GEOMETRIC AND MATHEMATICAL ANALYSIS OF FORGING TOOLS FOR ROLLER BODIES IN BEARINGS

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 4, April 2018, pp , Article ID: IJMET_09_04_071 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed GEOMETRIC AND MATHEMATICAL ANALYSIS OF FORGING TOOLS FOR ROLLER BODIES IN BEARINGS Isad Saric, Nedim Pervan, Adil Muminovic, Department of Mechanical Design, Faculty of Mechanical Engineering, University of Sarajevo, Sarajevo, Bosnia and Herzegovina Vahidin Hadziabdic, Department of Mathematics and Physics, Faculty of Mechanical Engineering, University of Sarajevo, Sarajevo, Bosnia and Herzegovina ABSTRACT The scope of research of this paper is designing, modelling and analysis of tools for cold forging of rolling bodies of roller bearings. Basic principles of metal processing using plastic deformation are presented for better understanding of the forging process. Geometric tool modelling required knowledge of interconnections between individual tool elements, and their role in the forging process. The paper presents geometric and mathematical modelling of tools, and simulations of their operation. This presented a complete overview of movements of individual tool elements, which improved its functionality. In order to minimise errors in tool making and its stability, stress analysis and material yield at forging were taken into consideration. Key words: Tools, Modelling, Simulation, CATIA, DEFORM. Cite this Article: Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic, Geometric and Mathematical Analysis of Forging Tools for Roller Bodies in Bearings, International Journal of Mechanical Engineering and Technology, 9(4), 2018, pp INTRODUCTION Cold forging processes are employed to produce workpieces with superior material properties and small geometrical tolerances. These processes are highly efficient and economical for large batches. Additionally, cold forging is an environmentally friendly production process, since a heating process of the workpieces is not necessary. Also, the utilization of material is effective. Due to the forming of cold material, the loads for the tools and the tribological system are crucial. The significant tribological loads are the contact normal stress, the surface enlargement, the relative velocity, the sliding distance and the temperature. [1] editor@iaeme.com

2 Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic In recent years, one of the more important areas of research and development of modern forging technology has been precision forging. Precision forging is used to produce forgings of high precision complex shapes, classified as components requiring minimum or zero subsequent machine processing. [2-6] The development and application of precision forging have led to significant technological, economic and environmental improvements in the forging process, which brings numerous benefits to the manufacturers. Research has shown that precision forgings, compared to forms processed from plate, can reduce production costs of the component by (80-90)%, and machine operation by 95%. Compared to the conventional approach, precision forgings reduce production costs of the component by (60-70)%, and machine operation by 90%. [7] Precision forging is best applied on rotating symmetrical components, since it simplifies the process and shaping of tools [8, 9]. Furthermore, higher accuracy of rotating components is achieved. The procedure is usually undertaken through individual or double forming operations. However, in case of asymmetrical forgings, it is more difficult to meet the criteria of this technology, because of the need for multiphase forming. In the beginning precision forging was associated with process of cold forging, but by the time hot forging is being used more frequently with goal of getting forgings which quality and dimensional accuracy are close to these obtained by cold forging. In recent time process of precision warm forging has also been introduced. Warm forging offers better utilization of material, improve a surface finish, and dimensional accuracy when compared with hot forging and reduced press loads when compared with cold forgings. [7] In Figure 1 typical forging components obtained by precision cold, warm and hot forgings are given. Figure 1 Cold (a) and warm (b) precision forged components [7] When designing forgings, the following must be taken into account: geometric shape of forging with regard to possibilities of the forging process; proper selection of forging material, procedure for thermal preparation and method of forging in terms of mechanical and technological properties of the forgings; technological properties of forging design with regard to the possibility of cost-effective forging and subsequent machine processing. This paper is aimed at designing, modelling and analysis of tools for cold forging of rolling bodies of roller bearings, Figure editor@iaeme.com

3 Geometric and Mathematical Analysis of Forging Tools for Roller Bodies in Bearings Figure 2 Drawing of finished component (a) and respective forging (b) 2. GEOMETRIC MODELLING OF FORGING TOOLS 2.1. Basic elements of forging tools Tools for forging on crank presses are usually of assembly type, which is the main difference between them and tools for forging on hammers. They have numerous advantages: savings in tool steel, since only inserts with recess are made of these, and other tool parts are made of construction steel; possible easy replacement of damaged and worn inserts with continued use of other tool parts (with usually a universal application), etc. Figure 3a presents a modelled 3D geometric model [10] of the lower part of assembly tool for forging on crank press (NACIONAL 750) in section, for inspection of working and construction elements of the tool. Figure 3 3D model lower part of assembly tool for forging: a) axonometric layout in half section after assembly, b) axonometric layout before assembly Figure 3b presents working (1 block presses, 3 matrix, 4 former of narrow forehead, 7 ejector, 8 pusher) and construction (2 casing, 5 insert, 6 cover) elements of the lower part of assembly tool editor@iaeme.com

