Machined Surface Finish Research Articles

Machining response of Ti64 alloy under Nanofluid Minimum Quantity Lubrication (NFMQL)

Rapid wear progression of cutting insert associated with attainment of excessive tool-tip temperature are indispensable causes which limit operational domain of cutting velocity during dry turning of Ti64 alloy. Again, to counteract demerits of flood cooling, jet of air-oil mist (MQL technology) is employed in which water-based coolants or vegetable oils are highly preferable. On the other hand, inclusion of nano-additives within base fluid, and supply the same through MQL system (NFMQL) is also a trendy area of research. Application potential of NFMQL is understood over conventional MQL in terms of better cooling, and lubrication effects due to improved thermo-physical, and tribological properties of the resultant cutting fluid. In this context, present study aims to assess performance of MQL jet containing biodegradable Jatropha oil (carried by pressurized air) when applied during longitudinal turning of Ti64 work alloy. In addition, advantages of 2D layered-structured graphene nanoplatelets (when dispersed into Jatropha oil), in purview of machining performance on difficult-to-cut Ti64 alloy under NFMQL, are studied in this work. Experimental data are compared on the basis of different lubrication conditions (dry, conventional MQL, and NFMQL). Morphology of tool wear is studied in detail. The work extends towards studying chip morphology and machined surface finish of the end product, as influenced by variation in lubrication conditions.

Silver nanoparticle-based Tween 80 green cutting fluid (AgNP-GCF) assisted MQL machining - An attempt towards eco-friendly machining

In modern research, the instigation of eco-friendly and sustainable manufacturing options have drawn a great attention and become a global interest. Thus, usage of environmental pleasant cutting fluids and their least consumption in machining operation is a promising attempt towards cleaner and sustainable machining. In this work, experimental investigations during silver nanoparticle-based Tween 80 green cutting fluid (AgNP-GCF) assisted minimum quantity lubrication (MQL) machining were conducted. In the first stage of the work, synthesis and characterization of AgNPs was carried out. Secondly, novel AgNP-GCF has been developed by dispersing AgNPs in different proportions (0.2 ​wt %, 0.4 ​wt %, 0.6 ​wt % and 0.8 ​wt %) in the water based Tween 80 emulsifier oil. Lastly, the process performance of developed AgNP-GCF under different cutting speeds was investigated during MQL machining of Inconel 718. Process performance with regard to surface finish quality (surface roughness) of the machined workpiece material in five different machining environments such as dry machining (without cutting fluid), MQL machining with Tween 80 based cutting fluid (without AgNPs), MQL machining with 0.2 ​wt % AgNP-GCF, MQL machining with 0.4 ​wt % AgNP-GCF and MQL machining with 0.6 ​wt % AgNP-GCF was examined and results were related with each other. The substantial improvement in quality of machined workpiece material was observed during AgNP-GCF assisted MQL machining. Under tested cutting speeds, the 0.6 ​wt % AgNP-GCF assisted MQL machining was 55% more effective in reducing surface roughness when compared to dry machining and 26% more effective when compared to MQL machining with Tween 80 based cutting fluid (without AgNPs). The high quality of machined surface during MQL machining with AgNP-GCF was due to appreciable heat transfer through AgNPs and their strong inherent lubricant properties. This study is expected to promote the cleaner and more competent MQL machining through the application of developed eco-friendly cutting fluid. • Silver nanoparticles were added to water based Tween 80 emulsifier oil to prepare an eco-friendly cutting fluid. • Effect of developed cutting fluid on the machining surface finish quality was studied. • Silver nanoparticle-based cutting fluid assisted MQL machining was more effective in improving the surface quality on the machined surface. • Silver nanoparticle-based cutting fluid assisted MQL machining was effective in improving the machining performance. • Promotes cleaner and sustainable machining through the application of developed eco-friendly cutting fluid.

Ultra-precision Machining of Micro-step Pillar Array Using a Straight-Edge Milling Tool

Ultra-precision machining has been well known as a very precise and effective way to prototype and fabricate different types of components with microstructures. In this paper, an ultra-precision micro-milling method has been presented to produce a micro-step pillar array as an embossing mold for semiconductor application. Theoretical analysis on machining mechanics indicates that work material property, machining strategy, and cutting tool geometry largely affect machining distortion on the machined microstructure. Experimental investigation has been conducted on micromachining of the micro-step pillar array using different types of cutting tools and work materials. Experimental results demonstrate that the material property, cutting tool edge radius, and cutting force play a significant role in the machined micro-structure accuracy and surface finish, while grain boundary of brass has no significant effect on the micro-milling performance. The best outcome among the tests done is achieved when using brass as work material and cutting with a straight-edge single crystalline diamond tool. The main reasons to achieve this outcome are based on: the brass material having a higher elastic modulus and the diamond tool having a smaller cutting edge radius, which contributes to better machinability of brass. One micro-step pillar array has been successfully obtained with very precise feature and dimensional accuracy using brass work material and single-crystal diamond tool. It is believed that the outcomes of this study would largely benefit the research community and end-users.

