Steel Ball Cold Forging Process Monitoring System Based On The Piezoelectric Effect

As the first process for steel ball processing, the forming defects of cold heading are the main sources of quality problems and defects. Because of Lacking process monitoring, the domestic cold heading equipments only executive the reciprocating mechanical movement. Its traditional detection often use the special test apparatus for manual inspection after completion of the processing, which serious wear the measuring tools and has lower detection efficiency. More importantly, the forming defects and faults in the production process could not be found by the traditional detection method. The limited detecting ability has become the bottleneck that impedes the cold upsetting to upgrade. By analyzing the theory study and application of monitoring equipment for the on-line monitoring of metal forming process, a quality monitoring methods for cold heading are proposed by on-line collecting and analyzing the load signal.The forming principle of steel ball cold heading is analyzed in this paper to establish the mathematical model of motion system of cold forging machine. The steel ball cold heading process was simulated by Using the finite element software DEFORM-3D that populated in the special plastic forming field. The forming process in the normal condition and the two common forming defect conditions (burr defects and spherical eccentric defects) are numerical simulated respectively by changing two indicators (the length of Raw materials and Concentricity of two die). After post-processing operation, the load curves of the bottom die (static die) are obtained, which correspond common quality defects of forming. Analyzing Simulation results, different burr sizes are mainly reflected in the two characteristics of load curve, which are the peak value and sequence in time. In the case of same length of the bar materials,spherical eccentric defect is mainly reflected in dynamic load value in the initial stages of cold heading Thus, the Feasibility is theoretically proved by collecting the load curve in the axial Location to analysis the forming quality of steel ball blank.Waveform acquisition is the basis of analyzing quality. Considering the special condition for extracting the load signal in bottom die, this paper contrastive analysis the characteristics of force sensors and their effects to the steel ball cold heading and the principle and application of the piezoelectric effect. The piezoelectric sensor is used to obtain load signal in bottom die. Considering the structure of steel ball cold heading machine, stiffness and other required factors, the piezoelectric material is selected and design of the PVDF piezoelectric membrane sensor is designed. After that, the appropriate installation location is selected and the cold upsetting force is calculated to check the bearing capacity of the sensor. Equivalent circuits of piezoelectric sensor and the charge amplifier and voltage pre-amplifier are analyzed theoretically, the application of the voltage amplifier AD623 with high impedance input as a pre-amplifier is proposed, which feasibility is through theory and experimental verification.Based on the analysis of system functional requirements and hardware architecture, hardware platform of the system are established. We selected the appropriate the MCU, designed A/D conversion unit, interactive interface circuit, the system clock unit, keyboard and other hardware circuit. According to the realistic condition of the factory, PCB circuit boards are designed taking the hardware anti-jamming measures.Software operating system platform is successfully established based on Analysis of the overall system software architecture and modular programming. The software modules: system initialization module, TFT display module, data acquisition and analysis module, HMI module and clock reading and writing module are programmed, which are time-ordered called by the main program and the subprograms. The load signal is scattered and the identification algorithm is achieved. System parameters are adjusted by the human-computer interaction module, the quality and processing information is traced by reading and writing the system clock to achieve, and the forming monitoring system is successfully designed.The data of three kinds forming defects are obtained in the industrial field and the learning and discrimination algorithm for the load signal are programmed. Using MATLAB, the data are analysised and the effectiveness and accuracy of the cold heading quality monitoring system are verified.