Hole surface morphology and tool wear mechanisms during cutting 3D carbon/carbon composites using diamond core drill

Carbon fiber reinforced carbon matrix (carbon/carbon) composites are a new class of ceramic engineering materials and applied in aerospace structures due to high strength in non-oxidizing atmospheres at extremely high temperatures, while it is a typical difficult-to-machine material due to its anisotropy and heterogeneity. Defects such as burrs, tears and fiber pullout are likely to be produced on machined surface when inappropriate machining parameters are employed. The material removal mechanisms during mechanical cutting of carbon/carbon composites are still not fully understood. In this work, the three-dimensional braided carbon/carbon composite was employed, hole surface morphology and tool wear mechanisms during drilling with a bronze sintered diamond core tool were studied. Result showed that fiber tearing and burrs were mainly observed at hole entrance and exit under low level of feed speed down to 20 mm/min. When the feed speed increased to 40 mm/min and 60 mm/min, severe tearing, uncut fibers, and delamination appeared at hole exit. Fiber orientation showed significant influence on material removal mechanisms as well as fiber shearing/bending fracture, fiber pullout and matrix fragmentation. The ground, pullout and fracture of abrasive particles were the main tool wear mechanisms, cutting chips were attached and blocked inside the core drill probably due to high cutting temperature in dry condition, as the temperature increased to ～260 °C under the feed speed of 60 mm/min.     

Hole exit quality and machined surface integrity of 2D Cf/SiC composites drilled by PCD tools

The brittle matrix and the anisotropic reinforcing phase of C_f/SiC composites bring great challenges to the machining process. Polycrystalline diamond (PCD) tool was used to drill 2D C_f/SiC composites. The influence of thrust force on hole exit defects was analyzed, and the transformation rule of material removal mechanism and surface generation of hole were studied. With the increase of feed rate, the thrust force increased and the hole exit defects increased. Specific drilling energy was used as an index to quantitatively describe the energy consumption of material removal. With the increase of feed rate and the decrease of cutting speed, the brittle fracture mode of carbon fibers changed from micro-brittle fracture inside carbon fiber to macro-brittle fracture. Although the machined surface of carbon fibers produced by micro-brittle fracture was composed of many micro-fracture, the hole surface was flat overall. Therefore, the hole surface roughness was small.     

Regression analysis of surface roughness and micro-structural study in rotary ultrasonic drilling of BK7

Ceramic materials have tremendous demand in manufacturing sectors. However, poor machinability impedes their widespread applications on an industrial scale. BK-7 falls in the same category and is normally processed by ultrasonic machining. But nowadays rotary ultrasonic machining is overtaking the ultrasonic machining for processing difficult to cut materials because of its superlative material removal mechanism. Current study aims to improve the surface quality of BK7 by studying the effect of input factors on surface roughness during rotary ultrasonic machining. Response surface methodology has been used to observe the effect of input variables ― spindle speed, feed rate and ultrasonic power ― on surface roughness (SR). Thereafter, central composite design was employed to estimate the regression coefficients of quadratic model for surface roughness. Fitness of developed quadratic model was checked by ANOVA test, which also revealed that all the model terms of input factors were significant except feed and speed interaction. Feed has the maximum impact over surface roughness descended by moderate impact of power and spindle speed. The study was further reinforced on observing the surface integrity of processed surfaces using scanning electron microscopic images. Mixed flow of material was observed to occur at lower feed rate and higher levels of rpm and ultrasonic power.     

CFRP旋刨刀具钻孔的可行性实验研究

CFRP是典型的难加工材料,特别是钻削直径d≥8 mm的孔。探究性设计了一种新型钻削CFRP的旋刨刀具,基于对旋刨刀刀具、麻花钻、套料钻进行的钻削实验,在不同的主轴转速和进给速度下,得到三种刀具轴向力的大小,然后利用MATLAB分别拟合出三种刀具的经验公式,并分析对比不同的转速和进给速度下轴向力对三种刀具的影响。结果表明旋刨刀刀具对CFRP制孔效果更优。     

Hardwood fibre fractionation using rotating cone

Rotating cones were used to carry out fibre fractionation of a 100% hardwood pulp having a consistency of 0.93± 0.02%. The unique features of the rotating cone fractionator adopted in this study were that its surface was constructed from a sieve mesh, thereby introducing a “rough” surface, and the feed pipe was located at an off-centre position to the axis of rotation. In all earlier studies reported in the literature, the fibre fractions were collected at different radial locations. However, in the present study, collection of the various fractions was made either at different radial or at angular positions. Tests were conducted for 120 mm diameter cones having a cone angle of 30°. Visual observations, photographs and fibre length measurements suggested that fibre fractionation performance strongly depended on the flow characteristics formed on and surrounding the rotating cone. In turn, they were found to be strongly dependent on the surface roughness, rotational speed and feed flow rate. Results for fibre fractionation showed quite conclusively that rotating cones made from 20-mesh and 32-mesh screens were more effective for fibre fractionation than “smooth” surface rotating cones.     

