Slot Milling Research Articles

Assessment of tool wear and microstructural alteration of the cutting tools in conventional and sustainable slot milling of Ti-6Al-4V alloy

This research presents both qualitative and quantitative analyses of tool wear during slot milling of Ti-6Al-4V alloy under conventional flood coolant and sustainable dry and minimum quantity lubrication (MQL) machining conditions. The microstructures of the cutting tools near the cutting edges have been analyzed for understanding the effectiveness of tool coating and the influence of tool wear and machining conditions on the tool microstructure. The abrasion wear was measured using maximum flank wear (VBmax) and the length over which the flank wear occurred. The chipping wear was measured using the surface area of the material chipped off from the cutting edge or tool nose. In addition, the correlations between the abrasion and chipping wear with plastic failure were investigated. It was found that the average magnitudes of VBmax and length were lower in MQL machining. The calculations of the surface area of chipped materials indicate comparatively lower chipping wear in MQL machining. Both the abrasion and chipping wear occurred along with plastic failure, indicating correlations among those wear mechanisms. It turned out that the TiAlN-coating was more effective in the reduction of tool wear under dry machining conditions. Delamination wear was observed under flood and MQL conditions, illustrating the effectiveness of coated tools under dry machining conditions. The microstructural analysis of the worn-out uncoated tools indicates plastic deformation and grain refinement underneath the tool wear, whereas this effect is less severe in coated tools. Conclusively, sustainable dry machining with TiAlN-coated tools and MQL machining resulted lesser tool wear, indicating the effectiveness of sustainable machining processes for Ti-6Al-4V alloy.

New observations on wear characteristics of solid Al2O3/Si3N4 ceramic tool in high speed milling of additive manufactured Ti6Al4V

Additive Manufacturing (AM) technologies applied to the titanium alloys have attracted attention from industries in recent years. Despite one of the main goals of AM is the reduction of manufacturing steps, semi-finish/finish machining operations are still required so as to obtain the desired geometrical tolerance and surface features. In this study, the solid end mill was manufactured by Al2O3/Si3N4 (Sialon) ceramic materials and employed in high-speed slot milling of Ti6Al4V alloy fabricated by the Direct Metal Laser Sintering (DMLS) AM technology to study the tool wear characteristics during processing. The Raman spectroscopic method was employed to characterize the molecular structures of Sialon ceramics for the manufacturing of the cutting tool. The morphologies and elemental maps of wear region of the ceramic tool were examined by scanning electron microscope and energy dispersive spectroscopy techniques. The results show that the adhesion wear and diffusion wear are the dominant wear mechanisms, and the chemical stability of Al2O3/Si3N4 (Sialon) ceramics fabricated as the solid ceramic tool to the attack of the atoms from additive manufactured Ti6Al4V is relatively weak under the atmosphere. The difference of thermal expansion coefficients of diffusion layer and tool substrate accelerates the initiation and propagation of thermal cracks formed on the diffusion interface. Moreover, fracturing and crater-like groves near the tool edge were finally formed due to the removal of adhered workpiece material.

The use of support vector machine, neural network, and regression analysis to predict and optimize surface roughness and cutting forces in milling

In the present study, prediction and optimization of the surface roughness and cutting forces in slot milling of aluminum alloy 7075-T6 were pursued by taking advantage of regression analysis, support vector regression (SVR), artificial neural network (ANN), and multi-objective genetic algorithm. The effects of process parameters, including cutting speed, feed per tooth, depth of cut, and tool type, on the responses were investigated by the analysis of variance (ANOVA). Grid search and cross-validation methods were used for hyperparameter tuning and to find the best ANN and SVR models. The training algorithm of developed NNs was one of the hyperparameters which was chosen from Levenberg-Marquardt and RMSprop algorithms. The performance of regression, SVR, and ANN models were compared with each other corresponding to each machining response studied. The ANN models were integrated with the non-dominated sorting genetic algorithm (NSGA-II) to find the optimum solutions by means of minimizing the surface roughness and cutting forces. In addition, the desirability function approach was utilized to select proper solutions from the statistical tools.

