本科毕业论文-耳机外壳成型工艺分析及模具设计.doc

齐鲁工业大学2013届本科生毕业设计（论文）本科毕业设计(论文)题目 耳机外壳成型工艺分析及模具设计 学院名称 机械与汽车工程学院 专业班级 机械（高职）09-2班 学生姓名 导师姓名 2013 年 6 月 1 日目 录摘 要 1ABSTRACT 2第一章 前言31.1平面零件图 31.2立体零件图 3第二章 工艺分析与计算32.1工艺性分析 42.2计算毛坯直径 42.3计算模具的刃口尺寸5第三章 压力、压力中心计算及压力机选择 63.1落料拉深工序63.1.1工艺力的计算63.1.2压力机的选择7第四章 工艺分析与计算 84.1落料拉深复合工序84.1.2模具的总体设计84.2主要零部件的设计和选用 124.2.1凸凹模 124.2.2落料凹模 144.2.3拉深凸模154.2.4固定板和垫板174.2.5卸料装置214.2.6压力圈234.2.7推杆装置244. .2.8模架 25参考文献 31摘 要模具设计是模具制造的基础，合理正确的设计是正确制造模具的保证；模具制造技术的发展对提高模具质量、精度以及缩短制造模具的周期具有重要的意义；模具的质量、使用寿命、制造精度及合格率在很大程度上取决于制造模具的材料及热处理工艺；模具成本直接关系到制件的成本以及模具生产企业的经济效益；模具工作零件的精度决定制件的精度；模具的寿命又与模具材料及热处理、模具结构以及所加工制作材料等诸多因素有关；模具的安装与使用直接关系到模具的使用性能及安全；而模具的标准化是模具设计与制造的基础，对大规模、专业化生产模具具有极重要的作用，模具标准化程度的高低是模具工业发展水平的标志。外壳是耳机的基本组成部分，其质量优劣对整个耳机性能的影响十分明显。外壳为精密冲压件，虽然一般具有比较规则的外部形状，但尺寸较小而精度要求较高，各部位结构分布很紧凑，与内部部件相互配合；并且外壳应能承受一定的外力，因而需通过合理的工艺方案和模具结构来保证。 本课题研究的主要内容是通过对工件进行工艺分析与工艺计算，并结合数值模拟方法，只是确定了该模具的落料拉深复合工艺。利用二维绘图软件CAD进行模具的二维装配图及零件图的设计,用通用三维造型软件Proe对部分零件进行三维设计。并利用Proe中的装配模块将零件装配起来，以检验其具体配合情况，最终得出的是合理的模具装配图及所有零部件的零件图。关键词：模具 冲压 复合模 拉深复合 - 1 -ABSTRACTMolddesignisthefoundationwhichthemoldmakes,thereasonablecorrectdesigniscorrectlymakesthemoldtheguarantee;Themoldmanufacturetechnologydevelopmenttoimprovesthemoldquality,theprecisionaswellasreducesmakesmoldthecycletohavethevitalsignificance;Themoldquality,theservicelife,themanufactureprecisionandthequalifiedratearedecidedintheverygreatdegreetomakesthemoldthematerialandtheheattreatmentcraft;Themoldcostdirectlyrelatesthework-piecethecostaswellasthemoldproductionenterpriseseconomicefficiency;Themoldworkcomponentsprecisiondecidesthework-piecetheprecision;Themoldlifewiththemoldmaterialandtheheattreatment,themoldstructureaswellasprocessesthemanufacturematerialrelatedandsoonmanyfactors;Themoldinstallmentandtheusedirectlyrelatesthemoldtheoperationalperformanceandthesecurity;Butthemoldstandardizationisthemolddesignandthemanufacturefoundation,tolarge-scale,thespecializedproductionmoldhastheextremelyvitalrole,themoldstandardizationdegreeheightisthemoldindustrialdevelopmentlevelsymbol.The shell is an the basic component of earphone, the impact of whose quality is very obvious to the performance of the entire earphone. Although generally having regular profile, the shell as a precision