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Robotic Arc Welding Automation: A Complete Knowledge Summary (Worth Collecting)

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Robotic arc welding is mainly applied in the automated production of various auto parts, construction machinery, and metal industries. As a core piece of equipment in industrial automation, robotic arc welding is primarily divided into two types: consumable electrode welding operations and non-consumable electrode welding operations. It features the ability to perform welding work for long periods, while ensuring high productivity, quality, and stability of welding operations. With technological development, robotic arc welding is evolving toward intelligence by leveraging machine vision and cloud data, gradually becoming a key support for high-efficiency industrial production.

1. System Composition of Robotic Arc Welding

A typical robotic arc welding system consists of the following components:
  • Robot
  • Automatic wire feeding device
  • Welding power supply
  • Welding torch
  • Positioner
  • Fixture
Based on differences in welding methods and specific welding process requirements for workpieces, the system can be optionally expanded with the following devices:
  • Torch cleaning and wire cutting device
  • Cooling water tank
  • Flux delivery and recovery device (for SAW)
  • Mobile device
  • Welding positioner
  • Sensing device
  • Dust removal device and weld inspection equipment

2. Three Welding Methods for Robotic Arc Welding

2.1 Gas Shielded Arc Welding

Methods such as argon arc welding (using argon as the welding area shielding gas) and carbon dioxide shielded welding (using carbon dioxide as the welding area shielding gas) fall into this category. Its basic principle is: when using an arc as the heat source for welding, shielding gas is continuously sprayed from the torch nozzle to isolate air from the molten metal in the welding area, protecting the arc and the liquid metal in the weld pool from contamination by oxygen, nitrogen, hydrogen, etc. in the atmosphere, so as to improve welding quality.

2.2 Tungsten Inert Gas (TIG) Welding

This is an arc welding method that uses a high-melting-point tungsten rod as one electrode for arc generation during welding, and is protected by argon. It is often used for strict welding of stainless steel, high-temperature alloys, etc.

2.3 Plasma Arc Welding

Developed from tungsten inert gas welding, plasma arc is a high-temperature ion flow generated by the ionization of ion gas. It is ejected from the fine nozzle hole and compressed into a slender arc column, with a temperature higher than that of conventional free arcs (e.g., argon arc welding only reaches 5000-8000K). Due to its slender arc column and high energy density, plasma arc is widely used in the welding field.

3. Three Gas Shielded Welding Methods for Robotic Arc Welding

Robotic arc welding mostly adopts gas shielded welding methods (MAG, MIG, TIG). Common welding power supplies (thyristor-type, inverter-type, waveform-controlled, pulsed or non-pulsed) can be mounted on robots for arc welding. Since robot control cabinets use digital control while welding power supplies are mostly analog-controlled, an interface is required between the welding power supply and the control cabinet.
In recent years, foreign robot manufacturers have their own specific supporting welding equipment, which already have corresponding interface boards built in, so no additional interface box is needed in the robotic arc welding system shown above.
It should be noted that the arc time accounts for a large proportion in the working cycle of robotic arc welding, so when selecting a welding power supply, the power capacity should generally be determined according to a 100% duty cycle.

3.1 MIG Welding (Metal Inert Gas Arc Welding)

This welding method uses the arc burning between the continuously fed wire and the workpiece as the heat source, and the gas ejected from the torch nozzle protects the arc during welding. The inert gas is generally argon.

3.2 TIG Welding (Tungsten Inert Gas Shielded Welding)

The heat source of TIG welding is a DC arc, with a working voltage of 10-15V but a current of up to 300A. The workpiece is used as the positive electrode, and the tungsten rod in the torch is used as the negative electrode. The inert gas is generally argon.

3.3 MAG Welding (Metal Active Gas Shielded Welding)

Metal active gas shielded welding uses a mixture of inert gas and a certain amount of active gas (such as O₂, CO₂) as the shielding gas.

