Drill-Ability Studies of Laser Drilled Micro Holes on CFRP Composites

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1 Drill-Ability Studies of Laser Drilled Micro Holes on CFRP Composites Anarghya A, Yatheesha R.B., Gurumurthy B.M., Nitish Rao, Ranjith B.S. Abstract This paper begins with the introduction on composite materials and their production techniques. It further describes, the experimentation concerned with fiber reinforced polymer (FRP) composites where high strength reinforcing fibers are combined with polymer (plastic) matrix for achieving suitably high strength. The machinability of the CFRP is of the major concern with surface finishing of the order of micro-scale. The analysis of FRP laminates is based on the micro drilled holes by laser drill and the result so obtained is analyzed through scanning electron microscope (SEM). The consideration of the heat accumulated zones as a result of laser drilling is analyzed. The suitable parameters for obtaining a good surface finish with the least amount of heat accumulated zone by laser drilling on the Carbon Reinforced Plastics concludes the paper. Keywords CFRP; Composite Material; Laser Drilling; SEM; Reinforcement. I. INTRODUCTION A composite material is made by combining two or more materials, often ones that have very different properties. Unique properties of the resulting material can be obtained upon combination. As the materials do not blend into each other due to their different properties, they can be easily differentiated in the composite. The individual components remain distinct even though the structure is complete. The new material i.e. the composite obtained after the combination of the individual materials will be preferable, as a result of the following reasons: - Strength, lightness, inexpensive, as compared to the traditional method. Composites are made up of individual materials referred to as constituent materials. There are two main categories of constituent materials: matrix and reinforcement. One portion of each type is required. By maintaining the relative positions, the matrix material surrounds and supports the reinforcement materials. The matrix properties are enhanced by the reinforcements which imparts their special mechanical and physical properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the product or structure to choose an optimum combination. The matrix material can be introduced to the reinforcement before or after the reinforcement material is placed into the mould cavity or onto the mould surface. [1]. The matrix material experiences a melding event, after which the part shape is essentially set. Depending upon the nature of the matrix material, this melding event can occur in various ways such as chemical polymerization or solidification from the melted state. This work was supported by Professor S.S. Sharma, Mechanical Engineering Department, Manipal Institute of Technology, and the Mechanical Laboratory of Manipal Institute of Technology, Manipal for the providing with all the useful resources for the successful fulfilment of the experimentation. Anarghya A completed his B.E. in Mechatronics Engineering from Manipal Institute of Technology, Manipal (phone: ; anarghya.murthy@yahoo.com) Yatheesha R.B. is an assistant professor, Department of Mechanical Engineering, Don Bosco Institute of Technology, Bangalore ( rambheerb@gmail.com) Gurumurthy B.M. is an assistant Professor, Department of Mechanical Engineering, Manipal Institute of Technology, Manipal, India ( gurumurthy.bm@manipal.edu) Nitish Rao is a student of Automotive Technology, Technical University Eindhoven, The Netherlands (phone: nitish.rao16@gmail.com) Ranjith B.S. completed his B.E. in Mechanical Engineering from Manipal Institute of Technology, Manipal (phone: ; ranjithbssg@yahoo.com) ISBN:

2 II. METHODS TO PRODUCE COMPOSITE MATERIALS Composite materials can be produced by a range of process. These processes vary from manual lay-up of reinforcement and hand application of resin to fully automated continuous processes. The most common techniques are: Hand or spray lamination Compression molding Resin injection Pultrusion Vacuum infusion 1.1. Hand or spray lamination Hand lamination is the most common process, accounting for over 40% of composites production worldwide. This is due to its ease of use and flexibility, which allows all types of reinforcement to be utilized. Here, in the experimentation as well the hand lamination method is used. III. FIBRE REINFORCED PLASTICS (FRP) Fiber-reinforced polymers/plastics is a recently developed material for strengthening of RC and masonry structure. It has been found to be a replacement of steel plate bonding and is very effective in strengthening of columns by exterior wrapping. The main advantage of FRP is its high strength to weight ratio and high corrosion resistance. FRP plates can be 2 to 10 times stronger than steel plates, while their weight is just 20% of that of steel. However, at present, their cost is high. The commonly used fibers are Carbon fibers, Glass fibers and Agamid fibers and the commonly used resins are polyester, vinyl ester and epoxy. uncommon that laser, as a thermally acting tool, may damage the matrix element in the composite, which reduce the composites mechanical properties [2]-[4]. B. 3.2 Heat affected zone (HAZ) The heat-affected zone (HAZ) is the area of the base material, which is not melted and but has its properties altered by welding or heat intensive cutting operations in its microstructure[5]. The large differences in material properties of the carbon fiber and the epoxy resin in carbon fiber reinforced plastic (CFRP) composite make laser processing very challenging. It was found that laser parameters such as laser power, repetition rate, and work piece temperature determine the extent of HAZ[6]. Fig. 2. Scanning Electron Microscope (SEM) image of a laser drilled hole The figure is of SEM laser drilled hole in composite showing matrix volatilization and fiber swelling. When the carbon fiber composites are heated rapidly as in laser drilling the impurities evaporate creating high gas pressure. This high pressure leads to swelling of the fibers within the HAZ which are retained even when the material cools down and returns to normal pressure. Laser delivers high power-density beam which upon impact on the work piece is converted into heat. As the impact zone is very small very high temperature capable of melting or volatilizing the material can be attained. This leads to material removal. Laser drilling which is a non-contact process produce small holes in various materials having high degree of precision and reproducibility. IV. METHODOLOGY The following processes were followed: - Fig. 1. Fiber Reinforced Plastic classification A. 3.1 Machining on Carbon fiber reinforced plastics Parts fabricated from FRP composites are normally laid in the near-net-shape, however cutting operations such as trimming, drilling, grinding and slotting are still required to remove excess material and meet dimensional tolerances and requirements. The use of laser machining for cutting composites is attractive due to its high cutting/travel speed, flexibility and ease of automation. However, it is not Materials requirement Hand layup process Laser drilling Scanning electron microscope (SEM) Analysis 4.1 Materials used Carbon fabric Epoxy resin (LY545) Hardener (HY045) Wax ISBN:

3 Acetone Teflon sheet 4.2 Hand Lay-Up Materials are purchased for making FRP laminates by Hand lay-up process. The carbon fiber fabric is usually trimmed to the appropriate size and laid down over a mold where it is formed to the desired shape[7]. Several layers may be required depending on the desired product Fabric is positioned manually in the open mold, and resin is poured, brushed, or sprayed over and into the fabric[8]. Entrapped air is removed manually with rollers to complete the laminates structure. Laminates are usually left to cure under standard room temperatures. The experimental trials were carried out on a state-of-art Marbach Compact CO2 laser cutting system (2115 DC-020). The machine is CNC controlled employing high-speed flatbed offering maximum cutting speed of 20,000 mm/min together with maximum cutting power of 2500 watt. CFRP work piece materials were manually laid up to provide nominally 3 mm thick symmetric UD CFRP laminates. The laminates were then cured according to the manufacturers specifications to give a fiber weight fraction of ~ 65 % and subsequently cut into plates [11]-[15]. A scanning electron microscope (SEM) and a conventional optical microscope were employed to characterize the surface damage induced laser trimming[16]. Entry and exit Kerfs width for all work pieces were linearly measured using optical microscope and kerfs angle was subsequently calculated, as shown in figure 6. Fig. 3. Hand Layup in progress Fig. 4. Preparation of laminate by hand layup process 4.3 Laser drilling Laser drilling is a process in which a laser is used to make holes, instead of conventional drilling[9]. Laser drilling of cylindrical holes generally occurs through melting and vaporization of the work piece material through absorption of energy from a focused laser beam. The energy required to remove material by melting is about 25% of that needed to vaporize the same volume, so a process that removes material by melting is often favoured[10]. Fig. 6. The laser drilling process close up view Figure 7 shows a schematic diagram of the structure of CFRP used in this study. CFRP with 3, 3.5, 4 mm thickness were used for laser processing. Figure 8 shows the optical setup of laser cutting of CFRP. In the experiments, a Q-switch Nd: YAG laser (Continuum, Minilite) was used. Figure 9 shows a schematic diagram of the laser cutting procedure. The laser beam was scanned with a constant speed on the surface[17]. The distance between the laser focus and the surface was kept constant during the scanning. Figure 10 shows the definition of focus positions of laser beam to the CFRP surface. The origin was defined on the CFRP surface and plus sign represented the focus inside of the CFRP, while minus sign represented that the focus located above the surface. Fig. 7. A schematic diagram of the CFRP used in the experiments Fig. 5. Laser drilling being carried out ISBN:

4 Fig. 8. Optical setup for the laser cutting of CFRP with nano-second pulse Fig. 10. The definition of focus positions of laser beam to the CFRP surface. V. RESULT AND DISCUSSION Fig. 9. A schematic diagram of laser processing procedure Table 1.-Heat Affected Zone Values obtained after laser drilling SL. NO. Thickness Diameter of Hole Frequency Assist gas HAZ (A) (B) (C) Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar From the above table it is clear that the greater the diameter of the hole, the more the HAZ induced into the material. 5.1 Graphs and explanation Fig. 11. Frequency v/s Heat Affected Zone ISBN:

5 The frequency plays a major role in influencing the HAZ in a composite material, although there other factors also which influences the inducing of HAZ in the material. The above graph is plotted between frequency and HAZ. In the graph for a constant frequency of LASER, HAZ is increasing, which implies that HAZ depends on some other parameter other than frequency. Graph 3-Heat Affected Zone v/s Thickness Fig. 12. Heat Affected Zone v/s Hole Diameter This graph explains that for a constant thickness of laminate, with the increase in the hole diameter HAZ increases. The above graph explains that for a constant whole diameter of 0.4mm which is drilled over 3 laminates of different frequency, HAZ remains constant. A. 5.2 Comparison among different laser drilled holes Table 2.-laser Drilled Holes for 0.4 mm Diameter Sr. No. Thickness Diameter HAZ Broken Status HAZ Effect NO LESS YES MORE LESS MODERATE Table 3.-laser Drilled Holes for 0.6 mm Diameter Sr. No. Thickness Diameter HAZ Broken Status HAZ Effect NO LESS YES MORE ISBN:

6 LESS MODERATE Table 4.-laser Drilled Holes for 0.8 mm Diameter Sr. No. Thickness Diameter HAZ Broken Status HAZ Effect YES LESS NO MORE YES MORE VI. CONCLUSION 1. Result shows that by careful control of Processing Parameters Laser Drilling of both Thin and Thicker composite materials is possible and the Scanning Electron Microscope Analysis shows that it is possible to micro-texture the surface of carbon composites to promote the bond strength. 2. Laser machining process induces heat in the composite material and may alter the properties of the material due to the creation of HAZ in the localized areas. 3. HAZ in the localized areas results in inducing of stress, thus the structural integrity of the material gets compromised due to improper machining. 4. Since the heat is accumulated in material during Laser processing especially in the case of carbon fibers, so minimum HAZ can be achieved in machining of CFRP composites by using short pulsed Lasers. 5. SEM analysis has enabled the proper visualization of the material and the stress induced in it due to improper machining technique and incorrect selection of parameters. 6. From the SEM analysis it is clear that the selection of the suitable parameters as well as proper bonding of the layers will result in a good finished micro hole and less material removal due to the thermal effect created by the Laser. The optimum parameters for a good surface finish with less HAZ are as follows: - 1. Frequency Range: 200 to Diameter of the Hole: Drilling Speed: 200m/sec 4. Thickness of specimen: 3 ACKNOWLEDGEMENTS All the authors would like to express their heartfelt thanks to Professor S.S. Sharma, Mechanical Engineering Department, Manipal Institute of Technology, who guided in the various stages of the experimentation and for pointing in the right direction. The Mechanical Laboratory of Manipal Institute of Technology, Manipal also helped in providing with all the useful resources for the successful fulfilment of the experimentation. REFERENCES [1] [2] M. H. El-Hofy, S. L. Soo, D. K. Aspinwall, W. M. Sim, D. Pearson, and P. Harden, "Factors Affecting Workpiece Surface Integrity in Slotting of CFRP," Procedia Engineering, vol. 19, pp , [3] I. Shyha, S. L. Soo, D. Aspinwall, and S. Bradley, "Effect of laminate configuration and feed rate on cutting performance when drilling holes in carbon fibre reinforced plastic composites," Journal of Materials Processing Technology, vol. 210, pp , [4] S. L. Soo, I. S. Shyha, T. Barnett, D. K. Aspinwall, and W.-M. Sim, "Grinding performance and workpiece integrity when superabrasive edge routing carbon fibre reinforced plastic (CFRP) composites," CIRP Annals - Manufacturing Technology, vol. 61, pp , 2012 ISBN:

7 [5]. F. Abedin et al., Review On Heat Affected Zone (HAZ) In Laser Machining, 2010 [6]. Pan & H. Hocheng et al., The Anisotropic Heat Affected Zone (HAZ) In The Laser Grooving Of Fiber-Reinforced Composite Material, 1995 [7]. Engineers handbook, Manufacturing methods, hand layup method. [8] [9] [10] Islam Shyha et al., An Investigation Into Co Laser Trimming Of CFRP & GFRP Composites, June 2013 [11] William M. Steen, Laser Material Processing, Springer-Verlag London Limited, p. 99, [12] Jose Mathew a & G.L. Goswami et al., Parametric Studies On Pulsed Nd: Yag Cutting Of CFRP Composites, Sept 1998 [10] Keisuke Ushida & Wataru Inami et al., Characteristic analysis of CFRP cutting with nanosecond pulsed laser, 2012 [11] Paul French & Mo Naeem et al., Macro And Micro Applications For Fiber Lasers In Laser Material Processing Of Aerospace Composite Material, 2007 [12] Desh Bandhu, Sandeep Singh Sangwan & Mukesh Verma at el., A Review Of Drilling Of Carbon Fiber Reinforced Plastic Composite Material, 2006 [13] T. Graf, R. Weber, V. Onuseit, M. Hafner, C. Freitag, A. Feuer; Laser Applications from Production to Machining of Composite Materials, EALA [14] R. Weber, M. Hafner, A. Michalowksi, T. Graf; Minimum damage in CFRP laser processing, Physics Proceedia 12(2), 2011, Pages [15] A. Goeke and C. Emmelmann, Influence of Laser Cutting Parameters on CFRP Part Quality, Physics Proceedia 5 (2010), pp [16] H.Y. Zheng a, G.C. Lim a & P.L. Chu at el., Study On UV Laser Machining Quality Of Carbon Fiber Reinforced Composites, 2010 [17] R. Weber, C. Freitag et al., Laser Processing Of CFRP, June 2012 ISBN: