JP4728926B2 - Lap resistance spot welding method - Google Patents

Description

  The present invention relates to a lap resistance spot welding method in which a plurality of steel plates are overlapped and spot-welded by resistance welding, and in particular, a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of electrodes and pressed. The present invention relates to a lap resistance spot welding method in which energization is performed while welding.

  The lap resistance spot welding method is a welding method in which a pair of electrodes is sandwiched between a pair of electrodes and energized while being pressed with this pair of electrodes to join the materials to be joined together. Due to the resistance heat generated by energization, a spot-like melted portion (nugget) is formed at the contact portion of the material to be joined.

  Welding machines that perform such lap resistance spot welding methods include power supply systems, single-phase AC systems, single-phase and three-phase rectification systems, inverter DC systems, and capacitor systems. From the viewpoint of power saving, inverter type DC resistance spot welding is becoming mainstream. However, the direct current resistance welding method has a problem that the electrode life is shorter than the alternating current resistance welding method. Therefore, conventionally, in order to extend the electrode life, when the zinc-based single-side surface-treated steel sheets are overlapped and welded together, the direct current is arranged such that the zinc-based surface treated surface is in contact with the positive electrode and the non-surface-treated surface is in contact with the negative electrode. A method of performing resistance spot welding has been proposed (see, for example, Patent Document 1).

  However, when three or more materials to be joined are welded by the conventional lap resistance spot welding method as described in Patent Document 1, when a thin plate is arranged on the outermost side, the thin plate and the adjacent thick plate There is a problem that a good nugget is not formed between them and a sufficient bonding strength cannot be obtained. Further, if the welding conditions are set so that the nugget grows to the outermost thin plate, the nugget formed between the thick plates on the inner side grows too much and scattering occurs.

  Therefore, conventionally, methods have been proposed for obtaining sufficient joint strength when three or more members to be joined are subjected to resistance spot welding (see, for example, Patent Documents 2 to 5). For example, in Patent Document 2, when a thin plate is overlapped and welded on two thick plates, a convex portion is formed at a portion to be welded of the thin plate, and the convex portion is crushed with a low pressure in the initial stage of welding. A spot welding method is disclosed in which a thin plate and a thick plate are welded, and then two thick plates are welded with high pressure.

  Further, in the spot welding method described in Patent Document 3, when a thin plate with low rigidity is superposed on a thick plate with high rigidity and welded, the tip diameter of the electrode tip that contacts the thin plate is brought into contact with the thick plate. By making it smaller than the tip diameter of the electrode tip, the contact area between the thin plate and the electrode tip is made smaller than the contact area between the thick plate and the electrode tip, thereby improving the welding strength. Furthermore, in the spot welding method described in Patent Document 4, the bonding strength is improved by changing the applied pressure between the thin plate side and the thick plate side. FIG. 6 is a diagram schematically showing the spot welding method described in Patent Document 4. As shown in FIG. 6, in the spot welding method described in Patent Document 4, a plate assembly 104 in which a thin plate 103 with low rigidity is superimposed on thick plates 101 and 102 with high rigidity is used as a pair of electrode tips 105 and 106. When the welding is performed between the electrode tips 105 and 106, the pressing force FU of the electrode tip 106 contacting the thin plate 103 is made smaller than the pressing force FL of the electrode tip 105 contacting the thick plate 101. Energized.

  On the other hand, in the method of manufacturing a resistance spot welded joint described in Patent Document 5, spot welding is performed in two stages in order to prevent the occurrence of scattering, and the second stage welding is performed at a higher pressure than the first stage welding. , Low current or the same current, long energization time or the same energization time. Further, in the resistance spot welding methods described in Patent Documents 5 and 6, even if the plate pressure ratio is a plate assembly, an electrode tip that contacts a thick metal plate for the purpose of forming a nugget of a required size without occurrence of scattering. The tip of the electrode is a curved surface having a radius of curvature larger than the radius of curvature of the tip of the electrode tip in contact with a flat or thin metal plate, spot welding is performed in two stages, and the second stage welding is higher than the first stage welding. It is done with pressure.

