Diamond Tool Research Articles

Investigation of the applicability of Cu–Fe–Mn–Ni based high entropy and compositionally complex alloys as metal matrix composites for cobalt free hot-pressed diamond tools

Due to the rising demand and carcinogenic effect of cobalt, alternative metal matrixes need to be developed for hot-pressed diamond tools. Due to this reason High-Entropy alloys without cobalt were calculated via phase fraction diagrams. Three alloys of the Al–Cu–Fe–Mn–Ni system Al30Cu30Fe5Mn25Ni10, Al11.25Cu35Fe5Mn20Ni28.75 and Al5Cu20Fe25Mn25Ni25 were chosen due to their different crystal structures ranging from pure bcc, eutectic fcc-bcc to pure fcc crystal structure. Cr5Cu20Fe25Mn25Ni25 was chosen to verify the change of one element on the consolidation properties. The alloys were mechanically alloyed and hot-pressed at 800 °C for 3 min without and at 900 °C for 3 min with diamonds. Porosity increased with the fraction of bcc solid solution in the investigated alloys of the Al–Cu–Fe–Mn–Ni system. Samples consisting of Cr5Cu20Fe25Mn25Ni25 showed the lowest porosity, which was attributed to precipitation of a second copper-rich fcc solid solution around the remaining pores. At a process temperature of 800 °C and 3 min isothermal hold the samples featured a porosity of only 2.72%. Within the XRD patterns and SEM images of the hot-pressed samples with diamonds no graphitization or formation of carbides could be observed. Therefore, Cr5Cu20Fe25Mn25Ni25 was identified as a promising cobalt free metal-matrix candidate for diamond tools.

Finite element analysis and experimental verification of residual stress in brazed diamond with Ni-Cr filler alloy

Residual stress is the main factor affecting the processing performance and service life of brazed diamond tools. Due to the high melting point of Ni-Cr filler alloy, the difference in thermal expansion coefficient between diamond and brazing layer is large during high brazing temperature, and excessive residual stress tends to be generated at the brazed joint. The existing process parameters are difficult to meet the demand for the lower residual stress under high brazing temperature. Suppressing effectively excessive residual stress has become the focus of current researches for process optimization of brazed diamond. In this paper, the conventional spherical finite element model of diamond is replaced by a six-octahedral finite element model of diamond, and a 3D finite element model of brazed diamond is established. The effects of brazing temperature, brazing layer thickness and holding time on the residual stresses in brazed diamond are analyzed. The results show that higher brazing temperatures result in larger differences in thermal expansion coefficients between the diamond and brazing layer, resulting in larger residual stress. The higher brazing layer thickness will enlarge the stress affected area inside diamond and thus generate higher stress. The residual stress decreases with rising holding time, however, the subsequent thermal damage to the diamond increases. Experimental measured tendency of residual stress for brazed diamond through Raman spectroscopy is well consistent with that of calculated results. After observing of the surface morphology for brazed diamond through super-depth of field microscope, the brazed diamond presents the low residual stress, weak graphitization and excellent processing performance at the condition of brazing temperature of 1010 °C, brazing layer thickness of 0.3 mm and holding time of 5 min.

Machinability improvement of titanium alloys in ultra-precision machining with micro-structured surface

Titanium alloys get wider applications in different areas due to its excellent mechanical properties. However, poor thermal conductivity and low elastic module of titanium alloy induce high tool wear and make it being one of hard-to-machine materials; especially the segmented chip formation accelerates the diamond tool wear in ultra-precision machining (UPM) of precision parts. This study applies micro-structured surface to improve machinability of titanium alloys in UPM by reducing the chip segmentation induced cutting forces fluctuations. Finite element (FE) model is built to study chip formation mechanism and characterize geometries of segmented chips in orthogonal diamond cutting of Ti6Al4V alloy with the aims at the design of micro-structures array. Turning experiments are conducted to compare cutting force, surface roughness, and tool wear for diamond turning of Ti6Al4V alloy on smooth surface and micro-structured surface. The results show that the FE simulated saw chips agree well with the measured ones. Moreover, the micro-structured surface helps to decrease cutting force, reduce diamond tool wear, and improve surface quality for UPM of titanium alloy. Especially, the new method fabricates micro-grooves array on the machined surface in half-finishing process of UPM without the need of any material pre-processing and extra manufacturing equipment, which can also provide the guidance for efficient and sustainable UPM of titanium alloys parts with high surface quality.

