JP7273311B2 - Method for evaluating electrodeposition paintability of welded joints, apparatus for evaluating electrodeposition paintability of welded joints, and method for manufacturing welded joints - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating the electrodeposition paintability of a welded joint, an apparatus for evaluating the electrodeposition paintability of a welded joint, and a method for manufacturing a welded joint.

Electrodeposition coating is an effective means for improving the corrosion resistance of mechanical structural members. Electrodeposition coating involves placing an object and an electrode in a tank containing an electrodeposition paint, generating an electric potential between the two, and causing electrophoresis of the coating film components of the electrodeposition paint to the object to be coated. is a method of depositing a coating film on the surface of Since the electrodeposition coating can form a coating film with high adhesion, it is possible to impart a high anticorrosion effect to the object to be coated. Furthermore, electrodeposition coating is highly economical when coating a large number of objects to be coated. In addition, electrodeposition coating can form a highly uniform coating film even on objects having complicated shapes.

However, when applying electrodeposition coating to a welded joint comprising a base material and a weld bead, there is a problem that electrodeposition coating defects tend to occur in the weld bead. This poor electrodeposition coating is caused by weld slag adhering to the weld bead surface. In particular, when the base material is a steel plate for automobiles, insulating Si, Mn-based welding slag derived from Si and Mn contained in the steel plate for automobiles adheres to the weld bead. It causes defective electrodeposition coating.

In view of the above circumstances, the development of welded joints having high electrodeposition paintability is underway, but in this process, the problem of how to evaluate the electrodeposition paintability of welded joints has arisen.

The most reliable method for evaluating the electrodeposition coating properties of welded joints is to actually apply electrodeposition coating to the welded joints. By observing the bead appearance of the welded joint after electrodeposition coating, and by conducting a corrosion resistance test (for example, a salt spray test and a combined cycle test (CCT)) on the welded joint after electrodeposition coating, the electrical It is possible to judge the quality of the paintability. However, it is time consuming and costly to implement electrodeposition coating. Therefore, there is a demand for a method that can accurately predict the electrodeposition coating properties of welded joints without electrodeposition coating.

Patent Literature 1 relates to a solid wire used for performing arc welding. In Patent Document 1, the area ratio of the slag generated on the bead is measured in order to evaluate the risk of the coating peeling off due to the peeling of the slag in the electrodeposition coating performed after welding. Specifically, by measuring the ratio of the total area of the slag to the surface area of the bead (slag encapsulation rate), the electrodeposition coatability of the solid wire, which is the material of the bead, is evaluated.

Patent Document 2 discloses a gas-shielded arc welding method for fillet-welding a bare steel sheet and a galvanized steel sheet while supplying a shielding gas, and a welded structure part obtained by this gas-shielded arc welding method, A welded structure part is disclosed in which the slag coverage of the weld bead on the bare steel sheet side is 1% or less, and the slag coverage of the weld bead on the galvanized steel sheet side is 15% or less. The slag coverage rate is the ratio of the slag area existing (covered) on the weld bead to the area of the entire weld bead. It is said that it can be calculated by dividing the weld bead on the steel plate side) and multiplying the ratio of the slag area to the bead area in each part by 100.

Both Patent Literature 1 and Patent Literature 2 focus on the relationship between the adhesion area of welding slag and the electrodeposition paintability to evaluate the electrodeposition paintability of welded joints. However, the electrodeposition coatability is affected not only by the adhesion area of the welding slag but also by the electrical properties of the welding slag. For example, in Patent Document 3, in a consumable electrode type gas shielded arc welding method for arc welding two steel plates using a welding torch having a consumable electrode, the surfaces of the weld bead and the weld bead toe are electrically oxidized with iron. (In Patent Document 3, the term iron oxide slag is described, but it is correctly iron oxide or scale. Hereinafter referred to as iron oxide or scale.) By covering with It is disclosed that the occurrence of defective coating can be suppressed. The methods for evaluating electrodeposition coating properties disclosed in Patent Documents 1 and 2 cannot perform evaluations that consider the electrical properties of welding slag.

In order to solve the above-mentioned problems, it has been considered to collect welding slag from the weld bead and measure its electrical resistance. However, the weld slag sampled from the weld bead has a non-uniform shape and a small amount (eg, 0.01 to 0.04 g per 12 cm bead for MAG welding when the base material is an automotive steel plate). In general, at least 1 g or more of oxide must be sampled in order to accurately measure the electrical resistance of the oxide. In order to collect welding slag of 1 g or more, it is necessary to perform welding and collection work for a long time, and much labor is required for evaluation. Furthermore, complex oxides such as welding slag are a mixture of oxides having various crystal phases. is difficult to measure stably. Therefore, it is not easy to evaluate the electrical properties of weld slag sampled from the weld bead.

