CN102049591B - Dissimilar metal spot welding system of light metal and coated steel and welding method thereof - Google Patents

Abstract

The invention provides a dissimilar metal spot welding system of light metal and coated steel and a welding method thereof, wherein the system comprises a CMT (cold metal transfer) arc welding system, an air bottle, a robot control module, a robot and a clamping device; the arc welding system is connected to the robot control module and used for transmitting a welding control signal; the air bottle is communicated with the CMT arc welding system; the robot control module is connected to the robot for transmitting a control signal of the movement of the robot. In the invention, a spot melting soldering joint is formed between light metal and coated steel to realize the spot connection of the light metal and the coated steel; the serious deformation of the joint during continuous seam welding is solved while the connecting quality of dissimilar metal is ensured; traditional vehicle body part joints primarily using resistance spot welding process are not influenced; and the design and manufacture costs of vehicle bodies are greatly reduced.

Description

Dissimilar metal spot welding system and welding method for light metal and coated steel plate

technical field

The invention relates to a device and method in the technical field of metal welding, in particular to a dissimilar metal spot welding system and welding method for light metal and coated steel plate.

Background technique

Because the density of light alloy materials such as aluminum and magnesium is much lower than that of steel, they are favored by major automobile manufacturers. However, the overall mechanical properties of advanced steel materials are still better than those of light alloy materials. Therefore, the multi-material connection of light alloy and advanced high-strength steel is adopted. Structures become the preferred solution for automotive lightweighting, which involves heterogeneous connections between light alloys and steels.

Because of the huge difference in melting point, thermal expansion coefficient and electrical conductivity between aluminum and steel, and the formation of hard and brittle phases - intermetallic compounds during welding, it is difficult to form a joint with good performance. Foreign countries have proposed a mechanical cold forming process to form a firm interlock between the rivet and the sheet - semi-hollow rivet self-piercing riveting. This method effectively avoids the problems existing in the fusion welding of dissimilar materials. However, when riveting cast aluminum alloys and magnesium alloys and other low-elongation light alloy materials, the joints are prone to cracks or even brittle cracks; when riveting steel, due to the high strength of the steel and the difficulty of deformation, a large riveting force is required. On the one hand, it is necessary to increase the strength of the rivet. In order to avoid serious thickening and cracking of the rivets, on the other hand, higher requirements are put forward for various performance indicators of the equipment, thereby increasing the connection cost of the car body. Laser welding aluminum alloy and steel can effectively control the thickness of the intermetallic compound, and the joint strength can easily meet the requirements, but the energy of the laser beam and the gap between the plates need to be strictly controlled, resulting in very high process costs. Friction stir welding has the advantages of low energy input and small deformation, and is more suitable for welding aluminum materials. However, when using this method, the shape of the joint is greatly restricted. For the complex shape of the automobile body, it is difficult to ensure the assembly accuracy between the thin plate parts through the fixture, which greatly limits the application of friction stir welding in the automobile body.

After searching the existing technology, it was found that Fronius proposed an arc welding process called cold metal transfer (CMT for short), and realized the connection between the aluminum plate and the galvanized steel plate through the CMT fusion brazing method. , that is, the aluminum plate melts during the welding process, but the steel plate does not melt, and the connection between the aluminum alloy and the galvanized steel is realized through the welding wire brazing filler metal. Since the CMT method realizes the transition of metal droplets through the mechanical withdrawal of the welding wire, the heat input is greatly reduced compared with the conventional arc welding process, so the thickness of the intermetallic compound at the aluminum-steel interface can be effectively reduced, thereby ensuring the mechanical properties of the joint , has become a very promising method for joining aluminum alloys and steel dissimilarities. However, the CMT fusion brazing method has the following defects: (1) At present, this method is only used for seam welding. Due to the large difference in thermal expansion coefficient between aluminum alloy and steel, there is a large welding deformation in the joint; (2) During seam welding, aluminum There must be a lap joint between the alloy and the steel plate, which poses a challenge to the traditional body parts design and is difficult to promote and apply.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention provides a dissimilar metal spot welding system and welding method for light metal and coated steel plate. By forming spot fusion brazing joints between light metal and coated steel plate, the spot welding of light metal and steel is realized. Connection, while ensuring the connection quality of dissimilar metals, it solves the problem of serious deformation of the joint caused by continuous seam welding, and does not affect the traditional joint design of body parts mainly connected by resistance spot welding process, thus greatly reducing Body design and manufacturing costs.

The present invention is achieved through the following technical solutions:

The invention relates to a dissimilar metal spot welding system for light metal and coated steel plate, including: CMT arc welding system, gas cylinder, robot control module, robot and clamping device, wherein: the arc welding system is connected with the robot control module and transmits welding control Signal, the gas cylinder is connected with the CMT arc welding system, and the robot control module is connected with the robot to transmit the control signal of the robot movement.