The effect of tool wear on the damaged layer thickness and tool wear rate in ultra-precision turning of quartz glass

Quartz glasses have been extensively used for many fields, such as semiconductor technology, optical instruments, inertial navigation and others. Ultra-precision turning with diamond tools can achieve high surface accuracy when processing non-ferrous materials. In recent years, ultra-precision turning has also been tried to be applied to process brittle materials, but there are constraints including small removal amount and tool wear. When diamond tools are used to cut quartz glass, tool wear occurs under the combined action of thermal effect and mechanical friction, which will affect the damaged layer thickness of the processed quartz glass. In this paper, the tool wear factor is led into the calculation of the extrusion volume, and the damaged layer thickness is calculated by the extrusion volume. Combined with the results of quartz glass turning experiments and the calculated results by simulation, the effect of tool wear factor on the damaged layer thickness and the tool wear rate is analyzed. The analysis shows that tool wear will lead to chip fracture thickness decrease and extrusion volume increase. Combined action of these two aspects, the damage layer thickness keeps unchanged at first and then rises with the increase of tool wear. In addition, the experimental results show that the tool wear rate rises with the increase of tool wear.

Investigating elastic recovery of monocrystalline silicon during plunging experiments with chamfered diamond tools

This study investigates the relationship between elastic recovery and friction during ductile mode machining of monocrystalline silicon. Plunging experiments were performed on an ultra-precision CNC machining center as the silicon work material was rotated. This approach allowed for investigating the combined effect of varying crystal directions and increasing depth on elastic recovery, pressures, and friction. A diamond cutting tool with a chamfered edge that maintains a constant negative rake along the cutting edge was used in plunging tests. Considering the importance of flank face contact area on friction and pressure distributions at the cutting zone, a non-linear expression is proposed to model the elastic recovery ratio as a function of groove depth. It is then employed in an analytical machining model to calculate the variation of pressure and coefficient of friction. The influences of pressure variation and changes in pressure direction as the machining mode transitions from ductile to brittle are investigated based on resolved stresses on the identified active slip plane. The methodology proposed in this study can be extended to study other monocrystalline materials, and the findings can be utilized in the process planning of advanced optics manufacturing.

Evaluation of milling performance of 50-μm D-shaped carbide tool, polycrystalline diamond-coated carbide tool, and polycrystalline diamond tool

Evaluation of milling performance of 50-μm D-shaped carbide tool, polycrystalline diamond-coated carbide tool, and polycrystalline diamond tool

Wear evolution of metal bond diamond tool in grinding of sapphire

The wear characteristics of the metal bond diamond tools changes with the grinding process, resulting in affecting the grinding efficiency, tool's life, and surface integrity of the workpiece. In this study, the wear evolution of a metal bond diamond tool, for the case of grinding of sapphire, is investigated by using a novel design of the grinding setup. The wear characteristics of the diamond grits and the metal bond at a fixed zone of the grinding tool were examined. In addition, the evolution of the grinding process, the grinding force, the grinding ratio, and the surface integrity of the sapphire were also evaluated. As the material removal volume increases, the number of participating diamond grits, the proportion of micro-fractured diamond grits, and the average diamond grit protrusion height increase during the grinding process. And the proportion of newly exposed diamond grits decreases and the distribution of protrusion height of diamond grits becomes narrower during the grinding process. Consequently, a higher grinding ratio, stable grinding force, and excellent ground surface integrity are achieved positively when the wear of the metal bond diamond tool transforms from the initial stage to the stable stage with the material removal volume of up to 3600 mm3.

