The methods of globoid surface modeling in CAD

Purpose: Modeling of globoid worm surface is a difficult issue of modeling of complex surfaces in CAD. Worm gears are a challenge for designers because of the construction and the functions that have to be met, as well. There are very few specialized applications to generate this type of gears. The software intended to model of the worm gear wheel only is not accessible, so basing on general intending CAD systems is a necessity. Modeling of globoid worm surface can cause the problem. The examples of globoid helical surfaces modeling in CAD are accessible on the Internet, but often they are not correct in terms of geometry and they do not reflect the actual geometry. These surfaces are modeled on the helix with uniform pitch but diameter variable only. The worm gear development, including these atypical ones, requires looking for new solutions in their modeling. Design/methodology/approach: The three methods of the globoid surface modeling, using CAD systems - AutoCAD and CATIA were presented. The modeling was carried out on the example of the warm lateral surface of the globoidal worm gears. In the first presented method the external program, that generates the script commands for AutoCAD system and lets generate the points of the globoid helix, was used. In the following two methods to model helixes, the possibilities of CATIA were used: creating the graph of two-dimension functions and comprising them into tree-dimension function and kinematic simulation, as well. In the globoid helix the pitch variation is included. Findings: The described methodologies are universal and allow to generate the globoid lateral-surface of worm on the basis of wormwheel constructional assumption and taken tooth profile. The advantages of CAD systems and their usefulness in the globoid worm gear designing are highlighted in the article. Research limitations/implications: The main problem concerned the method No. 3 that uses a kinematic simulation of CATIA. The number of simulation “frame” is the limitation. Practical implications: The proper modeling of worm gear geometry in CAD allows to analyse the geometric cooperation, strength (by the finite element method), or to make a prototype for the preliminary tests with using of the rapid prototyping techniques. Originality/value: All three presented methods are innovative and allow to provide a correctly modeled globoid surface as a basis to create a complete model of the globoid worm.

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Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę (zadania 2017).