A state-of-the-art digital factory integrating digital twin for laser additive and subtractive manufacturing processes

Additive manufacturing technology overcomes the limitations imposed by traditional manufacturing techniques, such as fixtures, tools, and molds, thereby enabling a high degree of design freedom for parts and attracting significant attention. Combined with subtractive manufacturing technology, additive and subtractive hybrid manufacturing (ASHM) has the potential to enhance surface quality and machining accuracy. This paper proposes a method for simulating the additive and subtractive manufacturing process, enabling accurate deformation prediction during processing. The relationship between stress distribution and thermal stress deformation of thin-walled 316L stainless steel parts prepared by Laser Metal Deposition (LMD) was investigated using linear scanning with a laser displacement sensor and finite element simulation. The changes in stress and deformation of these thin-walled parts after milling were also examined. Firstly, 316L stainless steel box-shaped thin-walled parts were fabricated using additive manufacturing, and the profile information was measured using a Micro Laser Displacement Sensor. Then, finite element software was employed to simulate the stress and deformation of the box-shaped thin-walled part during the additive manufacturing process. The experiments mentioned were conducted to validate the finite element model. Finally, based on the simulation of the box-shaped part, a simulation prediction was made for the box-shaped thin-walled parts produced by two-stage additive and subtractive manufacturing. The results show that the deformation tendency of outward twisting and expanding occurs in the additive process to the box-shaped thin-walled part, and the deformation increases gradually with the increase of the height. Meanwhile, the milling process is significant for improving the surface quality and dimensional accuracy of the additive parts. The research process and results of the thesis have laid the foundation for further research on the influence of subtractive process parameters on the surface quality of 316L stainless steel additive parts and subsequent additive and subtractive hybrid manufacturing of complex parts.

Beam shaping technology and its application in metal laser additive manufacturing: A review

Additive manufacturing (AM) has recently been accorded considerable interest by manufacturers. Many manufacturing industries, amongst others in the aerospace sector, are already using AM parts or are investing in such manufacturing methods. Important material properties, such as microstructures, residual stress, and surface topography, can be affected by AM processes. In addition, a subtractive manufacturing (SM) process, such as machining, is required for finishing certain parts when accurate tolerances are required. This finish machining will subsequently affect the surface integrity and topography of the material. In this research work, we focused on the surface integrity of Ti-6Al-4V parts manufactured using three different types of AM and finished using an SM step. The aim of this study was to gain an understanding on how each process affects the resulting surface integrity of the material. It was found that each AM process affects the materials’ properties differently and that clear differences exist compared to a reference material manufactured using conventional methods. The newly generated surface was investigated after the SM step and each combination of AM/SM resulted in differences in surface integrity. It was found that different AM processes result in different microstructures which in turn affect surface integrity after the SM process.

Hybrid manufacturing (HM), which combines additive manufacturing (AM) and subtractive manufacturing (SM), is effective for the fabrication of thin-walled complex shapes, such as impeller blades. Generally, a process planning for HM is to build a near-net shape through AM and finish its surface through SM. However, in this approach, the cutting tools are limited with long tool lengths and small tool diameters to avoid collisions between the cutting tool and workpiece. In addition, the fabrication shapes are also limited. Therefore, one possible solution is to alternate between AM and SM processes multiple times. In this approach, the workpieces are built gradually as the process progresses. Therefore, the cutting tool can easily avoid collision with the workpiece. However, melting penetration and temper color remain on the finished surfaces using the conventional process planning method with alternate multiple switching. In this process planning, AM and SM processes are alternated. Thus, the finished surfaces are remelted in the subsequent AM process. This heat input causes melting penetration and temper color. These thermal effects must be prevented because these can lead to unfinished part and deterioration of the appearance of the workpieces. Therefore, in this study, a novel process planning method that allows alternate multiple switches without thermal effects is proposed. In addition, a process planning support system that simulates SM process was developed. The SM simulation can detect collision between the cutting tool and workpiece. Using the proposed process planning method, the system plans a process in which thermal effects will not occur. In addition, a case study was conducted using a simulated impeller blade geometry. The results of the case study showed that the developed system could plan by using several cutting tools and parameters of the machining head. The system can estimate the processing time based on the cutting tool path, deposition path, SM process conditions, and AM process conditions. The results validated the developed system and demonstrated its usefulness.