4. Explanation of Robotic Arc Welding Systems

The arc welding process is much more complex than spot welding: the movement trajectory of the Tool Center Point (TCP, i.e., the end of the wire), the posture of the welding torch, and the welding parameters all require precise control. Therefore, in addition to the general functions mentioned earlier, robots for arc welding must also have functions suitable for arc welding requirements.
Theoretically, a 5-axis robot can be used for arc welding, but it will be difficult to handle complex-shaped welds with a 5-axis robot. Therefore, unless the weld is relatively simple, a 6-axis robot should be selected as much as possible.
When a robotic arc welding robot performs “zigzag” corner welding or small-diameter circular weld welding, its trajectory should be able to closely follow the taught trajectory. In addition, it should have software functions for different swing patterns for selection during programming, so as to perform swing welding. Moreover, the robot should also automatically stop moving forward at the pause point in each swing cycle to meet process requirements. In addition, it should have functions such as contact sensing, automatic search for weld start position, arc tracking, and automatic re-ignition.

5. Arc Welding Current in Debugging

Judgment of arc welding current magnitude during debugging:
  1. Small current:
    Narrow weld bead, shallow penetration, easy to form excessive height, incomplete fusion, incomplete penetration, slag inclusion, porosity, electrode adhesion, arc breakage, failure to ignite arc, etc.;
  2. Large current:
    Wide weld bead, deep penetration, undercut, burn-through, shrinkage cavity, large spatter, overburning, large deformation, weld lump, etc.

6. Offline Programming

Robotic arc welding systems mostly use offline programming
Offline programming can save more than 40% of on-site debugging time. If combined with virtual arc software such as Virtual Arc, it can simulate weld penetration based on welding current, wire, welding speed, pulse form, robot posture, etc., predict the welding state in advance, reduce a large amount of debugging work, and improve the cycle time and quality of the entire robotic welding system.

7. Two Key Technologies of the System

Two key technologies of robotic arc welding systems:
  1. Coordinated control technology:
    Control the coordinated movement of multiple robots and positioners, which can not only maintain the relative posture of the welding torch and the workpiece to meet the requirements of the welding process, but also avoid collision between the welding torch and the workpiece, and control the deformation impact of the welding area of each robot.
  2. Precise weld trajectory tracking technology:
    Combine the advantages of the offline working methods of laser sensors and vision sensors, use laser sensors to realize weld tracking during the welding process, improve the flexibility and adaptability of welding robots for welding complex workpieces, and combine vision sensors to observe offline to obtain the residual deviation of weld tracking. Based on deviation statistics, obtain compensation data and correct the robot’s movement trajectory, so as to obtain the best welding quality under various working conditions.

8. Welding Power Supply

  1. Welding power supply

    Consumable electrode gas shielded welding usually uses a DC welding power supply, and the arc welding rectifier-type DC power supply is widely used in production at present. In recent years, inverter-type arc welding power supplies have also developed rapidly. The rated power of the welding power supply depends on the current range required for various applications. The current required for consumable electrode gas shielded welding is usually between 100-500A, the duty cycle of the power supply is in the range of 60%-100%, and the no-load voltage is in the range of 55-85V.

  2. External characteristics of welding power supply

    The welding power supply for consumable electrode gas shielded welding can be divided into three types according to the type of external characteristics: flat characteristic (constant voltage), steep drop characteristic (constant current), and gentle drop characteristic.

    (1) Flat characteristic

    When the shielding gas is inert gas (such as pure Ar), Ar-rich gas, and oxidizing gas (such as CO₂), and the wire diameter is less than φ1.6mm, flat characteristic power supplies are widely used in production. This is because flat characteristic power supplies have many advantages when matched with constant-speed wire feeders: the arc voltage can be adjusted by changing the no-load voltage of the power supply, and the welding current can be adjusted by changing the wire feed speed, so the welding specification adjustment is relatively convenient. When using this external characteristic power supply, it has a strong self-adjustment effect when the arc length changes; at the same time, the short-circuit current is large, and arc ignition is relatively easy. The external characteristics of the flat characteristic power supplies actually used are not all truly flat, but have a certain downward slope, and the downward slope rate is generally not more than 5V/100A, but they still have the above advantages.

(2) Drop characteristic

When the wire diameter is relatively thick (greater than φ2mm), drop characteristic power supplies are generally used in production, matched with variable-speed wire feed systems. Since the wire diameter is relatively thick, the self-adjustment effect of the arc is weak, and the recovery speed after arc length change is slow. It is difficult to ensure a stable welding process relying solely on the self-adjustment effect of the arc. Therefore, like general submerged arc welding, an additional arc voltage feedback circuit is required to timely feed back the change of arc voltage (arc length) to the wire feed control circuit, adjust the wire feed speed, so that the arc length can be restored in time.

