Rapid Prototyping Oriented Research On Slicing 3D CAD Model Directly

Slicing 3D CAD directly in Rapid Prototyping (RP) makes it possible to avoid the data precision decreasement caused by data format conversion between CAD system and RP system, and to provide more accurate scanning data for layer generation, being of significance for its capability of improving forming quality.Aiming at the complexity and low efficiency in determining adaptive layer thickness when considering containment problems, a new adaptive slicing method was proposed based on the Z-key curves on the 3D model surface. The mehod expressed the 3D complex features on the model with 2D Z-key curves. Not taking containment problems into account, the layer thickness determination models could be simplified into 5 cases; and then the direct mapping between the geometric features of the Z-key curves and the adaptive layer thickness was developed. It has been found that the method can improve slicing efficiency for avoiding redundant computation.Aiming at the part surface quality decreasement caused by staircase effect, the containment relationships between RP part and CAD model and their realizations were researched. The RP part layer's cusp distribution with the positive or negative tolerance can be achieved by taking the boundary of the union or the intersection of the projected adjacent sections in CAD model as scanning contour; and the layer's mixed tolerance distribution with approximately equal cusp height can be realized by compensating the volumetric difference between the layers in RP part and the ones in CAD model. A method of blending the adjacent sections in CAD model based on the rotary ray through an inner point of the projected sections was proposed, being efficacious for the CAD model satisfying that the rotary ray intersects the projected contours at two points; and then, another method of blending the adjacent sections based on the parallel curves in the projected section contours was developed, having no requirement to the geometric features of the CAD model. Choosing the value of the tolerance controller properly, the methods can realize the layer's cusp distribution of the positive tolerance, the negative tolerance and the mixed tolerance.Aiming at the impossibility of comparing the RP part with the CAD model directly, a method of simulating the RP part purely based on the data processing results was developed. The method firstly generated each layer's digital model according to its forming order and relative position, and then the part's model was fabricated by stacking up all of the virtual layers. The shape of the part's emulation model is not influenced by transmission error of the RP machine, numerical control code error, and so on. This kind of model is able to give prominence to the effect of the data processing error to forming quality, and can provide a basis for evaluating and improving the data processing algorithm.The file conversion from CAD to RP system decreases the data precision of the model, and the integration degree of the design-manufacturing system. The significance and technique of integrating CAD system and RP machine directly were researched. The logical structure of the integrated system in real-time mode was established, and the RP data processing and motion control module was developed, realizing the direct integration of CAD and RP system. Aiming at the influence of scattering the layer's theoretical scanning curves to the shape and size of the layer's contour, the method of fitting the scanning curves with micro line segments was proposed, and the scanning data used in driving the RP machine to work was obtained. And the method of compensating the scattering deviation of scanning curves was researched, which improves the fitting precision of the layer'practical scanning path to the theoretical one.