Frédéric Vignat

Towards stiffness prediction of cellular structures made by electron beam melting (EBM)

Abstract Additive manufacturing is a novel way of processing metallic cellular structures from a powder bed. However, differences in geometry have been observed between the CAD and the produced structures. Struts geometry has been analysed using X-ray microtomography. From the 3D images, a criterion of ‘mechanically efficient volume’ is defined for stiffness prediction. The variation of this criterion with process parameters, strut size and orientation has been studied. The effective stiffness of struts is computed by finite element analysis on the images obtained by X-ray tomography. Comparison between the predicted stiffness and the effective one tends to show that the efficient volume ratio leads to a slight underestimation of the stiffness. Finally, the effective stiffness is used at the scale of a unit cell. This can help define the build orientation and loading direction that lead to the highest stiffness.

Manufacturing process simulation for tolerance analysis and synthesis

The choice of a manufacturing process (machine tools, cutting tools, part-holders, process plan) which allows the production of parts conform with the objective in terms of quality and price depends on many criteria. One of these is the compliance with the functional part tolerances. To check this point, the manufacturing process is simulated (positioning and machining operations). This simulation results in a Model of Manufactured Part (MMP). The deviations of all the MMP surfaces are described with regards to their nominal position (nominal part) using a small displacement torsor. Then, for all the functional tolerances to be checked, a virtual gauge is designed and developed and assembled with the MMP and the gap between the tolerance zone and the toleranced surface is calculated. The verification of each tolerance is performed via a system of inequalities representing the non-penetration conditions between the toleranced surface and the tolerance zone limits. The ability to machine a series of parts close to the functional tolerances being verified, the ISO or non-ISO manufacturing tolerances to specify the workpiece at the end of each set-up is determined. These tolerances are useful to follow the conformity of the workpiece at the end of each step of the machining process.

Simulation of the Manufacturing Process, Generation of a Model of the Manufactured Parts

Designing a new product in an industrial context supposes to be certain to be able to produce it according to a level of quality and controlled cost. To achieve this goal, it is necessary to simultaneously design the product and the process of production and to be able to simulate the envisaged process in order to predict the productivity and the quality that can be obtained. The proposed method is based on the generation of a virtual model of the manufactured parts (model MMP). The deviations of the manufactured surfaces of the MMP are expressed compared to the nominal part. These deviations are collected by simulation of the suggested manufacturing process. The range of variation of these deviations represents the 3d capabilities of the manufacturing means.

3D Transfer of Tolerances Using a SDT Approach: Application to Turning Process

The following paper aims to apply the concept of the small displacements torsor (SDT) in order to predict the defects of a part resulting in successive machining set-up. The proposition is to enlarge the 1D dispersion method to a 3D analysis of the feasibility of a machined part. This paper follows our previous works on the development of a method using this concept to simulate a manufacturing process. These developments are adapted to the turning process and its particularities. The relevant parameters allowing to describe the manufacturing and positioning defects are determined. These defects are analyzed with regards to the functional specifications of a part.

Tolerance analysis in machining using the model of manufactured part MMP – comparison and evaluation of three different approaches

This article aims to compare three different approaches already proposed by the authors regarding the three-dimensional error stack-up analysis in machining. Although the developed error stack-up analysis method comprises of different manufacturing processes, this article is limited to machining operations. This article is built on the previous research of the authors namely the model of manufactured part (MMP) which models the different geometrical deviation 3D impacts on the geometrical and dimensional quality of part produced (error stack-up) in a multi-stage (MS) machining process. In this study, the MMP will be used for developing numerical solution techniques for the aim of tolerance analysis in a MS machining process. The developed solution techniques are classified in two main categories: worst case analysis (WCA) (worst part produced) and stochastic analysis (STA). This article provides an overview of the MMP model and the different solution techniques. The different strategies to simulate the deviation parameters of the model are then discussed. For each of the three proposed solution techniques, its advantages and disadvantages are explored in detail. The performance of the solution techniques is then compared from different points of view (i.e. rapidity, convergence to the global minimum and analysed case … ) through a 3D example, and finally some perspectives are presented.

