Review of in-situ process monitoring and in-situ metrology for metal additive manufacturing

ENGIN-X, a new time-of-flight (TOF) neutron diffractometer optimized to measure elastic strains at precise locations in bulky specimens recently commissioned at the ISIS Facility in the Rutherford Laboratory, UK, is described. Fast counting times, together with a flexible and accurate definition of the instrumental gauge volume are the main requirements of neutron strain scanning and have been addressed on ENGIN-X through the design of a novel TOF diffractometer with a tuneable resolution and interchangeable radial collimators. Further, the routine operation of the instrument has been optimized by creating a virtual instrument, i.e. a three-dimensional computer representation of the diffractometer and samples, which assists in the planning and execution of experiments. On comparing ENGIN-X with its predecessor ENGIN, a 25× gain in performance is found, which has allowed the determination of stresses up to 60 mm deep in steel specimens. For comparison with constant-wavelength diffractometers, special attention has been paid to the absolute number of counts recorded during the experiments. A simple expression is presented for the estimation of counting times in TOF neutron strain scanning experiments.

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ENGIN-X: a third-generation neutron strain scanner

Microstructure and residual stress improvement in wire and arc additively manufactured parts through high-pressure rolling

This article provides a literature review of finite element simulation studies for metallic powder bed additive manufacturing processes. The various approaches in the numerical modeling of the processes and the selection of materials properties are presented in detail. Simulation results are categorized according to three major findings’ groups (i.e. temperature field, residual stresses and melt pool characteristics). Moreover, the means used for the experimental validation of the simulation findings are described. Looking deeper into the studies reviewed, a number of future directions are identified in the context of transforming simulation into a powerful tool for the industrial application of additive manufacturing. Smart modeling approaches should be developed, materials and their properties should be further characterized and standardized, commercial packages specialized in additive manufacturing simulation have to be developed and simulation needs to become part of the modern digital production chai...

Simulation of metallic powder bed additive manufacturing processes with the finite element method: A critical review

Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.

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Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

INTRODUCTION Residual Stress: Friend or Foe? Historical Development of Stress Measurement by Diffraction Special Characteristics of Neutron Strain Measurement Nature and Origin of Residual Stress Effects of Residual Stress FUNDAMENTALS OF NEUTRON DIFFRACTION Introduction Scattering and Absorption of Neutrons and X-Rays by Atoms Neutron Diffraction from Crystalline Solids Penetration of Neutron Beams Effects of Lattice Vibrations Extinction, Texture, and Multiple Scattering DIFFRACTION TECHNIQUES AND INSTRUMENT DESIGN Neutron Sources Diffractometers for Strain Measurement Neutron Detectors The Instrumental Resolution Instrument Gauge Volumes Sampled Gauge Volume and Effective Measurement Position Specialized Instruments for Strain Measurement PRACTICAL ASPECTS OF STRAIN MEASUREMENT USING NEUTRON DIFFRACTION Introduction Measurement of Diffraction Bragg Peak Profile Analyzing Bragg Peak Profiles Accuracy of Diffraction Peak Center Determination Analysis of Complete Diffraction Profiles for Strain Strain-Free Reference Reproducibility Tests INTERPRETATION AND ANALYSIS OF LATTICE STRAIN DATA Inferring Stresses from Lattice Strains Introduction to Mechanics of Crystallite Deformation Elastic Anisotropy of Single Crystals The Bulk Elastic Response of Polycrystals hkl-Specific Response in a Polycrystal Undergoing Elastic Deformation hkl-Specific Response in a Polycrystal Undergoing Plastic Deformation APPLICATIONS TO PROBLEMS IN MATERIALS SCIENCE AND ENGINEERING Introduction Welded Structures Composites and Other Multiphase Materials Plastically Deformed Components and Materials Near-Surface Stresses In Situ and Through-Process or Life Studies THE FUTURE SYMBOLS AND ABBREVIATIONS GLOSSARY APPENDICES Note on Reactor Flux Spectrum Relation between the Centroid of Sampled Gauge Volume and Translator Reading Points for Consideration When Making a Neutron Diffraction Stress Measurement Macroscopic Scattering Cross-Sections of All Elements Index

Thomas Holden

Papers

Introduction to the Characterization of Residual Stress by Neutron Diffraction