Research On Structural Optimal Design Of A Car Plastic Back Door

With the increasingly tense energy and the sharp deterioration of the environmentissues, the automotive industry,which is rapidly growing, has the responsibility to take onthe important task of energy saving and environmental protection.in modern automotivedesign, the concept of lightweight can solve these two problems at the same time.According to the sources: when the car is10%weight loss, fuel consumption can bereduced by6%to8%. This figure makes the lightweight become one of the hot spots of theautomotive design. Auto body parts account for40%to60%of the total vehicle quality, andtherefore the car weight loss has significant impact. To get Lightweight auto body, there aretwo ways, one is the use of lightweight materials, the other is the structure optimizationtechniques. As more and more research is conducted, the combination of the two ways inthe car design has become a new trend. With the relative low density, applicable to manyprocessing method, sound-absorbing and vibration isolation, heat insulation, electricalinsulating properties and resistance to corrosion, can be composite modified, low energyconsumption of production, and many other features, engineering plastics is increasinglyimportant in the automobile production, and has become one of the important materialsamong many lightweight materials.The two ways of lightweight design are combined in the paper, and then is applied to theplastic design of a car trunk lid. The structure of the traditional steel plastic back door isre-designed first, and then applies PET glass fiber reinforced plastic provided by a companyto the new structure. Compared to steel, the engineering plastic has a much smallerelasticity modulus, therefore the new structure needs to guarantee the mechanical propertiesfirst to achieve the lightest quality. Based on orthogonal experimental design, the combination of topology optimization and topography optimization is applied to the innerpanel basic structure, referring to the optimal results, beads and holes are distributed to thebasic structure. The new structure is composed of the inner panel, outer panel and lampholder, which need the thickness design as well. The thickness change is a continuousvariable, using the finite element method in the optimization, the time required for practicalproblem is unacceptable. Therefore, based on the theory of experimental design andapproximate model, the five variables, including the maximum displacement of the threeanalysis conditions, quality, modal, is fitted by the approximate model to replace the finiteelement model in the thickness design. In the optimization process of thickness design, themaximum displacement of the three analysis conditions, quality and modal, should betaken into account at the same time, therefore, this problem is in the scope ofmulti-objective optimization, in this paper,NSGA∏is selected to solve the problem.After optimization, the new structure is endowed the property of PET glass fiber reinforcedplastic, and then is conducted the same analysis as the traditional structure. Compared to theoriginal results, the quality of the new structure is reduced by8.97%, mode is increased by58.3%，the maximum displacement of the three analysis conditions is reduced in differentdegrees, which indicates that the plastic back door is reasonable and efficient.