Grinding and Turning.doc

Grinding and TurningGrinding and turning are two types of manufacturing process. They are commonly used in manufacturing. Grinding is considered to be a finishing process that is usually used for obtaining high-dimensional accuracy and better surface finish. Turning is often to be a rough process or finishing process sometimes, so turning is one of the most common manufacturing processes in manufacture.There are some comparisons between grinding and turning as follows:1. Process SystemGrind part: Grinding machines differ in construction as well as capabilities, and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground. So grinding machines can be simply classified as the cylindrical grinding machine and the surface grinding machine.Surface grinding machine usually has a planer-type reciprocating table on which the workpiece is held. The “tools” of grinding machine is abrasive wheel which simulates a milling cutter with an extremely large number of miniature cutting edges. When the machine works, the work table on which the workpiece is held moves reciprocally and the abrasive wheel rotates with the machine spindle.Cylindrical grinding machine holds the workpiece between centers. During the grinding operation, both workpiece and the grinding wheel rotate and longitudinal linear feed are applied to enable grinding of the whole length.Turn part: The turning machine is a machine tool used primarily for producing surfaces of revolution and flat edges. We commonly call turning machine as lathe. Based on their purpose, construction, number of tools that can simultaneously be mounted, and degree of automation, lathes or, more accurately, lathe-type machine tools can be classified as many type. In spite of that diversity of lathe-type machine tools, they all have common features with respect to construction and principle operation. These features can best be illustrated by considering the commonly used representative type, the engine lathe.There is a headstock in engine lathe. The spindle is driven through the gearbox, which is housed with in the headstock. The workpiece is often held in a chuck or a face plate and rotates with the spindle. The lathe tools are designed all kinds of shape and geometry depended on the purpose for which they are employed. Lathe tools motion includes axial feed and cross feed motion. Tools cut the workpiece by these two motions to complete the manufacturing process.2. Manufacturing Operations These two types of manufacturing process are often used to complete three frequently-used operationssurface, cylindrical, and internal operation. There are some features of the three operations as follows: Grind part: Surface grinding: There are two possible variations either a horizontal or vertical machine spindle can use to grind flat or plane surfaces. No matter what the grinding mode is, during the surface-grinding operations, heavy workpieces are held in fixtures or clamped by strap clamps on the machine table, however, small ones often held by magnetic chucks. When the workpiece is held stably and machine table moves reciprocally, the grinding wheel will move to feed. Cylindrical grinding: There are three cylindrical grinding methods to achieve different situations. One of cylindrical grinding method which is often used is transverse method. During the grinding operation, the workpiece is held between two plain centers and rotates slowly with axial moving reciprocally, the cross feed of the grinding wheel determines the depth of cut. Other two types method of cylindrical grinding are the plunge-cut method which grinding is achieved through the cross feed of the grinding wheel and no axial feed is applied and the full-depth method which is similar to the transverse method except that the grinding allowance is removed in a single pass. Internal grinding: This operation is employed for grinding relatively short holes. During the grinding operation, the movement state of workpiece is similar to one in cylindrical grinding except that its held in a chuck or a special fixture. The grinding wheel which is relatively small grinds internal surface of the hole. The depth of cut is also adjusted by the cross feed of the grind wheel. If the workpieces are too heavy to hold in chucks, in the case, the grinding wheel not only spins around its own but also rotates around the centerline of the hole that is being ground. There is another grinding methodcenterless grinding. In this grinding, the cylindrical workpiece is supported by a rest blade, between two wheelsthe grinding wheel and the regulating or feed wheel. This method can make cylindrical workpiece move automatically so that it can manufacture large number of workpieces in a short time. Turning part: Surface turning: This operation is also named facing. Facing operation is used to turn the whole end surface of the workpiece or an annular intermediate surface like a shoulder. During the facing operation, the workpiece is held in a chuck or on a face plate, and the cross slide of lathe tools provide the feed. Facing can move the tools from the periphery in ward or inside-out. Because the cutting force tends to push the tool away