SYNOPSIS
Over the years rocker arms have been optimized in its design and material for better performance. Durability, toughness, high dimension stability, wear resistance, strength and cost of materials as well as economic factors are the reasons for optimization of rocker arm. This paper reviews the various types of rocker arms, based on published sources from the last 40 years in order to understand rocker arm for its problem identification and further optimization. This paper present what rocker arm is, where it is used and why it is used, History related to rocker arm and it working is described. Various types of rocker arm used in vehicles and different materials used for making rocker arm are studied in this paper. Reasons for Failure of rocker arm are also discussed in this paper. In fast moving world the time is very important criteria. But in the manual program time takes more and more for every work in the world In the production department drawing is very important for design the various parts. In the manual work, its takes more time and is also very difficult to draw various components compare to CAD. So, to avoid these difficulties, CAD implements for quick & accurate design. Computer aided design have various packages are Auto CAD, Pro-E, etc. Auto CAD is using for 2D drawing and Pro-E is the latest implement in CAD, Which is especially using for 3D modeling. Most of the industry Pro-E is using for creating a new Design and modification of existing Design. ANSYS software is used for analyzing the 3d modeling objects. The ANSYS program has much finite element analysis, capabilities, ranging from a simple, linear, static analysis to a complex non–linear, transient dynamic analysis.
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INTRODUCTION
As a rocker arm is acted on by a camshaft lobe, it pushes open either an intake or exhaust valve [1][2]. This allows fuel and air to be drawn into the combustion chamber during the intake stroke or exhaust gases to be expelled during the exhaust stroke. Rocker arms were first invented in the 19th century and have changed little in function since then. Improvements have been made, however, in both efficiencies of operation and construction materials [1] [3] [4].
Rocker arm
A rocker arm is a valve train component in internal combustion engines. As the arm is acted on by a camshaft lobe, it pushes open either an intake or exhaust valve. This allows fuel and air to be drawn into the combustion chamber during the intake stroke or exhaust gases to be expelled during the exhaust stroke. Rocker arms were first invented in the 19th century and have changed little in function since then. Improvements have been made, however, in both efficiency of operation and construction materials. Many modern rocker arms are made from stamped steel, though some applications can make use of heavier duty materials.
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In many internal combustion engines, rotational motion is induced in the crank shaft as the pistons cause it to rotate. This rotation is translated to the camshaft via a belt or chain. In turn, lobes on the camshaft are used to push open the valves via rocker arms. This can be achieved either through direct contact between a camshaft lobe and rocker arm or indirectly though contact with a lifter driven pushrod. Overhead cam engines have lobes on the camshaft which contact each rocker arm directly, while overhead valve engines utilize lifters and pushrods. In overhead cam engines, the camshaft can be located in the head, while overhead valve engines have the camshaft in the block. Both varieties are seen in the US, but regulations have contributed to the decline of overhead valve applications elsewhere in the world. Throughout the history of the rocker arm, its function has been studied and improved upon. These improvements have resulted in arms that are both more efficient and more resistant to wear. Some designs can actually use two rocker arms per valve, while others utilize a "rundle" roller bearing to depress the valve. These variations in design can result in rocker arms that look physically different from each other, though every arm still performs the same basic function. Since energy is required to move a rocker arm and depress a valve, their weight can be an important consideration. If a rocker arm is excessively heavy, it may require too much energy to move. This may prevent the engine from achieving the desired speed of rotation. The strength of the material can also be a consideration, as weak material may stress or wear too quickly. Many automotive applications make use of stamped steel for these reasons, as this material can provide a balance between weight and durability. Some applications, particularly diesel engines, may make use of heavier duty materials. Engines such as these can operate at higher torques and lower rotational speeds, allowing such materials as cast iron or forged carbon steel to be used.
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HISTORY
Jonathan "Rundle" Bacon created Rocker arms in the 19th century, rocker arms have been made with and without "rundle" roller tips that depress upon the valve, as well as many lightweight and high strength alloys and bearing configurations for the fulcrum, striving to increase the RPM limits higher and higher for high performance applications, eventually lending the benefits of these race bred technologies to more high-end production vehicles. Even the design aspects of the rocker arm's geometry has been studied and changed to maximize the cam information exchange to the valve which the rocker arm imposes, as set forth by the Miller US Patent, #4,365,785, issued to James Miller on December 28, 1982, often referred to as the MID-LIFT Patent. Previously, the specific pivot points with rocker arm design was based on older and less efficient theories of over-arching motion which increased wear on valve tips, valve guides and other valve train components, besides diluting the effective cam lobe information as it was transferred through the rocker arm's motion to the valve. Jim Miller's MID-LIFT Patent set a new standard of rocker arm geometrical precision which defined and duplicated each engine's specific push-rod to valve attack angles, then designing the rocker's pivot points so that an exact perpendicular relationship on both sides of the rocker arm was attained: with the valve and the pushrod, when the valve was at its "mid-lift" point of motion [5].
