Design optimization of excavator bucket using Finite Element Method

76
International Journal of Research and Innovation (IJRI)
Design optimization of excavator bucket using Finite
Element Method
S.Sekhar Babu1
, Y.Venu2
1 Research Scholar, Department Of Mechanical Engineering, Vikas college of Engineering and Technology,Vijayawada rural,A.P,India.
2 Assistant professor , Department Of Mechanical Engineering, Vikas college of Engineering and Technology,Vijayawada rural,A.P,India.
*Corresponding Author:
S.Sekhar Babu,
Research Scholar, Department Of Mechanical Engineering,
Vikas college of Engineering and Technology,
Vijayawada rural,A.P,India.
Published: December 22, 2014
Review Type: peer reviewed
Volume: I, Issue : IV
Citation: S.Sekhar Babu, Research Scholar,Design optimiza-
tion of excavator bucket using Finite Element Method
INTRODUCTION
A hydraulic shovel of a bucket type excavator is an
earth moving machine
Comprising an upper rotatable chassis mounted on
a drivable body with wheel or
Track and hydraulically powered mechanism con-
sisting of boom, arm and bucket,
Mounted to the upper chassis.
The mechanism is actuated by the help of hydraulic
cylinders. The machines are
Widely used for the digging, lifting and cleanup pur-
pose. Trench digging in the
Application of placing pipes, digging applications in
construction areas, rearranging
Face of the earth are some examples for the use of
excavators.
Excavators can also be used for tasks other than
digging. In such cases different end
Attachments can also be used. One common appli-
cation is breaking rocks, for which
A breaker is used instead of a bucket
General view of an excavator
An excavator boom consists of an upper chassis
mounting bracket, an arm mounting
bracket at the tip end of the body, an arm cylinder
connection bracket welded on the
upper plate and a boom cylinder boss placed in the
middle of the vertical side plates.
The boom body is constructed with upper, lower
and vertical side plates welded to each other at right
angles to form a rectangular cross section. Addi-
tionally,
reinforcement plates may be connected to form a
closed box section in pursuant of
the design criteria
Abstract
An excavator is a typical hydraulic heavy-duty human-operated machine used in general versatile construction opera-
tions, such as digging, ground leveling, carrying loads, dumping loads and straight traction. Normally backhoe excava-
tors are working under worst working conditions. Due to severe working conditions, excavator parts are subjected to
high loads and must work reliably under unpredictable working conditions. Thus, it is necessary for the designers to
provide not only an equipment of maximum reliability but also of minimum weight and cost, keeping design safe under
all loading conditions.
The aim of the project is to improve excavator bucket life by optimizing the design and design parameters.
In first step data collection will be done.
In the next step excavator bucket model will be generated for further study in FEM software.
In the next step load calculations will be done to utilize the load value in FEM software.
In the next step transient analysis will be done to find the failure locations.
Model parameters will be modified and model will be modified using optistruct method.
Analysis will be conducted on modified model.
By using above analysis results best design along with best material will be concluded.
1401-1402

77
Hinge
Optimized reinforced construction for high strength
and performance matched to the machine‘s power.
Pin on or dedicated hinges are available
Hinge plates
Pass through torque tube for better load distribu-
tion and durability.
Sidebar
Re-drilled to add sidebar protection.
Side plate
Side wear plates
Side plates meet up with bottom wear plates for
seamless corner protection.* High strength steel
utilized for added protection.
Base edge
Straight or “spade”, depending on application.
Gussets
For maximum rigidity.
Adjuster group
Allows for easy correction for wear between the stick
and bucket.
Teeth (tips)
Forged from steel with properties that maintain
hardness for long wear life in tough digging applica-
tions.
Side cutters& sidebar protectors
For protection and penetration.
TYPES OF TEETH (TIPS)
Force calculations
To find the forces at different points of the attach-
ment is very important as it plays a crucial role in
the analysis, for getting results close to the actual
it is required to have accurate values of forces at
all pivot points. The methodology adopted is to find
maximum digging force for the given cylinder pres-
sures, and this is done using design view. The sec-
ond stage is to find the forces at all pivot points of
the attachment, this is done using mathcad.
Calculation of digging and breakout force
Digging force (rx)
The digging force is the available force at the tip of
the bucket teeth created by the stick cylinder(s).
Maximum digging force is calculated with dimen-
sion “a” at its maximum and with the bucket in a
position calculated for maximum breakout force.
Fs
-stick cylinder force
a -Perpendicular distance stick cylinder axis - stick
pivot
b -Distance stick pivot - tooth tip
Digging Force

