Tool-chip Contact Length Research Articles

Machining Ti-6Al-4V Alloy Using Nano-Cutting Fluids: Investigation and Analysis

Minimum Quantity Lubrication nanofluid (MQL-nanofluid) is a viable sustainable alternative to conventional flood cooling and provides very good cooling and lubrication in the machining of difficult to cut materials such as titanium and Inconel. The cutting action provides very difficult conditions for the coolant to access the cutting zone and the level of difficulty increases with higher cutting speeds. Furthermore, high compressive stresses, strain hardening and high chemical activity results in the formation of a ‘seizure zone’ at the tool-chip interface. In this work, the impact of MQL-nanofluid at the seizure zone and the corresponding effects on tool wear, surface finish, and power consumption during machining of Ti-6Al-4V was investigated. Aluminum Oxide (Al2O3) nanoparticles were selected to use as nano-additives at different weight fraction concentrations (0, 2, and 4 wt.%). It was observed that under pure MQL strategy there was significant material adhesion on the rake face of the tool while the adhesion was reduced in the presence of MQL-nanofluid at the tool-chip interface, thus indicating a reduction in the tool chip contact length (TCCL) and reduced seizure effect. Furthermore, the flank wear varied from 0.162 to 0.561 mm and the average surface roughness (Ra) varied from 0.512 to 2.81 µm. The results indicate that the nanoparticle concentration and the reduction in the seizure zone positively influence the tool life and quality of surface finish.

Performance profiling of solid lubricant for eco-friendly sustainable manufacturing

Abstract The intense heat generation during machining is critical to the workpiece quality. Coolant and lubrication therefore play decisive roles in machining. The conventional cutting fluids employed in machining have certain limitations with regards to their use for ecological and economic reasons. However the need for sustainable manufacturing and better surface quality urged to explore the merits of the lubricants that are eco-friendly such as solid lubricants that are proved to be a feasible alternative to the conventional cutting fluids. Solid lubricants, if employed properly, could control the machining zone temperature effectively by intensive removal of heat from the machining zone. If friction at the tool and workpiece interaction can be minimized by providing the effective lubrication, the heat generated can be reduced to some extent. It will also help reduce wear, thus improving the tool life and the surface finish. These are also used to reduce the force and the energy consumption. So the performance of the solid lubricant needs to be evaluated from tribological point of view. For this, an open tribometer has been envisaged to get the friction coefficient between the coated carbide tool and the austenitic stainless steel AISI 304 workpiece at machining - type situations. Hence this study investigate the effects of the machining parameters and the different machining environments on the machinablity aspects namely surface roughness, tool wear, tool - chip contact length, net cutting specific energy, chip morphology and the chip thickness ratio while machining austenitic stainless steel AISI 304 by TiAlN coated tungsten carbide inserts of the different tool geometry. To show the effectiveness of the solid lubricant, a comparative performance analysis, under the different environments was conducted. Results indicate that there is considerable reduction in the average flank wear (35%–60%), net cutting specific energy (40%–49%); tool-chip contact length (40%–60 %), chip thickness ratio (32%–65%) and the surface roughness (10%–39%) with the solid lubricant assisted machining compared to that of wet and dry machining. This study established that the solid lubricant assisted machining is an eco-friendly sustainable manufacturing process for the industry.

Optimization of process parameters for turning of titanium alloy (Grade II) in MQL environment using multi-CI algorithm

