KR100982503B1 - Evaluation Apparatus for Spot Welding Strength - Google Patents

Abstract

The present invention relates to an apparatus for evaluating spot weld strength, which can accurately and non-destructively inspect spot weld strength of a metal sheet with a simple operation.

The spot welding strength evaluation apparatus of the present invention has six electrodes arranged in a straight line contacting the same surface of the object to be measured, supplies current I (A) from one current supply electrode at both ends, and inside the current supply electrode. The voltage measuring electrode on one side of the voltage measuring electrode is placed in contact with the spot welding part to measure the terminal voltage V1 (V), and the reference terminal voltage V2 (V) is simultaneously measured on the other voltage measuring electrode away from the spot welding part. The quality of the spot welding fixation is determined by determining the surface electrical resistance reduction rate α of the Sot welded portion and comparing it with the calibration curve of the welding fixed strength and the electrical resistance reduction ratio obtained by using the same material as the measured object in advance.

Spot, welding strength, evaluation device, voltage measurement, surface electrical resistance drop rate

Description

Evaluation Apparatus for Spot Welding Strength

The present invention relates to an apparatus for evaluating spot weld strength, which can accurately and nondestructively inspect spot weld strength of a sheet of metal material with a simple operation.

Spot welding is a welding method that heats and melts by overlapping a welding material to locally flow a current, and is suitable for efficiently bonding thin plates, and is used in large quantities in automobiles and home appliances.

Conventional welding static strength inspection method is a tensile shear test or a peel test by simply peeling the weld, etc., all have a problem that the inspection time and economic (inspection cost) loss due to the fracture test. In addition, non-destructive inspection methods such as ultrasonic waves have been tried, but the evaluation method is complicated, so it is difficult to apply them at the spot welding work site.

In order to solve this problem, the method of evaluating the fixed strength is measured by measuring the electric resistance of the spot welded part from the surface electric resistance using the constant current 4-terminal method and the relationship between the electric resistance previously obtained and the size of the weld area (Nugget diameter). The problem was that the measurement accuracy and long inspection time were required.

In addition, since the electrical resistance measured by the constant current four-terminal method is a temperature coefficient of a general industrial metal material such as a steel plate to be spot-welded, for example, even the same material fluctuates by tens of percent due to the temperature difference between summer and winter, and thus the electrical resistance. Absolute value of did not lead to sufficient precision of welding service size or spot fixed strength evaluation. Therefore, when measuring the electrical resistance of the non-welded portion and the electrical resistance of the welded portion, and trying to find the relationship between the weld strength from the difference, there is a problem that the measurement is accompanied by a change in temperature characteristics and the complexity of the measurement.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an apparatus for evaluating spot weld strength, which can accurately and nondestructively inspect spot weld strength of a metal material with a simple operation.

In order to achieve the above object, the spot welding strength evaluation apparatus according to the present invention is provided with at least six electrodes arranged in a straight line contacting the same surface of the object to be measured, and a current is applied to any one of the electrodes located at both ends. Spot welding part voltage measurement in which at least two electrodes of the current supply electrode to which I (A) is supplied and the electrodes arranged side by side inside the current supply electrode contact the spot welding part to measure the terminal voltage V1 (V) of the spot welding part. It comprises an electrode and a measuring probe having a reference terminal voltage measuring electrode for measuring the reference terminal voltage V2 (V) of the object to be measured in the non-contact area spaced apart from the spot welding portion, the surface of the spot welding portion by the following equation By calculating the electric resistance reduction rate α and comparing it with the calibration curve of the welding fixed strength obtained by using the same material as the measured object and the electric resistance reduction rate in advance, Characterized in that for determining the quality of the welded to the pot.

