Analysis and Weight Reduction of a Tractors Front Axle

8/12/2019 Analysis and Weight Reduction of a Tractors Front Axle

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Analysis and Weight Reduction of a Tractors Front AxleDilip K Mahanty, Vikas Manohar, Bhushan S Khomane, Swarnendu Nayak

Tata Consultancy Services, India

Swarup Udgata

International Auto Limited,India

Abstract

Engineering components with optimum use of material and easy manufacturability is a direction where

prior simulation through finite element method is found to be very useful. Front Axle of Tractor is one of

the major and very important component and needs very good design as this part experiences the worst load

condition of the whole tractor. The objective of this paper was to analyse the new design of the front axleof tractor for Thirteen (13) different Certification Test load conditions. The existing design has no field

failure reports; so the results of the existing design were taken as basis for comparison with results of the

proposed models. Based on the finite element analysis results, redesign was carried out for the front axle

for weight optimisation and easy manufacturability. This led to five proposed designs of the front axlewhich were evolved based on the above objectives. The proposed designs were evaluated for selected worst

load cases of the existing design. The finite element analysis of new models yielded displacements and

stresses close to the existing design. The increase in stresses were close to 15 % for all five models. Theincrease in displacement was not significant but all the new designs conceived had met the structural

requirement. It was also observed that for the proposed designs there was a significant reduction in weight

(approximately 40 %) and the proposed models did not involve a lot of welding, thereby significant savingsof manufacturing was observed. The components used in the assembly were also found to be cost effective

like smaller diameters bearing, smaller knuckle size etc. The reduction in cost of production and weight

significantly reduced the cost of the new design of Front Axle. This analysis work showcases the use of

finite element analysis as a method for reduction of cost in terms of materials and manufacturing.

Introduction

Front Axle of Tractor is one of the major and very important component and needs very good design as thispart experiences the worst load condition of the whole tractor. The objective of this work was to analyse thecurrent design of the tractor front axle and evaluate the proposed designs for reduction in weight and for

better manufacturability.

The current design was analysed for 13 different Certification Test load cases. Five different models were

proposed based on ease of manufacture and weight reduction. The welding and forming operations required

in the proposed models were less than the current model. Also some of the connected components likebearings, bushes etc. have been redesigned for improved performance and decrease in cost. These were

done based on field feedback.

The Certification load cases as defined for the project is specified below:

a) Drop TestIn this case a pit of 2.5 feet deep and 2 feet wide and 5 feet long is dug on a very hard ground. The tractor

comes on to it at maximum speed of 35 Kmph and one of the front wheel is allowed to fall into it. The

tractor engine pushes the tractor further till the end of the pit and the engine keeps on humming in this caseeven after tractor has reached the end of the pit for some time and finally the engine stops. This is for

tractors with 35/55 HP capacity.


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b) Torture Test

The tractor is run on a test track which is having various types of humps/road conditions.

The conditions are described below:

Wheel 1 Condition Wheel 2 Condition

Ok Pot Hole ok Pot Hole

Ok Pot Hole ok Hump

Ok On a small radius Hump ok On a big radius Hump

(i.e. the radius of hump vary across the width of road )

Ok On a Plane Road ok On a Slope

(Like agriculture plot boundary)

Ok On a V road with Humps ok On a V road with

Humps

(The road height is less at the centre and on an inverted V road with humps)

c) 8 Shaped Track Test

The Tractor runs at 35 Kmph speed on a 8 shaped track with three medium sized humps positioned at

120o to each other in each circle of 8. The Steering has to be turned till its locking position is reachedwhile negotiating a curve.

d) The Impact Test

One side of the tractor collides head on against a rigid wall at a speed of 35 Kmph.

e) Extender wide open Test

The front axle extenders are fully extended and the tractor runs on either type of the V road at a speed of 15Kmph and also on one side slope condition.

f) Pit Test

At speed of 30 Kmph the tractor goes in side a pit of 10 feet deep with 20 degree slope on either side and

comes out.

g) Worst load test

In this load case all the worst load conditions, except the impact load would be applied on the axle and theanalysis would be carried out. Also an extender wide open test with worst load case would be carried out.


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Procedure

The geometric model for the current configuration was created based on the drawings provided. Small

fillets and blends were ignored while creating the model. The geometric model was made using

Unigraphics V16.0 (See Figure 1).

