Machined Surface Research Articles

The performance of grooved turning tools under distinct cooling environments

This work investigates the performance of modified tungsten carbide inserts when turning supermartensitic stainless steel with cutting fluid and/or air jet applied in two directions: either cutting fluid under high pressure or compressed air under low pressure supplied on the back of the chip (through a hole produced near the principal cutting edge), together with either cutting fluid or compressed air, both under low pressure, directed at the clearance face. Tool performance is evaluated by means of the principal cutting force, temperature distribution (using FEM), visual evaluation of the rake face, morphology of the chips and the quality of the machined surface. The findings indicate that the groove reduces the cutting force when dry cutting. Cutting fluid applied under low pressure at the clearance face is more efficient in decreasing both the cutting force and chip temperature than cutting fluid at high pressure supplied at the back of the chip. A chrome oxide layer is formed on the chip when air jet is applied, thus leading to an unfavorable cutting condition. The simultaneous application of cutting fluid under high pressure to reach the back of the chip and compressed air supplied through the clearance face provides the best surface quality.

ИССЛЕДОВАНИЕ ДИНАМИЧЕСКОЙ УСТОЙЧИВОСТИ ТЕХНОЛОГИЧЕСКОЙ СИСТЕМЫ ПРИ ТОЧЕНИИ НЕЖЁСТКИХ ВАЛОВ

The article considers a method for suppressing regenerative vibrations when turning non-rigid shafts that improves the quality of the machined surface, tool life, equipment durability, ergonomic indica-tors of working conditions and productivity

Analysis and experimental investigation of powder concentration and stirring velocity on powder mixed electrical discharge machining performance with 3D printed electrodes

In this work, CuO mixed lemon peel dielectric is used along with the 3D printed aluminium electrodes to enhance the electrical discharge machining (EDM) performance. This work mainly focuses on improving the surface quality by optimizing the powder concentration and stirring velocity. A full factorial of 27 experiments is carried out with input parameters such as pulse off time with 3 levels (28, 58 and 98 μs), powder concentration with 3 levels (1, 2 and 3 g/L) and stirring velocity with 3 levels (900, 1800 and 2700 rpm), while keeping the current, pulse on and voltage as constant. For all trials, the output responses viz. surface roughness (SR) and material removal rate (MRR) are noted. It is evidenced that EDM performance is influenced by the stability of powder mixed dielectric. To understand the most influential input parameter and its level, analysis of variance (ANOVA) and grey relational analysis (GRA) are carried out. The output analysis exhibited that powder concentration of 2 g/L, stirring velocity of 1800 rpm and pulse off time of 28 μs as the best combination for the best quality of finish (4.72 μm) with high MRR (0.0035 g/min) than the 1 g/L PC with 900 rpm SV for the best quality finish (5.87 μm) along high MRR (0.0029 g/min) and 3 g/L PC with 2700 rpm SV for the best quality finish (5.38 μm) with high MRR (0.0030 g/min) having pulse off time of 28 μs. The experimental findings are validated with a 3D surface plot and SEM images taken on the machined surface. Also, a simulation model is built to understand the flow velocity profiles. This helps ensure the minimum stirring velocity to be maintained to enhance the stability of powder mixed dielectric.

Development of an Alternative Manufacturing Technology for Niobium Components.

Due to their physical and mechanical properties, niobium products are used in the nuclear power industry, chemical industry, electronics, medicine and in the defence industry. Traditional manufacturing technology for these products is characterized by long production cycles and significant material losses during their surface machining. This paper presents the results of a study on the fabrication of niobium products by Spark Plasma Sintering (SPS). Structural and mechanical tests were conducted on the products obtained, as well as a comparative analysis with the properties of products obtained using traditional technology. Based on the analysis of the test results obtained, recommendations were made for the sintering of Nb powders. It was found that the optimum temperature for sintering the powder is 2000 °C as the density of the material obtained is close to the theoretical density. The microstructure obtained is comparable to samples obtained by the traditional method after recrystallization annealing. Samples obtained according to the new technology are characterized by higher mechanical properties Rp0.2 and Rm and the highest hardness.

