【作者】 黄立新；

【导师】 王成勇；

【作者基本信息】 广东工业大学 ， 机械电子工程， 2011， 博士

【摘要】 随着电子技术的发展,印制电路板(PCB)的应用越来越多,PCB的钻孔加工量也随之快速增长。常见的PCB板钻孔加工包括微小孔(直径0.3mm以下)和定位安装孔(直径2mm以上)加工。目前使用普通钻头加工定位安装孔中存在排屑不畅、钻头磨损和烧伤严重等问题,而且随着为了提高加工效率而提高转速和进给速度,这些问题更趋严重。虽然电路板上定位安装孔的数量远远小于微孔,但由于材料去除量大,钻头的消耗量同样很大。本文从印刷电路板制造业对PCB定位安装孔钻削加工技术的迫切实际需要出发,采用各种先进的数值仿真分析技术、材料微观分析技术、高速摄影和红外测温法等多种测试分析手段,对高速钻削PCB定位安装孔的钻屑形成机理、钻削力、钻削温度、钻头磨损、孔加工质量控制等,进行了深入的系统研究和分析；分析了钻屑形成过程与钻削力特征、钻头磨损和毛刺的关系,分析了钻削加工中钻削力、钻削温度的动态变化规律以及钻头磨损机理；建立了高速钻削加工条件与印刷电路板钻屑形态、钻屑形成规律、已加工表面质量、钻头磨损的关系；建立了基于热—力多物理场耦合理论的钻削加工PCB板中铜箔材料表面创成过程模型并对加工过程的多种特征进行了仿真；最后,基于对钻削过程及其主要特征的应用基础理论研究,分析了钻头结构与钻屑排屑的畅通关系,提出了改进钻头几何参数的基本原则和方法,并经过实际验证获得良好的加工效果。本文对PCB板高速钻削加工进行的系统深入的理论和实验研究,对于提高PCB孔加工理论、孔加工工艺技术和钻削工具的水平,有重要的学术和应用价值。本文主要研究结论如下：1.PCB安装定位孔高速钻削加工中产生的切屑是由铜屑、铝盖板屑和玻纤与树脂钻屑等不同PCB组分材料的切屑组成；因此,其呈不同的长度、厚薄和卷曲形态。铜箔钻屑分为长带状铜屑、短带状铜屑和C型屑三类。玻璃纤维／树脂钻屑主要有小螺距的长锥螺旋扇面形、长螺距的短锥螺旋扇面形、扇面块状屑和连续带状。钻屑挤过钻头的螺旋刃沟空间,盘旋而出,形成长短不同的带状钻屑；钻屑经受不住剧烈的变形,首先在其内缘的裂口受张力而破裂,并迅速扩展而达到断裂,成为断裂单元屑(扇形屑,或C形屑)。钻屑的形态与钻削的钻削用量、钻头几何角度和钻头磨损等有密切关联。2.钻削PCB板时的不同组分材料表现出不同的钻削力特征。钻削上表层铜箔时由于叠加冲击力,钻削轴向力达到最大；钻削玻纤与树脂的轴向力较小,纤维互相交错存在导致钻削扭矩变化比较大。钻屑的排屑方向也影响轴向力的大小,当钻屑从上面排出时,和钻屑从下部排出,轴向力和扭矩差别巨大,轴向力很大程度上取决于排屑是否通畅。3.钻削用量中对钻削力影响最大的是进给速度,轴向力随着进给速度的增大呈线性增长趋势,而钻头直径在大直径尺度范围内(2-3mm)对轴向力的影响并不十分显著。钻头几何参数中,横刃对轴向力影响最大,对扭矩的影响不是十分显著,横刃的减少可以有效地降低钻孔的轴向阻力。顶角增加使轴向力增加,顶角影响排屑方向,但对扭矩影响不是十分显著；对轴向力影响最小的是螺旋角。4.不同的印刷电路板材料,其力信号的特征是不同的。针对不同的PCB板材,存在相应最小轴向力的最优钻头几何参数。钻削无卤素板时,螺旋角为15°时轴向力最大,而其它两种板则在15°螺旋角时轴向力最小；顶角为150°时三种板的轴向力均最小。获得了加工FR4和HF板的钻削轴向力经验公式。5.钻头与工件接触面间的平均温度在200℃左右；钻削铜箔时的钻削温度最高为198.5℃,且明显高于钻削中间玻璃纤维树脂层的钻削温度,随着进给速度的增加,钻削区温度有下降的趋势。钻削热大部分是由钻屑带走。横刃厚度和螺旋角的增加,导致钻屑温度提高；顶角减小,则钻屑温度降低。钻削速度对钻削温度的影响大于进给速度的变化对钻削温度的影响。6.运用有限元数值计算技术建立了基于热—力多物理场耦合理论的钻削加工PCB板中铜箔材料表面创成过程模型；对钻屑生成、钻削力和钻削温度的仿真结果和PCB钻孔实测结果基本吻合。7.高速钻削PCB时硬质合金钻头磨损经历初期磨损、正常磨损和剧烈磨损三个阶段。硬质合金钻头磨损机理主要有磨粒磨损、粘附磨损、挤压变形和微崩刃。后刀面磨损是稳定磨损期的主要磨损形式。引起PCB钻头磨损的主要原因还是钻头在钻削玻纤布时引起的磨粒磨损。各部分切刃的磨损形式有所不同,刀尖处和主切削刃存在磨粒磨损和粘结磨损；而横刃处存在挤压塑性变形。在正常磨损阶段,随着钻孔数的增加,钻头后刀面磨损量基本呈线性上升必须选择合适的钻削参数,才能减少钻头磨损,提高钻头的寿命。8.高速钻削印刷电路板时毛刺属于铜箔毛刺,在一定范围内,进给速度与毛刺高度是正相关的,减小进给速度,有利于改善出口毛刺。横刃对毛刺生成影响作用显著,其次是顶角,螺旋角影响不大。减小进给速度,选择较小的横刃和顶角,保证刀具在正常磨损范围内使用,有利于改善出口毛刺。采用压力脚和垫板,可以减小毛刺的高度。9.基于前面的应用基础理论研究成果,提出了基于降低轴向力和改善钻屑排屑畅通的钻头设计的基本原则；指出对于PCB板定位安装孔的加工,磨制分屑槽和修磨横刃长度,是使钻屑排出畅顺和降低钻削轴向力的重要方法。提出了降低钻削轴向力,改善钻头磨损的相应的推荐钻削用量。设计了多种对横刃和分屑槽进行了改进的新型钻头；改进设计的近单分屑槽钻头使得PCB安装定位孔的钻屑获得了良好的断屑效果,使轴向力降低了20-30%；修磨横刃有效地降低轴向力,从而改善PCB钻头的钻削性能。成功设计的单分屑槽改进型钻头大大减少了钻削的铜屑缠丝现象,排屑通畅,改善了钻削孔的质量,钻头的寿命比标准钻头提高一倍。更多还原

【Abstract】 As the electronics develops, the PCB is widely used. Very frequently, drilling is a preliminary operation to PCB production The common PCB drilling can be divided into two types:one is the micro hole drilling (D≤0.3mm). Micro hole is an important part of the PCB. The other type is the fixed hole process. The fixed hole diameter is usually over 2mm. Comparing with microhole, the position hole process is the big diameter process. There is unsmooth chip removal, drill wear, serious burr while using common drill to do the