CHAPTER-5 CONNECTING ROD- A FORGING COMPONENT

Transcription

1 CHAPTER-5 CONNECTING ROD- A FORGING COMPONENT

2 Chapter-5. Connecting Rod-A Forging Component 73 CHAPTER-5 CONNECTING ROD- A FORGING COMPONENT 5.1 SCOPE Metal working is one of the three major technologies used to fabricate metal products. The others are casting and powder metallurgy. However, the metal working is perhaps the oldest and major out of three. This forming technology has developed slowly. During industrial revolution the iron and steel age started with the larger need for forging components. To satisfy these needs the fast track technologies are invented. Now days the forging processes are approaching towards boom to satisfy the need of quality forging of light metals and micro alloys for space, automotive vehicles and industrial purposes [1]. The modified slab method is well applicable for the forging component having plane strain and axisymmetric flow sections. The connecting rod is a perfect example of combination of these two sections. Connecting rod is highly dynamically loaded component used for power transmission in combustion engines. The flow sections are shown in Fig 5.1. The flow pattern shows that the complete deformation of connecting rod during forging process is a summation of axisymmetric flow at big and small end and a plane strain flow at the shank. Axisymmetric flow at both ends Plane strain flow in center section Fig-5.1- Modes of Metal Flow in Forging of Connecting Rod.

3 Chapter-5. Connecting Rod-A Forging Component 74 The connecting rod is subjected to a complex state of loading. It undergoes high cyclic loads of the order of 108 to 109 cycles, which range from high compressive loads due to combustion, to high tensile loads due to inertia. Therefore, durability of this component is of critical importance. Due to these factors, the connecting rod design and its manufacturing process has been the topic of research for different aspects such as production technology, materials, performance simulation, and fatigue. It can be produced either by casting, powder metallurgy or forging. Connecting rods for automotive applications are typically manufactured by forging from either wrought steel or powdered metal. It could also be cast. However, castings could have blow-holes which are detrimental from durability and fatigue points of view. The fact that forgings produce blow-hole-free and better rods gives them an advantage over cast rods. The connecting rod is divided into three major parts; Big end (Circular / modified), Small end (circular), Middle I- section. Big end connected or fixed to the crankshaft and it has to withstand against high compressive loads due to combustion and tensile loads due to inertia at crank shaft end. Small end is connected to the piston pin and it has to withstand against high compressive loads due to combustion and high tensile loads due to inertia at piston end. Middle I section connects big end to small end. It offers maximum rigidity with minimum weight. The investigation of forging process is designed to perform such that the modified analytical method is to implement to the standard component i.e connecting rod. It is to validate experimentally and then obtained deviation is used to develop knowledge base of the expert system. 5.2 PRODUCT INFORMATION The connecting rod under investigation and its geometrical specification is given in Fig 5.2. The material for the connecting rod is C70S6 (AISI standard) having

4 Chapter-5. Connecting R6d-A F orging Component 7 5 controlled cooling type heat treatment. The hardness range of the material is 286 BHN to 321 BHN. The mechanical properties include ultimate tensile strength of 900- looon/mm2; the yield strength is of '6 Kg/mm2 with the permissible elongation of 10%. The chemical composition of the connecting rod to be forged is consisting of alloying elements as carbon, Silicon, Manganese, Sulphur, Phosphorus, Nickel, at a different percentage as given in Table 5.1 The configuration of connecting rod which considered the net weight, length, width and thickness along with the initial stock size required is registered in Table 5.2. Table 5.1 Chemical composition of Connecting rod to be forged. ALLOYING ELEMENTS PERCENTAGE (%) Carbon 0.56 Silicon 0.26 Manganese 0.28 Sulphur Phosphorus Chromium 0.12 Nickel 0.09 Table 5.2 Configuration of the connecting rod Net weight Length of connecting rod Width of connecting rod Height/thickness of connecting rod Initial stock size 2.54 Kg mm mm 41.8 mm 0 56 mm X 210 mm

