TWI Frequently asked questions
by Richard Smith
Manual metal arc (MMA) welding (known as SMAW in the USA) is by far the most popular method for welding cast irons. In general, the best results are obtained when welding with low current and the lowest practical heat inputs. ManyMMA consumables for cast iron welding have special coatings to minimise arc penetration.
Less penetrating arcs, and low heat input levels can be achieved with metal inert gas (MIG) and metal active gas (MAG) welding (referred to as GMAW in the United States), especially if the dip transfer process is used.
For depositing cast iron fillers, oxy-acetylene welding provides the best control over weld metal and heat affected zone properties.
Advantages and disadvantages of the main options are:
| Process | Advantages | Disadvantages |
|---|
| MMA | Versatile, flexible, with a wide range of consumables especially designed to counter the disadvantages of the process | High penetration arc leads to high weld metal dilution by the casting |
| MIG/MAG | Easily mechanised, low penetration short circuit transfer mode | Less versatile than MMA |
| Oxy-acetylene - fusion | Cast iron fillers - good colour match, machinable, slow cooling rates | Wide HAZ, though relatively soft. Occasional distortion due to a large volume of heated material |
| Non-fusion - bronze welding | No dilution of the weld metal, and minimal HAZ hardening due to low melting point fillers | Poor colour match and high temperature properties. Low strength WM and interface |
See also Welding of cast irons - a guide to best practice, from which this FAQ is extracted.
