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5.1 Introduction
Conventional machining is the group of machining operations that use single- or multi-point tools to remove material in the form of chips. Metal cutting involves removing metal through machining operations. Machining traditionally takes place on lathes, drill presses, and milling machines with the use of various cutting tools. Most machining has very low set-up cost compared with forming, molding, and casting processes. However, machining is much more expensive for high volumes. Machining is necessary where tight tolerances on dimensions and finishes are required. 5.1 译文
传统机械加工是一组利用单刃或者多刃刀具以切屑形式去除材料的加工方式。金属切削意味着通过机械加工去除金属。传统的机械加工都是利用不同的刀具在车床、钻床和铣床上进行的。与成型加工、锻压和铸造工艺相比，大多数机械加工的生产准备成本都较低，然而如果是大批量生产，其成本要高得多。当对零件的尺寸公差和光洁度要求较高时，机械加工是很有必要的。 5.2 Turning and Lathe
Turning is one of the most common of metal cutting operations. In turning, a workpiece is rotated about its axis as single-point cutting tools are fed into it, shearing away excess material and creating the desired cylindrical surface. Turning can occur on both external and internal surfaces to produce an axially-symmetrical contoured part. Parts ranging from pocket watch components to large diameter marine propeller shafts can be turned on a lathe.
Apart from turning, several other operations can also be performed on lathe.
axially ['?ksi?li] adv.轴向地 symmetrical [si'metrik?l] a. 对称的
cylindrical [si'lindrikl] a.圆柱形的 contoured ['k?ntu?d] a.显示轮廓的，与某种形体轮廓相吻合的 译文:
在金属切削加工操作中，车削是最常见的一种。在车削过程中，工件绕其轴线回转，单刃车刀沿工件进给，切除掉多余的材料，最后形成要求的圆柱形表面。车削可以加工外面和内表面以形成具有轴对称的成形工件。从怀表的零件到大直径的船用螺旋桨轴都可以在车床上加工。
除了车削，还有另外几种加工操作都可以在车床上进行。
Boring and internal turning. Boring and internal turning are performed on the internal surfaces by a boring bar or suitable internal cutting tools. If the initial workpiece is solid, a drilling operation must be performed first. The drilling tool is held in the tailstock, and the latter is then fed against the workpiece. When boring is done in a lathe, the work usually is held in a chuck or on a face plate. Holes may be bored straight, tapered, or to irregular contours. Boring is essentially internal turning while feeding the tool parallel to the rotation axis of the workpiece. 译文:
利用镗杆或合适的内圆车刀可以进行镗削和车内圆。如果工件毛坯是实心的，首先要钻孔。钻头安装在尾架上，后者向工件进给。如果在车床上进行镗削加工，工件通常装夹在卡盘或者花盘上。镗出的孔可以是直孔、锥孔或者不规则轮廓。当将刀具沿工件的回转轴线平行进给时，镗削实际上就是车内圆。
Facing. Facing is the producing of a flat surface as the result of a tool’s being fed across the end of the rotating workpiece. Unless the work is held on a mandrel, if both ends of the work are to be
faced, it must be turned around after the first end is completed and then the facing operation repeated. The cutting speed should be determined from the largest diameter of the surface to be faced.
Facing may be done either from the outside inward or from the center outward. In either case, the point of the tool must be set exactly at the height of center of rotation.
Because the cutting force tends to push the tool away from the work, it is usually desirable to clamp the carriage to the lathe bed during each facing cut to prevent it from moving slightly and thus producing a surface that is not flat. In the facing of casting or other materials that have a hard surface, the depth of the first cut should be sufficient to penetrate the hard material to avoid excessive tool wear.
mandrel ['m?ndr?l] n.车床心轴 clamp [kl?mp] v. 夹紧，夹住
carriage [‘k?rid?] n.大刀架，拖板 penetrate ['penitreit] v. 穿透，渗透 tool wear 刀具磨损 译文:
车端面可以加工出一个平面，它是当车刀沿回转工件的端面横向进给的结果。除非工件固定在心轴上，如果工件两端都要车端面，必须将一端加工完成后，将工件调头，重复进行车端面加工。车削速度必须由所加工表面的最大直径来决定。车端面可以由外向内也可以由中心向外进行。无论哪种情况，刀尖必须准确地与回转中心对正。由于切削力有将车刀推离工件的趋势，通常最可行的就是在车端面时将拖板卡紧在床身上以避免车刀轻微移动造成加工表面不平整。在对具有硬质表面的铸件或其他材料进行车端面加工时，首次切深要足以穿透硬质材料从而避免过度的刀具磨损。
Parting. Parting is the operation by which one section of a workpiece is severed from the remainder by means of cutoff tool. Because cutting tools are quite thin and must have considerable overhang, this process is less accurate and more difficult. The tool should be set exactly at the height of axis of rotation, be kept sharp, have proper clearance angles, and be fed into the workpiece at a proper and uniform feed rate.
