12 research outputs found
Characterization of shape and dimensional accuracy of incrementally formed titanium sheet parts with intermediate curvatures between two feature types
Single point incremental forming (SPIF) is a relatively new manufacturing process that has been recently used to form medical grade titanium sheets for implant devices. However, one limitation of the SPIF process may be characterized by dimensional inaccuracies of the final part as compared with the original designed part model. Elimination of these inaccuracies is critical to forming medical implants to meet required tolerances. Prior work on accuracy characterization has shown that feature behavior is important in predicting accuracy. In this study, a set of basic geometric shapes consisting of ruled and freeform features were formed using SPIF to characterize the dimensional inaccuracies of grade 1 titanium sheet parts. Response surface functions using multivariate adaptive regression splines (MARS) are then generated to model the deviations at individual vertices of the STL model of the part as a function of geometric shape parameters such as curvature, depth, distance to feature borders, wall angle, etc. The generated response functions are further used to predict dimensional deviations in a specific clinical implant case where the curvatures in the part lie between that of ruled features and freeform features. It is shown that a mixed-MARS response surface model using a weighted average of the ruled and freeform surface models can be used for such a case to improve the mean prediction accuracy within ±0.5 mm. The predicted deviations show a reasonable match with the actual formed shape for the implant case and are used to generate optimized tool paths for minimized shape and dimensional inaccuracy. Further, an implant part is then made using the accuracy characterization functions for improved accuracy. The results show an improvement in shape and dimensional accuracy of incrementally formed titanium medical implants
Tool path generation for single point incremental forming using intelligent sequencing and multi-step mesh morphing techniques
A new methodology of generating optimized tool paths for incremental sheet forming is proposed in this work. The objective is to make parts with improved accuracy. To enable this, a systematic, automated technique of creating intermediate shapes using a morph mapping strategy is developed. This strategy is based on starting with a shape different from the final shape, available as a triangulated STL model, and using step-wise incremental deformation to the original mesh to arrive at the final part shape. Further, optimized tool path generation requires intelligent sequencing of partial tool paths that may be applied specifically to certain features on the part. The sequencing procedure is discussed next and case studies showing the application of the integrated technique are illustrated. The accuracy of the formed parts significantly improves using this integrated technique. The maximum deviations are brought down to less than 1 mm, while average absolute deviations of less than 0.5 mm are recorded
Single point incremental forming: An assessment of the progress and technology trends from 2005 to 2015
The last decade has seen considerable interest in flexible forming processes. Among the upcoming flexible forming techniques, one that has captured a lot of interest is single point incremental forming (SPIF), where a flat sheet is incrementally deformed into a desired shape by the action of a tool that follows a defined toolpath conforming to the final part geometry. Research on SPIF in the last ten years has focused on defining the limits of this process, understanding the deformation mechanics and material behaviour and extending the process limits using various strategies. This paper captures the developments that have taken place over the last decade in academia and industry to highlight the current state of the art in this field. The use of different hardware platforms, forming mechanics, failure mechanism, estimation of forces, use of toolpath and tooling strategies, development of process planning tools, simulation of the process, aspects of sustainable manufacture and current and future applications are individually tracked to outline the current state of this process and provide a roadmap for future work on this process
Overcoming challenges of prototyping with single point incremental forming through formability and geometric accuracy analysis
With recent developments in rapid prototyping technologies, the
automotive industry has been able to move away from costly and
inefficient methods of prototyping. In fact, rapid prototyping
techniques now exist for nearly all the components in a car,
meaning time and money is saved in product development. One
exception to this trend, despite their ubiquity in automotive
applications, is formed sheet metal components.
Single point incremental forming (SPIF) is a sheet metal forming
technique with a fast turnaround that uses little to no custom
tooling.
It is a promising method for filling the gap in rapid prototyping
capability for sheet metal components.
