Research

14 pages, 1664 KiB

Open AccessArticle

A New Thermal Model for Predicted Discharge Craters in Micro/Nano-EDM Considering the Non-Fourier Effect

by Zhi Chen, Cheng Wu, Hongbing Zhou and Hongzhi Yan

Crystals 2022, 12(6), 794; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12060794 - 01 Jun 2022

Viewed by 1542

Micro/nano-electrical discharge machining is an alternative preparation method for surface micro/nano-structures, but it is difficult to precisely control the size of the micro/nano-structures due to its unclear material removal mechanism. Thus, it is useful to study its machining mechanism to achieve high-efficiency and [...] Read more.

Micro/nano-electrical discharge machining is an alternative preparation method for surface micro/nano-structures, but it is difficult to precisely control the size of the micro/nano-structures due to its unclear material removal mechanism. Thus, it is useful to study its machining mechanism to achieve high-efficiency and controlled processing. At present, most of the established EDM thermal models for predicting the discharge crater size are based on the classical Fourier heat conduction law, assuming that the conduction velocity of heat energy is infinite. However, the single-pulse discharge time of micro/nano-EDM is transitory (<1 μs), and thus, the steady state heat balance condition cannot be achieved in a single-pulse discharge time. In order to predict the size of the micro/nano electrical discharge craters more accurately, the non-Fourier effect was considered to study the temperature field distribution of micro/nano-EDM of single-pulse discharge machining. Firstly, the classical Fourier heat conduction law was modified by introducing a relaxation time. Secondly, several key factors were considered to establish the thermal model of micro/nano-EDM in single-pulse discharge machining. Subsequently, numerical simulation software was used to solve the thermal model for obtaining the temperature field distribution of the workpiece material and predicting the size of the discharge craters. Finally, the predicting accuracy of the new thermal model was evaluated by comparing the relative error between the simulated values and experimental values. The comparison results show that considering the non-Fourier effect can reduce the average error of the thermal model from 33% to 10%. The non-Fourier effect is more obvious under the shorter discharge time of a single pulse. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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21 pages, 5193 KiB

Open AccessArticle

Research on EDM Performance of Renewable Dielectrics under Different Electrodes for Machining SKD11

by Wuyi Ming, Zhuobin Xie, Chen Cao, Mei Liu, Fei Zhang, Yuan Yang, Shengfei Zhang, Peiyan Sun and Xudong Guo

Crystals 2022, 12(2), 291; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020291 - 18 Feb 2022

Cited by 20 | Viewed by 2524

Abstract

Electrical discharge machining (EDM) is a non-traditional process, which can cut materials with a high melting point, high hardness, high strength, and low brittleness. However, the kerosene (dielectric of EDM) produces aerosols and toxic gases at high temperatures, which seriously affect the health [...] Read more.

Electrical discharge machining (EDM) is a non-traditional process, which can cut materials with a high melting point, high hardness, high strength, and low brittleness. However, the kerosene (dielectric of EDM) produces aerosols and toxic gases at high temperatures, which seriously affect the health of operators and air quality. This means that it is not conducive to the green manufacturing and sustainable development of EDM. In this study, thereafter, sunflower seed oil (SSO) and kerosene were used as dielectrics of EDM for machine SKD11, and the machining performance of the two dielectrics under different current, duty ratio, pulse duration and electrodes were comparatively analyzed, such as material remove rate (MRR), surface roughness (Ra), energy efficiency per volume (EEV) and exhaust emissions characteristics (EEC). This investigation found that the minimum value of EEV in SSO was 0.3879 kJ/mm³, which was about 25% lower than the minimum value of 0.4849 kJ/mm³ in kerosene. The emission rate of Cu electrode in SSO was 62.017 µg/min, which was lower than that in 78.857 µg/min, decreasing by about 21.36%, in kerosene. In addition, a super depth of field optical micro-scope was subsequently used in the experiments to observe the diameter of the debris. The results indicated that SSO has a larger proportion of debris of more than 35 µm in diameter. Therefore, SSO can be adopted as a substitute for kerosene dielectric to improve the sustainability of electrical discharge machining and realize green manufacturing. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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15 pages, 4517 KiB

Open AccessArticle

Comparative Analysis of Bubbles Behavior in Different Liquids by Laser-Induced Plasma Micromachining Single-Crystal Silicon

by Ying Liu, Hongjing Guo, Han Wang, Yi Zhang and Zhen Zhang

Crystals 2022, 12(2), 286; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020286 - 18 Feb 2022

Cited by 5 | Viewed by 1363

Abstract

Laser-induced plasma micromachining (LIPMM) can be used to fabricate high-quality microstructures of hard and brittle materials. The liquid medium of the LIPMM process plays a key role in inducing the plasma and cooling the materials, but the liquid medium is overheated which induces [...] Read more.

