Micromilling: material microstructure effects

Proceedings on Engineering Sciences

Development of micro-devices parts is intensified with developments in medical device and energetic industry. In production of micro-parts (micro-pump, micro-gears, micro-manipulators, etc.), a wide range of engineering materials is encountered. Strict requirements are set in terms of characteristic of micro-parts machined surfaces, such are low surface roughness, advanced tribological characteristic, etc. In this paper is analysed possibilities of different metallic materials mechanical micro-machining. The analysis includes the analysis of the generating and characteristics of the machined surfaces, and influence of a whole set of parameters on surface characteristic. The results showed the benefits of mechanical micromachining and proved that it can achieve satisfactory results of the surface characteristics indicators.

2015

The objective of this paper is to experimentally investigate the micro-machinability of stainless steel 316 under both dry and minimum quantity lubrication conditions. The machinability was assessed in terms of tool wear, tool life, cutting forces and surface finish. The tool life was characterised as the amount of material removed, instead of the conventional cutting times. The machining performance under MQL is superior to the dry machining for both process conditions in terms of the tool life. The magnitude of the machining forces showed cyclic pattern for both MQL and dry machining. The SEM images and the cutting force signals suggested that the dominant mode of the tool wear in micro-milling is edge chipping and abrasive wear at the tool tip. The surface roughness at the bottom of the slots improved significantly with the application of MQL for all levels of the tool wear.

Journal of Materials Science & Technology, 2012

He has 25 years of teaching and research experience in manufacturing, materials and mechanical engineering with special emphasis on Machining & Tribology. Currently, he has also interest in sustainable manufacturing and industrial engineering. He is the editor in chief of six international journals, guest editor of journals, books editor, book series editor and scientific advisory for many international journals and conferences. Presently, he is an editorial board member of 20 international journals and acts as a reviewer for more than 70 prestigious ISI Web of Science journals. In addition, he has also published as an author and co-author more than 30 book chapters and 350 articles in journals and conferences (more than 170 articles in ISI Web of Science, h-index 21). The trend towards miniaturization has increased dramatically over the last decade, especially within the fields concerned with bioengineering, microelectronics, and aerospace. Micromilling is among the principal manufacturing processes which have allowed the development of components possessing micrometric dimensions, being used to the manufacture of both forming tools and the final product. The aim of this work is to present the principal aspects related to this technology, with emphasis on the work material requirements, tool materials and geometry, cutting forces and temperature, quality of the finished product, process modelling and monitoring and machine tool requirements. It can be noticed that size effect possesses a relevant role with regard to the selection of both work material (grain size) and tooling (edge radius). Low forces and temperature are recorded during micromilling, however, the specific cutting force may reach high values because of the ploughing effect observed as the uncut chip thickness is reduced. Finally, burr formation is the principal concern with regard to the quality of the finished part.

Research in this report is preliminary experimental research on high performance milling and micro-milling of hard-to-machining materials (tool steels), constructive materials (aluminum) and materials for EDM electrodes (copper). The main idea of future research is possibility of micro-milling of hard-to-machine materials on precision high-speed milling machines. It will be done in order to avoid of non-conventional machining processes, which are dominantly used for micro-structures in practice today. In some cases, using of non-conventional processes (EDM, LBM, etc.) for micro-structures require large investments in machine systems.

Production Engineering, 2009

The occurrence of tool vibrations in the micromilling process is undesirable because of its negative influence on the quality of microstructures. Due to the small dimensions of the undeformed chip parameter, the influence of the cutting edge on the chip formation and on the regenerative effect seems to be larger than in macrodimensions. Within this paper the results of an experimental investigation with micro end-milling cutters (d = 1 mm) are presented. Additionally, the influences of the cutting edge radius, the corner radius, and the feed per tooth on the tool vibration trajectories, the process forces, and chatter and its causes are discussed.

Micromilling concerns the machining of parts with features that range from tens of micrometres to a few millimetres in size, with chiploads usually varying from below one micron to a few microns. Due to the fact that most commonly used materials have crystalline grains similar in size to chiploads, the cutting process sometimes takes place inside the individual grain itself. This phenomenon can be considered one of the main differences between microcutting and macrocutting. Recently it has been revealed that microstructure, especially grain size, has a dominant effect on the quality of the machined part. So far, there has been no detailed study of the influences of microstructure in the micromilling of polycrystalline materials. This paper reviews previous work on this topic. Special attention is given to surface finishes and burrs, as these are important issues for micro machined parts. The paper concludes with a summary of some of the key research problems in micromilling and suggests a systematic study of the effects of microstructure on surface generation and burr formation in the micromilling of polycrystalline materials.

2011

This paper reports an investigation of material microstructure effects on tool wear in micro-scale machining of multi-phase materials. A new generic approach is proposed to estimate the tool wear that utilises empirical data about the effects of micro milling process on cutting edge radius. Experiments were conducted to study independently the influence of two main phases in steel, pearlite and ferrite, on tool wear under different cutting conditions. Based on this empirical data two regression models were created to estimate the increase of cutting edge radius when machining single and multi-phase steels. To validate the models they were applied to predict the tool wear when machining two different multi-phase steel samples. The results showed a good agreement between the estimated and the actual tool wear.