The advancement of materials science during the last few decades has led to the development of many hard-to-machine materials, such as titanium, stainless steel, high-strength temperature-resistant alloys, ceramics, refractories, fibre-reinforced composites, and superalloys. Titanium is a prominent material and widely used for several industrial applications. However, it has poor machinability and hence efficient machining is critical. Machining of titanium alloy (Grade II) in minimum quantity lubrication (MQL) environment is one of the recent approaches towards sustainable manufacturing. This problem has been solved using various approaches such as experimental investigation, desirability, and with optimization algorithms. In the group of socio-inspired optimization algorithm, an artificial intelligence (AI)-based methodology referred to as Cohort Intelligence (CI) has been developed. In this paper, CI algorithm and Multi-CI algorithm have been applied for optimizing process parameters associated with turning of titanium alloy (Grade II) in MQL environment. The performance of these algorithms is exceedingly better as compared with particle swarm optimization algorithm, experimental and desirability approaches. The analysis regarding the convergence and run time of all the algorithms is also discussed. It is important to mention that for turning of titanium alloy in MQL environment, Multi-CI achieved 8% minimization of cutting force, 42% minimization of tool wear, 38% minimization of tool-chip contact length, and 15% minimization of surface roughness when compared with PSO. For desirability and experimental approaches, 12% and 8% minimization of cutting force, 42% and 47% minimization of tool wear, 53% and 40% minimization of tool-chip contact length, and 15% and 20% minimization of surface roughness were attained, respectively.

Development and analysis of tool wear and energy consumption maps for turning of titanium alloy (Ti6Al4V)

Machine tools are the main source of electric power consumption in industrial operations. Thus, in manufacturing, energy-efficient and cleaner production methods are preferred to mitigate production costs. Titanium alloys are known for their poor machinability and are generally characterized by low tool life, high energy consumption and poor surface quality due to its unique physical and mechanical properties. This research aims to evaluate the tool wear rate (R) and the specific cutting energy (SCE) at varying cutting conditions by developing tool wear and energy maps using unified cutting tests. Uncoated H13A tools were used during single-point turning of Ti-6Al-4V alloy by employing Full Factorial Design of Experiments. Based on experimental data, comprehensive process maps were developed for monitoring wear and energy data. These maps showed regions of (low moderate and high) wear and specific energy consumption. It was observed that while machining Ti-6Al-4V alloy the recommended cutting condition (V=100 m/min and f =0.16 mm/rev) enhances the tool life and reduces energy consumption together with high material removal rate. It was also deduced that instead of low speed, using a higher speed of 125 m/min will increase MRR by 127 % and SCE by 16 %, which is more feasible in a production environment. From tool-chip contact length and chip morphology analysis, a strong correlation indicated the reason behind the occurrence of various zones on the maps. It has been found that high wear and energy zone occurred due to the larger contact length and higher chip compression ratio when machining at high speed. The developed maps can be used to help the manufacturers achieve the economic and energy-efficient goal of machining.

Adhesion of Inconel 718 on Uncoated Tungsten Carbide Inserts in Interrupted Orthogonal Machining under MQL

Nickel-base super-alloys such as Inconel 718 are used for demanding applications in the industry. Their superior corrosion resistance and mechanical properties, especially under high heat and pressure, make them very attractive for highly stressed components. In contrast, their low thermal conductivity, work hardening tendency and high strength impose challenges for machining. In particular, occurring adhesion of the workpiece material on tungsten carbide (WC) inserts and tools is common hindering their life. In order to counteract this undesirable effect, cutting fluids are usually implemented. However, due to increased awareness of cutting fluids negative impact on the operator’s health and the environment, minimum quantity lubrication (MQL) is getting more attention among researchers and in the industry. In this study, the adhesion on the rake face of uncoated WC inserts under the application of MQL is observed. Inconel 718 workpieces prepared for orthogonal cutting trials are interrupted at variable intervals to allow more access for MQL to reach chip-tool interface. Mechanical load, coefficient of friction, adhesion area and chip-tool contact length on the rake face are investigated. It has been observed that interrupted machining can positively influence adhesion area and chip-tool contact length.

Sub-zero metalworking fluids for high performance cutting of difficult to cut materials

Sub-zero metalworking fluids (MWF) are applied above the temperatures used for cryogenic machining, but at temperatures below 0 °C. In this paper, various sub-zero MWF formulations based on pure ethane-1,2-diol, ethane-1,2-diol and emulsified ester as well as propane-1,2-diol are used for high performance cutting of Ti-6Al-4V. These formulations are investigated regarding tool temperatures, process forces, tool wear and surface topography. Furthermore, the tool-chip contact length is investigated in order to determine the effects of the MWF on the chip formation. It can be shown that the formulation containing propane-1,2-diol, which has favorable ecological and health properties, leads to good results.