In the above-mentioned Patent Document 3, in order to evaluate the effect of the gas-shielded arc welding method, the welding slag on the surface of the weld bead and the weld toe (actually considered to be scale) and the steel plate It is disclosed that continuity was measured by applying a general-purpose tester (POCKET TESTER MODEL: CDM-03D) across 10 resistors. Further, in the evaluation results of Examples of Patent Document 3, it is described that the area ratio of defective electrodeposition is small when there is iron oxide (scale) on the welding slag.

According to the evaluation method disclosed in Patent Literature 3, it is possible to easily evaluate the electrodeposition coating property while the welding slag or the like remains adhered to the weld bead. However, the present inventors have found that even with the evaluation method disclosed in Patent Document 3, it is sometimes difficult to accurately evaluate the electrodeposition coating properties of welded joints.

One of the reasons is that the applied voltage in the evaluation method of Patent Document 3 is too low. The applied voltage of the general-purpose tester used to evaluate the electrodeposition coating property of the welded joint in Patent Document 3 is expected to be 0.17V. Since the iron oxide adhering to the welded joint, which is evaluated in Patent Document 3, has a high conductivity of 40Ω to 1 kΩ, it can be evaluated even with the above applied voltage. However, it is difficult to evaluate Si, Mn-based welding slag, etc. with low conductivity with the above applied voltage.

Japanese Patent Application Laid-Open No. 2008-178906 JP 2017-164798 International Publication No. WO2017/126657

In view of the above circumstances, it is an object of the present invention to provide a method and apparatus for evaluating the electrodeposition paintability of welded joints, which can easily predict the electrodeposition paintability of various types of welded joints. Make it an issue. Another object of the present invention is to provide a method for producing a welded joint having high electrodeposition coating properties.

The gist of the present invention that can solve the above problems is as follows.
(1) A method for evaluating the electrodeposition coating properties of a welded joint according to one aspect of the present invention includes the steps of bringing a first terminal of an insulation resistance meter into contact with the weld slag adhering to the surface of a weld bead of the welded joint; A step of contacting the second terminal of the insulation resistance meter with the base material of the welded joint, a step of applying a voltage of 50 to 500 V between the first terminal and the second terminal, and the first terminal and measuring an electrical resistance value between the terminal and the second terminal.
(2) In the method for evaluating the electrodeposition coating property of a welded joint described in (1) above, the length of the period from the start to the end of the measurement of the electrical resistance value is set to 30 seconds or more, and the electrical resistance during the period is An average of the measurements may be taken as the electrical resistance value between the first terminal and the second terminal.
(3) In the method for evaluating electrodeposition coating properties of a welded joint described in (2) above, the first terminal may be pressed against the weld slag with a constant load during the period.
(4) In the method for evaluating electrodeposition coating properties of welded joints according to any one of (1) to (3) above, the axial direction of the first terminal is set perpendicular to the surface of the weld bead. may
(5) An apparatus for evaluating the electrodeposition coating properties of a welded joint according to another aspect of the present invention includes an insulation resistance meter having a first terminal and a second terminal and capable of applying a voltage of 50 to 500 V, a stage, and position control means capable of controlling the positional relationship between the first terminal and the stage.
(6) The welded joint electrodeposition paintability evaluation apparatus according to (5) above may further include load constant means for constant load applied to the first terminal.
(7) In the apparatus for evaluating electrodeposition coating properties for welded joints described in (6) above, the load constant means measures an elastic body that supports the first terminal or the stage and a displacement of the elastic body. and a displacement measuring means.
(8) In the apparatus for evaluating electrodeposition paintability for welded joints according to any one of (5) to (7) above, the position control means controls the position of the stage with respect to the first terminal along the vertical direction. The position may be configured to be controllable.
(9) In the apparatus for evaluating electrodeposition paintability for welded joints according to any one of (5) to (8) above, the position control means controls the first The position of the stage with respect to the terminals may be controlled.
(10) In the apparatus for evaluating electrodeposition paintability for welded joints according to any one of (5) to (9) above, the position control means adjusts the relative angle between the first terminal and the stage. It may be configured to be controllable.
(11) A method for manufacturing a welded joint according to another aspect of the present invention comprises a step of welding a base material to obtain a welded joint, and manufacturing the welded joint according to any one of (1) to (4) above. A step of measuring the electric resistance of the weld slag adhering to the surface of the weld bead of the weld joint using an evaluation method for electrodeposition coating, and measuring the electric resistance of the weld slag having a measured value of 400 MΩ or more on the weld bead. removing from the surface; and electrodeposition coating the welded joint.
(12) In the method for manufacturing a welded joint described in (11) above, the weld slag having the measured electrical resistance of 300 MΩ or more may be removed from the surface of the weld bead.
(13) In the method for manufacturing a welded joint described in (11) or (12) above, the welded joint is manufactured using the electrodeposition paintability evaluation apparatus described in any one of (5) to (10) above. You may carry out the evaluation method of the electrodeposition paintability of.

