While welding generally involves joining materials to each other, overlay welding is a welding method that applies welding characteristics as a surface treatment technology. Purposes for which it is used include surface modification and shape restoration (repair). Coating (i.e. overlaying) only the surface of an item with a suitable metal makes it possible to improve performance more cheaply than by making the entire item out of an expensive metal. Moreover, by repairing an item with a damaged (e.g. corroded or worn) surface using overlay welding, it is possible to use the item repeatedly. As overlay welding can produce thicker layers than thermal spraying or plating and because it creates a metallurgical bond between the base metal and the overlay, it can provide high durability and significant surface modification effects.
OVERLAY WELDING METHODS
Shielded metal arc welding
- The most common welding method.
- Employs rods as weld material.
- Core wire covered by coating material that adds special elements to weld metal.
- Weld metal protected by slag created during welding.
- Mainly used with ferrous materials.
CO2 WELDING (carbon-dioxide-gas-shielded arc welding) - MAG WELDING (Metal Active Gas welding)
- As wire is used for the weld material, continuous welding is possible. For this reason, the technique is sometimes referred to as semi-automatic welding.
- During welding, the shield gas (carbon dioxide gas or a mixture of argon and carbon dioxide gas) atmosphere protects from oxidation.
- Weld materials include solid wire, metal-cored wire, and flux-cored wire.
- Often used with ferrous materials.
MIG WELDING (Metal Inert Gas welding) - TIG WELDING (Tungsten Inert Gas welding)
- Also referred to as inert gas welding.
- During the welding process, the area to be welded is shielded by an inert gas (helium, argon).
- MIG welding uses the same mechanism as semi-automatic welding.
- TIG welding uses a tungsten electrode to generate an arc. The electrode is non-consumable, and the weld material is supplied externally (inserted into the arc) during welding.
- Often used with non-ferrous material also non-ferrous materials.
SUBMERGED ARC WELDING
- Welding is performed when the arc is submerged in the flux.
- Submerged arc welding comprises the union melt method, which uses wire as the weld material, and the band arc method, which uses hoops.
- Like shielded metal arc welding and semi-automatic welding, special elements are added using flux, and the method is used for all types of alloy steel.
- As welding uses a large current and employs thick-gage wires and hoops (steel bands) as weld materials, submerged arc welding is notable for its high efficiency.
PTA WELDING (Plasma Transferred Arc welding)
- This plasma arc method enable overlaying of hard complex carbide alloys, which have conventionally been difficult to weld.
- Like TIG welding, an arc is generated from a non-consumable tungsten electrode and welding is performed with flux supplied externally into the arc.
- A main feature of PTA welding is that the weld material is a powder. The method has the following benefits:
(1) Material powders can be blended to create original flux for easy overlay welding
(2) Allows welding of hard brittle materials such as complex car bide-metal alloys, which are difficult to shape into weld mate rial forms like wire and rods
OVERLAY WELDING MATERIALS
OSAKA FUJI Corporation deals with various general materials, but is mainly involved with welding the materials indicated below. We are also happy to be contacted regarding the welding of materials other than those indicated here. We handle everything from the welding test stage to commercialization.
Main weld materials handled by OFIC
Selection of main weld materials handled by OFIC