Electrospark deposition (ESD) is a pulsed micro-welding process that is used for small scale and precision repair of high value worn or misfabricated components. Electrospark deposition is also known as spark hardening, electrospark toughening, electrospark alloying, pulsed fusion surfacing and pulsed electrode surfacing. Principal industrial applications include repair of defects in casting moulds and injection moulding tooling.
Electrospark deposition systems contain a capacitor-based power supply that produce short duration high current pulses through a rotating wire consumable electrode. The consumable electrode material is deposited onto the work piece by means of electric sparks in a manner reverse to spark erosion. In the electrospark deposition process, the electrode is the anode and the work piece is the cathode.
When the capacitor energy is released, the direct current generates a plasma arc at a high temperature (8000 to 25,000°C) between the tip of the electrode and the work piece. The plasma arc ionizes the consumable and a small quantity of molten electrode material is transferred onto the work piece. The transfer of material is rapid and the self-quenching is extremely fast.
Based on short duration, high current pulses, the process imparts a low heat input to the substrate material, resulting in little or no modification of the substrate microstructure. Therefore, the process offers an advantage over fusion welding processes (including arc, laser and resistance welding) when repairing materials that are difficult to weld because of poor heat affected zone properties (e.g. liquation cracking, high hardness, low toughness). Components can be restored to their original dimensions, because with such low heat input the bulk substrate material remains near to ambient temperature with thermal distortion, shrinkage and high residual stresses avoided. Moreover, the process generates a good metallurgical bond between the coating and the substrate.
Electrospark deposition is particularly suitable for repair of small and shallow defects, but it is not appropriate for large defects, since the process is slow and the maximum thickness of the coating is about 2mm. Electrospark deposition can also be considered as a process to increase the wear and the erosion resistance of small surface areas.
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Schematic representation of Electrospark deposition