Mechanisms of tool-workpiece interaction in ultraprecision diamond turning of single-crystal SiC for curved microstructures

Single-crystal silicon carbide (SiC) is one of the most attractive materials for electronics and optics but extremely difficult to cut owing to its hard and brittle properties. While in previous studies, the focus has been placed on machining flat surfaces, in this study, the mechanisms of tool-workpiece interaction in cutting curved microstructures on 4H–SiC (0001) were explored through the ultraprecision diamond turning of micro-dimples. The surface/subsurface of both machined workpieces and used diamond tools were characterized, and the machining characteristics, such as chip formation and cutting forces, were also investigated. It was found that microcracks occurred easily in the feed-in/cut-in area of the dimples, which is caused by a large friction-induced tensile stress due to a large thrust force. The dimples located on the secondary cleavage directions <10−10> (S-dimples) were easy to produce crack-free surfaces, while the dimples located on the primary cleavage directions <−12−10> (P-dimples) were very prone to cause cracks on surfaces, even though the chips were formed in a ductile mode. The dimples located on the in-between direction (I-dimples) were moderately prone to surface cracking. It was also found that although the S-dimple has a crack-free surface, it has the thickest subsurface damage (SSD) layer containing a disordered layer, dislocations, and stacking faults; the SSD layer of the P- and I-dimples do not contain stacking faults; and the SSD layer of the I-dimple is the thinnest. Flank wear with nanoscale grooves on the diamond tool was significant without edge chipping and diamond graphitization detected. By optimizing the cutting conditions, a crack-free micro-dimple array was fabricated with nanometric surface roughness. The findings from this study provide guidance for the manufacture of curved SiC parts with high surface integrity, such as molds for replicating microlens arrays and other freeform surfaces on glass.

Development and Experimental Study of Electrochemical Diamond Drilling Process on Ti6Al4V

Electrochemical diamond drilling (ECDD) process is a chemical energy-based hybrid machining technique where the removal of material from the workpiece occurs with the help of both anodic dissolution and mechanical abrasion. Titanium alloys have remarkable mechanical as well as chemical properties, however, excellent properties enhance the difficulty in machining of titanium. Ti6Al4V, alloy of titanium contains [Formula: see text] and [Formula: see text] phase which have different dissolution potentials and produces poor surface when electrochemically machined. Here electrochemical diamond drilling of Ti6Al4V is done with a diamond abrasive tool which helps in mechanical abrasion and further by electrochemical dissolution hence this increases the rate of material removal and minimizes surface roughness. From the experiments, the suitable machining range was found to be, voltage 13–17[Formula: see text]V, tool feed rate 0.09–0.15[Formula: see text]mm/min, and electrolyte concentration of electrolyte from 225[Formula: see text]g/l to– 275[Formula: see text]g/l, with tool rotation ranging between 800[Formula: see text]RPM and 1200[Formula: see text]RPM. The MRR range found was between 30.57[Formula: see text]mg/min and 53.11[Formula: see text]mg/min with Ra values ranging between 2.66[Formula: see text][Formula: see text]m and –5.76[Formula: see text][Formula: see text]m. The variation of machining with ECDD tool and bare ECD tool has also been graphically represented which highlights the benefits of diamond abrasive-based ECDD tool.

Wear suppression and interface properties of diamond tool in micro-milling of TC4 alloy under graphene nanofluid MQL environment

The sustainable micro-milling process of TC4 alloy has garnered significant attention in aerospace engineering. However, the poor machinability of TC4 alloy results in particularly severe tool wear. Tool wear directly affects the machining quality of the parts, and traditional cutting fluids of suppressing tool wear indirectly increase production costs and pollute the environment. Therefore, to suppress the negative effects caused by tool wear, this paper proposes the application of water-based graphene nanofluid in the micro-milling of TC4 alloy in diamond tools. Firstly, micro-milling experiments and molecular dynamics simulations were conducted in different environments, including dry and water-based graphene nanofluid environments. Finally, tool surface wear morphology, milling forces, surface elements and structural phase changes were compared in detail. The results show that tool wear, including adhesive wear, abrasive wear, and edge chipping, was suppressed by graphene nanofluids compared to dry conditions, thereby increasing tool life. The graphene nanofluid improved the contact state between the tool and workpiece interface, reducing the milling forces. In addition, molecular dynamics indicates that the catalytic effect of the transition elements in the workpiece on the diamond tool was also weakened, and the carbon atoms of graphene were used as a sacrificial source to balance the catalytic effect. Graphitization and diffuse wear of the diamond were suppressed. More importantly, the water-based graphene nanofluid not only improves the wear resistance of the tool, but the LCA results show its potential for sustainability. Consequently, it holds promise for advancing the sustainable processing of challenging materials.

