轴端端盖专业模具毕业设计

上传人:仙*** 文档编号:38872956 上传时间:2021-11-09 格式:DOC 页数:34 大小:514KB
返回 下载 相关 举报
轴端端盖专业模具毕业设计_第1页
第1页 / 共34页
轴端端盖专业模具毕业设计_第2页
第2页 / 共34页
轴端端盖专业模具毕业设计_第3页
第3页 / 共34页
点击查看更多>>
资源描述
天津工程师范学院 2008 届本科生毕业设计 I 引言 . 1 1 模具简要概述 . 2 1.1 冷冲压及模具的概念 . 2 1.2 冲压及模具在工业生产中的地位 . 2 2 冲裁模具设计过程 . 4 2.1 零件分析 . 4 2.2 确定工艺方案 . 4 2.3 主要工艺参数计算 . 4 2.3.1 计算毛坯直径 . 4 2.3.2 确定是否加修边余量 . 5 2.3.3 确定是否需要压边圈 . 5 2.3.4 确定拉深次数 . 5 2.3.5 排样及材料的利用率 . 5 2.3.6 计算工序冲压力 . 7 2.3.7 压力中心 . 8 2.4 冲压设备的选择 . 9 2.5 确定冲裁间隙,计算主要工作部分尺寸 . 9 2.5.1 间隙对冲压力的影响 . 9 2.5.2 间隙对模具寿命的影响 . 9 2.5.3 间隙对冲裁件质量的影响 . 9 2.5.4 冲裁工序 . 10 2.6 模具结构设计 . 12 2.6.1 凹模周界尺寸计算 . 12 2.6.2 凹模厚度尺寸 H 的计算 . 12 2.6.3 凹模外形尺寸的计算 . 12 2.6.4 模具闭合高度的计算 . 12 2.6.4 拉深凹、凸模的圆角半径 . 12 2.6.5 选择模架及确定其他冲模零件 . 13 2.6.6 卸料零件的计算 . 13 2.6.7 弹性元件的设计计算 . 13 2.6.8 定位零件的确定 . 14 2.6.8 导向装置的种类及标准的确定 . 14 2.6.9 固定与支承零件的确定 . 14 2.7 端盖冲裁模的工作原理 . 16 3 模具装配与调试 . 18 3.1 安装顺序 . 18 3.2 装配要点 . 18 3.3 装配过程 . 18 结 论 . 20 参考文献 . 21 附录 1:冲压模零件的加工精度及其相互配合 . 22 天津工程师范学院 2008 届本科生毕业设计 II 附录 2:英文资料 . 23 附录 2:中文资料 . 28 致谢 . 32 天津工程师范学院 2008 届本科生毕业设计 1 引言 模具在现代生产中,是生产各种工业产品的重要工艺装备,它以其特定的形状通过一定的方式使原材料成形。由于模具成形具有优质、高产、省料和低成本等特点,现以在国民经济各个部门,特别是汽车、拖拉机、航空航天、仪器仪表、机械制造等工业部门得到极其广泛的应用。随着社会经济的发展,人们对工业产品的品种、数量、质量和款式都有越来越高的要求。为了满足人类的需要,世界上各工业发达国家都十分重视模具技术的开发,大力发展模具工业。积极采用先进技术和设备,提高模具制造水平,并取得了显著的经济效益。模具是制造业中使用量大、影响面广的工具产品。在现代批量生产中,没有高水平的模具,就没有高质量的产品,它对企业提高生产效率、降低生产成本也有重要的作用。模具工业也被称为“皇冠工业” 。随着我国加入 WTO 我国模具工业的发展将面临新的机遇和挑战。 近年来,中国的模具工业发展十分迅速,一直以每年 15%左右的增长速度快速发展。目前,模具在汽车、拖拉机、飞机、家用电器、工程机械、动力机械、冶金、机床、兵器、仪器仪表、轻工、日用五金等制造业中,起着极为重要的作用。国民经济的高速发展对模具工业提出了越来越多且越来越高的要求,巨大的市场需求推动着中国模具工业更快地发展。 模具 CAD/CAE/CAM 技术是改造传统模具生产方式的关键技术, 能显著缩短模具设计与制造周期,降低生产成本,提高产品质量。它使技术人员能借助于计算机对产品、模具结构、成形(型)工艺、数控加工及成本等进行设计和优化。我国自开发的有上海交大的冲裁模 CAD/CAM 系统;北京北航海尔软件有限公司的CAXA 系列软件;吉林金网格模具工程研究中心的冲压 CAD/CAE/CAM 系统等,为进一步普及模具 CAD/CAM 技术创造了良好条件。 根据我国模具技术的发展现状及存在的问题,今后应朝着如下几个方向发展: 1) 开发、发展精密、复杂、大型、长寿命模具,以满足国内市场需求。 2) 加速模具标准化和商品化,以提高模具质量,缩短模具制造周期。 3) 大力开发和推广应用模具 CAD/CAM 技术,提高模具制造过程的自动化。 4) 积极开发模具新品种、新工艺、新技术和新材料。 5) 发展模具加工成套设备,以满足高速发展的模具工业需要 天津工程师范学院 2008 届本科生毕业设计 2 1 模具简要概述 1. .1 冷冲压及模具的概念 冷冲压是先进的金属加工方法之一,也是塑性加工的基本方法之一。它主要是在室温下(对金属系指再结晶温度以下)加工金属板料, 故又称为板料冲压或冷冲压。 冷冲压是借助压力机, 通过模具在室温下对材料施加压力使其产生塑性变形或分离,从而获得零件所需要的形状、尺寸的一种的压力加工方法。用冲压方法加工的工件称为冲压件。 在冷冲压加工中,使被加工零件成形的一种特殊工具称为冷冲压模具(简称冷冲模)。模具工作部分的成形尺寸与被加工零件尺寸一致,所以,零件表现出“一模一样”的特征。在实现冷冲压的加工过程中,冷冲模是一种必需的工艺装备,没有先进的模具技术,先进的冲压工艺就无法实现。 1.2 冲压及模具在工业生产中的地位 和其他加工方法相比,冲压加工有如下特点: 1.可以冲压出其他加工工艺难以加工或无法加工的形状复杂的零件, 例如体积小、质量高的仪器仪表零件,汽车覆盖件,纵梁等。 