Zhuojin Pipe Fitting Co., LtdThree-Channel Electric Direct-Drive Synchronous Pressure Control System for Diamond Synthesis Presses
Literature Overview
This paper by Xu Hong and colleagues from China Jiliang University, published in Machine Tools and Hydraulics in 2019, presents an experimental study on a three-channel electric direct-drive synchronous pressure control system designed for synthetic diamond production presses. The research was supported by the National Natural Science Foundation of China (Grant No. 61640314) and the Zhejiang Provincial Natural Science Foundation (Grant No. LY15F030012). The work addresses a long-standing challenge in high-pressure synthesis: pressure pulsation during the hold-pressure stage, which degrades diamond crystal quality and yield.
Technical Background and Problem Statement
In the manufacturing of synthetic diamond using six-anvil and two-anvil presses, the hold-pressure stage is critical for crystal growth. Traditional hydraulic systems employ auxiliary pumps to maintain constant pressure, but these inevitably introduce pressure pulsations caused by pump displacement fluctuations and valve response delays. These pulsations, typically in the range of 0.1–0.5% of the set pressure, can cause nucleation irregularities and crystal defects.
The proposed system replaces conventional valve-controlled or pump-controlled hydraulic circuits with a distributed electric direct-drive architecture, where three independent drive channels provide synchronous pressure compensation during the hold-pressure phase.
System Architecture and Control Strategy
The three-channel direct-drive system operates on the following principles:
| Parameter | Conventional Hydraulic System | Three-Channel Electric Direct-Drive System |
|---|---|---|
| Pressure regulation method | Auxiliary pump with proportional valve | Three independent electric motors driving direct-drive actuators |
| Response time | 50–200 ms | 5–20 ms |
| Pressure pulsation amplitude | 0.1–0.5% of set pressure | <0.05% of set pressure |
| Energy consumption during hold stage | High (continuous pump operation) | Low (motors only active during compensation) |
| Control complexity | Moderate (single-loop PID) | High (three-channel coordination and synchronization) |
| Wear and maintenance | High (seals, valves, pumps) | Low (electric motors with minimal wear) |
The control strategy involves real-time pressure feedback from high-precision pressure transducers, with each channel independently computing its compensation signal based on a distributed control algorithm. The synchronization among the three channels ensures that the total pressure contribution remains constant while allowing each channel to adapt to local pressure deviations.
Experimental Results and Performance Evaluation
The experimental validation demonstrates that the three-channel system achieves pressure stability within ±0.03% of the set pressure during the hold stage, representing a significant improvement over the conventional auxiliary pump method. The system also eliminates the energy waste associated with continuous hydraulic pump operation, reducing power consumption by approximately 40% during the hold phase.
From a diamond synthesis perspective, the reduction in pressure pulsation translates directly to improved crystal quality. Studies have shown that pressure fluctuations above 0.1% can cause lattice distortion in growing diamond crystals, leading to higher defect densities and reduced optical quality. The sub-0.05% stability achieved by this system opens the possibility of producing higher-grade synthetic diamonds with fewer inclusions.
Engineering Significance and Broader Applications
While the immediate application is synthetic diamond production, the three-channel electric direct-drive pressure control concept has broader implications for other high-pressure processes in materials engineering and manufacturing. Applications in the steel pipe and fitting industry may include:
- Precision forging of complex pipe fittings where pressure uniformity is critical for dimensional accuracy and microstructure control.
- Hydrostatic extrusion of pipe blanks where pressure stability affects the uniformity of the extrusion ratio and wall thickness.
- High-pressure heat treatment processes for alloy pipes where pressure fluctuations can cause uneven phase transformation.
The key engineering challenge in adopting this technology is the cost of high-precision electric actuators and the complexity of the multi-channel synchronization control system. However, for applications where product quality is directly linked to pressure stability, the investment is justified by reduced scrap rates and improved yield.
Study Insights and Reflections
The paper represents a paradigm shift from hydraulic to electric direct-drive actuation in high-pressure applications. The elimination of hydraulic valves and pumps removes a major source of energy waste and mechanical wear, aligning with the broader industry trend toward electrification of manufacturing processes. The three-channel architecture provides redundancy and allows for graceful degradation if one channel fails, which is an important consideration for safety-critical high-pressure operations.
A potential area for further investigation is the integration of this pressure control system with process monitoring and adaptive control, where real-time measurement of crystal growth parameters could feed back into the pressure control loop for closed-loop optimization of diamond synthesis conditions.