Performance Evaluation of Graphene Nanofluid to Mitigate the Wear of a Diamond Tool in Micro-Machining of Ti6Al4V Alloy

Diamond tools are extensively used in ultra-precision machining due to their exceptional performance. However, when machining challenging materials like Ti6Al4V, diamond tools experience significant wear due to poor machining properties and catalytic effects. Tool wear not only impacts machining quality but also escalates machining costs and energy consumption. Cutting fluids are commonly employed to mitigate interfacial reactions and suppress tool wear. However, traditional cutting fluids are difficult to penetrate the cutting area and have limited lubrication and cooling capabilities. Therefore, in this paper, a technique combining graphene nanofluid and minimum-quantity lubrication (MQL) is used to suppress diamond tool wear. Firstly, micro-milling experiments for Ti6Al4V alloy are conducted using diamond tools in the graphene nanofluid MQL and under a dry environment. The experimental results show that tool wear is effectively suppressed by graphene nanofluids. Subsequently, the cutting process in both environments (graphene nanofluid MQL, dry) is simulated. The suppression mechanism of graphene nanofluid MQL for diamond tool wear is evaluated from phase transition, atomic transfer process, and amorphous behavior of diamond structure. The simulation results show that the contact characteristics, cutting force, and cutting temperature are improved by graphene nanofluids. Tool wear is effectively reduced. In addition, the removal efficiency of workpiece materials has also been improved. This work provides a technical basis for exploring the application of graphene nanofluids in diamond tool damage suppression and micro-milling.

Microstructure and properties of brazed diamond with Pr-modified Ni[sbnd]Cr filler metals

The aim of this study is to improve the mechanical properties of diamond tools by brazing diamonds with a modified NiCr filler alloy to achieve the reduction of thermal damage. In this paper, rare earth Pr doping into NiCr filler alloy is brazed at 1080 °C under vacuum and tested for organization and properties. The results show that the doping of Pr refines the grain size and carbide. Moreover, Cr7C3 and Cr3C2 are generated at the brazed interface, which realizes the chemical metallurgical bonding and improves the bonding strength of the diamond. The generation of the NiPr phase reduces the thermal damage of brazed diamonds. When the addition of Pr is 1 wt%, the diamond grits have a more complete morphology. The exposed height reaches 46.6 % of its own height and the carbonized layer is thinner. The thermal damage is reduced. In addition, the frictional wear experiments and strength tests also shows that the performance of this filler alloy brazed diamond is better than the unmodified filler alloy brazed diamond.

Effect of Turning Parameter and Fiber Pullout on Machinability of Unidirectional EGFRP under Cryogenic Condition

The non-homogeneous and anisotropic nature of composites poses challenges during machining, requiring the use of specialized cutting tools. GFRP materials were selected for their excellent elasticity, corrosion resistance, and high strength, making them ideal for applications in the aerospace and automotive industries. In this work, the surface quality of UD-GFRP composite bars during CNC machining in diverse machining conditions (dry, wet, and cryogenic) was investigated while considering the fiber-pullout issue. The UD-EGFRP composite materials have been machined with a polycrystalline diamond tool. The Taguchi-L9 orthogonal-array technique is used to investigate and further analysis. Three independent-variables feed rate, rotational speed or cutting speed, and depth of cut have been taken into account for their optimal design to get better machinability of EGFRP. This study also investigates the delamination criterion in composites and establishes the correlation between its input parameters and output responses. The findings revealed that cryogenic machining led to a notable improvement of 25.21% in surface roughness compared to the other lubrication methods. Also, the reduction from 84 µm to 34 µm in fiber-pullout signifies that cryogenic cooling effectively mitigated the occurrence of fiber-pullout.