The CMT arc welding system includes: welding torch, wire feeder, welding wire, host power supply and coolant tank, wherein: the welding torch is connected to the wire feeder, host power supply and coolant tank respectively, and the welding torch is fixedly arranged on the end of the robot , the wire feeder is connected to the host power supply and receives control instructions. The welding wire is located in the wire feeder and is heated and melted by the welding torch. After being heated and melted by the welding torch, it is dropped into the process hole of the perforated light metal plate as a filler metal and fused with the base metal to form a joint. The coolant tank and The host power supply is connected to receive control commands and is connected to the CMT arc welding system to cool the CMT arc welding system during the welding process. The host power supply is connected to the robot control module to transmit input and output signals during the welding process.

The perforated light metal plate is provided with a cylindrical or frustoconical process hole.

The steel plate is a coated steel plate, the base metal is low-carbon steel, high-strength steel, advanced high-strength steel or ultra-high-strength steel, etc., the coating is zinc, tin, copper or nickel-based alloy coating, and the thickness of the coating is 5-50 microns;

The gas cylinder is equipped with protective gas to provide an inert protective atmosphere for the welding process.

The robot is an industrial mechanical arm with six rotation axes, and its load-bearing capacity and working radius meet the requirements of arc welding. During the welding process, it drives the welding torch installed on the sixth axis to precisely locate the center of the hole in the light metal plate.

The present invention relates to a welding method for the above system

1) Punch out some process holes on the light metal plate in advance;

2) The light metal plates with holes are stacked on the coated steel plate and clamped by the clamping device, so that the upper and lower metal plates are in contact;

3) The robot drives the welding torch to move and make the welding wire in the welding torch perpendicular to the metal plate surface and aligned with the center of the process hole of the perforated light metal plate;

4) The robot control module sends a control signal to the CMT arc welding host power supply to start the welding process and opens the gas cylinder to pre-pass the shielding gas to form a shielding gas atmosphere on the perforated light metal plate;

5) The welding torch is controlled by the power supply of the CMT arc welding host. In the CMT arc mode, the arc is ignited with the set arc starting current and voltage;

6) Adjust the arc to the set welding current and welding voltage, weld with the set wire feeding speed and wire withdrawal frequency, the welding wire melts to fill the process hole, and realizes welding with the upper aluminum plate by melting the boundary of the process hole, and through the coating and the lower coating Brazing of steel plates;

7) After the welding is completed, the welding current decays to the arc current, the process hole on the light alloy plate is completely filled and the arc is extinguished after the surface is smooth, and the protective gas is kept flowing to prevent the joint from being oxidized;

8) The robot drives the welding torch to move to the position of the next preset hole and repeats the operations from step 3) to step 7) to realize dissimilar metal spot welding.

Compared with the prior art, the present invention has the following advantages: by converting seam welding into spot welding, the present invention greatly reduces the influence of thermal deformation on joint quality caused by the difference in thermal expansion coefficients of the two materials. Compared with the self-piercing riveting mechanical connection process, the cost of punching and welding wire is very low, and has no impact on the long-standing design method of body parts based on the resistance spot welding process, and is easy to popularize and apply. It is especially important that the method can effectively control the thickness of the intermetallic compound at the interface between the light metal and the steel plate, and the joint has superior mechanical properties.

Description of drawings

Fig. 1 is a schematic diagram of the process of the present invention.

Fig. 2 is a schematic diagram of the system of the present invention.

Fig. 3 is a working principle diagram of the method of the present invention.

Fig. 4 is a curve diagram of process parameters of the present invention.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1

As shown in FIG. 2 , this embodiment includes: a CMT arc welding system 1 , a welding wire 2 , a light metal plate with holes 3 , a steel plate 4 , a gas cylinder 5 , a robot control module 6 , a robot 7 , and a clamping device 8 . Among them: the CMT arc welding system 1 is connected with the robot control module 6 and transmits welding control signals, the welding wire 2 is installed in the CMT arc welding system 1, the perforated light metal plate 3 and the steel plate 4 are fixed on the clamping device 8, and the gas cylinder 5 and The CMT arc welding system 1 is connected, and the robot control module 6 is connected with the robot 7 to transmit control signals for the movement of the robot 7 .

The CMT arc welding system includes: welding torch 9, wire feeder 10, host power supply 11 and coolant tank 12, wherein: welding torch 9 is connected to wire feeder 10, host power supply 11 and coolant tank 12, and is mounted on a robot 7; the wire feeder 10 is controlled by the host power supply 11, and the welding wire 2 installed in it is melted and dropped into the hole of the light metal plate 3 through the welding torch 9 as a filler metal, and is fused with the base metal to form a joint; the coolant tank 12 is powered by the host The power supply 11 provides power and control signals to cool the CMT arc welding 1 system during the welding process; the host power supply 11 is connected to the robot control module 6 to transmit input and output signals during the welding process.