JP-A-4-94877 JP 2003-71569 A JP 2003-251468 A JP 2003-251469 A JP 2005-262259 A JP 2006-55898 A

  However, the conventional techniques described above have the following problems. That is, the spot welding method described in Patent Document 2 described above has a problem in that it is necessary to previously provide a convex portion at a position to be welded on the thin plate side, and there is a problem that the welding portion is limited thereby. The process for forming the material is necessary before welding, and the accuracy of abutting the electrode accurately on the center of the convex part is required. There is also a problem that it is necessary. Further, in the spot welding method described in Patent Document 3, since the contact area of the electrode in contact with the thin plate side is small, the current density is relatively large, so that the sheet separation (plate lift) on the thin plate side is large. This causes the problem that the finished accuracy of the product is deteriorated. Furthermore, since the electrode on the thin plate side has a high current density, the electrode is significantly fouled and worn. As a result, the electrode must be frequently dressed or replaced, resulting in problems such as production delays and increased costs. Occur frequently. Further, in the spot welding method described in Patent Document 4, the applied pressure of the electrode that contacts the thin plate side is made smaller than the applied pressure of the electrode that contacts the thick plate side, thereby reducing the contact resistance value on the thick plate side. The contact resistance value on the side is controlled so as to decrease, and heat generation is promoted.To that end, a servo motor and a gun controller that operates the servo motor are used to apply a force that pushes up the gun body from the bottom. In addition, as for the welding machine, a stationary spot welding machine cannot be applied, and it is limited to a robot type spot gun. There is a problem that the cost increases.

  On the other hand, in the spot welding methods described in Patent Documents 5 and 6, in order to carry out a welding process consisting of a first stage and a second stage, the spot welding machine is generally not provided in a short time. There is a problem that it is necessary to provide a variable pressure mechanism that operates, and the equipment becomes expensive. Also, in these welding methods, the nugget is formed on the thin plate side in the first stage, and then the nugget is formed on the thick plate side in the second stage without being scattered. It is necessary to apply the conditions and to apply a long-time energization or the same energization time condition at a low current or the same current. For this reason, although the welding has already been completed in the first stage welding, a large pressure and excessive heat input and load are generated in the second stage welding on the thin plate side which is still in a high temperature state. As a result, the indentation on the thin plate side becomes large, and there is a problem that the degree of deformation as a product becomes large. In particular, in the welding method described in Patent Document 6, this tendency increases because the radius of curvature of the thin plate side electrode is small. Further, in the welding methods described in Patent Documents 5 and 6, the electrode on the thin plate side is heavily soiled and worn, and frequent dressing or replacement of the electrode is required. .

  The present invention has been made in view of the above-mentioned problems. When three or more steel plates are subjected to resistance spot welding, even if the welding pressure is constant, the thin steel plate side is also provided. It is an object of the present invention to provide a lap resistance spot welding method in which necessary penetration is obtained and no scatter occurs.

The lap resistance spot welding method according to the present invention is a single-phase alternating current method in which a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes and energized while being pressed to weld the contact points of each steel plate. In the lap resistance spot welding method using a power source, the method includes the step of placing the thinnest steel plate among the steel plates on one electrode side, and the step of performing multi-stage energization welding with a constant applied pressure. The energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel plate by a heat generation mode utilizing contact resistance between the steel plates during the first stage energization, and a plate thickness t ₁ ( mm), the energization time _Ta and the current value _Ia are set so as to satisfy the following formula (1), and then energization is performed with energization time: 1 to 5 cycles and rest time: 1 to 5 cycles. Parsesh repeats the pause three times or more It is characterized in that the power is turned on.

In another lap resistance spot welding method according to the present invention, a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes, and energized while applying pressure to weld contact points of each steel plate. In the lap resistance spot welding method using an inverter controlled direct current method, the method includes the step of placing the thinnest steel plate among the steel plates on the plus electrode side, and the step of performing multistage energization welding with a constant applied pressure. The multi-stage energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel sheet due to a heat generation form utilizing contact resistance between the steel sheets during the first stage energization, and the thickness of the thinnest steel sheet. Energization time _Ta and current value _Ia are set so that the relationship with t ₁ (mm) satisfies the above formula (1), and then energization time is 10 to 100 milliseconds, and rest time is 10 to 100. Energized as milliseconds and Pulsation energization that repeats the pause three times or more is performed.

These lap resistance spot welding process, the current value I _b in the pulsation welding operation is preferably satisfies the following formula (2).

