尾座体加工工艺及镗模夹具设计

天津职业技术师范大学 Tianjin University of Technology and Education 毕 业 设 计 专 业： 机械设计与制造及其自动化 班级学号： XXXXXX 学生姓名： XXX 指导教师： XXX 副教授 二一二年六月 天津职业技术师范大学本科生毕业设计 尾座体加工工艺及镗模夹具设计 Designing lathe tailstock body processing technology and boring fixture design 专业班级：机自 0803 学生姓名： XXX 指导教师： XXX 副教授 学 院：机械工程学院 2012 年 6 月 摘 要 本课题主要是设计 CW6163车床尾座体的加工工艺及镗孔夹具设计。本设计中包括对进行夹具设计必须的毛坯选择、加工余量的确定、切削刀具和机床的选择及机动时间计算等方面知识。本次设计内容包括两部分，首先是对尾座体零件的工艺分析，其次是根据尾座体镗孔工序进行夹具体设计。本设计所选用的资料主义到贯彻最 新国家标准及部分标准。 本次设计师根据生产纲领成批量，年产量 1000台左右设计的。设计中考虑大批量生产，在加工过程中，为了保证被加工孔对其定位基准和尺寸精度和位置精度的要求，同时提高效率，对尾座体的镗孔工序进行夹具设计。设计采用平面和定位销组合定位，压板加紧和螺母锁紧的设计来提高加工效率和减轻工作人员劳动强度。 关键词 ：尾座体 加工工艺 镗床夹具 ABSTRACT The main task is to design CW6163lathe tailstock body processing technology and boring fixture design. This design including the fixture design to the blank selection, determination of machining allowance, cutting tool and machine tool selection and maneuvering calculation knowledge. This design includes two parts, the first is the tailstock body parts of the process analysis, the second is based on the tailstock body boring process clamp design. The design of the data to carry out the new national standards and standards. The designer according to production plan into the bulk, the annual output of 1000sets of left and right design. Design considerations for mass production, in the process, in order to ensure the hole on the locating datum and dimensional accuracy and position accuracy requirements, while improving the efficiency, the tailstock body bore for fixture design process. The design adopts the plane and positioning pin positioning, plate intensified and nut locking design to improve processing efficiency and reduce the labor intensity of workers. Key Words： The tailstock body Processing technology Jig boring machine I 目 录 1 绪论 . 1 1.1设计的目的 . 1 1.2设计任务及要求 . 1 1.3设计的内容及步骤 . 1 1.3.1工艺规程的设计 . 1 1.3.2专用夹具设计 . 2 2 零件加工工艺规程的制定 . 4 2.1 零件的分析 . 4 2.1.1零件的功用 . 4 2.1.2零件的工艺分析 . 4 2.2 零件的工艺规程 . 4 2.2.1确定零件的生产纲领 . 4 2.2.2确定零件毛坯的制造形式 . 5 2.2.3拟定零件机械加工工艺路线 . 5 3 零件工序设计 . 7 3.1 零件加工余量的确定 . 7 3.2 确定各工序所用机床及工艺设备 . 8 3.3 用量及工时定额 . 8 4 镗模夹具设计 . 11 4.1 设计夹具目的 . 11 4.2 镗模设计方案的选择和确定 . 11 4.2.1定位方案、定位误 差及定位元件的选择 . 11 4.2.2 装置的选择及夹紧力的布置 . 12 4.2.3 确定刀具的导引方式 . 12 4.2.4 设计夹具体 . 13 4.2.5 定夹具其它部分的结构形式 . 13 4.2.6 夹紧力计算（估算） . 14 结 论 . 16 翻译文献 . 19 II 参考文献 . 35 致谢 . 36 天津职业技术师范大学 2012 届本科生毕业设计 1 1 绪论 1.1 设计的目的 能熟练的运用机械制造工艺学的基本理论和夹具设计原理的知识，正确的解决一个零件在加工中的定位、夹紧以及合理制定工艺规程等问题的方 法，培养分析问题和解决问题的能力。通过对零件某道工序的夹具的设计夹具的训练，提高结构设计的能力。本次设计也是理论联系实践的过程，并学会使用手册、资料 ,增加解决工程实际问题的独立工作能力的过程。 1.2 设计任务及要求 制作成批量生产（ 1000 台）中等复杂程度零件（尾架体）的机械加工工艺规程和镗孔工序中所需要的专用夹具的设计。 设计任务要求： 1.零件的工艺性分析及选择毛坯 2.机械加工工艺过程卡及镗孔工序卡 3.夹具装配图和零件图 4.设计说明书 1.3 设计的内容及步骤 1.3.1 工艺规程的设计 1）对零件进行工艺分析。 （ 1）对零件机器结构中的作用及零件图上技术要求进行分析。 （ 2）对零件主要加工表面尺寸，形状及相对位置精度，表面粗糙度及主要技术条件进行分析。 （ 3）对零件的材质、热处理及工艺性进行分析。通过以上分析，以便在工艺过程中切实加以保证。 2）选择毛坯的制造方式，绘制零件毛坯综合示意图。 选择毛坯应以生产批量的大小来确定，跟据批量大小的生产规模决定毛坯形式及制造方法，根据有关资料 确定各个加工表面的总余量，并把各余量加在零件图各有关位置上，在毛坯图上标出相关尺寸。 3）制定零件的机械加工工艺路线 （ 1）制定工艺路线，在对零件和毛坯进行分析的基础上制定零件的加工工艺，它包括确定加工方法、确定安排加工顺序、确定定位夹紧方法，以及安排天津职业技术师范大学 2012 届本科生毕业设计 2 热处理、检验以及其他辅助工序等。 （ 2）选择定位基准，合理选定各工序的定位基准，当工序定位基准与设计基准不重合时，需要对它的工序尺寸进行换算。 （ 3）选择机床及夹具、刀具、量具。机床设备及工艺装备的选用应当既要保证加工质量，还要经济合理。 （ 4）加工余量 及工序间尺寸与公差的确定。根据工艺路线的安排，计算镗孔相关工序加工余量。其工序间尺寸公差按经济精度确定。 （ 5）确定切削用量机动时间。用公式计算各工序的切削用量，其余各工序的切削用量可由切削手册查到。然后计算该工序的时间定额。 （ 6）绘制零件的机械加工工艺过程卡片，及镗孔工序的工序卡片。 1.3.2 专用夹具设计 在该加工过程中需要设计镗模专用夹具。 夹具结构设计的方法和步骤： 1）确定夹具设计方案、绘制结构原理图。 确定夹具设计方案应遵循几个原则： （ 1）保证工序加工精度和技术要求。 （ 2）结构简单、制造 容易。 （ 3）造作方便、省力安全。 （ 4）满足零件在生产中高效低成本。 确定夹具设计方案的主要内容为： （ 1）确定工件的定位方案。 （ 2）确定刀具的对刀或引导方式。 （ 3）确定刀具的夹紧方案。 （ 4）确定夹具其他组成部分的结构形式。 （ 5）确定夹具体。 最后绘制出结构原理示意图 2）选择定位原件，计算定位误差。 在确定设计方案的基础上，应按照加工精度的高低，根据六点定位原理。约束自由度的数目以及确定所需的定位元件。选择好定位原件后，应计算定位误差。 3）计算夹紧力，决定夹紧机构及其主要尺寸 夹紧是按照静力 平衡条件，从具体定位夹紧力方案和切削条件出发进行分析，主要根据切削力决定理论夹紧力，但由于在加工过程中有冲击震荡存在，为了保障安装稳定理论夹紧力还要乘以一个安全系数 K， K 值可以在相关手册中查到。 天津职业技术师范大学 2012 届本科生毕业设计 3 计算出夹紧力后，根据所确定的加紧机构决定其主要尺寸。 4）绘制夹具装配图： （ 1）要求夹具装配图按照比例绘制。 （ 2）要有必要的视图和剖面图。 5）在装配图上标注各部位尺寸、公差配合和技术条件参考机床夹具设计或其他有关手册 天津职业技术师范大学 2012 届本科生毕业设计 4 2 零件加工工艺规程的制定 2.1 零件的分析 2.1.1 零件的功用 本课题所给零件是 cw6163 车床的尾架体。它的作用主要是。对工件起到固定支撑，保证定位的作用，减少在加工中因为工件自重或是刀具切削力引起工件形变，而导致的加工误差。 2.1.2 零件的工艺分析 1） 尺寸精度 加工孔 100H7 30H7 45H7 都是配合尺寸，必须有较高的尺寸精度，尺寸精度均为 IT7 级公差，精度要求较高，加工中应注意保证。 2） 形位精度 孔和右端面的垂直度误差为 0.08mm， 100H7 孔的内表面平行度误差为0.12mm， 100H7 孔的内表面圆柱度误差为 0.012mm 。 3） 表面粗糙度 配合表面要求较高的表面粗糙度， 100H7 孔的粗糙度为 Ra0.8 m, 30H7 45H7 孔的粗糙度为 Ra1.6 m，下表面粗糙度为 Ra1.6 m，上表面及左右两端面的粗糙度为 Ra3.2 m。 4） 热处理 为了消除毛坯铸件中的残余应力，进一步改善切削性能，铸造后应安排去应力退火或时效处理。 