Form grinding is a high-efficiency machining technology for products as fir-tree blade slots. The excessive heat generated in the grinding contact zone is the key issue for form grinding. In this paper, a profile rotating heat pipe grinding wheel (PRHP-GW) was proposed to help dissipate the grinding heat; nanofluids were applied to enhance its thermal performance. The heat transfer performance of PRHP was experimentally studied. Diamond and Al2O3 nanofluids with different mass concentrations and nanoparticle sizes were applied and compared with deionized water. The experiments were performed under the conditions of different heat inputs, rotational speeds, and different filling ratios. At the same filling ratio, there was a significant reduction in thermal resistance with nanofluids as compared with deionized water. Under the heat input of 140 W, the thermal resistance decreases by about 17.6

Carbon fiber–reinforced plastic (CFRP)/Ti6Al4V stacks are widely used in the aircraft industry to increase structural strength, reduce overall weight, and lower life cycle costs. A high drilling temperature has always been an unavoidable issue in stack drilling, resulting in severe delamination of CFRPs, the formation of large Ti6Al4V burrs, and poor hole surface quality. Therefore, accurately predicting the drilling temperature is crucial when drilling CFRP/Ti6Al4V stacks. However, differences in the thermal properties of the two materials and their heat transfer at the interface present challenges. This study proposes a novel temperature predictive model for low-frequency vibration-assisted drilling (LFVAD) of CFRP/Ti6Al4V stacks. The influences of heat transfer at the CFRP/Ti6Al4V interface and separation motion in LFVAD are considered in the model to predict the stack drilling temperature distribution, and the heat partition ratios of the two materials are also calculated. Internal air cooling, minimal quantity lubrication (MQL), and supercritical carbon dioxide (ScCO2) cooling strategies are applied in the drilling experiments to verify the accuracy of the proposed model and to study the influence of the drilling temperature on the hole quality. The results show that the prediction errors of the temperature in the CFRP and Ti6Al4V picked regions during LFVAD under the internal air cooling strategy are within 6.2

Owing to the difficult-to-machine characteristics of nickel-based superalloy, the deep hole drilling (DHD) is prone to various issues, including high thrust force and torque, high cutting temperature, difficult chip breaking, tool fracture and poor surface quality caused by poor chip evacuation. Low-frequency vibration-assisted drilling (LFVAD) facilitates the tool-workpiece periodic contact and separation, as well as effective chip breaking, which provides a high potential for the DHD of difficult-to-machine materials. In the present study, the DHD of nickel- based superalloy with LFVAD and conventional drilling (CD) is comparatively analyzed in detail. Firstly, the theoretical analysis shows that the good chip breaking ability of LFVAD can effectively enhance the chip evacuation of DHD. The chip unfolded areas of LFVAD are much smaller compared to those of CD. Then, LFVAD can effectively reduce the average drilling forces (by 14.6 % and 16.3 % for average thrust force and average torque, respectively) due to the less friction and enhanced cooling effect. As for chip morphologies, there are irregular small burrs at the edge of the chip for CD with dense and tight segmentation, while LFVAD shows a relatively smooth bottom edge with hypertrophic segmentation. Finally, LFVAD is benefit for improving surface quality under appropriate vibration condition. The findings of this paper indicate that LFVAD offers several machinability advantages, making it a promising technique for the DHD of difficult-to-machine materials.

For the light weight and chemical stability, Ti-6Al-4V titanium alloy microchannel is an ideal element for fluids controlling, transporting and manipulating, which has been widely used in the aerospace field. However, the poor surface quality of machined microchannels and tool wear pose challenges to performance improvement. In this study, ultrasonic vibration-assisted milling (UVAM) of titanium alloy microchannels was investigated, comparing the effects of ultrasonic vibration amplitude, spindle speed, feed rate, and cutting depth on surface morphology, surface roughness, sidewall verticality, and tool wear with conventional milling (CM) processes. The results demonstrated that axial ultrasonic vibration can effectively improve the machined surface uniformity and reduce tool wear, resulting in a 29.06 % decrease in microchannel surface roughness and a 7.76 % increase in sidewall perpendicularity. This study lays the foundation for manufacturing high-quality Ti-6Al-4V titanium alloy microchannels and also expands the application of ultrasonic-assisted machining techniques in the field of microchannel manufacturing.

