Performance study of various tool materials for electrical discharge machining of hot pressed ZrB_2

摘要

Purpose - This study aims to explore the machinability of ZrB_2 using electrical discharge machining (EDM) with different tool materials. Design/methodology/approach - The workpiece for this study was fabricated through powder metallurgy compaction method. The disc is machined using diamond load grinding to have parallel surfaces, then, 2 mm diameter holes are machined on the disc using EDM spark erosion machine with different tool materials (graphite, aluminium, tantalum, niobium, copper, brass, silver, tungsten and titanium). Roundness, geometry of hole, and diameter of the hole at different diametric planes, surface roughness (SR), material removal rate (MRR), tool wear rate (TWR), taper angle and recast layer (RCL) thickness are measured. The photographic analysis of tools, holes in the top view, bottom view and sectional view. SEM analysis was conducted to study the recast layer. Desirability function analysis was employed to rate the performances of tools. Findings - A new theory is developed which relates recast layer thickness with melting point and thermal conductivity of the tool materials. Machining of ZrB_2 by EDM is feasible; graphite is identified as the best tool. Recast layer thickness of the machined surfaces are indirectly proportional to the product of melting point and thermal conductivity of tool. Ablation behaviour of ceramic workpiece lead additional material losses in the tool. Originality/value - Extremely high strength and hardness of ZrB_2 due to the coexistence of strong covalent and metallic bond make mechanical machining very difficult or even impossible. No machinability studies were conducted previously on ZrB_2 using EDM; this work reveals machinability study of ZrB_2 with different tool materials.