Analysis of Factors Affecting Plane Milling Accuracy in High Speed Machining
Key words: high speed; plane milling; accuracy; factor
In today's high-speed development of mechanization, in the processing of workpieces, the blanks are generally first processed by rough milling, and then the semi-finished products are processed by semi-Precision Machining and precise machining with small feed rate, high-speed rotation, and finally, "finishing." "It is also called "empty knife", this is the most important step. However, the dimensions of the milled surface and the roughness of the surface must be taken into account before machining. The correct tool parameters and cutting parameters of the face mill must also be selected. Therefore, before milling, the material of the workpiece to be processed and the processing flow must be analyzed in detail. The flatness of the surface roughness and shape accuracy of the workpiece, as well as the parallelism and perpendicularity of the positional accuracy determine the quality of the milling.
1 Selection of plane milling tools for high speed machining
1.1 Influence of plane milling tools in high speed machining
In the high-speed machining process, if the tool wears out, the surface of the machined workpiece is ground by a large rounded tip instead of the cutting edge, resulting in an increase in the roughness of the bow surface and becoming thick. Secondly, the force applied to the face milling cutter in high-speed machining comes from the frictional force of the metal and the resistance generated by the deformation. These unnecessary forces will make the rounding of the milling cutter larger and dull. If the milling cutter is worn more seriously, it may cause The flatness of the milling cutter blade causes problems, resulting in poor surface flatness of the machined workpiece.
1.2 Type selection of plane milling tools in high speed machining
In the "small feed rate, high speed rotation" processing mode adopted by modern society, a machine tool with high cutting rate is required. Since the coarse-tooth milling cutter has a larger cutting load per tooth than the fine-tooth milling cutter, a coarse-tooth milling cutter is used for roughing and a cutting depth of 1.0 to 3.0 mm. The semi-precision machining depth is between 0.10 and 0.20 mm, but the precision machining is between 0.005 and 0.05 mm. Therefore, the fine-tooth milling cutter can be selected if the cutting load is small. Therefore, different tools must be selected according to the needs in the process to improve the accuracy.
2 Milling and reversing options
Milling has both milling and reverse milling, however, in order to make the milling machine more precise, it is necessary to choose smooth milling. Smooth milling is to facilitate the cutting of the workpiece, reduce the extrusion friction on the machined surface that has been machined, and reduce the cutting thickness of each cutter of the milling cutter to zero. This also requires the rotation direction of the milling cutter and the moving direction of the workpiece. the same. And the advantage of smooth milling and counter-milling is smooth and vibration is small. In order to prevent the table from moving in order to prevent the table feed screw and the fixing nut from causing a very large gap during the milling, the gap between the feed screw and the fixing nut must be adjusted.
3 High-speed machining in plane milling to select the appropriate cooling method and coating
3.1 Selection of cooling method for plane milling in high speed machining
Cooling method for plane milling in high speed machining: coolant type, air blow type, fuel injection type. In the current production and processing, two types of cooling methods, fuel injection and air blowing, are usually used. Because the coolant type is used to mill the workpiece with a large diameter milling cutter, the coolant cannot be sprayed to the entire milling cutter, especially when the milling continues to be processed and the blade is continuously cut into and out, if the coolant is used at this time. Hot cracks will occur. The air blowing type is mainly because the chemical composition of each metal is different. The color of the chips generated during processing is different. If dark brown chips are produced, the speed of processing carbon steel is appropriate. If the dark brown turns blue, it means The cutting speed is increased. When the temperature is too high, the chips will turn black. The air blowing cooling method can make the workers more intuitively observe the change of color and shape.
3.2 Selection of plane milling coatings for high speed machining
Coating the milling tool in high speed machining can greatly reduce the chance of hot cracking. The titanium aluminum nitride coating is the most difficult to use in the single layer film, such as tool steel, nickel alloy and aluminum alloy, because the friction coefficient of the aluminum nitride coating is 0.07 to 0.3. The hardness is 2800 to 4500 HV, the heat resistance is 750 to 900 degrees Celsius, the surface hardness is up to 80HRC, the coating thickness is 2 to 6 microns, and the coating process is black, purple or purple gray.
4 Reasons for affecting face milling cutting in high speed machining
The main reasons for the influence of cutting in high speed machining are: feed rate, speed, depth and so on.
If the feed of the cutting is increased during the roughing cutting process, the working efficiency is increased, and if the feed is reduced during the semi-precision machining and the precision machining, the surface roughness is increased. Also because the direction of the tool and the workpiece are relative displacements per unit time. For high speed steel milling, a feed rate of 30 to 65 mm per minute can be used at a speed of 0.15 to 0.8 meters per second.
Since the tool wear is not conducive to improving the precision of the machining, the cutting speed is increased under the tool bearing capacity, thereby improving the surface roughness.
The depth of cut refers to the vertical distance between the surface to be machined and the surface that has been machined. Roughing increases efficiency by increasing depth, and semi-precision machining and precision machining increase surface roughness by reducing depth.
5 High-speed machining of medium-face milling press blades and sharpening blades
The pressed insert has low dimensional accuracy and high edge strength. It is suitable for roughing with large impact, depth of cut and feed, which can reduce the cost of roughing. The high precision of the sharpening insert can improve the machining accuracy and surface roughness, and it can cut at a high speed with a small feed depth. It is more suitable for semi-precision machining and precision machining. Therefore, in the case of high speed machining, precise selection of the pressing blade and the sharpening blade is required.
In today's highly mechanized, there are many factors that affect the precision of high-speed machining plane milling, mainly in the selection of tools, roughing selection, cooling mode selection, coating selection in roughing, semi-precision machining and precision machining. The determination of the cause of the cutting, and the selection of the pressing blade and the sharpening blade. Through the analysis and discussion of it, it has further understanding and understanding of improving the precision of plane milling in high-speed machining, and also provides reference for the development of modern enterprises.
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