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Jichang Liu

Bio: Jichang Liu is an academic researcher from Hunan University. The author has contributed to research in topics: Coaxial & Laser. The author has an hindex of 7, co-authored 8 publications receiving 216 citations.

Papers
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Journal ArticleDOI
Jichang Liu1, Lijun Li1
TL;DR: In this article, a model of effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding was developed, and the relationship between powder concentration and power density distribution was established.
Abstract: In this paper, model of effects of powder concentration distribution on fabrication of thin-wall parts in coaxial laser cladding was developed. There exists relationship between powder concentration distribution and power density distribution, which affects fabrication of thin-wall parts in coaxial laser cladding. Changes in powder concentration distribution lead to changes in wall thickness and wall growing rate. Fluctuation of powder feed rate deteriorates the growing wall in laser cladding. Deviation of the powder flow stream makes the powder concentration distribution, the thermal flux density and consequently the molten pool not symmetrical against the x-axis, resulting in irregular upper faces of the formed wall. This was verified by the results of experiment.

55 citations

Journal ArticleDOI
Jichang Liu1, Lijun Li1
TL;DR: In this article, an in-time motion adjustment strategy was presented to remedy and eliminate defects occurring during laser cladding to improve the dimensional accuracy and surface finish of the built part.
Abstract: This paper presents in-time motion adjustment in laser cladding manufacturing process as a means to improve dimensional accuracy and surface finish of the built part. Defects occurring during laser cladding degrade the part quality such as dimensional accuracy and surface finish. In this paper, in-time motion adjustment strategy was presented to remedy and eliminate defects occurring during laser cladding to improve the dimensional accuracy and surface finish. Based on the relationship between the motion of laser head relative to the growing part and other parameters in effects on clad profile, the laser traverse speed, stand-off distance and laser approach orientation to the existing clad layer were adjusted by instructions from a close-loop control system in real time to remedy and eliminate defects. The results of the experiments verified the effects of in-time motion adjustment on dimensional accuracy and surface finish.

51 citations

Journal ArticleDOI
Jichang Liu1, Lijun Li1
TL;DR: In this paper, the effects of process variables on wall thickness, powder primary efficiency and speed of forming a thin metallic wall in single-pass coaxial laser cladding are investigated, and some resolution models are established and testified experimentally.
Abstract: In this paper, effects of process variables on wall thickness, powder primary efficiency and speed of forming a thin metallic wall in single-pass coaxial laser cladding are investigated, and some resolution models are established and testified experimentally. With some assumptions, each of wall thickness, powder primary efficiency and formation speed can be defined as a function of the process variables. Wall thickness is equal to width of the molten pool created in single-pass laser cladding and determined by laser absorptivity, laser power, initial temperature, scanning speed and thermo-physical properties of clad material. Powder primary efficiency and formation speed are both dependent on an exponential function involving the ratio of melt pool width, which is decided by the process variables, to powder flow diameter. In addition, formation speed is influenced by powder feed rate. In present experiment, a 500 W continual-wave (CW) CO2 laser is used to produce thin-wall samples by single-pass coaxial laser cladding. The experimental results agree well with the calculation values despite some errors.

49 citations

Journal ArticleDOI
Jichang Liu1, Lijun Li1
TL;DR: In this paper, a model of cross-section profile on the substrate in coaxial single-pass cladding with a low-power laser was studied, and the static model of powder mass concentration distribution at cold-stream conditions was defined as a Gaussian function.
Abstract: In this paper, a model of cross-section clad profile on the substrate in coaxial single-pass cladding with a low-power laser was studied. The static model of powder mass concentration distribution at cold-stream conditions was defined as a Gaussian function. In coaxial single-pass cladding with a low-power laser, since the influence of surface tension, gravity and gas flow on the clad bead could be neglected, the cross-section profile of the clad bead deposited by a low-power laser on the substrate was dominated by the powder concentration at each point on the pool and the time when the material was liquid at this point. The height of each point on the cross-section clad profile was defined as a definite integration of a Gaussian function from the moment at which the melt pool was just arriving at the point to the moment at which the point left the melt pool. In the presented experiment, powder of Steel 63 (at 0.63 wt% C) was deposited on a substrate of Steel 20 (at 0.20 wt% C) at the laser power of 135 W. The experimental results testified the model.

34 citations

Journal ArticleDOI
TL;DR: In this article, the effect of adding Mn or Si powder on mechanical properties and microstructure of the weld was investigated, and the average tensile-shear strength of Si-add joint is 3.84% higher than that of Mn-added joint.
Abstract: The experiments of laser penetration welding for dual phase steel and aluminum alloy were carried out, and the effect of adding Mn or Si powder on mechanical properties and microstructure of the weld was investigated. Some defects, such as spatter, inclusion, cracks and softening in heat affected zone (HAZ), can be avoided in welding joints, and the increased penetration depth is obtained by adding Mn or Si powder. The average tensile-shear strength of Si-added joint is 3.84% higher than that of Mn-added joint, and the strength of both joints exceeds that of no-added joint. In the case of adding Mn powder, small amount of liquid Al is mixed into steel molten pool, and the Al content increases in both sides of the weld, which leads to the increased weld width in aluminum molten pool. Thus, transverse area increases in jointing steel to aluminum, which is significant for the improved tensile-shear strength of joints. As far as adding Si powder is concerned, it is not the case, the enhancement of the joint properties benefits from improvement of metallurgical reaction.

