Improving the accuracy of parametric surfaces using cutting force synthesis and surface offset techniques

The next stage of curved surface machining would be to develop error compensation schemes within the tool path generation phase to enhance the accuracy of parametric surface machining. It was found during the course of this study to accurately implement the compensation scheme, an accurate and flexible surface offset model needs to be developed. The technique used to develop the offset model is based on De-Casteljau type subdivision. In this technique a uniform subdivision process is executed for the original control points until the generated control points are very close to the original surface. The control points are then entered into polygonization routine where the surface is polygonized, and an average normal is calculated for each polygon. Each polygon is then offset in the direction of the polygon normal followed by a trimming operation to either close or remove the self intersection cases. The proposed model and the least squares model were tested against the exact calculation of offset points. The new technique was found to be more accurate. In this thesis three error compensation schemes were developed.; The first error compensation scheme is based on the De-Casteljau technique to generate the tool path for roughing. The advantage of using this technique is that it allows for leaving an almost uniform thickness layer of metal on top of the finished surface. This is compared with the staircase model obtained from the traditional techniques based on pocketing routines.; The second error compensation scheme is developed based on measuring the first finished surface using a coordinate measuring machine (CMM). An error map of the surface is generated during the measuring cycle. The error map is then fed to the tool path generation program. If all the errors are aligned in one direction, an average value for surface offset value is computed based on the least squares principle, and is used as an offset value for the original surface. The new offset surface is then used to generate the tool path for the next surface.; The variable offset technique is based on the fact that each time a subdivision process is carried out, four patches are generated. So, after three levels of subdivision, the number of patches generated for a single patch is sixty-four. Using the error map generated from the CMM machine the nearest error value for each patch is selected as a possible candidate to offset this patch.; The third error compensation scheme is based on developing a cutting force model for both end mill and ball mill tools. The cutting force model is used to predict the surface error generated due to the tool deflection as a main source of error.; The proposed model was also used to speed the reverse engineering cycle by eliminating some of the re-measuring activities and for tolerancing free form surfaces where it showed varied degrees of success.; Finally the proposed technique was used to machine a number of parts with a varied degree of complexity and the measurement results showed increase in the machining accuracy up to 70 percent for the first and the second scheme, while the third scheme showed an improvement up to 20 percent. (Abstract shortened by UMI.)...