Search

Cutting toolholders, with designed in-built compliant mechanisms, are frequently used for machining microfeatures. In this paper, compliant structures are designed using trusses as they exhibit a superior strength-to-weight ratio. Systematically stacked two-stage truss structures along with flexure hinges are designed to yield the desired precise cutting motion. The materially reduced efficient design amplifies the output force and greatly assists in overcoming cutting resistance during machining. The characteristics of the designed compliant tool holder are analysed by considering the output force and displacement for a given input. Both mathematical modelling to determine the force and finite element analysis to identify the critical stress regions when subjected to a prescribed input displacement are presented. As part of dynamic analysis, modal analysis and harmonic response studies were performed to determine how the trussed compliant structure deforms when subjected to dynamic loadings. The designed tool holder was additively manufactured using functionally rigid polyamide-12-glass-bead (PA12-GB) material. The performance of the developed cutting tool holder is then verified by machining radially graded surfaces following which, the machining results are presented in this paper. [ABSTRACT FROM AUTHOR]

In order to reduce the machining deformation of thin-walled parts during milling, a non-uniform allowance planning method for thin-walled parts based on the workpiece deformation constraint with the idea of adding materials in reverse material removal sequence is proposed in this paper. This method does not require accurate deformation prediction and extensive experiments compared to traditional error compensation methods. It strives to maximize the allowance to enhance the stiffness of the in-process workpiece. First, a cutting force threshold calculation method is proposed according to the finite element method. The cutting force threshold at different positions is calculated by obtaining the local stiffness characteristics at the cutter-contact point under the constraint of allowable deformation. And then, the maximum machining allowance at the cutter-contact point is calculated depending on the cutting force model. Considering that the stiffness of the workpiece is position-dependent and affected by material removal, the stiffness of the workpiece is updated by adding elements in the reverse cutting direction, and the finishing stock is obtained by surface fitting. Experimental results show that compared with the traditional uniform allowance method, the error of the proposed method is reduced by about 83%, which can effectively reduce the deformation and improve the machining accuracy. [ABSTRACT FROM AUTHOR]

Finite Element (FE) modeling of machining processes has received growing attention over the last two decades. Since machining processes operate at severe deformation conditions, involving very high strain, strain rate, stress, and temperature, the modeling procedure is still a challenging task even with new advanced software and computers. Therefore, most of the published research works were mainly performed for the simplest configuration of machining known as orthogonal cutting, in which a plane strain deformation state is assumed. This configuration leads to reducing the number of elements in the FE model and the computational time of the solution, compared to conventional machining processes (turning, milling, and drilling). Nevertheless, FE modeling of orthogonal turning is still considered as an open-ended subject as most of the phenomena involved in the orthogonal turning process, which also exist in other machining operations, are not fully well understood. The present review article deals with finite element modeling of orthogonal machining process. The paper consists of several related parts. First, the fundamentals of the FE simulation of orthogonal turning process are briefly described. Then, a detailed review on the FE prediction of machining characteristics including chip morphology, cutting forces, cutting temperature, tool wear, and burr formation is provided. Also, the FE prediction of surface integrity characteristics including residual stresses and microstructural changes is discussed. The influence of input model and parameters including thermal, material, and frictional models as well as size and arrangement of elements on machining and surface integrity characteristics are explained as well. Both technical and statistical aspects of the FE simulation of orthogonal turning are treated. Since there is no review paper thoroughly and specifically discussing the methods and findings of the finite element simulation of turning operations, the present article can be used as a reference for researchers who are active and/or interested in this filed. [ABSTRACT FROM AUTHOR]

The machining of micro thin-walled parts constitutes a key process in the microelectronic field. Deformations and machining errors easily occur, due to the low stiffness of micro thin walls. In this paper, a new iterative finite element method (iterative FEM) was proposed for the deformation predictions based on previous conducted works in the authors' laboratory. The new method, with aim at the effect of low radial immersion milling, was improved in three aspects compared to the traditional predicted methods: interaction calculation between the deformation extent and the cutting force; the grid division was significantly intensive; the cutting force was dispersed on certain nodes similarly to real cases. Firstly, the static deformation analysis and iterative FEM were introduced. Following, a diamond-coated micro milling tool was utilized to machine the micro thinwalled structures of 30 to 105 µm in thicknesses. Subsequently, several tungsten steel-coated milling tools were also utilized. Various tool diameters and edge radii were selected for comparison to the diamond-coated micro milling tool. The experimental results demonstrated that the deformations were approximately consistent with the simulation results, although certain errors still existed. [ABSTRACT FROM AUTHOR]

