外文翻译--模具的历史发展

桂林电子科技大学毕业设计用纸 第 1 页 共 26 页 1 模具的历史发展 David O.Kazmer.Injec tion mold design engineering. Hanser Gardner Public ations， 2007. 模具的出现可以追溯到几千年前的陶器和青铜器铸造，但其大规模使用却是随着现代工业的掘起而发展起来的。 19 世纪，随着军火工业 (枪炮的弹壳 )、钟表工业、无线电工业的发展，冲模得到广泛使用。二次大战后，随着世界经济的飞速发展，它又成了大量生产家用电器、汽车、电子仪器、照相机、钟表等零件的最佳方式。从世界范围看，当时美国的冲压技 术走在前列 许多模具先进技术，如简易模具、高效率模具、高寿命模具和冲压自动化技术等，其大多起源于美国；而瑞士的精冲、德国的冷挤压技术、苏联对塑性加工的研究也处于世界先进行列。 50 年代，模具行业工作重点是根据用户的要求，制作能满足产品要求的模具。模具设计多凭经验，参考已有图纸和感性认识，对所设计模具零件的机能缺乏真切了解。从 1955 年到 1965 年，是冲压工业的探索和开发时代 对模具主要零部件的机能和受力状态进行了数学分桥，并把这些知识不断应用于现场实际，使得冲压技术在各方面有飞跃的发展。其结果是总结出了模 具的设计原则，并使得压力机械、冲压材料、加工方法、模具结构、模具材料、模具制造方法、自动化装置等领域更新换代，并向实用化的方向前进，从而使冲压加工进入生产优良产品的第一阶段。 进入 70 年代，模具进入高速化、机械化、精密化、安全化发展的第二阶段。在这个过程中不断涌现各种高效率、高寿命、高精度、多功能的自动化模具。其代表是多个工位的级进模和十几个工位的多工位传递模。在此基础上又发展出既有连续冲压工位又有多滑块成形工位的压力机 弯曲机。在此期间，日本站到了世界最前列 其模具加工精度进入了微米级，模具寿命，合金钢 制造的模具达到了几千万次，硬质合金钢制造的模具达到了几亿次。在冲压模具中，每分钟冲压次数，小型压力机通常为 200 至 300次，最高为 1200 次至 1500 次。在此期间，为了适应产品更新快、用期短 (如汽车改型、玩具翻新等 )的需要，各种经济型模具，如锌铬合金模具、聚氨酯橡胶模具、钢皮冲模等也得到了很大发展。 从 70 年代中期至今可以说是计算机辅助设计、辅助制造技术不断发展的时代。随着模具加工精度与复杂性不断提高，生产周期不断加快，模具业对设备和人员素质的要求也不断提高。依靠普通加工设备，凭经验和手艺越来越不能满足模具 生产的需要。 90年代以来，机械技术和电子技术紧密结合，发展了 NC 机床，如数控线切割机床、数控电火花机床、数控铣床、数控坐标磨床等。进而出现了采用电子计算机自动编程、控制的 CNC 机床，提高了数控机床的使用效率和范围。近年来又发展出由一台计算机以分时的方式直接管理和控制一群数控机床的 NNC 系统。 随着计算机技术的发展，计算机也逐步进入模具生产的各个领域，包括设计、制造、 桂林电子科技大学毕业设计用纸 第 2 页 共 26 页 管理等。国际生产研究协会预测，到 2000 年，作为设计和制造之间联系手段的图纸将失去其主要作用。模具自动设计的最根本点是必须确立模具零件标准及设计 标准。要摆脱过去以人的思考判断和实际经验为中心所组成的设计方法，就必须把过去的经验和思考方法，进行系列化、数值化、数式化，作为设计准则储存到计算机中。因为模具构成元件也干差万别，要搞出一个能适应各种零件的设计软件几乎不可能。但是有些产品的零件形状变化不大，模具结构有一定的规律，可总结归纳，为自动设计提供软件。如日本某公司的 CDM 系统用于级进模设计与制造，其中包括零件图形输入、毛坯展开、条料排样、确定模板尺寸和标准、绘制装配图和零件图、输出 NC 程序 (为数控加工中心和线切割编程 )等，所用时间由手工的 20%、工时 减少到 35 小时；从 80 年代初日本就将三维的 CAD CAM 系统用于汽车覆盖件模具。目前，在实体件的扫描输入，图线和数据输入，几何造形、显示、绘图、标注以及对数据的自动编程，产生效控机床控制系统的后置处理文件等方面已达到较高水平；计算机仿真 (CAE)技术也取得了一定成果。在高层次上，CAD CAM CAE 集成的，即数据是统一的，可以互相直接传输信息实现网络化。目前国外仅有少数厂家能够做到。 2 冲压 冲压是通过模具使板材产生塑性变形而获得成品零件的一种成形工艺方法。由于冲压通常在冷态下进行，因此也称冷冲压 。只有当板材厚度超过 8-100 毫米时，才采用热冲压。冲压加工的原材料一般为板材或带材，故也称板材冲压。某些非金属板材 (如胶木板、云母片、石棉、皮革等 )亦可采用冲压成形工艺进行加工。 冲压广泛应用于金属制品各行业中，尤其在汽车、仪表、军工、家用电器等工业中占有极其重要的地位。 冲压成形需研究工艺、设备和模具三类基本问题。 板材冲压具有下列特点： (1)材料利用率高； (2)可加工薄壁、形状复杂的零件； (3)冲压件在形状和尺寸精度方面的互换性好； (4)能获得质量轻而强度高、刚性好的零件； (5)生产率高，操 作简单，容易实现机械化和自动化； 冲压模具制造成本高，因此适合于大批量生产。对于小批量、多品种生产常采用简易冲模，同时引进冲压加工中心等新型设备，以满足市场求新求变的需求。 板材冲压常用的金属材料有低碳钢、铜、铝、镁合金及高塑性的合金钢等。如前所述，材料形状有板材和带材。 冲压生产设备有剪床和冲床。剪床是用来将板材剪切成具有一定宽度的条料，以供 桂林电子科技大学毕业设计用纸 第 3 页 共 26 页 后续冲压工序使用，冲床可用于剪切及成形。 生产实践中所采用的冲压成形工艺方法有很多，具有多种形式和名称，但其塑性变形本质是相同的。冲压成形具有如下几个非常突出的特点。 (1)垂直于板面方向的单位面积上的压力，其数值不大便足以在板面方向上使板材产生塑性变形。由于垂直于板面方向上的单位面积上压力的数值远小于板面方向上的内应力，所以大多数的冲压变形都可以近似地当作平面应力状态来处理，使其变形力学的分析和工艺参数的计算等工作都得到很大的简化。 (2)由于冲压成形用的板材毛坯的相对厚度很小，在压应力作用下的抗失稳能力也很差，所以在没有抗失稳装置 (如压边圈等 )的条件下，很难在自由状态下顺利地完成冲压成形过程。因此，以拉应力作用为主的伸长类冲压成形过程，多于以压应力作用为主的压缩类成 形过程。 (3)冲压成形时，板材毛坯内应力的数值等于或小于材料的屈服应力。在这一点上，冲压成形与体积成形的差别很大。因此，在冲压成形时变形区应力状态中的静水压力成分对成形极限与变形抗力的影响，已失去其在体积成形时的重要程度，有些情况下，甚至可以完全不予考虑，即使有必要考虑时，其处理方法也不相同。 (4)在冲压成形时，模具对板材毛坯作用力所形成的约束作用较轻，不像体积成形(如模锻等 )是靠与制件形状完全相同的型腔对毛坯进行全面接触而实现的强制成形。在冲压成形中，大多数情况下，板材毛坯都有某种程度的自由度，常常是 只有一个表面与模具接触，甚至有时存在板材两侧表面都不与模具接触的变形部分。在这种情况下，这部分毛坯的变形是靠模具对其相邻部分施加的外力实现其控制作用的。例如，球面和锥面零件成形时的悬空部分和管坯端部的卷边成形等都属这种情况。 由于冲压成形具有上述一些变形与力学方面的特点，致使冲压技术也形成了一些与体积成形不同的特点。 (1)由于不需要在板材毛坯的表面施加很大的单位压力即可使其成形，所以在冲压技术中关于模具强度与刚度的研究并不十分重要。相反地却发展了许多简易模具技术。由于相同的原因，也促使靠气体或液体压力成形 的工艺方法得以发展。 (2)因冲压成形时的平面应力状态或更为单纯的应变状态 (与体积成形相比 )，当前对冲压成形中毛坯的变形、力与电能参数方面的研究较为深人，有条件运用合理的科学方法进行冲压加工。借助于电子计算机与先进的测试手段，在对板材性能与冲压变形参数进行实时测量与分析的基础上，实现冲压过程智能化控制的研究工作也在开展。 (3)人们已经认识到冲压成形与原材料有十分密切的关系。所以，对板材冲压性能即成形性与形状稳定性的研究，目前已成为冲压技术的一个重要内容。对板材冲压性能的研究工作不仅是冲压技术发展的需要，而 且也促进了钢铁工业生产技术的发展，为其提高板材的质量提供了一个可靠的基础与依据。 桂林电子科技大学毕业设计用纸 第 4 页 共 26 页 3 我国模具工业现状及发展趋势 由于历史原因形成的封闭式、 “ 大而全 ” 的企业特征，我国大部分企业均设有模具车间，处于本厂的配套地位，自 70 年代末才有了模具工业化和生产专业化这个概念。生产效率不高，经济效益较差。模具行业的生产小而散乱，跨行业、投资密集，专业化、商品化和技术管理水平都比较低。 据不完全统计，全国现有模具专业生产厂、产品厂配套的模具车间（分厂）近 17000家，约 60 万从业人员，年模具总产值达 200 亿元人民币。但是 ，我国模具工业现有能力只能满足需求量的 60左右，还不能适应国民经济发展的需要。目前，国内需要的大型、精密、复杂和长寿命的模具还主要依靠进口。据海关统计， 1997 年进口模具价值6.3 亿美元，这还不包括随设备一起进口的模具； 1997 年出口模具仅为 7800 万美元。目前我国模具工业的技术水平和制造能力，是我国国民经济建设中的薄弱环节和制约经济持续发展的瓶颈。 3.1 模具工业产品结构的现状 按照中国模具工业协会的划分，我国模具基本分为 10 大类，其中，冲压模和塑料成型模两大类占主要部分。按产值计算，目前我国冲压 模占 50左右，塑料成形模约占20，拉丝模（工具）约占 10，而世界上发达工业国家和地区的塑料成形模比例一般占全部模具产值的 40以上。 我国冲压模大多为简单模、单工序模和符合模等，精冲模，精密多工位级进模还为数不多，模具平均寿命不足 100 万次，模具最高寿命达到 1 亿次以上，精度达到 3 5um，有 50 个以上的级进工位，与国际上最高模具寿命 6 亿次，平均模具寿命 5000 万次相比，处于 80 年代中期国际先进水平。 我国的塑料成形模具设计，制作技术起步较晚，整体水平还较低。目前单型腔，简单型腔的模具达 70以上， 仍占主导地位。一模多腔精密复杂的塑料注射模，多色塑料注射模已经能初步设计和制造。模具平均寿命约为 80 万次左右，主要差距是模具零件变形大、溢边毛刺大、表面质量差、模具型腔冲蚀和腐蚀严重、模具排气不畅和型腔易损等，注射模精度已达到 5um 以下，最高寿命已突破 2000 万次，型腔数量已超过 100腔，达到了 80 年代中期至 90 年代初期的国际先进水平。 3.2 模具工业技术结构现状 我国模具工业目前技术水平参差不齐，悬殊较大。从总体上来讲，与发达工业国家及港台地区先进水平相比，还有较大的差距。 在采用 CAD/CAM/CAE/CAPP 等技术设计与制造模具方面，无论是应用的广泛性，还是技术水平上都存在很大的差距。在应用 CAD 技术设计模具方面，仅有约 10%的模具在设计中采用了 CAD，距抛开绘图板还有漫长的一段路要走；在应用 CAE 进行模具方案设 桂林电子科技大学毕业设计用纸 第 5 页 共 26 页 计和分析计算方面，也才刚刚起步，大多还处于试用和动画游戏阶段；在应用 CAM 技术制造模具方面，一是缺乏先进适用的制造装备，二是现有的工艺设备（包括近 10 多年来引进的先进设备）或因计算机制式（ IBM 微机及其兼容机、 HP 工作站等）不同，或因字节差异、运算速度差异、抗电磁干扰能力差异等 ，联网率较低，只有 5%左右的模具制造设备近年来才开展这项工作；在应用 CAPP 技术进行工艺规划方面，基本上处于空白状态，需要进行大量的标准化基础工作；在模具共性工艺技术，如模具快速成型技术、抛光技术、电铸成型技术、表面处理技术等方面的 CAD/CAM 技术应用在我国才刚起步。计算机辅助技术的软件开发，尚处于较低水平，需要知识和经验的积累。我国大部分模具厂、车间的模具加工设备陈旧，在役期长、精度差、效率低，至今仍在使用普通的锻、车、铣、刨、钻、磨设备加工模具，热处理加工仍在使用盐浴、箱式炉，操作凭工人的经验，设备简 陋，能耗高。设备更新速度缓慢，技术改造，技术进步力度不大。虽然近年来也引进了不少先进的模具加工设备，但过于分散，或不配套，利用率一般仅有 25%左右，设备的一些先进功能也未能得到充分发挥。 缺乏技术素质较高的模具设计、制造工艺技术人员和技术工人，尤其缺乏知识面宽、知识结构层次高的复合型人才。中国模具行业中的技术人员，只占从业人员的 8%12%左右，且技术人员和技术工人的总体技术水平也较低。 1980 年以前从业的技术人员和技术工人知识老化，知识结构不能适应现在的需要；而 80 年代以后从业的人员，专业知识、经验匮乏， 动手能力差，不安心，不愿学技术。近年来人才外流不仅造成人才数量与素质水平下降，而且人才结构也出现了新的断层，青黄不接，使得模具设计、制造的技术水平难以提高。 3.3 模具工业配套材料，标准件结构现状 近 10 多年来，特别是 “ 八五 ” 以来，国家有关部委已多次组织有关材料研究所、大专院校和钢铁企业，研究和开发模具专用系列钢种、模具专用硬质合金及其他模具加工的专用工具、辅助材料等，并有所推广。但因材料的质量不够稳定，缺乏必要的试验条件和试验数据，规格品种较少，大型模具和特种模具所需的钢材及规格还有缺口。在钢材 供应上，解决用户的零星用量与钢厂的批量生产的供需矛盾，尚未得到有效的解决。另外，国外模具钢材近年来相继在国内建立了销售网点，但因渠道不畅、技术服务支撑薄弱及价格偏高、外汇结算制度等因素的影响，目前推广应用不多。 模具加工的辅助材料和专用技术近年来虽有所推广应用，但未形成成熟的生产技术，大多仍还处于试验摸索阶段，如模具表面涂层技术、模具表面热处理技术、模具导向副润滑技术、模具型腔传感技术及润滑技术、模具去应力技术、模具抗疲劳及防腐技术等尚未完全形成生产力，走向商品化。一些关键、重要的技术也还缺少知识产 权的保护。 桂林电子科技大学毕业设计用纸 第 6 页 共 26 页 我国的模具标准件生产， 80 年代初才形成小规模生产，模具标准化程度及标准件的使用覆盖面约占 20%，从市场上能配到的也只有约 30 个品种，且仅限于中小规格。标准凸凹模、热流道元件等刚刚开始供应，模架及零件生产供应渠道不畅，精度和质量也较差。 3.4 模具工业产业组织结构现状 我国的模具工业相对较落后，至今仍不能称其为一个独立的行业。我国目前的模具生产企业可划分为四大类：专业模具厂，专业生产外供模具；产品厂的模具分厂或车间，以供给本产品厂所需的模具为主要任务；三资企业的模具分厂，其组织模 式与专业模具厂相类似，以小而专为主；乡镇模具企业，与专业模具厂相类似。其中以第一类数量最多，模具产量约占总产量的 70%以上。我国的模具行业管理体制分散。目前有 19个大行业部门制造和使用模具，没有统一管理的部门。仅靠中国模具工业协会统筹规划，集中攻关，跨行业，跨部门管理困难很多。 模具适宜于中小型企业组织生产，而我国技术改造投资向大中型企业倾斜时，中小型模具企业的投资得不到保证。包括产品厂的模具车间、分厂在内，技术改造后不能很快收回其投资，甚至负债累累，影响发展。虽然大多数产品厂的模具车间、分厂技术力 量强，设备条件较好，生产的模具水平也较高，但设备利用率低。 我国模具价格长期以来同其价值不协调，造成模具行业 “ 自身经济效益小，社会效益大 ” 的现象。 “ 干模具的不如干模具标准件的，干标准件的不如干模具带件生产的。干带件生产的不如用模具加工产品的 ” 之类不正常现象存在。 4 工程 工程这门科学，是运用科学，数学，经济，社会和实用知识的总称，常用于设计和建造建筑物，机器，设备，系统等等，可以稳定地实现对社会的需求提供解决方案的专业。 美国工程师专业发展理事会（ ECPD， ABET 的前身）定义了“工程”为： 创造性地运用科学原理，设计或开发的结构，机器，仪器或生产工艺，或单独或联合的利用他们的产品，或建造或操作其设计，或预测其具体的操作条件下的行为，作为全方位的预定功能，是安全操作和经济学的生命和财产。 4.1 历史 在维基词典中查找工程，工程的概念已经存在，解释为制造，如滑轮，杠杆和车轮等等古代人类发明的。这些发明每一方都与现代的工程定义相一致，利用基本力学原理，开发有用的工具和对象 桂林电子科技大学毕业设计用纸 第 7 页 共 26 页 长期的工程技术本身有一个更近词源，工程师。而它本身的历史可以追溯到 1325年，当 一个 engineer（字面上看，一个经营发动机）原指“军用发动机的构造”，现在已经过时了，一个“发动机”指的是一个军事机器，也就是说，在战争中使用的机械武器（例如，一个投石器）。 过时的用法有存活至今例外，其中值得注意的是军事工程兵，例如，美国陆军工程兵。 这个“ engineer”本身更老的起源是，最终从拉丁语派生 ingenium（约 1250），意思是“生的素质，特别是精神力量”后来，随着桥梁和建筑技术学科成熟的平民建筑设计，土木工程一词进入，以此来区分在这些非专业的军事工程建设，并参与了这些词库 旧的军 事工程学科。 4.2 古代时代 在亚历山大灯塔，埃及金字塔，巴比伦的空中花园，雅典卫城帕特农神庙和希腊，罗马渡槽，威盛阿皮亚和罗马斗兽场，特奥蒂瓦坎的城市和玛雅，印加和阿兹特克帝国， 中国的长城，其中许多东西能作为一个独立的聪明才智和古代民事和军事工程师技能的证明。 最早的土木工程师的美称，是印和阗。左塞尔作为法老的官员之一，他可能在公元前约 2630 至 2611 年于萨卡拉设计和监督建造阶梯金字塔 。他可能也已为第一位的建筑工程师。 古希腊的发展无论在民用和军事领域，都使用了 安提 凯希拉机制，第一个已知的机械计算机，与阿基米德的机械的发明是早期机械工程的例子。 阿基米德的发明以及安提凯希拉机制的若干规定以及差行星齿轮传动装置或更复杂的知识，两机理论的主要原则，帮助设计了工业革命的齿轮火车，今天仍然被广泛地应用于不同领域，如机器人 和汽车工程。 中国，希腊和罗马军队，如火炮是由希腊人围绕公元前 4 世纪发明， 中世纪 弩和投石车、 投石机 的复杂的军事机器的发明和 设计制造。 4.3 文艺复兴时代 第一个电气工程师被认为是 1600 年的 Magnete，对“电”的出版创始人威廉吉尔伯特。 第一台蒸 汽发动机，由机械工程师托马斯萨弗里发明于 1698 年。此装置的研制牵扯到了在未来几十年的工业革命，大规模生产的开始。 随着工程师这种职业的地位不断上升，在十八世纪，这个词的意义变得更加狭窄，其中应用到数学和科学应用到这些目标的领域。同样，军事和民用工程机械工业也作为已知的领域融入到了工程。 桂林电子科技大学毕业设计用纸 第 8 页 共 26 页 4.4 现代时代 国际空间站是一个由多学科组成的现代工程技术。 电气工程可以在 1800 年追溯到亚历山德罗伏，迈克尔法拉第，格奥尔格欧姆的实验，他人和电动机发明的实验起源于 1872 年。詹姆斯麦克斯韦和赫兹于 19 世纪的作品引扩宽了电子领域。在真空管和晶体管的发明，后来进一步加速了电子产业发展到这样的程度，目前电气和电子工程师数量超过任何其他工程专业的同类。 托马斯萨弗里和苏格兰工程师瓦特的发明提升了现代机械工程。 在工业革命的发源地英国和海外发展的专业机器和他们的维修工具导致机械工程的快速增长。 化学工程，像它的对手机械工程一样在十九世纪工业革命时期发展。由 1880 年的化学品的大规模生产的需要以及工业革命生产要求的新材料，新工艺，人民创建了一个新的行业 ，致力于大规模开发化学品。化学工程师的角色是设计 这些化学工厂和建造。 航空航天工程是一个更现代化的工程，扩展了包括航天器设计，使其达到高度。它的起源可以追溯到大约在世纪之交的航空先驱， 19 世纪末至 20 初。早期航空的工程知识，主要是一些概念和其他部门的工程技术经验的引进。 1863 年在耶鲁大学应用科学工程中的第一个博士在美国获得前往威拉德吉布斯的机会，他也是第二批博士在美国进修。仅仅十年后，莱特兄弟成功的飞行， 20 世纪 20年代通过第一次世界大战军用飞机的发展，航空工业获得广泛发展。 同时，提供基本的背景研究，科学实验相结合，理论物理仍在继续。 1990 年，随着计算机技术的兴起，师艾伦设计了第一个电脑工程。 4.5 工程主要分公司 工程，就像其他科学，是一个广泛的学科，通常分为几个子学科。这些不同学科的关注自己工作领域的工程。最初的工程师将在一个特定的学科培训在整个工程师的生涯中，工程师有可能成为多学科。历史上工程的主要分支分类如下： 航天工程 - 飞机，航天器和相关主题的设计。 化学工程 - 化工原理开发及大规模的化学过程，以及设计新的特殊材料和燃料。 土木工程 - 设计以及公共和私人工程，如基础设施（道路，铁路，供水和水处理 等），桥梁和建筑物的建设。 电气工程 - 一个非常广泛的领域，可能包括设计和各种电器及电子系统，如电子线路，发电机，电动机，电磁 /机电设备，电子器件，电子电路，光纤，光电器件，计算机系统，研究 ，电信和电子产品。 机械工程 - 以物理，机械系统设计，如发动机，压缩机，动力系统，运动链，真空技术，设备和振动隔离设备的工程。 有时新专业与传统领域相结合，形成新的分支。一个新的或新兴的应用领域通常会暂时被定义为一个置换或对现有学科的一个子集，往往有灰色地带时，以一个给定的子场变 桂林电子科技大学毕业设计用纸 第 9 页 共 26 页 大或突出到足以作为一个新的“分支 分类”。出现这样的一个关键指标是重点大学时开始在新的领域建立部门和方案。 对于其中的每个领域存在着相当多的重叠，尤其是在物理、化学和数学科学应用到了自己的学科领域。 4.6 方法 例如涡轮的设计需要从许多领域的工程师合作，因为系统是受机械，电磁和化学过程。叶片，转子和定子以及蒸汽循环都需要精心设计和优化。 工程师运用物理学和数学科学领域找到合适的解决问题的方法并作出举措改善现状。比以往任何时候，工程师们现在要求为他们设计项目有关的科学知识更丰富，因此，他们在整个职业生涯的不断学习新知 识。 工程师设计选择不同的解决方案，如果有多个选项存在的利弊权衡的，必须选择出最符合要求的那一个，工程师的重要而独特的任务就是将其识别，理解和解释上的设计，以便产生一个成功的设计。但它通常是不够的，建立一个在技术上成功的产品，还必须满足进一步的要求并克服限制。限制可能包括可用资源有限，有想象力或技术的限制，为今后的修改和补充的灵活性，以及诸如成本，安全性，市场化，生产能力和可维护性要求的其他因素。通过了解的限制，工程师导出了在其中一个可行的物体或系统。 4.7 问题解决 工程师利用他们的科学，数 学和相应的经验知识，以寻找合适的解决方案的一个问题。 工程被认为是应用数学和科学的一个分支。 建立适当的数学模型的一个问题让他们去分析它，并测试可能的解决方案。 一个问题 通常存在多种合理的解决方案，因此工程师必须评估其优劣，选择不同的设计选择最佳的解决方案能满足其需求。收集大量专利统计数据，以“低层次”工程设计的核心，而在更高层次上做出最好的设计，消除矛盾，找出导致了问题的核心。 工程师一般尝试预测他们的设计有多好并发挥自己的所有能力后全面生产。他们使用包括：原型，比例模型，模拟，破坏性试验 ，无损检测，压力试验。 测试确保产品将达到预期效果。 作为专业工程师要有认真对待设计产品的责任，并完成生产预期的设计，以免造成意外伤害殃及市场。因此通常需要校核，包括工程师在其设计的安全系数，工程师的设计需要更大的安全系数，以减少意外的失败的风险。 对不合格产品的研究被称为法医工程，并能通过帮助评估它的实际情况而设计的产品设计师。例如桥梁工程，在桥梁坍塌后，应当仔细分析，找出桥梁坍塌的原因以及造成灾害的损失。 桂林电子科技大学毕业设计用纸 第 10 页 共 26 页 4.8 电脑使用 航天飞机在周围的高速空气中重返大气层进行流量计算机模拟。 解决方案要求的流量建模的流体流动与传热方程的综合影响进行计算。这样的计算只能依靠计算机的使用。 如同所有的现代科学技术，计算机和软件发挥着越来越重要的作用。以及典型的商业应用软件也有计算机辅助申请数目（计算机辅助技术），专门用于工程。计算机可用于生成基本物理过程，可以用数值方法解决模式。 行业最广泛使用的工具之一，是计算机辅助设计（ CAD）软件使工程师创建三维模型，二维图纸，绘制设计原理图。民航处联同数字样机（ DMU）的和 CAE 如有限元分析方法或分析元素软件允许工程师创建的外观设计，可以无需进行 昂贵且费时的物理原型的分析模型。 这些让产品和组件为缺陷检查 ；评估适应和组装，研究人体工程学，并分析系统的静态和动态的特征，如压力，温度，电磁辐射的电流和电压，数字逻辑电平，流体流动和运动学。所有这些访问和信息的发布是普遍组织了产品数据管理软件的使用。也有许多工具支持，如电脑辅助制造（ CAM）软件工程任务的具体产生数控加工指令 ；生产工程制造流程管理软件的 EDA 印刷电路板（ PCB）和电子工程师电路原理图 ；维修申请维修管理，民用工程 AEC 软件。 近年来，利用计算机软件来辅助品开发已集体来被视为产品生命周期管理 （ PLM）而闻名。 4.9 社会背景 工程是一大课题，合作范围从小型个人项目到大型国家企业。几乎所有工程项目都依赖于一些融资机构类别：一个公司，一个投资者的集合，或者一个政府。工程的最低限度是由少数种类的限制等问题是无偿开放式设计，工程和工程。 由于工程其本身的性质，必然与社会和人的行为相接触。 每个工程设计产品都将影响到社会。工程设计是一个非常强大的工具，使环境，社会和经济变化，它的应用带来了很大的责任。许多工程协会建立了工作守则和道德守则，以指导广大成员，并告知公众。 工程项目可能会 受到争议。从不同的工程学科的例子包括核武器的发展，三峡大坝的设计和运动型多用途车的使用和石油开采。对此，一些西方工程公司已制定严重的企业和社会责任政策。 工程是人类发展的主要驱动力。撒哈拉以南的非洲地区，许多国家仅有非常小的工程能力，这导致很多重要基础设施无法发展，仅靠外来援助。 对千年发展目标的实现需要很多足够的工程成就，发展基础设施能力和可持续的技术发展。所有海外发展和救济的非政府组织作出的工程设计中，工程师大量使用适用于灾害和开发方案的解决方案。一个慈善机构的目标是将良好的工程更好的服务于人类 。 桂林电子科技大学毕业设计用纸 第 11 页 共 26 页 1 The historical development of mold David O.Kazmer.Injection mold design engineering. Hanser Gardner Publications The emergence of mold can be traced back thousands of years ago, pottery and bronze foundry, but the large-scale use is with the rise of modern industry and developed. The 19th century, with the arms industry (guns shell), watch industry, radio industry, dies are widely used. After World War II, with the rapid development of world economy, it became a mass production of household appliances, automobiles, electronic equipment, cameras, watches and other parts the best way. From a global perspective, when the United States in the forefront of stamping technology - many die of advanced technologies, such as simple mold, high efficiency, mold, die and stamping the high life automation, mostly originated in the United States； and Switzerland, fine blanking, cold in Germany extrusion technology, plastic processing of the Soviet Union are at the world advanced. 50s, mold industry focus is based on subscriber demand, production can meet the product requirements of the mold. Multi-die design rule of thumb, reference has been drawing and perceptual knowledge, on the design of mold parts of a lack of real understanding of function. From 1955 to 1965, is the pressure processing of exploration and development of the times - the main components of the mold and the stress state of the function of a mathematical sub-bridge, and to continue to apply to on-site practical knowledge to make stamping technology in all aspects of a leap in development. The result is summarized mold design principles, and makes the pressure machine, stamping materials, processing methods, plum with a structure, mold materials, mold manufacturing method, the field of automation devices, a new look to the practical direction of advance, so that pressing processing apparatus capable of producing quality products from the first stage. Into the 70s to high speed, launch technology, precision, security, development of the second stage.Continue to emerge in this process a variety of high efficiency, business life, high-precision multi-functional automatic school to help with. Represented by the number of working places as much as other progressive die and dozens of multi-station transfer station module. On this basis, has developed both a continuous pressing station there are more slide forming station of the press - bending machine. In the meantime, the Japanese stand to the worlds largest - the mold into the micron-level precision, die life, alloy tool steel mold has reached tens of millions of times, carbide steel mold to each of hundreds of millions 桂林电子科技大学毕业设计用纸 第 12 页 共 26 页 of times p minutes for stamping the number of small presses usually 200 to 300, up to 1200 times to 1500 times. In the meantime, in order to meet product updates quickly, with the short duration (such as cars modified, refurbished toys, etc.) need a variety of economic-type mold, such as zinc alloy die down, polyurethane rubber mold, die steel skin, also has been very great development. From the mid-70s so far can be said that computer-aided design, supporting the continuous development of manufacturing technology of the times. With the precision and complexity of mold rising, accelerating the production cycle, the mold industry, the quality of equipment and personnel are required to improve. Rely on common processing equipment, their experience and skills can not meet the needs of mold. Since the 90s, mechanical and electronic technologies in close connection with the development of NC machine tools, such as CNC wire cutting machine, CNC EDM, CNC milling, CNC coordinate grinding machine and so on. The use of computer automatic programming, control CNC machine tools to improve the efficiency in the use and scope. In recent years, has developed a computer to time-sharing by the way a group of direct management and control of CNC machine tools NNC system. With the development of computer technology, computers have gradually into the mold in all areas, including design, manufacturing and management. International Association for the Study of production forecasts to 2000, as a means of links between design and manufacturing drawings will lose its primary role. Automatic Design of die most fundamental point is to establish the mold standard and design standards. To get rid of the people of the past, and practical experience to judge the composition of the design center, we must take past experiences and ways of thinking, for series, numerical value, the number of type-based, as the design criteria to the computer store. Components are dry because of mold constitutes a million other differences, to come up with a can adapt to various parts of the design software almost impossible. But some products do not change the shape of parts, mold structure has certain rules, can be summed up for the automatic design of software. If a Japanese companys CDM system for progressive die design and manufacturing, including the importation of parts of the figure, rough start, strip layout, determine the size and standard templates, assembly drawing and parts, the output NC program (for CNC machining Center and line cutting program), etc., used in 20% of the time by hand, reduce their working hours to 35 hours； from Japan in the early 80s will be three-dimensional cad / cam system for automotive panel die. Currently, the physical parts scanning input, map lines and data input, 桂林电子科技大学毕业设计用纸 第 13 页 共 26 页 geometric form, display, graphics, annotations and the data is automatically programmed, resulting in effective control machine tool control system of post-processing documents have reached a high level； computer Simulation (CAE) technology has made some achievements. At high levels, CAD / CAM / CAE integration, that data is integrated, can transmit information directly with each other. Achieve network. Present. Only a few foreign manufacturers ca 2 Stamping Stamping is a kind of plastic forming process in which a part is produced by means of the plastic forming of the material under the action of a die Stamping is usually carried out under cold state, so it is also called cold stamping. Heat stamping is used only when the blank thickness is greater than 8-100mm. The blank material for stamping is usually in the form sheet or strip, and therefore it is also called sheet metal forming. Some non-metal sheets (such as plywood, mica sheet, asbestos, leather) can also be formed by stamping. Stamping is widely used in various metalworking industry, and it plays a crucial role in the industries for manufacturing automobiles, instruments, military parts and household electrical appliances, etc. The process， equipment and die are the three foundational problems that needed to be studied in stamping.The characteristics of the sheet metal forming are as follows: (1) High material utilization. (2) Capacity to produce thin-walled parts of complex shape. (3) Good interchangeability of stamping parts precision in shape and dimension. (4) Parts with lightweight， high strength and fine rigidity can be obtained. (5) High productivity, easy to operate and to realize mechanization and automatization. The manufacture of the stamping die is costly, and therefore it only fits to mass production. For the manufacture of products in small batch and rich variety, the simple stamping die and the new equipment such as a stamping machining center, are usually adopted to meet he market demands. The materials for sheet metal stamping include mild steel, copper, aluminum, magnesium alloy and high-plasticity alloy steel, etc. Stamping equipment includes plate shear and punching press. The former shears plate into strips with a definite width, which would be pressed later. The later can be used both in shearing and forming. There are various processes of stamping forming with different working patterns and names, 桂林电子科技大学毕业设计用纸 第 14 页 共 26 页 but these processes are similar to each other in plastic deformation There are following conspicuous characteristics in stamping： (1) The force per unit area perpendicular to the blank surface is not large but is enough to cause the material plastic deformation. It is much less than the inner stresses on the plate plane directions In most cases stamping forming can be treated approximately as that of the plane stress state to simplify vastly the theoretical deformation mechanics analysis and the calculation of the process parameters. (2) Due to the small relative thickness， the anti-instability capability of the blank is weak under compressive stress As a result， the stamping process is difficult to proceed successfully without using the anti-instability device (such as blank holder) Therefore the variety of the stamping processes dominated by tensile stress are more than those dominated by compressive stress (3) During stamping forming， the inner stress of the blank is equal to or sometimes less than the yield stress of the material In this point， the stamping is different from the bulk forming. During stamping forming， the influence of the hydrostatic pressure of the stress state in the deformation zone to the forming limit and the deformation resistance is not so important as to the bulk forming In some circumstances ， such influence may be neglected Even in the case when this influence should be considered， the treating method is also different from that of bulk forming. (4) In stamping forming， the restrain action of the die to the blank is not severe as in the case of the bulk forming(such as die forging) In bulk forming, the constraint forming is proceeded by the die with exactly the same shape of the part Whereas in stamping， in most cases， the blank has a certain degree of freedom, only one surface of the blank contacts with the die In some extra cases, such as the forming of the suspended region of sphere or cone，and curling at the end of tube, neither sides of the blank on the deforming zone contact with the die. The deformation in these regions are caused and controlled the die applying an external force to its adjacent area. Due to the characteristics of stamping deformation and mechanics mentio ned above， the stamping technique is different from the bulk metal forming： (1) The importance of the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure unit area on its surface Instead， the techniques of the simple die and the pneumatic and hydraulic forming are developed. (2) Due to the plane stress or simple strain state in comparison with bulk forming， more research on deformation or force and power parameters has been done, stamping forming can 桂林电子科技大学毕业设计用纸 第 15 页 共 26 页 be performed by more reasonable scientific methods Based on the real time measurement and analysis on the sheet metal properties and stamping parameters, by means of computer and some modem testing apparatus research on the intellectualized control of stamping process is also in proceeding. (3) It is shown that there is a close relationship between stamping forming and raw material. The research on the properties of the stamping forming， that is， forming ability and shape stability, has become a key point in stamping technology. The research on the properties of the sheet metal stamping not only meets the need of the stamping technology development，but also enhances the manufacturing technique of iron and steel industry, and provides a reliable foundation for increasing sheet metal quality 3 Chinas mold industry and its development trend Due to historical reasons for the formation of closed, big and complete enterprise features, most enterprises in China are equipped with mold workshop, in factory matching status since the late 70s have a mold the concept of industrialization and specialization of production. Mold production industry is small and scattered, cross-industry, capital-intensive, professional, commercial and technical management level are relatively low. According to incomplete statistics, there are now specialized in manufacturing mold, the product supporting mold factory workshop (factory) near 17 000, about 600 000 employees, annual output value reached 20 billion yuan mold. However, the existing capacity of the mold and die industry can only meet the demand of 60%, still can not meet the needs of national economic development. At present, the domestic needs of large, sophisticated, complex and long life of the mold also rely mainly on imports. According to customs statistics, in 1997 630 million U.S. dollars worth of imports mold, not including the import of mold together with the equipment； in 1997 only 78 million U.S. dollars export mold. At present the technological level of China Die & Mould Industry and manufacturing capacity, Chinas national economy in the weak links and bottlenecks constraining sustainable economic development. 3.1 Research on the Structure of industrial products mold In accordance with the division of China Mould Industry Association, China mold is divided into 10 basic categories, which, stamping die and plastic molding two categories 桂林电子科技大学毕业设计用纸 第 16 页 共 26 页 accounted for the main part. Calculated by output, present, China accounts for about 50% die stamping, plastic molding die about 20%, Wire Drawing Die (Tool) about 10% of the worlds advanced industrial countries and regions, the proportion of plastic forming die die general of the total output value 40%. Most of our stamping die mold for the simple, single-process mode and meet the molds, precision die, precision multi-position progressive die is also one of the few, die less than 100 million times the average life of the mold reached 100 million times the maximum life of more than accuracy 3 5um, more than 50 progressive station, and the international life of the die 600 million times the highest average life of the die 50 million times compared to the mid 80s at the international advanced level. Chinas plastic molding mold design, production technology started relatively late, the overall level of low. Currently a single cavity, a simple mold cavity 70%, and still dominant. A sophisticated multi-cavity mold plastic injection mold, plastic injection mold has been able to multi-color preliminary design and manufacturing. Mould is about 80 million times the average life span is about, the main difference is the large deformation of mold components, excess burr side of a large, poor surface quality, erosion and corrosion serious mold cavity, the mold cavity exhaust poor and vulnerable such as, injection mold 5um accuracy has reached below the highest life expectancy has exceeded 20 million times, the number has more than 100 chamber cavity, reaching the mid 80s to early 90s the international advanced level. 3.2 mold Present Status of Technology Technical level of Chinas mold industry currently uneven, with wide disparities. Generally speaking, with the developed industrial countries, Hong Kong and Taiwan advanced level, there is a large gap. The use of CAD / CAM / CAE / CAPP and other technical design and manufacture molds, both wide application, or technical level, there is a big gap between both. In the application of CAD technology design molds, only about 10% of the mold used in the design of CAD, aside from drawing board still has a long way to go； in the application of CAE design and analysis of mold calculation, it was just started, most of the game is still in trial stages and animation； in the application of CAM technology manufacturing molds, first, the lack of advanced manufacturing equipment, and second, the existing process equipment (including the last 10 桂林电子科技大学毕业设计用纸 第 17 页 共 26 页 years the introduction of advanced equipment) or computer standard (IBM PC and compatibles, HP workstations, etc.) different, or because of differences in bytes, processing speed differences, differences in resistance to electromagnetic interference, networking is low, only about 5% of the mold manufacturing equipment of recent work in this task； in the application process planning CAPP technology, basically a blank state, based on the need for a lot of standardization work； in the mold common technology, such as mold rapid prototyping technology, polishing, electroforming technologies, surface treatment technology aspects of CAD / CAM technology in China has just started. Computer-aided technology, software development, is still at low level, the accumulation of knowledge and experience required. Most of our mold factory, mold processing equipment shop old, long in the length of civilian service, accuracy, low efficiency, still use the ordinary forging, turning, milling, planing, drilling, grinding and processing equipment, mold, heat treatment is still in use salt bath, box-type furnace, operating with the experience of workers, poorly equipped, high energy consumption. Renewal of equipment is slow, technological innovation, technological progress is not much intensity. Although in recent years introduced many advanced mold processing equipment, but are too scattered, or not complete, only about 25% utilization, equipment, some of the advanced functions are not given full play. Lack of technology of high-quality mold design, manufacturing technology and skilled workers, especially the lack of knowledge and breadth, knowledge structure, high levels of compound talents. Chinas mold industry and technical personnel, only 8% of employees 12%, and the technical personnel and skilled workers and lower the overall skill level. Before 1980, practitioners of technical personnel and skilled workers, the aging of knowledge, knowledge structure can not meet the current needs； and staff employed after 80 years, expertise, experience lack of hands-on ability, not ease, do not want to learn technology. In recent years, the brain drain caused by personnel not only decrease the quantity and quality levels, and personnel structure of the emergence of new faults, lean, make mold design, manufacturing difficult to raise the technical level. 3.3 mold industry supporting materials, standard parts of present condition Over the past 10 years, especially the Eighth Five-Year, the State organization of the ministries have repeatedly Material Research Institute, universities and steel enterprises, research and development of special series of die steel, molds and other mold-specific carbide special tools, auxiliary materials, and some promotion. However, due to the quality is not 桂林电子科技大学毕业设计用纸 第 18 页 共 26 页 stable enough, the lack of the necessary test conditions and test data, specifications and varieties less, large molds and special mold steel and specifications are required for the gap. In the steel supply, settlement amount and sporadic users of mass-produced steel supply and demand contradiction, yet to be effectively addressed. In addition, in recent years have foreign steel mold set up sales outlets in China, but poor channels, technical services support the weak and prices are high, foreign exchange settlement system and other factors, promote the use of much current. Mold supporting materials and special techniques in recent years despite the popularization and application, but failed to mature production technology, most still also in the exploratory stage tests, such as die coating technology, surface treatment technology mold, mold guide lubrication technology Die sensing technology and lubrication technology, mold to stress technology, mold and other anti-fatigue and anti-corrosion technology productivity has not yet fully formed, towards commercialization. Some key, important technologies also lack the protection of intellectual property. Chinas mold standard parts production, the formation of the early 80s only small-scale production, standardization and standard mold parts using the coverage of about 20%, from the market can be assigned to, is just about 30 varieties, and limited to small and medium size. Standard punch, hot runner components and other supplies just the beginning, mold and parts production and supply channels for poor, poor accuracy and quality. 3.4 Die & Mould Industry Structure in Industrial Organization Chinas mold industry is relatively backward and still could not be called an independent industry. Mold manufacturer in China currently can be divided into four categories: professional mold factory, professional production outside for mold； products factory mold factory or workshop, in order to supply the product works as the main tasks needed to die； die-funded enterprises branch, the organizational model and professional mold factory is similar to small but the main； township mold business, and professional mold factory is similar. Of which the largest number of first-class, mold production accounts for about 70% of total output. Chinas mold industry, decentralized management system. There are 19 major industry sectors manufacture and use of mold, there is no unified management of the department. Only by China Die & Mould Industry Association, overall planning, focus on research, cross-sectoral, inter-departmental management difficulties are many. 桂林电子科技大学毕业设计用纸 第 19 页 共 26 页 Mold is suitable for small and medium enterprises organize production, and our technical transformation investment tilted to large and medium enterprises, small and medium enterprise investment mold can not be guaranteed. Including product factory mold shop, factory, including, after the transformation can not quickly recover its investment, or debt-laden, affecting development. Although most products factory mold shop, factory technical force is strong, good equipment conditions, the production of mold levels higher, but equipment utilization rate. Price has long been Chinas mold inconsistent with their value, resulting in mold industry own little economic benefit, social benefit big phenomenon. Dry as dry mold mold standard parts, standard parts dry as dry mold with pieces of production. Dry with parts manufactured products than with the mold of the class of anomalies exist. 4 Engineering Engineering is the discipline, art and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge to design and build structures, machines, devices, systems, materials and processes that safely realize solutions to the needs of society. The American Engineers Council for Professional Development (ECPD, the predecessor of ABET) has defined engineering as: The creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination； or to construct or operate the same with full cognizance of their design； or to forecast their behavior under specific operating conditions； all as respects an intended function, economics of operation and safety to life and property. One who practices engineering is called an engineer, and those licensed to do so may have more formal designations such as Professional Engineer, Chartered Engineer, Incorporated Engineer, or European Engineer. The broad discipline of engineering encompasses a range of more specialized subdisciplines, each with a more specific emphasis on certain fields of application and particular areas of technology. 桂林电子科技大学毕业设计用纸 第 20 页 共 26 页 4.1 Engineering History The concept of has existed since ancient times as humans devised fundamental inventions such as the pulley, lever, and wheel. Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanical principles to develop useful tools and objects. The term engineering itself has a much more recent etymology, deriving from the word engineer, which itself dates back to 1325, when an engineer (literally, one who operates an engine) originally referred to “a constructor of military engines.” In this context, now obsolete, an “engine” referred to a military machine, i.e., a mechanical contraption used in war (for example, a catapult). Notable exceptions of the obsolete usage which have survived to the present day are military engineering corps, e.g., the U.S. Army Corps of Engineers. The word “engine” itself is of even older origin, ultimately deriving from the Latin ingenium (c. 1250), meaning “innate quality, especially mental power, hence a clever invention.” Later, as the design of civilian structures such as bridges and buildings matured as a technical discipline, the term civil engineering entered the lexicon as a way to distinguish between those specializing in the construction of such non-military projects and those involved in the older discipline of military engineering. 4.2 Ancient era The Pharos of Alexandria, the pyramids in Egypt, the Hanging Gardens of Babylon, the Acropolis and the Parthenon in Greece, the Roman aqueducts, Via Appia and the Colosseum, Teotihuacn and the cities and pyramids of the Mayan, Inca and Aztec Empires, the Great Wall of China, among many others, stand as a testament to the ingenuity and skill of the ancient civil and military engineers. The earliest civil engineer known by name is Imhotep. As one of the officials of the Pharaoh, Djosr, he probably designed and supervised the construction of the Pyramid of 桂林电子科技大学毕业设计用纸 第 21 页 共 26 页 Djoser (the Step Pyramid) at Saqqara in Egypt around 2630-2611 BC. He may also have been responsible for the first known use of columns in architecturecitation needed. Ancient Greece developed machines in both the civilian and military domains. The Antikythera mechanism, the first known mechanical computer, and the mechanical inventions of Archimedes are examples of early mechanical engineering. Some of Archimedes inventions as well as the Antikythera mechanism required sophisticated knowledge of differential gearing or epicyclic gearing, two key principles in machine theory that helped design the gear trains of the Industrial revolution, and are still widely used today in diverse fields such as robotics and automotive engineering. Chinese, Greek and Roman armies employed complex military machines and inventions such as artillery which was developed by the Greeks around the 4th century B.C., the trireme, the ballista and the catapult. In the Middle Ages, the Trebuchet was developed. 4.3 Renaissance era The first electrical engineer is considered to be William Gilbert, with his 1600 publication of De Magnete, who was the originator of the term electricity. The first steam engine was built in 1698 by mechanical engineer Thomas Savery. The development of this device gave rise to the industrial revolution in the coming decades, allowing for the beginnings of mass production. With the rise of engineering as a profession in the eighteenth century, the term became more narrowly applied to fields in which mathematics and science were applied to these ends. Similarly, in addition to military and civil engineering the fields then known as the mechanic arts became incorporated into engineering. 4.4 Modern The International Space Station represents a modern engineering challenge from many disciplines. Electrical engineering can trace its origins in the experiments of Alessandro Volta in the 1800s, the experiments of Michael Faraday, Georg Ohm and others and the invention of the electric motor in 1872. The work of James Maxwell and Heinrich Hertz in the late 19th 桂林电子科技大学毕业设计用纸 第 22 页 共 26 页 century gave rise to the field of Electronics. The later inventions of the vacuum tube and the transistor further accelerated the development of electronics to such an extent that electrical and electronics engineers currently outnumber their colleagues of any other Engineering specialty. The inventions of Thomas Savery and the Scottish engineer James Watt gave rise to modern Mechanical Engineering. The development of specialized machines and their maintenance tools during the industrial revolution led to the rapid growth of Mechanical Engineering both in its birthplace Britain and abroad. Chemical Engineering, like its counterpart Mechanical Engineering, developed in the nineteenth century during the Industrial Revolution. Industrial scale manufacturing demanded new materials and new processes and by 1880 the need for large scale production of chemicals was such that a new industry was created, dedicated to the development and large scale manufacturing of