Abstract

This paper presents a control system for a powder sintering machine utilizing the alternating current (AC) sintering technique assisted by uniaxial compression. The AC flows simultaneously through both the sintered material and the die assembly. The procedural model of the control system and its functionalities are described. Thermal models of the die assembly were developed using First-Order Plus Dead-Time (FOPDT) and Second-Order Plus Dead-Time (SOPDT) frameworks, followed by the synthesis of the control system. A prototype machine, developed at the University of Radom in cooperation with the University of Life Sciences in Lublin, is discussed, including its control algorithm and key process parameters affecting sample properties, established based on literature data. To achieve temperatures of 1700 °C and above, a specialized high-power supply (180 A, 400 VAC) with phase-angle and integral-cycle (group) control was implemented. The control system is based on a PLC equipped with temperature control loops, alongside measurements of shrinkage (displacement), compaction force, and auxiliary signals (vacuum and cooling systems). A dedicated control algorithm was developed to ensure process repeatability and optimization. For the ZrO2-based composite analyzed in this manuscript, an FOPDT process model was determined, yielding an equivalent transport delay of approximately 83 s and an equivalent time constant of nearly 333 s. Based on this model, PID controller parameters were derived, and a time-profile program control algorithm was developed. Furthermore, based on literature data, selected mechanical properties of composites obtained via AC sintering are presented, which served as foundational design criteria for the developed machine.

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