Application of AutoCAD in Scanning NC Machining

Qiqihar Railway Vehicle Group Corporation Cold Process Department (161002) Jin Zhengzhe Zhang Yingbin face machining center, its numerical control system is FANUC18M, the number of controllable axes is four axes, and the number of coordinated axes is three axes. At the same time, the machine is also equipped with RENISHAW's TRACE-CUT22 computer scanning profiling system, which can realize computer-aided automatic programming after scanning 3D solid model.

In the numerical control machining, the manual programming is carried out by using the code programming method matched with the machine numerical control system, including the macro programming technology to realize the programming of the general simple three-dimensional surface. But the latter is often computationally complex and error prone. Today's more popular CAD/CAM software, such as: PRO/ENGINEER, UG, I-DEAS, MASTERCAM, etc., this type of CAD/CAM system has powerful modeling functions, and both have CNC machining post-processing modules for different CNC systems. The setting can realize the automatic programming of the computer aided NC machining program code. However, such software is generally expensive, and the application and maintenance of the system are complicated. The TRACE-CUT22 system is slightly different from the CAD/CAM system described above. It can't directly construct and edit the machining model using the solid modeling method in the computer. It depends on the sample model of the actual workpiece and then collects the surface value points. To build a machining model. However, as a relatively open system, it also has interfaces with other CAD systems, which can easily exchange input and output of graphic files in multiple formats. Thus, by using the modeling and editing functions of the CAD system, To some extent, improve the applicability of the TRACE-CUT22 system.

This paper only discusses the application of AutoCAD in TRACE-CUT22 system with an example.

The above four methods of building a database have their own characteristics and are suitable for different occasions. To sum up, there are two ways: 1 Use UG/OPEN to develop a dedicated program for the graphics library. 2 Using the parametric library management tool provided by UG system to establish graphical parameterization technology and data technology, establish a parameterized library.

Engineering drawing, and has a certain three-dimensional modeling function, which can realize the modeling of the model) and the solid model. Among them, the wireframe model only contains the information of the edge, and there is no information about the face and the body, so the NC machining tool path cannot be generated. The surface model contains information about lines and faces, and is suitable for constructing complex surface solid models, so it can handle various calculations related to surfaces, such as generating motion trajectories of CNC tools. This is especially important in TRACECUT22. The entity model covers all the information of lines, faces and bodies, which will not be described here.

The surface generated by the AutoCAD system is scanned point by point and converted into the model file of the system. Therefore, the accuracy of the construction model and post-processing is directly limited by the CAD system. Thus, in the CAD modeling process, the settings of the surface texture density control variables surftabl and surftab2 should be calculated after comprehensively considering the requirements of the machining tool size, machining accuracy, machine setting, and the like.

The following is an example of a numerical control processing of a hook-and-loop type mold manufactured by our branch factory. The application process and parameter calculation method are introduced. The mold cavity diagram is as follows: in the modeling process, the curved cavity partition is formed by connecting seven curved slices, wherein the curved slice 1 and the curved slice 7 are constructed by a revsurf surface, and the rest is boundedge surface (edgesurf) Construct. For example, as mentioned above, in the surface modeling process, the parameters surftabl, surftab2 and modeling methods will directly affect the accuracy of product processing, so the following calculation settings should be made: surface precision control. 48. In processing, surface roughness and dimensional accuracy are affected by the radius of the tool tip and the amount of tooling, eg.

The theoretical value of roughness can be calculated as follows: Although there is no direct mathematical relationship between the amplitude it and the surface roughness a, it can generally be compared with the following table: Here it is necessary to introduce the trend of the tool path generated by TRACECUT22: Upper, the tool will first select the first surface fitting curve in the surftabl direction, and follow the mesh vertex in the direction of SUrftab2. The value of SUrftab2 will determine the number of mesh vertices of the fitting surface, and then cycle down. Therefore, the relationship between the surface texture density control variables surftabl and surftab2 and the theoretical value of the machining tool radius and surface roughness is as follows: The value of surftab2 can be appropriately determined according to the amount of surface deformation, and can be adjusted after simulation by VMM22 simulation. However, it should be noted that when the value of surftabl and surftab2 is increased, the calculation and regeneration time of the surface will be increased. By the way, in the process of surface modeling, the programming language of AutoLISP, VB, VC, etc. can be used to easily shape the surface.

The TRACECUT22 system will be determined as the workpiece coordinate system by the coordinate system WCS in AutoCAD. Therefore, before the data exchange between CAD and TRACECUT22, the WCS adjustment should be set to the appropriate position in time as the workpiece coordinate system position for NC machining. 'In AutoCAD, after the end of modeling, in order to exchange data with TRACE-CUT, the model file should be saved in ASC Graphics Conversion File (DXF) format. DXF file is a standard ASC text file, which can be converted by TRACECUT22. Converted to a curved 3D data point file - SUD file, SUP file. In this case, confirm the diameter of the probe that scans the surface.

Before the machine tool NC machining program is generated, the machining of the AutoCAD surface model needs to be further set in the TRACECUT22. It is generally divided into the following steps: setting the necessary parameters of the machine tool includes: setting the workpiece coordinate system (G54~G59), program number , clearance plane, clearance distance, safe position, etc.

Selecting the tool includes: defining the tool number, diameter, tool length and radius compensation number, spindle speed, feed rate, etc. in the program. It should be noted that. The diameter of the ball end mill for machining must be the same as the diameter of the probe used to acquire the data, ie the diameter of the probe confirmed when converting the file format.

To define the machining, you must select the profiling in 3D machining.

The machining path can be simulated in the VMM22 and the interference can be checked. If there is interference, the direction of surftabl and surftab2 can be adjusted appropriately, or the parameters in TRACECUT22 can be used to adjust.

In the scanning process, CAD modeling assisted modeling can eliminate the need to manufacture the real model model before scanning, which not only improves the economic benefits, but also improves the precision of the products to be processed.

Mechanical worker