JP6019740B2 - Welding method - Google Patents

Description

  The present invention relates to a method for welding an aluminum-based material made of aluminum or an aluminum alloy and a steel material.

  Conventionally, as one method for joining an aluminum-based material made of aluminum or an aluminum alloy and a steel material, they are overlapped and sandwiched between a pair of electrodes, and a resistance spot that welds them by supplying current to the electrodes. Welding research is ongoing.

  Here, in welding of an aluminum-based material and a steel material, a large current is required due to the low material resistance compared to resistance spot welding between steel materials. Therefore, when these are subjected to resistance spot welding, there is a problem that the aluminum-based material is excessively heated and becomes dust and is lost. On the other hand, for example, Patent Document 1 discloses a welding method in which an aluminum-based material and a steel material are resistance spot welded, and a predetermined current set in advance is intermittently supplied to an electrode for each predetermined time. Thus, a method is disclosed in which the generation of excessive heating and thus generation of dust is suppressed by preventing the current from being continuously supplied for a long time.

Japanese Patent No. 4425159

  In the conventional method disclosed in Patent Document 1, the present inventors can suppress the generation of dust and improve the bonding strength associated with the suppression. However, in each step, each material, in particular, an aluminum-based material. Is excessively heated, the amount of deformation of the aluminum-based material around the joint portion increases and the aluminum-based material adheres to the electrode, causing adverse effects on subsequent welding, resulting in poor productivity. And it was found that the thickness of the aluminum-based material decreased.

  This invention is made | formed in view of the above situations, and it aims at provision of the resistance spot welding method of the aluminum-type material and steel material which can ensure joint strength, improving productivity.

In order to solve the above-described problems, the present invention provides welding in which an aluminum-based material made of aluminum or an aluminum alloy and a steel material are sandwiched between a pair of electrodes in a state of being overlapped with each other and resistance spot welding is performed by energizing the electrodes. A method comprising: sequentially performing a plurality of steps each having an energization period and an energization stop period to supply current to the electrode intermittently in a plurality of steps, and the energization in the plurality of steps By making each length of the period longer in later steps in the execution order, and making each length of the energization stop period in the plurality of steps constant, the accumulated current amount of each step is There is provided a welding method characterized in that the number of steps in the order is increased in stages .

  According to this method, the accumulated current supplied to the electrode during the reference period is stepwise while avoiding excessive heating of each material by intermittently supplying current to the electrode in a plurality of steps. By increasing the resistance, it is possible to increase the amount of heating of each material against the decrease in resistance between the materials due to nugget formation in the previous step, and it is possible to appropriately expand the nugget as current is supplied. Therefore, according to this method, due to excessive heating of each material, particularly an aluminum-based material, when a large current is applied for a long time in one step, generation of dust, deformation of the aluminum-based material, aluminum It is possible to improve the bonding strength accompanying the expansion of the nugget while suppressing the reduction of the thickness of the system material and the adhesion of the aluminum system material to the electrode to increase the productivity.

Further , according to this method, the accumulated current amount can be increased stepwise by a simple method in which the lengths of the energization periods in a plurality of steps are changed so as to become longer as the subsequent steps in the execution order. Current control can be easily performed.

Further, the present invention is a welding method in which an aluminum-based material made of aluminum or an aluminum alloy and a steel material are sandwiched between a pair of electrodes in a state where they are overlapped with each other, and these materials are resistance spot welded by energizing the electrodes. Then, by sequentially executing a plurality of steps each having an energization period and an energization stop period, current is intermittently supplied to the electrodes in a plurality of steps, and each of the energization periods in the plurality of steps is By making the length constant and shortening each length of the energization stop period in the plurality of steps as the subsequent steps in the execution order, the accumulated current amount in each step is changed to the later in the execution order. There is provided a welding method characterized in that the number of steps is increased step by step.

  According to this method, the amount of heat generated at each step, which is equivalent to the integrated current amount, can be increased stepwise by a simple method of changing the energization stop time stepwise, and current control is easily performed. be able to.

  In the above method, the clamping pressure between the pair of electrodes may be substantially constant. However, if the clamping pressure for each step is changed with the progress of the step (increase in the number of steps), the nugget Effective in promoting formation.

