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 >> 机械制造工艺与设备 提交时间： 2018-03-14
摘要： 由于水火弯板等传统成形工艺的一些固有缺陷，复杂曲面钢板的弯曲成形一直是造船厂面临的一个难题。本文提出了一种新的基于冲压的渐进成形弯板工艺，以获得复杂的弯曲钢板，以取代传统的船体成型过程。所提出的渐进成形弯板工艺是由一系列步进冲头进行的，因此也被定义为增量冲裁。通过这个过程，由柔性支承系统固定和保持的薄板可以按预定的刀具轨迹一步一步地被折弯成目标形状。同时，为了提高成形工件的几何精度，采用三维扫描反馈系统测量工件在成形过程中的变形。利用三维扫描反馈系统，可以对大量工件点云数据进行成像和重建，从而形成成形件的三维形状。然后获得成形工件模型与目标CAD模型之间的差异，必要时可用于成形精度的反馈控制。为了验证所提出的形成过程，原来的增量冲样机的设计和制造，其主要由三轴数控机床、柔性支撑体系和三维扫描反馈系统。利用该原型进行了渐变曲率钢板的成形试验，并对其进行了详细的讨论，以论证复杂弯钢板增量弯曲成形的可行性。
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