Procedia CIRP最新文献

The deep rolling process can influence the surface and subsurface of hardened steels, such as the bearing steel AISI 52100, due to mechanical loading and elastoplastic deformation. By intentionally adjusting the surface and subsurface properties, the fatigue life of bearing inner rings can be increased. This is among others attributed to the strengthening of surface and subsurface. Residual stresses induced by deep rolling and modifications of the material microstructure also contribute to this effect. In the investigations presented the deep rolling process parameters of rolling pressure, overlap ratio, and ball diameter were specifically selected based on previous works. Fatigue life investigations were conducted on honed and deep rolled bearing inner rings to enhance the understanding of failure mechanisms and to quantify the influence of the deep rolling process on fatigue life. It was found that the deep rolled bearing inner rings exhibit higher compressive residual stresses in the subsurface than honed rings and also showed longer fatigue life under rolling loads. Optical analyses of bearing rings that failed due to fatigue were performed to detect the failure mechanisms. The tested bearings showed classical fatigue, where cracking is initiated below the surface and propagates to the surface under further stress. Residual stresses can influence both the crack initiation and propagation.

This study investigates the surface changes and fretting phenomena at neck-head interface of Ti6Al4V alloy. In particular, hip necks subjected to burnishing process are the objective of the experimental campaign. Ti6Al4V is a widely used material in orthopedic implants due to its excellent biocompatibility and mechanical properties. However, the potential for fretting fatigue is a common concern in hip implants requiring the exploitation of surface modification techniques to enhance the implant’s performance and durability. Burnishing process involves the controlled application of mechanical pressure to the implant’s surface, which can generate residual stresses and changes in surface topography. By employing advanced surface characterization techniques, including micrograph and profilometry, the surface modifications induced by burnishing were evaluated. Furthermore, fretting fatigue assessment was carried out through mechanical testing, simulating the conditions encountered in the hip joint during typical daily activities. Finally, an emerging sensing technology in the field of non-destructing optical testing, phase-based motion estimation (PBME) was employed in order to assess the surface gradual degradation before failure.

Finish turning is one of the key operations governing the residual stress of functional surfaces. The residual stress state is determined by the cutting conditions and the selected cutting tool system (macro geometry, cutting edge preparation, tool substrate, multi-layer coating…). However, this initial configuration evolves over time due to tool wear. Therefore, it seems fundamental to reproduce the wear process of the tool in order to understand the evolution of thermo-mechanical loadings applied to the machined surface. This work presents a numerical methodology for predicting the wear-induced residual stress drift in longitudinal turning. The complete 3D cutting tool is discretized into elementary 2D sections. A finite element based procedure is developed to calculate, considering each local tool geometry, the local loads withstood by the machined material. The latter are merged to generate equivalent 3D thermomechanical loadings implemented in a second macroscopic model able to calculate the residual stress state under different wear levels. Experimental cutting tests with artificially worn tools have confirmed that good agreement can be achieved.

Inconel 718 represents a large portion of high-temperature metals in key industries, where the machining-induced surface integrity is quite important. As the different grain size results in various densities of grain boundaries in the deformed area, the surface integrity can be significantly affected. This paper studies the effect of workpiece grain size on machining-induced surface integrity when cutting Inconel 718. Workpiece materials with fine or coarse grain features are prepared with various heat treatment methods. Orthogonal cutting experiments are conducted with uncoated carbide tools under different cutting speeds (20 - 100 m/min). The cutting force results indicate that Inconel 718 with larger grain size will cause lower cutting forces and the percentage reduction approximately ranges from 20 % to 33 %. An interesting phenomenon is found that the workpiece with coarse grains exhibits large-scale geometrical defects due to tearing within the grains at low cutting speed (v_c = 20 m/min). This phenomenon can be diminished if the cutting speed v_c is increased to 60 m/min. In addition, the subsurface deformation layer is reduced with decreasing workpiece grain size due to the barrier effect of grain boundary on plastic deformation.

The relationships between machining conditions, boundary layer and mechanical component functionality are known qualitatively for selected Wire Electrical Discharge Machining (Wire EDM/WEDM) applications and continuous further developments of this manufacturing technology minimize the thermal influences significantly. Nevertheless, the use of WEDM processes has so far been severely limited in safety-critical applications, especially in the field of turbomachinery construction and aerospace. For example, the removal of the generated surface layers is often still mandatory, although cutting processes can also leave a distinct thermo-mechanically influenced rim zone on the component. This conservative approach currently unnecessarily reduces the manufacturing potential of WEDM processes considerably and calls for an objective comparison of component function. In this paper, therefore, the flexural bending fatigue strengths of differently wire-eroded surfaces based on roughing-finishing sequences and optional post-processing treatment are compared with industrially established reference process chains.