According to the present invention, it is possible to easily predict the electrodeposition coating properties of various types of welded joints. INDUSTRIAL APPLICABILITY For example, when various means for improving electrodeposition paintability are examined, the present invention can make the effect measurement more efficient, thereby contributing to the improvement of the electrodeposition paintability of welded joints. Furthermore, according to the present invention, welded joints with high electrodeposition paintability can be manufactured with high productivity by removing welding slag that impairs electrodeposition paintability.

FIG. 4 is a schematic diagram showing an example of variations in measured values of electrical resistance; BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of an apparatus for evaluating the electrodeposition coating property of a welded joint according to one aspect of the present invention; 4 is a graph showing the relationship between the electrical resistance value between terminals and the defective area ratio of electrodeposition coating.

As a means for simply evaluating the electrodeposition coating properties of welded joints, it was conceived to evaluate the electrical resistance of welding slag adhering to the weld bead. However, conventional methods for evaluating electrodeposition paintability can only be applied to welded joints to which, for example, iron oxides with relatively low electrical resistance are adhered.

As a result of investigation, the present inventors have found that by applying a high voltage of 50 V or more to the welding slag, electrodeposition coating of welded joints to which welding slag having high electrical resistance (for example, Si, Mn-based welding slag, etc.) adheres. It was found that it is also possible to evaluate the sexuality.

However, it has also been found that if the voltage is too high, the electrical resistance of the weld slag cannot be evaluated due to dielectric breakdown. Therefore, it was also found that the voltage applied between terminals for evaluating welding slag should be about 500 V or less.

It has also been found that it is preferable to press the terminals against the slug with a constant load when measuring the electrical resistance between the terminals. In this case, variations in the measured values of electrical resistance can be suppressed, and the evaluation accuracy of electrodeposition coating properties can be further improved.

A method for evaluating electrodeposition coating properties according to one aspect of the present invention, which was completed based on the above knowledge, includes a step of contacting a first terminal of an insulation resistance meter with weld slag adhering to the surface of a weld bead of a welded joint. S1, step S2 of contacting the second terminal of the insulation resistance meter with the base material of the welded joint, step S3 of applying a voltage of 50 to 500 V between the first terminal and the second terminal, and the first and a step S4 of obtaining an electrical resistance value between the terminal and the second terminal. Hereinafter, the method for evaluating the electrodeposition coating property of the welded joint according to the present embodiment will be described in detail.

In the method for evaluating the electrodeposition paintability of a welded joint according to the present embodiment, first, (S1) the first terminal of an insulation resistance meter is brought into contact with the weld slag adhering to the surface of the weld bead of the welded joint, and (S2) The base material of the welded joint is brought into contact with the second terminal of the insulation resistance meter. The order of performing S1 and S2 is not particularly limited.

An insulation resistance meter is an instrument that has two terminals and measures the electrical resistance value between these terminals. For convenience, of the two terminals that the insulation resistance meter has, the one that contacts the welding slag is called the first terminal, and the one that contacts the base material is called the second terminal. terminal and negative terminal) may be used as the first terminal. In order to evaluate electrodeposition paintability, it is necessary to evaluate the electric resistance of welding slag, and this electric resistance may be extremely large. For example, when the base material is a steel plate for automobiles, the welding slag has a high electrical resistance (for example, Si, Mn-based welding slag, etc.). Therefore, the insulation resistance meter needs to be able to apply a high voltage of 50 to 500 V between the first terminal and the second terminal in order to measure a large electrical resistance value. Details of the applied voltage will be described later.

The configuration of the insulation resistance meter is not particularly limited as long as the above requirements are satisfied. As will be described later, in order to accurately evaluate the electrodeposition coatability, it is preferable to measure the electrical resistance value for 30 seconds or more and calculate the average value of the measured values during the measurement time. Therefore, it is preferable that the insulation resistance meter can record changes in measured values over time.

The state in which the first terminal is brought into contact with the welding slag is not particularly limited. However, when the first terminal of the insulation resistance meter is brought into contact with the weld slag adhering to the surface of the weld bead of the weld joint, the contact area between the first terminal and the weld slag is kept constant. can be further suppressed, which is preferable. For example, by making the axial direction of the first terminal substantially perpendicular to the surface of the weld bead, it becomes easy to make the contact area between the first terminal and the weld slag constant. A means for making the axial direction of the first terminal perpendicular to the surface of the weld bead is not particularly limited. For example, an evaluator may hold the first terminal by hand and visually adjust the contact angle of the first terminal. On the other hand, in order to further improve the evaluation accuracy, some fixing means and positioning means may be used to control the contact angle of the first terminal. Specific examples of fixing means and positioning means for the first terminal will be described later.

