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Article
Publication date: 26 July 2019

Bo Chen, Yongzhen Yao, Yuhua Huang, Wenkang Wang, Caiwang Tan and Jicai Feng

This paper aims to explore the influences of different process parameters, including laser power, scanning speed, defocusing distance and scanning mode, on the shape…

Abstract

Purpose

This paper aims to explore the influences of different process parameters, including laser power, scanning speed, defocusing distance and scanning mode, on the shape features of molten pool and, based on the obtained relationship, realize the diagnosis of forming defects during the process.

Design/methodology/approach

Molten pool was captured on-line based on a coaxial CCD camera mounted on the welding head, then image processing algorithms were developed to obtain melt pool features that could reflect the forming status, and it suggested that the molten pool area was the most sensitive characteristic. The influence of the processing parameters such as laser power, traverse speed, powder feed rate, defocusing distance and the melt pool area was studied, and then the melt pool area was used as the characteristic to detect the forming defects during the cladding and additive manufacturing process.

Findings

The influences of different process parameters on molten pool area were explored. Based on the relationship, different types of defects were accurately detected through analyzing the relationship between the molten pool area and time.

Originality/value

The findings would be helpful for the quality control of laser additive manufacturing.

Details

Sensor Review, vol. 39 no. 4
Type: Research Article
ISSN: 0260-2288

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Article
Publication date: 16 March 2015

Edward W Reutzel and Abdalla R Nassar

The purpose of this paper is to surveys classic and recently developed strategies for quality monitoring and real-time control of laser-based, directed-energy…

Abstract

Purpose

The purpose of this paper is to surveys classic and recently developed strategies for quality monitoring and real-time control of laser-based, directed-energy deposition.Additive manufacturing of metal parts is a complex undertaking. During deposition, many of the process variables that contribute to overall build quality – such as travel speed, feedstock flow pattern, energy distribution, gas pressure, etc. – are subject to perturbations from systematic fluctuations and random external disturbances.

Design/methodology/approach

Sensing and control of laser-based, directed-energy metal deposition is presented as an evolution of methods developed for welding and cladding processes. Methods are categorized as sensing and control of machine variables and sensing and control of build attributes. Within both categories, classic methods are presented and followed by a survey of novel developments.

Findings

Additive manufacturing would not be possible without highly automated, computer-based controllers for processing and motion. Its widespread adoption for metal components in critical applications will not occur without additional developments and integration of machine- and process-based sensing systems to enable documentation, and control of build characteristics and quality. Ongoing work in sensing and control brings us closer to this goal.

Originality/value

This work serves to introduce researchers new to the field of additive manufacturing to common sources of process defects during metal powder-based, directed-energy deposition processing, and surveys sensing and control methods being investigated to improve the process. The work also serves to highlight, and stress the significance of novel developments in the field.

Details

Rapid Prototyping Journal, vol. 21 no. 2
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 11 September 2019

Tobias Kolb, Reza Elahi, Jan Seeger, Mathews Soris, Christian Scheitler, Oliver Hentschel, Jan Tremel and Michael Schmidt

The purpose of this paper is to analyse the signal dependency of the camera-based coaxial monitoring system QMMeltpool 3D (Concept Laser GmbH, Lichtenfels, Germany) for…

Abstract

Purpose

The purpose of this paper is to analyse the signal dependency of the camera-based coaxial monitoring system QMMeltpool 3D (Concept Laser GmbH, Lichtenfels, Germany) for laser powder bed fusion (LPBF) under the variation of process parameters, position, direction and layer thickness to determine the capability of the system. Because such and similar monitoring systems are designed and presented for quality assurance in series production, it is important to present the dominant signal influences and limitations.

Design/methodology/approach

Hardware of the commercially available coaxial monitoring QMMeltpool 3D is used to investigate the thermal emission of the interaction zone during LPBF. The raw images of the camera are analysed by means of image processing to bypass the software of QMMeltpool 3D and to gain a high level of signal understanding. Laser power, scan speed, laser spot diameter and powder layer thickness were varied for single-melt tracks to determine the influence of a parameter variation on the measured sensory signals. The effects of the scan direction and position were also analysed in detail. The influence of surface roughness on the detected sensory signals was simulated by a machined substrate plate.

