Effect of laser texturing on the performance of ultra-hard single-point cutting tools

This paper investigates the cutting performance and anti-adhesive properties of textured single point polycrystalline diamond (PCD) cutting tools in machining Aluminium 6082 alloys. The micro/nano textures were first milled using a fibre laser (1064 nm wavelength) at different power intensities, feed speeds and pulse durations, and finally characterised using scanning electron microscopy, white light interferometry and energy dispersive X-ray spectroscopy. The effect of different textures on the cutting performance was investigated in turning tests under dry cutting conditions. The test was stopped at regular lengths of cut to allow analysis of height of adhesion through 3D white light interferometry. The data processing of the cutting forces and the microscopical characterisation of the tested cutting tools enabled the evaluation of the effects of texture design, friction coefficient and adhesive properties. The results indicated that feed force in tools with grooves perpendicular to the chip flow direction (CFD) was more stable (20-40N) than the benchmark (6-41N). Similarly, the thrust force for tools with grooves parallel to CFD and grooves perpendicular to CFD showed a homogeneous trend fluctuating between 60N to 75N as compared to the benchmark (ranging between 73N to 90N). For texture depth in the order of 260 nm and post process roughness in the order of tens of nanometers a reduction of average friction coefficient (0.28±0.14) was reported when using lasered inserts with grooves parallel to the chip flow direction compared to the benchmark tools (0.34±0.26) corroborated by reduced stiction of workpiece material on the rake face. In machining via textured tools with grooves perpendicular to CFD, the cutting forces were reduced by 23%, and the surface quality of the machined workpiece was improved by 11.8%, making this geometry the preferred choice for finishing applications. Using grooves parallel to CFD reduced the cutting forces by 11.76%, adhesion by 59.36% and friction coefficient by 14.28%, however it increased the surface roughness of the machined workpiece, making this geometry suitable for roughing operations. For the first time, laser manufacturing is proposed as a flexible technique to functionalise the geometrical and wear properties of PCD cutting tools to the specific applications (i.e. roughing, finishing) as opposed to the standard industrial approach to use microstructurally different PCDs (i.e. grain size and binder%) based on the type of operation. </div

ENHANCEMENT OF TOOL-LIFE OF HARD TURNING PROCESS VIA CRYOGENIC COOLANT AND MICROPATTERNED INSERT

Department of Mechanical EngineeringHigh hardness and high strength of materials are essential for advanced engineering applications to guarantee the safety and durability of the manufactured products. The hard turning process enables the machining of hardened materials which makes it one of the most widely used operation in automobile and heavy machinery industries. However, the problem with the hard turning is extreme machining conditions such as high cutting force and temperature generation leading to accelerated tool wear. Cubic boron nitride (CBN) is the essential insert of the hard turning operations. However, due to the higher production cost of CBN cutting tool, its performance should be maximized to achieve the higher machining and economic efficiency. The cryogenic liquids were mainly applied to machining of difficult-to-cut materials. The cryogenic liquids such as liquid nitrogen and carbon dioxide have been used as the cutting fluids to remove the heat generated in the cutting zone. Furthermore, some researchers have found that the textured (or patterned) functional surfaces can improve the frictional and tribological conditions between the two contacting surfaces. Hence, a proper development of the textured surfaces on the cutting tool can enhance the machining performances in the hard turning process. This dissertation presents a framework for the development of a numerical model and experimental investigations for enhancing the performance of the hard turning process using a cryogenic coolant and micropatterned tool. The first of this research presents the developed cutting model based on the modified Oxley???s theory. The cooling effects of cryogenic coolant were included in the model by implementing the proper heat transfer coefficient. Thermal effects generated in the primary and secondary zones were also modeled using the moving heat source technique. The model provides the predictions of cutting force, temperatures and tool wear, which were validated by experimental works. It was found that the use of LN2 coolant can reduce the effect of thermal softening in secondary deformation zone, which in turn increases the cutting forces. However, the cryogenic cooling mainly contributed the decrease in the diffusive and abrasive wear mechanisms to the improvement of tool life. The tool wear of CBN cutting tool was reduced by 20~34% in cryogenic cooling condition as compared to dry condition. Furthermore, finite element method (FEM) simulations were used to analyze the various pattern geometries and dimensions of micropatterned inserts. The simulation results showed that the micopatterned tool can decrease the stress distribution, force, and friction in the tool-chip interfaces. When the perpendicular and parallel type micropatterned tool having 100 ????m edge distance, 100 ????m pitch size and 50 ????m in height was used, the force and the friction was reduced by 6% and 25%, respectively. The experiments were conducted using micropatterned tool for the hard turning process and the variations in the chip morphology, cutting force, friction, and tool wear were analyzed. The results showed that the micropatterned tool was able to reduce the forces by 18.7%, friction by 34.3% and tool wear by 11.4% within the given ranges of experimental conditions. The model and the experimental findings of this research can be beneficial for the enhancing efficiency of the hard turning processes used in different industries. The techniques developed in this work can be further extended to see its applicability in other cutting operations such as drilling and milling.ope