Hybrid additive manufacturing (AM) and subtractive manufacturing (SM) processes utilize the combination of AM (e.g., LPBF and DED) and SM (e.g., milling and turning operations) to produce the final part. Due to the poor surface roughness resulting from the uneven melting of powders in AM, the subtractive process is a necessary finishing operation to improve the surface roughness of the AM part. The hybrid AM/SM technology combines the benefits of AM and SM processes to create complex geometry while introducing good surface finish and compressive stress to prevent crack initiation. However, the relationship between large process parameter space and the residual stress/distortion in the part is not well understood, which impedes the adoption of hybrid AM/SM to minimize the residual stress in the final product. To expedite the process optimization, we establish a pipeline for the sequential modeling of additive manufacturing (AM) and subtractive manufacturing (SM) processes. Key accomplishments achieved under this study include (1) development of thermal abstraction technique for the AM process to speed up the macroscale level heat transfer analysis based on the manufacturing factors including scanning vector, laser power, dwelling time, etc.; (2) development of the sequentially coupled thermal-mechanical model to predict the residual stress and distortion after AM process by passing the temperature history obtained from heat transfer analysis to the mechanical analysis at each time point; (3) validation of the thermal-mechanical model for AM using thin-wall structure from literature and cantilever beam structure from UNT’s experiments data; (4) conduction of the parametric study on the chamber temperature and part design in the AM process to demonstrate how the temperature gradient and supporting structure affect the residual stress and distortion; (5) exploration of macro and micro scale models to predict the bulk and surface residual stress after cutting; (6) applying the developed modeling framework to tailoring the hybrid AM/SM process. To support model verification and demonstration, we print cantilever beam structure with different supporting structure designs and cutting strategies to study how these factors affect the final part residual stress and distortion. The data collected in the printing and cutting process is used to examine the applicability of the developed simulation tool.

Laser-based additive manufacturing (LBAM) is a group of advanced manufacturing processes used to produce metal components and functionally graded products. Production in LBAM is either limited to the formation of thin or thick coatings on a substrate by laser metal deposition or the production of a fully functional metallic product by selective laser melting. In every case, LBAM fabricated components require optimization for the process parameters to avoid defects, such as porosity, crack holes, thermal deformation, and mechanical strength. As a key link in the laser additive manufacturing (LAM) process, laser scanning path planning is an effective strategy for balancing the temperature field of the formed part, avoiding stress concentration, and preventing deformation and cracking. Efficient, accurate, and reasonable planning of the laser scanning path is of great significance for improving the processing efficiency of the process data, prolonging the life of the laser scanning system, and improving the forming quality of the specimen. Through many studies, it was found that the scanning pattern of the lasers has a significant impact on the mechanical properties and deformations caused by a thermal mismatch during the process. Therefore, it is essential to have in-depth knowledge about path planning in LBAM. Our review mainly focuses on the influence of scanning patterns on deformation, temperature, and mechanical properties in LBAM. Finally, our paper discusses the current study limitations and some future studies in LAM technology.

