Design and Development of Engine hood with light weight SMC Polymer composite

Transcription

1 Design and Development of Engine hood with light weight SMC Polymer composite #1 B.B.Borhade, #2 G.Hagnoor, #3 Dr. P.P.Hujare 1 Student (Automotive Engg), Sinhgad Academy of Engineers, Pune 2 GM, TACO Composites Ltd, Pune 3 Prof., Sinhgad Academy of Engineers, Pune Abstract Use of Sheet Moulding Compound (SMC) has regained a renewed interest reducing or eliminating steel usage in automotive industry. Flexibility in design shape, lower tooling costs, design freedom, integration of functions and low weight are the factors, which made SMC as a material of choice. UPGF25% SMC grade material is considered for the development Engine hood aiming at weight benefit over steel bonnet. Noise & heat insulation are secondary benefits.various design options are prepared in Catia V5 surfacing module. Finite element analysis (FEA) is used for determination of deflection & stress with the loading of 150 kg human stepping load. Lighter option is selected for further development of tooling & experimentation. Benchmark cases referred before investment decision. Proto partprepared for experimentation & verification. Component is tested on UTM for deflection. Experimental results are compared with FEA simulation. Reasonable correlation for deflectionfound with 30% benefit in weight over steel bonnet. Better aesthetic, design freedom to enhance usability are inherent features of SMC process. Heat & noise insulation assessment is ongoing in vehicle testing. Keywords SMC, Design freedom, user friendly, deflection, light weight, noise. I. INTRODUCTION Sheet moulding compounds (SMC) refer to a family of composites made from a thermoset polymer matrix reinforced by short glass fibres around 25 mm long. SMC are manufactured as 2 3 mm thick pre-impregnated sheets in which glass fibres are randomly distributed [1]. SMC sheets are formed by compression in a mould heated at 150 ⁰ c, allowing rapid curing of the part. These materials are mainly used in the automotive industry for production of car body parts and semi-structural parts as roof module inner & car dec Lid. SMC is selected for automotive body parts because of its high thermal stability and its low thermal expansion coefficient, low density comparable to steel. A fundamental advantage of the high thermal stability is the proven online paint ability. Flexibility, lower tooling costs, design freedom, integration of functions, and gluing ability and low weight are additional factors, which made SMC as a material of choice[2]. This paper presents the case study for a commercial passenger vehicle wherein existing sheet metal engine hood is being replaced by light weight SMC composite material. It s UP GF25 unsaturated polymer 25% glass fiber. It is lighter in weight, low thermal conductivity & thermal expansion coefficient. With the many examples in automotive parts for SMC, it is decided to go for SMC engine hood design and development. Basic material properties & behavior under loading condition is referred from various published papers, reference books & industry case studies. M.Oldenbo and J. Varma[3] in paper 2D constitutive model for FE-simulations of SMC composite accounting for linear viscoelasticity and damage development, experimented behavior of SMC as linear vs non- linear concept. FE-simulation of a 4-point bending test is performed using shell elements. The result is compared with linear elastic solution and test data using a plot of maximum surface strain in compression and traction versus applied force. Simulation and test results are in very good agreement regarding the slope of the load-strain curve and the slope change. Considerable correlation in material behavior found for FE results of Linear and Non-linear behavior, also test and FE results. 1. METHODOLOGY Following wok process is devised to meet the objective of developinglight weight engine hood in SMC. The presented work is carried out in following stages, Collection of customer input for making design user friendly. Here we get technical design targets in addition aesthetic & ergonomic input. Selection of appropriate material, manufacturing process keeping cost & timelines targets from management perspective. 2015, IERJ All Rights Reserved Page 1