4 Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic 2.2. Basic forging operations for of rolling bodies of bearings Forging on crank presses may be undertaken perpendicularly to the axis (transverse forging) and in the direction of preform (longitudinal forging), whereby open forging moulds are used. For the purpose of easier filling of moulds for final forging, and to reduce the quantity of material discharged in the form of a ring and uniform deforming, the process of changing the shape of preform should be gradual. Therefore, segmentation of the forging process in several phases (operations) is recommended, in which each previous operation ensures easier and more complete filling of moulds in the next operation. The assembly tools for forging on crank presses (Figure 4a), is used for the making of rolling bodies of bearings forged cold, and include: top block, bottom block (fixed on machine casing) and shear blade. Figure 4 Set of tools for cold forging (a) and elements of assembly tool for forging on crank press (b) The top block includes working and construction elements. The working elements include: former of wider forehead, calotte former and pusher. The construction elements include: frame for former of wider forehead, plate, cone wedge and frame for cone wedge. The bottom block includes the following working elements: pusher, ejector, former of narrow forehead and matrix. The construction elements of the bottom block include: cover, casing and shear sleeve. (Figure 4b) The starting material is C45 wire. Forging is performed on NACIONAL 750 crank press, with productivity of 4080 pcs/h or 1.13 pcs/s. When forging on crank press, the forging process includes four phases or operations: I wire cutting, II preparatory forging, III final forging and IV removal of forging from mould. The operations are performed in the specified order. The wire, as a starting material for forging processing, passes through the shear sleeve (calibrated depending on the wire diameter), and then enters the shear blade cutting the wire in a particular length. This length is defined by a stopper on the machine, located near the tool. The next operation is the preparatory forging. The purpose of this operation is to prepare the forging component for the final forging. The precompressor is a working element of a press through which force is transferred to the blade needle. The needle of the shear blade compresses the wire into the calotte. The matrix and former of narrow forehead are designed by the process in which in final forging, if possible, the recess is filled by compression rather than extrusion. In order to achieve this, the preform (obtained by preparatory forging) needs to be pressed against the bottom of the recess, thereby ensuring proper final forging (Figure 5a) editor@iaeme.com

5 Geometric and Mathematical Analysis of Forging Tools for Roller Bodies in Bearings Figure 5 Preparatory forging (a) and final forging (b) The purpose of the final forging is to obtain the forging component with the shape and dimensions in line with forging measures. It is particularly important to point out that a gap should be envisaged between the top and bottom part of the tool, which prevents contacts between the inserts (due to continuous operation of the pusher, damage might occur). In order to ensure complete filling of the recess, the quantity of the starting material for final forging needs to be higher or equal to the quantity encased in the contours of the working elements (interrupted line, Figure 5b). This provides high quality filling of the mould and prevents fallouts. The final phase of forging a single rolling bearing bodie is discharge of the forging component. The forging process is repeated in the described order until a required number of forging components are made. Then, the forgings are forwarded to further mechanical and thermal treatment to obtain required geometric and mechanical characteristics. 3. MATHEMATICAL TOOL ANALYSIS FOR FORGING 3.1. Force required for forging It is well known that crank forging presses have the highest force at the end of travel of the presser. Maximum force is required at the final moment of metal deformation, when the forging component is the largest in horizontal plane, and excess material forms a ring. Therefore, for calculation of forging force, sizes of the forging in the final operation are relevant. The press force is determined based on the following [11]: = 1 where Specific pressure on forging component at the final forging phase, Surface of forging component projection on dividing plane and Coefficient of forging force increase due to formation on forging component ring. The specific pressure on forging component depends on relevant factors, which is the same as with forging on forging hammers: = 2 Coefficient of speed for forging on crank forging presses can be calculated based on the following expression: =2,8 (1 0,001 ) editor@iaeme.com

