Machinability improvement in three-dimensional (3D) ultrasonic vibration assisted diamond wire sawing of SiC

Ultrasonic vibration assisted (UVA) cutting has been proven to be an effective method for improving machining behavior in processing hard and brittle materials. However, there is no investigation on three-dimensional (3D) UVA diamond wire sawing (DWS). In this paper, a novel 3D vibration assisted DWS system is developed. A theoretical model is established for predicating sawing forces. Experiments have been carried out on DWS of silicon carbide (SiC) ceramics. The effects of ultrasonic vibration assistance, input vibration direction and cutting parameters on sawing forces, surface morphologies and tool wear are studied respectively. The simulation results indicate that elliptical motion in 3D space can be obtained for the diamond abrasive. The experimental results reveal that the proposed model has sufficient accuracy to predict sawing forces. It is demonstrated that sawing forces can be reduced by ultrasonic vibration assistance either in vertical direction or in longitudinal direction. However, 3D ultrasonic vibration condition provides the lowest sawing force because of the combined advantages. Due to intermittent cutting mode, sawing forces are decreased by 31%, 40% and 29.8% in X, Y and Z direction, respectively. Because debris can be removed more easily from the contact surface and large ductile smooth area can be obtained, 3D ultrasonic vibration assistance generates higher surface integrity than that of traditional sawing process. Moreover, the wear of diamond wire saw can be effectively decreased.     

Experimental investigation on diamond wire sawing of Si3N4 ceramics considering the evolution of wire cutting performance

When diamond wire saw is used in machining silicon nitride ceramics (Si₃N₄ ceramics), the ultra-hardness of Si₃N₄ causes the saw wire to wear out, which leads to the saw wire cutting performance constantly changing during its life cycle, and thus the machined quality of Si₃N₄ ceramics is affected. Surface roughness and topography are important indicators of the quality of the machined surface. In this paper, the diamond wire saw cutting experiment of Si₃N₄ ceramics was carried out, the effect of the evolution of saw wire cutting performance on the surface roughness and topography of Si₃N₄ ceramics as-sawn slices was investigated based on the analysis of the changes of saw wire wear topography, breaking force, bow angle and kerf loss during the sawing process. The results show that the surface roughness along the saw wire motion direction and the workpiece feed direction tends to decrease and then increase with the evolution of the cutting performance of the saw wire, which accords well with the trend of the as-sawn slices surface morphology. The results of the study can provide experimental reference for the development of high precision diamond wire saw cutting technology for Si₃N₄ ceramics.     

Influence of Thermally Assisted Machining Parameters on the Machinability of Inconel 718 Superalloy

The present study describes the effect of thermally assisted machining (TAM) parameters on the cutting force, tool wear and surface integrity characteristics (surface roughness, surface topography, and microhardness) of Inconel 718. An inexpensive flame heating technique using oxy-acetylene flame is used to heat the workpiece material. The TAM parameters such as cutting speed, feed rate, depth of cut, and workpiece temperature were selected as process parameters over cutting force, tool wear and surface integrity characteristics.The experimental results reveal that the cutting forces and surface roughness decrease with increases in cutting speed and workpiece temperature, while the workpiece temperature increases as tool wear decreases. The tool wear mechanisms observed were abrasive, adhesive, diffusion and notch wear. The XRD results of thermally assisted machining reveal that neither phase change nor broadening of the peaks were observed at different machining conditions.     

Fundamental research on machining performance of diamond wire sawing and diamond wire electrical discharge sawing quartz glass

In reciprocating diamond wire sawing of quartz glass, the reversing and acceleration and deceleration will cause the position change of diamond wire, resulting in the discontinuous wire sawing in the reversing stage, so as to leave residual material on the processing surface and form wire marks. Also, the cutting load will cause diamond wire deformation as bow shape, and affect the machining accuracy. In this paper, the evaluation of DWS machining performance of quartz glass focus on the sawing time, cutting force and vibration, wire tension, machining surface flatness and roughness, surface morphology and wire state. The theoretical analysis of wire mark was carried out, and the simplified wire bow model of quartz glass sawing was established. The existence of wire mark and wire bow were verified by detecting the 3D contour of the slice. In addition, a diamond wire electrical discharge sawing (DWEDS) was performed to find the differences to DWS in the above indicators. Experiments were presented in jet cooling and bath cooling conditions. It was found that the cutting force, vibration, and wire tension of DWEDS are more stable than that of DWS. The DWEDS has been proved helpful to improve machining performance of quartz glass from surface roughness, sawing time, processing state, and wire bow control as it reduces the macro cutting force acting on the diamond wire although the discharge effect is weak. The SEM of slice surface and diamond wire showed no significant difference between DWEDS and DWS. Also, the influence of feed speed and cooling methods on machining performance was investigated.     