The perforated light metal plate 3 has a cylindrical hole with a diameter of 6.5mm.

The steel plate is a coated steel plate 4, which is galvanized low carbon steel.

The gas cylinder 5 is filled with argon as a shielding gas to provide an inert shielding atmosphere for the welding process.

The robot 7 is an industrial mechanical arm with a load-bearing capacity of 5kg. It has six rotating axes and a working radius of 1444mm. During the welding process, it drives the welding torch 9 mounted on the sixth axis to precisely position the holes in the light metal plate 3. Central location.

In this embodiment, the upper light metal plate 3 is aluminum alloy AA6061-T6, the lower galvanized steel plate 4 is galvanized low-carbon steel plate HDG-GMW2, the thickness of the plates is matched: 1mm+1.2mm, and the surface of the aluminum alloy plate 3 is removed by mechanical grinding. Use acetone reagent to remove the oil stain on the surface of the metal plate. The material of the welding wire 2 is A1Si5, and the diameter is 1.2mm.

Process parameters: Welding current is 127A, voltage is 15.3V, wire feeding speed is 6.0m/min, arc length is corrected to -30%, wire withdrawal frequency is 70Hz, argon is used as shielding gas, its flow rate is 15L/min, welding time It is 0.8s.

The technical process of this embodiment is as shown in Figure 3 (a)-(h) and Figure 4:

1) Punch out a cylindrical process hole with a diameter of 6.5 mm on the aluminum alloy plate 3 in advance;

2) The aluminum alloy plate 3 is stacked on the coated steel plate 4 and clamped by the clamping device, so that the upper and lower metal plates are in contact;

3) The robot 7 drives the welding torch 9 to move and makes the welding wire 2 in the welding torch 9 perpendicular to the metal plate surface and aligned with the center position of the process hole of the aluminum alloy plate 3 with holes;

4) The robot control module 6 sends a control signal for the start of the welding process to the CMT arc welding host power supply 11 and opens the gas cylinder 5 to pass the shielding gas in advance, forming a shielding gas atmosphere near the process hole of the aluminum alloy plate 3 with holes;

5) After pre-passing the protective gas for a certain period of time (GPr=0.1s), the welding torch 9 is controlled by the CMT arc welding host power supply 11. In the CMT arc mode, the ignition current (135% of the welding current) and voltage arc;

6) After the ignition arc passes through the I-S section, the current is attenuated (SL section), and the CMT arc welding system 1 welds, burns and fills the process hole with the set welding current, welding voltage, wire feeding speed and wire withdrawal frequency, At the same time, the boundary of the melting hole is melted and brazed with the lower steel plate 4 through plating;

7) After reaching the preset welding time (section I), the welding current decays to the arc-ending current (50% of the welding current) through the SL section, and the process hole on the aluminum alloy plate 3 is completely filled and the surface After leveling (section I-E), the arc is extinguished, and the protective gas (GPo=0.5s) continues to flow for a certain period of time to prevent the joint from oxidizing;

Welding under this welding parameter condition, the zinc element on the galvanized steel sheet improves the wettability of aluminum on the steel and obtains a good welded joint. The shape of the joint is flat and symmetrical, without spatter, and there are few welding defects such as pores and cracks. After welding, the universal testing machine is used to stretch, and the tensile and shear strength of the joint can reach up to 3.364KN; while the self-piercing riveting process (SPR) uses the same material and plate thickness, the maximum tensile and shear strength is 2.704KN, so this process method can achieve a higher high strength. At the same time, the galvanized layer on the back of the galvanized steel sheet is not burned, and the corrosion resistance of the steel sheet is maintained.

Example 2

In this embodiment, the upper light metal plate 3 is aluminum alloy AA6061-T6, the lower galvanized steel plate 4 is high-strength steel DP780, the thickness of the plate is matched: 1mm+2mm, the hole diameter is 6.5mm, and the center distance between holes is 20mm. The aluminum alloy plate 3 is mechanically polished to remove the oxide layer on the surface, and acetone reagent is used to remove the oil stain on the surface of the metal plate.

Process parameters: The material of welding wire 2 is A1Si5, the diameter is 1.2mm, the welding current is 144A, the voltage is 16.4V, the wire feeding speed is 6.5m/min, the arc length is corrected to -30%, the wire withdrawal frequency is 70Hz, and argon is used as protection Gas, the flow rate is 15L/min, and the welding time is 0.8s.

