分类: 机械工程 >> 机床技术 提交时间: 2024-05-14
摘要: In-process detection of cutting forces, temperature, roughness, wear etc. during machining of titanium alloys are very important. The Finite element (FE) analysis plays an important role in monitoring and detection of machining responses. It offers a high accuracy in modeling of dry cutting processes and its performance in modeling of cryogenic machining process is a matter of interest. In this context, current investigation focuses on the dry turning and LN2/CO2cooling assisted turning process of commonly used Ti6Al4V alloy. It is very useful material in the biomedical sector, and the simulation of cutting forces and cutting temperature via finite element method (FEM) has been performed. In addition, the simulation results are validated with experimental work. The results show that the deviations between FE modeling and experimental results for the cutting temperature are the average of 5.54%, 5.18% and 8.42% for the dry, LN2and CO2cooling conditions, respectively. On the other hand, the deviations from FE modeling and cutting force test results were 3.74%, 3.358%, and 3.03% under dry, LN2and CO2cooling conditions, respectively.
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2024-05-12
摘要: Being easily fabricated, welded, biocompatible, having a high strength-to-weight ratio, withstanding comparatively high temperatures up to 800 °C and low modulus of elasticity make grade titanium and its alloys an important choice for automotive, biomedical and aerospace industries. In contempt of the different pleasant assets of Ti–6Al–4V alloy, the operation of this alloy is restricted especially when it comes to tribological and surface morphological characteristics. Enhancing these properties is important, for this purpose, a diversity of attempts and studies have been conducted. This paper mounts a review of morphological and tribological behaviors of titanium alloys including Ti–6Al–4V against different materials counting with carbide tools and other types of materials under dry and lubricated sliding conditions. The surface morphological, wear, and other properties have been discussed in this review article.
分类: 机械工程 >> 机床技术 提交时间: 2024-05-10
摘要: Today, superalloys (also known as hard-to-cut materials) such as nickel, titanium and cobalt based cover a wide range of areas in engineering applications. At the same time, challenging material properties namely high strength and low thermal conductivity cause low quality in terms of cutting tool life and surface integrity of the machined part. It is important to improve the machinability of this type of materials by applying various methods in the perspective of sustainability. Therefore, current study presents surface integrity, tool wear characteristics and initiatives to improve them during the machining of superalloys. In this manner, it is outlined the surface integrity characteristics containing surface defects, surface roughness, microstructure alterations and mechanical properties. Also, tool wear mechanisms for example abrasive, adhesive, oxidation, diffusion and plastic deformation are investigated in the light of literature review. Finally, possible improvement options for tool wear and surface integrity depend on machining parameters, tool modifications, cooling methods and trade-off strategies are highlighted. The paper can be a guide for the researchers and manufacturers in the area of sustainable machining of hard-to-cut materials as explaining the latest trends and requirements.
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2024-05-10
摘要: In this work, the sustainable machining approach is promoted by implementing the dry and minimum quantity lubrication (MQL) cooling conditions in the turning of duplex stainless steel. Initially, the turning experiments were performed under dry as well as MQL conditions and then, the influence of different positions of MQL nozzles on tribological and machining performance of 2205 duplex steel was investigated. The cutting parameters were kept fixed and the performance is evaluated in terms of surface roughness, micro-hardness, energy consumption, tool wear, machined surface microstructure and chips morphology. The results demonstrated that the highest average surface roughness values were obtained under dry conditions, with a value of 2.20 μm while MQL (flank + rake directions) produces the lowest surface roughness value of 1.55 μm with an improvement of 30%. Moreover, dual-jet MQL gives the lowest energy consumption (229 kJ) and tool wear (0.15 mm) with 23.67% and 52.38% enhancement, respectively.
