减速器箱体卧式钻孔专用组合机床结构设计【说明书+CAD】
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单面多轴钻孔组合机床动力滑台液压系统一、设计要求及工况分析1设计要求要求设计的动力滑台实现的工作循环是:快进 工进 快退 停止。主要性能参数与性能要求如下:切削阻力FL=30000N;运动部件所受重力G=10000N;快进、快退速度1= 3=0.07m/s,工进速度2=0.8310-3m/s;快进行程L1=150mm,工进行程L2=30mm;往复运动的加速时间t=0.2s;动力滑台采用平导轨,静摩擦系数s=0.2,动摩擦系数d=0.1。液压系统执行元件选为液压缸。2负载与运动分析(1) 工作负载 工作负载即为切削阻力FL=3000N。(2) 摩擦负载 摩擦负载即为导轨的摩擦阻力:静摩擦阻力 N2000100002.0sfs =GFm动摩擦阻力 N 1000 100001.0dfd =GFm(3) 惯性负载 N357.1N2.007.08.910000i=DD=tgGFu(4) 运动时间 快进 s21s07.0101503111=-uLt工进 s1.36s1083.0103033222=-uLt快退 s6.2s07.010)30150(33213=+=+=-uLLt设液压缸的机械效率cm=0.9,得出液压缸在各工作阶段的负载和推力,如表1所列。表1液压缸各阶段的负载和推力工况负载组成液压缸负载F/N液压缸推力F0=F/cm/N启 动加 速快 进工 进反向启动加 速快 退20001357.110003100020001357.110002222.21507.91111.134444.42222.21507.91111.1图1 F-t与-t图根据液压缸在上述各阶段内的负载和运动时间,即可绘制出负载循环图F-t 和速度循环图-t,如图1所示。二、确定液压系统主要参数1初选液压缸工作压力所设计的动力滑台在工进时负载最大,在其它工况负载都不太高,参考表2和表3,初选液压缸的工作压力p1=4MPa。2计算液压缸主要尺寸鉴于动力滑台快进和快退速度相等,这里的液压缸可选用单活塞杆式差动液压缸(A1=2A2),快进时液压缸差动连接。工进时为防止孔钻通时负载突然消失发生前冲现象,液压缸的回油腔应有背压,参考表4选此背压为p2=0.6MPa。表2 按负载选择工作压力负载/ KN50工作压力/MPa0.811.522.5334455表3 各种机械常用的系统工作压力机械类型机 床农业机械小型工程机械建筑机械液压凿岩机液压机大中型挖掘机重型机械起重运输机械磨床组合机床龙门刨床拉床工作压力/MPa0.82352881010182032表4 执行元件背压力系统类型背压力/MPa简单系统或轻载节流调速系统0.20.5回油路带调速阀的系统0.40.6回油路设置有背压阀的系统0.51.5用补油泵的闭式回路0.81.5回油路较复杂的工程机械1.23回油路较短且直接回油可忽略不计表5 按工作压力选取d/D工作压力/MPa5.05.07.07.0d/D0.50.550.620.700.7表6 按速比要求确定d/D2/11.151.251.331.461.612d/D0.30.40.50.550.620.71注:1无杆腔进油时活塞运动速度;2有杆腔进油时活塞运动速度。由式得242621cm1m1093m10)26.04(9.031000)2(-=-=-=ppFAh 则活塞直径 mm109m109.0m10934441=-ppAD参考表5及表6,得d0.71D =77mm,圆整后取标准数值得 D=110mm, d=80mm。由此求得液压缸两腔的实际有效面积为根据计算出的液压缸的尺寸,可估算出液压缸在工作循环中各阶段的压力、流量和功率,如表7所列,由此绘制的液压缸工况图如图2所示。表7液压缸在各阶段的压力、流量和功率值工况推力F0/N回油腔压力p2/MPa进油腔压力p1/MPa输入流量q10-3/m3/s输入功率P/KW计算公式快进启动2222.20.44加速1507.9p1+p0.74恒速1111.1p1+p0.660.350.23工进34444.40.63.910.7910-20.031快退启动2222.20.50加速1507.90.51.40恒速1111.10.51.310.450.59注:1. p为液压缸差动连接时,回油口到进油口之间的压力损失,取p=0.5MPa。2 快退时,液压缸有杆腔进油,压力为p1,无杆腔回油,压力为p2。三、拟定液压系统原理图1选择基本回路图2 液压缸工况图(1) 选择调速回路 由图2可知,这台机床液压系统功率较小,滑台运动速度低,工作负载为阻力负载且工作中变化小,故可选用进口节流调速回路。为防止孔钻通时负载突然消失引起运动部件前冲,在回油路上加背压阀。由于系统选用节流调速方式,系统必然为开式循环系统。(2) 选择油源形式 从工况图可以清楚看出,在工作循环内,液压缸要求油源提供快进、快退行程的低压大流量和工进行程的高压小流量的油液。最大流量与最小流量之比qmax/qmin=0.35/(0.7910-2)44;其相应的时间之比(t1+t3)/t2=(2.1+2.6)/36.1=0.13。这表明在一个工作循环中的大部分时间都处于高压小流量工作。从提高系统效率、节省能量角度来看,选用单定量泵油源显然是不合理的,为此可选用限压式变量泵或双联叶片泵作为油源。考虑到前者流量突变时液压冲击较大,工作平稳性差,且后者可双泵同时向液压缸供油实现快速运动,最后确定选用双联叶片泵方案,如图2a所示。(3) 选择快速运动和换向回路 本系统已选定液压缸差动连接和双泵供油两种快速运动回路实现快速运动。考虑到从工进转快退时回油路流量较大,故选用换向时间可调的电液换向阀式换向回路,以减小液压冲击。由于要实现液压缸差动连接,所以选用三位五通电液换向阀,如图2b所示。(4) 选择速度换接回路 由于本系统滑台由快进转为工进时,速度变化大(1/2=0.07/(0.8310-3)84),为减少速度换接时的液压冲击,选用行程阀控制的换接回路,如图2c所示。(5) 选择调压和卸荷回路 在双泵供油的油源形式确定后,调压和卸荷问题都已基本解决。即滑台工进时,高压小流量泵的出口压力由油源中的溢流阀调定,无需另设调压回路。在滑台工进和停止时,低压大流量泵通过液控顺序阀卸荷,高压小流量泵在滑台停止时虽未卸荷,但功率损失较小,故可不需再设卸荷回路。 图3 整理后的液压系统原理图图2 选择的基本回路2组成液压系统将上面选出的液压基本回路组合在一起,并经修改和完善,就可得到完整的液压系统工作原理图,如图3所示。在图3中,为了解决滑台工进时进、回油路串通使系统压力无法建立的问题,增设了单向阀6。为了避免机床停止工作时回路中的油液流回油箱,导致空气进入系统,影响滑台运动的平稳性,图中添置了一个单向阀13。考虑到这台机床用于钻孔(通孔与不通孔)加工,对位置定位精度要求较高,图中增设了一个压力继电器14。当滑台碰上死挡块后,系统压力升高,它发出快退信号,操纵电液换向阀换向。四、计算和选择液压件1确定液压泵的规格和电动机功率(1) 计算液压泵的最大工作压力小流量泵在快进和工进时都向液压缸供油,由表7可知,液压缸在工进时工作压力最大,最大工作压力为p1=3.96MPa,如在调速阀进口节流调速回路中,选取进油路上的总压力损失p=0.6MPa,考虑到压力继电器的可靠动作要求压差Dpe=0.5MPa,则小流量泵的最高工作压力估算为()MPa01.5MPa5.06.096.3e11p=+=D+D+pppp 大流量泵只在快进和快退时向液压缸供油,由表7可见,快退时液压缸的工作压力为p1=1.43MPa,比快进时大。