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Design optimization of excavator bucket using Finite Element Method

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An excavator is a typical hydraulic heavy-duty human-operated machine used in general versatile construction operations,
such as digging, ground leveling, carrying loads, dumping loads and straight traction. Normally backhoe excavators
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.

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Design optimization of excavator bucket using Finite Element Method

  1. 1. 76 International Journal of Research and Innovation (IJRI) 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
  2. 2. 77 International Journal of Research and Innovation (IJRI) 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
  3. 3. 78 International Journal of Research and Innovation (IJRI) 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
  4. 4. 79 International Journal of Research and Innovation (IJRI) 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
  5. 5. 80 International Journal of Research and Innovation (IJRI) 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
  6. 6. 81 International Journal of Research and Innovation (IJRI) 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
  7. 7. 82 International Journal of Research and Innovation (IJRI) 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
  8. 8. 83 International Journal of Research and Innovation (IJRI) 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
  9. 9. 84 International Journal of Research and Innovation (IJRI) Authour S.Sekhar babu Research Scholar, Department of Mechanical Engineering, Vikas college of Engineering and Technology, Nunna,Vijayawada rural,Krishna (DIST), AP,India Y. Venu Assistant Professor, Department of Mechanical Engineering, Vikas college of Engineering and Technology, Nunna,Vijayawada rural,Krishna (DIST), AP,India

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