The choice of numerical control tool and the determination of the cutting amount are important contents in the numerical control processing technology. It not only affects the machining efficiency of the numerical control machine tool, but also directly affects the processing quality. The development of CAD/CAM technology makes it possible to directly use CAD design data in CNC machining, especially the connection of DNC system microcomputer and CNC machine tools, making the entire process of design, process planning and programming completed on the computer, generally not Need to output a special process file. At present, many CAD/CAM software packages provide automatic programming functions. These softwares generally indicate the relevant problems in the programming interface in the programming interface, such as tool selection, machining path planning, cutting amount setting, etc., as long as programmers set relevant information. The parameters can automatically generate the NC program and transfer it to the CNC machine for processing. Therefore, the tool selection and cutting amount determination in the numerical control machining are completed under the human-machine interaction state, which is in sharp contrast with the ordinary machine tool processing. At the same time, the programmer is required to master the basic principles of tool selection and cutting amount determination. When programming, the characteristics of CNC machining are fully considered, and the cutting tool and cutting amount can be selected correctly. The types and characteristics of the commonly used tools for numerical control machining The numerically-controlled tool must adapt to the features of high-speed, high-efficiency, and high-degree of automation of CNC machine tools. Generally, it should include general-purpose tools, universal connection tool holders, and a small number of special tool holders. The tool holder is connected to the tool and mounted on the power head of the machine, so it has been gradually standardized and serialized. There are several ways to classify CNC tools. According to the tool structure can be divided into: Integral; Inlaid, using welding or clamp connection, clamp type can be divided into non-inversion and indexable two; Special type, such as composite tool, damping tool Wait. According to the materials used to manufacture the tool, it can be divided into: high-speed steel tools; carbide tools; diamond tools; other material tools, such as cubic boron nitride tools, ceramic tools and so on. From the cutting process can be divided into: Turning tools, extra-circular, inner hole, thread, cutting tools and many other; Drilling tools, including drills, reamers, taps, etc.; Boring tools; Milling tools. In order to meet the requirements of CNC machine tools for durable, stable, easy-to-adjust, interchangeable tools, in recent years, the machine-clamp indexable tools have been widely used, reaching 30% to 40% of the total number of CNC tools in the number of metal cuts. The amount accounts for 80% to 90% of the total. Compared with the tools used on ordinary machine tools, numerical control tools have many different requirements. The main characteristics are as follows: Rigidity (especially rough machining tools), high precision, low vibration and thermal deformation, good interchangeability, and quickness Change tool; High life, stable and reliable cutting performance; Tool size is easy to adjust, to reduce tool change adjustment time; Tool should be able to reliably chip or chip, in order to facilitate the removal of chips; Serialization, standardization, in order to facilitate programming And tool management. Selection of CNC machining tools The selection of tools is performed in the human-machine interaction state of NC programming. The tool and shank should be selected correctly based on the machine tool's machining ability, workpiece material's performance, machining process, cutting amount, and other related factors. The general principle of tool selection is: easy installation and adjustment, good rigidity, high durability and high precision. In the premise of meeting the processing requirements, try to choose a shorter tool holder to improve the rigidity of the tool processing. When selecting a tool, the dimensions of the tool must be adapted to the surface dimensions of the workpiece being machined. In production, the peripheral contours of plane parts are often machined with end mills. When milling planes, hard alloy insert milling cutters are selected. When machining bosses and grooves, high-speed steel end mills are selected; surface roughing or rough machining is performed. In the case of holes, corn milling inserts with carbide inserts can be selected. For the machining of some three-dimensional profiles and variable bevel profiles, ball-end cutters, ring cutters, taper cutters, and disc-type cutters are often used. In the free-form (mold) machining, because the cutting speed of the end of the ball-end tool is zero, therefore, in order to ensure the machining accuracy, the cutting distance generally adopts the tip close distance, so the ball head is often used for the surface finishing. The flat-blade cutter is superior to the ball-end cutter in terms of surface machining quality and cutting efficiency. Therefore, as long