Curved Surface Machining Tool Path Planning Under Constraint Of Cutting Force

Complex surfaces are widely used in the aerospace, automobile, shipbuilding and mold manufacturing industry field for their special functional or aesthetic feature. Through decades of development, compared with the maturate complex surface modeling, complex surfaces machining has still been a major problem. Nowadays, multi-axis NC machining has become the most effective method for complex surfaces parts. Tool path generation is important for complex surface NC machining, and the methodology of tool path generation affects the machining efficiency and the machining quality. As key technology of NC program, tool path planning of complex surface machining is a research hotspot and difficulty in this field.Tool path planning includes two parts, one is the parameter of the tool path, the other is the topological structure of the tool path. The parameters of the tool path include cutting step length and cutting row spacing, the topological structure of the tool path, in other words, it is the tool path pattern and the distribution shape of the tool path. Ideal curved surface machining tool path requires for the features as follows:reasonable cutting step length and cutting row spacing, uniform scallop height and high processing efficiency, continuous and steady cutting and little fluctuation of cutting force. This paper studied key technologies of tool path planning for complex surface machining aiming at improving the machining efficiency and quality. The specific contents are as follows:An unique cutter location net is estabished based on cutter location points by the least-squares plane fitting that is characterized with the optimal forward and side step length according to the machining error and scallop height constraints. The CL-net nodes are used as CL points for machining, these CL points have optimal path interval and step length under the condition of the given scallop height, and the tool path can get uniform scallop height. Then the location information, coordinate data, calculation of normal vector and curvature of the CL-net nodes are determined by means of computation, and in order to provide the foundation for the path planning, neighbor nodes of each CL-net node and their correlation are also analysed through MATLAB programming.Based on the geometrical characteristics of the curved surface, the influence of different cutting modes on the cutting force fluctuation is analysed. Tool path planning requires the consideration and integration of fluctuation of cutting force and tool path topology shape. The surface machining quality is improved by reducing the cutting force fluctuation generated during the machining process. The principle of the tool path planning is established under constraint of minimizing the cutting force fluctuation generated during the machining process. In the planning processes, cutter feeds to direction of normal vector of surface changing less. According to the actual processing conditions, some other constraints are attached.The planning tool path not only guarantees the geometric requirements such as the scallop height of the machined surface, the dynamic characteristics and physical factors are also considered in the process, the fluctuation of cutting force generated during the machining process is reduced, which is of great benefit to machining quality, machining equipment and tools. The G code generation procedures are compiled though post process that is applied in three-axis machining. Finally, the saddle surface numerical calculating example is given, through the experiment of the machining efficiency and the processing quality of the workpiece, the correctness and validity of the proposed method are verified.