LIGHTWEIGHT DESIGN OF SEAT CUSHION EXTENSION MODULES USING THE PROPERTIES OF PLASTIC AND HCA-SIMP

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 5, May 2018, pp , Article ID: IJMET_09_05_068 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed LIGHTWEIGHT DESIGN OF SEAT CUSHION EXTENSION MODULES USING THE PROPERTIES OF PLASTIC AND HCA-SIMP Dong-Seok Shin, Yu-Jun Song Department of Mechanical Engineering, Graduate School, Kongju National University (KNU), Korea Euy-Sik Jeon Department of Mechanical Engineering, Graduate School (Industrial Technology Research Institute), Kongju National University (KNU), Korea ABSTRACT Design using lightweight materials is limited by their associated structural properties. Topology optimization design has been proposed to consider this problem at the conceptual design stage; however, current research into the nonlinear structural environment is insufficient. In this study we consider the structural problems caused by changing the materials used for the extension module of an automotive seat cushion; static and dynamic tests are proposed and applied, then we present a corresponding conceptual design method. Finally, we use the results of the static and dynamic tests to verify the validity of the results. Keyword: FEA, Plastic, Seat-back, Multi-purpose, Topology optimization, Lightweight, Concept design Cite this Article: Dong-Seok Shin, Yu-Jun Song and Euy-Sik Jeon, Lightweight Design of Seat Cushion Extension Modules Using the Properties of Plastic and Hca-Simp, International Journal of Mechanical Engineering and Technology, 9(5), 2018, pp INTRODUCTION The design of lightweight mechanical parts for transportation vehicles has been studied by academics and those within the industry. [1] Research into weight reduction can be divided into changes in materials, structure, and methods. Of these, material changes have attracted the most research as they have the greatest potential for weight reduction. [5] However, when weight reduction is achieved by material change there needs to be an improvement in the strength of the design in order to maintain the physical performance. [6] As an alternative solution, Kim(2007) studied topology optimization and proposed changing the structure and the shape of the parts while maintaining existing design specifications. [2] However, no editor@iaeme.com

2 Dong-Seok Shin, Yu-Jun Song and Euy-Sik Jeon dynamic tests were carried out and only one test load was studied, so further investigation into the practicality of this approach is required. A study by Lee(2010) explored phase optimization design within a dynamic test environment, but this was also limited to one test condition and did not take into account static loads. [7] Aullg(2018) proposed a topology optimization scheme which accounts for various static and dynamic test environments for vehicle frames. Finite element analysis has shown that the results of topology optimization for a complex environment can satisfy both static and dynamic tests. [3] However, it is difficult to utilize the topology optimization design model in its existing form; hence it is necessary to study post-processing of the results and investigate the resulting performance changes. This paper presents a conceptual design study of weight-reduction that uses plastic for the extension module of automotive seat cushions and includes: 1. Static and dynamic tests based on FMVSS regulations which are simulated using finite element analysis on the seat cushion extension module designed using the layout concept. These results are presented alongside the performance of existing parts. 2. A proposed solution to the structural problems caused by changing from metal to plastic modules. 3. Changes to the geometry which satisfy the strength-requirements and the implementation of a conceptual design using HCA-SIMP. 4. A comparison of the performance of the plastic and metal modules to verify the validity of the new model. 2. PREFERENCE MODEL 2.1. The extension module in seat-cushion The initial extension module is based on the arbitrary extension module shown in Fig. 1. The extension module is mounted on the front of the seat cushion frame as a device which supports the user's thighs, and is an element which increases the weight of the vehicle. Extension modules are generally made of either metal or plastic parts. As shown in Table 1, the weight ratio of the metal parts is relatively high Static and dynamic test environment of seat frame The FMVSS does not specify a method for evaluating the strength of the cushion frame, so we based our models on the static structural analysis study as shown Fig. 2 (a). [4] Since there are no published regulations or case studies relating to dynamic tests of the extension module, the human body model was set to limit the speed to 0.5 m/s on impact with the extension module. We utilized two existing models for the finite element analysis, one based on metal and one on plastic. Fig. 3 shows the results of the finite element analysis for the conventional metal model (Type 1) and the plastic model (Type 2). The material properties of each model are shown in Table 2. The displacement of the Type 1 model was less than 5 mm. However, the modified plastic model showed a displacement of approximately 10 mm and poor strength. Fig. Fig. 3 shows the structural problems associated with weight reduction when only the material is changed. These problems mean that the design must be revisited and the basic geometry rethought editor@iaeme.com

3 Lightweight Design of Seat Cushion Extension Modules Using the Properties of Plastic and Hca- Simp Figure 1 Schematic diagram of extension module Table 1 Description of parts of extension module No Description Material % 1 Extension Steel Center block Plastic Guide block Plastic 17 Extension module 4 Front cover Steel Lever Plastic Spring guide Plastic Ignore 7 Connector Steel Ignore 8 Cushion Frame Holder Steel Ignore 9 Side frame Steel Ignore 10 Static block Steel Ignore Test parts 11 Leg model Steel Ignore A quick and easy engineering approach to determine the basic shape is the topology optimization technique. Topology optimization is used to determine the basic shape of an object; it is most commonly used with finite element analysis based on the density method (SIMP). (a) Static test of extension module. (b) Dynamic test of extension module. Figure 2 Simulating the test environment of the extension module editor@iaeme.com

4 Dong-Seok Shin, Yu-Jun Song and Euy-Sik Jeon (a) Static test analysis. (b) Dynamic test analysis. Figure 3 Static and dynamic test analysis. Table 2 Mechanical properties for extension module. Assortment Units Steel model plastic model Material - Steel GFRPwt40%GF Young s modulus (E) MPa 2.07e Poisson s ratio (ν) Density (ρ) kg/mm 7.83e E-6 Thickness mm TOPOLOGY OPTIMIZATION METHODS The model used to determine the basic shape of the plastic module is shown in Fig. 4. As in Fig. 5, the weight value of this model is higher than the existing value, but the strength can be significantly improved. Areas with low stress and small energy effects under static and dynamic loads can be eliminated in the topology optimization process to reduce weight. Figure 4 Shape of a fill-in extension block (Type 3) editor@iaeme.com

5 Lightweight Design of Seat Cushion Extension Modules Using the Properties of Plastic and Hca- Simp (a) Static test performance difference depending on material and structural changes. (b) Dynamic test performance difference depending on material and structural changes. Figure 5 Material change for basic shape Formulation The limiting variables for the topology optimization are chosen to be the z-directional displacements of the nodes where the maximum displacement occurs. The objective was set to minimize the volume. (a) Topology optimization results using finite element analysis of the static environment (Type 4). (b) Topology optimization results using finite element analysis of the dynamic environment (Type 5). Figure 6 Topology optimization results for the plas5tic model. The material density in each element of the design space =x 1 Minimize object function f=min (Volume) 2 Constraints f(x) =( /5) <1 3 f(x) " =( " /5) <1 4 The results of the topology optimization design for the static and dynamic tests are shown in Fig. 6. The performance values for each result are shown in Fig. 7. The results of the static test show that it does not meet the expectations of the dynamic test and the results of the editor@iaeme.com

6 Dong-Seok Shin, Yu-Jun Song and Euy-Sik Jeon dynamic test did not meet the expectations of the static test. The topology optimization method used to consider such a multipurpose environment is the density method (HCA- SIMP) using HCA. (a) Comparison of the static analysis results. (b) Comparison of the dynamic analysis results. Figure 7 Comparison of the FEA analysis results 3.2. Simplification of the model on which topology optimization is performed The topology optimization design results that include both the static and dynamic test environments are shown in Fig. 8 (a). The formulation of the static and dynamic environments in the optimization process of the multipurpose environment has been considered. Fig. 9, the Type 6 model satisfies both the static and dynamic environmental conditions, indicating that it can attain a light weight of 20%. However, since the shape is discontinuous, it is difficult to model it as a real product. A simple finite element model based on the topology optimization results of Fig. 8 (a) is shown in Fig. 8 (b). However, the complementary shape resulting from the simplification process may cause the physical performance to deteriorate and the weight to increase. The physical properties of these two models are shown in Fig. 9. (a) Optimization results considering both static and dynamic environment using HCA- SIMP (Type 6). (b) Simplified model of HCA-SIMP results (Type 7). Figure 8 Simplification modeling of HCA-SIMP results editor@iaeme.com

