Design and Analysis of High Speed Helical Gear By Using Ansys

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1 Design and Analysis of High Speed Helical Gear By Using Ansys A. Sai Bharath*1, T.v.s.r.k. Prasad*2 M.Tech Student (Cad/ Cam) Mechanical Engineering, NCET, Jupudi, Ibrahimpatnam, Vijayawada, Krishna (dt),a.p, India. Professor, Mechanical Engineering in NCET, Jupudi, Ibrahimpatnam, Vijayawada, Krishna (dt),a.p, India ABSTRACT Marine engines are among heavy-duty machineries, which need to be taken care of in the best way during prototype development stages. These engines are operated at very high speeds which induce large stresses and deflections in the gears as well as in other rotating components. For the safe functioning of the engine, these stresses and deflections have to be minimized. In this project, static-structural analysis on a high speed helical gear used in marine engines, have been performed. The dimensions of the model have been arrived at by theoretical methods. The stresses generated and the deflections of the tooth have been analyzed for different materials. Finally the results obtained by theoretical analysis and finite element Analysis are compared to check the correctness. A conclusion has been arrived on the material which is best suited for the marine engines based on the results. The present used material for helical gears is Mild Steel. In this project, gear is designed using two different aluminum alloys 7475 and Theoretical calculations and analysis are done for Helical gear using Mild Steel, Aluminum alloys 7475 and Parametric 3D modeling is done in Pro/Engineer and analysis is done in Ansys. Key words: Gear design, Computer aided analysis, Gear Hobbing, Gear shaving, Structural Analysis. 1. INTRODUCTION A gear is a rotating machine part having cut teeth, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, magnitude, and direction of a power source. The most common situation is for a gear to mesh with another gear however a gear can also mesh with a non-rotating toothed part, called a rack, thereby producing translation instead of rotation. The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping. When two gears of unequal number of teeth are combined, a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship. In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission. 2. METHODOLOGY OF SYSTEM DESIGN In order to design a helical gear system the following procedure should be followed; The input conditions are power, speed, helix angle, gear ratio. Gear design starts with material selection. Proper material selection is very important; Aluminum has been selected as a material. If the material for gear and pinion is same then the design should be based since it is weak. Find out the minimum central distance based on the surface compression stress is a (i+1)3 (0.7/σc) 2 E (Mt) iψ. [Design data] Here Mt=torque transmitted by the pinion=97420(kw/n)*kd*k Where Kd*K=1.3, ψ=b/a..[design data]. Minimum normal modules may e determined as mn 1.15Cosβ {Mt/Yv σb ψm Z1} ^1/3..[design data] Assume Z1=18, ψm=b/mn=10 from..[design data] Virtual number of teeth Zv=Z1/cos3β, Lewis form factor Yv= /Zv.[ Design data] Number of teeth on pinion Z1=2acosβ/mn*(i+1), Number of teeth on gear Z2=iZ1 Diameter of pinion D1=mn*Z1/cosβ, Diameter of gear D2=mn*Z2/cosβ Centre distance a=d1+d2/2, Face width b= ψa checking the calculations: i): based on the compressive stress, σc=0.7(i+1)/a* {(i+1/ib)*e[mt]} IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 1

2 ii): based on the bending stress, σb=0.7(i+1) (Mt)/{a.b.mn.Yv} Here the bending and compressive stress values obtained are less than the material property values, then the design is safe Theoretical design calculation The theoretical design calculations are performed using the input parameters such as power for marine high speed engine, pinion speed, gear ratio, helix angle, pressure angle etc. i.e Power P = 9000 KW, Speed of Pinion N = 3500 rpm, Gear Ratio i = 7, Helix Angle, β = 25oMinimum centre distance based on surface compression strength is given by a (7+1) ] 2.x 2.2 Material Selection Let the material for Pinion & Gear is Aluminum Alloy ; Its design compressive stress & bending stresses are [σc = kgf/cm 2 ], [σb = 3500 kgf/cm 2 ] Properties for Aluminum Alloy 6061 Speed of the pinion = 2000rpm Diameter of gear, mm No of teeth on gear = No of teeth on pinion = =15 Diameter of pinion = center distance = mm GR = Normal pitch m m Power = p =240KW = 240 W mm Gear ratio =6 Center distance = x = Helix angle = 45 0 = α Material used = mild steel Properties = BHN =30 Minimum tensile strength = 500MPa Young s modulus = 68.9GPa=68.9 MPa Normal pressure angle = фn tan фn = tan ф (ф=20) tan фn = tan 20 фn = a) Face width Usually recommended that the overlap should be 15 percent of the circular pitch Compressive stress = Bending stress = = N/mm 2 Module = m = 18 WKT gear ratio = GR = We have GR =6 and b = The maximum face width may taken as 12.5 m to 20m b = 20m = 360mm Formative or equivalent no of teeth for helical gears = Equivalent no of teeth on pinion = GR = No of teeth on gear = Equivalent no of teeth on gear = IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 2

