The choice of welding wire is an important factor for success when welding different pieces together, but it is still necessary to know the relationship between the parameter feed and performance.
When the wire speed (parameter feed) is set incorrectly, we can have a weld that looks good but actually has under- or over-penetration, which is a problem. On the contrary, when the speed (and therefore the electrical current) is adequate, the weld will look good and be mechanically good.
In this article we assume that the reader knows the MIG welding technique beforehand, that the parts to be welded are properly prepared and clean, that the equipment is appropriate for the welding to be attempted, and that the electrode and gas have been chosen. appropriate (if applicable).
Choosing the correct welding wire feed speed
We know that the vast majority of MIG machines are constant voltage (CV), so this is not a parameter to consider. We also know that the correct choice of electrode diameter and material can be established according to the material by means of pre-designed tables. Finally, we know that the ideal is to reduce the speed to its minimum possible expression without affecting the welding.
Each welding equipment will have its own parameters since there are no two welders that give the exact same output power; it is still possible to get values close enough to get good results the first time, and good performance. From there it will be a matter of experimenting with each combination of material and welding wire.
First it is necessary to measure the thickness of the pieces to be joined. As a general rule, for every 25 hundredths of a millimeter (0.25 mm) it is necessary to increase the current by 10 amps. Please note that the thickness is calculated for parts without chamfers or chamfers.. If parts have been prepared with bevels (V cuts), halve the thickness of the part.
Then the coefficient A is determined according to the diameter of the welding wire; this coefficient A will be multiplied by the amperage, and the result will give us the necessary speed of the wire, in millimeters per minute. The following table provides some examples.
|Wire diameter in mm||Coefficient A||Speed, in cm/min, for 3.175 mm plates||Speed, in cm/min, for 10 mm plates|
Problems derived from the wrong choice of welding wire feed
A good weld stands out for its appearance and for the penetration in the material, appreciable when making a cut in section. Bad ones, on the other hand, will look too wide (if the feed speed is too high) or too narrow (if the feed speed is too low).
By applying little voltage we do not achieve a good working temperature, so the welding will be cold, and will not penetrate properly. Conversely, excessive tension will also cause excess temperature, and the solder will appear spattered and spattered. In both cases there will be no consistent penetration through the metal.
Let’s go on to see the problems derived from the two speeds that we handle when welding: the feed of the welding wire, and the advance of the torch on the seam.
If we apply too much speed to the wire feed, in addition to wasting it and causing frequent jams in the mouth of the torch, we will have a beaded weld, too cylindrical; This causes there to be excess filler material, which must then be discarded, thus wasting welding wire.
If we apply a low speed we can have problems with the melting of the wire in the mouth of the torch; but if this does not happen, the seam will be poor, too flat and without penetration, with side splashes.
Ultimately, insufficient travel speed will result in a tight, wide weld with excess material on top. Excessive feed rate will produce a narrow weld that is too small and will not give the filler an opportunity to melt and penetrate properly.
Good practices when welding
The table we saw earlier should be taken as a general guide. The values, of course, will vary according to the material of the pieces to be welded, the material of the wire, the advance speed of the torch and will even vary according to the voltage and even the inert gas that we use.
Getting the most out of welding wire is more of an art than a technique that can be replicated in any workshop or factory. Each operator will know how to find the ideal welding parameters with practice, so it is always recommended to keep a notebook where the parameters are written down together with the results obtained.
By making use of the table provided in this article, the operator will be able to obtain the approximate speed and amperage parameters; From there, and depending on the machine used —some automatically manage the working voltage, while others allow it to be adjusted manually— the feed speed can be fine-tuned until it reaches the best possible value.
Although it seems incredible, it is also important to take into account the direction in which the welding will be carried out; welding from right to left is not the same as welding from left to right. An experienced welder will always try —if he is right-handed— to do it from right to left, since this achieves a neater bead and greater penetration of the filler material.