Diamond Tool Wear Research Articles

Impact of ultrasonic assisted cutting of steel on surface integrity

Diamond tools are typically used to fabricate optical molds. However, the excessive tool wear of diamond tools during machining steel still prevents their application for optical mold manufacturing. As steel molds potentially offer a higher lifetime than non-ferrous molds, the machining of steel to optical molds with diamond tools is desirable. This implies a great challenge for the production of tools for injection molded parts with complex geometry and high surface quality. As the most suitable method to prevent tool wear, ultrasonic assisted diamond cutting has been established. Since it is not yet known how the ultrasonic vibration during machining affects the surface integrity of manufactured components, an experimental study was carried out for this purpose. The conventional machining mode and the ultrasonic assisted elliptical vibration mode were compared. In addition to diamond tools, tools made of cubic boron nitride (CBN) were also included in the investigations to check whether ultrasonic assisted cutting with these significantly cheaper tools can achieve a similar supreme surface finish. For the evaluation of the surface integrity, the surface topography was measured post-process with 3D white light interferometry and the generated subsurface zone was characterized by metallographic analysis of the processed samples. Additionally, the forces were measured in-process to determine the local mechanical load on the material. The results show that in ultrasonic assisted cutting, compared to conventional machining, an improvement in surface quality is achieved with diamond tools as well as CBN tools. In terms of plastic deformation, it was also found that the influence on the surface layer is significantly different compared to conventional cutting with both diamond tools and CBN tools. The differences are attributed to the ultrasonic impact. Regarding the process forces, an elliptical vibration lowers the process forces with a factor supposedly depending on the cutting edge radius and the material hardness.

Responses of pre-crystallized and crystallized zirconia-containing lithium silicate glass ceramics to diamond machining

This paper reports on the responses of pre-crystallized and crystallized zirconia-containing lithium silicate glass ceramics (ZLS) to diamond machining in simulated dental milling and adjusting processes. Machining mechanics, tool wear and tribological characteristics, and surface and subsurface damage were investigated. Machining forces and coefficients of friction were measured using a force sensor and high-speed data acquisition system. Diamond tool wear and debris adhesion, and machining-induced surface and subsurface damage were examined using field emission scanning electron microscopy. The results show that both tangential and normal forces of crystallized ZLS were significantly higher than those of pre-crystallized ZLS (p < 0.05) while these forces for both materials significantly increased with the material removal rate (p < 0.05). Coefficients of friction in machining of crystallized ZLS were significantly higher than those in machining of pre-crystallized ZLS. In spite of the minimum wear of applied diamond tools in machining both materials, more crystallized ZLS debris adhesion on tool surfaces was observed. The principal removal mechanisms in machining of both materials were primary fracture and minor plastic deformation of pre-crystallized and crystallized ZLS. However, there was more severe fracture in machining of pre-crystallized ZLS than in machining of crystallized ZLS. Although machining-induced subsurface edge chipping damage in both materials remarkably increased with the feed rate (p < 0.05), such damage was significantly severer in pre-crystallized ZLS than in crystallized ZLS (p < 0.05). These microstructure-property-processing relations provide practical guidance of process selection for high-quality fabrication of ZLS materials.

Simulation and Experimental Study on the Surface Generation Mechanism of Cu Alloys in Ultra-Precision Diamond Turning.

The surface generation mechanism of the Cu alloys in ultra-precision diamond turning is investigated by both simulation and experimental methods, where the effects of the cutting parameters on the surface characteristics are explored, including the workpiece spindle speed, the cutting depth, the feed rate and the nose radius of the diamond tool. To verify the built model, the cutting experiments are conducted at selected parameters, where the causes of the error between the simulation and the machining results are analyzed, including the effects of the materials microstructure and the diamond tool wear. In addition, the nanometric surface characteristics of the Cu alloys after the diamond turning are identified, including the finer scratching grooves caused by the tool wear, the formation of the surface burs and the adhesion of graphite. The results show that the built model can be basically used to predict the surface topography for the selection of the appropriate machining parameters in the ultra-precision diamond turning process.

Износ абразивного слоя при глобоидном зубохонинговании

The paper reports the calculation-experimental method for the definition of abrasion layer wear parameters and presents the results of these parameters changes depending on machining conditions at globoidal gear honing. As a parameter for the definition working surface wear in a globoidal gear hone with organic rubber-based binding there is chosen a parameter widely used for the assessment of diamond tool wear – specific consumption of abrasion. The use of this parameter allows defining dimension wear of tool abrasion layer in a computation way, including operation surfaces of the globoidal hone.