 α = ((R2-R1) / R2) × 100

    = ((V2 / I-V1 / I) / V2 / I) × 100

    = ((V2-V1) / V2) × 100 (%)

(α: reduction rate of surface electrical resistance of spot welds,

 R2 is the resistance of the measured object located between the reference terminal voltage measuring electrodes,

 R1: resistance of the spot weld located between the spot welding electrodes and the voltage measuring electrode)

In addition, the power supply is supplied by a battery to supply the voltage and current to the electrode, the measuring probe, the electrical display of the electrical resistance reduction rate α, the main switch and the electronic circuit of the measuring switch to control the power supply It can be integrated and portable.

The management set value β may be set so that the NG display is possible when the electrical resistance reduction rate α is greater than or equal to the management set value β and when the electrical resistance reduction rate α is less than or equal to the management set value β.

According to the spot welding strength evaluation apparatus according to the present invention, it is possible to simultaneously measure the surface electrical resistance R1 in the welding region of the spot-welded metal material and the surface electrical resistance R2 of the non-welding region away from the welding region of the metal material described above. By evaluating the surface electrical resistance drop rate of the surface electrical resistance R1 of the non-welded region R1 in the welding region, the fluctuation caused by the temperature characteristics of the surface electrical resistance as described above is eliminated, thereby improving the measurement efficiency. High precision evaluation is possible.

In addition, it has a built-in power supply or electronic circuit that allows the control limits of welding strength to be set, making it easy to carry and easy for quality control and measurement in spot welding production sites.

Hereinafter, with reference to the drawings will be described a spot weld strength evaluation apparatus according to the embodiment of the present invention.

1 is an external view of an example of a portable spot welding strength evaluation apparatus according to the present invention.

This is a small and lightweight portable spot welding strength evaluation device that can be carried at the welding work site.The surface electric resistance measurement probe is pressed on the surface of the inspection target of spot welding and when the switch is pressed, a short time constant current (I) flows between the current probes. The terminal voltage (Vb) of the measurement probe and the reference voltage (Va) of the reference probe disposed between the probes are measured to digitally display the electrical resistance reduction rate of the spot weld (hold until reset). do). When the electric resistance reduction rate is α (%), the comparator can set the management set value (level) β by volume knob or ten-key, etc. If the measured value α is more than β, the green LED is turned on and it is OK. In the case of red LED. In addition, a battery checker by the LED for displaying the service life of the battery is attached. In addition, there is a ten-key for input such as management set values and measurement conditions, and there is a memory device that can record together with the measurement results of surface electrical resistance and electrical resistance reduction rate. You can print In particular, the ten-key part or the like becomes a cover (not shown) type after setting the input to prevent contact malfunction.

This evaluation device has the following features.

First, the battery can be driven (assuming 2 to 4 single or single yarn batteries or rechargeable batteries, considering the allowable number of measurements).

Second, a digital display of the electrical resistance drop rate is possible.

Third, it is possible to set the electric resistance reduction rate management set value. At this time, the setting of the management setpoint can be digitally switched.

Fourth, OK and NG LEDs can be displayed for the management set point.

Fifth, the measurement result can be saved through memory and external output is possible.

Sixth, it is portable and the total weight can be 300g or less.

2 shows a surface electrical resistance measurement electrode portion.

Each electrode is contacted with the surface of the subject by a spring force by about 0.2 N. An example of the distance between each probe is 15 mm between A and B, and 3 mm between C, D, E, and F. Between A, E, D, and B: 2 mm and between F and C: 5 mm. The electrodes A and B installed at both ends are current supply electrodes for supplying current I to the measurement target, and C and D are voltage measurement electrodes 1, and E and F are voltage measurement electrodes 2. In V1), the other side is applied to the reference voltage measurement V2, which is a part away from the welded portion. In FIG. 2, C and D are spot welding voltage measurement electrodes, and E and F are reference terminal voltage measurement electrodes. From these currents I, voltages V1 and V2, the surface electrical resistance R1 serving as the spot welding portion and the surface electrical resistance R2 serving as the reference portion can be obtained, and the surface electrical resistance reduction rate? Can be obtained as follows.

