03-11-2016, 03:40 PM
1464155064-analysisofboomabstract.docx (Size: 132.45 KB / Downloads: 6)
Introduction
Excavator is one of the most important machinery in engineering machinery. Excavators are widely used in construction, railway, water Conservancy, mining and other industries. Hydraulic excavator consists of three main parts: undercarriage, upper structure and the working device, the upper structure rotates on the undercarriage. The working device of a hydraulic excavator mainly consists of boom, arm, bucket, boom cylinder, arm cylinder, and bucket cylinder .The excavator boom is one of the key components of an excavator, and also main load bearing part.
In today’s world of growing competition, all industries are trying their best to give the components of high quality with minimum expenditure. So in present work design and analysis of boom for hydraulic excavator will be been done using SOLVER Software to get the variation of stress and displacement in the various parts of the boom and possible actions are taken to avoid the high stress level and displacement. During operation of hydraulic excavators many loads will be acting such as tensile load, compressing load, torsional load and shocking load, hence there will requirement of higher intensity of working device in hydraulic excavator.
The boom of an excavator is complex structure to examine. During operation, the boom of an excavator is stressed throughout their life. In the process of operation, boom is subjected to tensile, compressive, torsional and bending loads due to lifting and digging process whereas it is subjected to shock load due to excessive vibrations in the operation of the hydraulic excavator .so it is necessary to study about the stress-strain distribution, fatigue and vibration characteristics of the boom. Since many loads are acting on boomthere will requirement of higher intensity of working device in hydraulic excavator, so it is important to study about boom to avoid high stress levels on boom.
Most of the researches on excavator are done in past few years with the development of finite element method (FEM). Several researchers have conducted a variety of different analysis on excavator boom using different FEA tools.
2) Objective
Objective of the present work is to analysis and optimization of boom of any one hydraulic excavatorsby using any one of solver to test whether boom is safe for the various loading condition or not and exploring ways to reduce the stress levels in various parts of the boom.
3 Literature review
3.1) GuiJu-Zhang, Cai Yuan-Xiao and etc[1], in their works authors established finite element analysis of boom. Establishment of boom’s geometrical model on Pro/E.The boom's geometrical model of hydraulic excavator by using 3D modeling software Pro/E. Boom is mainly welded together by thin plates of different thickness and also it contains some other structural parts. During modeling process, threaded hole are omitted, transportation lifting lug, chamfers and other insignificant factors are also neglected.
They proposed mechanical analysis of working device. The static strength finite element analysis of excavator boom was carried through by using ansys from which stress 1and deformation contour diagrams are obtained to check hardness. According to their work maximum stress mainly occurred in the hinge point connected boom cylinder with boom and hinge point connected the boom with base. They attempt to analyse the stress and strain distribution by using FEA software workbench. Through analysis results boom structure meets static strength or not.
They proposed for Work condition where Tip of bucket teeth locates on the extension cord which is determined by one hinge point produced by bucket and bucket rod and the other hinge point produced by bucket rod and boom, and force applying dipper fluid cylinder pressure lever is largest. In this work condition, loads are gravity, lateral force and tangential force. The digging resistance reached the maximum. And this type work condition is dangerous one and hence small group of fatigue cracks will be appeared in parts of boom.
3.2) Amolb.bhosale,Drmaruthi B H,Drchannakeshavalu k etc[2] The main objective of their work is to analysis of existing design and optimizing the excavator boom.Stresses will be included in the excavator attachmentswhich vary during its operations at different positions. Thickness of the material is reduced in modelling for optimum weight of excavators.Material considered for excavator is hardox400. Hardox400 is high strength steel, combination of hardness and toughness.
The linear static analysis is done on existing model to study maximum displacement, maximum stress acting on boom, and also get reaction forces acting at support(at boom end and cylinder end). The optimization is done with varying thickness of boom plate and lug plate thickness. They proposed that linear static characterstics of the boom component, from those static characteristics the structural weight optimization is carried out with factor of safety 1.5. Results obtained by numerical analysis are validated analytically.stuctural weight optimization gave the total weight reduction of 36.4%.
3.3)BhaveshkumarP.Patel, jagadeeshPrajapati[3] ,their works focuses on structural weight optimization of excavator attachment using FEA approach by trial and error method. The work aims at strength calculations of the structures working under known load and boundry condition. In their works,parts of boom of mini hydraulic excavators are modified to get the optimized model. The parts of boom are modified by varying the thickness and dimensions of parts of boom.
Their results shows that weight optimized to reduce approximately 10kg of weight of boom and maximum voin mises stress acting on boom is 287Mpa ,which is less than yield stress 500Mpa,this indicates that optimized boom is safe for strength.