  Specifically, the clamping pressure by the electrode at each step is lowered as the step proceeds.

  According to this method, the contact resistance between the materials (aluminum-based material and steel material) increases with the progress of the step, and the heat generation of each material is promoted. As a result, nugget formation is effectively promoted. Moreover, it becomes possible to suppress a deformation | transformation of an aluminum-type material by making clamping pressure low with progress of a step.

  Moreover, you may make it raise the clamping pressure by the said electrode for every said step with the progress of the said step.

  According to this method, it is possible to effectively suppress the generation of dust that tends to occur as the amount of current increases due to the progress of the step. Furthermore, the contact area between materials can be increased. Therefore, it is possible to heat the material by supplying a relatively large current to the electrode while suppressing generation of dust, thereby promoting nugget formation.

  As described above, according to the present invention, it is possible to ensure the joint strength while improving productivity in resistance spot welding between an aluminum-based material and a steel material.

It is a figure for demonstrating the welding method which concerns on embodiment of this invention. It is a surface view for demonstrating the resistance spot welding method. It is a time chart of the energization current in the conventional welding method. It is a time chart of the energization current in the welding method concerning a 1st embodiment of the present invention. It is the time chart which showed the electric current in the welding method which concerns on 2nd Embodiment of this invention. It is the time chart which showed the electric current in the welding method which concerns on 3rd Embodiment of this invention. It is the time chart which showed the energizing current and the applied pressure (clamping pressure) of an electrode in the welding method which concerns on 4th Embodiment of this invention. It is the time chart which showed the energizing current and the applied pressure (clamping pressure) of an electrode in the welding method which concerns on 5th Embodiment of this invention. It is the time chart which showed the conduction current of Examples 1-18. It is a time chart which showed the energization current of comparative examples 1 and 2. 4 is a photograph showing the joining result of Comparative Example 1. 2 is a photograph showing a joining result of Example 1. FIG.

Hereinafter, preferred embodiments of a welding method for resistance spot welding of an aluminum-based material made of aluminum or an aluminum alloy and a steel material according to the present invention will be described with reference to the drawings.

  The outline of the welding method according to the present invention will be described. Here, as shown in FIG. 1, the case where the plate-shaped aluminum-type material 10 and the plate-shaped steel material 20 are resistance spot-welded is demonstrated. Although the specific material of each board | plate material 10 and 20 is not specifically limited, For example, JIS6000 type | system | group (Al-Mg-Si type alloy) is used as the aluminum-type material 10, and galvanization is given as the steel material 20. Steel is used.

  First, the aluminum-based material 10 and the steel material 20 are arranged so as to overlap each other. Next, these plate members 10 and 20 are sandwiched between a pair of electrodes 30a and 30b. At this time, the electrodes 30a and 30b are pressed in a direction approaching each other, and the plate members 10 and 20 are pressed in a direction approaching each other via the electrodes 30a and 30b with a predetermined pressure (the clamping pressure of the present invention). Then, a current is supplied to the electrodes 30a and 30b in a state where the pressurization to the plate members 10 and 20 is maintained.

  When a current is supplied to the electrodes 30a and 30b, the aluminum-based material 10 and the steel material 20 generate heat around the contact portions with the electrodes 30a and 30b due to their own material resistance and contact resistance between the plate materials. That is, with the supply of current to the electrodes 30a and 30b, the aluminum-based material 10 and the steel material 20 are heated. By heating, as shown in FIG. 2, the aluminum-based material 10 melts and sticks to the steel material 20, and a nugget 40 is formed between these plate materials 10, 20, and the aluminum-based material 10 and the steel material 10 are separated. Be joined.

  Here, in order to increase the bonding strength between the aluminum-based material 10 and the steel material 20, it is preferable that the aluminum-based material 10 is sufficiently melted to increase the nugget diameter R (the diameter of the nugget 40 in the plate surface direction). In order to increase the nugget diameter R, it is necessary to increase the amount of current supplied to the electrodes 30a and 30b.

