Precision Modification of a Two-Stage Pressure Boosting System on a Domestic Cubic Press and Synthesized of Nano-Polycrystalline Diamond

The traditional domestic hinge-type cubic presses are typically operated using limit switch for positioning, fully-open rapid hydraulic oil filling, and fixed-rate pressurization/depressurization modes. Such configurations are limited by poor six-cylinders positioning accuracy and hydraulic filling synchronization, and the pressurization and depressurization rates fail to meet the stringent requirements of ultra-high two-stage pressurization for eccentric load control and mechanical stability. In this study, systematic modification and upgrade were implemented on a domestic cubic press with 650 mm cylinders. To suppress or eliminate the floating and deformation of the frame under overpressure conditions, self-locking pin shaft was designed and assembled, and pre-compensation for frame deformation under high pressure was performed. In addition, aim at improving alignment accuracy and hydraulic filling synchronization, a dual-pump multi-mode hydraulic circuit and an equal-volume cylinder oil-filling process were built. Furthermore, a three-stage feeding method combined with an independent displacement action mode was innovatively proposed. A closed-loop control program was developed to operate in parallel with the original press control system, enabling the real-time acquisition, synchronous monitoring, and closed-loop adjustment of data sets including press operational status, oil pressure, and heating temperature. Additionally, a strategy combining proportional-integral-derivative (PID) control with precision pressure-control module components was proposed to achieve ultra-slow pressurization and depressurization. The correlation between synthesis chamber pressure and oil pressure, and the correlation between heating temperature and power were experimentally calibrated. Furthermore, the high-temperature and high-pressure (HTHP) synthesis of centimeter-sized nano-polycrystalline diamond bulk specimen was conducted. The results indicate that the optimized and upgraded domestic 650 mm cubic press is capable of synthesis large-volume samples at 15 GPa and over 2000 ℃, which significantly expands the application area of domestic cubic presses.