Special Issue "Hybrid Additive Manufacturing and Machining Machine-Tools and Processes"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: 31 May 2020.

Special Issue Editors

Prof. Aitzol Lamíkiz
E-Mail Website
Guest Editor
University of the Basque Country, Spain
Interests: laser material processing; metal additive manufacturing; laser material deposition; laser process simulation
Prof. Eneko Ukar
E-Mail
Co-Guest Editor
Dpt. Of Mechanical Engineering, University of the Basque Country (UPV/EHU), Spain
Interests: surface texturing; laser polishing; laser material deposition; selective laser melting; laser process simulation

Special Issue Information

Dear Colleagues,

Hybrid manufacturing systems are becoming an industrial solution for high-complexity part manufacturing. Now, it is possible to observe how main machine tools builders have developed different solutions of hybrid machines that incorporate additive manufacturing and machining processes. The combination of these two processes simultaneously incorporates a series of advantages, such as the possibility of manufacturing very complex parts by adding material and machining details, using the the same fixturing to mafacture the whole part, applying the same CAM system, combining additive manufacturing with high accuracy machining operations, etc.

Therefore, the objective of this Special Issue is the publication of first level research articles in the field of hybrid manufacturing processes, especially those that are applied in advanced materials for the industry. The following topics (not exhaustive) are within the scope of this Special Issue: Experimental research in additive manufacturing and/or machining of parts built by additive manufacturing, simulation of additive manufaturing and hybrid processes, machine solutions and mechatronics adaptations for hybrid systems, process comparison and energy saving using hybrid systems.

Prof. Aitzol Lamíkiz
Prof. Eneko Ukar
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Hybrid Machines
  • Laser Material Deposition
  • Additive Manufacturing + Machining
  • Simulation of Additive Manufacturing
  • Powder Bed Fusion Processes

Published Papers (12 papers)

