JP5806064B2 - Upset welding method - Google Patents

Description

  The present invention relates to an upset welding joining method in which two bars are butt-welded.

  In a member such as a column or beam of a reinforced concrete structure or a prestressed concrete structure, a shear reinforcement bar that surrounds the periphery of the main bar in the longitudinal direction is used to increase bending rigidity. Conventional shear reinforcement bars are provided with hooks at both ends, and the overall shape has a square shape, a Japanese character shape, an eye shape, a rice field shape, a square shape, or a combination of these, and surrounds the main reinforcement. The hook is locked to the main muscle to resist the shearing force. Instead of providing the hooks at both ends, a closed shear reinforcement having a loop formed by welding both ends to each other may be used. Such a closed shear reinforcement bar does not have a hook that engages with the main bar, and can be welded at any position regardless of the position of the main bar. It is used as a continuous shear reinforcement. However, there is a problem that strength and elongation are generally reduced when welding is performed. In particular, a high-strength shear reinforcement with high tensile strength and large yield strength has problems such as a welded portion and a heat-affected zone having lower strength than the base material, and being easily damaged by tension. For this reason, even if an excellent high-strength base material is used, there is a problem that the final characteristics are restricted by the characteristics of the welded part and the heat-affected part.

  Conventionally, for example, upset welding or flash welding is known as a butt resistance welding method in which welded portions of two rods to be welded are butted and heated by energization, and a high pressure is applied to the welded portion. (For example, refer nonpatent literature 1.).

  In upset welding, the two bars to be welded are held with electrodes, the welds are butted together, energized while applying pressure, and the welded parts are heated only by resistance heating while being short-circuited. This is a butt resistance welding method in which a strong pressurization is applied when an appropriate temperature is reached.

  In flash welding, two bars to be welded are held by electrodes, the welds are brought into contact with each other, energized, and the welds are melted and scattered by repeated short-circuiting and arcing by repeating contact and separation of the welds. It is a butt resistance welding method in which heating is performed while the entire welded portion is sufficiently heated and melted to strongly press and join.

Suzuki Shigeru, Hasegawa Kazuyoshi, Resistance welding practice (Part 2)-Flash welding and upset welding, "Journal of the Japan Welding Society", Welding Society, March 1995, Vol. 64, No. 2, p. 94-97

  The upset welding is a welding method in which the welded portion is heated only by resistance heat generation, and no melt scattering occurs in the welded portion, so that contamination associated with welding does not occur. Further, in upset welding, a bump-shaped increased diameter portion in which the outer diameter of the welded portion is enlarged is formed in a uniform shape. In addition, upset welding does not require a mechanism for advancing and retracting an electrode for gripping a bar and a reactance circuit for generating an arc, and therefore, welding equipment is less expensive than flash welding.

  However, in upset welding, depending on the end face shape of the welded portion, the uniform temperature rise and temperature distribution in the welded portion may be hindered, resulting in incomplete joining, and the welded portion may have lower strength than the base metal. In particular, when the area of the welded portion is large, it is difficult to achieve matching when they are abutted, so that it is more noticeable that uniform temperature rise and temperature distribution in the welded portion are hindered.

  The above-mentioned flash welding is a welding method in which the entire welded portion is sufficiently heated and melted to press and join strongly, so that the welding strength is strong and stable welding is performed regardless of the end face shape and area of the welded portion. be able to.

  However, flash welding is a welding method in which a welded portion is heated while being melted and scattered by repeated short-circuiting and arcing, and therefore contamination due to welding occurs. In addition, since the welded portion heated in such a manner is heated to 1500 ° C. or higher, a so-called white band softened due to a decrease in carbon content (decarburization) in the vicinity of the welded portion after welding and A so-called white layer (decarburized part) is produced, and depending on the degree of decarburization, there is a risk of so-called interface fracture that breaks at the welded part when an axial tensile force acts on the bar. Further, in flash welding, a so-called flower bloom phenomenon occurs in which protrusions associated with melt scattering in the welded portion are formed on the outer surface of the bump-shaped increased diameter portion where the outer diameter of the welded portion is enlarged. When such a flower bloom phenomenon occurs, the outer diameter of the bump-shaped increased diameter portion increases accordingly, so that it is necessary to thicken the concrete cover, leading to an increase in the amount of concrete used. In addition, in flash welding, a mechanism for advancing and retracting an electrode for holding a bar and a reactance circuit for generating an arc are necessary, so that welding equipment is very expensive.