Throughout the history of the rocker arm, its function has been studied and improved upon. These improvements have resulted in rocker arms that are both more efficient and more resistant to wear. Some designs can actually use two rocker arms per valve, while others utilize a "rundle" roller bearing to depress the valve. These variations in design can result in rocker arms that look physically different from each other, though ever y rocker arm still performs the same basic function. 4
Since energy is required to move a rocker arm and depress a valve, their weight can be an important consideration. If a rocker arm is excessively heavy, it may require too much energy to move. This may prevent the engine from achieving the desired speed of rotation. The strength of the material can also be a consideration, as weak material may stress or wear too quickly. Many automotive applications make use of stamped steel for these reasons, as this material can provide a balance between weight and durability. Some applications, particularly diesel engines, may make use of heavier duty materials. Engines such as these can operate at higher torques and lower rotational speeds, allowing such materials as cast iron or forged carbon steel to be used.
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WORKING
The rocker arm is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by a rotating lobe of the camshaft (either directly or via a tappet (lifter) and pushrod) while the other end acts on the valve stem. When the camshaft lobe raises the outside of the arm, the inside presses down on the valve stem, opening the valve. When the outside of the arm is permitted to return due to the camshafts rotation, the inside rises, allowing the valve spring to close the valve [2].
The drive cam is driven by the camshaft. This pushes the rocker arm up and down about the turn-on pin or rocker shaft. Friction may be reduced at the point of contact with the valve stem by a roller cam follower. A similar arrangement transfers the motion via another roller cam follower to a second rocker arm. This rotates about the rocker shaft, and transfers the motion via a tappet to the poppet valve. In this case this opens the intake valve to the cylinder head. The standard small-block Chevy (SBC) uses a 1.5:1 ratio rocker arm. In other words, the rocker-arm tip (output) moves 1.5 times the displacement of its pushrod socket (input), or camshaftlobe lift. The 1.5:1-ratio rocker arm translates 0.350 inches of camshaft-lobe lift into 0.525 inch of valve lift (0.350 inch x 1.5 = 0.525 inch). By increasing the rockerarm ratio, it's possible to increase valve lift without ever touching the camshaft. A 1.6:1-ratio rocker arm translates the same 0.350 inch of camshaft-lobe lift into 0.560 inch of valve lift (0.350 inch x 1.6 = 0.560 inch). This is a lift increase of about 6.7 percent. Valve lift can typically be increased as much as 10 percent by increasing rocker ratio.
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Since rocker arms are used to control both the intake and exhaust valves, swapping high-ratio rocker arms onto an engine increases both the intake-air command and the exhaust-scavenging potential. Generally speaking, a bump in rocker-arm ratio results in a noticeable performance gain. The almighty General knows this; GM swapped in a set of high-ratio 1.6 (up from the LT1's 1.5) rockers on the LT4 and later specified the LS7 ratio at a healthy 1.8 (up from the LS2's 1.7).
TYPES OF ROCKER ARM
Rocker arms are of various types, there design and specifications are different for different types of vehicles (bikes, cars trucks, etc). Even for same type of vehicle category rocker arms differs in some way. Types of rocker arm also depend upon which type of Internal-combustion engine is used in a vehicle (i.e. Push Rod Engines, Over Head Cam Engines, etc).
A. Stamped Steel Rocker Arm- The Stamped Steel Rocker Arm is probably the most common style of production Rocker Arm. They are the easiest and cheapest to manufacture because they are stamped from one piece of metal. They use a turn-on pivot that holds the rocker in position with a nut that has a rounded bottom. This is a very simple way of holding the rocker in place while allowing it to pivot up and down.
Fig.3. Stamped Steel Rocker Arm 7
B. Roller Tipped Rocker Arm- The Roller Tipped Rocker Arm is just as it sounds. They are similar to the Stamped Steel Rocker and add a roller on the tip of the valve end of the rocker arm. This allows for less friction, for somewhat more power, and reduced wear on the valve tip. The Roller Tipped Rocker Arm still uses the turn -on pivot nut and stud for simplicity. They can also be cast or machined steel or aluminium.
