Monday, December 11, 2023

How to choose the coil of wire for MIG welding?

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The success of this operation and the reduction of costs due to faulty joints or subsequent repairs depend on the correct choice of the coil of wire for MIG welding. Various factors intervene: quality, homogeneity in diameter, chemical composition and correct preparation of the equipment.

In this article we will focus on the three factors that we must take into account when buying a coil of wire for MIG welding: chemical composition, diameter and cost-quality ratio.

Coil selection criteria for MIG welding

mig welding roll

There is no single criterion. If you have in mind to use the MIG welding roll on a clean surface free of grease and other contaminants, you must choose an appropriate roll for it. If, on the other hand, the surfaces to be welded will be contaminated, you will need a more expensive product that allows welding under those conditions.

There are basically three criteria when choosing the appropriate MIG welding roll: its chemical composition, its diameter and its value for money. We will see below the aspects to take into account according to each of these selection parameters.

1. Chemical composition

to. Homogeneity

It is extremely important that the chemical composition is homogeneous throughout the wire roll. Why? Simple: With a MIG welding coil whose composition does not vary along the length of the wire and the other coils, it is possible to establish optimal parameters in the machine for certain parts and operations.

Think that in this way work times, errors and, with it, operating and production costs will be reduced.

b. slag formation

look for those Wire rolls for MIG welding that contain chemical elements such as aluminum, manganese, silicon, titanium and zirconium, which facilitate the elimination of excess oxygen forming a slag that can be easily removed after the operation, since, being less dense than the material contribution, rise to the surface, from where it is possible to remove them with the use of the hammer.

c. Material

This seems obvious at first, but if you are going to weld aluminum, use aluminum wire; if you will be welding carbon steel, use the wire indicated for that material. For example, ER70S-3 and ER70S-6 wires are used to join carbon steel parts, but not stainless steel.

At the same time, ER70S-3 is used for steels that have been properly degreased and cleaned. The ER70S-6, on the other hand, can be used in those cases where this previous operation is not possible.


A roll of ER70S-6 type MIG welding wire with a diameter of 0.76mm: it allows welding carbon steel.

The wire roll ER70S-6 is more expensive than ER70S-3, but ensures higher quality in welding, due to its chemical characteristics and the greater presence of deoxidizers.

There are special wires for Weld without argon gas —or the mixture of argon and carbon dioxide—, but, in addition to being more expensive due to the inclusion of a flux core, they produce more spatter and make it difficult to correctly visualize the puddle of material, with which the weld will tend to be less reliable and neat.

wire type Applications and considerations
ER70S-6 Use with CO2 or C-25 gas (75% argon, 25% carbon dioxide).
When used with CO2, greater penetration is achieved, although the C-25 achieves less splashing.
It can only be used properly indoors, without winds.
Allows welding of thin sheets, such as 0.8mm, more easily than flux-filled wires such as E71T-GS.
E71T-GS Does not require gas.
Indicated for welding outdoors, in windy conditions.
It allows welding rusty, dirty or painted parts.
It reaches higher temperatures than ER70S-6, so it is not indicated for thicknesses less than 1.5 mm.
It should be used only with argon gases or mixtures of argon and helium.
ER5356 is stiffer, allowing for better welds and more reliable feeding.


It must be used with mixed gases argon, helium and carbon dioxide.
Allows welding different stainless steels: AISI 301, 302, 304, 305 and 308.

2. Diameter

Another important factor to take into account is the homogeneity of the diameter in the wire to weld. An abrupt variation in its size (caused by the need to join one wire to another in the manufacturing process of the roll) can cause sudden variations in the electric current, which will compromise the quality of the welding.

The following table shows the most common commercial diameters and the appropriate thickness of the material to be welded for each of them.

