JP2016064435A - Joining body, magnetic rotary arc joining method, and method of producing joining body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joining body including an adequate strength.SOLUTION: A joining body 10 includes a first metal tube 21, a second metal tube 22, and a joint portion in which end faces of the first and second metal tubes are joined. In a joint interface 11 of the joint portion between the first metal tube 21 and the second metal tube 22, a dendrite layer 15 does not exist in a region inside outer peripheral faces of the first and second metal tubes 21, 22 and outside inner peripheral faces of the first and second metal tubes 21, 22.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a joined body, a magnetic rotating arc joining method, and a manufacturing method of a joined body, and more particularly, to a joined body of metal pipe, a magnetic rotating arc joining method, and a manufacturing method of a joined body.

  Conventionally, a magnetic rotating arc joining method is known (see, for example, JP-A-6-55267).

JP-A-6-55267

  In the magnetic rotating arc joining method described above, the end surfaces of the two steel pipes that are the joining target materials are uniformly melted by the arc, and the steel pipes are joined together by pressing one steel pipe to the other steel pipe at that timing. Join to obtain a joined body. In this case, a dendrite structure is generated at the bonding interface by supercooling the molten layer at the end faces to be bonded. This dendrite structure is low in strength as compared with regions other than the vicinity of the joint interface of the steel pipe (for example, the base material of the steel pipe and the heat-affected zone), and defects such as cracks may occur. As a result, there has been a problem that the strength of the bonded portion including the bonded interface of the bonded body is insufficient.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a magnetic rotating arc bonding method capable of forming a sufficiently strong bonded portion in a bonded body, sufficient It is to obtain a joined body including a joint portion having strength and a method for manufacturing the joined body.

  The joined body according to one embodiment of the present invention includes a first metal tube, a second metal tube, and a joined portion obtained by joining the end surfaces of the first and second metal tubes. At the joint interface between the first metal tube and the second metal tube at the joint, it is inside the outer peripheral surfaces of the first and second metal tubes and from the inner peripheral surfaces of the first and second metal tubes. There is no dendrite layer in the outer region.

  In the magnetic rotating arc joining method according to one embodiment of the present invention, the first and second metal tubes 21 and 22 are prepared (S10), the main heating step (S30), and the joining step (S40). ). In the main heating step (S30), an arc discharge is generated between the end faces of the first and second metal tubes 21 and 22, and a magnetic field is applied between the end faces to move the position of the arc discharge between the end faces. Then, the temperature at a position 2 mm away from the end faces of the first and second metal tubes 21 and 22 is fully heated to the bonding temperature (temperature T3 in FIG. 8D). In the joining step (S40), after the main heating step (S30), the end faces are butted together and joined. In the joining step (S40), the relative pressure-contact speed of the first metal tube 21 with respect to the second metal tube 22 when the end surfaces are brought into contact with each other is 20 mm / s or more.

  The manufacturing method of the joined body which concerns on one Embodiment of this invention uses the said magnetic rotating arc joining method. In this way, it is possible to obtain the joined body 10 having a sufficiently strong joint.

  According to the above, it is possible to obtain a joined body including a joint portion having sufficient strength.

It is a perspective schematic diagram of the joined body concerning this embodiment. It is a cross-sectional schematic diagram in line segment II-II of FIG. It is a schematic diagram for demonstrating the magnetic rotating arc joining method which concerns on this embodiment. It is a cross-sectional schematic diagram of the joined body of a comparative example. It is a cross-sectional schematic diagram of the joined body which concerns on this embodiment. It is a flowchart for demonstrating the magnetic rotating arc joining method which concerns on this embodiment. It is a schematic diagram which shows an example of the joining apparatus which enforces the magnetic rotating arc joining method which concerns on this embodiment. It is a timing chart for demonstrating the magnetic rotating arc joining method which concerns on this embodiment. It is a photograph of the sample of the joined object to which the magnetic rotating arc joining method concerning this embodiment is applied. 10 is an organizational photograph of the material shown in FIG. 9. It is a photograph of the sample of the joined body which is a comparative example. It is a structure | tissue photograph of the sample shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

<Composition of joined body>
With reference to FIG. 1 and FIG. 2, the joined body which concerns on this embodiment is demonstrated. Referring to FIG. 1, a joined body 10 is obtained by joining a first metal tube 21 and a second metal tube 22 by a magnetic rotating arc joining method. That is, the joined body 10 includes a first metal tube 21, a second metal tube 22, and a joint portion including a joint interface 11 in which the end surfaces of the first and second metal tubes 21 and 22 are joined together. . An outer peripheral bead portion (not shown) that protrudes to the outer peripheral side and an inner peripheral bead portion 13 that protrudes to the inner peripheral side are formed in the joint portion. The outer peripheral bead portion is removed by grinding. For this reason, the part by which the said outer periphery bead part was removed by grinding becomes the grinding part 12. FIG. And in the junction interface 11 of a junction part, it is an area | region inside the outer peripheral surface of the 1st and 2nd metal pipes 21 and 22, and outside the inner peripheral surface of the 1st and 2nd metal pipes 21 and 22. The dendrite layer 15 is not present. Thus, since the dendrite layer 15 does not exist near the center in the thickness direction of the first and second metal tubes 21 and 22, the strength of the joint can be sufficiently increased.

