英文版;

This paper relates to a method for strength welding of automobile body-in-white structure using ultra-high-strength steel. It is used to complete the body-in-white spot welding which increases the structural strength of the vehicle body after GEO welding. It belongs to the field of automobile manufacturing technology.



Background technique:

With the improvement of requirements for safety and energy saving of automobiles, ultra-high-strength steels based on solid solution strengthening, precipitation strengthening, grain refinement, dislocation strengthening and phase transformation strengthening (martensite) have entered the practical production application stage. In order to improve and meet crash safety performance and increase the strength of body parts, the importance of ultra-high strength thermoforming just spot welding performance and technology is highlighted.

The traditional car body-in-white uses a galvanized sheet, and when the two-layer galvanized sheet is welded, it is clamped and positioned using iron filings. Due to the material properties of high-strength thermoformed steel, the welding technology of thermoformed steel body-in-white requires stronger welding pressure, longer welding time and energy, so the traditional positioning pin can not meet the high-strength fixture positioning requirements. The wear and strength are not up to the process requirements, and the welding size and the fixed positioning dimensional accuracy cannot be met. In the case of an environment that does not meet the accuracy, if the two layers of steel plates are directly overlapped and pre-stressed, there will be voids or welding in an unplanned position, which has a great influence on the overall product quality and structural strength of the automobile.



Technical realization elements:

The technical problem to be solved by the present invention is how to position and spot weld the automobile white body of ultra high strength steel.

In order to solve the above technical problem, the technical solution of the present invention is to provide a hot-formed steel body-in-white spot welding method, characterized in that the steps are:

Step 1: bonding the welding faces of the two layers of steel plates of the hot-formed steel automobile body-in-white;

Step 2: clamping and positioning the two-layer steel plate through a ceramic positioning pin;

Step 3: respectively, an electrode cap is respectively disposed on the outer side of the two-layer steel plate to be spot-welded;

Step 4: Apply welding current and welding pressure between the two electrode caps, so that the spot welding on the two steel plates is melted and solidified into a welded joint.

Preferably, the electrode cap is subjected to a heat treatment process for increasing hardness.

Preferably, in the step 4, the joint shear strength displacement is ≤5 s/mm.

Preferably, in the step 4, the electrode retraction amount is consistent by ≥97%.

Preferably, in the step 4, when the thickness of the thin plate in the two-layer steel plate is 0.75 to 1 mm, the welding pressure is 3.9 to 4.3 KN, the welding time is 330 to 440 ms, the welding current is 10 to 12 ms, and the electrode cap diameter is 16 mm. .

Preferably, in the step 4, when the thickness of the thin plate in the two-layer steel plate is 1.1 to 2 mm, the welding pressure is 4.4 to 6 KN, the welding time is 460 to 660 ms, the welding current is 12.5 to 15.5 ms, and the electrode cap diameter is 16 ~20mm.

Preferably, in the step 4, the welding parameters are as shown in Table 1:

Table 1 Thermoforming steel welding parameters table

In Table 1, the plate thickness indicates the thickness of the thin plate in the two-layer steel plate, and the diameter of the contact surface indicates the diameter of the contact face of the electrode cap and the steel plate.

Compared with the prior art, the present invention has the following beneficial effects:

1. The use of matching thermoformed steel, the electrode cap adopts high hardness heat treatment to improve the overall precision and wear life of the supporting fixture;

2. The ceramic pin is used as the positioning of the fixture, which has the characteristics of high bending strength and electrical insulation, is safe, and can reduce the workload of subsequent cleaning of the welding slag;

3. Adopt new welding process parameters and high-strength supporting fixture mode to improve the first pass rate of products and improve production efficiency;

4. The matching use of high-precision welding fixtures starts with shortening the station downtime, which effectively reduces the comprehensive cost of the welding shop;

5. For the first time, ceramic locating pins and electrode cap briquettes with high hardness heat treatment process were introduced into the field of thermoforming steel spot welding, which promoted the progress of the overall welding process.

DRAWINGS

Figure 1 is a schematic view of a hot-formed steel body-in-white spot welding;

Figure 2 is a comparison diagram of the relationship between the welding pressure and the plate thickness of the conventional sheet and the thermoformed steel;

Figure 3 is a comparison diagram of the relationship between welding time and plate thickness of conventional sheet and thermoformed steel;

Figure 4 is a comparison of welding current and plate thickness of conventional sheet and thermoformed steel.

detailed description

The invention is further illustrated below in conjunction with specific embodiments. It is to be understood that the examples are not intended to limit the scope of the invention. In addition, it should be understood that various changes and modifications may be made by those skilled in the art in the form of the present invention.

