Machining Forces Research Articles

Temperature analysis in Computer Numerical Control milling of medical-grade poly(methyl methacrylate)

Conventional machining of materials is often characterized by the generation of heat and elevation of cutting point temperatures. This induces thermal transformations and development of residual stresses. Therefore, there is a necessity to evaluate the interaction of machining temperatures with heat generation to identify the optimal values for the least heat generation. This is the main aim of this study, where an analysis of temperature is conducted during the computer numerical control (CNC) milling of medical-grade poly(methyl methacrylate) (PMMA). The samples were obtained from used optical lenses with an average Shore D hardness and transparency of 79.1 and 89.2%, respectively. The experiments were designed using the Taguchi methodology. The milling parameters used were the spindle speed, depth of cut, and feed rate. A special adjustable jig and several fixtures were developed for workpiece holding. During the milling process, in-situ temperature monitoring was undertaken using a FLIR-E63900 Infrared Thermometer. From the analysis, the parameter combination for the least values of maximum and average temperatures was a spindle speed of 1250 rev/min, a depth of cut of 0.3 mm, and a feed rate of 350 mm/min. A one-way analysis of variance depicted that the spindle speed was the most significant parameter toward the maximum and average milling temperatures owing to the generated friction and cutting forces. The depth of cut and feed rate were insignificant to the temperature of the process. It is also reported that the spindle speed exhibited a direct relationship produced by the machining forces whereas the feed rate exhibited an inverse relationship with the machining temperature, which was attributed to the reduced contact time and high chip removal, hence high heat dissipation. Lastly, a regression analysis was conducted, which showed that the maximum ( R2 = 0.7566) and average temperatures ( R2 = 0.7383) during the CNC milling of medical-grade PMMA could be predicted using linear regression models.

Design of 2D Wave Booster Ultrasonic Vibration-Assisted Cutting Tool in Small Size Surface Machining

Ultrasonic Vibration-Assisted Machining (UVA) is a machining process that adds a micro-scale high frequency vibration to the motion of a cutting tooltip to interrupt the continuous interaction of tool - workpiece surface. A good point of machining with UVA is more effective than conventional processes such as lower machining forces, higher machining stability, less tool wear and better surface finishes. In molds fabrication with some narrow cavities having a conversion space diameter of less than 3mm will face many difficulties while low surface roughness is required. Low stiffness of technological system in these cases of finishing machining is the reason of a weak machining in high-speed cutting. The ability to achieve cutting speeds for surface finishing of this type in tight spaces is also an interesting application for UVA tools. This paper discusses the finishing machining tool design with UVA for milling machine in such as analyze of the main parameters, adding diagonal split and simulation of the generated vibration effects to evaluate the achieved results before fabrication by using the help of ANSYS.

Performance of Al2O3/TiC mixed ceramic inserts coated with TiAlSiN, WC/C and DLC thin solid films during hard turning of AISI 52100 steel

The present work evaluates the turning performance of alumina (Al2O3) and titanium carbide (TiC) based mixed ceramic cutting inserts with TiAlSiN, WC/C and DLC thin-film depositions during machining of AISI 52100 steel hardened to 55 ± 2 HRC hardness. Based on the generated machining forces, coefficient of friction, geometrical characteristics of the chips, and tool wear, a comparative analysis of the performance of uncoated and coated cutting tools was carried out. The machining outcomes were interpreted in relation to the adhesion strength of coating with the substrate, surface roughness and hardness of the top surface of the coatings. It was observed that the reduction of friction and machining forces accounted to lower localized strain along the shear plane leading to lower deformation of the chips. The TiAlSiN coating exhibited superior wear-resistance at the highest cutting speed when compared to DLC and WC/C coatings owing to its higher hardness and higher coating/substrate adhesion strength. However, the DLC and WC/C coatings, although softer, accounted to significant reduction of machining forces due to their self-lubricating properties.

