Optimal Fixture Design Research Articles

Convex relaxation for optimal fixture layout design

This article proposes a general fixture layout design framework that directly integrates the system equation with the convex relaxation method. Note that the optimal fixture design problem is a large-scale combinatorial optimization problem; we relax it to a convex Semi-Definite Programming (SDP) problem by adopting sparse learning and SDP relaxation techniques. It can be solved efficiently by existing convex optimization algorithms and thus generates a near-optimal fixture layout. A real case study in the half-to-half fuselage assembly process indicates the superiority of our proposed algorithm compared to the current industry practice and state-of-art methods.

Optimal Fixture Design for Drilling of Elastomer using DOE and FEM

An elastomer is a polymer with the property of viscoelasticity generally having notably low Young's modulus and high yield strain compared with other materials. The elastomer which is used in our project is styrene-butadiene rubber. The drilling of elastomer work piece is not easy since it can easily deform. Hence the desired output cannot be obtained. By designing a proper fixture layout, the drilling of elastomer can be done accurately. The fixture design requires accurate positioning of locators and clamps to reduce the deformation of work piece during drilling. In this work six locators and three clamps are used. The primary design layout is done and then it is analyzed in ANSYS to find out the work piece deformation. The various possible design layouts are formed using L27 orthogonal array by MINITAB Software. Then all the 27 layouts are analyzed using ANSYS and the deformation values are found. The optimal layout is found using DOE – Taguchi method from MINITAB Software by giving the 27 layouts and the corresponding deformation values as inputs. From the obtained SN ratio graph, the optimal fixture layout is found for minimum deformation of the work piece.

Off line simulation system of machining processes

The primary objective for modeling of machining processes is to develop a predictive capability of machining performance in order to facilitate effective planning of machining operations. This capability leads to faster implementation, higher performance, quality at a lower cost. This comes about due to improved selection of machining parameters, optimal fixture design and the avoidance of tool failure. The simulation system presented simultaneously considers the effect of cutter geometry, the cutter's initial position errors, workpiece geometry, machine tool dynamics, and workpiece/fixture system dynamics on the machining process. The integration of all of the above in one model provides an off-line tool to simulate and optimize the machining parameters and the fixture configuration cutting both lead and production time. The modular nature of the simulation system presented allows for the study of many different machining processes. The cutting forces in this system are modeled using a mechanistic approach. NURBS curves and surfaces are utilized for the geometric modeling and simulation of the machining process. While a finite element method is used to model and analyze the workpiece/fixture dynamics. Two case studies are presented to demonstrate the practical application of the presented simulation. The first case presents the optimization of the fixture configuration of a generic automotive component. While the second case presents the results of simulations performed on a novel mill/grind machining process. This process is a combination of face milling and grinding in one operation. Some simulated results are presented along with experimental validation.

Optimal fixture design in peripheral milling of thin-walled workpiece

In order to optimize the positions of the locators in peripheral milling of a thin-walled workpiece, a finite element model along with an accurate cutting forces model is proposed in this paper. The finite element model takes into account the thickness variations of the workpiece in peripheral milling. The locators on the secondary locating surface directly influence the surface errors in peripheral milling of thin-walled workpiece, so this paper deals with the optimization of the positions of the locators on the secondary locating surface. A method including two steps is presented. In the first step, the initial positions of the locators are determined by adding the locators at the position with the maximum deformation. In the second step, a heuristic algorithm is proposed to optimize the positions of the locators. Finally, a simulation example is used to illustrate the method.