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.

Modification of diamond tool by focused ion beam in dry single-point diamond turning

The modified diamond tools (MDT) by focused ion beam (FIB) can reduce tool wear to a certain extent while avoiding the pollution of traditional cutting fluid. This paper investigates the dry single-point diamond turning (DSPDT) process for Al6061 alloy with MDT. DSPDT tests showed that MDT produced lower cutting forces and generated smoother machined surfaces. Furthermore, MDT has a lighter wear compared with the unmodified diamond tools. The reasons why the cutting performance of MDT is better than the unmodified diamond tools are the reduced surface energy of modified diamonds proved by the first principle calculations and contact angle tests, and the change of the C–C bond energy and bond length according to the first principle calculations. Therefore, it is feasible and promising to apply the MDT in the DSPDT of Al6061 alloy, which will contribute to carbon neutralization manufacturing.

Researches on tool wear progress in mill-grinding based on the cutting force and acceleration signal

Tool wear progression has greatly impact on the machining quality, tool wear evaluation is useful to obtain tool states. Mill-grinding experiments are performed using the electroplated diamond tool to reveal tool wear progression. Both time and frequency domain, dimensional and dimensionless characteristics of cutting force and acceleration signals are analysed. Among time domain characteristics, peak and average values exhibit low and stable amplitudes at the initial wear stage, and evolve to large and fluctuant amplitudes at the severe wear stage. For frequency domain analysis, gravity frequency exhibits a decrease trend with tool wear progression. Among dimensionless characteristics, kurtosis and margin factors show a maximum value when tool wear progression goes into the severe wear stage, and can be applied to evaluate tool wear progression. Tool wear modes include the wearing flat process and fracture of diamond grains, tool wear mechanisms include the abrasive wear, adhesive wear and grain fracture.

Design of discrete-edge polycrystalline diamond tool and its cutting performance in milling Cf/SiC composites

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites are used extensively in many fields because of their superior properties, such as high specific strength and high specific modulus. However, Cf/SiC composites are typically difficult to machine materials due to their high hardness and anisotropy. Its machining easily leads to high cutting force, short tool life, and poor surface quality. The tool structure shows a significant impact on the cutting performance, which can further affect the cutting force and surface quality. In this study, a novel polycrystalline diamond (PCD) tool with discrete-edge structure was designed for milling Cf/SiC composites, which was devised with tiny microgrooves on the peripheral edge, and the geometric parameters were optimized by finite element simulation method. The cutting performance of the designed discrete-edge PCD tool in milling of Cf/SiC composites was studied. Cutting force, machined surface quality, tool wear mechanisms, and tool life were comprehensively investigated. Comparative experiments were also carried out with conventional straight-edge PCD tools by using identical cutting parameters. The cutting force when using the discrete-edge PCD tool gradually decreased with increasing cutting speed. The machined surface roughness Sa reached 3.5 μm at cutting speed of 125 m⋅min−1 with the discrete-edge tool. Surface defects in terms of fiber pullout, debonding, and cavities were reduced by the discrete-edge tool. The life of the discrete-edge PCD tool was 1.875 times that of the conventional PCD tool. The study illustrates that the cutting performance of the designed discrete-edge PCD tool is better than that of the conventional straight-edge PCD tool.

