Metals

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23 pages, 25998 KiB

Open AccessArticle

Light Source Modules for Defect Detection on Highly Reflective Metallic Surfaces

by Lih-Ping Huang, Quang-Cherng Hsu, Bao-Hsing Liu, Chin-Fu Lin and Chien-Hsianh Chen

Metals 2023, 13(5), 861; https://doi.org/10.3390/met13050861 - 28 Apr 2023

Cited by 2 | Viewed by 1877

High strength and highly reflective metal sheets are widely applied in industry; industrial requirements for defect detection are extremely demanding, particularly in the aviation and automotive industries. Classifying and recognizing surface defects on steel plate surfaces is highly challenging. Currently, defect detection is [...] Read more.

High strength and highly reflective metal sheets are widely applied in industry; industrial requirements for defect detection are extremely demanding, particularly in the aviation and automotive industries. Classifying and recognizing surface defects on steel plate surfaces is highly challenging. Currently, defect detection is still inspected visually by personnel. However, given the high temperatures at inspection sites and the high risks in the operating environments, machine vision inspection systems are expected to replace manual inspection processes eventually. Therefore, this study developed an automated defect detection system that reduces the high reflectivity of examined objects. The light sources emitted light rays to the rays diffused and reflected multiple times inside the hemispherical cover to produce uniform illumination. Subsequently, image processing was conducted to highlight defect features on the stainless-steel plates. Relatively favorable light source positions were identified, which reduced the difficulty of class identification, the omission rate in defect detection to be decreased, and frequently encountered reflection problems in the automated optical inspection of metallic products to be overcome. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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17 pages, 9527 KiB

Open AccessArticle

An Anisotropic Damage Model for Prediction of Ductile Fracture during Cold-Forging

by Atsuo Watanabe, Kunio Hayakawa and Shinichiro Fujikawa

Metals 2022, 12(11), 1823; https://doi.org/10.3390/met12111823 - 27 Oct 2022

Cited by 3 | Viewed by 1388

Abstract

Researchers have formulated equations of ductile fracture to simulate and predict defects in cold-forged parts, e.g., the Cockcroft–Latham criterion. However, these equations are not applicable to certain cases of fracture in forged products. This study formulates a new equation for predicting ductile fractures [...] Read more.

Researchers have formulated equations of ductile fracture to simulate and predict defects in cold-forged parts, e.g., the Cockcroft–Latham criterion. However, these equations are not applicable to certain cases of fracture in forged products. This study formulates a new equation for predicting ductile fractures with better prediction accuracy than the convention by which the cost for trial-and-error design can be reduced. The equation is expressed as a second-rank symmetric tensor, which is the inner product of the stress and strain-increment tensors. The theoretical efficacy of the equation in predicting ductile fractures is verified via a uniaxial tensile test. The practicability of the equation is confirmed by applying it to the simulations of two real cold-forged components: a cold-forged hollow shaft and a flanged shaft. For the hollow shaft, the equation predicts the position where the ductile fracture would initiate, which—to the best of the authors’ knowledge—is unique to this study. For the flanged shaft, the equation predicts the occurrence of diagonal cracks due to different lubrication conditions. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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9 pages, 1616 KiB

Open AccessArticle

Study on the Application of the GTAW Process in Strengthening the Welding Quality of Short Duplex Stainless Pipe

by Ming-Che Lin, Chia-Chieh Cheng and Ching-Chien Huang

Metals 2022, 12(10), 1691; https://doi.org/10.3390/met12101691 - 10 Oct 2022

Cited by 2 | Viewed by 1379

Abstract

This study focuses on the results of the welding process when the Taguchi method is added to the design of experimental welding parameters when creating the welding procedure for gas tungsten arc welding (GTAW) by ASME Code for duplex stainless steel (UNS31803). A [...] Read more.

This study focuses on the results of the welding process when the Taguchi method is added to the design of experimental welding parameters when creating the welding procedure for gas tungsten arc welding (GTAW) by ASME Code for duplex stainless steel (UNS31803). A Vickers hardness tester is employed to collect and convert the tensile strength data for each test piece (weld bead, base material, and heat-affected area). A ferritic rate meter can quickly determine the ferric contents, which affect corrosion resistance and susceptibility to cracking. The test data are entered into the Taguchi technique to analyze the influence of each component on the welding quality. The L₉ (3⁴) orthogonal table is used to design the parameters for the experiment. We fixed the same shielding gas and flow rate. Backing gas at root, workpiece clamping angle, heat input, and interlayer temperature are employed as control factors for the four essential variables of the GTAW process. The ideal set of quality analysis and optimization parameters can be found. The welding parameters could be used to improve the welding quality of thin and short duplex stainless steel pipe fittings during argon welding. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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16 pages, 5271 KiB

Open AccessFeature PaperArticle

High-Order Groove-Shape Curve Roll Design for Aluminum Alloy 7075 Wire Rolling

by Jinn-Jong Sheu, Chien-Jen Ho, Cheng-Hsien Yu and Chi-Yuan Kao

Metals 2022, 12(7), 1071; https://doi.org/10.3390/met12071071 - 23 Jun 2022

Cited by 2 | Viewed by 1936

Abstract

A Bézier curve groove-shape roll design method was proposed and compared to round-oval-round designs for the wire rolling process. CAE simulations were adopted to predict the rolling forces and torques required for the rolling process. The rolling torque required for the case of [...] Read more.

