Crack Detection Methodology for Green-State
This paper briefly reviews a new instrumentation approach developed for the electric resistivity testing of green-state P/M compacts. Rapid testing of the green-state specimens is made possible through a special-purpose sensor configuration, which incorporates a matrix of 10 by 10 spring-loaded needle contacts with pin spacing of 0.1 inches. The sensor permits the detection of hairline flaws with surface openings as small as 20 microns. A quantitative analysis of defect resolution is conducted to lay the foundations for the experimental and validation phase of the sensor development. In particular, a dipole model representation for flaws embedded in the compact is proposed. Further, by incorporating Gaussian random noise to the voltage recordings, measurement uncertainties can be explored. This model is utilized to investigate the depth a flaw can be detected based on a given signal-to-noise ratio of the instrument.
Non-destructive evaluation of green-state powder metal compacts using the electrical-resistivity method
This paper presents a new apparatus developed for non-destructive evaluation (NDE) of green-state powder metal compacts. A green-state compact is an intermediate step in the powder metallurgy (PM) manufacturing process, which is produced when a metal powder–lubricant mixture is compacted in a press. This compact is subsequently sintered in a furnace to produce the ﬁnished product. Non-destructive material testing is most cost effective in the green state because early ﬂaw detection permits early intervention in the manufacturing cycle and thus avoids scrapping large numbers of parts. Unfortunately, traditional NDE methods have largely been unsuccessful when applied to green-state PM compacts. A new instrumentation approach has been developed, whereby direct currents are injected into the green-state compact and an array of spring-loaded needle contacts records the voltage distributions on the surface. The voltage distribution is processed to identify potentially dangerous surface and sub-surface ﬂaws. This paper presents the custom-designed hardware and software developed for current injection, voltage acquisition, pre-ampliﬁcation and ﬂaw detection. In addition, the testing algorithm and measurement results are discussed. The success of ﬂaw detection using the apparatus is established by using controlled samples, which are PM compacts with dielectric inclusions inserted.
Laser photothermal non-destructive inspection method for hairline crack detection in unsintered automotive parts
A statistical non-contacting and non-intrusive method for revealing the presence of cracks in un-sintered (green) parts manufactured by powder metallurgy (PM) technology was developed based on photo thermal radiometry (PTR). The technique relies on the interaction of a modulated laser generated thermal wave with the crack resulting in change of amplitude and phase of the detected signal. The crack existence at points in high stress regions of a group of green sprockets was evaluated through the proposed method. The results were validated by an independent destructive technique—- microscope observation of the tested green sprockets following sintering, sectioning, and polishing at the locations where signal changes were observed in the green state. Statistical analysis conﬁrmed the excellent sensitivity (91%) of the method in detecting the presence of hairline (5–10 mm) cracks. This PTR diagnostic technique may lead to a simple and reliable on-line inspection methodology in high-stress locations of PM manufactured industrial steel products. Ultimately, the method can be developed for non-destructive quality and feedback control of the metal forming process of green automotive parts.
Infra-Red and On-Line Testing of Green-State and Sintered P/M Parts for Process Control
This research will concentrate on the formulation of a mathematical model capable of predicting the temperature distribution and heat flow in P/M parts and its relations to the supplied current, injection method, geometry and the thermo-physical properties of these parts. This model will subsequently be employed as a reference to aid in actual measurements of infrared signatures over the surface and its correlation to the detection of surface and subsurface flaws and inhomogeneity. In this progress report we will develop the theoretical background of IR testing of green state and sintered P/M compacts in terms of the governing equations, boundary conditions, and analytical and numerical solutions. Our main emphasis is placed on modeling various flaw sizes and orientations in an effort to determine flaw resolution limits as a function of minimum temperature distributions. Preliminary measurements have shown that this IR testing methodology can successfully test both green-state and sintered samples.
Electrostatic density measurements in green-state pm parts
The goal of this research is to show the feasibility of detecting density variations in green-state powder metallurgy (P/M) compacts from surface voltage measurements. By monitoring a steady electric current flow through the sample and recording the voltages over the surface, valuable information is gathered leading to the prediction of the structural health of the compacts. Unlike prior research that concentrated on the detection of surface-breaking and subsurface defects, the results presented in this thesis target the density prediction throughout the volume of the sample. The detection of density variations is achieved by establishing a correlation between the conductivity and their respective density. The data obtained from the surface measurements is used as part of an inversion algorithm, calculating the conductivity distribution, and subsequently the density within the compact.