3.4) Sun Jianghong and Pan Shangfeng [4] carried out basic research on the lightweight design of the excavator boom, but they didn’t give any specific lightweight design scheme. In further work the Luigi Solazzi [5] was the first who proposed the use of aluminium alloy in place of steel alloy for excavator boom and arm. Assuming the load conditions conducted finite element analysis at five operating conditions. The weight of final geometry was reduced by 50% while price increased about € 2.500–3.000.
3.5) Yu Shuo et al. [6] showed static analysis of actual (without internal ribs) and improved boom model using finite element method. The study revealed that high stress concentration is occurring at arm cylinder hinge point and exceeding the limit of yield stress in the boom cylinder hinge point in actual model. While in the improved boom model there is significant reduction in maximum stress, only about 60% of the original.
3.6) Li Dan et al. and Zhu Chun-Hua et al. [7]-[8] conducted the FEA of excavator boom at the dangerous operating state of boom using ANSYS software, including the calculation model for determining the load at each hinge point. Pro/E software was used to build the finite element model of boom. The results depicted that the boom in this condition does not have a large displacement, the maximum stress is less than the allowable stress of the material and deformation is in the elastic range.
3.7)Shengbin Wu and Xiaobao Liu [9] suggested four improvement for reducing stress concentration along with the improvement in high stress distribution by comparing main and improved model of boom, Through finite element analysis of a hydraulic excavator's boom in ANSYS Workbench. The force at all hinge point of boom was calculated by applying moment balance and force balance principle. The analysis shows that high stress is appearing in the top and bottom cover plates which near the rear seat and the junction of boom cylinder's connecting seat and the bottom plate.The practices demonstrate that the proposed improvements can reduce the destruction of hydraulic excavator's boom.
3.8) Shiva Soni et al. [10] carried out the static analysis of excavator boom. The modeling and simulation of boom was done in Autodesk INVENTER software which was interfaced with the softwares like Altair Hyper-mesh for meshing and ANSYS FEA tool for the analysis. The study reported that the stress is under acceptable limit.
3.9) GauravK.Mehta, V,R, Iyer and Jatin Dave[11], the paper describes Finite element analysis of the robotic mechanism of an excavator that contains bucket, arm and boom using CAD/CAM and CAE tools. Design changes are suggested in regions of components where stresses are not under allowable limit.
Static force analysis of mechanism is done on considering different critical operating conditions. It has been found that the condition at which mechanism produces breakout forces is most critical condition for static force analysis. Each link has been analysed as a free body for this condition and forces coming on each link has been foundout. These forces are used as boundary condition for finite element analysis.
Finite element analysis of boom is carried out using CAE package. After interpreting the FEA, design modification are made in components for minimum weight.
After interpreting FEA results, design modification are made to minimize the weight of designed component. Stiffener of 8mm is added in arm mounting on both sides. Shape and thickness of stiffener is changed.it is increased to 12mm from 6mm. thickness of side and top plates of front and rear section is reduced to 6mm from 10mm.thickness of inside stiffness is also changed to 6mm from 10mm. After all modification in boom, maximum voin mises stress is reduced to 247Mpa from 249Mpa and weight of boom is reduced to 836kg from 1008kg.
Methodology
The analysis of the boom depends upon the loading conditions.The different type of loads acting upon the boom aretensile load, compressing load, torsional load and shocking load etc.
Initially the computer aided drawings of the boom are prepared with the help of the CAD tools like pro-e, catia, solid works, or AutoCAD. The production drawings can be prepared with due preparation for the requirement. After with the help of the solvers the workpiece will be solved. The solver tools consist of pre-processing and post processing. Pre-processing consists of the dividing the existing component into finite elements of specified shape and size. This depends upon the number of nodes and shape of the elements, some shapes of the finite elements are triangular, rectangular, trapezoidal, octahedral with 3 noded,6 noded,10 nodded, 160 nodded elements. These elements will provide us the accurate position and accuracy of the analysis. The pre-processing part will be done with the help of hyper mesh nastron software packages.
After the pre-processing, application of boundary condition to the elements. After applying the boundary conditions the very next step is to apply the loading conditions. The maximum loading condition can be approximated by considering the maximum bending moment with ultimate payload conditions. The minimum loading condition can be approximated by self-weight of the vehicle. The suitable factor of safety must be assumed. The approximation of FOS can be considered by different loading approximation and impact loading conditions also. The maximum stress concentrated point is selected for the increment of stiffness in that place. We must increase the FOS with less cost and ease of access to assemble the other components.