Research On The Design Method Of Forming Process Parameters Of Autobody Panels Based On SMT

As an important part of automobile,autobody panels have many requirements in appearance,shape and performance.Due to the complex shape and large size of the autobody panels,the quality problems such as crack and wrinkle are easy to occur in the forming process.In order to prevent wrinkling and cracking,it is necessary to adjust the moderate technological parameters in the forming process to control the forming quality.At present,the commonly used design method of technological parameters in the forming process is to optimize the design based on numerical optimization algorithm.However,when the optimization algorithm is used to solve the technological parameters,the optimization process takes longer time to increase the design time,and the optimization process is more difficult under complex constraints.Therefore,this paper proposes a method for designing the forming process parameters of autobody panels based on the Satisfiability Modulo Theories(SMT).The main contents are as follows:Firstly,the surrogate model is used to construct the functional relationship between technological parameters and forming evaluation criteria.By quantifying the evaluation index of forming quality required by the engineer,the constraint satisfaction problem is constructed by combining the fitting function relations,so that the optimization design of multi-objective and multi-constraint functions can be transformed into a satisfiable solution design of the mathematical inequality set.Then,the SMT solver named dReal is used to solve the inequality quickly,and finally obtainintg the technological parameter value which is satisfiable the requirements of the engineer.Secondly,to generate a variety of solutions for engineers to choose,this paper introduced a concept of flexible constraints.According to the concept of flexible constraints,there will be divided into two categories,soft and hard constraints.By changing the values or scope of soft constraint,the inequality set based on the surrogate model is transformed into a dynamic variable equation set,thus generating multiple sets of technological parameter values.Based on the concept of human-computer interaction,the forming technological parameters design system of autobody panels was established.Through real-time modification of design variables and forming quality indexes under the human-computer interaction interface,the ideal design scheme for engineers was finally achieved.Thirdly,the feasibility analysis of the design method of technological parameters based on SMT is carried out with the case of square box.Blank holder force and stamping speed are selected as design variables,and sample value range is selected according to engineering experience.The sample matrix was collected by the Latin hypercube sampling method,and the center deviation criterion is used to evaluate the homogeneity of the sample matrix.The wrinkling value and crack value are quantified according to the forming limit curve.Then,A set of mathematical inequalities is constructed with BP neural network surrogate model.Combined with flexible constraints,the constraint satisfaction problem is solved rapidly by dReal,SMT solver.Finally,the feasibility of this method is proved under the simple model.Finally,based on the technological parameter design process of SMT,this paper develops the technological parameter design system of autobody panels.The system mainly includes the selection of model and design variables under the initial setting interface.Selection of experimental design method,fitting and result display of BP neural network and selection of evaluation criteria for model fitting under the interface of surrogate model.Solve the inequality design space under the design interface,the setting of the constraint space,the definition of soft and hard constraints,and the satisfiable design based on the SMT solver dReal.Results the selected process parameters were simulated and verified under the simulation interface,and displayed the FLD pictures.Using the fender model,regarded the blank holder force,stamping speed and drawing rib force as design variables,regarded wrinkle and crack value as forming quality index,the validity of this method is verified by judging and solving the constraint satisfiability problem,and the feasibility of application of the design system is verified.