2.产品具有足够的形状、尺寸精度,互换性能好,表面质量好,尺寸稳定。尺寸精度一般可达 ITl014 级,精冲最高可达 IT6 级。 3.材料利用率高。冷冲压是少、无切屑加工,材料耗损少,材料利用率一般可达 7085。 4.操作简单,生产过程便于实现机械化与自动化,生产效率高,特别适合大批量生产。高速冲裁小型制件,每分钟可达上千件,零件成本低。 5.冲压加工的缺点是模具制造周期长,成本高,且冲压过程中噪声很大,所以不适合单件或小批量生产。另外,由于压力机滑块往复运动快,手工操作容易发生事故,效应该特别重视安全生产。 由于冲压加工具备上述特点,冲压加工的应用范围十分广泛,它可以冲压黑色金属和有色金属, 也可以冲压非金属材料。 据统计, 在汽车制造、 机电和仪器、仪表生产中有 6070的零件是采用冲压加工制成的;在电子产品中,冲压件数量占零件总数的 85以上。 模具是生产各种工业产品的重要工艺装备, 是衡量一个国家工业发展水平的重要指标,模具工业在整个国民经济发展中的作用愈来愈显著。据近年来的统计表明,美、日等国的模具工业年产值已经超过机床工业年产值的 612;我天津工程师范学院 2008 届本科生毕业设计 3 国 2003 年模具工业总产值也已达 450 亿元左右,其中,冷冲压模具因其用途广、技术成熟而在模具中占比例最大。可以预见,高速发展的经济将对模具提出更为大量、更为迫切的需要和挑战。研究和发展冲压生产技术,对发展国民经济和加速工业现代化建设,具有十分重要的意义。 天津工程师范学院 2008 届本科生毕业设计 4 2 冲裁模具设计过程 2.1 零件分析 轴端端盖零件大批量生产,采用 08 软钢材料。 冲压件的工艺分析 该冲压件为底部带孔的圆筒拉深件,拉深高度不高,冲压材料为 08 钢,拉深成型性能比较好。又由于产品批量较大,工序分散的单一工序生产不能满足生产需要,应考虑集中的工艺方法 2.2 确定工艺方案 经分析冲压该零件需要的基本工序有(1)落料(2)冲孔(3)拉深,根据以上工序我们有以下两种方案。 方案一、先落料冲孔,然后正反拉伸。 方案二、落料、正反拉深、冲孔复合模。 分析比较上述两种工艺方案,可以得到如下结论。 方案一从模具的制造和维修上考虑,冲孔落料复合时,凸凹模刃磨方便,同时模具结构比较简单,但是该方案的正反拉伸安排在冲孔之后进行定位不易保证,影响零件的精度。 方案二的落料、正反拉深、冲孔的复合顺序有利于成形,既能满足产量的要求,又能保证产品质量和模具的合理性。 经综合分析论证:采用第二种方案,落料、正反拉深、冲孔复合模。 2.3 主要工艺参数计算 2.3.1 计算毛坯直径 该工件为无凸缘圆筒形件,根据等面积原则,用解析法求毛坯直径。如图 1所示: 按工件厚度中心层计算。 已知:h1=6 ,h2=2mm,d=34 ,r=2 ,t=1 , 根据公式 D=f4 (2-1) f 为各简单几何形状的表面积,mm2 天津工程师范学院 2008 届本科生毕业设计 5 则毛坯直径为 D=25644.1251218 .89524.459824.54350 图 1 2.3.2 确定是否加修边余量 根据冲压件相对高度: h/d=5.5/340.16 经查表得 h/d0.16 ZmaxZmin,不满足间隙公差条件,应缩小凹,凸提高制造精度才能保证间隙在合理范围。取 凹=0.6(Zmax-Zmin)=0.024 凸=0.4(Zmax-Zmin)=0.016 故凸D=49.950016. 0 凹D=49.95024. 00 凹D= 49.95024.00 凸D= 49.950016. 0 冲孔 836. 00 查公差表得: 凹=0.012mm;凸=0.008mm 凸d=(d+X )0凸=(8+0.5 0.3)0008. 0=8.150008. 0mm 凹d=(凸d+ Zmin)凹0=(8.15+0.1)0.0120 =8.250.0120mm 凹+凸=0.012+0.008=0.021.5D 时,应采用将橡胶分段,其间垫以钢垫圈。 安装橡胶时,周围应留有足够的空隙位置,以容许橡胶压缩时断面尺寸的 选用橡胶时的计算步骤 根据工作行程计算橡胶的自由高度, H自由=(3.54)S工作 根据 H自由计算橡胶的装配高度, H2 =(0.850.9)H自由 在模具装配时,根据模具空间大小确定橡胶的断面面积。 橡胶的选择 该模具采用橡胶作为弹性卸料装置,按冲模设计应用实例课本中的公式计算橡胶的自由高度, H自由=(3.54)S工作 (2-10) 式中 H自由橡胶的自由高度() ; S工作工作行程与模具修磨量或调整量(46 )之和再加一; 弯曲凸模与落料凸模之间的橡胶计算: H自由=(3.54)S工作=(3.54)(6+1)=(3.54)7=24.528 =(0.850.9)H自由 (2-11) 取 H2=23 2.6.7 弹性元件的设计计算 弹性元件的设计计算 为了得到较平整的工件,此模具采用弹压式卸料结构,使条料在落料、拉深过程中始终处在一个稳定的压力之下,从而改变了毛坯的变形稳定性,避免材料在切向应力作用下起皱的可能。落料卸料采用弹簧作为弹性元件 天津工程师范学院 2008 届本科生毕业设计 14 弹簧的选择 卸料板用于冲压件的卸料,且兼做压料板,是使工件保持平衡的关键零件,故选择弹簧时,其工作压力应加大一些。 根据结构初选为 4 根弹簧,卸料力 F卸2610N/4=652.5N。按预压力 F 预0.5652.5N=326.25N 和模具的结构尺寸, 查表 2-13 中可选序号 3438 的弹簧,其负荷为 F=330NF 预。 检验是否满足 S1S 总=S 预+S 工作+S 修磨。 