78
Breakout Force (L)
The breakout force is the available force at the tip of
the teeth created by the bucket cylinder. Maximum
breakout force is reached when the available tooth
force reaches at its maximum.
Breakout Force
Fl- Bucket cylinder force
c- Perpendicular distance bucket cylinder
axis - lever pivot
d- Perpendicular distance connecting link
axis - lever pivot
e- Perpendicular distance connecting link
axis – bucket pivot
r- Radius bucket pivot - tooth lip
MATERIAL FILL FACTOR
It is the factor by which the bucket is over or under
filled.
CALCULATION OF EXCAVATOR
BUCKET CAPACITY
Excavator buckets according to SAE
Capacity calculation of excavator buckets
according to SAE
SAE (Society of Automotive Engineers) and
PCSA (Power Crane & Shovel Association)
Capacity calculation of backhoe buckets accord-
ing
to CECE
(Committee for European Construction Equipment)
Definition of used symbols
A = BUCKET OPENING, measured from cutting edge
to end of bucket rear plate
B = CUTTING WIDTH, measured over the teeth or
side cutters
b = BUCKET WIDTH, measured over sides of buck-
et at the lower lip without teeth of Side cutters at-
tached
b1 = INSIDE WIDTH FRONT, measured at cutting
edge
b2 = INSIDE WIDTH REAR, measured at narrowest
part in the back of the bucket
F = SIDE PROFILE AREA OF BUCKET, bounded by
the inside contour and the strike
Plane of the bucket. Angular or curved indentation
of the side leading edge from the strike plane is not
being considered if less than A/12.
Comparison of bucket specification and
Digging force

79
MODELING
The above image shows sketch
The above image shows Extruded model
The above image shows Shell model
The above image shows Back ribs
The above image shows Final model
The above image shows Modified model
2D DRAWINGS
The above image shows 2d drafting of existing model
The above image shows 2d drafting of modified model

