CIRP Journal of Manufacturing Science and Technology最新文献

The interface slip state of high-speed friction stir welding (HSFSW) is challenging to determine, and accurate boundary conditions cannot be obtained. First, this paper studies the effects of velocity and temperature on the interface slip state, and establishes a new slip coefficient equation. Then, this equation was used to modify the velocity boundary conditions and improve the numerical calculation method of HSFSW. A numerical model of HSFSW was established and validated through experimental data. Finally, the effects of traverse speed and rotational speed on the temperature and void defects of HSFSW were elaborated, and the applicable process parameter range was determined. Specifically, void defects were observed at a rotational speed of 6000 rpm with traverse speeds of 1000 mm/min and 2000 mm/min, while surface peeling occurred at a traverse speed of 3000 mm/min with a rotational speed of 7000 rpm. This study establishes the optimal parameter range for aluminum alloy HSFSW, providing valuable guidance for future industrial applications.

In this study, an analysis was conducted to quantify errors in the additive manufacturing process, with a focus on comparing data files. The primary objective was to minimise the reliance on physical testing of produced components by favouring verification within a virtual environment. The initial focus was on the conversion from the CAD (Computer-Aided Design) model to the STL (Standard Tessellation Language) file, where discrepancies between the two formats were identified. To achieve optimal meshing, it is crucial to configure conversion parameters effectively, avoiding both detail loss and the handling of excessively large files. Following this, a comparison between STL files and reconstructed G-code files was conducted, uncovering further approximations introduced by the most commonly used slicers. In conclusion, the analysis highlights that both the quality of the mesh and the slicing phase significantly impact the final component. Understanding these factors is essential for achieving an optimal print outcome.

To broaden the process understanding with regard to a tool concept for finishing operations based on soft foams coated with diamonds, the application behaviour with respect to the surface preparation of a ground hardened steel surface is considered. By analysing the surface on the basis of established roughness parameters, the material removal behaviour is investigated in dependence on the process parameters and tool specifications. Furthermore, the influence on the micro roughness superimposed on the roughness profile can be analysed. The recorded process forces serve as a basis for understanding the underlying mechanisms and for interpreting the results.

Additive Manufacturing (AM) technologies, particularly laser powder bed fusion (LPBF), are revolutionising the production of complex geometries and lightweight structures. Furthermore, LPBF allows to tailor the microstructure and resulting properties of metallic materials. This study focuses on titanium alloys, crucial for high-performance applications like aircraft components and medical implants. Although AM enables near-net-shape fabrication, many titanium parts still require machining to meet surface and dimensional standards. Titanium’s challenging machinability is well-documented for cast and wrought alloys, but only less is known about additively manufactured variants. In this work, the machinability of an additively manufactured Ti-5Al-5V-5Mo-3Cr alloy (Ti-5553) is investigated, focusing on chip formation, cutting forces, and tool wear across different LPBF process parameters. Four LPBF parameter sets were validated, and results were compared to conventional wrought sample. The findings reveal significant variations in machinability linked to LPBF parameters. Specifically, the highest tool loads and wear were observed for samples produced with the highest energy density of E_V = 37.0 J/mm³, likely due to α-phase precipitation. In contrast, samples with lower energy densities (<29.1 J/mm³) exhibited up to 100% longer tool life. Concluding, this study highlights how the machinability of Ti-based components can be significantly influenced by the LPBF processing parameters.

To investigate the microstructural changes that occur in stainless steel (SS) 304 during single point incremental forming (SPIF), experiments and finite element (FE) simulations were conducted for a truncated square pyramid geometry. Results from material characterization experiments for four stress states, i.e., uniaxial tension, equibiaxial tension, shear, and uniaxial compression, were combined to construct a material model based on the constituent phases and transformation kinetics. The material model was implemented into numerical analyses, where a two-step FE approach was utilized to predict martensite transformation in SPIF with increased computational efficiency. Validation experiments showed good agreement with the martensite transformation predictions from the FE simulations. The four locations along the pyramid wall revealed varying martensite volume fractions because of the differing stress states of bending, stretching, and shear that the blank is subjected to during SPIF, which can affect the microstructure. The stress state can be defined in terms of the stress triaxiality and Lode angle parameter. The FE results indicate that stress triaxiality impacted the martensitic transformation kinetics in SS304 more than the Lode angle parameter for SPIF for this particular material and geometry. Thus, distinct stress states in incremental forming can affect the martensitic transformation locally and, when used strategically, achieve functionally graded materials. This is pertinent to industrial applications requiring custom components, e.g., trauma fixation hardware for medical applications.