55-36.62+10+4=18.416 合格 故选取 37 号弹簧外径 D=20mm,钢丝直径 d3mm,自由状态下高度 H自由=55mm 。 弹簧装配高度 H2H 自由-S 预=55mm-2mm=53mm,工作行程高度为 30mm。 2.6.8 定位零件的确定 定位零件的作用,是使条料或毛坯在精冲时确定正确的位置,从而保证冲出合格的制件,根据毛坏和模具不同的特点,必须采用不同形式的定位装置,冲模中常见的定位零件有定位板、定位销、挡料销、导料销,侧压板等。 而在该联接件的模具设计中,采用了挡料销定位零件进行定位。 2.6.8 导向装置的种类及标准的确定 模具中导向副的作用是保证上模相对于下模有一定位置关系, 分为滑动导向副和滚动导向副两类。 滑动导向副由导柱,导套组成,在中、小型模具中应用广泛。 滚动导向副由导柱、 导套和钢球保持圈组成, 适于要求精度高寿命长的模具,如高速冲裁模、精密冲裁模、硬质合金冲裁模等。 由于滚动导向副与滑动导向副相比,在滚动式导套、导柱间多了一层装在保持圈内的钢球作为滚动体,使原来的滑动磨擦变为滚动磨擦,磨擦系数小,提高模具导向副的使用寿命, 但是滚动导向副的价格高, 对于大批量生产的托架来说,滑动导向副就能满足生产要求,与滚动导向副相比,成本低。因此,采用滑动导向副。 2.6.9 固定与支承零件的确定 模柄的确定 模柄的作用是将模具的上模座固定在冲床的滑块上, 常用的模柄形式有整体式、旋入式、压入式、凸缘式、浮动式。压入式模柄通过配合与上模座联接固定,适用于模板较厚的中小型模具中,而且可以保证较高的同轴度和垂直度。此套模天津工程师范学院 2008 届本科生毕业设计 15 具选用凸缘式模柄,它与模座安装孔用 H7/ n6 配合。 垫板的设计与标准 垫板主要用于直接承受和扩散凸、凹模传来的压力,防止模座承受过大压力而出现凹坑, 影响模具正常工作。 模具是否用垫板, 根据模座承受压力大来确定,凸(凹)模支承端面对模座的单位压力为: = PA (2-12) 式中: P 冲裁力 A 凸(凹模)支承端面面积 小于等于模座许用应力则应在凸(凹)模与模座间加经淬硬磨平的垫板,外形尺寸按固定板形状决定,因此垫板厚度取 20mm,外形尺寸与落料凹模外形尺寸一致。 天津工程师范学院 2008 届本科生毕业设计 16 2.7 端盖冲裁模的工作原理 141619101115181719?6H7n6?4H9h8?25H7h6?38H7r6?25H7r621021222423252830312026272912138765432?8H7n6?8H7n6?8H7n6?8H7n6?8H7n6?8H7n6?8H7n6?82H7n6?10H7n6?10H7n6?10H7n6 图 2 1.下模座 2.定位销 3.下垫板 4. 下固定板 5. 落料凹模 6. 卸料板 7.挡料销 8. 落料拉伸凸凹模 9.上垫板 10.上模座 11.定位销 12.13.内六角紧固螺钉 14.模柄 15.打杆 16. 推杆 17.卸料螺钉 18.导套 19.导柱 20.推件块 21.卸料弹簧 22.顶件块 23.冲孔凸模 24.止动块 25.内六角紧固螺钉 26.弹簧 27.拉伸凸模 28.推杆29.托板 30.双头螺栓 31.螺母 32.导料销 如图为一副落料、正反拉伸、冲孔复合冲裁模的结构。端盖冲裁模的工作原理:冲模开始工作时,上、下模在压力机作用下分开,将条料放在落料凹模 5 上并通过挡料销 7 及导料销 32 定位,待上模在压力机滑块作用下下降时,落料拉伸凸凹模 8 与落料凹模 5 首先接触,并进行落料。然后下模中的拉伸凸模 27 便接触条料,待继续加压时,拉伸凸模 27 与落料拉伸凸凹模 8 开始对条料进行正天津工程师范学院 2008 届本科生毕业设计 17 拉伸成形。上模继续下降,推件块 20 与拉伸凸模 27 进行反拉伸成型,上模继续下降,由固定在下垫板上的冲头对冲裁件进行冲孔,废料由推杆从推件块 20 中的落料孔中排出。待上模在压力机滑块作用下回升时,打杆通过上顶杆下移顶出工件,同时安装在下模座中的下顶杆在橡胶力的作用下向上顶起,拿出制品,卸料板将废料提起,条料又恢复到原来的位置,准备下一冲程的冲裁。 天津工程师范学院 2008 届本科生毕业设计 18 3 模具装配与调试 对于导柱复合模,一般先安装上模,然后找正下模中凸凹模的位置,按照冲孔凹模型孔加工出顶杆孔,这样既可以保证上模中推件装置与模柄中心对正,又可避免顶杆错位,而后以凸凹模为基准分别调整落料与冲孔的间隙,使之均匀,再安装其它的零件。 3.1 安装顺序 组件装配 模架的组装,模柄的装入,凸模及凸凹模在固定板上的组装 总装配 先装上模,再以上模为准装下模 调整凸凹模的间隙 安装其它辅助零件 检查、试件 3.2 装配要点 按照装配过程安装,先装上模,然后装下模。 上模座、上模垫板、落料凸模和上模固定板上的销钉孔在调整完凸、凹模间隙均匀后一起配钻;同理,下模的销钉孔在下模座、下模垫板和凸凹模固定板经配合后配钻。 装落料凹模前先把挡料销装入,使其保证过盈配合。 冲孔凸模装在上模固定板以后, 应将冲孔凸模底部高出上模固定板的部分磨平。 3.3 装配过程 表 3 序号 工序 工艺说明 1、 检查零件及组件 检查冲模各零件及组件是否符合图样要求,并检查凸凹模间隙的均匀程度,各辅助零件是否配齐。 2、 装配上模 (1)先把已装上导柱的导套装在上模座上,再装模柄; (2)把冲孔凸模装在上模固定板上,调节间隙及中心直线度以及磨平端面; (3)最后把上模座、上模垫板、上模固定板、落料凸凹模,完成后把销钉装入定位,所有螺钉都拧紧。 