  However, when a method of continuously supplying a constant current amount to the electrodes 30a and 30b is used and this current amount is increased, the aluminum-based material 10 is excessively heated and becomes dust and is lost. The heating amount of the central portion of the electrodes 30a and 30b is excessively larger than that of the surrounding portion, and the thickness of the aluminum-based material 10 in the central portion is reduced. The aluminum-based material 10 in the surrounding portion of the electrodes 30a and 30b The problem arises that the aluminum-based material 10 is greatly deformed, for example, by rising, and the molten aluminum-based material 10 adheres to the electrode 30a.

  To solve this problem, as shown in FIG. 3, there is a method of supplying a constant current to the electrodes 30a and 30b while instantaneously stopping energization of these electrodes 30a and 30b. Specifically, in this method, a cycle of supplying the current Ib to the electrodes 30a and 30b for the time t1_b for the time t1_b and then stopping the energization for the time t2_b is performed a plurality of times. As a result of conducting various tests using this method, the present inventors have confirmed that the use of this method can suppress the generation of dust to some extent and can increase the bonding strength to some extent along with the suppression of dust. did. On the other hand, the present inventors can further improve the bonding strength even when using this method, that is, a method of instantaneously stopping the energization while supplying a constant current to the electrodes 30a and 30b. It has been found that it is impossible to achieve both suppression of reduction in the thickness of the aluminum-based material 10, suppression of deformation of the aluminum-based material 10, and suppression of adhesion of the aluminum-based material 10 to the electrode. Specifically, it has been found that problems such as a reduction in the thickness of the aluminum-based material 10 cannot be avoided when increasing the amount of current supplied to the electrodes 30a and 30b.

  As a result of diligent research on this result, the inventors of the present invention have, as described above, a method of supplying a constant current to the electrodes 30a and 30b while instantaneously stopping energization, that is, dividing the electrode into a plurality of steps. In the method of energizing 30a and 30b, the heating amount in each step becomes excessive, so that the deformation amount of the aluminum-based material 10 increases, the plate thickness of the aluminum-based material 10 decreases, and the aluminum-based material 10 is an electrode. It has been found that the problem of sticking to 30a still occurs.

  And based on this knowledge, the present inventors intermittently set the current amount supplied to these electrodes 30a, 30b while providing sufficient energization stop time by dividing into a plurality of steps, and a preset reference. By supplying current to the electrodes 30a and 30b so that the accumulated current amount integrated over the period increases stepwise, the joint strength is further improved, the reduction in the thickness of the aluminum-based material 10 is suppressed, and the aluminum-based material Both suppression of deformation 10 and suppression of adhesion of the aluminum-based material 10 to the electrode were realized. The integrated current amount corresponds to an integrated value of the current value supplied to the electrodes 30a and 30b and time.

  In the welding method according to the first embodiment, by supplying a current having a waveform as shown in FIG. 4 to the electrodes 30a and 30b, the current is intermittently supplied to the electrodes 30a and 30b in a plurality of steps, and Realized to increase the integrated current amount step by step. That is, in the welding method according to the first embodiment, the step of continuously supplying current to the electrodes 30a and 30b for a certain time t1 is performed a plurality of times with a certain energization stop time t2, and The amount of current I at each step is gradually increased.

  Here, supplying the current to the electrodes 30a and 30b so that the integrated current amount obtained by integrating the amount of current supplied to the electrodes 30a and 30b in a stepwise manner for a predetermined reference period increases stepwise is the preceding step. In the next step, the amount of heat generated between the plate members 10 and 20 is increased against the decrease in the resistance between the plate members 10 and 20 due to the nugget formation in the first step S1, and the reference period is the start of the first step S1. The time from the start of the second step S2 to the start of the second step S2 is equal to or more than the total energization time, that is, the time from the start of energization of the first step S1 to the end of energization of the final step. For example, in the first embodiment, the sum (t1 + t2) of the energization time t1 and the energization stop time t2 can be used.

  In the example shown in FIG. 4, the current supply step is performed four times, and the current amounts I1 to I4 in the first to fourth steps S1 to S4 are set to satisfy I1 <I2 <I3 <I4. . For example, the current amounts I1, I2, I3, and I4 in steps S1, S2, S3, and S4 are sequentially set to 15 kA, 15.5 kA, 16 kA, and 16.5 kA.

