Elsevier

Composite Structures

Volume 211, 1 March 2019, Pages 318-336
Composite Structures

Effect of wall thickness and cutting parameters on drilling of glass microballoon/epoxy syntactic foam composites

https://doi.org/10.1016/j.compstruct.2018.12.022Get rights and content

Abstract

Effect of glass microballoon (GMB) wall thickness and cutting parameters (cutting speed, feed and drill diameter) on thrust force (Ft), surface roughness (Ra), specific cutting coefficient (Kf), cylindricity (CYL), circularity error (Ce-Exit) and damage factor (Fd-Exit) in drilling of GMB/epoxy syntactic foam is presented. CNC vertical machining centre is utilised for conducting experiments based on full factorial design. Significant process parameters are identified through response surface methodology. Wall thickness significantly affects the Ce-Exit and CYL of the drilled hole. Increasing wall thickness significantly reduces the Ra (30%), CYL (41%) and Ce-Exit (56%) due to the increased thermal stability of syntactic foams. This observation is very crucial for the syntactic foams used in structural applications pertaining to structural stability. Drill diameter is observed to be significant for Ft, Ra, CYL and Fd-Exit; while Kf is governed by feed. Furthermore, grey relation analysis (GRA) is used to identify the specific combination of process parameters to obtain good quality drilled hole. Combination of higher particle wall thickness and feed, lower cutting speed and drill diameter produces a sound hole quality as observed from GRA. Hole quality is highly influenced by drill diameter followed by cutting speed and GMB wall thickness. The present study offers guidelines for the industries (structural applications) to produce quality holes in GMB reinforced epoxy matrix.

Introduction

Syntactic foams (SFs) are a special class of particulate composites developed by incorporating the rigid hollow particles in a matrix medium [1], [2], [3]. Syntactic foams are most commonly used in various marine, aerospace, automobile and civil structural applications owing to their low density combined with excellent compressive properties and low moisture absorption. These closed cell foams are also used in electronic packaging and insulation due to high thermal stability [3]. Hollow particles (also called microballoons) of glass, metal, polymers, carbon, ceramics and fly ash cenospheres have been used in SF fabrication [4], [5], [6], [7], [8], [9], [10], [11], [12]. Among different available hollow particles, glass microballoons (GMBs) are the most commonly used as compared to naturally available cenospheres due to better surface morphology [4]. Incorporation of these GMBs offers a wide range of properties to SFs like reduced density, improved impact strength, thermal and dimensional stability [13].

Epoxy resin with GMBs as fillers are extensively investigated for compressive, tensile, flexural, electrical and thermal properties in the recent past [14], [15], [16], [17], [18], [19], [20], [21]. Studies on the compressive properties reveal that the strength increases with density. Variation of filler content is not having any significant effect on the compression strength of the syntactic foam. Compressive modulus of syntactic foam depends on the GMBs wall thickness and found to be increasing with increasing content of thick-walled particles [14], [15], [16], [17]. Tensile test of syntactic foams reveals that the modulus and strength are found to be increasing with decreasing microballoon content. Modulus and strength can be improved by using thick-walled hollow particles [14], [18], [19]. Thermal studies reveal that incorporation of GMBs in epoxy helps to reduce the coefficient of thermal expansion and increases dimensional stability. It is also found that the dimensional stability of syntactic foam can be increased by increasing the wall thickness of GMBs [20], [21].

Structural components in weight sensitive applications of aerospace and automobile industries demand assembly of syntactic foams requiring drilling operation. However, syntactic foams drilling is quite challenging as drill experiences variable resistance while passing through the matrix, wall thickness of GMB and void space within GMB. Such variations in resistance might affect drilled hole quality significantly and hence needs to be addressed. Further, abrasive nature of GMBs may result in tool wear which significantly deteriorates the hole quality. Hence, the drilling behavior of syntactic foams needs to be thoroughly studied particularly in case of GMB wall thickness variations.