2 CAE of the design concepts. Proto tool & part preparation for initial evaluation. Component testing on UTM to measure the deflection within acceptable limit of packaging on vehicle. For pre-processing and post-processing Hyper works tool was used and for FEA simulationoptistruct solver is used. Step.1 CAD Model Generation- Catia V5 Step.2 FEA Model Building- Meshing, Boundary condition & load application Step.3 DetermineStaticdeflection under the applied load of 150 kg Step.4 Design iterations by changing thickness & rib parameters for minimum weight & acceptable deflection Step.5 Experimental validation of Results and Development of tool for part manufacturing. Fig. 1: Methodology Flowchart II. CAD MODEL PREPARATION The 3D models of engine hood are prepared in CATIA V5 surface module. Existing sheet metal hood is 1mm thick. It is being manufactured by conventional sheet metal press die & punch draw method. It has quality, cost & design freedom (space usability) concern. Two designs of SMC hood are made for FEA with and without ribs. In SMC model various design features like bottle holder, coin space, tiffin box holder etc are modeled as per customer requirement which was not possible in conventional sheet metal hood. Ribbing structure on top area where driver may step on is modeled limit the deflection in vehicle packaging area. Weight of the sheet metal & SMC engine hoods are calculated in CATIA by applying respective material density. 2015, IERJ All Rights Reserved Page 2

3 Fig. 2Existing engine hood sheet metal(1mm thk) Fig.3 SMC engine hood(3 mm thkwithout ribs) Rib Height:8 mm, width: 3 mm Fig.4 SMC engine hood(3 mm thk with ribs) 2015, IERJ All Rights Reserved Page 3

4 III. CAE ANALYSIS Based on customer s input static analysis done with load of 150 Kg. Stress is checked against acceptable limit of materials yield strength, keeping deflection to minimum from vehicle level packaging perspective. Following Steps are being followed: 1. Importing Catia 3D model into Hypermesh and Meshing with solid elements 2. Applying Boundary conditions in line with vehicle level fitment points. 3. Applying load of 150 kg (distributed on top patch- rib area where driver can step on the hood) 4. Checking deflection and stress to be within permissible limit. Following configurations are analyzed: 1. Design 1 - Base thickness 3mm without Rib 2. Design 2 - Base thickness 3mm with Rib The FE analysis was carried out to determine static deflection of the engine hood. Hyper-mesh is used as pre-processor for meshing. Solver used is Optistruct for simulation. Results are viewed & analysed as post processing in Hyper-view. 4.1 Meshing details The imported 3D model is meshed with second order tetrahedral structural element. The details of total no. of nodes, total no. of elements are mentioned in table I. Stepping load 150kg - UDL Fixed points Fig.5 load case & boundary conditions Table I: - FEA Parameters Sr. Parameter Value No. 1 Total no. of nodes Total no. of elements 4.2 Selection of Material Properties. Sr. No. 1 2 Material Steel IS513CR5 SMC UP GF25 Table II: - Selection of Material Properties Yield Strength (Mpa) Density (Kg/m3) Thermal conductivity w/m-k 2015, IERJ All Rights Reserved Page 4

5 4.3 Analysis of design1 (3 mm base without rib) Max deflection 15 mm Fig.6 Deflection analysis of design1 4.4 Analysis of design2 (3 mm base with rib) Maximum Von-Misesstress 32.10Mpa Fig.7 Stress analysis of design1 Max deflection6.37 mm Fig.8Deflection analysis of design 2 Max Von-Misesstress 21.3Mpa Fig.9 Stress analysis of design , IERJ All Rights Reserved Page 5

6 Design 2 (3 mm base with Rib) having 6.37 mm deflection with 21.3 Mpa Von Mises stress is selected for part manufacturing. IV. PART MANUFACTURING SMC sheet formation Glass fiber SMC Sheet Fig.10 SMC Sheet formation with raw material SMC sheet formation is continuous process wherein glass fibers are added to the base polymer material as shown in table III. Table III: - Raw material composition Material Resin 22.6 Glass Fiber 25 Mineral filler 48.6 Additives 3.8 Total 100 Weight Fraction SMC Part Manufacturing Fig.11 SMC Part manufacturing press 2015, IERJ All Rights Reserved Page 6