Machinability investigation and surface modification of nano-TiB2 and AlN grafted MWCNT hybridized Al 7075 matrix ternary composite through powder-mixed EDM

This paper accentuates powder-mixed electrical discharge machining (EDM) performance of a newly designed nano-TiB2 and AlN grafted multiwall carbon nano-tube (MWCNT) hybridized Al 7075 matrix ternary composite. The hybrid metal matrix composite (MMC) was fabricated through squeeze casting route, preceded by two-stage reinforcement addition, mechanical agitation, and ultrasonic treatment. EDM was carried out using cryogenic treated Cu electrode and Al2O3 particle-mixed dielectric medium. Influence of EDM process variables, that is, peak current ( I P), pulse-on time ( T ON), and powder concentration ( P C) on machinability of the hybrid MMC was studied considering material removal rate (MRR), tool wear rate (TWR), and average surface roughness ( Ra) as quality indicators. Effects of machining and Al2O3 particle addition on surface morphology of the hybrid MMC were also explored through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and elemental mapping. Results reveal elevation of MRR, reduction of TWR and improvement of surface finish during powder-mixed EDM in comparison to the non-mixed (conventional) EDM. Maximum traces of Al2O3 particle deposition was identified on the machined surfaces while using the powder concentration of 1.5 g/l within the dielectric.

Electropolishing of complex-shaped bulk metallic glasses in NaCl-ethylene glycol electrolyte

Electropolishing (EP) has been widely used to obtain good surface roughness of metallic structures; however, precisely-shaped cathodes are still necessary for the EP of bulk metallic glass (BMG) devices and components. In this work, the EP behavior of a Zr-based BMG was investigated using a plain steel cathode in NaCl-ethylene glycol electrolyte. The recast layer of wire electrical discharge machined (WEDMed) BMG surfaces with crystallization was effectively removed through the EP process, restoring the surface properties of BMGs. The effects of processing parameters, such as voltage, temperature, time, and electrolyte concentration, on the EP performance were explored, and the optimal EP parameters were determined. The EP mechanisms were discussed, where pitting formation was found to consist of three stages. Finally, the EP of a curved BMG part was successfully achieved based on the optimized processing parameters, further validating the feasibility to electropolish complex-shaped BMG structures using direct current (DC) power and NaCl-ethylene glycol electrolyte.

Study on the grinding surface quality of CNTs/2009AL composite material based on minimum quantity lubrication

Carbon nanotube aluminum matrix (CNTs/AL) composites are ideal lightweight and high-strength materials due to their excellent properties. However, the research on CNTs/AL composites only stays in the simulation and preparation stages, and no grinding research has been carried out. Revealing the grinding mechanism of CNTs/AL composites has far-reaching significance for the development of high-end equipment industries such as aerospace. Taking CNTs/2009AL composites as the research object, a minimum quantity lubrication (MQL) flat grinding platform was built for comparing the surface quality and defects of dry grinding and MQL grinding. The experimental results show that grinding wheel velocity was the grinding parameter that had the greatest influence on surface roughness in dry grinding and MQL grinding. The subsurface defects of dry grinding mainly included microcracks, burrs, pits, coatings, cavities, etc., and the rebound phenomenon of agglomerated carbon nanotubes. The subsurface defects of MQL grinding were only burrs and pits. The surface coating phenomenon of dry grinding increased with the increase in grinding wheel velocity, and the surface quality was improved. MQL grinding could significantly reduce grinding heat, reduce friction, and make the machined surface smoother. In dry grinding and MQL grinding, the subsurface damage depth decreased obviously with the increase in grinding wheel velocity. When the grinding wheel velocity was 30 m/s, the minimum subsurface damage depth of dry grinding and MQL grinding was 40.091 and 26.906 μm, respectively. Mastering the grinding mechanism of grinding CNTs/AL composites and the influence of grinding parameters on surface quality provides a basis for the selection of parameters and methods in grinding in industry. MQL grinding of CNTs/AL composites reduces the formation of many surface defects and improves the surface quality of the workpiece. It is an efficient, clean, and environmentally friendly processing method.

