The strategy of adding a numerical control sequence from the digital area of ​​the drawing

Optimization principle The machining information extracted from AutoCAD cannot be directly converted into CNC machining instructions, because machining has its particularity: First, multiple tools are used in general machining. If the tool is changed frequently, the auxiliary machining time will be over. Long, affecting processing efficiency, but also bring some installation errors.

The second is the block diagram of the processing letter program software extracted from the above, the tool path is discontinuous, and the processing is segmented. According to these characteristics, the following optimization principles can be determined: (1) the minimum number of tool changes; (2) machine tool error The processing impact is minimal; (3) the idle stroke is relatively minimal.

Optimization strategy (1) In order to minimize the number of tool changes, when we design the tool processing trajectory in human-computer interaction, we put the processing trajectory of the same tool in the same layer and filter the processing information from the DXF file once. Come out, so that the same tool only needs to be changed once.

(2) In order to minimize the influence of the machine tool transmission error on the machining, on the one hand, the machine tool clearance compensation method can be used in the machine tool control; on the other hand, the same feed direction is used for the parallel machining, as far as possible along the X axis or The Y axis is fed forward.

(3) In order to minimize the idle travel, dynamic selection is used to optimize the machining path. Here is a brief introduction to the basic idea of ​​the dynamic selection method. There are known n line segments (including straight lines, arcs, and double lines). The tool is machined from the starting point of one line segment to the end point, and then the end points and tools are selected from the remaining line segments. The nearest line segment of the current position is used as the next machining path.

When the tool reaches the end of each line segment, its distance from the end points of other line segments is different each time, it is changed, so it is called dynamic selection method. In general, the free path of the machining path determined by the dynamic selection method is relatively small.

The NC machining instruction generates the tool machining path and the geometric parameters of various pixels into a CNC machining instruction file in a specified format. Commonly used numerical control command formats are as follows: GOO? Fast forward command for fast positioning of the tool along the coordinate axis; G01? machining space straight line; G02? machining circular arc in the coordinate plane; G03? machining coordinate plane Reverse arc; Go4? Machine tool direction clearance compensation; T? tool change command; F? Tangential feed speed command During the conversion of CNC machining instructions, the starting point and end point coordinates in the NC command should be expressed in relative coordinates. For a straight line, the origin of the relative coordinate is the starting point of the line, and for the arc, the origin of the relative coordinate is the center of the arc, and the cutting depth, cutting amount and tool number of each line segment can be communicated through man-machine dialogue. The way to determine.

Summary Because the use of AutoCAD for the design of mechanical parts has been widely adopted, this article has omitted this part. At the same time, the generation of DXF files and the interface design of high-level languages ​​are also introduced in many books. This article mainly introduces an aim. A method of converting an AutoCAD drawing file into a CNC machining instruction.

The programming of the above 2, 3, and 4 parts should be modular, using the QBASIC high-level language. It should be noted that the format of the machining instructions of different CNC machine tools is different, and should be slightly changed when generating CNC machining instructions. This will create conditions for the CAD/CAM integration of machining.

(Finish)

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