A project seminar on FINITE ELEMENT ANALYSIS OF A GEAR TOOTH USING ANSYS AND STRESS REDUCTION BY STRESS RELIEF HOLE By P.BRAHMESHWAR RAO (08145A0310) G.SURYA MOHAN REDDY (07141A0309) M.HEMANTH (07141A0305) K.V.ANURAG REDDY (07141A0310) Under the guidance of Mr. Y.NAVEEN (Asst.Proffessor)
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A project seminar on
FINITE ELEMENT ANALYSIS OF A GEAR TOOTH USING ANSYS AND STRESS REDUCTION BY
STRESS RELIEF HOLE By
P.BRAHMESHWAR RAO (08145A0310)
G.SURYA MOHAN REDDY (07141A0309)
M.HEMANTH (07141A0305)
K.V.ANURAG REDDY (07141A0310)
Under the guidance of
Mr. Y.NAVEEN
(Asst.Proffessor)
ABSTRACT
The main aim of this project is to model a spur gear by
PRO-E. The model is then imported to ANSYS.
To reduce the stress in a gear tooth, with the help of a
stress relief hole, to the minimum value, without affecting the
quality.
PROJECT OVERVIEW A plane area element (plane stress with thickness) was chosen
and the model for the gear tooth whose stress was to be studied, was created and the Von Misses stress was calculated.
Then various case studies were conducted using a stress relief hole at different positions and the Von Misses stress value in each case was compared with the Von Misses stress value without hole.
After a number of case studies, we were able to optimize the position of the hole, because of which, stress in the gear tooth was the minimum.
INTRODUCTION ABOUT GEARS
Gears are used to transmit motion from one shaft to another or between a shaft and slide, this can be accomplished by successively engaging teeth.
Gears use no intermediate link or connector & transmit the motion by direct contact.
The two bodies have either a rolling or a sliding motion along the tangent at point of contact and no motion is possible along the common normal.
Gear design has evolved to such a level that throughout the motion of each contacting pair of teeth the velocity ratio of the gears is maintained fixed and the velocity ratio is still fixed as each subsequent pair of teeth come into contact.
GEAR TERMINOLOGY:-
Addendum circle Dedendum circle Addendum Dedendum Clearance Face of tooth Flank of tooth Circular pitch Pitch point Base circle
CLASSIFICATION OF GEARS Gears are classified according to the relative position of their shaft axes as
follows.
1) Parallel shaft
Spur gears
Helical gears
Herringbone gear
2. Intersecting shaft
Straight bevel gears
Spiral gears
Zerol bevel gears
3) Skew shaft
Crossed helical gears
Worm gears
SPUR GEAR Spur gears have straight teeth parallel to the axis and thus, are not subjected
to axial thrust due to tooth load.
At the time of engagement of the two gears, the contact extends across the entire width on a line parallel to the axis of rotation.
This results in sudden application of load, high impact stress and excessive noise at high speeds.
HELICAL GEAR In helical gear, the teeth are curved,
each being helical in shape.
At the beginning of engagement, contact occurs only at the point of leading edge of the curved teeth. As the gear rotates, the contact extends along the diagonal line across the teeth.
Thus the load application is gradual which results in low impact stresses and reduction in noise . Therefore helical gears can be used at high velocities than spur gears and have greater load carrying capacity
BEVEL GEARS
STRAIGHT BEVEL GEARS : The teeth are straight , radial to the point of intersection of the shaft axes and vary in cross section through out their length.
SPIRAL BEVEL GEAR: When the teeth of the bevel are inclined at an angle to the face of the bevel , they are known as Spiral or helical bevels.
ZEROL BEVEL GEARS: Spiral bevel gears with curved teeth but with a zero degree spiral angle are known as Zerol bevel gears
WORM GEAR Worm gear is a special case of a spiral gear
In which the larger wheel, usually, has a hallow or concave shape such that a portion of the pitch diameter of the other gear is enveloped on it.
The smaller of the two wheel is called the worm which also has a large spiral angle
ADVANTAGES:
Provide Positive Drive without slip. Suitable for high speed , high torque & high power transmission. Properly designed & properly maintained gear system can run over decades. Very high transmission ratio is practicable. Compact machine train in limited space.
DISADVANTAGES:
Needs Proper Lubrication System. which involve high cost. Needs Proper alignment- misaligned gear train will damage within very short time. Misaligned gear mesh or lack of lubrication will make noise & vibration. Spare gear is costly and proper replacement gear is difficult to procure in many
cases it is available only from OEM source. Require skilled technician to maintain.
TYPES OF FAILURES IN GEARS
Moderate wear Pitting
Rippling Ridging
Materials Notes Applications
Ferrous
Cast Iron Low cost easy to machine with high damping
Large moderate power, commercial gears
Cast Steels Low cost reasonable strength Power gears with medium rating to commercial quality
Plain carbon steels Good machining can be heat treated
Power gears with medium rating to commercial/medium quality
Alloy Steels Heat Treatable to provide highest strength and durability
Highest power requirement. For precision and high precision
Stainless Steels (Aust) Good corrosion resistance. Non magnetic.
Corrosion resistance with low power ratings. Up to precision quality
Stainless Steels (Mart) Hardenable , reasonable, corrosion resistance , magnetic
Low to medium power ratings Up to high precision levels of quality
Non-ferrous metals
Aluminium alloys Light weight ,non corrosive and good mach inability
Light duty instrument gears up to high precision quality
High production, low quality to moderate commercial quality
Gear has been developed by using PRO-E
COMMANDS USED Curve id(by using program)
Sketch 1
Extrude 1
Extrude cut 2
Pattern of Extrude 2
Round 1
Round 2
PROGRAM TO GENERATE CURVE ID /* For cylindrical coordinate system, enter parametric equation /* in terms of ‘t’ (which will vary from 0 to 1) for ‘r’, theta and ‘z’ /* For example: for a circle in x-y plane, centered at origin /* and radius = 4, the parametric equations will be: /* r = 4 /* theta = t * 360 /* z = 0 /*------------------------------------------------------------------- N o t=17 P angle=20 M =8 x=.15 O d=128 R d=92
P cd=not*m
B cd=p cd*cos(p angle)
R base=b cd/2
T t=(((3.141592654)*m)/2)+(2*m*x*tan ( pangle ))
K =b cd*((tt/ pcd)+((tan(pangle)-((pangle*(3.141592654)))/180)))
The fracture of a material is dependent upon the forces that exist between the atoms.
Because of the forces that exist between the atoms, there is a theoretical strength that is typically estimated to be one-tenth of the elastic modulus of the material.
The stress is concentrated around the crack tip or flaw developing the concept of stress concentration.
METHODS TO REDUCE STRESS CONCENTRATION
A number of methods are available to reduce stress concentration in machine parts. Some of them are as follows:
1. Provide a fillet radius so that the cross-section may change gradually.
2. Sometimes an elliptical fillet is also used.
3. If a notch is unavoidable it is better to provide a number of small notches rather than a long one. This reduces the stress concentration to a large extent.
4. If a projection is unavoidable from design considerations it is preferable to provide a narrow notch than a wide notch.