stamping part, has small dimensions and calls for high accuracy, the distribution of whose structure , is close. Because it should be fitted with the inner structure and bore some external forces, thus its very important to design a reasonable process and die structure to ensure that. The research was major in analyzing of the forming process and calculating the technology of the shell, and combined with numerical simulation, developing an reasonable process and die structure, and determining the working process is : blanking-ironing. In this paper, the writer designs two-dimensional assembly drawing and part drawing by using CAD,and three-dimensional part drawing by using the common 3D modeling softwareProe, which are assembled by using assembly plat to test fitting situation. Finally we rerceive the reasonable assembly drawing and all parts part drawings.Keywords: molddesign; stamping, compound die, ironing, blanking-ironing- 2 -第一章 前言1.1平面零件图 外壳是耳机的重要组成部分，主要起着支撑内部结构，稳定内部结构的作用。采用金属外壳，不但使耳机外形美观，而且金属的刚性对降低腔体的谐振起到抑制作用，对提升音质有着积极的影响。结合它的使用特征及材料特点，通过正确的工艺分析和工艺计算，制定出合理的加工工艺过程和模具结构，有助于提高工件的质量、延长工件的使用寿命、提高生产效率、降低生产成本，从而可以创造出好的生产效益。本次设计的主要任务是：对外壳（图1.1）成形过程进行研究，通过工艺分析与工艺计算，并结合数值模拟方法，确定合理的工艺路线和模具结构，用二维或三维设计软件设计外壳成形模具，画出模具装配图与主要零件零件图。工件材料为08F，材料厚度为，本次设计对工件进行了详细的工艺性分析，采用落料拉伸复合工艺成形工件。模具结构简单，生产效率高，成本低廉，产品质量稳定，操作方便。图1.1 1.2立体零件图- 37 -第2章 工艺分析与计算2.1工艺性分析该零件为圆筒形零件，零件的材料为冷压薄钢板08F，价格低廉，表面质量好，但偏析比较严重。其化学成分主要是C、Si、Mn、P、S、Al、Ni、Cr、Cu 等。其中C可增加碳化铁的数量，提高钢板的屈服强度和抗拉强度，降低塑性，使冲压性能恶化，特别是当出现于晶界时，对冲压性能的不利影响更大；硅溶于铁素体中，强化铁素体的作用很大，增加强度，降低塑性，故含硅量越低越好，深冲压钢板不能用硅脱氧，08钢中硅的质量分数；锰的直接影响不大，锰和硫形成锰化硫夹杂物，其数量和形态对冲压性能有影响，为了保证08钢的拉深性能，其锰的质量分数不应超过；磷显著的增高钢板的强度，增加脆性，并有偏析倾向，会形成较多的带状组织，这些都对冲压性能不利；硫形成硫化物，对板料的冲压性能无疑是有害的，它是影响最大的一种元素；铝是钢中最终脱氧剂，与碳形成碳化铝，显著的降低“应变时效”的倾向，容易获得“饼形”铁素体晶粒，能改善冲压性能，08钢中铝的质量分数一般为，最佳值为。材料的力学性能如下：抗拉强度MPa，屈服点，断后伸长率，断面收缩率，具有很好的拉深性能。 零件为圆筒形件，不变薄部分：底部厚度为0.7mm；。变薄部分：侧壁厚度为0.4mm；高度为4.8mm。由以上对零件形状的分析可知该件结构复杂程度一般，材料厚度变化较大。其主要尺寸可由落料、变薄拉深冲压工序获得。由于变薄拉深只改变筒壁的厚度，所以应将变薄部分作为筒壁，进行变薄拉深。2.2计算毛坯直径（1）计算制件体积按制件图（图1.1）上基本尺寸进行计算：2.3计算模具的刃口尺寸1）落料模具刃口尺寸：圆形凸模和凹模，可采用分开加工，按式19.1-3、19.1-4计算工作部分尺寸。所落下的料（即为拉深件的坯料）按IT12级取得极限偏差，故落料件的尺寸取为。首先根据表19.1-32确定拟采用的间隙类别为：类（中等间隙），然后按表19.1-42中，选取类（中等间隙类）比值为7.010.0。则双面间隙为：查表19.1-92，根据落料件的基本尺寸为17.5mm，得凸模极限下偏差；凹模极限上偏差。由，满足条件。