Finite element prediction of deformation mechanics in incremental forming processes

This thesis presents new insights into gaps in the knowledge of conventional spinning and single point incremental forming (SPIF) processes through numerical modelling of their deformation mechanics. The deformation mechanics of conventional spinning is investigated by constructing finite element (FE) models of a cylindrical cup using both single and dual roller passes. A design of experiments (DOE) technique is used to generate an experimental plan based on all the relevant process parameters, followed by an analysis of variance (ANOVA) approach which is then used to determine the most critical parameters. The results indicated that the area in which most of the plastic deformation is taking place changes during the subsequent passes. The deformation mechanics of SPIF is investigated by constructing a novel dual-level finite element model of the forming of a truncated cone. The first-level FE model is validated against experimental data and the second level FE model is used to investigate the deformation modes through the sheet thickness. DOE and ANOVA techniques are used to investigate the influence of the different process parameters on the predicted through-thickness shear. Simple strategies are applied to reduce the geometrical errors without affecting the process flexibility. The results of the second-level FE model indicated that through-thickness shear is an important component in the deformation mechanism in SPIF.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Selective Laser Melting Fabrication of the Nickel Base Superalloy CMSX486: Optimisation of Process Parameters using Image Analysis and Statistical Methods

Purpose – The purpose of this paper is to optimise the selective laser melting (SLM) process parameters for CMSX486 to produce a “void free” (fully consolidated) material, whilst reducing the cracking density to a minimum providing the best possible fabricated material for further post-processing. SLM of high temperature nickel base superalloys has had limited success due to the susceptibly of the material to solidification and reheat cracking. Design/methodology/approach – Samples of CMSX486 were fabricated by SLM. Statistical design of experiments (DOE) using the response surface method was used to generate an experimental design and investigate the influence of the key process parameters (laser power, scan speed, scan spacing and island size). A stereological technique was used to quantify the internal defects within the material, providing two measured responses: cracking density and void per cent. Findings – The analysis of variance (ANOVA) was used to determine the most significant process parameters and showed that laser power, scan speed and the interaction between the two are significant parameters when considering the cracking density. Laser power, scan speed, scan spacing and the interaction between power and speed, and speed and spacing were the significant factors when considering void per cent. The optimum setting of the process parameters that lead to minimum cracking density and void per cent was obtained. It was shown that the nominal energy density can be used to identify a threshold for the elimination of large voids; however, it does not correlate well to the formation of cracks within the material. To validate the statistical approach, samples were produced using the predicted optimum parameters in an attempt to validate the response surface model. The model showed good prediction of the void per cent; however, the cracking results showed a greater deviation from the predicted value. Originality/value – This is the first ever study on SLM of CMSX486. The paper shows that provided that the process parameters are optimised, SLM has the potential to provide a low-cost route for the small batch production of high temperature aerospace components. </jats:sec

Porosity, cracks, and mechanical properties of additively manufactured tooling alloys:a review

Additive manufacturing (AM) technologies are currently employed for the manufacturing of completely functional parts and have gained the attention of high-technology industries such as the aerospace, automotive, and biomedical fields. This is mainly due to their advantages in terms of low material waste and high productivity, particularly owing to the flexibility in the geometries that can be generated. In the tooling industry, specifically the manufacturing of dies and molds, AM technologies enable the generation of complex shapes, internal cooling channels, the repair of damaged dies and molds, and an improved performance of dies and molds employing multiple AM materials. In the present paper, a review of AM processes and materials applied in the tooling industry for the generation of dies and molds is addressed. AM technologies used for tooling applications and the characteristics of the materials employed in this industry are first presented. In addition, the most relevant state-of-the-art approaches are analyzed with respect to the process parameters and microstructural and mechanical properties in the processing of high-performance tooling materials used in AM processes. Concretely, studies on the AM of ferrous (maraging steels and H13 steel alloy) and non-ferrous (stellite alloys and WC alloys) tooling alloys are also analyzed