分类: 机械工程 >> 机械工程其他学科 提交时间: 2024-04-02
摘要: In this study, first, an orthopedic plate was 3D printed with Polylactic acid (PLA) and coated with polycaprolactone (PCL)/Akermanite (AKT) nano-fibers. The composition included 8 wt.% of PCL and 3 wt.% of nAKT, while diameter of the PCL/AKT nano-fibers was approximately 253 nm ± 33 nm. Thermomechanical properties such as pressure, three-point bending flexural, and thermal conductivity of coated and non-coated specimens were examined and compared. In the next step, the bioactivity of the coated samples was evaluated following a 28-day immersion in simulated body fluid (SBF). Further, scanning electron microscope (SEM) images were taken to assess morphology of nanofibers and apatite formation on samples. By adding PCL to PLA, the maximum pressure force is enhanced by 16.83%. Further by adding nAKT to PLA+PCL sample, the maximum pressure force is enhanced by 4.72%. Further, by adding PCL to PLA, the maximum bending flexural force is enhanced by 21.06%. Further by adding nAKT to PLA+PCL sample, the maximum bending flexural force is enhanced by 21.39%. The results of this study are used to improve modeling of the orthopedic plates.
分类: 机械工程 >> 机械设计 提交时间: 2024-04-01
摘要: Overstaffing production in underground coal mining is not convenient for daily management, and incomplete information of coal miners hinders the rescue process of firefighters during mine accidents. To address this safety sustainability issue, a novel face recognition method based on an improved multiscale neural network is proposed in this paper. A new depthwise seperable (DS)-inception block is designed and a joint supervised loss function based on center loss theory is developed to constructe a new multiscale model. The miniers can be recognized in the harsh underground environment during the life rescue. Experimental results show that the accuracy, recall and F1-score indexes of the proposed method for the miner face recognition in the underground mining environment are 97.26%, 94.17% and 95.42%, respectively. Transfer model with joint supervised loss can effectively improve the recognition accuracy by about 0.5~1.5%. In addition, the average recognition accuracy of the proposed face recognition method achieves to 91.34% and the miss detection rate is less than 5% in the dugout tunnel of coal mine.
分类: 机械工程 >> 刀具技术 提交时间: 2024-03-31
摘要: The present article describes a new and innovative method of producing an inseparablejointwith the use of expansion jaws. The effect of jaw tool geometry on the reaction forces and ultimate strength of an inseparable joint formed on a prototype stand was analyzed. The results are also compared of joints produced by jaws with single movement method and with complex movement method. The tool responds with bending and pressing one part into the other, which results in their permanent connection. In the tests, differentiation was introduced with regard to the height of the applied force to the collar of the connection pipe. A novelty is also a solution based on a complex, parameterized trajectory of the stamp movement consisting of horizontal and vertical displacements. This paper presents the tests of the joints formed at the stand. The new approach described in this article has resulted in a joint strength increase of approximately 30% using the innovative complex jaw movement of the biaxial clinching process. A jointtensile strengthclose to 1000N was achieved.
分类: 机械工程 >> 机械设计 提交时间: 2024-03-31
摘要: The bottom pivot is a vital support device in the miter gate but often subject to poor lubrication and wear failures. Calculating thehydrodynamic lubricationcharacteristics of the bottom pivot is a complex three-dimensional (3D) problem, and most of existing models adopt simplified assumptions to reduce the calculation difficulty. To solve this issue, this work develops a 3D model to calculate thehydrodynamic lubricationcharacteristics of the miter gate bottom pivot. Thefinite difference methodis used to solve theoil film thicknessand pressure distribution based on the spherical coordinatesReynolds equation. The component forces in three directions are calculated from the pressure distribution and compared with the theoretical values to generate the calculation difference. Then, thegenetic algorithm(GA) is used to minimize the difference to determine the optimal initial parameters for the 3D model. The analysis results show that the calculation accuracy can be significantly improved by using the optimal initial model parameters. When our initial pressure is 5.64MPa, the results meet the engineering accuracy requirements.
