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14 pages, 3866 KiB

Open AccessArticle

Effects of High Toughness and Welding Residual Stress for Unstable Fracture Prevention

by Gyubaek An, Jeongung Park and Ilwook Han

Appl. Sci. 2020, 10(23), 8613; https://doi.org/10.3390/app10238613 - 1 Dec 2020

Cited by 3 | Viewed by 1788

Abstract

Unstable fractures generally occur in brittle materials under low-temperature service conditions. Toughness and welding residual stress are the main factors that should be evaluated when defining a brittle crack propagation path. In this study, a rainbow welding technique was proposed and confirmed as [...] Read more.

Unstable fractures generally occur in brittle materials under low-temperature service conditions. Toughness and welding residual stress are the main factors that should be evaluated when defining a brittle crack propagation path. In this study, a rainbow welding technique was proposed and confirmed as being significantly useful in preventing unstable fractures in weld joints. The residual compressive stress in the crack front was particularly useful for decreasing the possibility of brittle fracture. The objective was to examine the effect of high welding consumable toughness welding residual stress, especially for avoiding brittle fracture through welding residual compressive stress. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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19 pages, 3031 KiB

Open AccessArticle

The Analytical Prediction of Thermal Distribution and Defect Generation of Inconel 718 by Selective Laser Melting

by Huadong Yang, Zhen Li and Siqi Wang

Appl. Sci. 2020, 10(20), 7300; https://doi.org/10.3390/app10207300 - 19 Oct 2020

Cited by 9 | Viewed by 2418

Abstract

In selective laser melting, the rapid change of the temperature field caused by the rapid movement of the laser causes the instability of the melt pool flow, resulting in a generation of defects, such as lack of fusion, keyholing and balling effect, which [...] Read more.

In selective laser melting, the rapid change of the temperature field caused by the rapid movement of the laser causes the instability of the melt pool flow, resulting in a generation of defects, such as lack of fusion, keyholing and balling effect, which greatly affect the performance of parts. In order to fully understand the temperature distribution and defect generation process of selective laser melting (SLM), experimental research, numerical simulation and analytical methods are mainly applied. The analytical method is suitable for the determination of the optimal process parameters because it is simple and consumes fewer resources. In a simulation, the absorptivity of the material is usually regarded as a constant, but experimental studies have shown that absorptivity is related to temperature, laser power, scanning speed, layer thickness and other process parameters. Considering the dynamics of thermal physical properties of Inconel 718, an improved analytical method was proposed and successfully applied to thermal analysis and the prediction of melt pool size. By comparing with the results of finite element simulation, experiment and other analytical solutions, the ease of use and effectiveness of the method are verified. Based on the prediction of the melt pool and the criterion of internal defects, the combination of process parameters that produce internal defects is calculated, which will make it possible to quickly obtain ideal process parameters. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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17 pages, 5930 KiB

Open AccessArticle

Influence of Process Parameters on Forming Load of Variable-Section Thin-Walled Conical Parts in Spinning

by Yingxiang Xia, Xuedao Shu, Ying Zhu and Zixuan Li

Appl. Sci. 2020, 10(17), 5932; https://doi.org/10.3390/app10175932 - 27 Aug 2020

Cited by 5 | Viewed by 1798

Abstract

Thin-walled conical parts with variable-section are usually made of superalloy material, with poor plasticity and complex forces, which are difficult to form and control. In this research, a thin-walled conical casing of superalloy GH1140 with variable-section is studied; the real stress–strain curve of [...] Read more.

Thin-walled conical parts with variable-section are usually made of superalloy material, with poor plasticity and complex forces, which are difficult to form and control. In this research, a thin-walled conical casing of superalloy GH1140 with variable-section is studied; the real stress–strain curve of the material is fitted and the load-displacement curves of superalloy GH1140 are obtained through a universal testing machine. To clarify the equivalent stress distribution on the upper surface of the thin-walled casing during the forming process and after unloading the rotary wheel, the finite element model of the thin-walled conical casing during the spinning forming process is established with the Simufact Forming finite element analysis software. The effects of processing parameters, such as the mandrel rotational speed ω, the roller feed ratio f and the gap deviation rate δ between the roller and mandrel, on the spinning forming load were obtained. The distribution and numerical trend of the tangential residual stress after forming were detected by X-ray diffraction, and the causes of defects such as flange instability were analyzed. The results of the forming test and the test of residual stress conform well with the simulation, which verifies the stability of the model. The research provides a theoretical basis for improving the forming quality of thin-walled parts with variable-section. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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15 pages, 6783 KiB

