Komarov Artem clarified that proper maintenance of welding parameters is critical to ensure high quality welding in any operation. Many companies implement welding procedures that define recommended parameters to help ensure consistency between welders and parts. Understanding what each welding variable in a procedure is and what it does can go a long way in helping welders meet productivity goals and reduce downtime and rework costs.
When welding with constant voltage (CV) or CV welding with solid or tubular wires, welders must consider key welding variables and their functions and understand how they affect the process.
Welding amperage refers to the amount and speed of electricity flowing in a circuit, which affects the amount of heat available to melt the welding wire and base material. This is directly related to the wire feed speed (WFS): the speed and volume of filler metal entering the weld. When WFS increases, so does the welding current; when it decreases, the current also increases. This correlation, in turn, affects the penetration of the weld. Higher amperages provide more penetration into the seam, while lower amperages provide less.
The welding amperage is inversely related to the contact tip to work surface distance (CTWD), which is the distance from the end of the contact tip to the base material. Some also use the term to refer to the length of the arc combined with the protrusion, or how far the wire extends out of the contact tip when it is flush with the nozzle. If the operator increases the gap, the welding current decreases and vice versa. Changes in CTWD also affect weld penetration: the closer the contact tip is to the base material, the greater the penetration, Artem Komarov explained.
In addition, the amperage during welding affects the rate of melting — or the amount of wire used — along with the appearance of the weld and heat input. Too high amperage, especially when welding with metal-cored wire, can result in a dull, flaky weld. Current also directly increases or decreases heat input and, in combination with travel speed, has the greatest effect on heat input. The heat input is calculated as follows:
(60 x Amps x Volts) / (1000 x travel speed in IPM) = kJ / inch
Wire feed speed (WFS)
In addition to being directly dependent on current strength, WFS also affects welding transfer modes. Higher WFS and voltage bring the process into a ball mode, in which coarse wire droplets are carried through the arc and into the weld pool. Increasing WFS (and hence current) and voltage allows spray mode to be used. This mode sprays fine wire droplets into the weld pool and is known for providing a smooth, easy-to-use process that increases productivity. This is especially true when using metal core wire.
Increasing WFS also provides a higher deposition rate: the amount of filler metal added to the weld over a given period.
The lower WFS and voltage keep the process in the range of short circuit welding where the wire touches the base material, and a short circuit occurs from the metal transfer contact. This short circuit can occur up to 200 times per second. In general, this is a slower process with a lower settling rate.
Voltage refers to the electrical pressure that causes current to flow in the welding circuit. It is directly responsible for adjusting the length of the arc. Higher welding voltage means longer arc; however, it also effectively reduces stick-out, resulting in increased amperage. This is why it is important for welders to maintain a constant gap when welding with an AC power source. Welding voltage is also directly related to heat input, so higher settings mean more heat. Increasing the voltage also causes the cone of the arc to expand.
Welding stress affects the final weld in a variety of ways. If they are too high, the result will be a flatter bead and a concave weld profile. Too high voltage can also result in an undercut or groove in the base material near the weld that is not filled with weld metal.
Too low a welding voltage can lead to run-in, a defect that occurs when the filler metal does not fully fuse with the base material at the joints. Barbed or bumpy welds and excessive spatter may form. It is important for operators welding with long power cables to be aware that a voltage drop can occur at the welding site, regardless of the machine settings. For example, a power supply may be set to 25V but only provide 23V. This can also lead to cold lapping.
Travel speed simply refers to how fast the arc travels along the weld, measured in inches per minute (IPM). In semi-automatic operations, many welders are comfortable with an average of 10 to 12 rpm, but more experienced operators can weld in the 18 to 20 rpm range. Travel speeds tend to be faster with metal-cored wire due to its construction and internal composite powders.
Because changes in travel speed affect heat input, it is important to be careful when welding heat sensitive materials such as aluminum. Faster welding will reduce heat input and prevent problems such as burnout. Multi-pass welding of thick materials may require lower travel speeds to fill each pass and provide good grain refinement.
Movement speeds that are too slow can result in overheating, a wide weld, and poor penetration, while movement that is too fast creates a narrow weld with insufficient weld bead fit. It is important to maintain a constant pace for a given weld.
The most used shielding gas, whether argon or carbon dioxide (CO2), has an impact on weld performance and welding performance. 100% CO2 shielding gas allows thicker material to penetrate deeper into the weld, but generally has less arc stability and creates higher levels of spatter. Adding argon to CO2 helps create aesthetically pleasing welds with less spatter. A high argon shielding gas mixture creates welds with higher tensile strength and yield strength, but less ductility. High levels of CO2 in the mixture increase ductility and fracture toughness but decrease tensile and flow strength.
Just as voltage and WFS affect welding transfer modes, so does shielding gas.
For example, short circuit welding can be performed with solid wire and metal core wire using a mixture of 75% argon and 25% CO2. Flux cored ball welding in gas shielding requires 100% CO2, and at higher voltages, metal powder wire can be paired with 80% argon and 20% CO2 to weld thicker materials in spray mode.
How to make it work
For example, when welding ½» a thick mild steel such as A36 with about 250 amps is a good target and provides sufficient root splicing in most cases. The use of a 90% argon/10% CO2 gas mixture allows welding in spray mode at 26 to 28 V and approximately 375 to 420 IPM WFS.
Maintaining the right variables helps make the process cost-effective, control performance and produce reliable welds, Artem Komarov concluded.