Resistance welding method, resistance-welded member and control apparatus for resistance welder, resistance welding evaluation method, and resistance welding evaluation program

Abstract

In a resistance welding method, by controlling the power amount from a melting start time onward, the weld quality may be stabilized efficiently, even when a disturbance is present, because of the correlation between the amount of power input from the melting start start time and a resulting nugget. The resistance welding method includes: pressing an electrode against a workpiece; inputting power to the workpiece through the electrode to subject the workpiece to Joule heating; detecting the melting start time, which is the time at which at least a portion of the faying portion of a workpiece starts to melt when subjected to Joule heating; calculating a first power amount input into the workpiece from the melting start time; and determining whether the first power amount has reached a first set value; and continuing the Joule heating until the first power amount reaches the first set value.

1 . A resistance welding method for forming a nugget by causing a faying portion to melt and solidify, comprising:
 pressing an electrode against a workpiece;   subjecting the workpiece to Joule heating by inputting power through the electrode into the workpiece;   detecting a melting start time, which is a time at which at least a portion of a faying portion of the workpiece starts to melt;   calculating a first power amount, which is an integrated value of the power input into the workpiece via the electrode from the melting start time;   determining whether the first power amount or a welding index value that indexes a welding condition of the faying portion corresponding to the first power amount has reached at least a first set value; and   continuing the Joule heating from the melting start time until the first power amount or the welding index value reaches at least the first set value.   
     
     
         2 . The resistance welding method according to  claim 1 , wherein detecting the melting start time further comprises:
 calculating a second power amount, by integrating the total power input into the workpiece, in accordance with an elapsed time from an energization start time, which is a time at which energization of the electrode for Joule-heating the faying portion begins; and   determining the melting start time as a time at which the second power amount reaches at least a melting start power amount, which is a power amount input until at least a part of the faying portion actually begins to melt and is determined in advance in accordance with the elapsed time from the energization start time, or a second set value set on the basis of the melting start power amount.   
     
     
         3 . The resistance welding method according to  claim 1 , wherein the Joule heating of the workpiece includes modifying a heating parameter of the workpiece based on whether the first power amount or the welding index value has reached at least the first set value. 
     
     
         4 . A workpiece that has been welded using the resistance welding method according to  claim 1 . 
     
     
         5 . A control apparatus for a resistance welder that includes an electrode that contacts an external surface of a workpiece and a power supply apparatus that supplies a current to the electrode for Joule-heating a faying portion of the workpiece, the control apparatus comprising:
 a melting start time detection unit that detects a melting start time, which is a time at which at least a portion of the faying portion starts to melt when subjected to Joule heating;   a first power amount calculation unit that calculates a first power amount, by integrating the total power input into the workpiece via the electrode from the melting start time;   a first determination unit that determines whether the first power amount or a welding index value that indexes a welding parameter of the faying portion that corresponds to the first power amount has reached at least a first set value; and   a heating unit that performs the Joule heating from the melting start time until the first power amount or the welding index value reaches at least the first set value.   
     
     
         6 . A resistance welder comprising:
 an electrode that is pressed against a workpiece;   a power supply apparatus that supplies a current to the electrode for Joule-heating a faying portion of the workpiece; and   the control apparatus according to  claim 5 .   
     
     
         7 . A control method for a resistance welder that includes an electrode, which contacts an external surface of a workpiece and a power supply apparatus that supplies a current to the electrode for Joule-heating a faying portion of the workpiece, the method comprising:
 detecting a melting start time, which is a time at which at least a portion of the faying portion starts to melt while being subjected to Joule heating by a power input into the workpiece from the electrode;   calculating a first power amount, by integrating the total power input into the workpiece via the electrode from the melting start time;   determining whether the first power amount or a welding index value that indexes a welding condition of the faying portion corresponding to the first power amount has reached at least a first set value; and   continuing the Joule heating from the melting start time until the first power amount or the welding index value reaches at least the first set value.   
     
     
         8 . A control program for a resistance welder that controls a computer to execute the control method for a resistance welder according to  claim 7 . 
     
     
         9 . A resistance welding evaluation method, comprising:
 pressing an electrode against a workpiece;   subjecting the workpiece to Joule heating by inputting power through the electrode into the workpiece;   detecting a melting start time, which is a time at which at least a portion of a faying portion of the workpiece starts to melt;   calculating a first power amount, by integrating the total power input into the workpiece via the electrode from the melting start time; and   estimating a welding parameter of the faying portion based on the first power amount.   
     
     
         10 . The resistance welding evaluation method according to  claim 9 , wherein the welding parameter estimated is a size of a nugget, which is formed when the faying portion melts and solidifies, the size of the nugget is estimated based on the first power amount. 
     
     
         11 . The resistance welding evaluation method according to  claim 9 , wherein detecting the melting start time further comprises:
 calculating a second power amount, by integrating the total power input into the workpiece, in accordance with an elapsed time from an energization start time, which is a time at which energization of the electrode for Joule-heating the faying portion begins; and   determining the melting start time as a time at which the second power amount reaches at least a melting start power amount, which is a power amount input until at least a part of the faying portion actually begins to melt and is determined in advance in accordance with the elapsed time from the energization start time, or a second set value set on the basis of the melting start power amount.   
     
     
         12 . A resistance welding evaluation method, comprising:
 calculating a second power amount, by integrating the total power input into a workpiece from an electrode pressed against the workpiece, in accordance with an elapsed time from an energization start time, which is a time at which energization of the electrode for Joule-heating a faying portion of the workpiece using the power input from the electrode begins; and   determining a melting start time as a time at which the second power amount reaches at least a melting start power amount, which is a power amount input until at least a part of the faying portion actually begins to melt and is determined in advance in accordance with the elapsed time from the energization start time, or a second set value set based on the melting start power amount,   wherein the melting start time at which at least a portion of the workpiece to be resistance-welded begins to melt is detected.   
     
     
         13 . A resistance welding evaluation program that controls a computer to execute the resistance welding evaluation method according to  claim 9 . 
     
     
         14 . A resistance welding evaluation program that controls a computer to execute the resistance welding evaluation method according to  claim 12 .