考虑到快退时进油不通过调速阀,故其进油路压力损失比前者小,现取进油路上的总压力损失p=0.3MPa,则大流量泵的最高工作压力估算为()MPa70.1MPa3.043.112p=+=D+ppp (2) 计算液压泵的流量由表7可知,油源向液压缸输入的最大流量为0.4510-3 m3/s ,若取回路泄漏系数K=1.1,则两个泵的总流量为L/min33/sm1055.0/sm1045.01.133331p= =-Kqq考虑到溢流阀的最小稳定流量为3L/min,工进时的流量为0.7910-5 m3/s =0.47L/min,则小流量泵的流量最少应为3.47L/min。(3) 确定液压泵的规格和电动机功率根据以上压力和流量数值查阅产品样本,并考虑液压泵存在容积损失,最后确定选取PV2R12-6/33型双联叶片泵。其小流量泵和大流量泵的排量分别为6mL/r和33mL/r,当液压泵的转速np=940r/min时,其理论流量分别为5.6 L/min和31L/min,若取液压泵容积效率v=0.9,则液压泵的实际输出流量为由于液压缸在快退时输入功率最大,若取液压泵总效率p=0.8,这时液压泵的驱动电动机功率为KW17.1KW108.06010331070.1336ppp=-hqpP根据此数值查阅产品样本,选用规格相近的Y100L6型电动机,其额定功率为1.5KW,额定转速为940r/min。2确定其它元件及辅件(1) 确定阀类元件及辅件根据系统的最高工作压力和通过各阀类元件及辅件的实际流量,查阅产品样本,选出的阀类元件和辅件规格如表8所列。其中,溢流阀9按小流量泵的额定流量选取,调速阀4选用Q6B型,其最小稳定流量为0.03 L/min,小于本系统工进时的流量0.47L/min。表8液压元件规格及型号序号元件名称通过的最大流量q/L/min规格型号额定流量qn/L/min额定压力Pn/MPa额定压降Pn/MPa1双联叶片泵PV2R12-6/335.1/27.9*162三位五通电液换向阀7035DY100BY1006.30.33行程阀62.322C100BH1006.30.34调速阀1Q6B66.35单向阀70I100B1006.30.26单向阀29.3I100B1006.30.27液控顺序阀28.1XY63B636.30.38背压阀1B10B106.39溢流阀5.1Y10B106.310单向阀27.9I100B1006.30.211滤油器36.6XU80200806.30.0212压力表开关K6B13单向阀70I100B1006.30.214压力继电器PFB8L14*注:此为电动机额定转速为940r/min时的流量。(2) 确定油管在选定了液压泵后,液压缸在实际快进、工进和快退运动阶段的运动速度、时间以及进入和流出液压缸的流量,与原定数值不同,重新计算的结果如表9所列。表9各工况实际运动速度、时间和流量快进工进快退L/min24.0L/min957.445.01212=*=AAqqm/s10824.0m/s1095601047.0343 112-3-35=Aqus38.1s109.01015031=-ts1.34s1088.01030332=-ts46.1s123.01018033=-t表10允许流速推荐值管道推荐流速/(m/s)吸油管道0. 51.5,一般取1以下压油管道36,压力高,管道短,粘度小取大值回油管道1. 53 由表9可以看出,液压缸在各阶段的实际运动速度符合设计要求。根据表9数值,按表10推荐的管道内允许速度取=4 m/s,由式计算得与液压缸无杆腔和有杆腔相连的油管内径分别为为了统一规格,按产品样本选取所有管子均为内径20mm、外径28mm的10号冷拔钢管。(3) 确定油箱油箱的容量按式估算,其中为经验系数,低压系统,=24;中压系统,=57;高压系统,=612。现取=6,得五 液压缸设计基础5.1液压缸的轴向尺寸液压缸轴向长度取决于负载运行的有效长度(活塞在缸筒内能够移动的极限距离)、导向套长度、活塞宽度、缸底、缸盖联结形式及其固定安装形式。图示出了液压缸各主要零件轴向尺寸之间的关系。活塞宽度。活塞有效行程取决于主机运动机构的最大行程,m18.03.0015.01= +=L。导向套滑动面长度C的取值:当,。导向长度,缸筒长度。5.2主要零件强度校核5.2.1缸筒壁厚=4因为方案是低压系统,校核公式,式中: -缸筒壁厚()-实验压力 ,其中是液压缸的额定工作压力D-缸筒内径 mD11.0= -缸筒材料的许用应力。,为材料抗拉强度(MPa),n为安全系数,取n=5。对于P116MPa.材料选45号调质钢,对于低压系统因此满足要求。5.2.2缸底厚度1=11对于平缸底,厚度 有两种算法1.缸底有孔时:其中2.缸底无孔时,用于液压缸快进和快退;其中5.2.3杆径d ,式中F是杆承受的负载(N)F=34444.4N 是杆材料的许用应力,=1005.2.4缸盖和缸筒联接螺栓的底径d1式中 K-拧紧系数,一般取K=1.251.5; F-缸筒承受的最大负载(N); z-螺栓个数; -螺栓材料的许用应力, ,为螺栓材料的屈服点(MPa),安全系数n=1.22.5 5.2.5液压缸稳定性计算液压缸承受的负载F超过某临界值时将会失去稳定性。稳定性可用下式校核:式中 nc- 稳定性安全系数 ,-4,取nc=3;由于缸筒固定活塞动,由杆材料知硬钢,因此 式中 l-安装长度(m); Rc-活塞杆横截面的最小回转半径(m); -材料柔性系数,取=115; -液压缸支承末端系数,取=; E-活塞杆材料的弹性模量,可取E=; J-活塞杆横截面惯性矩,对于实心杆;对于空心杆,D为杆的外径,d为杆的内径;-材料强度决定的试验值,=; A-活塞杆横截面积; -系数,取=; 因此满足稳定性要求。5.2.6液压缸缓冲压力液压缸设置缓冲压力装置时要计算缓缓从压力,当值超过缸筒、缸底强度计算的时,则以取代。在缓冲时,缓冲腔的机械能力为,活塞运动的机械能为。活塞在机械能守恒中运行至终点。 式中: 通过验算,液压缸强度和稳定性足以满足要求。六、验算液压系统性能1验算系统压力损失由于系统管路布置尚未确定,所以只能估算系统压力损失。估算时,首先确定管道内液体的流动状态,然后计算各种工况下总的压力损失。现取进、回油管道长为l=2m,油液的运动粘度取=110-4m2/s,油液的密度取r=0.9174103kg/m3。(1) 判断流动状态在快进、工进和快退三种工况下,进、回油管路中所通过的流量以快退时回油流量q2=70L/min为最大,此时,油液流动的雷诺数也为最大。因为最大的雷诺数小于临界雷诺数(2000),故可推出:各工况下的进、回油路中的油液的流动状态全为层流。(2) 计算系统压力损失将层流流动状态沿程阻力系数和油液在管道内流速同时代入沿程压力损失计算公式,并将已知数据代入后,得可见,沿程压力损失的大小与流量成正比,这是由层流流动所决定的。在管道结构尚未确定的情况下,管道的局部压力损失p常按下式作经验计算各工况下的阀类元件的局部压力损失可根据下式计算其中的Dpn由产品样本查出,qn和q数值由表8和表9列出。滑台在快进、工进和快退工况下的压力损失计算如下:1快进滑台快进时,液压缸通过电液换向阀差动连接。在进油路上,油液通过单向阀10、电液换向阀2,然后与液压缸有杆腔的回油汇合通过行程阀3进入无杆腔。