Development of rotary weeder blades by Finite Element Method

Transcription

1 941 Development of rotary weeder blades by Finite Element Method Mr. Mahesh Gavali 1, Mr. Satish Kulkarni 2 1 PG Student, Textile and Engineering Institute, Ichalkaranji, Maharashtra 2 Professor, Mechanical Engg, PVPIT College of Engg. Budhgaon, Maharashtra ABSTRACT Weeds are plants which are considered undesirable in agriculture and gardening. The process of removal of these weeds from crops is called weeding. Weeders are mechanical machines which are used for weed removal. The paper discusses about design develop and optimize blades used for these an effort is made to reduce power required to drive these machines and to increase the life of these blades using the blades with lowest stress profiles. Various blade parameters are selected for optimizing the blade design. The stress profiles are obtained by using finite element software Hyper- works. By increasing the life and lowering the power required the effectiveness of the mechanical weeders can be increased. The costs associated with mechanical weeding such as operating cost can be lowered; as such mechanical weeding can represent a viable and cost effective option to majority of medium and small scale farmers in developing countries like India. Keywords - weeding, weeders, blade, CAD, FEM, stress analysis. I. INTRODUCTION Agriculture is the main occupation in majority of developing nations such as India, Brazil, etc. One major reasons for lack of yield per unit agricultural area in these nations are weeds. Weeds compete for space, nutrients, water and light with crops. The losses caused by weeds can be particularly significant in vegetable crops and cash crops such as sugarcane Majority of the population in developing nations depends on agriculture and agro-based industries and businesses. Lack of mechanization or automation is one of the major roadblocks to improving the productivity of agriculture. Major reason for lack agricultural productivity is weeds. Most farmers can t afford these machines as the costs associated namely; operating and initial costs are high compared to other weed removal methods Rotary tilling is a widely used tillage operation in Indian farming because of its superior ability to mix, flatten and pulverize soil. Rotary Tilling is a more effective mechanism for mixing and digging soil. No matter the soil type, soil conditions or the amount of residue, Rotary operation will always produce the best result. The Rotary weeder can be made to operate various working depths widths and soil conditions. The rotating blades chop and mix the residues evenly throughout the working depth, outperforming any other mechanism[ 3] [4]. II. BLADE DESIGN AND CONFIGURATION Blades of the rotor are the components which directly interact with soil and as such have major impact on the operation of the weeders. The material used for manufacturing machines could be changed but this increases the associated costs significantly. The way of reducing the power requirement and to improve the life of machine is to improve geometry of blade. The interaction between soil and machines takes place at the blades; thus by improving their geometry the power required and the size of machine will reduce. The blade is designed & developed using the popular blades designs used in market available weeders as base. Using CAD and FEM techniques afterwards for finalizing the geometry. The finalized geometry not only reduces the power required but also decreases the cost of manufacture. The weight of machine is also reduced as smaller power source (engine) will be required to power the machine which will reduce the operating cost of the machine. In rotary weeders, blades are attached to a flange mounted on a rotating shaft usually by nuts & bolts shown in Fig. 1. Commonly three types of blade geometries are used as blades for weeders and tillers; namely: 1) L-shaped Blades 2) C-Shaped Blades

2 942 3) J- Shaped Blades TABLE I: Soil Types & Properties Type of Soil Soil Resistance (Kg/cm 2) Optimum Moisture Content (%) 1 Sandy soil Sandy loam Clay soil Heavy loam Fig. 1 Blades Assembly used in Weeders III. BLADE GEOMETRY & CAD MODELLING Fig.2 Blade Geometries used in Tilling and weeding machines. C shaped blades have greater curvature, so they are recommended for penetration in hard field and better performance in heavy and wet soils. J Shaped blades are used for loosening, destroying the soil surface compaction and giving better ventilation to the soil generally used for tilling hard and wet soils. L shaped blades are the most common widely used for the fields with crop residue, removing weeds [2] [6]. Based above investigation L shaped blade design is selected as base for geometry generation. Most soils found in India such as Black Cotton soil, Alluvial soil, Literate or red soil, etc. are classified on the basis of their base content such as sand base, loam base or clay base. The properties of these soils which are found most important in the design of weeding machine are base content, moisture content & bulk density [1] [6].Some of the properties of common soils are described in Table I [1] [3]. Blade geometry is based on the L shaped blade as it is most suitable for weed removal purpose. Solid model of the blade is prepared in CAD Software CATIA. L shaped blades commonly used for rotavators and weeders are taken base and hence are taken as a base model for this design. Fig. 3 shows the three views of the selected blade profile. Four different blade profiles made using CATIA software. Each of these models were analyzed for Maximum stress and displacement using a FEM Software Hyperworks. Based on the results found the final blade profile has been selected. The important parameters such as blade width, overall vertical length, overall horizontal length, thickness, etc., related to blade profile are given in Table II. These parameters are selected on basis of common requirements for weeder such as depth of 40-50mm, width of mm, etc. These blades are to be fastened on cutter or flange as shown Fig.1. Total Diameter of the Blade fastened flange should around 400 to 450mm. TABLE II Blade Parameters Symbol Used Name and Unit Values 1 Blade Width w mm mm Overall Vertical 2 Length Lv mm 120 mm Overall Horizontal Length Lh mm mm Blade clearance 4 angle α Blade Thickness t mm 5 mm 6 Max Curvature Radius R mm 40 mm

