Mechanistic models for additive manufacturing of metallic components

Directed energy deposition (DED) additive manufacturing: Physical characteristics, defects, challenges and applications

Next generation, additively-manufactured metallic parts will be designed with application-optimized geometry, composition, and functionality. Manufacturers and researchers have investigated various techniques for increasing the reliability of the metal-AM process to create these components, however, understanding and manipulating the complex phenomena that occurs within the printed component during processing remains a formidable challenge-limiting the use of these unique design capabilities. Among various approaches, thermomechanical modeling has emerged as a technique for increasing the reliability of metal-AM processes, however, most literature is specialized and challenging to interpret for users unfamiliar with numerical modeling techniques. This review article highlights fundamental modeling strategies, considerations, and results, as well as validation techniques using experimental data. A discussion of emerging research areas where simulation will enhance the metal-AM optimization process is presented, as well as a potential modeling workflow for process optimization. This review is envisioned to provide an essential framework on modeling techniques to supplement the experimental optimization process.

Invited Review Article: Metal-additive manufacturing — Modeling strategies for application-optimized designs

The additive manufacturing and the robotic applications are tremendously increasing in the manufacturing field. This review paper discusses the concept of robotic-assisted additive manufacturing. The leading additive manufacturing methods that can be used with a robotic system are presented and discussed in detail. The information flow required to produce an object from a CAD model through a robotic-assisted system, different from the traditional information flow in a conventional additive manufacturing approach is also detailed. Examples of the use of robotic-assisted additive manufacturing systems are presented.

Robot assisted additive manufacturing: A review

Powder-blown laser additive manufacturing adds flexibility, in terms of locally varying powder materials, to the ability of building components with complex geometry. Although the process is promising, porosity is common in a built component, hence decreasing fatigue life and mechanical strength. The understanding of the physical phenomena during the interaction of a laser beam and powder-blown deposition is limited and requires in-situ monitoring to capture the influences of process parameters on powder flow, absorptivity of laser energy into the substrate, melt pool dynamics and porosity formation. This study introduces a piezo-driven powder deposition system that allows for imaging of individual powder particles that flow into a scanning melt pool. Here, in-situ high-speed X-ray imaging of the powder-blown additive manufacturing process of Ti-6Al-4V powder particles is the first of its kind and reveals how laser-matter interaction influences powder flow and porosity formation.

In-situ high-speed X-ray imaging of piezo-driven directed energy deposition additive manufacturing.

Accurate temperature measurements based on careful experimentation and microstructural analysis were conducted for Ti-6Al-4V and Inconel 625 alloys deposited using the laser-based directed energy deposition process. In the case of the Ti-6Al-4V alloy, thermal measurements were made in the first layer during the first and four subsequent deposits to ascertain microstructural evolution during the heating and cooling cycles. Four energy densities were utilized during deposition of the Inconel 625 alloy to alter cooling rates and determine the impact of processing conditions on solidification morphology. The precise experimental measurements enabled a comprehensive analysis of the solid state reactions for Ti-6Al-4V, and the solidification phenomena to be elucidated for Inconel 625. The results for the Ti-6Al-4V alloy indicated that the measured thermal response could be used to anticipate initial microstructure based on cooling rates from the β-transus, and subsequent thermal cycles could be utilized to define potential transformations between α, α′, and β. Analysis of the measured thermal cycles from the liquid through solidification for the Inconel 625 alloy showed that processing parameters could be linked to factors governing the solidification process and microstructural features. Using these relationships, an accurate processing map for laser-based directed energy deposition for Inconel 625 was constructed to enable the identification of solidification morphology and microstructural scale based on critical processing parameters.

Joshua Z. Park

Papers

Thermal and microstructural analysis of laser-based directed energy deposition for Ti-6Al-4V and Inconel 625 deposits