Design, modeling and analysis of excavator arm

International Journal of Design and Manufacturing Technology (IJDMT), ISSN 0976 –
6995(Print), ISSN 0976 – 7002(Online) Volume 4, Issue 2, May - August (2013), © IAEME
14
DESIGN, MODELING AND ANALYSIS OF EXCAVATOR ARM
Sachin B. Bende1
, Nilesh P. Awate2
1
M.Tech scholar, Mechanical Engineering Department, GHRCE, Nagpur, India
2
Asst. Professor, Mechanical Engineering Department, GHRCE, Nagpur, India
ABSTRACT
The present work concentrate on the study of the components of the excavator in
order to identify the problems faced while performing the lifting and digging operations and
to provide a design solution by using CAD-CAE systems.For light duty construction work,
generally mini hydraulic backhoe excavators are used and mostly there are soil surfaces for
excavation. So, design of backhoe excavator is critical task in context of digging force
developed through actuators during the digging operation. The important criteria for the
design to be safe is that, the digging forces developed by actuators must be greater than that
of the resistive forces offered by the surface to be excavated. The two important factors
considered during designing an excavator arm are productivity and fuel consumption. As the
present mechanism used in excavator arm is subjected to torsional and bending stresses
during lifting and digging operation respectively, because of which failure occurs frequently
at the bucket end of the arm. So, the new mechanism of excavator arm is designed and the
Pro-e software is used for making the 3D model of the excavator arm linkage. By using
ANSYS workbench software static analysis of each of the excavator arm component is done
at existing digging force and also at newly calculated digging force. Also the bucket volume
is increased to compensate for the loss in production due to the reduction in digging force.
Keywords: Excavator arm, lifting, digging, actuators, productivity, CAD-CAE systems.
I. INTRODUCTION
An excavator is heavy equipment consisting of an articulated arm (backhoe), bucket
and cab mounted on a pivot (a rotating platform, like a Lazy Susan) a top and undercarriage
with tracks or wheels. Their design is a natural progression from the steam shovel.
Excavators are intended for excavating rocks and soils. Excavators may have a mechanical or
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ISSN 0976 – 6995 (Print)
ISSN 0976 – 7002 (Online)
Volume 4, Issue 2, May - August (2013), pp. 14-20
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hydraulic drive. Hydraulic excavators are the most important group of excavators. The typical
hydraulic excavator of VOLVO is shown in the fig.1.
Fig.1. A typical hydraulic excavator of VOLVO
II. DESIGN OF EXCAVATOR ARM
2.1 Calculation of pin diameter
F = 10,300N, r = 391mm, L = 315mm, P = 15.69N/mm2
, A = 66836mm2
,
Shear stress = 42N/mm2
, Bending stress = 84N/mm2
.
Let, d = diameter of pin
Torque, T=F × r=10300×391=4027300N-mm, Load, W=P×A=15.69×66836=1048656.8N
Now, Max. bending moment = M = WL/4 = (1048656.8 × 315)/4 = 82581723N-mm
Since, pin is subjected to suddenly applied load. Considering Km = 1.5, Kt = 2
We know that, equivalent twisting moment
Te = √(Kt × T)2
+ (Km × M)2
= √(2 × 4027300)2
+ (1.5 × 82581723)2
Te = 124134176.5 N-mm
But, Te = π/16 × d3
× shear stress
124134176.5 = π/16 × d3
× 42
Therefore, d = 246.9mm
we know that, equivalent bending moment
Me = 1/2[Km × M + Te] = ½[ 1.5 × 82581723 + 124134176.5]
Me = 124003380.5N-mm
But, Me = π/32 × d3
× bending stress
124003380.5 = π/32 × d3
× 84
Therefore, d = 246.86mm
Taking larger of the two values, we have diameter of pin = d = 246.9mm
2.2 Calculation for the total amount of material the bucket can lift
Since, we have considered a light duty construction work. So, calculate for a soil surface.
Density of soil is 1463kg/m3
.
For existing model,
Volume of bucket, V= 0.022m3
Total weight of soil, W= Density × Volume = 1463 × 0.022 = 32.186 Kg
For proposed model,
Calculated volume of bucket, V= 0.028m3
Total weight of soil, W= Density × Volume = 1463 × 0.028 = 40.964 Kg
Self weight of bucket = 17 Kg