Profile grinding of titanium alloys are now utilized for aero-engine structural components. However, owing to its low thermal conductivity, the grinding contact zone generates an intense deal of heat, resulting in burns on the surface of the workpiece. At the same time, titanium alloys are prone to abrasive adhesion at high temperatures, which aggravates the wear of the grinding wheel. A novel grinding wheel named profile rotating heat pipe-grinding wheel (PRHP-GW) was created to improve heat transfer in the grinding contact zone. Therefore, it is expected to achieve efficient heat exchange. The kind of working medium in the rotating heat pipe (RHP) is the key factor that might seriously influence the heat transmission capacity of the RHP-GW. In this article, the numerical simulation is applied to investigate the heat transfer characteristics of PRHP-GW from the perspective of different grinding heat flux, rotating speed and grinding wheel types (normal grinding wheel without RHP, PRHP-GW filled with deionized water, and PRHP-GW filled with diamond nanofluid). The results demonstrate that the heat transfer capacity of PRHP-GW is superior to that of the normal grinding wheel. In addition, the heat transfer performance of PRHP-GW filled with diamond nanofluid is better than the case filled with deionized water.

Carbon fiber–reinforced polymer (CFRP) and titanium alloy stacks play a significant role in the aerospace field to improve the mechanical properties of assembly components. Low-frequency vibration-assisted drilling (LFVAD) can realize the periodic contact and separation characteristic between tool and workpiece, thus pose a high potential for manipulating the machinability of CFRP/Ti stacks. In the present study, two types of drilling tools (polycrystalline diamond (PCD) tool and diamond-coated tool) are adopted, and tool wear behaviors are deeply evaluated during drilling CFRP/Ti stacks. Meanwhile, the specific influences of tool wear on the drilling performances are comprehensively analyzed under the LFVAD with minimum quantity lubrication (MQL). The results show that Ti-adhesion is observed for both drilling tools. Meanwhile, edge fracture is the key wear mode dominating for the PCD tool, and coating peeling is the main wear mode for the diamond-coated tool, with less Ti-adhesion. In addition, with the increasing number of drilled holes, the diamond-coated tool demonstrates better drilling performances with lower cutting force, better hole quality, and more hole-making number. The findings of this paper can contribute to providing a guidance for tool optimal selection in low-frequency vibration-assisted drilling of CFRP/Ti stacks with MQL.

Plain-woven carbon fiber-reinforced plastic (PW-CFRP) exhibits high damage tolerance and is widely used in the aerospace field. To address the issue that single-scale drilling simulation is difficult to reflect the practical drilling force due to the change in material elastic properties in PW-CFRP drilling simulation, this paper studies the prediction of elastic properties of PW-CFRP and multi-scale three-dimensional drilling simulation. Based on the prediction model of elastic performance parameters with periodic boundary conditions, the three-dimensional drilling simulation of PW-CFRP is carried out using the predicted material elastic performance parameters and the multi-scale finite element method, with experimental verification. The results show that the finite element method based on periodic boundary conditions can accurately predict the elastic constants of braided composites. For the woven unit cell, its boundary surface changes from plane to surface under shear load, and convex-concave warping deformation occurs. The PW-CFRP three-dimensional drilling simulation model, based on the stiffness prediction model, can accurately predict the axial force and torque during the drilling process. Under the same process parameters, the maximum relative errors between the simulation prediction and the experimental results of the drilling thrust force and torque are 14.2% and 8.5%, respectively. The multi-scale drilling simulation of PW-CFRP, from microscopic to mesoscopic to macroscopic, is realized.

为深入学习贯彻落实海南省委书记沈晓明在省委宣传思想工作领导小组(扩大)会议暨全省宣传部长会议上的重要讲话精神,2021年4月10日,由海南省社科联(社科院)、海南大学指导,海南省文物研究会创办,海南大学人文传播学院、海南省文物研究会、海南文化研究院主办的"建设文化强省和具有强大文化软实力的自由贸易港:第一届新时代海南文化发展论坛(2021)"在海口市举办.