由表19.1-102，由工件制造公差为，得：系数，因此，据式19.1-32及19.1-42得：落料凹模刃口尺寸为：落料凸模刃口尺寸为：2）变薄拉深 首次拉深件按IT12级的极限偏差考虑，且零件标注外形尺寸，故拉深件的外形尺寸取为。凸凹模圆角半径前面已经确定：，间隙取（因为变薄后，筒壁厚度为）由表19.4-402查出凸凹模的制造公差，当料厚为，制件直径为时，制件标注外形尺寸，由表19.4-392公式进行计算：拉深凹模刃口尺寸为： 拉深凸模刃口尺寸为：拉深凸模的出气孔尺寸： 取 。第三章 压力、压力中心计算及压力机选择3.1 落料拉深工序由于该零件为轴对称件，故不必进行压力中心的计算。3.1.1 工艺力的计算落料力：卸料力：式中 拉深力：查表19.4-462，得式中 k7系数，钢为1.82.25，取k7=2压边力按照防皱最低压边力公式（根据表19.4-432）： 这一工序的最大压力，是在离下死点4.9mm稍后就需达到：3.1.2 压力机的选择在实际生产中，为了防止设备超载，一般按如下公式进行估算压力机的公称压力：由前面的计算知，得：同时，这个零件尺寸较小，无须考虑台面尺寸。只需按照公称压力进行选择。因此，查表2-316选用40kN的开式压力机 进行加工。40kN压力机的技术参数如表3.1所示。表3.1 40kN压力机技术参数名 称40开式压力机标称压力40标称压力行程（）3.5滑块行程（）40标称行程次数（次/min）200最大封闭高度（）160封闭高度调节量（）34工作台尺寸（）左右280前后180由上述40kN开式压力机技术参数知：压力机最大封闭高度为，最小封闭高度为，所以，模具的闭合高度H0数值应满足下式：，即若实际设计的模具闭合高度小于134mm，不在设备闭合高度范围内，可以通过加垫板的方式解决。故冲压设备定为40kN开式压力机。第四章 模具结构设计 根据确定的工艺方案和零件的形状特点、精度要求、所选设备的主要技术参数、模具制造条件以及安全生产等选定其中冲模的类型及结构形式。4.1落料拉深复合工序4.1.2模具总体设计落料拉深复合模，首先要考虑落料凸模（兼拉深凹模）的壁厚是否过薄。凸凹模壁厚，查表20.3-22得料厚为0.60.8的低碳钢复合模最小壁厚为（1.01.2）mm，能保证足够强度，故可以采用复合模。落料拉深复合模，常采用落料正装，拉深倒装式。模座下的弹顶器提供压边力及顶件力，压边圈兼有顶件作用。由于料很薄（），采用弹性卸料板，弹簧提供弹力。其装配图见图4.1。图4.1a 落料拉深复合模1导套，2上模座，3弹簧，4卸料螺钉，5挡料销，6上垫板，7模柄，8推杆，9打料块，10、11、22圆柱销，12、19螺钉，13凸凹模固定板，14导柱，15卸料板，17凸凹模，18压边圈，20凸模，21顶杆，23凹模，24下垫板， 25下模座图4.1b落料拉深复合模图4.1b落料拉深复合模4.2主要零部件的设计和选用 4.2.1凸凹模落料拉深复合模，首先要考虑落料凸模（兼拉深凹模）的壁厚是否过薄。凸凹模壁厚，查表20.3-22得料厚为0.60.8的低碳钢复合模最小壁厚为（1.01.2）mm，能保证足够强度，故可以采用复合模。为了增加凸凹模的刚度和强度，将拉深凸模做成台阶式（图4.2a），用固定板固定，台阶处阶梯过渡，小端是工作部分，其尺寸和公差根据工件尺寸和制造方法确定为如图4.2a所示。中间台阶和凸凹模固定板过渡配合（H7/m6）。最大台阶是用台肩保证凸模在卸料时不被拉出。凸凹模材料为Cr12。取凸凹模长L为45mm，其长度计算过程如下： 式中 h1凸模固定板厚度，初定为20mm； h2卸料板厚度，初定为10mm；h3凸模进入凹模深度（查表20.1-82，得h3=（0.52）mm，取h3=0.5mm）；h凸模修磨量和在模具闭合状态下固定板与卸料板间的安全距离等因素需要增加的长度，一般取1020mm。）具体尺寸见图4.2 (a)。三维示意图见图4.2(b)。 a 凸凹模尺寸 b 三维图 图4.2 凸凹模 4.2.2落料凹模查表20.1-142，根据料厚，冲件尺寸，得凹模壁厚，高度。即凹模外型尺寸，按标准取。凹模强度校核：，式中凹模最小壁厚；冲裁力，即。此处凹模壁厚为，符合要求。即凹模的外形尺寸为。内外形尺寸均已定；有4个螺纹孔，以便于下模座固定；2个与下模座同时加工的销钉孔；有3个挡料销用的销孔。具体尺寸见图4.3a，三维示意图见图4.3b。 a 凹模尺寸 b 三维图图4.3 落料凹模4.2.3拉深凸模拉深凸模用固定板固定，其尺寸和公差根据工件尺寸和制造方法确定如图4.4a所示。中间部分和凸模固定板过渡配合（H7/m6）。最大台阶是用台肩保证凸模在卸料时不被拉出。凸模材料为Cr12，长度L取为32，其长度计算过程如下： 式中 h1凸模固定板厚度，初定为16mm； h2凸模进入凹模深度（查表20.1-8，得h2等于拉深件的高度，即h2=4.8mm）；h凸模修磨量和在模具闭合状态下固定板与卸料板间的安全距离等因素需要增加的长度，一般取1020mm。具体尺寸见图4.4 (a)。三维示意图见图4.4(b)。 a 凸模尺寸 b 三维图 图4.4拉深凸模4.2.4固定板和垫板凸凹模固定板厚度：，查表22.5-192，取标准值Hp=20mm。外形尺寸均与凹模外形尺寸一直，即D=80mm。有4个螺纹孔，以便于与上模座固定；有2个与上模座同时加工的销钉孔；有4个安装弹簧用的孔。