Carbon fiber reinforced plastic (CFRP) is widely used in aircraft fuselage, wings and tail etc. Milling is a necessary mechanical machining method after CFRP parts have been molded. The strength of CFRP materials is variable under different milling parameters and it’s difficult to judge the variation tendency when changing the parameters. To explore the influence of the milling parameters on the mechanical strength, prediction models of tensile and compressive strength are established in this article, which is based on the extreme gradient boosting algorithm (XGBoost). In addition, the differences in prediction performance between the extreme gradient boosting algorithm model and the artificial neural network (ANN) model are compared. The results show that the milling parameters will not change the tensile strength of CFRP. The better prediction ability is obtained in the test dataset by XGBoost, and the maximum error of the model for the prediction of CFRP compressive strength among the milling parameters range is less than 7.56%. The XGBoost model also indicates that the spindle speed has more pronounced influence on the compressive strength of CFRP. It is proven by the fracture topography under different spindle speeds: the increase of spindle speed result in the heat damage of the machining surface and reduce the fiber-resin bonding strength and finally decrease the compressive strength of CFRP. The prediction model proposed in this article is expected to provide more guidance for milling CFRP materials to reduce the machining damage and obtain better mechanical strength of the parts after machining.

Carbon fiber reinforced plastic (CFRP)/Ti6Al4V stacks are widely used in the aircraft industry, and drilling these stacks is essential during the assembly process. To solve the problem of high drilling temperatures in CFRP/ Ti6Al4V stacks, which lead to poor tool life and hole quality, the effects of three cooling strategies compose minimum quantity lubrication (MQL), water-based coolant, and internal air cooling, were investigated in this study. Tensile/compressive strength and fatigue-life tests were conducted to evaluate the applicability of the cooling medium before drilling. Then, low-frequency vibration-assisted drilling of CFRP/Ti6Al4V stacks was performed to investigate and analyze their machinability under the three cooling strategies by analyzing the drilling temperature, thrust force, tool wear, chip removal capacity, and hole quality. The results show that the selected cooling media, including Rhenus XT46 and Accu-Lube LB2000, are applicable in CFRP drilling, whereas the adopted media, compared with water, have little influence on the tensile/compressive strength and fatigue life of the CFRP. Compared with internal air cooling and MQL, water-based coolant can more effectively improve the machinability of CFRP/Ti6Al4V stacks, decreasing the CFRP drilling temperature by 41.6 % and 40.1 %, respectively, while the reductions in the Ti6Al4V drilling temperature are 76.7 % and 57.4 %, respectively. Meanwhile, under water-based coolants, the thrust force reductions in the drilling of CFRP are 13.1 % and 11.7 %, whereas those in the drilling of Ti6Al4V are 11.0 % and 7.8 %, respectively, compared with the internal air and MQL. In addition, under the water-based coolant condition, the tool wear rate is the slowest and the hole quality is the best among the three cooling strategies, whereas a high injection pressure further decreases the VBmax value. Furthermore, under the water-based coolant conditions, the Ti6Al4V exit burr height and CFRP exit delamination are the lowest. These findings provide useful insights into improving the machinability of CFRP/Ti6Al4V stacks in the aerospace industry, particularly for drilling that requires high-quality holes and a long tool life.

Low frequency vibration-assisted drilling (LFVAD) of CFRP/Ti stacks is a promising method of one-shot drilling to increase efficiency and extend tool life while adaptive approaches are applied to adjust the cutting parameters in each layer. Thus, the interfacial recognition method is significant to automatically change the cutting parameters. In this paper, two recognition methods are proposed based on the analysis of the features of cutting forces under the LFVAD process in both time and frequency domains. With the recorded thrust force signals at different wear stages, both the proposed methods identify the transition point when the drill bit starts to contact the Ti layer within allowable time delay. Compared with the traditional threshold method, the time domain method and the frequency domain method respectively increase the identifying speed by 19.8% and 46.7%, besides the reduction of implementation cost. In contrast, the time domain method reduces the programming and calculation time, while the frequency domain method improves the average recognition speed. Furthermore, an adaptive drilling system embedded with the established time-domain method is designed and the accuracy of the method is proved of 100% in a drilling test of all 20 CFRP/Ti stack holes. Moreover, the effect of the adaptive LFVAD process in improving tool wear and increasing machining efficiency is verified by reducing the force growth rate by 11.7% and time decrease of 37% in a hole-making cycle compared with the traditional LFVAD process.

Hole-making of stacks composed of carbon-fiber-reinforced plastic (CFRP) and titanium alloy under Low-frequency vibration-assisted drilling (LFVAD) is beneficial to both machining quality and tool wear. However, complicated deformation of the bottom Ti layer and even severe interfacial damage appears under the thrust forces with periodic fluctuations. Owing to lack of theoretical guidance in suppressing the deformation, this study established an analytical model to explain the influence of the fluctuating thrust force on the deformation of the workpiece. Data from validation trials performed on the CFRP/Ti stacks show that the deformation and thrust forces exhibit the same fluctuation behavior. The prediction errors of the average value and vibration amplitude of the Ti deformation were within 0.9 % and 10.7 %, respectively. Finally, a case study was conducted to optimize the drilling parameters in LFVAD of CFRP/Ti stacks based on the proposed model. As a result, the CFRP delamination damage was reduced by 17.0 %, and the stack drilling efficiency increased by 40.8 %.

In low-frequency vibration-assisted drilling (LFVAD) of CFRP/Ti6Al4V stacks, owing to the different mechanical and thermal performances of the involved carbon fiber–reinforced plastic (CFRP) composite and Ti6Al4V alloy, the short tool life of commonly used carbide (WC) tools and rapidly deteriorated machining quality are the major problems. This paper aims to explore whether the polycrystalline diamond (PCD) tool can achieve a competitive effect on drilling CFRP/Ti6Al4V stacks compared with previous CFRP drilling studies. To avoid the frequent occurrence of chisel edge fracture in LFVAD of Ti6Al4V alloy, a model of plowing behavior is established and parametric experiments based on it are performed with both PCD and WC drills. It is found that the periodically dynamic force is the major factor causing the chisel edge fracture of the PCD drill, which can be alleviated by reducing the feed rate. Besides, by using PCD drills instead of WC drills in Ti6Al4V drilling, the exit burr height, drilling diameter deviation, and surface roughness value are reduced under each given parameter. Finally, PCD and WC drill bits are used to perform a wear test on the CFRP/Ti6Al4Vstacks under optimized parameters. The PCD drill achieves superior performance, including lower wear rate, better hole quality, and higher consistency. The experiments discussed in this paper provide some suggestions for selecting tools and cutting parameters when drilling CFRP/Ti6Al4V stacks.

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.