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Research Papers

Mask-Less Pocket Milling of Composites by Abrasive Waterjets: An Experimental Investigation

[+] Author and Article Information
D. S. Srinivasu

Senior Researcher
Department of Mechanical, Materials and
Manufacturing Engineering,
University Park, University of Nottingham,
Nottingham NG7 2RD, UK
e-mail: dsivasrinivas@gmail.com

D. A. Axinte

Professor
Department of Mechanical,
Materials and Manufacturing Engineering,
Coates Building, Room A63,
University Park,
University of Nottingham,
Nottingham NG7 2RD, UK
e-mail: dragos.axinte@nottingham.ac.uk

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received April 3, 2013; final manuscript received March 10, 2014; published online May 21, 2014. Editor: Y. Lawrence Yao.

J. Manuf. Sci. Eng 136(4), 041005 (May 21, 2014) (13 pages) Paper No: MANU-13-1144; doi: 10.1115/1.4027181 History: Received April 03, 2013; Revised March 10, 2014

Milling pockets in advanced engineering composite materials (AECMs) by conventional methods is difficult due to machinability issues, such as heterogeneous constituents, softening of heat sensitive resin matrix, delamination, fiber pull-out, carcinogenic gases, and dust. On the other hand, waterjet (WJ) machining, among the unconventional approaches, is well known for machining a wide range of AECMs due to its unique features, exertion of low cutting force, low heat generation, no dangerous fume development and low airborne dust. However, from the preliminary studies, it was found that the conventional pocket milling tool path strategies existing in standard computer aided design (CAD) packages cannot be employed directly in milling AECMs with the WJs due to various reasons, such as less strength of composite materials in the transverse direction to the fiber orientation, and aggressive nature of high energy WJs. To address these issues, a novel jet path strategy for mask-less milling of pockets was proposed. This approach takes into account the nature of the highly aggressive fluidjets, the physical structure of the AECMs, and the limitations of the existing hardware controllers, which are not specifically designed for jet machining, while manoeuvring the jet over the surface to avoid undesired excessive erosion and contributes to the elimination of sacrificial masks. The proposed strategy is demonstrated by pocket milling of difficult to machine AECMs (glass and carbon fiber) by the WJ and abrasive waterjets (AWJ) along with geometric analysis on the pockets. The influence of various process parameters, such as water pressure, jet traverse rate, standoff distance (SOD), number of passes, on the milled surfaces was studied. Furthermore, the damage at various regions of the pocket was analyzed by scanning electron microscopy, to find out the causes of surface damages and re-cast of resin layer to address the damage was suggested. The effect of consideration of composite material's physical structure while milling was successfully demonstrated by generating pockets with minimum damage to the reinforcing fibers and delamination. A selection procedure between AWJs and WJs was proposed depending on the scaling of the targeted milling depth and precision required. Finally, modifications to the machine tool hardware controllers are suggested for efficient milling of AECMs.

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Figures

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Fig. 1

High energy jet path strategy for pocket milling in advanced engineering composite materials

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Fig. 2

Photograph of the abrasive waterjet setup for milling pockets in composite materials

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Fig. 3

Pocket milled in carbon-glass fiber composite material (Cytec 977-2 Toray HTS – 12K CF GF7781) materials: (a) photograph of the pocket and (b) geometrical characteristics

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Fig. 4

Schematic illustration of the wall slope formation in pocket milling: (a) characteristics and behavior of the jet, (b) photograph of the cross section of the milled pocket with jet deflection representation and (c) gradual evolution of the increased wall slope by secondary jet

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Fig. 5

Milling strategy for removing material in perpendicular direction to the fiber orientation of glass-carbon fiber composite (Cytec 977-2 Toray HTS – 12K CF GF7781) material

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Fig. 6

Cross section of the pocket milled in glass fiber composite (MTM 56FRNY/GF1100/32%-34plies @ 0 deg) material for damage analysis at various regions of milled surface

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Fig. 7

Influence of various waterjet process parameters on quality of the milled pocket on glass-carbon fiber composite (Cytec 977-2 Toray HTS – 12K CF GF7781) material

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Fig. 8

Influence of change in various waterjet process parameters on fiber damage of glass-carbon fiber composite (Cytec 977-2 Toray HTS – 12K CF GF7781) material

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Fig. 9

Pocket milled in glass fiber composite material (MTM 56FRNY/GF1100/32% - 34plies @ 0 deg) material: (a) photograph of the pocket and (b) geometrical characteristics

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Fig. 10

Pocket milled in carbon fiber composite material (MTM 56B/CF0700/40% - 15 plies @ 0 deg) material: (a) photograph of the pocket and (b) geometrical characteristics

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