Investigation on the cutting quality characteristics of abrasive water jet machining of AA6061-B4C-hBN hybrid metal matrix composites

Aluminum metal matrix composites (AMMCs) explicitly show better physical and mechanical properties as compared to aluminum alloys and results in a more preferred material for a wide range of applications. The addition of reinforcements embargo AMMCs employment to industry requirements by increasing order of machining complexity. However, it can be machined with a high order of surface integrity by nonconventional approaches like abrasive water jet machining. Hybrid aluminum alloy composites were reinforced by B₄C (5–15?vol%) and solid lubricant hBN (15?vol%) particles and fabricated using a liquid metallurgy route. This research article deals with the experimental investigation on the effect of process parameters such as mesh size, abrasive flow rate, water pressure and work traverse speed of abrasive water jet machining on hybrid AA6061-B₄C-hBN composites. Water jet pressure and traverse speed have been proved to be the most significant parameters which influenced the responses like kerf taper angle and surface roughness. Increase in reinforcement particles affects both the kerf taper angle and surface roughness. SEM images of the machined surface show that cutting wear mechanism was largely operating in material removal.     

旋转超声磨削Si3 N4陶瓷用金刚石磨具磨损行为研究

热压烧结Si₃N₄陶瓷材料常应用于航天飞行器中关键耐高温零部件,但由于高硬度和低断裂韧性,其加工效率和加工表面质量难以满足制造需求。为了提高热压烧结Si₃N₄陶瓷旋转超声磨削加工质量,减小由于金刚石磨具磨损带来的加工误差,开展了磨具磨损行为研究。基于热压烧结Si₃N₄陶瓷旋转超声磨削加工实验,分析了金刚石磨具磨损形式;基于回归分析建立了金刚石磨具磨损量数学模型,揭示了加工参数及磨具参数与金刚石磨具磨损量间映射关系;并研究了磨损形式与磨具磨损量及加工表面粗糙度影响规律。结果表明：磨粒磨耗是旋转超声磨削Si₃N₄陶瓷用金刚石磨具最主要磨损形式,比例超过50%;主轴转速和磨粒粒度对磨具磨损量影响最为显著;且磨损量较小时,加工表面粗糙度值反而增加。以上研究可为提高旋转超声磨削Si₃N₄陶瓷加工精度和加工质量提供指导。     

An investigation on machined surface quality and tool wear during creep feed grinding of powder metallurgy nickel-based superalloy FGH96 with alumina abrasive wheels

In this study, the machined surface quality of powder metallurgy nickel-based superalloy FGH96 (similar to Rene88DT) and the grinding characteristics of brown alumina (BA) and microcrystalline alumina (MA) abrasive wheels were comparatively analyzed during creep feed grinding. The influences of the grinding parameters (abrasive wheel speed, workpiece infeed speed, and depth of cut) on the grinding force, grinding temperature, surface roughness, surface morphology, tool wear, and grinding ratio were analyzed comprehensively. The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels. This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material. Moreover, both the BA and MA abrasive wheels exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion. Finally, an analytical model for prediction of the grinding ratio was established by combining the tool wear volume, grinding force, and grinding length. The acceptable errors between the predicted and experimental grinding ratios (ranging from 0.6 to 1.8) were 7.56% and 6.31% for the BA and MA abrasive wheels, respectively. This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel, and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00305-2     

Electrolytic concentration effect on the abrasive assisted-electrochemical machining of an aluminum–boron carbide composite

All engineering materials can be machined by one or combination of processes in such a way that the material’s potential is fully exploited. Electrochemical machining is found to be a most promising process that produces various components from the hard-to-machine materials for the various applications. Electrolyte concentration is playing a positive role by improving the electrolyte conductivity, but negatively forming the passivation layer on the cut surfaces. In order to improve the surface finish and removal of generated residual materials from the cut surfaces, abrasive particles were fed along with electrolyte into the machining zone. This present paper investigates the sodium chloride (NaCl) electrolyte with varied concentration (10–30%) in association with SiC abrasive particles on the material removal rate, surface roughness, and radial overcut while machining of aluminum 6061–boron carbide (5–15?wt%) composites. This study conclusively derived that electrolyte concentration up to 20% exhibited a positive role in the material removal rate for the machining of composites because the rate of dissolution was of higher magnitude. Externally supplied abrasive particles along with electrolyte reduced the surface roughness and radial over cut to an extent. Conversely, at higher electrolyte concentration, the externally supplied abrasive particles have a little effect on the removal of the formed passivation layer as confirmed by SEM analysis.     

