Jordan Weaver, Alec Schlenoff, David Deisenroth and Shawn Moylan
This paper aims to investigate the influence of nonuniform gas speed across the build area on the melt pool depth during laser powder bed fusion. This study focuses on whether a…
Abstract
Purpose
This paper aims to investigate the influence of nonuniform gas speed across the build area on the melt pool depth during laser powder bed fusion. This study focuses on whether a nonuniform gas speed is a source of process variation within an individual build.
Design/methodology/approach
Parts with many single-track laser scans were printed and characterized in different locations across the build area coupled with corresponding gas speed profile measurements. Cross-sectional melt pool depth, width and area are compared against build location/gas speed profiles, scan direction and laser scan speed.
Findings
This study shows that the melt pool depth of single-track laser scans produced on parts are highly variable. Despite this, trends were found showing a reduction in melt pool depth for slow laser scan speeds on the build platform near the inlet nozzle and when the laser scans are parallel to the gas flow direction.
Originality/value
A unique data set of single-track laser scan cross-sectional melt pool measurements and gas speed measurements was generated to assess process variation associated with nonuniform gas speed. Additionally, a novel sample design was used to increase the number of single-track tests per part, which is widely applicable to studying process variation across the build area.
Details
Keywords
Brandon Lane, Shawn Moylan, Eric P. Whitenton and Li Ma
Quantitative understanding of the temperatures, gradients and heating/cooling rates in and around the melt pool in laser powder bed fusion (L-PBF) is essential for simulation…
Abstract
Purpose
Quantitative understanding of the temperatures, gradients and heating/cooling rates in and around the melt pool in laser powder bed fusion (L-PBF) is essential for simulation, monitoring and controls development. The research presented here aims to detail experiment design and preliminary results of high speed, high magnification, in-situ thermographic monitoring setup on a commercial L-PBF system designed to capture temperatures and dynamic process phenomena.
Design/methodology/approach
A custom door with angled viewport was designed for a commercial L-PBF system which allows close access of an infrared camera. Preliminary finite element simulations provided size, speed and scale requirements to design camera and optics setup to capture melt pool region temperatures at high magnification and frame rate speed. A custom thermal calibration allowed maximum measurable temperature range of 500°C to 1,025°C. Raw thermographic image data were converted to temperature assuming an emissivity of 0.5. Quantitative temperature results are provided with qualitative observations with discussion regarding the inherent challenges to future thermographic measurements and process monitoring.
Findings
Isotherms around the melt pool change in size depending on the relative location of the laser spot with respect to the stripe edges. Locations near the edges of a stripe are cooled to lower temperatures than the center of a stripe. Temperature gradients are highly localized because of rough or powdery surface. At a specific location, temperatures rise from below the measurable temperature range to above (<550°C to >1100°C) within two frames (<1.11 m/s). Particle ejection is a notable phenomenon with measured ejection speeds >11.7 m/s.
Originality/value
Several works are detailed in the Introduction of this paper that detail high-speed visible imaging (not thermal imaging) of custom or commercial LBPF processes, and lower-speed thermographic measurements for defect detection. However, no work could be found that provides calibrated, high-speed temperature data from a melt-pool monitoring configuration on a commercial L-PBF system. In addition, the paper elucidates several sources of measurement uncertainty (e.g. calibration, emissivity and time and spatial resolution), describes inherent measurement challenges based on observations of the thermal images and discusses on the implications to model validation and process monitoring and control.
Details
Keywords
Gijeong Seo, Md. RU Ahsan, Yousub Lee, Jong-Ho Shin, Hyungjun Park and Duck Bong Kim
Due to the complexity of and variations in additive manufacturing (AM) processes, there is a level of uncertainty that creates critical issues in quality assurance (QA), which…
Abstract
Purpose
Due to the complexity of and variations in additive manufacturing (AM) processes, there is a level of uncertainty that creates critical issues in quality assurance (QA), which must be addressed by time-consuming and cost-intensive tasks. This deteriorates the process repeatability, reliability and part reproducibility. So far, many AM efforts have been performed in an isolated and scattered way over several decades. In this paper, a systematically integrated holistic view is proposed to achieve QA for AM.
Design/methodology/approach
A systematically integrated view is presented to ensure the predefined part properties before/during/after the AM process. It consists of four stages, namely, QA plan, prospective validation, concurrent validation and retrospective validation. As a foundation for QA planning, a functional workflow and the required information flows are proposed by using functional design models: Icam DEFinition for Function Modeling.
Findings
The functional design model of the QA plan provides the systematically integrated view that can be the basis for inspection of AM processes for the repeatability and qualification of AM parts for reproducibility.
Research limitations/implications
A powder bed fusion process was used to validate the feasibility of this QA plan. Feasibility was demonstrated under many assumptions; real validation is not included in this study.
Social implications
This study provides an innovative and transformative methodology that can lead to greater productivity and improved quality of AM parts across industries. Furthermore, the QA guidelines and functional design models provide the foundation for the development of a QA architecture and management system.
Originality/value
This systematically integrated view and the corresponding QA plan can pose fundamental questions to the AM community and initiate new research efforts in the in-situ digital inspection of AM processes and parts.