Furthermore, another lap resistance spot welding method according to the present invention is a method in which a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes and energized while being pressed to weld contact points of the respective steel plates. In the lap resistance spot welding method using an inverter controlled direct current method, the method includes the step of placing the thinnest steel plate among the steel plates on the plus electrode side, and the step of performing multistage energization welding with a constant applied pressure. The multi-stage energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel sheet due to a heat generation form utilizing contact resistance between the steel sheets during the first stage energization, and the thickness of the thinnest steel sheet. t ₁ after the relationship between (mm) was subjected to first energizing step sets the energization time T _a and the current value I _a to satisfy the above equation (1), the current value I _b for the first co If below the current value I _a in energizing step , And performs second energizing step is set to a range that indicates the current time T _b the following equation (3).

This lap resistance spot welding method, the relationship between the current value I _b in the said current value I _a in the first energizing step second energizing step preferably satisfies the above equation (2).

In the lap resistance spot welding method described above, the ratio (t ₂ / t ₁ ) of the total plate thickness t ₂ (mm) of the plate assembly to the plate thickness t ₁ (mm) of the thinnest steel plate is 4 or more. preferable.

  According to the present invention, the steel plate with the thinnest thickness is arranged on one electrode side, and the current-carrying conditions are optimized and the multi-stage current welding is performed. Three or more steel plates can be spot-welded without being generated, and further, a penetration enough to obtain a sufficient bonding strength can be formed on the thin steel plate side.

The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. First, the lap resistance spot welding method according to the first embodiment of the present invention will be described. FIG. 1 is a diagram schematically showing the lap resistance spot welding method of this embodiment, and FIG. 2 is a diagram showing an energization pattern in the lap resistance spot welding method of this embodiment. As shown in FIG. 1, in the lap resistance spot welding method of the present embodiment, first, the three steel plates 1, 2, 3 having different thicknesses are arranged so that the steel plate 3 having the smallest thickness is on the outside. That is, the steel plates 3 having the thinnest thickness are overlapped so as to be in contact with the electrode 5 or the electrode 6. Although not particularly limited plate thickness of these steel sheets, a sheet thickness t _1, for example, less than 1.0mm of the thinnest steel plate 3 is the plate thickness, the thickness of the thick steel plates 1 and 2 than for example It is 1.0 mm or more. The pair of welding electrodes 5 and 6 sandwich the plate assembly 4 composed of the three steel plates 1, 2 and 3 and pressurize the electrodes 5 and 6 with a single-phase AC power source (not shown). Energize in between, and perform multi-stage energization welding with energization frequency of 4 or more.

At that time, as shown in FIG. 2, in the first stage energization, the diameter (nugget diameter) of the nugget 7 formed on the steel plate 3 having the smallest thickness at the end of the first stage energization is dn (mm). When the plate thickness of the thinnest steel plate 3 is t ₁ (mm), the energization time _Ta and the current value I _a are set so that the relationship between the nugget diameter dn and the plate thickness t ₁ satisfies the following formula (4). Set and energize. Specifically, energization time set the T _a for example, a short 5 cycles or less, the steel plate 2 and the condition expulsion generation does not occur between the steel plate 3, and nugget diameter dn is 3.5 × √t ₁ The current value _Ia is set so as to be above. When the first-stage energization is performed under these conditions, the contact portion of each steel plate is melted to form the nugget 7. If energization is performed under the condition that the nugget diameter dn is less than 3.5 × √t ₁ , the weld strength of the joint is insufficient, and if energization is performed under the condition that the nugget diameter dn exceeds 5 × √t ₁ , the indentation on the steel plate 3 side In addition, the floating of the plate (short separation) is increased, the joint shape is deteriorated, and in addition, the electrode wear on the side of the steel plate 3 is particularly severe.

  The energization after the second stage is performed by repeating pulsation energization with an energization time of 1 to 5 cycles and a pause time of 1 to 5 cycles three or more times. Thereby, the nugget of the magnitude | size which can obtain sufficient joint strength between the steel plate 1 and the steel plate 2 can be grown, maintaining the nugget formed by the 1st stage electricity supply. On the other hand, since the energization after the second stage is pulsation energization with a downtime, in the portion where the steel plate 1 and the steel plate 2 are in contact with each other, the rapid heat generation, which is a characteristic of pulsation welding, is suppressed. A sufficiently large nugget can be formed while preventing the occurrence. Even if the energization time exceeds 5 cycles, the effect of growing the nugget is not improved. On the other hand, when the rest time exceeds 5 cycles, the temperature of the steel sheet is lowered and the welding efficiency is lowered. Furthermore, when the number of times of energization and pause is less than 3, the effect of pulsation energization cannot be obtained and a good nugget cannot be obtained.

