Norbert Pirch

Investigation on reducing distortion by preheating during manufacture of aluminum components using selective laser melting

The additive manufacturing process selective laser melting (SLM) can be used to directly produce functional components made out of metal. During the construction process, however, thermally induced residual stress occurs due to the layered build-up and the local input of energy by means of a focused laser beam, which can lead to distortion of the component or sections of the component itself. Normally, distortion is prevented due to supporting structures between the component and the substrate plate. It is not always possible, however, to provide all the areas of a component with supporting structures or to remove them later, depending on how complex the geometry or how accessible the structures are. When the substrate plate is heated during the construction process, the distortion can be reduced or eliminated entirely. Nonetheless, a systematic investigation of the extent to which preheating influences distortion of aluminum components has not yet been conducted. This works aims at systematically investigating the effects of preheating during SLM of aluminum components and determining an appropriate preheating temperature at which distortion practically no longer occurs. A significant reduction in distortion compared to the distortion without preheating can be seen beginning at a preheating temperature of 150 °C. At a preheating temperature of 250 °C, distortion can no longer be detected within the scope of the measuring accuracy independent of the twin cantilever test geometry investigated. In addition to reducing distortion, the preheating avoids the stress-related cracks in the component, which can lead to tearing of the parts of the test geometry. With 90 HV 0.1 at a preheating temperature of 250 °C, the hardness is greater than the required minimum hardness according to DIN EN 1706 of die-cast parts from the material AlSi10Mg. From these results, it can be concluded that a preheating temperature of 250 °C is suitable for reliably manufacturing components made out of the material AlSi10Mg using SLM free of defects and for preventing distortion completely.

Study of process window development for high deposition-rate laser material deposition by using mixed processing parameters

For several years, the interest in additive manufacturing is continuously expanding, owing to the paradigm shift that new production processes, such as laser material deposition (LMD), provide over conventional manufacturing technologies. With LMD, three-dimensional, complex components out of a wide range of materials can be manufactured consecutively layer-by-layer. However, aiming for the production of large components with LMD, the currently achieved deposition-rates of approximately 0.5 kg/h remain a major concern in regards to processing time and economic feasibility. In this respect, an experimental setup for high-deposition rate LMD is built up in the current work. Furthermore, an approach for developing a process window for resource efficient, high-deposition rate LMD is investigated in this paper. For the production of sound layers with LMD, the processing parameters need to be considered in an appropriate relation. Thus, by setting the main processing parameters: powder mass flow, traversal spee...

Melt dynamics in surface processing with laser radiation: calculations and applications

The purpose of this paper is more to stimulate a discussion than to set out well proven and undisputed facts. A great many papers are being published on the subject of diffracting optics and these usually fall into one of two classes: those concerned with bulk or with surface relief components. In most cases the authors have experience with one or other technology and often tend to describe the benefits of their own advances without fully putting them into the context of what is offered by alternative technologies. When comparing different forms of diffracting component it is also necessary to compare them with the equivalent conventional ones and to compare all relevant aspects of performance and cost. This critique is intended to be as impartial as possible but it must be admitted that the authors main experience is with surface relief technology.

Mechanisms during laser bending

In order to investigate the thermomechanical phenomena during the laser bending process, a simulation is performed. The governing thermoelastic-plastic equations are integrated by the finite element method. The results are related to predictions as given by the so-called temperature gradient mechanism (TGM), which is often used in the context of laser bending. It turns out that approximative identical temperature time cycles result in a plane and a prebended sheet in completely different forming behavior, whereby the forming behavior for the bended sheet depends on which side is laser treated. This means that a quantification of the extension and homogeneity of laser generated temperature field is insufficient for the prediction of forming behavior. The TGM model does not take into account the influence of the different stiffness of a plane or bended sheet on the stress and strain history in the laser treated zone. For this reason the TGM model can’t predict the different forming behavior of the plane and...

Laser-based production of thin wear-protection films

Wear-protection coatings are widely applied in the automotive industry to improve tribo-mechanical properties of highly stressed engine components. Today these coatings are produced by physical vapor deposition (PVD) which is a very time consuming production-step. Wet-chemical processes based on nanoparticulate materials have a high potential to be an energy and resource efficient technique to produce functional coatings, as they are free from any need for expensive vacuum technology and any other elaborate equipment. The major challenge of the process under investigation in this paper is to adapt a laser-based thermal post treatment to turn the applied dried film into a densely-packed layer with the desired properties. Thus the in-line capable process that is introduced is a key step to obtain protection layers on various substrate-materials with low thermal stability. Short interaction times between laser beam and work piece offer the possibility to achieve the necessary high peak-temperatures in connection with short heat penetration depths.In order to select an appropriate coating material different materials provided by Merck KGaA, Darmstadt are characterized regarding their optical properties by fitting a physical model for the layer permittivity to measured transmittance and reflectance spectra in the wavelength range 250 – 2500 nm. A finite element method is used to simulate the induced temperature-time-profiles at the surface of a coated substrate. Based on the simulation laser treatment experiments are carried out to achieve densification of the films.Wear-protection coatings are widely applied in the automotive industry to improve tribo-mechanical properties of highly stressed engine components. Today these coatings are produced by physical vapor deposition (PVD) which is a very time consuming production-step. Wet-chemical processes based on nanoparticulate materials have a high potential to be an energy and resource efficient technique to produce functional coatings, as they are free from any need for expensive vacuum technology and any other elaborate equipment. The major challenge of the process under investigation in this paper is to adapt a laser-based thermal post treatment to turn the applied dried film into a densely-packed layer with the desired properties. Thus the in-line capable process that is introduced is a key step to obtain protection layers on various substrate-materials with low thermal stability. Short interaction times between laser beam and work piece offer the possibility to achieve the necessary high peak-temperatures in connec...

Analysis of track formation during laser metal deposition

A fundamental understanding of the physical phenomena associated with the coaxial laser metal deposition (LMD) process is essential to enhance the science base and thereby improve the process itself. The interaction between the laser beam and the powder particles leads to an attenuation of the beam intensity and to a temperature rise of the powder particles before reaching the melt pool. To understand this mutual influence and their influence on the process result better, the powder gas stream was analyzed with an image-based particle density measurement system. This system illuminates the powder gas stream from the side with a line laser light source and monitors the particles plane by plane with a coaxially aligned camera through the powder nozzle. A high image rate allows to record the number and position of individual powder particles. The particle density distributions in the planes are determined by averaging over the images. With this, a statistical model can be derived with regard to the particles...

Temperature field and residual stress distribution for laser metal deposition

Laser metal deposition (LMD) process has been widely used in many industrial applications such as automotive, defense, aerospace, and so on. Modeling has to address physical phenomena like laser-powder interaction, heat transfer, fusion, solidification, and track formation. LMD induces a complex thermal stress field that results in residual stress distributions. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stresses can cause unpredicted in-service failures. Therefore, the prediction of its distribution in the deposited structure as a function of the process strategy is essential to improve the process and the part quality. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The authors developed a three-dimensional time-dependent finite element model for LMD with coaxial powder feeding supply. The model encompasses the powder stream, its interaction with the laser radiation, and the melt pool computation. The model was validated by a comparison of the experimental and computed shapes of the melt pool surfaces concerning cross section, longitudinal section and high-speed photographs [Pirch et al., in Proceedings of the ICALEO Conference, 16–20 October 2016]. In this paper, the model was applied to overlapping tracks for single and multilayer processing for different process strategies. The simulation allows us to analyze the time- and space-resolved evolution of temperature and stresses. The influence of the powder feed rate on the residual stresses is investigated.Laser metal deposition (LMD) process has been widely used in many industrial applications such as automotive, defense, aerospace, and so on. Modeling has to address physical phenomena like laser-powder interaction, heat transfer, fusion, solidification, and track formation. LMD induces a complex thermal stress field that results in residual stress distributions. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stresses can cause unpredicted in-service failures. Therefore, the prediction of its distribution in the deposited structure as a function of the process strategy is essential to improve the process and the part quality. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The authors developed a three-dimensional time-dependent finite element model for LMD with coaxial powder feeding supply. The model encompasses the powder stream, its interaction with the laser radiation, and the melt pool...