Elastic deformation machining method is a simple machining method in manufacturing aspheric surfaces process. In this method, the top surface of workpieces will deform and be in contact with the mold surface once vacuum is applied, while the bottom of workpiece is polished to flatness with the vacuum pressure is maintained stability. The machining process is finished when the thickness of workpiece is polished to size as required. When the vacuum is turned off and the workpiece is released from the mold, the bottom surface of the workpiece will be shaped into the aspheric surface as the top surface returns to its original flat surface form due to material elasticity. During machining, the form accuracy of aspheric surface is dependent on the value of vacuum pressure and contact between workpiece and mold surface. Therefore, the study of behavior of the glass in contact with the mold surface is necessary to determine the suitable mold surface. In this paper, the simulation results of the glass in contact with the mold in the different pressure values have been carried out. Based on the simulation and experiment results, the appropriate pressure values and mold surface are established for machining process by elastic deformation machining method. In order to improve the precision of form surface produced in elastic deformation machining, the mold profile is modified by selecting the finite element analysis results of workpiece in the case of vacuum pressure P = −95 kPa and the conic constant K = −3. [ABSTRACT FROM AUTHOR]

The sidewalls of thin-walled deep cavity components can easily deform during the milling process because of their low rigidity, which seriously affects the machining accuracy. To resolve this problem, this paper proposes a novel method to predict milling errors based on the finite element method (FEM). A dynamic model of the tool is first established, and the motion state of an arbitrary point on the tool during the continuous milling process is obtained by solving for the key parameters. In addition, both the deflection of the workpiece/tool system and the springback deformation of the workpiece are considered. The material is then removed based on a Boolean operation and a hexahedral mapping algorithm for the points; finally, the continuous tooling process and the milling error of the arbitrary point on the finished surface are obtained. This study uses a typical waveguide cover as the simulation object and verifies the veracity of the simulation method through experiments. [ABSTRACT FROM AUTHOR]

Significance of application of metal matrix composites (MMCs) in various industries has already been demonstrated. In order to address the challenges faced during machining MMCs, development of novel modeling techniques for understanding the mechanics of the process is crucial. This paper presents a new approach towards finite element modeling of MMC machining process to facilitate the analysis of plastic deformations. Transient Lagrangian modeling is used with adaptive remeshing control in order to reduce the effects of mesh distortions on accurate estimation of plastic deformation during machining. The thorough understanding of MMC plastic deformations, which is achieved using the developed model, is an asset in analysis of MMC behavior during the process. [ABSTRACT FROM AUTHOR]

This paper describes the machining and forming process of a Pitman arm, proposed to be used in the automotive industry, from austempered ductile cast iron (ADI) as an alternative to the commonly used material, AISI 1045 steel. Samples were austenitized at 900 °C for 180 min and subsequently austempered in a salt bath over a range of temperatures, from 340 to 360 °C, for 60 min, to obtain favorable mechanical properties. The results of metallographic testing show that the pieces formed with ADI have an average nodularity of 92.5%, and the average nodule count is 159 nodules/mm. Mechanical tests results of strength, elongation, hardness, and impact energy are comparable to that of ASTM standard A897-15 grade 1. A finite element simulation and an experimental analysis were performed to determine the forming force and the material strength. The deformation limits for ADI were identified. These limits and the simulation results show that ADI is an attractive alternative high-strength material for the Pitman arm application. [ABSTRACT FROM AUTHOR]

Design of fixture configuration (layout) is a procedure to establish the workpiece fixture contact through positioning of clamps and locating elements such that the workpiece elastic deformation is minimized. This work is done based on the assumption that the workpiece is an elastic body. Since the fixture layout influences the dimensional and form accuracy of the workpiece during the machining process, the fixture layout has to be optimized to minimize the workpiece deformation. In this paper, the workpiece deformation is modeled using finite element method (FEM), for the problem of fixture layout optimization problems with the objective of minimizing the dimensional and form errors. This paper presents a fixture layout optimization method that uses genetic algorithm (GA) and ant colony algorithm (ACA) separately. In this paper, three different number of node systems are defined on the same workpiece geometry to find the consistency in the performance of GA and ACA. The optimal solution, i.e., the most minimum value among the entire possible layout is determined separately for all three different number of node systems. The solution obtained for each node system using GA and ACA is compared with their respective optimal solution separately and ACA reports faster and accurate solutions. [ABSTRACT FROM AUTHOR]

