CNC加工中刀具的选择与切削用量的确定

CNC加工中刀具的选择与切削用量的确定刀具的选择和切削用量的确定是数控加工工艺中的重要内容，它不仅影响数控机床的加工效率，而且直接影响加工质量。CAD/CAM技术的发展，使得在数控加工中直接利用CAD的设计数据成为可能，特别是微机与数控机床的联接，使得设计、工艺规划及编程的整个过程全部在计算机上完成，一般不需要输出专门的工艺文件。现在，许多CAD/CAM软件包都提供自动编程功能，这些软件一般是在编程界面中提示工艺规划的有关问题，比如，刀具选择、加工路径规划、切削用量设定等，编程人员只要设置了有关的参数，就可以自动生成NC程序并传输至数控机床完成加工。因此，数控加工中的刀具选择和切削用量确定是在人机交互状态下完成的，这与普通机床加工形成鲜明的对比，同时也要求编程人员必须掌握刀具选择和切削用量确定的基本原则，在编程时充分考虑数控加工的特点。本文对数控编程中必须面对的刀具选择和切削用量确定问题进行了探讨，给出了若干原则和建议，并对应该注意的问题进行了讨论。一、数控加工常用刀具的种类及特点数控加工刀具必须适应数控机床高速、高效和自动化程度高的特点，一般应包括通用刀具、通用连接刀柄及少量专用刀柄。刀柄要联接刀具并装在机床动力头上，因此已逐渐标准化和系列化。数控刀具的分类有多种方法。根据刀具结构可分为：整体式；镶嵌式，采用焊接或机夹式连接，机夹式又可分为不转位和可转位两种；特殊型式，如复合式刀具，减震式刀具等。根据制造刀具所用的材料可分为：高速钢刀具；硬质合金刀具；金刚石刀具；其它材料刀具，如立方氮化硼刀具，陶瓷刀具等。从切削工艺上可分为：车削刀具，分外圆、内孔、螺纹、切割刀具等多种；钻削刀具，包括钻头、铰刀、丝锥等；镗削刀具；铣削刀具等。为了适应数控机床对刀具耐用、稳定、易调、可换等的要求，近几年机夹式可转位刀具得到广泛的应用，在数量上达到整个数控刀具的30%40%，金属切除量占总数的80%90%。数控刀具与普通机床上所用的刀具相比，有许多不同的要求，主要有以下特点：刚性好（尤其是粗加工刀具），精度高，抗振及热变形小；互换性好，便于快速换刀；寿命高，切削性能稳定、可靠；刀具的尺寸便于调整，以减少换刀调整时间；刀具应能可靠地断屑或卷屑，以利于切屑的排除；系列化，标准化，以利于编程和刀具管理。二、数控加工刀具的选择刀具的选择是在数控编程的人机交互状态下进行的。应根据机床的加工能力、工件材料的性能、加工工序、切削用量以及其它相关因素正确选用刀具及刀柄。刀具选择总的原则是：安装调整方便，刚性好，耐用度和精度高。在满足加工要求的前提下，尽量选择较短的刀柄，以提高刀具加工的刚性。选取刀具时，要使刀具的尺寸与被加工工件的表面尺寸相适应。生产中，平面零件周边轮廓的加工，常采用立铣刀；铣削平面时，应选硬质合金刀片铣刀；加工凸台、凹槽时，选高速钢立铣刀；加工毛坯表面或粗加工孔时，可选取镶硬质合金刀片的玉米铣刀；对一些立体型面和变斜角轮廓外形的加工，常采用球头铣刀、环形铣刀、锥形铣刀和盘形铣刀。在进行自由曲面加工时，由于球头刀具的端部切削速度为零，因此，为保证加工精度，切削行距一般取得很能密，故球头常用于曲面的精加工。而平头刀具在表面加工质量和切削效率方面都优于球头刀，因此，只要在保证不过切的前提下，无论是曲面的粗加工还是精加工，都应优先选择平头刀。另外，刀具的耐用度和精度与刀具价格关系极大，必须引起注意的是，在大多数情况下，选择好的刀具虽然增加了刀具成本，但由此带来的加工质量和加工效率的提高，则可以使整个加工成本大大降低。在加工中心上，各种刀具分别装在刀库上，按程序规定随时进行选刀和换刀动作。因此必须采用标准刀柄，以便使钻、镗、扩、铣削等工序用的标准刀具，迅速、准确地装到机床主轴或刀库上去。编程人员应了解机床上所用刀柄的结构尺寸、调整方法以及调整范围，以便在编程时确定刀具的径向和轴向尺寸。目前我国的加工中心采用TSG工具系统，其刀柄有直柄（三种规格）和锥柄（四种规格）两种，共包括16种不同用途的刀柄。在经济型数控加工中，由于刀具的刃磨、测量和更换多为人工手动进行，占用辅助时间较长，因此，必须合理安排刀具的排列顺序。一般应遵循以下原则：尽量减少刀具数量；一把刀具装夹后，应完成其所能进行的所有加工部位；粗精加工的刀具应分开使用，即使是相同尺寸规格的刀具；先铣后钻；先进行曲面精加工，后进行二维轮廓精加工；在可能的情况下，应尽可能利用数控机床的自动换刀功能，以提高生产效率等。三、数控加工切削用量的确定合理选择切削用量的原则是，粗加工时，一般以提高生产率为主，但也应考虑经济性和加工成本；半精加工和精加工时，应在保证加工质量的前提下，兼顾切削效率、经济性和加工成本。具体数值应根据机床说明书、切削用量手册，并结合经验而定。切削深度t。在机床、工件和刀具刚度允许的情况下，t就等于加工余量，这是提高生产率的一个有效措施。为了保证零件的加工精度和表面粗糙度，一般应留一定的余量进行精加工。数控机床的精加工余量可略小于普通机床。切削宽度L。一般L与刀具直径d成正比，与切削深度成反比。经济型数控加工中，一般L的取值范围为：L=（0.60.9）d。(3)提高v也是提高生产率的一个措施，但v与刀具耐用度的关系比较密切。随着v的增大，刀具耐用度急剧下降，故v的选择主要取决于刀具耐用度。另外，切削速度与加工材料也有很大关系，例如用立铣刀铣削合金刚30CrNi2MoVA时，v可采用8m/min左右；而用同样的立铣刀铣削铝合金时，v可选200m/min以上。主轴转速n(r/min)。主轴转速一般根据切削速度v来选定。计算公式为：式中，d为刀具或工件直径（mm）。数控机床的控制面板上一般备有主轴转速修调（倍率）开关，可在加工过程中对主轴转速进行整倍数调整。进给速度vF 。vF应根据零件的加工精度和表面粗糙度要求以及刀具和工件材料来选择。vF的增加也可以提高生产效率。加工表面粗糙度要求低时，vF可选择得大些。在加工过程中，vF也可通过机床控制面板上的修调开关进行人工调整，但是最大进给速度要受到设备刚度和进给系统性能等的限制。随着数控机床在生产实际中的广泛应用，数控编程已经成为数控加工中的关键问题之一。在数控程序的编制过程中，要在人机交互状态下即时选择刀具和确定切削用量。因此，编程人员必须熟悉刀具的选择方法和切削用量的确定原则，从而保证零件的加工质量和加工效率，充分发挥数控机床的优点，提高企业的经济效益和生产水平。In CNC processing cutting tool choice and cutting specifications determinationThe cutting tool choice and the cutting specifications determination is in the numerical control processing craft important content, it not only influence numerical control engine bed processing efficiency, moreover affects the processing quality directly. CAD/The CAM technology development, enables in the numerical control processing to become directly using the CAD design data possibly, specially the microcomputer and the numerical control engine bed joint, causes the design, the craft plan and the programming entire process completes completely on the computer, does not need to output the special technological document generally.Now, many CAD/The CAM software