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Now, Total load acting on bucket = Self weight of bucket + Total weight of soil
=17+40.964=57.964Kg
=57.964×9.81=568.62N
By using this load, the dynamic analysis will be done.
III. MODELING
3.1 CAD modeling
CAD technology is very important while designing Excavator Mechanism.
Following are advantages of CAD technology :
1) To increase the productivity of the designer
2) To improve the quality of the design
3.2 CAD/CAE softwares for Excavator mechanism design
• PRO/E – For 3D Component Design.
• PRO/Mechanism – For Mechanism
Pro/ENGINEER is a parametric, feature based, solid modeling System. It is the only
menu driven higher end software. Pro/ENGINEER provides mechanical engineers with an
approach to mechanical design automation based on solid modeling technology and the
features such as 3D modeling, parametric design, feature-based modeling, associativity,
capturing design intent, combining features into parts, and assembly. The three dimensional
model of the assembly of Excavator arm is shown in the fig.2.
Fig.2 Excavator arm assembly
IV. FINITE ELEMENT ANALYSIS
The finite element method (FEM), sometimes referred to as finite element
analysis(FEA), is a computational technique used to obtain approximate solutions of
boundary value problems in engineering. Simply stated, a boundary value problem is a
mathematical problem in which one or more dependent variables must satisfy a differential
equation everywhere within a known domain of independent variables and satisfy specific
conditions on the boundary of the domain. Boundary value problems are also sometimes
called field problems. The field is the domain of interest and most often represents a physical
structure.
The field variables are the dependent variables of interest governed by the differential
equation. The boundary conditionsare the specified values of the field variables (or related
variables such as derivatives) on the boundaries of the field. Depending on the type of
physical problem being analyzed, the field variables may include physical displacement,
temperature, heat flux, and fluid velocity to name only a few.

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4.1 Static structural analysis of Excavator arm
The steps involved in static structural analysis are as follows :
• The IGES file of the Excavator arm is imported and geometry is generated.
• The joint connection type used in the Mechanism Design to place a component in an
assembly is specified.
• Meshing of the model is done.
• Fixed support is provided to the mechanism.
• The initial digging force of 10300N is applied first and then the newly calculated
digging force of 7626N is applied.
• Solution of the problem is done in which the stresses induced due to the force applied
is found.
The fig.3 and fig.4 shows the stresses developed due to application of 10300N
force and 7626N force respectively.
Fig.3 Maximum Shear Stress at 10300N digging force
Fig.4 Maximum Shear Stress at 7626N digging force
It is seen from the fig.3 and fig.4 that dislocation of pin at the bucket end is occurring
at 10300N digging force and when the digging force is reduced to 7626N, the dislocation is
eliminated. Also, the digging force 7626N is greater than the resistive force offered by the
soil surface which is 4000N. Hence, the design is safe.
4.2 Dynamic analysis of bucket
After the digging operation the bucket will lift the material. So, the total load acting
on bucket will be the sum of self weight of bucket and total weight of material in the bucket.
The load acting on bucket while working is 568.62 N. Hence, the dynamic analysis of bucket
is done by applying a load of 570 N. The steps involved in dynamic analysis are as follows :
• Defining the geometry of bucket.
• Meshing of the geometry is done. The component is divided into 2147 elements
having 4457 nodes.

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• Providing fixed support at one end of the bucket.
• Applying force on the bucket.
• Solution involves determination of the stresses occurred due to the application of load
and also finding out the total deformation.
The fig.5, fig.6, and fig.7 shows equivalent (Von-Mises) stress, Maximum Shear stress
and total deformation respectively which are developed because of the 570N force applied.
Fig.5 Equivalent (Von-Mises) Stress
Fig.6 Maximum Shear Stress
Fig.7 Total Deformation
V. RESULTS AND DISCUSSIONS
The static structural analysis of the excavator arm is done and the maximum shear
stress developed in the model is shown. Also, the dynamic analysis of the bucket is done
when the Excavator is working. The stresses developed and deformation occurred is also
shown in the models of the bucket. The graphs of various stresses and deformation is drawn
with respect to the time interval and are shown in the fig.8, fig.9 and fig.10 respectively.

