Directed Energy Deposition (LiM 2021)

Development of laser-arc hybrid process for additive manufacturing of aluminum alloy and copper alloy
Dehua Liu, Shengnan Wu, Guangyi Ma, Fangyong Niu, Dongjiang Wu

Laser-arc hybrid process was recently suggested as a feasible method for additive manufacturing the metal structure with high properties and low defects. To promote an understanding of the effect of laser on manufacturing process, this paper is performed to prepare the Al-Zn-Mg-Cu alloy and Cu-Cr-Zr alloy using the laser and tungsten inert gas (TIG) arc hybrid heat source. The microstructure evolution of Al-Zn-Mg-Cu alloy and Cu-Cr-Zr alloy under laser-arc process are analyzed. Moreover, the elongation of the Cu-Cr-Zr alloy deposited sample can reach more than 40%. Laser-arc hybrid process provides a new idea for additive manufacturing alloys which are difficult to manufacture (high reflectivity, high thermal conductivity, et al.), and expand the application of laser additive manufacturing.

Keywords: Laser-arc hybrid; Additive manufacturing; High strength aluminum alloy; Copper alloy


Influence analysis of the layer orientation on mechanical and metallurgic characteristics of DED manufactured parts
Florian M. Dambietza,b,*, Tobias S. Hartwicha, Julian Scholl-Corrêab, Peter Hoffmann, Dieter Krause

With an increasing trend in product individualization, manufacturing custom-designed solutions and focusing on the
explicit industry’s needs are crucial to the manufacturer’s success. Especially within high-tech industries such as aerospace
industry, high-strength, large-sized but still lightweight metal parts are required. Although the Direct-Energy-Deposition
(DED)-technology offers a proven outset point for targeting this issue, there are few material-, metallurgic-, process-, and
geometry specific data available to support the initial design process of such parts. This contribution presents a profound
study of different steel- and aluminium materials with respect to their metallurgic and mechanical characteristics. Using a
state-of-the art DED-Laser system, tensile test specimens have been manufactured with alternative layer orientations.
These specimens are analyzed with regard to the required milling oversize, heat-induced stress deformation, metallurgic
characteristics and their tensile characteristics. As a result of this investigation, a suitable baseline for the future
generation of a DED design-by-feature catalogue is given.

Keywords: DED; Additive manufacturing; metallurgy; tensile characteristics; layer orientation


In-situ clad geometry measurement in wire laser metal deposition process
Iker Garmendia, Jon Flores, Carlos Soriano, Mikel Madarieta

Wire Laser Metal Deposition (w-LMD) is a promising technique that could generate significant cost reductions. However, process control still needs to be developed to ensure product quality. Due to the high temperature of the melt pool and the resulting light radiation, current commercial equipment can only measure the geometry of the clad after the process or between the deposition of different layers. They also require a stop in the process which affects the heating and cooling cycles of the part and the total manufacturing time. In this work, a measurement system based on a side mounted vision camera and laser light projection is developed, which allows an in-situ measurement of the clad geometry data. This enables to know the nozzle-to-part distance, the surface condition where the successive layers are deposited and the relation between bead characteristics and the quality of the deposition.

Keywords: LMD; coaxial; wire; control; monitoring


A measuring system based on chromatic confocal displacement sensor integrated with laser head for monitoring of laser metal deposition process
Piotr Koruba, Adrian Zakrzewski, Piotr Jurewicz, Michał Ćwikła, Jacek Reiner

The measurement of geometrical properties of a sample during laser material processing is still an open research issue. Thus, the knowledge about the laser focus in relation to sample before, during and after the process is considered as one of the most crucial parameters. In this study, we indicate that the chromatic confocal displacement sensor integrated with laser head can serve as an alternative for current solutions used in monitoring of laser metal deposition process. Therefore, the design procedures of measuring system is described, consisting in numerical modelling, selection of system components. Moreover, in order to determine the functionality parameters of the system it was experimentally characterized in two regimes i.e. off-line and on-line (with and without presence of laser beam, respectively). Additionally, the various methods for spectral data processing were presented. Finally, the preliminary measurement results obtained with the measuring system during laser metal deposition were presented and discussed.