Investigation on fiber fracture mechanism and milling force model of CF/PEEK by ultrasonic milling

Ultrasonic milling can achieve high machining efficiency and surface quality on CF/PEEK composites due to its advantages of low cutting force, high material removal rate, improved surface quality, long tool life, and eco-friendly machining technology. This method is widely used in many scenarios such as aerospace, navigation, and new types of weapons. However, the changes in fiber fracture mode and the effects of fiber friction caused by high-frequency ultrasonic vibration cannot be ignored. To study this, first, a fiber fracture model is constructed based on experiments to describe the fiber fracture mechanism. Then, the machined surface and subsurface are analyzed to establish the relationship between feed speed and fiber deformation depth. Increasing the feed can increase the fiber deformation depth by 3.17 times. Finally, an analysis of the single fiber fracture mechanics is carried out and a force model is created that considers the friction between the tool tip and the fiber during ultrasonic milling. The predictive force model, integrated with the fiber distribution, was validated against experimental results, showing a maximum force error of 5.722 %. This model effectively explains the fracture mechanism of CF/PEEK fibers during ultrasonic milling at the microscopic level.

Prediction of the cutting forces in milling operation based on multi-objective optimization of the time series analysis parameters

Accurate simulation of the cutting forces in the milling process is extremely complicated because of variations in cutting process parameters, including the change in modal characteristics of the workpiece along the machining path and the high-temperature gradient around the cutting zone, especially for the modeling of milling forces in flexible thin-walled workpieces. Therefore, proposing effective methods for prediction and control of cutting forces is highly important to ensure the high performance and stability of the cutting process as well as the quality of the machined surface. In this article, a novel method is presented for rapid prediction of cutting force signals based on the combination of the multi-variable time series analysis, the Imperialist Competitive Algorithm (ICA) and Multi-View Embedding (MVE) algorithm. A state-space model of the dynamic system is presented in order to quickly predict the instantaneous dynamic characteristics of the cutting process. The maximum error between the amplitude of experimental and predicted force signals (peak-to-peak) in stable and unstable cutting conditions is less than 8% and 17%, respectively. Therefore, it is illustrated that the presented method has remarkable computational accuracy and convergence speed for predicting the future of the cutting forces under both stable and unstable conditions.

High-performance Ti6Al4V surface manufacture by laser carburising-assisted grinding

High-precision Ti6Al4V surfaces with superior properties are in urgent demand in the manufacturing industry. The existing production model that separates surface strengthening from processing has limitations. Therefore, an integrated Ti6Al4V surface machining and strengthening method, laser carburising grinding, is proposed. Remelt layers containing diffusely distributed granular TiC phases are prepared on Ti6Al4V surfaces by coupling laser carburising alloying with grinding processes, improving the material surface's mechanical properties and grindability. Compared with the separated method, the surface shape accuracy is increased by 16 %, the surface hardness reaches 652 HV, and the surface wear resistance is greatly improved. The results improve the surface machining-strengthening integration theory of titanium alloy. The related technology is of great practical significance in guiding production.

Experimental Investigation on Wire Electric Erosion Behaviour of Silicon Dioxide Particulate Reinforced Composite

The intend of current study was focused on the prediction of material removal rate (MRR) and surface roughness (SR) for the AA7050-SiO2 composite during wire electric erosion or discharge machining (WEDM) process using a brass (Br) wire electrode. Here, stir casting process was employed to develop the AA7050 matrix composite with inclusion of 10wt.% SiO2 particle reinforcement. The multi-objective optimization method of Technique for order preference by similarity to ideal solution (TOPSIS) approach has been applied to find out the optimal setting of input machining parameters such as peak current (Ip), pulse-on time (Ton) and pulse-off time (Toff). Furthermore, the significant effects of parameters were identified by analysis of variance (ANOVA). Taguchi L9 (33) orthogonal design has been formulated to perform the experimental work. TOP SIS results stated that the optimal setting of Ip at 30 amps, Ton of 130 μs and Toff of 55 μs provide the better MRR with lesser SR. The ANOVA results noticed that Ip has the prime noteworthy parameter over the adopted responses having a contribution of 45.67%, followed by Ton (32.34%) and Toff (12.26%), respectively. The confirmation test was carried out by the optimal parameters setting to verify the predicted results. Finally, the scanning electron microscopy (SEM) test was carried out for the machined surface of the composite specimen and it was reveals that the formation of craters and recast layer thickness in the machined surfaces.

