CFRP Machining on Indigenously Developing Cryogenic Machining Facility: An Initial Study

Available online at www.sciencedirect.com

ScienceDirect Materials Today: Proceedings 18 (2019) 4598–4604

www.materialstoday.com/proceedings

ICMPC-2019

CFRP Machining on Indigenously Developing Cryogenic Machining Facility: An Initial Study Navneet Khannaa*, Krupansh Desaia, Arjun Shetha, Johan Øllgaard Larsenb a

b

Department of Mechanical Engineering, IITRAM, Ahmedabad 380026, Gujarat, India Danish Advanced Manufacturing Research Center, Sandagervej 10, DK - 7400 Herning, Denmark

Abstract

This experimental research work presents results of cryogenic machining of carbon fibre reinforced plastic (CFRP), focusing on thrust force and delamination. Trials were carried out under cryogenic cooling and dry environments using indigenously developing cryogenic machining facility. Thrust force and delamination (entry and exit) were thoroughly examined to establish the effects of cryogenic environment on the delamination of the machined component, and results were matched with those from dry machining. It is observed that, at higher cutting parameters cryogenic machining leads to lesser delamination and may extend product life and performance. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: CFRP composite; Drilling; Cryogenic machining; Liquid nitrogen; Delamination

1. Introduction In recent times, use of CFRP composite material has been increased substantially. Products of these fibers have applications in defence, aerospace and space equipment [1]. Drilling of polymer matrix composites is highly practiced as rivets are utilized in various assemblies made from composites. Hole quality is influenced by cutting parameters, tool geometry [2]. Most prominent damage mechanism in composites is delamination because it reduces service life of composite parts [3]. Rahme P et al. [4] concluded that delamination at entry and exit happens due to peeling-up and pushing out of fibers respectively; latter one is more severe [5, 6].

* Corresponding author. Tel.:+91-79-6777-5448 E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

4599

Nomenclature A B

LN2 - Liquid Nitrogen CFRP – Carbon Fibre Reinforced Plastic

Study of Ho-Cheng et. al. revealed that at high rpm and less feed, cuts are fuzzy and rough because of the temperature rise [7,8]. Heizel et. al. [9] studied the relation of point angle of the drill with thrust forces and the condition of holes where hole quality was calculated in terms of delamination and fraying for woven CFRP laminates. As point angle of drill increases, generated force also increase while the torque remained constant. Durao et. al. has utilized drill bits having point angle of 85° and 120°, and observed that latter drill bit has drilled holes with less entry delamination though thrust force was more for former drill bit [10]. Mayuet et al. [11] did experimental studies on woven CFRP by carbide drills and concluded that for wear in drill bit, abrasion of fibers is more severe than matrix adhesion. Further, they have also found that wear of drills was affecting the quality of drilled holes because delamination factor (DF) was rising as more number of holes were drilled. Feito et. al. [12] conducted ANOVA analysis and concluded that while drilling of woven CFRP laminates thrust force and delamination factor were highly influenced by feed and tool geometry, whereas cutting speed was having negligible influence. Velayudham et al. concluded that thrust force and delamination increases with increase in feed [3]. Work-piece and tools which are exposed to high cutting temperatures are cooled during machining by a cryogenic coolant because of its benefits like increase in cutting speed and material removal rate, increasing of tool life and a sustainable machining methodology [13]. Impero et. al. found that torque and thrust force reduces under cryogenic condition while drilling CFRP/Al stacks [14]. Gisip et. al. observed that tool wear decreases while drilling medium density fiberboard using cryogenic coolant and refrigerated air for cooling tools [15]. Further, as per the literature, Y. Kaynak et al. did comparisons of drilling in cryogenic and dry conditions by measuring drilling induced delamination, thrust force, surface integrity, cutting edge radius and torque. The holes were drilled at cutting speed of 60 m/min and feed rates of 0.025 mm/rev and 0.05 mm/rev. The study revealed that drilling in presence of LN2 improved surface integrity but increased delamination, thrust force compared to dry conditions [16]. While performing cryogenic drilling of 6 mm thick KEVLAR composite with standard HSS drill bit of 10 mm diameter, D Bhattacharya et al. achieved higher drill life employing cryogenic coolant [17]. Tian Xia evaluated drilling performance of CFRP laminate in dry and cryogenic conditions with uncoated solid carbide drill which has through holes for liquid nitrogen to pass. This study concluded that drilling in cryogenic condition gave holes with less burr formation, accurate diameter and lower surface roughness [18]. K. Glasin investigated the effects of drilling GLARE composite with cryogenic liquid nitrogen coolant and minimum quantity lubrication, and revealed that usage of both MQL and cryogenic fluid reduces surface roughness, build up formation and adhesions [19]. Gulketin et al. used new machining technique known as dipped cryogenic cooling and found that this cooling condition improved machinability, however it also increased thrust force developed during drilling of woven carbon fiber reinforced plastic laminate of 5 mm thickness [20]. Very few researchers have carried out experiments on cryogenic drilling of thin Carbon-Epoxy laminate and compared the outcomes with drilling in dry condition. In current study comparison of cryogenic and dry conditions while drilling CFRP composite laminate using uncoated tungsten carbide drill bits for various cutting parameters is conducted. 2. Experimental Details 2.1. Specimen Details The Carbon/Epoxy composite laminate with 46-52 % fiber volume fraction of 3 mm thickness is fabricated with dead weight hand lay-up process. During fabrication curing and post curing was done for 24-24 hours at 25°C. Pressure is applied as per manufacturing sequence. The specimen consists of 6 woven carbon fabric layers and the raw size of each layer is 250 mm x 250 mm. Further, the resin to hardener ratio is 10:1 by weight.