  Here, in order to suppress excessive heating of the aluminum-based material 10, it is preferable to lengthen the energization stop time t2 and further reduce the temperature of the aluminum-based material 10 during this energization stop time. Therefore, in the first embodiment, the energization stop time t2 is set to the same time as the energization time t1 to ensure a long time, and excessive heating of the aluminum-based material 10 is reliably suppressed. For example, t1 and t2 are set to the same value of about 167 ms.

  Further, when the electrodes 30a and 30b are so-called R-type and the tip end surface has a curved surface, a large current is required, the load on the apparatus is increased, and dust is easily generated. Therefore, in this embodiment, as the electrodes 30a and 30b, those having a flat tip surface and in surface contact with each material are used. For example, a tip having a diameter of 5 to 6 mm (electrode diameter is 13 to 16 mm) is used. Note that the pressure applied by the electrodes 30a and 30b during energization in each of steps S1 to S4 is constant, and is set to, for example, 4.9 kN.

  As described above, in the welding method according to the first embodiment, the electrodes 30a and 30b are intermittently energized for a certain energization time t1 across the certain energization stop time t2, and the electrodes 30a and 30b are energized. The amount of electric current is gradually increased as the number of steps increases. According to this method, it is avoided that the aluminum-based material 10 is excessively heated by intermittently energizing the electrodes 30a, 30b, generation of dust, deformation of the aluminum-based material, reduction of the nugget thickness, and The adhesion of the aluminum-based material 10 to the electrode can be suppressed, and the resistance between the materials accompanying the nugget formation in the previous step is increased by increasing the energizing current and thus the heating amount of the aluminum-based material 10 stepwise. Therefore, the amount of heat generated between the materials can be secured, and the nugget can be appropriately expanded every time the energization is performed, so that the bonding strength can be increased. In particular, since the energization stop time t2 is secured for a long time, the excessive heating can be avoided.

  4 and FIGS. 5 and 6 to be described later show a case where the electrodes 30a and 30b are energized using an inverter type power source, but the type of power source is not limited to this. For example, a single-phase AC power source may be used, and a part of the 1/2 cycle AC wave may be stopped.

  Next, a welding method according to the second embodiment will be described. The welding method according to the second embodiment differs from the first embodiment only in a specific energization method for the electrodes 30a and 30b. Therefore, only this energization method will be described here.

  In the welding method according to the second embodiment, by supplying a current having a waveform as shown in FIG. 5 to the electrodes 30a and 30b, the current is intermittently supplied to the electrodes 30a and 30b in a plurality of steps, and Realized to increase the integrated current amount step by step. That is, in the welding method according to the second embodiment, the step of continuously supplying the current I20 having a constant current amount to the electrodes 30a and 30b is performed a plurality of times with a constant energization stop time t20, and each step Gradually increase the energization time in steps.

  In the example shown in FIG. 5, the current supply step is performed four times, and the current amount I20 is controlled to be constant in the first to fourth steps S1 to S4, while the energization times t21 to t24 of each step S1 to S4. Is controlled to satisfy t21 <t22 <t23 <t24. For example, the energization current I20 at each step S1 to S4 is constant at 15.5 kA, the energization stop time t20 is constant at 167 ms, and the energization times t21, t22, t23, and t24 at each step S1 to S4 are 167 in order. , 200 ms, 233 ms, and 266 ms.

  Also in the welding method according to the second embodiment, the heating amount of the plate members 10 and 20 is increased stepwise by gradually increasing the energizing time at each step while the electrodes 30a and 30b are energized intermittently. Is done. Therefore, it is possible to avoid excessive heating of the aluminum-based material 10 and to suppress generation of dust, deformation of the aluminum-based material, reduction in nugget thickness, and adhesion of the aluminum-based material 10 to the electrode. On top of that, the resistance between the materials due to the nugget formation in the previous step can be counteracted to ensure the amount of heat generated between the materials, and the nugget can be expanded appropriately each time energization is performed to increase the joint strength. Can do.

  Next, a welding method according to the third embodiment will be described. The welding method according to the third embodiment also differs from the first embodiment only in a specific energization method for the electrodes 30a and 30b. Therefore, only this energization method will be described here.