Wear, 2011

An approach to defer tool wear in the micromilling process is investigated in this paper. Three different microstructure patterns, i.e. a number of micro-scale grooves which are in the directions of horizontal (0◦), perpendicular (90◦) and sloping at 45◦ to the cutting edge of the rake face, are generated by focused ion beam on three identical end mill cutters. The effects of these microstructures on tool wear resistance performance are investigated through three sets of slot milling trials on a NAK80 by using a CNC milling machine. Cutting forces are measured by a Kistler dynamometer. The machined surface roughness (Ra) is obtained by a white light interferometer. The milling cutters are inspected by a Scanning Electron Microscope (SEM) after each set of slot milling trial. The measurement results show that low cutting force is achieved when the microstructures are in the perpendicular direction rather than in the horizontal direction to the cutting edge is used. The tool with perpendicular microstructures to its cutting edge possesses the best tool wear resistance performance against other tested microstructured tools and the normal tool.

Journal of Machine Engineering, 2020

The article presents the results of measurements of the geometric structure of the surface after micro end-milling. In the experiments, coated monolithic super micrograin cemented carbide micro end mills with 2 flutes were employed. The machined parts were additively made of CoCr alloy using Selective Laser Melting technology (SLM). Analyzed variables were the volumetric density of energy supplied by the laser during the SLM process and the feed rate during micro-milling. The results showed a strong influence of SLM process parameters on the surface roughness, which, according to the authors, results from the significant variability of the mechanical properties of the material as a function of the volumetric density of energy supplied during melting.

Precision Engineering, 2019

Micromachining is a key technology in contemporary society, due to the new requirements of the modern industry. The need of higher accuracy and precision, even for details on the finished product (which may also have very small dimensions), can be fulfilled only with micromechanical machining. Among this family of technologies, micromilling is one of the most important and widespread: the potential of this process is due to the great precision level that can be obtained, when machining high strength materials too. One of the main challenges launched by micromilling concerns the understanding of the processes that generate breakages and deterioration of the tool, and the study of their causes, that are usually different from those observed in conventional milling processes, for which the definition and the prediction of the tool-life are regulated by the ISO-8688 standard (part 1 and 2). This standard is not referred to micromilling and a dedicated regulation has not been compiled yet. In this article the results of an experimental campaign, made to investigate the tool wear in micromilling process, are presented. The aim of the work is to provide fundamental knowledge for the development of a future standard that can fill the normative gap. In particular, results describe that the flank wear evolution follows the typical trend characterized by the decreasing, constant and increasing tool wear slope regions. Cutting force, roughness and tool corner radius evolution are related with tool wear. In particular, a statistical analysis based on the Pearson correlation coefficient is presented in order to quantify the correlation between the flank wear and the considered parameters. Details about the influence of feed rate and mill type in flank wear evolution are also provided. Furthermore, results show that flank wear could actually be used for a tool-life criterion in micromilling processes.

Procedia Technology, 2016

Ordered array of dots or grooves induces special functionality to the surface. Two types of textures viz. linear (perpendicular to the chip flow direction) and square were developed on plain WC inserts using focused ion beam machining. The inserts were coated with MoS 2 solid lubricants using pulsed DC magnetron sputtering. Dry turning tests were carried out on aluminum alloy (Al 6063) work material. Textured tools are found to be more effective in reducing the cutting forces and sticking behaviour of the work material as compared to the non-textured tools. The novel square textured tools performed better than the linear textured tools in terms of reduced cutting forces and improved surface finish. A reduction of about 30% in cutting forces was observed with square textured tools and that with the linear textured tools was about 20% as compared to the non-textured tools. The reduction in cutting forces and the associated change in sticking behaviour are attributed to the reduction in tool-chip contact area and reduced friction at the tool-chip interface owing to the improved lubrication provided by the interlayer of solid lubricant. Textures are functioning as reservoirs of the solid lubricant which in turn reduces the friction at the chip-tool interface.

micromachines, 2019

This paper presents the micromanufacturing of aluminum (Al) alloy microrods using micro turning as a competing process to other nontraditional micromachining methods. In that regard, the challenges in such manufacturing have been identified and overcome. The strategies of step-by-step cutting have also been delineated. In addition, the influence of step size and step length on the cutting and thrust forces were investigated. The chip morphology for micromachining was examined using scanning electron microscopic imagery. The safe dimension of the microrod was calculated and, subsequently, used to fabricate microrod, conical tip rod, and grooved rod from 3 mm long and 1.5 mm diameter rod using an appropriately coded computer numerical control (CNC) micromachining center. Our results showed that the thrust force was responsible for part deflection, emphasizing the necessity for computing safe dimensions. At shallow step sizes, the thrust force was more dominant, causing plastic deformation associated with rubbing and burnishing. The chips produced were irregular and sliced in nature. Conversely, at high step sizes, the cutting force superseded the thrust force, resulting in chips that were spread more along the width as opposed to the depth. The chips also had a smoother interacting surface. Finally, micro turning was successfully implemented to manufacture milli-scale structures (i.e., 3 mm long) with micro features (150 to 230 µm diameter) on aluminum alloy materials.

Advances in Manufacturing, 2020

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 d...

Micro-milling of metal structures with "thin" features represents a major challenge towards broadening the use of this technology in a range of micro-engineering applications, for example in producing multi-channel micro-structures, housings for mechanical micro-devices and surgical instruments. The most common thin features seen in micro- engineering products are ribs and webs. This research identifies the main factors affecting the reliability of micro-milling technology when employed for the machining of micro-components incorporating thin features. The general principles that should be followed in designing machining strategies for such features are discussed in the paper. Taking these general principles into account, new strategies are proposed to reduce the negative effects of identified factors on part quality and at the same time to overcome some of the problems associated with the use of conventional machining strategies for micro- milling of ribs and webs. To imp...