remainder [ri'meind?]剩余物 ，余数 overhang ['?uv?'h??] vt.悬于...之上 n.伸出;突出 uniform ['ju:nif?:m] a.相同的,一致的 n.制服;军服 clearance angles 后角 译文:
切断是一种利用切断刀（割刀）将工件的一部分与其剩余部分脱离的加工方法。由于切断刀非常薄而且处于悬臂状态，因此这种加工方法不太精确而且加工起来常常比较困难。切断刀必须准确地对正回转轴，保持锋利，具有合适的后角，以合适、不变的进给率沿工件进给。
Threading. Threading can be considered as turning since the path to be travelled by the cutting tool is helical. However, there are some major differences between turning and threading. While in turning, the interest is in generating a smooth cylindrical surface, in threading the interest is in cutting a helical thread of a given form and depth which can be calculated from the formulae. 译文:
车螺纹可以看作是车削，只是车刀所形成的加工轨迹是螺旋线。但二者也存在一些不同之处。车削主要考虑能否生成光滑的圆柱形表面，而车螺纹注重的是能否切出具有按公式计算出来的规定形状和深度的螺旋线。
There are two basic requirements for thread cutting.
? An accurately shaped and properly mounted tool is needed because thread cutting is a
form-cutting operation. The resulting thread profile is determined by the shape of the tool and its position relative to the workpiece.
? The second by requirement is that the tool must move longitudinally in a specific relationship to the rotation of workpiece, because this determines the lead of the thread. This requirement is met through the use of the lead screw and the split unit, which provide positive motion of carriage relative to the rotation of spindle
form-cutting operation 成形加工 longitudinally [l?:?d?i'tju:din?li] adv.纵向 lead screw 丝杠 split unit 开合机构 译文:
车螺纹有两个基本要求：首先，由于车螺纹是一种成形加工，因此车刀必须具有准确的形状而且要安装合适。所切出的螺纹外形是由车刀形状和它与工件的相对位置决定的。其次，车刀的纵向进给与工件的回转运动具有特定的关系，因此这决定了螺纹的导程。这个条件可以通过采用丝杠和开合机构得到满足，它们可以实现拖板相对于主轴回转运动的精确可靠的运动
1. Engine lathes 普通车床 2. Vertical lathes 立式车床 3. Turret lathes 转塔车床 5. Contouring lathes 仿形车床 6. Universal lathes 万能车床
Lathe bed is foundation of the engine lathe, which heavy, rugged casting is made to support the working parts of the lathe. The size and mass of the bed gives the rigidity necessary for accurate engineering tolerances required in manufacturing. On top of the bed are machined slideways that guide and align the carriage and tailstock, as they are move from one end of the lathe to the other. rugged adj. 健壮，坚固 mass n. 质量 slideways n.导轨 床身是普通车床的基础，它是由沉重而坚固的铸件制作而成的，其目的是为了支撑车床的工作部件。床身的尺寸和质量要使车床具有足够的刚性以保证制造过程中获得所需的工程公差。床身上的导轨可以引导和对准拖板和尾座，使它们可以从车床的一端移动到另一端。 ? Headstock is clamped atop the bed at left-hand end of the lathe and contains the motor that drives the spindle whose axis is parallel to the guideways through a series of gears housed within the gearbox. The function of gearbox is to generate a number of different spindle speeds. ? atop adv. 在(…)顶上 ? gearbox 齿轮箱
床头箱（主轴箱）紧固在床身上面的左端，内装有电机，它通过变速箱内的一组齿轮来驱动主轴转动，主轴的轴线平行于导轨。变速箱的功能是可以产生不同的主轴转速。
? A spindle gear is mounted on the rear of the spindle to transmit power through the change gears to the feeding box that distributes the power to the lead screw for threading or to the feed rod for turning.
? on the rear of 在…的尾部 ? change gears 挂轮 ? lead screw 丝杠 ? feed rod 光杠
主轴齿轮安装在主轴的尾部，通过挂轮把动力传递到进给箱，如果是车螺纹，进给箱将动力分配到丝杠上；如果是车削，就将动力分配到光杠上。
? The spindle has a through hole extending lengthwise through which bar stocks can be fed if continuous production is used. The hole can hold a plain lathe center by its tapered inner surface and mount a chuck, a face plate or collet by its threaded outer surface. ? taper n.坡度，锥形 v.锥度加工