Gas-shielded arc welding (GMAW) is a commonly used welding method that utilizes a gas-protected arc to melt the welding wire and base material, forming a weld. GMAW offers advantages such as simple operation, high welding speed, and high weld quality, making it widely used in welding various metal materials. However, GMAW also has some technical requirements and considerations, especially when welding thick plates, where mastering specific techniques and methods is essential to ensure welding effectiveness and safety.
This article will introduce the techniques and methods of GMAW welding thick plates, covering the following aspects:
Composition and Principles of GMAW
Adjustment of Current, Voltage, and Gas Flow in GMAW
Control of Welding Wire Extension Length and Torch Angle in GMAW
Selection of Welding Position and Direction in GMAW
Application of Welding Techniques and Oscillation Methods in GMAW
I. Composition and Principles of GMAW
GMAW typically consists of four parts: a welding machine, wire feeding mechanism, welding torch, and gas supply system. The welding machine serves as the power source, providing constant current or constant voltage with either direct current (DC) or alternating current (AC). The wire feeding mechanism adjusts the wire feed speed automatically based on the current. The welding torch, the primary tool, consists of an electrode, gas nozzle, trigger switch, and other components. The gas supply system provides shielding gases such as argon, carbon dioxide, or a mixture of these gases to protect the arc and molten pool from atmospheric contamination.
The principle of GMAW involves generating an arc between the electrode in the torch and the base material, with the arc's high temperature melting both the wire and the base material to form a molten pool. Simultaneously, the shielding gas forms a protective layer around the arc and molten pool, preventing oxidation or nitridation of the metal. The wire continuously feeds into the arc zone, replenishing the molten pool and forming the weld. The welding torch moves along the weld seam to complete the welding process.
II. Adjustment of Current, Voltage, and Gas Flow in GMAW
The current, voltage, and gas flow in GMAW are critical parameters influencing welding quality and efficiency. These parameters need to be adjusted according to factors such as the thickness of the workpiece, the diameter of the welding wire, and the welding position and direction.
Current Adjustment: The current determines the wire feed speed and melting rate. Higher currents increase the wire feed speed and melting rate, resulting in wider welds, deeper penetration, and faster welding speeds. Excessive current can cause overly wide welds, deep penetration, excessive spatter, and defects such as burn-through or undercut. Insufficient current results in narrow welds, shallow penetration, and insufficient fusion, leading to defects such as slag inclusion or porosity. Generally, thicker workpieces and larger diameter wires require higher currents. Current settings should also be adjusted for different welding positions, with vertical, horizontal, and overhead welding requiring 10%-20% lower current than flat welding.
Voltage Adjustment: Voltage affects the arc length and stability. Higher voltage results in longer, less stable arcs, narrower welds, shallower penetration, and slower welding speeds. Excessive voltage causes unstable arcs, excessive spatter, poor gas shielding, and defects like porosity or oxide films. Insufficient voltage results in short arcs, arc instability, wide welds, deep penetration, and defects such as burn-through or undercut. Voltage should match the current and be adjusted for different welding positions, with vertical, horizontal, and overhead welding requiring 2-3V higher voltage than flat welding.
Gas Flow Adjustment: The gas flow rate determines the thickness and stability of the shielding gas layer. Higher flow rates improve gas shielding, resulting in smoother welds with fewer porosities. Excessive flow increases gas consumption, affects welding visibility, and causes arc instability due to gas flow interference. Insufficient flow results in inadequate shielding, leading to porosity or oxide films. The gas flow rate should be adjusted based on the welding environment, wire diameter, and welding position, typically around 10L/min indoors and higher in windy outdoor conditions or with thicker wires.
Related article： How to Adjust the Current and Voltage of MIG Welding? 2 Methods for Precise and Fast Adjustment!
III. Control of Welding Wire Extension Length and Torch Angle in GMAW
Controlling the welding wire extension length and torch angle is crucial for maintaining welding quality and efficiency. These parameters should be adjusted based on the thickness of the workpiece, welding position, and direction.
Welding Wire Extension Length: The extension length, the distance from the nozzle tip to the arc point, affects arc stability and penetration. Longer extensions increase resistance, resulting in less stable arcs, deeper penetration, and more spatter. Shorter extensions reduce resistance, resulting in more stable arcs, shallower penetration, and less spatter. The extension length should be 5-10mm and adjusted for thicker workpieces or vertical, horizontal, and overhead welding to increase penetration and ensure sufficient fusion.