Influence of micro-textures on cutting insert heat dissipation

Metal machining is one of the most important manufacturing processes in today’s production sector. The tools used in machining have been developed over the years to improve their performance, by reducing the cutting forces, the friction coefficient, and the heat generated during the cutting process. Several cooling systems have emerged as an effective way to remove the excessive heat generated from the chip-tool contact region. In recent years, the introduction of nano and micro-textures on the surface of tools has allowed to further improve their overall performance. However, there is not sufficient scientific data to clearly show how surface texturing can contribute to the reduction of tool temperature and identify its mechanisms. Therefore, this work proposes an experimental setup to study the tool surface characteristics’ impact on the heat transfer rate from the tools’ surface to the cooling fluid. Firstly, a numerical model is developed to mimic the heat energy flow from the tool. Next, the design variables were adjusted to get a linear system response and to achieve a fast steady-state thermal condition. Finally, the experimental device was implemented based on the optimized numerical model. A good agreement was obtained between the experimental tests and numerical simulations, validating the concept and the implementation of the experimental setup. A square grid pattern of 100 μm × 100 μm with grooves depths of 50, 100, and 150 μm was introduced on cutting insert surfaces by laser ablation. The experimental results show that there is a linear increase in heat transfer rate with the depth of the grooves relatively to a standard surface, with an increase of 3.77% for the depth of 150 μm. This is associated with the increase of the contact area with the coolant, the generation of greater fluid turbulence near the surface, and the enhancement of the surface wettability.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant 2020.07155.BD and by the project POCI-01-0145-FEDER-030353 (SMARTCUT). Additionally, this work was supported by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020

Book of Abstracts of 11th Iberian Conference on Tribology

info:eu-repo/semantics/publishedVersio

Investigation on machinability of aluminum 7075 under dry environment

Aluminum is a light and soft material that is difficult to machine. It is the most produced non-ferrous metal and undergoes extensive machining for the development of a wide range of products. Advances in industry inspire the need to find sustainable ways of machining aluminum and its alloys using conventional machining processes. In the study reported in this paper, two sets of experiments were conducted to investigate the machinability of aluminum 7075 using a plain carbide tool under a dry environment, i.e., no lubrication. In the first set, four rough experiments were conducted where three important machining parameters, i.e., cutting speed CS (115-495 RPM), depth of cut DOC (0.8-1.5 mm), and Feed rate FR (0.08-0.2 mm/rev) have been varied at two levels each to check the behavior of responses or machinability indicators, i.e., surface roughness and tool wear, at machining parameters' highest and lowest values. Based on the results of the first set of experiments, the ranges and levels of parameters have been fixed in the second set for a detailed study of the machinability of aluminum. A total of nine experiments based upon Taguchi's robust design of experiment technique with orthogonal array L9 have been conducted where an additional machining parameter, i.e., machining time MT, has been introduced. The effect of machining parameters on tool wear and surface roughness has been studied in detail, and it is found that the dry machining of aluminum is possible without the early failure of the tool. Dry machining with low values of CS, DOC, FR, and medium MT is desirable for better machinability, i.e., minimum roughness and tool wear, an optimum combination of machining parameter cutting speed-115 RPM, depth of cut-0.8 mm, feed rate-0.12 mm/rev, and machining time-90 seconds. The findings of the present work will assist engineers and researchers in attaining quality, productivity, and sustainability while manufacturing parts and components from aluminum to be used in the automotive, defense, and aerospace sectors

BIODEGRADABLE MEDICAL DEVICE HAVING AN ADJUSTABLE DEGRADATION RATE AND METHODS OF MAKING THE SAME

Disclosed herein are biodegradable medical devices comprising biodegradable material (e.g., magnesium-calcium alloys) having an adjustable rate of degradation that can be used in various applications, including, but not limited to, drug delivery applications, cardiovascular applications, and orthopedic applications to make biodegradable and biocompatible devices. Also disclosed herein are methods of making biodegradable medical devices comprising biodegradable materials by using, for instance, hybrid dry cutting/hydrostatic burnishing

Study of Tribological Properties of Laser Micro-Texturing Titanium Surfaces under Lubrication with Protic Ionic Liquids