Open AccessArticle

Experimental Study of Tool Wear in Electrochemical Discharge Machining

by Jianxiao Bian, Baoji Ma, Xiaofeng Liu and Lijun Qi

Appl. Sci. 2020, 10(15), 5039; https://doi.org/10.3390/app10155039 - 22 Jul 2020

Cited by 12 | Viewed by 2747

Abstract

Electrochemical discharge machining (ECDM) is an emerging special processing technology for non-conductive hard and brittle materials, but it may encounter the problem of tool wear due to its process characteristics, which affects the processing accuracy. In this study, in the non-machining state, the [...] Read more.

Electrochemical discharge machining (ECDM) is an emerging special processing technology for non-conductive hard and brittle materials, but it may encounter the problem of tool wear due to its process characteristics, which affects the processing accuracy. In this study, in the non-machining state, the tungsten carbide spiral cathode with a diameter of 400 μm was selected to analyze the influencing mechanism of the process parameters on tool wear, and a suitable voltage range for the processing was obtained. The influence of the cathode’s loss behavior on the film formation time and the average current of spark discharge was discussed based on the current signal. The results show that the tool wear mainly appears from the bottom to the end and edge tip of the protrusion. Loss is mainly in the form of local material melting or gasification at high temperature. In addition, the loss may shorten the film formation time, but the effect on the average current of spark discharge is small. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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10 pages, 3193 KiB

Open AccessArticle

Thermal Behavior of Single-Crystal Diamonds Catalyzed by Titanium Alloy at Elevated Temperature

by Pengyu Hou, Ming Zhou and Haijun Zhang

Appl. Sci. 2020, 10(13), 4651; https://doi.org/10.3390/app10134651 - 6 Jul 2020

Cited by 2 | Viewed by 1933

Abstract

Single-crystal diamonds are considered as the best tool material for ultra-precision machining. However, due to its low thermal conductivity, small elastic modulus and strong chemical activity, titanium alloy has poor machinability and is a typically difficult-to-machine material. Excessive tool wear prevents diamonds from [...] Read more.

Single-crystal diamonds are considered as the best tool material for ultra-precision machining. However, due to its low thermal conductivity, small elastic modulus and strong chemical activity, titanium alloy has poor machinability and is a typically difficult-to-machine material. Excessive tool wear prevents diamonds from cutting titanium alloy. This study conducts a series of thermal analytic experiments under conditions of different gas atmospheres in order to research the details of thermochemical wear of diamonds catalyzed by titanium alloy at elevated temperatures. Raman scattering analysis was performed to identify the transformation of the diamond crystal structure. The change in chemical composition of the work material was detected be means of energy dispersive X-ray analysis. X-ray photoelectron spectroscopy was used to confirm the resultant interfacial thermochemical reactions. The results of the study reveal the diffusion law of the single-crystal diamond under the action of titanium in the argon and air environment. From the experimental results, the product of the chemical reaction corresponding to the interface between the diamond and the titanium alloy sheet could be found. The research results provide a theoretical basis for elucidating the wear mechanism of diamond tools in the titanium alloy cutting process and for exploring the measures to suppress tool wear. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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17 pages, 4415 KiB

Open AccessArticle

Study of the Mechanism of a Stable Deposited Height During GMAW-Based Additive Manufacturing

by Hongyao Shen, Rongxin Deng, Bing Liu, Sheng Tang and Shun Li

Appl. Sci. 2020, 10(12), 4322; https://doi.org/10.3390/app10124322 - 24 Jun 2020

Cited by 6 | Viewed by 2118

Abstract

Gas metal arc welding (GMAW)-based additive manufacturing has the advantages of a high deposition rate, low cost, the production of a compact and dense microstructure in the cladding layer, and good mechanical properties, but the forming process is unstable. The shape of the [...] Read more.