Fig.4. Roller Tipped Rocker Arm
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Fig.2. Valve train assembly
IV. ROCKER RATIO A rocker arm is simply a mechanically advantaged lever that translates camshaft data into valve actuation. The mechanical advantage is defined by a rocker's ratio. C. Full Roller Rocker Arm- The Full Roller Rocker Arm is not a stamped steel rocker. They are either machined steel or aluminium. They replace the turn-on pivot with bearings. They still use the stud from the turn-on pivot but they don't use the nut. They have a very short shaft with bearings on each end (inside the rocker) and the shaft is bolted securely in place and the bearings allow the rocker to pivot. 9
Fig.5. Full Roller Rocker Arm
D. Shaft Rocker Arms- The Shaft Rocker Arms build off of the Full Roller Rocker Arms. They have a shaft that goes through the rocker arms. Sometimes the shaft only goes through 2 rocker arms and sometimes the shaft will go through all of the rocker arms depending on how the head was manufactured. The reason for using a s haft is for rigidity. Putting a shaft through the rocker arms is much more rigid than just using a stud from the head. The more rigid the valve train, the less the valve train deflection and the less chance for uncontrolled valve train motion at higher RPM.
Fig.6. Shaft Rocker Arms 10
E. Centre Pivot Rocker Arms- The Centre Pivot Rocker Arm looks like a traditional rocker arm but there is a big difference. Instead of the pushrod pushing up on the lifter, the Cam Shaft is moved into the head and the Cam Shaft pushes directly up on the lifter to force the valve down. In this case the pivot point is in the centre of the rocker arm and the Cam Shaft is on one end of the rocker arm instead of the pushrod.
F. End Pivot (Finger Follower) Rocker Arms- The End Pivot or Finger Follower puts the pivot point at the end of the Rocker Arm. In order for the Cam Shaft to push down on the Rocker Arm is must be located in the middle of the rocker arm.
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MATERIALS
Beyond high ratios and friction-abatement technologies, performance-rockerswap talk must include discussions of materials, strength, and stability. The most common rocker materials are steel and aluminium Expounding on the material engineering of rocker arms, Scooter Brothers, cofounder of Comp Cams, explains some interesting facts about steel-bodied rocker arms. Scooter states that chrome-moly steel, although heavier than other materials, can offer some design advantages and have much thinner sections than aluminium due to its superior strength density. Generally speaking, it takes at least two times the aluminium to approach the strength of steel. The moment of inertia, or performance mass, of properly engineered steel parts can actually be close to that of aluminium. In other words, before jumping for lightweight aluminium rockers, it's important to realize that the effective weight of a quality steel unit may be comparable
A. Steel- Many automotive applications make use of steel for these reasons, as this material can provide a balance between weight and durability. Stamped steel was the OEM standard for Gen I and II, while cast steel was and is the standard for Gen III and IV While these are suitable for OEM and basic performance, the aftermarket and racing communities demand more exotic options [1].
B. Anodized-aluminium roller rockers-Nothing screams high performance more than a set of anodized-aluminium roller rockers, regardless of their true positive effect
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C. High-strength alloy aluminum rocker- High-strength alloy aluminium rocker arms are good, lightweight performers. Basic aluminium rocker arms are available with cast-alloy or extruded bodies, and high-end aluminium rocker arms are available machined from billet alloys [2].
D. Chrome-moly steel- Chrome-moly steel is a common material for highperformance parts, and rocker arms are no exception. The strength and rigidity of this material is hard to beat.
E. High-strength alloy steels- High-strength alloy steels are used in high-end, precision rocker arms, with rock-like rigidity for high-rpm race applications.
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FAILURE OF ROCKER ARM
Failure of rocker arm is a measure concern as it is one of the important components of push rod IC engines. Failure usual occurs at due to fracture at the hole or neck of the rocker arm. Various other factors are also mentioned below.
1. The fracture occurred at the hole of the rocker arm- The fracture occurred at the hole of the rocker arm. Multiple- origin fatigue is the dominant failure mechanism. The spheroidization of cementite in pearlite makes the hardness of the material of the failed rocker arms decrease to result in lower fatigue strength. Initiation and growth of the cracks was facilitated by a microstructure of low fatigue strength [1].The fracture of rocker arm at the hole is shown in fig.7.
Fig.7. Fracture at the hole of the rocker arm
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2. The fracture occurred at the neck of the rocker arm- The ultimate tensile strength (UTS) and elongation of the rocker arm material were 164.0 MPa and 2.5%, respectively. This UTS value is slightly lower than that of normal die -cast Al alloys. In the stress measurement test, the compressive stress exhibits the maximum value at the idling state and decreases as the engine speed increases. The maximum experimental stress at the neck was _21.0 MPa at the engine idle speed. Hence, this rocker arm is deemed to be safe in terms of fatigue fracture, taking into consideration the fatigue endurance limit of 58.8 MPa. The safety factors of this component are 2.6 and 3.8 based on the fatigue endurance limit and the modified fatigue endurance limit, respectively, suggesting that this S.F is appropriate. However, gas porosities introduced during the die-casting process provide sites of weakness at which premature fatigue crack initiation and finally fatigue fracture of this rocker arm can occur. Therefore, it is necessary to control the melt quality during the diecasting process in order to secure the safety of this type of rocker arm due to stresses acting on it [2].