Micro-textured cutting tools: Phenomenological analysis and design recommendations

One of the effective strategies to improve dry machining processes is the implementation of micro-textured cutting tools. Micro-textures decrease the chip-tool contact length and thus reduce friction and heat which lead to better surface quality and longer tool life. However, micro-cutting of the bottom side of the chip, known as derivative cutting, is an issue when using textured tools. Derivative cutting increases the cutting forces, heat, and ultimately tool wear. This paper investigates the effect of micro-texture design parameters on the occurrence of derivative cutting and offers design recommendations when preparing micro-grooves to eliminate/reduce the severity of this phenomenon.

Mechanisms and predictive force models for machining with rake face textured cutting tools under orthogonal cutting conditions

The cutting performance and mechanisms of rake face textured carbide cutting tools in orthogonal machining of a carbon steel are investigated. Micro-grooves at 15.5 μm top width and different depth-to-width ratios are fabricated on the tool rake face using a femtosecond laser. It is found that the textures can significantly enhance the surface wettability of the cutting tools to an emulsified cutting fluid, and a fast liquid infiltration along the micro-grooves takes place. The machining tests show that cutting tools with the rake face grooves can reduce the thrust force by up to 14.68% in comparison with the untextured cutting tools, as a result of the decreased frictional force between the tool and chip. It is shown that the reduced tool-chip actual contact area due to the rake face textures and reduced tool-chip contact length due to the thinning of chip are the main reasons for this frictional force reduction. It is further found that the ploughing action between the groove edges and chip material tends to increase the frictional force while the chip material deposition to the textural structures reduces the functionality of the textures. Plausible trends of the reduction of the cutting forces with respect to the textural parameters are discussed, from which grooves in parallel to the cutting edge at 0.6 depth-to-width ratio and about 90 μm spacing are found to perform the best. A cutting force model for orthogonal machining using rake face textured cutting tools are then developed using the classical thin shear zone theory and the unified mechanics of cutting approach. The model is finally verified experimentally which shows that the model predictions agree well with the corresponding experimental data for cutting with and without a cutting fluid.

Analytical prediction of shear angle and frictional behaviour in vibration-assisted cutting

• Transient tool-chip contact length and shear angle were studied in a vibration cycle. • An analytical model based on two shear zone theories was proposed for VAC process. • Average shear angle in VAC was less than that in CC for various process parameters. • Experiments demonstrated that VAC improved the effective shear angle significantly. Vibration-assisted cutting (VAC), a promising technique, proved to enhance the machinability of difficult-to-cut materials. Its significant superiority with regard to conventional cutting (CC) is considered to be closely related to variation of a shear angle in the primary shear zone and specific frictional behaviour at tool-chip interface. This paper analyses kinematics of VAC, focusing on critical stages of tool-workpiece interaction. Based on the evolution of kinematic parameters, a transient shear angle and a tool-chip contact length are investigated in a cycle according to these stages. To predict the transient parameters, an analytical model of the cutting process is proposed based on non-equidistant shear-zone and tool-chip sliding-sticking zone theories. This model for VAC can not only predict the dominant parameters of the cutting process (e.g., cutting force, friction coefficient), but also the secondary ones (e.g., shear strain). Experimental validation of the developed model is performed with orthogonal VAC of titanium alloy, and the shear angles are measured with optical microscopy of chip samples. For various process parameters, the effective shear angle in VAC is larger than that in CC. However, the average shear angle in VAC is smaller than the shear angle in CC. The proposed model can not only effectively predict the shear angle and frictional behaviour in VAC, but also other process parameters in a vibration cycle, enriching the theory of the VAC process.

