Martin Leary

Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: A review

One of the critical issues in orthopaedic regenerative medicine is the design of bone scaffolds and implants that replicate the biomechanical properties of the host bones. Porous metals have found themselves to be suitable candidates for repairing or replacing the damaged bones since their stiffness and porosity can be adjusted on demands. Another advantage of porous metals lies in their open space for the in-growth of bone tissue, hence accelerating the osseointegration process. The fabrication of porous metals has been extensively explored over decades, however only limited controls over the internal architecture can be achieved by the conventional processes. Recent advances in additive manufacturing have provided unprecedented opportunities for producing complex structures to meet the increasing demands for implants with customized mechanical performance. At the same time, topology optimization techniques have been developed to enable the internal architecture of porous metals to be designed to achieve specified mechanical properties at will. Thus implants designed via the topology optimization approach and produced by additive manufacturing are of great interest. This paper reviews the state-of-the-art of topological design and manufacturing processes of various types of porous metals, in particular for titanium alloys, biodegradable metals and shape memory alloys. This review also identifies the limitations of current techniques and addresses the directions for future investigations.

High-Value SLM Aerospace Components: From Design to Manufacture

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.

The Effect of Manufacturing Defects on the Fatigue Behaviour of Ti-6Al-4V Specimens Fabricated Using Selective Laser Melting

Additive Manufacturing (AM) technologies are considered revolutionary because they could fundamentally change the way products are designed. Selective Laser Melting (SLM) is a metal based AM process with significant and growing potential for the manufacture of aerospace components. Traditionally a material needs to be listed in the Metallic Materials Properties Development and Standardization (MMPDS) handbook if it is to be considered certified. However, this requires a considerable amount of test data to be generated on the materials mechanical properties. Therefore, the MMPDS certification process does not lend itself easily to the certification of AM components as the final component can have similar mechanical properties to wrought alloys combined with the defects associated with traditional casting and welding technologies. These defects can substantially decrease the fatigue life of a fabricated component. The primary purpose of this investigation was to study the fatigue behaviour of as-built Ti-6Al-4V (Ti64) samples. Fatigue tests were performed on the Ti-6Al-4V specimens built using SLM with a variety of layer thicknesses and build (vertical or horizontal) directions. Fractography revealed the presence of a range of manufacturing defects located at or near the surface of the specimens. The experimental results indicated that Lack-of-Fusion (LOF) defects were primarily responsible for fatigue crack initiation. The reduction in fatigue life appeared to be affected by the location, size and shape of the LOF defect.

Feasible Build Orientations for Self-Supporting Fused Deposition Manufacture: A Novel Approach to Space-Filling Tesselated Geometries

Support material is often utilised in additive manufacture to enable geometries that are not otherwise self-supporting. Despite the associated opportunities for innovation, the use of support material also introduces a series of limitations: additional material cost, cost of removal of support material, potential contamination of biocompatible materials, and entrapment of support material within cellular structures. This work presents a strategy for minimising the use of support material by comparing the geometric limits of an additive manufacture process to the build angles that exist within a proposed geometry. This method generates a feasibility map of the feasible build orientations for a proposed geometry with a given process. The method is applied to polyhedra that are suitable for close packing to identify space-filling tessellated structures that can be self-supporting. The integrity of an FDM process is quantified, and using the associated feasibility map, self-supporting polyhedra are manufactured. These polyhedra are integrated with non-trivial geometries to achieve a reduction in consumed material of approximately 50%. Nomenclature

Enhancing the Quality Function Deployment Conceptual Design Tool

The quality function deployment (QFD) conceptual design tool has been of significant benefit to customer satisfaction, while reducing the associated design time and cost. Observation of novice designers in tertiary engineering design courses identified a range of impediments to the robust transfer of QFD capabilities to the novice designers. These impediments appear to limit the perceived merit of QFD in novice designers and stymie its subsequent practical application. Given the improved design outcomes associated with QFD, a series of enhancements has been developed to overcome these impediments and assist the robust transfer of QFD capabilities to novice designers. The traditional QFD tool does not engage with customer requirements that constrain the feasibility of a design solution. This limitation restricts the applicability of QFD as an overarching design reference because an additional repository is required to document design constraints and may result in confusion in novice designers and flawed design outcomes if design constraints are used. A novel differential assessment method has been developed to overcome this limitation by enabling the inclusion of design constraints. The outcomes of this paper contribute to design education by facilitating the robust transfer of QFD capabilities and providing novel enhancements that expand the useful outcomes associated with QFD.