Based on the concept of effective abrasive grain number and the calculation method of surface roughness, two indexes, namely effective dressing rate Nr and dressing dispersion degree H, were proposed to evaluate the grinding performance and surface topography of the grinding head. The variation of Nr and H during the dressing process were analyzed. The relationship between both indexes and the surface roughness and the grinding force of carbon fiber reinforced plastics(CFRP) after grinding was also established. The experimental results show that Nr can effectively characterize the dressing state of the abrasive particles on the grinding head and reflect the passivation degree of the grinding head. H can effectively characterize the contour of the abrasive grain, and predict the quality of CFRP surface. When H is 18~25 μm, the grinding head surface roughness is the best. The grinding head force has smaller growth amplitude, and the grinding head has better performance.

In order to study the influence of milling and grinding process on the machining quality of CFRP (carbon fiber reinforced plastics), the single-layer brazed diamond abrasive router and diamond coated end mill were used during the trimming experiment of T800 carbon fiber reinforced plastics. The difference of the machining quality and occurrence of defects were discussed according to the observation of micro topography and measurement of surface roughness. The results show that surface quality under abrasive machining process is much better than that of milling process. Great pits and resin smearing are observed after milling process, while the section of carbon fiber is visible under abrasive machining process. The discussion shows that the fracture of carbon fiber bundles contributes to the formation of great pits and the continual reaction between flank face and finished surface lead to the occurrence of resin smearing. Grinding is the preferred machining process under the strict requirements for surface quality and processing deficiency.

Aiming at some problems in manufacturing the aircraft CR929, namely difficulty to predict exit delamination defect and high cost of hole load prediction test, a three-dimensional finite element drilling simulation and experimental research of carbon fiber reinforced plastics (CFRP) were carried out. Firstly, the macro-mechanical constitutive model of CFRP was established by Fortran language based on user-defined subroutine interface of ABAQUS software. Then a three-dimensional finite element model of large aperture drilling CFRP was established. By comparing the model in experiment, the correctness of the finite element model is verified under the same parameters. Finally, the finite element model was used to predict the axial force, torque and exit delamination of the hole at different processing parameters. The results show that the three-dimensional finite element simulation model of composite drilling based on three-dimensional solid element modeling can reliably predict the axial force and torque. The shape of exit delamination can be predicted by embedding cohesive elements at the exit of CFRP. Under the same parameters, the maximum relative error of simulation prediction for axial force, torque and exit delamination is 15.0%, 19.0% and 12.4%, respectively.

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

The influence of the binder concentration on the nanometric surface characteristics of WC/Co in ultra-precision grinding is investigated in the present work. The results firstly show that the surface finish of the ground WC/Co changed with increasing Co content, and the machined surfaces were covered by many micro-pits and surface burs induced by the plastic deformation and the prior removal of Co binder, which also led to the micro-chipping of the WC grains near the boundaries for the lack of support by Co. Many finer scratching grooves in the feed marks appeared, but the periodic grinding grooves caused by the feed of the diamond wheel became unclear with increasing Co content and the vibration induced marks on the machined surface turned to be primary, the spatial frequency of which is identified to be around 130 1/mm by the Fast Fourier transform. In addition, for the isotropic of the statistical size of the WC grains and the thickness of Co binder along each direction, a circular symmetry shape of the spatial frequency forms and the radius increases with increasing Co content.

通过开展低频振动钻削叠层材料单因素试验,研究了刀具的顶角、螺旋角和后角对钻削轴向力及温度的影响.结果表明:钻头顶角越大,轴向力越大,螺旋角的变化对钻削CFRP层轴向力影响较小;在钻削钛合金层时,轴向力随着螺旋角的增大呈先下降后上升的趋势,钻头后角越小,轴向力越大;钻头几何参数对钻削温度的影响可以忽略,得出较为适合CFRP/钛合金叠层材料振动制孔的钻头几何参数为顶角120°、螺旋角25°、后角20°.