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2024-03-28
摘要: The heat transfer mechanism andtemperature distributioninlaser weldingapplications have a great impact on the quality of the weld bead geometry, mechanical properties and the resultant microstructure characterizations of the welding process. In this study, the effects of pulsedlaser weldingparameters including the frequency and pulse width on the melt velocity field andtemperature distributionin dissimilarlaser weldingof stainless steel 420 (S.S 420) and stainless steel 304 (S.S 304) was investigated. A comprehensive comparison was conducted through the numerical simulation and artificial neural network (ANN). The results of numerical simulation indicated thatbuoyancy forceandMarangonistress are the most important factors in the formation of the flow of liquid metal. Also, increasing the pulse width from 8 to 12ms due to increasing the pulse energy, the temperature in the center of the melt pool increased about 250°C. This leads to increasing the convective heat transfer in the molten pool and heat affected zone (HAZ). The temperature difference at a distance of 1mm from the beam center at both metals at a frequency of 15 and 20Hz is bout 58 and 75°C, respectively. Furthermore, reducing the frequency to 5Hz, due to diminishment of thermal energy absorption time, has clearly decreased the weld penetration depth in the workpiece. According to the ANN results, increasing both pulse duration and frequency has the significant effect on increasing melting ratio from 0.4 to 0.8 compared to the other input parameters. The ANN results confirmed that under the same input conditions, because of the differences in thermal conductivity coefficient, absorption coefficient and melting point of the two pieces, S.S 304 has experienced higher temperatures about 10% more than S.S 420. Also, among the 13 back propagation learning algorithms, the Bayesian regularization algorithm had the best performance. Among the number of different neurons in the hidden layer, comparison was performed to prevent network overfitting. The maximum relative error of network output data and target data for S.S 304 and S.S 420 temperatures and melting ratio were 7.297, 10.16 and 11.33%, respectively.
分类: 机械工程 >> 机械工程其他学科 提交时间: 2024-03-28
摘要: Increasing the transfer (HT) coefficient used in thermal industries is very important. Various methods are used to improve the efficiency of thermal heat HT so that maximum HT takes place in a smaller space. Ethylene glycol (EG) is generally used as an agent for convective HT. EG obtains energy from a hot source and discharges it to the required location. At present, the most consumption of EG is to produce engine cooling fluid. In the upcoming research, the TB of EG fluid in two-dimensional microchannels (MCs) has been investigated using molecular dynamics (MD) simulations, and the effect of variables such as MC dimensions and MC wall temperature (Temp) on the TB of the simulated fluid has been investigated. The results revealed that by increasing the Temp difference of the MC wall from 10 to 50 K, the maximum temperature (Max-Temp) and velocity (Max-Vel) of the target sample increased to 640.94 K and 0.024 Å/ps. It can be concluded that the increase in the cross-sectional area and the wall Temp difference leads to an increase in the HT rate in the MC.
分类: 机械工程 >> 机械制造自动化 提交时间: 2024-01-07
摘要: 近年来,随着我国炼化行业与信息技术的深入融合与飞速发展,复杂炼化系统所产生的数据呈现爆炸性增长。报警系统是一类用于向操作者传递设备异常状态信息的监控系统;一旦设计不合理,设备在异常状态下可能会产生大量的过程报警甚至报警饱和的现象,严重影响操作者的信息处理能力,从而增加各种工业事故的发生概率。报警信息能够对复杂炼化过程给予正向的指导,因此如何从海量的报警日志中挖掘有价值的信息非常重要。深度学习是一种能够自动地从数据中学习和提取特征的方法,不需要人工构建复杂而精确的物理和数学模型,已在数据预测和分类领域得到广泛应用和关注。
分类: 机械工程 >> 机械制造自动化 提交时间: 2022-10-21
摘要: With growing interest in Laser Additive Manufacturing (LAM) of High-entropy alloys (HEAs) during most recent years, compositional elements design and process strategies innovation are primary methods to overcome undesirable microstructures and defects. Here we propose a new approach, a novel real-time laser shock modulation of melt pool (LSMMP) to obtain melt pool modifications for yielding HEAs with desired characteristics. LSMMP utilizes a pulsed laser shocking a liquid melt pool caused by a continuous wave laser, enabling non-destructive and real-time modulations for high-performance HEAs. The numerical simulation reveals the convection mechanism of the melt pool in the LSMMP process, and the intervention of the pulsed laser promotes melt pool flow type to convert the Marangoni effect into a multi-convective ring, which accelerates melt pool flow and inhibits columnar crystal growth. Experimental results show the evolution law of the microstructure in the LSMMP process. The microstructure of CrFeCoNi HEAs undergoes a Columnar-Equiaxed Transition (CET), and higher hardness is obtained. Laser shock is demonstrated to be an effective in-situ modulative tool for controlled additive manufacturing.