Figure 1 - Solid Model of Current design

The proposed models were based on the sketches, drawings and discussions with the manufacturingengineers. Five proposed models were created (See Figure 2).

Figure 2 - Solid Model of Proposed design


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The geometric models created in Unigraphics were imported into ANSYS V5.6 and FE meshing were

carried out with appropriate type of finite elements.

The current model was meshed using SOLID 45 and SOLID 92 Tetrahedral elements available in ANSYS.

The inner box, outer box and the torch portions were meshed using the SOLID45 elements and the knuckle,

pin, hub, bearings and bushes were meshed using the SOLID92 elements. The bearings, knuckle, hubs andthe bushes were restrained by coupling nodes (See Figure 3).

Figure 3 - Finite Element Model of Current Design

The proposed model was meshed using shell elements and solid tetrahedral elements. The boxes weremeshed using the SHELL63 elements. SHELL63 was considered for the analysis as it saved a lot of time

and effort for meshing of the proposed models with varying thickness. The knuckle, pin, hub, bearings,

torch and bushes were meshed using SOLID92 elements (See Figure 4).

Figure 4 - Finite Element Model of Proposed Design


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Major components of the Front axle where FE meshing have been carried out were,

Outer box

Inner box with torch

Hub

Knuckle and pin

Bushes and bearings.

The details of the loads applied on the model were calculated and given in the appendix-A. A typical loadand boundary condition is given in Figure 5.

Figure 5 - FE Model of Current Design with Boundary Conditions

The individual components have been coupled together so that there is no free motion between

components. The bearings and bushes have been coupled to the pin and the knuckle on the inner side andon the outer side they have been coupled with the sleeve / hub. The extender is coupled with the outer box

at the end of the extender and at the bolts. In the proposed model the torch is coupled to the extender. The

vertical restraints are applied on the bolts of the hub. The axial and transverse restraints are applied at the

pin in case of the current model and on the sleeve in the proposed model.

The loads as applied on the current and proposed model are given in Table 1


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Table 1: Directional loads applied for different Certification Test Conditions

Applied Loads

(N)Sr No. Load Case

FX FY FZ

1.Drop Test

(One Wheel in Pit)0 12000 7584

2.Torture Test

(Both Wheels in Pit)0 24000 20120

3.

Torture Test

(One Wheel in Pit;

Another Wheel in Hump)

0 24000 20120

4.

Torture Test

(One Wheel on Plane ;

Another on Slope)

11427 12000 0

5.Torture Test

(VRoad With Hump)4368 24000 20120

6.

Torture Test

( Small Radius Hump;

Big Radius Hump)

0 24000 7388.4

7.Extender Wide Open Test( One Wheel on Slope;

One on Plane )

11427 12000 0

8.Extender Wide Open Test

( VRoad with Hump)4368 24000 20120

9. Pit Test 1640 28510 0

10. 8 Shaped Track Test 25000 24000 20120

11.One Side Impact Test

(Stops in 0.1 Second)

0 12000 23751.3


( Stops in 1 Second )0 12000 2375.13

13. Worst Loading Condition 25000 28150 20120


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The loads applied on the proposed model were:

Worst loading condition

One side impact (stops in 0.1 second) and

Extender wide with worst loading for the models which could be extended.

Analysis

The static analysis of the Front axle was carried out for the 13 load cases mentioned in Table 1 for the

current model. Based on the analysis of the current model of the front axle, five different configurations for

the proposed models of the front axle were created. The challenge was to reduce the weight of the axle in

such a manner that manufacturability would be easier and design criteria were also met.

All the proposed designs were analysed for the worst load case simulation as obtained for the currentmodel.

Analysis Results & Discussion

Displacement and Stress Results for Current Model

The analysis of the Current model yielded results as specified in Table 2.

Table2: Maximum Stress and displacements in different componentsfor 13 load cases

Maximum Stress

( N/mm2)

Sr

No.Load Case

Max.

Stress

(N/mm2)

Max.

Disp.

(mm)Hub Knuckle Box

1.Drop Test

(One Wheel in Pit)

131

(Box )0.7061 27.5 127.5 131

2.Torture Test

(Both Wheels in Pothole)332.173 1.14 249 197 231

3.

Torture Test

(One Wheel in Pothole;

Another Wheel in Hump)

333 1.12358

(Bolt)182 245

4.