Diamond tool wear mode, path and tip temperature distribution considering effect of varying rake angle and duncut/Redge ratio

Diamond tool wear has been proven to strongly depend on the temperature at the cutting zone. This is because the elevated temperature so attained during machining not only lowers carbon cohesion energy thereby reducing the fracture toughness of diamond tool due to C–C bond weakening but also facilitates high rate of carbon diffusion from diamond tool into silicon workpiece leading to high tool wear. This research therefore studied the response of diamond tool wear path and mode to changing rake angle and ratio during ultraprecision single point diamond turning of a monocrystalline silicon. It was observed from the study that the tool with larger rake angle and high ratio experienced stronger cutting resistance from the workpiece thereby causing the kinetic friction to be high. Additionally, silicon carbide (Tribochemistry) formation was observed to be through both solid-state single phase and multiphase reaction which are in tandem with sp 3 –sp 2 disorder (graphitization) of diamond with bulk of the observed tool wear happening in the flank face which could be due to increasing rake angle influence on the changing ratio.

Diamond Tool Wear Measurement by Profilometry Method for Ultra-precision Machining of Silicon

Abstract Ultra-precision machining is used to generate the high quality surfaces in terms of nano-metric surface finish and sub-micron profile accuracy for various engineering applications. Due to unique properties of diamond i.e. high hardness, good heat conductivity and low friction co-efficient it is most suitable tool material for ultra-precision machining. Advancements in material science and growing needs for modern applications leads to development of new materials. Silicon is one of the prominent materials used for various optical applications. However processing of silicon by machining is quite difficult due to its hard and brittle nature. Diamond tool wear is one of the major issues for ultra-precision machining which leads to increase the process cost significantly. Control of tool wear mainly depends on machining parameter selection and understanding of tool wear mechanism. Wear measurement of diamond tool is essential to understand the wear mechanism, process behavior and tool life quantification. Wear measurement of nano-metric cutting edge is one of the challenging tasks. In current study machining experiments are performed on Silicon. Tool cutting edge is analyzed by profilometric measurements at different orientations. Wear of cutting edge, rake face and flank face is measured. Measurement results are very helpful for understanding the possible reasons of wear and hence to optimize the machining conditions to minimize the tool wear.

Oxygen-shielded ultrasonic vibration cutting to suppress the chemical wear of diamond tools

Ultrasonic vibration has been applied to reduce intense chemical tool wear in ultra-precision diamond cutting of steel and other alloys since a few decades ago. But still, its tool wear suppression mechanisms have not been fully understood. In this paper, the effect of oxygen in suppression of diamond tool wear for ultrasonic vibration cutting is investigated. Experimental results show that the wearing rate is reduced by applying oxygen shielding to the cutting zone in comparison with air and argon. Scientific explanations are also provided for the observed phenomenon through low-pressure metal oxidation experiments and X-ray photoelectron spectroscopy surface analyses.

Steady tool wear and its influence on tool geometry in ultra-precision fly cutting of CuZn30

In ultra-precision fly cutting (UPFC), steady tool wear progresses gradually when cutting ductile materials. The steady wear of diamond tools changes the tool geometry, and further affects the topography of the machined surface. In this study, a theoretical and experimental investigation was conducted on the forms of steady tool wear and their influence on the tool geometry in UPFC. The features of steady tool wear in UPFC were investigated, the displacement of the cutting edge under the effects of tool flank wear was modeled, and factors affecting the cutting edge roundness were investigated. The study results indicate the following: (1) the features of steady tool wear in UPFC include crater wear on the rake face, smooth and flat wear on the cutting edge, and flank wear on the tool clearance face. (2) A smooth wear-land on the cutting edge changes the top rake of the cutting tools, whereas flank wear on the tool clearance face affects the clearance angle and roundness of the cutting edge. (3) The maximum width of the tool material loss zone, the nose radius of the original fresh cutting edge, and the arc angle of the wear-land have a certain influence on the nose radius of the worn cutting edge. The results of this study will provide deep insight into steady tool wear and its influence on the tool geometry, which can potentially be used to predict or evaluate the finish of a machined surface under tool steady wear.