Sawing characteristics of diamond wire cutting sapphire crystal based on tool life cycle

Diamond wire saw cutting technology has been widely used in the slicing of sapphire crystal. The ultra-high hardness of sapphire makes the sawing characteristics of diamond saw wire constantly change. At present, there is a lack of in-depth understanding about the influence of sawing characteristics on the quality of sapphire as-sawn wafer, which leads to the unreasonable matching between the process parameters and the sawing characteristics of the saw wire, and reduces the as-sawn wafer quality and the saw wire life. In this paper, the slicing sapphire crystal experiment was carried out with constant process parameters and the variation of saw wire bow angle, nominal diameter and saw kerf loss, surface morphology and surface roughness of the as-sawn wafer during the whole life cycle of the saw wire from initial cutting to breakage was studied. The evolution mechanism of wear and sawing characteristics in the whole life cycle of saw wire was explored, and a reasonable processing scheme which can match the sawing characteristics was put forward. The research results show that in the whole life cycle of the saw wire, the abrasives emerge from the plating layer in turn, then the cutting edge are blunted, and finally the abrasives are greatly flattened and a small amount of falling off. Saw wire has experienced initial wear, stable wear and sever wear, and the proportion of three stages in the whole life cycle is about 0.3: 0.6: 0.1. Compared with the initial stage of wear and the late stage of rapid wear, the saw wire has higher sawing characteristics and better as-sawn wafer quality in the middle stable wear period. The sawing characteristics of new saw wire is relatively weak at the beginning of cutting, so the feed speed of workpiece should be increased gradually from low to high; When most of the abrasives finish sharpening edge, a relatively stable and high feed speed can be adopted; When the abrasives are obviously flattened or fall off, the feed speed should be decreased to accommodate the significantly reduced. cutting performance of diamond saw wire.     

Experimental study on laser assisted ultrasonic elliptical vibration turning (LA-UEVT) of 70% SiCp/Al composites

SiC_p/Al composites are more and more used in aerospace, military industry and other industries. However, the surface integrity of materials is poor, and the cutting force is large as the anisotropy of materials in the traditional machining (TM) process, which hinders the application of ceramic particle reinforced metal matrix composites. With the requirement of high dimensional accuracy, high efficiency and low damage for materials in these fields, non-traditional machining technology has become a research hotspot. Laser assisted machining (LAM) is a non-contact special machining method. Its advantages in machining SiC_p/Al composites have been proved by experiments, but there are still processing defects such as thermal cracks. Therefore, to further improve the machining quality of 70% SiC_p/Al composites with high volume fraction, a new machining method combining ultrasonic elliptical vibration turning (UEVT) and laser heating assisted turning (LAT) is proposed. High frequency intermittent machining and the adjustment of laser temperature influence on materials can be realized by adjusting the ultrasonic amplitude. Combining the characteristics of the two processing techniques, the feasibility study of the new machining method was studied by turning experiments. In this paper, compared with TM and LAT, the removal mechanism of materials and the effects of different laser heating temperatures and ultrasonic vibration on cutting force, surface quality, subsurface damage and chip morphology are explored. The results show that LA-UEVT can effectively reduce the cutting force and surface roughness, improve the plastic removal ability, and inhibit surface and subsurface damage. And the material removal process is mainly in the form of small particle crushing and particle pressing, which improves the stability of cutting force in the cutting process.     

New observations of the fiber orientations effect on machinability in grinding of C/SiC ceramic matrix composite

In this paper, the effect of machining parameters on cutting force, force ratio, 3D surface roughness was studied, and the surface formation mechanism was deeply analyzed in view of the position relation between machining directions and fiber orientations. New observations of the fiber orientation effect on machinability are attempted to obtain in grinding of 2D C/SiC ceramic matrix composite with electroplated diamond grinding tool. Two machining directions (A and B) on one surface are taken into account to study the effect of fiber orientation on the grinding process. The results indicate that the cutting forces obtained in machining direction of A are greater than that in machining direction of B under all experimental conditions. However, the tangential force is greater than the normal force, which is different from grinding ordinary material. Whether in the machining direction of A or direction of B in grinding C/SiC composite, on the whole the surface roughness values (Sa and Sq) decrease as the feed rate increases. As depth of cut increasing, the surface roughness values in the machining direction of A and B come out inconsistency. At different feed rates, the surface roughness values in the machining direction of A and B also represent inconsistency with the change of cutting speed. The theoretical model of undeformed cutting thickness is unfit for evaluating its effect on the surface roughness. After analyzing of the surface formation, except for some fibers forming extruding fault and fracture, being pulled out, and fracture or broken, a new phenomenon that some fibers forming extruding fault and fracture is observed.     