7 Lightweight Design of Seat Cushion Extension Modules Using the Properties of Plastic and Hca- Simp (a) Performance comparison in a static environment. (b) Performance comparison in a dynamic environment. 4. SIZE OPTIMIZATION Figure 9 Comparison of physical performance of each model Definition of the thickness factor Based on the simplified Type 7 model, the shape factor is defined as shown in Fig 10. The set parameters take into account the thickness values ± 30%, considering their interference with other shapes. Table 3 shows the initial set of shape parameters. Formulation was performed for dimensional optimization with the set shape factors. Initially, six variables were formulated, and each factor was arranged and interpreted based on the experimental design D-Optimal. GA algorithm was applied during the reaction surface method analysis. Figure 10 Shape factor setting for the topology optimization design results Final model The final model is shown in Fig. 11 (Type 8) and its physical performance is shown in Fig. 12. The material density in each element of the design space =x, ",, $, %, & 5 Minimize object function fmin Volume editor@iaeme.com

8 Dong-Seok Shin, Yu-Jun Song and Euy-Sik Jeon Constraints f(x) ' =(( ' /5) <1, i=1,2,3,,6 7 Table 3 The parameters of rib-thickness [mm] Assortment Initial value Upper boundary Under boundary x x " x x $ x % x & Figure 11 Shape factor set for the topology optimization design results (Type 8). (a) Performance comparison in a static environment. (b) Performance comparison in a dynamic environment. Figure 12 Performance comparison of the optimized models. 5. CONCLUSION In this study we proposed a conceptual design method to consider the static and dynamic environment using a topology optimization technique involving HCA-SIMP. The concept design process yielded the following results editor@iaeme.com

9 Lightweight Design of Seat Cushion Extension Modules Using the Properties of Plastic and Hca- Simp 1. We found that when only material change was considered and the existing structure was preserved, the parts were weak. Therefore, weight reduction may be achieved by applying the topology optimization technique of the fill-in model. 2. Optimization considering only the static environment satisfied the static or dynamic environment and could reduce the weight. 3. Optimization considering a multipurpose environment satisfied both the static environment and the dynamic environment and could reduce the weight. However, the shape must be corrected due to the non-continuous shape of the results. When the optimized geometry was simplified, the weight increased, while the static and dynamic performance decreased. 4. Dimensional optimization was performed using the simplified geometry. The weight of the final model (Type 8) was reduced by 20% compared to the Type 1 model and it met the criteria for static and dynamic criteria. This method can be considered as part of the conceptual design stage where structural defects are caused by changing the materials. ACKNOWLEDGEMENT This work was supported by the Purchase condition new product development Program (S ) funded by the Small and Medium Business Administration(SMBA, Korea) and supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea(NRF- 2015H1C1A ) REFERENCES Journal Articles [1] Jang, I.S. Min, B.J., A Study on the Weight Optimization for the Passenger Car Seat Frame Part. Journal of KSAE, 14(5), 2006, pp [2] Kim, H.J. Bae, C.H. Kim, S.H. Jung, H.S. Kwon, T.S. Suh, M.W. A Study on the Crashworthiness Enhancement of Rolling stock leading-cab using Topology Optimization. Journal of KSAE, 1, 2007, pp [3] Aullg, N. Nutwell, E. Menzel, S. Detwiler, D. Preference-based topology optimization for vehicle concept design with concurrent static and crash load case. Structural and Multidisciplinary Optimization, 57(1), 2018, pp [4] Jang, H.S. Choi, S.K. Park, S.C. Lim, H.P. Oh, E.D. A Study on the Development of Lightweight Seat Cushion Extension Module. Korea Academy Industrial Cooperation Society, 17(8), 2016, pp Thesis [5] Lim, J.Y., Lightweight Design of the Automotive Seat Back Frame using FEM. M.S. Dissertation, Jeon-Buk University, [6] Polavarapu, S. Topology and free-size optimization with multiple loading conditions for light weight design of die cast automotive backrest frame. M.S. Dissertation, Clemson University, [7] Lee, W.H. Topology optimization of cushioning foam package using hybrid cellular automata. M.S. Dissertation, A-ju University, editor@iaeme.com