Torture Test

(One Wheel on Plane;

Another on Slope)

84.652 1.769 30.87 31.22 56.66

5.Torture Test

(V Road with Hump)

331.7 1.142 243 197 230.44


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Maximum Stress

(N/mm2)Sr

No.Load Cases

Max.

Stress

(N/mm2)

Max.

Disp.

(mm) Hub Knuckle Box

6.

Torture Test

(Small Radius Hump;

Big Radius Hump)

143.3 0.44 134.5 133 119

7.

Extender Wide Open Test

(One Wheel on Slope;

One on Plane)

176.88 0.7181 39.6 77.58 158.74

8.Extender Wide Open Test

(V Road with Hump)453 2.372 259 270 385

9. Pit Test 283 0.64 283

(Bolt)

109 131

10. 8Shaped Track Test 353.5 1.286 341

(Bolt)

334.6

(Bearing)

241


(Stops in 0.1 Second)320 .55 119

(Bolt)

46

(Bearing)

320


(Stops in 1 Second )

119

(Bolt)

0.2725 119 45.03 56

13. Worst Loading Condition 384 1.278384

(Bolt)241

333

As can be seen the worst load case causes the maximum stress in the hub and the box. . The 8 shaped

track test causes worst load in the knuckle. The extender wide test causes the maximum stress in the box.But this is a very rare loading event. The maximum displacement for all the 13 load cases is due to the load

case 8 (extender wide open test on a V road). This is a very rare loading event. These are the results of the

current model and as the current model has reported no failures in the field, these results have been taken as

baseline to compare against the results obtained from the analysis of the proposed models.

Displacement and Stress Results for Modified Design

The displacement and stress values obtained for the modified designs are presented in the Table 3


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Table-3: Maximum Stress and displacements in different omponentsfor proposed models.

Maximum Stress

( N/mm2)Sr

No. Load Case

Max.

Stress

( N/mm2)

Max.

Disp.

( mm ) Hub Knuckle Box

Design: Square Box with Extender

1. Worst Loading Case604.174

(Hub Bolt)3.017

604

(Bolt)

243.4

(Bearing)387

2. Impact Test

345.155

(Rib & BoxConnection)

1.831

159.5

(Bolt) 40.177 345.155

3.Extended Position

(Worst Loading Case)864.4 8.06 864.4

338.5

(Bearing)524.4

Design: Square Box without Extender


(Hub Bolt)

3.29

(Cap End)

614.974

(Bolt)

248.756

(Bearing)407.413

2. Impact Test

318.223

(Rib & Box

Connection)

1.72

(Cap End)

174.5

(Bolt)

43.5

(Bearing)

318.223

Design: U Shaped Box with Extender

1. Worst Loading Case 619.1473.117

(Cap End)

619.417

(Bolt)251.2 435.4

2. Impact Test

413.58

(Bolt of

Extender)

1.587

(Cap End)

166.1

(Bolt)38.21 316.3


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Max. Stress (N/mm2)

Sr.

No.Load Case

Max Stress

(N/mm2)

Max Disp

(mm)Hub Knuckle Box

3. Extended Position(Worst Loading Case)

1073

(Bolt OF

Extender)

8.835(Cap End)

890.9(Bolt)

351.042 1073

Design : U Shaped Box without Extender


(Hub Bolt)

3.365

(Cap End)

643.0

(Bolt)

260.8

(Bearing)257.86

2. Impact Test240.422

(Box)

1.864

(Cap End)

178.638

(Bolt)44.394 240.422

(Rib& BoxConnection)

Design : Square Box with Offset Knuckle (Option 4)

1. Worst Loading Case

618.12

(Rib & Box

Connection)

3.642

(Cap End)

618.12

(Bolt)

240.258

(Bearing)319.5

2. Impact Test289.315

(Hub Bolt)

2.217

(Cap End)

172.6

(Bolt)

44.5

(Bearing)289.315


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Figure 6 - Total displacement plot for the current design

Figure 7 - Total displacement plot for the proposed design


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models did not involve a lot of welding, thereby significant savings of manufacturing was observed. The

components used in the assembly were also found to be cost effective like smaller diameters bearing,

smaller knuckle size etc. The reduction in cost of production and weight significantly reduced the cost of

the new design of Front Axle.