Fig.8. Fracture at the neck of the rocker arm 15
3. Failure of the rocker arm shaft is caused by the bending load- FEA results for the failure boundary condition obtained from orthogonal array indicated that the maximum and minimum stresses were 711 MPa and 161 MPa, respectively. The stress range Δσ was 550 MPa. The stress range Δσ obtained from the relationship between striation spacing and the range of the stress intensity factor was 592.42 MPa. The failure boundary condition estimated by using an orthogonal array and ANOVA was very useful because the relative error between the stress ranges obtained fro m striation and the stress ranges from FEA fell within 7%. Thus this result indicates Failure of the rocker arm shaft is caused by the bending load [4].
4. Wear of rocker arm pads- The superior wear resistance of silicon nitride pads for LPG taxi engines and it was found, that excessive calcium and phosphorus adsorptions on contact surfaces lubricated with diesel engine grade oil contained primary type zinc dialkyldithiophosphate and large amounts of calcium detergent. The excessive adsorption of some additives caused the micro-pits observed on the cam noses following every test conducted with that grade of oil. It is thought that the pits were formed by acid corrosion following mechanochemical reactions [6].
5. Fatigue failure of rocker arm shaft- Fatigue crack in rocker arm shaft for passenger car was initiated at through hole and subsequently propagated along its sidewall. If rocker arm shaft is operated under actual failure boundary condition, number of cycles to fracture is expected to be less than 129,650 cycles. The maximum stress measured in failure region under the most dangerous failure 16
boundary condition of rocker arm shaft between each loading condition is 221.2 MPa, which exceeds fatigue limit of 206 MPa and hence rocker arm shaft with this boundary condition has finite fatigue life
6. Carbon builds up at the end of valve stem- Due to carbon build up at the end of valve stem. Valve guide wear occurs on the inside diameter of the valve guide in a straight line with the centre line of the rocker arm.
7. Failure due to friction- The continuous interaction with the valve stem and push rod cause friction as they are touching each other this result in cheap formation.
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INTRODUCTION TO CAD/CAM CAD/CAM is a term which means computer-aided design and computeraided manufacturing. It is the technology concerned with the use of digital computers to perform certain functions in design and production. This technology is moving in the direction of greater integration of design and manufacturing, two activities which have traditionally been treated as district and separate functions in a production firm. Ultimately, CAD/CAM will provide the technology base for the computer-integrated factory of the future. Computer – aided design (CAD) can be defined as the use of computer systems to assist in the creation, modification, analysis, or optimization of a design. The computer systems consist of the hardware and software to perform the specialized design functions required by the particular user firm. The CAD hardware typically includes the computer, one or more graphics display terminals, keyboards, and other peripheral equipment. The CAD software consists of the computer programs to implement computer graphics on the system plus application programs to facilitate the engineering functions of the user company. Examples of these application programs include stress-strain analysis of components, dynamic response of mechanisms, heat-transfer calculations, and numerical control part programming. Computer-aided manufacturing (CAM) can be defined as the use of computer systems to plan, manage, and control the operations of manufacturing plant through either direct or indirect computer interface with the plant’s production resources.
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DESIGN PROCESS: The process of designing is characterized by six identifiable steps or phase 1. Recognition of need 2. Definition of problem 3. Synthesis 4. Analysis and optimization 5. Evaluation 6. Presentation APPLICATION OF COMPUTERS FOR DESIGN: The various design-related tasks which are performed by a modern computer-aided design system can be grouped into four functional areas: 1. Geometric modeling 2. Engineering analysis 3. Design review and evaluation 4. Automated drafting Geometric Modeling: In computer-aided design, geometric modeling is concerned with the computer- compatible mathematical description of the geometry of an object. The mathematical description allows the image of the object to be displayed and manipulated on a graphics terminal through signals from the CPU of the CAD system. The software that provides geometric modeling capabilities must be designed for efficient use both by the computer and the human designer.
