【作者】 汤宏群；

【导师】 王成勇；

【作者基本信息】 广东工业大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 微孔是印刷电路板的重要组成部分之一。随着印刷电路板制版技术和封装技术的快速发展,高密度、高集成、微细化、多层化的印刷电路板应运而生。印刷电路板机械钻孔面临越来越大的挑战,主要表现在：印刷电路板微孔孔径越来越小,微钻的直径也越来越小,对微钻寿命和微孔表面质量等要求越来越高。如何提高微钻寿命,提高微孔表面质量,改善微钻钻削行为,一直是钻削印刷电路板多层复合材料加工领域的研究热点。本文针对印刷电路板用微钻断裂失效问题,以降低微孔钻削加工过程中的振动,提高微孔钻削表面质量为目标,从动力学的角度出发,采用切削力学、机械振动、材料学和多体动力学等理论,运用非接触式激光测振技术和动态测振技术,通过大量的钻削实验和动力学仿真实验,深入研究了印刷电路板用微钻的动态特性以及微孔钻削机床在加工过程中的动态特性,分析了微孔钻削系统在加工过程中的动态特性对印刷电路板微孔钻削孔位精度的影响,并进行基于钻削参数的微孔钻削系统稳定性研究。研究结果对于丰富印刷电路板微钻钻削加工理论,指导印刷电路板用微钻设计与应用,指导印刷电路板微孔钻削机床的合理设计和选择,优化印刷电路板微孔钻削加工参数,提高微孔钻削质量具有一定的理论价值和实际应用意义。本文主要研究结论如下：在微钻瞬态动力学研究方面,引入耦合节点,提出微钻载荷施加新方法,得出当微钻接触工件开始入钻时,横刃瞬态位移较大,振动较大,瞬态应力也最大；当微钻开始去除工件材料时,主钻削刃的X、Y方向瞬态位移较大,振动较大,而主钻削刃Z方向及横刃部位瞬态位移较小,振动相对较小；钻削加工后期,主钻削刃瞬态位移减小,振动减小,瞬态应力相应减小。在钻削加工过程中,主钻削刃的等效应力值最大,磨损也大,最大磨损宽度出现在主钻削刃外缘处；指出微钻螺旋槽根部是微钻结构相对薄弱的部位,扭转载荷过大是微钻折断的主要原因,应加强微钻螺旋槽根部的刚度设计。在微钻动态特性研究方面,建立了印刷电路板微钻的全参数化模型,研究印刷电路板微钻的动态特性及其影响因素。发现具有螺旋刃准对称结构的微钻模态振型分别绕X轴方向或Y轴方向成对出现,且全部为弯曲模态振型,其中5、6阶为弯曲扭转模态振型。指出印刷电路板微钻轴向刚度远大于微钻径向刚度；微钻各阶固有频率随微钻悬伸长度的增加而减小,其中直径D=0.1 mm的微钻最佳加工悬伸长度为20 mm和23 mm,与工厂实际应用相一致；微钻各阶固有频率随过渡长度变化的规律不明显；微钻各阶固有频率随微钻芯厚的变化与微钻直径有关,其中直径D=0.1 mm的微钻,其各阶固有频率随微钻芯厚的变化不大,直径D=0.2 mm和D=0.3 mm微钻的各阶固有频率随着微钻芯厚的增加而增加；微钻倒角的变化对微钻结构参数影响不大,优化微钻倒角对微钻动态特性没有影响。在印刷电路板微孔钻削机床系统多体动力学分析方面,建立了印刷电路板微孔钻削机床系统多体动力学模型。通过对钻削机床进行动态特性分析,得出微孔钻削机床在钻削力作用下X、Y、Z方向位移和加速度的对数幅频曲线图,发现横梁是钻削机床的薄弱部位,提出增加横梁的刚度,优化横梁截面形状等设计原则,增加钻削机床稳定性。最后提出了印刷电路板微孔钻削机床钻削过程中的振动加速度频率响应数学模型,为印刷电路板微孔钻削机床进一步优化设计提供理论依据。在印刷电路板微孔钻削加工动力学与钻削稳定性研究方面,建立印刷电路板微孔钻削加工动力学模型,得出钻削过程中的振动加速度和钻削扭矩随主轴转速和进给速度变化的数学回归模型。钻削过程中的振动加速度随着主轴转速或进给速度的增加先增加,到一定值后,快速下降；钻削扭矩随主轴转速的变化也有类似的趋势,也是先增加到一定值后减小,但钻削扭矩和进给速度的关系则是呈线性关系,随进给速度的增加而增加。典型微孔钻削印刷电路板的振动变化曲线表明,钻削前2层铜箔时处于非稳态钻削阶段,振动加速度波峰较明显；随着钻削过程的进行,钻削加工过程中的振动加速度减小；主轴转速越高,振动加速度衰减越快,达到稳态钻削所需要时间越短；压力脚接触盖板时的振动峰值随进给速度的增加而增加；微孔钻削过程的振动情况随进给速度的变化趋势不明显；微孔钻削加工过程振动加速度的变化和退刀速度关系不明显。在微钻钻削印刷电路板微孔表面质量的研究方面,微孔钻削过程的振动、微钻直径和微钻磨损与孔位精度(CPK)的关系比较明显。直径小刚性较弱的微钻振动加速度大；直径大刚性强的微钻在钻削过程中轴向力大,振动加速度也大；中等直径的微钻振动加速度最小,孔位精度值最大。另外,钻削孔数少,平均振动加速度高,孔位精度值小；随着钻削孔数的增加,微孔钻削加工慢慢达到一个稳定状态,平均振动加速度下降,孔位精度值增大；但当钻削孔数继续增加时,微钻磨损增加,振动加速度增加,孔位精度值下降。更多还原

【Abstract】 Micro-holes are important parts of the printed circuit boards(PCBs). With the fast development of plating and packaging technologies, high density interconnection(HDI) PCBs has become popular. The mechanical drilling of PCBs is facing significant challenges due to the apertures of drilled holes of PCBs are becoming smaller and smaller, which means an increased demand on the life span of micro-drills and the quality of drilled holes. In the field of HDI PCBs drilling, increasing the life span of micro-drills, advancing the quality of drilled holes and improving micro-drilling behaviors have drawn much attention.Focusing on the fracture problem of PCB drills, the aim of this paper is to reduce the micro-drilling machining vibration and improve the micro-holes quality. Point of departure from dynamics, the cutting mechanics, mechanical vibration, material science and multi-body dynamics theory are adopted, and non-contact laser vibration measurement technology and dynamic vibration measurement technology are used. Massive drilling experiments and dynamic simulation experiments are set to study dynamic