The Manufacturing Automation course in the Mechanical Engineering program at the University of Connecticut (UConn) was one of the most popular courses in the ME curriculum. The students’ benefits from the course were already described in the companion paper [1]. In this paper the advantages of prototyping and part production through Subtractive Manufacturing (SM) and Additive Manufacturing (AM) are described. The paper discusses parts fabrication done as subtractive and additive manufacturing operations. This was done in the scope of the UConn Engineering i.e. in the ME and MEM programs where Manufacturing Automation and Senior Design courses are taught. Such operations were possible thanks to the equipment available at UConn School of Engineering and thanks to the cooperation with the creator of the Mastercam software - CNC Software Inc and aircraft engines and equipment manufacturer - Pratt & Whitney of East Hartford. The integration of design and manufacturing in the course was done through putting together the operations of conceptual design, geometric design and modeling of the parts designed during the course. The models of parts done by AM were created using 3D printing in ME Laboratory out of acrylonitrile butadiene styrene and different kinds of plastic and in PW/UConn laboratory using laser and electron beam AM machines. To demonstrate further integration of design and machining automation, the students were introduced to complicated problems of surfaces crossing, connections of surfaces and edges of cross sections of the tops and valleys. Thanks to the support and cooperation of the CNC Software, Inc., it was possible to show the students how to cut complicated surfaces on different computer numerically controlled (CNC) machines that ranged from three to nine degrees of freedom specifically designed for accurate and repeatable metal working. In addition, the additive manufacturing (AM) capabilities were introduced in the course thanks to the support of Pratt & Whitney/UConn Additive Manufacturing Laboratory located on the UConn campus. The AM machines are Arcam and laser machines that use electron and laser beams to meld titanium powder. The fabricated parts of high strengths are useful as rapid prototypes or in some cases as substitution parts in an existing mechanical systems. Thanks to the UConn Engineering program and support of the corporations: CNC Software, Inc. and P&W, students were introduced to the spectrum of modern Rapid Prototyping and part sintering operations going through subtractive and additive manufacturing. The process details of the theory, practice of operations, and recommendation for use of the technologies discussed above, as well as possibilities of further applications, are described in this paper. After learning the fundamentals of these processes, students are prepared to design and analyze parts as well as the process required for different machining capabilities. Methods to introduce students to the concepts of using laser and electron beams AM machine as well the prototype machining are described in the paper. Conclusions recommending the teaching methods of product SM and AM machining concepts and lessons learned are also pointed out.

The combination of distributed digital factories (D2Fs) with sustainable practices has been proposed as a revolutionary technique in modern manufacturing. This review paper explores the convergence of D2F with innovative sensor technology, concentrating on the role of Field Programmable Gate Arrays (FPGAs) in promoting this paradigm. A D2F is defined as an integrated framework where digital twins (DTs), sensors, laser additive manufacturing (laser-AM), and subtractive manufacturing (SM) work in synchronization. Here, DTs serve as a virtual replica of physical machines, allowing accurate monitoring and control of a given manufacturing process. These DTs are supplemented by sensors, providing near-real-time data to assure the effectiveness of the manufacturing processes. FPGAs, identified for their re-programmability, reduced power usage, and enhanced processing compared to traditional processors, are increasingly being used to develop near-real-time monitoring systems within manufacturing networks. This review paper identifies the recent expansions in FPGA-based sensors and their exploration within the D2Fs operations. The primary topics incorporate the deployment of eco-efficient data management and near-real-time monitoring, targeted at lowering waste and optimizing resources. The review paper also identifies the future research directions in this field. By incorporating advanced sensors, DTs, laser-AM, and SM processes, this review emphasizes a path toward more sustainable and resilient D2Fs operations.

Determination of alternation sequence for additive and subtractive manufacturing based on subtractive manufacturing simulation

Hybrid manufacturing machine tools have great potential to revolutionize manufacturing by combining both additive manufacturing (AM) and subtractive manufacturing (SM) processes on the same machine tool. A prominent issue that can occur when going from AM to SM is that the SM process toolpath does not account for geometric discrepancies caused by the previous AM step, which leads to increased production times and tool wear, particularly when wire-based directed energy deposition (DED) is used as the AM process. This work discusses a methodology for approximating a part’s surface topology using on-machine contact probing and formulating an optimized SM toolpath using the surface topology approximation. Three different geometric surface approximations were used: triangular, trapezoidal, and a hybrid of both. SM toolpaths were created using each geometric approximation and assessed according to three objectives: reducing total machining time, reducing surface roughness, and reducing cutting force. Different prioritization scenarios of the optimization goals were also investigated. The optimal surface approximation that yielded the most improvement in the optimization was determined to be the hybrid surface topology approximation. Furthermore, it was shown that when the machining time or cutting force optimization goals were prioritized, there was little improvement in the other optimization goals.