在进油路上,压力损失分别为在回油路上,压力损失分别为将回油路上的压力损失折算到进油路上去,便得出差动快速运动时的总的压力损失2工进滑台工进时,在进油路上,油液通过电液换向阀2、调速阀4进入液压缸无杆腔,在调速阀4处的压力损失为0.5MPa。在回油路上,油液通过电液换向阀2、背压阀8和大流量泵的卸荷油液一起经液控顺序阀7返回油箱,在背压阀8处的压力损失为0.6MPa。若忽略管路的沿程压力损失和局部压力损失,则在进油路上总的压力损失为此值略小于估计值。在回油路上总的压力损失为该值即为液压缸的回油腔压力p2=0.66MPa,可见此值与初算时参考表4选取的背压值基本相符。按表7的公式重新计算液压缸的工作压力为此略高于表7数值。考虑到压力继电器的可靠动作要求压差Dpe=0.5MPa,则小流量泵的工作压力为此值与估算值基本相符,是调整溢流阀10的调整压力的主要参考数据。3快退滑台快退时,在进油路上,油液通过单向阀10、电液换向阀2进入液压缸有杆腔。在回油路上,油液通过单向阀5、电液换向阀2和单向阀13返回油箱。在进油路上总的压力损失为此值远小于估计值,因此液压泵的驱动电动机的功率是足够的。在回油路上总的压力损失为此值与表7的数值基本相符,故不必重算。大流量泵的工作压力为此值是调整液控顺序阀7的调整压力的主要参考数据。2验算系统发热与温升由于工进在整个工作循环中占96%,所以系统的发热与温升可按工进工况来计算。在工进时,大流量泵经液控顺序阀7卸荷,其出口压力即为油液通过液控顺序阀的压力损失液压系统的总输入功率即为液压泵的输入功率W4.564W8.060109.27100588.060101.51099.43636p2p2p1p1pr=+=+=-hqpqpP液压系统输出的有效功率即为液压缸输出的有效功率由此可计算出系统的发热功率为按式计算工进时系统中的油液温升,即C其中传热系数K=15 W/(m2C)。设环境温T2=25C,则热平衡温度为C 油温在允许范围内,油箱散热面积符合要求,不必设置冷却器。六、设计小结课程设计是机械设计当中的非常重要的一环,本次课程设计时间一周略显得仓促一些。但是通过本次每天都过得很充实的课程设计,从中得到的收获还是非常多的。 这次课程设计,由于理论知识的不足,再加上平时没有什么设计经验,一开始的时候有些手忙脚乱,不知从何入手。在老师的谆谆教导,和同学们的热情帮助下,使我找到了信心。现在想想其实课程设计当中的每一天都是很累的,其实正向老师说得一样,机械设计的课程设计没有那么简单,你想copy或者你想自己胡乱蒙两个数据上去来骗骗老师都不行,因为你的每一个数据都要从机械设计书上或者机械设计手册上找到出处。虽然种种困难我都已经克服,但是还是难免我有些疏忽和遗漏的地方。完美总是可望而不可求的,不在同一个地方跌倒两次才是最重要的。抱着这个心理我一步步走了过来,最终完成了我的任务。Fundamentals of Machine Tools In many cases products from the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications.To meet such precise tolerance the removal of small amounts of material is needed.Usually machine tools are used for such operation. In the United States material removal is a big businessin excess of 36109 per year,including material,labor,overhead,and machine-tools shipments,is spent.Since 60 percent of the machanical and industrial engineering and technology graduate have something connection with the machining industry either through sale,design,or operation of machine shops,or working in related industry,it is wise for an engineering student to devote some time in his curriculum to studying material removal and machine tools. A machine tool provide the means for cutting tools to shape a workpiece to required dimensions;the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members,which are as follows: (a)Bed,Structure or Frame.This is the main member which provides a basis for,and a connection between,the spindles and slides;the distorion and vibration under load must be kept to a minimum. (b)Slides and Slideways.The translation of a machine element(e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surface(the slideways). (c)Spindles and Bearings.Angular displacement take place about an axis of rotation;the position of this axis must be constant within extremely fine limits in machine tools,and is ensured by the provision of precision spindles and bearings. (d)Power Unit.The electric motor is the universally adopted power unit for machine tools.By suitably positioning individual motors,belt and gear transmissions and reduced to a minimum. (e)Transmission Linkage.Linkage is the general term used to denote the mechanical,hydraulic,pneumatic or electric mechanisms which connect angular and linear displacements in defined relationship. There are two broad divisions of machining operations:(a)Roughing,for which the metal removal rate,and consequently the cutting force,is high,but the required dimensional accuracy relatively low.