3 943 Fig. 4 3-D view of Blade showing the various forces and constraints Fig. 3 Blade Deign Details From Table II it can be seen that blade width, overall horizontal length and clearance angle are varied and four different blade configurations are prepared based on L4 array of Taguchi methods. With this array three parameters; width, horizontal length & clearance angle are varied within two limits. The rest of the parameters are same as those shown above in Fig. 3 and Table II. The four different blade configurations are shown in Table III. Four CAD models are made based on above parameters and keeping other parameters constant. Fig. 4 shows Isometric view of the blade geometry and the forces acting on the blade. TABLE III Different Blade Designs based on L4 array Blade Design Blade Width w mm Overall Horizontal length Lh mm Clearance Angle 1 Blade Blade Blade Blade IV. CALCULATION OF FORCES & ANALYSIS Two major forces are known to act on a rotating blade used for tilling or digging operations. [3] [6] : Tangential Force acting at the tip of the blade as shown Fig. 4. Soil force acts perpendicular to the cutting edge of the blade. Soil force for analysis is considered as a uniformly distributed load acting along the cutting edge. Tangential Force K t is given by [6] ; K t 75CsN c c z u min [1] Soil force K s acting on the sharpened edge of the blade is given by [6] ; KtCp Ks [2] izene Where; C s is the non-reliability factor equal to 1.5 for non-rocky soils and 2 for rocky soils, N c is the power of the machine taken as 1 kw for small weeding machine, η c is traction efficiency taken as 80%, η z is coefficient of reservation of power taken as 0.8, u min is minimum peripheral velocity taken as 0.5 m/s, C p is coefficient of tangential force taken as 0.8, I is numbers of flanges taken as 1, Z e is number of blades on each side of the flange taken as 3

4 944 Following input data are used for the force analysis: Speed of cutter = 250rpm Number of flanges = 1 Total number of blades =6 Blades on each side of flange =3 Number of Bladesinteracting with soil n e Totalnumber of Blades The properties of material used for analysis shown in Table IV. The material is most common structural material mild steel (C20 Steel) which is case hardened to improve hardness. TABLE IV: Blade Material Properties Material Modulus of Elasticity MPa Poisson s Ratio Bulk Density kg/m 3 Mild Steel 2.1 E E-09 Fig.6 Displacement Contours of different Blades V. FEM ANALYSIS The CAD Model prepared in CATIA is imported into Hyperworks. The model is divided into elements using 3D meshing. Using tetra-type volume meshing triangular 2D & 3D elements are created. Materials, properties and loads are created & applied to models of Blade 1, 2, 3 & 4. A load step was created to perform a linear static analysis in RADIOSS module of Hyperworks. The results viewed and analyzed using Hyperview module of Hyperworks. Displacement and Von Mises Stress contours shown respectively in Figs 6 & 7 were analyzed to select best possible blade geometry to reduce power requirement and increase life of the blades. Calculated values of Tangential Force (K t ) & Soil Force (K s ) are N & N respectively. Fig.7 Stress Contours of different Blades VI. RESULTS Fig. 5 Blade model meshed Fig.6 & Fig. 7 indicate displacement and stress contours of different blade profiles. The red regions in the Fig.6 & Fig. 7 represent high levels of displacement & stress, the yellow & green represent moderate levels and blue regions represent low levels. Maximum displacement and stress for various blade designs enumerated and compared in Table V.