However, despite significant research over the last two decades,
barriers to industrial viability still include the key issues of
fracture occurring in the sheet metal, or a final part being
rejected due to unacceptable dimensional error. These two issues
are affected by SPIF process parameters, but the extent of their
influences are not well understood.
By investigating the effect of process parameters on material
formability and geometric accuracy, this thesis seeks to address
these issues.
Case studies emphasise the impact of formability and geometric
accuracy on prototyping automotive components with SPIF.
Also emphasised is the importance of effective support walls and
optimal design of the forming surface that is used to generate
toolpaths for forming components.
A systematic review of the literature regarding the first key
issue, formability in SPIF, highlights significant
inconsistencies in published research about the effects of
process parameters. A hypothesis to explain this result presents
the idea of non-linear effects and parameter interactions, which
is supported by original experimental work. This shows the
difficulty of empirical prediction of formability when, for
example, a small change in one parameter may interact with
another to significantly influence the outcome of the final
part.
Identifying and following safe formability limits will minimise
the likelihood of fracture for the forming surface of a
component. Research in this thesis looks at the thickness
distribution of variable wall angle conical frustum (VWACF) parts
as a basis for defining a safe formability limit. However,
experimental results show this is not viable due to irregular
trends in the thickness distribution close to the fracture point
of the VWACF.
The second key issue of geometric error in SPIF is approached by
focusing on a single mode of error, namely `wall bulge', or
springback in flat walls of components. Experiments studied how
a variety of tool shapes and sizes affected its severity, and
found a trade-off with `pillowing', another mode of geometric
error. At the same time as flat-ended tools reduce pillowing in
the base, the experimental results show an increase in the amount
of bulging in the walls.
The findings of this thesis demonstrate the impact that a single
parameter change can have on multiple aspects of a component.
Also highlighted are the complexities of the SPIF process that
remain as barriers to industrial viability. This work contributes
to overcoming these barriers and achieving efficient rapid
prototyping of sheet metal components
Heat-assisted incremental sheet forming of TI-6AL-4V sheets
Single point incremental forming (SPIF) is a sheet forming technique that deforms sheet materials incrementally to a designated shape. The process has shown high ability to deform low-strength materials for good geometrical accuracy and formability at room temperature. Deforming high-temperature alloys, such as Ti-6AI-4V, requires integrated heat sources to increase the ductility of the metal sheets for deformation. However, the integration of heating results in unpredictable thermomechanical behaviours on the formability, geometric accuracy, thickness distribution and surface quality. Considerable research efforts have been in developing in different heating methods and designing novel tools and analytical modelling to resolve the limitations. The current challenge remains to improve the localised and stable heating and functional tool design to reduce the thermal expansion and friction at the tool-surface contact area and the analysis of relationship between thermal and mechanical effects. This PhD research aims to develop and improve the induction heating-assisted SPIF system for Ti-6AI-4V sheets in tool design, lubrication, tool path optimisation and numerical analysis. Total four research methods include the study of microstructural and mechanical properties for low temperature (600 ℃ and 700 ℃) deformation using Zener-Hollomon parameter (Z-parameter). A novel tool design with water-cooling lubricant system to assist lubricant service. A combination of crystal plasticity finite element simulation method (CPFEM), representative volume element (RVE) and cellular automata (CA) to predict the grain orientation, crystal texture and grain size evolution in experimental scale and microstructure. A radial basis function (RBF) artificial neural network to optimise the tool path for improvements of geometric accuracy and surface quality above beta-transus (950 ℃) temperature
Heat-assisted incremental sheet forming of TI-6AL-4V sheets