characteristics of PCB micro-drills and micro-drilling machine during process. Then, a detailed analysis on dynamic characteristics of the micro-drilling system and CPK is presented. In according to the drilling parameters, the micro-drilling system stability is studied. The research results enrich the drilling theory of PCB micro-drills, provide guidance to the design and application of PCB micro-drills, instruct reasonable design and choice of drilling machine for PCB micro-holes, and optimize parameters of PCB micro-drilling. It is theoretically valuable and useful in improving the micro-holes quality..The main achievements of the research are as follows:In the study of instant dynamics characteristics of micro-drills, Introducing coupling node to propose a new method for exerting load on micro-drills. At the beginning of micro-drilling, the instant displacement of the chisel edge is relatively big, the vibration is significant too and the instant stress is the biggest. During the process of drilling, the instant displacement of X and Y directions are relatively big, and the vibration is obvious while that of Z direction is relatively small and the vibration is small as well. At the end of drilling, the instant displacement and vibration of the main cutting edge reduce, and the instant stress value decreases accordingly. During the process of drilling, the equivalent stress value of the main cutting edge is the biggest, and the wear is big too. The largest width of wear appears on the brim of the main cutting edge. It is pointed out that the root of the spiral grooves of micro-drills is the relatively weak part. The main reason for micro-drills fracture is the torque overloaded.Thus, the rigidity of the root of the spiral grooves should be enhanced.In the study of dynamical characteristics of micro-drills, a full parameterized model of PCB micro-drills is created for researching dynamical characteristics and influence factors of dynamical characteristics. It is found that the mode shapes of vibration of PCB micro-drills with the spiral blade quasi symmetrical structure are respectively around the X axis or Y axis in pairs, and all are bent mode shapes of vibration, especially the vibration mode shapes of 5th order and 6th order are bent and twisting. It is pointed out that the axial stiffness of micro-drill is bigger than the radial stiffness. The natural frequencies of the micro-drills in all stages reduces as the overhanging length of the micro-drill increases. The best overhanging length of the D=0.1mm micro-drill is 20 mm and 23 mm which are consistent with the values applied in the factory. No obvious rules of the influence of transition lengths on the natural frequencies in all stages of micro-drills are observed. The natural frequencies in all stages of micro-drills are related to the diameter of micro-drills as the web thickness changing. For D=0.1 mm micro-drill, the natural frequencies of all stages does not change obviously with the web thickness of micro-drill changing. For D=0.2 mm and D=0.3 mm micro-drills, the natural frequencies of all stages increases as the web thickness of micro-drill increasing.The