Patent Number: 
Section: claims

1. A method of monitoring resistance welding quality of a nuclear fuel rod using a resistance welding apparatus, the resistance welding apparatus includinga tube electrode configured to contact a cladding tube of the nuclear fuel rod,a plug electrode configured to contact an end plug of the nuclear fuel rod,a current sensor for detecting welding current,a voltage sensor for detecting welding voltage,a welding force sensor for detecting welding force applied to the end plug, anda monitoring unit monitoring welding quality in real time by processing detected signals,the method comprising:providing the cladding tube to be inserted in the tube electrode and aligning the end plug on the cladding tube to come in contact with the cladding tube at one side of the end plug while an opposite side of the end plug is supported by the plug electrode;supplying alternating current (AC) electric power to the tube electrode and the plug electrode during a welding time such that the welding current flows through the tube electrode, the cladding tube, the end plug and the plug electrode, and moving the plug electrode such that the welding force is applied to the end plug, thereby welding the end plug to the cladding tube;detecting, at every predetermined sample cycle by the monitoring unit, the welding current using the current sensor, the welding voltage applied between the tube electrode and the plug electrode using the voltage sensor, and the welding force using the welding force sensor;calculating, by the monitoring unit, an entire effective current value, an entire effective voltage value, an entire average dynamic resistance, and an entire average heating value, whereinthe entire effective current value is an effective current of the welding current for the welding time,the entire effective voltage value is an effective voltage of the welding voltage for the welding time,the entire average dynamic resistance value is calculated using the entire effective current value and the entire effective voltage value, andthe entire average heating value is calculated using the entire effective current value, the entire effective voltage value and the welding time;comparing, by the monitoring unit, the entire effective current value, the entire effective voltage value, the entire average dynamic resistance value and the entire average heating value with predetermined reference values, respectively, wherein when the entire effective current value, the entire effective voltage value, the entire average dynamic resistance and the entire average heating value are not within a reference range of the predetermined reference values, respectively, the welding is determined to be defective;calculating, by the monitoring unit, an interval dynamic resistance value, a gradient value of instantaneous dynamic resistances, and a gradient value of instantaneous welding forces, whereinthe interval dynamic resistance value is calculated using an interval effective current and an interval effective voltage, the interval effective current value being an effective current of the welding current for each half cycle of the AC electric power, and the interval effective voltage value being an effective voltage of the welding voltage for said each half cycle of the AC electric power,the gradient value of the instantaneous dynamic resistances is an average gradient of the instantaneous dynamic resistances for said each half cycle of the AC electric power, each of the instantaneous dynamic resistances being calculated using the welding current and the welding voltage at said every predetermined sample cycle,the gradient value of the instantaneous welding forces is an average gradient of the instantaneous welding forces for said each half cycle of the AC electric power, each of the instantaneous welding forces being the welding force detected by the welding force sensor at said every predetermined sample cycle; andcomparing, by the monitoring unit, the interval dynamic resistance value, the gradient value of the instantaneous dynamic resistances and the gradient value of the instantaneous welding forces with a preset interval dynamic resistance value, a preset gradient value of instantaneous dynamic resistances, and a preset gradient value of instantaneous welding forces, respectively, wherein when the interval dynamic resistance value, the gradient value of the instantaneous dynamic resistances and the gradient value of the instantaneous welding forces are not within a predetermined range of the preset interval dynamic resistance value, the preset gradient value of instantaneous dynamic resistances, and the preset gradient value of instantaneous welding forces, respectively, the welding is determined to be defective. 2. The method of claim 1, wherein the gradient value of the instantaneous welding forces is the average gradient of the instantaneous welding forces at a first half cycle of the AC electric power. 3. The method of claim 1, wherein the performing of the welding includes forming a welding bead protruding in a ring shape at welded portion between the cladding tube and the end plug. 4. The method of claim 1, wherein the welding force sensor is a load cell, and the load cell includes a welding force indicator. 