Experimental Studies of the Machinability of SiCp/Al with Different Volume Fractions under Ultrasonic-Assisted Grinding.

High-volume fraction silicon carbide particle-reinforced aluminum (SiCp/Al) has a promising application for its high specific strength, wear resistance, and thermal conductivity. However, SiCp/Al components with a high-volume fraction are prone to poor surface quality and defects such as fractures, cracks, and micro-pits. It has been reported that ultrasonic-assisted grinding machining (UAG) helps to improve the quality of SiCp/Al machined surfaces. However, the differences between SiCp/Al with different volume fractions obtained by UAG machining are not clear. Therefore, a comparative study of surface roughness, morphology, and cutting force was carried out by UAG machining on SiCp/Al samples with volume fractions of 45% and 60%. Compared to the 45% volume fraction SiCp/Al, the 60% volume fraction SiCp/Al has a higher cutting force and roughness under the same machining parameters. In addition, experiments have shown that cutting forces and surface roughness can be reduced by increasing the tool speed or decreasing the feed rate. UAG machining with an ultrasonic amplitude within 4 μm can also reduce cutting forces and surface roughness. However, more than 6 μm ultrasonic amplitude may lead to an increase in roughness. This study contributes to reasonable parameter settings in ultrasonically-assisted grinding of SiCp/Al with different volume fractions.

Tribology-driven strategies for tool wear reduction and surface integrity enhancement in cryogenic CO2-cooled milling of laser metal deposited Ti64 alloy

Additive manufacturing (AM) is chosen for its ability to streamline production processes and design freedom. This reduces material waste, enables rapid prototyping, and facilitates intricate geometries, ultimately offering cost-effective and customizable solutions for manufacturing complex components in diverse industries. Overlapping melting trajectories result in a low-quality surface (Ra=∼13.34 µm) in the laser metal deposition (LMD) of the Ti64 alloy. Therefore, post-processing is often essential for AMed parts for engineering applications. Milling trials were conducted on AMed specimens under four environmental conditions: dry, flood, minimum quantity lubrication (MQL), and cryogenic medium. The machinability was evaluated in terms of the cutting temperature, machined surface roughness, tool wear, chip morphology, and microhardness. The flank wear under cryogenic CO2 condition is 52.78–54.29 % lower than dry condition, 33.86–36.24 % lower than flood cutting, and 23.64–26.86 % lower than MQL. The outcomes show that cryogenic cooling augments the tool life and the surface integrity of milling LMD parts. Moreover, the hardness under cryogenic CO2 was higher, indicating dimensional stability and maintenance of shape integrity under applied loads.

A study on Effect of Surface Finishing Processes on Surface Roughness of AISI D2 Tool Steel

According to recent studies, dry hard turning is more beneficial practical process compared to a grindingoperation, it increases quality, reduces cost and lead-time formachined parts. In this study, effects of workpiece hardness,feed rate, depth of cut and cutting speed on surface roughnesswere studied using chamfered and honed CBN inserts. Fourfactors (hardness, depth of cut, feed rate and cutting speed)were considered and - two level fractional experiments wereconducted and analysis of the variance was performed.Furthermore this study shows that the effects of grinding ofheat treated AISI D2 specimens on surface roughness wereconducted and a comparison took place with hard turning. To investigate the effect temperature increase on bothtechniques, the machined surface of workpieces is examinedusing optical and scanning electron microscopy SEM.Practical results shows the lower workpiece hardness andlower cutting conditions resulted in a better surface roughness. Finally results showed that in hard machining not only themachining parameters have an influence on the surfaceroughness but also the material hardness found effective factorin finishing process.