Optimization of Cutting Parameters Affecting Cutting Force and Surface Roughness in Machining of AISI P20 Die Steel

This study focuses on optimizing cutting parameters effective on cutting force (Fc) and surface roughness (Ra) in the machining of AISI P20 steel. The turning experiments have been performed in CNC lathe at three different cutting speeds (Vc) (120, 180, and 240 m/min), three different feed rates (f) (0.12 0.21 and 0.3 mm/rev), and three different depths of cut (a) (0.4, 0.8, and 1.2 mm) according to Taguchi L9 orthogonal array. The effect levels of the cutting parameters on Fc and Ra have been determined with analysis of variance (Anova). The analysis results indicate that the depth of cut is the most significant parameter affecting Fc while the feed rate is the most significant parameter affecting Ra. Moreover, the result analysis shows that cutting speed of 240 m/min, feed rate of 0.12 mm/rev, and depth of cut of 0.4 mm) factor levels were the optimum cutting parameters for the output parameters (Fc and Ra). In turning experiments performed at optimum cutting parameters, the lowest Fc and Ra values were measured as 178N and 0.412 µm, respectively.

Mechanical properties and machinability of lithium silicate glass-ceramics with varying MgO content

This study focused on the role of lithium metasilicate crystalline phase and microstructural evolution on altering the mechanical properties and machinability of two glass-ceramic system, (Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2), previously developed by our research group. Our previous study showed that increasing MgO content introduced phase separation and thus controlling the crystallization and microstructure of the glass-ceramics. For this study we chose the glass ceramic system with 1.5 and 4.5 mol% MgO. The glass-ceramics were prepared by melt cast method followed by heat treatment at 650 °C to induce partial crystallization. The crystalline phase in the glass-ceramics was identified by x-ray diffraction and the quantification of crystalline and amorphous phase content was done using Rietveld refinement. The hardness and elastic moduli were measured by nanoindentation. Vickers hardness and fracture toughness were determined by micro indentation. Nano scratch test was performed and scratch morphology was characterized using AFM and FEG-SEM. In order to compare the machinability of the prepared glass-ceramic samples, milling experiments were carried out using CNC milling machine, and machining characteristics were compared by analysing machining force, surface roughness and microstructure of the machined surface. Presence of higher amount of lithium metasilicate (LS) crystals in higher magnesia containing glass-ceramic (G2) resulted in lower average force (Fyrms) as compared to lower MgO containing glass-ceramic. However, due to a wide range of variation in crystal size (150 nm - 2 μm) in higher MgO containing glass-ceramic, the force fluctuation was more than lower MgO containing glass-ceramics.

AN INVESTIGATION OF ULTRASONIC VIBRATIONS EFFECT ON SURFACE ROUGHNESS IN ALUMINUM 7075 AND AISI 1045 CARBON STEEL DURING END MILLING AND SIDE MILLING OPERATION

Milling is one of the discontinuous machining methods which makes tools contact with workpiece continuously along with the regular change of shear force. Providing strong materials for fabricating the required pieces challenge machining and producing complex shapes. Therefore, operations intended for reducing machining forces as well as increasing the final surface smoothness are remarkably important of which using ultrasonic vibrations is one method. This study centers on ultrasonic vibration-assisted milling operation. The required ultrasonic vibrations are applied using a transducer to an AISI 1045 steel workpiece and a 7075 aluminum. Also, by using an arithmetic modal analysis simulation on the related workpiece and fixture, the designing process was performed in a way to equate the natural frequency of the whole set to that of the ultrasonic transducer. The resonant frequency obtained for the steel and aluminum workpieces was 19840 and 19757[Formula: see text]Hz, respectively, and the milling operation was done by applying ultrasonic vibrations to the workpiece. The results obtained from surface roughness measurement indicated that an increase in the ultrasonic intensity from 15[Formula: see text]W/cm2 to 22.5[Formula: see text]W/cm2 in the aluminum workpiece resulted in improved surface roughness ([Formula: see text] by 70%. In addition, an increase in the ultrasonic intensity from 15[Formula: see text]W/cm2 to 22.5[Formula: see text]W/cm2 improved the surface smoothness ([Formula: see text] by 72%. Moreover, concerning the steel workpiece while the tool is perpendicular to the direction ahead of the workpiece, it was clear that applying 22.5[Formula: see text]W/cm2 ultrasonic vibrations to the end-milled surfaces resulted in an approximate increase in the average and maximum surface smoothness by 53% and 45%, respectively. Furthermore, applying 30[Formula: see text]W/cm2 ultrasonic vibrations to face-milled surfaces, either perpendicular to or parallel to the tool, led to an approximate increase in the average and maximum surface smoothness by 35% and 25%, respectively.