具体尺寸见图4.5 (a)。三维示意图见图4.5 (b)。凸模固定板厚度：，查表22.5-192，取标准值Hp=16mm。外形尺寸均与凹模外形尺寸一直，即D=80mm。有4个螺纹孔，以便于与上模座固定；有2个与上模座同时加工的销钉孔；有4个安装顶杆用的发顶杆孔。具体尺寸见图4.6 (a)。三维示意图见图4.6(b)。垫板厚度 查表22.5-202得，H=6mm，直径与凹模直径一致。上垫板均布有4个螺钉通孔，2个销钉通孔和4个卸料螺钉通孔。上垫板均布有4个螺钉通孔，2个销钉通孔和4个顶杆通孔。具体尺寸如下图4.7a 凸凹模固定板尺寸 b 三维图图4.5 凸凹模固定板a 凸模固定板 b 三维图图4.6 凸模固定板 a 上垫板 b 三维图图4.7 上垫板 a 下垫板 b三维图图4.8 下垫板4.2.5卸料装置1）卸料板由于材料较薄，采用弹性卸料板。查表20.1-332，由料厚t=0.7mm和卸料板宽度，得最小厚度。其外形尺寸与凹模外形一致，即为。有4个卸料螺钉的螺纹孔和3个安装固定挡料销的孔。具体尺寸见图4.9 (a)。三维示意图见图4.9(b)。 a 卸料板尺寸 b三维图图4.9 卸料板2）卸料螺钉按照习惯选为内六角圆柱头轴肩螺钉M850GB/T5281-1985。3）弹簧根据模具结构和卸料力，初定弹簧根数为n=4，且装在卸料螺钉上。则每根弹簧上的卸料力。弹簧工作中必须得压缩量 式中 lw工艺行程，一般取； l考虑模具的刃磨和调整的余量，一般取。取。查表14-353，选用弹簧外径，弹簧线材直径的弹簧，其最大允许工作负荷为，最大允许工作负荷下的弹簧每圈变形量为。4.2.6压边圈内形与拉深凸模间隙配合，外形受落料凹模内孔限制。压边圈在此处兼有顶料板的作用，与顶杆连用（三根及其以上），由弹顶器提供压边及顶料力。顶杆的长度=下模座厚度+垫板厚度+凹模厚度+凸模固定板厚度-压边圈厚度。经计算得顶杆长度至少为，由于安装空间的限制，此处只能使用直径为4mm的顶杆，查表22.5-612得，直径为4mm的顶杆最大长度小于60mm。鉴于此处所需的压边力和顶件力都很小，所以顶杆受力很小，故使用了4根顶杆。具体尺寸见图4.10 (a)。三维示意图见图4.10(b)。 a 压边圈尺寸 b三维图图4.10 压边圈4.2.7推杆装置前部外形与拉深凹模间隙配合且后部必须更大。具体尺寸见图4.11 (a)。三维示意图见图4.11(b)。与推杆联合使用，推杆的长度=模柄高度+凸凹模高+垫板厚度-打料块厚度。查表22.5-592，根据计算数值选用带肩推杆A6110。 a 打料块尺寸图 b三维图图4.11 打料块4.2.8模架考虑到送料及操作方便，且该模具精度要求一般，小型模具。据表22.4-30，选用后侧导柱模架8080130150 IGB/T2851.3，按其标准具体结构如下表4.1。表4.1 后侧模架具体结构选择名称数量规格（）标准上模座1GB/T2855.5下模座1GB/T2855.6导柱2GB/T2861.1导套2GB/T2861.6上模座采用4个对称布置的螺钉固定，并加2个的圆柱销进行准确定位。因此，在规定位置加工4-M6的螺钉沉孔，2-的销孔，4-M8的卸料螺钉沉孔。其中，销钉孔要求内壁粗糙度为1.6，导套孔要求内壁粗糙度为1.6，且导套孔有两个尺寸要求，要求公差符合H7，即分别为。具体尺寸如图4.12(a)所示。三维示意图见图4.12(b)。下模座采用4个对称布置的M8螺钉固定，并加2个的圆柱销进行准确定位。因此，在规定位置加工4-M8的螺钉沉孔，2-的销孔以及2个导柱孔。另外还包括4个顶杆孔。下模座如图4.13所示。a 上模座尺寸 b 三维图（正反面）图4.12 上模座 a 下模座尺寸 b 三维图（正反面）图4.13 下模座（9）其他模柄 采用压入式模柄 查表22.5-24 选用A2060JB/T7646.1；挡料销 选用圆柱式固定挡料销 查表22.5-58 选用A6JB/T7649.10；连接上模座和凸凹模固定板的螺钉 M635（4个）；连接下模座和凹模及凸模固定板的螺钉 M855（4个）；上模座和凸凹模固定板的定位销钉635（2个）；下模座和凹模及凸模固定板的定位销钉850（2个）；压入式模柄和上模座的止转销钉612（1个）。参考文献1 高军主编.金属塑性成形工艺及模具设计.北京:国防工业出版社,200772肖祥芷,王孝培主编.中国模具设计大典（第三卷）.南昌:江西科学技术出版社,20033王孝培.冲压手册（修订本）.北京:机械工业出版社,19904 廖希亮,邵淑玲主编.机械制图.济南:山东科学技术出版社,20025肖景容,姜奎华.冲压工艺学.北京:机械工业出版社,19906张鼎承主编.冲模设计手册.北京:机械工业出版社,19887王新华,袁联富.冲模结构图册.北京:机械工业出版社,20038王新华,陈登主编.简明冲模设计手册.北京:机械工业出版社,20089杨玉英主编.实用冲压工艺及模具设计手册.北京:机械工业出版社,200510湖南省机械工程学会锻压分会.冲压工艺.11机械电子工业部.模具公差与检测.北京:机械工业出版社,199312代勇.壳体变薄拉深工艺.锻压技术,2000,6:19-2013代勇.壳体落料拉深整形冲孔复合模.模具技术,2001,3:41-4314郭来平.