Cost Modeling and Evaluation of Hybrid Manufacturing Process With Laser Metal Deposition and CNC Machining
Authors: Shahriar Mohammad Ahnaf , Yang Yiran 
Published: August 2024

Abstract
Additive manufacturing (AM) is not just used for prototyping, but rather adopted as rapid tooling or manufacturing in industries such as Aerospace, Automobile, Medical, and Consumer Products. Laser Metal Deposition (LMD) – a Directed Energy Deposition (DED) process, has become increasingly popular because of its high manufacturing flexibility and efficiency. In LMD, the feedstock metal powder is melted by a high-power laser source while it is being deposited on the substrate. The combination of DED and CNC machining leads to a new hybrid process, which leverages the unique advantages of both additive and subtractive processes. Hybrid DED has great potentials to achieve the fabrication and repair of materials and designs that are challenging or even impossible when using only CNC or DED with good quality and tolerance assurance. In order to enable larger scale production, it is essential to assess the costs involved in hybrid DED. In the literature, some studies have been conducted to estimate DED costs, while there is lack of research focused on the cost calculation of DED fabrication and CNC surface finishing. It is found that the additive process and the subtractive process are considered separately and discussion on the selection of process parameters of machining is missing. However, these process parameters are critical factors depending on whether the target is to remove defect or perform surface finishing. This paper presents a cost model to calculate the fabrication and the repair of a part using 5-axis hybrid LMD, by integrating the two processes seamlessly. Through different case studies, the impact of process parameters on surface roughness and the relation of surface roughness with the DED process and CNC machining are discussed in this paper. Three case studies are performed while the first case compares the proposed model with the literature. The second case evaluates cost for machining a portion of a part using a milling cutter (roughing subtractive process), then depositing material (additive process) and finally surface finishing (finishing subtractive process). Similarly, the third case also has the same sequence of operations; roughing subtractive process, additive process and finishing subtractive process. The difference is that the third case involves relatively complicated machining to create angled slots. Results show that the material cost is the highest cost component while the overhead cost and the labor cost also contribute largely to the overall cost being second and third highest component respectively. The material cost is dominated by the metal powder cost. The overhead cost is mainly affected by the machine purchase cost. Since, the model has involved some sort of labor action in all the phases of fabrication, the labor cost is also quite considerable. However, the energy cost is small. Since metal additive manufacturing is very expensive, this study can help the researchers with funding and budgeting for their experimental work of fabrication.