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There are several different methods of representing the object in geometric modeling. The basic form uses wire frames to represent the object. Wire frame geometric modeling is classified into three types, depending on the capabilities of the interactive computer graphics system. The three types are: 2D- Two Dimensional representation is used for a flat object. 2½D- This goes somewhat beyond the 2D capability by permitting a threedimensional object to be represented as long as it has no side wall details. 3D- This allows for full three dimensional modeling of a more complex geometry. The most advanced method of geometric modeling is solid modeling in three dimensions. Another feature of some CAD systems is color graphics capability. By means of color, it is possible to display more information on the graphics screen. Colored images help to clarify components in an assembly, or highlight dimensions, or a host of other purposes. i. ENGINEERING ANALYSIS: CAD/CAM systems often include or can be interfaced to engineering analysis software which can be called to operate on the current design model. Examples of this type are Analysis of mass properties Finite element analysis The analysis may involve stress –strain calculations, heat-transfer computations, or the use of differential equations to describe the dynamic behavior of the system being designed. 20
7. INTRODUCTION TO PRO-ENGINEER Pro-Engineer is a powerful application. It is ideal for capturing the design intent of your models because at its foundation is a practical philosophy. Founder of this Pro-Engineer is Parametric Technology Corporation. After this version they are released Pro-E 2000i2, Pro-E 2001, Pro-e Wildfire, Pro-e Wildfire1.0, Pro-e Wildfire2.0,Pro-e Wildfire3.0,Pro-e Wildfire4.0,Pro-e Wildfire5.0, Creo Element pro 5.0, Creo 1.0 & Creo 2.0. 7.1 SCREEN LAY OUT: 7.1.1. Main Window: When the Pro-E is started, the main window opens on desktop. The four distinct elements of the window are: Pull-down menu Tool bar Display area Message area 7.1.1.1 Pull-Down Menus: The Pro-E pull-down menus are valid in all modes of the system. File: Contains commands for manipulating files Edit: Contain action commands.
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View: Contains commands for controlling model display and display performance. Datum: Creates datum features. Analysis: Provide access to options for model, surface, curve and motion analysis, as well as sensitivity and optimization studies. Info: Contains commands for performing queries and generating reports. Application: Provide access to various Pro-E modules. Utilities: Contains commands for customizing our working environment. Windows: Contains commands for managing various Pro-E windows. Help: Contains commands for accessing online documentation. Tool bar: The Pro-E toolbar contains icons for frequently used options from the pulldown Menus. The tool bar is also customized. 22
7.1.1.2
Display area:
Pro-E displays parts, assemblies, drawings, and models on the screen in the display area. An object’s on the current environment settings. 7.1.1.3
Message area:
The message area between the toolbar and the display area performs multiple Functions by: Providing status information for every operation performed. Providing
queries/hints
for additional
information
to complete a
command/task. Displaying icons in the message area, which represent different forms of information such as warnings or status prompts. Sketcher Sketcher consists of Sketch Dimension Constrain Modify Move Delete Geometric Tools Section Tools Undo Redo
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SKETCH: The sketch includes basic geometrical primitives such as Point Line Rectangle Arc Circle Advanced geometry which are used in two dimensional as well as three dimensional drawing. Point: It has been drawn by picking the point directly on desired place. Line: There are two options to draw a line Geometry Centerline Both geometry and center line has the following options 2 points 2 tangent Rectangle: Rectangle is drawn directly using the command rectangle.
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Arc: The following are the options in drawing the arc: Tangent End Concentric 3 tangent Fillet Circle: There are two basic types of drawing a circle. They are geometry and construction. Both the above said types include the following options Center/point Concentric 3 tangent Fillet 3 point Advanced geometry: It includes several advanced features such as Conic Coordinate system Elliptic fillet Ellipse Spline Text 25
Axis point DIMENSIONING: Dimensions can be added to sections as before. When a dimension is added, a weak dimension or constraint will be removed automatically. Although extra dimensions are no longer allowed, it is now possible to make reference dimensions in Sketcher. MODIFYING DIMENSIONS: When dimension values are modified, the section is updated immediately. If we don't want the section to update until we have modified several dimensions, we have to choose Delay Modify first. After the desired changes have been made, Regenerate should be chosen. MOVE: The Move command allows modifying the section by dragging an entity or vertex to a new position without having to specify which dimensions to be changed. Move will automatically determine which dimensions to be varied so that the section changes in a natural way while preserving all constraints. Move can also be used to drag a dimension to a different location. DELETE: Delete command is used to remove the features from the basic window. Delete has many options such as Delete item Delete many Delete all 26
