Architecture for Direct Model-to-Part CNC Manufacturing
In the traditional paradigm for Computer Numerical Control (CNC) machining, tool paths are programmed offline from the CNC machine using the Computer-Aided Design (CAD) model of the workpiece. The program is downloaded to the CNC controller and the part is then machined. Since a CAD model does not exist inside the CNC controller, it is unaware of the part to be machined and cannot predict or prevent errors. Not only is this paradigm labor intensive, it can lead to catastrophic damage if there are errors during machining. This paper presents a new concept for CNC machine control whereby a CAD model of the workpiece exists inside the controller and the tool positions are generated in real-time by the controller using the computer’s graphics hardware without human intervention. The new concept was implemented on an experimental lathe machine specifically designed to machine complicated ornamental wood workpieces with a personal computer. An example workpiece was machined and measured using a 3D camera. The measured data was registered to the CAD model to evaluate machining accuracy.
Adaptive ball drop algorithm for toolpath generation of axisymmetric triangulated parts to eliminate overcutting
Computer Numeric Control (CNC) milling lathes are used for pseudo-symmetric ornamental woodworking. A stereolithography (STL) part model is used for gouge-free toolpath generation using methods such as the geometry offset method and the ball drop method. The tool movement between cutter location (CL) points results in gouging of the STL part at convex intersections of triangles (path-gouging). This path-gouging can be controlled to be within user-specified tolerance, with large number of equispaced points in forward and sidestep directions. The resulting toolpath with large number of tool positions considerably slows the machining process. There exists a need for a universal method for efficiently eliminating this gouging and slowdown. In this work, a refined ball drop method is presented that eliminates path-gouging and reduces slowdown by automatically generating a variable step size in the side step and forward directions. To further optimise the number of side steps generated by the presented method, banding is used to reduce machining time while minimising un-machined material and eliminating gouging. The developed algorithm was tested on sample parts and verified by simulation and machining of wooden parts.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.