Of the proposed models, the model U-box with extender was considered as the best based on the utilizationand application. This analysis work showcases the use of finite element analysis as a method for reduction

of cost in terms of materials and manufacturing.

.

References

1. ANSYS Theory Manual.

2. J. E. Shigley, C. R. Mischke, Mechanical Engineering Design, McGraw-Hill, 1989, Singapore.

Appendix-A

1. DROP TESTFor details of the loads (See Figure 9)

Velocity of the Tractor is 35 km/hr (9.722 m/sec).

Acceleration = - u2/2S = - 31 m/sec2

Force = mass X acceleration = 7584 N.

Hence, vertical force on both wheels = 12000 N

Frontal force on Wheel, W1= 7584 N

Figure 9 - Drop test details

2. TORTURE TEST WITH POT HOLE & HUMP

For details of the loads (See Figure 10)


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Assuming, velocity reduces from 35 km/hr ( 9.722 m/sec ) to 17.5 km/hr ( 4.861 m/sec) in 431

mm distance.

Acceleration = - (u2-v2)/2S = - 82.24 m/sec2.

Hence, frontal force on both wheel = 20120 N

And Vertical force due to impact load = 24000 N.

Figure 10 - Torture test with pothole & hump details

3. TORTURE TEST WITH TWO POT HOLES


As size of potholes are same, from calculation of point no. 2,Frontal force on both wheel = 20120 N

And Vertical force due to impact load = 24000 N.

Figure 11 - Torture test with 2 potholes details


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4. TORTURE TEST WITH SMALL & BIG HUMPS


Assuming velocity reduces from 30 km/hr ( 8.33 m/sec ) to 15 km/hr (4.17 m/sec ) at big hump.

Acceleration = - (u2-v2)/2S = - 30.16 m/sec2.

Hence, Frontal force on both wheel= mass X acceleration = 7388.4 NAnd Vertical force due to impact load = 24000 N.

Figure 12 - Torture test with small & big humps details

5. IMPACT TEST (ONE SIDE COLLIDES AGAINST A RIGID WALL)


Considering time required to stop = 0.1 sec.

Acceleration = - (u-v)/t = - 97.22 m/sec2. Hence, Frontal force on one wheel = 23751.28 N

And Vertical force = 12000 N.

Figure 13 - Impact test (one side collides against a rigid wall) details


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6. TEST ON V SHAPED ROAD


By solving, R1= 12770 N = R2

Hence, Transverse component= R1 sin200=R2 sin20

0= 4368 N

Due to humps on the road, Frontal component on both wheels = 20120 N( from point no. 2).Vertical force = 24000 N.

Figure 14 - Test on V shaped road details

7. TEST FOR ONE WHEEL ON PLANE & ANOTHER WHEEL ON SLOPE


Considering, slope starts from the centre of the tractor ( the middle point of the wheels ),

The angle of the slope = tan 1{914.4/(663 X cos43.60)} = 62.30

So, R2= 12906.4 N. Hence, Transverse component =R2sin62.30= 11427 N

Vertical force on both wheels = 12000 N.

Figure 15 - Test for one wheel on plane & another on slope details

8. PIT TEST ON 200SLOPE ROAD


Total reaction force = R1= 2mg = 4800 N.

So, R1sin200= 1640 N & R1cos20

0= 4510 N

Hence, Frontal force on both wheel = 1640 N


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Vertical force on both wheels= 24000 + 4510 = 28510 N. (For impact loading.)

Figure 16 - Pit test on 200slope road details

9. TEST ON 8SHAPED TRACK WITH HUMPS


Assuming, radius of the track = 2.5 m.And, velocity of the tractor = 35 km/hr ( 9.722 m/sec).

Cetrifugal force = ( m v2/ r ) = 9345 N .

Maximum bearing force = 25000 N ( given ).

Hence, Ttransverse component = 25000 N ( considering higher value).

Due to humps on the road, Frontal component on both wheels = 20120 N (From point no. 2).

Vertical force = 24000 N.( for impact loading ).

Figure 17 - Test on 8 shaped track with humps details

10. WORST LOADING CASE


Considering all loading cases, maximum loads at all three directions are,


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Transverse component = 25000 N, Frontal component on both wheels = 20120 N .

Vertical force = 28510 N.

Figure 18 - Worst loading case details

Analysis and Weight Reduction of a Tractors Front Axle

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