活塞机械加工工艺规程及粗镗销孔夹具设计.doc

www.88doc88.comwww.yanziedu.com目录目录·······································································································11对零件进行工艺分析···············································································31.1活塞的作用···················································································31.2活塞的结构特点············································································31.3活塞的主要技术条件分析·································································41.3.1活塞裙部外圆与气缸的配合·······················································41.3.2活塞销的要求········································································41.3.3销孔(活塞的)的位置公差的要求···················································41.3.4活塞重量的要求·····································································426120活塞工艺规程的设计·········································································52.1活塞的材料及毛坯的制造·································································52.2定位其面的选择············································································52.3制定工艺路线···············································································62.3.1工艺路线方案一·····································································62.3.2工艺路线方案二·····································································72.3.3工艺方案的比较与分析·····························································82.4机械加工余量、工序尺寸及毛坯尺寸的确定········································112.4.1止口的加工余量····································································112.4.2端面及顶面的加工余量···························································122.4.3销孔的加工余量···································································122.4.4外圆的加工余量···································································122.5重点工序的加工说明·····································································122.5.1止口的加工·········································································122.5.2环槽的加工·········································································142.5.3裙部外圆的精加工·································································142.5.4销孔的精加工········································································142.6确定切削用量及基本工时.(重点工序)·············································152.6.1加工条件············································································152.6.2计算切削用量······································································162.6.3基本工时············································································162.7活塞的检验················································································162.7.1裙部直径和椭圆度的测量························································172.7.2销孔轴线与裙部轴心线的测量···················································182.7.3销孔轴心线对裙部轴心线的垂直度的测量·····································193夹具的设计························································································20粗镗销孔夹具·················································································203.1问题的提出················································································203.2夹具的设计················································································203.3切削力和夹紧力的计算和校核··························································223.3.1切削力················································································22www.88doc88.comwww.yanziedu.com3.3.2夹紧力·············································································234参考文献···························································································25致谢····································································································26附录·····································································································27www.88doc88.comwww.yanziedu.com1对零件进行工艺分析1.1活塞的作用由于柴油的物理化学特性，所以柴油机的构造是一个非常复杂的系统。