A Bézier curve groove-shape roll design method was proposed and compared to round-oval-round designs for the wire rolling process. CAE simulations were adopted to predict the rolling forces and torques required for the rolling process. The rolling torque required for the case of 28% vertical compression rate is 73% higher than the case of 12% compression rate. The curve fittings of the rolling torque and the compression force with respect to the compression rate were obtained with very high R-square values (0.99 and 0.98) in the first rolling pass. The rolling force required for the Bézier curve groove-shape design is no different compared to the oval design with the same compression rate, but the rolling torque requirement for the next rolling station is 6% less than the oval groove design. Furthermore, the equivalent strain distribution on the cross section of the product was uniform, and no fin flash defects occurred. The proposed Bézier curve groove-shape is a better design from the viewpoint of uniform product mechanical property requirement, and a larger compression rate per pass could be achieved. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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12 pages, 7244 KiB

Open AccessFeature PaperArticle

Microforming a Miniature Cup-Shaped Internal Gear Using a Cold Lateral Extrusion Process

by Cho-Pei Jiang, Po-Shen Chen, Yaroslav Erisov and Chang-Cheng Chen

Metals 2022, 12(5), 826; https://doi.org/10.3390/met12050826 - 11 May 2022

Cited by 5 | Viewed by 2005

Abstract

This study determines the micro forming of copper alloy to form a cup-shaped internal gear. The as received material, copper alloy C1100, is annealed to obtain the initial grains and to determine the effect of the initial grain size on the mechanical properties, [...] Read more.

This study determines the micro forming of copper alloy to form a cup-shaped internal gear. The as received material, copper alloy C1100, is annealed to obtain the initial grains and to determine the effect of the initial grain size on the mechanical properties, the deformability and the filling rate for a tooth cavity. The experimental results show that the specimen that is annealed at a temperature of 500 °C has an initial grain size of 25.5 µm, which increases ductility and allows a cup-shaped internal gear to be formed with the highest filling rate of 99.2%. Except for the as received material, the Vickers hardness, the extrusion force and the filling rate decrease as the initial grain size increases. The hardness is approximately homogeneous along the addendum and dedendum edges but gradually becomes less homogeneous along the edge of the tooth profile from the addendum to dedendum. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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16 pages, 8875 KiB

Open AccessArticle

Evaluation of Fracture Strain for Cold Drawn Thin-Walled Steel Tubes via Small Round-Bar Tensile Test

by Takashi Matsuno, Tomoko Matsuda, Hiroto Shoji and Mitsuru Ohata

Metals 2022, 12(5), 776; https://doi.org/10.3390/met12050776 - 30 Apr 2022

Cited by 6 | Viewed by 1835

Abstract

The evaluation of tube burring formability is a crucial task for finding a suitable material for tube-based automobile parts. The local strain at the ductile fracture site (fracture strain) should be evaluated for this purpose. Moreover, a cold-drawn steel tube has a strong [...] Read more.

The evaluation of tube burring formability is a crucial task for finding a suitable material for tube-based automobile parts. The local strain at the ductile fracture site (fracture strain) should be evaluated for this purpose. Moreover, a cold-drawn steel tube has a strong anisotropic shaped microstructure and possibly causes anisotropic fracture strain behavior. Based on this background, the study evaluated the axial and hoop directional fracture strains of cold-drawn steel tubes using the small round-bar tensile specimen. The burnished surface ratio on the pierced surface was also investigated for possibility estimation of in-line formability inspection. As a result, three tubes are presented with inferior, nearly the same, and superior hoop directional fracture strains compared with the axial strains, where exceeding 40% deterioration in the hoop direction occurs by a combination of grain elongation and carbide aggregation. The scanning electron micrographs suggest that the microvoid growth and linkage percolated thorough carbides on the elongated grain boundaries. For the piercing test, the 30% fracture strain deterioration resulted in a 4% decrease in the burnished surface ratio on the pierced surface. This result suggested that the estimation of the pierced surface can detect material defects before the actual tube-burring process. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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17 pages, 3024 KiB