Machining of titanium alloys using phosphonium-based halogen-free ionic liquid as lubricant additives

PurposeNowadays, ionic liquids (ILs) are used as lubricant additives because of their ability to improve tribological characteristics. However, majority of the ILs contains halogen-based anions. They are extremely sensitive to moisture and produce detrimental halides and halogen acids when reacted with moisture and water. These halides and halogen acids are harmful to the health and environment of the operator’s. This paper aims to study four different lubricants including two halogen-based ILs blended in canola oil and two phosphonium-based halogen-free ILs blended in canola oil and in pure canola oil.Design/methodology/approachViscosity and contact angle were measured by using rheometer and contact angle goniometer, respectively. Machining experiments were performed using turning centre with four different lubricants at two different cutting speeds and temperatures, and the machining forces, tool morphology and roughness of the machined surface were analysed.FindingsThe results showed that the inclusion of 1% phosphonium-based halogen-free ILs blended in canola oil increased the viscosity by 44.8% and reduced the cutting and thrust force by 21.7% and 26.8%, respectively, compared to pure canola oil lubricant. Microscopic analysis of tool showed lower adhesive and abrasive wear when machined with phosphonium-based halogen-free ILs blended in canola oil. The workpiece surface roughness reduced by 32% for phosphonium-based halogen-free ILs blended in canola oil compared with pure canola oil.Originality/valueHalogen-free ILs are possible green lubricants, as they do not contain harmful elements such as F, S, B and Cl like halogen-based ILs. To the best of the authors’ knowledge, this is presumably the first work which shows machining performance of halogen-free ILs as lubricant additives.

Hybrid turning process by interacting ultrasonic vibration and laser energies

ABSTRACT Hybrid machining processes are developed to achieve enhanced machining performance for various materials. In this study, ultrasonic vibration and laser sources interact simultaneously during the hybrid turning process and the process is termed ultrasonic vibration laser-assisted turning (UVLAT). Ultrasonic vibration-assisted turning (UVAT) fixture is mounted along with laser assisted turning (LAT) fixture on the lathe machine during the developed hybrid process. An experimental investigation on aluminum 3003 alloy is performed to analyze the machining performance for conventional turning (CT), UVAT, LAT, and UVLAT. Cutting speed and laser power are varied to machine aluminum alloy during various processes. The investigation shows that lower machining forces, higher machining temperature, smooth and lesser segmented chips, and lower surface roughness are obtained during UVLAT in comparison to CT, UVAT, and LAT. At higher cutting speed, machining forces and surface roughness are increased and decreased at higher laser power, whereas vice versa to machining temperature with variation in speed and power. Smooth edges and less segmentation are observed at higher laser power and cutting speed. Outcomes suggest that the machining performance of aluminum alloy is enhanced during the UVLAT process when compared with other processes.

Analysis of the operation principle for tubular flux-switching permanent magnet linear machine

PurposeThis study aims to unveil the generation mechanism of the thrust force in a tubular flux-switching permanent magnet (PM) linear (TFSPML) machine; the operation principle of the TFSPML machine is analyzed.Design/methodology/approachFirst, the air-gap flux density harmonic characteristics excited by PMs and armature windings are investigated and summarized based on a simple magnetomotive force (MMF)-permeance model. Then, the air-gap field modulation theory is applied in analyzing the air-gap flux density harmonics that contribute to the electromagnetic force. In addition, a simple method for separating the end force of the TFSPML machine is proposed, which is a significant foundation for the comprehensive analysis of this type of machine. As a result, the operation principle of the TFSPML machine is thoroughly revealed.FindingsThe analysis shows that the average electromagnetic force is mainly contributed by the air-gap dominant harmonics, and the thrust force ripple is mainly caused by the end force.Originality/valueIn this paper, the operation principle of the TFSPML machine is analyzed from the perspective of air-gap field modulation.

