In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the deposited layers, high precision, and suitability for full automation. Hence, the proposed repairing method based on DED appears to be a capable method of repairing. Therefore, the focus of this study was to present an overview of the DED process and its role in the repairing of metallic components. The outcomes of this study confirm the significant capability of DED process as a repair and remanufacturing technology.

Application of Directed Energy Deposition-Based Additive Manufacturing in Repair

Laser cladding and surface alloying are surface modification techniques employed to fabricate thin coating/layer with improved surface properties or to refurbish surface defects by forming highly resistant gradient coatings/layers on the substrate. High energy density and cooling rates make these techniques suitable to process a wide range of materials. In recent years, due to the development of high power lasers, improved controlling and delivery mechanisms have attracted extensive research in laser surface treatment. Researchers have analyzed various process factors to improve process performance. The experimental and theoretical studies show that the performance of laser cladding and surface alloying techniques can be enhanced significantly by the proper selection of input process parameters. This paper summarizes various research works carried out so far in the area of laser cladding and surface alloying of different materials and their applications. It reports the research outcomes of experimental and theoretical studies conducted to improve the process performance. A brief introduction of various laser surface treatment processes is also included. Besides these various problems, their solutions and trend for future works have also been discussed.

Recent trends in laser cladding and surface alloying

Predicting residual distortion in metal additive manufacturing (AM) is important to ensure quality of the fabricated component. The inherent strain method is ideal for this purpose, but has not been well developed for AM parts yet. In this paper, a modified inherent strain model is proposed to estimate the inherent strains from detailed AM process simulation of single line depositions on top of each other. The obtained inherent strains are employed in a layer-by-layer static equilibrium analysis to simulate residual distortion of the AM part efficiently. To validate the model, depositions of a single wall and a rectangular contour wall models with different number of layers deposited by a representative directed energy deposition (DED) process are studied. The proposed model is demonstrated to be accurate by comparing with full-scale detailed process simulation and experimental results. To make the method practical, a small-scale detailed simulation model is proposed to extract the mean inherent strains. Based on this approach, simulation results applied to the rectangular contour wall structures of different heights show that the modified inherent strain method is quite efficient, while the residual distortion of AM parts can be accurately computed within a short time. The improvement of the computational efficiency can be up to 80 times in some specific cases.

https://par.nsf.gov/servlets/purl/10208118

A modified method for estimating inherent strains from detailed process simulation for fast residual distortion prediction of single-walled structures fabricated by directed energy deposition

Directed energy deposition (DED) has matured into an essential additive manufacturing (AM) branch. DED has been broadly implemented in the design and fabrication of novel materials. These include metals, ceramics, and composites. Successful DED operation requires a good understanding of many critical phenomena, including laser-material interactions, fundamentals of casting and solidification of alloys, welding metallurgy and joining interfaces, along with microstructure-mechanical properties relations. Also critical are powder flowability, heat transfer, and various machine-related parameters. Several review articles have been published in recent years on metal AM via powder bed fusion (PBF) and DED, focusing on either a specific material system, mapping the recent technologies for AM, or issues related to the deposition process or material properties. Yet, no recent review is dedicated to a comprehensive presentation of material systems, design, fabrication, challenges, and the relationship between microstructures and mechanical properties of various DED'ed material families. Since the DED-based approach is becoming popular to manufacture bimetallic and multi-material structures, repair high-value structures, and alloy design, this comprehensive review focuses on materials design via DED, including a survey of a variety of monolithic and multi-material compositions. Finally, the critical challenges and opportunities in this area are highlighted. 

http://manuscript.elsevier.com/S0921509322003744/pdf/S0921509322003744.pdf

Laser-based directed energy deposition (DED-LB) of advanced materials

https://cyberleninka.org/article/n/674158.pdf

The Role of Laser Additive Manufacturing Methods of Metals in Repair, Refurbishment and Remanufacturing – Enabling Circular Economy

Laser reconditioning of crankshafts: From lab to application

Influence of Laser Reconditioning on Fatigue Properties of Crankshafts

In marine diesel engines, damaged crankshafts are common and expensive defects. Worn surfaces of main bearings and crankpin journals often require a complete replacement of these components. This paper presents the development of a repair procedure on its way to application. As an alternative to the method of grinding the accordant surfaces and using matched bearing shells, a rebuild to the original diameter is the goal of this investigation.This paper describes the development of a controlled diode laser cladding process in the lab and the characterization of flat specimens particularly by metallographic analysis and hardness testing.In preparation of the industrial application, previously ground crankpin journals of crankshafts could successfully be cladded with identical parameters as found on flat specimens in the lab. The claddings show a high quality in terms of connection to the base material and dilution. In hardness tests steep gradients from heat affected zone to unaffected base material could be measured.In marine diesel engines, damaged crankshafts are common and expensive defects. Worn surfaces of main bearings and crankpin journals often require a complete replacement of these components. This paper presents the development of a repair procedure on its way to application. As an alternative to the method of grinding the accordant surfaces and using matched bearing shells, a rebuild to the original diameter is the goal of this investigation.This paper describes the development of a controlled diode laser cladding process in the lab and the characterization of flat specimens particularly by metallographic analysis and hardness testing.In preparation of the industrial application, previously ground crankpin journals of crankshafts could successfully be cladded with identical parameters as found on flat specimens in the lab. The claddings show a high quality in terms of connection to the base material and dilution. In hardness tests steep gradients from heat affected zone to unaffected base material could b...

Regarding the fatigue strength of laser cladded components only very few investigations exist today. This situation induced an investigation whose most important technical results are presented in this paper. The final goal of this work is to predict the optimal process and material parameters for the laser cladding process regarding the fatigue strength and locations of crack initiation. With the intent of calculating the residual stresses in the coating and the adjacent substrate, a FEM-based weld simulation model was developed. On the basis of the calculated residual stresses, the mechanical load situation during cyclic bending is simulated. In order to verify the FE models, round specimens have been laser cladded and analysed regarding clad quality, dilution and hardness as well as fatigue strength during a four-point bending test. The results from simulations and experiments are used as input for calculating the fatigue strength and locations of crack initiation. The Cobalt-based alloy Stellite 21 has been cladded on two substrate materials: the austenitic steel X5CrNi18-10 and the hardened and tempered steel 42CrMo4. Experimental analyses showed that the fatigue limits of the specimens strongly depend on the core materials. The fatigue strength of the steel 42CrMo4 has been figured out to be lower compared to that of the austenitic steel. It is assumed that these results are associated with different residual stresses. A model to simulate residual stresses induced by the cladding process has successfully been set up. Possibilities of fatigue-limit calculation using two approved models for hardened steels have been investigated.

An approach to calculate fatigue properties of laser cladded components

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Laser reconditioning of crankshafts: From lab to application

Influence of Laser Reconditioning on Fatigue Properties of Crankshafts

Laser reconditioning of crankshafts: From lab to application

An approach to calculate fatigue properties of laser cladded components