Welding Torch Angle: The torch angle, the angle between the torch and the weld seam direction, influences the arc direction and molten pool shape. Larger angles cause the arc to deviate from the weld seam direction, resulting in flatter molten pools, narrower welds, and shallower penetration. Smaller angles align the arc with the weld seam direction, resulting in deeper molten pools, wider welds, and deeper penetration. The torch angle should be 60-80° and adjusted for different welding positions, with vertical, horizontal, and overhead welding requiring 10-20° smaller angles than flat welding.
IV. Selection of Welding Position and Direction in GMAW
Selecting the appropriate welding position and direction is essential for achieving high-quality welds. These choices should be based on the workpiece's shape, structure, and joint type.
Welding Position: Welding positions refer to the relative position of the weldment in space, which determines the gravity action and the flow of the molten pool during welding. The Welding positions include flat, horizontal, vertical, and overhead. Flat welding is the easiest, followed by horizontal and vertical welding, with overhead welding being the most challenging. The welding position should be chosen based on the workpiece's shape and structure, favoring flat or horizontal welding and avoiding vertical or overhead welding. If vertical or overhead welding is necessary, appropriate parameters and techniques should be used to prevent molten pool sagging or loss.
Welding Direction: Welding direction refers to the movement direction of the torch along the weld seam, which determines the heat input during welding and the cooling of the weld pool. Welding direction includes forward (push) and backward (pull). Forward welding (push) results in lower heat input, faster cooling of the molten pool, and smaller weld shrinkage, but a higher risk of insufficient penetration. Backward welding (pull) results in higher heat input, slower cooling of the molten pool, and larger weld shrinkage, but a higher likelihood of sufficient penetration. The welding direction should be chosen based on the workpiece's thickness and joint type, favoring forward welding to avoid backward welding. If backward welding is necessary, appropriate parameters and techniques should be used to prevent overheating or cracking of the weld seam.
V. Application of Welding Techniques and Oscillation Methods in GMAW
Applying suitable welding techniques and oscillation methods is critical for achieving high-quality welds. These should be adjusted based on the workpiece thickness, weld seam width, and shape.
1）Welding Techniques:
The welding technique refers to the movement speed and pattern of the welding gun during the welding process. It determines the heat input and the distribution of the weld pool. Generally, there are two types of welding techniques: uniform movement and intermittent movement. Uniform movement means the welding gun moves along the weld seam at a constant speed, while intermittent movement means the welding gun moves along the weld seam at an irregular speed, sometimes pausing and sometimes accelerating.
Uniform movement provides a more consistent heat input, leading to a more evenly distributed weld pool and a more regular weld seam shape. However, the weld seam tends to be narrower, increasing the likelihood of insufficient penetration.
Intermittent movement results in more uneven heat input, causing a less uniformly distributed weld pool and a less regular weld seam shape. However, the weld seam tends to be wider, increasing the likelihood of sufficient penetration.
The choice of welding technique should be based on the thickness of the workpiece and the width of the weld seam. It is advisable to choose uniform movement and avoid intermittent movement whenever possible. If intermittent movement is necessary, the pause duration and position should be carefully controlled to prevent the weld pool from becoming too large or too small.
2）Weaving Pattern
The weaving pattern refers to the side-to-side motion of the welding gun during the welding process. It determines the coverage area of the weld pool and the shape of the weld seam. Generally speaking, there are four kinds of swing modes: straight weaving, triangular weaving, Zigzag weaving, and circular swing.
Straight Weave: The welding gun moves side-to-side in a straight line along the weld seam. This pattern provides a smaller coverage area and produces a narrower weld seam, suitable for welding narrow weld seams or thin plates.
Triangular Weave: The welding gun moves side-to-side in a triangular pattern along the weld seam. This pattern provides a larger coverage area and produces a wider weld seam, suitable for welding wider weld seams or thicker plates.
Zigzag Weave: The welding gun moves side-to-side in a zigzag pattern along the weld seam. This pattern results in a less uniform coverage area and a less regular weld seam shape, suitable for welding irregular weld seams or uneven plates.
Circular Weave: The welding gun moves side-to-side in a circular pattern along the weld seam. This pattern provides a more uniform coverage area and a more even weld seam shape, suitable for welding regular weld seams or flat plates.
The choice of weaving pattern should be based on the shape of the weld seam and the thickness of the plate. It is advisable to select a weaving pattern that matches the weld seam and plate characteristics and to avoid excessive weaving to prevent an uneven weld pool or weld seam deformation.
These are the techniques and methods for welding thick plates with gas-shielded arc welding. I hope they are helpful to you. Gas-shielded arc welding is an efficient welding method, but it requires certain skills and experience to ensure the quality and safety of the weld. In practice, welding parameters and techniques should be flexibly adjusted and applied according to specific welding conditions and requirements to achieve the best welding results. Additionally, safety precautions should be taken to avoid accidents such as electric shocks, burns, and eye injuries.
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