  As shown in FIG. 2, in the joined body 10, the width of the outer peripheral bead portion (that is, the width L <b> 1 of the grinding portion 12) and the inner peripheral bead in the direction from the first metal tube 21 to the second metal tube 22. The difference between the width L2 of the portion 13 (the absolute value of L1-L2) is the average value ((L1 + L2) / 2) of the width of the outer peripheral bead portion (width L1 of the grinding portion 12) and the width L2 of the inner peripheral bead portion. However, it is 40% or less. In this way, the difference in the width of the bead portion between the inner peripheral side and the outer peripheral side of the first and second metal tubes 21 and 22 in the joint portion is sufficiently small, and the joint state of the joint portion is the inner periphery. There is no big difference between the side and the outer peripheral side, and the joined body 10 in which the soundness of the joint portion is ensured is obtained.

  Here, the width L2 of the inner peripheral bead portion 13 refers to the inner peripheral bead portion from the inner peripheral surface of the first metal tube 21 and the second metal tube 22 in the joined body 10 in the cross section shown in FIG. This is the distance between the positions at which 13 starts to project (boundary points 14a, 14b). Similarly, the width L1 of the grinding portion 12 on the outer peripheral side also corresponds to the distance between the positions at which the outer peripheral bead portions start to protrude from the outer peripheral surfaces of the first metal tube 21 and the second metal tube 22.

  In the joined body 10, any metal material can be used as the material of the joined body 10. For example, carbon steel for mechanical structure is used. In the joined body 10, the outer diameters of the first and second metal tubes 21 and 22 are 10 mm or more and 250 mm or less. The lower limit of the outer diameter is, for example, 20 mm or more, preferably 50 mm or more, more preferably 100 mm or more. Moreover, the thickness of the 1st and 2nd metal tubes 21 and 22 is 1 mm or more and 16 mm or less. The lower limit of the thickness is, for example, 2 mm or more, preferably 5 mm or more, more preferably 10 mm or more.

<Outline of Magnetic Rotating Arc Joining Method According to this Embodiment>
The outline of the magnetic rotating arc joining method for forming the joined body shown in FIGS. 1 and 2 will be described with reference to FIGS.

  In the magnetic rotating arc joining method, the Fleming left-hand rule is used. In the magnetic rotating arc joining method according to the present embodiment, as shown in FIG. 3, an annular shape is formed so as to surround a part of the outer peripheral side surfaces of the first and second metal tubes 21, 22 arranged so that the end faces face each other. While arranging the permanent magnet 7 and applying a magnetic field, a large direct current is passed from the power source 34 to the first and second metal tubes 21 and 22. And if the distance between the opposing end surfaces of the 1st and 2nd metal pipes 21 and 22 is kept at a certain fixed value, the arc 31 of 1.5 mm-2.0 mm will be ignited between the said end surfaces. In FIG. 3, the direction of the current is indicated by the arrow 33, and the direction of the force acting on the arc 31 is indicated by the arrow 32. That is, the generated arc 31 receives the force of the rotating magnetic field generated by the permanent magnet 7 and rotates at a high speed in the circumferential direction on the end face as indicated by the arrow 35 in FIG. As a result, both end faces of the first and second metal tubes 21 and 22 are heated.

  Here, in the initial stage after the arc is ignited, the arc 31 rotates on the inner diameter side of the first and second metal tubes 21 and 22, and the inner diameter side of the end face is heated. This is because the arc 31 receives a force in the inner diameter side direction due to a magnetic blowing phenomenon caused by a difference in magnetic flux density inside and outside the first and second metal tubes 21 and 22. In the present embodiment, as will be described later, the preheating step and the main heating step are performed using the heating by the arc. In the preheating step, the preheating temperature is set below the magnetic transformation point, and the heating temperature in the main heating step is set to, for example, about 1100 ° C.

  In this heating process, after the heating by the arc 31 is started, the magnetic susceptibility decreases with the temperature rise at the end faces of the metal tubes 21 and 22, and the ferromagnetism disappears at the magnetic transformation point (770 ° C.). For this reason, the magnetic flux density on the inner diameter side is higher than the magnetic flux density on the outer diameter side of the metal tubes 21 and 22, and the arc 31 is moved and heated to the outer diameter side of the metal tubes 21 and 22 by the magnetic blowing phenomenon.

  In the present embodiment, since the end surfaces of the first and second metal tubes 21 and 22 are sufficiently heated in advance by the preliminary heating step, the end surfaces reach a molten state almost uniformly by the main heating step. That is, it is possible to suppress the occurrence of the problem that the temperature of the inner diameter end face exceeds the melting point during the heating of the outer diameter end faces of the metal tubes 21 and 22 and the arc 31 disappears while the outer diameter end faces are insufficiently heated. Then, at the timing when the end surfaces of the first and second metal tubes 21 and 22 are almost uniformly melted, the metal tube on one side (for example, the first metal tube 21) is replaced with the metal tube on the other side (for example, the second metal tube). 22), the end surfaces of the first and second metal tubes 21 and 22 are joined. At this time, since the melted state is substantially uniform from the outer peripheral side to the inner peripheral side of the end face, the width of the bead portion is substantially equal between the inner main side and the outer peripheral side, and a uniform and good joint can be formed.