Optimal fixture design for drilling through deformable plate workpieces, part II: Results

Optimal fixture design for drilling through deformable plate workpieces, part II: Results

Optimal fixture design for drilling through deformable plate workpieces, part I: Model formulation

Considering that drilling constitutes about 40% of all metal-cutting operations, there is a surprisingly small number of published articles addressing drilling in general and high-speed drilling in particular relative to other areas of metal cutting such as turning and milling. And although the speed at which aluminum gets drilled has been climbing through the years, there appears to be yet a large margin to grow. Applications that involve drilling large number of holes encompass industries such as the aerospace, automotive, and potentially many other industries. As such, these same industries would stand to benefit handsomely from drilling holes at increasingly more rapid rates.Combinations of properly set high cutting speed and tool feed resulting in proportionally large material removal rate summarize aggressive drilling (AD). The basic ingredients for commercially viable, aggressive, yet economical drilling are coming together nowadays, promising a quantum leap in the speed (thousands of meters per minute) and, consequently, the feed at which drilling takes place. Drilling at many times the conventional rates undoubtedly translates into faster productivity, the savings of which typically would dwarf the cost associated with excessive tool wear. The trends, issues and challenges of aggressive drilling are reviewed in this paper.

Optimal Fixture Design Accounting for the Effect of Workpiece Dynamics

This paper presents a fixture layout and clamping force optimal synthesis approach that accounts for workpiece dynamics during machining. The dynamic model is based on the Newton-Euler equations of motion, with each fixture-workpiece contact modelled as an elastic half-space subjected to distributed normal and tangential loads. The fixture design objective in this paper is to minimise the maximum positional error at the machining point during machining. An iterative fixture layout and clamping force optimisation algorithm that yields the best improvement in the objective function value is presented. Simulation results show that the proposed optimisation approach produces significant improvement in the workpiece location accuracy. Additionally, the method is found to be insensitive to the initial fixture layout and clamping forces.

Optimal fixture design for drilling through deformable plate workpieces part II: results

This is the second of two manuscripts which employ finite element analysis and optimization algorithms to design optimal fixtures for drilling through deformable workpieces. Part I has addressed the problem formulation, suggesting five different objective functions that capture different geometric characteristics of the machined surface. The performance of the five obtained fixture layouts under different drilling conditions is studied in this paper. The drilling studies include single, sequential, and simultaneous (gang) drilling. These studies demonstrate the known fact that more frequent setups and longer machining time periods result in higher workpiece accuracies. The simulations also suggest that the proposed optimal fixturing model developed in this study can be used to command greater control over the drilling process, resulting in elevated drilling quality. The numerical value of the latter is captured by the objective function values. The computer simulations further identify optimal fixturing layouts that can be implemented in an industrial environment.

Optimal fixture design for drilling through deformable plate workpieces part I: model formulation

This is the first part of two manuscripts that address the development of scientifically based methodologies that use finite element methods and optimization algorithms to design optimal fixturing layouts for the drilling process. Part I focuses on the problem formulation and Part II discusses the results. The fixturing problem formulation is posed as a constrained optimization problem, in which the physical fixture constraints define the domain, and the desired fixturing characteristics are optimized in accordance with a selected objective function. The optimal fixturing model developed includes a material removal strategy that enables one to calculate the shape and dimensions of the machined hole surface. The boundary value problem associated with the optimal fixturing simulations is first formulated. Five different objective functions capable of describing various geometrical aspects of the machined hole have been developed and tested. These functions evaluate the square differences between the simulated and nominal radii and diameter values, minimize the maximum values of the latter quantities, and minimize the deviations of the drilled surface from a perfect cylinder.

Deformable Sheet Metal Fixturing: Principles, Algorithms, and Simulations

Fixture design is an important consideration in all manufacturing operations. Central to this design is selecting and positioning the locating points. While substantial literature exists in this area, most of it is for prismatic or solid workpieces. This paper deals with sheet metal fixture design. An “N-2-1” locating principle has been proposed and verified to be valid for deformable sheet metal parts as compared to the widely accepted “3-2-1” principle for rigid bodies. Based on the “N-2-1” principle algorithms for optimal fixture design are presented using finite element analysis and nonlinear programming methods to find the best “N” locating points such that total deformation of the deformable sheet metal is minimized. A simulation package called OFixDesign is introduced and numerical examples are presented to validate the “N-2-1” principle and optimal sheet metal fixture design approach.