Search Results for manufacturing processes

Fusion-based additive manufacturing (AM) processes rely on the formation of a metallurgical bond between a substrate and a feedstock material. Energy sources employed in the fusion AM process include conventional arcs, lasers, and electron beams. Each of these sources is discussed, with an emphasis on their principles of operation, key processing variables, and the influence of each source on the transfer of heat and material. Common energy sources used for metals AM processes, particularly powder-bed fusion and directed-energy deposition, are also discussed. Brief sections at the end of the article discuss the factors dictating the choice of each of these energy sources and provide information on alternative sources of AM.

This article focuses on four industrial additive manufacturing approaches that are used to create polymer parts. The first section focuses on material extrusion, providing information on lumped-parameter material flow models and higher-fidelity models developed to estimate temperature distribution. The second section covers polymer powder-bed sintering/ fusion, discussing the different levels of scale used to address modeling and the impact of process settings: thermodynamics at the powder-bed surface, consolidation of adjacent particles in the fusion process, and fusion and molecular-level behavior within particles. The third section on vat photopolymerization (VPP) discusses two primary approaches to modeling VPP processes, namely a lumped-parameter approach to estimate cured regions in the vat, known as the Jacobs model, and a high-fidelity, continuum approach that uses finite-element methods. The final section is devoted to material jetting, focusing on simulations used to study droplet generation at the nozzle and droplet impact.

The formation of defects within additive-manufactured (AM) components is a major concern for critical structural and cyclic load applications. Thus, understanding the mechanisms of defect formation in fusion-based processes is important for prescribing the appropriate process parameters specific to the alloy system and selected processing technique. This article discusses the formation of defects within metal additive manufacturing, namely fusion-based processes and solid-state/sintering processes. Defects observed in fusion-based processes include lack of fusion, keyhole collapse, gas porosity, solidification cracking, solid-state cracking, and surface-connected porosity. The types of defects in solid-state/sintering processes are sintering porosity and improper binder burnout. The article also discusses defect-mitigation strategies, such as postprocess machining, surface treatment, and postprocessing HIP to eliminate defects detrimental to properties from the as-built condition. The use of noncontact thermal, optical, and ultrasound techniques for inspecting AM components are also considered. The final section summarizes the knowledge gap in our understanding of the defects observed within AM components.

Additive manufacturing produces a change in the shape of a substrate by adding material progressively. This article discusses the simulation of laser deposition and three principal thermomechanical phenomena during the laser deposition process: absorption of laser radiation; heat conduction, convection, and phase change; and elastic-plastic deformation. It provides a description of four sets of data used for modeling and simulation of additive manufacturing processes, namely, material constitutive data, solid model, initial and boundary conditions, and laser deposition process parameters. The article considers three aspects of simulation of additive manufacturing: simulation for initial selection of process parameter setup, simulation for in situ process control, and simulation for ex situ process optimization. It also presents some examples of computational mechanics solutions for automating various components of additive manufacturing simulation.

This article provides readers with a brief review of the applications of thermography in additive manufacturing (AM), which still is largely a research and development (R&D) effort. There is a particular focus on metals-based laser powder-bed fusion (L-PBF), although applications in directed-energy deposition (DED) and electron beam PBF (E-PBF) also are mentioned. The metrological basis of thermography is discussed in the article. Background information on radiation thermometry is provided, including how the various equations are applied. Finally, specific examples and lessons learned from various AM thermographic studies at the National Institute of Standards and Technology (NIST) are provided.

Additive manufacturing (AM) is a revolutionary technology that fabricates parts layerwise and provides many advantages. This article discusses polymer AM processes such as material extrusion, vat photopolymerization (VPP), powder-bed fusion (PBF), binder jetting (BJ), material jetting (MJ), and sheet lamination (SL). It presents the benefits of online monitoring and process control for polymer AM. It also introduces the respective monitoring devices used, including the models and algorithms designed for polymer AM online monitoring and control.

The use of additive manufacturing (AM) is increasing for high-value, critical applications across a range of disparate industries. This article presents a discussion of high-valued engineering components predominantly used in the aerospace and medical industries. Applications involving metal AM, including methods to identify pores and voids in AM materials, are the focus. The article reviews flaw formation in laser-based powder-bed fusion, summarizes sensors used for in situ process monitoring, and outlines advances made with in situ process-monitoring data to detect AM process flaws. It reviews investigations of ML-based strategies, identifies challenges and research opportunities, and presents strategies for assessing anomaly detection performance.

X-ray imaging is a nondestructive evaluation (NDE) technique in which x-ray waves interact with an observed sample to generate images from which information about the examined object can be derived. This article discusses x-ray imaging systems and applications, presenting the history and role of x-ray imaging. It describes different setups that are implemented at various facilities that conduct x-ray imaging for different types of metal AM processes. The article also discusses different types of dynamics observed in experimental metal AM processes using x-ray imaging systems. It presents the future of x-ray imaging in metal AM.

The qualification of additive manufacturing (AM) processes and the certification of AM parts is recognized as a significant impediment to the rapid, low-cost deployment of AM manufacturing. The challenges are multifaceted; however, it is an attempt to apply conventional qualification approaches to an inherently different process that has caused the most difficulty. This article examines the conventional qualification methodology and explores how the unique characteristics of AM pose a set of qualification challenges. The extant approach to the qualification of AM processes is described, followed by a discussion on a possible future state.

This article explores the possibilities and limitations imposed by manufacturing processes and materials. Detailed design rules for the processes are presented. The article lists the main features of process groups in a tabular form. The physical characteristics and ratings of relative cost and production factors are also tabulated. The process groups include casting; deformation; powder processing; machining; noncutting; joining; ceramic, glass, and polymer processing; and composites manufacturing.

Manufacturing processes typically involve the reshaping of materials from one form to another under a set of processing conditions. This article discusses the two classification schemes of modeling for manufacturing processes, namely, on-line or off-line models and empirical, mechanistic, or deterministic models along with their important considerations. It describes the various aspects of modeling of deformation processes, casting operations, and fusion welding processes, with examples.