  The inventor makes a moving speed (also referred to as a pressing speed or a pressure contact speed) and a pressure contact force when pressing the metal pipe on one side to the metal pipe on the other side at the time of the above-described press contact, and a value equal to or higher than a certain value. From the central portion of the joint interface (the region of the joint interface that overlaps with the portion not deformed by the joining of the first and second metal tubes 21 and 22 when viewed from the axial direction of the joined body), the dendrite structure is exposed to the outside. Extrusion succeeded in forming a bonded interface without the dendrite layer. In order to form such a bonding interface, the melting state of the end face, the moving speed, and the pressing force are important control parameters. The moving speed is, for example, 20 mm / s or more, and the pressing force can be, for example, 5 MPa or more.

  Here, according to the conventional pressure welding method, the dendrite layer 15 is formed on the bonding interface 11 as shown in FIG. The presence of such a dendrite layer 15 causes a decrease in strength of the bonding interface 11. Such a dendrite layer 15 is formed because the moving speed and the pressure contact force when pressing the end surfaces of the first and second metal tubes 21 and 22 in the direction indicated by the arrow 16 make the dendrite layer 15 external. This is because it is not enough to be removed.

  Therefore, the present inventor makes the dendrite layer 15 formed at the time of bonding the outer side (inner peripheral side and the inner side) as shown in FIG. As shown by the arrow 18, the extrusion was successful. As a result, the region 17 including the central portion of the bonding interface 11 is in a state where the dendrite layer 15 does not exist. For this reason, in the joined body 10 according to the present embodiment shown in FIG. 5, the strength of the joined portion could be sufficiently increased.

  After performing the above steps, the bead portion 13 (see FIG. 5) located on the outer peripheral side is removed by grinding, whereby the joined body 10 as shown in FIGS. 1 and 2 can be obtained.

<Description of Magnetic Rotating Arc Joining Method and Joined Body Manufacturing Method According to this Embodiment>
Next, with reference to FIGS. 6-8, the magnetic rotating arc joining method which concerns on this embodiment, and the manufacturing method of the conjugate | zygote using the said magnetic rotating arc joining method are demonstrated in detail. Note that the vertical axis in FIG. 8A represents the energization current between the end faces, the vertical axis in FIG. 8B represents the arc voltage between the end faces, and the vertical axis in FIG. 8D, the vertical axis in FIG. 8D represents the temperature at a position 2 mm from the end surface, the vertical axis in FIG. 8E represents the pressing pressure between the end surfaces, and FIGS. ) Represents the time.

  With reference to FIG. 6, in the magnetic rotating arc welding method (joint body manufacturing method) according to the present embodiment, a preparation step (S <b> 10) is first performed. In this step (S10), first and second metal tubes 21 and 22 are prepared. The prepared first and second metal tubes 21 and 22 are set in the joining apparatus shown in FIG. In the joining apparatus shown in FIG. 7, the first metal tube 21 is fixed to the chuck 9 to which the plus terminal 8 is connected. The second metal tube 22 is fixed to the chuck 9 to which the minus terminal 6 is connected. An annular permanent magnet 7 is installed in the two chucks 9 so as to surround the first and second metal tubes 21 and 22. In addition, the load cell 5 is connected to the second surface side opposite to the first surface where the permanent magnet 7 is installed in the chuck 9 to which the minus terminal 6 is connected. A ball screw 3 is installed on the side opposite to the chuck 9 when viewed from the load cell 5. A motor 1 is connected to the ball screw 3 via a speed reducer 2. Further, a displacement sensor 4 for measuring the displacement of the chuck 9 to which the minus terminal 6 is connected is disposed at a position adjacent to the load cell 5. The 1st and 2nd metal tubes 21 and 22 are arrange | positioned so that a mutual end surface may oppose.

  Next, as shown in FIG. 6, a preheating step (S20) is performed. In the step (S20), arc discharge is generated between the end faces while the end faces of the first and second metal tubes 21 and 22 are opposed to each other, and a magnetic field is applied between the end faces to set the position of the arc discharge between the end faces. The temperature at a position 2 mm away from the end faces of the first and second metal tubes 21 and 22 is preheated to the preheating temperature (temperature T1 in FIG. 8D).

  Specifically, at the time t1 in FIG. 8, the distance (gap) between the end faces of the first and second metal tubes 21 and 22 is set to a predetermined size indicated by the gap D1 in FIG. At the same time, by applying an arc voltage V1 (see FIG. 8B) between the first and second metal tubes 21 and 22, the arc is ignited as shown in FIG. A current I1 (see FIG. 8A) flows. Further, the arc rotates at the end face as shown in FIG. 3 by the magnetic field generated by the permanent magnet 7 (see FIG. 7). As a result, the end face is heated, and the temperatures of the first and second metal tubes 21 and 22 at a position away from the end face by a predetermined distance (position 2 mm away from the end face) are shown in FIG. It is heated to a temperature T1 (preheating temperature), and the magnetism is lowered. At the time t2 when the temperature at the position reaches the temperature T1, the arc voltage and the arc current are set to zero (see FIGS. 8A and 8B). In addition, you may implement the preheating process (S20) mentioned above in multiple times.