天津工程师范学院 2008 届本科生毕业设计 19 3、 装配下模 上模装配完成后,下模座我们是根据上模座来装的,具体如下: (1)把拉伸冲孔凸凹模(凸凹模已装上下顶杆)装入凸凹模固定板中,磨平底面; (2)把凸凹模固定板和下模垫板找正位置后一起安装在下模座上; (3)下模座、凸凹模固定板、下模垫板和落料凹模合在一起配合,间隙调试完毕后打入销钉并拧紧所有螺钉。 4、 整体装配 上模与下模都装配好以后,要进行上模与下模和在一起的整体装配,使导柱可靠的固定在下模座上,落料拉伸凸凹模与落料凹模及各刃口间隙均匀,各配合精度达到图纸规定的要求。 5、 试冲与 调整 (1)切纸试冲 (2)装机试冲 天津工程师范学院 2008 届本科生毕业设计 20 结 论 在做毕业设计的前期阶段,通过构思和查阅资料之后初步定下设计的最佳方案-落料-正反拉伸-冲孔四道工序所组成的复合冲裁模具。 为了保证在加工的过程中不影响弯曲的形状、 大小和尺寸的要求,是将弯曲凸模和落料凸模先小过盈的装配起来,然后在将弯曲凹模与弯曲凸模通过配合再装配起来,双边留的间隙就可以保证弯曲件的各项要求。结构的定形和参数的确定等均是参考有关的书本和文献 ,有些知识也是经过和老师的讨论之后定下来的。后期阶段,进行有关数值的校核和工艺卡片的编写等工作。本次冲裁模具的设计,让我对自己所学的知识有一次总结性的验收过程, 同时在这个过程中也检验了我处理问题的能力。自接到毕业设计任务书到毕业论文总体的撰写,感觉到有一定的收获-把以前学过的课程又重新回顾了一次,是对我所学知识的融会贯通并使知识面进一步加深、拓宽的过程。所有的同学都感觉到在这两个多月的毕业设计中,学到的知识比课堂上学到的要实用、要印象深的多,正是因为有了前面的专业基础,才能在很短的时间内完成毕业设计。这说明了大学学习中凝聚了老师们的心血和我们自己的努力。知识的积累需要一个量的累积过程,知识的应用要求的是最终的累积结果。 我的毕业设计内容难度不是很大,但通过这次的模具设计,通过自己的学习和研究,一样给了自己很大的收获。使我对模具有了更深的了解,尤其是冲模的定义、分类、结构组成及工作原理。整个设计过程是一项艰难的工作,很多工作都是靠经验,书本上是学不到的。经过老师的悉心指导和自己查阅有关书籍解决了在设计中遇到的问题,培养了自己独立思考问题、解决问题的能力让自己有一个质的飞跃。为今后的工作、学习和生活打下了良好的基础。 天津工程师范学院 2008 届本科生毕业设计 21 参考文献 1冯炳尧,韩泰荣等.模具设计与制造简明手册.上海:上海科学技术出版社, 1998. 2模具实用技术丛书编委会.冲模设计应用实例.北京:机械工业出版社,1999.5. 3郑可锽.实用冲压模具设计手册.宇航出版社,1990.5. 4许发樾.实用模具设计与制造手册. 北京:机械工业出版社 ,2001. 5冯小明.冷冲压工艺及模具设计. 重庆:重庆大学出版社,2004.8. 6郑家贤.冲压工艺与模具设计实用技术.北京:机械工业出版社,2005.1. 7冲压模设计编写委员会.冲压工艺及冲模设计.北京:国防工业出版社,1993.7. 8丁松聚主编.冷冲模设计.北京:机械工业出版社,2001.9. 9史铁梁主编.冲模设计手册.北京:机械工业出版社,2003.8. 10姜奎华,肖景容主编.冲压工艺学.北京:机械工业出版社,2004.1. 11马正元.冲压工艺与模具设计. 北京:机械工业出版社,2003.8. 12薛啟翔.冲模制造实用技能.北京:机械工业出版社,2005.1. 13卢险峰.冲压工艺模具学.北京:机械工业出版社,2000.1. 14涂光祺.冲模技术.北京:机械工业出版社,2004.9. 15沈兴东,韩森和主编.冲压工艺与模具设计. 济南:山东科学技术出版社,2005.3. 16王孝培主编.冲压手册.北京:机械工业出版社,1990. 17夏琴香主编.冲压成形工艺及模具设计.广州: 华南理工大学出版社, 2004.9. 18徐政坤主编. 冲压模具设计与制造.北京:化学工业出版社,2003.8. 19中国机械工业教育协会组编.专业英语.北京:机械工业出版社,2001.4. 20马玉录,刘东学主编.机械设计制造及其自动化专业英语.北京:化学工业出版社,2001.8. 21陈统坚主编.机械工程英语.北京:机械工业出版社,2003. 天津工程师范学院 2008 届本科生毕业设计 22 附录 1:冲压模零件的加工精度及其相互配合 表四 模柄与上模座 H7/m6 冲孔凸模与上模固定板 H7/n6 挡料销与卸料板 H7/r6 下模座与导柱 H7/r6 导柱与导套 H7/h6 导套与上模座 H7/r6 天津工程师范学院 2008 届本科生毕业设计 23 附录 2:英文资料 Introduction to Mrchanical Design Mechanical design is the application of science and technology to devise new or improved products for the purpose of satisfying human needs. It is a vast field of engineering technology which not only concerns itself with the original conception of the product in terms of its size,shape and construction details,but also considers the various factors involved in the manufacture,markiong and use of the product. People