4600

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

2.2. Drill bit specification Nine uncoated tungsten carbide standard drill-bits are utilized during this study. The characteristic of the cutting tool are displayed in table 1. Table-1: Drill-bit specification Diameter (mm)

No. of cutting edge

Point angle (degree)

Helix angle (degree)

Length (mm)

5

2

118

30°

60

3. Experimental plan 3.1. Experimental set-up

Fig. 1. Experimental design

The experiments of drilling were done on Carbon-Epoxy laminate by 5 mm diameter drill bits made from solid tungsten carbide. Numerically controlled VMC machine (Mitsubishi V544) was used for performing drilling experiments. During drilling, thrust force was measured by Kistler dynamometer (type-9272). Before the drilling experiments, the whole setup shown in fig. 1 was calibrated. For cryogenic machining a circular clamp was attached to the vertical moving part of VMC machine through nut and bolts for liquid nitrogen flow arrangements. INOX devar cylinder of 200 liters capacity was used for delivering LN2 to cutting zone. Delivery pipeline of liquid nitrogen is passed through the small clamp which is attached to larger clamp by a thin metal plate, thus synchronizing the flow of liquid nitrogen with vertical motion of the spindle. Diameter of the nozzle is 1 mm. Drilling parameters are selected as per literature review. For each drilling parameter combination, 3 holes were drilled for better accuracy of the experiments. Nine drill bits were used for 27 trials. Each experiment was executed 3 times by the same drill bits as several research concluded that there is no significant tool wear while drilling initial holes [21-23]. Between center of two consecutive holes, distance of 15 mm was kept to allow the complete propagation of hole delamination. Khanna et.al [24] discussed the ways to increase the effectiveness of machining process using sustainable cryogenic delivery setup. 3.2. Delamination Quantification In this study, a stereomicroscope was employed for capturing images of drilling induced damages of holes for determining delamination. Images of high-resolution of drilled holes at drill entry and exit were acquired using 3-D microscope (Rapid-I V2015J LX) as shown in fig. 1. Specifications of this microscope are presented in table 2. A computer system was connected to the microscope to instantly save the images.

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

4601

Table -2: Microscope specifications Model

2015J LX

Resolution

800 x 600 pixels

Magnification

11 - 67x

Work-stage size

275 x 220 (in mm)