Findings

Parameter variations are confirmed to be detectable. Because of strong directional and positional dependencies of the melt-pool monitoring signal a calibration algorithm is necessary. A decreasing signal is detected for increasing layer thickness. Surface roughness is identified as a dominating factor with major influence on the melt-pool monitoring signal exceeding other process flaws.

Research limitations/implications

This work was performed with the hardware of a commercially available QMMeltpool 3D system of an LPBF machine M2 of the company Concept Laser GmbH. The results are relevant for all melt-pool monitoring research activities connected to LPBF, as well as for end users and serial production.

Originality/value

Surface roughness has not yet been revealed as being one of the most important origins for signal deviations in coaxial melt-pool monitoring. To the best of the authors’ knowledge, the direct comparison of influences because of parameters and environment has not been published to this extent. The detection, evaluation and remelting of surface roughness constitute a plausible workflow for closed-loop control in LPBF.

Details

Rapid Prototyping Journal, vol. 26 no. 1
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 26 April 2011

Shyam Barua, Todd Sparks and Frank Liou

The melt pool created by a laser is one of the most important factors affecting the quality of the deposit in a laser metal deposition (LMD) process. The high‐intensity…

Abstract

Purpose

The melt pool created by a laser is one of the most important factors affecting the quality of the deposit in a laser metal deposition (LMD) process. The high‐intensity infrared (IR) radiation emitted by the melt pool saturates a conventional camera sensor preventing useful data acquisition. The purpose of this paper is to discuss the development of a low‐cost vision system to monitor the size of the melt pool for in‐process quality control of the deposit.

Design/methodology/approach

According to the black body radiation theory, there is no radiation emitted in the ultraviolet (UV) region from the melt pool created in the LMD process. IR radiation and visible light are the only radiations inherent to the LMD process. UV illumination is utilized along with narrow band pass filters on a USB camera to achieve a clear image of the melt pool while IR radiation of the process is blocked out. The melt pool size and shape were closely monitored during the deposition process.

Findings

A clear image of the melt pool was obtained using a relatively low‐cost imaging system during laser deposition process.

Originality/value

Traditional approaches to vision systems in high‐intensity processes use a high‐speed video camera fitted with IR filters to prevent saturation of the camera sensor. Such systems are usually complex and expensive to run and maintain. This paper demonstrates an alternative and lower cost method to achieve in process monitoring in an LMD process.

Details

Rapid Prototyping Journal, vol. 17 no. 3
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 6 December 2019

Muhammad Omar Shaikh, Ching-Chia Chen, Hua-Cheng Chiang, Ji-Rong Chen, Yi-Chin Chou, Tsung-Yuan Kuo, Kei Ameyama and Cheng-Hsin Chuang

Using wire as feedstock has several advantages for additive manufacturing (AM) of metal components, which include high deposition rates, efficient material use and low…

Abstract

Purpose

Using wire as feedstock has several advantages for additive manufacturing (AM) of metal components, which include high deposition rates, efficient material use and low material costs. While the feasibility of wire-feed AM has been demonstrated, the accuracy and surface finish of the produced parts is generally lower than those obtained using powder-bed/-feed AM. The purpose of this study was to develop and investigate the feasibility of a fine wire-based laser metal deposition (FW-LMD) process for producing high-precision metal components with improved resolution, dimensional accuracy and surface finish.

Design/methodology/approach

The proposed FW-LMD AM process uses a fine stainless steel wire with a diameter of 100 µm as the additive material and a pulsed Nd:YAG laser as the heat source. The pulsed laser beam generates a melt pool on the substrate into which the fine wire is fed, and upon moving the X–Y stage, a single-pass weld bead is created during solidification that can be laterally and vertically stacked to create a 3D metal component. Process parameters including laser power, pulse duration and stage speed were optimized for the single-pass weld bead. The effect of lateral overlap was studied to ensure low surface roughness of the first layer onto which subsequent layers can be deposited. Multi-layer deposition was also performed and the resulting cross-sectional morphology, microhardness, phase formation, grain growth and tensile strength have been investigated.