Effect of microstructure on mitigating tool wear in diamond turning of nitrided steels

Tools used in diamond turning of steels undergo severe tool wear. In this study, several steels were heat-treated and nitrided to investigate the wear mitigating effect of the microstructure of nitrided steels. The results indicate that the tool wear is mitigated with increase in the chromium content of steel. The results also indicate that chromium carbides are transformed into chromium nitrides by nitriding. Thermodynamic analyses demonstrated that chromium nitrides are stable when in contact with diamond at the cutting temperature. Further, the ratio of iron nitrides to iron increased because the iron levels decreased as the chromium levels increased. Although diamond reacts with iron nitrides, the interaction is considerably weaker than that with iron.

Graphitization Behavior of Single Crystal Diamond for the Application in Nano-Metric Cutting.

Background: Graphitization behavior of diamond has received an increasing interest in nanoscale machining of some hard and brittle materials. Diamond has always been an important and excellent tool material in cutting area. However, the graphitization of the diamond tool is inevitable when it was used in special conditions. It is indicated that the graphitization of diamond crystal has great influence on the wear resistance of diamond cutting tool. The graphitization behavior needs to be investigated extensively in nanoscale with an atomic view. Molecular dynamics simulation provides a useful tool for understanding of the graphitization mechanism of diamond. The investigation on graphi-tization behavior of single crystal diamond can also provide a useful reference for the application of diamond cutting tool.Materials and Methods: In this paper, a molecular dynamics (MD) diamond crystal model is built to examine the graphitization behavior of diamond under various conditions. The sixfold ring method was employed to identify the structural characteristics of graphite and diamond. The effects of temperature and crystal orientation on the graphitization of diamond have been revealed. Considering the effect of temperature, the anisotropy of diamond graphitization against various crystal planes is presented and discussed carefully. The nano-metric cutting model of diamond tool evaluated by the sixfold ring meth-od also proves the graphitization mechanisms in atomic view.Results: Results indicate that the sixfold ring method is a reliable method to evaluate the graphitization behavior of diamond crystal. There exists a critical temperature of the graphitization of diamond. The results also show that {111} plane is more easy to get graphitization as compared with other crystal planes. However, {100} plane of diamond model presents the highest anti-graphitization property.Conclusion: The obtained results have provided the in-depth understanding on the wear of diamond tool in nano-metric machining and underpin the development of diamond cutting tool

New technology for cutting ferrous metal with diamond tools

In recent years, cutting objects for diamond tools have gradually expanded from non-ferrous metal and optical glass to ferrous metal materials. Moreover, the requirements of accuracy have continued to increase. To reduce the tool wear of diamond-cutting ferrous metals, a real-time adjustment method using nitrogen cold plasma was proposed. Atmospheric flexible cold plasma jet (AFCPJ) was developed to restrain diamond tool wear by reducing the chemical affinity on the tool–workpiece interface and by adjusting the complex thermal condition in the cutting zone. To obtain better cooling, lubrication, and modification effects, an ultrasonic elliptical vibration cutting device with separation characteristic was designed to promote the entry of the active particles in AFCPJ into the too–workpiece interface. Unlike dry cutting, diamond cutting assisted by cold plasm and ultrasonic elliptic vibration can help reduce the diffusion wear of carbon elements in a diamond tool to workpieces and chips and also effectively reduce the cutting temperature and the surface roughness of the workpiece. Results show that the AFCPJ can significantly restrain the tool wear of diamond-cutting ferrous metals. In addition, the diamond tool wear achieves the best restraining effect when cold plasma and ultrasonic elliptical vibration work together.

Surface integrity under diamond tool wear effects in ultra-precision raster milling of a Zn–Al–Cu alloy

In ultra-precision raster milling, the material removal process determines surface integrity. In this study, surface integrity was discussed under diamond tool wear effects in ultra-precision raster milling of a Zn–Al–Cu alloy. The results firstly showed that under high speed cutting in ultra-precision raster milling, quenching took place with phase decomposition (namely twin phase changes) with a deformation thickness of even less than 100 nm. Flank wear enhanced phase changes, promoted surface hardening, degraded surface quality, and increased deformation thickness, but crater wear gave better surface integrity. The intrinsic reason is that flank wear caused more external stress but crater wear was reverse, well supported by finite element simulation in orthogonal cutting. Significantly, it provides a further insight into diamond tool wear effects on surface integrity in ultra-precision raster milling of a Zn–Al–Cu alloy.