This paper describes a process damping force model calibrated using an in situ measurement of velocity during an unstable milling test. The process damping coefficient is selected to match simulated and measured velocity signals. The coefficient is inserted in the cutting force model and time-delay differential equations of motion that describe the milling system. The modeling approach is described and experimental results are presented for: 1) selecting the process damping coefficient; and 2) comparing measured velocities and milling stability to predictions from time domain simulation.

The current study on free bending focuses on traditional macroscopic tubes and profile components. Nevertheless, as the geometric size of the tube decreases, the resulting size effect affects the free bending deformation behavior of the microtube in the less constrained state. In this investigation, a constitutive model of microtubes considering the surface layer model was established. The corresponding model parameters were determined by fitting the flow curves of surface single crystals and internal polycrystals. According to the principle of free bending, the springback internal bending moment of the microtube was derived to explain the phenomenon whereby the bending radius of the microtube decreases with decreasing size factor. With decreasing size factor, the influence of the surface layer grains on the bending behavior of the microtube becomes more intense. Furthermore, by comparing the results of the microscale free bending experiment and simulation, it can be concluded that the material properties of microtubes in the finite element (FE) simulation should be defined based on the surface layer and inner layer. With decreasing microtubule size factor, the bending radius of the tube decreases, and the wall thickness changes more significantly. The cross-sectional distortion of the microtubes decreases with increasing grain size and wall thickness. This study explored the feasibility of the free bending process to achieve bending of microtubes and revealed that the size effect on the deformation behavior of microtubes should be considered in the microscale free bending process.

With a growing global awareness of the ecological challenges posed by plastic waste, the integration of recycled materials represents a crucial step to sustainable additive manufacturing of plastic products. To assess the applicability of recycled materials in 3D printing, we extruded recycled polylactic acid (PLA) into filament and printed specimens based on the fused filament fabrication (FFF) printing technology. For comparison purposes, we selected the virgin PLA filament as a reference. With the filament extruder, we produced filaments using virgin PLA pellets, a mixture of virgin pellets and recycled PLA, as well as fully recycled PLA. The extrudability and transferability of filaments were comprehensively investigated under various extrusion temperatures and speeds. Subsequently, using extruded filaments, we printed parts of different shapes such as cubes, tensile specimens, and flexural specimens. We measured the surface roughness, dimensional deviations, and mechanical properties of the printed parts. Results demonstrated that filament extruded from virgin pellets exhibited similar quality and mechanical properties as the virgin filament. Recycled PLA required higher extrusion temperature and speed to extrude filament than virgin PLA and mixed virgin PLA and recycled PLA. The tensile and flexural strength of printed parts from fully recycled PLA were more than 15 % lower than that from virgin filament. These findings contribute valuable insights towards the continued development of environmentally conscious practices in the field of additive manufacturing.

The hype around additive manufacturing technologies suggests that any complex shaped structure can be fabricated regardless of the type of material used. Moreover, it is often suggested that additive manufacturing processes will certainly disrupt the supply chain logistics and that everyone will be able to print on the demand at the comfort of their home. In this viewpoint, we describe and demystify some of the common assumptions associated with these set of technologies. We also show that conventional manufacturing processes cannot be fully replaced by additive manufacturing technologies, but rather there is a need for a complementarity between well-consolidated manufacturing technologies and additive manufacturing. While some of the contents presented here are basic for specialists working in the manufacturing field, we expect that this viewpoint can aid researchers working on topics related to additive manufacturing, but with less focus on the manufacturing aspects, helping them understand the actual limitations and advantages associated to these technologies. The four key issues that are addressed in this viewpoint, and their consequences, also intend to shape and mold future entrepreneurial efforts on additive manufacturing, as well as define future impacts (environmental, logistics, commercial and disruptive) associated to additive manufacturing technologies.

Bone drilling mechanism study is the basis for the optimization of cortical bone drilling process and drill geometry. In this paper, a drilling force model for modified drills with thinned chisel edge is established considering the heterogeneous structure of cortical bone. The bone mineral density is embedded into the established model, the model can predict the axial thrust force change along the drilling depth direction, and the model is verified through cortical bone drilling experiments. The thrust force and torque predicted by the model are in good agreement with the drilling experimental results of cortical bone drilling. Then, the drilling performance of the modified drill and the common drill is compared through cortical bone drilling experiments. Compared with common drill bits, the maximum reduction in average thrust force of the modified drill bit during stable drilling is 21.21 % (n = 2500 rpm, V_f=60 mm/min). The maximum reduction in average roughness of the hole wall is 21.87 % (n = 500 rpm, V_f=10 mm/min). The drill chisel edge thinning design reduces the negative impact of the negative normal rake angle on the cutting lip of common drill on drilling force and stability. Therefore, the drill bit chisel edge thinning design can effectively improve the drilling performance.