(b)Finishing,for which the metal removal rate,and consequently the cutting force,is low,but the required dimensional accuracy and surface finish relatively high.It follows that static loads and dynamic loads,such as result from an unbalanced grindingwheel,are rmore significant in finishing operations than in roughing operations.The degree of precision achieved in any machining process will usually be influenced by the magnitude of the deflections,which occur as a result of the force acting.Machine tool frames are generally made in cast iron,although some may be steel casting or mild-steel fabrications.Cast iron is chosen because of its cheapness,rigidity,compressive strength and capacity for damping the vibrations set-up in machine operations.To avoid massive sections in castings,carefully designed systems of ribbing are used to offer the maximum resistance to bending and torsional stresses.Two basic types of ribbing are box and diagonal.The box formation is convenient to produce,apertures in walls permitting the positioning and extraction of cores.Diagonal ribbing provides greater torsional stiffness and yet permits swarf to fall between the sections;it is frequently used for lathe beds.The slides and slideways of a machine tool locate and guide members which move relative to each other,usually changing the position of the tool relative to the workpiece.The movement genenally takes the forms of translation in a straight line,but is sometimes angulai rotation,e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding with the helix angle of the workpiece thread.The basic geometric elements of slides are flat,vee,dovetail and cylinder.These elements may be used separately or combined in various ways according to the applications.Features of slideways are as follows:(a)Accuracy of Movement.Where a slide is to be displaced in a straight line,this line must lie in two mutually perpendicular planes and there must be no slide rotation.The general tolerance for straightness of machine tool slideways is 00.02mm per 1000mm;on horizontal surfaces this tolerance may be disposed so that a convex surface results,thus countering the effect of “sag”of the slideway.(b)Means of Adjustment.To facilitate assembly,maintain accuracy and eliminate “play” between slideing members after wear has taken place,a strip is something inserted in the slides.This is called a gib-strip.Usually,the grib is retained by socket-head screw passing through elongated slots;and is adjusted by grub-screws secured by lock nuts.(c)Lubrication.Slideways may be lubricated by either of the following systems:1)Intermittently through grease or oil nipples,a method suitable where movements are infrequent and speed low.2)Continuously,e.g. by pumping through a metering value and pipe-work to the point of application;the film of oil introduced between surfaces by these means must be extremely thin to avoid the slide “floating”.If sliding surfaces were optically flat oil would be squeezed out,resulting in the surfaces sticking.Hence in practice slide surfaces are either ground using the edge of a cup wheel,or scraped.Both processes produce minute surface depresssions,which retain “pocket” of oil,and complete separation of the parts may not occur at all points;positive location of the slides is thus retained.(d)Protection.To maintain slideways in good order,the following conditions must be met:1)Ingress of foreign matter,e.g. swarf,must be prevented.Where this is no possible,it is desirable to have a form of slideway,which does not retain swarf,e.g. the inverted vee.2)Lubricating oil must be retained.The adhensive property of oil for use on vertical or inclined slide surface is important;oils are available which have been specially developed for this purpose.The adhesiveness of oil also prevents it being washed away by cutting fluids.3)Accidental damage must be prevented by protective guards.A machine tool performs three major functions:1)it rigidly supports the workpiece or its holder and the cutting tool; 2)it provides relative motion between the workpiece and the cutting tool; 3)it provides a range of feeds and speeds.Machines used to remove metal in the form of chips are classified in four general groups:those using single-point tools,those using multipoint tools,those using random-point tools(abrasive),and those that considered special.Machines using basically the single-point cutting tools include:1)engine lathes, 2)turret lathes , 3)tracing and duplicating lathes, 4)single-spindle automatic lathes, 5)multi-single automatic lathes , 6)shapers and planers, 7)boring machines.Machines using multipoint cutting tools include:1)drilling machines, 2)milling machines, 3)broaching machines, 4)sawing machines, 5)gear-cutting machines.Machines using random-point cutting tools include:1)cylindrical grinder, 2)centreless grinders, 3)surface grinders.Special metal removal methods include:1)chemical milling, 2)electrical discharge machining, 3)ultrasonic machining.The lathe removes material by rotating the workpiece against a cutter to produce external or internal cylindrical or conical surfaces.It is also commonly used for the production of flat surfaces by faing,in which the workpiece is rotated while the cutting tool is moved perpendicularly to the axis of rotation.The engine lathe is the basic turning machine from which other turning machines have been developed.The drive motor is located in the base and drives the spindle through a combination of belts and gears,which provides the spindle speeds from 25 to 1500 rpm.The spindle is a sturdy hollow shaft,mounted between heavy-duty bearings,with the forward end used for mounting a drive plate to impart positive motion to the workpiece.The drive plate may be fastened to the spindle by threads,by a cam lock mechanism,or by a thread collar and key.The lathe bed is cast iron and provides accurately ground sliding surfaces(way)on which the carriage rides.The lathe carriage is a H-shaped casting on which the cutting tool is mounted in a tool holder.The apron hangs from the front of the carriage and contains the driving gears that