Glass Fiber Reinforced Plastic machining optimization report


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Prepared a Glass Fiber Reinforced Plastic board and determined the optimal drilling conditions that would cause the least delamination using Design of Experiments.

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Glass Fiber Reinforced Plastic machining optimization report

  1. 1. d ABSTRACT The main objective of the project is to prepare a GFRP - Glass Fiber Reinforced Plastic (composite material) using glass fiber woven with a binder called bisphenol as a matrix, with the help of a Mechanical Press. The next step is to perform drilling operation on the composite using different drill bit materials such as High Speed Steel, Tungsten Carbide and Poly- Crystalline Diamond. The parameters such as feed of the operation and the spindle speed of the machine are varied and the test is undertaken. Simultaneously a dynamometer is attached to the drilling machine to check the torque and thrust force. The drilled holes are then subjected to a device called Profile Projector to study the delamination factor of the holes. The last test is called Flexure test (which is a bending test) in which the strength of the specimen is tested using the UTM - Universal Testing Machine. After obtaining all the data, the values are tabulated and graphs are plotted accordingly. 18
  2. 2. APPENDIX 3 TABLE OF CONTENTS CHAPTER NO. TITLE PAGE NO. ABSTRACT iii LIST OF TABLE LIST OF FIGURES LIST OF SYMBOLS xvi xviii xxvii 1. INTRODUCTION 1 1.1 GENERAL 1 1.2 . . . . . . . . . . . . . 2 1.2.1 General 5 1.2.2 . . . . . . . . . . . 12 General 19 . . . . . . . . . . 25 . . . . . . . . . . 29 1.2.3 . . . . . . . . . . . . 30 1.3 . . . . . . . . . . .. . . . . . . 45 1.4 . . . . . . . . . . . . . . . . . . 58 2. LITERATURE REVIEW 69 2.1 GENERAL 75 2.2 . . . . . . . . . . 99 2.2 ……………. 100 18
  3. 3. 1. INTRODUCTION 1.1. INTRODUCTION TO COMPOSITE MATERIALS Composite materials or Composites are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. Composites, unlike metals are not homogeneous, anisotropic and consist of both unique resins and fibers. Composites are normally manufactured in near net shape processes but they require secondary machining operations for assembly. Hence drilling, cutting and machining composites in any post processing operations to get to final shape or configuration is different from other materials. 1.2. HISTORY OF COMPOSITE MATERIALS The earliest man-made composite materials were straw and mud combined to form bricks for building construction. This ancient brick- making process was documented by Egyptian tomb paintings. Wattle and daub is one of the oldest man-made composite materials, over 6000 years old. Concrete is also a composite material and is used more than any other man-made material in the world. As of 2006, about 7.5 billion cubic meters of concrete are made each year—more than one cubic meter for every person on Earth. 18
  4. 4. 1.3. CLASSIFICATION OF COMPOSITE MATERIALS Composite materials are usually classified by the type of reinforcement they use. This reinforcement is embedded into a matrix that holds it together. The reinforcement is used to strengthen the composite. For example, in a mud brick, the matrix is the mud and the reinforcement is the straw. Common composite types include random-fiber or short-fiber reinforcement, continuous-fiber or long-fiber reinforcement, particulate reinforcement, flake reinforcement, and filler reinforcement. 1.3.1. METAL MATRIX COMPOSITES A metal matrix composite is a composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another metal, such as ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. A metal matrix composite is complementary to a cermet. They are made by dispersing a reinforcing material into a metal matrix. The reinforcement surface can be coated to prevent a chemical reaction with the matrix. 1.3.2. CERAMIC MATRIX COMPOSITES Ceramic Matrix Composites are subgroup of composite materials as well as a subgroup of technical ceramics. They consist of ceramic fibers embedded in a ceramic matrix, thus forming a ceramic fiber reinforced ceramic material. The matrix and fibers can consist of any ceramic material, whereby carbon and carbon fibers can also be considered a ceramic material. 1.3.3. POLYMER MATRIX COMPOSITES 18
  5. 5. Polymer Matrix Composite is the material consisting of a polymer (resin) matrix combined with a fibrous reinforcing dispersed phase. They are very popular due to their low cost and simple fabrication methods. Use of non-reinforced polymers as structure materials is limited by low level of their mechanical properties. The reinforced fibers may be arranged in unidirectional fibers or roving or chopped strands. They are used for manufacturing secondary load bearing aerospace structures, boat bodies, canoes, kayaks, automotive parts, radio controlled vehicles, sport goods, bullet proof vests and other armor parts, brake and clutch linings 1.4. FIBER REINFORCED COMPOSITES A fiber-reinforced composite (FRC) is a composite building material that consists of three components: (i) the fiber as the discontinuous or dispersed phase, (ii) the matrix as the continuous phase, and (iii) the fine interphase region, also known as the interface. This is a type of advanced composite group, which makes use of rice husk, rice hull, and plastic as ingredients. This technology involves a method of refining, blending, and compounding natural fibers from cellulosic waste streams to form a high- strength fiber composite material in a polymer matrix. The designated waste or base raw materials used in this instance are those of waste thermoplastics and various categories of cellulosic waste including rice husk and saw dust. FRC is high-performance fiber composite achieved and made possible by cross-linking cellulosic fiber molecules with resins in the FRC material matrix through a proprietary molecular re-engineering process, yielding a product of exceptional structural properties. Through this feat of molecular re-engineering selected physical and structural properties of wood are successfully cloned and vested in the FRC product, in addition to other critical attributes to yield performance properties superior to contemporary wood. 18