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Fig.8 Graph showing equivalent (Von-Mises) stress
Fig.9 Graph showing maximum shear stress
Fig.10 Graph showing total deformation
The comparison of the proposed model with the existing model is shown in the table 1.
Description Existing model Proposed model
Arm length 650 mm 723 mm
Boom length 1400 mm 1347 mm
Overall height 2150 mm 1996 mm
Bucket capacity 0.22 m3
0.28 m3
32.186 Kg 40.964 kg
Digging force 10300 N 7626 N
Max. Shear Stress 6975.7 Pa 5164.7 Pa
Total Deformation 2.8178 e-005
m 2.0863 e-005
m
Table 1. Comparison of Proposed model with the Existing model
Thus, it can be seen from the results that the digging force can be reduced by doing
some changes in the geometry of the Excavator arm. From the table 1, it can be seen that the
arm length is increased in the proposed model, and the length of boom and overall height of
the structure is slightly reduced.

20
VI. CONCLUSION
Design of the excavator arm has been modified and analysis of the design is also
done. From the analysis results, it is proved that the design is safe for the calculated digging
force. During designing of excavator arm, the important factors taken into account are
productivity and fuel consumption. Since, dislocation of the pin at bucket end and the
cracking at the adapter end is eliminated by reducing the digging force. But reduction in
digging force directly affects the productivity. So, the bucket capacity is increased to
compensate for the loss in production due to the reduction in digging force. Also, fuel
consumption is less due to the reduction in digging force. Finally, the results of the proposed
model is compared with the existing model.
REFERENCES
Research papers
[1] Enrique Busquets, ‘Finite Element Method Applied to a conceptual design of a
Hydraulic Excavator arm’, The University of Texas at El Paso International Test and
Evaluation Association.
[2] Guohua Cui and Yanwei Zhang, ‘Integrated Finite Element Analysis and Experimental
Validation of an Excavator Working Equipment’, IEEE 2009.
[3] Luigi Solazzi, ‘Design of aluminium boom and arm for an excavator’, Journal of
Terramechanics 47 (2010) 201–207.
[4] Srdan M. Bosˇnjak, ‘Comments on ‘‘Design of aluminium boom and arm for an
excavator”, Journal of Terramechanics 48 (2011) 459–462.
[5] Shahram Tafazoli, Peter D. Lawrence, and S. E. Salcudean, ‘Identification of Inertial
and Friction Parameters for Excavator Arms’, IEEE TRANSACTIONS ON
ROBOTICS AND AUTOMATION, VOL. 15, NO. 5, OCTOBER 1999.
[6] Yahya H. Zweiri, Lakmal D. Seneviratne and Kaspar Althoefer, ‘A Generalized
Newton Method for Identification of Closed-chain Excavator Arm Parameters’,
Proceedings of the 2003 IEEE lnlernstional Coorerenee on Robotics & Automation
Taipei, Taiwan, September 14-19, 1003.
[7] Chang Lv and Zhang Jihong, ‘Excavating force analysis and calculation of dipper
handle’, IEEE 2011.
[8] Dr Amged S. El-Wakeel, Dr A.E. Elawa and Y.S. Eng. El-Koteshy, “Position Control
of a Single Arm Manipulator using Ga-Pid Controller”, International Journal of
Electrical Engineering & Technology (IJEET), Volume 4, Issue 2, 2013, pp. 120 - 135,
ISSN Print : 0976-6545, ISSN Online: 0976-6553.
[9] Srushti H. Bhatt, N. Ravi Prakash and S. B. Jadeja, “Modelling of Robotic Manipulator
ARM”, International Journal of Mechanical Engineering & Technology (IJMET),
Volume 4, Issue 3, 2013, pp. 125 - 129, ISSN Print: 0976 – 6340, ISSN Online: 0976 –
6359.
Books
[1] A textbook of Theory of Mechanisms and Machines by Amitabha Ghosh.
[2] A Textbook of “Introduction to “Finite Elements in Engineering” by Tirupati R.
Chandrupatla and Ashok D. Belegundu. Prentice-Hall of India Pvt. Ltd.

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