  In view of the above circumstances, the present invention does not cause contamination due to welding, is formed in a shape with a bump-shaped increased diameter portion in which the outer diameter of the welded portion is enlarged, and is stable without depending on the end face shape or area of the welded portion. It is another object of the present invention to provide an upset welding joining method that realizes strong welding with inexpensive welding equipment.

The upset welding joining method according to the present invention that achieves the above object comprises gripping two bars at positions spaced apart from the welded portions of these bars by a pair of opposing upset welding electrodes, respectively. the proximally to each other, below the pressure needed to upset welding, protruding toward the welded portion of the other bar which is welded partner from the welding portion of one of the bars of the upper Symbol two bars By supplying power to the upset welding electrode and heating the local convex portion while pressurizing with a first pressure such that only the local convex portion is in contact with the welded portion of the other bar causes repeated flushing effect of locally melting the localized protrusion by a fuse effect by electromagnetic pinch force, then this upset welding electrodes close to each other while supplying power to the upset welding electrode Direction, the first higher than pressure, pressurized with a second pressure required for upset welding, characterized in that butt welding the two bars above.

In the upset welding joining method of the present invention, the first pressurizing force is such that only the local convex portions of the welded portions of the two bar members are in contact with each other, so pressurization is performed with the first pressurizing force. Sometimes, the contact of the most protruding protrusions in the welded portion, the cutting by local melting, and the movement of the energization point are repeated. Thereby, the unevenness of the end surface of the welded portion is leveled and aligned, and local melting is distributed over the entire end surface of the welded portion, so that the entire end surface is in an appropriate molten state. That is, when pressurization by the first pressurizing force is completed, a good welded part in pressurization by the second pressurizing force is obtained. Therefore, stable and strong welding is performed without depending on the end face shape or area of the welded portion. Further, the upset welding joining method of the present invention does not require a mechanism for moving the upset welding electrode for holding the bar, or a reactance circuit for generating an arc. Therefore, the welding equipment is cheaper than that of flash welding, and contamination and flower bloom phenomenon associated with welding does not occur, and a well-shaped bump-shaped enlarged portion is formed. Moreover, since the temperature of the heated weld is not as high as that of flash welding, softening due to decarburization does not occur.

  Here, in the upset welding joining method of the present invention, it is preferable that the first pressure is a pressure of 500 N or less.

  According to such a preferable form, the contact of the most protruding protrusions in the welded portion, the cutting by local melting, and the movement of the energization point can be efficiently repeated.

Further, upset welding method of the present invention, the upset welding electrode when pressurized in the first pressing force, the upset welding electrode to the upset welding electrode when pressurized by the second pressure higher power than the power supplied, it is also preferable to feed the upset welding electrode of this.

  According to such a preferable form, when it pressurizes with a 1st applied pressure, the cutting | disconnection by local melting can be produced stably.

  According to the present invention, contamination due to welding does not occur, and a bump-shaped increased diameter portion in which the outer diameter of the welded portion is enlarged is formed in a uniform shape, which is stable and strong regardless of the end face shape and area of the welded portion. An upset welding joining method that realizes welding with an inexpensive welding facility is provided.