  6. 6. This material, unlike other composites, can be recycled up to 20 times, allowing scrap FRC to be reused again and again. The failure mechanisms in FRC materials include delamination, intra- laminar matrix cracking, longitudinal matrix splitting, fiber/matrix de- bonding, fiber pull-out, and fiber fracture. 1.4.1. CARBON FIBER REINFORCED PLASTIC Carbon fiber reinforced plastic is an extremely strong and light fiber- reinforced polymer which contains carbon fibers. The polymer is most often epoxy, but other polymers, such as polyester, vinyl ester or nylon, are sometimes used. The composite may contain other fibers, such as aramid e.g. Kevlar, Twaron, aluminum, or glass fibers, as well as carbon fiber. The strongest and most expensive of these additives, carbon nanotubes, are contained in some primarily polymer baseball bats, car parts and even golf clubs where economically viable. Carbon fiber is commonly used in the transportation industry; normally in cars, boats and trains Although carbon fiber can be relatively expensive, it has many applications in aerospace and automotive fields, such as Formula One. The compound is also used in sailboats, rowing shells, modern bicycles, and motorcycles, where its high strength-to-weight ratio and very good rigidity is of importance. Improved manufacturing techniques are reducing the costs and time to manufacture, making it increasingly common in small consumer goods as well, such as certain ThinkPad’s since the 600 series, tripods, fishing rods, hockey sticks, paintball equipment, archery equipment, tent poles, racquet frames, stringed instrument bodies, drum shells, golf clubs, helmets used as a paragliding accessory and pool/billiards/snooker cues. 1.4.2. GLASS FIBER REINFORCED PLASTIC 18
  7. 7. Glass Fiber Reinforced Plastic is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes. The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinyl ester) or thermoplastic. Common uses of fiberglass include high performance aircrafts (gliders), boats, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding, casts, Surfboards, and external door skins. Fiberglass is an immensely versatile material which combines its light weight with an inherent strength to provide a weather resistant finish, with a variety of surface textures. The development of fiber reinforced plastic for commercial use was being extensively researched in the 1930s. It was particularly of interest to the aviation industry. Mass production of glass strands was accidentally discovered in 1932 when a researcher at the Owens-Illinois directed a jet of compressed air at a stream of molten glass and produced fibers. Owens joined up with the Corning Company in 1935 and the method was adapted by Owens Corning to produce its patented "Fiberglas". A suitable resin for combining the "Fiberglas" with a plastic was developed in 1936 by du Pont. The first ancestor of modern polyester resins is Cyanamid's of 1942. Peroxide curing systems were used by then. During World War II it was developed as a replacement for the molded plywood used in aircraft radomes (fiberglass being transparent to microwaves). Its first main civilian application was for building of boats and sports car bodies, where it gained acceptance in the 1950s. Its use has 18
  8. 8. broadened to the automotive and sport equipment sectors as well as aircraft, although its use there is now partly being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight. Fiberglass uses also include hot tubs, pipes for drinking water and sewers, office plant display containers and flat roof systems. Fiberglas is also used in the telecommunications industry for shrouding the visual appearance of antennas, due to its RF permeability and low signal attenuation properties. It may also be used to shroud the visual appearance of other equipment where no signal permeability is required, such as equipment cabinets and steel support structures, due to the ease with which it can be molded, manufactured and painted to custom designs, to blend in with existing structures or brickwork. Other uses include sheet form made electrical insulators and other structural components commonly found in the power industries. Because of fiberglass's light weight and durability, it is often used in protective equipment, such as helmets. Many sports utilize fiberglass protective gear, such as modern goaltender masks and newer baseball catcher's masks. 1.5. TYPES OF REINFORCING GLASS FIBERS Glass-reinforced composites gain their strength from thin glass fibers set within their resin matrix. These strong, stiff fibers carry the load while the resin matrix spreads the load imposed on the composites. A wide variety of properties can be achieved by selecting the proper glass type, filament diameter, sizing chemistry and fiber forms (e.g., roving, fabric, etc.). Fibers made primarily from silica-based-glass containing several metal oxides offer excellent thermal and impact resistance, high tensile strength, good chemical resistance and outstanding insulating properties. 18