5 Chapter-5. Connecting Rod-A Forging Component 76 Fig 5.2 Connectig Rod - component for forging 5.3 MANUFACTURING OF CONNECTING ROD The manufacturing of connecting rod includes the series of manufacturing processes consisting of stretch rolling, flattening, performing, final forging, flash removal and hole punching. The sequence of manufacturing operation and the component shape is shown in Fig. 5.3 The stretch rolling operation is performed for the production of preform [19]. The stage 1-5 shows the progressive change of shape during stretch rolling process. The resulting shape in stage 5 undergoes flattening operation performed between flat tools for the objective of uniform mass distribution. The stage 7 and stage 8 are the main stages of die forging. The stage 7 shows the blocker operation where the stroke marks the initial impression of the shape. This stage involves the production of flash around the periphery of blocker component. The stage 8 represents the finisher operation where the press stroke giving rise the final impression on the component. After the die

6 Chapter-5. Connecting Rod-A Forging Component 77 forging operation the resulting output undergoes flash removal process and the punching of holes at big end and small end. The forged connecting rods are usually produced in several die-forging stages as shown in Fig 5.4. The dies are constructed in two halves and are mounted as a one to the platform and one to the punch. The flattening die, blocker die, and finisher die are mounted on a die set over which the billet is to be placed and transferred in a sequence. In many of the cases that is for small sized components, the flattening operation is eliminated and the die consists of only blocker and fmisher. Fig Workpieces after forming stages.[l-5: stretch-rolling, 6: flattening, 7,8: die- forging, 9: flash removal and hole punching] 5.4 DIE DESIGN The sources of inaccuracy introduced by the forging process are many: die mismatch, uneven scaling of forged stock, uneven shrinkage, die wear, and uneven temperature distribution in work piece. In order to prevent these factors, the forging process tolerances are applied to dimension of forged part. The die design is based on the proper consideration of these tolerances.

7 Chapter-5. Connecting Rod-A Forging Component 78 Fig. 5.4 Dieset -Flattening (left), Blocker (Middle), Finisher (right). The design allowances are necessary material addition, included on the part design, which accommodate the functional requirement of the forging process. These allowances are mainly influenced by the choice of work piece material and includes, finish allowance, draft angles, and comer and fillet radii. These tolerances are mainly determined by the complexity of part s shape and include the tolerances on length, thickness or width to account for the effect of die wear, mismatch and straightness. The first step in the forging die design is to establish the location and shape of the parting line. The parting line is the plane of separation between upper and lower part of closed die set. Generally the parting line is located after the weighing of economical and technical considerations as it can measurably affect the initial cost, ultimate wear of dies, grain flow, and machining requirement for finish parts. The parting line for the connecting rod is through the largest cross section of the forging to avoid narrow, deep die impression. The die design progressed with the selection of draft angle [52], The draft angle is refers to a taper given to internal and external sides of closed die forging to facilitates its removal from the die cavity. It is expressed as an angle from the direction of ram travel. It is not only ensures good forging with minimum of production difficulty but also reduces die sinking expense. Among the standard draft angles of 1, 3, 5, 7 and 10 the 3-5 is used for finisher and maximum of 7 is used for blocker.