Wear mechanisms and effects of monolithic Sialon ceramic tools in side milling of superalloy FGH96

FGH96 is one kind of nickel-based superalloy, being widely used in aero engine hot end components due to its superior mechanical properties, while its machinability has been a challenge because of rapid tool wear and low machining efficiency. Recently, ceramic tools have gained widespread attention for their superior performance maintained at high temperatures. This work aims to study the wear mechanisms and the wear effects of monolithic Sialon ceramic tool in the side milling of superalloy FGH96. The specific influences of average flank wear on the side milling forces, machining temperatures, surface quality and micro-hardness of subsurface and the wear modes in the early and serious stage are analyzed. The results indicate that the milling temperatures, machined surface roughness and the depth of hardening layer will increase as the wear increases. While parallel to the cutting direction, the machined surface roughness is about 1.8 μm without significant changes until entering the serious wear stage. The milling force tends to undergo a decrease when the VB is about 0.22 mm, since the temperature is close to the solute temperature of γ’ phase in this stage. The main wear modes of monolithic ceramic tools are adhesive wear and flanking in the flank surface.     

Laser induced oxidation of cemented carbide during micro milling

Cemented carbide is widely used as precision mold material due to its superior properties. The excessive tool wear and short tool life are the main problems during micro cutting of cemented carbide. Firstly, the high temperature oxidation behavior of cemented carbide under laser irradiation was studied in this paper. Cemented carbide surface can be induced to fully oxidize and generate highly porous oxide layer which is much easier to remove with micro milling tool. Then, the micro milling hybrid process assisted with laser induced oxidation of cemented carbide was proposed. Micro milling experiments assisted with and without laser oxidation were performed on WC-15Co cemented carbide. It is found that the hybrid machining process can greatly reduce the tool wear and cutting force, and also achieve fine surface finish.     

Enhanced machinability of SiCp/Al composites with laser-induced oxidation assisted milling

In this study, an innovative machining process called laser-induced oxidation assisted milling (LOM) is proposed. A polycrystalline diamond (PCD) cutting tool is applied to machine 55% SiC_p/Al composites. The laser-induced oxidation mechanism is investigated. Under the condition of average laser power of 10 W, laser scanning pitch of 15 μm, laser scanning speed of 6 mm/s and oxygen-rich atmosphere, the effect of laser-induced oxidation is optimal. A loose oxide layer and a sub-layer with the hardness of 160 ± 40 HV are generated where the composition of the oxide layer is mullite (2Al₂O₃·SiO₂). Comparative investigation on the cutting force, surface quality and tool wear are performed. Compared with the conventional milling (CM), the normal force and thrust force of LOM decrease by 39% and 55%, respectively. The reduction of cutting forces is attributed to thermal failure of the interface layer. The dominant surface defects of the machined surface are particle fracture, particle pull-out, matrix tearing and matrix coating. Among the investigated parameters, the minimum surface roughness S_a is 0.37 μm when the feed per tooth and the cutting depth are 0.005 mm/z and 0.2 mm, respectively. The dominant tool wear modes of LOM include diamond spalling and edge chipping. The tool wear modes of CM are diamond spalling, edge chipping, abrasive wear, and adhesive wear. LOM can prolong the tool life and achieve better surface quality under the same cutting length.     

Experimental investigation of different morphology textured ceramic tools by in-situ formed for the dry cutting

Surface texture is considered an important measure to improve the cutting performance of a tool. In this study, we have prepared three types of textured and conventional tools on the rake face by an in-situ formed method. During the experiment, the best parameters of three types of textured tools were selected for dry cutting AISI 1045 steel at different cutting speeds. Cutting forces, cutting temperatures, workpiece surface roughness, and tool wear were measured during the cutting process. The results showed that textured tools have significantly reduced cutting force, cutting temperature, and tool wear, and the roughness of the workpiece was improved compared with the conventional tool. The micro-pit texture tool has less stress contact region than the micro-groove width texture tool, but the micro-groove width texture tool exhibiting the best cutting performance. This investigation clearly showed that the textured tool prepared by the in-situ formed method has improved cutting performance.     