Stack materials composed of CFRP (Carbon Fiber Reinforced Plastic) and titanium alloys are widely used in the aerospace field due to their excellent properties. However, the machining properties of the two materials are quite different in all aspects. During the single-shot drilling of compound stacks, some defects like entrance spalling and hole wall scratching are easily induced by the evacuation of titanium alloy chips. In order to improve the hole quality of stack materials, this research studied the influence of different amplitudes (A=0μm, 20μm, 40μm, 60μm) on cutting force, cutting temperature and hole quality by comparing the low frequency vibration drilling with the traditional drilling. The results show that the average axial force decreases with the increase of amplitude while the maximum axial force increases. Low-frequency vibration drilling drills the temperature to drop somewhat compared to the traditional drilling. Vibration drilling has no improvement on decreasing delamination defects and it tends to increase defects, but it can improves the quality of CFRP hole walls.

Low frequency vibration assisted drilling (LFVAD) is regarded as one of the most promising process in CFRP/Ti stacks drilling. This work carries the investigation of the difference between conventional drilling and LFVAD based on kinematic model. The experiments are conducted under varied vibration amplitude to a specific feed rate, also under varying spindle speeds, feed rates when the ratio of amplitude to feed rate is fixed. Then the hole quality of CFRP is evaluated based on the analysis of drilling force, chip morphology, chip extraction. The results show that there is rarely no difference between conventional drilling and LFVAD in drilling mechanism when the drilling diameter is over 1 mm. Because the impact effect caused by drill vibration is already weak. It is found that the severe mechanical damage of the CFRP holes surface could be significantly reduced due to the fragmented chips obtained in vibration drilling. The maximum instantaneous feed rate combined with feed rate and amplitude plays a significant role in CFRP hole quality. Lower maximum instantaneous feed rate results in better hole wall quality and less entry delamination. Spindle speed has no visible influence on entry delamination, while higher spindle speed improves the hole surface quality due to the resin coating phenomenon.

在叠层材料一体化制孔过程中,CFRP制孔质量极易受到钛合金切屑排出的影响,出现入口撕裂、孔径超差等加工缺陷.为了提高叠层材料的制孔质量,本文分析了振动钻削的运动学特征,确定了理论最小断屑振幅,通过低频振动钻削和传统钻削叠层材料的对比试验重点探讨了不同振幅参数对切削力、切削温度以及制孔质量的影响.结果表明:随着振幅增大,钻削平均轴向力小幅下降,最大轴向力呈现上升趋势;当振幅大于最小断屑振幅时,低频振动钻削在实现有效断屑排屑的同时能够显著降低切削温度,提高孔壁质量和孔径精度;CFRP入口撕裂受振幅的影响最为明显,加工振幅过大会导致入口撕裂的扩大;当振幅为30μm时,入口撕裂区域最小,孔壁粗糙度达到Ra2.16μm,叠层材料总体制孔质量最好,切削温度同时降低了20.8％.

The low interlaminar adhension and anisotropy of carbon fiber reinforced plastics (CFRP) could result in serious machining defects such as delamination, burrs, tearing, and other problems such as short tool life.On the idea of "grinding instead of cutting", delamination can be improved by using brazed diamond cutting tool whose grits are orderly arranged.In order to manufacture appropriate brazed diamond tool which is suitable for CFRP edge grinding, five kinds of tools with different grit size and varied arranging distance are prepared and the influences of tool structure changes on grinding forces and surface integrity when edging machining CFRP are investigated comparatively.The results show that under the same grain arrangement and the machining parameters, increasing grit size has few influence on grinding force but leads to a worse surface quality.In addition, decreasing grit arranging distance contributes to the improvement of machining quality and the grinding force increases firstly then decreases under the conditions of commonly grain size and machining parameters.

The chip morphology and tool wear for milling Invar die steel are studied.The research results indicate that under the condition of optimized cutting parameters,the chip forms for rough and finish milling are arc-shaped,and bringing about good chip control and evacuation.When roughing with Vc.=60m/min for 5 hours,the flank wear VB amounts to 0.26mm,and when finishing with Vc.=120m/min for 2 hours,the flank wear VB amounts to 0.2mm.The tool wear analysis shows that there exist light adhesive wear and abrasive wear in rake face.When roughing and finishing,there exist craters in the rake faces,chipping at the tip edges and notching at depth of cut.