CN111288907B - A metallographic detection method for measuring the diameter of a resistance spot welding nugget - Google Patents

Abstract

A metallographic detection method for measuring the diameter of a resistance spot welding nugget of the present invention includes the following steps: Step 1: Select a resistance spot welding part, select a surface of the welding spot, and calculate the average value L1 of the diameter of the indentation area of the welding spot ; Step 2: Select a cutting line that passes through the center of the solder joint and has a length of L1, and use a cutting machine to cut the solder joint along the cutting line; Step 3: Smooth, coarsely grind, finely grind, polish and corrode the cutting surface of the solder joint Processing; Step 4: Measure the cutting surface of the solder joint under a microscope to obtain the measured length L2 of the diameter of the indentation area and the measured length d2 of the nugget diameter; Step 5: Determine whether the error between L1 and L2 is less than the error threshold, If so, d2 is the length of the nugget area, otherwise, step 6 is performed; step 6: Calculate the nugget diameter length d1 according to the designed formula.

Description

A metallographic detection method for measuring the diameter of a resistance spot welding nugget

technical field

The invention belongs to the technical field of resistance spot welding, and relates to a metallographic detection method for measuring the diameter of a nugget of resistance spot welding.

Background technique

Resistance spot welding is widely used in the automotive field or other processes that require spot welding to connect. In the inspection of the solder joint quality under the welding process, one of the inspection content is the measurement of the diameter of the nugget, which requires cutting the solder joint. , and then grind, polish and corrode the solder joint profile, and finally measure the diameter of the welding nugget under an optical microscope. The measurement of resistance spot welding is a destructive experiment, so the cutting of the solder joint is very important, but during the cutting process, it is easy to deviate from the part to be cut, so that the detected part cannot be completely matched with the required part, resulting in The misalignment of the detection part, and once the cutting part deviates from the part to be detected will cause the entire measurement to fail. When the deviation from the measurement line occurs, there is currently no relevant method to correct the detection results.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems, the purpose of the present invention is to provide a metallographic detection method for measuring the nugget diameter of resistance spot welding, which can correct the measurement data, make the calculation result closer to the actual value, and play a role in the unmeasured nugget. The role of evaluation and estimation.

The invention provides a metallographic detection method for measuring the diameter of a resistance spot welding nugget, comprising the following steps:

Step 1: Select resistance point welding parts, select one surface of the welding point, and calculate the average value L1 of the diameter of the indentation area of the welding point;

Step 2: Select the cutting line that passes through the center of the solder joint and has a length of L1, and use a cutting machine to cut the solder joint along the cutting line;

Step 3: Polish, rough, finely grind, polish and corrode the cutting surface of the solder joint;

Step 4: Measure the cutting surface of the solder joint under a microscope to obtain the measured length L2 of the diameter of the indentation zone and the measured length d2 of the diameter of the nugget;

Step 5: Determine whether the error between L1 and L2 is less than the error threshold, if so, d2 is the length of the nugget zone, otherwise go to Step 6;

Step 6: Calculate the nugget diameter length d1 according to the following formula:

In the metallographic detection method of the resistance spot welding nugget diameter measurement of the present invention, step 1 is specifically:

Measure the length of the major axis and the length of the minor axis of the indentation area respectively, and calculate the average value of the length of the major axis and the length of the minor axis as the mean value L1 of the diameter of the indentation area.

In the metallographic detection method for measuring the nugget diameter of resistance spot welding of the present invention, the error threshold in step 5 is specifically 5% of the average value L1 of the diameter of the indentation area.

Since metallographic detection is a destructive experiment, once the sample is cut incorrectly, the experiment will fail. By using the metallographic detection method for measuring the diameter of the nugget of resistance spot welding of the present invention, when an error occurs in the preparation of the sample, the The formula corrects the measured data appropriately to make the calculation result closer to the actual value, and plays a role in evaluating and estimating the unmeasurable nugget diameter.

Description of drawings

Figure 1 is a schematic diagram of spot welding work;

2 is an equivalent diagram of the shape of a solder joint in a metallographic detection method for measuring the diameter of a resistance spot welding nugget of the present invention;

3 is a schematic diagram of a cut surface of a welding spot in a metallographic detection method for measuring the diameter of a resistance spot welding nugget of the present invention.

