Electro-Spark Deposition Machine Design, Physical Controls and Parameter Effects

Abstract

Electro-spark deposition (ESD) is a micro welding process characterized by short duration high current pulses, often generated by capacitors, arcing between a conductive electrode and substrate. The high intensity, low net power process results in metallurgical bonded coatings or alloyed layers with practically no heat affected zone. The unique characteristics of this process facilitate the bonding of high ceramic content cermet materials, as well as heat sensitive high value materials. The process is used to repair components where low heat input, low distortion depositions are required, as well as apply coatings for the improvement of corrosion resistance, tribological properties and local alloy content. The objective of this study was to evaluate the effects of ESD power supply designs on the control of ESD process parameters. Electrical power supply parameters such as voltage, capacitance and voltage were examined, along with physical parameters including; application force, movement speed, movement pattern and shielding gas were explored. Three different custom power supplies were developed to encompass performance improvements reported in previous studies and compare advanced circuit and parameter behavior against the traditional ESD machine. This was done by analyzing the possible voltage and current signals recorded from the power supply with a data acquisition system. The electrical signals were used to compare advances in voltage, capacitance, frequency and pulse sequence control. Key parameters were identified and implemented in a universal power supply as a simplified user interface. A wider range of electrical parameters were tested in order to meet the needs of a wider variety of material pairings. The new universal ESD power supply was tested to determine the parameter effects on the coating quality of titanium carbide nickel sintered electrodes deposited on copper substrates. Pulse voltage and frequency were identified as having the most significant effect on the coating thickness and defect formation. The deposition experiments for relating the electrical parameters to coating quality revealed errors in the coating measurements caused by variations in the ESD physical parameters. A computer numerical controlled machine was developed with a force feedback system to control the physical parameters. Using this system the effect of controlled deposition patterns, movement speed, application force, and argon shielding gas was tested against the effects of the ESD voltage and frequency. The experimental data concluded that the physical controls paired with the management of electrical parameters improved the coating thickness, and lack of defects. Implementation of a physical control system including movement and force control would be beneficial for future experiments and for some industrial applications. The combined electrical power effects of varying the voltage, frequency with the use of shielding gas resulted in improved coating thickness and quality. This demonstrated that testing to determine the effective parameter ranges for new applications and material pairings is integral to the deposition of thicker coatings with reductions in the typical pore, crack and oxidation defects.