  In the welding method according to the third embodiment, by supplying a current having a waveform as shown in FIG. 6 to the electrodes 30a and 30b, the current is intermittently supplied to the electrodes 30a and 30b in a plurality of steps, and Realized to increase the integrated current amount step by step. That is, in the welding method according to the third embodiment, the step of continuously supplying the current 30 with a constant current amount to the electrodes 30a and 30b for a predetermined time t30 is performed a plurality of times with a predetermined energization stop time, and The energization stop time between each step is gradually reduced.

  In the example shown in FIG. 6, the current supply step is performed four times, and the current amount I30 and the energization time t30 are controlled to be constant in the first to fourth steps S1 to S4, while the first step S1 and the second step. The first energization stop time t31 during S2, the second energization stop time t32 between the second step S2 and the third step S3, and the third energization stop time t33 between the third step S3 and the fourth step S4. Are controlled so that t31> t32> t33. For example, the energization current amount I30 in each step S1 to S4 is set to 15.5 kA, the energization time t30 is fixed to 167 ms, and the energization stop times t31, t32, and t33 are set to 167, 125 ms, and 83 ms in this order.

  Also in the welding method according to the third embodiment, the electrodes 30a and 30b are intermittently energized, and the energization stop time (cooling time of the plate members 10 and 20) is gradually shortened so that the material at the initial energization of each step is performed. The resistance gradually increases, and as a result, the heating amount of the plate members 10 and 20 is increased stepwise. Therefore, it is possible to avoid excessive heating of the aluminum-based material 10 and to suppress generation of dust, deformation of the aluminum-based material, reduction in nugget thickness, and adhesion of the aluminum-based material 10 to the electrode. On top of that, the resistance between the materials due to the nugget formation in the previous step can be counteracted to ensure the amount of heat generated between the materials, and the nugget can be expanded appropriately each time energization is performed to increase the joint strength. Can do.

  Next, a welding method according to the fourth embodiment will be described.

  In the welding method according to the fourth embodiment, the specific energization method to the electrodes 30a and 30b is the same as that of any of the first to third embodiments, and the pressure applied by the electrodes 30a and 30b for each step is determined as follows. As it progresses (as the number of steps increases), it becomes lower.

  FIG. 7 is a time chart showing the relationship between the energization current and the applied pressure in the welding method according to the fourth embodiment. As shown in the figure, the energization method of this embodiment is the same as the energization method of the first embodiment described above. Specifically, steps S1 to S4 of continuously supplying current to the electrodes 30a and 30b for a certain time t1 are performed a plurality of times with a certain energization stop time t2, and the current in each step The amount I is gradually increased. For example, the current amounts I1, I2, I3, and I4 are sequentially set to 15 kA, 15.5 kA, 16 kA, and 16.5 kA, and t1 and t2 are set to about 167 ms.

  And, for each cycle in which the pressing force of the plate members 10 and 20 by the electrodes 30a and 30b during energization is supplied for each step, specifically, the current is supplied to the electrodes 30a and 30b for a time t1, and then the energization is stopped for a time t2. Decrease gradually by a certain value. For example, the pressures P1, P2, P3, and P4 in steps S1 to S4 are set to 4.9 kN, 3.92 kN, 2.94 kN, and 1.96 kN. That is, the applied pressure is decreased by 0.98 kN for each step. The pressure P4 in step S4 is equal to the initial pressure P0 set as the pressure during the initial pressurization period in this resistance spot welding, and is set to 1.96 kN, for example.

  According to the welding method according to the fourth embodiment, the pressure applied by the electrodes 30a and 30b decreases by a certain value as the step proceeds, so that the contact resistance between the plate members 10 and 20 increases as the step proceeds. To increase. Therefore, compared with the case of the welding method of the first embodiment in which the pressurizing force of all steps S1 to S4 is substantially constant, it is possible to heat the plate members 10 and 20 with the progress of the steps better. Become. Therefore, according to the welding method according to the fourth embodiment, the nugget formation in each of steps S1 to S4 can be effectively promoted, thereby forming a larger nugget 40 and obtaining a high joint strength. It becomes possible. Moreover, there is also an effect that the deformation of the aluminum-based material 10 can be suppressed by decreasing the applied pressure by a certain value.