Study of chip formation mechanism in one-dimensional vibration-assisted machining

Abstract It is known that the shear angle is smaller in 1D vibration-assisted machining (VAM) than in conventional machining (CM). The intermittent nature of cutting in 1D VAM with the unique characteristic of elastic recovery is a very different machining process than CM. In this research, the chip formation in 1D VAM, which reveals the mechanism of the cutting process has been studied by Finite Element (FE) simulation to investigate the state of deformation of the chip followed by experimental analysis on a variety of metals with a set of parameters. The cutting experiments include both low-frequency and ultrasonic 1D VAM to investigate the chip formation, the forces, and the corresponding machined surfaces. It has been found from both FE simulation and experimental results that the intermittent cutting with elastic recovery and strain hardening facilitate the increased shear angle and smaller chip thickness in 1D VAM than CM. The smaller tool-chip contact length is also responsible for smaller chip thickness in 1D VAM than CM.

On the Steady-State Workpiece Flow Mechanism and Force Prediction Considering Piled-Up Effect and Dead Metal Zone Formation

Abstract The manufacturing of miniaturized components is indispensable in modern industries, where the uncut chip thickness (UCT) inevitably falls into a comparable magnitude with the tool edge radius. Under such circumstances, the ploughing phenomenon between workpiece and tool becomes predominant, followed by the notable formation of dead metal zone (DMZ) and piled-up chip. Although extensive models have been developed, the critical material flow status in such microscale is still confusing and controversial. In this study, a novel material separation model is proposed for the demonstration of workpiece flow mechanism around the tool edge radius. First, four critical positions of workpiece material separation are determined, including three points characterizing the DMZ pattern and one inside considered as stagnation point. The normal and shear stresses as well as friction factors along the entire contact region are clarified based on slip-line theory. It is found that the friction coefficient varies symmetrically about the stagnation point inside DMZ and remains constant for the rest. Then, an analytical force prediction model is developed with Johnson–Cook constitutive model, involving calibrated functions of chip-tool contact length and cutting temperature. The assumed tribology condition and morphologies of material separation including DMZ are clearly observed and verified through various finite element (FE) simulations. Finally, comparisons of cutting forces from cutting experiments and predicted results are adopted for the validation of the predictive model.

PVD AlTiN coating effects on tool-chip heat partition coefficient and cutting temperature rise in orthogonal cutting Inconel 718

Significant cutting temperature rise is induced in dry machining Inconel 718 with high cutting speed due to its low thermal conductivity and high hot hardness. PVD AlTiN coating can avoid direct contact between tool substrate and moving chip, which will affect tool-chip interface heat partition and temperature rise. However, few studies were relevant with the effect of AlTiN coating on tool-chip interface heat partition and temperature rise in dry cutting Inconel 718. In this study, the tool-chip interface temperature rises due to heat generations in primary and secondary deformation zones (PDZ and SDZ) are predicted with various heat partition coefficients, respectively. The cutting temperatures measured by two-color thermometer are utilized to determine the heat partition coefficient, and to verify the proposed interface temperature predictive model for dry orthogonal cutting Inconel 718 at cutting speed 40, 80 and 120 m/min with uncoated and PVD AlTiN coated tools. It is found that AlTiN coating decreases crater wear, and tool-chip contact length compared with that using uncoated tool. AlTiN coating decreases the maximum tool-chip interface temperature 39.00 °C and 5.47% compared with that using uncoated tool at 120 m/min. Heat partition model RG-W and RR was suitable for temperature prediction with least summary relative errors in cutting Inconel 718 with uncoated and AlTiN coated tools. The results illustrate that the PVD AlTiN coated tool could be beneficial in high-speed dry cutting Inconel 718 due to its less tool-chip interface temperature rises and tool crater wear.