  9. 9. Fibers can also be produced from carbon, boron and aramid. While these materials offer high tensile strength and are stiffer than glass, they cost significantly more. For that reason, carbon, boron and aramid are typically reserved for high-tech application demanding exceptional fiber properties for which the customer is willing to pay a premium. An alternative is to use hybrid fiber (combining an expensive fiber with glass fiber), which improves overall cost yet cost less than using premium fibers alone. 1.5.1. E-GLASS FIBER E-glass is a popular fiber made primarily of silica oxide, along with oxides of aluminum, boron, calcium and other compounds. Named for its good electrical resistance, E-glass is strong yet low in cost, and accounts for over 90% of all glass fibers reinforcements, especially in aircraft radomes, antennae and application where radio-signal transparency is desired. E-glass is also used extensively in computer circuit boards where stiffness and electrical resistance are required. In addition to E-glass, several other types of glass can be used for composite reinforcement. The most popular are high strength glass and corrosion resistant glass. 1.5.2. HIGH STRENGTH GLASS FIBER High- strength, carbon or other advanced fibers are used in application requiring greater strength and lower weight. High-strength glass is generally known as S-type in the United States, R-glass Europe and T-glass in Japan. S-glass was originally developed for military application in the 1960’s and a lower cost version, S-2 glass, was developed for commercial applications. High- strength glass has appreciably higher amounts of silica oxide, aluminum oxide and magnesium oxide than E-glass. S-2 glass is approximately 40-70% stronger than E-glass. 18
  10. 10. 1.5.3. CORROSION RESISTANT GLASS FIBER When glass fibers are exposed to water, they become eroded to leaching. To protect against water erosion, a moisture- resistant coating such as silane compound is coated on to the fibers during composite formation provides additional protection. The result is corrosion-resistant glass (called C-glass) Some types of glasses perform better than others when exposed to acids or bases. Both C-glass and S-2 glass offer good corrosion resistance when exposed to hydrochloric or sulfuric acid. E-glass and S-2 glass resist sodium carbonate solution better than C-glass. 1.6. MACHINING OF GLASS FIBER REINFORCED COMPOSITES Machining of GFRPs (Glass fiber reinforced plastics) differs significantly from machining of conventional metal and alloys. In the former the material behaviors depend on diverse fiber and matrix properties, fiber orientation and relative volume of matrix and the fibers. The tool continuously encounters alternate matrix and fiber material whose response to machining can vary greatly. For example in a glass/epoxy composite the tool encounters a low temperature soft epoxy matrix and brittle glass fibers. Conventional machining of GFRPs (Glass fiber reinforced plastics) is difficult due to the presence of comparatively high volume fraction of hard fibers in the matrix, their orientation and diverse fiber and matrix properties. The earliest of the literature in FRP (Fiber reinforced plastics) machining was by Wason. He was of the opinion that the best way to saw FRP plates was by diamond tipped circular saw with large amount of cutting fluid. The speed should be high and feed rate slow. Mackrin also stated that diamond wheel may be used for cutting GFRP. The most significant work in 18
  11. 11. the machining of GFRP is by Konig, Wulf, Grab and Willerscheid. They have identified that the major problems associated with different FRPs namely glass, carbon and Kevlar reinforced ones. They found that type of fiber used for reinforcement is the major factor which determines the machinability of the composite. 1.6.1. DRILLING OF FRP Drilling is far the most important item of machining and it is very important because it is often a final operation during assembly. Any defects lead to rejection of the part. In the aircraft industry for example drilling associated delamination accounts for 60% of all part rejections during the final assemble of an aircraft. The economic impact of this is significant considering the value associated with the part when it reaches the assemble stage. 2. LITERATURE REVIEW Glass Fiber Reinforced Plastic refers to a plastic which has been reinforced with glass fibers. It uses a plastic matrix, which may be an epoxy resin, a thermosetting or thermoplastic resin to bind the glass fiber together and improve its mechanical properties. It is far less brittle than carbon fiber 18
  12. 12. reinforced plastic and less expensive than metals. Its bulk strength and weight properties are very favorable compared to metals. Morton [1] discusses about GFRP, how it is fabricated, the advantages of using GFRP and design considerations to be considered in using equipment are made from them in his article. Also he discusses the different resins that can be used for its fabrication. He discusses the thermosetting resins (epoxies, polyesters, vinyl esters). He discusses the hand layup method of fabrication that is being used for this project to apply resin on thin glass fiber mats stacked on top of another till desired dimensions are achieved. This is the most basic of fabrication techniques. It is also referred to as ‘contact molding’. The author continues to mention about the strength characteristics of GFRP and its various properties that make it preferable in various fields of application like corrosion resistance, weight advantages, high strength, inexpensiveness and flexibility. A lot of research has been conducted to achieve efficient drilling of composites materials. Drilling tests were carried out on GFRPC composites in order to verify the effect of machining parameters on cut quality. Experiment results showed that, the quality index was strongly affected by cutting speed to feed ratio (V/s). In particular large damage zones were observed when low V/s values were adopted. However beyond a limiting value, extend of the damage is no longer influenced by V /s. A ratio of V/s greater than 150 was suggested in order to obtain best cut quality in drilling of GFRPC. The type of drill used has an important influence on the various process parameters. Here the influence of three drill types of same diameter is studied. Davim et al. [2] gives details about the study on a straight flute jobber length type drill and a twist type drill used for composite drilling. The drills used are of the same diameter (here 5 mm) and varies only in their type. The “jobber length” drill has a 118 degree point angle. Important results obtained showed that the Twist drill presents less specific cutting 18