6 where Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic Largest diameter of forging component in horizontal plane. The expression (3) must comply with the requirement (4): (1 0,001 ) 0,7 4 This means that for the forging components with 300 mm the following is included: =2,8 0,7=1,96 5 The stress inequality coefficient and coefficient taking into account losses due to friction have the same value as with forging on forging hammers, i.e.: =1,2; =2,4 6 Specific deformation resistance, for the temperature interval of forging, can be replaced with strength of material under the set forging conditions, wherefore the specific pressure is: =2,8 (1 0,001 ) 1,2 2,4 =8 (1 0,001 ) 7 The coefficient has the same value as with forging on forging hammers: =!1,1+ #$ % &# 8 Taking into account all above, the expression for force (1) could be presented as follows: =8 (1 0,001 )!1,1+ #$ % &# 9 Based on expression (9), the force of crank forging press is determined, which is required for forging the component in Figure 2. The required forging force in this case is = MN Sizing of bearings Calculation of the bearing means to find (select) the one able, with certain reliability, to achieve its purpose. The required size of the bearing for a particular bearing position is determined based on the type of bearing and its capacity, present loads, designed life span and operational safety. Dynamic and static $ bearing capacity are used as capacity measures for their sizing. Dynamic capacity is a capacity criterion for the selection of dynamic capacity bearings, or bearings with rotation under load. It is determined depending on the bearing life span, based on the expression: = * + *, * - 10 Where Equivalent dynamic bearing load,. / Factor of durability,. Factor of temperature and. Factor of number of revolutions. At the design phase, an appropriate bearing is selected for the known value of dynamic capacity editor@iaeme.com

7 Geometric and Mathematical Analysis of Forging Tools for Roller Bodies in Bearings 4. ANALYSIS OF TOOL OPERATIONS FOR FORGING The analysis of tool operations for forging included observations of behaviour of starting material during the forging process. In the analysis, the DEFORM system was used. Simulation of the forging process using the DEFORM system has a key role in improving the quality, delivery and cost reduction. It has been proven as extremely efficient in a wide range of research and industrial application. The first step in FEM analysis of tool operation is to define parameters of the starting material (wire diameter 0=14.2 mm; wire material C45). A necessary step for the process is to define material and its condition before the forging. Since this is a cold forging process, the starting temperature of the wire is 120 C. In addition to material characteristics, a mesh of finite elements needs to be generated, i.e. number of finite elements and number of nodes need to be defined. Geometry of the model is approximated with finite elements. The actual surface of the component and its FEM approximation do not match completely and the coincidence can be improved by increasing the number of finite elements of FEM model. [12-16] Figure 6 Starting materials of defined characteristics (a) and press travel (b) Figure 6a presents generated elements and their geometric characteristics, and layout of the starting material with set parameters. In addition to the starting material, the forging tools have to be defined as well. The forging force has been set by defining the tool movement or press travel, as presented in Figure 6b. This way, the intensity of the forging force is obtained as output data. The press travel in this case is 412,5984 mm. The importance of precise identification of press travel needs to be pointed out, since otherwise an unwanted collision between the top and bottom parts of the tool might occur and cause serious tool damage. Figure 7 presents dependence of the load and time of action of the forging force on the starting material. The diagram includes two forging phases (preparatory and final forging). Behaviour of the top tool part was monitored. Phase I is preparatory forging, in which the starting material, under the effect of blade needle, is placed in the matrix of the bottom tool part, wherefore preparations are made for the final forging. As presented in the diagram, slight forces occur in this phase compared to the final forging. Phase II is final forging, in which the starting material is embedded in recess for final forging and plastic deformation. At the end of phase II, the forging is made with appropriate additions for subsequent processing editor@iaeme.com

8 Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic Figure 7 Diagram of top tool part load in time The obtained forging force, required for plastic deformation of the starting material into the forging of desired size, in this case is =0.856 MN. Based on the obtained value, it is clear that the press of NACIONAL 750 type with force of 6 =6.3 MN achieves much higher force (5-10 times higher) than the force required for forging of the particular forging component. The obtained ratio of the required forging force and press force has a positive effect on tool stability, since the working elements are not exposed to the maximum value of press force. In this particular case, the time parameter is defined subjectively, for a clearer presentation of change in the forging force. In the real time, this parameter is 5-10 times lower. Figure 8 Cross-section of the finished forging (a) and stress of the forging in tool (b) Figure 8a presents the cross-section of the finished forging, including: 1 ring, 2 dance and 3 addition for processing, and Figure 8b presents stress of the forging in tool after completed forging process. The interrupted line is a contour of the finished component after mechanical processing. In order to obtain the final contour, the forging component must undergo a series of treatments, which after the forging have a very important role in defining a finished component with acceptable envisaged dimensions editor@iaeme.com

