Pulsed laser welding of sheet metals

IMPULSE LASER WELDING OF THINCASTIC METALS 

TECHNOLOGICAL PROCESSES WITH THE USE OF PULSE LASER WELDING CAN BE SUCCESSFULLY FOR SOLVING THE PROBLEMS OF OBTAINING SMALL-SIZED COMPOUNDS. THE EXPERIENCE OF THEIR IMPLEMENTATION SHOWS THE WIDE OPPORTUNITIES OF CONTROLLING THE QUALITY OF CONNECTIONS IN DIFFERENT PURPOSE PRODUCTS. Pulsed laser welding is often used to join parts made of different metals and alloys with a thickness of 0.05 mm. 1.0 mm. When it is used for thin sheet metal products, defects in the form of through burns can occur in welded points.

Consideration of the conditions under which the formation of point welded joints takes place shows that under the influence of highly concentrated pulsed laser radiation, the metal heats up to high temperatures in the zone of its action. The material is melted over the entire thickness of the sheet, and the surface layers evaporate as a result of overheating of the metal. Above the surface of the weld pool, a high-growth gas jet of superheated steam is formed. vapor-gas torch, which exerts a gas-dynamic pressure on the molten metal. The exposure of the vapor-gas factor to the surface of the weld pool can lead to its deflection and the formation of a through-hole in the center [1]. On closer examination it is established that the following factors mainly influence the melt:

gas-dynamic pressure of a combined-cycle flame </ li>
pressure of laser radiation (light flux) </ li>
hydrostatic pressure of the molten metal weld pool </ li>
pressure due to surface tension forces </ li> </ ul>
Comparison of the penetration depth of the investigated metals at the same pulse duration showed that the pulse energy required to obtain the same penetration depth & mdash; 0,4 mm, for tungsten it is tens times more in comparison with titanium. In addition, the specific energy consumption for the melting of the STL alloy 7? 3 is significantly larger than that of titanium. 

The effect of laser radiation when welding on the butt-welded parts inevitably leads to uneven melting of the welded edges, therefore, it is almost impossible to obtain a symmetrical weld seam. As a result of experimental studies, it has been established that with a symmetrical beam guide, the welded point moves toward the titanium by 18% to 20% of the diameter of the welded point. You saw titanium slips, the depth of penetration from the side of the titanium was 0.49 mm, while on the part of the residence permit 7 n 3 was negligible. In order to increase the depth of penetration of the alloy STL 7 ~ 3, the beam was angled (Fig. 2). 

In the course of the work, the technique of forming a welded joint during welding was studied and the method of beam alignment at an angle was developed, ensuring the required shape of the weld pool and the necessary strength of the welded joint. The angle of the surface of the butt-welded metals should be within the range of 18-22 degrees to the horizontal. On the side of the VNZ alloy 7? 3 in the formation of the weld pool, the binding component of Fe-Ni is mainly involved as more fusible, and the grains of tungsten can pass into the weld pool before they can dissolve in the liquid melt. The state of the microstructure at the boundary of the STL alloy 7? 3 shows that a good structural bond is formed, which can provide the necessary strength of the welded joint. In the macro- and microstructure of the welded specimens, it can be seen that the formation of the welded seam occurs mainly due to BT1 → 0, in the presence of a noticeable transition layer between the welded point and the alloy BHZ 7 n 3. In the structure, traces of intensive mixing of welded metals in a liquid bath are observed. This photo shows a good fusion of the welded alloys. The formation of the weld pool is mainly due to the alloy BT1? 0. Thus, it is recommended to introduce a new parameter in the laser welding modes of titanium and the alloy of permissible solids, & mdash; the angle of inclination of the surface of the welded products with respect to the angle of the beam guide. When it is secured, the largest fusion zone is obtained with the VNZ alloy at a smaller depth of its melting, but at the same depth of penetration of both metals. Such a connection clearly provides the greatest strength in the shearing test, which was confirmed by mechanical tests (shear strength 350 ± 370 MPa, tensile strength 540 MPa). 

X-ray spectral analysis determines the distribution of basic chemical elements (titanium, tungsten) and their relative amount in the weld. It can be seen that the weld seams contain both analyzed elements. Consequently, in the process of welding, metal is mixed in the entire volume of the liquid bath. In this case, the refractory tungsten gets spread throughout the entire volume of the bath, reaching the opposite boundary of the welded point. In the titanium distribution over the cross section, a greater unevenness is observed than in tungsten. On a site with a very high concentration of tungsten, the content of titanium decreases accordingly. The nature of the distribution of tungsten shows that in the welded joint, the wool is present not only as individual grains as a very refractory metal, but also in a solid solution. 

Reduction of metal consumption and reduction of dimensions while maintaining performance characteristics is one of the tendencies of instrument making. Similar problems are considered in the manufacture and renovation of jewelry, the manufacture of surgical instruments, sensors for various purposes, etc. This example shows the possibilities of pulsed laser technology and approaches to its implementation. 

A. Yu. Albagachiev, N.I. Minaeva, 
In. I. Privezentsev, NN Chunikhin 
Moscow Technological University

07.12.2017