电解-磁力研磨钛合金的工艺参数优化

为了改善钛合金零部件的表面质量,降低其表面粗糙度,基于电解-磁力研磨复合加工工艺,选用烧结法制备的Al_2O_3系球形磁性磨料,对钛合金样件进行表面光整加工。采用响应面法获得了工件表面粗糙度关于电解电压、主轴转速及进给速度的2阶响应曲面函数及显著影响工件表面粗糙度的关键因素。实验结果表明,优化的电解-磁力研磨参数如下:主轴转速1000 r/min,电解电压15 V,进给速度2.5 mm/s。在优化的工艺参数下对钛合金样件电解-磁力研磨10 min,样件的表面粗糙度由原始的1.7μm下降到0.13μm,表面微裂纹和微观形貌得到明显改善,提高了零件的寿命。     

单向碳纤维增强塑料磨削加工性能

碳纤维增强塑料因具有优异的力学性能,在航空航天等领域有重要应用。通过单向碳纤维增强塑料(CFRP)的平面磨削实验,研究了塑料增强方向对CFRP磨削加工性能的影响。研究发现,单向塑料基复合材料磨削时,由于纤维增强塑料的各向异性,磨削力与加工表面粗糙度均呈现明显的规律性。其中,在加工参数砂轮转速为1500 r/min,进给速度为5 m/min和切削深度50μm的条件下,最大和最小磨削力分别为42和10 N,而且,磨削力符合规律:法向>纵向>横向。通过对磨削加工表面显微形貌的分析,揭示了塑料基复合材料磨削微观多向材料的去除机理。研究结果不仅对拓展CFRP的应用具有重要的经济意义,同时,能够为复合材料精密加工提供一定的理论和实验支撑。     

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.     

Parameter Optimization of Rotary Ultrasonic Machining on Quartz Glass Using Response Surface Methodology (RSM)

In the current research, rotary ultrasonic machining was used to drill holes in quartz material. The effect of different RUM parameters namely tool feed rate, tool rotational speed and ultrasonic power on material removal rate and surface roughness has been studied experimentally. The response surface methodology with central composite design has been used to design the experiments. From the desirability approach, the optimum setting of the rotary ultrasonic machining parameters was found to be the tool rotational speed of 4968 rpm, feed rate of 0.55 mm/min, and ultrasonic power of 80% for achieving the maximum MRR of 0.2135 mm3/s and minimum SR of 0.3685 μm. Microstructure analysis of the machined surface was performed by using scanning electron microscopy in order to study the mechanisms of material removal under the different settings of RUM parameters. It was observed that at very low feed (0.08 mm/min) and high rpm (5681) the material is predominantly removed by plastic deformation whereas at high feed (0.92 mm/min) and low rpm (2318) the material is removed by brittle fracture.     

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.     

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.     

Influence of in-plane and out-of-plane machining on the surface topography,the removal mechanism and the flexural strength of 2D C/C-SiC composites

Ceramic Matrix Composites (CMCs) are increasingly demanded especially for the production of structural components for several industries such as aerospace because of their excellent thermo-mechanical and fatigue properties. As one of the last production steps final machining is necessary to meet the required tolerances. From the economic point of view final machining of CMCs is highly critical and special knowledge is assumed to avoid irreparable damage, because of their heterogeneous, anisotropic and brittle nature. In this work diamond grinding and diamond milling have been applied to a 2D C/C-SiC composite at various feed rates and cutting speeds and in both main laminate directions, in-plane and out-of-plane. The microstructures of in-plane and out-of-plane machining indicate different material removal mechanisms due to different composite architecture. Increasing feed rate leads generally to more surface defects and consequently to higher roughness. Little influence on the four-point-bending strength was observed when changing the machining speed.     