而油缸就是这个系统中一个很关键的部位，对整个动力系统起着决定性影响，在某种意义来说它是柴油机里面的“心脏”。而活塞则是柴油机机里“心脏中的心脏”。活塞位于发动机汽缸内,作往复运动,当燃烧室里的混合气体(空气和燃料)点燃并膨胀时,活塞受到气体的压力,并经过活塞销及连杆将压力传送给曲柄。气体的吸入,压缩,废气的排除,也都由活塞的运动来完成.因此活塞工作的主要特点是在高温高压下作长时间的连续变负荷往复运动。为了提高活塞的工作性能和寿命,它必须具有如下的要求:(1)在高温高压下具有足够的强度和刚度；(2)较轻的结构重量；(3)良好的耐磨性和耐蚀性；(4)良好的导热性,热膨胀系数小；(5)保证气缸内部空间密封。本次设计加工的是6120柴油机的活塞。1.2活塞的结构特点6120活塞顶部有燃烧室,混合气体在里面进行燃烧,它的容积大小就决定着里面能够容纳混合气体多少,也就决定了燃烧后所产生的压强大小。近顶部的环槽分为气环槽和油环槽，为放置活塞环用,在气环槽内放置的活塞环使活塞头部与气缸不接触,并用以密封活塞的顶部,防止漏气。远离顶部的环槽钻有油孔,它把飞溅到气缸套内壁上的多余润滑油刮去,并通过油孔流回,使之不致进入燃烧室。活塞的裙部在活塞的工作过程中起导向的作用,底部有精加工的止口,它是为加工活塞而设置的辅助精基面,在结构和功能上没有起到直接的作用。由于燃料燃烧会产生很大压力，所以在工作过程中活塞将产生受力变形和热变形,由于活塞裙部在圆周方向刚度不同,在活塞的轴线方向的弹性变形比垂直于该方向的弹性变形大,使活塞裙部在受力后变成椭圆,另一方面,在高温的工作www.88doc88.comwww.yanziedu.com环境下也要产生热变形。销孔轴线方向的金属层比较厚,热鼓胀比垂直于该方向上的大,也将使活塞裙部变形后成为椭圆,这样的话将必然使活塞与气缸套的间隙不均匀的减少甚至消失,以至产生强烈的摩擦甚至咬住。为了补偿上述的变形,所以把活塞的裙部设计制造成椭圆形,椭圆的长轴在垂直于活塞销孔轴心线的方向上。此外，活塞在工作时顶部是直接和高温气体接触的,而裙部是间接传来的热量,故而头部的热鼓胀量要比裙部的大,为了补偿这种不均匀的变形,故把活塞头部的外径设计得比裙部小,同时头部也设计成上小下大的锥形。同时在活塞裙部的销孔附近加工出凹坑,用来增加裙部与气缸套内壁的间隙。1.3活塞的主要技术条件分析1.3.1活塞裙部外圆与气缸的配合活塞裙部外圆与气缸要求是一种精密地配合,因而裙部外圆一般要求公差等级IT6,为减少机械加工的困难,将活塞裙部和气缸套孔径的制造公差均放大二倍,装配时按裙部的尺寸分成二组对应装配,以保证大致要求的间隙。要求裙部外圆的粗糙度Ra1.6m。1.3.2活塞销的要求为了使活塞销在工作过程中能在孔中自由转动,销孔的公差等级大小要求IT6级,同时为了减少机加工工作量,活塞和活塞孔的装配也采用分组装配法,要求销孔内圆的粗糙度Ra0.2m。1.3.3销孔(活塞的)的位置公差的要求销孔(活塞的)的位置公差也应有严格要求，销孔轴心线到顶面的距离影响气缸的压缩比,也就影响着发动机的效率,因此应该控制在90±0.05内。销孔轴心线对裙部轴心的垂直度影响着活塞销,销孔和连杆的受力情况过大将使活塞销、销孔、连杆单侧受力。活塞在气缸套中倾斜,加剧磨损,因此这里垂直度在100mm长度上公差为0.03mm。销孔轴心线对裙部轴心线的对称度误差也会引起不均匀摩损,故而应该限制。1.3.4活塞重量的要求为了保证发动机运转平稳,在同一发动机上各活塞的重量不应相差太大,对于6120柴油机活塞,同级活塞的重量差不能超过20克,即活塞的重量差不得大于活塞名义重量的±2.5%.活塞在装配的时候应按重量进行分组.www.88doc88.comwww.yanziedu.com26120活塞工艺规程的设计2.1活塞的材料及毛坯的制造活塞在发动机内是做高速的往复运动,根距它的工作特性，为了减少其惯性的作用采用的材料为共晶铝硅合金。它的化学成分为:共晶铝硅合金（）i11-13；Cu1-2；Mg0.4-1；Mn0.2-0.7；Fe0.8；其余l与铸铁相比具有以下的优点：(1)导热性好，使活塞顶面降温快，可以提高发动机的压缩比，不至于引起混合气体自燃,可以提高发动机效率；(2)重量轻，惯性力小；(3)切削性能好；(4)铸造流动性好，可以得到精确的毛坯。由于是大批大量的生产万件每年，为了提高毛坯的精度，铸出活塞的销孔及燃烧室，减少机加工余量，故而毛坯的铸造是采用金属模铸造。毛坯在机械加工前先要去铣浇冒口，并进行时效处理，消除铸造时因冷却不均匀而产生的内应力，增加活塞的强度及硬度。时效处理的方法是将活塞加热到°°，保温小时后自然冷却。2.2定位基面的选择定位基准选择的准确性对保证零件表面间的位置精度、位置尺寸和安排加工顺序都有很大的影响，直接影响零件的加工精度和生产效率。基准是用来确定生产对象上几何要素间的几何关系所依据的那些点、线、面。一个几何关系就有一个基准。活塞是一种薄壁型零件，在外力作用的情况下是很容易产生变形的，而活塞主要表面的尺寸精度和位置精度的要求都很高，因此应以一个统一的基面定位来加工这些要求高的表面，如直接采用外圆定位的话（即设计基准）将有可能产生很大的变形。故在这里采用活塞的止口和端面来作为统一基准。在精车外圆和精磨外圆这两工序中用止口处的锥面和顶面上的中心孔定位，www.88doc88.comwww.yanziedu.com其余工序都采用止口和端面定位。精镗销孔则由于精度要求很高，为避免产生基准不重合误差，而采用的是设计基准做为定位基准。采用止口和端面（或锥面和中心锥）作为基面有下列优点：(1)用这种定位方法可以加工裙部、头部、顶面、销孔等主要及其它次要表面，而且在这一道工序中，一次安装就可以车削外圆、顶面、环槽,实现了工序的集中。既可提高生产率，又能保证这些表面的位置精度。(2)活塞裙部在半径方向的刚性差，利用止口和端面定位可以沿活塞轴向夹紧，就不至引起严重的变形，同时又可以进行多刀切削提高生产效率。当然这些定位也有一些缺点：如果加工一些本来不需要加工的表面，而且是一些精度要求级高的要经过两次加工的。止口对裙部外圆的同轴度误度将影响环槽的位置精度。但总的说来，采用止口端面作为统一基准虽然增加了加工工时和设备，但它更有利于保证加工质量，故而采用它来定位是可行的。2.3制定工艺路线关于工艺路线的拟订，目前还没有一套精确的计算方法，而是采用经过生产实践总结出来的一些带有经验和综合性的原则。制订工艺路线的出发点是使零件的几何形状、尺寸精度及位置精度等技术要求能得到合理的保证，在生产纲领已确定为大量生产和条件，故可以适当地采用专用机床配以专用夹具。除此还应考虑经济效果，使生产成本尽量下降。它是制定工艺规程的关键阶段。此次设计拟订了几套工艺路线方案：2.3.1工艺路线方案一工序号内容1粗车止口2粗外切槽及顶部3钻斜面油孔4钻环槽油孔5钻销座油孔6滑销座油孔7粗镗销孔8精车止口及顶锥9精切细外环岸及倒角10精镗销孔（顺镗）11挖销孔卡簧12切小槽13靠模车裙部www.88doc88.comwww.yanziedu.com14车凹部15车燃烧室16精车顶部及导角17钻R7凹坑18车燃烧室口19铣喷油道曲线20清洗21滚压2.3.2工艺路线方案二工序号内容1粗车止口2粗镗销孔3粗切外槽及顶部4钻斜面油孔5钻环槽油孔6钻销座油孔7滑销座油孔8精车止口及顶锥9精切梯形槽10精镗销孔（顺镗）11挖卡簧槽12切小槽13靠模车裙部14车凹部及去毛刺15滑油池底16车燃烧室17精车顶部及倒角18钻R7凹坑19车燃烧室口20铣喷油道曲线21去毛刺锐边22清洗23滚压销孔