Clearance Face Research Articles

Study of the influence of cutting parameters on tool wear and the state of the machined surface

This work presents a study of wear on the clearance face of turning tools. This study will contribute to the development of improved machining precision and efficiency while extending tool life and also ensuring the surface quality produced, despite wear and edge deposition phenomena. A tool flank wear model is developed as a function of the cutting conditions, including the cutting speed, depth of cut, feed rate, and machining time. Factors influencing tool clearance face wear are determined through experimental testing. We also investigate the edge phenomenon reported on the tool cutting face by plotting a curve of the edge variation versus the machining time. Tool wear and built-up edge phenomena both affect the quality of the surface finish produced. Additionally, the edge phenomenon degrades the geometric quality of the tool and generates wear on the tool clearance face. Therefore, models are developed to aid in selection of appropriate cutting conditions that ensure the expected surface finish is realized while also providing control over tool wear. Overall, this method combines experimental and theoretical approaches to study and control turning tool wear with the aim of improving both machining quality and efficiency.

The influence of physical vapor deposition (PVD) coating on the microgeometry of high-speed steel (HSS) cutting tools during the machining of wood-based composites

ABSTRACT The aim of this work was to analyze the impact of a multilayer TiN/AlTiN nano coating deposited using the physical vapor deposition (PVD) method on the microgeometry and durability of replaceable knives made of high-speed steel (HSS). The blunting process took place while milling standard medium density fireboard with a thickness of 16 mm. Seven reference knives and seven coated ones were used. During durability tests, the wear index value, i.e. the maximum wear on the clearance face VBmax = 0.3 mm was adopted as the blunting criterion. After the blunting stage, the tools were subjected to a precise geometric analysis based on a contact profilometer. In this way, a number of geometric parameters and rounding factors K were obtained for coated and uncoated blades at various points along the cutting edge on a distance 10 mm with 0.5 mm increments. Then, these data were subjected to statistical analysis using the Bonfferoni method. The results showed statistically significant changes in the values of some asymmetry coefficients K at the stage of tool lapping.

The performance of grooved turning tools under distinct cooling environments

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

Numerical Modeling of Cutting Characteristics during Short Hole Drilling: Part 2—Modeling of Thermal Characteristics

The modeling of machining process characteristics and, in particular, of various cutting processes occupies a significant part of modern research. Determining the thermal characteristics in short hole drilling processes by numerical simulation is the object of the present study. For different contact conditions of the workpiece with the drill cutting inserts, the thermal properties of the machined material were determined. The above-mentioned properties and parameters of the model components were established using a three-dimensional finite element model of orthogonal cutting. Determination of the generalized values of the machined material thermal properties was performed by finding the set intersection of individual properties values using a previously developed software algorithm. A comparison of experimental and simulated values of cutting temperature in the workpiece points located at different distances from the drilled hole surface and on the lateral clearance face of the drill outer cutting insert shows the validity of the developed numerical model for drilling short holes. The difference between simulated and measured temperature values did not exceed 22.4% in the whole range of the studied cutting modes.

Influence of WC-Co knifes pre-treatment with drag finishing method subjected to tool coatings deposition on blunting process

ABSTRACT This paper details the analysis of the micro geometry in modified tools coated with the nano multi-layer TiN/AlTiN obtained by the PVD method. In standard replaceable cutting blades made of WC-Co before deposition, the radius of the blade rounding was increased from about 4 µm to about 13 µm using the drag finishing method with usage of OTEC company device. Next, the tools coated with the multilayer nano-coating TiN/AlTiN were subjected to blunting process. Mentioned above procedure was carried out on a standard 18 mm thick chipboard, assuming the blunting criterion (maximal tool wear on clearance face) Vbmax = 0.2 mm. In addition, previously blunted tools (modified and unmodified) were subjected to a detailed geometric analysis on a contact profilometer. Results show significant differences in the changes of various geometric parameters, in particular in the coefficients determining the asymmetry of the edge roundness denoted with letter K. Especially analysis of changes that concerns coefficient KR based on loss of cutting edge from rake face in comparison to clearance face suggests more intensive abrasive tool wear on rake face. Based on durability tests it can be supposed that changes in values of asymmetry coefficients in general described with letter K can decide about tool life.