GEOMETRIC TOOLS: Geometric tool has the following options: Intersect Trim Divide Use edge Offset edge Mirror Move entity SECTION TOOLS: Section tool has the following options: Copy draw Integrate Place section Start point Toggle Undo All Sketcher operations can now be undone with the Undo command. We can hit Undo repeatedly to reverse actions one after another. Redo is provided, as well. 7.1.2 PART: PROTRUSION: Protrusion consists of following options: 27
Extrude Revolve Sweep Blend EXTRUDE: Extrusion means adding the material from a specified side. Condition: The drawn sketch must be a closed loop. Enough references should be mentioned. Protrusion adds the material perpendicular to the selected plane. Options for giving depth. Blind: By choosing the option blind, we can give directly numerical value. Thru until: Adds the material that goes through all the surfaces until it reaches the specified surface. Up to point/vertex: Adds the material with a flat bottom that continues until it reaches the specified point or vertex. Up to Curve: Adds the material with a flat bottom that continues until it reaches the specified curve that you draw in a plane parallel to the placement plane. 28
Up to Surface: Add the material from the selected plane to the selected surface. Exemption: For the basic (first) component, there is no option for giving thru next, thru all and thru until. There is no chance for giving two side blends if one side was chosen. REVOLVE: The revolve option creates a feature by revolving the sketched section around a centerline. A revolved feature can be created either entirely on one side of the sketching plane, or symmetrically on both sides of the sketching plane. To create or redefine a revolved feature, specify the elements in the following order: Attributes Section Direction Angle Rules for sketching a revolved feature: The revolved section must have a centerline. The geometry must be sketched on only one side of the axis of revolution. If more than one centerline in the sketch, Pro-E uses the first centerline sketched as the axis of rotation. The section must be closed. 29
Options for specifying the angle of revolution: Variable: Any angle of revolution less than 360 degrees is specified by using this variable 90: Create the feature with a fixed angle of 90 degrees. 180: Create the feature with a fixed angle of 180 degrees. 270: Create the feature with a fixed angle of 270 degrees. 360: Create the feature with a fixed angle of 360 degrees. Up To Point/Vertex: Create the revolved feature up to a point or vertex. The revolved feature ends when the section plane reaches the point or vertex. Up to Plane: Create the revolved feature up to an existing plane or planar surface that must contain the axis of revolution.
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INTRODUCTION TO ANSYS The ANSYS program has many finite element analysis capabilities, ranging from a simple, linear, static analysis to a complex non – linear, transient dynamic analysis. A typical ANSYS analysis has three distinct steps: Building the model Applying loads and obtains the solution Review the results. BUILDING THE MODEL: Building a finite element model requires a more of an ANSYS user’s time than any other part of the analysis. First you specify the job name and analysis title. Then, define the element types, real constants, and material properties, and the model geometry. Defining element types: The analysis element library contains more than 100 different element types. Each element type has a unique number and a prefix that identifies the element category. Example: beam, pipe, plant, shell, solid. Defining element real constants: Element real constant are the properties that depend on the element type, such as cross sectional properties of a beam element. For example real constants for BEAM3 , the 2-d beam element, or area, moment of inertia(IZZ), height , shear deflection constant (SHEAR Z), initial strain (ISTRN) different elements of same type may have different real constant values. 31
Defining material properties: Most elements types require material properties.
Depending on the
application, material properties may be: Linear or non linear Isotropic, Orthotropic, or an isotropic Constant temperature or temperature – dependant As with element type and real constant, each set of material properties has a material reference number. The table of material reference number verses material property set ids called material property table. Within, one analysis you may have multiple material properties set. Material property test: Although you can define material properties separately for each element analysis, the ANSY program enables you to store a material property set in an archival material library file, then retrieve the set and reuse it in multiple analysis. The material library files also enable several ANSYS user to share common used material property data. Overview of model generation: The ultimate purpose of the finite element analysis is which to recreate mathematical behavior of an actual engineering system.
In other words, the
analysis must be an accurate mathematical model of a physical prototype. In the broadest sense, this model comprises all the nodes, elements, material properties, real constant, boundary conditions, and other features that are used to represent the physical system.