Laser-induced plasma micromachining (LIPMM) can be used to fabricate high-quality microstructures of hard and brittle materials. The liquid medium of the LIPMM process plays a key role in inducing the plasma and cooling the materials, but the liquid medium is overheated which induces lots of bubbles to defocus the laser beam and reduce machining stability. In this paper, a comparative investigation on bubble behavior and its effect on the surface integrity of microchannels in three types of liquids and at different depths during LIPMM has been presented. Firstly, the formation mechanism of microbubbles was described. Secondly, a series of experiments were conducted to study the number and maximum diameter of the attached bubbles and the buoyancy movement of floating bubbles in the LIPMM of single-crystal silicon under deionized water, absolute ethyl alcohol, and 5.6 mol/L phosphoric acid solution with a liquid layer depth of 1–5 mm. It was revealed that the number and maximum diameter of attached bubbles in deionized water were the highest due to its high tension. Different from the continuous rising of bubbles at the tail of the microchannels in the other two liquids, microbubbles in 5.6 mol/L phosphoric acid solution with high viscosity rose intermittently, which formed a large area of bubble barrier to seriously affect the laser focus, resulting in a discontinuous microchannel with an unablated segment of 26.31

μ

m. When the depth of the liquid layer was 4 mm, absolute ethyl alcohol showed the advantages in narrow width (27.15

μ

m), large depth (16.5

μ

m), and uniform depth profile of the microchannel by LIPMM. This was because microbubbles in the anhydrous ethanol quickly and explosively spread towards the edge of the laser processing zone to reduce the bubble interference. This research contributes to a better understanding of the behavior and influence of bubbles in different liquid media and depths in LIPMM of single-crystal silicon. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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17 pages, 5169 KiB

Open AccessArticle

Analysis and Optimization of the Machining Characteristics of High-Volume Content SiCp/Al Composite in Wire Electrical Discharge Machining

by Hongzhi Yan, Bakadiasa Djo Kabongo, Hongbing Zhou, Cheng Wu and Zhi Chen

Crystals 2021, 11(11), 1342; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11111342 - 03 Nov 2021

Cited by 5 | Viewed by 1313

Abstract

With the properties of high specific strength, small thermal expansion and good abrasive resistance, the particle-reinforced aluminum matrix composite is widely used in the fields of aerospace, automobile and electronic communications, etc. However, the cutting performance of the particle-reinforced aluminum matrix composite is [...] Read more.

With the properties of high specific strength, small thermal expansion and good abrasive resistance, the particle-reinforced aluminum matrix composite is widely used in the fields of aerospace, automobile and electronic communications, etc. However, the cutting performance of the particle-reinforced aluminum matrix composite is very poor due to severe tool wear and low machining efficiency. Wire electrical discharge machining has been proven to be a good machining method for conductive material with any hardness. Even so, the high-volume SiCp/Al content composite is still a difficult-to-machine material in wire electrical discharge machining due to the influence of insulative the SiC particle. The goal of this paper is to analyze the machining characteristics and find the optimal process parameters for the high-volume content (65 vol.%) SiCp/Al composite in wire electrical discharge machining. Experimental results show that the material removal method of the SiCp/Al composite includes sublimating, decomposing and particle shedding. The material removal rate is found to increase with the increasing pulse-on time, first increasing and then decreasing with the increasing pulse-off time, servo voltage, wire feed and wire tension. Pulse-on time and servo voltage are the dominant factors for surface roughness. In addition, the multi-objective optimization method of the nondominated neighbor immune algorithm is presented to optimize the process parameters for a fast material removal rate and low surface roughness. The optimized process parameters can increase the material removal rate by 34% and reduce the surface roughness by 6%. Furthermore, the effectiveness of the Pareto optimal solution is proven by the verified experiment. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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10 pages, 4318 KiB

Open AccessArticle

Preparation of Superhydrophobic Surfaces Based on Rod-Shaped Micro-Structure Induced by Nanosecond Laser

by Zhi Li, Gang Xue, Yanming Wu, Xinghua Wang and Hengpei Pan

Crystals 2021, 11(11), 1274; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11111274 - 20 Oct 2021

Cited by 5 | Viewed by 1637

Abstract

Solid–liquid frictional resistance is mainly attributed to the adhesion caused by the boundary layer effect. Superhydrophobic surfaces are expected to be an effective method to reduce frictional resistance. In this paper, a rod-shaped micro-structure was prepared on surfaces of Al alloy (5083) and [...] Read more.

Solid–liquid frictional resistance is mainly attributed to the adhesion caused by the boundary layer effect. Superhydrophobic surfaces are expected to be an effective method to reduce frictional resistance. In this paper, a rod-shaped micro-structure was prepared on surfaces of Al alloy (5083) and Ti alloy (TC4) by line-by-line scanning with nanosecond laser. The inherent properties of the metal materials—such as their coefficient of thermal conductivity (CTC) and specific heat capacity (SHC)—had a major influence on the surface morphology and shape size of the rod-shaped micro-structure. Both two metals showed apparent oxidation on their surfaces during laser ablation, however, the degree of surface oxidation of the Al alloy was greater than that of the Ti alloy due to its more fragmentary rod-shaped micro-structure. The laser-treated surfaces could turn from hydrophilic to hydrophobic or even superhydrophobic after being left in the air for 20 days, which might be caused by the adsorption of low-surface energy matter in the air. In addition, the contact angle of the Al alloy was larger than that of the Ti alloy, which is due to the larger ratio of height to width of the micro–nano composite rod-shaped micro-structure on the surface of the Al alloy. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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15 pages, 3244 KiB