Role of porosity in machinability of additively manufactured Ti-6Al-4V

Despite numerous benefits, the additively manufactured (AM) parts present poor surface quality and dimensional errors, requiring semi-finishing or finishing operations. Machining of AM metals presents multiple challenges due to porosity, anisotropy, microcracks, and uneven layer thickness. This paper studies the role of porosity in the machinability of AM porous Titanium alloy (Ti6Al4V). Microendmilling experiments are conducted using the AM Ti6Al4V with four porosity levels. The machining response is analyzed in terms of machining force, chip morphology, tool wear, and machined surface finish; and compared with that of solid/continuous Ti6Al4V. A new metric has been proposed to quantify and statistically correlate the random variations in the machining force with AM part porosity. At higher porosities, tool chipping increases due to thermo-mechanical shocks as the tool encounters random pore-material boundaries. This results in microburrs and an increase in surface roughness (Ra). The chip and surface morphology show pore closure phenomenon at lower porosity levels, while chip segmentation is observed at higher porosities. Overall, the findings of this research provide valuable insights into the cutting mechanism of AM porous metals. Moreover, the correlation between the machining response and the porosity-driven part quality could be instrumental in in-situ process monitoring/control of hybrid additive-subtractive processes.

WITHDRAWN: Multiscale cutting and damage mechanisms of flax fiber reinforced biocomposites under hygrothermal conditioning

Manufacturing processes of biocomposite materials made of natural plant fibers and biobased polymers are subjected to many issues that slow down their industrial expansion. Among these issues, the hygrothermal conditions are the most relevant because natural plant fibers are highly sensitive to humidity due to their hydrophilic properties, and their ability to absorb water molecules is accelerated by increasing the temperature, which affects their mechanical performances. This paper addresses the cutting and damage mechanisms that occur when machining flax fiber reinforced polylactic-acid (PLA) biocomposites under hygrothermal conditioning. The moisture content, the chip morphology, the tool-chip friction calculated from the machining forces, and the machined surface state observed with a scanning electron microscope are considered in this study to evaluate the machinability and identify the involved mechanisms. Results show that the conditioning temperature and the fiber orientation affects considerably the moisture diffusion behavior inside the biocomposite structure, which modifies the cutting contact interaction and leads to a change in the form of the chip in terms of curling. The tool-chip friction is also dependent on both the hygrothermal conditioning and the fiber orientation that control the different involved mechanisms such as adhesion, plastic deformation, and fiber shear. The microscopic observation of the machined surfaces describes the shearing efficiency of flax fibers regarding the hygrothermal conditioning in addition to the effect of interface and microstructural fiber damages after a long hygrothermal conditioning time.

Study on helical milling performance of wood-plastic composites

In order to provide scientific guidance for Wood-plastic composite(WPC) helical milling, this paper studied the effects of cutting parameters and tool parameters on cutting force and surface quality in WPC machining with diamond tools. Multiple linear regression model and response surface method are used to evaluate three factors, namely-spindle speed, cutting depth and tool helical angle when the feed speed is fixed at 5 m/min. The applicability of the model is predicted and verified respectively in a given range, and the change law of cutting force and surface quality in helical milling is predicted accurately. The results show that the cutting force increases with the increase of the three factors. The surface quality only increases with the increase of the spindle speed. The optimum conditions for low cutting force and excellent surface quality are: spindle speed is 6254 r/min, the feed speed is 5 m/min, the cutting depth is 0.5 mm, and the tool helical angle is 54°. These parameters are recommended to be used in actual WPC machining to improve cutting efficiency.

MulTi-FAST: A Machinability Assessment of Functionally Graded Titanium Billets Produced from Multiple Alloy Powders.

Technological developments in the area of functionally graded multi-material manufacture are poised to disrupt the aerospace industry, providing the means for step-change improvements in performance through tailored component design. However, the challenges faced during the downstream processing, i.e., machining of such functionally graded multi-materials are unclear. In this study, the challenges involved when face-turning billets consisting of multiple alloys are assessed. To achieve this, a cylindrical billet consisting of Ti-64, Ti-6242, Ti-5553 and Beta C alloys was manufactured from powder feedstock using field-assisted sintering technique (FAST) and termed MulTi-FAST billets. A detailed study of the structural integrity during machining at the diffusion bond interfaces of multiple titanium alloy bond pairings in the MulTi-FAST billet was conducted. The machining forces were measured during face-turning to investigate the impact and behaviour of different alloy pairings during a continuous machining operation. The results showed the significant differences in force machining response, surface topography and the type of surface damage was dependent on the direction the titanium alloy graded pairings were machined in. In terms of subsurface microstructural damage, regardless of the machining direction, no critical damage was found in the vicinity of the bonded alloys. The findings provide an insight into the deformation characteristics and challenges faced in the machining of functionally graded components with multiple titanium alloys.

