die 20 and the outer peripheral surface of the metal pipe 1, and between the inner die 25 and the inner peripheral surface of the metal pipe 1 in view of moldability. In forming the shoulder 100 as the stress concentration portion, the pressure is used to form the shoulder 100. Thus, a stress caused in part of the metal pipe 1 downward of the shoulder 100 is reduced, and change in thickness of the part of the metal pipe 1 except for the expanded part is reduced.
The drive 33 moves the second die 28 only, and the first die 27 is kept stationary. Thus, the first die 27 does not axially rub part of the inner peripheral surface except for part thereof for forming the thick portion 10. This can prevent the part of the metal pipe 1 except for the part for forming the thick portion 10 from damage or deformation.
The expansion device 15, the outer die 20, the inner die 25, the base plate 23, the plate 30, and the drive 33 constitute a processing device of the present invention.
As shown in
When a downward load is applied to the downstream end of the metal pipe 1 with the metal pipe 1 fixed to the flange component 2, a stress is generated in every part of the metal pipe. At this time, parts enclosed with circles A and B in
According to the present embodiment described above, the metal pipe 1 including the shoulder 100 formed in the axial center of the metal pipe 1 is set in the outer die 20, and an axial pressure is then applied to the metal pipe 1 with the inner die 25 inserted in the metal pipe 1 to concentrate the stress on the shoulder 100 to deform the shoulder 100. Then, the thick portion 10 is formed from the deformed portion as a starting point. Thus, unlike the conventional examples, there is no need to heat the metal pipe 1 to high temperature to reduce the deformation resistance. This can improve production efficiency and dimensional accuracy, and can reduce energy consumption. Thus, the metal pipe which is lightweight, and has a required strength in a required portion can be obtained with high precision at low cost.
The shoulder 100 is formed in the metal pipe 1, and the shoulder 100 is used as the stress concentration portion. Thus, the stress concentration can reliably be caused when the pressure is applied, and the thick portion 10 can be formed as desired.
Since the shoulder 100 is formed by expanding the metal pipe 1, the shoulder 100 can easily be obtained, and the metal pipe 1 can be obtained at lower cost.
In the above embodiment, the inner die 25 is configured to be dividable into the first die 27 and the second die 28. However, the inner die 25 is not limited thereto, and the first die 27 and the second die 28 may be integrated as those of an alternative shown in
In the above-described embodiment, the shoulder 100 is formed in the metal pipe 1, and the shoulder 100 is used as the stress concentration portion. However, the stress concentration portion is not limited to the shoulder. For example, as shown in
In the above-described embodiment, the thick portion 10 is formed to bulge outward from the outer peripheral surface of the metal pipe 1. However, the thick portion 10 is not limited thereto, and may be formed to bulge inward from the inner peripheral surface of the metal pipe 1.
Materials of the metal pipe 1 are not limited as long as they can be used for deformation processing, and various types of materials can be used.
The metal pipe 1 can be used not only as a part of exhaust systems of automobiles, but can also be used as, e.g., air pipes, liquid pipes, etc.
The diameter of the metal pipe 1 is not particularly limited. For example, the diameter may be about several tens cm.
As described above, the present invention can be applied to, for example, metal pipes constituting an exhaust system of an automobile.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP10/07385 | 12/20/2010 | WO | 00 | 12/29/2011 |