80
INTRODUCTION TO FEA
Finite element analysis (fea) was first developed in
1943 by r. Courant, who utilized the ritz method
of numerical analysis and minimization of variation
calculus to obtain approximate solutions to vibra-
tion systems. Shortly thereafter, a paper published
in 1956 by m. J. Turner, r. W. Clough, h. C. Martin,
and l. J. Top established a broader definition of nu-
merical analysis. The paper centered on the "stiff-
ness and deflection of complex structures".
By the early 70's, fea was limited to expensive main-
frame computers generally owned by the aeronaut-
ics, automotive, defense, and nuclear industries.
Since the rapid decline in the cost of computers and
the phenomenal increase in computing power, fea
has been developed to an incredible precision. Pre-
sent day supercomputers are now able to produce
accurate results for all kinds of parameters.
Fea consists of a computer model of a material or
design that is stressed and analyzed for specific re-
sults. It is used in new product design, and existing
product refinement. A company is able to verify a
proposed design will be able to perform to the cli-
ent's specifications prior to manufacturing or con-
struction. Modifying an existing product or struc-
ture is utilized to qualify the product or structure
for a new service condition. In case of structural
failure, fea may be used to help determine the de-
sign modifications to meet the new condition.
There are generally two types of analysis that are
used in industry: 2-d modeling, and 3-d modeling.
While 2-d modeling conserves simplicity and allows
the analysis to be run on a relatively normal com-
puter, it tends to yield less accurate results. 3-D
modeling, however, produces more accurate results
while sacrificing the ability to run on all but the
fastest computers effectively. Within each of these
modeling schemes, the programmer can insert nu-
merous algorithms (functions) which may make the
system behave linearly or non-linearly. Linear sys-
tems are far less complex and generally do not take
into account plastic deformation. Non-linear sys-
tems do account for plastic deformation, and many
also are capable of testing a material all the way to
fracture.
Fea uses a complex system of points called nodes
which make a grid called a mesh. This mesh is pro-
grammed to contain the material and structural
properties which define how the structure will react
to certain loading conditions. Nodes are assigned at
a certain density throughout the material depend-
ing on the anticipated stress levels of a particular
area. Regions which will receive large amounts of
stress usually have a higher node density than
those which experience little or no stress. Points of
interest may consist of: fracture point of previously
tested material, fillets, corners, complex detail, and
high stress areas. The mesh acts like a spider web
in that from each node, there extends a mesh ele-
ment to each of the adjacent nodes. This web of vec-
tors is what carries the material properties to the
object, creating many elements.
A wide range of objective functions (variables within
the system) are available for minimization or maxi-
mization:
• Mass, volume, temperature
• Strain energy, stress strain
• Force, displacement, velocity, acceleration
• Synthetic (user defined)
There are multiple loading conditions which may be
applied to a system. Some examples are shown:
• Point, pressure, thermal, gravity, and centrifugal
static loads
• Thermal loads from solution of heat transfer anal-
ysis
• Enforced displacements
• Heat flux and convection
• Point, pressure and gravity dynamic loads
Each fea program may come with an element li-
brary, or one is constructed over time. Some sample
elements are:
• Rod elements
• Beam elements
• Plate/shell/composite elements
• Shear panel
• Solid elements
• Spring elements
• Mass elements
• Rigid elements
• Viscous damping elements
Many fea programs also are equipped with the capa-
bility to use multiple materials within the structure
such as:
• Isotropic, identical throughout
• Orthotropic, identical at 90 degrees
• General anisotropic, different throughout
Types of engineering analysis
Structural analysis consists of linear and non-lin-
ear models. Linear models use simple parameters
and assume that the material is not plastically de-
formed. Non-linear models consist of stressing the
material past its elastic capabilities. The stresses in
the material then vary with the amount of deforma-
tion as in.
Vibrational analysis is used to test a material against
random vibrations, shock, and impact. Each of
these incidences may act on the natural vibrational
frequency of the material which, in turn, may cause
resonance and subsequent failure.
Fatigue analysis helps designers to predict the life
of a material or structure by showing the effects of
cyclic loading on the specimen. Such analysis can
show the areas where crack propagation is most
likely to occur. Failure due to fatigue may also show
the damage tolerance of the material.
Heat transfer analysis models the conductivity or
thermal fluid dynamics of the material or struc-
ture. This may consist of a steady-state or transient
transfer. Steady-state transfer refers to constant

