This paper presents a mechanistic model for prediction of fluctuating thrust force and torque during drilling of unidirectional carbon fiber–reinforced polymer (UD-CFRP). A micro-scale model ...consisting of fiber, matrix, and fiber-matrix interface is proposed to simulate the orthogonal cutting behavior for the entire range of fiber orientation. Based on the FE model, a detailed energy analysis is conducted to quantify the various energy-absorbing mechanisms. The relationship between the percentage of each mechanism and factors such as depth of cut, tool rake angle, and fiber orientation is revealed. Afterwards, force coefficients related to these factors are obtained based on the orthogonal cutting database and used to calculate the instantaneous thrust forces and torque generated on the cutting lips, which are divided into a continuous set of infinitesimal elements conducting orthogonal cutting. Orthogonal cutting and drilling experiments with various machining parameters have been performed to validate the proposed FE and mechanistic models. Good correlation between the experimental and predicted results is found and thus the model is capable of predicting the fluctuation of thrust forces and torque for the whole drilling process.
The T800 Carbon fiber reinforced polymer/plastic (CFRP) has been increasingly used for its considerable specific strength/modules to manufacture the primary load-carrying structures in aerospace ...industry. The abrasive carbon fibers can cause rapid tool wear in CFRP drilling, which deteriorate the quality of hole wall and result in unpredictable decrease of bearing capacity. In order to effectively reduce the tool wear, a cooling method namely external cooling lubrication (ECL) is applied in this study by using two different lubricants (Boelube 70104 and Castrol Syntilo 9828). The results show that Boelube 70104 lubricant exhibits the maximum flank wear (VB) reduction (34.5%) as compared to dry drilling after drilling 30 holes. And, the maximum CER reduction (57.4%) is obtained by using Castrol Syntilo 9828 lubricant. Different from previous researches, the maximum thrust force of drilling process using ECL presents obvious decrease as compared to dry drilling. And, the value of surface roughness (Ra) exhibits an obvious decrease when using Boelube 70104 lubricant. Two main different mechanisms for Ra decrease namely reducing surface cavity at FCA of 90° <
θ
< 180° and reducing saw-tooth surfaces at FCA of 0° <
θ
< 90° are separately observed for Boelube 70104 and Castrol Syntilo 9828 separately.
Application of carbon fiber reinforced plastic (CFRP) in aircraft load-carrying structure makes the component become thicker and damage tolerance get stricter. The heat accumulation highly increases ...the hole wall temperature along feeding direction during thicker CFRP component drilling due to the low thermal conductivity, which highly deteriorates the hole quality. Therefore, this paper proposed a hole wall temperature measurement experiment at various fiber cutting angles with different measuring distances to investigate the effects of heat accumulation on the cutting temperature and damages. Results show hole wall temperature in the vicinity of hole-exit increases by almost 20⁓40 °C and 30⁓65 °C separately for
S
=3000 rpm and
S
=5000 rpm. The fiber shearing and bending when against fiber cutting seriously increases temperature near the hole wall by increasing the fiber-rich regions and contact time between workpiece and cutting lip. Moreover, the maximum temperature distribution maps along feeding direction and radial direction were separately drawn for the first time to analyze the heat accumulation and overheating areas. The hole wall along the hole edge and feeding direction were detected, and severe matrix cracking, fiber bending, and fiber-matrix debonding occurred at the position where maximum temperature was located. In the future, the findings of borehole temperature characteristics can be used to refine the existing temperature model of CFRP drilling.
BESIII is an experiment at the high precision frontier of hadron physics in
τ
-charm region. Machine learning techniques have been used to improve the performance of BESIII software. In this ...proceeding, we present novel approaches with XGBoost for multi-dimensional distribution reweighting, muon identification and cluster reconstruction for CGEM (Cylindrical Gas Electron Multiplier) inner tracker.
With the increasing requirements for aircraft assembly accuracy, pre-assembly analysis technology based on measured data has become one of the most important process precision compensation methods. ...How to accurately obtain and analyze the measured data of key features of parts according to assembly intention is the key step of pre-assembly analysis technology. Existing researches only explain the importance of the correct selection of measurement datum qualitatively, but none of them analyzed theoretically and provided specific methods when the measurement datum is inconsistent with the design datum, which is easy to misjudge the originally qualified parts. Therefore, this paper proposes a novel assembly-oriented measurement datum transformation and tolerance reallocation method for aircraft assembly. Firstly, based on the assembly type and geometric feature classification, the measurement datum of parts without Geometric Dimensioning and Tolerancing (GD&T) is identified, and the importance of correct selection of measurement datum is proved by a case theoretically. Secondly, when the measurement datum is not coincident with the assembly datum, a spatial homogeneous transformation method of measured data is proposed, which transforms the measured data from a temporary measurement coordinate system (TMCS) to an assembly datum coordinate system (ADCS). Finally, the tolerance redistribution of the measurement target features relative to the TMCS is carried out directly on the basis of the original tolerance. The experimental results show that the key features exceeding the upper tolerance limit of 0.042 mm are within the theoretical tolerance again after datum transformation, which solves the problem that the part has been misjudged as unqualified in the measurement process.
