The methods of globoid surface modeling in CAD

Abstract

Purpose: Modeling of globoid worm surface is a difficult issue of modeling of complexsurfaces in CAD. Worm gears are a challenge for designers because of the constructionand the functions that have to be met, as well. There are very few specializedapplications to generate this type of gears. The software intended to model of the wormgear wheel only is not accessible, so basing on general intending CAD systems is anecessity. Modeling of globoid worm surface can cause the problem. The examplesof globoid helical surfaces modeling in CAD are accessible on the Internet, but oftenthey 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 newsolutions 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 carriedout on the example of the warm lateral surface of the globoidal worm gears. In thefirst presented method the external program, that generates the script commands forAutoCAD system and lets generate the points of the globoid helix, was used. In thefollowing two methods to model helixes, the possibilities of CATIA were used: creatingthe graph of two-dimension functions and comprising them into tree-dimension functionand kinematic simulation, as well. In the globoid helix the pitch variation is included.Findings: The described methodologies are universal and allow to generate the globoidlateral-surface of worm on the basis of wormwheel constructional assumption andtaken tooth profile. The advantages of CAD systems and their usefulness in the globoidworm 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 thelimitation.Practical implications: The proper modeling of worm gear geometry in CAD allows toanalyse the geometric cooperation, strength (by the finite element method), or to makea prototype for the preliminary tests with using of the rapid prototyping techniques.Originality/value: All three presented methods are innovative and allow to provide acorrectly modeled globoid surface as a basis to create a complete model of the globoidworm.