It is a schematic diagram which shows the state which faced the welding part of the two bar materials in the upset welding joining method which is one Embodiment of this invention. It is an enlarged view of the A section shown in FIG. It is an enlarged view of the A section shown in FIG. It is an enlarged view of the A section shown in FIG. It is an enlarged view of the A section shown in FIG. It is the state just before the primary pressurization in the upset welding joining method which is one embodiment of the present invention is finished, and the secondary pressurization. It is a schematic diagram which shows the state which the secondary pressurization in the upset welding joining method which is one Embodiment of this invention was complete | finished. It is a graph which shows the relationship between the axial direction tensile strength of the joint which welded two bar materials, and the width | variety of a heat affected zone.

  Embodiments of the present invention will be described below with reference to the drawings.

  Here, an embodiment in which the present invention is applied to butt welding of two bar members having a wire diameter of 15.9 mm will be described. Moreover, the welding equipment used here is a conventionally known welding equipment for upset welding.

  FIG. 1 is a schematic diagram showing a state in which welded portions 2 of two bar members 1a and 1b are butted in an upset welding joining method according to an embodiment of the present invention.

  First, the bars 1a and 1b are held by a pair of opposing clamps 3a and 3b at positions spaced apart from the welds 2 of the two bars 1a and 1b, respectively, and the two bars 1a and 1b are held. The welded part 2 is abutted. The clamps 3a and 3b are operated in directions close to each other by a hydraulic cylinder (not shown). More specifically, one of the clamps 3a and 3b is operated in a direction close to the other clamp 3b by a hydraulic cylinder, and the other clamp 3b is fixed in position. By such an operation, a pressure is applied between the clamps 3a and 3b. In addition, the clamps 3a and 3b are connected to a power source (not shown) and function as electrodes that heat the welded portion 2 by receiving power. The two bars 1a and 1b are examples of two bars according to the present invention, and the clamps 3a and 3b are examples of upset welding electrodes according to the present invention. A current supplied from a power source (not shown) flows to the bars 1a and 1b via the clamps 3a and 3b, and heats the welded portion 2.

  After the bars 1a and 1b are gripped by the clamps 3a and 3b and the welded portion 2 is abutted, one clamp 3a is moved in the direction close to the other clamp 3b by the hydraulic cylinder, and the clamps 3a and 3b are moved to each other. Primary pressurization is performed with a first pressure in the proximity direction. The first pressurizing force is a pressurizing force such that the welded portions 2 of the bars 1a and 1b are in contact with each other. Further, the first pressing force is a constant pressing force and continues to pressurize for a predetermined time. The first pressurizing force is, for example, one tenth or less of the pressurizing force of the primary pressurization in the conventional upset welding, and is approximately 135 N here. This first pressurizing force is an example of the first pressurizing force referred to in the present invention. Moreover, the pressurization time of primary pressurization is 2 seconds, for example.

  Moreover, in the state which continued primary pressurization, electric power is supplied from the power supply which is not shown in figure, and the welding part 2 is heated via clamp 3a, 3b. The current value at this time is, for example, a current value that is 1.5 times or more the current value in conventional upset welding, and is about 8000 A here. The current value of about 8000 A is an example of a current value that stably causes a fuse effect due to an electromagnetic pinch force described later.

  2 to 5 are enlarged views of a portion A shown in FIG. 2 shows the state of the welded portion 2 immediately after power is supplied from a power source (not shown), and FIGS. 3 to 5 show the state of the welded portion 2 thereafter.

  Even if the end surface of the welded portion 2 is processed with high accuracy, it has irregularities. In the present embodiment, since the first pressurizing force is a pressurizing force at which the welded portions 2 of the rods 1a and 1b are in contact with each other, when power is supplied from the power source in a state where primary pressurization is continued, First, as shown in FIG. 2, the protrusions 21 a and 21 b that protrude most in the welded portion 2 come into contact with each other, and a current I flows through that portion. That is, the current I flows locally. Thereafter, as shown in FIGS. 3 and 4, the convex portions 21a and 21b through which the current I flows are locally melted and cut by the fuse effect due to the electromagnetic pinch force. As described above, since the current I is about 8000 A, which is 1.5 times or more the current value in the conventional upset welding, the fuse effect due to the electromagnetic pinch force is stably generated as compared with the conventional current value. .