A number of research publications for evaluating the drilling behavior of polymer composites have been published. El-Sonbaty et al. [22] analysed the effects of cutting and work material parameters on torque, thrust force and roughness in glass fiber reinforced polymer (GFRP) drilling using high-speed steel twist drills. Gaitonde et al. [23] established the relation between speed and feed with surface roughness in high-speed drilling of polyamides using response surface methodology (RSM). For the same polyamide material, Rubio et al. [24] used Taguchi method to analyse the effects of tool geometry and cutting parameters on thrust force, circularity error and hole diameter. Liu et al. [25] optimized the cutting parameters in machining of titanium alloy under minimum quantity lubrication condition using a new flexible method called coupling response surface methodology. Results show that surface roughness and cutting forces can be minimized by adopting lower values of feed and depth of cut. Taguchi method coupled with GRA has been used by Palanikumar et al. [26] to optimize the process parameters for minimizing the surface roughness and thrust force in GFRP composite drilling. The effect of multi-walled carbon nanotube (MWCNT) in laser drilling of MWCNT reinforced GFRP nanocomposite composites has been reported by Palanikumar [27]. Results show that the addition of MWCNT significantly improves the hole quality due to enhanced heat transfer characteristics of the composite. Basavarajappa et al. [28] proposed RSM based mathematical expressions to correlate v and f with Ft, Ra and Kf for GFRP composites drilling.

Krishnaraj et. al. [29] conducted high-speed drilling of carbon fiber reinforced polymer (CFRP) laminates to analyse process parameters influence on thrust force, circularity, delamination, and hole size. Furthermore, multi-response optimization has been performed to improve the quality of drilled holes [30]. The effect of cutting speed and feed on drilling forces, burrs, hole wall surface morphology and delamination damage in drilling of high-strength T800S/250F CFRP laminate has been analysed by Xu et al. [31] using coated twist and dagger drill. Xu et al. [32] proposed evaluation criteria for quantifying the defects induced during drilling of T800/X850 CFRP laminates using three different types of drills. The effect of different cutting sequence, tool geometry and tool materials in drilling of hybrid CFRP/Titanium stacks have been studied by Xu and El Mansori [33]. Results reveal that the drill geometry significantly effects drilling of CFRP/Titanium stacks than tool material composition. Drilling from titanium to CFRP phase produces sound quality holes in terms of consistent hole diameters and better surface finish. Ameur et al. [34] analysed the effect of process parameters on cylindricity error and delamination in dry drilling of CFRP composites. Saoudi, Zitoune [35] proposed a unique analytical model for predicting critical thrust force responsible for delamination considering the effect of the chisel and cutting edges in drilling of CFRP composites. Effect of cutting speed and feed on the temperature generated during drilling of CFRP and GFRP composites has been reported by Sorrentino, Turchetta [36]. Finally, a numerical model has been proposed based on experimental data for predicting the temperature generated during drilling of composites. An effort has been made by Merino-Perez et al. [37] to study the effect f, v and workpiece constituents in CFRP composites drilling.

Despite the availability of exhaustive literature on drilling of polymer composites, studies influence of wall thickness variations (different density particles) on epoxy based syntactic foams is not yet reported. Thereby in the present investigation, an effort has been made to analyse the drilling behavior of GMB/epoxy syntactic foam with particle wall thickness variation. Influence of process parameters (v, f, w and D) on responses such as Ft, Ra, Kf, CYL, Ce-Exit and Fd-Exit are presented. Furthermore, based on the experimental analysis, grey relation optimization is performed to propose a specific combination of process parameters to achieve better machinability and hole quality which might act as a guideline in industrial practices.