2.2 零件的工艺规程 2.2.1 确定零件的生产纲领 机器零件的生产纲领按下式计算： N=Qn（ 1+a%+b%） 式中： N 零件的生产纲领（件 /年） Q 产品的年产量（台 /年） n 每台中该零件的数量（件 /台） a% 备品的百分率 b% 废品的百分率 天津职业技术师范大学 2012 届本科生毕业设计 5 其中：产品的年产量 Q=1000 台 /年 , 每台中该零件的数量 n=1 件 /台 , 备品的百分率 a%=4%，平均废品的百分率 b%=3%， N=1000 1(1+4%+3%)=1070 件 通过计算可知，生产类型为大批量生产。 2.2.2 确定零件毛坯的制造形式 毛坯种类确定：选用灰口铸铁，牌号为 HT200，灰铸铁具有较好的可切削性，铸造性，耐磨性，而且吸振性好，成本较低。 毛坯制造方法：砂型机器铸造，铸造 精度高，且生产效率较高，铸件成型后的材质比木模稳定可靠。在铸造时，应防止砂眼和气孔的产生，浇注的位置是大平面朝下，基面朝上。为了减少毛坯制造时产生的残余应力，其结构，厚度要均匀，浇铸后应安排退火工序。 2.2.3 拟定零件机械加工工艺路线 1） 工艺路线的制定 : （ 1）先粗后精 加工尾架体顶面和底面时：先粗刨顶面，粗刨底面；再磨削顶面，磨削底面。粗加工时切削力较大，产生较多的切削热。粗加工时需要较大的夹紧力。粗加工后铸造毛坯的内应力重新分配在这些热和力的周围。工件会发生较大的变形。粗精加工分开，是为了保证这些有 粗加工引起的工件变形，能够在精加工后被消除掉。 （ 2）先基面后其他 先将精基准尾架体底面加工出来，然后再加工 100 的孔等。 （ 3）先主后次 尾架体的底面尺寸及 100 孔是主要配合面，它的加工应安排在 45 30孔之前。 工艺过程，（参见工艺过程卡） 2） 定位基准的选择 （ 1）选择定位基准： 工件的加工部位和各表面相对位置的准确性，取决于工件在机床上相对刀具位置的准确性，也就是取决于工件在夹具中定位的准确性，定位的准确与否，由于定位基准的选择正确与否有直接联系，所以定位基准选择合理与否不仅影响到零件的加 工位置精度，而且决定了工件各表面加工先后顺序。 （ 2）选择粗基准： 粗基准的选择，可以保证重要表面能够分配到必须且均匀的加工余量，也保证了工件加工表面与不加工表面的相互位置精度。是为了能够在此基准的定位下，加工出精基准，从而对工件进行进一步的加工。 天津职业技术师范大学 2012 届本科生毕业设计 6 车床尾架体为了保证被加工表面最主要位置要求是 100H7 孔轴线与 B 端面的垂直度为 0.08 （ 3）选择精基准： 应保证各表面的相互位置精度，使夹具结构简单，安装方便，采用基准统一原则，即设计基准与定位基准相互统一。 尾架体零件应尽量选择设计基准为精基准，以 100H7 孔的轴心线为定位基准，能保证孔的加工精度。 另外，还应考虑到在测量已加工表面位置时的测量基准。 天津职业技术师范大学 2012 届本科生毕业设计 7 3 零件工序设计 零件机械加工工艺路线拟定后还需对每一工序进行设计。其主要内容包括：确定每一工步的加工余量、计算各工序的工序尺寸及公差、选择各工序所使用的机床及工艺装备、确定切削用量、计算工时定额等 。 3.1 零件加工余量的确定 机械加工余量对工艺过程有一定的影响，余量不够，不能保证零件的加工质量，余量过大，不但会增加机械加工劳动量，而且增加了材料、刀具、能源的 消耗，从而增加了成本，所以必须合理的安排加工余量。 根据零件毛坯条件：材料灰口铸铁 HT200，生产类型为中批生产。采用金属模型铸造毛坯。本设计采用查表修正和经验估计法相结合来确定各加工表面的机械加工余量、工序尺寸及毛坯尺寸。 1）工序尺寸计算 以加工 035.00100孔为例，设计加工方法为： 粗镗 半精镗 精扩 精铰 细铰 具体计算值见表 2-1 表 2-1 工序尺寸计算表 工序名称 工序余量 mm 工序达到的公差等级 mm 最小极限尺寸mm 工序尺寸及极限偏差 mm 细铰 0.1 )(7 035.00IT 100 035.00100 精铰 0.6 )(9 054.00IT 100-0.1=99.9 054.009.99 精扩 0.8 )(10 14.00IT 99.9-0.6=99.3 14.003.99 半精镗 1.5 )(11 23.00IT 99.3-0.8=98.5 23.005.98 粗镗 5 )(13 46.00IT 98.5-1.5=97 46.0097 毛坯孔 )1(16 IT 97-5=92 192 2）工序间尺寸计算 精铰孔时，是以 E 面定位的，而设计基准为轴线，因而定位基准与设计基准不重合，因而要进行尺寸换算。 如下图所示，在尺寸链中，要间接保证的尺 寸为 3.02.0250 ，因此，设其为封闭环 A ，由竖式法求得： 80.0)0()1(20.0)()()()( 4321 lEslEslEilEi 3.0)0()0(3.0)()()()( 4321 lEilEilEslEs 1968462501 l 天津职业技术师范大学 2012 届本科生毕业设计 8 所以，工序尺寸 3.08.0196 3.2 确定各工序所用机床及工艺设备 由于该工件生产规模为中批生产，根据工件的结构特点和技术要求，各工序所用机床及工艺装备确定如下：工序 030，铣床 X6120、通用夹具；工序 050、055、 060、 065 卧式镗床 T4680 专用夹具；工序 70，钻床 Z3063。 3.3 用量及工时定额 以加工 100H7 孔为例，确定加工中各个工步的切削用量，机动时间及工时定额。 1） 切削用量计算： （ 1） .粗镗铸出孔 毛坯孔 D=92mm，粗镗加工至 D=97mm，查机械加工工艺手册， P1-132,选择硬质合金刀头，从表中可以选择切削速度 v=60m/min,进给量 f=0.4mm/r,根据公式： 1000dnv ， m in/1979714.3 100060 rn 查机械加工工艺人员手册， P1128 确定在粗镗孔时的实际进给长度： 加工长度 l =500 mm， 刀具切入长度 1l =2.5 mm,刀具超出长度 2l =2.5 mm, 天津职业技术师范大学 2012 届本科生毕业设计 9 m i n409.61974.0 5.25.2500210 nf lllT (2).半精镗孔 孔径 D=98.5mm，查机械加工工艺手册， P1-132,选择硬质合金镗刀头，从表中可以选择切削速度 v=80m/min,进给量 f=0.3mm/r,根据公式： 1000dnv ， m in/25 95.9814.3 10 0080 rn 查机械加工工艺人员手册， P1128 确定在半精镗孔时的实际进给长度： 加工长度 l =500 mm， 刀具切入长度 1l =2.5 mm,刀具超出长度 2l =2.5 mm m i n499.62593.0 5.25.2500210 nf lllT (3).精扩孔 孔径 D=99.3mm，查实用机械 加工工艺手册， P1307，选用硬质合金扩孔刀，从表中可以选择切削速度 v=120m/min,进给量 f=0.2mm/r,根据公式： 1000dnv m i n/38 53.9914.3 10 0012 0 rn 查金属机械加工工艺人员手册， P1128 确定在精扩孔时的实际进给长度： 加工长度 l=500 mm，刀具切入长度 1l =2.5 mm,刀具超出长度 2l =2.5 mm m i n558.63852.0 5.25.2500210 nf lllT (4).精铰孔 孔径 D=99.9mm，查实用机械加工工艺手册， P1307，选用硬质合金精铰刀，从表中可以选择切削速度 v=40m/min,进给量 f=4.0mm/r,根据公式： 1000dnv ， m in/1289.9914.3 100040 rn 查金属机械加工工艺人员手册， P1132，确定在精铰孔时的实际进给长度： 加工长度 l=500 mm，切深 a p=0.3mm,刀具切入长度 1l =0.3 mm,刀具超出长度2l =45 mm m i n650.11280.4 453.0500210 nf lllT (5).细铰孔 孔径 D=100mm，查实用机械加工工艺手册， P1307，选用硬质合金浮动天津职业技术师范大学 2012 届本科生毕业设计 10 镗刀，从表中可以选择切削速度 v=30m/min,进给量 f=2.5mm/r,根据公式： 1000dnv ， m in/9610 014.3 10 0030 rn 查金属机械加工工艺人员手册， P1132，确定在细铰孔时的实际进给长度： 加工长度 l=500 mm， 切深pa=0.3mm,刀具切入长度 1l =0.05 mm,刀具超出长度2l =45 mm m i n271.2965.2 4505.0500210 nf lllT 2）单件时间定额： Tm=Tm1+Tm2+Tm3+Tm4+Tm5 =6.409+6.499+6.558+1.650+2.271 =23.387 min 查手册，可以得到以下计算公式： Ta=2min Te=7% (Tm+Ta)=0.07 25.387=1.78 min Ts=1.5% (Tm+Ta)=0.015 25.387=0.38 min Tr=2% (Tm+Ta)=0.02 25.387=0.51 min 所以： T 定额 =23.387+2+1.78+0.38+0.51=28.057 min Td1 单位时间 Tm 基本时间 Ta 辅助时间 Tr 休息与生理需要 Ts 布置工作的时间 Te 准备与终结时间 天津职业技术师范大学 2012 届本科生毕业设计 11 4 镗模夹具设计 4.1 设计夹具目的 机床夹具是在切削加工中，用以准确的确定工件位置，并将其牢固的加紧的工艺装备。它可靠的保证工件的加工精 度，提高加工效率，减轻劳动强度。充分发挥机床的工艺性能。为了提高生产率，尾架体加工，有必要采用专用夹具来满足生产率及合理的经济要求，减轻工人劳动强度。 由于孔加工比其它表面要复杂的多，加工环境条件差，刀具尺寸受被加工孔的限制，致使刀杆细长而刚性差，以至于影响孔的加工精度。如果采用划线找正的方法加工有一定位置精度的孔时；不仅生产效率低，而且加工质量也不高。有必要采用镗模夹具。设计该镗模夹具，有利于保证加工精度，提高生产率，保证定位准确，保证夹紧可靠，并尽可能使夹具结构简单合理，降低成本。 4.2 镗模设计方 案的选择和确定 4.2.1 定位方案、定位误差及定位元件的选择 工件在机床相对刀具占有正确的加工位置，这就是定位。工件在夹具中定位的目的，就是要使同一批工件在夹具中占有一定正确的加工位置。 该方案是以 C 面（底面）作为主要定位面，有 3 个定位点。 E 面作为导向面。有两个定位点，而且 C 面的面积要大于 E 面面积。根据定位基准选择的一般原则：选最大尺寸的表面为安装面（限制 3 个自由度），选最长距离的表面为导向面（限制 2 个自由度）。该定位方案可行。 C 面为主要定位面，限制了三个自由度。 E 面（侧面）为导向面，限制两个自由度。这 样就确定了工件与刀具间的相对位置。 由于 C 面为精基面，因此，可在 C 面设立两个支承板，以确保定位稳定，而不会出现过定位。两个支承板位置分布在两侧，比较分散，其形成的受力四边形面积尽可能大。 E 面两点定位，为确保质量，两个支承点间距离应尽可能远些。 在镗削加工工序中，是以平面定位的，而这一平面又是精基面，很难保证大平面的平整。因此，不能用大平面作为定位元件来定位。选用支承板作为小平面式定位。在 C 面用两个支承板定位。 E 面一侧用两个开槽盘头定位螺钉定位。 定位误差的计算： 工件以平面定位，所以 Y=0； 天津职业技术师范大学 2012 届本科生毕业设计 12 由于镗孔的 工序基准和定位基准重合，所以 B=0.015+0.1=0.025 定位误差为 D= B=0.025 4.2.2 装置的选择及夹紧力的布置 夹紧装置选择的是否合理，对于确保加工质量和提高生产率有很大的关系，一般来说在不破坏定位精度，保证加工质量前提下，应尽可能使夹紧装置的夹紧作用准确，安全可靠，操作方便省力，夹紧变形小，结构简单，制造容易。 镗削的切削力产生的翻转扭矩不很大，因此，手动夹紧已经可以满足。 设计和选用夹紧装置的核心问题是如何正确地施加夹紧力即适当布置夹紧力。夹紧力应保证定位准确可靠。 ,而不能 破坏原定位，考虑到中批生产，夹紧力方向应便于工人操作。因此，将夹紧螺母设计在顶面，减轻劳动强度，便于操作。与 C 面两个支承板相对应产生夹紧力。 4.2.3 确定刀具的导引方式 镗模中的导引元件，选用固定式镗套，这是因为加工零件时，一次性镗通孔，不用频繁的更换刀具及镗套，而且我们在制定工艺规程中，采用的镗削加工速度也不高。如果用回转式镗套，则不能满足上述要求。 镗杆是依靠镗套和支架来引导和支承的。镗套结构对于被镗孔的几何形状，尺寸精度以及表面粗糙度有很小的影响。因此镗套的设计是镗模设计中的重要环节之一。 镗套的 布置形式是由镗孔的孔径 D，以及孔的长度 L 与孔径之比 L/D 所决定的，镗杆的长度很长，为了防止镗杆受切削力而变形，影响其刚度，采用双面单镗套的布置形式。由于前后镗套已经确定了镗杆的位置，因此镗杆与机床主轴之间不可用刚性连接，只能是浮动连接，以避免镗套中心与机床主轴不重合时发生孔径增大，镗套拉毛等现象。 为了满足装配要求和强度要求，在结构上设置了较大的安装基面和加强筋，详见夹具装配图。 镗套的内径是镗杆的导杆的导引部分直径决定的，一般来说，为使刀具从镗套内穿过，则其内径应大于刀具直径。 如 100 孔精镗时，刀具直径为 75 。则其镗套内径应大于刀具直径，选镗套内径 80 与镗杆的配合应为间隙配合。间隙要适宜，太大，镗杆导引不好影响加工精度。太小，镗杆与镗套磨损严重，产生热量可能会使镗杆与镗套咬死，这里取56nH。 天津职业技术师范大学 2012 届本科生毕业设计 13 镗套外径与衬套的配合，衬套与支架内径的配合应为过渡配合。为避免个别出现过盈现象，装配时应采用修配法，一般配合取66hH。 镗套长度要选取适宜，太短导引不好，影响镗杆回转精度，从而影响孔加工质量；太长不易散热，镗套磨损严重，影响加工精度。一般对于双面单镗套导引，镗套长度 H 一般取 H=(1.5-2)d。 d 为镗杆导引部分直径。 4.2.4 设计夹具体 夹具体应能保证夹具的整体刚度和强度，在此前提下，要尽量减轻重量。因此，夹具体大部分采用铸件，以便能根据需要铸出各种形状的筋条和边框、铣床、磨床等机床夹具通常是开式或半开式的，以便刀具通过。而钻床夹具则常设计成框架式，以便钻套的配置。为了提高夹具制造的工艺性，夹具体很少做成整体的，而是分成座底立柱，模板等零件，它们之间用螺钉和销钉进行联接定位。 由于粗镗时，切削深度较半精镗时大，所以粗镗时切削力最大。 (1)夹具轮廓（最大）尺寸，之所以需要标注轮廓尺寸，是因为它影响机床规格的确定。 (2)配合尺寸及性质如定位元件与夹具体的配合，钻套与衬套、衬套与夹具体的配合等标注配合的意义在于给夹具零件设计者作出规定，并给总图的阅读提供方便。 有关配合的选取，通常可参照机床夹具设计手册进行 (3)装配位置要求。其中包括定位元件之间，定位元件与对定元件之间，多个对定元件之间以及定位元件与夹具在机床 工作台或主轴上安装用元件之间等几方面的位置要求，标注这些要求，一方面是作为封闭环，在规定夹具零件相关尺寸位置和公差时，要予以保证另一方面是用作夹具装配时的最终精度检验指标，装配位置要求通常按被加工工件上相应尺寸及位置公差的 1/5 1/3选取，一般当工件相应尺寸精度要求高应取大值，以便于夹具制造。 4.2.5 定夹具其它部分的结构形式 镗模支架是组成镗模的重要零件之一，它是安装镗套和承受切削力用的。因此，它必须具有足够的刚性和稳定性。因此要防止镗模支架的受力振动和变形，在结构上应考虑有较大的安装基面和设置必要 的加强筋。 镗模底座要承受包括工件、镗杆、镗套、镗模支架定位元件和夹紧装置内的全部重量，以及加工过程中的切削力。因此，底座刚性要好，变形要小，通常镗模底座的壁厚较厚而底座内腔设有十字形加强筋。 为了安装各元件，镗模底座上平面，在相应位置做出了相配合的凸台表面，其凸出高度为 5mm。镗模材料选用灰铸铁 HT200。 天津职业技术师范大学 2012 届本科生毕业设计 14 4.2.6 夹紧力计算（估算） 总切削力的计算： 由于粗镗时，切削深度较半精镗时大，所以粗镗时切削力最大。切削时，镗刀块一端切深为 3mm，另一端为 2mm。刀具材料 YG6硬质合金刀。主偏角 45粗镗进给量 s=0.4mm/r。所以切削力 75.0stCPz PZ 式中： mmKgC PZ /100 ， 75.0)4.0(/1 0 0 tmmkgP Z 当 t=3mm 时， mmKgP Z 87.1 5 04.031 0 0 75.01 当 t=2mm 时， mmKgP Z 58.1 0 04.021 0 0 75.02 孔加工时的总切削力 mmKgPPP ZZZ 45.25121 镗孔时通常轴向力很小且方向不变，因此它对夹紧力影响不大。镗孔关键在于根据其圆周切削力 ZP 方向的变化，按照可能出现的最坏情况来确定所需夹紧力。 当圆周力 ZP 向上时，是工件绕的支承板右端最远的那一端点回转，并有可能抬起工件，此时，利用公式l LKPW Z进行计算。查机床夹具设计手册。 安全系数 K的计算： 根据公式6543210 KKKKKKKK 进行计算。其中，工件材料系数 3.10 K，加工精度系数 2.11 K ，因为计算工序选择是粗加工；刀具钝化程度 0.12 K 切削特点系数 0.13 K，因为是连续切削；夹紧力稳定系数 3.14 K ，因为是手动夹紧；操作方便系数 0.15 K因为方便夹紧；支承面接触点系数 0.16 K因为接触点确定。 所以， 02.20.10.13.10.10.12.13.1 K mmKgl LKPW Z 51.1591150 47045.25102.2 当个圆周力 ZP 方向处于水平方向时，有使工件产生平移的可能。在不允许定位螺钉承受切削力时，工件按照静力平衡方程Zj PffW )( 21 进行计算。查机床夹具设计手册。 天津职业技术师范大学 2012 届本科生毕业设计 15 mmKgff KPW Z 83.1 2 6 92.02.0 45.2 5 102.221 因为： WW ，所以夹紧力选择 mmKgW 51.1591 选择的是 M16 的螺柱，配合压板，六角螺母一起把工件夹紧。查机床夹具设计手册螺母可提供的夹紧力可知，假设扳手长度为 90mm, 假设加在扳手上的力为 100 mmKg ，则产生的夹紧力 mmKgQ 523 0 ， WQ 所以能够完全满足夹紧需要。 天津职业技术师范大学 2012 届本科生毕业设计 16 结 论 毕业设计不仅仅是一个综合性的设计，也不只是理论的设计，他还包括解决实际问题的方案设计，这就要求我们把理论知识的应用与实际相结合，灵活运用。 通过本次毕业设计，使我们认识到毕业设计是我们走上工作岗位之前在学校期间对所学基础知识、专业知识、基 本技能和专业技能进行的一次全面综合学习过程。 毕业设计是一个综合性的设计，不只是理论的设计，而且还用于实际，这就要求我们把理论知识的应用与实际相结合。次毕业设计，是我对所学基础知识、专业知识、基本技能和专业技能进行的一次全面综合学习过程。 在这次毕业设计过程中，对于计算机的操作时必不可少的，计算机的辅助设计，文字的输入、排版的良好的运用，极大的提高了设计的效率。并且可通过互联网在较短的时间里搜索到自己所需要的资料，从而对整个设计过程有了很大的帮助。在设计过程中，我到图书馆查阅大量的资料，独立的分析问题解决问 题。在整个设计过程中发现自己知识的漏洞，有问题会向指导老师学习、同学讨论。得到一种解决方案。在和老师、同学交流的过程中取长丰富自己的知识面。 设计期间，我总结梳理过去所学的知识，综合应用于此次的毕业设计中，通过查阅图书馆的手册，一步一步的完成自己的设计，有不对的地方及时改正，设计在六月中旬完成。通过毕业设计我初步体会到解决工程实际工作的方法，并学会了如何把所学知识技能应用于工程实际中，初步掌握了科学研究的方法与技巧。 总之，通过毕业设计使我们初步体会到工程实际工作的经历，并学会了如何把所学知识技能应用于工程 实际中，了解理论与实际是否有差别，初步掌握了科学研究的方法与技巧。对今后的工作实践十分有益。 天津职业技术师范大学 2012 届本科生毕业设计 17 天津职业技术师范大学 2012 届本科生毕业设计 18 天津职业技术师范大学 2012 届本科生毕业设计 19 翻译文献 Style of materials Materials may be grouped in several ways. Scientists often classify materials by their state: solid, liquid, or gas. They also separate them into organic (once living) and inorganic (never living) materials. For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products. Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product. Engineering materials may be further subdivided into: Metal Ceramics Composite Polymers, etc. Metals and Metal Alloys Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility. Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors. What is the difference between an alloy and a pure metal? Pure metals are elements which come from a particular area of the periodic table. Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans. Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples of metal alloys include stainless steel which is an alloy of iron, nickel, and chromium； and gold jewelry which usually contains an alloy of gold and nickel. Why are metals and alloys used? Many metals and alloys have high densities and are used in applications which require a high mass-to-volume ratio. Some metal alloys, such as those based on aluminum, have low densities and are used in aerospace applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable. What are some important properties of metals? Density is defined as a materials mass divided by its volume. Most metals have relatively high densities, especially compared to polymers. Materials with high densities often contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities, and are used in applications that require other metallic properties but also require low weight. Fracture toughness can be described as a materials ability to avoid fracture, especially when a flaw is introduced. Metals can generally contain nicks and dents without weakening very much, and are impact resistant. A football player counts on 天津职业技术师范大学 2012 届本科生毕业设计 20 this when he trusts that his facemask wont shatter. Plastic deformation is the ability of bend or deform before breaking. As engineers, we usuallydesign materials so that they dont deform under normal conditions. You dont want your car to lean to the east after a strong west wind. However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break. The atomic bonding of metals also affects their properties. In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires. It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through. Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. For example, adding a small amount of iron to aluminum will make it stronger. Also, adding some chromium to steel will slow the rusting process, but will make it more brittle. Ceramics and Glasses A ceramic is often broadly defined as any inorganic nonmetallic material By this definition, ceramic materials would also include glasses； however, many materials scientists add the stipulation that “ ceramic” must also be crystalline. A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous. Properties of Ceramics and Glasses Some of the useful properties of ceramics and glasses include high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance. Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials； some are piezoelectric materials； and a few special ceramics are superconductors at very low temperatures. Ceramics and glasses have one major drawback: they are brittle. Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid state. Hence, all the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be used for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used. In sintering, ceramic powders are processed into compacted shapes and then heated to temperatures just below the melting point. At such temperatures, the powders react internally to remove porosity and fully dense articles can be obtained. An optical fiber contains three layers: a core made of highly pure glass with a high refractive index for the light to travel, a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches 天津职业技术师范大学 2012 届本科生毕业设计 21 and other surface imperfections, and an out polymer jacket to protect the fiber from damage. In order for the core glass to have a higher refractive index than the cladding, the core glass is doped with a small, controlled amount of an impurity, or dopant, which causes light to travel slower, but does not absorb the light. Because the refractive index of the core glass is greater than that of the cladding, light traveling in the core glass will remain in the core glass due to total internal reflection as long as the light strikes the core/cladding interface at an angle greater than the critical angle. The total internal reflection phenomenon, as well as the high purity of the core glass, enables