Hole exit damage and tool wear during the drilling of CFRP with a double-point angle drill

Pengnan Li,Xinyi Qiu,Changping Li,Qiulin Niu,Anhua Chen,고태조 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5

The control of hole exit damage and hole wall quality poses a considerable challenge during the drilling of carbon fiber-reinforced plastic (CFRP). This study aims to study the effect of the cutting edge type on the aforementioned issues. First, a comparative study between hole exit damage caused by a twist drill and a double-point angle drill was conducted to investigate the influences of the chisel, principal, and secondary cutting edges on hole exit damage. The maximum damage ring caused by the double-point angle drill is smaller than that caused by the twist drill because the drop speed of the cutting force in the secondary cutting edge drill during the exit stage of the double-point angle drill is less than that of the twist drill. Then, the double-point angle drill was used to determine the effects of tool wear on thrust force and hole wall damage. Outer corner wear and flank wear were investigated, and hole wall damage mechanisms were discussed. The damage of missing fibers does not worsen with an increase in tool wear, but the damage of fiber pullout becomes more serious due to increased cutting force. Consequently, a double-point angle drill bit is preferable for drilling holes on CFRP.

Formation Mechanism and Adhesion Evaluation of Debris in Ti–6Al–4V Alloy Turning

Changping Li,Xiangyu Liu,Moran Xu,Jielin Chen,Shujian Li,Pengnan Li,Tae Jo Ko 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.5

In this paper, the formation mechanism of adhered debris on the surface of turned titanium alloy was studied. The adhesion rate of debris was calculated and evaluated using image extraction technology. The effects of cutting parameters and cooling conditions on the debris adhesion rate were also studied. Moreover, the chip temperature and trajectory in the turning process are analyzed using a finite element simulation and a thermal camera. The results show that there are three primary sources of adhered debris: the adhesion of the built-up edge, the micro-chips formed during the cutting process, and the micro-chips generated by the friction between the chip and the machined surface. In addition, the cutting speed is also one of the most significant factors affecting the adhesion of debris. The debris adhesion rate drops significantly as the cutting speed decreases. It was also found that the coolant can effectively reduce the debris adhesion rate, and this effect is more evident at low feed rates.

Novel Environmentally Friendly Manufacturing Method for Micro-Textured Cutting Tools

Changping Li,Xinyi Qiu,Zhen Yu,Shujian Li,Pengnan Li,Qiulin Niu,Rendi Kurniawan,고태조 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.1

Surface texturing on cutting tools has a great influence on reducing the friction force between tool and chip interfaces. In this study, a grinding method was developed to fabricate micro-groove textures on cutting tools using a special diamond grinding wheel on the tool rake face. A comparative experiment was done using a laser and other grinding method to fabricate micro-grooves. The developed grinding method does not produce harmful gases, it is environmentally friendly, and it fabricates groove textures with high efficiency and quality. Various micro-grooves with depths of 30–90 μm, groove pitches of 0.5–1 mm, and groove angles of 30–60 o were made on the rake faces of non-coated end-mill tools using the developed grinding method. Milling experiments on aluminum alloy (Al6061-T6) and tool steel (SKD11) with non-water-soluble coolant were carried out using the textured tools, and the cutting force and tool wear were investigated. In most cases, the cutting force produced by the micro-grooved tools is significantly reduced. In addition, the wear resistance of the micro-groove cutting tool is better than that of a conventional cutting tool, and there is no chipping.

Tool life evaluation of CFRP drilling with three kinds of drill

Xinyi Qiu,Pengnan Li,Changping Li,Qiulin Niu,Shujian Li,Tae Jo Ko,Lingyan Tang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.7

Serious tool wear in CFRP drilling is one of the key problems to be solved urgently. Firstly, a suitable indirect evaluation index of tool life is selected according to the literature. The critical delamination force was obtained by blind hole pushing experiment. Then, tool wear experiments were carried out with double point angle drill, stepped drill and reverse edge compound drill to analyze the variation rules of the thrust force, exit burr, exit delamination and tear with tool wear. Threshold values of exit delamination, tearing and critical thrust force were compared with each evaluation index one by one to study the causes of drills failure. The results indicated that the maximum tool wear position was the outer corner. Among the three types drills, the thrust force, delamination factor and burr angle of the reverse edge compound drill are smaller. The double point angle drill fails due to the excessive thrust force, while the stepped drill and the reverse edge compound drill fail due to the hole exit delamination exceeding the threshold. The number of drilled holes of the reverse edge compound drill is 100 % and 25 % higher than that of the double point angle drill and the stepped drill, respectively. Therefore, the reverse edge compound drill is suitable for drilling CFRP.

Tool Wear in Longitudinal-Torsional Ultrasonic Vibration Assisted Drilling of CFRP/Ti Stacks and Its Influence on Drilling Quality

Chunhao Wang,Pengnan Li,Shujian Li,Xinyi Qiu,Changping Li,Qingquan Jiang,Qiulin Niu,Tae Jo Ko 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.1

Longitudinal-torsional ultrasonic vibration assisted drilling (LTUVD) has received extensive attention as a new machining technology in recent years. Especially for the stacks structure similar to carbon fiber reinforced polymer/titanium alloy material (CFRP/Ti6Al4V), it has more significant machining advantages. However, the effect mechanism of longitudinal-torsional ultrasonic vibration (LTUV) on tool wear, the tool wear condition in LTUVD machining and its influence on machining quality are not clear. In this work, the effect of LTUV on the tool wear of CFRP/Ti stacks was analyzed, and the tool wear of CFRP/Ti stacks and its effect on the entrance, interface and hole wall were investigated by drilling experiments under LTUVD condition. The analysis demonstrated that LTUVD can reduce tool wear by reducing the force and temperature during CFRP/Ti stacks drilling. The typical characteristics of LTUVD drill wear were the reduction of the flank face width, the adhesion of Ti to the tool, the blunting and the fracture of the cutting edge. The worn tool shows different wear characteristics in different parts. Spindle speed is one of the key factors that affect the wear rate of the typical parts, such as chisel edge, outer edge corner and main cutting edge. The mean damage factor of the entrance and interface of the 17–20 holes drilled by LTUVD were 11.5% and 8.7% higher than those of the 1–4 holes respectively. As the tool wear intensifies, the hole wall of CFRP produced more pits and the flatness decreased. The hole wall roughness increased by 30.9% when the 17–20 holes were drilled compared with the 1–4 holes.