Machining and surface finishing of brittle solids

Ceramic materials are finished primarily by abrasive machining processes such as grinding, lapping, and polishing. In grinding, the abrasives typically are bonded in a grinding wheel and brought into contact with the ceramic surface at relatively high sliding speeds. In lapping and polishing, the ceramic is pressed against a polishing block with the abrasives suspended in between them in the form of a slurry. The material removal process here resembles three-body wear. In all these processes, the mechanical action of the abrasive can be thought of as the repeated application of relatively sharp sliding indenters to the ceramic surface. Under these conditions, a small number of mechanisms dominate the material removal process. These are brittle fracture due to crack systems oriented both parallel (lateral) and perpendicular (radial/median) to the free surface, ductile cutting with the formation of thin ribbon-like chips, and chemically assisted wear in the presence of a reactant that is enhanced by the mechanical action (tribochemical reaction). The relative role of each of these mechanisms in a particular finishing process can be related to the load applied to an abrasive particle, the sliding speed of the particle, and the presence of a chemical reactant. These wear mechanisms also cause damage to the near ceramic surface in the form of microcracking, residual stress, plastic deformation, and surface roughness which together determine the strength and performance of the finished component. A complete understanding of the wear mechanisms leading to material removal would allow for the design of efficient machining processes for producing ceramic surfaces of high quality. The research was supported in part by the National Science Foundation through grants MSS 9057082, Jorn Larsen-Basse, Program Director and DDM 9057916, Bruce Kramer, Program Director.     

Experimental Investigation on Rotary Ultrasonic Face Grinding of SiCp/Al Composites

SiCp/Al composites have been widely used in many fields such as aerospace, automobile, advanced weapon system, etc. But this kind of material, especially with high volume fraction, is difficult to machine due to the reinforced particles existing in matrix, which has limited its further application. Rotary ultrasonic machining (RUM) has many excellent features and it has never been used to machine SiCp/Al composites. In order to improve the machinability and application of SiCp/Al composites, the rotary ultrasonic face grinding experiments of SiCp/Al composites reinforced with 45% volume SiC particles were carried out to investigate cutting force, surface quality, tool wear, and abrasive chip shapes. The experimental results indicate that ultrasonic vibration could reduce cutting force, surface roughness, surface defects, and increase plastic removal ratio. The cutting force could be lowered by an average of 13.86% and the surface roughness could be lowered by an average of 11.53%. The examined results of tool wear patterns suggest that tool wear is mainly caused by grain breakage and grain fall-off. Grinding wheel blockage and grinding burn were not observed in machining process.     

Electrical Discharge Machining (EDM) Characteristics Associated with Electrical Discharge Energy on Machining of Cemented Tungsten Carbide

In this investigation, cemented tungsten carbides graded K10 and P10 were machined by electrical discharge machining (EDM) using an electrolytic copper electrode. The machining parameters of EDM were varied to explore the effects of electrical discharge energy on the machining characteristics, such as material removal rate (MRR), electrode wear rate (EWR), and surface roughness. Moreover, the effects of the electrical discharge energy on heat-affected layers, surface cracks and machining debris were also determined. The experimental results show that the MRR increased with the density of the electrical discharge energy; the EWR and diameter of the machining debris were also related to the density of the electrical discharge energy. When the amount of electrical discharge energy was set to a high level, serious surface cracks on the machined surface of the cemented tungsten carbides caused by EDM were evident.     