81
thermo properties in the material that yield linear
heat diffusion.
Results of finite element analysis
Fea has become a solution to the task of predicting
failure due to unknown stresses by showing prob-
lem areas in a material and allowing designers to
see all of the theoretical stresses within. This meth-
od of product design and testing is far superior to
the manufacturing costs which would accrue if each
sample was actually built and tested.
In practice, a finite element analysis usually con-
sists of three principal steps:
1. Preprocessing: the user constructs a model of the
part to be analyzed in which the geometry is divided
into a number of discrete sub regions, or elements,"
connected at discrete points called nodes." Certain
of these nodes will have fixed displacements, and
others will have prescribed loads. These models can
be extremely time consuming to prepare, and com-
mercial codes vie with one another to have the most
user-friendly graphical “preprocessor" to assist in
this rather tedious chore. Some of these preproces-
sors can overlay a mesh on a preexisting cad file, so
that finite element analysis can be done convenient-
ly as part of the computerized drafting-and-design
process.
2. Analysis: the dataset prepared by the preproces-
sor is used as input to the finite element
Code itself, which constructs and solves a system of
linear or nonlinear algebraic equations
Where u and f are the displacements and externally
applied forces at the nodal points. The
Formation of the k matrix is dependent on the type
of problem being attacked, and this
Module will outline the approach for truss and lin-
ear elastic stress analyses. Commercial
Codes may have very large element libraries, with
elements appropriate to a wide range
Of problem types. One of fea's principal advantages
is that many problem types can be
Addressed with the same code, merely by specifying
the appropriate element types from
The library.
3. Post processing: in the earlier days of finite ele-
ment analysis, the user would pore through reams
of numbers generated by the code, listing displace-
ments and stresses at discrete positions within the
model. It is easy to miss important trends and hot
spots this way, and modern codes use graphical
displays to assist in visualizing the results. A typi-
cal post processor display overlays colored contours
representing stress levels on the model, showing a
full field picture similar to that of photo elastic or
moiré experimental results.
Introduction to ansys
Ansys is general-purpose finite element analysis
(fea) software package. Finite element analysis is
a numerical method of deconstructing a complex
system into very small pieces (of user-designated
size) called elements. The software implements
equations that govern the behaviour of these ele-
ments and solves them all; creating a comprehen-
sive explanation of how the system acts as a whole.
These results then can be presented in tabulated,
or graphical forms. This type of analysis is typically
used for the design and optimization of a system far
too complex to analyze by hand. Systems that may
fit into this category are too complex due to their
geometry, scale, or governing equations.
Ansys is the standard fea teaching tool within the
mechanical engineering department at many col-
leges. Ansys is also used in civil and electrical en-
gineering, as well as the physics and chemistry de-
partments.
Ansys provides a cost-effective way to explore the
performance of products or processes in a virtual
environment. This type of product development is
termed virtual prototyping.
With virtual prototyping techniques, users can iter-
ate various scenarios to optimize the product long
before the manufacturing is started. This enables a
reduction in the level of risk, and in the cost of in-
effective designs. The multifaceted nature of ansys
also provides a means to ensure that users are able
to see the effect of a design on the whole behavior
of the product, be it electromagnetic, thermal, me-
chanical etc.
Steps involved in ansys:
In general, a finite element solution can be broken
into the following these
Categories.
1. Preprocessing module: defining the problem
The major steps in preprocessing are given below
- Defining key points /lines/areas/volumes
- Define element type and material /geometric /
properties
- Mesh lines/areas/volumes/are required
The amount of detail required will depend on the di-
mensionality of the analysis (i.E. 1D, 2d, axis, sym-
metric)
2. Solution processor module: assigning the loads
,constraints and solving. Here we specify the loads
(point or pressure), constraints (translation, rota-
tional) and finally solve the resulting set of equa-
tions.
3. Post processing module: further processing and
viewing of results
In this stage we can see:
List of nodal displacement
Elements forces and moments
Deflection plots
Stress contour diagrams
Overview of structural analysis
Structural analysis is probably the most common