Influence of crystallographic effect on tool wear, cutting stress, cutting temperature, cutting force and subsurface damage in nano cutting of single crystal silicon carbide

Single crystal 3C-SiC as a typical hard and brittle material. Due to its extremely high hardness and brittleness, diamond tools can have drastic wear problems in a short period of time when performing nano-machining processes. Single-crystal 3C-SiC has good anisotropy. In order to gain insight into the effect of crystal orientation on the tool wear behavior during nano-cutting, this paper investigated the tool wear for six cutting crystals downward using molecular dynamics simulation. The tool wear process was analyzed in terms of tool wear, cutting stress, cutting temperature, cutting force and subsurface damage. The results showed that the tool is subjected to large hydrostatic stress concentrations, radial forces and tool temperature concentrations during machining. Under these effects, abrasive wear, graphitic wear and amorphous phase change were produced. In addition, the clearance face of the tool is more severely worn than the rake face. By reasonably selecting the cutting crystal orientation, well control and improvement of tool wear and machined surface quality can be achieved.

Improved life of circular saws used in primary wood processing

The effects of the Engineered Micro-Geometry (EMG) of the carbide teeth of circular saws on their wear rate and resulting sawing variation for 2-time intervals were studied. The objective was to improve the wear resistance of circular saws used during the primary transformation of wood. The tests were carried out under industrial production conditions with two series of circular saws; 1- with up-sharp tips, and 2- with cutting edges honed to adopt a waterfall geometry. The duration of the tests was 255 min and 645 min. Wood studs were sampled to measure sawing variation. Recession on the rake and clearance faces of the tips as well as the width of the wear land were measured. The wear mechanisms of the cutting edges of both types of saws were studied. Chipping and cracking were the two dominant wear mechanisms observed on the up-sharp tips. Saws with waterfall hone tips showed remarkably reduced chipping and cracking. Wear rate of the latter was notably lower than that of saws with up-sharp tips at both periods of sawing. Between-stud, within-stud, and total sawing variations decreased when saws with modified cutting edges were used.

Machinability characterization in end milling of Invar 36 fabricated by wire arc additive manufacturing

Aircraft manufacturing sector manufactures a huge number of preforms near to the final profile or accuracy molds to avoid waste and to be more sustainable in terms of environment. However, this near net shape (NNS) profiles need requirements to avoid expansions and contractions in the manufacturing process, restricted tolerances and high dimensional stability. Therefore, the aim of this paper is to propose a machinability characterization finished milling study of Invar 36 samples fabricated by Wire Arc Additive Manufacturing (WAAM) technology using Minimum Quantity Lubrication (MQL). The results state that the WAAM sample roughness values reach the smallest values for all the cutting conditions although the average WAAM sample force increment is 9% comparing the wrought one owing to the high hardness level of WAAM samples (20%). Moreover, not only the statistical analysis demonstrates that the cutting speed is irrelevant in this machinability investigation, but it also optimizes the best roughness value (0.8 mm) when milling at the cutting speed of 50 m/min and feed per tooth of 0.06 mm/z. Finally, the main wear mechanism when finished milling WAAM sample of Invar 36 is adhesion on the rake a clearance faces.