Single point incremental forming (SPIF) is a sheet forming technique that deforms sheet materials incrementally to a designated shape. The process has shown high ability to deform low-strength materials for good geometrical accuracy and formability at room temperature. Deforming high-temperature alloys, such as Ti-6AI-4V, requires integrated heat sources to increase the ductility of the metal sheets for deformation. However, the integration of heating results in unpredictable thermomechanical behaviours on the formability, geometric accuracy, thickness distribution and surface quality. Considerable research efforts have been in developing in different heating methods and designing novel tools and analytical modelling to resolve the limitations. The current challenge remains to improve the localised and stable heating and functional tool design to reduce the thermal expansion and friction at the tool-surface contact area and the analysis of relationship between thermal and mechanical effects. This PhD research aims to develop and improve the induction heating-assisted SPIF system for Ti-6AI-4V sheets in tool design, lubrication, tool path optimisation and numerical analysis. Total four research methods include the study of microstructural and mechanical properties for low temperature (600 ℃ and 700 ℃) deformation using Zener-Hollomon parameter (Z-parameter). A novel tool design with water-cooling lubricant system to assist lubricant service. A combination of crystal plasticity finite element simulation method (CPFEM), representative volume element (RVE) and cellular automata (CA) to predict the grain orientation, crystal texture and grain size evolution in experimental scale and microstructure. A radial basis function (RBF) artificial neural network to optimise the tool path for improvements of geometric accuracy and surface quality above beta-transus (950 ℃) temperature
Numerical and experimental studies of asymmetrical Single Point Incremental Forming process
The framework of the present work supports the numerical analysis of the Single Point Incremental Forming (SPIF) process resorting to a numerical tool based on adaptive remeshing procedure based on the FEM. Mainly, this analysis concerns the computation time reduction from the implicit scheme and the adaptation of a solid-shell finite element type chosen, in particular the Reduced Enhanced Solid Shell (RESS). The main focus of its choice was given to the element formulation due to its distinct feature based on arbitrary number of integration points through the thickness direction. As well as the use of only one Enhanced Assumed Strain (EAS) mode. Additionally, the advantages include the use of full constitutive laws and automatic consideration of double-sided contact, once it contains eighth physical nodes.
Initially, a comprehensive literature review of the Incremental Sheet Forming (ISF) processes was performed. This review is focused on original contributions regarding recent developments, explanations for the increased formability and on the state of the art in finite elements simulations of SPIF. Following, a description of the numerical formulation behind the numerical tools used throughout this research is presented, summarizing non-linear mechanics topics related with finite element in-house code named LAGAMINE, the elements formulation and constitutive laws. The main purpose of the present work is given to the application of an adaptive remeshing method combined with a solid-shell finite element type in order to improve the computational efficiency using the implicit scheme. The adaptive remeshing strategy is based on the dynamic refinement of the mesh locally in the tool vicinity and following its motion. This request is needed due to the necessity of very refined meshes to simulate accurately the SPIF simulations. An initially mesh refinement solution requires huge computation time and coarse mesh leads to an inconsistent results due to contact issues. Doing so, the adaptive remeshing avoids the initially refinement and subsequently the CPU time can be reduced.
The numerical tests carried out are based on benchmark proposals and experiments purposely performed in University of Aveiro, Department of Mechanical engineering, resorting to an innovative prototype SPIF machine. As well, all simulations performed were validated resorting to experimental measurements in order to assess the level of accuracy between the numerical prediction and the experimental measurements. In general, the accuracy and computational efficiency of the results are achieved
Metodologia avançada para simulação de processos de estampagem incremental
Doutoramento em Engenharia MecânicaThe framework of the present work supports the numerical analysis of the
Single Point Incremental Forming (SPIF) process resorting to a numerical tool
based on adaptive remeshing procedure based on the FEM. Mainly, this
analysis concerns the computation time reduction from the implicit scheme and
the adaptation of a solid-shell finite element type chosen, in particular the
Reduced Enhanced Solid Shell (RESS). The main focus of its choice was given
to the element formulation due to its distinct feature based on arbitrary number
of integration points through the thickness direction. As well as the use of only
one Enhanced Assumed Strain (EAS) mode. Additionally, the advantages
include the use of full constitutive laws and automatic consideration of doublesided
contact, once it contains eighth physical nodes.