5. A method of monitoring resistance welding quality of a nuclear fuel rod using a resistance welding apparatus, the resistance welding apparatus includinga tube electrode configured to contact a cladding tube of the nuclear fuel rod,a plug electrode configured to contact an end plug of the nuclear fuel rod,a current sensor for detecting welding current,a voltage sensor for detecting welding voltage,a welding force sensor for detecting welding force applied to the end plug, anda monitoring unit monitoring welding quality in real time by processing detected signals,the method comprising:providing the cladding tube to be inserted in the tube electrode and aligning the end plug on the cladding tube to come in contact with the cladding tube at one side of the end plug while an opposite side of the end plug is supported by the plug electrode;supplying alternating current (AC) electric power to the tube electrode and the plug electrode during a welding time such that the welding current flows through the tube electrode, the cladding tube, the end plug and the plug electrode, and moving the plug electrode such that the welding force is applied to the end plug, thereby welding the end plug to the cladding tube;detecting, at every predetermined sample cycle by the monitoring unit, the welding current using the current sensor, the welding voltage applied between the tube electrode and the plug electrode using the voltage sensor, and the welding force using the welding force sensor;calculating, by the monitoring unit, an entire effective current value, an entire effective voltage value, an entire average dynamic resistance, and an entire average heating value, whereinthe entire effective current value is an effective current of the welding current for the welding time,the entire effective voltage value is an effective voltage of the welding voltage for the welding time,the entire average dynamic resistance value is calculated using the entire effective current value and the entire effective voltage value, andthe entire average heating value is calculated using the entire effective current value, the entire effective voltage value and the welding time;comparing, by the monitoring unit, the entire effective current value, the entire effective voltage value, the entire average dynamic resistance value and the entire average heating value with predetermined reference values, respectively, wherein when the entire effective current value, the entire effective voltage value, the entire average dynamic resistance and the entire average heating value are not within a reference range of the predetermined reference values, respectively, the welding is determined to be defective;calculating, by the monitoring unit, an interval dynamic resistance value, a gradient value of instantaneous dynamic resistances, and a gradient value of instantaneous welding forces, whereinthe interval dynamic resistance value is calculated using an interval effective current and an interval effective voltage, the interval effective current value being an effective current of the welding current for each half cycle of the AC electric power, and the interval effective voltage value being an effective voltage of the welding voltage for said each half cycle of the AC electric power,the gradient value of the instantaneous dynamic resistances is an average gradient of the instantaneous dynamic resistances for said each half cycle of the AC electric power, each of the instantaneous dynamic resistances being calculated using the welding current and the welding voltage at said every predetermined sample cycle,the gradient value of the instantaneous welding forces is an average gradient of the instantaneous welding forces for said each half cycle of the AC electric power, each of the instantaneous welding forces being the welding force detected by the welding force sensor at said every predetermined sample cycle; andcomparing, by the monitoring unit, the interval dynamic resistance value, the gradient value of the instantaneous dynamic resistances and the gradient value of the instantaneous welding forces with a preset interval dynamic resistance value, a preset gradient value of instantaneous dynamic resistances, and a preset gradient value of instantaneous welding forces, respectively, whereinwhen the interval dynamic resistance value is within a predetermined range of the preset interval dynamic resistance value, a first quantified value is added to a total quantified value,when the gradient value of the instantaneous dynamic resistances is within a predetermined range of the preset gradient value of instantaneous dynamic resistances, a second quantified value is added to the total quantified value,when the gradient value of the instantaneous welding forces is within a predetermined range of the preset gradient value of instantaneous welding forces, a third quantified value is added to the total quantified value, andwhen the total quantified value is greater than a predetermined total quantified value, the welding is determined to be normal. 6. The method of claim 5, wherein when the total of the first, second and third quantified values is less than the predetermined total quantified value, the welding is defective or warning depending on a level of the total. 7. The method of claim 5, wherein the first quantified value, the second quantified value and the third quantified value are weighted.