In the welding process, welding current, voltage, and welding speed are the key parameters that determine the quality and size of the weld. Their interaction directly affects the penetration, width, reinforcement of the weld, as well as the stability and efficiency of welding. This article will deeply explore the specific influence of these parameters on the weld and the application and control points in different welding methods.
Influence of Welding Current
When the welding current increases (with other conditions unchanged), the penetration and reinforcement of the weld will increase, while the width of the weld will not change much (or increase slightly). This is because the increase in current leads to an increase in the arc force and heat input, the heat source moves downward, and the penetration is approximately proportional to the current; at the same time, the amount of wire melted increases, and the reinforcement increases when the width of the weld remains unchanged; although the diameter of the arc column increases, the increase in the depth of the arc penetration limits the movement range of the arc spot, so the width of the weld remains basically unchanged. However, too large a current is easy to cause undercut, burn-through, and spatter in the weld, while too small a current will lead to unstable arc, small penetration, incomplete penetration, slag inclusion, and other problems, and also reduce productivity. Therefore, the welding current needs to be appropriately selected according to the diameter of the electrode and other factors, and adjusted according to the position of the weld, joint form, etc.
Influence of Arc Voltage
When the arc voltage increases, the arc power increases, the heat input to the workpiece increases, the arc length lengthens and the distribution radius increases. As a result, the penetration decreases slightly, the width of the weld increases, and the reinforcement decreases. This is because when the width of the weld increases, the amount of wire melted decreases slightly. The arc voltage mainly affects the width of the weld. Too long an arc will make the combustion unstable, increase metal spatter, and may lead to pores in the weld. Therefore, a short arc should be used as much as possible during welding, and generally, the arc length should not exceed the diameter of the electrode.
Influence of Welding Speed
When the welding speed increases, the energy decreases, and both the penetration and width of the weld will decrease, and the reinforcement will also decrease. Because the amount of wire deposited per unit length of the weld is inversely proportional to the welding speed, and the width of the weld is approximately inversely proportional to the square root of the welding speed. To improve productivity, a larger diameter electrode and current should be selected under the premise of ensuring quality, and the welding speed should be adjusted appropriately to ensure the consistency of the weld size.
Short-circuit Transfer Welding
Short-circuit transfer is widely used in CO₂ arc welding for thin plates and all-position welding. Its specification parameters include arc voltage, welding current, welding speed, welding circuit inductance, gas flow rate, and wire extension length. For a specific wire diameter and welding current, a suitable arc voltage needs to be matched to achieve a stable short-circuit transfer process and reduce spatter. The welding circuit inductance can adjust the growth rate of the short-circuit current and control the penetration of the base metal; too fast or too slow welding speed will lead to weld defects; the gas flow rate depends on many factors; a suitable wire extension length should be 10 - 20 times the diameter of the wire, and it has a significant impact on the current and penetration; CO₂ arc welding generally adopts DC reverse polarity to obtain better results.
Spray Transfer
In CO₂ gas, when the current reaches a certain value and is accompanied by a higher arc voltage, the molten metal of the wire is transferred in small droplets, which is suitable for medium and thick plate welding. This process has strong arc penetration and large penetration, and DC reverse polarity is adopted. When the current increases, the arc voltage needs to be increased correspondingly, otherwise, the weld formation will deteriorate, and if the voltage is too high, the spatter will increase significantly. Moreover, there are essential differences between the spray transfer in CO₂ and that in argon arc welding.
Measures to Reduce Metal Spatter
Correct selection of process parameters can reduce spatter. The spatter rate is relatively small in the low-current and high-current regions (spray transfer region). The spatter is the least when the welding torch is vertical, and the forward or backward inclination is preferably not more than 20 degrees. The wire extension length should be shortened as much as possible, and an increase in the wire extension length will increase the spatter amount.
Types of Shielding Gases and Welding Methods
CO₂ arc welding uses CO₂ as the shielding gas, and a preheater needs to be installed in the gas supply to prevent gas path blockage. The MAG welding method uses a mixture of CO₂ and Ar as the shielding gas and is suitable for stainless steel welding. The MIG welding method uses Ar as the shielding gas and is suitable for aluminum and aluminum alloy welding.
Summary
Welding current, voltage, and welding speed play a crucial role in the welding process. Reasonable control of these parameters can ensure the quality of the weld, improve welding efficiency, and reduce welding defects. In actual operation, welders must accurately adjust these parameters according to the material, thickness, and welding position of the workpiece, and combine the characteristics of different welding methods and shielding gases to obtain the ideal welding effect. This not only requires a deep understanding of the welding principle but also rich practical experience to deal with various complex welding conditions and ensure the high-quality completion of welding work.
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