分类: 机械工程 >> 机械制造自动化 提交时间: 2022-09-26 合作期刊: 《桂林电子科技大学学报》
摘要: 为验证某款燃料电池商用车动力系统选型的合理性,以该款车型动力系统的关键参数为基础,在Matlab仿真平台上搭建包含复合能量源(包含燃料电池和蓄电池包)、电机系统(包含驱动电机和电机控制器)及车辆传动系统(包含主减速器和车轮)的模型。采用基于动态规划算法的全局优化能量管理策略,设定空载、半载和满载3种载重模式,以欧洲典型行驶工况EUDC_LOW 为仿真工况,分析车辆在不同载重模式下的动力经济性。仿真结果显示,在3种载重模式下,车辆配置的复合能量源均能满足车辆在指定行驶工况下的功率要求,但随着车辆载重的增大,蓄电池包终端SOC逐渐偏离初始值,考虑到商用车需要在大载重的模式下工作较长时间,较低的SOC不利于车辆保持最佳的动力性。针对该车型的验证结果表明,在后续的研究和实车验证中,应考虑配置功率更大的车载燃料电池。
分类: 机械工程 >> 机械制造自动化 提交时间: 2022-09-26 合作期刊: 《桂林电子科技大学学报》
摘要: 针对机器人动力学模型复杂、冗余计算导致运算效率低的问题,提出一种程式化建模方法(PMM)。以六自由度斯 坦福机械臂为例,利用该方法建立基于拉格朗日方程的动力学模型,按照正向分析,逆序输出的核心思想,重点分析模型 递推过程;在验证模型正确性的基础上,比较使用PMM和未使用PMM 的常规拉格朗日方程所建立的斯坦福机械臂力学 模型在计算机中的尺寸和运行时间等指标。实验结果表明,相对常规拉格朗日方法,由PMM 所建模型的复杂程度降低 了67.6%,计算效率提高了66.3%;斯坦福机械臂为完整约束系统,将PMM推广到欠驱动非完整约束系统,采用与模型紧 密相关的部分反馈线性化控制算法进行数值仿真和物理样机实验分析,验证了PMM 的可靠性和有效性,为不同类型的机 器人提供了一种效率高、通用性强的动力学建模方法。
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2022-08-24
摘要: 本文结合提升劳动者就业创业能力、提升技能培训质量、加快知识型、技能型、创新型高技能劳动建设大军培养的相关政策、路线、要求,从任务分析,方法研究、能力培养、技术内涵分析、培训问题解决、教学实施步骤和关键等几个方面提出数控机床装调维修技师和高级技师培训的数字化转型建议和方法。
分类: 机械工程 >> 机械制造自动化 提交时间: 2022-05-31
摘要: With growing interest in Laser Additive Manufacturing (LAM) of High-entropy alloys (HEAs) during most recent years, the design of compositional elements and process strategies are primary methods to overcome undesirable microstructures and defects. Here we propose a new approach, a novel real-time Laser Shocking of Melt Pool (LSMP), to obtain melt pool modifications for yielding HEAs with desired characteristics. LSMP utilizes a pulsed laser shocking a liquid melt pool caused by a continuous wave laser, enabling non-destructive and real-time modulations for high-performance HEAs. The numerical simulation reveals the convection mechanism of the melt pool in the LSMP process, and the intervention of the pulsed laser promotes melt pool flow type to convert the Marangoni effect into a multi-convective ring, which accelerates melt pool flow and inhibits columnar crystal growth. Experimental results show the evolution law of the microstructure in the LSMP process. The microstructure of CrFeCoNi HEAs undergoes a Columnar-Equiaxed Transition (CET), and higher hardness is obtained. Laser shock is demonstrated to be an effective in-situ modulative tool for controlled additive manufacturing.