Numerical Simulation of Orthogonal Machining of Gallium Nitride via Smoothed Particle Hydrodynamics

Gallium Nitride is one of the best candidates for upcoming industrial revolution due to itssuperior electrical properties over silicon. In the present work, we investigate the chipformation, cutting force and effective stress in diamond machining of gallium nitride bysmoothed particle hydrodynamics approach based on Mohr-Coulomb material model. Thecomparison of the effective stress as reported by molecular dynamics studies and thatpredicted by the smoothed particle hydrodynamics simulation demonstrates the effectivenessof the smoothed particle hydrodynamics model.

Soft machining-induced surface and edge chipping damage in pre-crystalized lithium silicate glass ceramics

Soft machining is a key procedure in fabrication of high-strength lithium-based silicate glass ceramic (LS) restorations. This paper reports on the diamond machining-induced surface and edge chipping damage in two pre-crystalized LS materials: pre-crystallized lithium metasilicate/orthophosphate glass ceramic (Pre-LS, IPS e.max CAD) and pre-crystallized zirconia-containing lithium metasilicate glass ceramic (Pre-ZLS, Vita Suprinity). Indentation techniques were used to measure the material mechanical properties. Soft machining was conducted using a robotic controlled apparatus mimicking dental CAD/CAM machining processes at different removal rates and enabling in-process force measurement. Machined surface roughness was assessed using 3D confocal optical profilometry in terms of the average and maximum surface heights. Scanning electron microscopy was used to assess diamond tool and machined surface and edge morphology. Soft machining of both materials was dominated by brittle fracture mixed with localized ductile flow. However, the higher brittleness index of Pre-ZLS than Pre-LS yielded higher degrees of machining-induced conchoidal fractures in Pre-ZLS in comparison with irregular fractures in Pre-LS. Thus, much larger surface roughness and deeper edge chipping damage were produced in Pre-ZLS than Pre-LS. Machining forces for Pre-ZLS were significantly smaller than Pre-LS, due to the lower machinability index associated with a complex relation of the mechanical properties as well as less debris adhesion for Pre-ZLS than Pre-LS. Further, increased material removal rates resulted in significantly increased machining forces, maximum surface roughness and fracture, and edge chipping damage in both Pre-ZLS and Pre-LS materials. Therefore, optimization of soft machining processes needs to be practiced to achieve accepted surface and edge quality at balanced removal rates.

Machinability study on Al7075/Al2O3-SiC hybrid composites

In the present research, the effects of volume fraction of SiC+Al2O3 particles and aging temperature on the machinability of stir-casted Al7075 metal matrix composites (MMC) have been investigated. The hybrid composites were fabricated using the liquid metallurgy route. Al7075 was reinforced with different wt. % of SiC (3%, 6%, and 9%) and Al2O3 (2%, 4%, and 6%) which were used to fabricate the hybrid metal matrix composites. The samples were aged at different temperatures (140 ºC, 160 ºC, and 180 ºC) for 4 h and cooled at furnace temperature (27 ºC). The machinability of hybrid metal matrix composites was studied by carrying out L27 orthogonal array experiments. Three process parameters were selected, such as 0.2 mm/min of the depth of cut, 0.1 mm/min of feed rate, and 1500 rpm of spindle speed. The obtained results indicate that the surface roughness and machining force of MMCs increase with an increase in weight percentage of Al2O3/SiC and decrease with the increase in aging temperature. Optimum machining force and surface roughness were obtained at 2% Al2O3 + 3 % SiC and 180°C of aging temperature.

