A project seminar onFINITE ELEMENT ANALYSIS OF A GEAR TOOTH USING ANSYS AND STRESS REDUCTION BY STRESS RELIEF HOLEByP.BRAHMESHWAR RAO G.SURYA MOHAN REDDY M.HEMANTH K.V.ANURAG REDDY (08145A0310) (07141A0309) (07141A0305) (07141A0310)

Under the guidance ofMr. 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 stressrelief 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 1)

2.

3)

Gears are classified according to the relative position of their shaft axes as follows. Parallel shaft Spur gears Helical gears Herringbone gear Intersecting shaft Straight bevel gears Spiral gears Zerol bevel gears 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

NotesFerrous

Applications

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 qualityPower gears with medium rating to commercial/medium quality

Plain carbon steels

Good machining can be heat treated

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 Low to medium power ratings Up to high precision levels of quality

Stainless Steels (Mart)

Hardenable , reasonable, corrosion resistance , magnetic

Non-ferrous metals Aluminium alloys Light weight ,non corrosive and good mach inability Light duty instrument gears up to high precision quality

Brass alloysBronze alloys Magnesium alloys Nickel alloys Titanium alloys Di-cast alloys Sintered powder alloys

Low cost, non-corrosive, excellent machinabilityExcellent machinability low friction and good compatibility with steel Light weight with poor corrosion resistance. Low coefficient of thermal expansion. poor machinability High strength, for low weight, good corrosion resistance Low cost with low precision and strength Low cost low quality, moderate strength

low cost commercial quality gears. Quality up to medium precisionFor use with steel power gears. Quality up to high precision Light weight low load gears. Quality up to medium precision Special gears for thermal applications to commercial quality Special light weight high strength gears to medium precision High production, low quality gears to commercial 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)))

Gamma =(((bcd*(3.141592654))-(not*k))/(not*2))*(360/(bcd*(3.141592654)))R =r base/(cos(t*40))

Inv =tan(t*40)-(((t*40)*(3.141592654))/180)Theta =(((inv*180)/3.141592654)+gamma) Z =0

Spline is generated by using program

STRESS CONCENTRATION

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 CONCENTRATIONA 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.

SURFACE WHICH IS TO BE ANALYSED1VOLUMES TYPE NUM MAR 16 2011 13:20:36

Y Z X

1NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) DMX =.075412 SMN =.211E-04 SMX =136.713 MAR 16 2011 13:18:11MN

YMX

Z

X

.211E-04

15.19

30.381

45.571

60.761

75.952

91.142

106.332

121.523

136.713

Without hole von misses stress = 136.716N/mm2

1

MN

NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics EFACET=1 AVRES=Mat DMX =.075724 SMN =.204E-04 SMX =133.361 YMX

Z

X

XV =1 YV =2 ZV =3 DIST=100.909 XF =-.366964 YF =.183072 ZF =-.001143 Z-BUFFER .204E-04 14.818 29.636 44.454 59.271 74.089 88.907 103.725 118.543 133.361

Position of the hole :x=30,y=60,dia=3 Von misses stress value=133.36 N/mm2

1

MN

NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics EFACET=1 AVRES=Mat DMX =.075491 SMN =.170E-04 SMX =136.212 XV =1 YV =2 ZV =3 DIST=100.909 XF =-.365144 YF =.185921 ZF =-.001269 Z-BUFFER .170E-04 15.135 30.269 45.404 60.539 75.673 90.808 105.943 121.077 136.212

YMX

Z

X

Position of the hole : x=30,y63,dia=1mm Von misses stress value = 136.212N/mm2

1

MN

NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics EFACET=1 AVRES=Mat DMX =.075717 SMN =.289E-04 SMX =135.663 XV =1 YV =2 ZV =3 DIST=100.91 XF =-.367417 YF =.182698 ZF =-.001001 Z-BUFFER .289E-04 15.074 30.147 45.221 60.295 75.368 90.442 105.516 120.589 135.663

YMX

Z

X

Position of the hole :x=28,y=58,dia=3 Von misses stress value = 135.663N/mm2

1

MN

NODAL SOLUTION STEP=1 SUB =1 TIME=1 SEQV (AVG) PowerGraphics EFACET=1 AVRES=Mat DMX =.075632 SMN =.221E-04 SMX =135.639 XV =1 YV =2 ZV =3 DIST=100.909 XF =-.367262 YF =.18355 ZF =.357E-03 Z-BUFFER .221E-04 15.071 30.142 45.213 60.284 75.355 90.426 105.497 120.568 135.639

YMX

Z

X

Position of the hole :x=35, y=60,dia=2mm Von misses stress = 135.639N/mm2

CONCLUSION:By creating hole in the gear, we can alter stress in the gear. Stress reduction is neither directly nor inversely proportional to the Stress Relief

Hole Diameter. Stress Reduction is neither directly nor inverselyproportional to the position of the stress relief hole. Horizontal shift of the hole position has larger effect on the stress value then the vertical shift.

Better results on stress reduction, were observed on the negative side of theload point, for each tooth By optimizing the diameter and position of the stress relief hole, we can reduce the stress value in a gear tooth by a considerable amount, without affecting the functioning of the gear (In this problem, we could reduce stress from 136.731N/mmA2 to 133.36 N/mmA2 at x=30,y=20 with hole dia 3)

QUERIES ?

THANK YOU