Thickness of the material to be welded, in mm
Wire diameter, in mm/inches
0.6/.023 0.75/.030 0.9/.035
0.8 Yes Yes No
one Yes Yes No
1.25 Yes Yes Yes
1.5 No Yes Yes
two No Yes Yes
3.25 No Yes Yes
4.75 No No Yes
6.5 No No Yes

3. Value for money

The rule of thumb is: whenever possible, buy the best quality available and choose the brands you trust. A mig welding wire low quality can mean a bad welding or, even worse: a structural failure and damage to the equipment of welding, by fusion of the wire with the torch nozzle or by jams in the feeder.

4. Presentation

While it’s a minor factor for the professional or hobbyist who will occasionally weld, for those who own a shop and MIG weld on a daily basis, the presentation of the wire to weld It is important.

If you plan to do a lot of work on a continuous basis, you may want to make an initial investment and buy a box or drum, which contains much more wire than individual coils. In this case, always keep safety in mind, and remember to unplug the appliance after working, since it is possible that the wire remains energized.

If you weld occasionally, buy the small rolls, which take up little space and, on small and semi-professional machines, allow you to install them inside.

Frequent questions

How many meters of wire for MIG welding are there in a roll of so many kg?

The answer depends on the diameter and material of the welding wire. The following table provides the length of a coil of wire based on weight, classified by the most common materials and diameters.

weight in kg
diameter in mm
Length according to material, in meters
Steel Stainless steel. Aluminum Copper
0.5 0.6 220 212 627 190
0.9 0.6 440 423 1254 380
4.5 0.6 2199 2116 6270 1903
twenty 0.6 9676 9325 27592 8374
0.5 0.75 129 124 369 112
0.9 0.75 259 249 737 224
4.5 0.75 1293 1244 3688 1119
twenty 0.75 5690 5475 16224 4925
0.5 0.9 95 91.5 271 82
0.9 0.9 190 183 541 164
4.5 0.9 950 915 2709 822
twenty 0.9 4180 4023 11919 3615
0.5 1.15 57.5 55 1640 fifty
0.9 1.15 115 110 327.5 99.5
4.5 1.15 574.5 552 1639 497
twenty 1.15 2528 2433 7210 2187.5
0.5 1.5 32.3 31 92 28
0.9 1.5 64.5 62 184 56
4.5 1.5 323.5 311 922 279.5
twenty 1.5 1422 1369 4056 1230.3

Is it possible to weld bronze?

Yes, but be careful! In Spanish, bronze is designated as different alloys of copper with one of these metals: aluminum (cuproaluminum), arsenic (arsenical bronze), zinc (brass), cobalt (bronze sun) and tin (bronze itself and bronze for weapons). There is also a polyalloy of copper with iron, tin or zinc with antimony, bismuth or lead that is used to make musical bells. In English, bronze proper is called brass, and brass, brass.

Confusion between both materials is very common, which often leads to inappropriate selection of the electrode, the method and the technique of welding.

The recommendation is to use the TIG method for these metals, although there are some mig wires that allow welding alloys such as cuproaluminium (CuAl-A2 type wires) and brass (CuZn-C type wires). For brass, use CuSi-A (silicon copper) type wires.

One option is to use the brazing technique (providing an alloyable metal to both parts), which, in the case of bronze, can be aluminium.

How do I weld galvanized?

Regardless of the base metal, the zinc coating represents a serious hazard when welding due to the gases that are produced.

For this, it is very important to have FCAW (flux-cored) type wire, which allows welding without gas, with good direct ventilation that removes any type of gas produced from the operator. The material of the wire, as always, must correspond to that of the elements to be welded.

Ideally, place a fan behind and to the side of the operator and, if possible, a fume extractor. Even with these precautions, the use of a mask is mandatory for this material.

If possible, sand the surfaces to be welded beforehand, in such a way that the presence of zinc on the surface is minimal.


The purchase must be governed in the first place by the material to be welded, and by the availability of a suitable gas cylinder (to generate the protective atmosphere around the welding). Then the diameter must be taken into account, depending on the thickness of the materials to be joined, and finally the price and presentation (reel, drum, box).

The correct choice according to this guide will allow a better welding, more reliable and durable, and more neat.

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