  As described above, since the pressurization is continued with the first pressurizing force that is the pressurizing force at which the welds 2 are in contact with each other, when the convex portions 21a and 21b are cut, as shown in FIG. The protrusions 22a and 22b that protrude most in the welded portion 2 after cutting 21a and 21b come into contact with each other, and a current I flows through these portions. That is, the energization point moves. Thereafter, similarly to the above-described cutting of the convex portions 21a and 21b, the convex portions 22a and 22b through which the current I flows are locally melted and cut by the fuse effect by the electromagnetic pinch force.

  Hereinafter, the contact of the most protruding protrusions in the welded portion 2, the cutting by local melting, and the movement of the energization point are repeated.

  FIG. 6 is a schematic view showing a state immediately before the secondary pressurization is completed after the primary pressurization in the upset welding joining method according to an embodiment of the present invention.

  When the primary pressurization is completed, as shown in FIG. 6, the end face of the welded portion 2 is obtained by repeating the above-described contact between the most protruding convex portions in the welded portion 2, cutting by local melting, and movement of the energization point. The unevenness is smoothed and alignment is achieved. Further, the above-described local melting is distributed over the entire end face of the welded portion 2, and the entire end face is in an appropriate molten state. That is, when the primary pressurization is completed, a good weld 2 in the secondary pressurization described later is obtained.

  The welding equipment used in this embodiment is a welding equipment for upset welding that is not provided with a reactance circuit for generating an arc, and is an apparatus that heats the welded portion 2 only by resistance heat generation while being short-circuited. . Therefore, the contamination accompanying welding does not occur. Moreover, since the temperature of the heated welding part 2 is not high temperature like flash welding, and is about 1300 degrees C or less, softening by decarburization does not arise. This temperature is confirmed, for example, by observing by thermography.

  When power is supplied and the welded portion 2 is heated, the clamp 3a is moved in the direction close to the other clamp 3b by the hydraulic cylinder, so that the clamps 3a and 3b are moved toward each other with the second applied pressure. Secondary pressure is applied. The second pressing force is higher than the first pressing force. The second pressing force is, for example, a pressing force equivalent to the pressing force of the secondary pressurization in the conventional upset welding, and is about 2.3 kN here. This second pressurizing force is an example of the second pressurizing force referred to in the present invention. The current at this time is smaller than the current at the time of primary pressurization, and is, for example, two-thirds or less of the current at the time of primary pressurization. This current value is, for example, a current value equivalent to the current value in conventional upset welding, and is about 4000 A here.

  FIG. 7 is a schematic diagram showing a state where the secondary pressurization in the upset welding joining method according to an embodiment of the present invention is completed.

  Due to the secondary pressurization, the heated welded portion 2 of the rods 1a and 1b is welded (warm-joined) by the applied pressure and spreads in the radial direction as shown in FIG. 7, and the outer diameter of the welded portion 2 is enlarged. The bump-shaped increased diameter portions 10a and 10b are formed. The amount of upset by secondary pressurization is controlled by detecting the position of the operating clamp 3a. For example, when it is detected by an encoder (not shown) that one clamp 3a has moved to the target position, the pressurization is terminated. Through the above steps, as shown in FIG. 7, the two bars 1a and 1b are butt welded.

  This embodiment does not require a mechanism for advancing and retracting the clamps 3a and 3b for gripping the bars 1a and 1b and a reactance circuit for generating an arc, and has been conventionally known for upset welding. Since it is a welding joining method using equipment, welding equipment is cheaper than flash welding. Further, in the present embodiment, as described above, the temperature of the heated welded portion 2 is not as high as that of flash welding, but about 1300 ° C. or less, and the welded portion 2 is only heated by resistance while being short-circuited. As a result, the flower bloom phenomenon does not occur, and the ridge-shaped enlarged portions 10a and 10b having a well-formed shape are formed. Further, according to the present embodiment, as described above, when the primary pressurization is completed, the unevenness of the end face of the welded portion 2 is leveled and aligned, and a good welded portion 2 in the secondary pressurization is obtained. In addition, since local melting is distributed over the entire end surface of the welded portion 2, welding is performed stably and firmly without depending on the end surface shape or area of the welded portion 2. Note that the end surface of the welded portion 2 was in a molten state because the welded portion 2 was melted when the textured portions 10a, 10b were cut along the axial direction after welding and the structure was examined. Confirmed by observation of tissue.

