The following is a brief introduction to the tool path generation method. NC tool path generation method for lines, surfaces and volumes
The technology started from 2D drawing, experienced the development stage of 3D wireframe, surface and solid modeling, and has been to the parametric feature modeling. NC machining is mainly driven by points and lines, such as hole processing, contour processing, plane area processing and so on. This kind of processing requires high level of operator and complex interaction. In the development stage of surface and solid modeling, solid based machining appears. The machining object of solid machining is an entity (generally represented by CSG and B-rep), which is obtained by some basic voxels through set operation (Union, intersection and difference operation). Solid machining can be used not only for rough machining and semi finishing machining of parts, but also for the research and development of feature-based NC programming system, which is the basis of feature-based machining.
Feature based NC tool path generation method
Parametric feature modeling has a certain period of development, but the research on Feature-based tool path generation method is just beginning. Feature processing makes NC programmers not to operate the low-level geometric information, but to directly carry out NC programming for the features that meet the habits of engineering and technical personnel, which greatly improves the programming efficiency.
W. In their research, r.mail and a.j.mcleod proposed a feature-based NC code generation subsystem. The working principle of this system is that each machining process of a part can be regarded as the sum of the machining of the shape feature group of the part. Then the whole shape feature or shape feature group is processed separately, then the part is finished. The NC code of each shape feature or shape feature group can be generated automatically. The developed system is only suitable for 2.5D parts processing.
Lee and Chang developed a tool path generation system for convex free-form surfaces by using virtual boundary method. The working principle of this system is that a minimum rectangle block is embedded in the convex free-form surface, so that the convex free-form surface feature is converted into a concave feature. The combination of the smallest rectangle and the final product model constitutes an indirect product model called virtual model. The tool path generation method is divided into three steps: (1) cutting polyhedron feature; (2) cutting freeform surface feature; (3) cutting intersection feature.
The basis of feature processing is solid processing, which can also be considered as higher-level entity processing. However, feature processing is different from solid processing, which has its own limitations. There are several differences between feature processing and solid machining
In concept, feature is the functional element of a part, which conforms to the operating habits of engineering and technical personnel and is well known by engineering and technical personnel; entity is a low-level geometric object, a geometric body obtained through a series of Boolean operations, without any functional semantic information; entity processing is often a one-time processing of the whole part (entity). But in fact, a part is not likely to be processed with only one knife at a time. It often needs to go through a series of steps such as rough machining, semi finishing and finishing. Different parts of parts are generally processed with different cutters; sometimes a part needs to be turned and milled. Therefore, solid machining is mainly used for rough machining and semi finishing of parts. Feature processing solves the above problems in essence, and feature processing has more intelligence. Certain fixed processing methods can be specified for specific features, especially those already specified in the step standard. If we have developed a specific processing method for all the standard features, we can imagine the convenience of machining those parts which are made up of standard features. If CAPP system can provide corresponding process characteristics, NCP system can greatly reduce interactive input and have more intelligence. However, these solid machining can not be realized; feature processing is helpful to lay a good foundation for the realization of CAD, CAPP, CIMS and even Concurrent Engineering (CE), while entity machining is powerless to these
