毕业设计英文翻译(原文).doc

桂林电子科技大学毕业设计（论文）报告用纸 第31页 共 29页 编号： 毕业设计(论文)外文翻译（原文）学 院： 机电工程学院 专 业： 机械设计制造及其自动化 学生姓名： 赵盛伟 学 号： 0801120319 指导教师单位： 桂林航天工业学院 姓 名： 梁 伟 职 称： 高级工程师 2012 年 5 月 15 日CNC LATHELessons 1 Components of Modern CNC LathesThe CNC lathe is machine tool that can remove material from work-piece, which is clamped and rotated about an axis. This machine tool is used primarily for producing surfaces of revolution and flat edges. Of all metal cuttings, most is done with a sharp single-point cutting tool. Modern CNC lathes use turrets to hold cutting tools rigidly and move cutting tools accurately. The turret also has automatic tool-changing capability; it is used to quickly take an old tool out and a new tool into its cutting position. A front turret is built to move tools from below the spindle centerline up to the work. A rear turret, on the other hand, moves tools from above the spindle centerline down to the work. Therefore, machines equipped with front and rear turrets can execute cutting operations from above and below the work simultaneously.Lathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool.The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod.The bed is the backbone of a lathe. It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets, They are precision-machined to assure accuracy of alignment. On most modern lathes the way are surface-hardened to resist wear and abrasion, but precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed.The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmissionthrough which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle.The tailsticd assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location, An upper casting fits on the lower one and can be moved transversely upon it, on some type of keyed ways, to permit aligning the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76mm(2to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw.The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways, The second size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers.Engine lathes are the type most frequently used in manufacturing. They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mm(12 to 24 inches)swing and from 610 to 1219 mm(24 to 48 inches) center distances, but swings up to 1270 mm(50 inches) and center distances up to 3658mm(12 feet) are not uncommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes-with swings usually not over 330 mm (13 inches ) also are available in bench type, designed for the bed to be mounted on a bench on a bench or cabinet. Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the work piece, thy are not suitable for quantity production. Often the actual chip-production tine is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operators time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing. The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered.The engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic of single-point tooling for maximum metal removal, and the use of form tools for finish on a par with the fastest processing equipment on the scene today.Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Turret Lathes Production machining equipment must be evaluated now, more than ever before, this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turrets lathe, the designer should strive for a minimum of operations.Automatic Screw Machines Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important part in the economy of the parts machined on the automatic screw machine. Quantities less than on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities.Automatic Tracer Lathes Since surface roughness depends greatly on material turned, tooling , and feeds and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances.In some cases, tolerances of 0.05mm are held in continuous production using but one cut . groove width can be held to 0.125mm on some parts. Bores and single-point finishes can be held to 0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of 0.125mm is economical on both diameter and length of turn.The components of lathe are follows:1. Slant bed The lathe bed is the main frame of the machine, which supports all the components on ti as well as providing a path for chips as they fall. The bed of a CNC lathe is usually slanted to allow chips to fall away easily. Lathe bed is usually made of gray or nodular cast iron to damp vibrations and is made by casting. It has guide ways to allow the carriage to slide easily lengthwise. The height of the lathe should appropriate to technician to do its job easily and comfortably.2. HeadstockThe headstock is fixed at the left hand side of the lathe bed and contains the spindle and transmission gearing, which provides a number of different spindle speeds (some provide variable spindle speeds, which employ friction, electrical, or hydraulic drives). The spindle is driven though the transmission.The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmissionthrough which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.3. Chuck The main function of the chucks is connecting to the spindle and clamping the work.4. Carriage The main function of the carriage is moving the cutting tool to the revolving work. It contains the saddle, cross-slide, and apron.5. Tailstock The tailstock assembly mainly supports the right end of the work.6. MCU (machine Control Unit) It consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment. Simply, in fact, it is a computer used to store and process the CNC programs entered.7. Turret A variety of machining operations means that a variety of tools are required. The main function of the turret is holding the cutting tool and replaying an old tool with a new tool during a tool change.As we know, the important function of turret on a CNC lathe is to quickly change tools when required. Most of the time, several different cutting tools are used to produce a part. The tool must be replaced quickly for the next machining operation. For this reason, the majority of CNC machine tools are equipped with automatic tool changers, such as magazines on machining centers and turrets on turning lathe. They allow tool changing without the intervention of the operation. Typically, an