  From the time t2 to the time t3, the first and second metal tubes 21 and 22 are held with the arc discharge stopped. Although the temperature at the position 2 mm from the end face decreases to the temperature T2 as shown in FIG. 8D by this holding time, the end face temperature becomes more uniform due to thermal diffusion at the end face. At this time, as shown in FIG. 8C, the gap between the end faces is once set to zero and set to a predetermined gap D1 again. This is because the gap is adjusted in order to reliably start the arc in the main heating process described later.

  Next, the main heating step (S30) is performed as shown in FIG. In the main heating step (S30), an arc discharge is generated between the end faces of the first and second metal tubes 21 and 22, and a magnetic field is applied between the end faces to move the position of the arc discharge between the end faces. The temperature at a position 2 mm away from the end faces of the first and second metal tubes 21 and 22 is fully heated to the bonding temperature (temperature T3 in FIG. 8D).

  Specifically, at a time point t3 in FIG. 8, the distance (gap) between the end faces of the first and second metal tubes 21 and 22 is set to a predetermined size indicated by a gap D1 in FIG. 8C. At the same time, by applying an arc voltage V1 (see FIG. 8B) between the first and second metal tubes 21 and 22, the arc is ignited as shown in FIG. A current I2 (see FIG. 8A) flows. In this case, the stability of the arc at the end face on the outer peripheral side was improved. Further, the arc rotates at the end face as shown in FIG. 3 by the magnetic field generated by the permanent magnet 7 (see FIG. 7). As a result, the end face is heated, and the temperatures of the first and second metal tubes 21 and 22 at a position away from the end face by a predetermined distance (position 2 mm away from the end face) are shown in FIG. It is heated to a temperature T3 (joining temperature).

  After this step (S30), from the time point t4 when the temperature at the above position rises to the temperature T3 to the time point t5, as shown in FIG. 8, it is larger than the energization current value (current I2) in the main heating step (S30). A step of passing a value upset current (current I3 in FIG. 8A) between the end faces is performed. As a result, as shown in FIG. 8D, the temperature at the position 2 mm from the end face (and the temperature of the end face) increases. At time t5 in FIG. 8, the arc voltage and the upset current are set to zero. Thus, even after the time point t5 when the arc voltage is set to zero, the temperature at the position 2 mm from the end face continues to rise and reaches the temperature T4 (see FIG. 8D) which is the maximum temperature.

  Next, the joining step (S40) shown in FIG. 6 is performed. In the joining step (S40), after the main heating step (S30), the end faces of the metal tubes 21 and 22 are butted together and joined. In the joining step (S40), the joined portions that are joined by abutting the end faces are energized and heated.

  Specifically, the second metal tube 22 is brought closer to the first metal tube 21 from a predetermined time after the time t5 shown in FIG. 8 to reduce the distance between the end faces (gap in FIG. 8C). At this time, the moving speed of the second metal tube 22 is set to 20 mm / s or more. Even after the gap becomes zero at time t6 (that is, in a state where the end faces are in contact with each other), the motor 1 (see FIG. 7) is further driven to press the metal tube 22 toward the metal tube 21 side. As a result, the gap becomes negative as shown in FIG. 8C (that is, the molten end faces are pushed out to the outer peripheral side and the inner peripheral side to form the bead portion, thereby joining the end faces). . At this time, as shown in FIG. 8E, pressure is generated between the end faces from time t6, and reaches a predetermined pressure P1 at time t7. The pressure P1 (pressure contact force) is, for example, 5 MPa or more. This is because it is considered that a pressure contact force of at least about 5 MPa is required to join the melted end faces.

  Thus, when the pressure between the end faces detected by the load cell 5 (see FIG. 5) reaches a predetermined pressure P1, the movement of the metal tube 22 by the motor 1 is stopped. As a result, the gap (see FIG. 8C) is substantially constant from time t7. Then, the state where the pressure between the end faces is a predetermined pressure P1 is maintained from the time point t7 to the time point t8, and the first and second metal tubes 21, 22 as shown in FIG. By passing a current I4 between them, the joint is heated by energization. Then, at the time t8, the energization heating is finished. Thus, the 1st and 2nd metal pipes 21 and 22 can be joined by performing a joining process (S40). Further, as shown in FIG. 5, the dendrite layer 15 is pushed out from the central part of the joint interface 11 from the joint interface between the metal tubes 21 and 22, and there is no dendrite layer in the central part.

  Thus, by performing a joining process (S40), the 1st and 2nd metal pipes 21 and 22 can be joined and a joined body can be obtained. Moreover, in the manufacturing method of the joined_body | zygote 10, after this joining process (S40), the post-process including the process of grinding the outer peripheral surface in the junction part of the obtained joined body 10, and removing the bead part of an outer peripheral side etc. Step (S50) may be performed. In this way, the joined body 10 shown in FIG. 1 can be obtained.

