DESIGN AND ANALYSIS OF A SPUR GEAR USING FEMAP WITH NX NASTRAN

DESIGN AND ANALYSIS OF A SPUR GEAR USING FEMAP WITH NX NASTRAN

Mrs. V. Balambica**, A. Vishnu*, G. Vijay*, R. Ravi Kumar*, E. Umar Farook*
** Lecturer, Department of Mechanical Engineering,
* Students, Department of Mechanical Engineering,
Bharath University, Chennai-73

ABSTRACT
A friction wheel with teeth cut is known as a tooth wheel or gear. Gear drives are widely used in various kinds of machines such as metal cutting, machine tools, automobiles, materials handling equipment, rolling mills, marine power plants etc., In this paper a spur gear is taken into consideration. The gear is modeled using a modeling software Pro-E. After the modeling is carried out the maximum stress in the root spur gear tooth for various modulus are to be analyzed using analysis software FEMAP with NX-NASTRAN (Finite Element with the Modeling and Post processing). This is old meshing software which is used for accurate meshing and analysis. The version going to be used is FEMAP 9.2. The software analyzed results are compared with the theoretical results. The comparison is shown using graphs.

1. INTRODUCTION

A gear is a component within a transmission device that transmits rotational force to another gear or device. A gear is different from a pulley in that a gear is a round wheel which has linkages ("teeth" or "cogs") that mesh with other gear teeth, allowing force to be fully transferred without slippage. Depending on their construction and arrangement, geared devices can transmit forces at different speeds, torques, or in a different direction, from the power source. Gears are a very useful simple machine. The most common situation is for a gear to mesh with another gear, but a gear can mesh with any device having compatible teeth, such as linear moving racks. A gear's most important feature is that gears of unequal sizes (diameters) can be combined to produce a mechanical advantage, so that the rotational speed and torque of the second gear are different from that of the first. In the context of a particular machine, the term "gear" also refers to one particular arrangement of gears among other arrangements (such as "first gear"). Such arrangements are often given as a ratio, using the number of teeth or gear diameter as units. The term "gear" is also used in non-geared devices which perform equivalent tasks.

1.1 SPUR GEAR

The spur gear is simplest type of gear manufactured and is generally used for transmission of rotary motion between parallel shafts. The spur gear is the first choice option for gears except when high speeds, loads, and ratios direct towards other. A single spur gear is generally selected to have a ratio range of between 1:1 and 1:6 with a pitch line velocity up to 25 m/s. The pinion is made from a harder material than the wheel.


2 INVOLUTE GEAR TEETH

For reasons of economy in production modern gear teeth are almost exclusively cut to an involute form. The involute is a curve, which is generated by rolling a straight line around a circle, where the end of the line will trace an involute. The figure below shows the construction of an involute. To use this method to draw a gear profile would be very time consuming. If two meshing gear were manufactured with square teeth instead of being cut to an involute form, the gears would not be able to rotate in mesh. The diagram below shows two such gears which locked together.

3 MODELING

Pro/ENGINEER (commonly referred to as Pro/E or Pro) is a parametric feature-based three-dimensional Solid modeling CAD software created by Parametric Technology Corporation (PTC). Pro/ENGINEER is a mechanical engineering and design CAD tool capable of creating complex 3D models, assemblies, and 2D measured drawings; it does not support architectural or civil engineering practices. It originally caused a major change in the CAD industry when first released by introducing the concept of Parametric Modeling. Rather than models being constructed like a mound of clay with pieces being added or removed to make changes, the user constructs the model as a list of features, which are stored by the program and can be used to change the model by modifying, reordering, or removing them.


4 MESHING

Femap is an engineering analysis pre- and post processor for the simulation of complex engineering problems using the finite element method. It runs on Microsoft Windows and provides CAD import, modeling and meshing tools to create a finite element model, as well as post processing functionality that allows mechanical engineers to interpret analysis results. The finite element method allows engineers to virtually model components, assemblies, or systems to determine behavior under a given set of boundary conditions, and is typically used in the design process to reduce costly prototyping and testing, evaluate differing designs and materials, and for structural optimization to reduce weight. Product simulation applications include basic strength analysis, frequency and transient dynamic simulation, system-level performance evaluation and advanced response, fluid flow and multi-physics engineering analysis for simulation of functional performance.

4.1 Types of Meshing

There are two types of meshing in Femap with Nx-Nastran software, they are
 Tetra meshing
 Hex meshing
Where here the type of meshing selected is hex meshing. This is selected because this will gives more accurate analyzed result.

Module Elements Nodes
4 840 1200
5 1728 2200
6 1200 1854
Elements and nodes of different modules

5 STATIC STRESS ANALYSIS

NX Nastran is a premium computer aided engineering (CAE) tool that major manufactures worldwide rely on for their critical engineering computing needs to produce safe, reliable and optimized designs within increasingly shorter design cycle times. For over 30 years, Nastran has been the analysis solution to choice in every almost every major industry including aerospace, defense, automotive, ship building, heavy machinery, medical and consumer products an industry standard for the computer aided analysis of stress, vibration, structural failure/durability, heat transfer, noise/acoustics and flutter/aero elasticity.


5.1 STATIC ANALYSIS

Static analysis, static projection, and static scoring are pejorative terms for statistical analyses which take existing trends and project them into the future too simplistically, or beyond what is possible to predict in any fashion, producing often wildly unrealistic results. Its opposite, dynamic analysis or dynamic scoring, attempts to take into accord how variables may change or interact

5.2 Element type

Here in our project we have created rigid elements for applying moment. Rigid elements-Rigid connection between a master and unlimited number of slave nodes. For meshing we had created solid elements eight-node brick (hexahedron element).

6 RESULTS AND CONCLUSION
VON MISES STRESS:

Serial No. Module Theoretical ValueN/mm2 Femap Analyzed valueN/mm2
1 4 169.4 177.6
2 5 123 133
3 6 73.8 82.07

BENDING STRESS ANALYSIS:

Serial No. Module Theoretical ValueN/mm2 Femap Analyzed valueN/mm2
1 4 93.4 87.57
2 5 66.5 57.22
3 6 33.8 27.9


7 CONCLUSION:

The theoretical stresses of both bending and von mises stress is found manually and then analyzed in FEMAP with NX NASTRAN software. The readings are shown in the tabular column; the graphs are drawn. It is found that comparing with manual results, FEMAP results are approximate or closer to it. Hence we conclude that Femap with NX-Nastran Software can be used for other analyzing purpose also.


References

1. Dr. T.J.Prabhu (2004) ‘ Fundamentals of Machine Design’, pg 5.3-5.5
2. Dr. T.J.Prabhu (2004) ‘ Design of transmission element’, pg 1.1-1.22
3. FEMAP with NX NASTRAN (2005), Reference guide for meshing. Vol.1
4. FEMAP with NX NASTRAN (2005), Reference guide for analysis, Vol.2
5. Gitin M Maithra (2002), ‘Hand Book of Gear Design’, pg 2.1-2.40, Appendix A1- A5
6. K.R.Gopalakrishnan (2003), ‘Machine Drawing’, pg 259-290
7. PSG College of Technology (2003) ‘Design Data’, Kalaikathir achagam
8. Pro/Engineer, Reference Guide.