The structures of the first terminal and the second terminal are not particularly limited, either, and may be of a normal shape and material. On the other hand, various configurations for improving evaluation accuracy and evaluation efficiency can be applied to the first terminal and the second terminal. For example, when the first terminal of the insulation resistance meter is brought into contact with the weld slag adhering to the surface of the weld bead of the weld joint, the first terminal preferably has a shape that keeps the contact area constant. On the other hand, when bringing the second terminal of the insulation resistance meter into contact with the base material of the welded joint, it is desirable from the viewpoint of evaluation accuracy and evaluation efficiency to use means for ensuring and facilitating the contact between the two. Specific examples of the first terminal and the second terminal will be described later.

Next, (S3) a voltage of 50 to 500 V is applied between the first terminal and the second terminal. If the applied voltage is less than 50 V, it is impossible to evaluate the electrodeposition coating properties of welded joints to which welding slag having high electrical resistance (for example, Si, Mn-based welding slag, etc.) adheres. On the other hand, if the applied voltage exceeds 500 V, the risk of dielectric breakdown increases. When dielectric breakdown occurs, the measured value of the electrical resistance of the welding slag is displayed as low, leading to the erroneous evaluation result that the electrodeposition paintability is good. can't Preferably, the applied voltage is 250V or less.

Further, (S4) an electric resistance value between the first terminal and the second terminal is obtained. It is judged that the smaller the electrical resistance value between the terminals, the better the electrodeposition coating property of the welded joint. Although the electrical resistance value between the terminals may not match the electrical resistance value of the welding slag, as a result of various investigations by the present inventors, it has been found that there is a good relationship between the electrical resistance value between the terminals and the electrodeposition coating property. A correlation was confirmed. In the evaluation method of the electrodeposition paintability according to the present embodiment, the electrodeposition paintability is evaluated based on the electrical resistance value between the terminals in consideration of both evaluation accuracy and ease of evaluation.

When a voltage is applied to the welding slag attached to the weld bead, the measured value of the electrical resistance between the terminals may vary greatly. For example, when the welding slag is small, or when the electrical resistance of the welding slag is high and a high voltage is applied between the terminals, the measured values tend to vary.

Ｒａｖｅ：測定開始から測定終了までの期間における電気抵抗の測定値の平均
Ｒ（ｔ）：測定開始から測定終了までの期間における電気抵抗の測定値
ａ ：測定開始時点
ｂ ：測定終了時点
なお、上記数式を用いて電気抵抗の測定値の平均Ｒａｖｅを求める場合、測定時間（＝ａ－ｂ）を３０秒以上とすることが好ましい。測定を、電圧の印加と同時に開始してもよいし、電圧の印加から所定時間（例えば３０秒以上）経過してから開始してもよい。 FIG. 1 is a schematic diagram showing an example of variations in measured values of electrical resistance. The horizontal axis of the graph in FIG. 1 is the elapsed time from the start of voltage application, and the vertical axis is the measured value of the electrical resistance between the terminals output by the insulation resistance meter. As shown by the dashed-dotted line in FIG. 1, the measured value of electrical resistance between terminals may vary greatly over time. In this case, the average value of the electrical resistance measurements during the period from the start of measurement to the end of measurement may be regarded as the electrical resistance value between the terminals. The average of the measured values of electrical resistance in the period from the start of measurement to the end of measurement can be obtained by the following formula.

Rave: Average R(t) of measured values of electrical resistance during the period from the start of measurement to the end of measurement: Measured value of electrical resistance during the period from the start of measurement to the end of measurement a: Start time of measurement b: End time of measurement Note that the above When calculating the average Rave of the measured values of electrical resistance using a formula, the measurement time (=a−b) is preferably 30 seconds or longer. The measurement may be started simultaneously with the application of the voltage, or may be started after a predetermined time (for example, 30 seconds or longer) has passed since the application of the voltage.

According to the studies of the inventors, one of the factors that cause variations in measured values is the oscillation of the first terminal. The means for bringing the first terminal into contact with the welding slag is not particularly limited, and this may be carried out according to the skill of the evaluator. It is preferably fixed using an arbitrary jig during the measurement. Specific examples of fixing means for the first terminal and the welded joint will be described later.

If the weld slag is extremely small, even if the first terminal and the welded joint are fixed using a jig, there is a possibility that variations in the measured values of electrical resistance cannot be sufficiently suppressed. In such a case, it is preferable to press the first terminal against the weld slag with a constant load at least during the period from the start to the end of the measurement of the electrical resistance value. As a result, variations in the measured values of electrical resistance can be further suppressed, for example, as indicated by the solid line in the graph of FIG.