Keywords: laser metal deposition, chromatic abberation, optical system design,


Investigation on laser cladding of rail steel without preheating
Christian Brunner-Schwer, Max Biegler, Michael Rethmeier

The contact between train wheels and rail tracks is known to induce material degradation in the form of wear, and rolling contact fatigue in the railhead. Rails with a pearlitic microstructure have proven to provide the best wear resistance under severe wheel-rail interaction in heavy haul applications. High speed laser cladding, a state-of-the-art surface engineering technique, is a promising solution to repair damaged railheads. However, without appropriate preheating or processing strategies, the utilized steel grades lead to martensite formation and cracking during deposition welding.
In this study, laser cladding of low-alloy steel at very high speeds was investigated, without preheating the railheads. Process speeds of up to 27 m/min and laser power of 2 kW are used. The clad, heat affected zone and base material are examined for cracks and martensite formation by hardness tests and metallographic inspections. A methodology for process optimization is presented and the specimens are characterized for suitability. Within the resulting narrow HAZ, the hardness could be significantly reduced.

Keywords: High speed laser cladding; rail tracks; pearlitic microstructure; preheating


Process development for laser hot-wire deposition welding with high-carbon cladding Material AISI52100
Laura Budde, Marius Lammers, Jörg Hermsdorf, Stefan Kaierle, Ludger Overmeyer

An increase in wear resistance and thus an increase in service life is of great importance for many components. The production of hybrid components with high-carbon steel as cladding material offers the possibility of achieving these goals. However, materials with a carbon equivalent of more than 0.65 are considered difficult to weld due to their tendency to crack. In this study, a laser hot-wire deposition welding process with bearing steel AISI 52100 as cladding material is used to investigate the influence of laser power, wire feed speed, scanning speed, overlap ratio and wire preheating as well as interactions of these parameters on process stability, the formation of cracks and pores, the cladding waviness and the dilution. Layers of eight adjacent weld seams are welded onto an austenitic stainless steel. A stable process is observed for most parameter combinations except for samples with low wire feed speed and major wire preheating.

Keywords: LMD-W; Cladding; high-carbon steel


Evaluation of steady state via thermography during laser-directed energy deposition with wire
Anton Odermatt and Nikolai Kashaev

Additive manufacturing of structures in a single continuous deposition process is appealing because defects at the start- and end-points of a track can be avoided. For the evaluation of process stability, a steady state process needs to be reached. A methodology for the determination of the interpass temperature for processes using a positioner for movement of the work piece has been developed. This methodology was applied to a laser- and wire-based directed energy deposition process. The approach of the steady state process can be described by an exponential growth law. From the interpass temperature, a cooling rate can be calculated. The evolution of the interpass temperature can be used for process control and the cooling rate can be related to material properties. A comparison with results from the literature shows that the convergence rate is mainly dependent on the power level of the energy source and the size of the structure.

Keywords: thermography; steady state; process control; interpass temperature; cooling rate


Analysis and recycling of bronze grinding waste to produce maritime components using directed energy deposition
Vinzenz Müller, Angelina Marko, Tobias Kruse, Max Biegler, Michael Rethmeier

Additive manufacturing promises a high potential for the maritime sector. Directed Energy Deposition (DED) in particular offers the opportunity to produce large-volume maritime components like propeller hubs or blades without the need of a costly casting process. The post processing of such components usually generates a large amount of aluminum bronze grinding waste. The aim of the presented project is to develop a sustainable circular AM process chain for maritime components by recycling aluminum bronze grinding waste to be used as raw material to manufacture ship propellers with a laser-powder DED process. In the present paper, grinding waste is investigated using a dynamic image analysis system and compared to commercial DED powder. To be able to compare the material quality and to verify DED process parameters, semi-academic sample geometries are manufactured.

Keywords: Additive Manufacturing; Directed Energy Deposition; Recycling; Powder Analysis; Maritime Components


Laser directed energy deposition produces improved cp Ti for dental prosthetic applications
O. Barro, F. Arias-González, F. Lusquiños, R. Comesaña, J. del Val, A. Riveiro, A. Badaoui, F. Gómez-Baño, J. Pou

Titanium and titanium alloys are widely employed in biomedical applications by virtue of their remarkable corrosion resistance, biocompatibility, exceptional specific strength and relatively low elastic modulus. Commercially pure titanium (cp-Ti) is a designation for titanium with a reduced content of alloying elements. This group of alloys are characterized for having a great resistance to corrosion in comparison with other titanium alloys. Additionally, cp-Ti also presents reduced cytotoxicity. Laser directed energy deposition (LDED) is an additive manufacturing method able to produce metallic materials of great quality. By controlling the cooling rates, the material microstructure can be tuned in order to improve its mechanical/chemical properties. In the present work, LDED using a high power diode laser as energy source, was used to produce cp-Ti parts of grade 4. The cp-Ti obtained by LDED showed a higher mechanical performance than the commercial counterpart: 7% increment of ultimate tensile strength, 12.9% increment of elongation after fracture and 30% increment of toughness. These results can be attributed to a specific microstructure modification inherent to the LDED process.