Studying mechanism of anisotropic crack generation on C-, R-, A-, and M-planes of sapphire during ultra-precision orthogonal cutting using a visualized slip/fracture activation model

With the growing demand for the fabrication of microminiaturized components, a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant. Single-crystal sapphire stands out as a promising material for microelectronic components, ultra-precision lenses, and semiconductor structures owing to its exceptional characteristics, such as high hardness, chemical stability, and optical properties. This paper focuses on understanding the mechanism responsible for generating anisotropic crack morphologies along various cutting orientations on four crystal planes (C-, R-, A-, and M-planes) of sapphire during ultra-precision orthogonal cutting. By employing a scanning electric microscope to examine the machined surfaces, the crack morphologies can be categorized into three distinct types on the basis of their distinctive features: layered, sculptured, and lateral. To understand the mechanism determining crack morphology, visualized parameters related to the plastic deformation and cleavage fracture parameters are utilized. These parameters provide insight into both the likelihood and direction of plastic deformation and fracture system activations. Analysis of the results shows that the formation of crack morphology is predominantly influenced by the directionality of crystallographic fracture system activation and by the interplay between fracture and plastic deformation system activations.

Micro-WEDM of Ti-29Nb-13Ta-4.6Zr Alloy for Antibacterial Properties: Experimental Investigation and Optimization

Recent developments of orthopedic implant applications have discovered a variety of new metallic biomaterials known as β-type titanium alloys. The μ-WEDM (micro-wire electro discharge machining) surface treatment technique, capable of improving the surface properties of orthopedic implants, was studied in a machining Ti-29Nb-13Ta-4.6Zr alloy. This study aimed to evaluate material removal rate (MRR), kerf width, average surface roughness, microhardness and antibacterial response at different machining parameters which are capacitance (1 nF, 10 nF and 100 nF) and gap voltage (80 V, 95 V and 110 V). The Taguchi method was used to optimize the mentioned output parameters, while ANOVA (analysis of variance) described the significance and contribution of capacitance and gap voltage. Grey relation analysis (GRA) was conducted to perform multiple output optimization. For antibacterial response, cultivations of B. subtilis, E. coli, P. aeruginosa and S. aureus bacteria on treated surfaces for 72 h were performed. As the results, optimal values of MRR, kerf width, crater area, average surface roughness and microhardness were equal to 0.0637 mm3/min, 93.0 μm, 21.8 μm2, 0.348 μm and 442 HV, respectively. Meanwhile, μ-WEDM treatment improved antibacterial properties while the highest antibacterial response was achieved at the lowest average surface roughness resulting in least biofilm formation on treated surfaces.

The Effect of Implantoplasty on the Fatigue Behavior and Corrosion Resistance in Titanium Dental Implants.

Implantoplasty is a technique increasingly used to remove the biofilm that causes peri-implantitis on dental implants. This technique of mechanization of the titanium surface makes it possible to eliminate bacterial colonies, but it can generate variations in the properties of the implant. These variations, especially those in fatigue resistance and electrochemical corrosion behavior, have not been studied much. In this work, fatigue tests were performed on 60 dental implants without implantoplasty, namely 30 in air and 30 in Hank's solution at 37 °C, and 60 with implatoplasty, namely 30 in air and 30 in Hank's solution at 37 °C, using triaxial tension-compression and torsion stresses simulating human chewing. Mechanical tests were performed with a Bionix servo-hydraulic testing machine and fracture surfaces were studied by scanning electron microcopyElectrochemical corrosion tests were performed on 20 dental implants to determine the corrosion potentials and corrosion intensity for control implants and implantoplasty implants. Studies of titanium ion release to the physiological medium were carried out for each type of dental implants by Inductively Coupled-Plasma Mass Spectrometry at different immersion times at 37 °C. The results show a loss of fatigue caused by the implantoplasty of 30%, observing that the nucleation points of the cracks are in the areas of high deformation in the areas of the implant neck where the mechanization produced in the treatment of the implantoplasty causes an exaltation of fatigue cracks. It has been observed that tests performed in Hank's solution reduce the fatigue life due to the incorporation of hydrogen in the titanium causing the formation of hydrides that embrittle the dental implant. Likewise, the implantoplasty causes a reduction of the corrosion resistance with some pitting on the machined surface. Ion release analyses are slightly higher in the implantoplasted samples but do not show statistically significant differences. It has been observed that the physiological environment reduces the fatigue life of the implants due to the penetration of hydrogen into the titanium forming titanium hydrides which embrittle the implant. These results should be taken into account by clinicians to determine the convenience of performing a treatment such as implantoplasty that reduces the mechanical behavior and increases the chemical degradation of the titanium dental implant.