8 Chapter-5. Connecting Rod-A Forging Component 79 The selection of fillet and comer radii is the most important factor in the design of forging die. Metal flowing in the die containing cavities of various depths will not undergo the abrupt changes in the flow direction and can lead the condition called flow-through. The comer radii is formed by the intersection of two surfaces with an included angle (with in forging) of less than 180 or extruded angle (outside the forging) of greater than 180. During establishment of minimum dimensions of comer radii, the two factors are considered, the radius as a stress concentrator in the die and the pressure necessary to fill the die cavity. The fillet radius is the intersection of two surfaces with an included angle (with in forging) of greater than 180 or extruded angle (outside the forging) of less than 180. Liberal fillets on the forging permits the forging stock to follow the die contour more easily during the forging forces. The last step in the forging die design is to consider the finish allowances. The finish allowances are the amount of additional material that is added to all surfaces of the part which are to be machined. This material is added so that the part can machined to desired tolerances with an acceptable surface finish. The surfaces parallel to the parting line are affected by the die closure and straightness tolerances, surface perpendicular to the parting line are affected by dimensional, straightness and material tolerances. The adverse effect of these tolerances is considered and the minimum machining allowances is considered to be 0.02 in (0.5mm). The above discussed allowances are considered and the die design for finisher components and registered infig DIE MODELING BY CATIA V5 R15. CATIA (Computer Aided three Dimensional Interactive Application) developed by Dassault systems is one of the world leading CAD/CAM/CAE packages. Being a solid modeling tool, it not only unites the 3D parametric features with 2D tools, but also addresses every design through manufacturing process. In addition to creating

9 Chapter-5. Connecting Rod-A Forging Component 80 solid models and assemblies, 2D drawing views can also be generated in the drafting workbench of the CATIA. The drawing views that can be generated include orthographic, section, dimensions in the drawing views. The bidirectional associative nature of this software ensures that the modification made in the model is reflected in the drawing views and vice versa. The CATIA serves the basic design tasks by providing different workbenches. A workbench is defined as a specified environment consisting of a set of tools, which allows the user to perform specific design task in a particular area The basic workbenches are Part Design workbench. Wire frame and Surface Design workbench. Assembly Design workbench, and Drafting workbench Part Design Workbench The part design workbench is a parametric and feature based environment use to create the solid model can be create. The basic requirement for this workbench is a sketch. The sketch for this feature is drawn in sketcher workbench which is invoked within the part design workbench. The various applicable constraints are automatically applied to it while drawing the sketch. The features are also provided to apply additional constraints and dimensions. The set of other tools are also provided for the features like fillets, champers etc. The provision is also available to assign the material to the model in the part design Wireframe and Surface Design Workbench The Wireframe and the surface design workbench is a parametric and feature based environment used to create wireframe or the solid model. The tools in this workbench are similar to those in part design workbench. The only difference is that the tools in this environment are used to create the basic and advanced surfaces. It is provided with the surface editing tools which are used to manipulate the surfaces to obtain the required shape. Design And Development Of Expert System for Forging Process.

10 Chapter-5. Connecting Rod-A Forging Component 81 Fig 5.5 Allowances on Finished Connecting Rod

11 Chapter-5. Connecting Rod-A Forging Component Assembly Design Workbench The Assembly design workbench is used to assemble the components using the assembly constraints available in this workbench. There are two types of assembly design approaches; Bottom-up and top-dawn. In the bottom-up approach of assembly the previously created components are assembled together to maintain there design inert. In the top-dawn approach, the components are created inside the assembly in the assembly design workbench Drafting Workbench The Drafting workbench is used for the documentation of the parts or assemblies created earlier in the form of drawing views and their detailing. There are two types of drafting techniques; Generative drafting and Interactive drafting. The generative drafting technique is used to automatically generate the drawing views of the parts and assemblies. The parametric dimensions added to the component in the part design workbench during its creation can also be generated and displayed automatically in the drawing views. The provision is also provided to generate the bill of material (BOM). In interactive drafting, it is required to create the drawing views by sketching them using the normal sketching tools and then adding the dimensions. The connecting rod under consideration is drafted using the CATIA and with the addition of proper allowances it is removed from the block to generate its corresponding die. The two dies are modeled on the single die block for blocker and the finisher operation. The finisher die is provided with the provision for gutters so as to ensure the excess material flow around its periphery as a flash. The drafted view of the connecting rod die is shown in Fig.5.6 The die blocks are separated by parting line and generate as a two halves. The assembly of the two dies is reported as a complete die for the connecting rod under investigation in its mating state is registered in Fig.5.7.

