CN108247226B - Laser welding pool control method based on Lorentz force - Google Patents

Abstract

A laser welding molten pool control method based on Lorentz force belongs to the technical field of laser processing. The method is to apply mutually perpendicular current and magnetic field in the laser welding molten pool at the same time, then a Lorentz force following Ampere's left-hand law is generated inside the molten pool, through which the force state, flow behavior and solidification process of the melt are affected Take active control. Applying the backward Lorentz force to the molten pool can make the welding "small hole" deep and elongated, the metal vapor/plume/plasma in the small hole escapes smoothly, and the molten pool flows smoothly, resulting in The effect is increased penetration, improved weld stability, and optimized weld formation. If the applied current and magnetic field parameters are AC or pulse waveform modulated, the Lorentz force can also produce stirring, vibration, directional drive and other effects on the melt in the molten pool. While controlling the welding defects, it can also realize the adjustment function of the weld structure and performance.

Description

A method for controlling molten pool of laser welding based on Lorentz force

technical field

The invention relates to a method for controlling a molten pool of laser welding based on Lorentz force, and belongs to the field of laser processing. It can be used for laser self-fusion welding, laser wire filling welding, laser narrow gap welding, etc.

Background technique

Due to its unique advantages, laser welding has been used more and more in aerospace, automobile, chemical industry, shipbuilding and other industrial fields, especially alloys containing low boiling point alloying elements such as aluminum alloys and magnesium alloys. The large amount of evaporation combined with the low viscosity of the melt and the small surface tension itself are prone to defects such as pores, splashes, undercuts, and difficulty in forming welds. In addition, with the emergence of ultra-high-power lasers (tens of kilowatts to 100 kilowatts), laser power is no longer the bottleneck restricting laser welding of large and thick plates. The aspect ratio of the "hole" and the volume of the molten pool also increase significantly, and then large splashes occur during the welding process, and the welds are prone to defects such as pores, undercuts, humps, and slumps. And the pit is even more difficult to find a good solution. Therefore, it is of practical significance to invent a method with good controllability for controlling the welding pool by applying the Lorentz force.

In response to these problems in laser welding, some scholars have proposed the method of electromagnetic field-assisted laser welding, but they are all assisted by a single magnetic field or a single electric field. Although its influence on laser welding has been confirmed by experiments, its law of action is difficult to control. Moreover, the control accuracy of the electromagnetic field is very high, and so far there is no unified explanation for the mechanism of the influence of the magnetic field or the electric field on the laser welding.

The invention mainly aims at the defects and deficiencies such as pores, cracks, unstable welding process and poor welding seam formation that are easy to occur in laser welding, and actively controls the welding "small holes" and molten pools during the welding process. The main principle of control is to simultaneously apply current and magnetic field in the liquid metal and generate the corresponding Lorentz force, through which the laser welding process and welding quality are controlled and optimized.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for regulating the laser welding "hole" and the motion behavior of the molten pool by using the Lorentz force generated by the interaction of current and magnetic field in the laser welding molten pool, in order to solve the problems that often occur in the laser welding process. The welding process is unstable, prone to defects and deficiencies such as pores, cracks, undercuts, humps and craters.

The technical scheme of the present invention is:

A method for controlling the molten pool of laser welding based on Lorentz force, adding mutually perpendicular current and magnetic field to the molten pool of laser welding, according to Ampere's left-hand law, the corresponding Lorentz force will be generated in the molten pool. The parameters are controlled in a targeted manner, and the corresponding Lorentz force is used to intervene in the welding "holes" and molten pools in a targeted manner, so as to achieve the purpose of optimizing the welding process stability, welding defect elimination and welding quality. The most typical implementation is: two opposite electrodes are arranged on both sides of the molten pool, and a magnet is inclined in front of the "small hole", the current is forced to flow through the molten pool during operation, and a part of the magnetic field also passes through the molten pool. Under the conditions of the magnetic field direction and the current direction, a backward and upward Lorentz force according to Ampere's law is generated in the weld pool, which has a positive effect on the welding process and the welding quality.