  Further, during the multistage energization welding, it is not necessary to change the applied pressure unlike the spot welding methods described in Patent Documents 5 and 6 described above. That is, in the resistance spot welding method of this embodiment, the applied pressure applied to the plate assembly 4 by the electrodes 5 and 6 is constant.

Further, in the lap resistance spot welding method of this embodiment, when the current value I _b during pulsation welding operation shown in FIG. 2 is less than 1/3 of the current value I _a in the energization of the first stage, the plate thickness There is not a required nugget formed thinnest steel plate 3, fittings may become insufficient strength, and if the current value I _b during pulsation welding current exceeds the current value I _a in the energization of the first stage Scattering may occur between the steel plate 2 and the steel plate 3. Therefore, the current value I _b during pulsation welding operation is preferably set within a range satisfying the following equation (5). Thereby, the nugget of the magnitude | size which can obtain sufficient intensity | strength can be formed, without generating scattering between the steel plate 1 and the steel plate 2, and between the steel plate 2 and the steel plate 3, respectively.

When the ratio (t ₂ / t ₁ ) of the total plate thickness t ₂ (mm) of the plate assembly 4 to the plate thickness t ₁ (mm) of the thinnest steel plate 3 is less than 4, the above-described technique of the present invention is applied. Even without this, for example, a well-known technique such as making the tip radius of the electrode in contact with the thinnest steel plate 3 smaller than the tip radius of the other electrode can be well welded. That is, the present invention has an advantage when the ratio (t ₂ / t ₁ ) of the total plate thickness t ₂ (mm) of the plate assembly 4 to the plate thickness t ₁ (mm) of the thinnest steel plate 3 is 4 or more. And advanced.

  As described above, in the lap resistance spot welding method according to the present embodiment, the steel plate 3 having the thinnest thickness is disposed on the outermost side so as to be in contact with the electrode 5 or the electrode 6, so that a normal spot welding technique is applied. In this case, since the thinnest steel plate 3 is cooled by the electrode in contact therewith, it is difficult to form a sufficiently large nugget on the steel plate 3 side, but the present invention is applied. This makes it possible to form a better nugget. In addition, after energizing under the condition that the nugget is formed on the thinnest steel plate 3 side, the nugget is grown between the steel plate 1 and the steel plate 2 by performing pulsation energization that repeats energization and pause three times or more. Even if the welding pressure is not changed, it is possible to form a nugget capable of obtaining sufficient bonding strength without causing scattering.

  In the lap resistance spot welding method of the first embodiment described above, the welding of a plate assembly in which three steel plates are overlapped is described as an example, but the present invention is not limited to this. If it is the lap resistance spot welding method of 3 or more steel plates, the effect mentioned above will be acquired.

  Next, the lap resistance spot welding method according to the second embodiment of the present invention will be described. FIG. 3 is a diagram schematically illustrating the lap resistance spot welding method of the present embodiment, and FIG. 4 is a diagram illustrating an energization pattern in the lap resistance spot welding method of the present embodiment. In the lap resistance spot welding method of this embodiment, as shown in FIG. 3, first, the three steel plates 11, 12, and 13 having different thicknesses are overlapped so that the steel plate 13 having the smallest thickness is on the outside. Match. Then, the plate assembly 14 composed of the three steel plates 11, 12, 13 is sandwiched and pressed by the pair of welding electrodes 15, 16, and the steel plate 13 having the thinnest plate thickness is obtained by an inverter control direct current method. Energization is performed between the electrodes 15 and 16 so that the electrode 16 that comes into contact is a positive electrode, and multi-stage energization welding in which the number of energizations is four or more is performed.