COMPARISON OF CUTTING TOOL GEOMETRIES BASED ON CUTTING FORCES AND ROUGHNESS OF HARD TURNED SURFACES

Surface quality and energy consumption are two widely studied topics of hard machining. Due to the increasing need of companies for new, more efficient materials, tools and procedures, their manufacturers or suppliers have to deliver innovative solutions from time to time. In this study the latest development of a hard turning insert manufacturer is used in comprehensive machining experiments to show how the new tool (a wiper insert) behaves compared to its standard counterpart. Based on surface roughness and machining force measurement and analysis, this efficiency is proved by quantitative results: the wiper geometry ensures significantly better surface quality, while the energy consumption of the used machine tool is considerably lower.

Evaluation of tool wear during micro-milling of ultrasonically assisted abrasive peened Ti-6Al-4V

When a cutting tool shears through a workpiece, the interaction causes wear of the tool which is based on relative hardness, surface characteristics of the tool and the workpiece, cutting environment and thermal behaviour at the work/tool interface. In this study, wear of a micro-end milling tool is investigated while milling of as-received and peened work material (in this case, Ti-6Al-4V). The peening is performed with the help of an in-house developed ultrasonic cavitation process. The process excites the abrasives suspended in the cavitating medium, which impart on the work surface and induce compressive residual stress and uniform grain refinement. As the cutting process advances, a built-up is formed more rapidly in the as-received workpiece, leading to higher cutting forces and earlier chipping of the cutting edge. Under the peened conditions, it is found that the increase in tool edge radius and flank wear width reduce by 50 % and 54 % respectively compared to the as-received one. Additionally, peening-induced grain refinement leads to a 26 % decrease in surface roughness of the machined surface and inhibits burr formation by 60 %. A tool wear chipping model is employed to predict the tool diameter, cutting edge radius and flank wear width of the worn tool. Results show that the magnitude of flank wear, edge radius of worn tool and tool diameter deviate from experiments by 15.2 %, 14 % and 13 % respectively.

DETERMINATION OF THE SIZE OF MEDIUM GRANULES IN FREE ABRASIVE PROCESSING TECHNOLOGY AND THE SIZE OF THE RESERVOIR OF A MACHINE FOR VIBRATION PROCESSING OF PARTS

It is noted that the process of vibration processing of parts is carried out by the relative movement and mutual pressure of granules of the medium and the parts being processed circulating in the oscillating reservoir. It is noted that the removal of defects from the surface of a part is carried out by the processes of microcutting and elastoplastic deformation. It is indicated that despite the effectiveness of vibration processing, its capabilities are limited to performing simple operations and have not been sufficiently studied. The effectiveness of vibration processing depends on a number of factors, among which the size of the medium granules and the size of the machine reservoir play a significant role. To determine these factors, the kinematics of the finishing and grinding process was considered, and the joint movement of the medium granule and the part was taken into account. The removal of microchips along the entire length of the machined surface during one period of oscillation of the machine reservoir and the damping properties of the material of the working medium used were also taken into account. It has been established that, depending on the shape of the part, its position and direction of movement in the reservoir, the angle of contact with the granules can vary from 0 to 90º. In this regard, cases of encounters between granules and parts are considered. It has been established that the unfavorable case of a meeting occurs at the right angle of their collision. It is concluded that the removal of microchips from the surface of parts is theoretically inversely proportional to the size of the medium granules. It has been determined that the increase in damping of the medium caused by a decrease in the size of the granules can be compensated by increasing the amplitude of the oscillations of the reservoir and the use of granules with a large specific gravity. The choice of granule size is also limited by the conditions of their access to the surfaces being treated, while the conditions for eliminating the possibility of granules jamming are met. It has been experimentally confirmed that the reservoir with a “U” – shaped cross-section turned out to be the best, due to the absence of stagnant zones in it. It has been established that as the cross-section of the reservoir increases, the productivity of the machine will decrease. Intensifying the process by increasing the amplitude is unacceptable, since this causes the appearance of deep defects on the treated surfaces. To increase processing efficiency, it is necessary to increase the volume of the reservoir by lengthening it, rather than increasing its cross-section.