package all provides the automatic programming function, these software are generally prompt the craft plan in the programming contact surface the related question, for instance, cutting tool choice, processing way plan, cutting specifications hypothesis and so on, programmers so long as have established the related parameter, may automatically produce completes the processing the NC procedure and the transmission to the numerical control engine bed. Therefore, in the numerical control processing cutting tool choice and the cutting specifications determination is completes under the man-machine interactive condition, this forms the sharp contrast with the ordinary engine bed processing, at the same time also requests the programmers to have to grasp the cutting tool choice and the cutting specifications determination basic principle, when programming full consideration numerical control processing characteristic. This article the cutting tool choice and the cutting specifications which must face to the numerical control programming in determined the question has carried on the discussion, has produced certain principles and the suggestion, and to the question which should pay attention has carried on the discussion.First, numerical control processing commonly used cutting tool type and characteristicThe numerical control processing cutting tool must adapt the numerical control engine bed high speed, is highly effective and the automatic high characteristic, should include the general cuttingtool, the general connection hilt and the few special-purpose hilts generally. The hilt must join the cutting tool and install on the engine bed power head, therefore already gradual standardization and seriation. The numerical control cutting tool classification has the many kinds of methods. May divide into according to the cutting tool structure: (1) Integral type; (2) The mosaic, uses the welding or machine clamps the type connection, machine clamps the type to be possible to divide into does not index and may index two kinds; (3) Special pattern, like compound expression cutting tool, absorption of shock type cutting tool and so on. According to makes the materialwhich the cutting tool uses to be possible to divide into: (1) High-speed steel cutting tool; (2) Hard alloy tools; (3) Diamond cutting tool; (4) Other material cutting tools, like cubic boron nitride cutting tool, ceramic cutting tool and so on. May divide into from the cutting craft: (1) The turning cutting tool, divides the outer annulus, in the hole, the thread, cuts the cutting tool many kinds of and so on; (2) Drills truncates the cutting tool, including drill bit, reamer, screw tap and so on; (3) Boring cutting tool; (4) Milling cutting tool and so on. In order to adapt the numerical control engine bed durably to the cutting tool, is stable, easy change, may trade and so on the request, in recent years machine clamps the type to be possible to index the cutting tool to obtain the widespread application, reaches higher authorities in the quantity to the entire numerical control cutting tool 30% 40%, the metal excision quantity accounts for the total 80% 90%.On the numerical control cutting tool and the ordinary engine bed uses the cutting tool compares below, some many different requests, mainly have the characteristic:(1) Rigidity good (in particular rough machining cutting tool), precision high, the vibration-proof and the