LMDCAM2: Software Tool for Near-Net Repair, Cladding and Built-Up by Laser Metal Deposition

Laser Metal Deposition (LMD) is growing in importance as a technique for the processing and manufacturing of parts in industry. LMD is used for a wide range of applications including the repair of worn parts, the built-up of 3D structures and the surface functionalization trough cladding. In many cases, the nominal CAD model from the design stage is no longer suitable for the representation of the part geometry due to distortion or defects especially in case of a worn part. This means for the generation of close contoured tool paths it is essential to create a digital model representing the surface of the actual part. This digitalization is often achieved by using a laser scanner whose raw output is represented by point cloud. Tool path planning software (CAM) available on the market generally demonstrate substantial deficits in generating paths on scanned surface data, because these programs are usually optimized on NURBS based surfaces and in most cases were originally designed for subtractive manufacturing applications. LMDCAM2 represents a new software tool especially designed for the LMD process. It is optimized for working with 3D scanned, triangulated data based models which could include noisy data and offers fundamental features for creating and manipulating tool paths adapted to the LMD process. Besides algorithms for calculating close contoured equidistant tracks, the software is also able obtain tracks for additive production through advanced slicing techniques of a 3D model.Copyright

Laser-based manufacturing of metallic conducting paths

Large-scale OLEDs, solar cells or heated windows have in common that they all are in need of conducting paths for collecting or distributing electricity on poorly or non-conducting surfaces.But common techniques for the production of conducting paths in OLED devices are time- and energy-consuming and therefore expensive since they include high vacuum sputtering and photolithographic processes: More than 90% of the carefully applied metal coating has to be removed in an etching process leaving used etchants for recycling. Common solar cells’ conducting paths are made by screen-printing a silver paste onto the surface and then treating the applied structure in an energy-consuming furnace process.The Fraunhofer ILT – in cooperation with Philips Lighting – developed a laser-based process to ‘write’ metallic conducting paths of widths down to 35 µm onto ITO-coated glass with speeds of up to 2.5 m/s in ambient atmosphere. The conducting paths consist of aluminum, copper, silver or a similar material and show specific resistances of about 0.0473·10−4 Ohm·cm and sheet resistances of about 0.04 Ohms per square which is sufficient for OLED applications. A multiple coating can even reduce resistances further.Large-scale OLEDs, solar cells or heated windows have in common that they all are in need of conducting paths for collecting or distributing electricity on poorly or non-conducting surfaces.But common techniques for the production of conducting paths in OLED devices are time- and energy-consuming and therefore expensive since they include high vacuum sputtering and photolithographic processes: More than 90% of the carefully applied metal coating has to be removed in an etching process leaving used etchants for recycling. Common solar cells’ conducting paths are made by screen-printing a silver paste onto the surface and then treating the applied structure in an energy-consuming furnace process.The Fraunhofer ILT – in cooperation with Philips Lighting – developed a laser-based process to ‘write’ metallic conducting paths of widths down to 35 µm onto ITO-coated glass with speeds of up to 2.5 m/s in ambient atmosphere. The conducting paths consist of aluminum, copper, silver or a similar material and show sp...

The production of layers made of Inconel 738LC by cladding with Nd : YAG laser radiation

The laser cladding process was used in order to create crack and pore free layers and webs out of Inconel 738LC with Nd:YAG laser radiation. During the experiments the processing parameters were varied, and experiments were done partly on cooled and partly on not cooled specimens. Showing the dependence of pore and crack formation on the temperature distribution, these results are compared with those of simulation by means of heat conduction calculations. With these investigations a successful reconditioning of turbine blades and vanes should be reached.