On cutting process damping for small cutters by including the influences of the dead metal zone and elastic recovery

Existing ploughing-based process damping models oriented for the cutting processes did not consider two important factors, i.e. the dead metal zone (DMZ) in front of the rounded cutting edge and the material elastic recovery rate under the clearance face, and thus, they cannot exactly detect the underlying mechanism of process damping in the cutting processes with small cutters. This article systematically investigates the generation mechanism of cutting process damping for small cutters, and proves that the DMZ and the elastic recovery rate have combined contribution to the process damping of small cutters’ cutting. It is theoretically found that in contrast to the full elastic recovery assumed in the macro cutting processes, the material under the cutter’s clearance face is partially recovered in the cutting processes with small cutters, due to the relatively high proportion of plastic deformation. The actual recovery height is numerically calibrated based on the ideal plastic assumption of the stress-strain relationship. Expressions of the statically and dynamically indented areas, which are required for deriving process damping model, are analytically formulated as the functions of the DMZ and the actual recovery height since they greatly change the indentation boundaries between the rounded cutting edge and the clearance face. Above derivations are then utilized to derive the expressions of dynamic cutting forces, and subsequently, the process damping effect is considered to analyze the milling stability. Finally, a series of milling tests with small cutter prove the reasonability of the proposed process damping model.

Material piling up and spreading effects in the cutting processes with small feed rates

Previous studies only reported that the material piling up effect will occur in the cutting processes with relatively small feed rates, and even in this case, there is no further theoretical report to touch its generation mechanism. In this work, it is the first time to experimentally report that obvious material spreading phenomenon together with the material piling up effect appears in the cutting process, whose uncut chip thickness is less than the minimum uncut chip thickness (MUCT). It is found that one part of the material to be cut will be piled up in front of the cutter’s rake face. Meanwhile, the remained part flows into the cutter’s clearance face, followed by further compression. As a result, the cutting tooth actually does not remove the material, but rolls the material by its rounded edge. Just because of this rolling effect, the flowed material is deformed and spread along the width direction of the workpiece surface, and this spreading behaviour leads to that the width of the machined workpiece is larger than its initial value. The spread width of the workpiece is quantitatively characterized by using Tselikov’s theory, which is widely used to capture the rolling behaviour. The volume of the material piled up in front of the cutter’s rake surface is calculated by subtracting the volume of the spread material, which is calculated based on the spread width, from the volume of the initial material to be cut according to the volume invariance principle. Subsequently, the height of the piled up material is calculated by geometrically modelling the piling up area as a triangle region. Based on the above analyses, the material spreading and piling up mechanisms in cutting are theoretically explored. The validity of the theoretically calculated spread width and piling up height is verified by the numerical results obtained from finite element simulations. Finally, a cutting force model that can characterize the influences of spreading and piling up effects is established. Several cutting experiments, including both the micro and conventional milling tests, confirm that the proposed methods can give better prediction accuracy of the cutting forces, especially when the ratio of feed rate to the radius of the rounded cutting edge is small.

Modelling and prevention of meshing interference in gear skiving of internal gears

Gear skiving is a highly productive process for machining of internal gears which are required in large quantity for electric mobility transmissions. Due to the complex kinematics of gear skiving, collisions of the tool and workpiece can occur during the process. Models exist to check for collisions of the tool shank or collisions in the tool run-out. While these models are sufficient for the process design of external gear skiving, at internal gears meshing interferences between tool and workpiece can appear outside the contact plane on the clearance face of the tool. To test for meshing interference requires comprehensive assessment of workpiece, tool and process kinematics. Currently, this is often done by time consuming CAD-simulation. In contrast, this paper presents an automated geometrical model for the analysis of meshing interference. The test for collisions is thereby performed along the whole height of the tool and especially includes constructive clearance angles and eccentric tool positions. The model is developed for user-friendly implementation and practical applications. The model for avoiding meshing interference in gear skiving is validated on two different process applications. In doing so, influences of the tool and process design on the interference situation are investigated, compared and discussed. Furthermore this new approach enables the prevention of meshing interference or tooth tip collisions in the early tool design by adjusting the process kinematics or the tool design itself. The maximal viable tool height can be quantified and recommendations for improving the clearance face situation are suggested.