chemicals in new industrial plants. The role of the chemical engineer was the design of these chemical plants and processes. Aeronautical Engineering deals with aircraft design while Aerospace Engineering is a more modern term that expands the reach envelope of the discipline by including spacecraft design. Its origins can be traced back to the aviation pioneers around the turn of the century from the 19th century to the 20th although the work of Sir George Cayley has recently been dated as being from the last decade of the 18th century. Early knowledge of aeronautical engineering was largely empirical with some concepts and skills imported from other branches of engineering. The first PhD in engineering (technically, applied science and engineering) awarded in the United States went to Willard Gibbs at Yale University in 1863； it was also the second PhD awarded in science in the U.S. Only a decade after the successful flights by the Wright brothers, the 1920s saw extensive development of aeronautical engineering through development of World War I military aircraft. Meanwhile, research to provide fundamental background science continued by combining theoretical physics with experiments. In 1990, with the rise of computer technology, the first search engine was built by computer engineer Alan Emtage. 桂林电子科技大学毕业设计用纸 第 23 页 共 26 页 4.5 Main branches of engineering Main article: List of engineering branches Engineering, much like other science, is a broad discipline which is often broken down into several sub-disciplines. These disciplines concern themselves with differing areas of engineering work. Although initially an engineer will be trained in a specific discipline, throughout an engineers career the engineer may become multi-disciplined, having worked in several of the outlined areas. Historically the main Branches of Engineering are categorized as follows:1417 Aerospace engineering - The design of aircraft, spacecraft and related topics. Chemical engineering - The exploitation of chemical principles in order to carry out large scale chemical process, as well as designing new specialty materials and fuels. Civil engineering - The design and construction of public and private works, such as infrastructure (roads, railways, water supply and treatment etc.), bridges and buildings. Electrical engineering - a very broad area that may encompass the design and study of various electrical & electronic systems, such as electrical circuits, generators, motors, electromagnetic/electromechanical devices, electronic devices, electronic circuits, optical fibers, optoelectronic devices, computer systems, telecommunications and electronics. Mechanical engineering - The design of physical or mechanical systems, such as engines, compressors, powertrains, kinematic chains, vacuum technology, and vibration isolation equipment. New specialties sometimes combine with the traditional fields and form new branches. A new or emerging area of application will commonly be defined temporarily as a permutation or subset of existing disciplines； there is often gray area as to when a given sub-field becomes large and/or prominent enough to warrant classification as a new branch. One key indicator of such emergence is when major universities start establishing departments and programs in the new field. For each of these fields there exists considerable overlap, especially in the areas of the application of sciences to their disciplines such as physics, chemistry and mathematics. 桂林电子科技大学毕业设计用纸 第 24 页 共 26 页 4.6 Methodology Design of a turbine requires collaboration of engineers from many fields, as the system is subject to mechanical, electro-magnetic and chemical processes. The blades, rotor and stator as well as the steam cycle all need to be carefully designed and optimised. Engineers apply the sciences of physics and mathematics to find suitable solutions to problems or to make improvements to the status quo. More than ever, engineers are now required to have knowledge of relevant sciences for their design projects, as a result, they keep on learning new material throughout their career. If multiple options exist, engineers weigh different design choices on their merits and choose the solution that best matches the requirements. The crucial and unique task of the engineer is to identify, understand, and interpret the constraints on a design in order to produce a successful result. It is usually not enough to build a technically successful product； it must also meet further requirements. Constraints may include available resources, physical, imaginative or technical limitations, flexibility for future modifications and additions, and other factors, such as requirements for cost, safety, marketability, productibility, and serviceability. By understanding the constraints, engineers derive specifications for the limits within which a viable object or system may be produced and operated. 4.7 Problem solving Engineers use their knowledge of science, mathematics, and appropriate experience to find suitable solutions to a problem. Engineering is considered a branch of applied mathematics and science. Creating an appropriate mathematical model of a problem allows them to analyze it (sometimes definitively), and to test potential solutions. Usually multiple reasonable solutions exist, so engineers must evaluate the different design choices on their merits and choose the solution that best meets their requirements. Genrich Altshuller, after gathering statistics on a large number of patents, suggested that compromises are at the heart of low-level engineerin