thermal deformation are small; (2) Inter changeability is good, is advantageous for fast trades the knife; (3) Life high, the cutting value stable, is reliable; (4) Cutting tool size is advantageous for the adjustment, by reduces trades the knife time(5)Cutting tool ought to be able reliably to break the filings or the volume filings, by favors the scrap removing; (6) Seriation, the standardization, by favors the programming and the cutting tool management.Second, the numerical control processes the cutting tool the choiceThe cutting tool choice is carries on in under the numerical control programming man-machine interactive condition. Should according to the engine bed processing ability, the work piece material performance, the processing working procedure, the cutting specifications as well as other correlation factors correctly selects the cutting tool and the hilt. The cutting tool choice always principle is: Installment adjustment convenient, rigidity good, the abrasive resistance and the precision are high. In satisfies the processing request under the premise, chooses the short hilt as far as possible, by enhances the rigidity which the cutting tool processes.When selects the cutting tool, must cause the cutting tool the size with to process the work piece the superficial dimension to adapt. In the production, the plane components peripheral outline processing, often uses the end mill; When milling plane, elected hard alloy bit milling cutter; When processes raised Taiwan, the scoop channel, chooses the high-speed steel end mill; When processing semifinished materials surface or rough machining hole, may select inlays the hard alloy bit the corn milling cutter; And changes the drift angle outline contour to some three-dimensional profiles the processing, often uses a ball milling cutter, the ring-like milling cutter, the coned milling cutter and the disc cutter.When carries on the free curved surface processing, because the ball cutting tool nose cutting speed is a zero, therefore, for the guarantee processing precision, the cutting row spacing obtains generally very can be dense, therefore ball commonly used in curved surface precision work. But the flat head cutting tool all surpasses a ball knife in the face work quality and the cutting efficiency aspect, therefore, so long as under the premise which the guarantee only cuts, regardless of is the curved surface rough machining precision work, all should first choose the flat head knife. Moreover, the cutting tool abrasive resistance and the precision and the cutting tool price relations are enormous, must bring to the attention is, in the majority situation, the cutting tool which chooses although increased the cutting tool cost, but from this the processing quality and the processing efficiency enhancement which brings, then may cause the entire processing cost to reduce greatly. In the processing center, each kind of cutting tool installs separately in the knife storehouse, according to the procedure stipulated carries on as necessary chooses the knife and trades the knife movement. Therefore must use the standard hilt, in order to makes to drill, the boring, to expand the standard cutting tool which, working procedure and so on milling uses, is rapid, accurately installs to the engine bed main axle or the knife storehouse comes up. The programmers should understand on the engine bed uses the hilt the structure size, the