Involute Spur Gear Template Development by Parametric Technique Using Computer Aided Design

Abstract

There are many methods available for developing profiles of gear and spline teeth. Most of the techniques are inaccurate because they use only an approximation of the involute curve profile. The parametric method developed in this paper provides accurate involute curve creation using formulas and exact geometric equations. In addition, the involute curve by equation technique allows using either Cartesian in terms of X, Y, and Z or cylindrical coordinate systems to create the involute curve profile. Since spur gear geometry is controlled by a few basic parameters, a generic gear can be designed by three common parameters namely the pressure angle (a), the module (m), and the number of teeth (z). Most of the present day CAD systems have no built-in tool for designing such gears. This paper is an attempt in utilizing the concept of parametric technology to develop a template gear. The gear so developed has true involute profile, which is a realistic design. This will allow making changes to the gear design by using Copyright: IAARR, 2009 www.afrrevjo.com 416 Indexed African Journals Online: www.ajol.info parametric input. If one gear file is developed using this parametric technology, with which, different size and variety of spur gears can be created. The specific objective is to design and develop a template spur gear with 3 module, 30 Teeth, 20° pressure angle based on parametric technique by using CATIA V5R14 package. The later portion it is shown how this model may be retrieved and utilized for developing gears of different modules and number of teeth with change in these input parameters. Introduction Template gear development using parametric method means that the dimensions control the shape and size of the gear. The template gear should have the ability to be modified, and yet remain in a way that retains the original design intent. The logical modifications which can be carried out will be the number of teeth and module. Since the design is parametric it is possible to create a variety of spur from one model (Earnest L. Walker and Bruce Cox, 1999). The involute gear is based on an involute curve, which is a mathematical shape. The involute profile is the path traced by unwrapping a string that is wound over a cylinder by maintaining its tension. There are many methods available in creating the involute profile. Method 1 is purely based on geometrical construction and is concerned in preparing the teeth profile individually for all the teeth in the gear, this takes longer time to complete the total profile of the gear and Method 2 is preparing one profile and by keeping this as template the other profiles are created. This method is adequate when ordinary representation of the gear is needed and not an accurate one. The third method and the most accurate system is the graphic method of drawing the involute. Though the procedure is laborious, it can be used for creating the uncorrected and corrected gear profiles. This could be also employed in developing form tools. (Gitin M. Maitra, 2000). Excel Spreadsheet can also be used to draw gears quickly and easily, it will be very useful in creating sets of gears for any projects that require accurate shapes and rapid prototyping of interlocking gears. Excel is a common program. The shortcomings are that any adjustments to the design cannot be immediately reflected in the program where the profile is generated. Instead, the new parameters must be entered into the Excel sheet, and then transferred to a plot file. It also needs to provide a visualization of what the new gear