Research On The Development And Optimization Of Aluminum Alloy Body At The Conceptual Design Stage

With the intensification of competition in the Chinese auto market,the requirements for excellent quality,aesthetic appearance and cost-effective price are getting higher and higher.And the body design level is a key indicator to measure the level of the car design.Most of the cost and time of body development is occupied by the conceptual design phase,so the concept design stage plays an important role in vehicle development.For the development and optimization of aluminum alloy body at the conceptual design stage,the simplified model of the vehicle body was created and its performance was analyzed,the simplified model of aluminum alloy body was created and its materials were replaced with aluminum alloy,the simplified model size optimization was implemented and the multi-objective optimization of the cross-sectional shape was carried out.The main work of this paper is as follows:(1)In order to deal with blindness in design work in the conceptual design stage,the vehicle's simplification model,which was reasonable and easy to modify,was built to reduce body design cycles and costs based on relevant data.The method of establishing the body wireframe model,the simplified method of the beam element and the simplified method of the joint were compared and analyzed.According to the data of the original model,the wireframe model based on key nodes of the car body was constructed.The body beam section database and the body joint database were established.And the simplified model of the body based on the real joint and the actual section was finally established.This model was suitable for concept development of similar vehicle bodies.Model analysis and data reference were provided to subsequent designs.(2)According to the simplified model of the vehicle body,the stiffness analysis of the simplified model was carried out under the bending condition and the torsion condition.The error between the simplified model and the detailed finite element model was less than 10%,which proved the accuracy and rationality of the simplified model.The material of the simplified model was replaced with the aluminum alloy material in the case of equal stiffness.Firstly,according to the equivalent stiffness material replacement formula,the initial thickness of the body parts under the aluminum alloy material was obtained.Due to the excessive thickness variable replaced by the formula,the error was large,and the obtained model stiffness was reduced by about 20% compared with the raw material.Therefore,the initial thickness needs to be optimized to eliminate the error.The stiffness of the raw material model was set to the constraint and object.The optimized thickness value was obtained,and a simplified model of the aluminum alloy body with equal stiffness was established.(3)Design variables were selected by sensitivity analysis of the simplified model.The relationship between body performance parameters and thickness was qualitatively judged by relative sensitivity analysis.Through the size optimization analysis of the simplified model,the thickness value that satisfies the stiffness requirement and the minimum mass target was calculated.According to the shape and thickness of the section,the section characteristic parameters of the beam component can be obtained,which provides parameter guidance for subsequent generation and optimization of section shapes.(4)In order to solve the problem of low flexibility and low efficiency of section shape in the conceptual design stage,the improved particle swarm optimization algorithm was applied to multi-objective optimization of the cross-section shape of the body beam.The algorithm was improved by improving the inertia weight of the algorithm and adding the crowding distance mechanism,which makes the algorithm have better global search and faster convergence speed.Different from the previous method of section optimization,the section shape was optimized by controlling the joint coordinates of the section to improve the flexibility of the section design.In order to avoid errors caused by the approximation model,the functional relationship between the section characteristic parameters and the node coordinates of the beam section was derived.The cross-sectional area,the moment of inertia to the x axis,the moment of inertia to the y axis and inertial product were set to optimize the target.In order to eliminate the influence of the magnitude of the response value,the three sub-objects of the x,y axis moment of inertia and the inertia product were normalized into an objective function using the compromise programming method.And the reasonable weight value of the objective function was given based on the analytic hierarchy process,so that the relative importance of each factor was considered comprehensively,and then the above four targets were converted into two target optimization problems.Finally,the non-inferior solution set of the optimization model was obtained by the improved particle swarm optimization algorithm and a non-dominated solution that meets the needs can be found according to the needs of the designer.The effectiveness of the method was verified by an example.