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Flood-weldingSkill to Salvage Forging Dies.SOLUTIONS with Effective, Practical Advice
Flood-welding includes a set of processes identified by their exceptionally high deposition rate. It can reach up to 14 kg/h (30 lb/h) and even more in certain cases. They are used to repair and recondition defective or worn out forging dies. Reclaiming and returning to service repaired dies, besides the time gain vs. purchasing new sets, provides more economic operation. High deposition rate is achieved using large size consumable electrodes in one of the possible processes selected for the application.
Such large size electrodes, as used almost exclusively for Flood-welding, require high currents and develop much heat. Special fixtures are required for protection, to keep the welder removed from the elevated temperature, by enabling electrode manipulation from a suitable distance. Forging dies may be built of low alloy steel like AISI Type 4350 or of Tool steel like AISI Type H-13, a type of air hardening heat resistant hot work steel. Before performing Flood-welding repair all cracked and worn out areas must be removed.
Carbon arc gouging is the process usually employed after the dies have been suitably preheated in a furnace. Attention must be exerted to make sure that sound surface has been reached. When advisable two different filler metals can be used. The first one, for the deepest parts, should be selected to provide ductility and toughness. The material for the superficial application could be one of the available heat and wear resistant filler metals. Preheating of the whole die, usually to be performed in a suitable furnace, is essential to successful Flood-welding repair. Due to the large mass of molten weld metal present at any given time in the die undergoing repair, the use of ceramic blanketing is necessary to reduce the cooling rate and to keep interpass temperature within the required limits. After solidification but while the weld is still hot, the Flood-welding slag has to be removed and manual peening is applied. This is done using a pneumatic hammer with a blunt tool to reduce residual stresses. Once the required amount of weld metal has been applied, a process that may last many hours, procedures for uniform, low cooling rate after welding must be applied. The procedure may require reheating in a furnace to 540 °C (~1000 °F) to reduce local thermal gradients, and slow cooling to room temperature for air hardening the tool steel.
Note: - Air hardening tool steels owe their capability to composition, that permits the development of acceptable hardness even after slow cooling in air. The massive dimensions of dies and other tools do not allow rapid cooling. Finally post weld heat treating for stress relieving and tempering must be selected according to the materials involved and must be applied with care. Correct heat treating is the essential factor for successful Flood-welding. Experience will suggest the most suitable electrode selection, depending on the base metal and on the service that the reclaimed die has to sustain. When professionally performed, Flood-welding reduces costs, improves turnaround time and keeps the forging industry competitive.
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