  13. 13. pressure and thrust force than the Jobber length drill considering the same cutting parameters (cutting speed and feed rater). The Twist drill produces less damage on the GFRP composites than the Jobber length drill as well as has better performances. Delamination is the cracking of the composites laminate due to the contact with the drill bit. It is a major problem associated with drilling fiber- reinforced composite material that, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long performance deterioration. In the machining composites parts, a finish comparable to metals cannot be achieved because of inhomogeneity and anisotropy of materials. Tsao et al. [3] mentions that induced delamination can occur at both entrance and exit planes of work piece. A rapid increase in feed rate at the end of drilling will cause cracking around the exit edge of the hole. Tsao et al. [3] mentions that delamination in drilling have been correlated to thrust force during exit of the drill. A significant portion of the thrust is due to the chisel edge. Increasing the chisel edge length, results in the rise of thrust force. The candle stick drill and saw drill have a smaller center than the twist drill; thus, a smaller extent of the last laminate is subjected to a bending force. Experiments indicate that there exists s critical thrust force below which no delamination occurs. Above that level, matrix cracks are generated by interface delamination growing from the crack tips. Davim and Reis et al. [2] mentions that the hole surface quality (surface roughness and dimensional precision) is strongly dependent on cutting parameters, tool geometry and cutting forces (thrust force and torque). The author studied the work developed by other authors drew the conclusion from drilling of glass fiber reinforced plastics manufactured by hand layup method that the specific cutting pressure decreases with the feed rate and slightly with the cutting speed, and the thrust force increases with 18
  14. 14. the feed rate. The feed rate is the cutting parameters which has greater influence on specific cutting pressure. The damage increases with both cutting parameters, which means that the composite damage is lesser for higher cutting speed and for lower feed. JOURNALS REFERRED “Effects of special drill bits on drilling-induced delamination of composite materials” Introduction Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for joining structures. Delamination is among the serious concerns during drilling. Practical experience proves the advantage of using such special drills as saw drill, candle stick drill, core drill and step drill. The experimental investigation described in this paper by Hocheng, Tsao et al. [3] examines the theoretical predictions of critical thrust force at the onset of delamination, and compares the effects of these different drill bits. The results confirm the analytical findings and are consistent with the industrial experience. Ultrasonic scanning is used to evaluate the extent of drilling-induced delamination. The advantage of these special drills is illustrated mathematically as well as experimentally, that their thrust force is distributed toward the drill periphery instead of being concentrated at the center. The allowable feed rate without causing delamination is also increased. The analysis can be extended to examine the effects of other future innovative drill bits. Results The experimental results of the drilling-induced delamination while using special drills have been presented. The results are compared with the theoretical predictions of critical thrust force at the onset of delamination, 18
  15. 15. and are consistent with the industrial experience as well. Due to the different drill geometry, these drills show different levels of the drilling thrust force which varies with the feed rate. The advantage of these special drill bits lies in their higher threshold feed rate at the onset of delamination. Among the five drills, the core drill offers the highest critical feed rate followed by the candle stick drill, saw drill and step drill, while the traditional twist drill allows for the lowest feed rate. In other words, the core drill, candle stick drill, saw drill and step drill can be operated at larger feed rate or in shorter cycle time without delamination damage compared to the twist drill. “The effect of vibratory drilling on hole quality in polymeric composites”:- Introduction Arul et. al. [4] mentions that anisotropy of fiber-reinforced plastics (FRP) affects the chip formation and thrust force during drilling. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced plastics, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce good quality holes with high efficiency by conventional drilling method. This research concerning drilling of polymeric composites aims to establish a technology that would ensure minimum defects and longer tool life. Specifically, the authors Arul, Vijayraghavan Malhotra et al. conceived a new drilling method that imparts a low- frequency, high amplitude vibration to the work piece in the feed direction during drilling. Using high-speed steel (HSS) drill, a series of vibratory drilling and conventional drilling experiments were conducted on glass fiber- reinforced plastics composites to assess thrust force, flank wear and delamination factor. In addition, the process-status during vibratory drilling was also assessed by monitoring acoustic emission from the work piece. 18