Cutting force prediction in milling CFRPs with complex cutter geometries

The ability to predict the cutting forces for an arbitrary cutting tool is essential for selecting process parameters that would result in minimum machining damage. This activity is also important for improving existing cutting tool geometries and developing new ones. This work utilizes the mechanistic modeling approach in combination with neural networks data fitting for simulating the cutting forces in the milling of unidirectional carbon fiber-reinforced polymers (UD-CFRP). A method is proposed for predicting the cutting forces for tools of complex geometry by transforming the specific cutting energies from orthogonal cutting to the oblique cutting and accounting for the effects of rake angle and edge radius. It is shown that the method developed is capable of predicting the cutting forces in slot milling of unidirectional composites with a segmented flute cutter and over the entire range of fiber orientations from 0° to 180°. Model predictions were compared with experimental data and were found to be in good agreement. The effect of varying tool geometry on cutting forces was also investigated.

Tool wear and resulting surface finish during micro slot milling of polycarbonates using uncoated and coated carbide tools

A growing application of polycarbonates is in the microfluidic disks and DNA detection devices, where surface finish of the micro-channels plays an important role. This study intends to investigate the tool wear and surface finish generated during micro slot milling of polycarbonate using uncoated, TiN-coated, and TiAlN-coated tungsten carbide tools. The effects of tool coating and the machining parameters on the possible reduction of tool wear and improvement of surface finish were investigated. It was found that with careful selection of cutting parameters and tool coating, micro-channels with smoother surface finish, minimum burrs around the edges, and controlled tool wear can be obtained using micro-milling. A combination of medium range of depth of cut and feed rate was found to improve the surface finish in polycarbonates, as well as minimize the tool wear. The TiAlN tool coating was found to only be effective in reducing tool wear without much effect on the machined surface. The adhesion was found to be the most dominating tool wear mechanism in uncoated carbide tool, followed by cutting edge chipping and tool nose’s plastic failure. The adhesion wear was found to be reduced in coated tools, especially in TiAlN-coated tools, although delamination wear started to dominate in the coated tools when higher feed rate and depth of cut were used. Both lower and higher of depths of cut were found to generate higher tool wear and leave traces of tool marks on the machined surface.

The effects of material anisotropy on secondary processing of additively manufactured CoCrMo

Components produced by near net shape additive manufacturing processes often require subsequent subtractive finishing operations to satisfy requisite surface finish and geometric tolerances. It is well established that the microstructure and properties of the as-built component are sensitive to the additive processing history. Therefore, downstream secondary processes may be affected by the as-built components’ mechanical behavior. In this work we study the sensitivity of secondary machining operations on CoCrMo samples produced via laser powder bed fusion. Utilizing novel high-throughput mechanical testing, microstructure characterization, and a rigorous statistical analysis we investigate the degree of material anisotropy present in the as-built material. We then study the effects of this anisotropy on secondary processing via slot milling experiments. Our results indicate that mechanical anisotropy is driven by both the morphology of the microstructure as well as crystallographic texture. The machining force response is correspondingly sensitive to these sources of anisotropy, which has the potential to impact how manufacturers finish additively built parts.

Experimental and theoretical investigation of milling tool selection towards energy-efficient process planning in discrete parts manufacturing

Recently, energy-efficient process planning has aroused numerous concerns from both industry and academia. However, as one of the most important tasks of process planning in discrete parts manufacturing system, tool selection has seldom been investigated in terms of energy efficiency. Without a good understanding of its effects on energy efficiency of machining process, energy-efficient manufacturing cannot be achieved to a satisfactory level. To bridge this research gap, this paper studies tool selection effects by analysing tools with different geometrical parameters, i.e. cutter radius, flute number and helix angle. Their effects on energy efficiency of slot milling process are analysed using experimental approach and theoretical approach, respectively. In experimental approach, Taguchi method is firstly applied to study the effects of each tool geometrical parameter. Then, analysis of variance (ANOVA) is performed to study the significance of each factor. In theoretical approach, the influence of tool selection on cutting power is analytically revealed. Subsequently, the energy efficiency of different cutters is quantitatively analysed through numerical experiments. The results are quite promising with both approaches leading to the same conclusion. The rank of influence is cutter radius > flute number > helix angle. Both methods suggest that a milling cutter with a larger cutter radius and fewer flutes will improve the energy efficiency in milling process. Although there is a small discrepancy in helix angle, it does not affect the good agreement of these two methods since the influence of the helix angle is nearly negligible. Compared to experimental approach, theoretical approach may have more application potential since it may help reduce time and waste of materials. To the best knowledge of the authors, the effects of tool selection on energy efficiency in milling process are systematically analysed for the first time, which significantly advances the state of the art in energy-efficient process planning.

