Importance of Feature Sequencing in Incremental Forming

Investigation of material deformation mechanism in double side incremental sheet forming

In incremental sheet forming (ISF), including single point incremental forming (SPIF) and double side incremental forming (DSIF), the material formability can be significantly enhanced when compared with conventional sheet forming processes. The material deformation in ISF is far more complicated because of the combined material deformation under stretching, bending, shearing, and cyclic loading, with an additional effect of compression in DSIF. Despite extensive investigation on material deformation during ISF, no theory has yet been widely agreed to explain different types of the material fracture behavior observed in ISF experiments. This paper presents a comprehensive review on the formability enhancement in ISF and proposes possible fracture mechanisms explaining the different types of fracture behavior observed in the experimental investigations. Discussions are presented to outline the current research progress and possible solutions to overcome the current ISF process limitations because of the material processing failure due to fracture.

Double Sided Incremental Forming (DSIF) is gaining importance over Single Point Incremental Forming (SPIF) due to its ability to form complex geometries and the capability to obtain better accuracies. In the present work, residual stresses are measured in pyramidal components formed using SPIF, DSIF using X-ray diffraction technique. Residual stress development mechanism during SPIF and DSIF is studied using Finite Element Analysis (FEA). Stress development along circumferential and meridional directions are explained using bending and unbending of sheet material taking place around forming tool. It is observed that the residual stresses are compressive on the outer surface and tensile on the inner surface of sheet in both circumferential and meridional directions. In DSIF, supporting tool restricts the unbending of sheet causing the residual stresses to be less compressive on the outer surface and less tensile on the inner surface compared to SPIF. It is also observed that with an increase in tool diameter, spring back increased, hence, meridional residual stress on the outer surface became more compressive and circumferential residual stress on the inner surface became more tensile. Residual stresses in ISF are compared with FEA predictions of conventional stamping process.

An analytical study of new material test method for tension under bending and compression in double side incremental forming

Nowadays, manufactured pieces can be divided into two groups: mass production and production of low volume number of parts. Within the second group (prototyping or small batch production), an emerging solution relies on Incremental Sheet Forming or ISF.ISF refers to processes where the plastic deformation occurs by repeated contact with a relatively small tool. More specifically, many publications over the past decade investigate Single Point Incremental Forming (SPIF) where the final shape is determined only by the tool movement. This manufacturing process is characterized by the forming of sheets by means of a CNC controlled generic tool stylus, with the sheets clamped by means of a non-workpiece-specific clamping system and in absence of a partial or a full die. The advantage is no tooling requirements and often enhanced formability, however it poses a challenge in term of process control and accuracy assurance. Note that the most commonly used materials in incremental forming are aluminum and steel alloys however other alloys are also used especially for medical industry applications, such as cobalt and chromium alloys, stainless steel and titanium alloys. Some scientists have applied incremental forming on PVC plates and other on sandwich panels composed of propylene with mild steel and aluminum metallic foams with aluminum sheet metal. Micro incremental forming of thin foils has also been developed.Starting from the scattering of the results of Finite Element (FE) simulations, when one tries to predict the tool force (see SPIF benchmark of 2014 Numisheet conference), we will see how SPIF and even micro SPIF (process applied on thin metallic sheet with a few grains within the thickness) allow investigating the material behavior. This lecture will focus on the identification of constitutive laws, on the SPIF forming mechanisms and formability as well as the failure mechanism. Different hypotheses have been proposed to explain SPIF formability, they will be listed however the lecture will be more focused on the use of SPIF to identify material parameters of well-chosen constitutive law. Results of FE simulations with damage models will be investigated to better understand the relation between the particular stress and strain states in the material during SPIF and the material degradation leading to localization or fracture.Last but not least, as industrial world does not wait that academic scientists provide a deep and total understanding on how it works, to use interesting processes, the lecture will review some applications. Examples in fields as different as automotive guard, engine heat shield, gas turbine, electronic sensor, shower basin, medical component (patient-fitted organic shapes) and architecture demonstrate that the integration of SPIF within the industry is more and more a reality.Note that this plenary lecture is the result of the research performed by the author in the University of Liege (Belgium) and in Aveiro (Portugal) with the team of R. de Souza during PhD theses of C. Henrard, J. Sena and C. Guzman and different research projects. It is also a synthesis of the knowledge gathered during her interactions with many research teams such as the ones of J.R. Duflou from KU Leuven in Belgium, J. Cao from Northwestern University in USA, M. Bambach in BTU Cottbus-Senftenberg in Germany, J. Jeswiet from Queen's University, Kingston, Canada who are currently working together on a state-of-the-art paper. The micro SPIF knowledge relies on contacts with S. Thibaud from the University of Franche Comte.

A toolpath strategy for improving geometric accuracy in double-sided incremental sheet forming

Incremental sheet-forming (ISF) processes have been developed rapidly in the past two decades. Its high flexibility and easy operability have a significant appeal for industrial applications, and substantial progress has been made in fundamental understanding and demonstration of practical implementation. However, there are a number of obstacles including achievable accuracy and instability in material deformation, which are considered as a main contributing factor for preventing the ISF process to be widely used in industry. As a variant of the general ISF process, double-sided incremental forming (DSIF) uses an additional supporting tool in the opposite side of the workpiece, maintains the flexibility, and at the same time improves the material deformation stability and reduces material thinning. In recent years, there has been increased research interest in looking into DSIF-specific material deformation mechanisms and investigation. This paper aims to provide a technical review of the DSIF process as benchmarked with single-point incremental forming (SPIF). It starts with a brief overview of the current state of the art of both SPIF and DSIF. This is followed by a comparative study between SPIF and DSIF with the key research challenges identified. This leads to a recommendation of future directions for DSIF focused research.