  16. 16. From the drilling experiments, it was found that vibratory drilling method is a promising machining technique that uses the regeneration effect to produce axial chatter, facilitating chip breaking and reduction in thrust force. Results The results of vibratory drilling studies on woven glass fabric composite using high speed steel drill were presented. Some of the observations are:- • The thrust in vibration drilling is smaller than that in the conventional drilling, which indicates that the vibration drilling method is suitable for defect constrained drilling of polymeric composites. • The trend of variation of thrust, flank wear, delamination factor, AE power and AE rms with number of holes for conventional and vibration drilling are similar. • Good correlation between thrust and delamination factor indicates that on-line monitoring of thrust can facilitate defect-constrained drilling. In conventional drilling, increase of thrust and delamination factor around 30 holes, indicates that 30 is the limiting number of holes to be drilled and in vibratory drilling 50 is the limiting number of holes to be drilled for defect tolerance. “Fiber reinforced composites in aircraft construction” Introduction Fibrous composites have found applications in aircraft from the first flight of the Wright Brothers' Flyer 1, in North Carolina on December 17, 1903, to the plethora of uses now enjoyed by them on both military and civil aircrafts, in addition to more exotic applications on unmanned aerial vehicles (UAVs), space launchers and satellites. Their growing use has risen from 18
  17. 17. their high specific strength and stiffness, when compared to the more conventional materials, and the ability to shape and tailor their structure to produce more aerodynamically efficient structural configurations. In this paper, Soutis et al. [5] gives a review of recent advances using composites in modern aircraft construction is presented and it is argued that fiber reinforced polymers, especially carbon fiber reinforced plastics (CFRP) can and will in the future contribute more than 50% of the structural mass of an aircraft. However, affordability is the key to survival in aerospace manufacturing, whether civil or military, and therefore effort should be devoted to analysis and computational simulation of the manufacturing and assembly process as well as the simulation of the performance of the structure, since they are intimately connected. Results The application of carbon fiber has developed from small-scale technology demonstrators in the 1970s to large structures today. From being a very expensive exotic material when first developed relatively few years ago, the price of carbon fiber has dropped to less than £10/kg, which has increased applications such that the aerospace market accounts for only 20% of all production. The main advantages provided by CFRP include mass and part reduction, complex shape manufacture, reduced scrap, improved fatigue life, design optimization and generally improved corrosion resistance. The main challenges restricting their use are material and processing costs, impact damage and damage tolerance, repair and inspection, dimensional tolerance, size effects on strength and conservatism associated with uncertainties about relatively new and sometimes variable materials. Carbon fiber composites are here to stay in terms of future aircraft construction, since significant weight savings can be achieved. For secondary structures, weight savings approaching 40% are feasible by using composites instead of light metal alloys, while for primary structures, such 18
  18. 18. as wings and fuselages, 20% is more realistic. These figures can always improve but innovation is the key to making composites more affordable. “Influence of cutting parameters on thrust force and torque in drilling of E-glass/polyester composites” Introduction Reinforced plastics find wide application in all manufacturing fields due to their distinct properties such as low weight, high strength and stiffness. Although components are produced to near net shape, machining is often needed to fulfill the requirements related to tolerances of assembly needs. Among all the machining processes, drilling is the most indispensable method for the fabrication of products with composite panels. The performance of these products is mainly dependent on surface quality and dimensional accuracy of the drilled hole. Murthy et al [6] studies the effect of process parameters such as spindle feed, drill diameter and point angle and material thickness on thrust force and torque generated during drilling of GFRP composite material using solid carbide drill bit. Full factorial Design of Experiments (DoE) has been adopted and the results indicate that spindle speed is the main contributing factor for variation in thrust force and drill diameter is the main contributing factor for variation for variation in torque. The optimum combination of process parameters settings has been found out using the integration on Taguchi method and Response Surface Methodology. Results Thrust force is significantly influenced by spindle speed and they are inversely proportional. Hence while working on glass fiber reinforced composites by using solid carbide drills, higher spindle speed are recommended for process parameter ranges under consideration. Cutting torque is significantly influenced by drill diameter. Higher the drill diameter, 18
  19. 19. larger the thrust force and cutting torque required. Thrust force increases whereas cutting force decreases with the increase in drill point angle. Both thrust force and cutting torque increase with the increase in feed rate and material thickness. Integrating taguchi method and RSM can be very effective in process parameter optimization, as combining of the results of the two methods can not only optimize the parameters, but also, indicate the values of response, through which process parameter selection can be refined and results justified. The results are based on the preselected range of values of speed, feed, material thickness drill diameter and drill point angle and hence the inference drawn cannot be completely generalized. The inferences drawn from this study is of great significance to the practitioners in minimizing tool wear and cutting energy, as solid carbide tool is being widely used in machining GFRP 3. EXPERIMENTAL DETAILS AND PROCEDURE 3.1. INTRODUCTION Major constituents in a fiber reinforced composite material are reinforcing fiber and the matrix which hold the fibers. Fibers are the principal constituents; they occupy a large volume fraction and the major portion of load acting on a composite. For this experimental study we select E type glass fiber and Bisphenol as the reinforcing fiber and the matrix respectively. In previous studies done in institutions outside, they used epoxy resins and other resins to hold the fibers. We use Bisphenol to study how it differs from other resins and the different properties that it imbibes to the final GFRP that is prepared. The most common form in which GFRP’s are used in structural application is called laminated. It is obtained by stacking a number of thin layers of fibers and matrix and consolidating them to the desired thickness. The fiber orientation in each layer as well as the stacking sequence of 18