9 Geometric and Mathematical Analysis of Forging Tools for Roller Bodies in Bearings 5. CONCLUSION The use of modern software solutions is a key to success of numerous companies. Software has become an important component in business decision making and basis of scientific research and engineering problem solving. It is also an important component in industrial, transportation, medical, telecommunication, military and many other systems. The paper clearly indicates advantages in the use of modern methods in modelling and analysis of operations of specialised forging tools. Such methods provide quicker and more efficient obtainment of output data of importance for the forging process. For the purpose of a more efficient use of technology and material savings, key parameters of the forging process are defined. One of the methods is a use of specialised software for modelling and analysis (CATIA, DEFORM, etc.), which can be applied to obtain high quality data with reference to the forging process. This method reduces the time for toll design and increases safety of operation and productivity of the tools. The possibility to model parts of a set and simulate its operation provides to the designer an accurate insight into its form and functionality. This means that errors that might occur during the product development are easily detected and eliminated. Because of these advantages and shorter time of product development, a number of computer programs and systems for this purpose is present on the market. The use of CATIA and DEFORM software facilitates understanding of tool design and forging process, and provides a complete insight into material flow and filling of graving, as well as into the stress of the forging component. This also makes accurate setting of parameters with reference to the starting material. Monitoring certain parameters makes it possible to predict the tool stress, and therefore extend its life span and efficiency in terms of repair and durability of spare parts. REFERENCES [1] Müller, C., Rudel, L., Yalcin, D. and Groche, P. Cold forging with lubricated tools. Key Engineering Materials, , 2014, pp [2] Behrens, B.-A., Doege, E., Reinsch, S., Telkamp, K., Daehndel, H. and Specker, A. Precision forging processes for high-duty automotive components. Journal of Materials Processing Technology, 185(1-3), 2007, pp [3] Hawryluk, M., Gronostajski, Z., Kaszuba, M., Polak, S., Widomski, P., Smolik J. and Ziemba, J. Analysis of the wear of forging tools surface layer after hybrid surface treatment. International Journal of Machine Tools and Manufacture, 114, 2017, pp [4] Hawryluk, M. and Mrzygłód, B. A durability analysis of forging tools for different operating conditions with application of a decision support system based on artificial neural networks (ANN). Eksploatacja i Niezawodnosc Maintenance and Reliability, 19(3), 2017, pp [5] Mori, T. and Li, S. A new definition of complexity factor of cold forging process. Precision Engineering, 33, 2009, pp [6] Bariani, P. F., Bruschi, S., Ghiotti, A. and Simionato, M. Ductile fracture prediction in cold forging process chains. CIRP Annals Manufacturing Technology, 60, 2011, pp [7] Milutinović, M., Vilotić, D. and Movrin, D. Precision forging Tool concepts and process design. Journal for Technology of Plasticity, 33(1-2), 2008, pp [8] Douglas, R. and Kuhlmann, B. Guidelines for precision hot forging with applications. Journal of Materials Processing Technology, 98(2), 2000, pp [9] Nee, J. G. Fundamentals of Tool Design, 6th Edition. Michigan [10] Society of Manufacturing Engineers (SME), editor@iaeme.com

10 Isad Saric, Nedim Pervan, Adil Muminovic and Vahidin Hadziabdic [11] Saric, I., Repcic, N. and Muminovic, A. 3D Geometric parameter modelling of belt transmissions and transmissions gear. Technics Technologies Education Management TTEM, 4(2), 2009, pp [12] Musafija, B. Obrada metala plastičnom deformacijom, 5. izdanje. Sarajevo Svjetlost, [13] Saric, I., Muminovic, A., Colic, M. and Rahimic, S. Development of integrated intelligent computer-aided design system for mechanical power-transmitting mechanism design. Advances in Mechanical Engineering, 9(7), 2017, pp [14] Saric, I., Pervan, N., Colic, M. and Muminovic, A. Conceptual design and stress snalysis of the composite frame of Dirt Jump Mountain Bike. International Journal of Mechanical Engineering and Technology, 9(3), 2018, pp [15] Delić, M., Čolić, M., Mešić, E. and Pervan, N. Analytical Calculation and FEM Analysis Main Girder Double Girder Bridge Crane. TEM Journal, 6(1), pp [16] Pervan, N., Čolić, M., Šarić, I. and Hadžiabdić, V. Analysis of the Haulage Ropes on Ropeways in Case of Accidental Loads. TEM Journal, 5(2), pp [17] Pervan, N., Mešić, E. and Čolić, M. Stress Analysis of External Fixator Based on Stainless Steel and Composite Material. International Journal of Mechanical Engineering and Technology, 8(1), 2017, pp [18] Mirlind Bruqi, Rame Likaj, Ahmet Shala and Nexhat Qehaja, Automatic Design of Technological Process of Forging, International Journal of Mechanical Engineering and Technology 8(9), 2017, pp