Adding micro textures by laser texturing technology to one or both sliding surfaces of relative motion has been recently studied as an environmentally friendly and efficient way to improve tribological behaviors of metals, including the reduction of friction and wear. Meanwhile, protic ionic liquids are gradually gaining increasing attention as neat lubricants and lubricant additives because of their simple synthetic procedures where the halogen elements can be easily avoided from their molecular components. The eco-friendly protic ionic liquids can be strongly adsorbed on the substrate surfaces to form ordered lubricant films which prevent the rubbing pair from direct contact. Also, protic ionic liquids may have tribo-chemical reactions with the contact materials to generate the tribo-layer on the top of the surface which may be responsible for good tribological performance. This study focuses on the influence of laser micro textures on the tribological performance of titanium alloy—Ti6Al4V lubricated by polyalphaolefin (PAO) 40 and its mixture of 2-hydroxyethylammonium 2-ethylhexanoate (Eet). Multiple texture types are created by varying the energy density of pulse and the distance between dimples. The parameter adaptations modify the outer layers of the Titanium alloy with specific topographies and properties, and the microstructural modifications and oxidation processes lead the textured surfaces with different surface roughness and wettability. A custom-designed reciprocating ball-on-flat tribometer was used to assess the tribological performance of the textured surfaces at room temperature. The wettability of these tribological systems is characterized by dropping lubricants on textured and untextured surfaces to measure the contact angle. The friction coefficient and wear volume of textured surfaces are decreased compared to the untextured surface under different lubricant conditions. Compared to the traditional lubricant – PAO40, when employing protic ionic liquid mixture, the more significant reduction of friction and wear volume can be observed, especially for the textured surface with variations of energy densities. It is believed that both laser surface texturing and the use of PILs have a positive effect to improve the tribological properties of titanium alloys under a variety of extreme conditions. Meanwhile, the combination of laser texturing technology and protic ionic liquid has been proved as a more efficient way to reduce the frictional behavior of titanium alloys, which exhibits the great potential of using protic ionic liquid for the titanium applications to extend their tribology applications in aerospace and other fields

Study on cutting performance of SiCp/Al composite using textured YG8 carbide tool

Precision machining of SiCp/Al composites is a challenge due to the existence of reinforcement phase in this material. This work focuses on the study of the textured tools’ cutting performance on SiCp/Al composite, as well as the comparison with non-textured tools. The results show that the micro-pit textured tool can reduce the cutting force by 5–13% and cutting length by 9–39%. Compared with non-textured tools, the cutting stability of the micro-pit textured tools is better. It is found that the surface roughness is the smallest (0.4 μm) when the texture spacing is 100 μm, and the residual stress can be minimized to around 15 MPa in the case of texture spacing 80 μm. In addition, the SiC particles with size of around 2–12 μm in the SiCp/Al composite may play a supporting role between the texture and the chips, which results in three-body friction, thereby reducing tool wear, sticking, and secondary cutting phenomenon. At the same time, some SiC particles enter into the micro-pit texture, so that the number of residual particles on the surface is reduced and the friction between the tool and the surface then decreases, which improves the surface roughness, and reduces the surface residual stress.TU Berlin, Open-Access-Mittel - 202

Microstructure and wear mechanisms of textured CVD alumina and titanium carbonitride coatings

The aim of this thesis is to find the reasons behind how the wear performance of hard coatings produced by chemical vapor deposition (CVD) is influenced by their texture, as this is today not fully known. Therefore, differently textured coatings were synthesized, and subsequently analyzed both before and after specially designed machining tests. The main research methods used are analytical electron microscopy, transmission Kikuchi diffraction, electron backscattered electron diffraction, X-ray diffraction, atom probe tomography and Schmid factor simulations.The microstructure, texture and facet development of the as-deposited α-Al2O3 coatings were determined, and the effect of catalyzing gas and diffusion of heavy elements from the substrate were described. After machining tests, terrace formation at the edges is attributed to crystallographic dependent etching. More deformation occurs for the textured coatings in the transition zone, with an associated sub-surface dislocation formation coupled to the number of activated slip systems. The surface morphology in the sliding zone is mainly affected by the surface developed in the previous zones. For the (0001)-textured coating, the observed low wear rate is attributed to homogeneous basal-slip dominating plastic deformation, while for the (01-12) and (11-20) textures the main deformation mechanism is heterogeneous plastic deformation, causing micro-rupture and abrasion, leading to higher wear-rates.For titanium carbonitride coatings, the (211)-textured coating exhibits a more significant and non-uniform deformation than (110), which is related to a heterogeneous response of the relevant slip system.In conclusion, the results presented in this thesis reveal the complex relationships between local wear mechanisms and coating texture. This fundamentalunderstanding can facilitate future development of texture-controlled CVD α-alumina and titanium carbonitride coatings, with the potential of further improving the performance of coated cutting tools