Open AccessArticle

A Cuckoo Search Algorithm Using Improved Beta Distributing and Its Application in the Process of EDM

by Dili Shen, Wuyi Ming, Xinggui Ren, Zhuobin Xie, Yong Zhang and Xuewen Liu

Crystals 2021, 11(8), 916; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11080916 - 06 Aug 2021

Cited by 7 | Viewed by 1605

Abstract

Lévy flights random walk is one of key parts in the cuckoo search (CS) algorithm to update individuals. The standard CS algorithm adopts the constant scale factor for this random walk. This paper proposed an improved beta distribution cuckoo search (IBCS) for this [...] Read more.

Lévy flights random walk is one of key parts in the cuckoo search (CS) algorithm to update individuals. The standard CS algorithm adopts the constant scale factor for this random walk. This paper proposed an improved beta distribution cuckoo search (IBCS) for this factor in the CS algorithm. In terms of local characteristics, the proposed algorithm makes the scale factor of the step size in Lévy flights showing beta distribution in the evolutionary process. In terms of the overall situation, the scale factor shows the exponential decay trend in the process. The proposed algorithm makes full use of the advantages of the two improvement strategies. The test results show that the proposed strategy is better than the standard CS algorithm or others improved by a single improvement strategy, such as improved CS (ICS) and beta distribution CS (BCS). For the six benchmark test functions of 30 dimensions, the average rankings of the CS, ICS, BCS, and IBCS algorithms are 3.67, 2.67, 1.5, and 1.17, respectively. For the six benchmark test functions of 50 dimensions, moreover, the average rankings of the CS, ICS, BCS, and IBCS algorithms are 2.83, 2.5, 1.67, and 1.0, respectively. Confirmed by our case study, the performance of the ABCS algorithm was better than that of standard CS, ICS or BCS algorithms in the process of EDM. For example, under the single-objective optimization convergence of MRR, the iteration number (13 iterations) of the CS algorithm for the input process parameters, such as discharge current, pulse-on time, pulse-off time, and servo voltage, was twice that (6 iterations) of the IBCS algorithm. Similar, the iteration number (17 iterations) of BCS algorithm for these parameters was twice that (8 iterations) of the IBCS algorithm under the single-objective optimization convergence of Ra. Therefore, it strengthens the CS algorithm’s accuracy and convergence speed. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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19 pages, 6373 KiB

Open AccessArticle

Study on Mechanism of Glass Molding Process for Fingerprint Lock Glass Plates

by Wuyi Ming, Haojie Jia, Heyuan Huang, Guojun Zhang, Kun Liu, Ya Lu and Chen Cao

Crystals 2021, 11(4), 394; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11040394 - 08 Apr 2021

Cited by 8 | Viewed by 2453

Abstract

Curved glass is widely used in 3C industry, and the market demand is increasing gradually. Glass molding process (GMP) is a high-precision, high-efficiency 3D glass touch panel processing technology. In this study, the processing parameters of fingerprint lock glass panels were deeply analyzed. [...] Read more.

Curved glass is widely used in 3C industry, and the market demand is increasing gradually. Glass molding process (GMP) is a high-precision, high-efficiency 3D glass touch panel processing technology. In this study, the processing parameters of fingerprint lock glass panels were deeply analyzed. This paper first introduces the molding process of the glass panel, discusses the glass forming device, and explains the heat conduction principle of the glass. Firstly, it introduces the forming process of the glass panel, discusses the glass forming device, and explains the heat conduction principle of the glass. Secondly, the simulation model of a fingerprint lock glass plate was simulated by MSC. Marc software. The stress relaxation model and structure relaxation model are used in the model, and the heat transfer characteristics of glass mold are combined to accurately predict the forming process of glass components. The effects of molding temperature, heating rate, holding time, molding pressure, cooling rate and other process parameters on product quality characteristics (residual stress and shape deviation) were analyzed through simulation experiments. The results show that, in a certain range, the residual stress is inversely proportional to the bending temperature and heating rate, and is directly proportional to the cooling rate, while the shape deviation decreases with the increase of temperature and heating rate. When the cooling rate decreases, the shape deviation first decreases and then increases. Furthermore, a verification experiment is designed to verify the reliability of the simulation results by measuring and calculating the surface roughness of the formed products. Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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13 pages, 19410 KiB

Open AccessArticle

Evolution Mechanism of Transient Strain and Residual Stress Distribution in Al 6061 Laser Welding

by Youmin Rong, Yu Huang and Lu Wang

Crystals 2021, 11(2), 205; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11020205 - 19 Feb 2021

Cited by 5 | Viewed by 2331

Abstract

Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are [...] Read more.

Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa). Full article

(This article belongs to the Special Issue Non-traditional Machining of Crystal Materials)

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