Investigating formability enhancement in double side incremental forming by developing a new test method of tension under cyclic bending and compression

Investigation of control of the incremental forming processes

Preliminary investigations on Double Sided Incremental Forming of thermoplastics

Incremental Sheet Metal Forming (ISMF) is a flexible sheet metal forming process that enables forming of complex three dimensional components by successive local deformations without using component specific tooling. ISMF is also regarded as die-less manufacturing process and in the absence of part-specific dies, geometric accuracy of formed components is inferior to that of their conventional counterparts. In Single Point Incremental Forming (SPIF), the simplest variant of ISMF, bending near component opening region is unavoidable due to lack of support. The bending in the component opening region can be reduced to a larger extent by another variant of ISMF namely Double Sided Incremental Forming (DSIF) in which a moving tool is used to support the sheet locally at the deformation zone. However the overall geometry of formed components still has unacceptable deviation from the desired geometry. Experimental observation and literature indicates that the supporting tool loses contact with the sheet after forming certain depth. Present work demonstrates a methodology to enhance geometric accuracy of formed components by compensating for tool and sheet deflection due to forming forces. Forming forces necessary to predict compensations are obtained using force equilibrium method along with thickness calculation methodology developed using overlap that occurs during forming (instead of using sine law). Results indicate that there is significant improvement in accuracy of the components produced using compensated tool paths.

Incremental sheet forming (ISF) has demonstrated significant potential to form complex three-dimensional parts without using component-specific tools and is suitable for economically fabricating low-volume functional sheet metal parts. Single-point incremental forming (SPIF) uses only one tool to form components and requires additional setup to form complex geometries. Double-sided incremental forming (DSIF), using two tools (one on either side of the sheet), can form features from top and bottom of sheet in single setup. While forming components with multiple features, the accuracy of component depends on the tool path strategy used for each feature and sequence in which features are formed. Methodologies are developed to recognise features from free-form components modeled using single and/or multiple surfaces. Recognised features are sliced using horizontal, inclined or offset strategies (developed during the present work) based on the geometrical characteristics of a given feature. Selection of best-forming sequence is automated based on the relation between features and process mechanics. Results presented in this paper show that complex free-form geometries can be formed with good accuracy using proposed methodologies. Maximum deviation between the measured and ideal profiles is less than 400 μm, while using right sequence and appropriate tool path strategy.

Forming accuracy improvement by double-side incremental forming

Incremental sheet forming (ISF) is a flexible sheet metal forming process that enables forming of complex three-dimensional components by successive local deformations without using component-specific tooling. ISF is also regarded as a die-less manufacturing process in the absence of part-specific die. Geometric accuracy of formed components is inferior to that of their conventional counterparts. In single-point incremental forming (SPIF), the simplest variant of ISF, bending near component opening region is unavoidable due to lack of support. The bending in the component opening region can be reduced to a larger extent by another variant of ISF, namely, double-sided incremental forming (DSIF) in which a moving tool is used to support the sheet locally at the deformation zone. However, the overall geometry of formed components still has unacceptable deviation from the desired geometry. Experimental observation and literature indicate that the supporting tool loses contact with the sheet after forming certain depth. This work demonstrates a methodology to enhance geometric accuracy of formed components by compensating for tool and sheet deflections due to forming forces. Forming forces necessary to predict compensations are obtained using force equilibrium method along with thickness calculation methodology developed using overlap of deformation zone that occurs during forming (instead of using sine law). A number of examples are presented to show that the proposed methodology works for a variety of geometries (axisymmetric, varying wall angle, free-forms, features above and below initial sheet plane, and multiple features). Results indicate that there is significant improvement in accuracy of the components produced using compensated tool paths using DSIF, and support tool maintains contact with sheet throughout the forming process.

Although the Incremental Sheet Forming (ISF) technology has been studied and applied from the last decade of the previous century with more than 30 years of experiences and ameliorations of the researchers of this field, but the ability of deformation of the formed material sheet still has remained in a restrictive modest value. This sheet forming technology could be divided into 2 mains branches: Single Point Incremental Forming (SPIF) and Two Point Incremental Forming (TPIF) wherein the first one is usually applying in research and the second branch is used in production. The ISF is suitable for forming sheet for a single product or for small batch production with a great advantage of a no-need pestle and mold manufacture in advance, but the formability of formed sheet material cannot bigger than a limited formed angle of about 80o that depends on the material and the forming parameters. There are some ameliorations for increasing the formability of the formed sheet such as heating the formed sheet in Hot SPIF or Multistage SPIF (MSPIF)… All the effort and amelioration measures are confronted with different difficulties. In this paper, we concentrate to study on the MSPIF technology on stainless steel SUS304 by simulation method with the proof of experimental method. The results were also compared to the simple SPIF to show its own pros and cons on the related field such as the technology, the productivity and the lubrication.