Knowledge-based Geometry Generation for Spur and Helical Gears

Abstract

Numerical analysis and true 3-D solid models of gear pairs are highly desirable to simulate real working conditions and reduce long and expensive test phases. This article presents methods, within a knowledge-based Automated Concurrent Engineering Software (ACES) for gear design and manufacturing system, for defining the gear tooth profile analytically from basic geometric parameters (diametral pitch, pressure and helix angles, number of teeth and tooth thickness) and determining the coordinates of all points on the working and the fillet portions of the tooth for standard and nonstandard gears, in order to generate FEM models for analysis, through automatic mesh generation and boundary condition assignment and produce a suitable gear construction (3-D model). The involute and trochoid curves can then be plotted on a Cartesian coordinate system emanating at the center of the gear. An accurate description of the tooth geometry and the associated mating-gears model for FEM analysis provide an early estimation of the full stress fields during the design phase, where there is still time to make significant changes. This 3-D solid model provides maximal value to a designer for machining the gear on a standard CNC milling machine without form cutters; far defining tool paths for Electric Discharge Machining (EDM); for rapid prototyping systems and for viewing VRML models. The system has a direct interface with a FEM processor (ANSYS) and a CAD tool (Pro/E). A case study is presented to demonstrate the system functionality with spur and helical gears.