job. With the increasing rotation speed, the problem is much more serious. Although the number of position holes is less than the microholes, the drill consuming is still larger due to the more material removal of bigger hole.In order to address the needs of high speed drilling of PCB fixed holes in practice, systematic researches were conducted on chip formation mechanisms of high speed drilling of PCB, tool wear mechanisms, surface finish, cutting forces and optimization of cutting parameters by numerical simulation analysis, micro-material analysis. High-speed photography, infrared temperature and optimization of drill geometry parameters. Chip formation, cutting forces and drill wear principles were studied. The relationship amony cutting conditions and chips, chip formation, surface finish, drill wear was established. Based on thermo-mechanical coupling theory, model can be applied to printed circuit board (PCB) which consists of thin copper foil. Finally, based on applications of basic theory about drilling process and characteristics, interaction between drill structure and chip removal was analyzed. Basic principle and method of drill improvement were put forward, which proved well production. All these researches will improve PCB drilling process, holes formation technique and drill production, which are great valuable.The key conclusions are as follows:1. The basic characteristics of PCB chip formation are combined with the Cu, Al, and fiber chips, which show different ship, size and types. As form of chip, fiber chips are rather long but very soft, medium length of copper chips, aluminum chips the length of the shortest, and was curled-type. Cu chips have types of long and short strip, and C-type. Glass fiber/resin chips have types of small cone-shaped spiral fan, longer cone-shaped spiral fan, small fan, and continuous chips. Different size and ship are produced through the helix groove of the drill when cutting. Great deformation first by the tension cracks and then enlarges the cracks to break down, which become various crack ships (fan, C-type). Drilling conditions, drill geometry and wear have great effects on them.2. Every material of PCB shows its unique drilling force property. The force reaches largest in the first force wave when drill the upper copper foil. It decreases in glass fiber/resin. The intertwined fibers cause great changes of drilling torques. The direction of chip movement shows large effect on the force. The same direction of feed and chip removal causes much larger force than opposite direction. The thrust depends more on the chip removal.3. For cutting conditions, feed has the greatest effect on the cutting force. It increases linearly with the increase of feed rate increases. The diameter of drills does not show the significant effect on the cutting force (D:2-3 mm). For the geometry of the drill, the web has greater effect on the