A study of abrasive water jet machining process on glass/epoxy composite laminate

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Abstract

Surface roughness (Ra) and kerf taper ratio (TR) characteristics of an abrasive water jet machined surfaces of glass/epoxy composite laminate were studied. Taguchi's design of experiments and analysis of variance were used to determine the effect of machining parameters on Ra and TR. Hydraulic pressure and type of abrasive materials were considered as the most significant control factor in influencing Ra and TR, respectively. Due to hardness of aluminium oxide type of abrasive materials, it performs better than garnet in terms of both machining characteristics. Increasing the hydraulic pressure and abrasive mass flow rate may result in a better machining performance for both criteria. Meanwhile, decreasing the standoff distance and traverse rate may improve both criteria of machining performance. Cutting orientation does not influence the machining performance in both cases. So, it was confirmed that increasing the kinetic energy of abrasive water jet machining (AWJM) process may produce a better quality of cuts.

Introduction

Abrasive water jet machining (AWJM) process is one of the non-traditional machining processes that have been used extensively in various industry related applications. The basic principles of abrasive water jet machining (AWJM) were reviewed in details by Momber and Kovacevic (1992). This technology is less sensitive to material properties as it does not cause chatter, has no thermal effects, impose minimal stresses on the workpiece, and has high machining versatility and high flexibility.

The use of composite materials becomes prominent in today's modern technological applications. Fibreglass is used widely as a reinforcement of composite materials. It has unique characteristics such as high strength to weight ratio, easy availability, good corrosive resistance, excellent design flexibility, good electrical resistance, high fatigue endurance limit, and extremely cost effective in certain manufacturing methods (Strong, 1989).

Machining of glass fibre reinforced polymer (GFRP) composites requires the need for better understanding of cutting processes regarding accuracy and efficiency. Drilling of FRP composites causes more wear of the drill compared to drilling on conventional materials mainly due to heterogeneity of the work material which leads the drill bit to experience variable forces resulting in damage of work material such as delamination, fibre pull out and poor hole quality (Ramkumar et al., 2004). Due to these limitations of conventional machining processes, alternative techniques that utilize non-conventional energy sources for material removal such as electrical discharge machining (EDM), laser cutting, ultrasonic machining, water jet and abrasive water jet machining has drawn much interest and has been studied the feasibility of the processes (Komanduri et al., 1991). Among these non-conventional machining processes, abrasive water jet machining is the only method used in industry today for trimming fibre reinforced composite materials as laser machining suffers from the problem of a large heat-affected zone, while EDM suffers from extremely low cutting rates (Colligan et al., 1993).

In the AWJM process, the possibilities of environmental contamination due to fibrous materials are significantly reduced or eliminated since water jet washes away the eroded material from the surface of the workpiece (Ramulu and Arola, 1994).

There are numerous associated parameters and factors of AWJM process that can influence the surface quality of the AWJ machined surfaces (Hashish, 1991, König and Rummenhöller, 1993). However, in the present study only six were considered for analysis: one two-level factor and five three-level factors. By using a conventional experimental methodology or full factorial experiment, 486 distinct test conditions are needed to study all of the factors and their levels. Hence, it was neither economical nor practical to conduct a full-factorial experiment. It was therefore, suggested to apply design of experiment (DoE) using Taguchi's orthogonal array to reduce the number of experiments to a more practical and affordable size. Moreover, DoE based on Taguchi's orthogonal array is a powerful and robust design methodology. In the present study, the effect and optimization of control and noise factors in terms of surface roughness will be investigated using Taguchi method and ANOVA.

Section snippets

Material

In the present study, E-glass fibres namely woven (plain weave) TGF-800 was used as the reinforcement materials. The continuous glass filament has a diameter of 10 μm. The woven glass fibre strand has a width of 4 mm and the woven thickness is 0.3 mm from direct roving. The matrix used was thermosetting epoxy resin WM-215 TA which was mixed with thermosetting hardener WM-215 TB at a ratio of 4:1 as recommended by the manufacturer.

Sample fabrication

Fibreglass/epoxy laminates were prepared using hand lay-up process.

Analysis of variance

The effect of control factors were investigated through the analysis of variance (ANOVA). It is a computational technique conducted mainly to learn about the influence of various design factors and to observe the degree of sensitivity of the result to different factors affecting the quality characteristics (Fowlkes and Creveling, 1995). Table 2 shows the ANOVA and F-ratio values on machining performance of Ra. This analysis was carried out for a 95% confidence level. It was found that factors A

Conclusions

On the basis of experimental results, analysis of variance (ANOVA) and the effect of machining parameters on surface roughness and kerf taper ratio, the conclusions can be drawn for effective machining of glass/epoxy composite by AWJM process as follows:

  • (1)

    Hydraulic pressure (MPa) and type of abrasive materials (i.e. garnet and aluminium oxide) were considered as the most significant control factor in influencing Ra and TR, respectively.

  • (2)

    Due to hardness of aluminium oxide type of abrasive

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