Essential causes for tool wear of single crystal diamond in ultra-precision cutting of ferrous metals

This paper presents indepth theoretical analyses and experimental verifications involving the essential causes for diamond tool wear from aspects of crystal graphitization, carbon diffusion and oxidation reaction. The catalytic effect of transition metal iron on the structure transformation of diamond crystal to graphite was investigated using the molecular dynamics simulation technique. Mathematic prediction model of carbon atoms diffusing from the diamond tool surface into the iron lattice was established. Moreover, types and conditions of the complicated chemical reactions at the cutting interface were analyzed by chemical thermodynamic calculation method. Raman scattering analysis was performed to distinguish the structural change of diamond crystal, Energy dispersive X-ray analysis was used to detect the change in chemical compositions of the work material, and X-ray photoelectron spectroscopy was adopted to confirm the resultants of interfacial thermochemical reaction. The results indicated the essential causes for diamond tool wear could be summarized as initial rapid reduction of cutting edge strength caused by a series of tribochemistry transformations at localized high temperature and high pressure, and then was attributed to the cumulative mechanical wear of diamond metamorphic surface. This research work provides an important theoretical basis for exploring appropriate wear inhibition processes for diamond tool.

A molecular dynamics investigation into nanoscale scratching mechanism of polycrystalline silicon carbide

In this study, 3D molecular dynamics simulations were conducted to investigate the nanoscale scratching mechanism of polycrystalline SiC constructed by Voronoi site-rotation and cut method. The scratching process, SiC crystal structure evaluation, scratching force, stress, and temperature, surface morphology, and subsurface damage (SSD) were discussed after simulation. The results indicate that the ductile scratching process of polycrystalline SiC could be achieved in the nanoscale depth of cut through the amorphous crystal structure phase transition, which is the primary material removal mechanism in nanoscale SiC scratching. The silicon atom can penetrate into the diamond grit which may cause the wear of diamond tool. The disorder grain boundary (GB) atoms can transit to hexagonal diamond structure and generate dislocation during the scratching. Furthermore, the higher scratching speed results in smaller scratching force, smaller normal stress, and higher temperature due to the larger impaction breaking more SiC bonds, which makes the SiC material more ductile and easier to remove. The tangential stress shows great dependence on the grain and GB geometry and position due to the stress concentration in the GB. It is also found that the higher scratching speed encourages the pileup atoms in the front of grit to flowing to the grit side to form the groove protrusion, which can get a shallower SSD thickness and a wider SSD layer. SSD results also indicate that at least three types of the material removal mechanism – amorphous transition, intergranular fracture, and transgranular fracture – exists in the polycrystalline SiC scratching process.

Mechanism-Based FE Simulation of Tool Wear in Diamond Drilling of SiCp/Al Composites.

The aim of this work is to analyze the micro mechanisms underlying the wear of macroscale tools during diamond machining of SiCp/Al6063 composites and to develop the mechanism-based diamond wear model in relation to the dominant wear behaviors. During drilling, high volume fraction SiCp/Al6063 composites containing Cu, the dominant wear mechanisms of diamond tool involve thermodynamically activated physicochemical wear due to diamond-graphite transformation catalyzed by Cu in air atmosphere and mechanically driven abrasive wear due to high-frequency scrape of hard SiC reinforcement on tool surface. An analytical diamond wear model, coupling Usui abrasive wear model and Arrhenius extended graphitization wear model was proposed and implemented through a user-defined subroutine for tool wear estimates. Tool wear estimate in diamond drilling of SiCp/Al6063 composites was achieved by incorporating the combined abrasive-chemical tool wear subroutine into the coupled thermomechanical FE model of 3D drilling. The developed drilling FE model for reproducing diamond tool wear was validated for feasibility and reliability by comparing numerically simulated tool wear morphology and experimentally observed results after drilling a hole using brazed polycrystalline diamond (PCD) and chemical vapor deposition (CVD) diamond coated tools. A fairly good agreement of experimental and simulated results in cutting forces, chip and tool wear morphologies demonstrates that the developed 3D drilling FE model, combined with a subroutine for diamond tool wear estimate can provide a more accurate analysis not only in cutting forces and chip shape but also in tool wear behavior during drilling SiCp/Al6063 composites. Once validated and calibrated, the developed diamond tool wear model in conjunction with other machining FE models can be easily extended to the investigation of tool wear evolution with various diamond tool geometries and other machining processes in cutting different workpiece materials.