Evaluation of processing factors on turning of thermoplastics

Experiments were carried out to study the effects of cutting speed, feed, depth-of-cut and tool-nose-radius on the cutting force and surface roughness produced during turning of the thermoplastics Nylon-6 and Teflon. Generalized equations for the cutting force and surface roughness in terms of processing factors have been established using the statistical technique of multiple regression analysis. The equations have been tested for acceptability by the F-test and the degree of significance of various factors has been assessed by the t-test.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

环形金刚石线锯切割蓝宝石试验研究

使用环形金刚石线直径为0.70毫米,长4米,切割直径53毫米的蓝宝石晶体,30分钟即可完成切割。论文研究切割线速度,进给速度等对蓝宝石切割面粗糙度的影响。通过试验找到环形金刚石线切割蓝宝石片的最佳工艺参数并对其切割机理进行了探讨。     

Machining of plastics: A new approach for modeling

A theoretical model was defined to predict cutting forces in drilling of polyamide. This model was not built in analogy to metal cutting but starting from the viscoelastic behavior of the workpiece material. The drilling thrust and torque were assumed to be a logarithmic function of the ratio between a characteristic time of the material and a process time. Drilling tests were carried out to experimentally evaluate the thrust and torque in dependence of drilling speed and feed rate. The experimental data are in good agreement with the predicted logarithmic trend, except at high feed rates at which a plateau is observed. The chip formation mechanism was recognized to affect the thrust and torque dependence on feed rate so that the theoretical model was opportunely corrected. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Wear resistant CVD diamond tools for turning of sintered hardmetals

Sintered hardmetals are very hard materials that are usually machined using diamond grinding wheels and electro-discharge machining. Dry cutting with super-hard cutting tools like cubic boron nitride (c-BN), polycrystalline diamond (PCD) and chemical vapour deposition (CVD) diamond is an ecological alternative to reduce operation times and, therefore, to improve the productivity. In the present work, cylindrical forging dies of WC–27 wt.% Co hardmetal grade were turned at fixed operating parameters (cutting speed=15 m/min; depth-of-cut=0.2 mm; feed rate=0.03 mm/rev.) using CVD diamond tipped hardmetal inserts. Commercial PCD and c-BN inserts were tested for comparison. The cutting tool behaviour was studied in terms of both the tool wear and the finishing quality of the workpiece. The tool damage was evaluated using a special probe for edge roughness evaluation, together with scanning electron microscopy observations. The CVD diamond tools survived the task showing slight cratering, whereas flank wear was the main wear mode for the other superhard tools. Amongst all the tested tools, PCD presented the worst performance in terms of tool wear and workpiece surface quality. Furthermore, the operation time was reduced to one tenth with respect to conventional diamond wheel grinding.     

陶瓷轴承外圈内圆磨削力与表面质量研究

为了探究陶瓷轴承外圈内圆(简称外圆)磨削力以及磨削力对表面质量的影响机制,通过磨削实验首先获得了不同磨削参数对外圆磨削力的影响规律,其次得出了旋转磨削力与表面粗糙度和表面去除方式的关系。结果表明,随着砂轮速度减小,进给量和工件转速增加,陶瓷外圆磨削法向与切向磨削力均增加,且法向磨削力是切向磨削力的3倍左右;当磨削力增大,磨削表面由塑性去除向脆性去除转变,表面粗糙度值增大,表面质量变差。在陶瓷轴承外圆磨削时可适当选用较高的砂轮速度、较小的进给量和工件转速以保证表面加工质量和加工效率。     

Performance of Si3N4/(W,Ti)C graded ceramic tool in high-speed turning iron-based superalloys

A Si₃N₄/(W, Ti)C graded nano-composite ceramic tool was fabricated and its performance in high speed turning iron-based alloys GH2132 was investigated compared with homogeneous and commercial ceramic tools. The chip morphology, cutting forces, cutting temperature, tool life and failure mechanisms and machined surface roughness were recorded and analyzed. The results showed that with the increasing cutting speed the resultant cutting force shows a tendency to first increase and then decrease while the cutting temperature increases gradually. Straight continuous chips, bending continuous chips, twist continuous chips and snarled chips form in turn. Saw-tooth chips tend to form when the cutting speed is more than 200?m/min. The graded tool shows longer tool life especially at the cutting speed of 150 and 200?m/min compared with the homogenous and commercial ceramic tools. Tool failure modes mainly include grooving on the rake face, notching on the flank face, abrasion and adhesion. The grooving on the rake face tends to decrease while notching on the flank face tends to increase as cutting speed increases. Surface roughness of the machined iron-based super-alloys is relatively high due to the serious adhesion. Better surface roughness can be got using the graded tool.     

连续玻璃纤维增强聚丙烯层合板非等温拉伸成型质量研究

采用自行设计的模具,对双层玻璃纤维增强聚丙烯（GFRTP）复合材料单向层合板进行了半球形非等温拉伸成型试验,结合显微观察等手段,就复合材料单向层合板预热温度、拉伸速率等对制件厚度分布、成型质量的影响进行了研究。结果表明,提高预热温度可导致制件变薄;提高拉伸速率可改善制件的表面质量,当拉伸速率超过150 mm/min时制件会产生拉裂和脱层的缺陷。