CFRP has been gradually used in the load-carrying structure with thicker component and stricter damage tolerance in aviation industry. However, the heat accumulation always occurs at hole exit-ply ...during thick CFRP drilling, resulting in temperature even higher than the glass transition temperature (Tg) of matrix, affected by which severe damages will occur based on an unknown cutting mechanism. Therefore, to investigate the new mechanism, this paper proposed a temperature controlled orthogonal cutting experiment by heating the cutting area to specified high temperature ranges (below and above Tg) before cutting. The results show that the resin matrix will be only softened by the high temperature below Tg and lose part of its strength, but the cutting mechanism is almost not changed. As for temperature above Tg, the resin matrix will be heated into molten state thereby losing the support function for machined fibers, which changes the cutting mechanism at 90° <θ < 180° into low efficiency cutting mode controlled by compressing stress. The fibers that lose support will be over bent and broken by flank face, and severe thermal mechanical damages including loose face, matrix cracking and fiber pull out can be captured at θ ~ 150° of hole wall near exit.
Due to the low thermal conductivity of CFRP and serious axial heat accumulation in dry drilling condition, the excessive cutting temperature simulation and suppression analysis have been the main ...research fields to analyze and improve borehole quality with the wide application of thick CFRP component in main load-carrying structures of aircraft. This paper proposed a three-dimensional drilling temperature simulation model to investigate the complex cutting temperature characteristics and predict the overheating area distribution during thick UD-CFRP drilling with dry condition and Boelube lubricant, thereby revealing its effects on occurrence of thermal-mechanical damages. Different from the previous drilling temperature simulation models, the material continuous removal process in this model was considered and discretized into finite chip layers removal process to model its effects on drilling heat transfer. Based on thermography method, a drilling temperature measurement experiment was conducted to validate the simulation model. Meanwhile, the overheating area distribution was predicted and the obvious reduction effects of ECL method on the overheating area ranges were confirmed. Moreover, the size of overheating area was proved to be a qualitative index of whether the hole wall subsurface damage at against fiber cutting zone is serious or not.
•The thermo-mechanical relationship of tool-materials was decoupled around the tool wear mechanism.•The effect of drilling parameters on interface temperature and tool wear progression was ...quantified.•The cutting behavior at four FCAs under various cutting temperature and worn edges was revealed.•The subsurface damage formation and propagation mechanism of drilling process was analyzed.•The interface damages of thin-walled CFRP/Ti under high thermo-mechanical erosion were evaluated.
Due to the poor thermal conductivity and machinability of CFRP and Ti6Al4V, significant heat accumulation at the interface and rapid tool wear are considered the main factors restricting the hole quality. This study conducted a thin-walled CFRP/Ti stack drilling experiment to investigate the evolution of the thrust force, temperature and tool wear versus different drilled hole numbers and spindle speeds, affected by which the novel material removal behavior was revealed. Results showed that the thrust force and interface temperature increased with the hole number and spindle speed, causing a significant increase in the cutting edge rounding and flank face wear dominated by the many fiber bundles and metal debris. In turn, the various tool wear led radial interface temperature to alternately transfer between Φ = 45° and 135°. Under the cyclic thermo-mechanical function, the fibers underwent significant bending deformation as they lost the support of the degenerated matrix resin, forming severe subsurface damage when the interface temperature exceeded the matrix glass transition temperature (Tg = 110 °C). Combined with the comprehensive evaluation of exit damages, a relatively higher spindle speed was preferred for selecting the initial drilling of thin-walled CFRP/Ti stack and gradually reducing the spindle speed with increasing tool wear extent.
This paper focuses on the analysis of exit-ply temperature characteristics and the occurrence of exit-damages during drilling of UD CFRP. Different diameter drills are used to reveal their effects on ...temperature variation, cutting mechanism and damage modes. The results show that exit-ply temperature is strongly dependent on the interaction between tool-workpiece system. In particular, an significant factor to affect the peak temperature is the location of unruptured region when main cutting edges act on exit-plies, which will result in high temperature appearing along hole edge at θ ~ 0°. The two-dimensional maps of high temperature along borehole edge are drawn at a continuous change of fiber cutting angles, based on which the dependences of exit-damages on the cutting temperature variations are discussed for the first time. The effects of high temperature on the exit-ply hole wall damages are concluded by examining the micrographs. And the width of loose surface near the hole-exit is identified to represent the functioning range of the excessive temperature. Moreover, the effects of high temperature on the exit-delaminations are analyzed by the adjusted delamination factor (Fda) at various drilling parameters.
Due to lack of effective backup when drilling aircraft thin-walled CFRP structure, serious dynamic structural deformation including vertical and in-plane deformation usually occur, which extremely ...changes the cutting behavior and materials removed mechanism, causing severe entrance and exit damages. Therefore, this paper proposed a dynamic deformation measurement experiment in vertical and horizontal direction at various processing parameters to analyze their effects on cutting mechanism and damages distribution. Results show the vertical and in-plane deformation occurrence are highly dependent on the actual positions of tool-CFRP system. Namely elastic deformation, local deformation and drawback reflection appear many a time in different stages, causing obvious sudden change of thrust force and different initiation and propagation characteristics of damages. With the feed rate increasing and workpiece thickness decreasing, the maximum displacements of every stages all increase and some thinner workpiece displacement exceed several times the plate thickness. The larger in-plane deformation will nonuniformly distribute along borehole exit due to the different cutting mechanism and strength of different fiber cutting angles. The larger elastic deformation and drawback action in vertical direction will change the out-ply material remove mechanism into mainly puncture rather than only cutting. Under the joint action of deformation in two directions, the loose surface damages composed of delamination and uncut fiber will gather heavily at exit.
•The vertical and in-plane deformation were characterized in divided stages by DIC.•The influence of drilling parameters on deformation and drawback was investigated.•The cutting behavior at various FCA under large drawback action was revealed.•The damage formation and propagation mechanism of drilling process was analyzed.•The in-plane damages in entrance and exit regions after deformation were evaluated.
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