move the tool and carriage along or across the way to provide the desired tool motion.A compound rest,located above the carriage provides for rotation of the tool holder through any desired angle.A hand wheel and feed screw are provided with a hand wheel and feed screw for moving the compound rest perpendicular to the lathe way.A gear train in the apron provides power feed for the carriage both along and across the way.The feed box contains gears to impart motion to the carriage and control the rate at which the tool moves relative to the workpiece.On a typical lathe feeds range from 0.002 to 0.160 in. per revolution of the spindle,in about 50 steps.Since the transmission in the feed box is driven from the spindle gears,the feeds are directly related to the spindle speed.The feed box gearing is also used in thread cutting and provides from 4 to 224 threads per in.The connecting shaft between the feed box and the lathe apron are the feed rod and the lead screw.Many lathe manufacturers combine these two rods in one,a practice that reduces the cost of the machine at the expense of accuracy.The feed rod is used to provide tool motion essential for accurate workpiece and good surface finishes.The lead screw is used to provide the accurate lead necessary for the thread cutting.The feed rod is driven through a friction clutch that allows slippage in case the tool is overloaded.This safety device is not provided in the lead screw,since thread cutting cannot tolerate slippage.Since the full depth of the thread is seldom cut in one pass,a chasing dial is provided to realign the tool for subsequent passes.The lathe tailtock is fitted with an accurate spindle that has a tapered hole for mounting drills,drill chucks,reamers,and lathe centers.The tailstock can be moved along the lathe ways to accommodate various lengths of workpieces as well as to advance a tool into contact with the worpiece.The tailstock can be offset relative to the lathe ways to cut tapers or conical surfaces.The turret lathe is basically an engine lathe with certain additional features to provide for semiautomatic operation and to reduce the opportunity for human error.The carriage of the turret lathe is provided with T-slots for mounting a tool-holding device on both sides of the lathe ways with tools properly set for cutting when rotated into position.The carriage is also equipped with automatic stops that control the tool travel and provide good reproduction of cuts.The tailstock of the turret lathe is of hexagonal design,in which six tools can be mounted.Althogh a large amount of time is consumed in setting up the tools and stops for operation,the turret lathe,once set,can continue to duplicate operations with a minimum of operator skill until the tools become dulled and need replacing.Thus,the turret lathe is economically feasible only for production work,where the amount of time necessary to prepare the machine for operation is justifiable in terms of the number of part to be made.Tracing and duplicating lathes are equipped with a duplicating device to automatically control the longitudinal and cross feed motions of the single-point