82
application of the finite element method. The term
structural (or structure) implies not only civil engi-
neering structures such as bridges and buildings,
but also naval, aeronautical, and mechanical struc-
tures such as ship hulls, aircraft bodies, and ma-
chine housings, as well as mechanical components
such as pistons, machine parts, and tools.
Types of structural analysis
Static analysis--used to determine displacements,
stresses, etc. Under static loading conditions. Both
linear and nonlinear static analyses. Nonlinearities
can include plasticity, stress stiffening, large deflec-
tion, large strain, hyper elasticity, contact surfaces,
and creep.
Modal analysis--used to calculate the natural fre-
quencies and mode shapes of a structure. Different
mode extraction methods are available.
Harmonic analysis--used to determine the response
of a structure to harmonically time-varying loads.
Transient dynamic analysis--used to determine the
response of a structure to arbitrarily time-varying
loads. All nonlinearities mentioned under static
analysis above are allowed.
Spectrum analysis--an extension of the modal anal-
ysis, used to calculate stresses and strains due to
a response spectrum or a psd input (random vibra-
tions).
Buckling analysis--used to calculate the buckling
loads and determine the buckling mode shape. Both
linear (eigenvalue) buckling and nonlinear buckling
analyses are possible.
Explicit dynamic analysis--this type of structural
analysis is only available in the ansys ls-dyna pro-
gram. Ansys ls-dyna provides an interface to the
ls-dyna explicit finite element program. Explicit dy-
namic analysis is used to calculate fast solutions
for large deformation dynamics and complex con-
tact problems.
In addition to the above analysis types, several spe-
cial-purpose features are available:
• Fracture mechanics
• Composites
• Fatigue
• P-method
• Beam analyses
MATERIAL PROPERTIES AND BOUNDARY
CONDITIONS
MATERIAL PROPERTIES
CARBON STEEL
Young’s modules – 200000MPa
Poisson ratio - 0.29
Density – 0.000007872kg/mm3
Thermal Conductivity – 0.42w/mmk
Specific Heat – 481j/kg k
Yield stress 240Mpa.
Tensile stress 360 MPa
Material: EN 19
Young’s Modulus (EX) : 18900N/mm2
Poissons Ratio (PRXY) : 0.3
Density: 0.000007500kg/mm3
Bulk Modulus 135 GPa
Shear Modulus 70.0 GPa
BOUNDARY CONDITIONS
Pressure on teeth
Constrained on back ribs
Structural Analysis excavator bucket for exist-
ing model (EN 19 structural steel)
The above image is the imported model of excavator
bucket. Modeling was done in Pro-E and imported
with the help of IGES (Initial Graphical Exchanging
Specification).
The above image showing the meshed modal.
The above image shows displacement

83
The above image shows von-misses stress
The above image shows strain
MODAL ANALYSIS
The above image shows the modal analysis
RESULT TABLES
STRUCTURAL ANALYSIS
E N19 Carbon steel
Exiting
model
Modified
model
Exiting
model
Modified
model
Displace-
ment
4.844 3.4451 13.644 9.7131
Stress 373.39 420.28 371.39 418.76
Strain 0.00187 0.0021 0.005249 0.00592
Conclusion
This project work deals with “design optimization
of excavator bucket using finite element method”.
Initially literature survey and data collection is
done to understand approach and rectification
methodology.
3D parametric model is generated using creo para-
metric modeling software.
Model was evaluated to study existing model be-
havior at working condition.
Modifications are done on model to improve qual-
ity.
Analysis is done on modified model to find stress,
deflections, strain, life, fos, buckle factor and fre-
quency.
Comparison is done between original and modified
model.
As per analysis results this project work concludes
that optimized design will give 300% improve-
ment in life only , strengthen ribs are going to get
damaged , periodically ribs have to be replaced to
protect to protect the bucket.
REFERENCES
1). A study of failures in excavator arm(1)
2). A soil model for a hydraulic simulator excavator based
on real-time multibody dynamics
3). Computer aided design of excavator arm: fem
Approach
5). Performance evaluation of hard faced excavator buck-
et teeth against abrasive wear using mmaw process
6). Simulation and optimization of hydraulic excavator’s
working device
7). Design, modification and concept generation of fixture
to mount sub-assemblies from the hydraulic excavator
bucket
8). The improvements of the backhoe-loader arms
9). A hydraulic simulator for an excavator
10). Optimization of component of excavator bucket

84
Authour
S.Sekhar babu
Research Scholar,
Department of Mechanical Engineering,
Nunna,Vijayawada rural,Krishna (DIST),
AP,India
Y. Venu
Assistant Professor,
Department of Mechanical Engineering,
Nunna,Vijayawada rural,Krishna (DIST),
AP,India

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