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In ANSYS terminology, the term model generation usually takes on the narrower meaning of generating the nodes and elements that represent the spatial volume and connectivity of actual system. Thus, model generation in this discussion will mean that the process of define the geometric configuration model’s nodes and elements. The ANSYS program offers you the following approaches to model generation: Creating a solid model within ANSYS. Using direct generation reporting a model created in CAD system. Meshing your solid model: The procedure for generating a mesh of nodes & elements consists of three main steps: Set the element attributes Set mesh controls Generate the mesh controls, The second step, setting mesh controls, is not always necessary because the default mesh controls are appropriate for many models. If no controls are specified, the program will use the default setting on the de size command to produce a free mesh. As an alternative, you can use the small size feature to produce a better quality free mesh. Before meshing the model, and even before building the model, it is important to think about whether a free mesh or a mapped mesh is appropriate for the analysis. A free mesh has no restrictions in terms of element shapes, and has no specified pattern applied to it. 33
Compared to a free mesh, a mapped mesh is restricted in terms of the element shape it contains and the pattern of the mesh. A mapped area mesh contains either only quadrilateral or only triangular elements, while a mapped volume mesh contains only hexahedron elements. In addition, a mapped mesh typically has a regular pattern, with obvious rows of elements. If you want this type of mesh, you must build the geometry as series of fairly regular volumes and or areas that can accept a mapped mesh. Setting element attributes: Before you generate a mesh of nodes and elements, you must first define the appropriate element attributes. That is, you must specify the following: Element type Real constant set Material properties set Element co-ordinate system. LOADING: The main goal of finite element analysis is to examine how a structure or component response to certain loading condition. Specifying the proper loading conditions, therefore, a key stepping analysis. You can apply loads on the model in variety of ways in ANSYS program. Loads: The word loads in ANSYS terminology includes boundary. Conditions and externally or internally applied forcing functions. Examples of loads in different disciplines are: Structural: displacement, forces, pressures, temperatures (for thermal strain), gravity 34
Thermal: temperatures, heat flow rate, convections, and internal heat generation, infinite surface Magnetic: Magnetic Potentials, magnetic flux, and magnetic current segment Electric: electric potentials, electric current, charges, charge densities, infinite Fluid: Velocities and pressures A DOF constraint fixes the degrees of freedom of a known value. Examples of constraints are specified displacement and symmetric boundary conditions in structural analysis, prescribed temperatures in thermal analysis, and flux parallel boundary conditions. A force is concentrated load applied at a node in a model. Examples are forces and moments in structural analysis, heat flow rates in thermal analysis. A surface load is distributed load applied over a surface. Examples are pressures in structural analysis and convections and heat fluxes in thermal analysis. Coupled field loads are simple case of one of the above loads, where results from analysis are used as loads in another analysis. For examples you may apply magnetic forces calculated in magnetic field analysis are force loads in structural analysis. How to apply loads: You can apply loads most loads either on the solid model (on key points, line, areas) or on the finite element model (on nodes and elements). For example, you can specify forces at a key point or a node. Similarly, you can specify
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convections (and other surface loads) on lines and areas or nodes and element faces. No matter how you specify loads, the solver expects all loads to be in term of finite element model. Therefore if your specify loads on the solid model, the program automatically transfers them to the nodes and element at the beginning of the solution. SOLUTION: In the solution phase of the analysis, the computer takes over and solves the simultaneous equations that the finite element method generates. The result of the Solutions are: nodal degree of freedom values, which form the primary solution, and b) derived values, which form the element solution. The element solution is usually calculated at the elements integration points. The ANSYS program writes the results to the database as well as to the result file. Several methods of solving the simultaneous equations are available in the ANSYS program: frontal solution, sparse direct solution, Jacobi Conjugate gradient (JCG solution, incomplete cholesky conjugate (ICCG) solution, preconditioned conjugate gradient (PCG) solution, automatic iterative solver option (ITER). The frontal solver is the default, but you can select a different solver. Post processing: After building the model and obtaining the solution, you will want answers to some critical question: will the design really work when put to use? How high are the stresses in this region?
How does the temperature of this part vary with
time? What is the heat loss across my model? How does the magnetic flow 36
through this device? How does the placement of this object affect fluid flow? The post processors in the ANSYS program can help you find answer these questions and others. Post processing means reviewing the results of an analysis. It is probably the most important step in the analysis, because you are trying to understand how the applied loads affect your design, how well you finite element mesh is, and so on. Two post processors are available review your results: Post 1, the general post processor, and post 26, the time history post processor. Post 1 allows you to review the results over the entire model at specific load steps and sub steps (or at specific time – points or frequencies). In a static structural analysis, for example, you can display the stress distribution for load step 3 or, in a transient thermal analysis; you can display the temperature distribution at time – 100 seconds. Result Files: The ANSYS solver writes results of an analysis to the results file during solution. The name of the results file depends on the analysis discipline: Job Name.rst for structural analysis. General Post Processor: You use Post1, the general post processor, to review analysis results over the entire model, or selected portion of the model, of a specifically defined combination of loads at a single time (or frequency). Post 1 has many capabilities, ranging from simple graphics display and tabular listing to more complex data manipulation such as load case combinations.
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Displaying Results Graphically: Graphics display is perhaps the most effective way to review results. You can display the following types of graphics in post1: Contour displays Deformed shape displays Vector displays Path plots Reaction force displays Particle flow traces. INTRODUCTION TO STRUCTURAL ANALYSIS Structural analysis is probably the most common application of the finite element method.
The term structural (or structure) implies not only civil
engineering structures such as bridges and buildings, but also naval, aeronautical and mechanical structures such as ship hulls, aircraft bodies and machine housings, as well as mechanical components such as pistons, machine parts and tools. Types Of Structural Analysis: The seven types of structural analysis provided by ANSYS are given below. 1. Static analysis: used to determine displacement, stresses etc. under static loading conditions. Both linear and non-linear static analyses.