  1. Adjustment of power supply output parameters
    The main technical parameters of consumable electrode gas shielded welding power supplies are:(1) Input voltage (number of phases, frequency, voltage)(2) Rated welding current range

    (3) Rated duty cycle (%)

    (4) No-load voltage

    (5) Load voltage range

    (6) Type of power supply external characteristic curve (flat characteristic, gentle drop external characteristic, steep drop external characteristic)

Usually, the requirements for the technical parameters of the welding power supply should be determined according to the needs of the welding process, and then a welding power supply that can meet the requirements should be selected.

(1) Arc voltage

Arc voltage refers to the voltage drop between the end of the wire and the workpiece, not the voltage indicated by the power supply voltmeter (the voltage at the output end of the power supply). The pre-adjustment of arc voltage is realized by adjusting the no-load voltage of the power supply or the slope of the power supply external characteristic. Flat characteristic power supplies mainly realize arc voltage adjustment by adjusting the no-load voltage. Gentle drop or steep drop characteristic power supplies mainly realize arc voltage adjustment by adjusting the slope of the external characteristic.

(2) Welding current

The current of flat characteristic power supplies is mainly adjusted by adjusting the wire feed speed, and sometimes the no-load voltage is appropriately adjusted for a small amount of current adjustment. For gentle drop or steep drop characteristic power supplies, it is mainly realized by adjusting the slope of the power supply external characteristic.

9. Wire Feeding System

The wire feeding system is usually composed of a wire feeder (including motor, reducer, straightening wheel, wire feeding wheel, wire feeding hose, wire spool, etc.). The wire coiled on the wire spool is sent to the welding torch through the straightening wheel and wire feeding wheel. According to different wire feeding methods, it can be divided into four types:

(1) Push-type

Push-type refers to the wire being pushed by the wire feeding wheel through the hose to reach the welding torch, which is the main wire feeding method for semi-automatic consumable electrode gas shielded welding.

This wire feeding method has a simple, lightweight welding torch structure, and is convenient for operation and maintenance, but the resistance of wire feeding is relatively large. As the hose becomes longer, the wire feeding stability becomes worse. Generally, the length of the wire feeding hose is about 3.5-4m.

(2) Pull-type

Pull-type can be divided into three forms:

  1. Separate the wire spool and the welding torch, and connect them through a wire feeding hose;
  2. Install the wire spool directly on the welding torch;
  3. Separate the wire spool from the welding torch, and also separate the wire feeding motor from the welding torch.
The first two are suitable for fine wire semi-automatic welding, but the first one is more convenient to operate, and the third wire feeding method can be used for automatic consumable electrode gas shielded welding.

(3) Push-pull type

The wire feeding hose of this wire feeding method can be extended up to about 15m, expanding the operating distance of semi-automatic welding. When the wire advances, it relies on both the thrust from the back and the pulling force from the front, using the combined force of the two to overcome the resistance of the wire in the hose. The two powers of push and pull need to be coordinated during debugging, and try to be synchronized, but pull is the main one. During wire feeding, the wire should always be kept straight in the hose.

This wire feeding method is often used in semi-automatic consumable electrode gas shielded welding.

(4) Planetary (linear) type

The planetary wire feeding system is designed based on the principle that “a rotating nut fixed axially can feed a screw axially”.

Three rollers at 120° to each other are cross-mounted on a base to form a driving disc. The driving disc is equivalent to a nut, and the wire passing through the middle of the three rollers is equivalent to a screw. There is a pre-adjusted helix angle between the three rollers and the wire.
When the main shaft of the motor drives the driving disc to rotate, the three rollers apply an axial thrust to the wire to push the wire forward. During wire feeding, the three rollers revolve around the wire on the one hand, and rotate around their own axes on the other hand. The wire feeding speed can be adjusted by adjusting the speed of the motor.
This wire feeding mechanism can be connected in series level by level to form a so-called linear wire feeding system, which can make the wire feeding distance longer (up to 60m).
If one-stage transmission is used, it can transmit 7-8m. This linear wire feeding method is suitable for conveying small-diameter wires (φ0.8-1.2mm) and steel wires, as well as long-distance wire feeding.