3 Tooth form factor for pinion for 20 0 full depth involute Y 1 P = Tooth form factor for gear for 20 0 full depth involute Y 1 G = = = ( ) Y 1 P The dynamic tooth load on the helical gear is given by Properties for helical gears: Pressure angle ф = 20 Helix angle α = 45 0 Addendum = 0.8M(maximum) = 14. 4mm Dedendum = 1M(minimum) = 18mm Minimum total depth = 1.8m =32.4mm Minimum clearance 0.2M =3.6mm Where v, b, c have usual meaning as discussed in spur gears C = deformation factor = K =0.111 for 20 0 full depth involute system in N/mm 2 Thickness of tooth = M = mm Strength of helical gears: C= = N/mm b = face width M = module Y 1 =tooth form factors The static tooth load or endurance strength of the tooth for bevel gear is given by Both the pinion and gear are made of the same material the pinion is weaker thus the design will be based upon pinion The allowable static stress ( ) for steel gears is approximately one third of the ultimate tensile strength =, endurance limit (BHN=30) =flexural N Peripheral speed = V = m/s D P, b, Q and K have usual meanings as discussed in spur gears in this case K =load stress factor = The value of velocity factor C depending upon peripheral velocities greater than 20 m/s is given by IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 3

4 K= Q = WKT the diameter of pinion hub =1.8 mm Length of the hub = 1.25 mm If the pitch circle diameter of the pinion is less than or equal to 14.7M+60mm = 14.7 b) Design for pinion shaft Tangential load on pinion Axial load of pinion Bending moment of pinion shaft X = over hang =1296 Bending moment of pinion shaft due to the axial load = c) Design for the gear shaft Let We have already calculated that the tangential load = Axial load = Bending moment due to the tangential load = = (x = 1296) = Bending moment due to axial load = Torque transmitted by pinion T = N mm Equivalent twisting moment = We know that equivalent twisting moment = Torque on the gear shaft = T =torque on the pinion shaft N mm Let us now check for the principle shear stress WKT the shear stress induced We Know that equivalent twisting moment = direct stress due to axial load = σ= 0.32 principle shear stress = We also know that equivalent twisting moment = = the principle shear stress is less than the permissible shear stress of 230 Mpa therefore the design is satisfactory IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 4

Let us know check for the principle shear stress; We Know that shear stress = τ = 230 Direct stress due to axial load σ = Principle shear stress = The principle shear stress is same as the

5 Let us know check for the principle shear stress; We Know that shear stress = τ = 230 Direct stress due to axial load σ = Principle shear stress = The principle shear stress is same as the permissible stress of 230 Mpa the design is satisfactory We Know that diameter of gear hub = 1.8 = mm 2D DRAWING Length of hub =1.25 =96.025mm Length of hub is < face width i.e = 360mm 3. MODEL OF HELICAL GEAR 3.1 Analysis Significant Development in analysis of strength properties of gear transmission follows the achievements in computation design, simulation of meshing and tooth contact analysis made by Lewiki,Handschuh.They carried out 2D analyses using finite element method, boundary element methods & Compared the results to experimental ones validated crack simulation based on calculated stress intensity factors and mixed mode crack angle prediction. In practice, simplified formulas are usually used in gear transmission design. They enables estimation of stresses at tooth root with accuracy acceptable for engineering design. In every case, strength properties of gear transmissions are strongly influenced by gear geometry, applied manufacturing processes, and dimensional accuracy of manufactured gears. 3.2 Gear Manufacturing Gears are manufactured by various processes. These are, casting, stamping, rolling, extruding, and machining. Gears can also be produced by powder metallurgy. Among the above said process, machining process in most commonly used. It is an accurate method. Basically gears are produced by machining by a) Forming method. b) Generating method Forming Method IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 5