A Numerical Simulation of Machining 6061 Syntactic Foams Reinforced with Hollow Al2O3 Shells

Aluminum closed cell syntactic foams possess reduced density, higher peak compression strength, and lower coefficient of thermal expansion and thermal conductivity compared to metal alloys. However, the industrial mass production of these complex material systems presents a significant problem in the form of poor machinability. In order to address this concern and to increase the use of this potential cost- and energy-saving system, a two-dimensional numerical model using the AdvantEdgeTM machining software was developed. For the verification of the numerical model, machining trials in dry conditions were conducted on different samples using a SandvikTM carbide-coated insert having a 6° rake angle and a 7° clearance angle. The hollow alumina shell diameter and volume fraction were found to profoundly affect the magnitude of the generated machining forces. This study showed an increase in machining force by almost 25% for syntactic foams reinforced with hollow alumina shells of higher volume fraction and coarser diameters. The cutting conditions to obtain a favorable stress diastribution in the syntactic foam’s machined sub-surface were identified.

Effects of process parameters on machining forces and surface roughness during turning 304L steel using SiO2 nanofluid

The use of cutting fluids in machining processes plays an important role in minimizing cutting temperature, cutting forces, and machining cost In this paper, a study has been performed to model and optimize the process parameters involved in the turning operation of alloy steel AISI-304L (4306) with SiO2 nanofluids using the minimum quantity lubrication (MQL) method. The effects of spindle speed, feed rate, and flow rate in three levels have been investigated on the surface roughness and the machining forces using the response surface method (RSM). The results show the feed rate has the most effect on output responses. The minimum level of the feed rate and the maximum level of the flow rate and the spindle speed results in the optimum value for the surface roughness and machining forces. Also, a comparison between lubricating with and without nanoparticles show addition of nanoparticles improves the cutting forces and surface roughness due to the increase of the thermal conductivity coefficient of cutting fluids. The use of SiO2 nanoparticles in cutting fluid decreases the surface roughness by 48.5% and the cutting force by 12.3% compared to pure cutting fluid in the same condition.

Impacts of flank wear and cooling strategies on evolutions of built-up edges, diffusion wear and cutting forces in Ti6Al4V machining

Titanium alloys are widely used in aerospace industries due to their excellent physical and mechanical performances, however, their poor machinability always induce fast tool wear. To better understand the interaction between progressive tool wear and cooling strategies in machining of titanium alloy Ti6Al4V, an in-depth analysis towards evolutions of built-up edges (BUEs), diffusion wear and cutting forces was carried out through experimental work. Design of experiments was used towards analyzing pertinent effects involved in machining Ti6Al4V. Uncoated carbide inserts were artificially treated with different initial flank wear (VB) in order to decouple the effects involved in progressive wear condition from rake and flank faces. Dry cutting, flood cutting with emulsion and cryogenic cutting with liquid nitrogen (LN2) were used as different cooling strategies. The results show that initial VB presents significant contributions to BUEs formation, diffusion wear and cutting forces fluctuation, especially under aggressive cutting conditions. Cryogenic assistance significantly eliminates these issues compared to dry and flood conditions.

Investigation of Gaussian mixture clustering model for online diagnosis of tip-wear in nanomachining

This paper studied an unsupervised machine learning method to achieve real-time diagnosis of tip wear in tip-based nanomachining with an Atomic Force Microscope (AFM). The unsupervised Gaussian Mixture Model (GMM) was applied for online pattern recognition using the collected process data. In this work, the time varying signal of machining force was collected and managed in the form of moving data windows. The characteristics of the nanomachining force signal, including the maximum force, peak to peak force, and the variance, were calculated as the data of extracted features to indicate the tip wear conditions. Outliers were identified and removed using the Mahalanobis Distance Detection. A GMM model was trained using the historical processing data, in which the tip wear states were identified by clustering the feature parameters of each data frame. The change of the tip conditions was detected and tracked through the changing numbers of the tip failure points in the data windows. Experiment results showed that the highest and the average recognition accuracy of the proposed model was 1 and 0.8367 with the longest and the average calculation time of 0.031 s and 0.025 s. Compared with supervised and semi-supervised machine learning algorithms, the GMM based on unsupervised machine learning model has slightly lower recognition accuracy, but much shorter calculation time, which is suitable for online automatic diagnosis of tool wear in large-scale nanomanufacturing in real time.