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Five-axis application in inclined surface machining

The high-performance five-axis CNC milling machining center and CNC system have spatial coordinate system rotation and inclined plane tool compensation functions, thus providing the possibility to process some parts that require inclined plane processing and relatively high machining accuracy. When processing on an inclined surface, because the coordinate system changes in space, it is difficult to program the processing. It is necessary to break through the conventional programming thinking mode for programming, and to perform special processing on the program. This article discusses this issue based on the actual processing of model products.

In the production process of model products, we often encounter such parts, which need to be punched, bored, and milled on inclined surfaces, or they need to be processed on several inclined surfaces in different directions and different inclinations in the same clamping. And there are higher geometric tolerance requirements between each inclined plane. The conventional methods for processing such parts are to turn the bed head, rotate the work table or use a combination fixture. If the processing direction or processing position is different, it requires secondary clamping and re-alignment. The processing process is extremely cumbersome, due to the clamping positioning and Due to the limitations of the machine tool itself, the machining accuracy of the parts cannot be guaranteed. For example, in the processing of the T×× table body, there are many holes on the inclined surface, and the special-shaped surface is difficult to clamp, and the positioning reference is not good. Multiple clampings cause errors to accumulate, and sometimes the hole margin error exceeds 1mm.

In order to solve the processing problem of this kind of parts, through continuous exploration and continuous improvement of process methods, combined with the existing machine tools in the factory, a five-axis CNC milling machining center was finally selected to solve this problem. The selected machine tool has five axes and five linkages. In addition to three linear axes, it also has a rotary table (C axis: -360°~360°) and a swing head (B axis: 0°~110°). The rotating axis adopts the control system FANUC160i, which has the functions of spatial coordinate system rotation and inclined plane tool compensation.

From the perspective of realizing bevel processing, the drilling, boring, tapping, milling and other processing needs of multiple bevels in different directions and angles can be completed in one clamping. It reduces the number of clampings, reduces labor intensity, shortens the production cycle of the product, and more importantly, improves the processing accuracy of parts and ensures the consistency of product quality.

Take the window processing of a base part of the Changsan series as an example. The part is as shown in the figure below: To process this window, it can be seen that the machine tool should complete a 2-axis linkage interpolation on the XZ, YZ plane and a spindle Head bobbing action. Because in order to make the tool perpendicular to the processing surface, the spindle must complete a swinging motion. If the swinging head is present, it involves a series of multi-axis machining issues such as swing length. Therefore, multi-axis programming must be used to complete the process. Programming and machine tool debugging are difficult, which puts higher requirements on programmers and machine tool operators. In practical applications, taking into account factors such as ensuring the safety of machine tools, it is necessary to Simulate the machining process and perform multiple air cuts to ensure that the program is correct before formal processing can be carried out. In addition, the multi-axis program algorithm is quite complex, and the influence of factors such as the pendulum length needs to be considered. A certain machine tool must have specific post-processing, but post-processing is often due to differences in algorithms and control positions, as well as calculation stability. Programs obtained after software post-processing are often difficult to meet the accuracy requirements of part drawings in terms of control accuracy.

From the analysis, it can be seen that the direct cause of the increase in programming difficulty is the emergence of the inclined plane. Therefore, if the processing plane and the inclined plane can be made to coincide, then this type of problem will be transformed into a two-axis and a half machining programming problem, and the programming difficulty will be greatly reduced. Therefore, it is conceivable to first use the machine tool’s coordinate system conversion function (G68 command) to make the processing plane coincide with the inclined plane, and secondly use the tool length compensation command (G432) to add the tool length in the vertical direction of the inclined plane. After the above processing , so that the problem of bevel processing can be solved by converting it into plane processing, thus greatly reducing the difficulty of programming. If you need to process multiple bevels at the same time, you only need to rotate the C axis to C0 (the zero position of the workbench, which is the same as the swing direction of the spindle), and then complete the processing by rotating the coordinate system and increasing the tool length. If the machining shape is relatively simple, the programming work can be completed manually. This makes it possible to process multiple inclined surfaces, multiple stations, and multiple tool changes in one CNC machine tool clamping.

The program structure is as follows:

%

N0100O0008 (program name)

N0102M6T1;(Tool change)

N0104G0G90G56X400Y200Z260B0C0; (Move to reference point)

N0106G432X200Z150H1Bω; (Add the tool length in the direction perpendicular to the bevel)

N0108M3S3000; (spindle forward rotation)

N0110M8; (Open cutting fluid)

N0112G68X188Y0Z60I0J1K0Rω; (Coordinate system conversion, ω is the angle through which the main axis rotates from zero to perpendicular to the inclined plane)

……

N0200G69; (Coordinate system rotation canceled)

N0202G492X200Z300; (Slope tool compensation is canceled and moves to a safe position)

N0204M9; (cutting fluid off)

N0206Cα; (C-axis rotation, α is the minimum angle between the vertical line of the n-th slope to be processed and the C0 position)

N0208G0G90G56X400Y200Z260B0C0; (Move to reference point)

N0210G432X200Z150H1Bωn; (Add the tool length in the direction perpendicular to the bevel)

N0212G68X188Y0Z60I0J1K0Rωn; (Coordinate system conversion, ωn is the angle through which the main axis rotates from zero to perpendicular to the inclined plane)

……

N0200G69; (Coordinate system rotation canceled)

N0202G492X200Z300; (Slope tool compensation is canceled and moves to a safe position)

N0204M9; (cutting fluid off)

N0204M30; (Program ends, return to program head)

Although bevel processing has been implemented in the above discussion, it is limited to drilling, boring, tapping, and milling simple shapes composed of straight lines and arcs on the bevel, and is limited to manual programming. If the milling shape is more complex, such as milling equation curves, three-dimensional surfaces, or lettering on an inclined surface, how should you program it?

Even when these shapes are processed on a flat surface, manual programming cannot be achieved and can only be completed through CAM software. Through careful study of machine tools and CAM software, an effective way to complete the processing and programming of such parts was found by combining software programming with manual programming.

The analysis shows that in ordinary three-axis milling programming, the tool axis direction is always perpendicular to the XOY plane. However, when the spindle deviates from the original vertical direction and the tool plane is tilted, how can the program generated on the XOY plane be on the inclined plane? runs correctly. The analysis shows that although the coordinate system has rotated, if the relative position of the figure made on the XOY plane (a) in the original coordinate system and the shape to be processed on the slope (b) are consistent with the relative position in the new coordinate system , then the program generated on the XOY plane can be directly applied to bevel processing. According to the influence of the machine tool’s head swing action on the position of the graphics, the analysis shows that when drawing on the XOY plane, the graphics should be rotated 90° counterclockwise with the programming origin as the rotation center (the rotation angle should be determined according to the specific conditions of the machine tool, etc.), so Just make the graphics position in the CAM software consistent with the actual processing position. By adding and modifying the program header and program tail, that is, adding coordinate system conversion and inclined plane tool compensation, software programming and manual programming are combined, thereby realizing the processing of arbitrary complex shapes such as milling equation curves, three-dimensional surfaces, lettering, etc. on the inclined plane. .

Through actual processing verification, it is confirmed that this method can be used to program any complex shape on any inclined surface within the permitted range of the machine tool function and stroke.

The figure below shows an example of processing a three-dimensional curved surface on a 52° inclined surface:

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