The technical process of this embodiment is as shown in Figure 3 (a)-(h) and Figure 4:

1) Pre-punching a number of cylindrical process holes with a diameter of 6.5 mm on the aluminum alloy plate 3;

2) The aluminum alloy plate 3 is stacked on the coated steel plate 4 and clamped by the clamping device, so that the upper and lower metal plates are in contact;

3) The robot 7 drives the welding torch 9 to move and makes the welding wire 2 in the welding torch 9 perpendicular to the metal plate surface and aligned with the center position of the process hole of the aluminum alloy plate 3 with holes;

4) The robot control module 6 sends a control signal for the start of the welding process to the CMT arc welding host power supply 11 and opens the gas cylinder 5 to pass the shielding gas in advance, forming a shielding gas atmosphere near the process hole of the aluminum alloy plate 3 with holes;

5) After pre-passing the protective gas for a certain period of time (GPr=0.1s), the welding torch 9 is controlled by the CMT arc welding host power supply 11. In the CMT arc mode, the ignition current (135% of the welding current) and voltage arc;

6) After the ignition arc passes through the I-S section, the current is attenuated (SL section), and the CMT arc welding system 1 welds, burns and fills the process hole with the set welding current, welding voltage, wire feeding speed and wire withdrawal frequency, At the same time, the boundary of the melting hole is melted and brazed with the lower steel plate 4 through plating;

7) After reaching the preset welding time (section I), the welding current decays to the arc-ending current (50% of the welding current) through the SL section, and the process hole on the aluminum alloy plate 3 is completely filled and the surface After leveling (section I-E), the arc is extinguished, and the protective gas (GPo=0.5s) continues to flow for a certain period of time to prevent the joint from oxidizing;

8) The robot 7 drives the welding torch 9 to move to the position of the next preset hole and repeats the operations from step 3) to step 7) to realize spot welding of dissimilar metals.

Other implementation modes of this embodiment are the same as Embodiment 1.

Under the conditions of the process parameters, the appearance of the multi-point continuous spot welding joint is smooth and beautiful, the process stability is good, and there is no welding defect such as spatter. The deformation after welding is small, and the upper and lower two-layer plates are basically kept flat. Compared with seam welding, there is no obvious bending. Therefore, the adoption of this process method can greatly reduce the deformation of the connected workpieces.

Claims (4)

1. the welding method of the dissimilar metal spot welding system of a light metal and clad steel sheet, it is characterized in that, this system comprises: the CMT electric arc welding system, gas cylinder, the robot control module, robot and clamping device, wherein: electric arc welding system links to each other with the robot control module and transmits the welding control signal, gas cylinder is communicated with the CMT electric arc welding system, the robot control module links to each other with robot, the control signal of transferring robot motion, described CMT electric arc welding system comprises: welding gun, wire-feed motor, welding wire, host power supply and tank for coolant, wherein: welding gun respectively with wire-feed motor, host power supply and tank for coolant link to each other, and welding gun is fixedly installed on the end of robot, wire-feed motor links to each other with host power supply and receives control instruction, welding wire is arranged in wire-feed motor and splashes into the fabrication hole of light metal plate with holes and form joint with the mother metal fusion as filling metal after the welding gun heat fused, tank for coolant is connected with host power supply and receives control instruction and be connected with the CMT electric arc welding system, cooling CMT electric arc welding system in welding process, host power supply links to each other with the robot control module with the input/output signal in the transmission welding process, said method comprising the steps of:

1) gets some fabrication holes at the light metal plate in advance;

2) overlapping being positioned on the clad steel sheet and by clamping device of light metal plate with holes clamped, contact between the metallic plate up and down;

3) robot drives the welding gun motion and makes welding wire in the welding gun vertical with metal plate and aim at the center of the fabrication hole of light metal plate with holes;

4) robot control module sends the control signal that welding process begins and opens in advance logical protective gas of gas cylinder to CMT arc welding host power supply, forms protective gas atmosphere at light metal plate with holes;

5) welding gun is by CMT arc welding host power supply control, under the CMT arc mode, with the striking current set and the voltage electric arc that ignites;

6) electric arc is adjusted to welding current, the weldingvoltage of setting, with wire feed rate and the welding of welding wire pumpback frequency of setting, welding is realized by border, melting process hole and light metal plate in wire melting fill process hole, realizes soldering by coating and lower floor's clad steel sheet;

7) after welding finished, welding current decayed to the receipts arc current, the fabrication hole on the light metal plate filled up fully and surfacing after arc extinction, keep passing into protective gas to prevent the joint oxidation;

8) robot drive welding gun moves to the position of next preset holes and repeats step 3) to the operation of step 7), realizes dissimilar metal spot welding.

2. method according to claim 1 is characterized in that, the parent metal of described clad steel sheet is mild steel, high-strength steel, advanced high-strength steel or super-high strength steel, and coating is zinc, tin, copper or nickel alloy plating layer, and thickness of coating is the 5-30 micron.

3. method according to claim 1 is characterized in that, described gas cylinder built-in protective gas.

4. method according to claim 1 is characterized in that, described machine people is the industrial machinery arm that has six axles that rotatablely move.

Images