Section snippets

Constituent materials

Syntactic foams specimens are fabricated using GMBs reinforced in LAPOX (L-12) epoxy resin with K-6 polyamine hardener procured from Atul Ltd., Valsad, India. Epoxy matrix is reinforced with three different density grades (particle wall thickness variations) of hollow borosilicate GMBs (SID-200Z, SID-270Z and SID-350Z) procured from Trelleborg Offshore, USA. Wall thickness, density and mean particle size of SID-200Z, SID-270Z and SID-350Z grade hollow particles are 0.716, 0.925, 1.080 µm; 200,

Syntactic foam microstructure and density

Extensive micrography is conducted on the as-cast syntactic foam samples. Fig. 2 shows a representative micrograph of as cast syntactic foam sample. Microballoons are observed to be uniformly distributed throughout the epoxy matrix without forming the clusters. Particle debris is not seen in the epoxy matrix indicating intact particles during processing. During syntactic foam fabrication air is entrapped in the matrix resin leading to matrix porosity. Densities of syntactic foams along with

Conclusions

Three types of syntactic foams are prepared using different grades of GMBs (varying wall thickness) in the epoxy matrix at 60 vol%. Fabricated syntactic foams are drilled using CNC vertical machining center with coated tungsten carbide twist drills. FFD based experiments are performed to analyse the effect of process parameters on the machining performance. Mathematical models developed based on experimental results to predict the responses in the chosen range are validated using ANOVA.

Acknowledgment

Authors thank the Mechanical Engineering Department at NITK for providing facilities and support. The views expressed in this article are those of authors, not of funding agencies.

Data Availability

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

References (57)

  • K. Palanikumar

    Experimental investigation and optimisation in drilling of GFRP composites

    Measurement

    (2011)
  • V. Krishnaraj et al.

    Optimization of machining parameters at high speed drilling of carbon fiber reinforced plastic (CFRP) laminates

    Compos B Eng

    (2012)
  • A. Hrechuk et al.

    Hole-quality evaluation in drilling fiber-reinforced composites

    Compos Struct

    (2018)
  • J. Xu et al.

    Study of drilling-induced defects for CFRP composites using new criteria

    Compos Struct

    (2018)
  • J. Xu et al.

    Experimental study on drilling mechanisms and strategies of hybrid CFRP/Ti stacks

    Compos Struct

    (2016)
  • J. Saoudi et al.

    Critical thrust force predictions during drilling: analytical modeling and X-ray tomography quantification

    Compos Struct

    (2016)
  • L. Sorrentino et al.

    In process monitoring of cutting temperature during the drilling of FRP laminate

    Compos Struct

    (2017)
  • J.L. Merino-Perez et al.

    Influence of workpiece constituents and cutting speed on the cutting forces developed in the conventional drilling of CFRP composites

    Compos Struct

    (2016)
  • K. Palanikumar et al.

    Assessment of factors influencing surface roughness on the machining of Al/SiC particulate composites

    Mater Des

    (2007)
  • A.M. Abrão et al.

    Drilling of fiber reinforced plastics: a review

    J Mater Process Technol

    (2007)
  • L. Sorrentino et al.

    A new method to reduce delaminations during drilling of FRP laminates by feed rate control

    Compos Struct

    (2018)
  • J.P. Davim et al.

    A novel approach based on digital image analysis to evaluate the delamination factor after drilling composite laminates

    Compos Sci Technol

    (2007)
  • V. Manakari et al.

    Dry sliding wear of epoxy/cenosphere syntactic foams

    Tribol Int

    (2015)
  • S. Karnik et al.

    Delamination analysis in high speed drilling of carbon fiber reinforced plastics (CFRP) using artificial neural network model

    Mater Des

    (2008)
  • R. Zitoune et al.

    Influence of machining parameters and new nano-coated tool on drilling performance of CFRP/Aluminium sandwich

    Compos B Eng

    (2012)
  • U. Khashaba et al.

    Machinability analysis in drilling woven GFR/epoxy composites: Part I-effect of machining parameters

    Compos A Appl Sci Manuf

    (2010)
  • A.Z. Sultan et al.

    Effect of machining parameters on tool wear and hole quality of AISI 316L stainless steel in conventional drilling

    Procedia Manuf

    (2015)
  • B.U. Gowda et al.

    Comparative study of surface roughness and cylindricity of aluminium silicon nitride material using MRA GMDH & pattern recognition technique in drilling

    Procedia Mater Sci

    (2014)
  • Cited by (29)

    • 3D printing of glass microballoon–based syntactic foams

      2023, Lightweight and Sustainable Composite Materials: Preparation, Properties and Applications
    View all citing articles on Scopus
    View full text