A hot-formed steel body-in-white spot welding method, the steps are:

Step 1: bonding the welding faces 1 of the two-layer steel plate of the hot-formed steel automobile body-in-white to each other, as shown in FIG. 1;

Step 2: The two-layer steel plate is clamped and positioned by the ceramic positioning pin 2;

Step 3: an electrode cap 3 is respectively disposed on the outer side of the two-layer steel plate to be spot-welded; the electrode cap 3 uses a high-hardness heat treatment process to ensure dimensional stability during the body-in-white welding process;

Step 4: Apply welding current and welding pressure between the two electrode caps 3, so that the spot welding on the two steel plates is melted and solidified into a welded joint.

The technical specifications of ceramic positioning pins are as follows:

1) Superior wear resistance:

Compressive strength (MPa): 2300

Bending strength (MPa): 240

Elastic ratio (GPa): 280

2) Anti-adhesion: It can effectively reduce the adhesion of welding slag and dust;

3) Electrical insulation: meet Volvo's strict global insulation technical specifications;

4) Ultra high strength at high temperature, heat resistance (°C): 1700

5) Long service life: ensuring the lowest scrap rate and the shortest downtime of the welding process, effectively reducing the overall cost of the welding shop.

The types of ceramic pins used in this embodiment are: D15-040960385 (31915024), D13-034422378 (31915023), D15-040962889 (31553145).

The technical specifications of hot-formed steel spot welding are as follows:

1) Spot welding speed: 2s/point;

2) Welding point shear strength displacement: ≤ 5s / mm;

3) The amount of electrode indentation (residual thickness of thermoformed steel base material) is ≥97%

4) The welding pressure of the welding torch is twice that of ordinary galvanized sheet.

The traditional galvanized sheet and the hot-formed steel (Boron-Steel) of the present invention were subjected to a plurality of experimental processes, and the same thickness was controlled to compare the welding parameters, thereby realizing the combination of welding theory and practice. The welding process parameter setting law of the hot-formed steel body-in-white is realized, and the application of the hot-formed body welding in the actual production process is realized. According to the spot welding resistance parameter standard ES-6M2A-1K251-A*, the electrode parameters are implemented according to ISO5821, and the experimental research on welding parameters of laminated welding of carbon steel, laminated welding of high-strength coated steel and GMT welding of alloy sheet, experimental data as follows:

Table 1 Thermoforming steel welding parameters table

Table 2 Traditional plate welding parameter table

The welding parameters of thermoformed steel and traditional plate are shown in Table 1 and Table 2. The relationship between welding pressure and plate thickness of traditional plate and thermoformed steel is shown in Figure 1. The relationship between welding time and plate thickness of traditional plate and thermoformed steel is For example, as shown in Figure 2, the relationship between welding current and plate thickness of conventional sheet and thermoformed steel is shown in Figure 3.

It can be seen from the above data:

First, the welding current, voltage and welding time on the hot-formed steel application settings, according to the thickness of the plate, the curve and trend is almost the same as ordinary galvanized sheet;

Second, the white body welding pressure of the hot-formed steel is higher than the starting pressure of the galvanized sheet. As the thickness increases, the welding pressure increase of the galvanized sheet decreases from 70% to about 30%;

Third, due to the characteristics of refinement grain, dislocation strengthening and phase transformation strengthening (martensite) of thermoformed steel, the welding time is about 100% higher than that of galvanized sheet, which requires a longer welding dwell time to melt Wearing steel plates, insufficient welding dwell time will cause various problems such as insufficient welding or insufficient welding strength in the experiment, so sufficient welding time is necessary for thermoforming;

Fourth, the welding current of the hot-formed steel is almost the same as that of the galvanized sheet, that is, the energy required for welding the same plate thickness is almost the same;

V. Comprehensive comparison of the welding parameters of hot-formed steel (boron steel). Compared with the traditional galvanized sheet, the welding parameters need to be increased by 30% to 100% to meet the hot-rolled steel. Welding requirements.

In order to support the use of thermoformed steel, the invention innovatively utilizes the ceramic pin as the positioning of the fixture, and at the same time uses a high hardness heat treatment process for the electrode cap compact to ensure dimensional stability during the body-in-white welding process and improve the supporting fixture. Overall accuracy and wear life.

In terms of process parameters, the welding current, welding pressure and welding holding time of the hot formed steel are solidified and retained by continuous testing and testing of welding quality, welding shear strength displacement and testing of electrode shrinkage after welding. Created and established a set of technical indicators for domestic thermoforming steel body-in-white welding.

Through the use of ceramic locating pins and welding process parameters, not only can the welding body positioning accuracy be improved, but also the practice gap in the field of hot-formed steel body-in-white can be complemented, which provides a basis for setting industry standards and increasing welding rate.

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