At that time, as shown in FIG. 4, in the first-stage energization, the diameter (nugget diameter) of the nugget 17 formed on the thinnest steel plate 13 is dn (mm), and the thinnest steel plate 13 is thick. the when _t 1 and (mm), the relationship between the nugget diameter dn and the plate thickness _{t 1} is to satisfy the above equation (4), energized by setting the energization time _{T a} and the current value _{I a,} the steel plate 12 A nugget is formed at a contact portion between the steel plate 13 and the steel plate 13. The energization after the second stage is performed by repeating the pulsation energization three times or more with the energization time being 10 to 100 milliseconds and the pause time being 10 to 100 milliseconds, and the nugget shape formed by the first stage energization. While maintaining the above, it is possible to form a nugget having a size in which no scattering occurs between the steel plate 11 and the steel plate 12 and sufficient welding strength can be obtained.

  In addition, in the pulsation energization, if the energization time for one time is less than 10 milliseconds, the nugget does not grow because no heat is generated at the contact portion of each steel sheet, and the energization time for one time exceeds 100 milliseconds. In such a case, the effect of suppressing sudden heat generation is lost, and intense scattering occurs. Accordingly, the energization time is 10 to 100 milliseconds. Also, if the pause time is less than 10 milliseconds, scattering tends to occur, and if the pause time exceeds 100 milliseconds, the temperature of the weld decreases and the welding efficiency decreases, so a sufficiently large nugget is formed. Not. Therefore, the pause time is 10 to 100 milliseconds. Furthermore, if the number of times of energization and pause is less than 3, the effect of pulsation energization to form a sufficiently large nugget without generating scattering is not obtained, so the number of repetitions is 3 or more. .

In the lap resistance spot welding method of this embodiment, the relationship between the current value I _a of the energization current value I _b and the first stage at the time of pulsation welding operation of the second stage or later, the equation (5) to be within a range satisfying, it is desirable to set the current value I _b during pulsation welding operation. Thus, forming a nugget having a size capable of obtaining sufficient bonding strength without causing any scattering between the steel plate 11 and the steel plate 12 while maintaining the nugget shape formed by the first-stage energization. Can do. Further, in the configuration of the present embodiment described above, the ratio (t ₂ / t ₁ ) of the total plate thickness t ₂ (mm) of the plate assembly 14 to the plate thickness t ₁ (mm) of the thinnest steel plate 13 is 4 or more. In some cases, it demonstrates its superiority and advancedness.

  As described above, in the lap resistance spot welding method of the present embodiment, the steel plate 13 having the thinnest thickness is disposed on the outermost side so as to come into contact with the plus electrode 16, and therefore the welding heat generated between the steel plates is In this way, the welding heat is transferred from the negative electrode side to the positive electrode side by riding on the flow of electrons due to the direct current. Due to this phenomenon, a sufficiently large nugget is formed between the steel plate 12 and the steel plate 13. Further, after energization is performed under the condition that a nugget is formed between the steel plate 12 and the steel plate 13, pulsation energization is performed by repeating energization and pause three times or more, and in particular between the steel plate 11 and the steel plate 12. Therefore, sufficient bonding strength can be obtained without changing the applied pressure during welding. Furthermore, since the energization after the second stage is pulsation energization with downtime, in the portion where the steel plate 11 and the steel plate 12 are in contact with each other, the rapid heat generation characteristic of pulsation welding is suppressed, A sufficiently large nugget can be formed while preventing the occurrence. Furthermore, in the lap resistance spot welding method of the present embodiment, since multistage energization welding is performed with an inverter-controlled DC current method, the lap resistance spot welding method of the first embodiment that performs multistage energization welding with a single-phase AC power supply is used. In comparison, the degree of freedom in selecting the energization time is large, and since there is no zero cross in the current waveform as in single-phase alternating current, heat generation efficiency is high and welding can be realized in a shorter time.

  The configuration and effects other than those described above in the lap resistance spot welding method of the present embodiment are the same as those of the lap resistance spot welding method of the first embodiment described above.

  Next, a lap resistance spot welding method according to the third embodiment of the present invention will be described. FIG. 5 is a diagram showing an energization pattern in the lap resistance spot welding method of the present embodiment. In the lap resistance spot welding method of this embodiment, as in the lap resistance spot welding of the second embodiment shown in FIG. 3, first, three steel plates 11, 12, and 13 having different thicknesses are used. Lamination is performed so that the thinnest steel plate 3 is on the outside. Then, the plate assembly 14 composed of the three steel plates 11, 12, 13 is sandwiched and pressed by the pair of welding electrodes 15, 16, and the steel plate 13 having the thinnest plate thickness is obtained by an inverter control direct current method. Energization is performed between the electrodes 15 and 16 so that the electrode 16 that comes into contact is a positive electrode, and multi-stage energization welding is performed with two energization times.

