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Article
Publication date: 15 August 2016

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…

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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

Rapid Prototyping Journal, vol. 22 no. 5
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 3 January 2017

Godson A. Tetteh

The purpose of this paper is to investigate the relationship between a student’s study time and the learning outcome from a perspective that will correspond to Bloom’s (1956…

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Abstract

Purpose

The purpose of this paper is to investigate the relationship between a student’s study time and the learning outcome from a perspective that will correspond to Bloom’s (1956) taxonomy and how teaching can be developed using variation theory.

Design/methodology/approach

The author designed a learning study using an experiment with three different classes of students. The experimental research question was “Does a student’s study time (massed or distributed spacing) have an impact on the learning process?”

Findings

Results indicated that students in the “strictly supervised study time” grouping improved on their learning outcomes more than those in the “not strictly supervised study time” equivalent and those in the control group. It is important for students to manage their own learning activities and follow a regular study routine to improve their learning outcomes.

Research limitations/implications

This study used undergraduate students at a university in Ghana, and its findings may not necessarily be applicable to other populations. One other limitation was that the author did not control for the lecturer’s expectations and how these may have influenced students’ learning outcomes. Another potential limitation was that total quality management was the only subject area used for this study.

Practical implications

The objective of the study was to use the motivated strategies for learning questionnaire (MSLQ) approach by Pintrich et al. (1991) to determine the relationship between a student’s study time and the impact on their learning outcomes. The results imply that students must take more active roles in their learning by having regular study time.

Originality/value

Currently, to the best of the author’s knowledge, there are not many experiment-based research studies on a student’s study time using the MSLQ approach by Pintrich et al. (1991). This study contributes to the existing literature by examining how a student’s study time (massed or distributed spacing) has an impact on the learning outcome as a lesson and learning study.

Details

International Journal for Lesson and Learning Studies, vol. 6 no. 1
Type: Research Article
ISSN: 2046-8253

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