16 Original Scientific Paper Kishore Debnath, Inderdeep Singh, Akshay Dvivedi EVALUATION OF SURFACE ROUGHNESS DURING ROTARY-MODE ULTRASONIC DRILLING OF GLASS/EPOXY COMPOSITE LAMINATES Received: 20 May 2014 / Accepted: 20 June 2014 Abstract: The application spectrum of fiber reinforced plastics (FRP's) has increased enormously in the last few years. The demand of FRP's has multiplied due to the fact that the properties of these materials are superior to the conventional metals and alloys. The increasing demand of FRP's expands the requirement of machining operation, especially when intricate parts are made up of FRP's. In a complex FRP product, components are mostly assembled through mechanical fastening. Mechanical fastening such as bolting demands the hole of desired size and good quality. The quality of the hole decides the ultimate load carrying capacity of the final assembly. The production of good quality hole in FRP's through traditional method is still a challenging task. The unwanted surface damage in and around the drilling zone is the major drilling problem. Therefore, continuous efforts have been put for the manufacturing of high precision good quality holes. In the present research investigation, an innovative method has been conceptualized and developed for the drilling of good quality holes in glass/epoxy laminates. Experimental investigation has been carried out to analyze the effect of several process parameters on the hole wall surface roughness. The major outcome of the study emphasize that the surface roughness near the hole entrance side is low as compared to the surface roughness at the hole exit side. Key words: Composites, Polymer, Laminates, Ultrasonic Drilling, Surface Roughness. Ocena hrapavost površine u toku rotacionog ultrazvučnog bušenja staklo/epoksi kompozitnih laminata. Upotrebni spektar vlaknima ojačanih plastika (FRP) se u poslednjih nekoliko godina znatno proširio. Potražnja FRP-a se povećala zbog činjenice da osobine ovih materijala su superiornije u poređenju sa konvencionalnim metalima i legurama. Povećana potražnja FRP-a proširuje zahteve operacija obrade, posebno kada su u pitanju složeni delovi od FRP-a. Kod kompleksnog FRP dela delovi su obično spojeni mehaničkim pričvršćivanjem. Mehaničko pričvršćivanje kao napr. spajanje vijcima zahteva otvor određene veličine i dobrog kvaliteta. Kvalitet rupe određuje nominalno opterećenje nošenja celog sklopa. Izrada kvalitetnog otvora kod FRP-a upotrebom klasičnih metoda je još uvek izazovni poduhvat. Neželjeno površinsko oštećenje u i oko zone bušenja je veliki problem. Stoga su ostvareni veliki napori u cilju poboljšanja izrade kvalitetnih otvora. U ovom radu je razvijena i opisana inovativna metoda bušenja kvalitetnih otvora u staklo/epoxy laminatima. Eksperimentalno istraživanje je sprovedeno da bi se analizirali efekti nekoliko parametara na hrapavost zidova otvora. Veliki rezulatat istraživanja naglašava da je hrapavost blizu ulaza otvora mala u poređenju sa hrapavošću na strani izlaza otvora. Ključne reči: Kompoziti, polimeri, laminate, ultrazvučno bušenje, površinska hrapavost. 1. INTRODUCTION The superior strength and stiffness, light-weight and anti-corrosion characteristic are the few properties that make FRP’s an excellent class of material system [1-4]. These materials have replaced many metallic components in aerospace and automobile industry. The use of FRP’s in structural and non-structural applications necessitates joining through mechanical fastening of several components [5,6]. The efficiency of mechanical fastening is highly dependent on the precision and accuracy of the drilled hole. Mostly, drilling of FRP is performed in a conventional way by rotating and feeding the drill against the work material. The major drawback of the conventional drilling is the drilling induced damage that cannot be completely avoided [7,8]. The main reason of drilling induced damage is the generation of thrust force during drilling. The thrust force is generated because of the direct interaction between the tool and work material. The interaction between the tool and work material cannot be avoided if the hole is made by means of conventional drilling process. This challenge leads to the development of new drilling methods where the direct contact between the tool and work material can be avoided. In order to achieve this, non-conventional machining methods can be useful for making of holes in FRP’s. Rotary ultrasonic machining (RUM) has been developed for drilling of FRP parts when there is a requirement of good quality holes. RUM is a hybrid machining process which is a combination of diamond grinding and ultrasonic machining process [9]. Cong et al. [10] has experimentally proved that RUM is much superior to the twist drilling of carbon fiber reinforced plastics (CFRP). The study shows that thrust force, torque, surface roughness, delamination and tool wear is less in RUM as compared to twist drilling. Liu et al. [11] has developed a new drilling method named rotary ultrasonic elliptical machining (RUEM) for drilling of CFRP. RUEM combines the advantages of both RUM and ultrasonic elliptical vibration cutting (UEVC). The