Lin Zhongqin

A study of a reverse engineering system based on vision sensor for free-form surfaces

Reverse engineering can quickly create a CAD model of a new product, in which, the sensor, sampling planning and surface reconstruction are three crucial elements. In this paper, a reverse engineering system involving a new vision sensor, an improved sampling planning module and a fine surface reconstruction module is developed. A characteristic of the proposed sensor is strong linearity between output and input, obtained by the structure optimization when a simple lens replaces the asperic lens. Back propagation (BP) neural network error compensation heightens accuracy. To increase efficiency of digitization, an improved sampling planning approach is proposed; it is based on surface curvature and tangent line slope of a measured point. In surface reconstruction, a new adaptive extracting approach based on curvature of surface reconstructs the non-uniform rational B-spline (NURBS) surface for the scattered data. The accompanying reverse engineering experiment proves the proposed system to be reliable and efficient.

Study on moving GTA weld pool in an externally applied longitudinal magnetic field with experimental and finite element methods

Under the control of external longitudinal magnetic field, substantial changes happen to ordinary gas tungsten arc welding (GTAW) process. In this paper, mathematical models of fluid flow and heat transfer of external longitudinal magnetic field moving GTAW three-dimensional weld pool were established. Current density distribution on weld pool surface was obtained by probe method. Using the multi-coupled analysis function of finite element analysis software ANSYS, distributions of current density and magnetic field as well as fluid flow and heat transfer in three-dimensional moving weld pool were systematically investigated to understand and reveal the effect of external longitudinal magnetic field on liquid metal in moving GTA weld pool and also to supply basis for the application of external longitudinal magnetic field welding technology.

Study on the influences of geometrical parameters on the formability of stretch curved flanging by numerical simulation

Abstract Flanging is an important sheet forming process in auto-body panel stamping industry, which can affect the assembly quality of auto-body. Unfortunately, simulation of flanging is a relatively difficult task, and the formability is not so clear so far. In this paper, the capability of a large-step static implicit FE code, AutoForm, on simulation of stretch curved flanging is studied, and some key technical points are listed. Then the effects of some geometrical parameters on the formability of stretch curved flanging have been analyzed. The simulation results are validated by experiments.

Stamping and stamping simulation with a blankholder gap

Abstract Applying a blankholder gap is the main method of control of the blankholder in stamping or its simulation. In this paper, the nature of stamping with a blankholder gap is provided as well as two advantages of stamping simulation with a blankholder gap. Finally, a reasonable blankholder gap for cup deep drawing and the reverse drawing process is proposed.

Robust fixture layout design for multi-station sheet metal assembly processes using a genetic algorithm

The optimal fixture layout is crucial to product quality assurance in the multi-station sheet metal assembly processes. Poor fixture layout may lead to product variation during the assembly processes. In this paper, a genetic algorithm (GA)-based optimisation approach has been presented for the robust fixture layout design in the multi-station assembly processes. The robust fixture layout is developed to minimise the sensitivity of product variation to fixture errors by selecting the appropriate coordinate locations of pins and slot orientations. In this paper, a modified state space model for variation propagation in the multi-station sheet metal assembly is developed for the first time, which is the mathematical foundation of optimal algorithm. An e-optimal is applied as the robust design criteria. Based on the state space model and design criteria, a genetic algorithm is used to find the optimal fixture layout design. The proposed method can greatly reduce the sensitivity level of product variation. A four-station assembly process of an inner-panel complete for a station wagon (estate car) is used to illustrate this method.

An improved equivalent drawbead model and its application

Abstract In this work, an improved equivalent drawbead model is presented to replace the actual drawbead shape. Three-dimensional finite element analysis of the deep drawing process was performed to determine the optimum distribution of drawbead restraining force for the stamping of the joint panel of a gate pillar. The optimum design of the drawbead geometry was executed by means of nonlinear constraint optimization in conjunction with the improved equivalent drawbead model. The drawbead geometry parameters obtained from the optimization design were validated by the achievement of defect-free production panels. The simulation results correspond well with those observed in actual practice, which demonstrates that the restraining force can be reflected effectively by the improved equivalent drawbead model.

Investigation of sheet metal forming by numerical simulation and experiment

Abstract Two large sheet-forming simulation CAE systems — Autoform and Ls-dyna3D — being representatives of implicit and explicit solutions, respectively, are employed in the comparison of simulation results for a side-frame constituting the outer panel of a Santana 2000; validating experiments are also presented in this paper. Through the simulation calculation, the engineering strain and the thickness change of the blank during forming are compared and the comparison between the strain state and the FLD is given. The possible areas of wrinkling and failure in the course of pressing are determined. According to the comparison, the difference produced by two systems in dealing with problems is discussed, the cause of existing difference is analyzed and methods of reducing the difference are presented. Finally, the advantages and disadvantages of the two systems are considered.

A new contact judgement method for sheet metal forming simulation

Abstract A new contact judgement method for sheet metal forming simulation is proposed. The method can overcome miss-judgement and error-judgement, and improve numerical stability and computational accuracy effectively. Based on the proposed contact judgement method, a static–implicit FE code is developed. Some typical sheet metal forming processes and the benchmark of NUMISHEET’93 are simulated, and satisfactory results being obtained.

Auto Body Stamping Robust Design Approach and Application

The uncertainties in the auto body stamping process affect the stamping quality significantly. The current stamping simulation and optimization may lead to design failure without considering these uncertainties. A systematic stamping robust design approach is proposed. The variation behavior of the local auto sheet properties is analyzed, and the parameters are obtained. A stochastic analysis method is developed, where FE‐simulation, uniform design, response surface methodology (RSM) and Monte‐Carlo simulation are used. The robust optimization model composed of mean and standard deviation is constructed and solved. The proposed approach is verified through feature box and deck lid inner panel forming process. The developed approach offers rapid and reliable results for engineers to deal with potential stamping problems during the early phase of product and tooling design, saving more time and resources.

Study on geometry modeling in the dynamic stamping simulation of a die

Abstract Geometric modeling used in the dynamic stamping simulation of a die is discussed. Several modeling methods based on engineering drawings used often to construct 3D surface models of an autobody panel in stamping simulation are also discussed. Based on this discussion, a front-door model of a car is constructed based on the CAD system, then it is transferred into the CAE system by means of VDA data format. The calculation results of dynamic stamping simulation, including the distributions of engineering major strain and thickness change of the blank and FLD are presented. In order to verify the accuracy in modeling and simulation, experiments have been done in a plant, which show that the results of the calculation are almost identical to those of the experiments.