Abrasive waterjet and wire electrical discharge machining of metal matrix composite

Soo, Lik (2023). Abrasive waterjet and wire electrical discharge machining of metal matrix composite. University of Birmingham. Ph.D.

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Abstract

Metal matrix composites (MMCs) are widely used in many applications such as aerospace and automotive industries for over the past few decades. However, the conventional machining of MMCs causes serious tool wear, poor surface integrity and dimensional deformity due to strain hardening. Three main phases of experimental work were conducted to evaluate the non-conventional machining: Abrasive Waterjet (AWJ) and Wire Electrical Discharge Machining (WEDM) methods on SiC particulate reinforced Al alloy AA2618 matrix composite. The first phase of the experiments focuses primarily on the optimisation of the selected process parameters. The key findings show that traverse rate and pulse-on time are the most important factor in AWJ and WEDM, respectively.
Following an extensive literature review, the effect of wettability based on the surface integrity was studied in Phase 2. The in-depth study of process parameters optimisation of AWJ and WEDM to achieve desirable surface integrity and chemistry has been proven useful in controlling the wettability of Al/SiCp metal matrix composite. Surface wetting properties were characterised by measuring the static contact angle and sessile droplet method was employed. The surface integrity varies significantly across the AWJ machined surfaces, the results show that the surface generated by AWJ are more hydrophobic compared to by WEDM. The wetting analysis demonstrates the Cassie-Baxter model that the surface roughness increases, contact angle increases due to air pockets entrapment. The anisotropic surface features generated by AWJ contribute to the complex behaviour of wetting property whereas the WEDM surfaces are more isotropic due to the consistency of material removal mechanism. The influence of material removal mechanisms by ploughing effect upon the workpiece subsurface characteristics were explored.
The state-of-the-art of proposed hybrid machining strategy in Phase 3 emphasised on the emerging approaches for generation of hydrophobic to superhydrophobic surface. Hydrophobic surface is crucial in the aerospace application of commonly used MMCs due to anti-icing. The research results revealed that the combination of AWJ rough cutting and dual pass WEDM polishing technique is able to create a close to superhydrophobic surface, with the advantages of time and cost saving as no anti-icing coating or tool adjustment is needed. This methodology is also capable of removing surface defects (striation and ploughing marks) and grits embedments generated by AWJ processes.
In conclusion, the comprehensive study of the AWJ and WEDM machining of this special purpose MMC will impact the future of aerospace industry and generate a research direction in the wettability study.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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