Open AccessArticle

Experiments and Crystal Plasticity Simulations on Plastic Anisotropy of Naturally Aged and Annealed Al–Mg–Si Alloy Sheets

by Kengo Yoshida, Yasuhito Yamazaki and Hidetaka Nakanishi

Metals 2021, 11(12), 1979; https://doi.org/10.3390/met11121979 - 8 Dec 2021

Cited by 7 | Viewed by 2164

Abstract

The influence of the heat treatment on the plastic anisotropy of an Al–Mg–Si sheet was investigated by experiments and crystal plasticity simulations. Uniaxial tension tests were conducted for the naturally aged (T4 temper) and annealed (O temper) Al–Mg–Si sheets. Solute atoms Mg and [...] Read more.

The influence of the heat treatment on the plastic anisotropy of an Al–Mg–Si sheet was investigated by experiments and crystal plasticity simulations. Uniaxial tension tests were conducted for the naturally aged (T4 temper) and annealed (O temper) Al–Mg–Si sheets. Solute atoms Mg and Si form clusters in the T4 temper sheet, while they bind to form precipitates in the O temper sheet. It is found that the in-plane variation of the R value, texture, and grain size are almost identical for both sheets. By contrast, the anisotropy of the flow stress is clearly dissimilar; the flow stress is the highest in the diagonal direction for the O temper sheet, whereas the flow stress in that direction is nearly lowest for the T4 temper sheet. Thus, the heat treatment alters the anisotropy of the flow stress. The plastic behaviors of the specimens were simulated using the dislocation density-based crystal plasticity model. The influence of the dislocation interaction matrix on the plastic anisotropy was examined. The orientation dependence of the flow stress is found to be sensitive to the interaction matrix. The flow stresses predicted by the interaction matrix determined based on the dislocation dynamic simulation agree with the experimental results for the O temper sheet. Whereas this interaction matrix does not reproduce the flow stress anisotropy for the T4 temper sheet. When the interactions among the dislocations are set to equivalent—i.e., the interaction matrix is filled with unity—the crystal plasticity simulation results in the flow stress anisotropy that is similar to the experimental trend of the T4 temper sheet. In contrast to the flow stress, the R value is insensitive to the interaction matrix, and the predicted R values agree with the experimental results for both specimens. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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21 pages, 5497 KiB

Open AccessArticle

The Deep Drawing of a Flanged Square Hole in Thin Stainless Steel Sheet

by Tsung-Chia Chen, Ching-Min Hsu and Cheng-Chi Wang

Metals 2021, 11(9), 1436; https://doi.org/10.3390/met11091436 - 10 Sep 2021

Cited by 4 | Viewed by 2220

Abstract

To manufacture metal products of accurate size and shape by deep drawing requires the precise control of a number of variables. The problem of spring-back after the load has to be avoided, and the prevention of cracks in the product requires careful control [...] Read more.

To manufacture metal products of accurate size and shape by deep drawing requires the precise control of a number of variables. The problem of spring-back after the load has to be avoided, and the prevention of cracks in the product requires careful control of the punch load. In this study, where drawing experiments and simulations were carried out on thin sheets of SUS304 stainless steel, the influence of the scale effect on the thin sheets also needed consideration. This was accomplished by the use of an updated Lagrangian formulation and finite element analysis. Material behavior was simulated using a micro-elastoplastic material model, the performance of which was compared with that of models involving conventional materials. The Dynaform LS-DYNA solver was used for simulation analysis, and pre and postprocessing were carried out to obtain material deformation history as well as to determine thickness change, distribution and material stress, and prepare strain distribution maps. Scaling was necessary to account for the effect of the thickness of the sheet and the relationship between punch load and stroke, the distribution of thickness, stress and strain, and the maximum size (d) of the flanged hole and the maximum height of the flange. The simulation results were compared with experimental results to confirm the accuracy of the three-dimensional finite element analysis of the elastoplastic deformation. The results showed that the size of the fillet radius of the hole (Br) had an effect on the punch load, which increased with an increase in Br. However, the minimum thickness of the formed flange decreased with an increase in Br. The maximum principal stress/strain and height of the flange also increased with an increase in Br. The punch fillet radius (R_p) also had an impact on the process. The punch load decreased with the increase in R_p, while the minimum thickness increased slightly. The average values of the minimum thickness for three models were 0.148, 0.0775, and 0.0374 mm. The forming ratio also had an influence on the process. When the forming limit of the square hole flange was FLR = 0.84, cracking occurred in the corners of the flange, and wrinkles formed over the undrawn area of the sheet. These findings can serve as a valuable reference for the design of deep drawing processes. Full article

(This article belongs to the Special Issue Innovative Mechanical Processing Technology of Metals)

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