Performance evaluation of the edge preparation of tungsten carbide inserts applied to hard turning

Owing to their inferior hot hardness in comparison with alumina-based ceramics and polycrystalline cubic boron nitride, the performance of coated carbide tools when turning hardened steels strongly relies on proper chemical composition and carbide grain size, together with adequate cutting edge preparation. This work investigates the effect of geometric parameters on the performance of cutting tools applied to turning of AISI 4140 steel hardened to 40 and 50 HRC, in terms of the components of the turning force and temperature. Additionally to well-established geometric parameters, such as the projection of the hone radius on the rake face (Sγ), the projection of the hone radius on the clearance face (Sα), and the form factor K (ratio of Sγ to Sα), a novel parameter is proposed, namely perimeter ratio (P), which represents the ratio of the perimeter of the modified cutting edge to the circumference of the standard honed edge. Moreover, the experimental results were compared with analytical and numerical findings in order to assess their effectiveness in predicting the components of the turning force and chip temperature. The results indicated that analytical modeling was capable to satisfactorily predict the variation of the force components with edge preparation, using as input the value of the corresponding experimental forces for the standard honed cutting edge. On the other hand, the numerical modeling was successfully applied to predict the components of the resultant force at the expense of higher computational effort. The cutting force was not drastically affected by edge preparation, whereas the feed and passive forces increased with P and Sα and the form factor K was not capable to provide a consistent relationship with both the feed and passive forces. Both the experimental and numerical temperatures of the chip and the numerical temperature at the tool-chip interface did not present a straightforward trend with regard to edge preparation.

Influence of the microstructure of tool coatings based on Ti and Al on the blunting process during chipboard processing

Influence of the microstructure of tool coatings based on Ti and Al on the blunting process during chipboard processing.This work concerns three different tool coatings containing Ti and Al. i.e. TiN, AlTiN, TiAlSiN applied to cutting tools used in the machining of wood materials. In the case of the AlTiN coating, a multilayer structure with alternately arranged AlTiN and TiN nano-layers was used. The above coatings were applied to standard replaceable knives used for CNC milling heads made of WC-Co cemented carbide. The deposition process was carried out using the RF Magnetron Sputtering method. During the measurement on a workshop microscope, the VBmax index measured on the clearance face was adopted as the wear criterion. The research proved a very good behaviour of the TiN/AlTiN multilayer coating, for which the longest average service life which was recorded exceeded the results obtained for the reference tool by about 30%. The addition of silicon, which was supposed to increase the abrasion resistance, only did not improve the durability of the blade, it actually worsened it by 6%. In addition, the coating, which has been widely used in the machine industry for a very long time, i.e. TiN, did not extend the tool life significantly (+ 7%).

Development of a Process-Oriented Tribological Test Rig for the Performance Assessment of Tool Coatings in Turning of Titanium Ti6Al4V

The interaction of cutting tool and workpiece in the contact zone is crucial with regard to tool wear. This is of particular relevance for difficult to machine materials such as titanium Ti6Al4V in continuous operations like turning. Due to the low thermal conductivity of titanium, the heat generated during cutting mainly flows into the tool leading to high tool temperatures. In addition, the low Young’s modulus in combination with the high yield strength of Ti6Al4V leads to high normal and shear stresses acting on the tool surfaces and to detrimental ploughing unless sharp cutting edges are used. Previous attempts to increase the tool life in turning of Ti6Al4V by coatings have not been satisfactory. Temperature active coatings are expected to reduce friction and thus tool wear, allowing for more productive cutting conditions or reduced use of coolant. Tribological conditions strongly differ between rake and clearance face in terms of sliding velocity, stress state and temperature, while insights into the contact zone during cutting are difficult to obtain. Thus, for preliminary assessment of the tool performance, tribological pin-on-disc tests are generally used. However, they suffer from the drawback of a closed friction system, as the pin repeatedly engages the same track on the material specimen, thereby affecting its tribological behavior. In order to suitably emulate mechanical and thermal conditions in continuous cutting, an open friction system has been designed, which is characterized by simultaneous adjustment and measurement of acting forces. At the same time, tool surface temperatures are captured by intermittent radiation measurement. Consequently, the open friction test rig enables the separate investigation of the tribological conditions of rake and clearance face. In this paper, the test rig design and first experimental results obtained from tribological investigations are reported. Separation of forces and subsequent evaluation of stresses acting on both tool surfaces is explained.

