CN111288907B - Metallographic detection method for measuring diameter of resistance spot welding nugget - Google Patents
Metallographic detection method for measuring diameter of resistance spot welding nugget Download PDFInfo
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- CN111288907B CN111288907B CN202010188641.XA CN202010188641A CN111288907B CN 111288907 B CN111288907 B CN 111288907B CN 202010188641 A CN202010188641 A CN 202010188641A CN 111288907 B CN111288907 B CN 111288907B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/08—Measuring arrangements characterised by the use of optical techniques for measuring diameters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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Abstract
The invention relates to a metallographic detection method for measuring the diameter of a resistance spot welding nugget, which comprises the following steps: step 1: selecting a resistance spot welding part, selecting one surface of a welding spot, and calculating an 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 is calculated according to the designed formula.
Description
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 resistance spot welding nugget.
Background
Resistance spot welding is widely applied in the field of automobiles or other processes needing spot welding for connection, one detection content is the measurement of nugget diameter in the process of detecting the quality of a welding spot in the welding process, the welding spot needs to be cut, then the section of the welding spot is ground, polished and corroded, and finally the diameter of the welding nugget is measured under an optical microscope. The measurement of resistance spot welding is a destructive experiment, and thus cutting of a welding spot is very important, but during the cutting process, the welding spot is easily deviated from a portion to be cut, so that the detected portion cannot be completely matched with the required portion, the detected portion is dislocated, and once the cutting portion deviates from the portion to be detected, the entire measurement fails. When the problem of deviation from the measurement line occurs, no related method currently corrects the detection result.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a metallographic detection method for measuring the diameter of a resistance spot welding nugget, which can correct measurement data, enable a calculation result to be closer to an actual value and play a role in evaluating and estimating the unmeasured nugget.
The invention provides a metallographic detection method for measuring the diameter of a resistance spot welding nugget, which comprises 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:
in the metallographic detection method for measuring the diameter of the resistance spot welding nugget, the step 1 specifically comprises the following steps:
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.
In the metallographic detection method for measuring the diameter of the resistance spot welding nugget, the error threshold value in the step 5 is 5% of the average value L1 of the diameter of the indentation area.
The metallographic detection is a destructive experiment, so that once a sample is cut wrongly, the experiment fails, and by adopting the metallographic detection method for measuring the diameter of the resistance spot welding nugget, when the sample is prepared wrongly, the measurement data can be corrected properly through a formula, so that the calculation result is closer to an actual value, and the effect of evaluating and estimating the diameter of the nugget which cannot be measured is achieved.
Drawings
FIG. 1 is a schematic view of a spot welding operation;
FIG. 2 is an equivalent diagram of the appearance of a welding spot in the metallographic detection method for measuring the diameter of a nugget of resistance spot welding according to the present invention;
FIG. 3 is a schematic diagram of a welding spot cutting surface in the metallographic detection method for measuring the diameter of a resistance spot welding nugget according to the present invention.
Detailed Description
Fig. 1 is a schematic view of spot welding operation, in which a power supply 10 supplies power to an electrode 20, and two members to be welded 40 are welded together by pressing down the upper and lower electrodes 20. As shown in fig. 2, from the distribution characteristics of the spot welding, the surface oxide layer can be approximately composed of three concentric circles, and the outermost layer is a black surface oxide layer region 1; the middle part is a thinning transition area of the resistance welding spot under the pressure of the electrode head, namely an indentation area 2; high temperature is generated between the steel plates to melt the center of the steel plates, and after cooling, a nugget 3 which is approximately circular is formed. Under the pressure of the electrode head of the electrode 20, an oxidation layer region 1 and an indentation region 2 are formed on the outer surface of the part to be welded 40, and a nugget 3 is positioned between the two parts to be welded 40. According to the principle of spot welding, under the condition of uniform stress, the shape of a nugget inside a welding spot determines the shape of a thinning area generated on the appearance of the welding spot, so that the nugget 3 and the indentation area 2 are concentrically distributed on the appearance. In the method, the diameter measurement value of the middle circle, namely the diameter of the indentation area is introduced as a characteristic parameter in the process of measuring the diameter of the nugget.
The invention relates to a metallographic detection method for measuring the diameter of a resistance spot welding nugget, which specifically comprises 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;
in specific implementation, the major axis length and the minor axis length of the indentation area are measured respectively, and then the average value of the major axis length and the minor axis length is calculated to be used as the average value L1 of the diameter of the indentation area.
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;
when the method is specifically implemented, the center of the welding spot selected in the step has certain error, and the welding spot is ensured to be close to the center of the welding spot as much as possible.
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; with particular reference to the schematic view of the weld cut surface of fig. 3;
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;
in specific implementation, the error threshold is specifically 5% of the average value L1 of the diameters of the indentation areas.
Step 6: the nugget zone length d1 is calculated according to the following formula:
in specific implementation, the measurement principle and the formula are derived as follows:
as shown in fig. 2, a geometric model is built according to the equivalent diagram of the welding spot shape, the geometric model is built on the basis of a circle or a quasi-circle with the geometric similarity between the nugget diameter and the indentation diameter, and the irregular welding spot shape in actual work can be converted into a concentric circle model in fig. 2 for calculation. In fig. 2, the outer surface great circle is in an indentation form, the inner circle is in a nugget form, and it is assumed that the nugget diameter d1 of the portion where the line BC is located is measured according to actual needs, but the actual cutting measurement portion is the position where the AD line is located after cutting or sample preparation in actual work. The measured nugget diameter at this point was d2, and the indentation diameter was L2:
AE is equal to GF equal to x, and the triangle AOE and the triangle GOF are both right-angled triangles, which can be known from the pythagorean theorem:
AE2+OE2＝AO2 (1)
GF2+OF2＝GO2 (2)
wherein the content of the first and second substances,
the tape of formula (1) can be obtained:
wherein the content of the first and second substances,
the tape-in formula (2) can be obtained:
d12＝d22+4x2 (4)
simultaneous equations (3) and (4) can be derived:
the above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, which is defined by the appended claims.
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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| CN112881389B (en) * | 2021-01-15 | 2023-05-26 | 本钢板材股份有限公司 | Metallographic detection method for diameter of steel plate resistance spot welding nugget region |
| CN113984837B (en) * | 2021-10-27 | 2024-02-23 | 重庆理工大学 | Welding spot quality detection method for resistance spot welding based on welding spot characteristic information fusion |
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| JPH1147975A (en) * | 1997-07-31 | 1999-02-23 | Masayoshi Iida | Method for evaluating spot welding of sheet |
| CN1609622A (en) * | 2004-11-22 | 2005-04-27 | 西北工业大学 | Real-time detection method for spot welding nugget diameter |
| CN100365382C (en) * | 2006-03-03 | 2008-01-30 | 北京工业大学 | Non-destructive testing method of dot weld nugget diameter |
| CN101241001A (en) * | 2008-02-28 | 2008-08-13 | 河北工业大学 | Aluminium alloy resistance spot welding nugget size real-time detection process |
| CN103822970B (en) * | 2014-03-05 | 2016-03-23 | 吉林大学 | A kind of portable resistor spot welding Automatic ultrasonic testing instrument and detection method |
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