Wire Cutting CAD/CAM Technology Based on AutoCAD

In recent years, single-machine numerical control systems have gradually been replaced by microcomputer-based group control systems (DNCs). Manual programming has been a transition from graphic to automatic programming, and CAD/CAM technology has been widely used in manufacturing technology. Due to the powerful drawing and editing capabilities of AutoCAD software and the open DXF data interface, it has become an important part of the graphics input platform and automatic programming. However, many current AutoCAD-based automatic programming systems draw according to the processing sequence without considering the automatic compensation of the tool path, and the machining direction needs to be manually set. For complex parts, it is often necessary to manually determine the drawing parameters, which has many inconveniences. This article adopts ARX development technology and VISUAL C++6.0, carries on the secondary development to AutoCAD, causes the graphical input, the editor, the automatic tracing, the NC programming, the master-slave communication process to complete in the AtuoCAD platform, transforms the line cutting system into The goal is to achieve CAD/CAM integration.

2 system structure

The system adopts the master-slave mode of control, in which the host uses a mid-range microcomputer, and the slave adopts a single-chip computer system to directly control the line cutting machine tool. A host controls multiple slaves through the RS-485 interface, making full use of the powerful functions of the microcomputer to perform graphics input, output, and establishment of cutting process parameter databases. The host's automatic programming module converts the graphic data information into NC machining instructions, and passes the machining instructions to the slaves, which are executed in turn to complete the machining process. At the same time, the slave feeds back data according to the host requirements, providing the basis for real-time control, automatic tracking, and establishment of the process parameter database. The host software system includes six function modules such as graphic input, process parameter processing, automatic programming, simulation, tracking and communication (Figure 1).

Figure 1 host software system structure

3 automatic programming technology

The automatic programming module mainly solves the functions of automatic tracing, machining direction discrimination, automatic tool trajectory compensation, and realizes CAD/CAM integration. The process is shown in Figure 2.

Figure 2 automatic programming software flow chart

3.1 Get Graphical Data and Generate Basic Process Closed Loop

The DXF file generated after the AutoCAD drawing input is used to acquire the feature information of the processing entity by using the feature-based information modeling method. What the system needs is the geometric information of the entity, so only the ENTITIES Section of the DXF file needs to be read and processed, and the relevant feature information is stored. Based on this information, the topological relationship between the outline of the part and its constituent elements is initially formed. CAD drawing entities are stored in the DXF file in the order in which they are drawn, regardless of the processing sequence. When deleting or adding an entity in the closed-loop machining cycle, the entities in the DXF file are not stored in the order of the machining closed loop. Reorder the endpoints to form a closed loop. In this way, drawing and processing are separated, and when AutoCAD is used for graphic input, it is not necessary to care about the actual processing sequence, which simplifies the data input process. The system uses double-linked list data structures to store entity information. Double-linked list data structures are found in the literature.

3.2 Judging the processing direction

This paper uses vector method to judge the machining direction. In the following, any machining closed loop shown in Fig. 3 is taken as an example to illustrate the processing direction discrimination algorithm.

First traverse the doubly-linked list and find the end point nearest to the X-axis or Y-axis as the starting point for processing, that is, D=MIN(|x-x0|, |y-y0|). Let this point be point B, which is point A and point C in the front and rear ends of the linked list. It can be inferred that the connection between the two vectors AB and BC connecting point B will uniquely determine the direction of the original figure.

Figure 3 any closed-loop schematic

The vector method is used to determine the direction of the triangle ABC. For ease of programming, the quadrant to which the vector direction belongs is classified according to the following principle. Set point A (xA, yA), B (xB, yB), C (xC, yc), then AB = OB-OA = (xBi + yBj) - (xAi + yAj) = (xB-xA) i - ( yB-yA)j

When xB-xA> 0, yB-yA ≥ 0, AB ∈ I quadrant;

When xB-xA ≤ 0, yB-yA> 0, AB ∈ II quadrant;

When xB-xA<0, yB-yA≤0, AB∈III quadrant;

When xB-xA> 0, yB-yA <0, the AB ∈ IV quadrant.

According to the selection principle of the processing starting point, it can be inferred that the vectors AB and BC cannot be in the same quadrant, thereby simplifying the judgment process. The closed-loop direction judgment process is shown in Fig. 4. In FIG. 4, KI, KII, KIII, and KIV respectively represent slopes of the respective quadrant vectors. This method is simple in programming, fast in operation, short in program execution time, and can accurately implement automatic tracing.

Figure 4 Vector method to determine the direction of processing

3.3 Form an actual machining track

In the formation of the actual machining trajectory, it is necessary to consider the effects of the concave and convex mold characteristics of the processing object, the diameter of the molybdenum wire, the discharge gap, and the machining direction. The tool trajectory compensation amount is determined in the automatic programming system, and the basic processing route is adjusted. To ensure the accuracy of processing. Assuming that the radius of the molybdenum wire is r molybdenum, and the unilateral discharge gap is δ, the machining path offset compensation amount is

f = r molybdenum + δ electricity (1)

The target workpiece contour is generally composed of straight lines and arcs (other curves can be obtained by fitting straight lines and arcs), so adjusting the tool's actual machining trajectory actually increases or decreases the radius R of the arc, and the straight line at normal Move f in the direction.
Let the line ends be Ps(xs,ys),Pe(xe,ye),

The general equation of the original line is L:Ax+By+C=0(2)

The linear equation after translating f is L': Ax+By+C'=0 (3)

Among them (4)

A=ye-ys,B=xs-xe,C=xeys-yexs(5)

For arcs, R'=R±f(6)

The choice of sign in equations (4) and (6) depends on the convex and concave model properties and machining direction of the workpiece. Adjustments in various situations are given in Reference [2]. The system is accurate to 1μm when making calculations. After corresponding adjustments to each entity, the actual trajectory of the tool is obtained, thereby eliminating the errors caused by the tool parameters such as the tool and the discharge gap, and improving the machining accuracy.

In the actual machining, the contour of the workpiece may not be smooth, corners, sharp corners, etc., may easily cause problems such as broken wires, short circuits, corner collapses, and air gaps. A transitional arc (R≥f) may be added to make the machining trajectory smoothly transition. Protect molybdenum wire and improve processing efficiency. The system performs interpolation operations on each entity in the processing sequence, stores the machining commands in a file, and sends them to the slave system for processing, thereby realizing CAD/CAM integration.

4 Conclusion

The AutoCAD-based CAD/CAM technology introduced in this paper has been applied in the precision instrument factory of our institute, and has realized the technical transformation and group control management of the CKX-1 type and DMK6732 CNC electric discharge wire cutting machine tools. During use, the user only needs to be familiar with the basic drawing operations and draw input according to design requirements without having to care about the machining process. Complicated calculations and trajectory compensation are all done by an automatic programming system to separate the graphics input from the processing. After the drawing, the host machine directly controls the machining and realizes CAD/CAM integration. The system also enables precise machining of complex workpiece contours. The system has a friendly interface and is easy to operate. It can accurately perform automatic tracing and tool path compensation. The operation is stable and reliable, reducing the burden on the operator and improving the processing efficiency.

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