This an engine, its purpose is to transfer force

This project mainly deals with the design, analysis and manufacture of connecting rod. Connecting rod is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders among other similar mechanisms. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a connecting rod and/or connecting rod. Here the connecting rod is designed, analyzed and the manufacturing process has been studied. Connecting rod temperature has considerable influence on efficiency, emission, performance of the SI engine. Purpose of the investigation is measurement of connecting rod transient temperature at several points on the connecting rod, from cold start to steady condition and comparison with the results of finite element analysis.In this project the connecting rod is modeled and assembled with the help of SOLID WORKS software and the component is meshed and analysis is done in ANSYS software and the modal and static behavior is studied and the results are tabulated. The various stresses acting on the connecting rod under various loading conditions has been studied.In the present thesis work has been taken up on the following aspects to cover the research gaps and to present the results based on the systematic studies:

1) Different modes of deformations for the connecting rod of an engine.

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2) FEA analysis of the connecting rod to measure stresses at the points where it is not possible to find out practically and to observe the behavior of the connecting rod.

1.      Introduction:

 

Connecting rods are widely used in variety of S.I engines. The function of connecting rod is to transmit the thrust of the piston to the crankshaft, and as the result the reciprocating motion of the piston is translated into rotational motion of the crankshaft. It consists of a pin-end, a shank section, and a crank-end. Pin-end and crank-end pin holes are machined to permit accurate fitting of bearings. One end of the connecting rod is connected to the piston by the piston pin. The other end revolves with the crankshaft and is split to permit it to be clamped around the crankshaft. The two parts are then attached by two bolts. Connecting rods are subjected to forces generated by mass and fuel combustion. These two forces results in axial and bending stresses. Bending stresses appear due to eccentricities, crankshaft, case wall deformation, and rotational mass force. Therefore, a connecting rod must be capable of transmitting axial tension, axial compression, and bending stresses caused by the thrust and pull on the piston and by Centrifugal force. A connecting rod is subjected to many millions of repetitive cyclic loadings. Manufacturing technology of this machinery and also its quantity must be reached to optimum level. Above statements show the importance of stress analysis in Connecting rod for optimizing them. In this regard, dynamic stress analysis in connecting rods of this tractor was studied.

 

1.1         Basic procedure for creating a 3-d model in solid works:

Creation of a 3-D model in SOLID WORKS PREMIUM 2010 can be performed using three work benches i.e., Part, Assembly and Drawing.

 

1.1.1        Part:

In this sketch is used to create two-dimensional representations of profiles associated within the part. We can create a rough outline of curves, and then specify conditions called constraints to define the shapes more precisely and capture our design intent. Each curve is referred to as a sketch object.

 

1.1.2        Creating a new sketch:

To create a new sketch, chose newàpartàSketch then select the reference plane or sketch plane in which the sketch is to be created.

 

1.1.3        Sketch plane:

The sketch plane is the plane that the sketch is located on. The sketch plane menu has the following options:

Face/Plane:With this option, we can use the attachment face/plane icon to select a                     planar face or existing datum plane. If we select a datum plane, we can use the reverse direction button to reverse the direction of the normal to the plane.

XC-YC, YC-ZC,and ZC-XC: With these options, we can create a sketch on one of the WCS planes. If we use this method, a datum plane and two datum axes are created as below.

2.      Modeling:

Feature creation:

“Feature” is an all-encompassing term that refers to all solids, bodies and primitives used in solid works premium 2010. Form Features are used to supply detail to the model in the form of standard feature types. These include hole, slot, groove, pocket, rib and extrude. We can also create our own custom features using the UserDefinedoption. All of these features are associative.

Reference Featuresallow creating reference planes, reference lines and reference points. These references can assist in creating features on cylinders, cones, spheres and revolved solid bodies. Reference planes can also aid in creating features at angles other than normal to the faces of a target solid. Dress up Featureoptions lets us modify existing solid bodies and features. These include a wide assortment of options such as edge fillet, variable fillet, chamfers, draft, offset face, shell and tapers.

Wire frame and Surface designlets us create surface and solid bodies. A surface body with zero thickness, and consists of a collection of faces and edges that do not close up to enclose a volume. Most Free Form Feature options create surface bodies.

2.1         Creation of Solid/Surface Bodies:

 

We can create solid bodies by extrude the sketch geometry to create associative features or Creating primitives for the basic building blocks, then adding more specific features (for example, holes and slots etc.).

Shafting the sketch and non-sketch geometry lets us to create a solid body with complex geometry. This method also gives us total control over the editing of the body. If any change of model we can directly change the sketch in part only, therefore it automatically get changed in all the part and assembly drawings. Dress-up features are used to modify the part bodies according to given specifications these are the most important advanced features to modify the objects through solid works.

 

2.2         Modeling Procedure:

 

Connecting Rod Shank

 

To create the above part following features are used.

a)      Part

b)      Assembly

c)      Drawing

Open Solid works Software

 

To enter into any one of module.

Ø  Start Menu

Ø  New

Ø  Part Design

Ø  It opens

part module as shown below.

Figure 1: Start the part drawing in Solid works

 

To set the required units go to

Tools menu

– Options

– select units as mm.

To draw the sketch as per the specifications

Select required plane – select sketch tool, it enters into sketch module now draw the required sketch as shown in fig.

To create the small ends draw the sketch as shown below with required dimensions and exit workbench now we enter into part design.

2.3         Extrude / Extrude cut:

This feature is used to add/remove the material normal to sketch or through a reference. In the part design use Extrude / Extrude cut tool from the sketch based features and select the sketch then give the required height (Length) as shown below fig.

2.4         Fatigue design requirement:

 

Connecting rod is acted upon by gas loads andinertial loads during its operation. The forces include gas forces due to combustion and inertia forces due to its own weight. In that point of view fatigue is an important parameter to be considered for estimating the life of the component. The magnitudes of inertia forces are constant but gas forces are varying in nature. Due to fluctuating nature of these forces the chances of component failure due to fatigue is very high. Thus fatigue is one of the significant factors to be taken into account while optimizing an existing design. Fatigue in a component arises due to the following reasons:

 

·         Material defect

·         Manufacturing defects

·         Poor detailing of dimensions while designing

·         Error in load calculation

 

The possible zones of stress concentrations are the change in cross-section from center shank to small end, change in cross-section from big end to center shank and the center shank itself. The connecting rod is subjected to higher duty cycles and the forces acting on the connecting rod is also tremendously high. Connecting rod is being categorized as a functional component and the failure rate is very high during the developmental stages.

 

Table 1: Percentage of Materials

Fatigue

24%

Improper material selection

37%

Fabrication defects

16%

Improper heat treatment

14%

Design Errors

12%

Improper heat treatment

9%

2.5         Material Properties:

 

The material used for selected connecting rod is steel and the properties of the material are presented in the Table2.

 

Table 2: Material Properties

Material Selected

Steel

Alluminium

Young’s Modulus€

1.78e+005Mpa

70 Mpa

Poisson’s Ratio

0.3

0.33

Density

7.197e-006Kg/mm3

2.61161 Kg/mm3

Tensile Strength

100 to 200 Mpa

422 Mpa

Compressive Strength

400 to 1000 Mpa

363 Mpa

Shear Strength

120 Mpa

90 Mpa

 

The connecting rod is being manufactured by different processes such as casting, powder metallurgy and drop forging. The process parameters used for these processes are different accordingly the residual stress levels inside component are also different. These residual stresses can be detrimental or beneficial to the fatigue performance of the component. Thus the life of connecting rod is evaluated by the type of process in which it is manufactured. Based on these assumptions the manufacturing processes effects have a tremendous influence on the fatigue life of connecting rod.

The process parameters have to be further evaluated for enhancing the fatigue life of connecting rod. The previous practice of designing was to incorporate only the strength reduction factor and that will lead to low allowable design stresses. This practice leads to increased mass of the component. In this new methodology, fatigue performance of critical components are improved by incorporating process parameters in design phase that will lead to higher allowable stresses and weight also can be reduced by redesigning.