复合模设计中几个问题的探讨.模具制造,2002,3:30-3115高广军,赵强.DYNAFORM数值模拟技术在冲压成形中的应用.模具制造,2003,5:5-916成虹.板料变薄拉深过程中的润滑与模具设计.成都电子机械高等专科学校学报,2003,2:1-417施子庆,张建慈.影响内外曲翻边的质量因素分析及采取的措施.金属成形工艺,2000,18（2）:44-4618洪慎章，曾振鹏汽车车轮盖落料-拉深-冲孔-切边复合模设计汽车工艺与材料，2001，3:25-2719岳睿,丁为民,周晓刚.升降器外壳冲压工艺设计.锻压技术，2007,32（2）:82-8520王卫卫.材料成形设备.北京:机械工业出版社,200621 Sven K. Esche,Sudheer Khamitkar,Gary L. Kinzel,Taylan Altan.Process and die design for multi-step forming of round parts from sheet metal.Journal of Materials Processing Technology,1996,59: 24-3322 Leonid Shulkin,Steven W.Jansen,Mustafa A.Ahmetoglu,Gary A.Kinzel,Tylan Altan.Elastic defections of the blank holder in deep drawing of sheet motal.Journal of Materials Processing Technology,1996,59:34-4023 Tung-Sheng Yang.The application of abductive networks and FEMto predict the limiting drawing ratio in sheet metalforming processes.Int J Adv Manuf Technol .2008,37:58-69 26 M.F. Shi and J.C. Gerdeen.A Theoretical Study of the Ironing Process in Sheet Metal Forming.J. Mater. Shaping Technol,1989, 7:203-211 为你提供优秀的毕业论文参考资料，请您删除以下内容，O(_)O谢谢！2 Many people have the same mixed feelings when planning a trip during Golden Week. With heaps of time, the seven-day Chinese为你提供优秀的毕业论文设计参考资料，请您删除一下内容，O(_)O谢谢！National Day holiday could be the best occasion to enjoy a destination. However, it can also be the easiest way to ruin how you feel about a place and you may become more fatigued after the holiday, due to battling the large crowds. During peak season, a dream about a place can turn to nightmare without careful planning, especially if you travel with children and older people. As most Chinese people will take the holiday to visit domestic tourist destinations, crowds and busy traffic are inevitable at most places. Also to be expected are increasing transport and accommodation prices, with the possibility that there will be no rooms available. It is also common that youllwait in the line for one hour to get a ticket, and another two hours at the site, to only see a tiny bit of the place due to the crowds. Last year, 428 million tourists traveled in China over the week-long holiday in October. Traveling during this period is a matter that needs thorough preparation. If you are short on time to plan the upcoming