  Here, the case where the energization method of the first embodiment is applied as a specific energization method for the electrodes 30a and 30b has been described. Of course, the energization method of the second and third embodiments is applied. Also good. In these cases, similar effects can be obtained.

  Next, a welding method according to the fifth embodiment will be described.

  In the welding method according to the fifth embodiment, the pressure applied by the electrodes 30a and 30b for each step is increased as the steps progress (as the number of steps increases), otherwise This is the same as the welding method according to the fourth embodiment.

  FIG. 8 is a time chart showing the relationship between the energization current and the applied pressure in the welding method according to the fifth embodiment. As shown in the figure, in this embodiment, the pressure applied to the plate members 10, 20 by the electrodes 30a, 30b during energization is gradually increased by a certain value. For example, the pressures P1, P2, P3, and P4 in steps S1 to S4 are set to 1.96 kN, 2.94 kN, 3.92 kN, and 4.9 kN. That is, the pressure is increased by 0.98 kN for each step.

  According to the welding method according to the fifth embodiment, the pressurizing force of the plate members 10 and 20 by the electrodes 30a and 30b increases as the step proceeds, so that it easily occurs as the current amount increases due to the step. It is possible to effectively suppress the generation of dust. In addition, the contact area between the materials can be increased. Therefore, it is possible to heat the plates 10 and 20 by supplying a relatively large current to the electrodes 30a and 30b while suppressing the generation of dust, thereby promoting nugget formation and obtaining high bonding strength. It becomes.

  In other words, the welding method according to the fourth embodiment and the welding method according to the fifth embodiment are different in method and action depending on whether the pressure applied by the electrodes 30a and 30b is gradually decreased or increased. Even in this case, the nugget formation can be promoted as a result, and a common effect that higher bonding strength can be obtained can be achieved.

  In the fifth embodiment, the case where the energization method of the first embodiment is applied as a specific energization method for the electrodes 30a and 30b has been described. Of course, the energization method of the second and third embodiments is applied. May be. In these cases, similar effects can be obtained.

  Next, the welding results of Examples 1 to 18 in which the aluminum-based material 10 and the steel material 20 are resistance spot welded using the welding methods according to the first to fifth embodiments, and the current having a constant current amount to the electrodes 30a and 30b. The welding results of Comparative Examples 1 and 2 in which the aluminum-based material 10 and the steel material 20 are resistance spot-welded by continuously supplying for a predetermined time will be described with reference to Tables 1 and 2.

  In Examples 1 to 18 and Comparative Examples 1 and 2, a plate-like JIS6000 (Al—Mg—Si alloy) material having a plate thickness of 0.9 mm was used as the aluminum-based material 10, and the plate thickness as the steel material 20. A plate-like steel material plated with 0.8 mm of zinc was used. Further, as a welding result, the tensile strength TS, the deformation amount of the aluminum-based material 10, and the occurrence of dust were examined. In Table 1, N1 and N2 in the tensile strength TS are values in different test pieces, respectively.

  First, according to Table 1, the welding results (Examples 1 to 6) of the first to third embodiments will be described. In the first to sixth embodiments, as illustrated in FIG. 9, first to fourth current supplies for supplying currents I_a, I_b, I_c, and I_d to the electrodes at time t_on_a, t_on_b, t_on_c, and t_on_d, respectively. Steps S1 to S4 were performed with energization stop times t_off_a, t_off_b, and t_off_c, respectively. In each of the current supply steps S1 to S4, the test piece was sandwiched between the electrodes 30a and 30b with the applied pressures P_a, P_b, P_c, and P_d. The applied pressure P_0 is the above-described minimum applied pressure. Table 1 shows specific values of the current amount, energization time, and energization stop time for each of Examples 1 to 6, respectively. Examples 1 to 3 are results of using the welding method according to the first embodiment in which the current value of each step is increased stepwise while the energization time and the energization stop time are constant. Examples 4 and 5 are results when using the welding method according to the second embodiment in which the energization time of each step is increased stepwise while the current value and energization stop time of each step are constant. Example 6 relates to the third embodiment, wherein the current value of the second step is set larger than the current value of the first step, and the current value of each subsequent step is constant, that is, the current value of the second step This is a result of using a welding method in which the energization time of each step is the same, and the energization stop time between each step is reduced stepwise. Although omitted in Table 1, the pressure applied at each step is constant (P_a = P_b = P_c = P_d = P_0).