light to travel long distances with little loss of intensity. Composites Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components. For example: polymer/ceramic composites have a greater modulus than the polymer component, but arent as brittle as ceramics. Two types of composites are: fiber-reinforced composites and particle-reinforced composites. Fiber-reinforced Composites Reinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase the modulus of the matrix material. The strong covalent bonds along the fibers length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved. Fibers are difficult to process into composites, making fiber-reinforced composites relatively expensive. Fiber-reinforced composites are used in some of the most advanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix. Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix. Fibers have a very high modulus along their axis, but have a low modulus perpendicular to their axis. Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus. Particle-reinforced composites Particles used for reinforcing include ceramics and glasses such as small mineral particles, metal particles such as aluminum, and amorphous materials, including polymers and carbon black. Particles are used to increase the modulus of the matrix, to decrease the permeability of the matrix, to decrease the ductility of the matrix. An example of particle-reinforced composites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer. 天津职业技术师范大学 2012 届本科生毕业设计 22 Polymers A polymer has a repeating structure, usually based on a carbon backbone. The repeating structure results in large chainlike molecules. Polymers are useful because they are lightweight, corrosion resistant, easy to process at low temperatures and generally inexpensive. Some important characteristics of polymers include their size (or molecular weight), softening and melting points, crystallinity, and structure. The mechanical properties of polymers generally include low strength and high toughness. Their strength is often improved using reinforced composite structures. Important Characteristics of Polymers Size. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/molthat can be more than 2,000 repeating units depending on the polymer structure! The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights. Thermal transitions. The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used. For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100 , 212 ), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300 (572 ). Crystallinity. Polymers can be crystalline or amorphous, but they usually have a combination of crystalline and amorphous structures (semi-crystalline). Interchain interactions. The polymer chains can be free to slide past one another (thermo-plastic) or they can be connected to each other with crosslinks (thermoset or elastomer). Thermo-plastics can be reformed and recycled, while thermosets and elastomers are not reworkable. Intrachain structure. The chemical structure of the chains also has a tremendous effect on the properties. Depending on the structure the polymer may be hydrophilic or hydrophobic (likes or hates water), stiff or flexible, crystalline or amorphous, reactive or unreactive. The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product. Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining. With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties. Alloy steel owe their properties to the presence of one or more elements other 天津职业技术师范大学 2012 届本科生毕业设计 23 than carbon, namely nickel, chromium, manganese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used commercially in many ways not possible with carbon steels. The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon steels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect. A Simplified Iron-carbon Diagram If we focus only on the materials normally known as steels, a simplified diagram is often used. Those portions of the iron-carbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel. The key transition described in this diagram is the decomposition of single-phase austenite() to the two-phase ferrite plus carbide structure as temperature drops. Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment. To begin to understand these processes, consider a steel of the eutectoid composition, 0.77% carbon, being slow cooled along line x-x in Fig.2.1. At the upper temperatures, only austenite is present, the 0.77% carbon being dissolved in solid solution with the iron. When the steel cools to 727 (1341 ), several changes occur simultaneously. The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution. The rejected carbon forms the carbon-rich cementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is austenite 0.77%C ferrite 0.02%C+cementite 6.67%C. Since this chemical separation of the carbon component occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling. This structure is composed of two distinct phases, but has its own set of characteristic properties and goes by the name pearlite, because oits resemblance to mother- of- pearl at low magnification. Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y in Fig.2.1. At high temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and austenite. Tie-line and level-law calculations show that low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon. At 727 (1341 ), the austenite is of eutectoid composition (0.77% carbon) 天津职业技术师范大学 2012 届本科生毕业设计 24 and further cooling transforms the remaining austenite to pearlite. The resulting structure is a mixture of primary or pro-eutectoid ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite. Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such steel cools, as shown in z-z of Fig.2.1 the process is similar to the hypo-eutectoid case, except that the primary or pro-eutectoid phase is now cementite instead of ferrite. As the carbon-rich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid composition at 727 (1341 ). As before, any remaining austenite transforms to pearlite upon slow cooling through this temperature. It should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions, which can be approximated by slow cooling. With slow heating, these transitions occur in the reverse manner. However, when alloys are cooled rapidly, entirely different results may be obtained, because sufficient time is not provided for the normal phase reactions to occur, in such cases, the phase diagram is no longer a useful tool for engineering analysis. Hardening Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly. If the carbon content of the steel is known, the proper temperature to which the steel should be heated may be obtained by reference to the iron-iron carbide phase diagram. However, if the composition of the steel is unknown, a little preliminary experimentation may be necessary to determine the range. A good procedure to follow is to heat-quench a number of small specimens of the steel at various temperatures and observe the result, either by hardness testing or by microscopic examination. When the correct temperature is obtained, there will be a marked change in hardness and other properties. In any heat-treating operation the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too fast, the outside becomes hotter than the interior and uniform structure cannot be obtained. If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results. Even after the correct temperature has been reached, the piece should be held at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature. The hardness obtained from a given treatment depends on the quenching rate, the carbon content, and the work size. In alloy steels the kind and amount of alloying element influences only the hardenability (the ability of the workpiece to be hardened to depths) of the steel and does not affect the hardness except in unhardened or partially hardened steels. Steel with low carbon content will not respond appreciably to hardening 天津职业技术师范大学 2012 届本科生毕业设计 25 treatment. As the carbon content in steel increases up to around 0.60%, the possible hardness obtainable also increases. Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed state. Pearlite responds best to heat-treating operations； and steel composed mostly of pearlite can be transformed into a hard steel. As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the same. There is a limit to the rate of heat flow through steel. No matter how cool the quenching medium may be, if the heat inside a large piece cannot escape faster than a certain critical rate, there is a definite limit to the inside hardness. However, brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature. Under these circumstances there would always be some finite depth of surface hardening regardless of size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching. Tempering Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel. The operation consists of reheating quench-hardened steel to some temperature below the critical range followed by any rate of cooling. Although this process softens steel, it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would. The final structure obtained from tempering a fully hardened steel is called tempered martensite. Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Low-temperature draws, from 300 to 400 (150205 ), do not cause much decrease in hardness and are used principally to relieve internal strains. As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600 (315 ) the change to a structure called tempered martensite is very rapid. The tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite. A substantial precipitation of cementite begins at 600 (315 ), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness. In the process of tempering, some consideration should be given to time as well as to temperature. Although most of the softening action occurs in the first few minutes after the temperature is reached, there is some additional reduction in hardness if the temperature is maintained for a prolonged time. 天津职业技术师范大学 2012 届本科生毕业设计 26 Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated. Two special processes using interrupted quenching are a form of tempering. In both, the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool. These processes, known as austempering and martempering, result in products having certain desirable physical properties. Annealing The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked. This is usually accomplished by heating the steel too slightly above the critical temperature, holding it there until the temperature of the piece is uniform throughout, and then cooling at a slowly controlled rate so that the temperature of the surface and that of the center of the piece are approximately the same. This process is known as full annealing because it wipes out all trace of previous structure, refines the crystalline structure, and softens the metal. Annealing also relieves internal stresses previously set up in the metal. The temperature to which a given steel should be heated in annealing depends on its composition； for carbon steels it can be obtained readily from the partial iron-iron carbide equilibrium diagram. When the annealing temperature has been reached, the steel should be held there until it is uniform throughout. This usually takes about 45min for each inch(25mm) of thickness of the largest section. For maximum softness and ductility the cooling rate should be very slow, such as allowing the parts to cool down with the furnace. The higher the carbon content, the slower this rate must be. The heating rate should be consistent with the size and uniformity of sections, so that the entire part is brought up to temperature as uniformly as possible. Normalizing and Spheroidizing The process of normalizing consists of heating the steel about 50 to 100 (10 40 ) above the upper critical range and cooling in still air to room temperature. This process is principally used with low- and medium-carbon steels as well as alloy steels to make the grain structure more uniform, to relieve internal stresses, or to achieve desired results in physical properties. Most commercial steels are normalized after being rolled or cast. Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution. If steel is heated slowly to a temperature just below the critical range and held there for a prolonged period of time, this structure will be obtained. The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined. Surface Hardening Carburizing The oldest known method of producing a hard surface on steel is case hardening or carburizing. Iron at temperatures close to and above its critical temperature has an 天津职业技术师范大学 2012 届本科生毕业设计 27 affinity for carbon. The carbon is absorbed into the metal to form a solid solution with iron and converts the outer surface into high-carbon steel. The carbon is gradually diffused to the interior of the part. The depth of the case depends on the time and temperature of the treatment. Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such as charcoal or coke. It is a long process and used to produce fairly thick cases of from 0.03 to 0.16 in.