adjustment method as well as the adjustment scope, in order to in programming time determines the cutting tool the radial direction and the axial size. At present our countrys processing center uses the TSG tool system, its hilt has the straight handle (three kind of specifications) and the bit holder (four kind of specifications) two kinds, altogether includes 16 kinds of different uses the hilts. In economy numerical control processing, because the cutting tool sharpens, surveys and replaces many manual carries on for the man-power, takes the non-cutting time to be long, therefore, must reasonably arrange the cutting tool the order of rank. Should follow the principle below generally: (1) Reduces the cutting tool quantity as far as possible; (2) After a cutting tool attire clamps, should complete all processing spot which its can carry on; (3) The thick precision work cutting tool should separate the use, even if is the same size specification cutting tool; (4) The mill drills after first; (5) The advanced good curved surface precision work, latter carries on the two-dimensional outline precision work; (6) In the possible situation, to be supposed automatically to trade the knife function as far as possible using the numerical control engine bed, by enhances the production efficiency and so on.Third, numerical control processing cutting specifications determinationThe reasonable choice cutting specifications principle is, when rough machining, by enhances the productivity generally primarily, but also should consider the efficiency and the processing cost; When half precision work and precision work, should in under the guarantee processing quality premise, the proper attention to both cutting efficiency, the efficiency and the processing cost. The concrete value should act according to the engine bed instruction booklet, thecutting specifications handbook, and the union experience but decides.(1) Depth of cut t. In the engine bed, the work piece and in the cutting tool rigidity permission situation, t was equal to processing remainder, this is enhances the productivity a effective action. In order to guarantee the components the processing precision and the surface roughness, should keep the certain remainder generally to carry on the precision work. The numerical control engine bed precision work remainder may be smaller than slightly the ordinary engine bed.(2)Cutting width L. General L and cutting tool diameter d has the direct ratio, has the inverse ratio with the depth of cut. In the economy numerical control processing, the general L value scope is: L= (0.6 0.9) d. (3) Enhances v also is enhances the productivity a measure, but v and the cutting tool abrasive resistance relations quite are close. Along with v increasing, the cutting tool abrasive resistance drops suddenly, therefore v choice mainly is decided by the cutting tool abrasive resistance. Moreover, the cutting speed and the processing material also have the very big relations, for example when anther jingang 30CrNi2MoVA with the end mill milling, v may use 8m/About min; When with same end mill milling aluminum alloy, v may choose 200m/Above min.(4) Main axle rotational speed n (r/Min). The main axle rotational speed general basis cuts the speed v to designate. The formula is: The in the formula, d is the cutting tool or the work piece diameter(mm). On the numerical control engine bed control panel has the main