At that time, as shown in FIG. 5, in the first stage energization, the nugget diameter formed on the thinnest steel sheet 13 after the first stage energization is dn (mm), and the plate of the thinnest steel sheet 13 is formed. When the thickness is t ₁ (mm), the energization time _Ta and the current value I _a are set so that the relationship between the nugget diameter dn and the plate thickness t ₁ satisfies the above formula (4). A nugget is formed by applying, to the contact portion of the steel plate, welding milk heat belonging to a short-time, break-point grain, which is a heat generation mode (unsteady heat generation) using contact resistance between the steel plates. At this time, since the inverter-controlled direct current type is energized, the welding heat generated between the steel plates rides on the flow of electrons due to the direct current, resulting in a form in which the welding heat moves from the negative electrode side to the positive electrode side. . Due to this phenomenon, a sufficiently large nugget can be formed between the steel plate 12 and the steel plate 13. Then, the energization of the second stage, a range indicated with the current value I _b below current I _a in the energization of the first stage, the following equation (6) the energization time T _b, i.e., the energization of the first stage at a current value I _a above, and energized by setting the following 6 times the current value I _a, growing nugget formed by the energization of the first stage. Thereby, the steel plate 11 and the steel plate are formed while forming a nugget having a size capable of obtaining sufficient bonding strength at a portion where the steel plate 13 having the thinnest thickness and the adjacent steel plate 12 are in contact with each other, and preventing the occurrence of scattering. A nugget can also be formed in the part where 12 contacts.

Here, when the energization time in the second stage energization exceeds (6 × T _a ) seconds, the occurrence of scattering is generated or the indentation on the surface of the steel sheet becomes large. The current value I _b for the energization of the second stage, even if it exceeds the current value I _a of the energization of the first stage, or to induce expulsion occurs, or indentation of the steel sheet surface increases. Note that the current value I _b for the energization of the second stage is preferably in the range satisfying the above equation (5). Thereby, generation | occurrence | production of scattering can be suppressed and the spot weld part with very few indentations formed on the steel plate surface can be formed. Further, in the configuration of the present embodiment, the ratio (t ₂ / t) of the total plate thickness t ₂ (mm) of the plate assembly 14 to the plate thickness t ₁ (mm) of the thinnest steel plate 13 that has conventionally been difficult to weld. _{When 1} ) is applied to a plate assembly of 4 or more, significant effects can be expected.

As described above, in the lap resistance spot welding method of the present embodiment, the inverter-controlled direct current method is applied, and the steel plate 13 having the thinnest thickness is disposed on the outermost side so as to contact the plus electrode 16, The welding heat generated between the steel plates rides on the flow of electrons due to the direct current and moves from the negative electrode side to the positive electrode side. Due to this phenomenon, a nugget having a sufficiently large nugget diameter dn can be formed between the steel plate 12 and the steel plate 13. In addition, after forming the nugget by the energization of the first stage to the steel plate conditions nugget is formed in the steel plate, the current value I _b for more than 1/3 of the current value I _a of the energization of the first stage and it sets the current value I _a following values, performs energization of the second stage to set the energization time T _b ranges energizing time Ta or more and a (6 × T _a) following the first stage, each Since the nugget formed on the steel plate is grown, sufficient bonding strength can be obtained without changing the welding pressure during welding. Furthermore, since the lap resistance spot welding method of the present embodiment is energized by the inverter controlled DC current method, the length of the energization time is selected compared to the lap resistance spot welding method of energizing with a single-phase AC power source. High degree of freedom and high heat generation efficiency because there is no zero cross in the current waveform like single phase AC. Moreover, in the lap resistance spot welding method of this embodiment, since a rest time is not inserted like the pulsation energization mentioned above, welding can be realized for a shorter time.

  The configuration and effects other than those described above in the lap resistance spot welding method of the present embodiment are the same as those of the lap resistance spot welding method of the second embodiment described above.

