A new high-speed observation system for evaluating the spark location in WEDM of Inconel 718

Abstract

Abstract Wire electrical discharge machining (WEDM) is a good machining method for nickel-base superalloy, which is a key material in aero-engine, rocket engine and nuclear reactor. Experimental data indicate that the spark location along the thickness direction is usually uneven in WEDM. This phenomenon will be harmful to the usability and reliability of the parts machined by WEDM, especially in aerospace. However, the spark location is very difficult to observe directly with high precision due to the narrow cutting kerf. In view of this situation, a new high-speed observation system is proposed to evaluate the spark location during the continuous discharge process for the first time. The discharge spark, in turn, passes through heat-resistant glass, optical filter, focusing lens and digital high-speed videocamera. A series of image processing methods and centroid methods are utilized to acquire the spark location in this system. It can be observed that the number of discharge sparks of all regions in decreasing order is: middle region, lower region and upper region. The maximal standard deviation (St) of spark location can reach up to 0.137. Thereafter, a group of discharge experiments are carried out to analyze the relations between the process parameters and spark location evenness. An optimal combination of process parameters for even spark location is obtained, which can produce a standard deviation (St) of spark locations as low as 0.039. Eventually, the relation between spark location and machining characteristics is also illustrated. Ra can be decreased by 32.6% without reducing machining efficiency based on the process parameter optimization for even spark location.