  α = ((R2-R1) / R2) × 100

    = ((V2 / I-V1 / I) / V2 / I) × 100

    = ((V2-V1) / V2) × 100 (%)

 Referring to the method for non-destructively evaluating the spot welding strength of the present invention by such a measuring device as follows.

3 shows the situation of the surface electrical resistance measured by the evaluation apparatus of FIGS. 1 and 2. In FIG. 3, R1 and R2 represent electrical resistances on one surface of the test, and R1 = R2 before spot welding. In this case, when spot welding is performed on the R1 portion, the thickness and area of the portion increase in appearance and R1 is lowered because the converter through which the current I flows is widened. 4 shows the phenomenon of lowering the electrical resistance of the spot welded portion. In Fig. 4, a plate-like welded member having t1 and t2 is superimposed to flow a large current through the electrodes sandwiched between them, thereby forming a molten portion called a nugget between the welded members by electric resistance heating, and according to the plate thickness of the spot welded. It shows a decrease in surface electrical resistance. If the area of the nugget portion is S, it can be said that the maximum shear strength? Max when the welded members are pulled in the longitudinal direction from each other is proportional to the nugget area S. In addition, since the current path of the spot weld portion increases only the back side thickness t2 in the nugget area S range, the surface electrical resistance of this portion falls. If the decrease rate of electrical resistance is α, α is S = 0 until spot welding, so R1 = R2, and when α = 0, t1 and t2 are welded to the front, R2 is the value when the thickness t1 + t2 is an integral part. The surface electrical resistance of is lowered, and α rises to a certain value in proportion to the decrease amount. The surface electrical resistance R of the SPCC steel sheet changes as shown in FIG. 4 depending on the thickness. In the case of a galvanized steel sheet, the same change is shown. In other words, in the case where the front spot welding is overlapped with the 0.5 mm thick welded material in double, the spot weld portion can be seen to increase to 1.0 mm thickness, so that the electrical resistance is halved from about 120 µm to 60 µm, and the electrical resistance reduction rate α is up to 50. It is thought to be%. Also, welding the thick material to the thin material to measure the reduction rate of the surface electrical resistance of the thin material has the best detection accuracy. For example, when spot welding a 2 mm steel plate to a 0.5 mm steel sheet, the surface electric resistance of the spot weld is 120 μ 120. You can expect α = 70%, down to a maximum of 36μΩ. In fact, since the electrical connection between the welded portions can be considered to be only the nugget area of the spot welded portion, the rate of decrease in electrical resistance? Varies with the nugget area S representing the quality of the spot welded fixation. Therefore, by arranging the calibration curves of the welding fixed strengths related to the electrical resistance reduction rate α and the nugget area α in the spot welds in advance, the weld fixed strength can be estimated by measuring the surface electrical resistance reduction rate. 5 is an example of a calibration curve showing the relationship between the surface electrical resistance reduction rate α and the maximum tensile shear strength of a sample prepared by varying the spot conditions of two galvanized steel sheets having a plate thickness of 0.65 mm. It can be seen that the maximum tensile shear strength of about 200 Kgf or more can be obtained as the control strength of 40% or more. In addition, in FIG. 4, when the thickness of the steel sheet to be measured is 2 mm or more, the change in the electrical resistance with respect to the thickness decreases, and thus, the examination for increasing the detection sensitivity due to the change of the inter-electrode dimensions or the like is required.

 In practice, when a predetermined current I (A) is flowed between the point state electrodes, the potential difference between the two measuring electrodes arranged in a straight line within the pole before the current supply is compared. It is described as an apparent surface electrical resistance.