Here, "pressing with a constant load" does not mean that the load applied to the first terminal is set to a strictly constant value. The accuracy of making the load constant can be appropriately selected according to the required evaluation accuracy and variations in the measured values of electrical resistance between terminals. If the weld slag is large and the measured value is stable, the first terminal is held by the hand of the evaluator, and if the load is stabilized by hand, the first terminal is pressed against the weld slag with a constant load. It can be said that On the other hand, if the weld slag is small and the measured values are not stable, it is preferable to control the load using some load stabilization means. In this case, the variation in the load pressing the first terminal against the welding slag during the period from the start to the end of the measurement of the electrical resistance value is preferably within a range of 2N or less, for example. A specific example of the load constant means will be described later.

The apparatus for carrying out the method for evaluating the electrodeposition coating properties of welded joints according to the present embodiment is not particularly limited, and can be appropriately selected according to the properties and amount of welding slag and the required evaluation accuracy. If the measured value of the electrical resistance between terminals is stable, the evaluation of the electrodeposition coating property may be carried out by the evaluator's technique. That is, the first terminal and the second terminal may be held by the evaluator's hand. However, considering the safety of evaluation work, evaluation accuracy, evaluation efficiency, etc., it is preferable to use some kind of evaluation device.

An electrodeposition paintability evaluation apparatus for welded joints according to another embodiment of the present invention will be described below. As shown in FIG. 2, the electrodeposition coatability evaluation apparatus 1 according to the present embodiment has a first terminal 111 and a second terminal 112, and an insulation resistance meter 11 capable of applying a voltage of 50 to 500 V. , a stage 12 having fixing means 121 , and a position control means 13 capable of controlling the positional relationship between the first terminal 111 and the stage 12 .

<Insulation resistance meter 11>
As described above, the insulation resistance meter 11 must be able to apply a voltage of 50-500V. As long as this requirement is satisfied, the configuration of the insulation resistance meter 11 is not particularly limited. On the other hand, it is preferable that the insulation resistance meter 11 be capable of recording changes over time in the measured value of electrical resistance between terminals. According to this, the length of the period from the start to the end of the measurement of the electrical resistance value is set to 30 seconds or more, and the average of the measured values of the electrical resistance in this period is the electrical resistance between the first terminal and the second terminal. It is possible to implement an evaluation method that regards the resistance value, and to further improve the evaluation accuracy.

The insulation resistance meter 11 has a first terminal 111 and a second terminal 112 . The first terminal 111 is brought into contact with the weld slag 23 adhering to the weld bead 22 of the welded joint 2 , and the second terminal 112 is brought into contact with the base material 21 of the welded joint 2 . As illustrated in FIG. 2, the first terminal 111 and the second terminal 112 may have the same shape. On the other hand, the configurations of the first terminal 111 and the second terminal 112 may be suitably changed according to their uses.

<First terminal 111>
When the first terminal 111 of the insulation resistance meter 11 is brought into contact with the weld slag 23 adhering to the surface of the weld bead 22 of the weld joint 2, it is preferable to keep the contact area between the weld slag 23 and the first terminal 111 constant. . For that purpose, it is preferable that the tip of the first terminal 111 has an acute angle. For example, the radius of curvature of the tip of the first terminal 111 may be 0.3 to 0.7 mm. However, it is conceivable that the optimum shape of the first terminal 111 for suppressing variations in measured values differs depending on the shape of the weld bead 22 of the weld joint 2 and the properties of the weld slag 23 . Since the oscillation of the first terminal 111 causes variations in the measured values, the first terminal 111 is directly fixed to the electrodeposition coatability evaluation apparatus 1, or is measured via a load constant means 14 described later. Indirect fixation is preferred. A means for fixing the first terminal 111 is not particularly limited, and a clamp or the like may be used, for example.

<Second terminal 112>
On the other hand, the tip of the second terminal 112 that contacts the base material 21 does not need to have an acute angle. Rather, it is preferable to stabilize the conduction between base material 21 and second terminal 112 . For example, the fixing means 121 of the stage 12 to be described later and the second terminal 112 may be electrically connected. According to this configuration, the second terminal 112 of the insulation resistance meter 11 can be brought into contact with the base material 21 of the welded joint 2 at the same time that the welded joint 2 is set in the electrodeposition paintability evaluation apparatus 1, so that the measurement efficiency is further improved. do.

<Stage 12>
The stage 12 has a configuration in which the welded joint 2, which is a sample, can be arranged. The shape of the stage 12 can be appropriately changed according to the shape and size of the welded joint 2 to be evaluated. As illustrated in FIG. 2, if the base material 21 of the welded joint 2 is a thin plate, the stage 12 preferably has a flat top surface. On the other hand, if the base material 21 is a round bar, the stage 12 may be provided with a groove for fixing the round bar.

