Advancements in powder mixed electrical discharge machining of metal matrix composites: a comprehensive review

The potential of Metal Matrix Composites (MMCs) to provide an excellent combination of mechanical properties, specifically strength-to-weight ratio, stiffness, and wear resistance, provides substantial motivation for their use in high-performance engineering applications. The heterogeneity in MMC’s microstructure and the presence of hard reinforcement phases create significant challenges for conventional machining processes, leading to poor surface finish quality, excessive tool wear, and reduced productivity. While Electrical Discharge Machining (EDM) is commonly used for machining MMCs, it has several limitations that include low material removal rates, unpredictable discharge behaviour, rapid tool wear, and compromises to surface integrity. Powder Mixed Electrical Discharge Machining (PMEDM) is a new technique that modifies the dielectric medium using either conductive or semi-conductive powders to enhance the electrical discharge characteristics. Although there have been a number of academic investigations into PMEDM, the mechanisms involved in PMEDM-assisted machining of MMCs are still not well understood, and reported results vary significantly from one material system to another and from one set of operating conditions to another. In this systematic review the basic principles of PMEDM are examined, and the effects of the powder type, powder concentration, powder particle size, and electrical parameters (i.e., discharge current, pulse-on/off time, and gap voltage) on key performance measures including material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR) are evaluated. Additionally, surface integrity aspects such as recast layer formation, micro-hardness variations, and defects are reviewed. These aspects are generally underreported and poorly correlated to process parameters in prior literature. Additionally, the review identifies several areas where further research is needed to develop stable processes, eliminate powder agglomerations and sedimentations, establish standard optimisation techniques, and model processes, as well as to make PMEDM scalable and repeatable. Finally, by integrating relevant experimental and analytical studies, this review provides a synthesis of recent developments and outlines future research directions to develop a thorough mechanistic understanding of the PMEDM process, to establish effective surface integrity control strategies, and to enable reliable industrial application of PMEDM for machining advanced MMCs.