A novel calibration method for angular misalignment in independently controlled fast tool servo-based diamond turning

With significant technological progress in optics fields, such as VR and 3D sensing technologies, the demand for optical components with complex shapes (e.g., freeform surfaces) has expanded significantly in recent years. Ultra-precision diamond turning is one of the common manufacturing methods used for freeform optics. There are two tool-motion mechanisms for freeform diamond turning: slow tool servo (STS), which moves the entire tool rest, and fast tool servo (FTS), which only drives the diamond tool. In particular, high-frequency and long-stroke FTS units driven by a separate control system from the machine tool controller have recently been developed as a new trend in FTS-based diamond turning. However, this type of independent FTS control system causes a time delay between the machine tool instruction and the FTS tool motion. Even a millisecond-scale time delay can cause a considerable angular misalignment owing to the high rotation rate of the spindle, resulting in a micron-scale form error on the workpiece surface. In this paper, a novel method for precisely measuring the time delay from the machined workpiece surface and compensating for the misalignment based on the measured time delay was proposed. To measure the time delay, spherical dimples were machined on the workpiece surface by using STS and FTS. Subsequently, the angular misalignment and time delay were obtained by comparing the measured surface profiles at specific positions of the spherical dimples. Thus, the time delay can be measured with microsecond-scale accuracy. Based on the measured time delay, the shifted tool position along the spindle axis by the time delay was compensated to the ideal tool position by considering the cutting velocity. Consequently, the angular misalignment was completely eliminated, and submicron-level form accuracy was achieved. This calibration method of angular misalignment for an independent FTS unit is expected to significantly improve the accuracy of ultra-precision machining of freeform optics.

A theoretical and deep learning hybrid model for predicting surface roughness of diamond-turned polycrystalline materials

Polycrystalline materials are extensively employed in industry. Its surface roughness significantly affects the working performance. Material defects, particularly grain boundaries, have a great impact on the achieved surface roughness of polycrystalline materials. However, it is difficult to establish a purely theoretical model for surface roughness with consideration of the grain boundary effect using conventional analytical methods. In this work, a theoretical and deep learning hybrid model for predicting the surface roughness of diamond-turned polycrystalline materials is proposed. The kinematic–dynamic roughness component in relation to the tool profile duplication effect, work material plastic side flow, relative vibration between the diamond tool and workpiece, etc, is theoretically calculated. The material-defect roughness component is modeled with a cascade forward neural network. In the neural network, the ratio of maximum undeformed chip thickness to cutting edge radius R TS, work material properties (misorientation angle θ g and grain size d g), and spindle rotation speed n s are configured as input variables. The material-defect roughness component is set as the output variable. To validate the developed model, polycrystalline copper with a gradient distribution of grains prepared by friction stir processing is machined with various processing parameters and different diamond tools. Compared with the previously developed model, obvious improvement in the prediction accuracy is observed with this hybrid prediction model. Based on this model, the influences of different factors on the surface roughness of polycrystalline materials are discussed. The influencing mechanism of the misorientation angle and grain size is quantitatively analyzed. Two fracture modes, including transcrystalline and intercrystalline fractures at different R TS values, are observed. Meanwhile, optimal processing parameters are obtained with a simulated annealing algorithm. Cutting experiments are performed with the optimal parameters, and a flat surface finish with Sa 1.314 nm is finally achieved. The developed model and corresponding new findings in this work are beneficial for accurately predicting the surface roughness of polycrystalline materials and understanding the impacting mechanism of material defects in diamond turning.

Mo2C interface layer: effect on the interface strength and cutting performance of diamond/Fe-Ni-WC composites

The weak interfacial strength between Fe-based matrix and diamonds causes diamond particles to fall off prematurely, significantly affecting the cutting efficiency of diamond composites. This work aimed to optimize the interfacial microstructure and mechanical properties of the diamond/Fe-Ni-WC composites by coating a Mo2C layer on the diamond particles. The Mo2C-coated diamonds were prepared via the molten salt method. Diamond/Fe-Ni-WC composites were sintered by the hot-pressing process under a vacuum. The bending strength of composites with Mo2C-coated diamonds was improved from 804 to 996 MPa with the increased coating time. The energy dispersive spectroscopy scanning indicated that the Mo2C coating layer changed the interfacial composition between the matrix and the diamonds from Fe–C alloy to Mo2C, improving the interface strength. Moreover, the diamond protrusion heights of composites were raised by adding a Mo2C interface, resulting in an improvement in the cutting efficiency of impregnated diamond tools.