  In Comparative Examples 1 and 2, as described above and as shown in FIG. 10, a constant current I_a was continuously supplied to the electrodes 30a and 30b for a time t_on_a. Table 1 shows these current values and energization time for Comparative Examples 1 and 2.

  As shown in Table 1, in Comparative Example 2 in which a relatively high current of 17.5 kA was continuously supplied for 300 ms, the amount of deformation of the aluminum-based material 10 was increased and dust was generated. Only a tensile strength as low as about 5 kN could be obtained. On the other hand, in Comparative Example 1 in which the supply current is lower than that in Comparative Example 2 and a current of 16.5 kA is continuously supplied for 300 ms, generation of dust is avoided and a tensile strength of about 2.6 kN can be obtained. Although it was possible, as in Comparative Example 2, the amount of deformation of the aluminum-based material 10 was large, and an appropriate bonded shape could not be obtained.

  On the other hand, in Examples 1-6, in any example, generation | occurrence | production of a dust is avoided and the tensile strength of 2.6 kN or more is obtained, suppressing the deformation amount of the aluminum-type material 10 to moderate or less. I was able to. In particular, in Comparative Examples 1 to 3 according to the first embodiment, it is possible to obtain a high tensile strength of 2.9 kN or more while avoiding generation of dust and suppressing the deformation amount of the aluminum-based material 10 to a slight amount. It was.

  Here, FIG. 11 is a photograph showing the joining result of Comparative Example 1, and FIG. 12 is a photograph showing the joining result of Example 1. From the comparison of region A of these photographs, Comparative Example is also shown. 1 shows that the deformation amount of the aluminum-based material 10 is larger than that of the first embodiment. Further, it can be seen from these photographs that the plate thickness d1 of the aluminum-based material 10 in Comparative Example 1 is smaller than the plate thickness d2 in Example 1. Furthermore, from these photographs, in Comparative Example 1, the melted area reaches the surface of the aluminum-based material 10 in the region B, and the molten aluminum-based material 10 is in a state of adhering to the electrode 30a. On the other hand, in Example 1, it can be seen that the melting region does not reach the surface, and an appropriate nugget is formed.

  Next, according to Table 2, the welding results (Examples 7 to 18) of the fourth and fifth embodiments will be described.

  Table 2 shows specific values of the amount of current, the energization time, the energization stop time, and the applied pressure for each of Examples 7 to 18 based on FIG.

  Examples 7-12 are the results of using the energization method according to the first embodiment as the energization method, and Examples 13-16 are the results of using the energization method according to the second embodiment as the energization method, In Examples 17 and 18, as a result of using the energization method according to the third embodiment as the energization method, specifically, the current value of the second step is the current value of the first step as in the sixth example. The current value of each step after that is constant, that is, the same as the current value of the second step, the energization time of each step is constant, and the energization stop time between each step is stepwise It is the result of using the method reduced to The alphabet “A” following the example number is the fourth embodiment, that is, an example in which the pressurizing force for each step is decreased as the step proceeds, and “B” is the fifth embodiment, That is, this is an embodiment in which the pressurizing force for each step is increased as the step proceeds. Comparative Examples 1 and 2 are the same as Table 1.

  As shown in Table 2, in any of Examples 7 to 18, the generation of dust was avoided, and the tensile strength of 2.9 kN or more was suppressed while suppressing the deformation amount of the aluminum-based material 10 to a moderate level or less. I was able to get it. And when the tension of Examples 7 to 12 and the tensile strength of Examples 1 to 3 in Table 1 that are common to these examples and the energization method are compared, Examples 1 to 3 are 2.89 kN or more. On the other hand, Examples 7-12 were 3.15 kN or more. Similarly, when the tensile strengths of Examples 13 to 16 and the tensile strengths of Examples 4 and 5 in Table 1 are compared, Examples 4 and 5 are 2.5 kN or more, while Examples 13 to 16 was 2.9 kN or more. Similarly, when the tensile strength of Examples 17 and 18 is compared with the tensile strength of Example 6 in Table 1, Example 6 is 2.65 kN or more, while Examples 17 and 18 are 2. It was 95 kN or more. That is, according to the welding methods of Examples 7 to 18 in which the pressurizing force for each step is changed as the step proceeds, the energization method similar to the welding method of Examples 1 to 6 in which the pressurizing force of all the steps is made substantially constant. However, compared with the welding method of the said Examples 1-6, it was able to increase joint strength effectively.