who perform the various functions of mechanical design are typically called designers,or design engineers.Mechanical design is basically a creative activity.However,in addition to being innovative,a design engineer must also have a solid background in the areas of mechanical drawing,kinematics,dynamics,materials engineering,strength of materials and manufacturing processes. As stated previously,the purpose of mechanical design is to produce a product which will serve a need for man. Inventions,discoveries and scientific knowledge by themselves do not necessarily benfit people;only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore,that a human need must be identified before a particular product is designed. Mechanical design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze the system and then make sound judgments on how the product is to be manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations.There are no facts or equations which alone can be used to provide all the correct decisions required to produce a good design. On the other hand, any calculations made must be done with the utmost care and precision. For example,if a decimal point is misplaced,an otherwise accrptable design may not function. Good designs require trying new ideas and being willing to take a certain amount of risk,knowing that if the new idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and wellestablished methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old,proven concepts should be used and what new,untried should be incorporated. 天津工程师范学院 2008 届本科生毕业设计 24 New design generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs can be enjoyed .Thus there is a chance for a superior product, but only at higher risk. It should be emphasized that,if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Even though many impractical ideas may arise,it is usually easy to eliminate them in the early stages of design before firm details are required by manufacturing. In this way, innovative ideas are not inhibited. Quite often, more than one design is developed,up to the point where they can be compared against each other. It is entirely possible that the design which is ultimately accepted will use ideas existing in one of the rejected designs that did not show as much overall promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the design engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimum. Another important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they are to be incorporated. Communicating the design to others is the final, vital step in the design process. Undoubtedly many great designs, inventions,and creative works have been lost to mankind simply because the originators were unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer,when presenting a new solution to administrative, management, or supervisory persons,is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted. Basically, there are only three means of communication available to us. There are the written, the oral, and the graphical firms. Therefore the successful engineer will be technically competent and versatile in all three forms of communication. A technically competent person who lacks ability in any one of these forms is severely handicapped. If ability in all three forms is lacking ,no one will ever know how competent that person is ! The competent engineer should not be afraid of the possibility of not successding in 天津工程师范学院 2008 届本科生毕业设计 25 a presentation . In fact, occasional failure should be expected because failure or criticism seems to accompany every really creative idea. There is a great deal to be learened form a failure, and the greatest gains are obtained by those willing to risk defeat. In the final analysis, the real failure would lie in deciding not to make the presentation at all. To communicate effectively,the following questions must be answered: (1) Does the design really serve a human need? (2) Will it be competitive with existing products of rival companies? (3) Is it economical to produce? (4) Can it be readily maintained? (5) Will it sell and make a profit? Only time will provide the true answers to the preceding questions, but the product should be designed, manufactured and marketed only with initial affirmative answers.The design engineer also must communicate the finalized design to manufacturing through the use of detail and assembly drawings. Quite often, a problem will occurt during the manufacturing cycle. It may be that a change is required in the dimensioning or tolerancing of a part so that it can be more readily produced. This falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected. In other cases,a deficiency in the design may appear during assembly or testing just prior