Keywords: Additive manufacturing, Laser Directed Energy Deposition, titanium, commercially pure titanium


Processing of low-alloyed case-hardening steel Bainidur AM by means of DED-LB/M
Dominic Bartels, Oliver Hentschel, Jonas Dauer, Wolfgang Burgmayr, Michael Schmidt

Low-alloyed steels are typically exposed to additional case-hardening post-processing to improve the mechanical properties in the case area of the material for increased hardness and wear resistance. Another possibility for improving these material properties is provided by in-situ alloying using laser-based directed energy deposition of metals (DED-LB/M). However, this requires basic understanding of the mechanisms when processing the base material. Within this work, different processing parameters for defect-free fabrication of the low-alloyed case-hardening steel Bainidur AM are presented. This includes the correlation of geometrical properties and internal defects like pores or cracks with the applied process parameters. Additional hardness measurements are performed for analyzing the influence of different processing strategies. It is found that a hardness gradient is formed and that the material hardness is depending on the process parameters used. Furthermore, the obtained material hardness is similar to the hardness values of conventionally bainitized samples obtained from literature.

Keywords: Additive manufacturing; DED-LB/M; Laser metal deposition; Case-hardening steel; Bainidur AM


Optical monitoring sensor system for laser-based directed energy deposition
Bohdan Vykhtar, Alexander Marek Richter

To achieve homogeneous material properties and thus high-quality components, a constant melt pool geometry and temperature are essential during the laser-based directed energy deposition processes. Especially at high deposition rates, process instabilities can appear, which lead to deviations in melt pool properties consequently resulting in the discrepancy in the target/actual comparison and, in the worst case, in the disposal of the component. To monitor the continuity of the melt pool properties, this paper presents an optical monitoring sensor system, which is capable of monitoring the process by guiding, filtering, and analyzing the optical signals of the melt pool. The presented sensor system is mounted on-axis to accomplish image acquisition and monitor the melt pool emissions but is also off-axis integrable in hybrid and wire-arc-based processes. The system is demonstrated for melt pool monitoring while processing stainless steel and an outlook is given on using that information to control the whole process.

Keywords: Real-Time Sensor, Additive Manufacturing, Monitoring; Robotics


Acoustic emissions of laser metal deposited NiTi structures
Julian Ulrich Weber, Alexander Bauch, Johannes Jahnke, Claus Emmelmann

near net-shape parts. Precise material deposition increases material efficiency and prevents the excessive use of costly materials. In a fully automated manufacturing process with minimized scrap production, these benefits are enabled by material specific process monitoring and parameter development.
Acoustic emissions were monitored for the LMD process of the costly shape memory alloy. Acoustic emission monitoring values were defined and evaluated regarding of NiTi structural defect formation. For the evaluation of defect formation, the degree of delamination for each specimen has been identified. Concurrent measurement of the oxygen content in the process chamber was carried out to correlate defects to the process atmosphere.
Distinct defect frequencies were detected for NiTi structures indicating delamination and cracks. The acquired data was used to design an LMD process control concept based on acoustic emission monitoring.

Keywords: Laser Metal Deposition; Acoustic Emissions; Nickel-Titanium; Nitinol; Defect monitoring


Structure-borne acoustic process monitoring of laser metal deposition
Irene Buchbender, Christian Hoff, Jörg Hermsdorfa Volker Wesling, Stefan Kaierle

Acoustic emissions have been used as a means for process monitoring and non-destructive testing in welding to determine process characteristics, detect anomalies and infer the quality of the welded part. While air-borne noise has been studied extensively, research on the application of body-borne sound in the process monitoring of laser metal deposition remains limited. This paper examines the use of structure-borne sound for in-process monitoring of the deposition of the nickel-based superalloy CMSX-4. Due to the low weldability of the material and its susceptibility to hot-cracking, there arises a need for an in-process, non-destructive method for monitoring cracking. A high-frequency-impulse-measuring device (QASS GmbH) up to 50 MHz was attached to the substrate mount. The frequency data of the signal over time was evaluated by analysing the short-time Fourier transform (STFT) of the raw acoustic data, the acoustic characteristics of the process were determined, acceptable thresholds set and cracking detected.