Maximum job weight

25 kg

Touch probe

3-axis touch probe with 1µm

4. Results and discussion 4.1. Response of thrust force on different drilling parameters: In this study, L9 orthogonal array was applied for making holes with tungsten carbide drills of standard tool geometry in cryogenic and dry conditions. Recorded readings of thrust forces in drilling of CFRP laminates of 3 mm with various parameters were analyzed thoroughly. The thrust forces observed for different combinations of chosen parameters while drilling of CFRP are mentioned in fig. 2. It is evident from results that with rise in feed, there is a rise in thrust force due to increase in uncut chip thickness [25] and more impact of the fibers in direction of feed [3,26]. Thrust force was observed to decrease with increasing spindle speed due to softening of matrix material because of increase in temperature. The S/N values were found out for every trial of L9 array and equation “lower is the best” was selected. Values for Signal/Noise ratio of thrust force infers that feed rate is more affecting the thrust force than rpm in drilling of CFRP laminate as shown in fig. 3(a) and 3(b). Minimal thrust force was recorded at 3000 rpm and feed equal to 0.05 mm/rev. ANOVA for developed thrust force while drilling is done with 95% confidence level. It can be clearly observed in figure 3(a), the feed was predominantly affecting thrust force in dry condition with highest contribution of 93.44%. The contribution of the cutting speed was very low, i.e. 4.75%. Thrust force rises with increase in feed rate and falls with increase in RPM. Many researchers have obtained the similar trend in their studies [27]. In cryogenic condition hardening of workpiece takes place. Thus, thrust force in cryogenic condition is observed greater than in dry condition. It can be observed from fig. 3(b) that contribution of feed rate and rpm on thrust force in cryogenic condition is 63.75% and 35.36%, respectively.

Thrust force (N)

60 50 40 30 20 10 0 1000 rpm 1000 rpm 1000 rpm 2000 rpm 2000 rpm 2000 rpm 3000 rpm 3000 rpm 3000 rpm 0.05 mm/rev 0.10 mm/rev 0.15 mm/rev 0.05 mm/rev 0.10 mm/rev 0.15 mm/rev 0.05 mm/rev 0.10 mm/rev 0.15 mm/rev

Dry

Cryogenic

Fig. 2. Average thrust force comparison under cryogenic and dry conditions. 4.75%

0.89%

1.81% 35.36%

93.44%

Feed

rpm

error

Fig. 3. (a) Effect of input factors on thrust force in dry condition

63.75%

Feed

rpm

error

Fig. 3 (b) Effect of input factors on thrust force in cryogenic condition

4602

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

4.2. Response of hole delamination on different drilling parameters: Peel-up and push-out delamination factors (DF = Dmax/Dnominal) are quantified for different combinations of RPM and feed rate and are presented in figure 4(a), 5(a) and in figure 4(b), 5(b), respectively. Both delamination at entry and exit increases with feed and decreases with rpm for dry and cryogenic conditions as shown in figure 8 and 9 respectively. Thus, it is clear that there is a direct relation between delamination and thrust force. Similar trend is observed by various researchers [21]. Push-out delamination at exit of hole is observed higher than the peel-up delamination at entry as there is absence of the support at the drill exit to reduce propagation of delamination. Delamination in cryogenic condition is observed higher as thrust force is higher. 1.13%

11.84%

87.03% Feed

Figure 4(a) Hole entry RPM-3000 &

Figure 4(b) Hole exit RPM-3000

feed

& feed rate-0.05 mm/rev in dry

rate-0.05mm/rev

in

dry

condition

condition

rpm

error

Fig. 6(a). Effect of input factors on entry delamination in dry condition

2.19% 20.41%

77.40%

Figure 5(a) Hole entry RPM-3000 &

feed

rate-0.05mm/rev

Figure 5(b) Hole exit RPM-

in

rpm

error

3000 & feed rate-0.05mm/rev

cryogenic condition

in cryogenic condition

2.45%

Feed

Fig. 6(b). Effect of input factors on entry delamination in cryogenic condition

4.85%

0.13% 38.44%

56.71%

97.42% Feed

rpm

error

Fig. 7(a). Effect of input factors on exit delamination in dry condition

Feed

rpm

error

Fig. 7(b). Effect of input factors on exit delamination in cryogenic condition

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

3

2 1.8

Delamination factor

Delamination factor

4603

1.6 1.4 1.2 1 1000 rpm 1000 rpm 1000 rpm 2000 rpm 2000 rpm 2000 rpm 3000 rpm 3000 rpm 3000 rpm 0.05 0.10 0.15 0.05 0.10 0.15 0.05 0.10 0.15 mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev

Dry

Cryogenic

Fig. 8. Entry delamination comparison under cryogenic and dry conditions.

