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.

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.

Carbon fibre-reinforced plastic (CFRP) composites have been widely used in the field of aerospace and transportation because of their excellent mechanical properties. However, excessive tool clogging commonly occurs because of low chip storage space, thereby leading to workpiece failure. The slot grinding experiments with and without ultrasonic vibration were performed by using abrasive tools with defined grain pattern to improve tool life. The mathematical model of the fibre cutting angle in ultrasonic vibration-assisted slot grinding (USG) was established. The influences of ultrasonic vibration on the grinding force, tool clogging and surface integrity of unidirectional CFPR were discussed quantitatively. Results show that the USG featured lower grinding force, shorter fibre chip and better surface integrity than the conventional slot grinding (CSG). In addition, the lowest and highest reduction rates of grinding forces are obtained by using the fibre orientation of 90° and 135°, respectively. The maximum fibre chip lengths produced in USG are approximately 78% and 66% lower than those in CSG with fibre orientations of 0° and 90°, respectively. Several adhesive chips are observed on the USG tool surface. The chip storage spaces in CSG are filled with adhesive chips. The USG has a positive influence on surface roughness and damage because of the changes in fibre cutting angle. Compared with CSG, the USG produces similar fibre fracture patterns, except at the fibre orientation of 0°. Furthermore, the surface defects in USG are lower than those in CSG.

In this study, control research of chip morphology and removal is conducted theoretically and experimentally on the basis of the low-frequency vibration-assisted drilling process of titanium alloy. The chip morphology prediction model is established on the basis of the modified kinematic model, in which the shear angle variation, critical cutting thickness, and stiffness of a vibration generator system are considered. In terms of chip removal monitoring, a new monitoring method based on high speed camera is proposed in this paper. And the reliability of the new method is verified by comparing the signals obtained by the power sensor and the force sensor. An empirical prediction model for chip removal is also established on the basis of the modified kinematical model, the chip morphology prediction model, and the force balance analysis of fragmental chips. Validation experiments show that the mean error of chip radian, which can reflect the difference between the predicted chip morphology and the experimental one, is 6%. The mean error of the predicted chip removal index compared with the experimental one is 10.4%. The results obtained show that chip removal can be controlled effectively by low rotation speed, small chip radian, light chip weight, high minimum quantity lubrication cooling pressure, and high oscillation frequency. On the basis of the prediction model of chip removal, the effects of drilling parameters on chip removal behavior are analyzed, and the optimal drilling parameter combination with highest processing efficiency is given.

Ultrasonic vibration assisted grinding (UVAG) is an effective method for edge trimming to improve the mechanical integrity of carbon fiber reinforced polymer (CFRP). However, due to the high heat resistance, abrasiveness and powdery chip of CFRP, serious tool clogging, rapid tool wear and poor surface are still considerable problems to the industry. In this paper, monolayer brazed diamond grinding tools with defined grain distribution are designed in order to solve the above problems. The maximum undeformed chip thickness based on UVAG was analyzed. A mathematical grinding force model was established based on monolayer brazed diamond tools. The UVAG experiments using different grain inter-row spacing diamond tools were carried out. The grinding force and surface morphology were investigated and compared. It was found that the predicted grinding force values were consistent with the experimental results. Additionally, the force was strongly related to the grain inter-row spacing. When employing the tool with the grain inter-row spacing of 1.2 mm, the grinding force was highest and the roughness of the surface was better due to more active grits and interaction-overlap areas.

Drilling of carbon fiber reinforced polymer (CFRP) is a challenging task in modern manufacturing sector and machining induced delamination is one of the major problems affecting assembly precision. In this work, a new three-dimensional (3D) finite element model is developed to study the chip formation and entrance delamination in drilling of CFRP composites on the microscopic level. Fiber phase, matrix phase and equivalent homogeneous phase in the multi-phase model have different constitutive behaviors, respectively. A comparative drilling test, in which the cement carbide drill and unidirectional CFRP laminate are employed, is conducted to validate the proposedmodel in terms of the delamination and the similar changing trend is obtained. Microscopic mechanism of entrance delamination together with the chip formation process at four special fiber cutting angles (0°, 45°, 90° and 135°) is investigated. Moreover, the peeling force is also predicted. The results show that the delamination occurrence and the chip formation are both strongly dependent on the fiber cutting angle. The length of entrance delamination rises with increasing fiber cutting angles. Negligible delamination at 0° is attributed to the compression by the minor flank face. For 45° and 90°, the delamination resulted from the mode III fracture. At 135°, serious delamination which is driven by the mode I and III fractures is more inclined to occur and the peeling force reaches its maximum. Such numerical models can help understand the mechanism of hole entrance delamination further and provide guidance for the damage-free drilling of CFRP.

AFRP(Aramid Fiber Reinforced Plastics) is widely used in the aerospace and automotive while there are many problems in machining AFRP such as furry, delamination, burns and so on. Milling experiments of AFRP have been conducted to study the influence of different helix angle (0°, 30°, 60°) and cutting tools (traditional end mill, multiple flute end mill and compression end mill) on cutting force and machined surface quality. The results indicated that the cutting force has been reduced and the surface quality has been improved with the increase of helix angle. The cutting tool structure can make greater influence on machined surface quality than the cutting parameters. A cutting tool with the structure of multiple flute or herringbone cutting edge could reduce the axial cutting force. However the cutting force is too small to cut off fibers when using a multiple flute end mill. A good processing surface can be achieved while cutting with a compression end mill or a tool with big helix angle.

In this work, diamond grits are brazed with either Ag–Cu–Ti alloy or Ni–Cr alloy. Variations in the morphology of the brazed diamond grits, such as graphitization, erosion, microcracking and fracture, are observed. The compressive strength and thermal toughness index (TTI) of the brazed diamond grits are evaluated. The results obtained show that the morphologies of the original, unaltered diamond grits are similar to those of the brazed diamond grits. When the diamond grits were brazed using the Ag–Cu–Ti alloy, several disadvantageous phenomena, i.e., graphitization, erosion, microcracking, and fracture, were not observed, and the compressive strength and the TTI values of the brazed diamond grits were decreased only slightly. However, when the diamond grits were brazed with the Ni–Cr alloy, surface graphitization, erosion, microcracking, and fracture of the brazed diamond grits resulted, in addition to a significant reduction of the mechanical strength of the brazed diamond grits.