Microstructure-based three-dimensional characterization of chip formation and surface generation in the machining of particulate-reinforced metal matrix composites

Particulate-reinforced metal matrix composites (PRMMCs) are difficult to machine due to the inclusion of hard, brittle reinforcing particles. Existing experimental investigations rarely reveal the complex material removal mechanisms (MRMs) involved in the machining of PRMMCs. This paper develops a three-dimensional (3D) microstructure-based model for investigating the MRM and surface integrity of machined PRMMCs. To accurately mimic the actual microstructure of a PRMMC, polyhedrons were randomly distributed inside the matrix to represent irregular SiC particles. Particle fracture and matrix deformation and failure were taken into account. For the model’s capability comparison, a two-dimensional (2D) analysis was also conducted. Relevant cutting experiments showed that the established 3D model accurately predicted the material removal, chip morphology, machined surface finish, and cutting forces. It was found that the matrix-particle-tool interactions led to particle fractures, mainly in the primary shear and secondary deformation zones along the cutting path and beneath the machined surface. Particle fracture and dilodegment greatly influences the quality of a machined surface. It was also found that although a 2D model can reflect certain material removal features, its ability to predict microstructural variation is limited.

Study of Cutting Forces and Prediction of Surface Quality Analysis Using Neural Network Model, Support Vector Regression Model by Various Textured Tool Condition for Ti-6Al-4V Alloy

To evaluate the performance of the textured tool on surface quality with three different types of the textured pattern using Wire-Cut Electrical Discharge Machining (W-EDM) on tungsten carbide cutting tools with two different groove depth dimensions 100 μm& 200μm respectively and the tools are coated with both TiN and TiAlN using Physical Vapour Deposition (PVD) technique. Surface roughness is predicted using the Support Vector Regression, multilayer Artificial Neural Network model (ANN) model. ANN training is carried out with a pure line transfer function and backpropagation algorithm. Easy off machining and good surface finish are achieved through TiAlN coated tool with linear texture along the perpendicular to chip flow direction than the tools considered for experimental and predicted conditions.

Dry, MQL, and Nanofluid MQL Machining of Ti–6Al–4V Using Uncoated WC–Co Insert: Application of Jatropha Oil as Base Cutting Fluid and Graphene Nanoplatelets as Additives

Nanocutting fluids are very popular due to their excellent thermo-physical and tribological properties which provide adequate cooling and lubrication during metal cutting. Conventional dry machining of difficult-to-cut superalloy Ti–6Al–4V faces several challenges. To overcome this, application of cutting fluid is indeed a necessity. However, performance of conventional minimum quantity lubrication (MQL) system, in which air–oil mist is sprayed into cutting zone, is somewhat limited due to inadequate penetration into tool–work and tool–chip interfacial regions, especially at high cutting speeds. MQL performance can further be enhanced by applying nanocutting fluid in which nano-sized additives are dispersed into the base cutting fluid; this is known as nanofluid MQL (NFMQL). In order to take care of several alarming issues related to environmental protection and occupational health hazards, the present study explores application feasibility of biodegradable Jatropha oil added with graphene nanoplatelets as nanocutting fluid. Machinability of Ti–6Al–4V is assessed under NFMQL; results are compared to that of dry and conventional MQL machining. Cutting force magnitude, tool-tip temperature, morphology of worn-out insert, chip’s macro/micro-morphology and surface roughness of the machined work part, etc., are studied in detail. For MQL and NFMQL, tool wear morphology detects existence of ‘unaffected zones’ which indicates sustenance of strong hydrodynamic tribo-film of cutting fluid, thus protecting the insert against wear. Up to 82 m/min cutting speed, NFMQL causes lower tool flank wear than dry and conventional MQL. On the other hand, superior machined surface finish is obtained under NFMQL up to 106 m/min cutting speed.

