Michaël Hinderdael

Hardware-in-the-loop control of additive manufacturing processes using temperature feedback

Laser-based additive manufacturing is a technology for the production of freeform metallic parts. In order to produce parts with high quality, it is important for the manufacturing processes to be controllable with a high degree of precision. Current additive manufacturing systems attempt to reach this goal by carefully tuning the operational parameters, often in combination with a feedback control system. These systems are based on low order, empirical models of the process, which may limit the performance that can be achieved. This paper introduces a control system based on a high order physical heat conduction model of the melt pool dynamics. The control system serves as a framework which can be applied to many laser material processes in which high precision is required such as laser cladding and selective laser melting. The controller is able to regulate the melt pool size by modulating the laser power using a number of surface temperature measurements as the feedback signal. A hardware-in-the-loop (...

Proof of Concept of Integrated Load Measurement in 3D Printed Structures

Currently, research on structural health monitoring systems is focused on direct integration of the system into a component or structure. The latter results in a so-called smart structure. One example of a smart structure is a component with integrated strain sensing for continuous load monitoring. Additive manufacturing, or 3D printing, now also enables such integration of functions inside components. As a proof-of-concept, the Fused Deposition Modeling (FDM) technique was used to integrate a strain sensing element inside polymer (ABS) tensile test samples. The strain sensing element consisted of a closed capillary filled with a fluid and connected to an externally mounted pressure sensor. The volumetric deformation of the integrated capillary resulted in pressure changes in the fluid. The obtained pressure measurements during tensile testing are reported in this paper and compared to state-of-the-art extensometer measurements. The sensitivity of the 3D printed pressure-based strain sensor is primarily a function of the compressibility of the capillary fluid. Air- and watertightness are of critical importance for the proper functioning of the 3D printed pressure-based strain sensor. Therefore, the best after-treatment procedure was selected on basis of a comparative analysis. The obtained pressure measurements are linear with respect to the extensometer readings, and the uncertainty on the strain measurement of a capillary filled with water (incompressible fluid) is ±3.1 µstrain, which is approximately three times less sensitive than conventional strain gauges (±1 µstrain), but 32 times more sensitive than the same sensor based on air (compressible fluid) (±101 µstrain).

Evaluation of Different Topologies of Integrated Capillaries in Effective Structural Health Monitoring System Produced by 3D Printing

Over the last years the structural health monitoring (SHM) systems investigations have been focused on providing structures with similar functionality as the biological nervous system. There are numerous studies that have investigated this. In those studies a large number of sensors collects an extensive amount of data. In this study we demonstrate a novel effective SHM (eSHM) system which can monitor a structure with one single pressure sensor. The eSHM system can detect cracks by means of a system of capillaries integrated in a structure. This structure with the integrated capillaries can be produced by 3D printing, also known as additive manufacturing (AM). The principle of the eSHM system is monitoring the pressure variations in a network of capillaries. The effectiveness of this system is linked with the greatest strength of AM, which is the capability to create complex geometrical structures. Before the implementation in real structures, it is of crucial importance to be sure that the capillaries do not negatively influence the fatigue behaviour of the structures and the crack initiation. For this, the main objective of this study is to investigate different locations for a straight capillary incorporated into a four-point bending test specimen. The investigated titanium specimens with the integrated eSHM system are produced by AM. The capillary is located in the longitudinal dimension of the test specimen on the tension area of a four-point bending setup. We evaluate three different distances of the capillary to the outer surface of the test specimens. Furthermore, the results are also obtained by finite element simulations. We can conclude that –for the considered structure– the presence of the capillary does not influence the fatigue life negatively. On the other hand, cracks nucleate in the capillary region. Our future work will focus on the improvement of the capillary’s robustness. Other parameters like roughness effect and residual stresses should be also taken into account. doi: 10.12783/SHM2015/22

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

Negative Pressure Waves Analysis for Crack Localization and Crack Size Estimation for 3D Printed SHM System

A new Structural Health Monitoring system was developed to allow a faster introduction of 3D printed components into safety critical applications. Additive manufacturing techniques are used to embed capillaries in a 3D printed structure that are then pressurized. Continuous monitoring of the capillary pressure allows the system to indicate the existence of a crack when the pressure deviates from the initial pressure level. A specifically developed experimental set-up enables the study of the impact of different parameters on the leak flow behavior and the occurring Negative Pressure Waves. Negative Pressure Waves are analyzed to demonstrate the crack localization and crack size estimation feasibility. It will first be theoretically proven that the size and location of the crack can be derived from the Negative Pressure Waves. Secondly, measurements will validate the crack localization and size estimation feasibility of the new Structural Health Monitoring system.Copyright