What is Electrode Extension (Stickout)?
Electrode extension or also called stick-out length or stick-out distance refers to the length of the welding wire that extends past the contact tube as shown in the below figure. This is the area where preheating of the welding wire/ filler wire occurs due to electric resistance. It controls the dimensions of the weld bead since the length of the filler wire extension affects the burn-off rate.
What is Contact-tip-to-work distance (CTWD)
Contact tip to work distance or CTWD means the distance from the contact tip to the workpiece as shown in the above figure. The right time to accurately check the contact-tip-to-work distance is before the start of the weld or programming the robot, and you can take a physical measurement before you strike the welding arc. Once the arc is struck, arc length is measured by voltage, and electrode extension can be measured by resistance in the circuit or with sight. When people use the term contact-tip-to-work distance, they often mean the sum of arc length and electrode extension.
The contact tip-to-work distance, because of its effect on the wire extension, affects the welding current required to melt the wire at a given feed speed. The figure below shows the extent to which the welding current requirement can vary with tip-to-work distance. Basically, as the tip-to-work distance is increased, the amount of I2R heating increases, and the welding current required to melt the wire is decreased. The converse is also true.
Importance of electrode stick out
The basic control setting for low conductivity electrode metals is very much dependent upon the electrode stick out. Variation in electrode stick out results in a change in the electrical characteristics of the balanced system, as determined by the resistivity of the electrode length between the contact tip and the arc (See Fig. 19). In essence, as the contact tip-to-work distance is increased the I2R heating effect is increased, thus decreasing the welding current (I) required to melt the electrode (in effect, increasing the deposition rate for a given current level). Conversely, as the contact tip-to-work distance is decreased, the I2R effect is decreased, thus increasing the welding current requirements
for a given wire feed speed (in effect, decreasing the deposition rate for a given current level). This point emphasizes the importance of maintaining proper nozzle-to-contact tip distance in welding gun maintenance, as well as the importance of maintaining good welding techniques through proper gun positioning.
Electrode stick-out is a parameter which makes it possible to change welding energy without changing the quantity of deposited metal delivered to a welding puddle. It is particularly important when welding with flux-cored wires. Knowledge of its impact on welding parameters and formation of weld geometry is very useful when making fillet welds of small thicknesses. Understanding the mechanism of electrode stick-out’s impact on weld geometry helps to avoid many problems when welding.
Electrical stick out the distance for short circuit transfer mode
Stick-out length for shirt circuit mode shall be kept low as the distance need to be kept minimum to allow a short circuit of the welding wire with the workpiece. a stick-out length of 6- 13 mm gives good results in GMAW short circuit metal transfer mode.
Electrical stick out the distance for Spray transfer mode
Stick-out length for spray mode requires to be kept longer as wire melts without any short circuit. a stickout length of 19- 25 mm gives good results in GMAW spray transfer mode as shown in the below figure.