Comparison between cryogenic coolants effect on tool wear and surface integrity in finishing turning of Inconel 718

Abstract The most important challenges when machining difficult-to-cut alloys used in critical applications consist mainly in increasing tool life as well as improving the component surface integrity. In particular, the nickel based alloys exhibit very low thermal conductivity inducing higher cutting temperature and thereby rapid tool wear. In this context, cryogenic machining is a promising approach that enhances cooling efficiency either when using the liquid nitrogen LN2 or the carbon dioxide LCO2. According to previous works, cryogenic machining has been carried out on several work materials such as titanium alloys and nickel based alloys. Their findings figured out that longer tool life and better surface integrity were obtained when machining titanium alloys, unlike nickel based alloys. In this work, a comparative study has been carried out in order to investigate the cryogenic machining performance during turning operation of Inconel 718 with respect to tool wear behavior and surface integrity of the machined part. In fact, two cryogenic fluids were employed namely LN2 and LCO2 considering as a reference the conventional lubrication. This study illustrates that conventional lubrication and LCO2 cryogenic cooling allowed to obtain similar machining time, tool wear and surface finish. Nevertheless, LN2 cryogenic machining resulted in the lowest tool life as well as the poorest surface finish. Moreover, residual stresses have been measured beneath the machined surfaces when machining using new tools and tools with different levels of tool flank wear. It was observed that compared to conventional lubrication, both cryogenic conditions showed better results with respect to residual stress profiles along the machined surfaces.

Effects of Cutting Speed on MQL Machining Performance of AISI 304 Stainless Steel Using Uncoated Carbide Insert: Application Potential of Coconut Oil and Rice Bran Oil as Cutting Fluids

In metal machining, minimum quantity lubrication (MQL) refers to supply of an optimal amount of cutting fluid into tool-work interfacial region. As compared to traditional dry machining, machining process executed under MQL has several advantages. Properties of cutting fluid play important role toward machining performance. In the present work, application potential of rice bran oil is compared with coconut oil in the context of MQL machining of AISI 304 stainless steel. Cutting force magnitude, approximate tool-tip temperature, flank wear depth, etc., are studied as machining performance indicators. In addition, different tool wear mechanisms, chip morphology, and surface roughness of the machined work part are studied in detail. It is experienced that MQL (rice bran oil) outperforms MQL (coconut oil). MQL (rice bran oil) exhibits lower cutting force, lesser tool-tip temperature, reduced extent of tool wear, and better machined surface finish than dry as well as MQL (coconut oil) machining.

Effect of flax fiber orientation on machining behavior and surface finish of natural fiber reinforced polymer composites

Manufacturing processes of natural fiber reinforced polymer (NFRP) composites are becoming the interest of industrials and scientists because these eco-friendly materials are emerging in automotive and aerospace industries. In this context, machining processes of NFRP composites present significant issues related to the complex structure of natural fibers that need thorough tribological studies. This paper aims to explore the effect of natural fiber orientation on the machinability of NFRP composites using Merchant model in order to separate the shearing energy from the friction energy. Orthogonal cutting process is conducted on unidirectional flax fibers reinforced polypropylene composites by changing the fiber orientation from 0° to 90° with respect to the cutting direction. Iosipescu shear tests are also performed to determine the mechanical shear behavior in function of the fiber orientation. Results show the applicability of Merchant model on the machining analysis of NFRP composites by verifying the main model assumptions. The fiber orientation affects significantly the shearing and the friction energies that control the cutting behavior and the chip formation of the NFRP composite. The resulted machined surfaces are hence intimately related to the natural fiber orientation.

Continuity-preserving tool path generation for minimizing machining errors in five-axis CNC flank milling of ruled surfaces

Five-axis CNC flank machining has been commonly used in the industry for shaping complex geometries. Geometrical errors typically occur in five-axis flank finishing of non-developable surfaces using a cylindrical cutter. Most existing tool path planning methods adjust discrete cutter locations to reduce these errors. An excessive change in the cutter center or axis between consecutive cutter locations may deteriorate the machined surface quality. This study developed a tool path generation method for minimizing geometrical errors on finished surfaces while preserving high-order continuity in the cutter motion. A tool path is described using the moving trajectory of the cutter center and changes in two rotational angles in compact curve representations. An optimization scheme is proposed to search for optimal curve control points and the resulting tool path. A curve subdivision mechanism progressively increases the control points during the search process. Simulation results confirm that the proposed method not only enhances the computational efficiency of tool path generation but also improves the machined surface finish. This study provides a computational approach for precision tool path planning in five-axis CNC flank finishing of ruled surfaces.