  In addition, the material which comprises the 1st and 2nd metal pipes 21 and 22 is steel, such as carbon steel for machine structures. The preheating temperature (temperature T1) in the preheating step (S20) is preferably a temperature lower than the magnetic transformation point of the material (for example, steel). For example, the preheating temperature (temperature T1) in the preheating step (S20) may be 100 ° C. or higher and 1000 ° C. or lower. In the case where the thickness of the metal tubes 21 and 22 is thick, even if the temperature of the inner diameter is increased, the temperature of the outer peripheral surface at a position 2 mm from the end surface of the metal tubes 21 and 22 for measuring the preheating temperature T1 or the like is not so high. This is because there are cases. Further, the preheating temperature is preferably 200 ° C. or higher and 900 ° C. or lower, more preferably 300 ° C. or higher and 800 ° C. or lower. Moreover, 1050 degreeC or more and 1150 degrees C or less (for example, 1100 degreeC) may be sufficient as the joining temperature (temperature T3) in this heating process (S30).

  Moreover, the current value between the end faces (current I1 or current I2 in FIG. 8A) in the preheating step (S20) and the main heating step (S30) may be 10 A or more and 10,000 A or less. The magnetic flux density of the magnetic field in the preheating step (S20) and the main heating step (S30) may be 1 mT or more and 1000 mT or less.

  Moreover, the moving speed (pressing speed) of the metal tube 22 in the joining step (S40) can be set to 20 mm / s or more and 1100 mm / s or less. The lower limit of the moving speed is set to 20 mm / s because if the moving speed is too slow, the temperature of the end faces decreases before the end faces come into contact with each other, resulting in poor bonding conditions. The upper limit of the moving speed is set to 1100 mm / s, which is determined as a feasible value in consideration of equipment performance of the motor 1 and the hydraulic drive device. The moving speed is preferably 30 mm / s or more and 1000 mm / s or less, more preferably 50 mm / s or more and 900 mm / s or less.

  Moreover, each condition in each process (S20-S40) of the joining method mentioned above can be suitably selected according to the material, size, etc. of the metal pipes 21 and 22. Further, in this method, by controlling the heating time based on the temperature history, the heating time can be easily controlled even when the current value, arc voltage value, magnetic flux density, material size, and the like are different.

  Although there is a part which overlaps with the description mentioned above, the characteristic structure of embodiment of this invention is enumerated.

  (1) A joined body 10 according to an embodiment of the present invention includes a first metal tube 21, a second metal tube 22, and a joined portion obtained by joining end surfaces of the first and second metal tubes. Is provided. At the joint interface 11 between the first metal tube 21 and the second metal tube 22 at the joint, the first and second metals are inside the outer peripheral surfaces of the first and second metal tubes 21 and 22. The dendrite layer 15 does not exist in a region outside the inner peripheral surfaces of the tubes 21 and 22.

  In this way, since the dendrite layer 15 having a relatively low strength does not exist in the central portion of the bonded interface 11 of the bonded body, the strength of the bonded portion including the bonded interface is attributed to the presence of the dendrite layer 15. This can reduce the possibility of defects such as cracks in the joint. For this reason, the joined body 10 provided with the joint part of sufficient intensity | strength can be obtained.

  (2) In the joined body 10, the material of the joined body 10 may be carbon steel for mechanical structure. In this case, the joined body according to the present embodiment can be applied to a machine part or the like.

  (3) In the joined body 10, the outer diameters of the first and second metal tubes 21 and 22 may be 10 mm or more and 250 mm or less. In this case, the joined body 10 having a relatively small diameter to a large diameter can be obtained.

  (4) In the joined body 10, the thickness of the first and second metal tubes 21 and 22 may be not less than 1 mm and not more than 16 mm. In this case, by preparing the joined body 10 having various thicknesses, the degree of freedom in selecting a mechanical device to which the joined body 10 according to the present embodiment is applied can be increased.

  In the joined body 10, the outer peripheral bead portion may be removed by grinding in the joined portion. The width L1 of the outer peripheral bead portion may be the width L1 of the ground portion from which the outer peripheral bead portion has been removed by grinding. In this case, since the outer peripheral bead portion can be removed from the outer peripheral surface of the joined body 10 by grinding to finish the outer peripheral portion smoothly, the appearance of the joined body 10 can be made cylindrical.

  (5) The magnetic rotating arc joining method according to one embodiment of the present invention joins the step of preparing the first and second metal tubes 21 and 22 (S10) and the step of heating (S30). And a step (S40). In the main heating step (S30), an arc discharge is generated between the end faces of the first and second metal tubes 21 and 22, and a magnetic field is applied between the end faces to move the position of the arc discharge between the end faces. Then, the temperature at a position 2 mm away from the end faces of the first and second metal tubes 21 and 22 is fully heated to the bonding temperature (temperature T3 in FIG. 8D). In the joining step (S40), after the main heating step (S30), the end faces are butted together and joined. In the joining step (S40), the relative pressure-contact speed of the first metal tube 21 with respect to the second metal tube 22 when the end surfaces are brought into contact with each other is 20 mm / s or more.