7 SMC sheet is placed and pressed in between the former set (made of steel) of the press set up. It supplies hot steam from bottom former at 150⁰c. Once the part is formed part is taken out by raising the top former. Total cycle 5 minutes. Part is finished by deflashing, filing, putty filling, inner and outer sanding. Utility Features Tiffin box Bottle Holder Paper space Coin space Fig.12 Part(Top view) Fixing points Fig.13 Part (Bottom view) V. TESTING SET UP To verify the design as per customer usage, part is tested on Universal Testing Machine (UTM) Instron make. Part clamped Fig.14 Deflection testing on UTM (Instron Make) Part is clamped on platform with clamps like it is mounted in vehicle cabin, two parts were measured for repeatability. Measurement of stress with strain gauging was not possible due to mounting difficulty on the inner rib area. Since the FEA stress values are well within the permissible limit of material strength, it is decided to go ahead with deflection results. 2015, IERJ All Rights Reserved Page 7

8 VI. TEST RESULTS 150 Kg load simulating a driver steeping load on engine bonnet is applied on UTM as given in set up. Proto parts of both designs are tested shows the deflection and compared with FEA results as shown in table IV TableIV :FEA & Test Deflection comparison Deflection (mm) Design 1 with Rib Design 2 Without Rib Test result FEA Results Correlation (%) Comparison of deflection Measured deflection is having good correlation with FEA predictions. Considering the deflection and space around engine, design 1 with rib is taken up for final tooling and further validation. Weight benefit achieved over the conventional steel bonnet is listed in the table V given below- TableV : Weight comparison Part Material Steel IS513CR5 SMC UP GF25 Density (Kg/m3) Weight (Kg) Benefit 30% reduction VII. CONCLUSION 1) The tested deflection has reasonable correlation with the FEA results. Design 2 (with Rib) giving minimum deflection is finalized for production. 2) SMC Polymer composite material weight reduction over steel. Additionally it provides many user friendly features like space for tiffin box, bottle, paper, coinetc which is not possible in steel in single part. 3) Since material has better properties (Thermal conductivity, expansion coefficient, thermal stability, paint ability) it provides better isolation from heat & noise as compared to steel. This is being evaluated in vehicle level testing as ongoing exercise. REFERENCES 1) Steven Le Corre, Laurent Orge as,, Denis Favier, Ali Tourabi, AbderrahimMaazouz, Ce cilevenet, "Shear and compression behavior of sheet moulding compounds", Composites Science and Technology 62 (2002) ) FonsHarbers, "Advances in SMC/BMC Automotive Applications", SAE paper ) M. Oldenbo, J. Varna, 2D constitutive model for FE-simulations of SMC composite accounting for linear viscoelasticity and damage development, Submitted to International journal for numerical methods in engineering, SE , PP ) M. Shirinbayan, J. Fitoussi, F. Meraghni, B. Surowiec, M. Bocquet, A. Tcharkhtchi," High strain rate visco-damageable behavior of Advanced Sheet moulding Compound (A-SMC) under tension", Composites Part B 82 (2015) , IERJ All Rights Reserved Page 8

9 5) Yuxuan Li, Zhongqin Lin, Aiqin Jiang, Guanlong Chen," Experimental study of glass-fiber mat thermoplastic material impact properties and lightweight automobile body analysis", Materials and Design 25 (2004) ) A.H.M FazleElahi, MilonHossain, Shahida Afrin, Mubarak A Khan, Study on the Mechanical Properties of Glass Fiber Reinforced Polyester Composites, ICMIEE-PI ) Sainath A. Waghmare, Prashant D. Deshmukh, Thickness determination of SMC replacing Sheet metal for Automobile roof, SSRG-IJME, Vol-I Oct ) Mangesh Kale, AkashMohanty, Nachiket Thakur, Deformation Analysis & validation of Fiber Reinforced Composite Component, 7th IRF International Conference, , IERJ All Rights Reserved Page 9