6 In this method a form cutter is used. The formed cutter may be single point cutting tool or a multipoint milling cutter. The cutting edges formed cutter has been finished to the shape between the gear teeth being cut. Forming method is used for producing very small number of gears. Gears produced by forming are less accurate. Forming process is simple and cheaper. This method is takes more time Gear Generating processes This method of gear manufacturing is based on the fact that any two involute gears of the same module will mesh together. Here one of the meshing gears is made as the cutter. The other gear rotates and also reciprocates along the width of the gear blank. Because of the relative rolling motion between cutter and the blank, gear teeth are generated on the gear blank. The gear may be generated by rack cutter, pinion cutter or a hob. Using the generated method, profile of the gear teeth can be very accurately produced. The following generating methods used for gear production are Gear shaping, Gear planning, Gear hobbing Gear Hobbing It is a process of generating a gear by means of a rotating cutter called hob. The hob has helical threads. Grooves are cut in the threads parallel to the axis. This will provide the edges. Proper rake and clearance angle are ground on these cutting edges. The rotating hob acts like a continuously moving rack as it cuts. The blank is mounted on a vertical arbour. The hob is mounted in a rotating arbour. The hob axis is tilted the hob lead angle so that its teeth are parallel to the axis of the gear blank. Then = (90º-1). Where 1 = helix angle of the hob thread. NOTE: (hob lead angle = 90º-hob helix angle) The hob is rotated at suitable cutting speed. It is fed across the blank face. The hob and blank are made to rotate in correct relationship to each other; they rotate like a worm and worm gear in mesh. For one relation of the hob, the blank rotates by one tooth. (In case of single start hob). For helical gears, the axis of the hob is inclined to horizontally. Where a= θ + (90º-1). (If the helix of the hob and the helix of the gear to be cut are different. One is right and another is left handed.) a= θ (90º-1) (if the helix of the hob and the helix of the gear to be cut are both right handed or both is left handed.) Where, a = helix angle of the helical gear to be cut.,1 = helix angle of the hob. The gear hobbing technique is used for generating spur, helical and worm gears. Gear hobbing is used in automobiles, machine tools, various components, instruments, clocks and other equipment. In the present the helical gears were produced by gear hobbing technique and finished by gear shaving operation. The gear teeth generating process by milling machine is shown in fig Fig Image showing milling machine Finishing Process Gears manufactured by different machining processes will have rough surfaces. The machined gears may have errors in tooth profiles, concentricity and helix angles. For quiet and smooth running of gears, these errors and rough surfaces should be removed. Gear finishing operations are done for this purpose. The various gear finishing processes like gear burnishing, gear shaving etc Gear Burnishing Is a method of finishing of gear teeth which are not hardened. This is a cold working process. This method is used to improve the surface finish of the gear teeth. This also increases the hardness at the teeth surface. The teeth of burnishing gears are very hard, smooth and accurate. They are arranged at 120º position around the work gear. The gears are rotated in one direction for some period. Then they are rotated in the reverse direction for the some period. The pressure is applied by the harder burnishing teeth on the work gear Gear Shaving This is the most common method of gear finishing. In this method a very hard gear shaving cutter is used to remove fine chips from the gear teeth. The shaving cutter may be in the form of a rack or a pinion. The rotary method using pinion cutter is used on all types of gears. The rotating cutter will have helical teeth of about 15º helix angle. The cutter has a number of serrations on its periphery. These act as cutting edges. In the rotary type of gear shaving the work gear is held between centres and is free to rotate. The shaving cutter meshes with the work gear. The axis of the cutter is inclined to the gear at an angle equal to the helix angle of the cutter (θ) when the cutter rotate, the cutter reciprocates in a direction parallel to the gear axis. The cutting edges of the shaving cutter remove burrs, nicks and high points on the surface of the work gear. It can remove from the teeth flank, chips up to 0.1mm thick. IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 6

4. ANALYSIS OF HELICAL GEAR MATERIAL ALUMINUM ALLOY 6061 STRUCTURAL AND RESULT ANALYSIS Displacement Vector Sum Imported Model from Pro/Engineer Von Mises Stress Element Type: Solid 20 node 95

7 4. ANALYSIS OF HELICAL GEAR MATERIAL ALUMINUM ALLOY 6061 STRUCTURAL AND RESULT ANALYSIS Displacement Vector Sum Imported Model from Pro/Engineer Von Mises Stress Element Type: Solid 20 node 95 Material Properties: : 68900N/mm 2 Youngs Modulus (EX) Poissons Ratio (PRXY) : 0.33 Density : kg/mm 3 Meshed Model Strain Loads Pressure N/mm 2 Solution Solution Solve Current LS ok MODAL ANALYSIS IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 7