Molecular dynamics simulation and experiment research of cutting-tool wear mechanism for cutting aluminum alloy

In order to reveal the wear mechanism of diamond tool in precision cutting large-aperture aluminum alloy mirror, molecular dynamics simulation is carried out in this work. The simulation results indicate that diffusion wear is the dominant way of the tool wear, which is in consistent with the cutting experiment. EDS of the aluminum alloy chips shows that Cu elements result in the phenomenon of chemical wear for diamond tool in the precision cutting process. Therefore, the wear mechanism of diamond tool in precision cutting large-aperture aluminum alloy mirror is a combination of diffusion wear and chemical wear. In addition, through the micro topography of the diamond tool wear zone, it can be found that the flank wear is the dominant form of the cutting tool. The results of the orthogonal experiment show that the influence of the tool clearance and feed rate on tool wear is greater than that of the cutting speed and tool arc radius. The results of single-factor experiment indicate that with the increase of the feed rate, the tool wear increases. While with the increase of the tool clearance, the tool wear decreases.

CAD/CAM diamond tool wear.

This study evaluated the wear of computer-aided design/computer-assisted manufacture (CAD/CAM) burs and the morphologic changes after a number of millings. Diamond burs (cylinder and step-bur) were divided into four milling groups: zero millings (G0); 15 millings (G1); 25 millings (G2); and 35 millings (G3). Seventy-five premolar crowns were milled using the Cerec Compact Milling unit and VitaBlock Mark II. Surface roughness, three-dimensional profile, and SEM were used for wear and surface damage evaluation. Two-way ANOVA and Tukey test (α = .05) showed that G3 produced statistically different values compared to G0 and G2, but not G1. The cylinder burs showed higher roughness values than step-burs for all groups. SEM showed similar diamond particle damage for cylinder burs and step-burs, and signs of surface damage, cracks, and particle losses for G3. Both cylinder burs and step-burs were able to sustain a larger number of milling procedures than indicated by the manufacturer.

Mechanism of suppressing wear of diamond tool in ultrasonic vibration cutting

Mechanism of suppressing wear of diamond tool in ultrasonic vibration cutting

Diamond tools wear in drilling of SiCp/Al matrix composites containing Copper

Although SiCp/Al matrix composites possess numerous excellent physical and mechanical properties, high hardness and high wear resistance characteristics of SiC reinforcement lead to low tool life and resultant poor machined surface quality in cutting. The aim of this paper is to investigate the micromechanism underlying the macro-scale wear of diamond tools in drilling of high volume fraction SiCp/Al composites. To achieve this, the worn morphologies and possible crystal structure evolution of diamond tools after drilled 10 holes were examined using Laser Scanning Microscope and Raman spectroscopy, respectively. Additionally, based on drilling forces and hole quality, the machinability assessment of SiCp/Al6063 composites was carried out. The results indicate that the mechanically induced abrasion and thermodynamically activated chemical graphitization is the dominant and common wear mechanisms for PCD and CVD diamond coated tools in drilling of 65vol% SiCp/Al6063 composites containing copper. The reciprocating actions of thin graphite layer formed by oxidizing hydrogen chemisorbed on diamond surface by Copper oxides and graphite removal due to SiC particulates’ high-frequency scrape lead to continual and significant occurrence of diamond graphitization. In air atmosphere, the thermodynamic conditions of diamond-graphite transformation in machining of SiCp/Al6063 composites containing Copper are investigated. The coupled abrasive-chemical wear model is formulated based on analytical description of diamond wear mechanisms above. In terms of machinability of high volume fraction SiCp/Al composites, CVD diamond coated carbide drill is preferred, due to its stable cutting force, less wear and its ability to produce acceptable machined quality with increasing hole number.

Suppression of diamond tool wear in machining of tungsten carbide by combining ultrasonic vibration and electrochemical processing

As an important ceramic material, tungsten carbide (WC) is utilized as the typical mold in precision glass molding, which has replaced conventional grinding and polishing to provide a highly replicative process for mass manufacturing of optical glass components. Ultra-precision grinding, which is time consuming and has low reproducibility, is the only method to machine such WC molds to high profile accuracy. Although diamond turning is the most widely used machining method for fabrication of optical molds made of metals, diamond turning of WC is still considered challenging due to fast abrasive wear of the diamond tool caused by high brittleness and hardness of WC. Ultrasonic vibration cutting has been proven to be helpful in realizing ductile-mode machining of brittle materials, but its tool life is still not long enough to be utilized in practical diamond turning of optical WC molds. In the current study, a hybrid method is proposed to combine electrochemical processing of WC workpiece surface into the diamond turning process. Cutting tests on WC using poly-crystalline diamond tools were conducted to evaluate its effect on improvement of tool wear and surface quality. Validation cutting tests using single crystal diamond tools has proven that the proposed hybrid method is able to significantly reduce the diamond tool wear and improve the surface quality of machined ultra-fine grain WC workpiece compared to ultrasonic vibration cutting without electrochemical processing.