  20. 20. various layers can be controlled to generate a wide range of physical and mechanical properties for the composite laminate. The design of experiment was done by taking three input parameters namely the drill material, spindle speed and feed rate. We discuss the details of the experimental procedure and the different equipment’s and tools used in this study as follows: 3.2. PROCEDURE • Manufacture GFRP using woven glass fiber and Bisphenol as matrix. • Acquire tools, drill bits (HSS, Tungsten Carbide, PCD) • Drill GFRP with the drill bits at varying cutting speed and feed rate • Find thrust force and torque by attaching 9257B Kistler Dynamometer to drilling equipment. • Perform wear test, flexural strength test, hardness test on GFRP • Optimize thrust force, torque and minimize delamination (both entry and exit) in the holes using Design of Experiments and Response Table Methodology • Find optimal machining parameters for obtaining best quality drilled hole. 3.3. MANUFACTURING METHOD FOR GFRP – HAND LAYUP METHOD The GFRP is prepared in the laboratory at room temperature using woven glass fiber mats and using Bisphenol along with promoters and catalysts to progress the method at room temperature. 18
  21. 21. Fig.1 Molding process  Mold is treated with a release agent-to prevent sticking.  Gel coat layers are placed on the mold- to give decorative and protective surface.  Put the reinforcement (woven roving's or chopped strand mat).  The thermosetting resin is mixed with a curing agent, and applied with brush or roller on the reinforcement.  The part is allowed to cure and then disassembled from the mold.  Since this process is not typically performed under the influences of heat and pressure, simple equipment and tooling can be employed. 3.4. TOOLS USED We use three different drill bits of increasing hardness to test the effect of drill bit material on the output parameters. HSS (High Speed Steel), Tungsten Carbide and PCD (Poly Crystalline Diamond) 18
  22. 22. Fig.2 HSS Fig.3 Tungsten Carbide 18
  23. 23. Fig. 4 PCD Fig. 5 Parts of Twist Drill We use 5mm diameter twist drill bits. Nomenclature of drill bit is as follows. 18
  24. 24. Axis: The imaginary straight line which forms the longitudinal center line of the drill Body: The portion of the drill extending from the shank or neck to the outer corners of the cutting lips Chisel Edge: The edge at the end of the web that connects the cutting lips Clearance: The space provided to eliminate undesirable contact between the drill and the work piece Clearance Diameter: The diameter over the cut away portion of the drill lands Drift: A flat tapered bar for forcing a taper shank out of its socket Flutes: Helical or straight grooves cut or formed in the body of the drill to provide cutting lips, to permit removal of chips, and to allow cutting fluid to reach the cutting lips Flute Length: The length from the outer corners of the cutting lips to the extreme back end of the flutes; it includes the sweep of the tool used to generate the flutes and, therefore, does not indicate the usable length of the flutes Helix Angle: The angle made by the leading edge of the land with a plane containing the axis of the drill Land: The peripheral portion of the body between adjacent flutes Lead: The axial advance of a leading edge of the land in one turn around the circumference Lips: The cutting edges of a two flute drill extending from the chisel edge to the periphery Margin: The cylindrical portion of the land which is not cut away to provide clearance Neck: The section of reduced diameter between the body and the shank of a drill Oil Grooves: Longitudinal straight or helical grooves in the shank, or 18
  25. 25. grooves in the lands of a drill to carry cutting fluid to the cutting lips Oil Holes or Overall Length. Point: The cutting end of a drill, made up of the ends of the lands and the web; in form it resembles a cone, but departs from a true cone to furnish clearance behind the cutting Point Angle: The angle included between the cutting lips projected upon a plane parallel to the drill axis and parallel to the two cutting lips Shank: The part of the drill by which it is held and driven Tang: The flattened end of a taper shank, intended to fit into a driving slot in a socket Taper Drill: A drill with part or all of its cutting flute length ground with a specific taper to produce tapered holes; they are used for drilling the original hole or enlarging an existing hole Taper Square Shank: A taper shank whose cross section is square Web: The central portion of the body that joins the lands; the extreme end of the forms the chisel edge on a two-flute drill. Point angle =118° Cutting edge angle = 59° Helix angle =25° Clearance angle =6° Process Parameters Spindle Speed (rpm) Feed (mm/rev) Drill Bit Level 1 450 0.04 HSS Level 2 852 0.08 TUNGSTEN CARBIDE Level 3 1250 0.12 PCD Table 1: The varying input parameters factor We use the above sets of spindle speed, feed rate and drill bit to perform a run test on the GFRP prepared. The spindle speeds and feed rate values are selected in such a way to keep the settings as low, medium and 18
