Method of laser welding of parts made of different metals

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and may be used in welding different materials by laser radiation. Plane of but joint between said parts is inclined along tangential line to segment of welded seam thermal effect. Laser radiation is focused to material with higher heat resistance at a distance from butt plane. But joint plane inclination angle and focus distance are determined with due allowance for inhibiting evaporation of low-melting metal. Laser radiation is fed onto welded surfaces to heat welding zone to melting temperature to produce, thereafter, a welded seam.

EFFECT: possibility to weld different metals together.

3 dwg

 

The invention relates to a method of welding dissimilar metals by laser radiation and can be used, including in the field of mechanical engineering.

How is that on the welded surface of the dissimilar metals is fed laser radiation, which heats the weld zone to the melting temperature, after cooling (solidification) which is obtained weld.

Known analogues, construction site preparation of edges for welding of copper and its alloys to steel [1] and the method of electron-beam welding [2]. Their disadvantage is the lack of taking into account the characteristics of the welded metals in the case of processing of heterogeneous materials, which can lead to more intensive evaporation of fusible metal in comparison with the more refractory.

The invention aims to remedy this drawback and to enable welding of dissimilar metals by laser radiation, taking into account their thermophysical and physicochemical characteristics. This is accomplished by completing form abutment surfaces of the welded parts in a plane tilted at a certain angle tangent to the segment of the heat-affected zone and apply laser radiation to a more refractory material. Then first melted refractory material, then through the heat transfer happens the molten fusible material.

The method is carried out by calculating the required angle of inclination of the abutment surface and the displacement zone of the laser radiation relative to this interface.

Metallographic examination of the zone of interaction with the metals showed that the zone has a cross section of a segment shape. As a result of experimental studies of the effect of LI (laser radiation) on phase transformations in metals revealed that the shape of the zone of influence or power of 1 kW at a speed of 1200 mm/min in steel W and zirconium has segmented character with the center of the circle O1and low segment area with the center of the circle O2(figure 1). The presence of the second segment area can be explained either by the beginnings of a dagger of penetration into the metal, or the emergence of a secondary energy source due to oxidation processes with heat release. The nature of the heat affected zones does not depend on energy, but the magnitude of the second zone depends on the physico-chemical properties of metals. Zirconia is chemically active metal.

From the analysis of the nature of the heat-affected zone should that welding of dissimilar metals should be the power supply for the refractory metal and the shape of the joint surfaces must repeat the form of the HAZ. In practice, it is better butt surface to make a flat, and based on the economic considerations. This is due to the difference of the melting temperature, in particular the melting point of molybdenum is equal 2620°C, and became equal to 1510°C. Therefore, to obtain a weld need to raise the energy density to melt molybdenum, while the evaporation steel. To eliminate this effect it is necessary to use the slope of the abutment plane of the welded components. The plane of the weld is inclined at an angle tangent to the segment of the heat-affected zone (figure 2). Then melted refractory metal, and due to heat transfer is partially melt the fusible metal.

Figure 2 presents the geometry of a butt-joint welding molybdenum and steel. Laser irradiation (LI) is more refractory molybdenum (TPL=2620°C). The melting point of steel is 1510°C, h - thickness of the parts. The angle φ and the displacement of the laser radiation should be selected in such a manner that respects the equality of squares S1=S2and the temperature at mid-depth joint was equal to the melting temperature of the second welded metal, in this case - steel (TPL=1510°C). Equality of squares S1=S2provides uniform fusion of steel.

Figure 3 presents the scheme of the calculation of the angle joint φ and the displacement of the laser radiation L. the velocity Vector SV is RCI v Stis perpendicular to the plane of the drawing. The calculation is as follows.

1. Depth pereplavlenny zone hpropsequal [3]:

where

P is the radiated power,

Rlis the radius of the focused radiation,

α is the coefficient of thermal diffusivity of refractory metal,

vSt- welding speed,

λT- coefficient of thermal conductivity of refractory metal,

Tkis the boiling point of the refractory metal.

2. Have a right-angled triangle with sides R and K. the Angle of intersection φ is defined as

where

here hdet- the thickness of the welded parts, Rlis the radius of the laser radiation.

3. The offset of the laser radiation from the junction on the surface of the parts denoted by L, is defined as the sum

where

4. Thus, substituting(1), (3), (4) in (2)and (6), (7) in (5), we obtain

By the formulas (8) and (9) can be calculated required for processing the proposed method, the surface angle of intersection φ and the displacement of the laser radiation L.

Sources of information

1. atent utility model RU 67002.

2. The patent RU 2285599.

3. Fghrhafen, Inthanon, Feesyou. Technological processes of laser processing: Textbook. the textbook for high schools / Under the editorship Veggiano. - M.: Publishing house of Moscow state technical University n.a. Bauman, 2006. - 664 S.: ill. - ISBN 5-7038-2701-9).

Method of laser welding of parts made of dissimilar materials, characterized in that the plane of the joint parts perform the inclined tangent to the segment of the heat-affected zone of the weld, and a laser focus on the more refractory material at a distance from the joint plane, the angle of inclination of the plane of the joint and the focusing distance calculated from conditions ensure that no evaporation of the low-melting metal.



 

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