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Research

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Open AccessArticle
Analysis of the Machining Process of Titanium Ti6Al-4V Parts Manufactured by Wire Arc Additive Manufacturing (WAAM)
Materials 2020, 13(3), 766; https://doi.org/10.3390/ma13030766 - 07 Feb 2020
Abstract
In the current days, the new range of machine tools allows the production of titanium alloy parts for the aeronautical sector through additive technologies. The quality of the materials produced is being studied extensively by the research community. This new manufacturing paradigm also [...] Read more.
In the current days, the new range of machine tools allows the production of titanium alloy parts for the aeronautical sector through additive technologies. The quality of the materials produced is being studied extensively by the research community. This new manufacturing paradigm also opens important challenges such as the definition and analysis of the optimal strategies for finishing-oriented machining in this type of part. Researchers in both materials and manufacturing processes are making numerous advances in this field. This article discusses the analysis of the production and subsequent machining in the quality of TI6Al4V produced by Wire Arc Additive Manufacturing (WAAM), more specifically Plasma Arc Welding (PAW). The promising results observed make it a viable alternative to traditional manufacturing methods. Full article
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Open AccessArticle
Areal Surface Roughness Optimization of Maraging Steel Parts Produced by Hybrid Additive Manufacturing
Materials 2020, 13(2), 418; https://doi.org/10.3390/ma13020418 - 16 Jan 2020
Abstract
We report on an experimental study and statistical optimization of the surface roughness using design of experiments and the Taguchi method for parts made of 1.2709 maraging steel. We employ a hybrid additive manufacturing approach that combines additive manufacturing by selective laser melting [...] Read more.
We report on an experimental study and statistical optimization of the surface roughness using design of experiments and the Taguchi method for parts made of 1.2709 maraging steel. We employ a hybrid additive manufacturing approach that combines additive manufacturing by selective laser melting with subtractive manufacturing using milling in an automated process within a single machine. Input parameters such as laser power, scan speed, and hatching distance have been varied in order to improve surface quality of unmachined surfaces. Cutting speed, feed per tooth, and radial depth of cut have been varied to optimize surface roughness of the milled surfaces. The surfaces of the samples were characterized using 3D profilometry. Scan speed was determined as the most important parameter for non-machined surfaces; radial depth of cut was found to be the most significant parameter for milled surfaces. Areal surface roughness S a could be reduced by up to 40% for unmachined samples and by 23% for milled samples as compared to the prior state of the art. Full article
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Open AccessArticle
A Study on Optimal Machining Conditions and Energy Efficiency in Plasma Assisted Machining of Ti-6Al-4V
Materials 2019, 12(16), 2590; https://doi.org/10.3390/ma12162590 - 14 Aug 2019
Abstract
This research objective was to determine the significant parameters for effective plasma assisted machining (PAM) of Ti-6Al-4V and to derive optimal processing conditions. PAM parameters such as feed rate, spindle speed, and depth of cut have significant effects on its machining characteristic. In [...] Read more.
This research objective was to determine the significant parameters for effective plasma assisted machining (PAM) of Ti-6Al-4V and to derive optimal processing conditions. PAM parameters such as feed rate, spindle speed, and depth of cut have significant effects on its machining characteristic. In this study, the design of experiments (DOE) was used to select optimal machining conditions for PAM. The signal-to-noise (S/N) ratio was analyzed using the Taguchi method and the contributions of the factors were determined using analysis of variance (ANOVA). Finally, the optimal PAM machining conditions were selected using response optimization. In addition, the energy efficiency of conventional machining (CM) and the PAM were compared. The energy efficiency was analyzed by specific cutting energy. The cutting force and surface roughness of PAM decreased by 60.2% and 70.5%, respectively, in optimal PAM machining conditions. Full article
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Open AccessArticle
Material Characterization of AISI 316L Flexure Pivot Bearings Fabricated by Additive Manufacturing
Materials 2019, 12(15), 2426; https://doi.org/10.3390/ma12152426 - 30 Jul 2019
Abstract
Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent [...] Read more.
Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench. Full article
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Open AccessArticle
Analysis of the Machining Process of Inconel 718 Parts Manufactured by Laser Metal Deposition
Materials 2019, 12(13), 2159; https://doi.org/10.3390/ma12132159 - 05 Jul 2019
Cited by 1
Abstract
Laser metal deposition (LMD) is an additive manufacturing process that allows the manufacturing of near-net-shape products. This could mean significant savings in terms of materials and costs in the manufacturing of high-performance components for the aeronautical industry. In this work, an analysis of [...] Read more.
Laser metal deposition (LMD) is an additive manufacturing process that allows the manufacturing of near-net-shape products. This could mean significant savings in terms of materials and costs in the manufacturing of high-performance components for the aeronautical industry. In this work, an analysis of how the LMD processing of alloy 718 affects the final machining has been carried out. For this purpose, a comparative study has been done by means of the monitoring of the end milling process of a part manufactured by LMD and a rough-milled part from forged material. Differences between process outputs such as chip morphology and cutting forces were studied. Material characteristics such as microstructure, hardness and mechanical properties were also analyzed. Full article
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Open AccessArticle
A Hybrid Process Integrating Reverse Engineering, Pre-Repair Processing, Additive Manufacturing, and Material Testing for Component Remanufacturing
Materials 2019, 12(12), 1961; https://doi.org/10.3390/ma12121961 - 18 Jun 2019
Abstract
Metallic components can gain defects such as dents, cracks, wear, heat checks, deformation, etc., that need to be repaired before reinserting into service for extending the lifespan of these parts. In this study, a hybrid process was developed to integrate reverse engineering, pre-repair [...] Read more.
Metallic components can gain defects such as dents, cracks, wear, heat checks, deformation, etc., that need to be repaired before reinserting into service for extending the lifespan of these parts. In this study, a hybrid process was developed to integrate reverse engineering, pre-repair processing, additive manufacturing, and material testing for the purpose of part remanufacturing. Worn components with varied defects were scanned using a 3D scanner to recreate the three-dimensional models. Pre-repair processing methods which include pre-repair machining and heat-treatment were introduced. Strategies for pre-repair machining of defects including surface impact damage, surface superficial damage and cracking were presented. Pre-repair heat-treatment procedure for H13 tool steel which was widely used in die/mold application was introduced. Repair volume reconstruction methodology was developed to regain the missing geometry on worn parts. The repair volume provides a geometry that should be restored in the additive manufacturing process. A damaged component was repaired using the directed energy deposition process to rebuild the worn geometry. The repaired part was inspected in microstructure and mechanical aspects to evaluate the repair. The hybrid process solved key issues associated with repair, providing a solution for automated metallic component remanufacturing. Full article
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Open AccessArticle
A Study on the Dimension Accuracy on the Inner Structure of the 3D Printed Parts Caused by the Scanning Strategy
Materials 2019, 12(8), 1333; https://doi.org/10.3390/ma12081333 - 24 Apr 2019
Abstract
Selective laser melting (SLM) has been used in many fields recently, especially in the aerospace field. Many studies have been done on mechanical properties of the printed parts, but the dimension accuracy of the inner structure received little attention during these years. In [...] Read more.
Selective laser melting (SLM) has been used in many fields recently, especially in the aerospace field. Many studies have been done on mechanical properties of the printed parts, but the dimension accuracy of the inner structure received little attention during these years. In this work, the dimension accuracy of the inner structure was measured and compared using different scanning strategies. Compared with the measured data, a new scanning strategy was used and finds that the dimension accuracy was better than the previous one that used a two-scanning strategy. To explain this phenomenon, finite element analysis (FEA) was used to show the temperature distribution after a 0.1 s cooling using two different scanning strategies, which caused the dimensional deviation in printing. Full article
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Open AccessArticle
Microstructural Tuning of a Laser-Cladding Layer by Means of a Mix of Commercial Inconel 625 and AISI H13 Powders
Materials 2019, 12(3), 544; https://doi.org/10.3390/ma12030544 - 12 Feb 2019
Cited by 3
Abstract
The aim of this work is to evaluate the microstructural evolutions developed by mixing a corrosion-resistant and high-performance material with a high-hardness material in a coating obtained by laser-cladding technology. In this paper, five different mixtures of Inconel 625 alloy and AISI H13 [...] Read more.
The aim of this work is to evaluate the microstructural evolutions developed by mixing a corrosion-resistant and high-performance material with a high-hardness material in a coating obtained by laser-cladding technology. In this paper, five different mixtures of Inconel 625 alloy and AISI H13 steel powders have been deposited on a plate of 42CrMo4 steel using a 2.2 kW diode pumped Nd:YAG laser. The effect of adding tool steel to a Ni-based superalloy has been analyzed by the characterization of each cladded sample using optical microscopy and scanning electron microscopy (SEM). The precipitates observed in the samples have been analyzed by energy dispersive X-ray spectroscopy (EDS X-ray). SEM micrographs and EDS analysis indicate the existence of Laves phase. It has been observed that the presence of these precipitates is stabilized in a certain range of AISI H13 addition. Full article
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Open AccessArticle
Development of an Intra-Layer Adaptive Toolpath Generation Control Procedure in the Laser Metal Wire Deposition Process
Materials 2019, 12(3), 352; https://doi.org/10.3390/ma12030352 - 23 Jan 2019
Abstract
Recently developed concentric laser metal wire deposition (LMWD) heads allow metal addition processes which are independent of the deposition direction, thus enabling complex paths to be generated. The sensitivity of the process to height deviations has experimentally been observed to be greater with [...] Read more.
Recently developed concentric laser metal wire deposition (LMWD) heads allow metal addition processes which are independent of the deposition direction, thus enabling complex paths to be generated. The sensitivity of the process to height deviations has experimentally been observed to be greater with this type of head than with powder ones, therefore requiring more precise and local process control algorithms to be implemented. This work developed a methodology for measuring the part, layer by layer, using a 3D scanner based on structured laser light. Height corrections were applied to the mean and intra-layer height deviations by recalculating the deposition trajectories of the next layer to be deposited. Local height deviations were adjusted by varying the scanning speed, thus increasing the feed rate in the lower areas and decreasing it in the higher ones. Defects generated in the purpose, with height differences within the layer, were successfully corrected. A flat layer was re-established through the application of the control strategy. The internal integrity of the parts due to the scanning speed variation was analyzed, resulting in fully dense parts. The structured light measurement and height correction systems are found to be an affordable and time-efficient solution that can be integrated into an LMWD environment, thereby improving the process robustness. Full article
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Open AccessArticle
Analysis of Melt Pool Characteristics and Process Parameters Using a Coaxial Monitoring System during Directed Energy Deposition in Additive Manufacturing
Materials 2019, 12(2), 308; https://doi.org/10.3390/ma12020308 - 19 Jan 2019
Abstract
The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 [...] Read more.
The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 3D hybrid machine used in combination with a CCD-based coaxial temperature measurement system was utilized in this work to investigate what information relating to the intensity distribution of melt pool surfaces could be appropriate to draw conclusions about process conditions. In this study it is shown how the minimal required specific energy for a stable process can be determined, and it is indicated that the evolution of a plasma plume depends on thermal energy within the base material. An estimated melt pool area—calculated by the number of pixels (NOP) with intensities larger than a fixed, predefined threshold—builds the main measure in analysing images from the process camera. The melt pool area and its temporal variance can also serve as an indicator for an increased working distance. Full article
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Review