Prediction of machining accuracy based on geometric error estimation of tool rotation profile in five-axis multi-layer flank milling process

In five-axis multi-layer flank milling process, the geometric error of tool rotation profile caused by radial dimension error and setup error has great influence on the machining accuracy. In this work, a new comprehensive error prediction model considering the inter-layer interference caused by tool rotation profile error is established, which incorporates a pre-existing prediction model dealing with a variety of errors such as geometric errors of machine tool, workpiece locating errors, and spindle thermal deflection errors. First, a series of tool contact points on the tool swept surface in each single layer without overlapping with others are calculated. Second, the position of the tool contact points on the overlapped layers is updated based on the detection and calculation of inter-layer interferences. Third, all evaluated tool contact points on the final machined surface are available for completing the accuracy prediction of the machined surface. A machining experiment has been carried out to validate this prediction model and the results show the model is effective.

Comparison of geometrical accuracy and surface finish of cam profile generated by wire-EDM and CNC milling machine

CAM is a machining element that has a curved groove or curved outline used for converting rotary motion into the form of linear motion or vice versa. The radial cam is a type of cam which having rotating plate or disc with an outer circumference shaped for producing a linear movement to a follower which is held against it. The quality of the final machined component surface depends on the accuracy and surface finish, position, orientation and run-out. The main aim of this paper is to machine a CAM profiles with CNC milling and wire cut EDM process and comparing the surface finish and accuracy of the machined surface with surface roughness tester and coordinate measuring machine (CMM).

Investigation of Advanced Control Schemes for High-speed Small-Hole EDM Drilling

High-speed small-hole electrical discharge machining (EDM) drilling is extensively applied to machine cooling film holes of turbine blades and diesel nozzle spray holes due to its non-contact characteristics and dedicated features, e.g. high-speed rotation and high-frequency pulse power generator. However, with increasing drilling depth, the process stability could be easily deteriorated by frequent debris due to restricted flushing conditions. Consequently, the machining efficiency and surface finish of high-aspect-ratio holes cannot be guaranteed. To address this problem, this paper proposes a sliding mode and self-tuning control scheme to regulate the discharging process. An integral function is presented as the switch mode to avoid chattering, and a direct algorithm that reparameterizes the model in terms of controller parameters is considered to reduce computation. The presented comparative drilling experiments with high aspect ratio (nearly 100) show the benefits of the adaptive controller.

Investigations on electrochemical machining (ECM) of Al7075 material using copper electrode for improving geometrical tolerance

This research work focuses on electrochemical machining performance evaluation of Al7075 material ECM has become the most important and high precision technique in the manufacturing sector, since many intricate 3D profiles can be machined using a copper electrode. ECM process widely applied in aerospace industries using of multiple hole drilling, turbine blades within close limits and drilling jet engine turbine blades, etc. The objective of this experiment is found the maximum Material Removal Rate (MRR), reducing the machining time, good hardness and surface finish. The machining parameter considered were current (12 V), duty cycle (75%), and electrolyte concentration (32%). The performance measures such as metal removal rate (MRR), the machining time (min), hardness, form and orientation tolerance were examined. Main effect plot, interaction plot and contour plot analysis were used to optimize the process parameters for ECM processes. As a result, metal removal rate is maximized by increasing the electrolyte concentration (36 g/l), duty cycle (95%) and machining voltage (16 v). Metal hardness is improved by decreasing the machining voltage (12 V), duty cycle (75%) and increasing the electrolyte concentration (36 g/l). Minimum circularity is achieved at machining voltage, electrolyte concentration, and duty cycle are reduced. Minimum cylindricity is obtained while increasing the electrolyte concentration and decreasing the machining voltage. Minimum perpendicularity is achieved to increase of voltage and decrease of electrolyte concentration.

Effect of edge preparation technologies on cutting edge properties and tool performance

Edge preparation has gained widespread use due to its low cost and high impact. Various edge preparation methods are reported in the literature. Choice of edge preparation techniques influences the edge properties and the ensuing tool performance. The current work investigates the influence of three different edge preparation methods, brushing, drag finishing, and wet abrasive jet machining on the performance of tungsten carbide inserts during orthogonal turning. Edge preparation not only changes the geometry but also the properties of the edge. Experimental results show that a drag finished edge has the lowest edge surface roughness (Ra = 0.42 μm), while abrasive jet machining can induce 63% greater compressive residual stress than the unprepared tool. Reduction in tool wear was observed at the same stage of cutting length in the prepared edges alongside improved edge hardness. A thermomechanical finite element analysis is performed to evaluate the thermomechanical behavior of all the cutting edges. Results demonstrate that the use of prepared cutting edges enhances stress distribution and reduces the temperature. Experimental results confirm that the drag finished edge has the best overall performance out of the three edge techniques with lower cutting temperature, better stress distribution, lower cutting forces, reduced flank wear, and reduced roughness of the machined surface finish.