  In this way, the dendrite layer 15 that is a layer containing a dendrite structure does not exist in the central portion of the bonding interface 11, and the bonded body 10 having a sufficiently strong bonded portion can be obtained. The lower limit of the relative pressure contact speed is set to 20 mm / s because the relative movement speed between the first metal tube 21 and the second metal tube 22 is set to 20 mm / s in order to bring the end surfaces in the molten state into contact with each other. This is because the above is necessary. For example, when the distance between the end faces is about 2 mm (the arc length is about 2 mm), it is difficult to bring the end faces into contact with each other when the relative movement speed is less than 20 mm / s. The upper limit of the relative movement speed may be 1100 mm / s or less, more preferably 1000 mm / s or less.

  In addition, although the position 2 mm away from the end face is adopted as the temperature measurement position, the inventor has a stable correspondence between the experiment and the simulation if the temperature is at the position from the simulation and the experiment, and is used for the control. It has been confirmed that the measured value has sufficient reliability.

  (6) In the magnetic rotating arc joining method, in the joining step (S40), the pressure contact force (pressure P1 in FIG. 8E) when the end faces are abutted may be 5 MPa or more. Further, the upper limit of the pressure contact force may be 950 MPa or less. The reason why the lower limit of the pressure is set to 5 MPa is that the minimum pressure that can be pressed is considered to be about 5 MPa. The reason why the upper limit of the pressure is 950 MPa is that the pressure is assumed when a material having a high yield stress is used as the material of the metal tube. The pressure is preferably 10 MPa or more and 900 MPa or less, more preferably 20 MPa or more and 800 MPa or less.

  (7) In the magnetic rotating arc joining method, after the joining step (S40), the first and second metal tubes 21 and 22 are joined at the joining interface between the first metal tube 21 and the second metal tube 22. It is preferable that the dendrite layer 15 is not present in a region inside the outer peripheral surface of the first metal tube 21 and outside the inner peripheral surfaces of the first and second metal tubes 21 and 22. In this case, the strength of the joint portion in the joined body can be sufficiently increased.

  (8) In the magnetic rotating arc joining method, after the preparation step (S10) and before the main heating step (S30), the end surfaces of the first and second metal tubes 21 and 22 are arranged to face each other. Thus, by generating an arc discharge between the end faces and applying a magnetic field between the end faces to move the position of the arc discharge between the end faces, a position 2 mm away from the end faces of the first and second metal tubes 21 and 22 A step (S20) of preheating the temperature to a preheating temperature (temperature T1 in FIG. 8D) may be further provided. In the magnetic rotating arc joining method, the preheating temperature (temperature T1) in the preheating step (S20) may be a temperature lower than the magnetic transformation point of the material.

  In this way, since the preheating step (S20) can be performed using the same equipment as the method used in the main heating step (S30), it is not necessary to prepare an independent heating means for preheating, and simple Depending on the configuration, it can be preheated. For this reason, since the joint portion (the end portion including the opposing end surfaces of the first and second metal tubes 21 and 22) can be sufficiently heated in advance by the preliminary heating, arc discharge is performed in the main heating step (S30). Stability can be improved and the occurrence of problems such as insufficient or uneven heating of the joint can be suppressed. For this reason, generation | occurrence | production of a joining defect can be suppressed.

  (9) In the said magnetic rotating arc joining method, the material which comprises the 1st and 2nd metal pipes 21 and 22 may consist of steel. The bonding temperature (temperature T3) in the main heating step (S30) may be 1050 ° C. or higher and 1150 ° C. or lower. The bonding temperature (temperature T3) is preferably 1070 ° C. or higher and 1130 ° C. or lower, more preferably 1080 ° C. or higher and 1120 ° C. or lower. In this case, the 1st and 2nd metal pipes 21 and 22 which used steel as a material can be joined reliably, and a joined body can be obtained.

  (10) In the magnetic rotating arc joining method, the material may be carbon steel for mechanical structure. In this case, the joining method according to the present embodiment can be used for manufacturing machine parts and the like by applying the magnetic rotating arc joining method to joining metal pipes using carbon steel for machine structure as a material. Here, the carbon steel for machine structure is carbon steel for machine structure defined in JIS standard G4051 (for example, S10C, S45C, S55C, etc.), and boron (B) is added to the carbon steel defined in the above JIS standard G4051. The carbon steel contained (for example, SAE standard 10B38, SBM40, etc.) is meant.

  (11) In the magnetic rotating arc joining method, the outer diameters of the first and second metal tubes 21 and 22 may be 10 mm or more and 250 mm or less. As described above, the joining method according to the present embodiment can be applied to the metal pipes 21 and 22 having a relatively small diameter to a large diameter.

  (12) In the magnetic rotating arc joining method, the thickness of the first and second metal tubes 21 and 22 may be not less than 1 mm and not more than 16 mm. Thus, the joining method according to the present embodiment can be applied from the relatively thin metal tubes 21 and 22 to the thick metal tubes 21 and 22.