2.6 2.2 1.8 1.4 1 1000 rpm 1000 rpm 1000 rpm 2000 rpm 2000 rpm 2000 rpm 3000 rpm 3000 rpm 3000 rpm 0.05 0.10 0.15 0.05 0.10 0.15 0.05 0.10 0.15 mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev mm/rev

Dry

Cryogenic

Fig. 9. Exit delamination comparison under cryogenic and dry conditions.

It is evident from fig. 6(a) and fig. 7(a) that the contribution of feed rate in dry condition in entry and exit delamination is 87.03% and 97.42%, respectively and contribution of RPM in entry and exit delamination is 11.84% and 2.45%, respectively while the contribution of feed rate in cryogenic condition in entry and exit delamination is 77.40% and 56.71%, respectively and of RPM in entry and exit delamination is 20.41% and 38.44%, respectively which can be observed from fig. 6(b) and fig. 7(b). Conclusions: This experimental research work presents results of cryogenic machining of carbon fibre reinforced plastic (CFRP), focusing on thrust force and delamination. Trials were carried out under cryogenic cooling and dry environments using indigenously developing cryogenic machining facility. It is observed that, at higher cutting parameters cryogenic machining leads to lesser delamination and can extend product life and performance. The other important conclusions are given below:     

 

In dry and cryogenic conditions thrust force and entry and exit delamination factors increase with increase in feed while decrease with increase in rpm. For dry and cryogenic drilling, thrust force and delamination at entry and exit were observed minimum for 0.05 mm/rev feed rate and 3000 rpm. In case of drilling CFRP in cryogenic condition at 0.05 mm/rev feed rate and 3000 rpm thrust force, delamination at entry and exit were found higher than in dry condition because of hardening of the material at the time of drilling due to lower temperature of LN2. At 0.05 mm/rev and 3000 rpm thrust force for cryogenic condition was observed 49.45% higher than in dry condition leading to higher peel up and push out delamination. The feed rate was observed the most contributing factor on thrust force in dry condition with contribution of 93.44% while the contribution of cutting speed was very low, i.e. 4.75% while in cryogenic drilling condition feed rate and cutting speed were having 63.75% and 35.36% contribution respectively. In case of drilling in dry condition the contribution of feed in hole delamination at entry and exit is 87.04% and 97.42% respectively and of RPM in peel-up and push-out delamination is 11.84% and 2.45% respectively. In cryogenic drilling contribution of feed rate on delamination at entry and exit is 77.40% and 56.71% respectively and contribution of RPM is 20.41 % and 38.44 % respectively.

Acknowledgements The authors would like to thank the SERB-DST, Government of India, for the financial support given under the Project (ECR/2016/000735), titled “Design and Development of Energy Efficient Cryogenic Machining Facility for Heat Resistant Alloys and Carbon Fibre Composites”.

