High-speed cutting (HSC) demands the ability to machine complex 3D curves and surfaces at high speeds, with precision, efficiency, and quality. These complex shapes, often referred to as free-form curves and surfaces, cannot be described by simple quadratic equations. For instance, forging dies used in the production of insulating parts for urban air tram systems are now manufactured directly from hardened steel (52HRC) using high-speed milling. Compared to traditional methods involving graphite electrodes and EDM, hard milling saves time but requires specialized tools and advanced milling strategies.
The precision required is ±0.02mm, with a surface roughness of Ra < 0.7μm. This places strict demands on the CNC system’s trajectory control and adjustment accuracy. During new product development, CAD software is first used to create a model sketch based on functional and design requirements. Then, CAM software calculates the tool path and coordinates for roughing and finishing. The part’s complex contour is approximated using straight lines, arcs, or higher-order curves. Each NC program segment is divided at intersection points, and larger intervals reduce the number of nodes and blocks, improving efficiency.
CNC systems calculate feed commands along each axis to generate the desired tool path through interpolation. This process differs from CAD/CAM's mathematical descriptions. Interpolation calculates intermediate points between start and end positions, based on feedrate and allowable error. The speed and accuracy of this calculation directly affect CNC performance.
Linear interpolation, commonly used in CNC systems, has limitations. When dealing with complex contours, it requires small string errors, increasing calculation points and program size. A typical interpolation period (T) is 1–10 ms, affecting maximum feed speed. If T is too short, the program becomes large and execution slows down, reducing productivity and accuracy—especially in low-volume production of molds, turbine blades, or aircraft parts.
Linear interpolation creates polygonal paths, leading to sharp acceleration changes at corners. This can cause vibration, reduce tool life, and damage the workpiece. Spline interpolation, such as NURBS (Non-Uniform Rational B-Spline), offers better accuracy and smoother motion, replacing multiple straight segments with fewer, more precise curves.
Modern CNC systems use digital drives and buses for improved resolution, reduced interference, and enhanced diagnostics. They also support pre-control functions, error compensation, and multi-axis transformations. These features ensure smooth motion, high accuracy, and safety during high-speed operations.
Error compensation includes thermal, friction, and geometric adjustments. Safety measures like enclosures and two-channel monitoring protect operators and equipment. In conclusion, NURBS interpolation, along with advanced CNC features, significantly improves machining efficiency, accuracy, and safety in high-speed cutting applications.
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