氮气保护对无铅再流焊焊点外观质量的影响

由于无铅钎料润湿性较差,在实际生产中普遍采用氮气保护。通过新制定的氮气保护无铅再流焊工艺,对焊点外观质量进行了统计分析。其结果显示氮气保护可以减少元件偏移和桥连等缺陷,对竖碑、焊球和锡珠等缺陷也有一定影响。

基于瑞利分布的SPC控制图应用研究

该文通过分析生产过程中印刷电路板(PCB)上元件位置偏移形成的原因,建立了元件位置偏移的数学模型,进而论证了元件位置偏移距离服从瑞利分布。由于休哈特X控制图要求所控制的质量属性服从正态分布,用其控制PCB元件位置偏移会出现误判。该文对它进行了优化改进,提出了更适合于控制元件位置偏移距离的瑞利控制图,实验结果表明瑞利控制图具有更好的效果。另外,该文也提出了一种利用数据库来构造专家系统的方法,采用该方法的控制图自动模式识别效率比一般的专家系统有所提高,这种新的思路对控制图模式的智能识别将有所帮助。

基于容差参数区间估计法的谐振式无线充电系统故障诊断

为了解决谐振式无线充电系统元件参数偏移故障定位诊断困难的问题,通过分析谐振式无线充电系统电路结构的特征,对电流信号进行傅里叶分析提取有效特征量,基于容差参数区间估计法对元件参数偏移故障进行诊断。通过模拟各种元件参数偏移故障,验证容差参数区间估计法对于此类故障诊断的有效性。结果表明,此方法不但简单易于操作且对于定位诊断谐振式无线充电系统元件参数偏移故障有很好的诊断能力。

The Topic of Contact Zone Problems in the Shaft and Hole Joint, Taking into Account Component Form Errors

In assemblies constructed from components manufactured with radial deviations, cross-section deviations and deviations being combination of both, there occur variable values of local stresses and displacements. Both the types of shape deviations and their values need to be taken into account in the designing process and play an important role during machine operation. They have a crucial effect on the value and scatter of maximum reduced von Mises stresses and contact stresses. Axisymmetric joints were examined, in which shafts in selected shape variants and in variable angular positions were associated with a non-deformable hole. The aspects of contact zone problems are presented using the example of numerical simulation of contact between an elliptical saddle-shaped shaft placed in a rigid, non-deformable hole in different angular positions. Occurrence of both variable relative stresses and contact stresses as well as shaft＇s axial shift and rotary movement resistance were demonstrated.