Brief analysis of CNC machine tool selection and rational use

CNC machining tools must adapt to the high speed, high efficiency and high degree of automation of CNC machine tools. Generally, they should include general-purpose tools, universal connecting shanks and a small number of special shanks. The shank is to be connected to the tool and mounted on the power head of the machine, so it has been standardized and serialized. There are several ways to classify CNC tools.

According to the tool structure, it can be divided into: 1 integral type; 2 inlaid type, using welding or machine clamp type connection, and the machine clamp type can be divided into two types: non-indexing and indexable; 3 special types, such as composite cutter, minus Shock tools, etc. According to the materials used in the manufacture of tools can be divided into: 1 high-speed steel tools; 2 hard alloy tools; 3 diamond tools; 4 other material tools, such as cubic boron nitride tools, ceramic tools.

From the cutting process can be divided into: 1 turning tools, sub-circles, internal holes, threads, cutting tools, etc.; 2 drilling tools, including drills, reamers, taps, etc.; 3 boring tools; 4 milling tools, etc. . In order to meet the requirements of CNC machine tools for tools that are durable, stable, easy to adjust, and changeable, in recent years, machine-clampable indexable tools have been widely used, reaching 30% to 40% of the entire CNC tool in number, metal removal The amount accounts for 80% to 90% of the total.

Compared with the tools used on ordinary machine tools, CNC tools have many different requirements, mainly including the following features: 1 good rigidity (especially rough machining tools), high precision, anti-vibration and small thermal deformation; 2 good interchangeability, It is convenient for quick tool change; 3 high life, stable and reliable cutting performance; 4 tool size is easy to adjust to reduce tool change adjustment time; 5 tool should be able to reliably break chip or chip to facilitate chip removal; 6 series Standardization for programming and tool management.

The selection of the tool is carried out in the human-computer interaction state of the NC programming. The tool and tool holder should be selected correctly according to the machining capacity of the machine tool, the performance of the workpiece material, the machining process, the amount of cutting and other relevant factors. The general principle of tool selection is: easy installation and adjustment, good rigidity, durability and high precision. Under 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 size of the tool should be adapted to the surface size of the workpiece being machined. In the production, the peripheral contour of the plane parts is often processed by an end mill; when milling the plane, the cemented carbide insert milling cutter should be selected; when the bosses and grooves are machined, the high-speed steel end mill is selected; the surface of the blank is machined or roughed. For the hole, the corn milling cutter with the carbide insert can be selected; for the machining of some three-dimensional and variable bevel contours, ball-end milling cutters, ring milling cutters, conical milling cutters and disc milling cutters are often used.

In the free-form surface (mold) processing, since the cutting speed of the end of the ball-end tool is zero, in order to ensure the machining accuracy, the cutting distance is generally the tip-tight distance, so the ball head is often used for the finishing of the surface. The flat-blade tool is superior to the ball-end knives in terms of surface quality and cutting efficiency. Therefore, the flat-blade knives should be preferred if the surface is roughed or finished under the premise of ensuring no cutting. In addition, the durability and accuracy of the tool are highly dependent on the tool price. It must be noted that in most cases, the choice of a good tool increases the tool cost, but the resulting processing quality and processing efficiency increase. , can make the entire processing cost greatly reduced.

In the machining center, various tools are mounted on the tool magazine, and the tool selection and tool change operations are performed at any time according to the program. Therefore, a standard tool holder must be used in order to quickly and accurately load the standard tool for drilling, boring, expanding, milling, etc. onto the machine tool spindle or tool magazine. The programmer should be aware of the structural dimensions, adjustment methods, and adjustment range of the tool holder used on the machine to determine the radial and axial dimensions of the tool during programming. At present, China's machining center adopts TSG tool system. Its tool holder has two types: straight handle (3 specifications) and taper shank (4 specifications), including 16 different handles. Previous 1 2Next

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.

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:

1 Cutting depth t. With the machine tool, workpiece and tool stiffness allowed, t is equal to the machining allowance, which is an effective measure to improve 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.

2 Cutting width L. The 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 value range of L is: L = (0.6 ~ 0.9) d.

3 cutting speed v. Increasing v is also a measure to improve productivity, but v is 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. .

4 spindle speed n (r / min). The spindle speed is generally selected based on the cutting speed v. The calculation formula is: v=∏nd/1000. The control panel of the CNC machine tool is generally equipped with a spindle speed adjustment (magnification) switch, which can adjust the integral speed of the spindle during the machining process.

5 Feed speed vF.vF should be selected according to the machining accuracy and surface roughness requirements of the part and 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, the 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 device and the performance of the feed system.

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