As mentioned above, although the spot welding strength evaluation method by the surface electrical resistance fall rate measurement was demonstrated in detail in this invention, the change of the detection precision by the temperature characteristic of the electrical resistance which an evaluation material has as follows is shown by the method of this invention. It can prevent, and the spot strength evaluation with high precision can be performed. In other words, the electric resistance of a general metal material spot welded increases with temperature, and in the case of iron, since the temperature coefficient η of the electric resistance is 15 × 10 ⁻³ , the surface electric resistance changes from R1 to R1 + ΔR1 in the spot weld. Even if the temperature of the measured object changes by ΔT, the electrical resistance changes by R = (R1 + ΔR1) (1 + ΔΔT). For example, if there is a temperature difference of 100 ° C due to climate change such as summer or winter, a measurement error of 5 to 25% occurs based on the evaluation of the surface electric resistance value alone. 6 shows an example in which the relationship between surface electrical resistance and temperature is measured for a general steel sheet SPCC material and a hot dip galvanized steel sheet, and the temperature coefficient of the surface electrical resistance is about 2.9 × 10 ⁻³ . In the electrical resistance reduction rate evaluation as in the present invention, since both the spot welding resistance R1 and the reference electrical resistance R2 change in proportion to the temperature coefficient of the electrical resistance, they are eliminated in the calculation of the electrical resistance reduction rate. Do not.

1 is a schematic diagram and a basic electronic circuit block diagram of a portable spot welding strength evaluation apparatus according to an embodiment of the present invention.

Figure 2 is a probe electrode specification of the portable spot welding strength evaluation apparatus according to an embodiment of the present invention.

3 is an explanatory diagram of surface electrical resistance in a spot welded portion and a reference portion;

4 is a graph showing the relationship between surface electrical resistance and steel sheet thickness in steel sheet (SPCC).

5 is a graph showing the relationship between the surface electrical resistance reduction rate α and the maximum tensile shear strength in a hot dip galvanized steel sheet (t1, t2: 0.65 mm).

Figure 6 is a graph showing the change with the temperature of the surface electrical resistance.

* Description of the symbols for the main parts of the drawings *

10: measuring probe

11: Digital display of surface electrical resistance reduction rate α

12: ten-key

13: Management Setpoint β Setting Knob

14: main switch

15: measuring switch

16: LED

Claims (3)

At least six electrodes arranged in a straight line contacting the same surface of the object to be measured are provided, and a current supply electrode to which current I (A) is supplied to any one of the electrodes located at both ends, and inside the current supply electrode. At least two electrodes arranged side by side are in contact with the spot weld to measure the terminal voltage V1 (V) of the spot weld, and a reference terminal of the object to be measured in the non-contact area spaced apart from the spot weld. And a measuring probe having a reference terminal voltage measuring electrode for measuring the voltage V2 (V), and the surface electrical resistance reduction rate α of the spot welding part is obtained by the following equation, Spot welding strength evaluation apparatus characterized in that the quality of the spot welding fixation is determined by comparing the calibration curve of the fixed strength and the electrical resistance reduction rate.  α = ((R2-R1) / R2) × 100     = ((V2 / I-V1 / I) / V2 / I) × 100     = ((V2-V1) / V2) × 100 (%) (α: reduction rate of surface electrical resistance of spot welds,  R2 is the resistance of the measured object located between the reference terminal voltage measuring electrodes,  R1: resistance of the spot weld located between the spot welding electrodes and the voltage measuring electrode) The method of claim 1, The power supply unit is supplied with a battery to supply voltage and current to the electrode, the measurement probe unit, the calculation / display unit of the electrical resistance reduction rate α, the main switch controlling the power supply of the power supply unit, and the electronic circuit of the measurement switch. Spot welding strength evaluation device, characterized in that the portable can be built. The method according to claim 1 or 2, The spot welding strength evaluation apparatus characterized by setting the management set value (beta) to be OK when the electrical resistance reduction rate (alpha) is equal to or greater than the management set value (beta) and NG display when the electrical resistance reduction rate (alpha) is less than or equal to the management set value (beta).

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