Initially, a comprehensive literature review of the Incremental Sheet Forming
(ISF) processes was performed. This review is focused on original contributions
regarding recent developments, explanations for the increased formability and
on the state of the art in finite elements simulations of SPIF. Following, a
description of the numerical formulation behind the numerical tools used
throughout this research is presented, summarizing non-linear mechanics
topics related with finite element in-house code named LAGAMINE, the
elements formulation and constitutive laws.
The main purpose of the present work is given to the application of an adaptive
remeshing method combined with a solid-shell finite element type in order to
improve the computational efficiency using the implicit scheme. The adaptive
remeshing strategy is based on the dynamic refinement of the mesh locally in
the tool vicinity and following its motion. This request is needed due to the
necessity of very refined meshes to simulate accurately the SPIF simulations.
An initially mesh refinement solution requires huge computation time and
coarse mesh leads to an inconsistent results due to contact issues. Doing so,
the adaptive remeshing avoids the initially refinement and subsequently the
CPU time can be reduced.
The numerical tests carried out are based on benchmark proposals and
experiments purposely performed in University of Aveiro, Department of
Mechanical engineering, resorting to an innovative prototype SPIF machine.
As well, all simulations performed were validated resorting to experimental
measurements in order to assess the level of accuracy between the numerical
prediction and the experimental measurements. In general, the accuracy and
computational efficiency of the results are achieved.O presente trabalho assenta na análise numérica do processo de Estampagem
Incremental por Único Ponto (SPIF) recorrendo ao refinamento adaptativo da
malha através do Método dos Elementos Finitos (FEM). Nomeadamente, a
atenção é dada à redução do tempo de cálculo baseado no esquema de
integração implícito em combinação com um elemento finito do tipo “sólidocasca”
predefinido. O principal motivo da escolha do tipo de elemento finito
deve-se à sua formulação possibilitar a atribuição de um número arbitrário de
pontos de integração na direção da espessura combinado com a utilização de
um único modo de deformação acrescentada e integração reduzida no plano.
Além disso, as vantagens incluem a utilização de leis constitutivas
tridimensionais, análise automática de contacto em dupla face e espessura,
uma vez que é um elemento hexaédrico de 8 nós.
Inicialmente, uma revisão da literatura relacionada com o processo de
estampagem incremental (ISF) é apresentada evidenciando as contribuições
recentemente desenvolvidas, explicações do aumento da formabilidade do
material em ISF e com maior ênfase o estado-de-arte das simulações
numéricas pelo FEM do processo SPIF. Seguidamente, é apresentado a
descrição dos conceitos teóricos que suportam e foram utilizados ao longo
desta pesquisa, resumindo tópicos de mecânica não-linear relacionada com o
código LAGAMINE, formulação de elementos finitos e leis constitutivas.
O principal objetivo do presente trabalho é a aplicação do método de
refinamento adaptativo combinado com um elemento finito sólido-casca, a fim
de melhorar a eficiência computacional usando o esquema de integração
implícito. A estratégia de refinamento adaptativo é baseada no refinamento
dinâmico da malha localmente na proximidade da ferramenta e acompanhando
o seu movimento. Este requisito é devido à necessidade de malhas muito
refinadas para simular com precisão as simulações SPIF. A malha inicialmente
refinada requer enorme tempo de cálculo e uma malha grosseira leva a
resultados inconsistentes devido a problemas de contato. Neste sentido, o
refinamento adaptativo evita o refinamento inicial total da malha e
consequentemente melhora a performance computacional da simulação.
Os testes numéricos realizados são baseados em casos estudo e em testes
experimentais realizados na Universidade de Aveiro, Departamento de
Engenharia Mecânica, recorrendo a uma máquina protótipo inovadora
construída propositadamente para SPIF. Todas as simulações realizadas são
validadas recorrendo às medições experimentais, de modo a avaliar o nível de
precisão entre a previsão numérica e as medições experimentais. Em geral, a
precisão e a eficiência computacional dos resultados são alcançados