12 Chapter-5, Connecting Rod-A Forging Component 83 Blocker Die Finisher Die JBEDL JSRuEEZDEL. Fig. 5.6 Connectin Rod Die Modelled by CATIA Fig 5.7 Die Assembly Design And Development Of Expert System for Forging Process.'

13 Chapter-5. Connecting Rod-A Forging Component SIMPLIFICATION OF COMPLEX DEE SHAPE OF CONNECTING ROD To implement the modified slab method, it is required to represent a complex forging in to a simplified and equivalent forging. The plan projected area As and perimeter Ps of a simplified geometry must be equal to the plan area of actual forging. The plan area of connecting rod is shown in Fig 5.8. The Fig-5.9 represents the top view of simplified die of connecting rod. As=n L2+ 2LsL (5-1) Ps=2ttL+2Ls (5-2) Perimeter of area Fig 5.8- Plan area of connecting rod Two half axisymmetric element Pane strain element Fig-5.9 Simplified equivalent forging (Top view)

14 Chapter-5. Connecting Rod-A Forging Component 85 During converting the complex die in to an simplified die, the parameter L and Ls are correlate with the area and the perimeter of the connecting rod The total load is to estimate by adding the load for two half axisymmetric elements of radius L and the load for plane strain element of length Ls and width 2L.The relation are registered as, Ls= (Ps-2 tt L)/2 (5.3) L = 2n (5.4) In general the L is taken as times the center distance of connecting rod. 5.7 EMPIRICAL ESTIMATIONS The empirical set of relations from literature, forging practice handbook are studied and implemented for estimation of fixed parameters of the process. The overall approach is made to find the shape complexity factor, flash weight, flash dimensions and selection of press capacity. The empirical relations are defined and applied to a connecting rod under investigation Estimation of Shape Difficulty Factor The overall design of forging process requires the prediction and estimation of Shape complexity and volume of the forging, number and configuration of perform or blocker, flash dimension in the dies and the additional flash volume required in the stock for performing and finishing operation, forming load. The size of production lot and the number of performing operation necessary and required tolerances are determined essentially by the geometrical complexity of the forging for a given material. It is therefore useful in planning the production of forging to define an objective of reproducible quantity representing its geometrical complexity.

15 Chapter-5. Connecting Rod-A Forging Component 86 The shape difficulty factor is determined from the ration of finished component weight to the envelope weight [49]. The density of material (alloy steel C7056) is, p = 7.85»10'6 Kg / mm3 The geometrical parameters as shown in Fig are, Length of initial block Lb = mm Width of initial block Bb = mm Height of initial block Hb = 1.8 mm 2 ] 6 Lb= Fig. 5.10: Major Dimensions for Calculations of Shape Difficulty Factor Equation for the Enveloped weight is estimated as, Wenvelope Lb *Bb Hb * p (5.5] = (316.3). (128.6) *(41.8).( '6) = kg The weight of forging component without flash weight i.e Net weight is, Wfinish = 2.54 Kg The shape difficulty factor is estimated as. S = Wfinish / Wenvelope = (^-6)

16 Chapter-5. Connecting Rod-A Forging Component Estimation of Slug Weight The sectional view of connecting rod die showing major dimensions is used in calculations of slug weight of the forging component. The geometrical parameters shown in the Fig.5.11 are, Diameter of slug at the big end Dbe = 68.5 mm Diameter of slug at the small end Dse = 34 mm Thickness of slug at both ends T =9.1 mm E>be= 68.5 mm DSE=34 Iam The Big end slug weight is calculated as, WBE = (ic) / 4} (Dbe) 2 * (T) * p (5.7) = Kg The small end slug weight is calculated as, WSE = m / 4}. (Dse) 2 (T) * p (5.8) = Kg The total slug weight is calculated as, WsiUg = WBE + WSE (5.9) = Kg.

