Three-Channel Electric Direct Drive Synchronous Pressure Control System for Diamond Synthesis Presses

Literature Overview

The paper by Xu Hong, Qian Jin, Du Zhijiang, Chen Xiai, Wang Ling, and Wang Guirong (Machine Tool and Hydraulics, 2019, Vol. 47, No. 10, pp. 1-4), funded by the National Natural Science Foundation of China (Grant No. 61640314) and the Zhejiang Provincial Natural Science Foundation (Grant No. LY15F030012), presents an experimental study on a three-channel electric direct drive synchronous pressure control system. While this work is primarily situated in the domain of ultra-high pressure equipment for synthetic diamond production, the underlying principles of precise pressure control and multi-channel synchronization have direct relevance to high-pressure pipe forming processes, hydrostatic testing systems, and pressure vessel manufacturing.

Technical Architecture and Control Strategy

The system employs a distributed electric direct drive configuration to replace the traditional pump-and-valve hydraulic control approach used during the pressure holding stage of diamond synthesis. In conventional six-anvil or two-anvil presses, a secondary pump maintains pressure during the hold stage, but this inevitably introduces pressure pulsation due to pump discharge characteristics and valve response lag. The proposed system uses three independent electric direct drive channels, each capable of precise force application, with a coordinated control strategy to maintain constant pressure.

Comparison of Control Approaches

The electric direct drive approach eliminates the need for a continuously running pump, thereby reducing energy waste. The response time of electric motors is significantly faster than hydraulic pumps, enabling rapid correction of pressure deviations. The three-channel configuration provides redundancy and allows for fine-tuning of the pressure distribution across the press platens, which is essential for achieving uniform pressure during the diamond growth process.

Relevance to Pipe and Fitting Manufacturing

Although the primary application is diamond synthesis, the control philosophy translates directly to high-pressure pipe forming operations. In processes such as hydroforming of tee fittings, pipe expanding, and cold expansion of pipe ends for flange attachment, precise and stable pressure control is critical to product quality. Pressure pulsation during the forming hold stage can lead to dimensional inaccuracy, surface defects, and inconsistent material flow. The three-channel direct drive approach could be adapted to hydroforming presses to achieve superior pressure stability, resulting in tighter dimensional tolerances on formed tees and elbows.

In my engineering practice, I have observed that pressure fluctuations during the hold stage of hydroforming are a persistent challenge, particularly for complex geometries such as tees with multiple branch connections. The conventional hydraulic approach often requires careful tuning of accumulator volume and valve response to minimize pulsation, but the fundamental limitations of hydraulic systems persist. An electric direct drive system with independent channel control offers a paradigm shift: each channel can be independently regulated to compensate for local pressure imbalances caused by asymmetric material flow in the tee geometry.

Control Performance Metrics

The experimental results demonstrate that the three-channel system achieves significantly lower pressure fluctuation amplitude compared to the conventional pump-controlled system. The key performance indicators include pressure stability (typically measured as peak-to-peak variation in MPa), response time to pressure setpoint changes (in milliseconds), and energy consumption during the hold stage. The electric direct drive system achieves pressure stability within a fraction of a percent of the setpoint, which is an order of magnitude improvement over conventional hydraulic systems.

Study Insights and Engineering Implications

This paper demonstrates that electric direct drive technology, previously considered impractical for ultra-high pressure applications, can now be deployed for precise pressure control in demanding industrial processes. The three-channel architecture is particularly noteworthy because it enables spatially resolved pressure compensation, which is essential for forming complex geometries such as tees where material flow is inherently asymmetric.

For pipe and fitting manufacturers, the adoption of electric direct drive pressure control systems could lead to significant improvements in product quality and manufacturing efficiency. The elimination of hydraulic pumps and valves reduces maintenance requirements, eliminates hydraulic fluid contamination risks, and lowers energy consumption. Furthermore, the digital control architecture facilitates integration with Industry 4.0 manufacturing systems, enabling real-time monitoring and adaptive control of forming parameters. However, the initial capital investment for electric drive systems is higher than for hydraulic systems, and the control algorithm development requires specialized expertise. Engineers considering this technology should conduct a thorough cost-benefit analysis, weighing the capital expenditure against the long-term savings in energy, maintenance, and scrap reduction.