Welding
Polarity by process
In short
DCEN, DCEP or AC by process, metal and consumable.
The three connections
DCENElectrode negative, work positive (DC−, “straight”)Heat goes mostly into the work: penetration, cool electrode. TIG on steels, stainless, copper, titanium.
DCEPElectrode positive, work negative (DC+, “reverse”)Solid-wire MIG/MAG, most covered electrodes and gas-shielded flux-cored wires.
ACAlternating currentThe EP half cycle strips the oxide, the EN half penetrates. TIG on aluminium and magnesium.
Usual connection by process
| Process | Polarity |
|---|---|
| 141 TIG steel, stainless, copper, titanium | DCEN |
| 141 TIG aluminium, magnesium | AC |
| 131 / 135 MIG-MAG solid wire | DCEP |
| 136 gas-shielded flux-cored (E71T-1) | DCEP |
| 114 self-shielded flux-cored (E71T-11) | DCEN |
| 111 basic electrode (E7018, E 42 x B) | DCEP (or AC if rated) |
| 111 cellulosic electrode E6010 | DCEP |
| 111 rutile electrode E6013 | AC, DCEN or DCEP |
The consumable datasheet rules: some flux-cored wires and electrodes need the opposite of this table.
Tungsten electrodes (ISO 6848)
| Code | Painted tip | Use |
|---|---|---|
| WP | Green | Pure tungsten, AC aluminium |
| WC20 | Grey | Cerium, DC and AC, low and medium current |
| WL15 | Gold | Lanthanum, DC and AC |
| WL20 | Dark blue | Lanthanum, DC and AC, replaces thoriated |
| WZ8 | White | Zirconium, AC aluminium |
| WT20 | Red | Thoriated, slightly radioactive: avoid |
Sources
- TWI : quelle polarité pour l’électrode enrobée ? : FAQ MMA (link)
- SpawBaza : AWS A5.1, courant par type d’enrobage : 4e chiffre : enrobage et courant (link)
- Miller : équilibre AC en TIG aluminium : Demi-ondes EP (décapage) et EN (pénétration) (link)
- Lincoln Electric : fil fourré autoprotégé E71T-11 : Fiche Powercraft T-11, DCEN (link)
- EWM : codes couleur des électrodes de tungstène : ISO 6848, tableau des oxydes (link)
Tools · Welding
Heat inputHeat input in kJ/mm (EN 1011-1) from current, voltage and travel speed.Carbon equivalent and preheatCE (IIW), CET and indicative preheat temperature (EN 1011-2, method B) with validity range check.Shielding gasRecommended gas (ISO 14175 class) and flow in L/min by process, material and wire diameter.Back purgeVolume to purge between dams, pre-purge time and gas use to shield the root side.Welding settingsCurrent, voltage, wire or electrode, gas and polarity by process, material, thickness and position; dimensioned joint preparation and passes.Weld shrinkageIndicative transverse and longitudinal shrinkage of a butt joint, with pre-setting advice.Filler metal weightJoint section (V, X, fillet), deposited weight and filler weight to order by process.Weld defect diagnosisTick what you see at the arc, in the pool and on the bead: ranked likely causes and remedies (TWI).ISO 5817 criteriaPermitted limit of an imperfection by quality level B, C or D, and verdict on the measurement (ISO 5817:2023).Weld pass layoutGroove area, number of layers and passes, numbered welding sequence sketch.Dissimilar metal weldingFiller metal to join two different metals (steel, stainless, duplex, nickel, aluminium) and precautions.