Machining characteristics of nickel-based alloy with positive polarity blasting erosion arc machining

Abstract

A nickel-based high-temperature alloy widely used in aerospace engines is a typical difficult-to-cut material by conventional machining processes due to its high-temperature mechanical strength and toughness. Blasting erosion arc machining (BEAM), a new type of electrical discharge machining (EDM) method, is capable of removing such materials with a very high material removal rate and a low tool wear ratio. This paper presents experimental investigations in machining characteristics and machined surface integrity of the nickel-based alloy GH4169 (similar to Inconel718) by positive polarity blasting erosion arc machining (positive BEAM). The test results imply a possibility to improve the surface integrity with positive BEAM compared with a regular negative one. In this work, a three-factor, three-level machining performance experiment was carried out to examine the effects of the machining parameters such as discharge peak current, flushing inlet pressure, and pulse duration on the machining performances of material removal rate, tool wear ratio, and surface roughness. The experimental results show that positive BEAM is capable of greatly improving the machined surface integrity. The surface roughness decreased from 274 μm (under negative polarity BEAM) down to 31 μm (under positive polarity BEAM). Additionally, fewer micro-cracks and a thinner heat-affected zone on the workpiece surface can be observed. It also reveals that by optimizing the combination of the negative and the positive BEAM, favorable machining performances of high material removal rate and finer surface roughness are possible. By utilizing the polarity effects, the machining allowance for the subsequent semi-finishing processes such as cutting can be further reduced.