Golden Week it may not be a bad idea to avoid some of the most crowded places for now. There is always a place so fascinating that everyone yearns for. Arxan is a place like this. The beauty of Arxan is everlasting regardless of the changing of four seasons. Bestowed by nature, its spectacular seasonal landscape and mountains are just beyond word. Arxan is a crucial destination for the recommended travelling route, China Inner Mongolia Arxan Hailar Manzhouli. It is also the joint of the four prairies across the Sino-Mongolian border, where people gravitate towards the exotic atmosphere mixed with Chinese, Russian, and Mongolia elements. As a historic site for the Yitian Battle, Arxan still embodies the spirit of Genghis Khan. Walking into Arxan, you will be amazed by a kaleidoscope of gorgeous colors all the year round - the Spring azaleas blooming red in the snow, the Summer sea wavering blue in the breeze, the Autumn leaves painted in yellow covering volcanic traces, and the Winter woods shining white on the vast alpine snowscape. Hinggan League Arxan city is situated in the far eastern area of Inner Mongolia Autonomous Region. Its full name Haren Arxan means hot holy water in the Mongolian language. Arxan is a tourism city in the northern frontier with a blend of large forest, grand prairies, vast snowfield, heaven lake cluster, thermium, as well as volcanic cluster. It is a rare and unique ecotourism base filled with healthy sunshine, clean air and unspoiled green. Nestled close to the countrys largest virgin forest, and known for its spring and ecological environment, Arxan is marveled at by many tourists as the purest land on earth. You cannot miss out the Autumn of Arxan. It is definitely the best with brightly-colored scenery full of emotions. Autumn in the northern part of the country comes earlier than the South. A September rain followed by the footprints of Autumn brings more colors to the once emerald green mountain and blooming grassland. Shutterbugs flock to see for themselves the marvel of splendid colors around the mountains and waters, many of whom have travel a long distance and even camp here only to capture a moment of the nature wonder. The silver birch turns golden, while