Characteristic of the wear of a tool coating based on amorphous carbon during chipboard milling

Characteristic of the wear of a tool coating based on amorphous carbon during chipboard milling. The study verified the durability and the course of wear during the durability tests of the TiAlN / a-C:N double tool coating. The aforementioned coating consisted of a bottom layer of TiAlN and a top layer based on nitrogenenriched amorphous carbon. Standard replaceable cutters for milling heads made of WC-Co sintered carbide were subjected to the modification process. The coating was applied using plasma by RF Magnetron Sputtering. During the tests, the blade wear was measured using a workshop microscope. The VB max indicator measured on the clearance face was adopted as the blunting criterion and its maximum value was set on 0,2 mm. The results show that the additional coating of amorphous carbon contributed to the increase of the tool durability determined with cutting distance. The use of only a single layer based on TiAlN shortened the durability by about 3%. On the other hand, applying both the bottom and top layers TiAlN /a-C:N) extended the cutting distance by about 24%. The research showed a clear advantage in terms of the durability of the blades modified with a multi-layer coating in relation to a single-layer. Moreover, the positive effect of the top layer containing amorphous carbon on tool durability has been demonstrated.

Study on the effect of laser-assisted machining on tool wear based on molecular dynamics simulation

During the nanometric cutting of single crystal silicon, the wear of the diamond tool is rapid. Despite laser-assisted machining (LAM) has been used to mitigate tool wear, the specific mechanism is not clear. In this paper, molecular dynamics simulations have been successfully used to explain the effect of LAM on tool wear. The long-range carbon bond order potential (LCBOP) is used to describe the interaction of atoms in the diamond tool. The simulation results show that it has the ability to accurately simulate the graphitization of diamond. LAM enhances ductile response of silicon and reduces the cutting force. But only at the appropriate laser power, LAM will inhibit the formation of silicon carbide and mitigate tool wear. The effect of laser power on the tool rake face and clearance face is different. When the laser power is about 50 eV/ps, the wear of tool clearance face is significantly suppressed, which is attributed to the reduction of frictional resistance. When the laser power is about 150 eV/ps, the reduction in cutting forces and silicon carbide results in smaller tool wear of the rake face. At other laser powers, a large increase in chip temperature may promote tool wear to some extent. Therefore, proper laser power is necessary during LAM.

High-Precision Cutting Edge Radius Measurement of Single Point Diamond Tools Using an Atomic Force Microscope and a Reverse Cutting Edge Artifact

This paper presents a measurement method for high-precision cutting edge radius of single point diamond tools using an atomic force microscope (AFM) and a reverse cutting edge artifact based on the edge reversal method. Reverse cutting edge artifact is fabricated by indenting a diamond tool into a soft metal workpiece with the bisector of the included angle between the tool’s rake face and clearance face perpendicular to the workpiece surface on a newly designed nanoindentation system. An AFM is applied to measure the topographies of the actual and the reverse diamond tool cutting edges. With the proposed edge reversal method, a cutting edge radius can be accurately evaluated based on two AFM topographies, from which the convolution effect of the AFM tip can be reduced. The accuracy of the measurement of cutting edge radius is significantly influenced by the geometric accuracy of reverse cutting edge artifact in the proposed measurement method. In the nanoindentation system, the system operation is optimized for achieving high-precision control of the indentation depth of reverse cutting edFigurege artifact. The influence of elastic recovery and the AFM cantilever tip radius on the accuracy of cutting edge radius measurement are investigated. Diamond tools with different nose radii are also measured. The reliability and capability of the proposed measurement method for cutting edge radius and the designed nanoindentation system are demonstrated through a series of experiments.