In precision manufacturing industry, requirements for surface quality are very high. It is important to accurately predict the machined surface errors to reduce manufacturing costs and lead times as well as develop fixturing scheme to optimize machining quality. This paper presents a contribution for predicting the machined surface errors where fixture-workpiece system dynamic effects during milling process are considered. The combined effect of clamping and milling on machined surface errors prediction is taken into account, and finite element analysis is developed to analyze the workpiece deformation. In finite element analysis environment, the static analysis and explicit dynamic analysis are used to calculate the static deformation due to clamping force and the dynamic deformation due to milling force. Milling forces are applied to the manufacturing points step by step. The chip removal effect is taken into account based on element death technique, and every fixture locator is modeled as a virtual spring-damper system to emulate the fixture-workpiece contact points. The developed methodology has been verified by a set of end milling experiments for ten fixture layouts. The measured and predicted results are in good agreement, and the results also illustrate that the closer the triangle formed by the three locators in the primary datum is to an equilateral triangle, the smaller machined surface errors will be. [ABSTRACT FROM AUTHOR]

In machining fixtures, minimizing workpiece deformation due to clamping and cutting forces is essential to maintain the machining accuracy. This can be achieved by selecting the optimal location of fixturing elements such as locators and clamps. Many researches in the past decades described more efficient algorithms for fixture layout optimization. In this paper, artificial neural networks (ANN)-based algorithm with design of experiments (DOE) is proposed to design an optimum fixture layout in order to reduce the maximum elastic deformation of the workpiece caused by the clamping and machining forces acting on the workpiece while machining. Finite element method (FEM) is used to find out the maximum deformation of the workpiece for various fixture layouts. ANN is used as an optimization tool to find the optimal location of the locators and clamps. To train the ANN, sufficient sets of input and output are fed to the ANN system. The input includes the position of the locators and clamps. The output includes the maximum deformation of the workpiece for the corresponding fixture layout under the machining condition. In the testing phase, the ANN results are compared with the FEM results. After the testing process, the trained ANN is used to predict the maximum deformation for the possible fixture layouts. DOE is introduced as another optimization tool to find the solution region for all design variables to minimum deformation of the work piece. The maximum deformations of all possible fixture layouts within the solution region are predicted by ANN. Finally, the layout which shows the minimum deformation is selected as optimal fixture layout. [ABSTRACT FROM AUTHOR]

In high-speed dry milling of thin-walled parts, the cutter-workpiece temperature rises asymptotically with cutting speed, causing excessive cutter tooth wear and workpiece thermal expansion, which in turn reduces the cutter life and produces dimensional and geometrical variabilities in the machined part. Therefore, a basic understanding of the thermal aspect of machining and the effecting parameters is essential for achieving better part quality with improved productivity. This paper presents a transient milling simulation model to assist manufacturing engineers in gaining in-depth understanding of the thermomechanical aspects of machining and their influence on resulted part quality. Based on the finite-element method approach, the model can predict transient temperature distributions and resulted elastic-plastic deformations induced during the milling of 2.5D prismatic parts comprising features like slots, steps, pockets, etc. The advantages of the proposed model over previous works are that it (1) performs feature-based machining simulation considering transient thermomechanical loading conditions; (2) allows modeling the effects of coolant on convective heat transfer rate; and (3) considers the nonlinear behavior of the workpiece due to its changing geometry, inelastic material properties, and flexible fixture–workpiece contacts. The prediction accuracy of the model was validated with experimental results obtained during the course of the research work. A good agreement between the numerical and experimental results was found for different test cases with varying part geometries and machining conditions. [ABSTRACT FROM AUTHOR]

Workpiece deformation must be controlled in the numerical control machining process. Fixture layout and clamping force are two main aspects that influence the degree and distribution of machining deformation. In this paper, a multi-objective model was established to reduce the degree of deformation and to increase the distributing uniformity of deformation. The finite element method was employed to analyze the deformation. A genetic algorithm was developed to solve the optimization model. Finally, an example illustrated that a satisfactory result was obtained, which is far superior to the experiential one. The multi-objective model can reduce the machining deformation effectively and improve the distribution condition. [ABSTRACT FROM AUTHOR]