In the machining process of economical CNC machine tools, since the sharpening, measurement and replacement of the tools are mostly manual and manual, the occupation time is long. Therefore, the arrangement order of the tools must be arranged reasonably. Generally, the following principles should be followed: 1 Minimize the number of tools; 2 After a tool is clamped, all the machining steps that can be performed should be completed; 3 The rough-finished tools should be used separately, even for tools of the same size; 4 First milling and drilling; 5 first surface finishing, then 2D contour finishing; 6 When possible, the automatic tool change function of CNC machine tools should be used as much as possible to improve production efficiency.
Third, the determination of the amount of cutting during processing
The principle of reasonable selection of cutting amount is: when roughing, it is generally to improve productivity, but economical and processing costs should also be considered; in semi-finishing and finishing, under the premise of ensuring processing quality, taking into account cutting efficiency, Economic and processing costs. The specific values ​​should be based on the machine manual, the cutting amount manual, and the experience. Specifically consider the following factors:
Cutting depth ap. With machine, workpiece and tool stiffness allowed, ap is equal to machining allowance, which is an effective measure to increase productivity. In order to ensure the machining accuracy and surface roughness of the parts, it is generally necessary to leave a certain amount of allowance for finishing. The finishing allowance of CNC machine tools can be slightly smaller than that of ordinary machine tools.
Cutting width L. Generally, L is proportional to the tool diameter d and inversely proportional to the depth of cut. In the processing of economical CNC machine tools, the general value range of L is: L = (0.6 ~ 0.9) d.
Cutting speed V. Increasing V is also a measure to increase productivity, but v is more closely related to tool durability. As v increases, tool durability drops dramatically, so the choice of v depends primarily on tool durability. In addition, the cutting speed is also very much related to the processing material. For example, when milling the alloy just 30CrNi2MoVA with an end mill, v can be about 8m/min; when milling the aluminum alloy with the same end mill, V can be more than 200m/min. .
Spindle speed n (r/min). The spindle speed is generally selected based on the cutting speed v. The calculation formula is: V=pnd/1000. The control panel of the CNC machine tool is generally equipped with a spindle speed trimming (magnification) switch, which can adjust the spindle speed during the machining process.
Feed rate Vf. The VF should be selected based on the machining accuracy and surface roughness requirements of the part as well as the tool and workpiece material. The increase in Vf can also increase production efficiency. When the surface roughness of the machined surface is low, the Vf can be selected to be larger. During the machining process, Vf can also be manually adjusted by the trim switch on the machine control panel, but the maximum feed rate is limited by the stiffness of the equipment and the performance of the feed system.
With the wide application of CNC machine tools in production practice and the formation of quantitative production lines, CNC programming has become one of the key issues in CNC machining. In the process of programming the NC program, it is necessary to select the tool and determine the amount of cutting in the human-computer interaction state. Therefore, the programmer must be familiar with the selection method of the tool and the principle of determining the amount of cutting, so as to ensure the processing quality and processing efficiency of the part, give full play to the advantages of the CNC machine tool, and improve the economic efficiency and production level of the enterprise.
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