Papers by Author: Qian Chu Liu

Abstract: Today additive manufacturing is shaping the future of global manufacturing and is influencing the design and manufacturability of tomorrows products. With selective laser melting (SLM), parts can be built directly from computer models or from measurements of existing components to be re-engineered, and therefore bypass traditional manufacturing processes such as cutting, milling and grinding. Benefits include: 1) new designs not possible using conventional subtractive technology, 2) dramatic savings in time, materials, wastage, energy and other costs in producing new components, 3) significant reductions in environmental impact, and 4) faster time to market. SLM builds up finished components from raw material powders layer by layer through laser melting. SLM removes many of the shape restrictions that limit design with traditional manufacturing methods, thereby allowing computationally optimised, high performance structures to be utilised. Functional engineering prototypes and actual components can then be built in their final shape with minimal material wastage. Samples and small product runs can be produced quickly at comparatively low cost to test and build market acceptance without major investment. In this chapter we present and discuss some of the concepts and findings involved in the design, manufacture and examination of high-value aerospace components from Ti-6Al-4V alloy produced at the RMITs Advanced Manufacturing Precinct.

Abstract: Maintenance of ageing military aircraft structures encompasses both engineering and scientific management. In support of this, surface modification and repair methods are used on an opportunity basis to extend the life of aircraft in terms of fatigue and safety. Often, certain surface modification technologies have proved to be both cost effective and amenable for safe application. Some candidate technologies include shot peening, cold spray, deep surface rolling, friction stir welding, laser shock peening, and laser cladding. Whilst some technologies have been successfully applied to Australian Defence Force (ADF) aircraft in the past, some newer technologies are also being considered. The supersonic particle deposition (SPD) technology also known as cold spray coating has been recently approved for application on a helicopter gear box. Another technology of significance to ADF application is Laser Cladding (LC) technology. This paper briefly summarises the research work on these technologies at DSTO and discusses potential applications for aircraft components in the near future. It also provides an analysis of technologies and their potential advantages and disadvantages.

Abstract: High-strength steels are used in several critical aerospace applications such as aircraft landing gear, primary structure and engine components. These steels, such as the AISI 4340 assessed here exhibit small critical crack sizes, and when they suffer in-service damage from impact or corrosion, repairing the damage is particularly challenging. One potential repair method is using laser assisted metal deposition (LAMD or ‘laser cladding’ LC), to rebuild the damaged region or the grinding depression remaining after the damage has been removed. The critical situations where these materials are used makes it essential that repairs do not introduce any degradation, such as microcracking, that could lead to failure in service. In this trial, 420 grade stainless steel cladding powder was used to produce a clad layer with both high strength and good corrosion resistance. The cladding was performed under various powder mass flow rates, traverse speeds, and laser powers. The clad thickness and the depth of the fusion zone varied, as expected, with all the cladding conditions. It was found that there was very little porosity, and importantly, no evidence of microcracking under any cladding condition. There were some small defects near the clad boundary, apparently associated with each clad pass. The absence of microcracking is a promising result, and the research will be continued to assess the effect of microstructure and defects on performance of the repaired plates.

Abstract: Laser shock peening (LSP) is an innovative surface treatment technique for metal alloys, with the great improvement of their fatigue, corrosion and wear resistance performance. Finite element method has been widely applied to simulate the LSP to provide the theoretically predictive assessment and optimally parametric design. In the current work, 3-D numerical modelling approaches, combining the explicit dynamic analysis, static equilibrium analysis algorithms and different plasticity models for the high strain rate exceeding 106s-1, are further developed. To verify the proposed methods, 3-D static and dynamic FEA of AA7075-T7351 rods subject to two-sided laser shock peening are performed using the FEA package–ABAQUS. The dynamic and residual stress fields, shock wave propagation and surface deformation of the treated metal from different material modelling approaches have a good agreement.