Investigation of the Oven Process in Indirect Metal Laser Sintering

This paper deals with the optimization of Indirect Metal Laser Sintering. Different experimental analyses have proven that the oven process is highly responsible for the part distortion. By means of polished micrograph sections and thermogravimetric and dilatometric investigations, the oven process has been divided into four main steps: polymer removal, solid-state sintering, infiltration and liquid-phase sintering. Further experiments were carried out at higher temperature phases of the oven process, using modified process parameters. The aim of this research is to improve the knowledge about the oven process. In another step, this process will be simulated by means of finite element analysis in order to minimize the part distortion.Mechanical Engineerin

Simulation of the Process Step Polymer Removal in Indirect Metal Laser Sintering

With the Indirect Metal Laser Sintering and by means of a heat treatment in an oven process metal components can be produced. In the first step the polymer is transformed from the solid state into the gas phase. This takes place all over the component at different velocities depending on the local temperatures and temperature gradients. The creation of the gas phase develops a pressure inside of the component because the diffusion of the polymer within the part has a finite velocity. The pressure may contribute to a damage of the component. This essay deals with the procedure to simulate the gas pressure on the basis of the implementation of kinetic models in the Finite-Element-Analysis.Mechanical Engineerin

Layer Formations in Electron Beam Sintering

Among direct metal processing manufacturing technologies (Rapid Manufacturing), Electron Beam Sintering (EBS) exhibits a high application potential. Especially, the fast beam deflection provided by electromagnetic lenses allows the realization of considerable building speeds and minor residual stresses. Therefore, this paper aims to examine and utilize the given potential for additive layer manufacturing. In this context, the deployed scanning strategy is a very important aspect. By means of an increasing computer power, innovative and flexible patterns for the solidification of the powder can be implemented. Thus, different patterns are being examined and evaluated. Finally, occurring effects in the exposed zone are introduced.Mechanical Engineerin

Transient Physical Effects in Electron Beam Sintering

The extensive use of the electron beam in manufacturing processes like welding or perforating revealed the high potentials for also using it for solid freeform fabrication. First approaches like feeding wire into a melt pool have successfully shown the technical feasibility. Among other features, the electron beam exhibits high scanning speed, high power output, and beam density. While in laser-based machines the fabrication is working in a stable way, transient physical effects in the electron beam process can be observed, which still restrict process stability. For instance, a high power input of the electron beam can result in sudden scattering of the metal powder. The authors have developed an electron beam freeform fabrication system and examined the above mentioned effects. Thus, the paper provides methods in order to identify, isolate and avoid these effects, and to finally realize a reproducible process.Mechanical Engineerin

Process Chain for Numerical Simulation of IMLS

Additive layer manufacturing methods imply, among other advantages, extensive flexibility concerning their ability to realize mass customization. Despite various efforts towards process enhancement, numerous deficiencies concerning part distortion or residual stresses are still observable. The present work deals with the definition of an efficient process chain for numerical simulation of indirect metal laser sintering (IMLS), in order to improve dimensional accuracy. The underlying method is based on investigations of dilatometric behavior of iron based powder, which is integrated into reaction kinetic models and coupled with a finite element analysis (FEA). Thus, singular process steps, e. g. solid phase sintering, phase transformations or infiltration, are numerically modelled with adequate accuracy. Referring to thermomechanical simulation, possibilities for pre-scaling of part geometries are presented.Mechanical Engineerin

A Method for the Prediction of Process Parameters for Minimal Distortion in Welded Frame Structures Using a FE-simulation

AbstractWelded frame structures are often subject to unintended distortions due to the thermal joining process. In order to precisely quantify and reduce the distortion of welded frame structures using Finite Element (FE) simulation, a fast and reliable method is required, especially for industrial applications. This paper presents a methodical, simulation based and time optimised framework for the prediction of appropriate process parameters for minimal component distortion of complex welded frame structures by means of e.g. a variation of the process parameters or the weld seam sequences. To achieve a minimal distortion of the final structure, different optimisation algorithms will be used in combination with a database