Detailed ways

FIG. 1 is a schematic diagram of spot welding work. The power source 10 supplies power to the electrodes 20 , and the two pieces to be welded 40 are welded together by pressing down the upper and lower electrodes 20 . As shown in Figure 2, from the distribution characteristics of spot welding, it can be approximately composed of three concentric circles, the outermost layer is the black surface oxide layer area 1; the middle is the resistance welding spot thinning under the pressure of the electrode tip The transition area is the indentation area 2; a high temperature is generated between the steel plates, which melts the core of the steel plate, and forms a nearly circular nugget 3 after cooling. Under the tip pressure of the electrode 20 , an oxide layer area 1 and an indentation area 2 are formed on the outer surface of the parts to be welded 40 , and the nugget 3 is located between the two parts to be welded 40 . According to the principle of spot welding, when the force is uniform, the shape of the nugget inside the solder joint determines the shape of the thinned area generated on the shape of the solder joint. Therefore, from the shape of the shape, the nugget 3 and the indentation area 2 are Concentric distribution. In the process of measuring the diameter of the nugget in the method of the present invention, the measured value of the diameter of the middle circle, that is, the diameter of the indentation zone, is introduced as a characteristic parameter.

A metallographic detection method for measuring the diameter of a resistance spot welding nugget of the present invention specifically includes the following steps:

Step 1: Select resistance point welding parts, select one surface of the welding point, and calculate the average value L1 of the diameter of the indentation area of the welding point;

In specific implementation, the long axis length and the short axis length of the indentation area are measured respectively, and the average value of the long axis length and the short axis length is calculated as the average value L1 of the diameter of the indentation area.

Step 2: Select the cutting line that passes through the center of the solder joint and has a length of L1, and use a cutting machine to cut the solder joint along the cutting line;

During specific implementation, there is a certain error in the center of the solder joint selected in this step, and it is sufficient to ensure that it is as close as possible to the center of the solder joint.

Step 3: Polish, rough, finely grind, polish and corrode the cutting surface of the solder joint;

Step 4: Measure the cutting surface of the solder joint under a microscope to obtain the measured length L2 of the diameter of the indentation zone and the measured length d2 of the diameter of the nugget; specifically refer to the schematic diagram of the cutting surface of the solder joint in FIG. 3 ;

Step 5: Determine whether the error between L1 and L2 is less than the error threshold, if so, d2 is the length of the nugget zone, otherwise go to Step 6;

In specific implementation, the error threshold is specifically 5% of the average value L1 of the diameter of the indentation area.

Step 6: Calculate the nugget length d1 according to the following formula:

In specific implementation, the measurement principle and formula are deduced as follows:

As shown in Figure 2, the geometric model is established according to the equivalent diagram of the shape of the solder joint. The geometric model is established on the basis of a circle or a quasi-circle whose nugget diameter and indentation diameter are geometrically similar, and are irregular in actual work. The shape of the solder joints can be converted into the model of concentric circles in Figure 2 for calculation. In Figure 2, the outer large circle is the indentation shape, and the inner circle is the nugget shape. It is assumed that the nugget diameter d1 at the position of the line BC is measured according to actual needs, but the actual cutting and measurement position is the AD line after cutting or sample preparation in actual work. location. The nugget diameter obtained from the measurement is d2, and the indentation diameter is L2:

Set AE=GF=x, the triangle AOE and the triangle GOF are both right-angled triangles, according to the Pythagorean theorem:

AE ² +OE ² =AO ² (1)

GF ² +OF ² =GO ² (2)

带入式(1)可得：in,

Bringing into equation (1), we can get:

带入式(2)可得：in,

Bringing into equation (2), we can get:

d1 ² =d2 ² +4x ² (4)

Simultaneous formulas (3) and (4) can be deduced:

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the idea of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the present invention. within the scope of protection.

Claims (3)

1. A metallographic detection method for measuring the diameter of a resistance spot welding nugget is characterized by comprising the following steps:

step 1: selecting a resistance spot welding part, selecting one surface of a welding spot, and calculating the average value L1 of the diameters of the indentation areas of the welding spot;

step 2: selecting a cutting line which passes through the center of the welding point and has the length of L1, and cutting the welding point along the cutting line by using a cutting machine;

and step 3: grinding, coarse grinding, fine grinding, polishing and corrosion treatment are carried out on the cutting surface of the welding spot;

and 4, step 4: measuring the cutting surface of the welding point under a microscope to obtain a measured length L2 of the diameter of the indentation area and a measured length d2 of the diameter of the nugget;

and 5: judging whether the error between L1 and L2 is smaller than an error threshold value, if so, d2 is the length of the nugget area, otherwise, executing step 6;

step 6: the nugget diameter length d1 was calculated according to the following formula:

2. the metallographic detection method for measuring the diameter of a resistance spot welding nugget according to claim 1, wherein the step 1 specifically comprises:

the major axis length and the minor axis length of the indentation area were measured, respectively, and the average of the major axis length and the minor axis length was calculated as the average L1 of the diameter of the indentation area.

3. The metallographic detection method for the measurement of the diameter of a resistance spot weld nugget according to claim 1, wherein the error threshold in step 5 is specifically 5% of the average value L1 of the diameter of the indentation area.

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