 

2.6         CAD Model of connecting rod:

 

The geometric model designed using CATIA is given in Figure 2. The model shows a transition zone between small end and shank, center shank and a transition between big end and shank. These transition zones are stress concentration zones since there is a change in cross-section.

Table 3: Engine Specifications in which connecting rod

Parameters

Dimensions

Bore

57 mm

Stroke

58.6mm

Crank length

64mm

Maximum power

[email protected] rpm

Maximum torque

[email protected] rpm

Top speed @idle

2875 rpm

Top speed @ full load

2500 rpm

Center- to- center connecting rod length

233mm

Peak firing pressure of the engine

130 bar or 13 Mpa

Normal value of firing pressure

120 bar or 12 Mpa

Compression ratio

9.35/1

Length of connecting rod

117.2

Outer Diameter of Big end

50mm

Inner Diameter of Big end

40mm

Outer Diameter of small end

22mm

Inner Diameter of Small end

19mm

3.      Description:

3.1         Experimental Procedure

 

Experimental procedure involves modeling of connecting rod using CATIA software. Static analysis of connecting rod is done using ANSYS in order tounderstand the fatigue locations in connecting rod. The maximum load acting on connecting rod was calculated analytically. The load thus calculated was used as an axial tensile force at the small end in order to do perform static analysis of connecting rod. The transition zone between small end and shank was selected for this study. The force acting on the small end of connecting rod is a combination of gas forces and inertia forces.

 

Forces on connecting rod small end = Gas forces – Inertial Forces of piston.

Gas forces are calculated using maximum gas pressure values taken from Table 2. The peak firing pressure for the engine is 130 bar and the same value is used for calculating the peak firing pressure acting on the piston surface. This peak firing pressure gets added up to the force acting on piston pin end.

 

Gas force acting on the piston surface = Peak firing pressure × ?/4×D2.

Where ‘D’ is the diameter of the piston and pressure 130 bar = 13 MPa.

 

Gas Force = 13×? /4 × (97)2

Where 97 mm is the effective surface diameter = 96067.54 N

 

Inertia forces of piston = mp ×ap

Where’mp’ is the mass of reciprocating parts and ‘ap’ is theAcceleration of reciprocating parts.

 

3.2         The following is the list of steps that are used to

Create the required model:

a)      Choose the reference plane.

b)      Set the dimension in mm.

c)      Go to sketcher and sketch circular entities.

d)      Then extrude these entities for making the both ends of connecting rod.

e)      Again reference plane is selected for shank of connecting rod.

f)       Entities is made that should be tangential to both ends.

g)      Extrude the entities symmetrically.

h)      Plane is selected for making entities of groove.

i)       Groove is made on the shank and mirrored for creating groove on both side.

j)       Datum plane is selected for creating small holes on piston end

k)      Then holes are made on the periphery of piston end.

 

4.      Dynamic Equivalent System on Connecting Rod

Continuous body may be replaced by a body by two masses assumed to be concentrated at two points connected rigidly together. Such a system of two masses is termed an equivalent dynamical system. The conditions to be satisfied by an equivalent system are:

1.      The total mass must be equal to that of the rigid body.

2.      The centre of gravity must coincide with that of the rigid body.

3.      The total moment of inertia about an axis through centre of gravity must be equal to that of the rigid body.

m = mass of the rigid body

K = radius of gyration about an axis through G

ma,mb = two masses for equivalent dynamical system

a,b = distances of ma, mb from g respectively.

ma+mb = m

ma x a = mb x b

ma x a2 + mb x b2

ma= mk2/a(a + b)

k2= ab

Figure 2: Truely Dynamical system

 

Basics of the static and dynamic balancing of rotating objects were discussed. In this part our focus is targeted at the reciprocating systems and in particular piston/connecting-rod/crank-shaft mechanism. However, before details discussion of this subject, we need to review some concepts in dynamics. Two systems of bodies are said to be dynamically equivalent if their motions are the same under the same set of forces and moments. This is illustrated in Fig. 1 where a real object is idealized by its dynamically equivalent system consisting of two masses m1 and m2

x

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