cutting tool and provide a finished part of required shape and size in one or two passes of the tools.The single-spindle automatic lathe uses a vertical turret as well as two cross slids.The work is fed through the machine spindle into the chuck,and the tools are operated automatically by cams.The multispindle automatic lathe is provided with four,five,six,or eight spindles,with one workpiece mounted in each spindle.The spindles index around a central shaft,with the main tools slide accessible to all spindles.Each spindle position is provided with a side tool-slide operated independently.Since all of the slides are operated by cams,the preparation of this machine may take several days,and a production run of at least 5000 parts is needed to justify its use.The principal advantage of this machine is that all tools work simultaneously,and one operator can handle several machines.For relatively simple parts,multispindle automatic lathes can turn out finished products at the rate of 1 every 5 sec.A shapers utilizes a single-point tool in a tool holder mounted on the end of the ram.Cutting is generally done on the forward stroke.The tool is lifted slightly by the clapper box to prevent excessive drag across the work,which is fed under the tool during the return stroke in preparation for the next cut.The column house the operating mechanisms of the shaper and also serves as a mounting unit for the work-supporting table.The table can be moved in two directions mutually perpendicular to the ram.The tool slide is used to control the depth of the cut and is manually fed.It can be rotated through 90 deg. On either side of its normal vertical position,which allows feeding the tool at an angle to the surface of the table.Two types of the driving mechanisms for shapers are a modified Whitworth quick-return mechanism and a hydraulic drive.For the Whitworth mechanism,the motor drives the bull gear,which drives a crank arm with an adjustable crank pin to control the length of the stroke.As the bull gear rotates,the rocker arm is forced to reciprocate,imparting this motion to the shaper ram.The motor on a hydraulic shaper is used only to drive the hydraulic pump.The remainder of the shaper motions are controlled by the direction of the flow of the hydraulic oil.The cutting stroke of the mechanically driven shaper uses 220 deg. of rotation of the bull gear,while the return stroke uses 140 deg.This gives a cutting stroke to return stroke ratio of 1.6 to 1.The velocity diagram shows that the velocity of the tool during the cutting stroke is never constant,while the velocity diagram for a hydraulic shaper shows that for most of the cutting stroke the cutting speed is constant.The hydraulic shaper has an added advantage of infinitely variable cutting speeds.The principal disadvantage of this type of machine is the lack of a definite limit at the end of the ram stroke,which may allow a few thousandths of an inch variation in stroke length.A duplicating device that makes possible the reproduction of contours from a sheet-metal template is available.The sheet metal template is used in conjunction with hydraulic control.Upright