1. A laser welding molten pool control method based on Lorentz force, adding mutually perpendicular current and magnetic field to the laser welding molten pool at the same time. Lorentz force. According to the control requirements of the welding pool, the parameters such as the magnitude and direction of the applied current and magnetic field are controlled in a targeted manner, and the generated Lorentz force is used to actively intervene in the behavior of the welding hole and the molten pool.

2. Further, the verticality of the magnetic field and the current means that the magnetic field line and the current line have mutually perpendicular component vectors. The current directions in the molten pool can be X, Y, and Z directions (the welding direction is the X direction, and the workpiece surface is perpendicular to the X direction is the Y direction), and the magnetic field is arranged to be perpendicular to the current field.

3. Further, the device for generating the magnetic field can be a permanent magnet or an electromagnet, the magnet can be arranged on one or both sides, the angle between the magnet and the surface of the workpiece is 10°～90°, and the magnetic field strength in the molten pool area is 100Gs～2T. The front end of the permanent magnet or electromagnet core is covered with a copper sleeve to enhance heat dissipation.

4. Further, the cross section of the permanent magnet or electromagnet core is rectangular, circular, elliptical, annular or polygonal. The permanent magnet or electromagnet core with the hollow structure can also realize the combination of the magnet and the gas protection nozzle.

5. Further, the current flows into the molten pool through the electrode directly contacting the workpiece surface, the electrode spacing is 3mm~20mm, the current size is 1A~600A, and the electrode contacting the workpiece surface is divided into sliding friction (the corresponding electrode shapes are strips, rods, etc.). ) and rolling friction (the corresponding electrode shape is a roller), the cross-sectional area of the bar and rod electrodes is 4mm ² ~ 200mm ² , the diameter of the roller is 10mm ~ 200mm, and the angle between the two roller electrodes in the direction of the laser beam is 20° ~ 90°. A spring is set above the electrode to ensure stable contact between the electrode and the workpiece surface and constant pressure. The electrode material is pure copper, copper alloy or tungsten alloy. In order to enhance the heat dissipation of the electrode, water cooling is added to the rear of the electrode.

6. Further, laser wire filling welding can use the welding wire as an electrode to introduce current into the molten pool, and the other electrode corresponding to it can be directly connected to the workpiece or arranged behind the molten pool by means of rollers. The angle between the welding wire and the workpiece is 10°~70°, the diameter of the welding wire is 0.6mm~2.5mm, the current size is 1A~500A, the distance between the roller and the contact point of the welding wire is 20mm~50mm, and the roller is perpendicular to the board surface.

7. Further, the electromagnetic field may be a steady magnetic field, an alternating magnetic field or a magnetic pulse. The current can be direct current, alternating current, current pulse or induced current. Steady magnetic field, alternating magnetic field or magnetic pulse magnetic field and direct current, alternating current, pulse current or induced current can be arbitrarily matched. The frequency of AC electric field/magnetic field is 2Hz～10kHz, and the pulse width of electric pulse is 100ns～100ms.

Advantages of the present invention:

1. The laser beam is not disturbed by magnetic fields and currents. Unlike electron beams and arcs, there are no charged particles in the laser beam, and the electromagnetic field does not affect it. Therefore, the addition of magnetic field and current will not affect the basic physical laws of laser-material interaction in laser welding.

2. Strong controllability and operability. The interaction of magnetic field and current to generate Lorentz force is a basic physical law, and the size, direction and position of Lorentz force can be flexibly designed according to specific requirements. For example, for metal materials such as aluminum and magnesium, which have low liquid surface tension and good fluidity, the use of Lorentz force to generate lift and damping is helpful for weld formation.

3. Enhance the stability of the welding process and increase the penetration. The backward Lorentz force is applied to the liquid metal around the "small hole", the "small hole" is elongated longitudinally and the fluctuation of the surrounding liquid metal is also suppressed, the stability of the welding process is improved, and at the same time, the "small hole" can be enhanced. "The ability to "dig" down, increasing penetration.

