[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Superhydrophobic and superoleophilic membranes for oil-water separation application: A comprehensive review

Micro milling cutters or micro mills are unique and important micro tools for fabricating miniaturised devices with sufficient geometrical and dimensional accuracy and machined surface integrity. Micro milling cutters, compared to conventional macro tools, have significantly different material removal mechanisms. They are also made of different raw materials and structures and exhibit distinctive machining characteristics and performances. Herein, we present the first comprehensive and up-to-date review of micro milling cutters in terms of their uniqueness, material removal mechanisms, materials and compositions, structures and design, fabrication techniques and machining performances, to provide adequate guidance for interested involvers. We also outline and discuss several possible future research directions to offer potential insights for the micro milling community and future researchers.

Advances in micro milling: From tool fabrication to process outcomes

During the additive manufacturing (AM) process, energy is transferred from the energy beam to the processed material. The high-energy input and uneven temperature distribution result in the high-temperature gradient, large thermal stress, and warping deformation. The scanning strategy, one of the representative AM processing parameters, plays an important role in the microstructures, mechanical properties, and residual stresses of 3D printed parts. It is necessary to review the current state of research about scanning strategy in additive manufacturing, and this paper seeks to address this need. This review mainly focuses on the scanning strategies in selective laser melting process. Various scanning strategies and their effects on mechanical properties, microstructures, and residual stresses of selective laser melted parts are summarized. Finally, some suggestions on the optimization of scanning strategy for better performance are provided based on the above analysis.

https://link.springer.com/content/pdf/10.1007/s00170-021-06810-3.pdf

Scanning strategy in selective laser melting (SLM): a review

Prior to any practical application, brittle material components may need to be machined to a high degree of precision in order to avoid functional breakdown as well as to maintain exacting surface dimensional integrity and retain strength. This usually means grinding in the ductile region. Optimization of the grinding process can shorten manufacturing time and cost and prolong component lifetime. This article reviews the current state of the art of ductile grinding and outlines the underlying science behind pertinent machining events. Engineering aspects of the grinding process will be surveyed, with consideration of wheel requirements and of such variables as grit characteristics, strain rate and temperature. Attention will be given to the fundamental role of removal processes from individual and cumulative microcontacts, using nanoscratch mechanics as the underlying basis for analysis. The critical influence of diversity in material microstructures in determining local deformation mechanisms and subsequent material removal will be highlighted. Practical requirements for optimal ductile grinding will be indicated.

Science and art of ductile grinding of brittle solids

In this paper nanosecond laser machining process was developed to improve the hydrophobicity of AISI 316L stainless steel surface. A geometrical model of laser machined Gaussian micro hole, together with constrain conditions, was established for the first time to predict surface contact angle and optimize structure geometries for maximizing its hydrophobicity. The effects of processing laser power and pitch of microstructures on the topography of the machined surface were investigated through laser machining experiment. Subsequently, the water droplet contact angle was measured to evaluate the hydrophobicity of different specimens. Results show that under the laser power of 10 W and 14 W, with the increase of the pitch of microstructures, the contact angle increases until it reaches its peak value then drops gradually. Under the large pitch of microstructure, the contact angle will increase with the increase of the processing laser power. Under the same pitch of microstructure, the contact angle will increase with the increase of ten-point height of surface topography, Sz which is a better parameter than Sa (arithmetical mean height) to characterise hydrophobicity of surface with Gaussian holes. This study shows that large Sz is an essential condition to form the stable and robust Cassie–Baxter state, i.e. a condition to achieve superhydrophobicity. The comparison between the predicted and measured contact angles in experiments shows that the proposed model can accurately predict contact angle and optimize the geometries of the microstructure to achieve maximum hydrophobicity.