Studies on chip morphology and modes of tool wear during machining of Ti-6Al-4V using uncoated carbide tool: application of multi-walled carbon nanotubes added rice bran oil as nanocutting fluid

In this work, machining performance of Ti-6Al-4V is studied in consideration with cutting force, tool-tip temperature, tool wear mechanisms, chip morphology and roughness of the machined surface. Machining experiments are carried out by varying cutting speed (Vc) with constant feed and depth-of-cut. Uncoated WC-Co insert is used as cutting tool. Multi-walled carbon nanotubes (MWCNTs) added rice bran oil is utilized to produce nanofluid minimum quantity lubrication (MQL) environment. Chip morphology along with measurable geometrical parameters including chip-tool contact length, equivalent chip thickness (H ch), segmentation spacing, segmentation frequency, shear band width, shear angle, chip hardness, etc. are studied in detail. Effects of Vc on cutting force, tool-tip temperature, depth of flank wear, and area of crater wear are discussed. Different tool wear mechanisms are identified as well. It is experienced that nanofluid MQL (NFMQL) outperforms traditional dry cutting as well as conventional MQL in purview of improved process performance.

Study on the influence of micro-textures on wear mechanism of cemented carbide tools

Wear behavior of micro-textured insert with lubrication was studied. Micro-pits with different diameters (80–200 μm), depths (3–10 μm), and area occupancies (10–30%) were manufactured on the tool rake face near the main cutting edge. Experimental research was conducted to reveal the effect of micro-pits on tool-chip interface friction characteristics. Besides, the texture parameter with better tribological characteristics was selected to study the wear mechanism of textured insert. Scanning electron microscopy analysis was conducted on the worn area of rake face. The results confirmed that the micro-textures can effectively reduce the average shear strength of rake face and actual tool-chip contact length during machining. The best average friction coefficient can be obtained with texture diameter of 170 μm, depth of 7 μm, and area occupancy of 20%. Adhesive wear, diffusion wear, and oxidation wear appeared on the worn area of rake face. The micro-textures can effectively reduce the diffusion wear and suppress the built-up edge (BUE) by improving tool-chip interface friction characteristics. The findings are of significance for enhancing the application of textured insert with excellent tribological characteristics.

Numerical investigation of the performance of micro-textured cutting tools in cutting of Ti-6Al-4V alloys

FEM is used to model and simulate the cutting of Ti-6Al-4V alloys using micro-textured cutting tools as well as the non-textured cutting tool. The dry cutting tests are also carried out to validate the FEM simulations. The simulated results show that the micro-textured cutting tools can reduce the cutting temperatures, the main cutting forces, the cutting resisting forces as well as the actual tool-chip contact lengths by 5~25%, 2~10%, 5~20%, and 10% as so, respectively. Meanwhile, the micro-textured cutting tools make the chips to be more easy to break. In addition, the fluctuations of the cutting resisting force of the micro-textured cutting tools are more obvious than that of the non-textured one. The secondary cutting of chips by the edge of textured groove is a common phenomenon in dry cutting with micro-textured cutting tools; however, the V-shaped cross-section grooves can reduce the severity of the secondary cutting compared to the rectangular cross-section grooves. The dry cutting tests show a good agreement with the FEM simulations. In future, more researches would be focused on the structural design of surface textures to avoid the secondary cutting in machining of different materials, and the micro-textured cutting tools would have important prospect of application in machining operations.

Cutting performance investigation based on the variable friction model by considering sliding velocity and limiting stress

Fast and accurate cutting force prediction is still one of the most complex problems and challenges in the machining research community. In this study, a modified finite element model is presented to predict cutting force and cutting length in turning operations of AISI 1018. Unlike the existing research, in which the mean friction coefficient μ was taken, a variable friction coefficient μ involving the sliding velocity between chip and tool is presented in this article. The sticking–sliding friction model is adopted, and the maximum limiting stress in sticking region is calculated by considering the thermal softening and normal stress distribution. Experiments have been performed for machining AISI 1018 using tungsten carbide tool, and simulation results have been compared to experiments. The simulation results of the modified finite element model have shown better outputs in predicting cutting force, tangential force, and tool–chip contact length on the rake face. The results of this article not only are meaningful to optimize tool design and cutting parameters but also can provide a clear understanding of contact behavior between tool rake face and chip.

