minimization of stresses in a helical gear by solid modelling in creo software

Minimization of Stresses in a helical Gear by solid modelling using CREO software

Presented by:

Denil Patel

Guide: Ass. Prof. Abhishek Upadhyay

17TH SEM MECHANICAL PROJECT PRESENTATION

Contents•Abstract

•Project definition

•Company Background

•Modelling of a helical gear in CREO with procedure

•Change in Design of Base model

•Analysis of base model and proposed model with procedure

•Tabulation of data

•Advantages of proposed change.

•Conclusion


7TH SEM MECHANICAL PROJECT PRESENTATION 3

AbstractFor the project work, the need is to make a design model of gear and

test it so the main objective of this work is to design and 3D modeling of Helical Gear from calculation and CREO software. The primary goal of this research involves the description and creation of CAD model of a helical gear. This model will be made in CREO software and then it will be given a change in design. This change will then be analyzed in CREO software if any improvements found in the test model it will be shown to the company so that they can use the research work on their real design. This will help then decide whether to improve the design or some other method to improve the performance.

Project Definition

The main goal of this project work was to minimize the stresses inside a helical gear, so that the life of the gear can be increased. Its endurance limit can be increased which will ultimately benefit the users due to an increased service life. The model of present design is made in CREO and then load is applied. This application of load gave us the type of bending in the helical gear. Thus to decrease that and in order to increase the strength of the gear we will build a CAD model in the software and then after applying a change in its geometry we will again test it against the same loading to confirm if the change has increased the endurance limit.



Figure shows direction of application of load

Company Background• About

KIRAN MOTORS LTD. PLATINUM Rated Authorized Dealer for MARUTI SUZUKI INDIA LTD.

Ahmedabad, Baroda, Surat, Himatnagar, Bodeli, Modasa, Viramgam, Mandal

• MissionCommit Less AND Deliver More....

Customer Satisfaction is our Ultimate Moto

• DescriptionWe wish to introduce ourselves as KIRAN MOTORS LTD. PLATINUM Rated

Authorized Dealer for MARUTI SUZUKI INDIA LTDAhmedabad, Baroda, Surat, Himatnagar, Bodeli, Modasa, Viramgam,

MandalKIRAN MOTORS LTD incorporates activities of Sales, Service, and

Repairs of Maruti Suzuki range of vehicles. 77TH SEM MECHANICAL PROJECT PRESENTATION


Introduction to Helical Gears

•Helical gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Helical gears can be meshed in a parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration are sometimes known as "skew gears".

•The angled teeth engage more gradually causing them to run more smoothly and quietly.

•The use of helical gears is indicated when the application involves high speeds, large power transmission, or where noise abatement is important.


•The crossed configuration is less mechanically sound because there is only a point contact between the gears, whereas in the parallel configuration there is a line contact.

•Quite commonly helical gears are used with the helix angle of one having the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal angles. The two equal but opposite angles add to zero: the angle between shafts is zero – that is, the shafts are parallel. Where the sum or the difference is not zero the shafts are crossed. For shafts crossed at right angles the helix angles are of the same hand because they must add to 90 degrees.

Specification of gear used

FACE WIDTH 100

Z1 20

NORMAL MODULE 3.5

HELIX ANGLE 13


Procedures to form involute profile Taken Pitch Circle Diameter , Root Circle Diameter , Outside circle Diameter & base circle Diameter

D = 59.50 mmRD = 51.401mmBC = 55.91 mmOD = 66.50 mm


Procedures to form involute profile •Draw a line from the circle centre (0,0) to the base circle perpendicular to your grid. In other words at 0, 90, 180 or 270 degrees.

•Draw a line 1/20th of the Base Circle Radius (RB) long at a right angle from the end of that line. This line is now tangent to the base circle. It will be very hard to see unless you zoom in on the intersection of the base circle and the lines.


Procedures to form involute profile

Extend the tangent line for each copy so it's

length is the 1/20th of the base circle radius

times the number that you have next to that

tangent line (0 x FCB, 1 x FCB, 2 x FCB…

14 x FCB) extend them from the tangent

point. Make sure you zoom in on the

drawing so you extend the correct line.

Starting at tangent line #0, draw a line from the end of tangent #0 to the end of tangent #1, and so on. Trim the involute curve to DO, the outside diameter of the gear.

Drawing shows the involute drawn along the ends of the tangent lines.7TH SEM MECHANICAL PROJECT PRESENTATION 13


•Erase all the tangent lines, leaving the involute curve generated by the process. Make a line that goes from the intersection of the involute curve and the pitch diameter circle (D) to the centre of the gear. Note that this will not be the same as the line going from the start of the involute at the base circle (DB) to the centre.

•Draw a second line ¼ of the Gear tooth spacing (GT) radially from the first line; usually this is best accomplished by radially copying the line from the first. 4.5 degrees is ¼ of the gear tooth spacing (GT=18 degrees).

•Now mirror a copy of the involute curve around this second line, make sure you leave the original curve, thus copying the other side of the involute 9 degrees (1/2 GT) from the pitch circle (D) intersection with the involute.



• Erase the radial lines, leaving the two involute curves. Draw a line from the start of each involute at the base circle to the centre of the gear. Trim those lines to the Root Diameter (DR) circle.