Burr edge occupancy: edge finishing index for milling machined parts

Machining burrs are formed at all machined workpiece edges. One useful solution to decrease machining time and cost, in particular for milling parts, is to generate machined parts edges with minimum burr. This article proposes burr edge occupancy ηs as an index to evaluate deburring difficulty and, consequently, adequate selection of suitable deburring methods. Initially the sensitivity of ηs to cutting parameters must be evaluated. We investigated the main governing factors on ηs when slot milling two types of aluminium alloys (from different families) that are used in the automotive and aerospace industries. The cutting parameters that led to edges with minimum ηs are presented. It was found that, unlike most burr size attributes, ηs is sensitive to variation of the cutting parameters used: cutting speed, family of material, and cutting tools. Lower ηs means less time and effort for deburring and edge finishing of machined parts. Furthermore, ηs measurement is more convenient than the procedures used to measure other burr size attributes, including burr height (bh) and burr thickness (bt).

Study on End Brush Deburring and Sintered Diamond Ball Deburring of Micro-features Milled

The presence of top burr in the micro-features produced by milling process can deteriorate and affect the surface quality of the products. Though there are some deburring methods can be used and reported successfully remove the burr in the micro scale features, however simpler and alternative method is still needed. Two of the deburring methods that can be used are end brushing and sintered diamond ball methods. Therefore the aim of this paper is to study the application of the end brush and sintered diamond ball for deburring top burrs exist on micro features produced by milling process. Slot milling experiments were conducted and subsequently deburring process using the two methods was conducted. Micro scale features were also produced using milling process followed by deburring. The deburred results were observed visually using optical microscope and Scanning Electron Microscope (SEM) and surface roughness was measured. Experimental results show that the end brush and sintered diamond ball deburring have successfully remove the top burrs. The end brush deburring method produced better surface quality compared to the sintered diamond ball.

Optimization of energy consumption and surface roughness in slot milling of AISI 6061 T6 using the response surface method

Industrial sectors are looking for reducing their energy consumption due to the concerns on fossil fuel depletion and climate change, along with the increasing energy costs. In recent years, research on optimizing the energy consumption of machining processes has received significant attention as a way to diminish their environmental impact.

Investigation of effect on energy consumption of surface roughness in X-axis and spindle servo motors in slot milling operation

The energy cost is a significant expense in the machining companies, and the reduction of energy consumption has a critical prescription in the industry. To increase energy efficiency, machine producers have contributed by developing advanced functions for machines. Besides these, one of the main purposes of machining is to bring the desired surface roughness to the best level. In this study, it is aimed to optimize cutting parameters to minimize the surface roughness and the energy consumption in the process of the 7075-aluminium material, which is commonly used in manufacturing industry, in CNC milling machine under dry cutting conditions. Therefore, a test list was created with Taguchi L9 experiment design the surface roughness and the power consumption of the machining centre were measured by processing in the CNC milling machine according to the tool diameter, cutting depth, cutting speed and feed rate parameters. The measured values were analyzed in the Minitab 17 program for the Taguchi method. According to the results of the analysis, X axis servo motor’s Pcutting value is affected by the amount of depth of 82%. However, the spindle servo motor’s Pcutting value was determined to be affected by the highest 34% cutting speed. The SEC (Specific Energy Consumption) value of both servo motors is affected by the maximum amount of depth. It is the amount of SCEC (Specific Cutting Energy Consumption) allows us to characterize machinability of the materials according to results from energy consumption. SCEC value is affected by the cutting speed 53% rate in the axis servo motor. In addition, it is affected by the feed rate of 43% in the spindle servo motor.

Experimental study on milling performance of 2D C/SiC composites using polycrystalline diamond tools

The present paper concerns assessment of the milling machinability of 2D C/SiC composites using polycrystalline diamond (PCD) tools. Influences of milling parameters on cutting forces, surface integrity and machined defects were studied. Experimental results showed that cutting forces varied greatly in a milling circle due to the sudden changes of fiber cutting angle. As cutting speed increased, cutting forces and surface roughness decreased. Cutting forces and surface roughness both increased as feed rate increased. Fiber fracture, matrix damage and fiber-matrix debonding were three main material removal mechanisms during slot milling. Pits and cracks were main machined defects at ground surface, and they more easily happened at the intersection of woven yarns. Surface integrity of 90° fiber orientation was better than that of 0° fiber orientation. Machined defects of side edges had three types: fiber protrusion combined with surface damage, fiber protrusion and surface damage. Quantity and size of surface damage were much larger than fiber protrusion. Both of surface damage and fiber protrusion increased with the increase in feed rate. Higher cutting speeds could decrease the fiber protrusion of side edges evidently, however have minor influence on the surface damage.