automatic tool changer grips the tool in the spindle, pulls it out, and replaces it with another tool. On most machines with automatic tool changers, the turret can rotate in either direction, forward or reverse. Each tool position on the face of the turret is numbered for identifying the tool it holds. Tools can be mounted on the face of the turret as well as on its sides. Upon receiving a tool change command from the MCU, the turret moves to a safe tool change coordinates programmed for programmable tailstocks, the tailstock might first have to be moved back before a tool change is executed.Lesson 2 CNC Lathe Axes of Motion CNC equipment executes machining operations by performing some form of sliding liner and rotary motion. The actual method of movement is designed by the manufactured and can vary form machine to machine. For example, the table can move in the horizontal plane (X Y-axis motion) and the spindle in the vertical plane (Z- axis motion). Primary machine axes of movement should follow right-hand rule, i.e., spindle movement is primarily along the Z-axis, whereas movement into the work is along the Z axis and movement away form the work is along the +Z axis. The system will respond to a command to move the spindle along the +X or +Y axis by moving the table in the opposite direction, X or Y axis.When dealing with CNC lathes, we will only consider two basic machine motions in this text. The important axes in CNC lathe are the Z and X axes. The Z-axis expresses the direction along the spindle axis. Positive +Z represents the direction away from the spindle and work, and negative Z is the direction toward the spindle and into the work. The X-axis is along the way of the way of the cross-slide movements. Positive +X shows the direction away from the spindle centerline and negative X is motion toward the spindle centerline and into the work. Apart from Z and X axes, in some machines with programmable tailstocks, the W-axis is used to designate the movement of the tailstock. This is a third axis on these machines. More complex turning centers may also have a fourth axis.Lesson 3 Tools for CNC Lathe Operations Modern tool technology has produced cutters replaceable carbide inserts. Initial investment in those tools is somewhat high but they yield substantial long-term savings in term of job setup time and tool regrinding cost. Worn inserts are simply replaced with factory-ordered prefaced inserts. Tool inventory is reduced because the same tool can be used to cut different materials by switching to different materials by switching to a different insert grade.The higher-strength carbide inserts allow the tool to be driven into the hardest materials. However, higher machining forces demand substantial spindle horsepower, so sufficient machine rigidity is needed. The main disadvantages of using carbide inserts are their brittleness and their sensitivity to shock. If not used properly, it tends to chip or crack.The advantages of using carbide insert tools were discussed. These included cutting capabilities at higher speed (approximately two three times faster than for high speed steel cutters) as well as reduction in tool inventory and elimination of regrinding time and cost. An additional advantage for single-point tools is the fact that inserts are made with a precise tool nose radius for cutting. Thus, the location of the tool nose center for any tool can be accurately determined. This makes tool offset specifications and CNC programming a much easier job.1. Insert Material With regard to lathe operation there are four important types of materials used for inserts.(1) Cemented carbides Cemented carbides are formed by using tungsten carbide sintered in a cobalt matrix.(2) Coated carbides The wear resistance of cemented carbides can be improved by 200% to 500% by costing them with wear-resistant materials. Coating materials include titanium carbide and aluminum oxide (a ceramic). Coatings offer excellent performance on steels, cast iron, and nonferrous materials.(3) Ceramics A ceramic is a very hard material formed without metallic bonding. It displays exceptional resistance to wear and heat load. The most popular material for forming ceramics is aluminum oxide. Often an additive such as titanium oxide or titanium carbide is used. Hard materials can be machined at extremely high cutting speeds with relatively little loss in tool life. In addition, the surface finish is better than that finished with other cutting materials. The main disadvantage with ceramics is that they have low resistance to impact and shock. Thus, they can only be used in operations where impact loading is low.(4) DiamondsThere are two main types of diamond cutting materials. The first is single crystal natural diamonds shaving with outstanding wear resistance but low shock resistance. The other consists of smaller synthetic diamond crystals fused together at high temperature and pressure into a carbide substrate. This type of material displays good resistance to shock loading. Diamond tools offer substantial improvements over carbides. Better surface finish and higher cutting speeds with substantial improvements in tool life can be achieved.2. Insert Shape Inserts are available in various shapes and sizes. The shape determines the strength and the number of cutting edges. There are six basic shapes for turning operation：Circular inserts，hexagonal inserts，square inserts，parallelogram inserts, diamond inserts，and triangular insertsCircular inserts are the strongest, followed by hexagonal, square, parallelogram, diamond, and triangular. Because these tools are very rigid, a high degree of accuracy can be achieved with their use. More exact diameters can be milled when a center cutting carbide tool is used for boring. Milling time is also shorter with carbide cutters. Some important rules to be considered when selecting insert of tooling for lathe operations are:(1) Select the strongest insert shape possible.(2) Select the smallest practical insert size.(3) Select the largest tool nose radius possible.(4) Select the largest boring bar diameter having the smallest possible overhang.Lesson 4 Basic Lathe OperationThis text will consider the most basic lathe operation: facing, turning, grooving, parting, drill