  In the magnetic rotating arc joining method, after the main heating step (S30) and before the joining step (S40), an upset current having a larger value than the energization current value in the main heating step (S30) (FIG. 8 ( A step of passing the current I3) of A) between the end faces may be further provided.

  In this case, before performing the joining step (S40), the melting region of the joining portion (the region including the end faces of the first and second metal tubes 21 and 22) can be made uniform by the upset current. For this reason, generation | occurrence | production of a joining defect can be suppressed reliably.

  In the magnetic rotating arc joining method, in the joining step (S40), the joining portion joining the end faces with each other may be energized and heated. In this case, it is possible to suppress an excessive temperature decrease in the joint portion in the joining step (S40), so that it is possible to prevent the joining conditions from deteriorating. For this reason, generation | occurrence | production of a joining defect can be suppressed more reliably.

  In the magnetic rotating arc joining method, the preliminary heating step (S20) may be performed a plurality of times before the main heating step (S30). In this case, when the first and second metal tubes 21 and 22 have a large diameter or when the metal tubes 21 and 22 are thick, the temperature of the joint portion can be sufficiently increased by a plurality of preheatings. it can. For this reason, generation | occurrence | production of a joining defect can be suppressed.

  In the magnetic rotating arc joining method, after the preheating step (S20) and before the main heating step (S30), the step of holding the first and second metal tubes with the arc discharge stopped ( A period between time t2 and time t3 in FIG. 8 may be further provided.

  In this case, in particular, when the thickness of the first and second metal tubes 21 and 22 is large, by performing thermal diffusion at the end face by the holding process as described above, the inner peripheral side and the outer peripheral side of the end face The temperature difference can be reduced. As a result, the occurrence of poor bonding can be suppressed. The length of the holding step may be, for example, more than 0 seconds and 10 seconds or less. This is because even the thick metal tube can sufficiently equalize the temperature of the end face by securing the holding time of about 10 seconds. If the metal tubes 21 and 22 are sufficiently thin, the main heating step (S30) may be performed immediately after the preheating step (S20) without performing the holding step.

  In the magnetic rotating arc joining method, the energization current value between the end faces in the preheating step (S20) and the main heating step (S30) may be 10 A or more and 10,000 A or less. In this case, an energization current value can be selected according to the size and material of the metal pipes 21 and 22 to be joined, and the occurrence of poor joining can be suppressed. Further, the energization current value may be controlled so as to fall within a range of ± 150 A with respect to the target value.

  In the magnetic rotating arc joining method, the magnetic flux density of the magnetic field in the preheating step (S20) and the main heating step (S30) may be 1 mT or more and 1000 mT or less. In this case, the magnetic flux density can be selected according to the size and material of the metal tube to be joined, the energization conditions, and the like. The magnetic flux density is preferably 10 mT or more and 900 mT or less, more preferably 20 mT or more and 800 mT or less.

  (13) A method for manufacturing a joined body according to an embodiment of the present invention uses the magnetic rotating arc joining method. In this way, it is possible to obtain the joined body 10 having a sufficiently strong joint.

(Experimental example)
In order to confirm the effect of the magnetic rotating arc joining method according to the present embodiment, the following experiment was conducted.

<Sample>
In this experiment, a cylindrical material using a JIS standard S45C material having an outer diameter of 40 mm and a wall thickness of 3 mm was prepared as the first and second metal tubes. The axial length of the cylindrical material was 300 mm. Moreover, the apparatus of the structure shown in FIG. 7 was used for the joining apparatus used for joining.

<Experiment method>
1) Sample of Example The prepared metal tube was set in the joining apparatus shown in FIG. 7, and joined by the magnetic rotating arc joining method according to the present embodiment shown in FIG. The set value of the current value in the preheating step (S20) was 115A, and the magnetic flux density on the outer diameter side of the metal pipe (steel pipe) end face was 40 mT. Further, the set value of the current value in the main heating step (S30) was set to 115A as in the preheating step (S20). Since the current value is proportional to the rotation speed of the arc, heating was performed for a long time at a lower current value to increase the temperature of the entire metal tube, thereby expanding the melting region. The magnetic flux density on the outer diameter side of the metal tube was 40 mT. In the preheating step (S20), heating was performed until the temperature (temperature T1 in FIG. 8D) at a position 2 mm from the outer diameter end face of the metal tube reached 550 ° C. The main heating step (S30) was started 3 seconds after the preheating step (S20) was completed (time point t3 3 seconds after time point t2). In this step, bonding was performed when the temperature at a position 2 mm from the outer diameter end face of the metal tube reached 1100 ° C. Immediately before bonding, an upset current (current I3 in FIG. 8A) was passed with a current value of 2 kA in order to make the melting region of the end faces uniform.

  About the upset which is a joining process (S40), regarding the example of the present invention, the pressure speed was 43 mm / s, and the pressure (pressure force) shown in FIG. 8E reached 60 kN (170 MPa). Alternatively, when the amount of pushing (the value on the minus side of the gap in FIG. 8C) has reached 11 mm, the operation is completed. Moreover, in order to suppress the temperature reduction of a metal pipe end surface, the energization heating with the electric current value of 2 kA was performed also during the joining process (S40).