Findings

An optimized lateral overlap of about 60-70% results in an average surface roughness of 8-16 µm along all printed directions of the X–Y stage. The single-layer thickness and dimensional accuracy of the proposed FW-LMD process was about 40-80 µm and ±30 µm, respectively. A dense cross-sectional morphology was observed for the multilayer stacking without any visible voids, pores or defects present between the layers. X-ray diffraction confirmed a majority austenite phase with small ferrite phase formation that occurs at the junction of the vertically stacked beads, as confirmed by the electron backscatter diffraction (EBSD) analysis. Tensile tests were performed and an ultimate tensile strength of about 700-750 MPa was observed for all samples. Furthermore, multilayer printing of different shapes with improved surface finish and thin-walled and inclined metal structures with a minimum achievable resolution of about 500 µm was presented.

Originality/value

To the best of the authors’ knowledge, this is the first study to report a directed energy deposition process using a fine metal wire with a diameter of 100 µm and can be a possible solution to improving surface finish and reducing the “stair-stepping” effect that is generally observed for wires with a larger diameter. The AM process proposed in this study can be an attractive alternative for 3D printing of high-precision metal components and can find application for rapid prototyping in a range of industries such as medical and automotive, among others.

Details

Rapid Prototyping Journal, vol. 26 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 24 July 2019

Rong Li and Jun Xiong

The purpose of this study is to present how the thermal energy transmission of circular parts produced in robotized gas metal arc (GMA)-based additive manufacturing was…

Abstract

Purpose

The purpose of this study is to present how the thermal energy transmission of circular parts produced in robotized gas metal arc (GMA)-based additive manufacturing was affected by the substrate shape through finite element analysis, including distributions of thermal energy and temperature gradient in the molten pool and deposited layers.

Design/methodology/approach

Three geometric shapes, namely, square, rectangle and round were chosen in simulation, and validation tests were carried out by corresponding experiments.

Findings

The thermal energy conduction ability of the deposited layers is the best on the round substrate and the worst on the rectangular substrate. The axial maximum temperature gradients in the molten pool along the deposition path with the round substrate are the largest during the deposition process. At the deposition ending moment, the circumferential temperature gradients of all layers with the round substrate are the largest. A large temperature gradient usually stands for a good heat conduction condition. Altogether, the round substrate is more suitable for the fabrication of circular thin-walled parts.

Originality/value

The predicted thermal distributions of the circular thin-walled part with various substrate shapes are helpful to understand the influence of substrate shape on the thermal energy transmission behavior in GMA-based additive manufacturing.

Details

Rapid Prototyping Journal, vol. 25 no. 7
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 7 May 2019

Chuanchu Su and Xizhang Chen

This paper aims to mainly report the impact of torch angle on the dynamic behavior of the weld pool which is recorded and monitored in real time with the aid of a…

Abstract

Purpose

This paper aims to mainly report the impact of torch angle on the dynamic behavior of the weld pool which is recorded and monitored in real time with the aid of a high-speed camera system. The influence of depositing torch angle on the fluctuation behavior of weld pool and the quality of weld formation are compared and analyzed.

Design/methodology/approach

The FANUC controlled robotic manufacturing system comprised a Fronius cold metal transfer (CMT) Advanced 4000R power source, FANUC robot, water cooling system, wire feeding system and a gas shielding system. An infrared laser was used to illuminate the weld pool for high-speed imaging at 1,000 frames per second with CR600X2 high-speed camera. The high-speed camera was set up a 35 ° angle with the deposition direction to investigate the weld pool flow patterns derived from high-speed video and the effect of torch angles on the first layer of wire additive manufacture-CMT.

Findings

The experimental results demonstrated that different torch angles significantly influence on the deposited morphology, porosity formation rate and weld pool flow.

Originality/value

With regard to the first layer of wire arc additive manufacture of aluminum alloys, the change of torch angle is critical. It is clear that different torch angles significantly influence on the weld morphology, porosity formation and weld pool flow. Furthermore, under different torch angles, the deposited beads will produce different defects. To get well deposited beads, 0-10° torch could be made away from the vertical position of the deposition direction, in which the formation of deposited beads were well and less porosity and other defects.