Gas metal arc welding (GMAW)-based additive manufacturing has the advantages of a high deposition rate, low cost, the production of a compact and dense microstructure in the cladding layer, and good mechanical properties, but the forming process is unstable. The shape of the welding bead critically affects the layer height and dimensional accuracy of the parts manufactured, and it is difficult to control. A series of experiments were designed and the results indicated that when the value of the predefined layer height is set in a certain range and other parameters are held constant, the height of the thin wall produced by GMAW-based additive manufacturing is almost equal to the predefined layer height multiplied by the number of layers. This research work shows that during the GMAW process, the changes in the distance between the torch and the top surface of the part cause a variety of dry extensions of the electrode; furthermore, the changes lead to a variety in the heat input into the molten pool. Therefore, the dry extension of the electrode is the key factor influencing the geometry of the welding bead, especially the layer height, and it has a compensating effect that makes the actual layer height close to the predefined value. A three-dimensional numerical model was established to study the influence of the predefined layer height to the fluid flow and heat transfer behaviors during the weld-deposition process. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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19 pages, 3102 KiB

Open AccessArticle

Numerical Investigation into the Effect of Different Parameters on the Geometrical Precision in the Laser-Based Powder Bed Fusion Process Chain

by David De Baere, Mandanà Moshiri, Sankhya Mohanty, Guido Tosello and Jesper Henri Hattel

Appl. Sci. 2020, 10(10), 3414; https://doi.org/10.3390/app10103414 - 15 May 2020

Cited by 6 | Viewed by 2441

Abstract

Due to the layer-by-layer nature of the process, parts produced by laser-based powder bed fusion (LPBF) have high residual stresses, causing excessive deformations. To avoid this, parts are often post-processed by subjecting them to specially designed heat treatment cycles before or after their [...] Read more.

Due to the layer-by-layer nature of the process, parts produced by laser-based powder bed fusion (LPBF) have high residual stresses, causing excessive deformations. To avoid this, parts are often post-processed by subjecting them to specially designed heat treatment cycles before or after their removal from the base plate. In order to investigate the effects of the choice of post-processing steps, in this work the entire LPBF process chain is modelled in a commercial software package. The developed model illustrates the possibilities of implementing and tailoring the process chain model for metal additive manufacturing using a general purpose finite element (FE) solver. The provided simplified computational example presents an idealised model to analyse the validity of implementing the LPBF process chain in FE software. The model is used to evaluate the effect of the order of the process chain, the heat treatment temperature and the duration of the heat treatment. The results show that the model is capable of qualitatively capturing the effect of the stress relaxation that occurs during a heat treatment at elevated temperature. Due to its implementation, the model is relatively insensitive to duration and heat treatment temperature, at least as long as it is above the relaxation temperature. Furthermore, the simulations suggest that, when post-processing, it is necessary to perform the stress relaxation before the part is removed from the base plate, in order to avoid a significant increase of the deformation. The paper demonstrates the capability of the simulation tool to evaluate the effects of variations in the process chain steps and highlights its potential usage in directing decision-making for LPBF process chain design. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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Review

Jump to: Research

14 pages, 2514 KiB

Open AccessReview

A Review on Laser Powder Bed Fusion of Inconel 625 Nickel-Based Alloy

by Zhihua Tian, Chaoqun Zhang, Dayong Wang, Wen Liu, Xiaoying Fang, Daniel Wellmann, Yongtao Zhao and Yingtao Tian

Appl. Sci. 2020, 10(1), 81; https://doi.org/10.3390/app10010081 - 20 Dec 2019

Cited by 116 | Viewed by 8924

Abstract

The Inconel 625 (IN625) superalloy has a high strength, excellent fatigue, and creep resistance under high-temperature and high-pressure conditions, and is one of the critical materials used for manufacturing high-temperature bearing parts of aeroengines. However, the poor workability of IN625 alloy prevents IN625 [...] Read more.

The Inconel 625 (IN625) superalloy has a high strength, excellent fatigue, and creep resistance under high-temperature and high-pressure conditions, and is one of the critical materials used for manufacturing high-temperature bearing parts of aeroengines. However, the poor workability of IN625 alloy prevents IN625 superalloy to be used in wider applications, especially in applications requiring high geometrical complexity. Laser powder bed fusion (LPBF) is a powerful additive manufacturing process which can produce metal parts with high geometrical complexity and freedom. This paper reviews the studies that have been done on LPBF of IN625 focusing on the microstructure, mechanical properties, the development of residual stresses, and the mechanism of defect formation. Mechanical properties such as microhardness, tensile properties, and fatigue properties reported by different researchers are systematically summarized and analyzed. Finally, the remaining issues and suggestions on future research on LPBF of IN625 alloy parts are put forward. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metal Components: Mechanical Behavior, Process Parameter Optimization, and Control Ⅱ)

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