NDT and materials characterization
Improved methods of nondestructive characterization of green ceramics should be developed, and correlations should be established between the characterization and the subsequent properties of the sintered ceramic and its service performance or performance-related property. Attention should be given not only to discontinuities and density variations (e.g., 33 resulting from porosity distribution) but also to homogeneity (e.g., of binder and sintering aids), mechanical properties, and sintering aids.
Detection of Cracks in Green Powder Metallurgy
Effective early detection of green cracks in powder metal compacts is a key issue for the powder metal industry. Early detection would dramatically improve costs, efficiencies, and reliability for powder metal components, making the energy efficient powder metal process attractive to more kinds of components. This project is directly relevant to increased reliability for gears and other parts using sinter-harden powders where some green machining is desired before sintering.
A review of nondestructive testing methods
The problem of forming defects in green parts during compaction and ejection has become more prevalent as parts producers have started to use higher compaction pressures in an effort to achieve high density, high performance P/M steels. In this review, several nondestructive inspection methods are evaluated, with the aim of identifying those, which are practical for detecting defects as early in the production sequence as possible. The most promising NDT methods for P/M applications include electrical resistivity testing, eddy current and magnetic bridge testing, magnetic particle inspection, ultrasonic testing, X-ray radiography, gas permeability testing, and gamma ray density determination. The capabilities and limitations of each of the techniques are evaluated in this review.
Powder metallurgy of Ge, Si, and Ge-Si
Planetary ball-milling and pressing behaviour of Ge, Si and Ge-Si powder mixtures are investigated. Scanning and transmission electron microscopy observations revealed the different microstructure of the two elements after milling: Ge remains in a microcrystalline state, whereas Si can be comminuted into grains consisting of nanocrystalline regions. Planetary milling of the two elements together, using agate balls and vial, did not reveal any compound formation. By hot-isostatic pressing, pure Ge and Ge-Si mixtures were densified to a higher value than pure Si. This denotes a plastic flow of the Ge component at a process temperature of 800°C. The microhardness of hot-pressed Ge reaches the bulk value; hot-pressed Si is very soft. Energy dispersive X-ray analysis and X-ray diffraction did not detect any impurity contamination from vial and milling media wear. Moreover, by electrical transport measurements it turned out that the net carrier concentration density resulting from electrical active impurities introduced by the milling and pressing process is below 2 x 1016 cm 3 at room temperature.
In – Line Phase -Contrast X – ray Imaging and Tomography for Materials Science
X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conve ntional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X -rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients.
X-ray inspection – lets you know what’s inside (Article)
X-ray inspection, also called radiography or radiographic testing, is a very effective method of uncovering subsurface defects in materials and products. Laboratory Testing Inc. performs industrial radiography, using both digital radiography (computed radiography) and film radiography (conventional radiography) techniques.
A Novel Multi-Probe Resistivity Approach to Inspect Green-State Metal Powder Compacts (Book)
This paper describes a new instrumentation approach to the nondestructive testing of green-state powdered metallurgy components. These samples are likely to generate surface-breaking and subsurface defects prior to sintering. Exploiting the principles of electric resistivity or potential drop measurements in solids, a system is configured which is capable of recording surface voltage distributions due to impressed current inputs. At the heart of this novel testing procedure is a multiple-pin sensor which allows for flexible measurement conditions in order to cover wide surface areas. Practical tests with production samples compare well with both analytical and numerical modeling techniques in predicting surface voltage distributions. Furthermore, initial studies of surface-breaking flaws exhibit excellent defect detectability.
Density evaluation of powder metallurgy compacts using in situ X-ray radiography (Article, Book)
The measurement of density in porous materials during mass production process is one of the most important factors in industry. The existing methods for measuring density such as hydrostatic weighing and microscopic examinations have some limitations and some inherent problems associated with them. Recently, processes based on radiography have emerged. This paper deals with the in situ measurement of density of porous materials using X-ray techniques. For this purpose, experiments have been performed at various density levels of powder metallurgy compacts. in situ X-ray radiography was then carried out on samples. A correlation has been made between the film density of radiographic film and the surface density of the compacts. A mathematical relationship was derived between the absorbed X-ray, the film intensity and the compact density. The comparison of values of the experimental data and mathematical relationship reveals 1?6% average discrepancies.
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