Geometrical Deviation Model of product throughout its life cycle

Nowadays, the requirements of customers concerning a product are more and more tight and high. The satisfaction of these, such as quality, reliability, robustness and cost, plays an important role in the context of global and concurrent economy. However, a product, during its life cycle, passes through manufacturing and assembly stages where geometrical deviations are generated and accumulated. These deviations that obviously have an influence on the performances of the product are not considered. Thus, a model based on the small displacement torsor that allows to model the geometrical deviations of the product is proposed in this paper. (Received 18 March 2010; Revised 20 August 2010; Accepted 1 October 2010)

3D Simulation of Manufacturing Defects for Tolerance Analysis

When a new product is designed in an industrial context, it must be possible to produce this product with the desired level of quality and at an acceptable cost for the market. One of the important quality criteria is compliance with functional tolerances. To evaluate the impact of manufacturing defects on the quality of parts produced, designers simulate the influence of the error stack-up in different machining operations to check compliance with functional tolerances. This paper builds on the Model of Manufactured Part (MMP) and the Jacobian-Torsor Model and presents a combined approach for analysing machined part tolerance taking into account the geometrical defects occurring in a multi-stage machining process (positioning defects and machining defects). This combined approach aims to help designers when evaluating the different process plans by predicting the worst quality of finished parts. This study uses interval arithmetic because it offers the advantage of expressing uncertainties and deviations.

Tolerance Analysis in Machining: An Approach Combining the Model of Manufactured Part and the Jacobian-Torsor Model

To perform tolerance analysis in machining, a combined approach which blends the benefits of the Model of Manufactured Part (the MMP model) and the Jacobian-Torsor model is proposed. The former is based on the CAD nominal model, where deviations are described relative to the nominal part using small displacement torsor. The later starts with the kinematic dimension chains and expresses the relative position and orientation of the various components of the chosen kinematic chain by Jacobian matrices. The Jacobian-Torsor model uses interval arithmetic for expressing the possible variation of the functional elements and for calculating the extreme bounds of the functional requirements. In the following sections, the two aforementioned models will first be outlined before the new combined approach for tolerance analysis in machining is presented. This new approach uses the advantages of the MMP model to simulate the machining operation, taking into account positioning and machining defects. Furthermore it takes advantages of the interval-based formulation which has been used in the Jacobian Torsor model. The combined approach is finally applied on an example.Copyright

A method to generate lattice structure for Additive Manufacturing

Additive Manufacturing (AM), popularly called 3D Printing, is a scientific term indicating the Rapid Prototyping (RP) technologies developed in 1980s. AM technologies can directly fabricate a complex 3D object from three-dimensional Computer Aided Design (3D CAD) model by adding layer-by-layer of material. Advances in AM technologies are capable of manufacturing highly complicated geometries of product without the need for process planning, the reduction of product development time and cost, the removal of tooling compared to conventional manufacturing technologies. The production of lattice structures is quickly performed by AM technologies in order to attain a product with lightweight and stronger and to provide the high specific mechanical properties such as strength and energy absorption. However, the current product modelling technologies have many difficulties for generation of lattice structure model. Thus, the paper proposes a new approach that allows to create different configuration types of conformal and non-conformal lattice structure model.

Integration of Multiphysical Phenomena in Robust Design Methodology

Due to the development of science and technology the requirements of customers and users for a product are more and more tight and higher. The satisfaction of these, such as quality, reliability, robustness and cost of the product plays an important role in the context of global and concurrent economy. However, there are many variation sources during the product life cycle such as material defects, manufacturing imperfection, different use conditions of the product, etc. It can make the designed product not to meet fully the requirements of the users. Thus, we propose, in this chapter, several analysis methods based on data mining tools in order to analyze the result of performance simulation of the product taking into account the geometrical deviations generated during its life cycle. These methods allow classifying and identifying factors that influence on performance of the designed product. With these methods, the product designers can analyze the “real” performance under geometrical variation sources generated in the practical environment. Moreover, the proposed methods can be used to transfer back the result of the “real” performance analysis of the product to the manufacturer and product designer in order to obtain a robust product.