SLM additive manufacture of H13 tool steel with conformal cooling and structural lattices

Purpose Additive manufacture (AM) such as selective laser melting (SLM) provides significant geometric design freedom in comparison with traditional manufacturing methods. Such freedom enables the construction of injection moulding tools with conformal cooling channels that optimize heat transfer while incorporating efficient internal lattice structures that can ground loads and provide thermal insulation. Despite the opportunities enabled by AM, there remain a number of design and processing uncertainties associated with the application of SLM to injection mould tool manufacture, in particular from H13/DIN 1.2344 steel as commonly used in injection moulds. This paper aims to address several associated uncertainties. Design/methodology/approach A number of physical and numerical experimental studies are conducted to quantify SLM-manufactured H13 material properties, part manufacturability and part characteristics. Findings Findings are presented which quantify the effect of SLM processing parameters on the density of H13 steel components; the manufacturability of standard and self-supporting conformal cooling channels, as well as structural lattices in H13; the surface roughness of SLM-manufactured cooling channels; the effect of cooling channel layout on the associated stress concentration factor and cooling uniformity; and the structural and thermal insulating properties of a number of structural lattices. Originality/value The contributions of this work with regards to SLM manufacture of H13 of injection mould tooling can be applied in the design of conformal cooling channels and lattice structures for increased thermal performance.

Computer Aided Tolerancing (CAT) platform for the design of assemblies under external and internal forces

Due to the stochastic nature of manufacturing processes, the functionality of mechanical assemblies is subject to variation defined by tolerances and manufacturing process characteristics. In many assemblies, functionality is also dependent on external and internal forces. Numerous Computer Aided Tolerancing (CAT) tools have been proposed that address tolerance analysis problems in complex mechanical assemblies; however current tools do not accommodate a general class of problem where the functionality of a design is fundamentally dependent on the effects of external and internal forces. This research addresses the limitation of CAT tools to accommodate assemblies under loading by developing a tolerance analysis platform which integrates CAD, CAE and statistical analysis tools using Process Integration and Design Optimisation (PIDO) software capabilities. The platform extends the capabilities of traditional CAT tools by enabling tolerance analysis of assemblies in which assembly characteristics are dependent on external and internal forces. To demonstrate the capabilities of the developed platform, examples of tolerance analysis problems involving external forces (compliance) and internal forces (multi-body dynamics) are presented.

Comparative Life Cycle Assessment (LCA) of passenger seats and their impact on different vehicle models

The main purpose of Life Cycle Assessment (LCA) to date has been to evaluate life cycle impacts of different design solutions and materials for a car, its sub-systems and components. Considerable number of publications are available on LCA of automotive components. This research aims to extend the LCA approach by evaluating and comparing the effects of mass reduction of passenger seats for different vehicle models in order to provide strategic support for decision making in the development process and to validate the environmental benefits of design alternatives under investigation. For this purpose, the paper presents a comprehensive LCA of passenger seats with detailed consideration of alternative scenarios for the use phase for different vehicle models.

A fundamental model of quasi-static wheelchair biomechanics

The performance of a wheelchair system is a function of user anatomy, including arm segment lengths and muscle parameters, and wheelchair geometry, in particular, seat position relative to the wheel hub. To quantify performance, researchers have proposed a number of predictive models. In particular, the model proposed by Richter is extremely useful for providing initial analysis as it is simple to apply and provides insight into the peak and transient joint torques required to achieve a given angular velocity. The work presented in this paper identifies and corrects a critical error; specifically that the Richter model incorrectly predicts that shoulder torque is due to an anteflexing muscle moment. This identified error was confirmed analytically, graphically and numerically. The authors have developed a corrected, fundamental model which identifies that the shoulder anteflexes only in the first half of the push phase and retroflexes in the second half. The fundamental model has been extended by the authors to obtain novel data on joint and net power as a function of push progress. These outcomes indicate that shoulder power is positive in the first half of the push phase (concentrically contracting anteflexors) and negative in the second half (eccentrically contracting retroflexors). As the eccentric contraction introduces adverse negative power, these considerations are essential when optimising wheelchair design in terms of the users musculoskeletal system. The proposed fundamental model was applied to assess the effect of vertical seat position on joint torques and power. Increasing the seat height increases the peak positive (concentric) shoulder and elbow torques while reducing the associated (eccentric) peak negative torque. Furthermore, the transition from positive to negative shoulder torque (as well as from positive to negative power) occurs later in the push phase with increasing seat height. These outcomes will aid in the optimisation of manual wheelchair propulsion biomechanics by minimising adverse negative muscle power, and allow joint torques to be manipulated as required to minimise injury or aid in rehabilitation.

Designing shape memory alloy linear actuators: A review:

In numerous studies, it was emphasised that only a few of patented shape memory alloy applications are commercially successful due to material limitations combined with a lack of material and design knowledge and associated tools. This work further emphasises that these limitations may be improved or even resolved with proper design approaches and techniques; thus, the functionality and the reliability of shape memory alloy actuators could be realised and optimised. A brief review of the recent progress and development in optimising shape memory alloy linear actuator with different design methods, techniques and/or approaches are presented and discussed in this review.