Experimental Investigations of Abrasive Mixed Electro Discharge Diamond Grinding of Nimonic 80A

This paper presents a novel hybrid machining process (HMP) called abrasive mixed electro discharge diamond grinding (AMEDDG) in which abrasive powder is mixed in dielectric fluid to perform electro discharge diamond grinding (EDDG) action on a workpiece. In-house-fabricated AMEDDG setup was used to experimentally evaluate the performance of the process during the machining of Nimonic 80A. The effects of wheel speed, powder concentration, current, and pulse-on-time (POT) were investigated on the material removal rate (MRR). The surface morphological properties of the machined workpiece were investigated based on some quality surface indicators. The experimental results show that MRR of the workpiece was influenced by wheel speed, current, and powder concentration, and optimum MRR can be achieved at a wheel speed of 1400 RPM, a powder concentration of 4 g/L, a current of 10 A, and a POT of 26 µs.     

Machinability of titanium alloy through electric discharge machining

Titanium alloy (Ti-6Al-4V), being considered as hard-to-machine material, offers many challenges especially during conventional machining. Electric discharge machining could be a good option if it offers a good match between material removal rate and surface finish of the machined feature. The issue of appropriate selection of electrode material for good machining of Ti-6Al-4V is not yet comprehensively explored which is the core focus of this study. Moreover, the effect of pulse time ratio is thoroughly examined which is not specifically studied before. Discharge current and pulse time ratio are considered as the input variables, whereas the material removal rate and surface roughness are selected as performance measures of machinability. Copper, aluminum, brass and graphite are employed to evaluate the machining behavior. Experimental results revealed that aluminum electrode provides the lowest surface roughness, whereas the maximum material removal rate is achieved using graphite electrode. However, graphite electrode can offer high material removal rate with low surface roughness by initially employing negative tool polarity for rough machining and then positive tool polarity for fine machining.     

Effects of Lubricant Condition and Tool Wear in Hard Turning of Novel-Abrasion-Resistance (N-AR) Cast Iron

Advanced materials, such as high abrasion resistant cast iron, have great applications for abrasive and erosive environments. Since the amount and the hardness of the microstructural carbides constituents in this material is extremely high, the abrasion-resistance cast iron is generally difficult to be machined with traditional cemented carbide tool. The hard and abrasive particles in this material can remarkably shorten the cutting tool life through abrasion of tool face and deterioration of cutting edge. In this article, Cubic Boron Nitride (CBN) cutting tool has been used to machine a novel-abrasion-resistance (N-AR) cast iron. The performances of CBN tool under different lubrication conditions were evaluated in view of tool wear, cutting force, and surface roughness (Rz). Further more, the wear rate of CBN tool under different machining condition and the mechanism of the CBN tool in machining of this type of work materials has also been investigated.     

An Experimental Study on Electrical Discharge Machining of Manganese-Zinc Ferrite Magnetic Material

The objective of this research is to investigate the machining characteristics of manganese-zinc (Mn-Zn) ferrite magnetic material using electrical-discharge machining (EDM). The material removal rate, the surface topography, the surface roughness, the recast layer, and the chemical composition of the machined surface were studied in terms of EDM processing variables. Experimental results indicate that the morphology of debris revealed the mechanism of material removal. The surface microgeometry characteristics are not always uniform and homogenous and the EDM process produces much damage on the machined surface. The material removal rate, the surface roughness, and the recast layer are proportional to the applied discharge energy.     

Influence of graphite powder mixed EDM on the surface integrity characteristics of Inconel 625

Surface integrity in electric discharge machining (EDM) has always been a major concern in the manufacturing industry. Although, EDM with a powder suspended dielectric has shown good potential in enhancing the material removal rate and improving surface finish, influence of the same on the overall surface integrity is not very clear. The current work utilized the graphite powder and evaluated its role in combination with concentration and machining parameters, on surface roughness (Ra), surface crack density (SCD), white layer thickness, microhardness depth profile, possible phase changes, and residual stress during powder-mixed EDM (PMEDM) of Inconel 625 (a nickel-based super alloy), that is now-a-days regularly used in aerospace, chemical and marine industries. The results showed that significant reduction in surface roughness, crack density, and white layer thickness is possible with the PMEDM process. It also promoted formation of carbides and other alloy compounds which is responsible for augmentation of hardness in surface and subsurface region. The added particles also caused a decline in tensile residual stress of the machined samples.     

Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings

Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings was carried out. The objectives were to demonstrate that such difficult-to-machine coating surfaces could be machined with commercial machines and tools, and to characterize the surface finish of the machined coatings. The coatings were obtained using two thermal spraying processes: arc spraying and high velocity oxy-fuel spraying. Different machining techniques were tried to optimize the surface finishing of the coatings based on surface finish and time required. Machined samples were then examined using stylus roughness testers. Surface roughness parameters R_a and R_q were measured using various cut-off lengths, sampling lengths, and numbers of sampling and cut-off lengths to characterize the scaling behavior of the surfaces. Diamond turning of WC–Co demonstrated the advantage of high material removal rates, and diamond grinding of WC–Co produced good surface finish with relatively high material removal rates. Precision-machined WC–Co and Alloy-625 surfaces could be identified as self-affine fractals in a statistical sense within the correlation length, i.e. within the length scales studied from 0.08 to 8 mm. The surface roughness heights of the machined surfaces were found to be dependent on the scale of cut-off length as a power law.     

Machinability study of abrasive aqua jet parameters on hybrid metal matrix composite

The present work involves investigation of the abrasive aqua jet (AAJ) machining of hybrid metal matrix which consists of Al 6063 reinforced with boron carbide (B₄C) and zirconium silicate (ZrSiO₄) in the form of particulates in the proportion of 5% B₄C and 5% ZrSiO₄. The Response surface method using a central composite design was adopted for conducting experiments by changing the aqua jet pressure, abrasive flow rate, and traverse rate. The results were taken with different types of abrasives of various mesh sizes in this study, which were analyzed using response surface graphs. The striation effect on the bottom-machined surfaces was also examined using the striation length and its frequency. Surface topography and morphology were analyzed on the AAJ-machined composite kerf wall cut surfaces. The machined surface exhibited the inherent characteristics of AAJ which included wear tracks, and contamination generated in the metal surface. The experimental results revealed that higher abrasive flow rate (400 g/min), lower traverse rate (30 mm/min), and higher aqua jet pressure (300 MPa), the production of a higher material removal rate, lower surface roughness and kerf taper angle.     

Material removal in grinding sapphire wafers with brazed–diamond pellet plates

Grinding is an important abrasive machining process in many manufacturing chains. In order to improve the material removal in the grinding of sapphire wafers, this study presents two brazed-diamond pellet (BDP) plates developed with different BDP surface textures, i.e., a non-grooved BDP plate and a grooved BDP plate. Their performances were tested in the coarse grinding of sapphire wafers. The surface topography, surface roughness, material removal rate (MRR) were comprehensively investigated. The experimental results show that sapphire is removed in its brittle mode. However, the grooved BDP plate can produce lower surface roughness under a higher MRR. The improvement in surface roughness is mainly due to the better coolant flowability and chip removal facilitated by the grooves. The higher MRR is partly due to the increased pressure in the sapphire-plate contact zone. It is found that the grooved BDP plate can increase MRR by about 45.7%.     

On machining of hard and brittle materials using rotary tool micro-ultrasonic drilling process

The present paper reports on a recently developed rotary tool micro-ultrasonic drilling (RT-MUSD) process. The RT-MUSD process was utilized for machining of micro-holes in zirconia, silicon and glasswork materials. The effects of work material properties on the performance characteristics (material removal rate (MRR), depth of hole and hole overcut) of RT-MUSD process were investigated by varying the power rating, rotation speed, abrasive size and slurry concentration. Additionally, machined micro-holes and tool surface were analyzed considering microscopic images. The experimental results revealed that the MRR and depth of hole increased by increasing the power rating. An increase in rotation speed up to 300 rpm, abrasive size up to #1200 mesh and concentration up to 20% increased the MRR, depth of hole and decreased hole overcut. The maximum machining rate and hole overcut were observed during machining of silicon followed by glass and zirconia. The fracture toughness and hardness of the work material affected the MRR and tool wear, respectively. Pure brittle fracture mode of material removal was observed in all the work materials during RT-MUSD process. Eventually, the RT-MUSD process was optimized using desirability approach and a micro-hole of depth 4355 µm was achieved using optimal parameter settings.     