Verification of structural simulation results of metal-based additive manufacturing by means of neutron diffraction

AbstractMetal-based additive processes are characterized by numerous transient physical effects, which exhibit an adverse influence on the production result. Hence, various research approaches for the optimization of e. g. the structural part behavior exist for layered manufacturing. Increasingly, these approaches are based on the finite element analysis to be able to understand the complexity. Hereby it should be considered that the significance of the calculation results depends on the quality of modeling the process in the simulation environment. Based on a selected specimen, the current work demonstrates in which way the numerical accuracy of the residual stress state can be analyzed by utilizing the neutron diffraction. Thereby, different process parameter settings were examined

Design of a five-axis ultra-precision micro-milling machine—UltraMill. Part 2: Integrated dynamic modelling, design optimisation and analysis

Using computer models to predict the dynamic performance of ultra-precision machine tools can help manufacturers to substantially reduce the lead time and cost of developing new machines. However, the use of electronic drives on such machines is becoming widespread, the machine dynamic performance depending not only on the mechanical structure and components but also on the control system and electronic drives. Bench-top ultra-precision machine tools are highly desirable for the micro-manufacturing of high-accuracy micro-mechanical components. However, the development is still at the nascent stage and hence lacks standardised guidelines. Part 2 of this two-part paper proposes an integrated approach, which permits analysis and optimisation of the entire machine dynamic performance at the early design stage. Based on the proposed approach, the modelling and simulation process of a novel five-axis bench-top ultra-precision micro-milling machine tool—UltraMill—is presented. The modelling and simulation cover the dynamics of the machine structure, the moving components, the control system and the machining process and are used to predict the entire machine performance of two typical configurations

Towards Additively Manufactured Metamaterials with Powder Inclusions for Controllable Dissipation: The Critical Influence of Packing Density

Particle dampers represent a simple yet effective means to reduce unwanted oscillations when attached to structural components. Powder bed fusion additive manufacturing of metals allows to integrate particle inclusions of arbitrary shape, size and spatial distribution directly into bulk material, giving rise to novel metamaterials with controllable dissipation without the need for additional external damping devices. At present, however, it is not well understood how the degree of dissipation is influenced by the properties of the enclosed powder packing. In the present work, a two-way coupled discrete element - finite element model is proposed allowing for the first time to consistently describe the interaction between oscillating deformable structures and enclosed powder packings. As fundamental test case, the free oscillations of a hollow cantilever beam filled with various powder packings differing in packing density, particle size, and surface properties are considered to systematically study these factors of influence. Critically, it is found that the damping characteristics strongly depend on the packing density of the enclosed powder and that an optimal packing density exists at which the dissipation is maximized. Moreover, it is found that the influence of (absolute) particle size on dissipation is rather small. First-order analytical models for different deformation modes of such powder cavities are derived to shed light on this observation

Tool path pattern and feed direction selection in robotic milling for increased chatter-free material removal rate

Robotic milling becomes increasingly relevant to large-scale part manufacturing industries thanks to its cost-effective and portable manufacturing concept compared to large-scale CNC machine tools. Integration of milling processes with industrial robots is proposed to be well aligned with the aims and objective of the recent fourth industrial revolution. However, the industrial robots introduce position-dependent and asymmetrical dynamic flexibility, which may reflect to the tool tip dynamics under several conditions. Under such circumstances, the stability limits become dependent on the machining location and the feed direction. In this respect, selection of machining tool path patterns is crucial for increased chatter-free material removal rates (MRR). This paper proposes an approach to evaluate and select tool path patterns, offered by the existing CAM packages, for increased chatter-free MRR. The machining area is divided into number of machining locations. The optimal feed direction is decided based on the absolute stability at each region considering the asymmetrical and position-dependent tool tip dynamics. Then, the alternative tool path patterns are evaluated and the corresponding optimum feed direction is decided for increased chatter-free material removal. The application of the proposed approach is demonstrated through simulations and representative experiments