17 Chapter-5. Connecting Rod-A Forging Component Estimation of Flash Weight Total weight of component including sludge weight is given as, Wfinish + Wslug = Kg The Fig 5.12 and 5.13 reported important considerations during flash weight and design variables on connecting rod die. Fig Important considerations for flash weight [59]. Section AA Section BB Fig.5.13 Design variables to determine the flash weight of connecting rod

18 Chapter-5. Connecting Rod-A Forging Component 89 The geometrical parameters shown are registered as, Final height of forging, hf = 41.8 mm Minimum distance between flat surfaces upon which stock is resting when dies are closed is given as, ho = 14 mm Distance between internal and external parting lines with considering the symmetry about its axis is, Iia = 00 mm Diameter of the initial round stock, Do =56 mm Final forging diameter Dj = mm The dimensionless parameter V, which represents height ratio, is calculated as, [60] V = hf /(ho + ha) (5.10) = The dimensionless parameter n is calculated as, - n =S(Do/Di)2V2 (5.11) = The constants ki and k2 are defined by Altan etal [58] to estimate the flash load. The terms are defined and evaluated as, k! = [15.44 (Wflm+Wsiug) ('a2) ( * n)] (5.12) = k2 = ( n). 3.7 (5.13) = The flash weight is estimated as [50],

19 Chapter-5. Connecting Rod-A Forging Component 90 Wflash ~~ [ki * kj] * (Wfini + Wslug) / 100 = Kg s l-2kg Estimation of the Forging Component Weight The estimation of forging component weight is comprised of consideration of sludge weight and flash weight with weight of finished component Thus the forging component weight is given as [51,52,57], Wall = Wfinish + Wflash + Ws]ug = P-O) = 4.1 Kg 5.7,5 Estimation of Flash Thickness and Land Width The shape difficulty factor is accounted for the estimation of flash dimensions. Hence the equation (4.48) and (4.49) pertaining to case -1 from chapter-4 are employed for this estimation. t = (Wall)1/ Wall t = 3.07 ram (5.16) The flash land width is given as, w = { [ (0.0038)(S)(Do/t) + [4.93/(Wall)0'2]} t w= mm (5.17) The ratio of flash land width to flash thickness is given as, w/t = [11.48/3.07] = 3.73 Design And Development Of Expert System for Forging Process,

20 Chapter-5. Connecting Rod-A Forging Component Selection of Forging Press The forging operation is performed as a series of edger, blocker and finisher stroke. Most of the connecting rods involve the blocker and finisher operation. The selection of forging press is depends on the load requirement for the blocker operation. The empirical relations are employed to obtain the load required for blocker. The die geometry for blocker operation is shown in Fig Fig.5.14 Plan area of finished die with flash land width. The various parameters required in load calculations are given as. Component plan area using AutoCAD is obtained as A Length of component including land width, L Component diameter including land width, Ds Yield strength y The overall component width is calculated as = mm2 = mm = mm = '6 Kg/mm (5.18) = mm

21 Chapter-S. Connecting Rod-A Forging Component 92 The load required to forge the component in Blocker die is given by [54], P 4 x [l - (0.001 x.ds)] x ' 20 v Ds x k X A x y 1000 = 4 x[l-(0.00 lx )] x ,, / f 26406x7.85] X / X V L 1000 J = Ton (5.19) Thus for forging this component in blocker die the press capacity of 1600 Ton is selected. 5.8 SUMMARY The connecting rod is considered for forging process to which the modified slab method equations are to be implementing to validate and to generate the knowledge base for the forging process. The detail dimensional parameters with its material properties are explained. The allowances are discussed for the design of die of the component. The studied allowances are implemented and modeled by CATIA V5 R15. The modeling of two half dies as an assembly is reported for the further investigation. The empirical equations are employed to the component to determine the fixed parameters like flash dimensions, and flash weight. The press selection is made for the blocker based on the empirical equation for the blocker operation. The connecting rod is selected as a component for forging process and is designed to analyze analytically by modified slab method. The validation of the results can be remarked by performing experimentation for the same. Thus the experimentation for the forging of connecting rod is designed and performed in the next chapter.