The stage 12 may have fixing means 121 capable of fixing the welded joint 2 arranged on the stage 12, as illustrated in FIG. The configuration of the fixing means 121 is not particularly limited, and can be changed as appropriate according to the shape and size of the welded joint 2 to be evaluated. On the other hand, if the welded joint 2 is small, the welded joint 2 may be adhered to the stage 12 using double-sided tape or the like. Therefore, the fixing means 121 may be omitted from the electrodeposition paintability evaluation apparatus 1 . Alternatively, the material of the fixing means 121 may be a conductor, and the fixing means 121 and the second terminal 112 may be electrically connected. The fixing means 121 and the second terminal 112 may be integrated.

<Position Control Means 13>
The position control means 13 is configured to be able to control the positional relationship between the first terminal 111 and the stage 12 . Here, the positional relationship is a concept including relative positions and relative angles. The position control means 13 is used to bring the first terminal 111 into contact with the weld slug 23 of the weld joint 2 placed on the stage 12 . By using the position control means 13, it is possible to suppress the oscillation of the first terminal 111 and improve the evaluation accuracy.

In FIG. 2 , the position control means 13 is connected to the stage 12 and controls the positional relationship between the first terminal 111 and the stage 12 by moving the stage 12 . On the other hand, the positional relationship between the first terminal 111 and the stage 12 may be controlled by connecting the position control means 13 to the first terminal 111 and moving the first terminal 111 . Connecting the position control means 13 to both the first terminal 111 and the stage 12 is also possible.

Although the configuration of the position control means 13 is not particularly limited, a preferred specific example is shown below. The position control means 13 may be configured to be able to control the position of the stage 12 with respect to the first terminal 111 along the horizontal horizontal direction (X-axis direction) and/or the horizontal vertical direction (Y-axis direction). Thereby, the first terminal 111 can be moved to any position on the weld bead 22 . Further, the position control means 13 may be configured to be able to control the position of the stage 12 with respect to the first terminal 111 along the vertical direction (Z-axis direction). This makes it possible to easily carry out the procedure of bringing the first terminal of the insulation resistance meter into contact with the weld slag adhering to the surface of the weld bead of the weld joint. Additionally, the position control means 13 may be configured to be able to control the relative angle (θ) between the first terminal 111 and the stage 12 . As a result, the procedure for making the axial direction of the first terminal perpendicular to the surface of the weld bead can be easily performed. On the other hand, by adjusting the arrangement position and arrangement angle of the welded joint 2 on the stage 12, the movement in the X-axis direction, the Y-axis direction, and the Z-axis direction and the change in θ may be unnecessary. Accordingly, one or more of the above-described configurations may be omitted from the position control means 13. FIG.

The electrodeposition coatability evaluation apparatus 1 may further include load constant means 14 for constant the load applied to the first terminal. Thereby, the first terminal can be pressed against the welding slag with a constant load during the period from the start to the end of the measurement of the electrical resistance value.

Although the configuration of the load constant means 14 is not particularly limited, preferred specific examples are shown below. The load constant means 14 may include an elastic body 141 that supports the first terminal 111 or the stage 12 and a displacement measuring means 142 that measures the displacement of the elastic body 141 . Elastic bodies are, for example, elastomers, springs, and the like. The displacement measuring means 142 is, for example, a scale arranged adjacent to the elastic body 141 in parallel with the deformation direction of the elastic body 141 .

When the first terminal 111 is pressed against the welding slag 23 using the electrodeposition coatability evaluation apparatus 1 having the load constant means 14, the elastic body 141 is deformed according to the pressing load. The multiplier of the elastic constant of elastic body 141 and the magnitude of displacement of elastic body 141 is the load that presses first terminal 111 against welding slug 23 . Therefore, by making the displacement of the elastic body 141 constant, the load that presses the first terminal 111 against the welding slug 23 can be easily made constant. Further, according to the above-described configuration, the load for pressing the first terminal 111 against the weld slug 23 can be easily changed according to the size of the weld joint 2, the amount and properties of the weld slag 23, and the like. It also becomes easy to match the evaluation conditions when performing multiple evaluations. The electrodeposition coatability evaluation apparatus 1 may further include a controller that operates the position control means 13 according to the output of the displacement measurement means 142 .

The elastic constant of the elastic body 141 is not particularly limited, and can be appropriately selected according to the pressing load. The value of the pressing load is also not particularly limited, and can be appropriately selected according to the amount and properties of the weld slag 23 of the welded joint 2 to be evaluated. For example, when the base material 21 of the welded joint 2 is an automotive steel plate and the weld bead 22 is produced by gas-shielded arc welding, the elastic constant of the elastic body 141 is set to 0.1 to 0.3 N/mm. , the amount of displacement of the elastic body 141 is preferably set to 1 to 10 mm. Therefore, in this case, it is considered preferable to keep the load for pressing the first terminal 111 constant within the range of 0.1 to 3N. The definition of "constant" here is as described above.