5 945 TABLE V Comparison after linear stress analysis Blade Maximum Displacement mm Von Mises Stress MPa 1 Blade Blade Blade Blade Blade 4 shows least maximum displacement and stress. Hence Blade 4 geometry should be used as optimized blade design. VII. CONCLUSION CAD CAE & FEM are useful tools for analyzing stresses and deformations in design of complex geometries. Weeders are used for removal of weeds in between rows of crops. For a single row rotary weeder the power required can be lowered by optimizing the blade and minimizing stresses. Above analysis revels that L shaped geometry Blade 4 configuration shows lowest displacement (deformation) and stresses. Hence Blade 4 geometry should perform better in the field than others. Further field study should be needed to verify these results. REFERENCES [1] Gopal U. Shinde and Shyam R. Kajale, Design Optimization in Rotary Tillage Tool System Components by Computer Aided Engineering Analysis, International Journal of Environmental Science and Development, Vol. 3, 3, June 2012 [2] Azar Khodabakhshi, Davood Kalantari, Seyed Reza Mousavi Effect of Design Parameters of Rotary Tillers on Unevenness of the Bottom of the Furrows, International journal of Agronomy and Plant Production. Vol., 4 (5), , 2013 [3] Subrata Kr. Mandal, Basudeb Bhattacharyya, Somenath Mukherjee, and Priyabrata Chattopadhyay Design & Development of Rotavator blade: Interrogation of CAD Method, ISSN: ; 2013 IJSRPUB [4] Subrata Kr Mandal and Dr. Basudev Bhattacharya Proceeedings of the 1stInternational and 16th National Conference on Machines and Mechanisms, IIT Roorkee, India, Dec 18-20, 2013 (5), , 2012 ISSN ECISI Journals [5] V.M. Salokhe, N. Ramalingam, Effect of rotation direction of a rotary tiller on draft and power requirements in a Bangkok clay soil, Journal of Terramechanics 39 (2003) [6] Bernacki H, Haman J, Kanafojski CZ. Agricultural machines, theory and construction. US department of Agriculture and national science foundation, Washington, D.C [7] Moses Okoth Marenya, Performance characteristics of a deep tilling rotavator Faculty of Engineering, Built Environment and Information Technology University of Pretoria, Pretoria, September, 2009 [8] Kaveh Mollazade, Ali Jafari, Ebrahim Ebrahimi,Application of Dynamical Analysis to a Choose Best Subsoiler s Shape using ANSYS,New York Science Journal, 2010; 3(3) [9] Mohammad Shekofteh, Hosein Shekofteh, Mohammad Razahojati, Modeling the Soil Cutting Process in Rotary Tillers Using Finite Element Method, International Journal of Agriculture: Research and Review. Vol., 2 [10] Kaveh Mollazade, Hojat Ahmadi, Reza Alimardani, Optimal design of rotary tiller s rotor and width proportionate to Tractor power using energy method, Int J Agric & Biol Eng Vol.2 2, June, 2009 [11] Gill, W. R., and G. E. Vanden Berg. (1996). Design of tillage tool. In soil dynamics in tillage and traction Washington, D.C., U.S.GPO [12] C. Cordill, T.E. Grift, Design and testing of an intra-row mechanical weeding machine for corn, Biosystems Engineering, September2011, PP [13] U. S. Kankal,V.P.Khmabalkar,,D.S.Karale,, S.M.Nage, Effect of operating speed, moisture content of soil and approach angle of sweep on specific draft and weeding efficiency, The International Journal Of Engineering And Science (IJES), Volume 3, Issue 6, Pages 01-09, 2014 [14] Raffaelli M., Fontanelli M., Martelloni L., Frasconi C., Peruzzi A., Innovative strategy and machines for physical weed control in agriculture and urban areas. International Conference RAGUSA SHWA 2012, Ragusa - Italy Safety Health and Welfare in Agriculture and in Agro-food Systems, September 3-6, 2012, PP [15] Zhang Libin,Jiang Jiandong,Li Yanbiao, Agricultural rotavator power requirement optimization using multiobjective probability parameter optimization, International Agricultural Engineering Journal Vol. 19, 3,, Pages 15-22, December, 2010.