To enhance the performance of HPHT Hydraulic Cubic Press and improve the quality of diamond single crystals and the acceptance rate of polycrystalline products, several methods of equipment modification can be implemented.
1. Improving Host Machine Repeatability
Problem and Background The company's presses are hinge-type HPHT Hydraulic Cubic Press. Before modification, the six hinge beams in the press's main unit were connected using straight pins, and there were gaps between the pins and holes. These gaps primarily originated from three aspects: 1) installation fit tolerances; 2) wear from long-term use and maintenance/disassembly; and 3) elastic and plastic deformation of the hinge beam inner holes when the press was overpressured. These gaps caused the working state of the main unit (such as the initial position of the top hammers) to potentially differ with each working cycle, leading to unstable quality of synthesized composite inserts and poor repeatability for batch products. Data from the 8# press before modification showed that the displacement of each hinge beam was uneven, with a large difference between the maximum and minimum displacements (0.22mm), and they did not return to zero each time, indicating poor structural rigidity and plastic deformation in the main unit. This non-uniformity in pin/hole fit across the 12 sets of pins and holes on the hinge beams resulted in both elastic and plastic deformation under force.
Modification Method The original straight pins were replaced with elastic non-clearance tapered pins.
Advantages of Tapered Pins
1.No-clearance connection: When the end screw tightens the inner pin shaft, the outer pin shaft expands, creating an interference fit between the pin shaft and the pin hole, achieving a "no-clearance" connection.
2.Reduced deformation: Multiple grooves are milled on the outer pin shaft. When the screw is tightened, the force-bearing area of the pin hole increases, reducing the force per unit area and significantly slowing down the elastic and plastic deformation of the pin hole.
3.Easier maintenance: The original outer diameter of the outer pin shaft is 0.5mm smaller than the pin hole. During installation, it is in a relaxed state and can be easily inserted into the pin hole. For disassembly, simply loosening the screw allows the outer pin shaft to return to its original size, making it easy to pull out. This simplifies and lightens the work of disassembling the pins, freeing maintenance personnel from strenuous, heavy hammering tasks.
Modification Effect The actual use of these elastic non-clearance tapered pins showed significant effects. After modification, the 8# press exhibited more uniform hinge beam displacements, a smaller difference between maximum and minimum displacements (0.10mm), and the ability to return to zero each time. This indicates that the tapered pins eliminated some of the gaps between pins and holes. The hinge beams now only undergo elastic deformation without plastic deformation under stress, thereby greatly enhancing the structural rigidity of the main unit. This leads to better repeatability during equipment operation and stable product quality.
2. Improving Control System Accuracy
Problem and Background Some of the company's presses originally used relay-based control systems with constant voltage heating control, which were outdated and had low precision.
Modification Method In collaboration with a company in Guilin, the original pressure and heating systems were modified.
Features and Improvements of the New Control System
1.Pressure Control: The new system utilizes small pump variable frequency dynamic pressure compensation, achieving a pressure steady-state control accuracy of ±0.05 MPa, significantly better than the old presses' ±0.2 MPa accuracy.
2.Heating Control: It offers two heating control modes: non-constant power and constant voltage. Theoretically, the non-constant power heating control can greatly improve the stability of the synthesis block temperature, with a steady-state control accuracy of ±50W. The constant voltage steady-state control accuracy reaches ±0.01V, compared to the old presses' ±0.08V.
3.Operation Interface: The adoption of a touch display screen provides operators with intuitive displays, precise process adjustment data, and convenient operation.
Modification Effect The control system modification led to improved stability and accuracy of synthesis pressure and temperature, which in turn promoted product quality improvement.
3. Reducing Equipment Failure Rate
Problem and Background In the operation of diamond presses, a significant proportion of faults were found to be caused by solenoid coil burnout.
Modification Method
1.Solenoid Replacement: The original M FJ 1-415 AC dry-type solenoids were replaced with the latest M FB 1-5.5 AC wet-type solenoids. These wet-type solenoids feature high insulation strength.
2.Control System Upgrade: The control system adopted programmable logic controllers (PLCs) – single-chip microcontrollers – manufactured by Omron Corporation of Japan.
Modification Effect
1.After more than half a year of use, the wet-type solenoids have not experienced any coil burnout, ensuring long-term normal operation and reducing equipment failure rates.
2.The adoption of PLC control reduced fault points and enabled automatic display of fault causes and alarms. Consequently, the failure rate significantly decreased, maintenance time was reduced, and equipment utilization increased.
3.The overall effect was improved work efficiency, reduced loss of synthesis blocks, and thus an increased product acceptance rate.

After the modifications, the phenomenon of solenoid coil burnout was reduced, the equipment failure rate decreased, maintenance time was shortened, and equipment utilization increased.
In summary, by adopting measures such as improving the repeatability of the main unit, enhancing the accuracy of the control system, and reducing the equipment failure rate, the overall performance of the hexagonal anvil hydraulic press can be significantly improved, leading to better performance of diamond single crystals and a higher acceptance rate of polycrystalline products.