Superhydrophobic structures on 316L stainless steel surfaces machined by nanosecond pulsed laser

The research and application of high speed metal cutting (HSMC) is aimed at achieving higher productivity and improved surface quality. This paper reviews the advancements in HSMC with a focus on the material removal mechanism and machined surface integrity without considering the effect of cutting dynamics on the machining process. In addition, the variation of cutting force and cutting temperature as well as the tool wear behavior during HSMC are summarized. Through comparing with conventional machining (or called as normal speed machining), the advantages of HSMC are elaborated from the aspects of high material removal rate, good finished surface quality (except surface residual stress), low cutting force, and low cutting temperature. Meanwhile, the shortcomings of HSMC are presented from the aspects of high tool wear rate and tensile residual stress on finished surface. The variation of material dynamic properties at high cutting speeds is the underlying mechanism responsible for the transition of chip morphology and material removal mechanism. Less surface defects and lower surface roughness can be obtained at a specific range of high cutting speeds, which depends on the workpiece material and cutting conditions. The thorough review on pros and cons of HSMC can help to effectively utilize its advantages and circumvent its shortcomings. Furthermore, the challenges for advancing and future research directions of HSMC are highlighted. Particularly, to reveal the relationships among inherent attributes of workpiece materials, processing parameters during HSMC, and evolution of machined surface properties will be a potential breakthrough direction. Although the influence of cutting speed on the material removal mechanism and surface integrity has been studied extensively, it still requires more detailed investigations in the future with continuous increase in cutting speed and emergence of new engineering materials in industries.

Advancements in material removal mechanism and surface integrity of high speed metal cutting: A review

Inconel 718 (IN-718) has excellent mechanical and chemical properties at high temperature, which has been widely applied in aerospace, ocean, and chemical industries. Meanwhile, the super high temperature properties lead to its poor machinability and machined surface integrity. Good machinability and surface integrity of IN-718 have always been challenging topics in the field of mechanical machining. The machinability and surface integrity of IN-718 was reviewed in this paper. The influences of chemical elements, microstructure, cutting parameters, and cutting environments on machinability were discussed. Cutting force, specific energy, and tool wear were analyzed as the main factors of machinability evaluation index. The characteristics of machined surface integrity including surface morphology (such as surface defects and surface roughness), microstructure modifications (such as plastic deformation, grain size, and white layer) and mechanical properties (such as microhardness and residual stress) related to IN-718 were presented. The state-of-the-art of machining IN-718 showed that most current research focused on its poor machinability and surface integrity in the aspect of material characteristics. There is lack of research on machinability from the viewpoint of geometrical structure of the part to be machined. Therefore, it is important to further study the manufacturability (the difficulty of the process from material to part) of IN-718 components with complex geometrical surface and profiles to achieve shape control and precise design.

Recent progress of machinability and surface integrity for mechanical machining Inconel 718: a review

Laser-assisted grinding (LAG) is a promising method for cost-effective machining of hard and brittle materials. Knowledge of material removal mechanism and attainable surface integrity are crucial to the development of this new technique. This paper focusing on the application of LAG to Reaction Bonded (RB)-SiC ceramics investigate the material removal mechanism, grinding force ratio and specific grinding energy as well as workpiece surface temperature and surface integrity, together with those of the conventional grinding for comparison. Response surface method and genetic algorithm were used to optimize the machining parameters, achieving minimum surface roughness and subsurface damage, maximum material removal rate. The experiments results revealed that the structural changes and hardness decrease enhanced the probability of plastic removal in LAG, therefore obtained better surface integrity. The error of 3-D finite element simulation model that developed to predict the temperature gradient produced by the laser radiation is found to be within 2.7%–15.8%.

Yukui Cai

Papers

Superhydrophobic structures on 316L stainless steel surfaces machined by nanosecond pulsed laser

Advancements in material removal mechanism and surface integrity of high speed metal cutting: A review

Recent progress of machinability and surface integrity for mechanical machining Inconel 718: a review

Material removal mechanism of laser-assisted grinding of RB-SiC ceramics and process optimization

Burr Controlling in Micro Milling with Supporting Material Method