10. Welding Torch

The welding torches of consumable electrode gas shielded welding are divided into semi-automatic welding torches (hand-held) and automatic welding torches (installed on mechanical devices).
A conductive nozzle (made of red copper or chrome copper, etc.) is installed inside the welding torch. The welding torch also has a channel and nozzle for delivering shielding gas to the welding area. The nozzle and conductive nozzle can be easily replaced as needed.
In addition, the resistance heat generated when the welding current passes through components such as the conductive nozzle and the arc radiation heat will cause the welding torch to heat up, so certain measures need to be taken to cool the welding torch. The cooling methods include air cooling, internal circulating water cooling, or a combination of the two. For air-cooled welding torches, in CO₂ gas shielded welding, a current of up to 600A can be used under intermittent load. However, when using argon or helium shielded welding, the current is usually limited to 200A.
  1. Classification of welding torches
    (1) Semi-automatic welding torchesSemi-automatic welding torches usually have two forms: gooseneck type and pistol type.
  • Gooseneck type welding torch
    Suitable for small-diameter wires, flexible and convenient to use, especially suitable for welding in compact parts, hard-to-reach corners, and some restricted areas;
  • Pistol type welding torch
    Suitable for larger-diameter wires, it has higher requirements for cooling effect, so internal circulating water cooling is often used. Semi-automatic welding torches can be installed together with the wire feeding mechanism or separated.

(2) Automatic welding torches

The basic structure of automatic welding torches is the same as that of semi-automatic welding torches, but they have a larger current-carrying capacity and longer working time, and sometimes need to use internal circulating water cooling. The welding torch is directly installed at the lower part of the welding head, and the wire is sent into the welding torch through the wire feeding wheel and wire guide tube.

  1. Gas supply system and cooling water system
    (1) Gas supply systemThe gas supply system is similar to that of tungsten inert gas welding. For CO₂ gas, a preheater and dryer usually need to be installed to absorb moisture in the gas and prevent porosity from forming in the weld. For consumable electrode active gas shielded welding, a gas mixing device also needs to be installed to mix the gas evenly before sending it into the welding torch.

(2) Cooling water system

The cooling water system is composed of a water tank, a water pump, a cooling water pipe, and a water pressure switch. The cooling water in the water tank flows through the cooling water pipe via the water pump, enters the welding torch after passing through the water pressure switch, and then flows back into the water tank through the cooling water pipe to form a cooling water cycle. The function of the water pressure switch is to ensure that the welding system cannot start welding when cooling water does not flow through the welding torch, so as to protect the welding torch and avoid burning due to no cooling.

  1. Torch service center
    Including torch cleaning and wire cutting device, oiling device, and TCP automatic calibration device. It can increase the normal operation time by 8%.
  • Automatic TCP definition
  • Automatic TCP inspection/update
  • TCP repeatability +/- 0.1mm
  • Stable workpiece quality
    Higher system reliable operation time

11. Positioner

The positioner is generally linked with the robot and is an additional axis of the robot. It can cooperate with the robot to complete the welding of complex workpieces. The repeat accuracy of high-performance positioners can reach 0.1mm.

12. Starting Point Sensing Function

  1. Pre-weld contact sensing;
  2. Automatically search for weld start point, end point, and weld position;
  3. Reduce the positioning accuracy requirements for fixtures;
  4. Can realize 3D guidance;
  5. Fast search, search speed 20-50mm/s, single-point one-direction search time 2-6s;
  6. Guidance accuracy ±0.25mm.

13. Arc Tracking and Adaptive Function

  1. Automatically track the weld during the welding process;
  2. Use the arc as a sensing device;
  3. Assembly, processing, and welding deformation errors can be corrected;
  4. Weld tracking accuracy ±0.1mm.

14. Laser Vision Weld Sensing

The robot adopts an active tracking method, and the robot controls the sensor:
  1. Real-time acquisition of torch position and welding speed, convenient control, and easy adjustment when the speed changes.
  2. Can be easily integrated and synchronized with external axes
  3. Bus communication method, rich information volume

15. Post-Welding Quality Inspection

With the development of vision technology, technologies such as line laser and white blue light have now emerged, which can complete weld quality inspection. They can detect the weld start point, weld height, weld width, welding defects, and weld continuity, and can even judge the rationality of welding parameters through spatter detection. This forms a manufacturing closed loop for the entire welding automation, laying a foundation for future machine learning.

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