drilling machines or drill presses are available in a variety of sizes and types,and are equipped with a sufficient range of spindle speeds and automatic feeds to fit the needs of most industries.Speed ranges on a typical machine are from 76 to 2025 rpm.,with drill feed from 0.002 to 0.20 in. per revolution of the spindle.Radial drilling machines are used to drill workpieces that are too large or cumbersome to conveniently move.The spindle with the speed and feed changing mechanism is mounted on the radial arm;by combing the movement of the radial arm around column and the movement of the spindle assembly along the arm,it is possible to align the spindle and the drill to any position within reach of the machine.For work that is too large to conveniently support on the base,the spindle assembly can be swung out over the floor and the workpiece set on the floor beside the machine.Plain radial drilling machine provide only for vertical movement of the spindle;universal machines allow the spindle to swive about an axis normal to the radial arm and the radial arm to rotate about a horizontal axis,thus permitting drilling at any angle.A mutispindle drilling machine has one or more heads that drive the spindles through universal joints and telescoping splined shafts.All spindles are usually driven by the same motor and fed simultaneously to drill the desired number of holes.In most machines each spindle is held in an adjustable plate so that it can be moved relative to the others.The area covered by adjacent spindles overlap so that the machine can be set to drill holes at any location within its range.The milling operation involves metal removal with a rotating cutter.It includes removal of metal from the surface of a workspiece,enlarging holes,and form cutting,such as threads and gear teeth.Within an knee and column type of milling machine the column is the main supporting member for the other components,and includes the base cotaining the drive motor,the spindle,and the cutter.The cutter is mounted on an arbor held in the spindle,and supported on its outer extremity by a bearing in the overarm.The knee is held on the column in dovetail slots,the saddle is fastened to the knee in dovetail slots,and the table is attached to the saddle.Thus,the build-up of the knee and column machine provide three motions relative to the cutter.A four motion may be provided by swiveling the table around a vertical axis provided on the saddle.Fixed-bed milling machines are designed to provide more rigidity than the knee and column type.The table is mounted directly on the machine base,which provides the rigidity necessary for absorbing heavy cutting load,and allows only longitudinal motion to the table.Vertical motion is obtained by moving the entire cutting head.Tracer milling is characterized by coordinated or synchronized movements of either the paths of the cutter and tracing elements,or the paths of the workpiece and model.In a typical tracer mill the tracing finger follow the shape of the master pattern,and the cutter heads duplicate the tracer motion.6
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