Hereinafter, the effects of the present invention will be specifically described with reference to examples of the present invention and comparative examples that are out of the scope of the present invention. First, as a first example of the present invention, three steel plates having different thicknesses and strengths are spot-welded by the welding method of the first embodiment shown in FIGS. The nugget diameter of the part was examined. The plate assembly at that time is shown in Table 1 below. In this embodiment, the steel plates 1 and 2 are galvanized steel plates galvanized on both sides of a high-strength steel plate with an adhesion amount of 45 g / m ² per side, and the steel plate 3 with the thinnest thickness is used for the steel plate 3 with the smallest thickness. A bare steel plate without plating was used. Also, as welding conditions, a single phase AC power source is used as the welding power source, the electrode has an electrode diameter D of 16 mm, a tip diameter of 6 mm, and a tip R of 40. The pressure was 6.0 kN. Other welding conditions are shown in Table 2 below. Note that N in the energization pattern of pulsation energization after the second stage shown in Table 2 below is the number of repetitions. In addition, as a comparative example, with the plate assembly B, the second stage energization is not normal pulsation energization but normal continuous energization, and lap spot welding is performed. Similarly, the presence or absence of scattering and the size of the joint nugget diameter I investigated. The above results are also shown in Table 2 below.

  As shown in Table 2 above, Example No. 2 in which the second and subsequent stages were subjected to pulsation energization and lap resistance spot welding with a single-phase AC power source. 1, no. The test material No. 2 had no occurrence of scattering, and a sufficiently large nugget was obtained at the joint of each steel plate. In contrast, Comparative Example No. 2 in which the second stage was continuously energized. The test material of No. 3 was scattered, and further, the above-mentioned Example No. 1, no. The nugget diameter of the joint portion of each steel plate was smaller than that of Sample No. 2. In particular, the nugget diameter of the joint of the thinnest steel plate 3 is the same as that of Example No. 1, no. It was about half of the sample material of No. 2, and a good nugget was not obtained.

  Next, as a second example of the present invention, the plate set shown in Table 1 above was subjected to overlap spot welding by the welding method of the second embodiment shown in FIG. 3 and FIG. The nugget diameter was examined. As welding conditions at that time, an inverter DC power source is used as a welding power source, and an electrode diameter D is 16 mm, a tip diameter is 6 mm, and a tip R is 40. The pressure was 6.0 kN. The electrode arrangement was such that the steel plate 3 side was a positive electrode and the steel plate 1 side was a negative electrode. Other welding conditions are shown in Table 3 below. Note that N in the energization pattern of pulsation energization after the second stage shown in Table 3 below is the number of repetitions. Furthermore, as a comparative example, with the plate assembly B, the overlap spot welding is performed only by the first stage energization without performing the second stage energization. Similarly, the presence or absence of scattering and the size of the nugget diameter of the joint are determined. Examined. The above results are also shown in Table 3 below.

  As shown in Table 3 above, Example No. 2 in which the second and subsequent stages were subjected to pulsation energization and lap resistance spot welding was performed by an inverter direct current DC method. 4, no. The test material No. 5 had no occurrence of scattering, and a sufficiently large nugget was obtained at the joint of each steel plate. On the other hand, comparative example No. which welded only by the 1st step of continuous energization without performing the 2nd step. In the test material of No. 6, scattering occurred, and the above-mentioned Example No. 4, no. The nugget diameter of the joint portion of each steel plate was smaller than that of the test material of 5. In particular, the nugget diameter dn of the joint of the thinnest steel plate 3 is the same as that of Example No. 4, no. It was 1/4 or less of the 5 specimens, and a good nugget could not be formed.

  Next, as a third example of the present invention, the plate set shown in Table 1 above is subjected to overlap spot welding by the welding method of the third embodiment shown in FIG. I checked the size. As welding conditions at that time, an inverter DC power source is used as a welding power source, and an electrode diameter D is 16 mm, a tip diameter is 6 mm, and a tip R is 40. The pressure was 6.0 kN. The electrode arrangement was such that the steel plate 3 side was a positive electrode and the steel plate 1 side was a negative electrode. Other welding conditions are shown in Table 4 below. Furthermore, as a comparative example, with the plate assembly B, the overlap spot welding is performed only by the first stage energization without performing the second stage energization. Similarly, the presence or absence of scattering and the size of the nugget diameter of the joint are determined. Examined. The above results are also shown in Table 4 below.