(0.764.06mm) in depth. Steel for carburizing is usually a low-carbon steel of about 0.15% carbon that would not in itself responds appreciably to heat treatment. In the course of the process the outer layer is converted into high-carbon steel with a content ranging from 0.9% to 1.2% carbon. A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment. Because there is some grain growth in the steel during the prolonged carburizing treatment, the work should be heated to the critical temperature of the core and then cooled, thus refining the core structure. The steel should then be reheated to a point above the transformation range of the case and quenched to produce a hard, fine structure. The lower heat-treating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just above the lower critical point. A third tempering treatment may be used to reduce strains. Carbonitriding Carbonitriding, sometimes known as dry cyaniding or nicarbing, is a case-hardening process in which the steel is held at a temperature above the critical range in a gaseous atmosphere from which it absorbs carbon and nitrogen. Any carbon-rich gas with ammonia can be used. The wear-resistant case produced ranges from 0.003 to 0.030 inch(0.08 0.76mm) in thickness. An advantage of carbonitriding is that the hardenability of the case is significantly increased when nitrogen is added, permitting the use of low-cost steels. 天津职业技术师范大学 2012 届本科生毕业设计 28 材料的类型 材料可以按多种方法分类。科学家常根据状态将材料分为：固体、液体或气体。他们也把材料分为有机材料 (曾经有生命的 )和无机材料 (从未有生命的 )。 就工业效用而言，材料被分为工程材料和非工程材料。那些用于加工制造并成为产品组成部分的就是工程材料。 非工 程材料则是化学品、燃料、润滑剂以及其它用于加工制造过程但不成为产品组成部分的材料。 工程材料还能进一步细分为：金属材料陶瓷材料复合材料 聚合材料，等等。 金属和金属合金 金属就是通常具有良好导电性和导热性的元素。许多金属具有高强度、高硬度以及良好的延展性。 某些金属能被磁化，例如铁、钴和镍。在极低的温度下，某些金属和金属化合物能转变成超导体。 合金与纯金属的区别是什么？纯金属是在元素周期表中占据特定位置的元素。例如电线中的铜和制造烹饪箔及饮料罐的铝。 合金包含不止一种金属元素。合金的性质能通过改变其 中存在的元素而改变。金属合金的例子有：不锈钢是一种铁、镍、铬的合金，以及金饰品通常含有金镍合金。 为什么要使用金属和合金？许多金属和合金具有高密度，因此被用在需要较高质量体积比的场合。 某些金属合金，例如铝基合金，其密度低，可用于航空航天以节约燃料。许多合金还具有高断裂韧性，这意味着它们能经得起冲击并且是耐用的。 密度定义为材料的质量与其体积之比。大多数金属密度相对较高，尤其是和聚合物相比较而言。 高密度材料通常由较大原子序数原子构成，例如金和铅。然而，诸如铝和镁之类的一些金属则具有低密度，并被用于 既需要金属特性又要求重量轻的场合。 断裂韧性可以描述为材料防止断裂特别是出现缺陷时不断裂的能力。金属一般能在有缺口和凹痕的情况下不显著削弱，并且能抵抗冲击。橄榄球运动员据此相信他的面罩不会裂成碎片。 塑性变形就是在断裂前弯曲或变形的能力。作为工程师，设计时通常要使材料在正常条件下不变形。没有人愿意一阵强烈的西风过后自己的汽车向东倾斜。 然而，有时我们也能利用塑性变形。汽车上压皱的区域在它们断裂前通过经历塑性变形来吸收能量。 金属的原子连结对它们的特性也有影响。在金属内部，原子的外层阶电子由所有原子共 享并能到处自由移动。由于电子能导热和导电，所以用金属可以制造好的烹饪锅和电线。 因为这些阶电子吸收到达金属的光子，所以透过金属不可能看得见。没有光子能通过金属。 合金是由一种以上金属组成的混合物。加一些其它金属能影响密度、强度、断裂韧性、塑性变形、导电性以及环境侵蚀。 例如，往铝里加少量铁可使其更强。同样，在钢里加一些铬能减缓它的生锈天津职业技术师范大学 2012 届本科生毕业设计 29 过程，但也将使它更脆。 陶瓷和玻璃 陶瓷通常被概括地定义为无机的非金属材料。照此定义，陶瓷材料也应包括玻璃；然而许多材料科学家添加了“陶瓷”必须同时是晶体物组成的约定。 玻 璃是没有晶体状结构的无机非金属材料。这种材料被称为非结晶质材料。 陶瓷和玻璃的特性 高熔点、低密度、高强度、高刚度、高硬度、高耐磨性和抗腐蚀性是陶瓷和玻璃的一些有用特性。 许多陶瓷都是电和热的良绝缘体。某些陶瓷还具有一些特殊性能：有些是磁性材料，有些是压电材料，还有些特殊陶瓷在极低温度下是超导体。陶瓷和玻璃都有一个主要的缺点：它们容易破碎。 陶瓷一般不是由熔化形成的。因为大多数陶瓷在从液态冷却时将会完全破碎(即形成粉末 )。 因此，所有用于玻璃生产的简单有效的 诸如浇铸和吹制这些涉及熔化的技术都不能用于由晶体 物组成的陶瓷的生产。作为替代，一般采用“烧结”或“焙烧”工艺。 在烧结过程中，陶瓷粉末先挤压成型然后加热到略低于熔点温度。在这样的温度下，粉末内部起反应去除孔隙并得到十分致密的物品。 光导纤维有三层：核心由高折射指数高纯光传输玻璃制成，中间层为低折射指数玻璃，是保护核心玻璃表面不被擦伤和完整性不被破坏的所谓覆层，外层是聚合物护套，用于保护光导纤维不受损。 为了使核心玻璃有比覆层大的折射指数，在其中掺入微小的、可控数量的能减缓光速而不会吸收光线的杂质或搀杂剂。 由于核心玻璃的折射指数比覆层大，只要在全内反射过 程中光线照射核心 /覆层分界面的角度比临界角大，在核心玻璃中传送的光线将仍保留在核心玻璃中。 全内反射现象与核心玻璃的高纯度一样，使光线几乎无强度损耗传递长距离成为可能。 复合材料 复合材料由两种或更多材料构成。例子有聚合物 /陶瓷和金属 /陶瓷复合材料。之所以使用复合材料是因为其全面性能优于组成部分单独的性能。 例如：聚合物 /陶瓷复合材料具有比聚合物成分更大的模量，但又不像陶瓷那样易碎。 复合材料有两种：纤维加强型复合材料和微粒加强型复合材料。 纤维加强型复合材料 加强纤维可以是金属、陶瓷、玻璃或是已变成石墨的 被称为碳纤维的聚合物。纤维能加强基材的模量。 沿着纤维长度有很强结合力的共价结合在这个方向上给予复合材料很高的模量，因为要损坏或拉伸纤维就必须破坏或移除这种结合。 把纤维放入复合材料较困难，这使得制造纤维加强型复合材料相对昂贵。 纤维加强型复合材料用于某些最先进也是最昂贵的运动设备，例如计时赛竞赛用自行车骨架就是用含碳纤维的热固塑料基材制成的。 竞赛用汽车和某些机动车的车体部件是由含玻璃纤维 (或玻璃丝 )的热固塑料基材制成的。 天津职业技术师范大学 2012 届本科生毕业设计 30 纤维在沿着其轴向有很高的模量，但垂直于其轴向的模量却较低。纤维复合材料的制造者往往 旋转纤维层以防模量产生方向变化。 微粒加强型复合材料 用于加强的微粒包含了陶瓷和玻璃之类的矿物微粒，铝之类的金属微粒以及包括聚合物和碳黑的非结晶质微粒。 微粒用于增加基材的模量、减少基材的渗透性和延展性。微粒加强型复合材料的一个例子是机动车胎，它就是在聚异丁烯人造橡胶聚合物基材中加入了碳黑微粒。 聚合材料 聚合物具有一般是基于碳链的重复结构。这种重复结构产生链状大分子。由于重量轻、耐腐蚀、容易在较低温度下加工并且通常较便宜，聚合物是很有用的。 聚合材料具有一些重要特性，包括尺寸 (或分子量 )、软化及熔化 点、结晶度和结构。聚合材料的机械性能一般表现为低强度和高韧性。它们的强度通常可采用加强复合结构来改善。 聚合材料的重要特性 尺寸：单个聚合物分子一般分子量为 10,000 到 1,000,000g/mol 之间，具体取决于聚合物的结构 这可以比 2,000 个重复单元还多。 聚合物的分子量极大地影响其机械性能，分子量越大，工程性能也越好。 热转换性：聚合物的软化点 (玻璃状转化温度 )和熔化点决定了它是否适合应用。这些温度通常决定聚合物能否使用的上限。 例如，许多工业上的重要聚合物其玻璃状转化温度接近水的沸点 (100 , 212 )，它们被广泛用于室温下。而某些特别制造的聚合物能经受住高达 300 (572 )的温度。 结晶度：聚合物可以是晶体状的或非结晶质的，但它们通常是晶体状和非结晶质结构的结合物 (半晶体 )。 原子链间的相互作用：聚合物的原子链可以自由地彼此滑动 (热可塑性 )或通过交键互相连接 (热固性或弹性 )。热可塑性材料可以重新形成和循环使用，而热固性与弹性材料则是不能再使用的。 链内结构：原子链的化学结构对性能也有很大影响。根据各自的结构不同，聚合物可以是亲水的或憎水的 (喜欢或讨厌水 )、硬的或软的、晶体状的或非结晶质的、 易起反应的或不易起反应的。 对热处理的理解包含于对冶金学较广泛的研究。冶金学是物理学、化学和涉及金属从矿石提炼到最后产物的工程学。 热处理是将金属在固态加热和冷却以改变其物理性能的操作。按所采用的步骤，钢可以通过硬化来抵抗切削和磨损，也可以通过软化来允许机加工。 使用合适的热处理可以去除内应力、细化晶粒、增加韧性或在柔软