Temporal and spatial crater wear prediction of WC/Co tools during dry turning of Ti6Al4V alloy

A new approach is developed to predict the crater wear variation on straight grade tungsten carbide tools during titanium machining. The effect of crater wear geometry has been considered on the variation of local state variables such as normal stress (σn), chip sliding velocity (vs), and cutting temperature (T) over the contact length at varying cutting times. Experimentally determined crater profiles at progressive wear stages were geometrically replicated on the cutting tool models and used for FEM analysis. In order to account for the variation of the state variables and wear rates with respect to the tool-chip contact length, the dimensionless fractional contact length parameter is introduced in the Usui characteristic wear equation. The thermo-mechanical state variables evaluated at different fractional contact lengths and cutting time were used to obtain the wear coefficients. The crater wear profile and wear depth are predicted and the same is experimentally validated over the contact length.

Experimental Investigation on Ultrasonic Atomization Assisted Turning of Titanium Alloy.

There are high cutting temperatures, large tool wear, and poor tool life in conventional machining, owing to the superior strength and low thermal conductivity of titanium alloy. In this work, ultrasonic atomization assisted turning (UAAT) of Ti6Al4V was performed with a mixed water-soluble oil-based cutting fluid, dispersed into tiny droplets by the high frequency vibration of a piezoelectric crystal. Different cutting speeds and two machining environments, dry and ultrasonic atomization assisted machining, were considered in the investigation of tool life, tool wear morphology, surface roughness, and chip morphology. In comparison with dry machining, UAAT shows lower tool wear and longer tool life due to the advantages of cooling and lubrication. Furthermore, better surface roughness, smoother chip edges, and shorter tool-chip contact length were obtained with UAAT.

Numerical Investigation of the Derivative Cutting Effect of Micro-Textured Tools in Dry Cutting of Ti6Al4V

In this study, FEM simulation of titanium alloy machining with micro-textured tool using Thirdwave AdvantEdge. Micro-scale textures on the rake face of the cutting tool is a single linear groove parallel to the cutting edge. Viewing simulation results ,derivative cutting did occur under the cutting parameters in this study. The tool-chip contact length decreases due to the existence of the micro-textures. Shear angle increases which indicates smaller deformation of the cutting layer and thus smaller cutting forces and cutting temperature. However, the derivative cutting effect increases the variations of the cutting forces. Therefore, strength of the cutting tool must be taken into consideration during the designation of the micro-textured cutting tool.

Influence of the Supplying Technique of a Sub-Zero Metalworking Fluid on the Performance of Face Turning of Ti-6Al-4V Titanium Alloy

Sub-zero metalworking fluids (MWF) are applied above the temperatures commonly used for cryogenic machining, but at temperatures below 0 °C. Both leads to a high cooling effect, resulting in a lower thermal load and eventually less tool wear. The high cooling effect also influences the chip formation, as the tool-chip contact length is reduced due to high thermally induced stresses in the chip which favors chip breaking. In this paper, a through-tool MWF supplying technique is investigated for face turning of Ti-6Al-4V at varied cutting speeds. Regarding the supplying technique, varied supply temperatures of the sub-zero MWF, varied mass flows, and varied nozzle positions are investigated. The process and process results are characterized by the temperature of the tool, process forces, wear parameters as well as the surface roughness. The results show that, besides the supply temperature of the sub-zero MWF and the applied mass flow, the nozzle position has a high influence on the performance of sub-zero MWF. In particular at high cutting speeds and thus high heat impacts, applying high mass flows at low supply temperatures with a combined MWF supply, over both the rake and the flank face, leads to reduced tool temperatures and less tool wear. The shortest tool-chip contact lengths, however, were achieved by means of a MWF supply only over the rake face. This promotes chip breaking.