Erase all the circles except the Root

Diameter (DR) circle. Draw a curve from

the outside tip of one involute to the other,

which has a centre at 0,0 (the centre of the

gear) thus drawing the outside of the tooth

(the curve has the radius of RO). You now

have a completed gear tooth.

Radially copy the completed gear tooth 19 times around the Root Diameter (DR) circle, spacing the copies 18 degrees apart (GT), making 20 gear teeth (T) in total.

Erase the Root Diameter (DR) circle and make a curve (or straight line) between ends of two teeth which has a centre at 0,0 (the centre of the gear).

Radially copy that curve or line around the gear as you did with the gear teeth. You now have a completed involute gear.


Modeling of tooth in CREO software



Part Drawing of the Base Model


Change in Base Model• Fillet is applied

at the bottom of the tooth.

• This is done for improving the fatigue strength as it reduces the Von mises stress for the gear tooth.


Figure shows the Part Drawing of the Proposed Model


Analysis of both the models in CREO 2.0 Software

The image shows the stress at various points on the geometry of the gear.

The Color code indicates the value of stress.

Base model stress analysis


• This image shows the stress distribution for the Proposed model.

• From the image we can understand that the max value of stress has decreased which indicates that the strength of the material has improved. Proposed model analysis image


Properties of the Material Selected for the Gear analysisMaterial Name FE20 (CREO Software Database)

Density 0.250803 lbm/in^3

Young’s Modulus 5.40524e+09 lbm/(in sec^2)

Poisson’s Ratio 0.25

Co-efficient of thermal Expansion 6e-06 /F


Steps for Analysis:

Step: 1

Bring the CAD Model of the part to be analysed and collect the design data, load data and the material to be used.

Step: 2

Click on simulation.

Step: 3

Provide constrains or support. Here the sides of the gear are given the constraints so when it is simulated all the DOF’s of the side face are constrained.

Step: 4

Define the Material. Assign the material in this step. Here the material used is FE20.


Step: 5

Apply load of 10kn on the edge of the gear or the places to be checked for the stress distribution.

Step: 6

Start the analysis.

Step: 7

Then finally you will run the analysis after its completion you have to click show results.

Step: 8

You need to click open the results of the file which is saved by the extension “ .rwd “and review the results imparted by the software.


Step: 9

Then from the same window if you click on edit and results window you can generate graphs of Von Mises and all other stress like the Max shear stress, principle stress.

Step: 10

Bring the new part which is modified form of the original with providing the fillet at the bottom of the tooth.

Step: 11

Now restart the analysis review the result.


Place on Gear Profile Base Model Proposed Model

Colour Max Stress Value Colour Max Stress Value

Tooth Edge Yellow 1294 Yellow- Parrot Green 1184

Near Fillet Light Green 980 Light Green 949

Face Blue 329 Blue 319

Table shows the comparison of the results of analysis of the base model and the proposed model from the before showed images at various points on the gear geometry.


Expected advantages due to modification

•The effect of the novel proposed circular fillet design on the contact stresses developed in helical gear teeth were investigated in comparison with the standard design. The new geometry incorporating the circular fillet was modelled for dimensionless tooth considering loading of 10 kN at the HPSTC of the tooth. •It is clear from the analysis data that the novel circular design surpasses the existing unfilleted design of the helical gear tooth fillet in terms of fatigue endurance without affecting overall geometry. This can be easily manufactured using standard involute hobbing tools with special tip design.


Conclusion The Software CREO 2.0 Parametric is a very useful tool for modelling and analysis of any mechanical linkage or part.The small changes that needed a practical prototype to be sanctioned can now be easily done with the help of this tool.Moreover the fillet provided proves that it increases the strength of the gear tooth as it decreases the maximum Von Mises Stress induced and gives more fatigue resistance.This will increase the life of the gear and improve its efficiency and performance in present conditions.

REFERENCES

PAPERS

• Juha Hedlund and Arto Lehtovaara “Modelling of helical gear contact with tooth deflection “Tampere University of Technology, Machine Design, and P.O. Box 589, 33101 Tampere, Finland Available online 4 January 2006

• K. Mao “Gear tooth contact analysis and its application in the reduction of fatigue wear “Mechanical Engineering, School of Engineering and Design, Brunel University, Uxbridge, Middlesex UB8 3PH, UK, Received 27 May 2005; received in revised form 7 June 2006; accepted 19 June 2006 Available online 25 July 2006

• Shanmugasundaram Sankar, Maasanamuthu Sundar Raj and Muthusamy Nataraj “Profile Modification for Increasing the Tooth Strength in Spur Gear Using CAD “Research Scholar, Anna University, Coimbatore, India Department of Mechanical Engineering, Government College of Technology, Coimbatore, India Received July 13, 2010; revised August 5, 2010; accepted August 18, 2010

◦ V. Spitas, Th. Costopoulos and C. Spitas “Increasing the Strength of Standard Involute Gear Teeth with Novel Circular Root Fillet Design “Laboratory of Machine Elements, Mechanical Engineering Department National Technical University of Athens, Iroon Politechniou 9, 15780, Athens, Greece, American Journal of Applied Sciences 2 (6): 1058-1064, 2005 ISSN 1546-9239


REFERENCESBOOKS

1. Gear design by Gitin M Maitra, TMH Publication, New Delhi

2. Handbook of Practical Gear Design By - Darle W.Dudley