Hybrid manufacturing approaches with additive and subtractive manufacturing is a promising technology for many sectors from personal care goods to aerospace. When it comes to the residual stresses, there are hardly about the additive manufacturing (AM). Although some researches have been conducted for the hybrid laser additive manufacturing and subtractive manufacturing (SM) processes, only the machining parameters, material properties, and surface quality were analyzed; there were a few experiments about the residual stresses. Taking this into account, this paper aims to analyze the surface residual stresses in hybrid manufacturing approaches. Additive machining process, electrochemical corrosion, and surface residual stresses testing were described in detail. The main results of the research would be references for the surface residual stresses when 316L stainless steel specimens are manufactured with laser metal deposition and milling after AM immediately. The oxidation is much serious in additive manufacturing, and the surface tensile stresses are quite small. Both the electrochemical corrosion and milling at high temperature will affect the distribution of the surface residual stresses. The residual tensile stresses are distributed symmetrically after milling process while they are asymmetric after electrochemical corrosion.

Recently, the fact that hybrid manufacturing (HM) combines different manufacturing processes mechanism of additive and subtractive processes has gained significant attentions. This work attempts to study a process of HM in order to overcome the disadvantages of each manufacturing process. Selective laser melting (SLM) of ANSI 316L stainless and machining are used as the additive and subtractive manufacturing process, respectively, in this work. Firstly, the mechanical properties and the standard samples manufactured by HM are analyzed. The results show that the finished surface roughness has no apparent influence on the tensile strength. The tensile strength of HM is reduced in comparison with the substrate materials. The yield strength of HM is higher than the substrate material. And the heat treatment is beneficial for the mechanical properties improvement. Further, the geometrical feature structure manufacture complexity indices (GFS-MCIs) are defined and calculated from the computer-aided design (CAD) model. In reference to GFS-MCIs, a satellite thruster structure (STS) is analyzed and decomposed into two geometrical feature structures. Based on the result of GFS-MCIs, STS is manufactured by HM approach as a complete component.

Toward Rapid Manufacturability Analysis Tools for Engineering Design Education

Additive manufacturing (AM), an enabler of Industry 4.0, recently opened limitless possibilities in various sectors covering personal, industrial, medical, aviation and even extra-terrestrial applications. Although significant research thrust is prevalent on this topic, a detailed review covering the impact, status, and prospects of artificial intelligence (AI) in the manufacturing sector has been ignored in the literature. Therefore, this review provides comprehensive information on smart mechanisms and systems emphasizing additive, subtractive and/or hybrid manufacturing processes in a collaborative, predictive, decisive, and intelligent environment. Relevant electronic databases were searched, and 248 articles were selected for qualitative synthesis. Our review suggests that significant improvements are required in connectivity, data sensing, and collection to enhance both subtractive and additive technologies, though the pervasive use of AI by machines and software helps to automate processes. An intelligent system is highly recommended in both conventional and non-conventional subtractive manufacturing (SM) methods to monitor and inspect the workpiece conditions for defect detection and to control the machining strategies in response to instantaneous output. Similarly, AM product quality can be improved through the online monitoring of melt pool and defect formation using suitable sensing devices followed by process control using machine learning (ML) algorithms. Challenges in implementing intelligent additive and subtractive manufacturing systems are also discussed in the article. The challenges comprise difficulty in self-optimizing CNC systems considering real-time material property and tool condition, defect detections by in-situ AM process monitoring, issues of overfitting and underfitting data in ML models and expensive and complicated set-ups in hybrid manufacturing processes.

Laser sintering (LS), laser melting (LM), and laser metal deposition (LMD) are presently regarded as the three most versatile laser-based additive manufacturing (AM) processes. Laser-based AM processes generally have a complex nonequilibrium physical and chemical metallurgical nature, which is material- and process-dependant. The influence of material characteristics and processing conditions on the metallurgical mechanisms and resultant microstructural and mechanical properties of AM-processed components needs to be clarified. This chapter starts with the definition of LS/LM/LMD processes and operative consolidation mechanisms for metallic components. Powder materials used for AM, in the categories of pure metal powder, prealloyed powder, multi-component metals, alloys, metal matrix composites (MMCs) powder, and associated densification mechanisms during AM are addressed. An in-depth review of material and process aspects of AM, including the physical aspects of materials for AM and the microstructural and mechanical properties of AM-processed components, is presented. The purpose of this chapter is to establish a general relationship among material, process, and metallurgical mechanism for laser-based AM of metallic components.