Laser-induced oxidation assisted micro milling of spark plasma sintered TiB2-SiC ceramic

In this work, a novel process of laser-induced oxidation assisted micro milling (LOMM) was proposed. TiB₂-SiC ceramic with hardness of 24.6 ± 0.8 GPa was prepared by spark plasma sintering and used as the workpiece material. The cutting force, surface quality and tool wear mechanisms were investigated. Under laser irradiation and oxygen assistance, a porous oxide layer and relatively dense sub-layer were formed. The hardness of the sub-layer was found to be 12.8 ± 0.7 GPa which was far lower than that of the substrate. Both the cutting and thrust forces increased with increasing the feed per tooth and depth of cut in micro milling of the sub-layer material. The material removal mechanism was dominated by a transition from ductile to brittle mode as the feed per tooth increased from 0.3 μm/z to 1.2 μm/z. The surface roughness Ra of 46 nm was achieved when the cutting speed, feed per tooth and depth of cut were 31.4 m/min, 0.3 μm/z and 2 μm, respectively. The tool wear mechanism was characterized by the flank wear and coating spalling. As a case study, a micro slot having width of 0.5 mm and aspect ratio of 2 was fabricated by the LOMM. For comparison, the conventional micro milling was also carried out using the same cutting parameters. The surface quality fabricated by LOMM was better than that by the conventional micro milling. The machining efficiency in LOMM was improved by 104% as compared to the conventional micro milling.     

Diamond tools for wire sawing metal components

In the last few years, a wire sawing process has been developed for many applications in the field of natural stone and construction materials, especially for very thick materials or components that are difficult to access. Diamond wire cutting was limited to small carbon-steel shapes, such as pipelines for transporting gas or oil under the sea. In particular, the task of cutting pure steel components offers new fields of applications, e.g. treatment of nuclear power or off-shore-components. The application of the wire sawing process for these specific cutting operations requires the development of diamond tools adapted to the cutting process. In this paper, the basic principles of wire sawing are explained and the background of diamond wire cutting of steel components is discussed. The interaction between the tool and the workpiece is described in detail. Results are presented of a project on further developments of the diamond wire sawing technique, emphasising the applications for metal components.     

Research on the machinability of A-plane sapphire under diamond wire sawing in different sawing directions

Due to its superior mechanical, optical and chemical properties, sapphire (α-Al₂O₃) is widely used in engineering, optics, medicine, and other scientific research fields. The atomic structure of sapphire gives rise to anisotropy in its mechanical properties, which affects the machinability of sapphire materials on different crystal planes. Different cutting directions will affect the wafer economy and surface quality achieved during wire sawing due to this anisotropy. In this study, the machinability of A-plane sapphire was investigated for diamond wire sawing in three different directions, following the C-plane, R-plane and M-plane. The results show that the direction following the M-plane could be the best direction for diamond wire sawing because this direction results in the minimal sawing forces, the lowest specific energy and the smallest volume of material that will need to be removed during subsequent processing. These characteristics correspond to the direction with the highest fracture strength since the material is removed by brittle machining. The force ratio for sawing in the direction of the R-plane is the smallest because this direction is associated with the minimum hardness and the lowest critical load for the transition from plastic to brittle removal of the workpiece material. The 3D height parameters show no obvious pattern among the three sawing directions. The mechanism of material removal is mainly brittle removal, with some plastic removal, and is obviously affected by the crystal orientation.     

Friction and wear properties of TiAlN coated tools with different levels of surface integrity

Surface integrity is a critical factor to assess the quality of mechanical products, which has a significant impact on the service performance. In this work, the surface integrity of coating, such as roughness, hardness and residual stress, are changed by micro-blasting. The high-speed sliding wear experiments and cutting experiments are carried out with the TiAlN coated tool with different levels of surface integrity. The influence of the surface integrity of the coating on the high-speed sliding wear and cutting performance is investigated. The result shows that the low surface roughness of the coating can effectively reduce the friction coefficient. The high surface hardness and compressive residual stress (absolute value) can reduce the fluctuation range of friction coefficient. The cutting performance of coated tool is mainly influenced by the surface hardness and surface residual stress. The high wear resistance of the TiAlN coated tool in sliding wear process or cutting process can be obtained at the low surface roughness, the medium hardness and residual stress. It has practical significance to improve the surface integrity and the wear resistance of the coated tools.     

Smoothed particle hydrodynamics simulation and experimental analysis of SiC ceramic grinding mechanism

Crack induced surface/subsurface damage in SiC ceramic grinding limits the industrial application. A single-grain scratching simulation based on the smoothed particle hydrodynamics (SPH) has been used to analyze the SiC grinding mechanism, including the material removal process, scratching speed effect on crack propagation, ground surface roughness, and scratching force. The simulation results showed that the material removal process went through the pure ductile mode, brittle assisted ductile mode, and brittle mode with the increase of the depth of cut. The critical depth of cut for ductile-brittle transition was about 0.35?µm based on the change of ground surface crack condition, surface roughness, and maximum scratching force. Increasing the scratching speed promoted the transformation of deep and narrow longitudinal crack in the subsurface into the shallow and wide transverse crack on the surface, which improved the surface quality. The SPH simulation results were indirectly validated by the cylindrical grinding experiments in terms of the critical single grain depth of cut for ductile-brittle transition, and the trend of ground surface roughness and grinding forces.     

Wear behavior of SiAlON ceramic tool and its effects during high-speed cutting

Nickel-based superalloys are widely employed in aerospace and other fields on account of excellent performance. However, the tool is easily worn out in cutting of superalloys, which will deteriorate the surface quality and lower the service life of the components. In this paper, the effect of ceramic tool wear on surface integrity during high-speed turning of superalloy GH4169 was studied. The results demonstrate that tool wear raises cutting temperature and cutting force. The wear mechanisms of the rake face of the ceramic tool are adhesive wear and oxidation wear, and the wear mechanisms of the flank face are adhesive wear, oxidation wear and abrasive wear. The enhancement effect of tool wear on thermal effect is greater than that on mechanical effect, which forms a larger tensile residual stress on the machined surface. In addition, tool wear increases the thickness of the plastic deformation layer, raising the KAM value from 0.43° to 0.63° at a cutting speed of 200 m/min.     

Investigation of machinability in milling of Inconel 718 with solid Sialon ceramic tool using supercritical carbon dioxide (scCO2)-based cooling conditions

Milling of hard-to-machining materials is still a challenge since the high cutting temperature caused by the cooling lubrication problems and the property of materials. This paper proposes the use of supercritical carbon dioxide (scCO₂), supercritical carbon dioxide based minimum quantity lubrication cutting fluid (scCO₂-MQL), and supercritical carbon dioxide based minimum quantity lubrication with oil droplets cutting fluid (scCO₂-OoW) as the eco-friendly cooling-lubrication methods for milling of Inconel 718 superalloy. The cutting forces, cutting temperatures, surface roughness, surface topographies, subsurface characteristics and tool wear were performed to quantify the effect of various cooling methods. The results indicated that the application of scCO₂-based cooling conditions was an effective cooling and lubrication technology for the ceramic tool since it could reduce the cutting force and temperature and improve the surface finish with lower peaks and valleys dispersion compared with other cooling conditions. Compared with the scCO₂-MQL, only scCO₂ and dry milling conditions, the topographies of machined surface under the scCO₂-OoW condition have been significantly improved. Furthermore, the scCO₂-OoW cooling technique has facilitated the removal of debris adhering to the ceramic tool and improved lubrication of the cutting zone.     

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

High efficiency and precision grinding of brittle materials is challenging due to material physical and chemical properties. To understand the effect of grain geometry and wear conditions on the material removal mechanism in brittle material precision grinding, a single diamond grain grinding experiment was conducted on Silicon Carbide (SiC). The cutting edge radius and deflection angle were measured by confocal scanning. Under six different cutting edge radius and three maximum undeformed chip thickness, grinding force and ground surface were measured. Diamond grain wear was investigated by observing the grain morphology, wear rate, grinding force, and ground surface change over accumulative material removal volume. The result showed the existence of a critical cutting edge radius for improving SiC ground surface quality.. Normal grinding force increased with the cutting edge radius increase. Tangential grinding force increased with the cutting edge radius increase and reached the peak value at the critical cutting edge radius. Flank wear was the major wear mode in precision SiC grinding. The grain wear was associated with the grinding force and ground surface.     

超声波功率对Cu-SiO_2复合镀层形貌与性能的影响

采用超声波辅助电沉积工艺制备Cu-SiO_2复合镀层,借助扫描电镜、粗糙度仪、显微硬度计和摩擦磨损试验机,研究超声波功率对复合镀层形貌、显微硬度和摩擦磨损性能的影响。结果表明,较低功率(0~160 W)超声波起不到改善和提高复合镀层形貌与性能的效果,较高功率(240~400 W)超声波能够明显改善复合镀层的形貌平整性和致密性,并且提高性能;超声波功率过高,反而使复合镀层形貌变差,性能下降。超声波功率为400 W时,复合镀层呈颗粒状形貌,表面粗糙度仅为0.42μm,显微硬度达到166.8 HV,磨损质量损失率为1.07 mg/min,表现出良好的摩擦磨损性能。