The capability of machining intricate features with high dimensional accuracy in hard and difficult-to-cut material has made electrodischarge machining (EDM) process as an inevitable and one of the most popular non-conventional machining processes. In recent years, both EDM and micro-EDM processes are being used extensively in the field of mould making, production of dies, cavities and complex 3D structures using difficult-to-cut tungsten carbide and its composites. The objective of this paper is to provide a state of the art in the field of EDM and micro-EDM of tungsten carbide and its composites. The review begins with a brief introduction on the EDM and micro-EDM processes. The research and developments in electrodischarge machining of tungsten carbide are grouped broadly into conventional EDM of tungsten carbide, micro-EDM of tungsten carbide and current research trends in EDM and micro-EDM of tungsten carbide. The problems and challenges in the area of conventional and micro-EDM of tungsten carbide and the importance of compound and hybrid machining processes are discussed. A summary of the future research directions based on the review is presented at the final section.

A review on the conventional and micro-electrodischarge machining of tungsten carbide

A study on the fine-finish die-sinking micro-EDM of tungsten carbide using different electrode materials

Surface modification of Ti-alloy by micro-electrical discharge process using tungsten disulphide powder suspension

Electrical discharge machining (EDM) is an alternative shaping route for manufacturing complex component shapes of hard and brittle materials such as WC–Co cemented carbides (hardmetals). However, it results in a poor surface integrity that often leads to mechanical degradation of these materials. In this investigation, the influence of multi-pass sequential EDM on the fracture and fatigue behavior of a WC–10wt%Co cemented carbide is studied. It is compared with the behavior exhibited by a reference condition, attained through conventional mechanical grinding and polishing using diamond as abrasive. Considering that rupture is related to existing defects, either introduced during sample fabrication or induced by machining, a detailed fractographic examination is conducted to discern failure origins. The experimental findings indicate that flexural strength of WC–Co hardmetals, under both monotonic and cyclic loading, is strongly affected by EDM. An analysis of the results using a linear-elastic fracture mechanics approach allows to establish a clear connection between surface integrity and mechanical strength. Quantitative discrepancies between the estimated and the experimentally measured critical flaw sizes for all the EDM samples are rationalized through the existence of residual tensile stresses of considerable magnitude at the shaped surface. From a fatigue viewpoint, these residual stresses are even more detrimental because they imply an additional mean stress; thus, higher effective load ratio at the EDMed surface. As a consequence, fatigue sensitivity of the EDMed specimens is higher than for the reference condition. Relief of these stresses through annealing treatments is assessed and shown to be a relatively effective alternative for improving the fracture and fatigue behavior of WC–Co cemented carbides shaped by EDM.

Fracture and fatigue behavior of electrical-discharge machined cemented carbides

Influence of the composition of WC-based cermets on manufacturability by wire-EDM

The correlation between electrical-discharge machining (EDM) and surface integrity and its influence on the sliding contact response of a fine-grained WC-10% wt Co hardmetal have been studied. Different surface finish conditions were evaluated corresponding to sequential EDM as well as grinding and polishing employing diamond as abrasive. Surface integrity was characterized in detail for all conditions through scanning electron microscopy (SEM). Sliding contact response was determined through microscratch measurements using a nanoindentation system. Contrary to the results obtained from conventional hardness evaluation, the above testing technique allows discrimination of EDM effects on the contact behavior of the studied cemented carbide. The experimental results, given in terms of scratch penetration-load curves and friction coefficient, indicate that microscratch resistance increases with finer-executed EDM, up to values similar to those exhibited by the reference ground and polished condition. The findings are discussed in terms of contact damage features as related to surface integrity and intrinsic microstructural features.

E. Idañez

Papers

Influence of electrical discharge machining on the sliding contact response of cemented carbides