4. Eliminate laser welding defects. Through alternating current or pulse waveform modulation of current and magnetic field, the corresponding Lorentz force can stir, oscillate, brake and directional drive the molten metal to eliminate pores, cracks, undercuts, humps and craters, etc. defect.

5. Adjust the weld structure and performance. The introduction of magnetic pulses and current pulses during the solidification of molten pool metal can refine the grains, reduce segregation, and inhibit the effect of columnar crystals, so as to achieve the purpose of regulating the solidification structure of the weld and improving the performance of the weld.

Description of drawings

Figure 1. Schematic diagram of the action principle of Lorentz force on the molten pool of laser welding.

Figure 2 is a schematic front view of the combined action of the transverse current and the oblique magnetic field.

Figure 3 is a schematic side view of the combined action of the transverse current and the oblique magnetic field.

Figure 4 is a schematic side view of the combined action of the transverse current and the laser coaxial magnetic field.

FIG. 5 is a schematic front view of the combined action of the filament oblique current and the transverse magnetic field.

FIG. 6 is a schematic side view of the combined action of a filament oblique current and a transverse magnetic field.

Figure 7 Schematic diagram of permanent magnet with copper cold jacket and electromagnet poles.

Figure 8. Effect of Lorentz force on laser welding.

Detailed ways

The process of controlling the laser welding molten pool by the method of the present invention is as follows: by passing a current into the laser welding molten pool and generating a Lorentz force with a magnetic field perpendicular to it, the welding "hole" and the molten metal in the molten pool are actively control. The current is applied by a pair of electrodes spanning both sides of the molten pool, and the magnetic field is applied by magnets (permanent or electromagnetic) arranged around the molten pool, as detailed below by way of specific examples.

Example 1

The specific implementation device of this embodiment is shown in FIG. 2 and FIG. 3 . The welding material is 316L stainless steel, the plate thickness is 20mm, and the surface is decontaminated; the laser power is 18KW, the spot size is 0.45mm, and the welding speed is 1m/min; Material: chromium zirconium copper, electrode form: a pair of rollers, the angle between the two electrodes is 60°, the electrode spacing (the distance between the electrode and the surface of the workpiece) is 12mm, the current is 100A DC, the distance between the electrode and the laser beam (electrode contact point) The distance between the connection line and the central axis of the beam) is 2mm; the strip-shaped NdFeB permanent magnet is arranged in the oblique front of the molten pool and forms a 30° angle with the surface of the workpiece.

Example 2

In this example, the electrode of the device is changed from the roller of Example 1 to a round bar, the electrode diameter is 5mm, the electrode material is chromium zirconium copper, the electrode spacing (the distance between the electrode and the surface of the workpiece) is 8mm, and a 50A is applied between the two electrodes. Constant current; the distance between the electrode and the beam (the distance between the electrode contact line and the central axis of the beam) is 1mm, the welding material is 6061 aluminum alloy, the plate thickness is 4mm, and the surface is removed from dirt and oxide film; the laser power is 4.5KW, and the spot size is 0.45mm , welding speed 2m/min; front shielding gas: Ar gas, flow rate 15L/min, back 10L/min Ar gas protection; strip-shaped NdFeB permanent magnets are placed in front of the molten pool at a 30° angle to the surface of the workpiece, and the size of the magnet is large It is 50×9×4mm, and the magnetic field strength of the welding area is 0.1T.

Example 3

The specific implementation device of this embodiment is shown in FIG. 4 . The magnetic field is provided by an electromagnet coaxial with the laser. The magnetic field is a sinusoidal alternating magnetic field with a frequency of 50 Hz. The maximum intensity of the magnetic field in the welding area is 0.2T. Welding material 2024 aluminum alloy, plate thickness 6mm, surface removal of dirt and oxide film; laser power 5KW, spot size 0.45mm, welding speed 1.5m/min; front shielding gas: Ar gas, flow 15L/min, back 10L/minAr Gas protection; electrode material: chrome zirconium copper, electrode form: a pair of rollers, the angle between the two electrodes is 60°, the electrode spacing (the distance between the electrode and the surface of the workpiece) is 12mm, the current is DC 100A, the electrode and the laser beam are The distance (the distance between the electrode contact line and the central axis of the beam) is 2mm.