2) Sample of Comparative Example Bonding was performed basically under the same conditions as the sample of the above example. However, for the upset of the sample of the comparative example, the condition of the comparative example was different from that of the example. Specifically, the pressure contact speed is 10 mm / s, and the pressure (pressure contact force) shown in FIG. 8E reaches 60 kN (or 170 MPa), or the pushing amount (the gap minus in FIG. 8C). When the value on the side became 10 mm, the process was completed.

<Result>
1) Sample of Example FIG. 9 shows an appearance of a joined body of the example in which the above-described metal tube is joined. In addition, in FIG. 9, the joined body is cut | disconnected along the axial direction, and it has arrange | positioned so that the cut surface of the cut | disconnected one part can be seen. FIG. 10 shows a cross-sectional microphotograph of the central part of the joint in the joined body shown in FIG. In FIG. 10, the cross-sectional microphotograph of (a) joining part, (b) heat affected part 1, (c) heat affected part 2, and (d) base material is shown in order from the joining interface. 10 is at a position of 0 mm from the bonding interface. Moreover, the said heat affected zone 1 is a 0.1-mm position from a joining interface. The heat affected zone 2 is at a position 0.2 mm from the bonding interface. Moreover, the said base material is a 0.4 mm position from a joining interface.

  As can be seen from FIG. 9 and FIG. 10, in the joined body according to the present embodiment, the dendrite layer does not exist in the central portion of the joined interface of the joined portion, and the joined portion is substantially uniform from the inner peripheral side to the outer peripheral side. It turns out that it has become a favorable structure | tissue and the favorable junction part is formed.

2) Sample of Comparative Example FIG. 11 shows the appearance of a bonded body of a comparative example in which the metal pipe described above is bonded. In addition, in FIG. 11, the joined body is cut | disconnected along the axial direction similarly to FIG. 9, and it arrange | positions so that the cut surface of the cut | disconnected one part can be seen. FIG. 12 shows a cross-sectional microphotograph of the central portion of the joint in the joined body shown in FIG. In FIG. 12, as in FIG. 10, a cross-sectional micrograph of (a) the joint, (b) the heat affected zone 1, (c) the heat affected zone 2, and (d) the base material in order from the joint interface is shown. Yes.

  As can be seen from FIGS. 11 and 12, in the comparative example, a dendrite layer is present at the joint interface, and the strength of the joint is lower than the strength of the joint in the joined body of the example shown in FIG. 9. it is conceivable that.

  Although the embodiments and examples of the present invention have been described above, the above-described embodiments can be variously modified. The scope of the present invention is not limited to the above-described embodiment. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is particularly advantageously applied to magnetic rotating arc welding of steel pipes.

1 motor, 2 speed reducer, 3 ball screw, 4 displacement sensor, 5 load cell, 6 minus terminal, 7 permanent magnet, 8 plus terminal, 9 chuck, 10 joined body, 11 joining interface, 12 grinding part, 13 bead part, 14a , 14b Boundary point between bead and inner peripheral surface, 15 dendrite layer, 16, 18, 32, 33, 35
Arrow, 17 area, 21, 22 metal tube, 31 arc, 34 power supply.

Claims (7)

A first metal tube;
A second metal tube;
A joining portion joining the end faces of the first and second metal tubes;
At the joint interface between the first metal tube and the second metal tube at the joint, the first and second metal tubes are inside the outer peripheral surfaces of the first and second metal tubes. A joined body in which a dendrite layer does not exist in a region outside the inner peripheral surface of.   The joined body according to claim 1, wherein a material of the joined body is carbon steel for machine structure. Preparing first and second metal tubes;
By generating an arc discharge between the end faces of the first and second metal tubes and applying a magnetic field between the end faces to move the position of the arc discharge between the end faces, the first and second The step of heating the temperature at a position 2 mm away from the end face of the metal tube to the joining temperature;
After the step of performing the main heating, the step of abutting and joining the end faces,
The magnetic rotating arc joining method, wherein, in the joining step, a relative pressure contact speed of the first metal tube with respect to the second metal tube when the end surfaces are brought into contact with each other is 20 mm / s or more.   The magnetic rotating arc joining method according to claim 3, wherein in the joining step, a pressure contact force when the end faces are brought into contact with each other is 5 MPa or more.   After the joining step, at the joining interface between the first metal tube and the second metal tube, the first and second metal tubes are inside the outer peripheral surfaces of the first and second metal tubes. The magnetic rotating arc joining method according to claim 3 or 4, wherein a dendrite layer is not present in a region outside the inner peripheral surface of the metal tube.   After the preparation step and before the main heating step, the end surfaces of the first and second metal tubes are opposed to each other, and arc discharge is generated between the end surfaces and between the end surfaces. A step of preheating the temperature at a position 2 mm away from the end faces of the first and second metal tubes to a preheating temperature by applying a magnetic field to move the position of the arc discharge between the end faces; The magnetic rotating arc joining method according to any one of claims 3 to 5, further comprising:   The manufacturing method of a joined body using the magnetic rotating arc joining method of any one of Claims 3-6.