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2022-05-25 合作期刊: 《桂林电子科技大学学报》
摘要: 在电子封装领域中,所用的无铅钎料主要是二元或者三元Sn基共晶或近共晶合金,其基体相为富Sn相。为得到富Sn相的力学性能及应力-应变关系,由纳米压痕试验测试获得了富Sn相的弹性模量与硬度,并得到载荷-位移曲线。采用有限元反演分析的方法确定了富Sn相的特征应力和特征应变,并由量纲函数确定应变强化指数。将特征应力和特征应变强化指数等参数代入幂强化模型中,计算得到富Sn相的屈服强度为31.51 MPa,并最终确定富Sn相的应力-应变关系函数表达式。
分类: 机械工程 >> 机械工程其他学科 分类: 计算机科学 >> 计算机软件 提交时间: 2022-02-16
摘要: 近年来,数字孪生受到了广泛关注,数字孪生也正在变得越来越复杂。目前的数字孪生案例大多集中在一个特定的场景上,面对多层次多场景的工作环境,甚至模型的交互与耦合,仍缺乏构建复杂数字孪生的方法。本文提出了一种标准化的基于模型分割和组装的复杂数字孪生模型的建模方法。首先,将数字孪生的复杂模型按照4C架构中的层次(Composition)、场景(Context) 、组件(Component)和代码(Code)划分为若干简单模型。层次和场景使数字孪生专注于特定尺度和场景中的有效元素。组件和代码用于开发简单数字孪生模型。其次,通过信息融合、多尺度关联、多场景交互,将数字孪生的简单模型组装成复杂模型。本体模型构建了不同数字孪生中实体的完整信息库。知识图谱在不同尺度的数字孪生之间架起了关系的桥梁。场景迭代实现行为交互和计算结果精度的提高。本文提供了一种可实现的方法来构建复杂的数字孪生模型,并支持组件和代码的复用促进数字孪生的快速开发。
分类: 电子与通信技术 >> 信息处理技术 分类: 工程与技术科学 >> 工程通用技术 分类: 机械工程 >> 机械工程其他学科 提交时间: 2022-02-08
摘要: The spectral leakage (SL) from windowing and the picket fence effect (PEF) from discretization have been among the standard contents in textbooks for many decades. The SL and PEF would cause the distortions in amplitude, frequency, and phase of signals, which have always been of concern, and attempts have been made to solve them. This paper proposes two novel decomposition theorems that can totally eliminate the SL and PEF, they could broaden the knowledge of signal processing. First, two generalized eigenvalue equations are constructed for multifrequency discrete real signals and complex signals. The two decomposition theorems are then proved. On these bases, exact decomposition methods for real and complex signals are proposed. For a noise-free multifrequency real signal with m sinusoidal components, the frequency, amplitude, and phase of each component can be exactly calculated by using just 4m1 discrete values and its second-order derivatives. For a multifrequency complex signal, only 2m1 discrete values and its first-order derivatives are needed. The numerical experiments show that the proposed methods have very high resolution, and the sampling rate does not necessarily obey the Nyquist sampling theorem. With noisy signals, the proposed methods have extraordinary accuracy.
分类: 机械工程 >> 机械设计 提交时间: 2021-11-17
摘要: The biomimetic design provides an adequate solution to achieve an excellent design. However, the prototype space for biomimetic design is relatively large, and it becomes more and more challenging to find the required biological prototypes quickly and efficiently. In order to improve the design efficiency and enrich the means of biomimetic innovation, this paper proposes a biological knowledge-enabled bidirectional encoder representation from transformers (BERT) model to assist biomimetic design, namely BioDesign. We extract the biological strategies, functions and extract dimensional information from the Asknature as the data source. The linguistic expression model-BERT was used to recommend biomimetic strategies or functions combined with the biological strategies data. Finally, we take the biomimetic erosion wear resistant design of the valve core as an example and use the proposed BioDesign model to recommend biomimetic inspired functions. According to the recommended content of the BioDesign model, we obtained the erosion wear resistance strategies and designed the biomimetic structure. The erosion wear experiment proved the feasibility and effectiveness of the proposed method.