Maciej Mazur

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.

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.

Mechanical properties of Ti6Al4V and AlSi12Mg lattice structures manufactured by selective laser melting (SLM)

Emerging additive manufacturing (AM) techniques such as selective laser melting (SLM) present an exceptional opportunity for the manufacture of lattice structures which exhibit attractive mechanical properties beyond the capabilities of solid materials. However, to apply SLM-manufactured lattices as structural elements, it is necessary to quantify their manufacturability as well as key mechanical properties, such as compressive strength and stiffness, under varying material, geometric and loading conditions. This work reports on the experimental investigation of the SLM manufacturability and mechanical properties of titanium (Ti6Al4V) and aluminium (AlSi12Mg) alloy lattice structures; the materials were selected because of their inherently high specific strength (pursuant to lattice structure design opportunities) and compatibility with SLM. A range of lattice structures are manufactured and experimentally assessed for compressive strength and stiffness, with varying materials, cell topology, cell size, number of unit cells and associated boundary conditions. The mechanical properties as well as deformation and failure characteristics are analyzed and compared with theoretically predicted behaviour.

Application of Polynomial Chaos Expansion to Tolerance Analysis and Synthesis in Compliant Assemblies Subject to Loading

Statistical tolerance analysis and synthesis in assemblies subject to loading are of significant importance to optimized manufacturing. Modeling the effects of loads on mechanical assemblies in tolerance analysis typically requires the use of numerical CAE simulations. The associated uncertainty quantification (UQ) methods used for estimating yield in tolerance analysis must subsequently accommodate implicit response functions, and techniques such as Monte Carlo (MC) sampling are typically applied due to their robustness; however, these methods are computationally expensive. A variety of UQ methods have been proposed with potentially higher efficiency than MC methods. These offer the potential to make tolerance analysis and synthesis of assemblies under loading practically feasible. This work reports on the practical application of polynomial chaos expansion (PCE) for UQ in tolerance analysis. A process integration and design optimization (PIDO) tool based, computer aided tolerancing (CAT) platform is developed for multi-objective, tolerance synthesis in assemblies subject to loading. The process integration, design of experiments (DOE), and statistical data analysis capabilities of PIDO tools are combined with highly efficient UQ methods for optimization of tolerances to maximize assembly yield while minimizing cost. A practical case study is presented which demonstrates that the application of PCE based UQ to tolerance analysis can significantly reduce computation time while accurately estimating yield of compliant assemblies subject to loading.

Numerical methods to predict overheating in SLM lattice structures

Additive manufacture provides significant design flexibility in comparison with traditional manufacturing methods. For example, Selective Laser Melting (SLM) is capable of producing highly complex lattice structures that are not otherwise manufacturable. Such lattice structures enable structural optimisation at a macro level, while reducing associated manufacture time by reducing the component volume. Structural lattices provide a significant commercial opportunity for SLM processing. However, to ensure robust manufacturing outcomes, it is necessary that specific technical constraints be satisfied. In particular, lattice structures typically have high resistance to heat transfer, and consequently may be subject to overheating. Gross overheating may result in visible damage to the lattice network, and rejection of the component. More critical is the possibility for overheating that causes microstructural and fusion defects that are not visually apparent, but will compromise performance and safety in-use. This work provides a useful contribution the available literature by presenting a numerical simulation method to predict overheating in SLM structures. This method can be used prior to manufacture to minimise the risk of overheating and to provide design guidance on how to modify proposed geometry to avoid overheating. The method is calibrated with reference to observed overheating failures in SLM lattice manufactured in aluminium. Computational expense is important to enable the method to be compatible with the early design phase. Opportunities to reduce computational expense are discussed, including symmetry, layer heating simplification and layer concatenation. While all these simplifications reduce the computational expense they are shown to provide simulation data that correctly indicates gross failure of aluminium lattice structures due to overheating.Additive manufacture provides significant design flexibility in comparison with traditional manufacturing methods. For example, Selective Laser Melting (SLM) is capable of producing highly complex lattice structures that are not otherwise manufacturable. Such lattice structures enable structural optimisation at a macro level, while reducing associated manufacture time by reducing the component volume. Structural lattices provide a significant commercial opportunity for SLM processing. However, to ensure robust manufacturing outcomes, it is necessary that specific technical constraints be satisfied. In particular, lattice structures typically have high resistance to heat transfer, and consequently may be subject to overheating. Gross overheating may result in visible damage to the lattice network, and rejection of the component. More critical is the possibility for overheating that causes microstructural and fusion defects that are not visually apparent, but will compromise performance and safety in-use. T...

Optimisation of Automotive Seat Kinematics

Automotive seating structures have evolved over an extended period of development, resulting in convergence of practical embodiments to a planar kinematic chain, typically based on a four-bar linkage. Seating structures are subject to a stringent set of constraints and objectives, including: allowable envelope of motion, structural integrity, modularity and product cost. Although four-bar linkage kinematics is well understood, the large design space, combined with multiple constraints and objectives, impose significant challenges to design optimisation. The following work illustrates a practical method to resolve these conflicting design requirements by mapping the feasible design space and quantifying the relative merit of feasible designs for various objectives.