  Here, conventionally, in butt welding, the diameter of the rods 1a and 1b held between the clamps 3a and 3b and the bump-shaped enlarged portions 10a and 10b is not increased, but the heat of welding is increased. It is known that heat-affected portions 11a and 11b softened by the influence are formed. Depending on the width of the heat-affected portions 11a and 11b, the heat-affected portions 11a and 11b may break when subjected to the action of an axial tensile force.

  Further, conventionally, by reducing the width of the softened heat-affected portions 11a and 11b generated in the rods 1a and 1b after welding, the strength of the heat-affected portions 11a and 11b is reduced to the base material (bars 1a and 1b). A technology that achieves the same strength is known. This technique will be described with reference to FIG.

FIG. 8 is a graph showing the relationship between the axial tensile strength and the width of the heat affected zone of a joint in which two bars are welded. The vertical axis of this graph indicates the axial tensile strength of the joint, and the horizontal axis indicates the width (mm) of the heat affected zone. In addition, σ _{B on} the vertical axis represents the base material strength. In FIG. 8, a bar (base material) having a wire diameter of 10 mm was used.

  As shown in FIG. 8, the strength of the heat-affected zone is approximately 0.2 times the width of the base metal diameter (2 mm in the example shown in FIG. 8). It has the same strength as the base metal. This is because the plastic deformation of the low-strength heat-affected zone is constrained by the high-strength base material portion. This technology is a so-called “soft joint theory”, for example, “Welding Society,“ Welding and Joining Technology ”, First Edition, Second Printing, Sangyo Publishing Co., Ltd., July 20, 1994. , P. 267 ”. In addition, the width | variety of the softened heat affected zone is confirmed by cutting the area | region containing a heat affected zone after welding along an axial direction, and measuring hardness.

  In upset welding, the width of the softened heat-affected zone generated in the bar after welding is less than 0.2 times the diameter of the base metal by bringing the position where the bar is gripped by the clamp closer to the weld. Is possible. However, in conventional upset welding, in order to make the width of the heat-affected zone less than 0.2 times the base metal diameter, if the position where the bar is gripped by the clamp is brought close to the weld, it is proportional to this. Thus, heat removal by the clamp is strengthened. As a result, heating of the welded portion due to the supply of electric power is hindered, resulting in incomplete joining due to insufficient heating, and the welded portion may have a lower strength than the base material. That is, when such an incomplete joining occurs, there is a risk of so-called interface fracture that breaks at the weld due to an axial tensile force. Therefore, in conventional upset welding, the width of the softened heat-affected zone generated in the bar after welding is set to 0.2 times the base metal diameter or less by bringing the position where the bar is gripped by the clamp closer to the weld. It was difficult to make the width.

  Hereinafter, a description will be given with reference to FIG.

  In the present embodiment, as described above, the first pressurizing force in the primary pressurization is the most prominent in the welded portion 2 by making the welded portion 2 of the rods 1a and 1b contact each other. Contact between the convex portions, cutting by local melting, and movement of the energization point are repeated. When the primary pressurization is completed, the unevenness of the end face of the welded portion 2 is leveled and aligned to obtain a good welded portion 2 in the secondary pressurization, and the local melting is performed on the welded portion. 2 is distributed over the entire end surface of the welded portion 2, it is welded stably and firmly without depending on the end surface shape or area of the weld 2. Therefore, in this embodiment, the width of the softened heat-affected portions 11a and 11b generated in the welded bars 1a and 1b is set to a width of 0.2 times or less the diameter of the base material (bars 1a and 1b). Even if the position where the bars 1a and 1b are gripped by the clamps 3a and 3b is brought close to the welded portion 2, the welded portion 2 is sufficiently heated.