to shipping. These realities simply bear out the fact that design is a living process. There is always a better way to do it and the designer should constantly strive towards finding that better way. Some Rules for Mechanical Design Designing starts with a need, real or imagined. Existing apparatus may need improvements in durability, efficiently, weight, speed, or cost. New apparatus may be needed to perform a function previously done by men, such as computation, assembly, or servicing. With the objective wholly or partly defined, the next step in design is the conception of mechanisms and their arrangements that will perform the needed functions. For this, freehand sketching is of great value, not only as a record of ones thoughts and as an aid in discussion with others, but particularly for communication with ones own mind, as a stimulant for creative ideas. When the general shape and a few dimensions of the several components become 天津工程师范学院 2008 届本科生毕业设计 26 apparent, analysis can begin in earnest. The analysis will have as its objective satisfactory or superior performance, plus safety and durability with minimum weight, and a competitive cost. Optimum proportions and dimensions will be sought for each critically loaded section, together with a balance between the strength of the several components. Materials and their treatment will be chosen. These important objectives can be attained only by analysis based upon the principles of mechanics, such as those of statics for reaction forces and for the optimum utilization of fricition; of dynamics for inertia, acceleration, and energy; of elasticity and strength of materials for stress and deflection; and of fluid mechanics for lubrication and hydrodynamic drives. Finally, a design based upon function and reliability will be completed, and a prototype may be built. If its tests are satisfactory, and if the device is to produced in quantity, the initial design will undergo certain modifications that enable it to be manufactured in quantity at a lower cost. During subsequent years of manufacture and service, the design is likely to undergo changes as new ideas are conceived or as further analysis based upon tests and experience indicate alterations .Sales appeal, customer satisfaction, and manufacture cost are all related to design, and ability in design is intimately involved in the success of an engineering venture. To stimulate creative thought, the following rules are suggested for the designer. 