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Technical Paper Archive

Welcome to the NDT-RAM Technical Paper Archive!

Please view the technical paper abstracts below to learn more about the theory and technology behind The Modal Shop's proven line of NDT-RAM systems. 

As always, if you should have any questions, please do contact us at ndt@modalshop.com or 513.351.9919.


Fundamentals of Resonant Acoustic Method

Abstract:
Rapid conversion of machined parts to powder metal and cast is driving industries, especially automotive. Due to the high expectations of both primary manufacturers and end consumers, defects cannot be tolerated even in million piece quantities. There is, in effect, a growing requirement for zero defect supply chain commitments. To achieve zero defect output, manufacturers are making the commitment to move to online NDT. This type of online inspection requires accuracy, reliability, and high throughput. Resonant Acoustic Method NDT (NDT-RAMTM) provides a proven technique exhibiting these pivotal performance requirements and automates economically. NDT-RAM tests, reports and screens for most common part flaws in a manner similar to the way NASA tests flight hardware and automotive manufacturers validate their new car designs. Utilizing structural dynamics and statistical variation, NDT-RAM provides mature, laboratory proven technology in a robust, economical, process-friendly manner.

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Physical Basis of Resonant Acoustic Method

Abstract:
Resonant inspection measures the structural response of a part and evaluates it against the statistical variation from a control set of good parts to screen defects. Its volumetric approach tests the whole part, both for external and internal structural flaws or deviations, providing objective and quantitative results. This structural response is a unique and measurable signature, defined by a component’s mechanical resonances. These resonances are a function of part geometry and material properties and are the basis for Resonant Acoustic Method for Flaw Detection. By measuring the resonances of a part, one determines the structural characteristics of that part in a single test. Typical flaws and defects adversely affecting the structural characteristics for powdered metal as would be introduced in the green state are geometry related and typically a result of handling. This paper introduces the physical basis of the technique.

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Effects of Crack Size Using Resonant Inspection

Abstract:
Resonant Inspection is commonly used by powdered metal part manufacturers to sort quality components from those with structural defects. One of the more common structural defects found in powdered metal parts are cracks, often produced while in the green state. A controlled experiment was designed to investigate the sensitivity of resonant frequency shifts to crack size. This evaluation was intended to generalize and quantify the effectiveness of resonant inspection by generating a variety of crack sizes within a tightly controlled set of production parts. Although data was acquired to quantify how small of a crack the resonant inspection technique can detect, it is important to recognize that these results cannot be applied across all powdered metal parts due to differences in part geometry, mass and stiffness as well as control of production process variations.

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Resonant Inspection of Nodularity

Abstract:
One common application for RAM-NDT is testing ductile iron for acceptable levels of nodularity. Cast iron is a metal alloy characterized by relatively high carbon content. During the metal’s solidification, this carbon content can form graphite, with tiny, irregular flakes that disrupt the crystalline structure, causing cracks and unwanted brittleness. In ductile iron the graphite forms spherical, rounded nodules that inhibit the formation of cracks and provide enhanced ductility and machinability.

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Resonant Inspection for Small Powder Metal Parts

Abstract:
Resonant Inspection is commonly used for quality assurance testing of powder metal components, providing a volumetric whole body approach that detects both external and internal structural flaws or anomalies. This technique measures a metal component’s mechanical resonances by striking the part with an impact and analyzing the acoustic ringing produced. Traditionally this technique has been limited to small to medium components with sizes ranging from about a “dime to a dinner plate” due to the requirements to align and impact the part. However, using a new methodology that employs a drop testing fixture to excite the part rather than an electromechanical impactor, very small components such as those commonly manufactured by powder metal MIM processes can be 100% inspected reliably, quickly and cost-effectively. This paper presents the new drop test methodology supported with case study and experimental results.

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Resonant Inspection for Improved NVH Performance

Abstract:
Resonant Inspection is a non-destructive test technique that measures the structural dynamic signature of an article. By comparing the resulting footprint to expected signatures, anomalous outliers are sorted due to some inherent structural defect, improving quality and consistency of manufactured components. Brake components, such as rotors and drums, are designed with specific structural dynamic properties for desired NVH qualities. Resonant Inspection via the Resonant Acoustic Method (RAM-NDT) provides a proven economical technique with the capacity for accurate, reliable and high-throughput 100% online inspection.

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Resonant Inspection for Sinter Brazing

Abstract:
With continued growth of powder metal components in the vehicle, particularly within the power train, the requirement for defect free manufacturing has driven suppliers to seek out cost effective methods of 100% inspection. To achieve zero defect (“Zero PPM”) output cost-effectively, manufacturers are making the commitment to move to online, automated nondestructive testing (NDT) methods. This type of online inspection requires accuracy, reliability, and high throughput. Resonant Inspection is emerging as a very efficient method of structural defect discrimination and lends itself very well to 100% inspection of powder metal components. This paper will present the fundamental principles of the resonant acoustic method (RAM NDT), on a structural basis, followed with RAM NDT applied to a variety of sinter braze integrity inspection applications.

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