  26. 26. high. The previous tests done in other journals influenced us to select the appropriate values. The drilling machine was modified so as to measure the thrust and torque during the drilling cycle. For this a dynamometer was attached to drilling machine. For proper measurement of the thrust and torque was fixed in such a way that the axis of the drill bit passes through the center of the dynamometer. 3.5. EQUIPMENTS USED The important equipment’s used in experimentation include 3.5.1. Drilling Machine The drilling machine used for the experiment is a radial upright type drilling machine. The machine can be used as an automatic feed machine or a manual feed machine. The control that allows its use as an automatic feed machine. The upper lever allows selection of automatic feed in three levels – 0.04mm/rev, 0.08mm/rev and 0.12mm/rev. Once the required level is selected the lower has to be pulled forward for the machine to start automatic operation. The drilling machine can be operated either on a belt drive or a geared drive. In the case of the belt drive the drive is taken directly from the drive motor of the drilling machine to it spindle through a belt drive. In the other case a geared drive also comes into picture. To prevent damage to the machine change over from belt drive to geared drive or vice versa should be done only when motor is switch off. Presently the machine is in belt drive; pull the lever to the blue colored area for the geared drive. It depends also on the rpm of the drive motor used for the drilling machine. A 960 rpm or a 1440 rpm motor can be used with this drilling 18
  27. 27. machine. When using the different drive motor the spindle speeds available are 960 rpm, Geared drive – 65 rpm, 95 rpm, 140rpm, 205 rpm, 300 rpm 960 rpm, Belt drive- 390 rpm, 570 rpm, 840 rpm, 1230 rpm, 1800 rpm 1440 rpm, Geared drive- 100 rpm, 142 rpm, 210 rpm, 310 rpm, 450 rpm 1440 rpm, Belt drive- 600 rpm, 852 rpm, 1260 rpm, 1860 rpm, 2700 rpm 3.5.2. Dynamometer A drill tool dynamometer was used to measure the thrust force and torque occurring during the drilling operation. It is designed to be directly mounted on the top of the drilling machine. It is basically a strain gauge based sensor. This dynamometer consists of 2 strain gauge based sensor; one measured the thrust force acting on the dill tool, while the other one measures the twisting force (torque) acting on the drill tool. The dynamometer has to be mounted in such a way that the drilling machine passes through the axis of the dynamometer; this will ensure accurate torque readings. Before starting experiment the instrument has to be put in “ON” position for about 10min for initial warm-up. Adjust the potentiometer in the front panel till the display reads “0” for thrust force as well as torque 3.5.3. Profile Projector The profile projector is used for measuring the drilled holes after completing the drilling operation. The GFRP piece is mounted on the work table of the profile projector. The specimen is focused by adjusting the position of the table to get a clear sharp image. The focusing should be done properly to ensure that the damage area around the drilled hole is clearly visible. A magnified image of the GFRP piece is obtained on the screen. Magnification on the range of 10x, 20x and 50x are possible using the instrument. Going for a higher magnification allows for easier measurement 18
  28. 28. of the drilled holes. Both linear and angular measurements can be done using the profile projector. 3.5.4. Variable Speed and Feed Controller 3.6. DELAMINATION FACTOR Delamination is a mode of failure for composite materials. It is caused due to weak bonding of constituents. It reduces the structural integrity of material and results in poor assembly tolerance and long term performance deterioration. Delamination causes layers of the glass fibers to separate after repeated cyclic stresses. This makes the material lose the mechanical toughness. Delamination factor is determined by the ratio of maximum diameter (D max) of Delamination and the diameter of the hole (D) Fd = D max/D 18
  29. 29. Fig.6 Delamination Factor Fig.7 Delamination Entry Fig.8 Delamination exit 3.7. TESTS PERFORMED ON GFRP Composite materials emerge as a promising alternative to correct the deficiencies caused by steel reinforcements in concrete structures. The advantageous properties of fiber reinforced polymer (FRP) such as high strength to weight ratio, and corrosion and fatigue resistance create an interest in engineers. For wide acceptance and implementation in construction, full characterizations of the mechanical properties of GFRP specimens are needed. In particular, it is necessary to define the mean value and 18
  30. 30. distribution of the tensile strength of GFRP bars for reinforced concrete, which engineers can use for design purposes and composite manufacturers for quality control. 3.7.1. FLEXURAL STRENGTH TEST Flexural strength, also known as modulus of rupture, bend strength or fracture strength, a mechanical parameter for brittle material, is defined as a materials ability to resist deformation under load. The transverse bending test is most frequently employed, in which a rod specimen having either a circular or rectangular cross section is bent until fracture using a three point flexural test technique. The flexural strength represents the highest stress experienced within the material at its moment of rupture. It is measured in terms of stress, here given the symbol σ. Fig.9 Three Point Flexure Test When an object formed of a single material like a wooden beam or steel rod, is bent, it experiences a range of stresses across its depth. At the edge of the object on the inside of the bend, the stress will be at its maximum compressive stress value. At the outside of the bend, the stress will be at its maximum tensile value. These inner and outer edges of the beam or rod are 18