Failure analysis of R-regions of CFRP hat-shaped structure under pull-off load

Chen Rong,Li Shujian,Tae Jo Ko,Li Pengnan,Jiang Yong,Li Changping,Niu Qiulin 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.3

As a kind of typical structure, the hat-shaped structure (HSS) is widely used in carbon fiber reinforced plastics (CFRP) aircraft parts. In this work, a scheme of filling fillers and adding reinforcing plies in R-regions was proposed to strengthen the R-regions of HSS. Moreover, the force analysis of R-region with or without strengthening in R-region under pull-off load was presented. A finite element model was developed to study the failure behavior of Rregions. A series of HSS samples were fabricated by co-curing process. The pull-off tests of HSS were conducted to validate the model, and the failure mechanism of R-regions was further studied by characterizing the macro-micro structure of R-regions in HSS under pull-off load. Results showed that the structural bearing capacity of HSS can be improved by strengthening in R-regions. After strengthening in R-regions, the pull-off load was borne by multiple interfaces, and the interlaminar interface pull-off strength can increase by 38.8 %.

Study on the Formation of the Crater and Modified Layer in EDM Titanium Alloys Based on Fluid–Solid Coupled Temperature Field Model

Yini Chen,Changping Li,Shuang Li,Moran Xu,Lei Huang,Shujian Li,Pengnan Li,Xinyi Qiu,Tae Jo Ko 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.3

Electric discharge machining (EDM) is used widely in machining titanium alloys, but the modified layer formed can weaken the mechanical properties of the parts. The present study examined the formation of craters and the evolution of the modified layer (melting layer + heat-affected layer) in RC-type EDM using a fluid–solid coupled temperature field model. This model adopts the level set method to track the liquid–solid two-phase and the driving force equation to control the recoil pressure. The results showed that the discharge energy has a significant effect on the formation of the modified layer. The formation of the modified layer showed phased characteristics with time. The variation law and formation mechanism of the modified layer are described in detail. A verification experiment showed that the diameter and depth of the crater were in good agreement with the simulation results. These results can provide an important reference for EDM to formulate the machining parameters.

Influence of fiber direction and processing parameters on drilling temperature of CFRP

Rong Chen,Shujian Li,Chang Ping Li,Pengnan Li,Yong Jiang,Tae Jo Ko 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.4

Drilling high quality holes is a necessary prerequisite to ensure efficient and accurate connection and assembly of CFRP components. In addition to cutting force, cutting heat is another important factor affecting the quality of CFRP drilling. In this paper, a drilling experiment of CFRP laminate is carried out, and the method of prefabricating thermocouple holes on the edge of the test-hole is used to study the influence of fiber direction and processing parameters on the drilling temperature. Results show that when drilling along the fiber direction of 0°, the heat conduction in the edge area of test-hole wall is better than that of drilling along the fiber direction of 90°. Accordingly, the drilling temperature is obviously higher. Under this experimental condition, the temperature difference of the edge area of test-hole caused by the fiber direction is as high as 44 °C. At the feed rate of 0.04 mm/rev, when the speed increases from 1500 rpm to 4500 rpm, the axial force decreases by 13.9 %, and the peak temperature at p1 and v1 increase by 63.2 % and 22.2 %, respectively. At the spindle speed of 3000 rpm, when the feed rate increases from 0.02 mm/rev to 0.06 mm/rev, the drilling axial force increases by 35.0 %, and the peak temperature at p1 and v1 decreases by 31.1 % and 30.0 %, respectively.

New Compound Drill Bit for Damage Reduction in Drilling CFRP

Xinyi Qiu,Pengnan Li,Changping Li,Qiulin Niu,Anhua Chen,Puren Ouyang,Tae Jo Ko 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.1

This paper focuses on finding a suitable drill bit for drilling Carbon Fiber Reinforced Plastic (CFRP). The drilling characteristics of the dagger drill, the double point angle drill, and the candle stick drill are studied. The results show that the side edge has poor ability to remove burrs, and the tip structure of the outer corner of the candle stick drill can greatly reduce the entry damage. However, the outer corner small tip structure of the candle stick drill cannot effectively remove the uncut fiber around θ = 0° of hole exit. The long secondary cutting edge of the dagger drill makes a small thrust force at the drilling exit stage and reduces the dropping speed of the thrust force, leading a lower impact on the laminate bottom. Then, a new tool is developed for drilling CFRP based on the advantages of the three kinds of drill bits. The drill has a long secondary cutting edge, a small tip diameter and a small tip structure of the outer corner. And its drilling characteristics are analyzed. The result shows that the new compound drill bit can effectively remove fibers and reduce thrust force at the drilling exit stage, form burr-free and small delamination hole. The drill reduces the waste of CFRP in manufacturing process since the exit damage is reduced substantially, which is in line with the concept of green manufacturing.