In addition, although the elastic body 141 supports the first terminal 111 in FIG. 2 , the elastic body 141 may support the stage 12 . Even if the elastic body 141 supports the stage 12, when the first terminal 111 is pressed against the welding slug 23, the stage 12 moves and the elastic body 141 deforms, thereby obtaining the above-described effects. is. Alternatively, the pressing load may be made constant by performing motor control using a torque meter, motor control using a load cell, control using a lever, and control using an air pump. That is, any one of these mechanisms may be used as the constant load means 14 .

The electrodeposition paintability evaluation apparatus 1 may further have another means for facilitating the evaluation work. For example, the electrodeposition coatability evaluation apparatus 1 further includes a light for illuminating the weld bead 22, a CCD camera and monitor for magnifying and displaying the weld bead 22, and a constant temperature and humidity chamber for equalizing the evaluation environment. may

<Method for manufacturing welded joint>
Next, a method for manufacturing a welded joint according to another aspect of the present invention will be described below. A method for manufacturing a welded joint according to another aspect of the present invention includes a step of welding a base material to obtain a welded joint, and using the method for evaluating the electrodeposition coating property of the welded joint according to the above-described embodiment, A step of measuring the electric resistance of the weld slag adhering to the surface of the weld bead of the weld joint, a step of removing the weld slag having a measured electric resistance of 400 MΩ or more from the surface of the weld bead, and electrodeposition coating on the weld joint. and the step of

The type of base material and welding method are not particularly limited. Also, the device for measuring the electrical resistance of welding slag is not particularly limited. For example, the electrical resistance of the welding slag may be measured using the electrodeposition paintability evaluation apparatus according to the present embodiment described above to evaluate the electrodeposition paintability of the welded joint.

After measuring the electrical resistance of the weld slag, the weld slag having a measured electrical resistance of 400 MΩ or more is removed from the surface of the weld bead. As can be seen from the experimental results shown in FIG. 3, when the measured value of the electrical resistance of the slag is 400 MΩ or more, the defective coating area ratio is approximately 5% or more. Therefore, it is preferable to perform electrodeposition coating after removing such slag. Also, the welding slag to be removed may be welding slag having a measured electrical resistance of 300 MΩ or more, 320 MΩ or more, or 350 MΩ or more. A further improvement in electrodeposition coating properties can be expected by lowering the threshold value for determining whether or not a substance is to be removed. Any removal method may be used, but removal using a grinder is exemplified. The means and conditions of electrodeposition coating are not particularly limited. According to the method for manufacturing a welded joint according to the present embodiment, welding slag having a measured electrical resistance of 400 MΩ or more (preferably 300 MΩ or more) is not included, and therefore the coating defect area ratio is low (for example, 5% or less), A welded joint with high corrosion resistance is obtained. Furthermore, according to the method for manufacturing a welded joint according to the present embodiment, it is possible to remove only the weld slag that impairs the electrodeposition coating properties, so that the productivity of the welded joint can be improved.

A weld bead with a length of 120 mm is produced by stacking two steel plates of the same type selected from thin steel plates of various compositions with a thickness of 2.6 mm and performing gas-shielded arc welding using solid wires of various compositions. Then, eight types of lap fillet welded joint samples having various weld slag properties were prepared. These welded joints were evaluated according to the following procedures. A mixed gas of 20% by volume CO ₂ and 80% by volume Ar was used as the shielding gas.

(Evaluation A: Evaluation of electrodeposition coating properties using the method and apparatus of the present invention)
First, an evaluation apparatus having an insulation resistance meter, a stage, a position control means, and a constant load means was used to evaluate the electrodeposition coating properties. The stage had a clamp that gripped the base material of the welded joint. The position control means can move the stage horizontally, vertically, horizontally, and vertically, and can change the angle of the stage. The load constant means had a spring attached to the clamp holding the first terminal and a scale for measuring the displacement of the spring. The spring was arranged to expand and contract in the axial direction of the first terminal. Since the load is applied by pressing a spring with a fixed spring constant by a constant amount, the pressing force of the first terminal is made constant.

The conditions for evaluating the electrodeposition coating properties were as follows.

Spring constant of spring: 0.1 N/mm
Pushing amount of the first terminal: 2mm
Pushing angle of the first terminal: The axial direction of the first terminal is perpendicular to the surface of the weld bead Type of insulation resistance tester: IR4054 (manufactured by Hioki)
Measurement method of the electrical resistance value between terminals: Measurement was performed for 1 minute, and the average of the electrical resistance values during this period was regarded as the electrical resistance value between terminals. Select a slag, measure one slag once for 1 minute, measure 5 times and average it. Measurement voltage of the electrical resistance value between terminals: 125 V

(Evaluation B: Evaluation of electrodeposition paintability by electrodeposition coating and observation of appearance after coating)
Next, the welded joint subjected to the above evaluation A was subjected to electrodeposition coating, and the appearance after the electrodeposition coating was observed. Then, by dividing the area of the coating defects by the weld bead area, the electrodeposition coating defect area ratio of the welded joint of one sample was obtained. The evaluation of the defective area ratio was performed by the method described in Patent Document 3.