4604

N. Khanna et al./ Materials Today: Proceedings 18 (2019) 4598–4604

References [1] Wang XM, Zhang LC (2003) An experimental investigation into the orthogonal cutting of unidirectional fibre reinforced plastics. Int J Mach Tool Manu 43(10):1015–1022 [2]Davim JP, Reis P (2003) Drilling carbon fiber reinforced plastics manufactured by autoclave - experimental and statistical study. Mater Des 24(5):315–324 [3]Velayudham, A., and R. Krishnamurthy. "Effect of point geometry and their influence on thrust and delamination in drilling of polymeric composites."Journal of Materials Processing Technology 185.1-3 (2007): 204-209. [4] Rahme P, Landon Y, Lachaud F, Piquet R, Lagarrigue P (2008) Study into causes of damage to carbon epoxy composite material during the drilling process. Int J Mach MachMater 3(¾):309–325 [5]Sorrentino L, Turchetta S, Bellini C (2018) A new method to reduce delaminations during drilling of FRP laminates by feed rate control. Compos Struct 186:154–164 [6]Hocheng H, Tsao C (2003) Comprehensive analysis of delamination in drilling of composite materials with various drill bits. J Mater Process Technol 140(1):335–339 [7] Ho-Cheng H, Dharan CKH. Delamination during drilling of composite laminates. J EngInd, ASME 1990;112:236–9. [8] Ho-Cheng H, Pwu HY, Yao KC. Machinability of some fiber reinforced thermoset and thermoplastics in drilling. Mater Manuf Process 1993;8(6): 653–82. [9] Heisel U., Pfeifroth T. Influence of Point Angle on Drill Hole Quality and Machining Forces when Drilling CFRP. Proc. CIRP. 2012;1:471– 476. doi: 10.1016/j.procir.2012.04.084. [10] Durão P., Gonçalves J.S., Tavares R.S., de Albuquerque C., Aguiar A., Torres A. Drilling tool geometry evaluation for reinforced composite laminates. Compos.Struct. 2010;92:15451550. doi: 10.1016/j.compstruct.2009.10.035. [11] Mayuet, P.; Gallo, A.; Portal, A.; Arroyo, P.; Alvarez, M.; Marcos, M. Damaged Area based Study of the Break-IN and Break-OUT defects in the Dry Drilling of Carbon fiber Reinforced Plastics (CFRP). Proc. Eng. 2013, 63, 743–751. [12] Feito , Norberto, et al. "Experimental analysis of the influence of drill point angle and wear on the drilling of woven CFRPs." Materials 7.6 (2014): 4258-4271. [13] Pušavec, Franci, Antun Stoić, and Janez Kopač. "The role of cryogenics in machining processes." Tehnički vjesnik 16.4 (2009): 3-9. [14] Impero, Filomena, et al. "A comparison between wet and cryogenic drilling of CFRP/Ti stacks." Materials and Manufacturing Processes 33.12 (2018): 1354-1360. [15] Gisip, Judith, Rado Gazo, and Harold A. Stewart. "Effects of cryogenic treatment and refrigerated air on tool wear when machining medium density fiberboard." Journal of Materials Processing Technology 209.11 (2009): 5117-5122. [16] Xia, T., Kaynak, Y., Arvin, C., & Jawahir, I. S. (2016). Cryogenic cooling-induced process performance and surface integrity in drilling CFRP composite material. The International Journal of Advanced Manufacturing Technology, 82(1-4), 605-616. [17] Bhattacharyya, D., and D. P. W. Horrigan. "A study of hole drilling in Kevlar composites." Composites science and technology 58.2 (1998): 267-283. [18] Xia, Tian, "INVESTIGATION OF DRILLING PERFORMANCE IN CRYOGENIC DRILLING ON CFRP COMPOSITE LAMINATES" (2014). Theses and Dissertations--Mechanical Engineering. 36. [19]Giasin, K., S. Ayvar-Soberanis, and A. Hodzic. "Evaluation of cryogenic cooling and minimum quantity lubrication effects on machining GLARE laminates using design of experiments." Journal of Cleaner Production 135 (2016): 533-548. [20]Basmaci, Gültekin, et al. "Impact of Cryogenic Condition and Drill Diameter on Drilling Performance of CFRP." Applied Sciences 7.7 (2017): 667. [21] Khanna Navneet, Krupansh Desai, and Arjun Sheth. "Industry supported experimental studies on drilling of thick multi-directional GFRP composite material." Procedia CIRP 77 (2018): 320-323 [22] Krishnaraj, Vijayan, Redouane Zitoune, and Francis Collombet. "Study of drilling of multi-material (CFRP/Al) using Taguchi and statistical techniques." Usak University Journal of Material Sciences 1.2 (2012): 95-109. [23] Ramesh, B., et al. "Drilling of pultruded and liquid composite moulded glass/epoxy thick composites: Experimental and statistical investigation." Measurement 114 (2018): 109-121. [24] Khanna N, Agrawal C, Joshi V. ZERO VAPOR LOSS INTEGRATED CRYOGEN PHASE SEPARATOR. Indian Patents 201721031291 A, 2017. doi:July 2017. [25] Arshinov V, Alekseev G. Metal cutting theory and cutting tool design. Moscow: MIR publishers; 1976. [26] Zitoune Redouane, Krishnaraj Vijayan, Collombet Francis. Study of drilling of composite material and aluminium stack. Compos Struct 2010;92:1246–55. [27] Kaybal, Halil Burak, et al. "A novelty optimization approach for drilling of CFRP nanocomposite laminates." The International Journal of Advanced Manufacturing Technology (2018): 1-18.