Laser powder bed fusion (LPBF) is an additive manufacturing technique that enables significant design freedom and high-complexity part production. However, the process requires unconventional analysis methods for surface characterization due to process-induced variations. One possible technique is to use in-situ optical tomography (OT) technique for quality control of LPBF surfaces during fabrication. In-situ characterization approach would enable better first time yield and inspection possibility of inner channels without the need of destructive testing. In this study, samples with varied angles and process parameters are produced by LPBF. Camera images are collected during the production per every process layer using the optical-tomography system. These OT images are interpreted to obtain roughness estimates of sample overhanging surfaces. OT roughness outputs are analyzed and correlated with optical coherence scanning interferometry (CSI) measurements. The relationship between OT surface roughness estimates and optical measurements for different process parameters are presented. The possibility of using an in-situ surface analysis method for the characterization of LPBF surfaces is discussed.

Nickel-based superalloys exhibit excellent corrosion resistance and mechanical strength at elevated temperatures, making them highly sought after for safety-critical applications in the aerospace, nuclear and chemical industries. However, these advantageous properties also lead to machining challenges such as extensive tool wear and surface integrity issues. Surface integrity includes aspects such as residual stress and surface microstructure, both of which are affected by thermo-mechanical loads during the cutting process. These loads are related to variables such as cutting parameters, tool material and tool geometry, etc. Understanding the relationship between these factors and surface integrity is critical to improving the quality of the machined part. This study investigates the effects of feed rate and cutting depth on the microstructure during milling of Inconel 718 both experimentally and using simulation techniques. In the experimental phase, orthogonal milling tests were performed to measure the cutting forces and temperature distribution. The results showed that the surface deformation increased at higher feed rates but decreased at lower cutting depths. The simulations showed that thermo-mechanical loads in the workpiece rim zone are responsible for the surface deformation. The simulations indicate that the mechanical loads decrease with increasing cutting depth due to the simultaneous increase in temperature. These findings provide a theoretical basis for a better understanding of the changes in surface integrity during the machining of such superalloys.

To sustain prosperous and lucrative business opportunities, companies are required to constantly evolve to remain competitive. The way this strategy emerges depends on how their offerings are positioned in the market. For example, certain companies are focusing on increasing operational efficiency to achieve improved key performance indicators, while others are exploring new ways of operating. In this paper, the latter aspect is targeted in the context of initiating remanufacturing. This research aims to describe the incentives behind initiating remanufacturing. The research was conducted through multiple case studies involving eight original equipment manufacturers that are either initiating or engaging in remanufacturing. The results show that the incentives can be grouped into five categories: (1) business development, (2) access to cores, (3) environmental reasoning, (4) preparing for regulations, and (5) technological development. These categories are conceptualised based on the experiences or visions of the case companies and are related to their short- and long-term expectations of remanufacturing.

Gaining knowledge about the sustainable context is fundamental for the success of a product development, as a lack of knowledge limits the possibilities of innovation. The contextual boundaries of a system often do not adequately describe the influence on sustainability, so that product developers are unaware of problem shifts within and between the areas of impact on sustainability. For reasons of complexity, a therefore needed holistic captured system context is insufficiently taken into account in existing approaches. Within the scope of this article, a framework for Sustainable Context Engineering is developed, that provides a formalization of a holistic sustainable system context for the analysis and synthesis of relations in product development. Furthermore, a requirements methodology based on SPES 2020 is proposed, which supports the decomposition of requirements by model-based templates via a subtractive structure. This promotes communication and situational awareness among developers in order to influence the sustainability goals in the early phase of the product development process. Further research will be made in order to implement the approach in a model-based manner and to define a finite number of measurement parameters based on interdisciplinary sustainability models.

Lightweight design is gaining in importance for design for sustainability due to its capability to reduce weight, conserve materials, and enhance energy efficiency. However, environmental sustainability encompasses a broader spectrum, including, for instance, a responsible resource management as well as material recyclability. Despite their shared objective of optimizing resource consumption, can lightweight design indeed be substantiated as sustainable, and if so, how?

Therefore, this contribution emphasizes a systematic approach for the analysis of environmental effects caused by property changes resulting from the implementation of lightweight design strategies (system, form, material and manufacturing lightweight design) in products. Thereby, life cycle issues of the lightweight design strategies are evaluated on the basis of a holistic life cycle perspective. Finally, the interrelationships between lightweight design strategies and sustainability strategies (eco-efficiency, eco-effectiveness, and sufficiency) are discussed. In future, the presented approach supports both positive synergies as well as negative conflicts of lightweight design and design for sustainability to be efficiently and strategically evaluated throughout the design process, so that holistically optimized lightweight and sustainable products can thus be created.