Journal of Manufacturing and Materials Processing

Due to recent developments across the aerospace, power generation and defense sectors, the demand for flat-surfaced components with extremely high surface quality is rapidly increasing. In this regard, although abrasive machining processes often produce fine, contaminated swarf that is frequently relegated to landfill, these processes remain critical for the engineering sector. Motivated by increasing sustainability and circularity pressures, this narrative review examines the current state of the art in recycling and repurposing the chips, tooling and cutting fluids that are typically generated or consumed within grinding processes. In doing so, a number of methodologies for extracting useful materials from swarf slurries are identified, including pyrometallurgical routes (applied successfully to Ni–Co alloys, for example), hydrometallurgical strategies (e.g., iron leaching from ferrous swarf) and, in the case of non-metallic materials such as CMCs and CFRPs, chemical processing methods. Various means of separating abrasive constituents and removing contaminants from grinding swarf are also highlighted, within which centrifugation and heat treatment are found to be particularly useful for non-ferrous materials such as titanium alloys or composites, whilst ferrous materials are largely magnetically separated. Prospective applications for spent abrasive tooling are also explored, including reuse as shot, waterjet machining feedstock, road surface additives, or mortar in the context of cement production. Likewise, heat- and radiation-based strategies for prolonging cutting-fluid life are highlighted, and their associated sustainability benefits and limitations discussed, despite ultimate disposal still being relegated to fuel usage or landfill. Ultimately, this review identifies the scarcity of grinding-specific recycling process data and highlights the need for robust, publicly accessible recycling strategies for novel material systems.

Energy density is a common but often inadequate parameter for predicting properties in laser additive manufacturing, as it fails to capture complex energy absorption dynamics. This study introduces energy utilization efficiency as a governing factor for melt pool characteristics in laser directed energy deposition (LDED) of 316L stainless steel. We demonstrate that at a constant energy density, energy utilization efficiency varies significantly with process parameters, ranging from conditions that cause lack-of-fusion to those that promote porosity. Experimentally, increasing energy utilization efficiency under constant energy density (90 J/mm) led to a five-fold increase in melt pool depth and a doubling of its area. This shift in energy utilization efficiency directly influenced tensile properties, with samples at moderate energy utilization efficiency achieving optimal yield strength (~428 MPa), ultimate tensile strength (~583 MPa), and elongation (~51.6%). Quantitative strengthening analysis revealed that dislocation strengthening contributed approximately 60% of the total yield strength, but its contribution decreased with excessive energy utilization efficiency due to grain coarsening. To overcome the limitations of energy density, we propose normalized enthalpy as a predictive design parameter. It shows a strong linear correlation with melt pool width, depth, and area, effectively integrating both process inputs and material thermal response. This work provides a fundamental insight into energy–material interactions and offers a physics-enhanced predictive tool that complements conventional energy density metrics for optimizing the LDED process.

This study evaluates the performance of a copper-based metal matrix composite (Cu-MMC) brake pad fabricated by powder metallurgy for high-speed railway braking applications. The material was produced via homogeneous powder mixing, compaction at 650 MPa, and sintering at 950 °C for 2 h to promote densification and metallurgical bonding. The fabricated Cu-MMC exhibited densities of 5.71–5.98 g/cm³, porosities of 5.85–10.1%, and hardness values of 62–73 HV, indicating effective microstructural control. Tribological performance was assessed using a brake dynamometer at an equivalent speed of 160 km/h and a contact pressure of 0.95 MPa. The composite demonstrated a low specific wear rate of 0.11–0.14 cm³/MJ, meeting the TJ/CL 307-2014 standard for high-energy braking. Surface analysis revealed stable frictional behavior dominated by oxidative–abrasive, adhesive, and delamination wear mechanisms. Thermal evaluation showed a maximum operating temperature of 225–235 °C, below the softening temperature of copper, confirming adequate thermal stability.