1. Apply ingenuity to utilize desired physical properties and to control undesired ones. The performance requirements of a machine are met by utilizing laws of nature or properties of matter (e.g., flexibility, strength, gravity ,inertia ,buoyancy, centrifugal force, principles of the lever and inclined plane, friction, viscosity, fluid pressure,and thermal expansion), also the many electrical, optical, thermal, and chemical phenomena. However, what may be useful in one application may be detrimental in the next . Flexibility is desired in value springs but not in the valve camshaft; friction is desired at the clutch face but not in the clutch bearing. Ingenuity in design should be applied to utilize and control the physical properties that are desired and to minimize those that are not desired. 2. Provide for favorable stress distribute and stiffness with minimum werght. On components subjected to fluctuating stress, particular attention is given to a reduction in stress concentration, and to an increase of strength at fillets, threads, holes, and fits. Stress reduction are made by modification in shape ,and strengthening may be done by prestressing treatments such as surface rolling and shallow hardening. Hollow shafts and tubing, and box sections give a favorable stress distribution, 天津工程师范学院 2008 届本科生毕业设计 27 together with stiffness and minimum weight. Sufficient stiffness to maintain alignment and uniform pressure between contacting surfaces should be provided for crank, cam, and gear shafts, and for enclosures and frames containing bearing supports. The stiffness of shafts and other components must be suitable to avoid resonant vibrations. 3. Use basic equations to calculate and optimize dimensions. The fundamental equations of mechanics and the other sciences are the accepted bases for calculations. They are sometimes rearranged in special forms to facilitate the determination or optimization of dimensions, such as the beam and surface stress equations for
展开阅读全文
相关资源
正为您匹配相似的精品文档
相关搜索

最新文档


当前位置:首页 > 压缩资料 > 基础医学


copyright@ 2023-2025  zhuangpeitu.com 装配图网版权所有   联系电话:18123376007

备案号:ICP2024067431-1 川公网安备51140202000466号


本站为文档C2C交易模式,即用户上传的文档直接被用户下载,本站只是中间服务平台,本站所有文档下载所得的收益归上传人(含作者)所有。装配图网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私,请立即通知装配图网,我们立即给予删除!