change of the chamfer angle has a modest impact on structure parameters of micro-drills, optimizing the chamfer angle of micro-drills have no influence on the dynamical characteristics.In the analysis of multi-body dynamics for PCB drilling machine, a multi-body dynamical model of PCB drilling machine is created. Through analyzing the dynamical characteristics of the PCB drilling machine, a curve of logarithm and amplitude-frequency obtained to show the direction displacement and acceleration of X, Y, Z as the PCB drilling machine operating. Thus it is found that the beam is the weak part of the drilling machine. It is proposed to strengthen the rigidity of the beam and optimize the principles of designing the shape design of cross section of the beam so as to improve the machining stability of the drilling machine. Finally, it is proposed that the drilling acceleration frequency of the PCB drilling machine responses to the mathematical model, providing theoretical basis for further optimizing designs of PCB drilling machines.In the study of dynamical processing and machining stability of PCB micro-drilling, a dynamical model of PCB micro-drilling of is built, and a mathematical regression model is built to show that drilling vibration acceleration and drilling torque varying with spindle speed and feed speed. Drilling vibration acceleration augments as spindle speed and feed speed increasing. However, it reduces fast after reaching a certain value. The trend of drilling torque as spindle speed changing is similar. However, drilling torque and feed speed have a linear relationship, drilling torque increases as feed speed increasing. The typical vibration curve of PCB micro-drills indicates that the drilling process is unsteady and the peak value are obvious when drilling the first and the second layers of copper foil. With the conduct of drilling process, drilling vibration acceleration decreased. Higher spindle speed, faster the vibration damping, and the less time needed to achieve stable drilling. The peak value of pressure foot increases with the feed speed increasing. There is no obvious change of vibration as the feed speed changing during micro-drilling. The change of vibration has little to do with return speed during micro-drilling.In the study of surface quality of PCB micro-holes, there is an obvious relationship between CPK and vibration characteristics of spindle, micro-drill diameter as well as the wear of micro-drill.The vibration acceleration of micro-drill with weak rigid and small diameter is large. Axial force of micro-drills with strong rigid and large diameter is large in drilling, so the vibration acceleration is large too. The minimum vibration acceleration of micro-drills which owns medium diameter, and its CPK is bigger. The less the drilled holes are, the higher the average vibration acceleration and the lower CPK. As the drilling holes increases, the drilling machine achieves a stable status and then the average vibration acceleration reduces while the CPK increases. However, as the drilling holes increases, the wear of the micro-drill and the vibration acceleration increase while the CPK decreases.更多还原