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Open AccessReview
Laser Cutting: A Review on the Influence of Assist Gas
Materials 2019, 12(1), 157; https://doi.org/10.3390/ma12010157 - 06 Jan 2019
Cited by 1
Abstract
Assist gas plays a central role in laser fusion cutting. In this work, the aerodynamic interactions between the assist gas and the workpiece are reviewed. An insight into those phenomena that hinder the cutting quality and performance is provided. These phenomena include shock [...] Read more.
Assist gas plays a central role in laser fusion cutting. In this work, the aerodynamic interactions between the assist gas and the workpiece are reviewed. An insight into those phenomena that hinder the cutting quality and performance is provided. These phenomena include shock waves, choking, boundary layer separation, etc. The most relevant and promising attempts to overcome these common problems related to the gas dynamics are surveyed. The review of the current scientific literature has revealed some gaps in the current knowledge of the role of the assist gas dynamics in laser cutting. The assist gas interactions have been investigated only under static conditions; and the dynamic interaction with the molten material on the cutting front has not been addressed. New nozzle designs with improved efficiency of molten material removal are required to improve cut quality; and cutting speed in current industrial laser cutting machines; especially in those assisted by new high-brightness laser sources. Full article
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Open AccessReview
Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations
Materials 2018, 11(12), 2583; https://doi.org/10.3390/ma11122583 - 18 Dec 2018
Cited by 4
Abstract
Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable [...] Read more.
Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilled. Full article
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