Keywords: Laser welding; process monitoring


Height variation in scanned hot-wire laser surfacing processes
Alexander Barroi, Kai Biester, Laura Budde, Marius Lammers, Jörg Hermsdorf, Ludger Overmeyer

The use of hot wire in laser cladding can raise the energy efficiency and the deposition rate of the process drastically. This study shows that when using hot wire, the process faces stronger restrictions to one of the process parameters, the wire nozzle height. A change of three millimeters in wire nozzle height can double the dilution. This is because of the impact of stick out length on the wire heating. But not only the heating has an effect when changing the height, it also changes the wire positioning, a parameter which is sensible for the process stability.

Keywords: height variation; hot-wire; laser cladding; heating power; process stability


Studies on the direction-independent temperature measurement of a coaxial laser metal deposition process with wire
Avelino Zapata, Christian Bernauer, Melanie Hell, Michael F. Zaeh

Among the Directed Energy Deposition (DED) processes, Laser Metal Deposition with wire (LMD-w) combines the ad-vantages of a high precision and a high deposition rate. Recently, optical systems have been developed that form a ring-shaped laser spot, facilitating a direction-independent LMD-w process. When a pyrometer is coupled to such an optical system, the measurement spot features a ring-shaped form corresponding to the laser spot. Using this pyrometer setup, the inline temperature signal during the LMD-w process was studied within this work. The two modalities of a one-color and a two-color measurement were compared regarding their reliability. The measurement setup was varied to study the influence of different process conditions on the signal. Based on this, a configuration was identified that allowed a valid measurement. A reliable inline temperature measurement opens the opportunity to monitor and control the process.

Keywords: Laser Metal Deposition; DED; Additive Manufacturing; temperature monitoring; one-color pyrometry; two-color pyrometry


Rotary straightening of fine wire for LMD-W applications
S. Pamin, M. Grafe, M. Lammers, J. Hermsdorf, S. Kaierle, and L. Overmeyer

In wire-based high-precision laser applications as micro welding or micro laser metal deposition the straightness of the wire used plays an essential role. Small process windows require constant input conditions and thus straight wire without deformations. Uncoiled commercial wire exhibits a spatial, often helix-like curvature as a result of previous recoil processes on comparatively small reels. With the rotary straightener developed in this work, stainless steel wires with diameters of 75 μm and 100 μm, respectively, were straightened from average curvature levels of 22.56 m-1 down to 0.61 m-1 by alternating bending. This cold forming process causes crystallographic irregularities (dislocations) and residual stresses, which additionally lead to a rise in hardness and yield strength of the wire. For subsequent laser processes the changed material properties are advantageous, as they increase process robustness and enable a longer wire stick-out.

Keywords: micro welding; laser metal deposition; fine wire; rotary straightener; alternating bending


Automatic changing of weld deposit for additive manufacturing of hybrid metal-glass components using direct laser deposition
Marius Lammers, Kai Biester, Nick Schwarz, Jörg Hermsdorf, Stefan Kaierle, Henning Ahlers

Direct Laser Deposition is a manufacturing process, that enables Additive Manufacturing of nearly any fusible material ranging from metal to glass feedstock. For generating hybrid components out of steel and fused silica, system technology with coaxial beam guidance using different laser beam sources can be used to enable the direct manufacturing of optical, structural and thermal elements. To suit both processes, a wide velocity range regarding the weld material feed from 0.1 to 5 m/min is required. In this paper a prototype machine for material feeding and changing is presented, that is capable of processing both metal wire and glass fiber. In order to determine process-critical parameters, preliminary tests are carried out to determine the requirements for the system. The paper also shows how the prototype system performs in terms of changing and feeding the wires as well as fibers with a focus on wear and changing cycles.

Keywords: laser glass deposition; laser metal deposition; weld material feed; metal-glass hybrid components; automatic material changing; wire; fiber


Effect of atmosphere conditions on additive manufacturing of Ti4Al6V by coaxial W-DED-LB process
Eva Vaamonde, Pilar Rey, Rosa M Arias, Iago Troncoso

Additive Manufacturing is being a strategic tool for industrial applications even for large size structural parts where high deposition rates, as achieved by Directed Energy Deposition (DED) techniques based on wire deposition, are required. However, manufacturing of large components on reactive materials as titanium alloys requires specific atmosphere conditions to reach the specified properties on the deposited material. In this paper coaxial laser wire deposition (W-DED-LB) of titanium grade 5 alloy has been studied to achieve the highest deposition rate and process stability and the effect of protective conditions has been assessed. Three different configurations (local, inert chamber, local + inert chamber) were tested in order to bring a deep understanding of the influence of protective conditions on process stability, surface quality, metallurgy, hardness and oxygen content of deposited material.

Keywords: laser additive manufacturing; coaxial wire; titanium alloy; oxigen content