trust, but not on the torque. Wet thinning can reduce the thrust. The point angle shows less influence on the force for its changing the direction of chips movement and hardly on the torque.4. The characteristics of force waves vary with different types of PCB. Evey material has its own best drill parameters. For the halogen-free plate (HF board), helix of 15°cause largest thrust, but other boards show the smallest. When point angle is 150°,all the three materials show the smallest force. Empirical formula of drilling thrust for FR-4 and HF has been obtained.5. The temperature between drill and workpiece is about 200℃. The maximum cutting temperature for copper foil of PCB is about 198.5℃, which is obviously larger than that of resin. With the increase of the feed rate, the temperature goes down. Most drilling heat is taken away by chips. The larger the web thickness and helix angle, the higher the drilling temperature. At the same time, it decreases with the point angle decrease. The influence of cutting speed on the temperature is greater than the feed rate.6. Based on thermo-mechanical coupling, the mechanism of the creation of holes of copper foil is verified by the finite element models. The SEM results of chip formation, cutting forces and temperature and experimental of PCB results are consistent.7. Carbide drill wear during high-speed PCB drilling has three stages, the initial wear, normal wear and severe wear. Carbide drill wear mechanism mainly includes abrasive wear, adhesive wear, chipping and micro-extrusion. Flank wear is the stable form of abrasion wear of the main, in the normal wear stage. Different parts of the drill wear are different. The drill point and the main edge of cutter exit abrasive and adhesive wear. Extruded plastic deformation occurs in the web. With the increase in the number of holes, tool flank wear a linear increase. The appropriate cutting parameters must be selected in order to reduce tool wear, improving tool life.8. Burr in drilling PCB is from the copper foil. Feed rate and the burr height are positively correlated in some degree. Small feed can improve the exit burr. Web has the greater effect on the burr generation, than the point angle, the least one is the helix angle. Less drill wear can also improve it. The fixed device and back-up board proves useful for it.9. A design method based on lower cutting forces and better chips removal was proposed. For the PCB fixed hole high speed drilling, chip groove and web thinning of the drill is the right choice. To decrease the cutting force and cutter wear, different kinds of drills are tried on. The single chip diving groove and web thinning drill show better results of chip break, the force decreased 20-30% from the thinning web. The new type drill shows the good performance in chip removing, avoiding of winding in the drill, which improves the quality of the drilling and drill life.更多还原