Centre cone generation and its force performance in single-point diamond turning

In single-point diamond turning (SPDT), vertical tool centre error owing to the tool feed trajectory is higher or lower than the workpiece centre will result in the conical or cylindrical appearance on the centre of machined surface. Different from the residual centre cylinder under tool below centre error existance, the interference between the tool and the workpiece when tool above centre error exists will cause interference zone around the formed centre cone, which greatly affects the form accuracy of the machined surface and the optical functions it owns. In order to explore the evolution and force performance of the central cone during tool interference, and realize the online identification of tool above centre error, this paper analyzed the relation between the centre structure mophology and the cutting force form under the existence of the tool above centre error. Meanwhile, the influence of the secondary interference between the tool clearance face and the centre cone generated from previous face turning was studied. Then, by establishing the geometric model of the tool clearance face, round platform and centre cone during the turning process, a interference spatial curve model between tool and workpiece was derived. Finally, a force model reflected by the mapping of extrusion area of tool and workpiece was established, whereby the mapping relation between the cutting force and the morphology of the interference zone was further clarified, and the tool above centre error could be online identified based on the cutting force forms. Theoretical and experimental results show an exact correspondence between the cutting force and the morphology of interference zone, the online identification of the tool above centre error can be potentially realized by the established cutting force model, which greatly improves the cutting efficiency of SPDT.

Wear of TiAlN and DLC coated microtools in micromilling of Ti-6Al-4V alloy

The trend toward the miniaturizing of commercial and engineering products is inevitable. Micromilling is the most versatile process to shape microcomponents subtractively. One of the main areas that benefit from micromilling is medical, with titanium and titanium alloy being its most frequently used materials. The popular Ti-6Al-4V alloy has excellent combination of strength and toughness, combined with a great resistance to corrosion and oxidation. This particular alloy dominates other Ti alloys and is used in 50% of all titanium applications. Taking into consideration that this alloy is considered a difficult to cut material, this study investigates the machinability of Ti-6Al-4V in micromilling operations. The wear of micro tools (152.4 μm diameter) coated with TiAlN and diamond-like carbon coating (DLC) are investigated and compared against uncoated tools. The tests are performed on a four-axis CNC milling system with a 60,000 min−1 maximum spindle speed. The tools are tested under dry conditions and wet conditions using the minimum quantity of lubrication. It is used cutting speed of 9.6 m/min, feed rate of 0.1 μm/tooth and axial depth of cut of 10 μm. The test consisted of machining slots 4.2 mm long until the end of the tool life. The results show that edge radius rounding and flank wear are the main wear types. The wear is predominant on the secondary clearance face of the microtool when applying cutting fluid. The lowest tool wear is obtained with the DLC coated microtools under dry conditions, presenting a wear reduction of 640% and 267% when compared to TiAlN coated and the uncoated microtool, respectively.

Modeling of the minimum cutting thickness in micro cutting with consideration of the friction around the cutting zone

Friction modeling between the tool and the workpiece plays an important role in predicting the minimum cutting thickness during TC4 micro machining and finite element method (FEM) cutting simulation. In this study, a new three-region friction modeling is proposed to illustrate the material flow mechanism around the friction zone in micro cutting; estimate the stress distributions on the rake, edge, and clearance faces of the tool; and predict the stagnation point location and the minimum cutting thickness. The friction modeling is established by determining the distribution of normal and shear stress. Then, it is applied to calculate the stagnation point location on the edge face and predict the minimum cutting thickness. The stagnation point and the minimum cutting thickness are also observed and illustrated in the FEM simulation. Micro cutting experiments are conducted to validate the accuracy of the friction and the minimum cutting thickness modeling. Comparison results show that the proposed friction model illustrates the relationship between the normal and sheer stress on the tool surface, thereby validating the modeling method of the minimum cutting thickness in micro cutting.