23 citations


Cited by
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TL;DR: In this article, the authors map available additive manufacturing methods based on their process mechanisms, review modelling approaches based on modelling methods and identify research gaps and implications for closed-loop control of the process.
Abstract: Additive manufacturing is a technology rapidly expanding on a number of industrial sectors. It provides design freedom and environmental/ecological advantages. It transforms essentially design files to fully functional products. However, it is still hampered by low productivity, poor quality and uncertainty of final part mechanical properties. The root cause of undesired effects lies in the control aspects of the process. Optimization is difficult due to limited modelling approaches. Physical phenomena associated with additive manufacturing processes are complex, including melting/solidification and vaporization, heat and mass transfer etc. The goal of the current study is to map available additive manufacturing methods based on their process mechanisms, review modelling approaches based on modelling methods and identify research gaps. Later sections of the study review implications for closed-loop control of the process.

984 citations

Journal ArticleDOI
TL;DR: A detailed overview of the thermal/fluid properties inherent in the direct laser deposition (DLD) process can be found in this article, with a focus on the mechanical properties and microstructure of parts manufactured via DLD.
Abstract: Laser-based additive manufacturing (LBAM) processes can be utilized to generate functional parts (or prototypes) from the ground-up via layer-wise cladding – providing an opportunity to generate complex-shaped, functionally graded or custom-tailored parts that can be utilized for a variety of engineering applications. Directed Energy Deposition (DED), utilizes a concentrated heat source, which may be a laser or electron beam, with in situ delivery of powder- or wire-shaped material for subsequent melting to accomplish layer-by-layer part fabrication or single-to-multi layer cladding/repair. Direct Laser Deposition (DLD), a form of DED, has been investigated heavily in the last several years as it provides the potential to (i) rapidly prototype metallic parts, (ii) produce complex and customized parts, (iii) clad/repair precious metallic components and (iv) manufacture/repair in remote or logistically weak locations. DLD and Powder Bed Fusion-Laser (PBF-L) are two common LBAM processes for additive metal part fabrication and are currently demonstrating their ability to revolutionize the manufacturing industry; breaking barriers imposed via traditional, ‘subtractive’ metalworking processes. This article provides an overview of the major advancements, challenges and physical attributes related to DLD, and is one of two Parts focused specifically on DLD. Part I (this article) focuses on describing the thermal/fluidic phenomena during the powder-fed DLD process, while Part II focuses on the mechanical properties and microstructure of parts manufactured via DLD. In this current article, a selection of recent research efforts – including methodology, models and experimental results – will be provided in order to educate the reader of the thermal/fluidic processes that occur during DLD, as well as providing important background information relevant to DLD as a whole. The thermal/fluid phenomena inherent to DLD directly influence the solidification heat transfer which thus impacts the part's microstructure and associated thermo-mechanical properties. A thorough understanding of the thermal/fluid aspects inherent to DLD is vital for optimizing the DLD process and ensuring consistent, high-quality parts.

781 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of the mechanical characteristics and behavior of metallic parts fabricated via direct laser deposition (DLD), while also discussing methods to optimize and control the DLD process.
Abstract: The mechanical behavior, and thus ‘trustworthiness’/durability, of engineering components fabricated via laser-based additive manufacturing (LBAM) is still not well understood. This is adversely affecting the continual adoption of LBAM for part fabrication/repair within the global industry at large. Hence, it is important to determine the mechanical properties of parts fabricated via LBAM as to predict their performance while in service. This article is part of two-part series that provides an overview of Direct Laser Deposition (DLD) for additive manufacturing (AM) of functional parts. The first part (Part I) provides a general overview of the thermo-fluid physics inherent to the DLD process. The objective of this current article (Part II) is to provide an overview of the mechanical characteristics and behavior of metallic parts fabricated via DLD, while also discussing methods to optimize and control the DLD process. Topics to be discussed include part microstructure, tensile properties, fatigue behavior and residual stress – specifically with their relation to DLD and post-DLD process parameters (e.g. heat treatment, machining). Methods for controlling/optimizing the DLD process for targeted part design will be discussed – with an emphasis on monitored part temperature and/or melt pool morphology. Some future challenges for advancing the knowledge in AM-part adoption are discussed. Despite various research efforts into DLD characteristics and process optimization, it is clear that there are still many areas that require further investigation.

737 citations

Journal ArticleDOI
TL;DR: In this paper, the state of the art in the field of laser machining of structural ceramics is presented, focusing on experimental and computational approaches in understanding physical nature of the complex phenomena.
Abstract: Outstanding mechanical and physical properties like high thermal resistance, high hardness and chemical stability have encouraged use of structural ceramics in several applications. The brittle and hard nature of these ceramics makes them difficult to machine using conventional techniques and damage caused to the surface while machining affects efficiency of components. Laser machining has recently emerged as a potential technique for attaining high material removal rates. This review paper aims at presenting the state of the art in the field of laser machining of structural ceramics and emphasizes on experimental and computational approaches in understanding physical nature of the complex phenomena.

401 citations