超声振动辅助磨削完全烧结氧化锆陶瓷牙冠的实验研究

针对现有全锆牙在制作过程中存在二次烧结、收缩精度难以控制等问题,提出了采用超声振动辅助磨削完全烧结氧化锆陶瓷牙冠的方法。从理论分析的角度对其运动学特性进行了研究,并通过超声振动辅助磨削和普通金刚石磨削实验,对该方法的可行性进行了分析。结合牙冠的加工特点,重点研究了主轴转速对材料去除率、表面粗糙度以及最大边缘碎裂的影响规律。实验结果表明,超声振动辅助磨削不仅能提升材料的去除率,有效抑制出口边缘碎裂,同时降低了工件表面的粗糙度,是实现完全烧结氧化锆陶瓷牙冠高效低损伤加工的新方法。     

CBN grain wear and its effects on material removal during grinding of FGH96 powder metallurgy superalloy

Grinding with cubic boron nitride (CBN) superabrasive is a widely used method of machining superalloy in aerospace industries. However, there are some issues, such as poor grinding quality and severe tool wear, in grinding of powder metallurgy superalloy FGH96. In addition, abrasive wheel wear is the significant factor that hinders the further application of CBN abrasive wheels. In this case, the experiment of grinding FGH96 with single CBN abrasive grain using different parameters was carried out. The wear characteristics of CBN abrasive grain were analyzed by experiment and simulation. The material removal behavior affected by CBN abrasive wear was also studied by discussing the pile-up ratio during grinding process. It shows that morphological characteristics of CBN abrasive grain and grinding infeed direction affect the CBN abrasive wear seriously by simulation analysis. Attrition wear, micro break, and macro fracture had an important impact on material removal characteristics. Besides, compared with the single cutting edge, higher pile-up ratio was obtained by multiple cutting edges, which reduced the removal efficiency of the material. Therefore, weakening multiple cutting edge grinding on abrasive grains in the industrial production, such as applying suitable dressing strategy, is an available method to improve the grinding quality and efficiency. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00412-2     

An experimental study on grinding of Zr-based bulk metallic glass

There are limited studies in the literature about machinability of bulk metallic glass(BMG).As a novel and promising structural material,BMG material machining characteristics need to be verified before its utilization.In this paper,the effects of cutting speed,feed rate,depth of cut,abrasive particle size/type on the BMG grinding in dry conditions were experimentally investigated.The experimental evaluations were carried out using cubic boron nitride(CBN) and Al_2O_3 cup wheel grinding tools.The parameters were evaluated along with the results of cutting force,temperature and surface roughness measurements,X-ray,scanning electron microscope(SEM)and surface roughness analyse.The results demonstrated that the grinding forces reduced with the increasing cutting speed as specific grinding energy increased.The effect of feed rate was opposite to the cutting speed effect,and increasing feed rate caused higher grinding forces and substantially lower specific energy.Some voids like cracks parallel to the grinding direction were observed at the edge of the grinding tracks.The present investigations on ground surface and grinding chips morphologies showed that material removal and surface formation of the BMG were mainly due to the ductile chip formation and ploughing as well as brittle fracture of some particles from the edge of the tracks.The roughness values obtained with the CBN wheels were found to be acceptable for the grinding operation of the structural materials and were in the range of 0.34-0.58 μm.This study also demonstrates that conventional Al_2O_3 wheel is not suitable for grinding of the BMG in dry conditions.     

液体磁性磨具小孔光整加工材料去除机理及实验

针对小孔内壁光整加工技术的难题,本文提出一种新型精密研磨孔光整加工技术,以磁致相变理论为指导,从微观角度阐述了液体磁性磨具研磨孔光整加工的材料去除机理.采用"双刃圆半径"模型进行单个磨料颗粒切削模型研究,得出小孔光整加工的材料去除率数学表达式.通过实验验证了磨料粒度、入口压力、电流强度等因素对材料去除率以及表面粗糙度的影响,实验结果表明:在合适的范围内,增大磨料颗粒直径、入口压力以及电流强度有利于提高材料的去除率和表面质量.而当磨粒直径、入口压力以及电流强度选取过大时,虽然能获得较高的材料去除率,但是最终获得的表面粗糙度值并不理想.该研究为通孔零件内壁表面精密光整加工提供了有益参考.