Main menu>preprocessor>loads>analysis Type> New Analysis> Select Modal> Click> OK Mode Main menu>preprocessor>loads>analysis Type> Analysis Options>

8 Main menu>preprocessor>loads>analysis Type> New Analysis> Select Modal> Click> OK Mode Main menu>preprocessor>loads>analysis Type> Analysis Options> No. Of Modes to Extract: 5 Click> OK Main menu>solution>solve>current Ls>Ok RESULTS Mode 1 3 Mode 4 Mode 2 Mode 5 IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 8

9 RESULTS TABLE STRUCTURAL RESULTS ALUMINUM ALLOY 6061 ALUMINUM ALLOY 7475 MILD STEEL DISPLACEMENT (mm) 0.898e e e -03 STRESS (N/mm 2 ) STRAIN 0.745e e e -06 ALUMINUM ALLOY 6061 ALUMINUM ALLOY 7475 MILD STEEL MODE 1 MODE 2 MODE 3 MODE 4 MODE 5 FREQUENCY (Hz) DISPLACEMENT (mm) FREQUENCY (Hz) DISPLACEMENT (mm) FREQUENCY (Hz) DISPLACEMENT (mm) FREQUENCY (Hz) DISPLACEMENT (mm) FREQUENCY (Hz) DISPLACEMENT (mm) MODAL RESULTS WEIGHT COMPARISON MILD STEEL AL ALLOY 6061 AL ALLOY 7475 Kg CONCLUSION In this project, static-structural analysis on a high speed helical gear used in marine engines, have been performed. The dimensions of the model have been arrived at by theoretical methods. The stresses generated and the deflections of the tooth have been analyzed for different materials.the present used material for helical gears is Mild Steel. In this project, gear is designed using two different aluminum alloys 7475 and Theoretical calculations and analysis are done for helical gear using Mild Steel, Aluminum alloys 7475 and While using Mild Steel for helical gears, the weight is more. By replacing with aluminum alloys, the weight is reduced. Parametric 3D modeling is done in Pro/Engineer and analysis is done in Ansys. By observing the analysis results, the stress values are less by using all the 3 materials than their respective yield stress values. So using aluminum alloys is better for helical gear used in high speed marine engines. In aluminum alloys, using aluminum alloy 6061 is better as its weight is less than aluminum alloy IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 9

10 REFERENCES 1. Emmanuel RIGAUD, Ecole Centrale de Lyon., 1999, Modelling and analysis of Static Transmission Erroreffect of wheel body deformation and interactions between adjacent loaded teeth, hal , Version 122 Dec Zeping Wei., 2004 Stresses and Deformations in Involute spur gears by Finite Element method, M.S, Thesis, College of Graduate Studies and research, University of Saskatchewan, Saskatchewan. 3. PSG,2008, Design data, Kalaikathir Achchagam publishers, Coimbatore India 4. Joseph E.Shigley.charles R.Mischike, 2003, Mechanical Engineering design, Tata McGraw Hill. 5. Andrzej kawalec, Jerzy Wiktor., 2006, Comparative analysis of tooth root strength Using ISO and AGMA 6. Standards in spur and helical gears with FEM based verification, ASME Journal of Mechanical Design,Vol 128/ Lazar Chalik, DE, 1996, Preloaded Gearing for high speed application Vol 88, ASME Power transmission &Gearing conference 8. P.N.Rao, 2003, Manufacturing Technology, 2 nd Edition, Tata Mc Grew Hill 9. Metals Handbook, 1990, Properties and Selection: Nonferrous Alloys and SpecialPurpose Materials, ASM International Vol.2, 10th Ed. 10. R.E. Sanders, Technology Innovation in aluminum Products, The Journal of the Minerals, 53(2):21 25, 2001 IJCSIET-ISSUE3-VOLUME3-SERIES3 Page 10

STRUCTURAL AND THERMAL ANALYSIS OF GEAR TECHNOLOGY

STRUCTURAL AND THERMAL ANALYSIS OF GEAR TECHNOLOGY D.Ashokkumar 1, M.Venkaiah 2 1 M.tech student, Mechanical Engineering, Narasaraopeta Engineering College, A.P, India 2 Assistant Professor, Mechanical