from the workpiece, during the facing operation, the carriage must be clamped. Cylindrical turning: Cylindrical turning is the most common of all lathe operations. During the cylindrical turning operation, the workpiece is held by chuck and rotates with the spindle. The axial feed of lathe tools is offered by the carriage, either manually or automatically, and the cross feed of tools depends on the depth of cut. Especially, during the rough process, the large depth of cut and small feeds should be used. Contrary to the former, finishing process needs smaller depth of cut and high cutting speed. Internal turning: Manufacturing the internal surface on the lathe need a boring bar suitable internal cutting tools. When the workpiece is held and rotates with spindle, the boring bar or internal cutting tools will get into the hole of workpiece and feed in axial direct to complete the operation. Besides the three turning method, there are other three methodsgroove cutting, taper turning, and thread cutting. Groove cutting is used to cut off and cut groove, so only cross feed of the tool is employed. As for taper turning, there are three methods to achieve the taper turning, but the principle is the same, that driving the tool in a direction that is not paralled to the lathe axis but inclined to it with an angle that is the same as the angle of the taper desired. Thread cutting must keep the axial feed at a constant speed so that we can obtain desired pitch of the thread, so the carriage must be droved by the lead screw. 3. Cutting Tools Grind part: The grinding wheel is a special tools used in grinding process. Grinding wheels are composed of abrasive grains in similar size and a binder. Every abrasive grain on the periphery surface is like a cutting tool. Because of the large number of “cutting tools”, grinding can be a finishing process. There are so many pores between the grains. these pores assist the easy flow of coolants to enable efficient and prompt removal of the heat generated during the grinding process. The grinding wheel are identified based on their shape an size, kind of abrasive, grain size, grade of the bond and structure. Shape and size are determined by the purpose for which they are to be used. Different kind of abrasive is used to grind different materials. Grain size of abrasive often determined the quality of ground surface obtained. The grade of the bond and the structure determined the resistance of pulling off the abrasive grains from the grinding wheel. Turn part: Because the turning has much kind of operations, different lathe tools have different shape and geometry for different manufacturing purpose. On the whole, the turning tools can be classified into external cutting tools and internal cutting tools. Turning tools have different nose radii for different manufacturing, such as small nose radii for rough process. Facing tools have different tools for left and right-hand-side surface. Cutoff tools are often used to cut off the workpiece and machine external annual grooves. There all kinds of thread-cutting tools, such as triangular, square, or trapezoidal cutting edges for different thread. Form tools have edges especially manufactured to take a certain form. Obviously, different form must use different form tools to manufacture. Grinding and turning are commonly used in manufacturing. Grinding is often used to complete finishing process. Usually, before the finishing process in grinding, turning usually completes the rough process, since turning can achieve many types of manufacture. In finishing process, grinding can achieve high accuracy in most of the surface and cylindrical manufacture. So we often combine the grinding and turning in a whole manufacturing process. If we can understand more knowledge of grinding and turning well, we can use them in manufacturing process more reasonably and efficiently.翻译：磨削与车削磨削和车削是两只机械加工的方法，它们广泛应用于机械生产中。磨削被认为是一种精加工方式，通常用来获得高尺寸精度和表面粗糙度要求较高的加工要求。车削常用于粗加工和半精加工中，有时也用于精加工，所以在机械加工生产中车削是应用最为广泛的机械加工方式之一。下面有一些关于磨削与车削特点的比较：1、 工艺系统磨削加工方面：磨床根据结构和功能的不同有所区别，使用何种型号的磨床主要取决于被加工工件的几何形状和物理性质。所以磨床可以大体上分为外圆磨床和平面磨床。平面磨床一般具有一个可装夹工件并可做刨床式往返运动的工作台。磨床的“刀具”砂轮类似于拥有大量微型刀刃的铣刀。当磨床工作是，夹持工件的工作台做直线往返运动，与此同时，砂轮随主轴高速旋转，对工件进给。在外圆磨床上加工的工件主要被夹持在两个顶尖之间，磨削加工的过程中，工件和砂轮都会旋转，工件沿轴向方向进给，使砂轮能在工件全长范围内加工。车削加工方面：车削机床是一种主要用来加工回转表面和平面的机床。我们通常简称车削机床为车床，基于它们的加工目的、机床结构、所能装夹的刀具数量、自动化程度以及加工精度的不同，车床可细分为很多种类。尽管车床种类繁多，但是它们在结构和工作原理上都有一些共同的特点，而最能集中表现这些特点的车床莫过于普通车床。在每一台普通车床左侧都有一个主轴箱，主轴的旋转正是由主轴箱中的齿轮组带动的。工件通常装夹在夹具或卡盘上并随主轴一起旋转。车削刀具根据其作用被设计成各种形状尺寸。车刀的运动包括轴向进给运动与横向进给运动，车刀正是通过这两种进给运动的复合来完成对工件的加工。2、 加工工艺以上两种机械加工方法都能用于完成三种常用的加工工艺平面加工、圆柱面加工和内表面加工。下面是三种加工工艺的部分特点：磨削加工方面：平面磨削：磨削平面或端面有两种可行方式立式主轴磨削和卧式主轴磨削。不论是立式或卧式，在平面磨削加工中，较重的工件都被夹具或压板固定在工作台上，而较小的工件一般用磁力吸盘固定在工作台上。当工件固定夹紧，工作台开始直线往返运动时，砂轮开始对工件进给。圆柱面磨削：为了完成不同要求的加工，一般有三种比较常用的圆柱面磨削方法。其中最常用的一种是横向磨削，磨削加工时，工件被固定在顶尖之间，工件在缓慢旋转的同时在轴线方向做往返运动，砂轮的横向进给决定背吃刀量。另外两种圆柱面磨削方法分别是切入式磨削和全深度磨削，切入式磨削只靠横向进给完成切削，而没有轴向进给。全深度磨削和横向磨削比较类似，只是整个磨削一次性完成，没有第二次进给。内表面磨削：这种加工工艺主要用来磨削较短的孔结构内表面。加工的工件装夹在卡盘或特殊夹具上，运动状态与圆柱面磨削的工件相同。用相对比较小的砂轮在孔内部进行磨削。其背吃刀量同样由砂轮的横向进给调节。如果工件太大而难以固定在夹具上，这种情况下砂轮除自转外还会绕工件孔的中心线旋转以完成磨削加工。除以上三种常用磨削工艺外，还有一种磨削工艺无心磨削，在这一工艺中，圆柱形工件支撑在长刀片上，并夹在两个轮之间砂轮和导轮或称为进给轮。这种加工方法可以使圆柱形工件自动进给以便于在短时间内加工大量的工件。车削加工方面：平面车削：平面车