  31. 31. known as ‘extreme fibers’. Most materials fail under tensile stress before they fail under compressive stress, so the maximum tensile stress value that can be sustained before the beam or rod fails is its flexural strength. For a rectangular sample under a load in a three point bending setup σ = (3FL) / (2bd²) F is the load (force) at the fracture point (N) L is the length of the support span (mm) b is width (mm) d is thickness (mm) 4. TABULATION AND GRAPHS 4.1. TABULATION RESPONSE TABLE FOR DELAMINATION ENTRY Drill Bit Material Speed (rpm) Feed (mm/rev) Exp. No HSS TC PCD 450 852 1250 0.04 0.08 0.12 1 1.059 1.059 1.059 2 1.068 1.068 1.068 3 1.11 1.11 1.11 4 1.058 1.058 1.058 5 1.09 1.09 1.09 6 1.099 1.099 1.099 7 1.035 1.035 1.035 8 1.068 1.068 1.068 9 1.095 1.095 1.095 10 1.04 1.04 1.04 11 1.06 5 1.065 1.065 12 1.08 5 1.085 1.085 13 1.03 5 1.035 1.035 14 1.06 2 1.062 1.062 15 1.07 5 1.075 1.075 16 1.01 5 1.015 1.015 17 1.04 3 1.043 1.043 18 1.06 8 1.068 1.068 19 1.02 1.02 1.02 20 1.026 1.026 1.026 21 1.031 1.031 1.031 22 1.012 1.012 1.012 23 1.015 1.015 1.015 24 1.029 1.029 1.029 25 1.01 1.01 1.01 26 1.016 1.016 1.016 27 1.022 1.022 1.022 TOTAL 9.697 9.48 8 9.181 9.504 9.475 9.372 9.284 9.453 9.614 AVERAGE 1.077 1.05 4 1.020 1.056 1.052 1.041 1.031 1.050 1.068 18
  32. 32. Table 2: Response table for Delamination Entry RESPONSE TABLE FOR DELAMINATION EXIT Drill Bit Material Speed (rpm) Feed (mm/rev) Exp. No HSS TC PCD 450 852 1250 0.04 0.08 0.12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Table 3: Response table for Delamination Exit RESPONSE TABLE FOR THRUST FORCE Drill Bit Material Speed (rpm) Feed (mm/rev) Exp. No HSS TC PCD 450 852 1250 0.04 0.08 0.12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Table 4: Response table for thrust force 18
  33. 33. RESPONSE TABLE FOR TORQUE Drill Bit Material Speed (rpm) Feed (mm/rev) Exp. No HSS TC PCD 450 852 1250 0.04 0.08 0.12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Table 5: Response table for torque 4.2. GRAPHS DELAMINATION ENTRY GRAPHS 18
  34. 34. 1.045 1.05 1.055 1.06 1.065 1.07 1.075 1.08 1.085 0 500 1000 1500 HSS: SPEED VS DELAMINATION ENTRY DELAMINATION Fig.10 Speed vs Delamination Entry (HSS) 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.1 0 0.05 0.1 0.15 HSS: FEED VS DELAMINATION ENTRY DELAMINATION Fig.11 Feed vs Delamination Entry (HSS) 18
  35. 35. Fig. 12 Speed vs Delamination Entry (TC) Fig.13 Feed vs Delamination Entry (TC) 18
  36. 36. Fig.14 Speed vs Delamination Entry (PCD) Fig.15 Feed vs Delamination Entry (PCD) 18
  37. 37. Fig.16 Drill Bit Material vs Delamination Entry DELAMINATION EXIT GRAPHS Fig.17 Speed vs Delamination Exit (HSS) 18
  38. 38. Fig.18 Feed vs Delamination Exit (HSS) Fig.19 Speed vs Delamination Exit (TC) 18
  39. 39. Fig.20 Feed vs Delamination Exit (TC) Fig.21 Speed vs Delamination Exit (PC) 18
  40. 40. Fig.22 Feed vs Delamination Exit (PCD) Fig.23 Drill Bit Material vs Delamination Exit 18
  41. 41. THRUST FORCE GRAPHS Fig.24 Speed vs Thrust Force (HSS) 0 20 40 60 80 100 0 0.05 0.1 0.15 HSS: FEED VS THRUST FORCE THRUST Fig.25Feed vs Thrust Force (HSS) 18
  42. 42. 56 58 60 62 64 66 68 0 500 1000 1500 TUNGSTEN CARBIDE: SPEED VS THRUST FORCE THRUST Fig.26 Speed vs Thrust Force (TC) Fig.27 Feed vs Thrust Force (TC) 18
  43. 43. Fig.28 Speed vs Thrust Force (PCD) Fig.29 Feed vs Thrust Force (PCD) 18
  44. 44. Fig.30 Drill Bit Material vs Thrust Force TORQUE GRAPHS Fig.31 Speed vs Torque (HSS) 18
  45. 45. Fig.32 Feed vs Torque (HSS) Fig.33 Speed vs Torque (TC) 18
  46. 46. Fig.34 Feed vs Torque (TC) Fig.35 Speed vs Torque (PCD) 18
  47. 47. Fig.36 Feed vs Torque (PCD) Fig.37 Drill Bit Material vs Torque 18
  48. 48. 4.3. TEST RESULTS 4.3.1. FLEXURAL STRENGTH Fig.38 Flexural Strength Graph The peak load obtained is 6.8 KN Flexural strength σ = (3FL) / (2bd²) = 3x6800x500/ (2x100x10x10) = 510 N/mm2 Flexural Strength is found out as 510.00 N/mm2 5. SUMMARY AND CONCLUSION 18
  49. 49. A brief summary and main conclusion drawn from this study are presented in this chapter. The main highlight of this work is that this study was conducted based on the composites manufacturing and drilling point of view. The samples for machining were prepared so that the required fiber orientation 60% by volume could be given. The drilling machine was modified so that it could measure thrust force and torque value. The influence of the input parameters on the damage factor and thrust force and torque is found out and how it is checked to obtain better quality drill hole. 5.1. CONCLUSIONS From the data received after optimizing the output parameters by adjusting the input parameters, we come to these following conclusions. The spindle speed, feed and drill bit material has influence on the final outcome of the quality of the drilled hole. The drill bit material is most influential parameter in the output parameters according to study done. It is observed that the delamination factor or the damage factor, thrust force and the torque increases as the feed rate is increased while it decreases with the increase of spindle speed. Also as the hardness of the drill bit increases, the delamination decreases both at the entry and exit level. It is also observed that delamination exit is more than the delamination entry. To achieve minimum delamination, thrust force and torque during drilling process, we see that we need to reduce the feed rate and increase the spindle speed. Thus we select the drill bit material as PCD, feed rate as 0.04 mm/rev and the spindle speed as 1250 rpm to achieve the best quality drilled hole. REFERENCES 18
  50. 50. [1] “Fiber-Glass Reinforced Plastics for Corrosion Resistance” :- Ted R. Morton, Beetle Plastics, Inc. 1974 [2] “Experimental study of drilling glass fiber reinforced plastics (GFRP) manufactured by hand lay-up”:-J.Paulo Davim, Pedro Reis - Composites Science and Technology 64(2004) 289-297 [3] “Effects of special drill bits on drilling-induced delamination of composite materials” :- H. Hocheng, C.C. Tsao – International Journal of Machine Tools &Manufacture 46 (2006) [4] “The effect of vibratory drilling on hole quality in polymeric composites” :- S. Arul, L. Vijayraghavan, S.K. Malhotra, R. Krishnamurthy – International Journal of Machine tools & Manufacture 46 (2006) 252-259 [5] “Fibre reinforced composites in aircraft construction”:-C.Soutis – Progress in Aerospace Sciences 41 (2005) 143-151 [6] “Process Parameters Optimization in GFRP drilling through integration of Taguchi and Response Surface Methodology” Murthy B.R.N, Lewlyn L.R. Rodrigues and Anjaiah Devineni – Research journal of Recent Sciences Vol1 (6) June 2012 18