Micro-machinability and edge chipping mechanism studies on diamond micro-milling of monocrystalline silicon

Excessive generation of undesirable surface and subsurface damages such as surface edge chipping often occurs when monocrystalline silicon, a hard and brittle material, is machined at tens to hundreds of microns in thickness. However, before developing strategies to reduce edge chipping and improve the machining efficiency by micro-milling, understanding of its cutting mechanism is required. In this study, the micro-machinability and edge chipping mechanism on a (001) silicon were investigated by full slot milling using the natural diamond tool. A volumetric measurement technique was also proposed to quantify edge chipping better. Three chipping types: 45°, 90° and mixed mode (dominant type) were observed, and its mechanism is attributed to cleavage and slip structure within silicon’s crystal architecture. The cutting forces, surface and edge quality were examined and characterised accordingly. From the reported results, the size effect on the specific cutting energy is greatly influenced by the shear strain work hardening of the workpiece. Enhancement of the strain work hardening effect is attributed and demonstrated using small feed rate, high cutting speed and cutting along the [100] feed direction. As a result, good surface quality of Ra = 20 nm and small edge chipping volume of 80 μm3 were achieved.

Modeling and Experiment of Milling Force under All Fiber Orientation Angles in Slot Milling of Unidirectional CFRP Laminates

Milling force is an important factor in determining the machined surface quality of carbon fibre reinforced polymer (CFRP) in milling process. This paper focuses on the radial force and tangential force under different fibre orientation angles during the milling of unidirectional T800/X850 CFRP laminates. The traditional straight slot milling is replaced by the circumferential slot milling in the experiment and the idea of small scale approximation is applied in analysis of data. Using this method, the milling force under all fibre orientation angles can be obtained approximately by a single experiment and the radial force and tangential force during the milling process can be obtained through mechanical modelling. Through processing experimental data, the coefficients in the theoretical formula of CFRP milling are fitted to get a function about milling force on cut depth, feed and tool rotation angle. And this function can be used to optimise milling parameters and fibre orientation during slot milling. [Submitted 16 January 2017; Accepted 18 December 2017]

Modelling and experiment of milling force under all fibre orientation angles in slot milling of unidirectional CFRP laminates

Milling force is an important factor in determining the machined surface quality of carbon fibre reinforced polymer (CFRP) in milling process. This paper focuses on the radial force and tangential force under different fibre orientation angles during the milling of unidirectional T800/X850 CFRP laminates. The traditional straight slot milling is replaced by the circumferential slot milling in the experiment and the idea of small scale approximation is applied in analysis of data. Using this method, the milling force under all fibre orientation angles can be obtained approximately by a single experiment and the radial force and tangential force during the milling process can be obtained through mechanical modelling. Through processing experimental data, the coefficients in the theoretical formula of CFRP milling are fitted to get a function about milling force on cut depth, feed and tool rotation angle. And this function can be used to optimise milling parameters and fibre orientation during slot milling. [Submitted 16 January 2017; Accepted 18 December 2017]

Sustainable selection of optimum toolpath orientation in milling AISI 1018 steel alloy

Toolpath orientations and axes weights have been identified as some of the parameters that could influence the electrical energy consumption and sustainable machining objectives. However, power evaluations of the machine tool axes when carrying different weights and in different toolpath trajectories have not been fully implemented for energy management in machining processes. This work proposes a framework for determining optimum toolpath orientations by conducting a comparative study and individualization analysis of axes weights for electrical power consumption management in slot milling operations of AISI 1018 steel alloy. Results show that performing slot milling at an angle aligned in the direction of the axis with the minimum weights tend to lower the feed axes power consumption.. Therefore, sustainable slot milling operations could be achieved by aligning the toolpaths at an angle oriented in the direction of the lighter axis for minimum feed axes power consumption. This work could further enhance the modeling of power consumption, and hence electrical energy demand in mechanical machining for resource efficiency and green manufacturing.

Material Stiffness and Cutting Parameters for Honeycomb Aluminum Sandwich Panel: a Comparison with Bulk Material

Abstract Aluminum sandwich panel provides a high-strength, light-weight structural material for use in aircraft and aerospace applications such as cabin bulkheads, rotor blades, and luggage and cargo unit load devices. This unique material also has application in many other industries such as machine tool enclosures, museum exhibits, marine craft bulkheads, and hurricane panels for storm survivability. This material, consisting of aluminum face sheets surrounding an aluminum honeycomb core, offers very high rigidity in a low density material. Machining this material is quite challenging due to variable cutting conditions in the low density, low lateral stiffness honeycomb core. Machining often requires a significant amount of post-processing in the form of manual removal of the partially released core walls (flags) along machined edges. The purpose of this work is to reduce the flagging created in the machining of this material. The first step to improving the cutting conditions is to better understand the causes that impact them. In this pursuit, a series of experiments was conducted to measure, quantify, and study the cutting forces during the machining of aluminum sandwich panel. A force dynamometer was used to measure forces during slot milling in bulk aluminum generating cutting coefficients for the force model. Cutting results in bulk aluminum showed generally good agreement with the model with over-predictions ranging from 5 to 20% depending on the feed rate. A series of cutting tests was then conducted on the aluminum sandwich panel in order to decouple the machining forces for the face sheets, the honeycomb core, and combinations of face sheets and core. The data revealed vibration in the honeycomb material that were significantly worse for shallower depths of cut involving the top face sheet and the upper portion of the honeycomb structure despite efforts at stiffening the fixture. The data showed force spikes that correlate with specific engagement conditions in the honeycomb structure. Peak forces were measured as high as 400N though it is not entirely clear whether these peak values are representative of actual peak forces or a combination of peak force with harmonic vibration. The resulting cut walls showed signs of tearing, rubbing, and remaining cell walls indicating that for much of the cut, ideal shearing of the material did not occur. The research highlights the need for further study of the actual mechanism of cell wall removal in this complex cutting environment.

The evolution of cutting forces during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composites

Cutting forces generated during traditional machining of fiber reinforced polymer composites play an important role in determining machined surface quality. The cutting force signals also provide a live indicator of the dynamic behavior of the chip formation process. Cutting forces in machining FRPs are dependent primarily on the instantaneous fiber cutting angle, chip thickness, cutting edge geometry and the current state of cutting edge wear. In this study, effects of the cutting edge rake angle and tool wear on cutting force evolution during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composite was investigated. The cutting forces were measured in the feed and normal directions and then transformed to the tangential and radial directions of the tool path. A simplified cutting force model consisting of a shearing region and a pressing was used to determine the shearing and friction force components. This allowed determination of the friction coefficient on the clearance face of the tool. It was found that the friction coefficient varied significantly with rake angle and fiber cutting angle. The effect of rake angle on cutting forces is more discernable in the shearing region with positive rake angle tool providing the most efficient cutting. Furthermore, correlations were found between machining damage and the magnitude and orientation of the resultant shearing force.

Effect of Tool Path Complexity on Top Burrs in Micromilling

Abstract Burr generation during micro milling operation is one of the major problem that poses challenge before engineers. The deburring operations performed in macro milling cannot be utilized in micro domain as this can affect the dimensional accuracy and possibly, damage the machined surfaces. However, the burr dimensions could be reduced by selecting appropriate machining parameters. Most of the studies done so far are focused on straight slot milling operations, while the complex tool paths, which are more often used in the industrial domain, have not been studied adequately. Therefore, the present work involves a detailed experimental analysis of burr formation in micro milling considering the effect of curvature in the tool path. The experiments performed are of two types. The Type I experiments investigate the top burrs as a function of tool path and machined length. The Type II experiments investigate the effect of machining parameters on the formation of burrs in both straight and curved paths. The burr values are found to increase with the curvature for the top burrs because of the increased plowing region due to the curvature effect. It is also noticed that burr dimensions at lower feed values are more in straight slots whereas, at higher feed values, circular tool paths here resulted in more burrs. Minimum burrs are observed at a depth of cut of 20 μm .

A Comparative study of Wear and tool life of HSS TiN coated end mills and WC uncoated end mills

The objective of this research is to compare the performance and economic value of TiN coated end mills and WC end mills on S45C slot milling. The commercial end mills that produce and provide by SAN Engineering and Supply Co., Ltd. and commercial S45C steels, were selected for this investigation. The models of wear were analyzed by the scanning electron microscope, SEM. The result showed that the wear models of the TiN coated end mills are abrasive and surface peeling, while the wear models of WC end mills are adhesive and uniform micro-chipping on the cutting edges. The analysis the economic value also represented that WC end mills are worth more than the others.