the larch is still proudly green. You will find yourself drowned in the intoxicating red of the wild fruits as well as the glamour of flowers in full blown. And your heart will be lingering on the woods as its time for the wild fruits to ripe. The picturesque Arxan in Autumn is indeed a fairyland only exists in a dream that satisfies all your fantasies. If itrains heavily on Saturday night, some elderly Chinese will say it is because Zhinu, or the Weaving Maid, is crying on the day she met her husband Niulang, or the Cowherd, on the Milky Way. Most Chinese remember being told this romantic tragedy when they were children on Qixi, or the Seventh Night Festival, which falls on the seventh day of the seventh lunar month, which is usually in early August. This year it falls on Saturday, August 2. Folklore Story As the story goes, once there was a cowherd, Niulang, who lived with his elder brother and sister-in-law. But she disliked and abused him, and the boy was forced to leave home with only an old cow for company. The cow, however, was a former god who had violated imperial rules and was sent to earth in bovine form. One day the cow led Niulang to a lake where fairies took a bath on earth. Among them was Zhinu, the most beautiful fairy and a skilled seamstress. The two fell in love at first sight and were soon married. They had a son and daughter and their happy life was held up as an example for hundreds of years in China. Yet in the eyes of the Jade Emperor, the Supreme Deity in Taoism, marriage between a mortal and fairy was strictly forbidden. He ordered the heaven troop to catch Zhinu back. Niulang grew desperate when he discovered Zhinu had been taken back to heaven. Driven by Niulangs misery, the cow told him to turn its hide into a pair of shoes after it died. The magic shoes whisked Niulang, who carried his two children in baskets strung from a shoulder pole, off on a chase after the empress. The pursuit enraged the empress, who took her hairpin and slashed it across the sky creating the Milky Way which separated husband from wife. But all was not lost as magpies, moved by their love and devotion, formed a bridge across the Milky Way to reunite the family. Even the Jade Emperor was touche