In this study, an eco-friendly electrolyte for electropolishing tungsten and the minimum material removal depth on the electropolished tungsten surface are investigated using an electrochemical etching method. Using a concentrated acid electrolyte, the polarization curve and current density transient are observed. For a NaOH electrolyte, the effects of interelectrode gap and electrolyte concentration on electropolishing are investigated. The differences in electropolishing characteristics are compared among different electrolyte types. Microholes are etched on the electropolished tungsten surface to determine the minimum material removal depth on the tungsten surface. Experimental results indicate the color effect due to a change in the thickness of the oxide film on the tungsten surface after electropolishing with a concentrated acid electrolyte. The surface roughness decreases with the interelectrode gap width owing to the increased current density when using the NaOH electrolyte. However, the electropolishing effect is less prominent with a significantly smaller gap because the generated bubbles are unable to escape from the narrow working gap in time. A material removal depth of less than 10 nm is achieved on the tungsten surface in an area of diameter 300 µm, using the electrochemical etching method.

The World Health Organization emphasized the importance of goggles and face shields for protection of medical personnel at the outbreak of the COVID-19 pandemic. Unsurprisingly, almost all countries suffered from a critical supply shortage of goggles and face shields, as well as many other types of personal protective equipment (PPE), for a long period, owing to the lack of key medical material supplies and the inefficiency of existing fabrication methods arising from the need to avoid crowds during the outbreak of COVID-19. In this paper, we propose a novel combined shield design for eye and face protection that can be rapidly fabricated using three-dimensional printing technology. The designed prototype eye-face shield is accessible to the general public, offering more possibilities for yield improvement in PPE during emergent infectious disease events such as COVID-19.

Auxetic structures are a special class of structural components that exhibit a negative Poisson's ratio (NPR) because of their constituent materials, internal microstructure, or structural geometry. To realize such structures, specialized manufacturing processes are required to achieve a dimensional accuracy, reduction of material wastage, and a quicker fabrication. Hence, additive manufacturing (AM) techniques play a pivotal role in this context. AM is a layer-wise manufacturing process and builds the structure as per the designed geometry with appreciable precision and accuracy. Hence, it is extremely beneficial to fabricate auxetic structures using AM, which is otherwise a tedious and expensive task. In this study, a detailed discussion of the various AM techniques used in the fabrication of auxetic structures is presented. The advancements and advantages put forward by the AM domain have offered a plethora of opportunities for the fabrication and development of unconventional structures. Therefore, the authors have attempted to provide a meaningful encapsulation and a detailed discussion of the most recent of such advancements pertaining to auxetic structures. The article opens with a brief history of the growth of auxetic materials and later auxetic structures. Subsequently, discussions centering on the different AM techniques employed for the realization of auxetic structures are conducted. The basic principle, advantages, and disadvantages of these processes are discussed to provide an in-depth understanding of the current level of research. Furthermore, the performance of some of the prominent auxetic structures realized through these methods is discussed to compare their benefits and shortcomings. In addition, the influences of geometric and process parameters on such structures are evaluated through a comprehensive review to assess their feasibility for the later-mentioned applications. Finally, valuable insights into the applications, limitations, and prospects of AM for auxetic structures are provided to enable the readers to gauge the vitality of such manufacturing as a production method.

Micro-milling is a precision manufacturing process with broad applications across the biomedical, electronics, aerospace, and aeronautical industries owing to its versatility, capability, economy, and efficiency in a wide range of materials. In particular, the micro-milling process is highly suitable for very precise and accurate machining of mold prototypes with high aspect ratios in the microdomain, as well as for rapid micro-texturing and micro-patterning, which will have great importance in the near future in bio-implant manufacturing. This is particularly true for machining of typical difficult-to-machine materials commonly found in both the mold and orthopedic implant industries. However, inherent physical process constraints of machining arise as macro-milling is scaled down to the microdomain. This leads to some physical phenomena during micro-milling such as chip formation, size effect, and process instabilities. These dynamic physical process phenomena are introduced and discussed in detail. It is important to remember that these phenomena have multifactor effects during micro-milling, which must be taken into consideration to maximize the performance of the process. The most recent research on the micro-milling process inputs is discussed in detail from a process output perspective to determine how the process as a whole can be improved. Additionally, newly developed processes that combine conventional micro-milling with other technologies, which have great prospects in reducing the issues related to the physical process phenomena, are also introduced. Finally, the major applications of this versatile precision machining process are discussed with important insights into how the application range may be further broadened.

The limitations of significant tool wear and tool breakage of commercially available fluted micro-end mill tools often lead to ineffective and inefficient manufacturing, while surface quality and geometric dimensions remain unacceptably poor. This is especially true for machining of difficult-to-machine (DTM) materials, such as super alloys and ceramics. Such conventional fluted micro-tool designs are generally down scaled from the macro-milling tool designs. However, simply scaling such designs from the macro to micro domain leads to inherent design flaws, such as poor tool rigidity, poor tool strength and weak cutting edges, ultimately ending in tool failure. Therefore, in this article a design process is first established to determine optimal micro-end mill tool designs for machining some typical DTM materials commonly used in manufacturing orthopaedic implants and micro-feature moulds. The design process focuses on achieving robust stiffness and mechanical strength to reduce tool wear, avoid tool chipping and tool breakage in order to efficiently machine very hard materials. Then, static stress and deflection finite element analysis (FEA) is carried out to identify stiffness and rigidity of the tool design in relation to the maximum deformations, as well as the Von Mises stress distribution at the cutting edge of the designed tools. Following analysis and further optimisation of the FEA results, a verified optimum tool design is established for micro-milling DTM materials. An experimental study is then carried out to compare the optimum tool design to commercial tools, in regards to cutting forces, tool wear and surface quality.

This paper presents the design and fabrication of an aluminium oxide cutting insert with an internal cooling channel formed through an additive manufacturing method. The formed insert is subjected to a controlled densification process and analysed through a series of characterisation investigations. The purpose of the study is to develop the design concept and analyse the forming and sintering parameters used in the lithographic ceramic manufacturing process. The results validated the feasibility of the geometrical design, providing the required structural conformity with the integrated internal feature using conditional specifications. It is confirmed that the forming parameters would affect the material properties of the green body. Furthermore, the results indicate that the heating rate and temperature variance of the de-binding and thermal treatment regime influences the microstructural growth kinetics and the quality of the densified insert. Using a novel application of liquid gallium as an internal coolant, experimental results showed a decrease in tool wear difference of 36% at  = 250 m/min, and 31% in tool wear difference at  = 900 m/min between cooling and non-cooling conditions. When external cooling was applied, the results showed at  = 250 m/min, the difference between the tool wear rates with the internal coolant relative to the external coolant was 29%. Increasing to  = 900 m/min, the results revealed a 16% tool wear difference. The results clearly indicate the potential of liquid gallium as a heat transfer agent in internal cooling applications for cutting inserts, and by extension demonstrable reduction in tool wear.