as it is not over-cut, the flat-end cutter should be the first choice for both rough and finish machining of the surface. In addition, the tool's durability and precision are highly related to the tool's price. It must be noticed that, in most cases, selecting a good tool increases the tool cost, but the resulting increase in machining quality and machining efficiency. , you can greatly reduce the cost of the entire process. In the machining center, various tools are installed on the tool magazine, and the tool selection and tool change actions are performed at any time according to the procedures. Therefore, a standard tool holder must be used so that the standard tool used for drilling, boring, expanding, milling, etc. can be quickly and accurately mounted on the spindle or tool magazine of the machine tool. The programmer should know the structural dimensions, adjustment methods, and adjustment range of the tool holder used on the machine tool to determine the radial and axial dimensions of the tool when programming. At present, China's machining center adopts TSG tool system, and its handle has two kinds of straight shank (3 specifications) and taper shank (4 kinds of specifications), including a total of 16 kinds of handles for different purposes. During the processing of economical CNC machine tools, the tool grinding, measurement and replacement are mostly performed manually, and the time required for assisted use is longer. Therefore, the arrangement order of the tools must be reasonably arranged. Generally should follow the following principles: 1 to reduce the number of tools as much as possible; 2 After a tool is clamped, it should complete all the processing steps it can perform; 3 rough finishing of the tool should be used separately, even the same size of the tool; 4 First, after milling; 5 first finish the surface finish, after the two-dimensional contour finishing; 6 where possible, should use the automatic tool change function of CNC machine tools to improve production efficiency. The determination of the cutting amount in the processing process The principle of reasonable selection of the cutting amount is: When roughing, the general improvement is to increase the productivity. However, the economy and processing cost should also be taken into consideration. When semi-finishing and finishing, the quality of the processing should be ensured. Under the premise, taking into account cutting efficiency, economy and processing costs. The specific value should be based on the machine tool specification, cutting amount manual, and combined with experience. Specifically consider the following factors: Cutting depth ap. In the case of machine tool, workpiece and tool rigidity, ap is equal to the machining allowance, which is an effective measure to increase productivity. In order to ensure the machining accuracy and surface roughness of the parts, a margin should generally be left for finishing. The finishing allowance of CNC machine tools can be slightly smaller than that of ordinary machine tools. Cutting width L. In general, L is proportional to the tool diameter d and inversely proportional to the cutting depth. In the processing of economical CNC machine tools, the general L value range is: L = (0.6 ~ 0.9) d. Cutting speed V. Raising V is also a measure to increase productivity, but v has a closer relationship with tool life. As v increases, the tool life drops sharply, so the choice of v depends mainly on tool life. In addition, the cutting speed and processing materials also have a great relationship, such as milling with an end mill just 30CrNi2MoVA alloy, v can be used about 8m/min; and with the same endmill milling aluminum alloy, V can be selected more than 200m/min . Spindle speed n (r/min). The spindle speed is generally selected according to the cutting speed v. The formula is: V=pnd/1000. CNC machine tool control panel is generally equipped with spindle speed adjustment (magnification) switch, the spindle speed can be adjusted during the whole multiple adjustment. Feed speed Vf. The vF should be selected based on the part's machining accuracy and surface roughness requirements as well as the tool and workpiece material. The increase in Vf can also increase production efficiency. When the surface roughness requirement is low, Vf can be selected to be larger. In the process, Vf can also be manually adjusted through the trim switch on the machine control panel, but the maximum feed rate is limited by the equipment stiffness and feed system performance. With the wide application of numerical control machine tools in production practice and the quantification of the production line, numerical control programming has become one of the key issues in numerical control processing. In the process of NC programming, it is necessary to select the tool and determine the cutting amount in real time under the condition of human-machine interaction. Therefore, programmers must be familiar with the selection method of cutting tools and the principle of determining the cutting amount, so as to ensure the processing quality and processing efficiency of parts, give full play to the advantages of CNC machine tools, and improve the economic efficiency and production level of enterprises.
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