Wen Cheng Tang

Assembly process optimization for reducing the dimensional error of antenna assembly with abundant rivets

This paper proposes a process optimization method to improve the dimensional precision of riveted assemblies. The method representation and investigation use an assembly with 1093 rivets yielded from the double curved reflector. Firstly the static and dynamic finite element (FE) models respectively represent the global large-scale assembly and the local riveting process. The dimensional precision is denoted by the root mean square (RMS) of the deformations of the key points selected from the static FE nodes. Then the quantitation between RMS and process parameters equates to the iterative static FE analyses interpolating the dynamic FE analysis result and the possible former static FE analysis result. Finally the integration of the genetic and ant colony algorithms optimizes the process parameters, i.e. the rivet upsetting directions (UDs) and the assembly sequence (AS). Investigation indicates (1) both the rivet UDs and AS are the main RMS influence factors; (2) the proposed method can efficiently optimize the specific process parameters for the large-scale assembly with abundant rivets; and (3) the effective optimization prefers to solve rivet UDs and AS step by step.

Performance of reducing the dimensional error of an assembly by the rivet upsetting direction optimization

Reduction in the dimensional error of an assembly mostly focuses on the variation of fixtures and parts inside, in which the variation is mainly controlled by the methods relating to the fixture design and variation analysis. Recently, more researches concentrate on the dimensional analysis of the aluminum assembly where the distortion of rivet joints cannot be neglected, that is, the riveting-induced dimensional error. Hence, both the device design and the variation analysis for the riveting are drawing much attention to reduce the overall distortion. This article presents a dimensional reduction method, a rivet upsetting direction optimization based on a local-to-global dimensional calculation. The method is developed from a recent framework of assembly process optimization according to the discovered sensitivity between global dimensional error and rivet upsetting directions. A potential function that gathers the overall effect of every locating error is included. Simulations for three riveted assemblies are presented for comparison and results show that the method is efficient for the specific assignment of every rivet upsetting directions, and the effects of locating errors and rivet upsetting directions are highly coupled. The coupled effect yields the key questions in the improvement of this method. Detailed suggestions are then summarized.

Assembly sequence optimization for minimizing the riveting path and overall dimensional error

Due to the complexities of calculations based on different representations of constituent parts in an assembly, the combined improvement of efficiency and precision for the riveting has seldom been studied by the sequence planning or dimensional engineering. This article develops an assembly sequence optimization method that simultaneously minimizes the path length and overall dimensional error for the solid riveting. The sequence is denoted by the order of classifications for the nodes around the rivet holes in the finite element model for the assembly. Ant colony algorithm is applied on the optimization by integrating two calculations, that is, the length calculation of riveting path and the calculation of the dimensional error related to rivet upsetting directions and assembly sequence. Results for three assemblies are presented which show a good degree of optimization in performance for different scales of assemblies with different numbers of rivets that share the same solid riveting process.

Two-Step Identification of Instantaneous Cutting Force Coefficients and Cutter Runout

Cutting force coefficients and cutter runout parameters are the key factors for accurate prediction of instantaneous milling forces. A new two-step identification method is presented to calibrate them in end milling. Based on analyzing effects of cutter runout on milling forces, a method of extracting nominal milling forces from measured milling forces is proposed. By calibrating average cutting force coefficients and corresponding average chip thickness, an approach to evaluate the instantaneous cutting force coefficients is proposed. Then, an iterative method is presented to identify cutter runout, and the procedure is also given in detail. Milling tests are performed to test the proposed method, and validity of the identification approach is proved by a good agreement between predicted results and experimental results.

Deep Study and Improvement of the Globally Convergent Version of MMA

The globally convergent version of MMA (GCMMA) is deeply studied in this paper. Based on 3-bar truss structures, the advantages and disadvantages of the rules for updating the parameters are analyzed. The factor that makes convergence rate slow is found. Then the improvement measure by using two points approximate optimization for reference is put forward to speed up convergence rate. Finally by application on structural optimization of a truss, improved GCMMA can converge to the global optimal solution. Meanwhile, the convergent rate of improved GCMMA is significantly faster than GCMMA.

Solving the Deflection Problem of Laptop Casing Structure by Finite Difference Method

Due to its large length/thickness ratio, the casing structure can be treated as plates andshells,thus the classical plates and shell theories can be applied. A general MATLAB program wasdesigned to solve the deflection problems of the isotropic casing with simple support usingdifferential method. To test its precision,two different load conditions as well as two materials wereused and their results was made comparison with that of finite element method and Navier solution.The results were in good agreement with each other and the method was efficient in solving thedeflection problems of a casing structure

Performance Analyses and Experimental Verification for the Clamping Mechanism of Die Casting Machine

The research object of this paper is double-toggle clamping mechanism of DC3500 die casting. The theoretical formulas of stroke ratio and force amplification are proposed and the prototype model is established in ADAMS to generate kinematic and mechanical curves. Moreover, experimental values are used to verify the validity of the theoretical formulas and simulation model, and the causes of experimental error are gaven. Thus, the theoretical model can be adopted directly for the design of larger double-toggle clamping mechanism to simplify the design cycle.

Computer-Aided Production Control of Automobile Injection Molds Based on Process Perception

This paper focuses on major issues in production process control of automobile injection molds based on process perception, such as manufacture resource perception, exchange in three-dimensional model (3D), production planning and scheduling, manufacture process planning (tool path and assembly sequence). After a survey of them, we propose a method for the construction of computer-aided production process control platform. 1) Define the networked manufacture semantic/data model and an encapsulating approach to efficiently manipulate manufacturing resources. 2) Develop structural multi-view data models for the design information of automobile molds transferring in 3D. 3) Propose a production planning and scheduling arithmetic. 4) Develop a variation accumulation model for manufacturing process control. 5) Integrate the tool path and assembly sequence planning of injection molds by using a variation accumulation model. 6) Integrate the existing and/or developed models to the new system. Finally we introduce a validation method and discuss the prospect to the accurate control of production process.

Truss Structural Optimization Based on Globally Convergent Version of MMA

The subproblem of the globally convergent version of method of moving asymptotes (GCMMA) was deeply studied and realized by Lagrange dual method, sequential unconstrained minimization technique (SUMT) and conjugate gradient method. Based on the convex, separable and conservative properties of subproblem, a dual problem was built by using Lagrange dual method. The dual problem was transformed into unconstrained optimization problem using SUMT and solved by conjugate gradient method. Finally, the feasibility of solution of subproblem is demonstrated by truss structural optimization problem. Comparing with other optimization algorithms, GCMMA can converge to the global optimal solution.

A Modified Volumetric Penalization Method for Gray Elements Suppression

The volumetric penalization approach is an important method for gray elements suppression in topology optimization. With the volumetric penalization approach, the topology optimization problem is consistent and regularized, and topology description is unambiguous. Considering the fact that an unreasonable topological form of structure is sometimes resulted with the traditional volumetric penalization function, a modified function is proposed. By utilizing the modified function, the gray elements are compelled to be 0 or 1, and the efficiency of optimization solving is also improved. To verify the validity of the modified method, it is compared with the famous volumetric penalization method, SINH method, through a typical example. Simultaneously, its numerical instabilities are also analyzed.