  As shown in Table 4 above, Example No. 2 in which the second and subsequent stages were subjected to pulsation energization and lap resistance spot welding was performed by an inverter-driven DC method. 7, no. The test material No. 8 had no occurrence of scattering, and a sufficiently large nugget was obtained at the joint of each steel plate. On the other hand, comparative example No. which welded only by the 1st step of continuous energization without performing the 2nd step. The test material of No. 9 was scattered, and the above-mentioned Example No. 7, no. The nugget diameter of the joint portion of each steel plate was smaller than that of the test material of 8. In particular, the nugget diameter dn of the joint of the thinnest steel plate 3 is the same as that of Example No. 7, no. It was 1/4 or less of 8 specimens, and a good nugget could not be formed.

It is a figure which shows typically the resistance spot welding method which concerns on the 1st Embodiment of this invention. It is a figure which shows the electricity supply pattern in the resistance spot welding method which concerns on the 1st Embodiment of this invention. It is a figure which shows typically the resistance spot welding method which concerns on the 2nd Embodiment of this invention. It is a figure which shows the electricity supply pattern in the resistance spot welding method which concerns on the 2nd Embodiment of this invention. It is a figure which shows the electricity supply pattern in the resistance spot welding method which concerns on the 3rd Embodiment of this invention. It is a figure which shows typically the spot welding method of patent document 4.

Explanation of symbols

1, 2, 3, 11, 12, 13, 101, 102, 103 Steel plate 4, 14, 104 Plate assembly 5, 6, 15, 16, 105, 106 Electrode 7, 17 Nugget

Claims (6)

In a lap resistance spot welding method with a single-phase AC power source, in which a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes and energized while pressing to weld the contact points of each steel plate,
Placing the thinnest of the steel plates on one electrode side; and
A step of performing multi-stage energization welding with a constant applied pressure,
The multistage energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel sheet by a heat generation form utilizing contact resistance between the steel plates during the first stage energization, and a thickness t of the thinnest steel sheet. ₁ Energization time _Ta and current value _Ia are set so that the relationship with ₁ (mm) satisfies the following formula (A), and then energization time: 1 to 5 cycles, pause time: 1 to 5 cycles A lap resistance spot welding method characterized by performing pulsation energization that repeats energization and pause three or more times.

In the overlap resistance spot welding method by the inverter control direct current method in which a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes, and a contact point of each steel plate is welded by applying electricity while applying pressure.
Placing the thinnest of the steel plates on the positive electrode side; and
A step of performing multi-stage energization welding with a constant applied pressure,
The multistage energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel sheet by a heat generation form utilizing contact resistance between the steel plates during the first stage energization, and a thickness t of the thinnest steel sheet. ₁ Energizing time _Ta and current value _Ia are set so that the relationship with ₁ (mm) satisfies the following formula (A), and then energizing time: 10 to 100 milliseconds, resting time: 10 to 100 mm A lap resistance spot welding method characterized by performing pulsation energization that repeats energization and pause three or more times per second.

Lap resistance spot welding method according to claim 1 or 2 current I _b in the pulsation welding operation is to satisfy the following formula (B).

In the overlap resistance spot welding method by the inverter control direct current method in which a plate assembly in which three or more steel plates are overlapped is sandwiched between a pair of welding electrodes, and a contact point of each steel plate is welded by applying electricity while applying pressure.
Placing the thinnest of the steel plates on the positive electrode side; and
A step of performing multi-stage energization welding with a constant applied pressure,
The multistage energization welding process includes a nugget diameter dn (mm) formed on the thinnest steel sheet by a heat generation form utilizing contact resistance between the steel plates during the first stage energization, and a thickness t of the thinnest steel sheet. ₁ after the relationship between (mm) was subjected to first energizing step sets the energization time T _a and the current value I _a to satisfy the following formula (C), passing a current value I _b the first while below the current value I _a in step lap resistance spot welding method, which comprises carrying out the second energizing step is set to a range that indicates the current time T _b the following equation (D).

Lap resistance spot welding method according to claim 4 in which the relationship between the current value I _b in the said current value I _a in the first energizing step second energizing step is characterized by satisfying the following formula (E) .

The ratio (t ₂ / t ₁ ) of the total plate thickness t ₂ (mm) of the plate assembly to the plate thickness t ₁ (mm) of the thinnest steel plate is 4 or more. 2. The lap resistance spot welding method according to item 1.

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