Example 4

The difference between this embodiment and Embodiment 3 is that the magnetic field is also provided by an electromagnet coaxial with the laser, but the magnetic field is a constant magnetic field, and the magnetic field strength in the welding zone is 0.12T. The current between the electrodes is changed from DC to AC square wave, the current peak value is 60A, the duty ratio is 1:1, and the pulse width is 20ms.

The above embodiments are only further detailed descriptions of the present invention, and it cannot be considered that the specific embodiments of the present invention are limited to these descriptions. On the premise of not departing from the concept of the present invention, a series of methods derived from simple deduction should be regarded as belonging to The scope of protection of the present invention.

Claims (5)

1. A laser welding pool control method based on Lorentz force is characterized in that: adding mutually perpendicular current and magnetic field into a laser welding molten pool, and generating Lorentz force which is mutually perpendicular to the current and the magnetic field in the molten pool according to the ampere law; controlling the magnitude and direction of the applied current and the applied magnetic field, and actively interfering the behavior of the small welding hole and the molten pool by utilizing the generated Lorentz force to enable the direction of the generated Lorentz force to face the obliquely upper part of the welding seam; the device for generating the magnetic field is a permanent magnet or an electromagnet, the magnet is arranged on one side or two sides, the angle range between the magnet and the surface of the workpiece is 10-90 degrees, and the magnetic field intensity of a molten pool area is 100 Gs-2T; the front end of the iron core of the permanent magnet or the electromagnet is coated with a copper sleeve to enhance heat dissipation;

the current flows into a molten pool by directly contacting the surface of a workpiece through an electrode, the electrode distance is 3-20 mm, the current is 1A-600A, the mode that the electrode contacts the surface of the workpiece is divided into sliding friction and rolling friction, and the cross section area of a bar-shaped electrode and a rod-shaped electrode is 4mm²～200mm²The diameter of the roller is 10 mm-200 mm, and the included angle of the two roller electrodes in the laser beam direction is 20-90 degrees; the laser wire-filling welding takes a welding wire as an electrode to lead current into a molten pool, and the other corresponding electrode is directly connected on a workpiece or arranged behind the molten pool in a roller way; the angle between the welding wire and the workpiece is 10-70 degrees, the diameter of the welding wire is 0.6-2.5 mm, the current is 1-500A, the distance between the roller and the contact of the welding wire is 20-50 mm, and the roller is vertical to the plate surface.

2. The method of claim 1, wherein the method comprises the steps of: the perpendicularity of the magnetic field and the current means that magnetic lines and current lines have mutually perpendicular components; the direction of current in the molten pool is X, Y, Z directions, and the arrangement of the magnetic field is based on the principle that the magnetic field is perpendicular to the current field.

3. The method of claim 1, wherein the method comprises the steps of: the section of the iron core of the permanent magnet or the electromagnet is rectangular, circular, elliptical, annular or polygonal; the permanent magnet or the electromagnet core with a hollow structure is adopted to realize the combination of the magnet and the gas protection nozzle.

4. The method of claim 1, wherein the method comprises the steps of: a spring is arranged above the electrode to ensure that the electrode is stably contacted with the surface of the workpiece and the pressure is constant; the electrode is made of pure copper, copper alloy or tungsten alloy; in order to enhance the heat dissipation of the electrode, the rear part of the electrode is cooled by water.

5. The method of claim 1, wherein the method comprises the steps of: the electromagnetic field is a steady magnetic field, an alternating magnetic field or a magnetic pulse; the current is direct current, alternating current, current pulse or induced current; the steady magnetic field, the alternating magnetic field or the magnetic pulse magnetic field and the direct current, the alternating current, the pulse current or the induction current are matched at will; the frequency of the alternating current electric field/magnetic field is 2Hz to 10kHz, and the pulse width of the electric pulse is 100ns to 100 ms.

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