  As described above, according to the welding method of the present invention, generation of dust is avoided and deformation of the aluminum-based material 10, reduction of the thickness of the aluminum-based material 10, and adhesion of the aluminum-based material 10 to the electrode are performed. High tensile strength, that is, bonding strength can be obtained while suppressing adhesion.

  Here, the energization time, the energization stop time, the energization current amount, the applied pressure, and the number of energization steps are not limited to the above.

  However, in order to reliably suppress excessive heating of the aluminum-based material 10, it is preferable to lengthen the energization stop time. Specifically, if the energization stop time is 60 to 500 ms (4 cycles to 30 cycles at 60 Hz), the aluminum material 10 is deformed due to excessive heating of the aluminum material 10, and the thickness of the aluminum material 10 is reduced. It has been found that high productivity can be ensured by avoiding the situation of adhesion of the aluminum-based material 10 to the electrodes 30a and 30b and generation of dust.

  Moreover, in order to suppress excessive heating of the aluminum-based material 10 with certainty, it is preferable to suppress the amount of energization current to some extent. Specifically, it is found that if the energization current amount is suppressed to 20 kA or less, more preferably 17.5 kA or less, deformation of the aluminum-based material 10 due to excessive heating of the aluminum-based material 10 can be reliably suppressed. ing.

  In order to secure the bonding strength, the number of current supply steps is preferably 3 or more.

  In addition, regarding the fourth and fifth embodiments, in the above-described embodiment, the pressing force is decreased or increased by a constant value, but the amount of change in the pressing force is not necessarily constant. For example, the amount of change corresponding to the energization time for each step may be set.

  In the fourth and fifth embodiments, the applied pressure is changed at the start of energization of each step. However, the timing of changing the applied pressure may be at the end of energization or during energization stop.

  Further, the present invention provides a current to the electrode so that an integrated current amount obtained by integrating the amount of current supplied to the electrode intermittently in a plurality of steps and accumulated in a preset reference period increases stepwise. The specific energization method is not limited to the above. For example, the energization methods according to the above-described embodiments may be combined.

10 Aluminum material 20 Steel material 30a, 30b Electrode 40 Nugget R Nugget diameter

Claims (4)

It is a welding method in which an aluminum-based material made of aluminum or an aluminum alloy and a steel material are sandwiched between a pair of electrodes in a state where they are overlapped with each other, and these materials are resistance spot welded by energizing the electrodes,
By sequentially performing a plurality of steps each having an energization period and an energization stop period , a current is intermittently supplied to the electrodes in a plurality of steps ,
By making each length of the energization period in the plurality of steps longer in later steps in the order of execution, and making each length of the energization stop period in the plurality of steps constant, A welding method , wherein the integrated current amount is increased stepwise as a subsequent step in the order of execution . It is a welding method in which an aluminum-based material made of aluminum or an aluminum alloy and a steel material are sandwiched between a pair of electrodes in a state where they are overlapped with each other, and these materials are resistance spot welded by energizing the electrodes,
By sequentially performing a plurality of steps each having an energization period and an energization stop period, a current is intermittently supplied to the electrodes in a plurality of steps,
By integrating the lengths of the energization periods in the plurality of steps, and shortening the lengths of the energization stop periods in the plurality of steps as the subsequent steps in the execution order, the integration of each step A welding method characterized in that the amount of current is increased stepwise in later steps in the execution order . The welding method according to claim 1 or 2 ,
The welding method, wherein the clamping pressure by the electrode at each step is lowered as the step proceeds. The welding method according to claim 1 or 2 ,
The welding method, wherein the clamping pressure by the electrode for each step is increased as the step proceeds.