  Therefore, in this embodiment, the width of the softened heat-affected portions 11a and 11b generated in the rods 1a and 1b after welding due to the influence of welding heat is 0.2 times or less the diameter of the rods 1a and 1b. This position can be gripped by the clamps 3a and 3b as a position for gripping the two bars 1a and 1b. As described above with reference to FIG. 8, the heat-affected portions 11a and 11b have the base material (bars 1a and 1b) having a strength that is obtained by welding the bars 1a and 1b thus gripped. Has comparable strength. That is, it is avoided that the tensile force acts in the axial direction and breaks at the heat affected portions 11a and 11b, and breaks at the base material (bars 1a and 1b).

  Therefore, it is not necessary to take measures such as containing an alloy component accompanying the generation of the softened heat-affected zones 11a and 11b, and it is only necessary to consider the strength of the base material (bars 1a and 1b) itself. Cost can be reduced. Moreover, since it does not break at the heat-affected portions 11a and 11b, it will be responsible for the elongation when the axial tensile force is applied, excluding the bump-shaped increased diameter portions 10a and 10b, and has good elongation value performance. Can be obtained.

  In the above-described embodiment, the bar material referred to in the present invention is described as an example of a bar material having a wire diameter of 15.9 mm. However, the bar material referred to in the present invention is not limited to this. There may be any bar material of any wire diameter. However, in the case of a bar having a wire diameter thinner than 15.9 mm, the first and second pressures are lower than those described in the above-described embodiments, and the wire diameter is thicker than 15.9 mm. In the case of a bar having the above, the first and second pressures are higher than those described in the above-described embodiments.

  Further, in the above-described embodiment, the example in which the first pressurizing force referred to in the present invention is 135 N has been described, but the first pressurizing force referred to in the present invention is not limited to this, and welding is performed. The pressurizing force is preferably 500 N or less, as long as it is a pressurizing force that can efficiently repeat the contact between the projecting projections that are the most prominent in the part, the cutting by local melting, and the movement of the energization point.

  Moreover, in embodiment mentioned above, when pressurizing the upset welding electrode said to this invention with a 2nd applied pressure, electric power higher than the electric power supplied to an upset welding electrode is used, and an upset welding electrode is used with a 1st applied pressure. The example of supplying the upset welding electrode when pressurizing has been described. However, the present invention is not limited to this, and the power supplied to the upset welding electrode according to the present invention is, for example, constant power. Good.

1a, 1b Bar 2 Welded part 21a, 21b, 22a, 22b Convex part 3a, 3b Clamp 10a, 10b Hump-shaped increased diameter part 11a, 11b Heat affected part

Claims (3)

With a pair of opposing upset welding electrodes, the two bars are gripped at positions apart from the welded portions of the bars, and the upset welding electrodes are moved closer to each other than the pressure required for upset welding. Only the local convex part which protruded toward the welding part of the other bar material which is a welding other party from the welding part of one bar material of the two bar materials which is low is the welding part of the other bar material while pressurizing at a first pressure to the extent that contact with the upset by heating the localized protrusion supplies power to the welding electrodes, said local specific convex portion by a fuse effect by electromagnetic pinch force was repeated flushing effect of locally melted, then the said upset welding electrode proximally to each other while supplying power to upset welding electrodes, higher than the first pressure, the upset weld Pressurized with principal a second pressure, upset welding method characterized by butt welding the two bars.   The upset welding joining method according to claim 1, wherein the first pressing force is a pressing force of 500 N or less. Wherein when pressurized with upset welding electrode said first pressing force, a power greater than the power supplied to the upset welding electrodes when pressurizing the upset welding electrode at the second pressure, the The upset welding joining method according to claim 1 or 2, wherein the upset welding electrode is supplied to the upset welding electrode.

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