The relationship between the inter-terminal electrical resistance value (average value of the measured values at 10 points) for each welded joint obtained by evaluation A and the electrodeposition coating defect area ratio of each welded joint obtained by evaluation B is shown in FIG. shown. According to FIG. 3, it can be seen that there is a good correlation between the electrical resistance value between terminals and the defective coating area ratio. Therefore, according to the present invention, it is possible to easily predict the electrodeposition coating properties of various types of welded joints.
Furthermore, slag on the weld bead was removed with a grinder in five samples (before electrodeposition coating) having an electrical resistance value of 400 MΩ or more in FIG. After that, when these samples were subjected to electrodeposition coating (evaluation B), the defective coating area ratio of these samples was 2% or less.

According to the method for evaluating the electrodeposition paintability of a welded joint and the apparatus for evaluating the electrodeposition paintability of a welded joint according to the present invention, it is possible to easily predict the electrodeposition paintability of various types of welded joints. INDUSTRIAL APPLICABILITY For example, when various means for improving electrodeposition paintability are examined, the present invention can make the effect measurement more efficient, thereby contributing to the improvement of the electrodeposition paintability of welded joints. Therefore, the present invention has high industrial applicability.

1 Electrodeposition paintability evaluation device 11 Insulation resistance meter 111 First terminal 112 Second terminal 12 Stage 121 Fixing means 13 Position control means 14 Load constant means 141 Elastic body 142 Displacement measuring means 2 Weld joint 21 Base material 22 Weld bead 23 welding slag

Claims (13)

contacting the first terminal of the insulation resistance meter with the weld slag adhering to the surface of the weld bead of the weld joint;
a step of contacting a second terminal of the insulation resistance meter with the base material of the welded joint;
applying a voltage of 50 to 500 V between the first terminal and the second terminal;
measuring an electrical resistance value between the first terminal and the second terminal;
A method for evaluating the electrodeposition paintability of a welded joint. The length of the period from the start to the end of the measurement of the electrical resistance value is 30 seconds or more,
2. The electrodeposition paintability of the welded joint according to claim 1, wherein the average of the measured values of the electrical resistance in the period is regarded as the electrical resistance value between the first terminal and the second terminal. Evaluation method. 3. The method for evaluating electrodeposition paintability of a welded joint according to claim 2, wherein the first terminal is pressed against the welding slag with a constant load during the period. 4. The method for evaluating electrodeposition paintability of a welded joint according to claim 1, wherein the axial direction of the first terminal is perpendicular to the surface of the weld bead. an insulation resistance meter having a first terminal and a second terminal and capable of applying a voltage of 50 to 500 V;
a stage;
position control means capable of controlling the positional relationship between the first terminal and the stage;
An apparatus for evaluating electrodeposition paintability of welded joints. 6. The apparatus for evaluating electrodeposition coating properties of welded joints according to claim 5, further comprising load constant means for constant the load applied to said first terminal. The load constant means is
an elastic body that supports the first terminal or the stage;
displacement measuring means for measuring the displacement of the elastic body;
7. The apparatus for evaluating electrodeposition paintability of welded joints according to claim 6, comprising: 8. The position control means according to any one of claims 5 to 7, wherein the position control means is configured to be able to control the position of the stage with respect to the first terminal along the vertical direction. Electrodeposition coating performance evaluation equipment for welded joints. 9. The position control means according to any one of claims 5 to 8, wherein said position control means is configured to be able to control the position of said stage with respect to said first terminal along horizontal vertical and horizontal directions. 2. The apparatus for evaluating electrodeposition paintability of welded joints according to item 1. The welded joint according to any one of claims 5 to 9, wherein the position control means is configured to be able to control the relative angle between the first terminal and the stage. Electrodeposition coating property evaluation equipment. a step of welding the base material to obtain a welded joint;
A step of measuring the electric resistance of the weld slag adhering to the surface of the weld bead of the welded joint using the method for evaluating the electrodeposition coating property of the welded joint according to any one of claims 1 to 4;
removing weld slag having a measured electrical resistance of 400 MΩ or more from the surface of the weld bead;
and a step of electrodeposition coating the welded joint. 12. The method of claim 11, further comprising removing weld slag from said surface of said weld bead wherein said measured value of said electrical resistance is greater than or equal to 300 M[Omega]. The method for evaluating the electrodeposition paintability of the welded joint is carried out using the electrodeposition paintability evaluation apparatus according to any one of claims 5 to 10, according to claim 11 or 12. method of manufacturing a welded joint.

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