Non –
Linearity’s can include plasticity, stress stiffening, large deflection, large strain, hyper elasticity, contact surfaces, and creep.
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2. Modal analysis: used to calculate the natural frequencies and mode shapes of a structure. Different mode extraction methods are available. 3.
Harmonic analysis: used to determine the response of a structure to harmonically time varying loads.
4. Transient dynamic analysis: used to determine the response of a structure to arbitrarily time varying loads. All non-linearity’s mentioned under static analysis above are allowed. 5. Spectrum analysis: an extension of the model analysis, used to calculate stress and strain due to response spectrum or a PSD input (random vibrations). 6. Buckling analysis: used to calculate the buckling load and determine the buckling mode shape. Both linear (Eigen value) buckling and non –linear buckling analyses are possible. Explicit dynamic analysis – ANSYS provides an interface to the LS-Dyna explicit finite element programs is used to calculate fast solution for large deformation dynamics and complex contact problems. INTRODUCTION TO THERMAL ANALYSIS A steady state thermal analysis calculates the effects of steady thermal loads on a system or component. Engineer/analysts often perform a steady state analysis before doing a transient thermal analysis, to help establish initial conditions. A steady – state analysis also can be the last step of a transient thermal analysis, performed after all transient effects have diminished.
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You use steady – state thermal analysis to determine temperatures, thermal gradients, heat flow rates, and thermal loads that do not vary over time cause heat fluxes in an object that. Such loads include the following. Convections Radiations Heat Flow rates Heat fluxes (heat flow per unit area) Constant temperature boundaries. A steady state thermal analysis may be either linear, with constant material properties; or non linear, with material properties that depend on temperature. The thermal properties of most material do vary with temperature, so the analysis usually is non linear, including radiation effects also makes the analysis non linear. FINITE ELEMENT ANALYSIS Finite element analysis (FEA) has become commonplace in recent years, and is now the basis of a multibillion dollar per year industry. Numerical solutions to even very complicated stress problems can now be obtained routinely using FEA, and the method is so important that even introductory treatments of Mechanics of Materials { such as these modules { should outline its principal features. In spite of the great power of FEA, the disadvantages of computer solutions must be kept in mind when using this and similar methods: they do not necessarily reveal how the stresses are influenced by important problem variables such as materials properties and geometrical features, and errors in input data can produce wildly incorrect results that may be overlooked by the analyst. Perhaps the most important function of theoretical modeling is that of sharpening the designer's intuition; users of finite element codes should plan their strategy toward this end, supplementing the 40
computer simulation with as much closed-form and experimental analysis as possible. Finite element codes are less complicated than many of the word processing and spreadsheet packages found on modern microcomputers. Nevertheless, they are complex enough that most users do to program their own code. A number of prewritten commercial codes are available, representing a broad price range and compatible with machines from microcomputers to supercomputers1. However, users with specialized needs should not necessarily shy away from code development, and may the code sources available in such texts as that by Zienkiewicz2 to be a useful starting point. Most finite element software is written in FORTRAN, but some newer codes such as felt are in C or other more modern programming languages.
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CONCLUSION Rocker arm is an important component of engine, failure of rocker arm makes engine useless also requires costly procurement and replacement. An extensive research in the past clearly indicates that the problem has not yet been overcome completely and designers are facing lot of problems specially, stress concentration and effect of loading and other factors. The finite element method is the most popular approach and found commonly used for analyzing fracture mechanics problems. Lightweight rocker arms are a plus for high rpm applications, but strength is also essential to prevent failure. In recent years, aftermarket steel roller tip rockers have become a popular upgrade for the most demanding racing applications. Some of these steel rockers are nearly as light as aluminium rockers. But their main advantage is that steel has better fatigue strength and stiffness than aluminium. So we can say that steel is the better material in terms of strength and aluminium is good for making low cost rocker arms.
The design of the project was successfully completed using pro/E. The problems which emerged during the design of the machine where successfully over come using PRO/E . The design of the project involved making use of most of the important features of pro/E is versatile and comprehensive software foe three-dimensional solid modeling. Protrusion and cut are used as main feature to develop the components. The components are drawn very using PRO/E. 42
PHTOGRAPHY
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ANALYSIS PICTURE CAD Model of Rocker Arm
Reaction Force Acting at the Pin
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Equivalent Stress
Maximum Shear Stress
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Force Acting at the Exhaust Valve End of Rocker Arm
Equivalent Stress
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Maximum Shear Stress
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BIBLIOGRAPHY 1. PTC Series Manual for Pro-E. 2. Machine Drawing by K.R.Gopalakrishna 3. CAD/CAM by Groover. 4. Www. PTC. COM 5. Www. Mech.nwu.edu/ Pro-E /toc.htm Website: 6. www.Ansys.com
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