Research On Off-Line Optimization Technology Of NC Milling Process

Numerical control (NC) machining occupies an important place in the manufacturing industry. As one of the key technologies, NC machining is the basement for manufacturing modernization, and is strategically important to develop military industry. Using existing NC machining equipments, machining process optimization can increase efficiency and guarantee machining quality, which is important to improve the machineability of the equipments and produce great economic benefits. Traditionally, adaptive control (AC) technology, especially adaptive control constraints (ACC) was applied to optimize and control the machining process. With the development of computer technology, optimizing machining process based on machining process simulation technique becomes a more potential method, which is an off-line optimization method relative to the on-line optimization in AC, and shows the advantage of low cost, agreement with the trend of green manufacturing and without real-time requirement.As a new stage of machining process simulation, virtual machining can supply vivid machining scene, and take full consideration of machine performance such as kinematic characteristics and dynamic characteristics in geometry simulation and physical simulation. In this paper, off-line machining process optimization technology, which based on virtual machining technique, is studied including off-line optimization principle and process, establishment of optimization mathematics model, selection for constraint rules.Because machining simulation is the basement to the off-line optimization, this paper focus on the research on machining process simulation based on solid simulation technology. Depending on the analysis to the reasons of self-intersection in constructing tool swept volume, the solved method is proposed. To eliminate the wrong result in solid simulation, a sweeping method based on a 3-dimision swept profile is introduced.In simulation and optimization to machining process, getting milling parameters is very important to apply cutting force model, to estimate tool life and to optimize cutting parameters. This paper presents a new method which is named"sliced method", which replaces the tool by its half cylindrical face in feed direction, and treats the intersection geometry between the half cylindrical face and the removed material body of tool path to calculate the milling parameters including radial width, axial depth, cut-in angle and cut-out angle."Sliced method"does not increase the complexity of workpiece, but is more efficient to calculate the parameters relative to the method according to the chip geometry. The validation of the"sliced method"is test by the good agreement between the measured forces and the predicted forces indirectly.To fit the characteristic of machining process optimization, particle swarm optimization (PSO) algorithm was improved by introduced the particle average distance to the standard PSO algorithm. By controlling the threshold of particle average distance, improved PSO algorithm can achieve the optimal result with smaller iterations.Because spindle revolutions and feed rates are not optimized in most NC file,but most optimization researches on federate optimization, this paper makes study on optimizing federates and spindle revolutions together. Combined with the PSO, feed rates and spindle revolutions in NC file are optimized during each"particle"seeking its optimal value.Based on ACIS solid model system, an off-line optimization system of NC end milling process is developed which has the function of solid simulation. Using the optimization system, spindle revolutions and feed rates in NC file for rough machining are optimized according to the multiple objectives: constant machining forces and increasing machining efficiency. Using the optimal NC file, milling experiments are carried out and the experiment result shows the validity and reliability of off-line milling process optimization system.