Effect of process parameters on chip formation during vibration-assisted drilling of Ti6Al4V

Vibration-assisted drilling (VAD) of Ti6Al4V is typically used in the aerospace industry to enhance the performance of the machining process. A mix of continuous and saw-tooth chip formation is associated with VAD of Ti6Al4V. In this paper, a comprehensive experimental study is developed to examine the effect of process parameters on the dominant chip formation mechanisms and the associated effects on the thrust forces and machined surface finish. The results indicate a significant change of the chips free surface produced by VAD. The kinematics of VAD showed a direct relation between the VAD amplitude and the effective rake angle. In agreement with the theory of saw-tooth formation due to cyclic crack formation, the scanning electron microscopy (SEM) examination showed a gross crack (GC) and micro crack (MC) along the shear plane. The GC increased from 20 μm for conventional drilling to 224 μm for VAD at the highest amplitude. Moreover, increasing the VAD amplitude to 160 μm showed an obvious enhancement of the machined surface finish. In addition, the study presents the influence of VAD on the tool wear mechanisms through the composition analysis of the chips machined surface using Energy Dispersion X-ray Spectroscopy (EDS).

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Dislocation structures, chemical segregation, γ′, γ″, δ precipitates, and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure are revealed. Knowledge derived from these process-structure-property relationships was used to engineer a super-solvus solution anneal at 1020 °C for 15 min, followed by aging at 720 °C for 24 h heat treatment for AM-IN718 that eliminates Laves and δ phases, preserves AM-specific dislocation cells that are shown to be stabilized by MC carbide particles, and precipitates dense γ′ and γ″ nanoparticle populations. This “optimized for AM-IN718 heat treatment” results in superior properties relative to wrought/additively manufactured, then industry-standard heat treated IN718: relative increases of 7/10 % in yield strength, 2/7 % in ultimate strength, and 23/57 % in elongation to failure are realized, respectively, regardless of as-printed vs. machined surface finishes.

Tool orientations’ generation and nonlinear error control based on complex surface meshing

Tool orientations’ planning of five-axis machining is a significant factor for impacting surface quality and overall machining accuracy of complex-curved surface parts. This paper particularly describes a practical method of tool orientation’s generation for ball cutters commonly used in complex surface finish machining. Based on the method of triangular meshing in surface, the points and the normal vectors are respectively extracted from the surface with unknown parameters. Each obtained normal vector is translated by Rodrigues’ rotational motion in space into the tool orientation for the ball cutter. The generated tool orientation is simple to be adjusted and can effectively avoid problems such as overcut and interference during machining. In addition, by analyzing the nonlinear error between adjacent tool orientations in machining, an interpolation is proposed approach to reduce the rotational error angle and guarantee the continuity of trajectory. After actual processing, the highlights of this method are verified.

Surface Shaping by Cutting: Theoretical Aspects

The terminology relating to surface shaping by cutting is considered. Gaps in the standard terminology give rise to different terms for the same concept and different concepts described by the same term in the technical literature. The concept of the initial tool surface needs to be eliminated, since it covers three independent concepts: the initial generative surface; the initial generative cutting surface; the initial supply surface. Definitions are provided for concepts such as the generative and initial generative lines of tools; the initial surface to be machined and the final machined surface and others. Those definitions should be included in the relevant standard (State Standard GOST 25762–83).

Post-processing effects on the surface characteristics of Inconel 718 alloy fabricated by selective laser melting additive manufacturing

This experimental study presents the effects of various post-processes including finish machining (FM), drag finish (DF) and vibratory surface finish (VSF) on surface characteristics and wear performance of Inconel 718 specimens fabricated by selective laser melting additive manufacturing. Concentrated characteristics are surface roughness, surface topography, microstructure, microhardness, XRD pattern and wear resistance. Analysis shows that partially melted powders on the surface and just beneath the surface create an undesired layer and its thickness varies from 80 to 130 µm that leads to poor surface topography and very high surface roughness. FM and DF post-processes are capable of completely removing this layer and in the meantime, up to 96 and 88% lower surface roughness. Post-processes particularly FM leads to occur strain hardening and resulted in up to 21% increase microhardness as compared to as-built material. XRD pattern of as-built and wrought alloys shows substantial difference when considering (111) and (200) planes. This study demonstrates that post-processes enhance the wear performance of SLM manufactured Inconel 718. Coefficient of friction and the wear rate of the as-built specimen decreased more than 10% after FM process.