Details

Industrial Robot: the international journal of robotics research and application, vol. 46 no. 2
Type: Research Article
ISSN: 0143-991X

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Article
Publication date: 23 July 2019

Cameron Myron Knapp, Thomas J. Lienert, Paul Burgardt, Patrick Wayne Hochanadel and Desiderio Kovar

Directed energy deposition (DED) with laser powder-feed is an additive manufacturing process that is used to produce metallic components by simultaneously providing a…

Abstract

Purpose

Directed energy deposition (DED) with laser powder-feed is an additive manufacturing process that is used to produce metallic components by simultaneously providing a supply of energy from a laser and mass from a powder aerosol. The breadth of alloys used in DED is currently limited to a very small range as compared to wrought or cast alloys. The purpose of this paper is to develop the new alloys for DED is limited because current models to predict operational processing parameters are computationally expensive and trial-and-error based experiments are both expensive and time-consuming.

Design/methodology/approach

In this research, an agile DED model is presented to predict the geometry produced by a single layer deposit.

Findings

The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed. The proposed model incorporates concepts from heat transfer, welding and laser cladding; and integrates them with experimental fits and physical models that are relevant to DED.

Originality/value

The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed.

Details

Rapid Prototyping Journal, vol. 25 no. 6
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 1 September 2001

P. Mohan Raj, S. Sarkar, S. Chakraborty and P. Dutta

A transient, three‐dimensional mathematical model of a single‐pass laser surface alloying process has been developed to examine the macroscopic heat, momentum and species…

Abstract

A transient, three‐dimensional mathematical model of a single‐pass laser surface alloying process has been developed to examine the macroscopic heat, momentum and species transport during the process. A numerical study is performed in a co‐ordinate system moving with the laser at a constant scanning speed. A fixed grid enthalpy‐porosity approach is used, which predicts the evolutionary development of the laser‐melted pool. It is observed that the melting of the added alloying element is not instantaneous in case its melting temperature is higher as compared to that of the base metal. As a result, the addition of alloying element at the top surface cannot be accurately modelled as a mass flux boundary condition at that surface. To resolve this situation, the addition of alloying elements is formulated by devising a species generation term for the solute transport equation. By employing a particle‐tracking algorithm and a simultaneous particle‐melting consideration, the species source term is estimated by the amount of fusion of a spherical particle as it passes through a particular control volume. Numerical simulations are performed for Ni as alloying element on Al base metal. It is revealed that the present model makes a distinctly different prediction of composition variation within the resolidified microstructure, as compared to a model that does not incorporate any considerations of distributed melting.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 11 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 15 June 2010

Kamran Mumtaz and Neil Hopkinson

The purpose of this paper is to investigate the selective laser melting (SLM) of Inconel 625 using pulse shape control to vary the energy distribution within a single…

Abstract

Purpose

The purpose of this paper is to investigate the selective laser melting (SLM) of Inconel 625 using pulse shape control to vary the energy distribution within a single laser pulse. It aims to discuss the effectiveness of pulse shaping, including potential benefits for use within SLM.

Design/methodology/approach

Laser parameters were varied in order to identify optimal parameters that produced thin wall parts with a low surface roughness without the use of pulse shape control. Pulse shape control was then employed to provide gradual heating or a prolonged cooling effect with a variety of peak power/pulse energy combinations. Properties of pulse shaped and nonpulse shaped parts were compared, with particular attention focused on part surface roughness and width.

Findings

High peak powers tended to reduce top surface roughness and reduce side roughness as recoil pressures flatten out the melt pool and inhibit melt pool instabilities from developing. Ramp up energy distribution can reduce the maximum peak power required to melt material and reduce material spatter generation during processing due to a localized preheating effect. Ramp down energy distribution prolonged melt pool solidification allowing more time for molten material to redistribute, subsequently reducing the top surface roughness of parts. However, larger melt pools and longer solidification times increased the side roughness of parts due to a possible lateral expulsion of material from the melt pool.

Originality/value

This paper is the first of its kind to employ laser pulse shape control during SLM to process material from powder bed. It is a useful aid in unveiling relationships between laser energy distribution and the formation of parts.

Details

Rapid Prototyping Journal, vol. 16 no. 4
Type: Research Article
ISSN: 1355-2546

Keywords

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