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Producing P/M compacts is generally a low-cost, high-volume manufacturing effort with very special quality assurance requirements. When considering the three basic P/M steps of mixing, compacting, and sintering, it is the compaction process producing the green-state parts that offer the highest pay-off for quality control through nondestructive evaluation (NDE) techniques. A detection of compacting-related problems in the green-state samples permits early process intervention, and thus prevents the creation of potentially significant numbers of faulty parts. Work at WPI currently has concentrated on extending the previously developed method for crack detections to measure density variations within the parts. In this paper a physical model and a mathematical formulation are reported that are capable of relating green-state density to electric conductivity for various lubricant concentrations. Electrostatic measurements of cylindrical compacts have so far confirmed the theoretical model assumptions. Specifically, the green-state conductivity increases as the sample density increases up to approximately 6.9 – 7.0 g/ccm. Any further density increase results in a decrease in conductivity. Preliminary measurements with a range of cylindrical samples support the theoretical model. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper progress is reported on relating the density of green-state compacts in the presence of various lubricant concentrations to electric conductivity. This relationship lies at the core of the electrostatic NDE methodology to predict density distributions. It will be shown that density and material conductivity follow a complex functional behavior that is determined by the type and concentration of the lubricant. Specifically, the material conductivity increases as the sample density increases up to approximately 6.9 - 7.0 g/cm[sup 3]. Any further density increases cause a decrease in conductivity. Theoretical and experimental data will be provided to explain this phenomenon. [ABSTRACT FROM AUTHOR]

In this research we discuss an electrostatic measurement approach whereby electric current is injected into green-state compacts and the resulting surface voltages are recorded in an effort to determine the density distribution. We present results of pure iron powder with and without lubricants compacted to various densities and their measured electric resistivities in an effort to establish a statistical correlation. The electric measurements will ultimately be utilized to predict density distributions throughout the green-state P/M compact. The constant current is injected through point and aperture electrodes and voltages are recorded along the surface of the compact. The recorded voltages of the controlled cylindrical samples are compared to a mathematical Green’s function model involving an analytical electrostatic solution of Poisson’s equation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]