Incremental Sheet Forming Process Research Articles

A New Incremental Sheet Forming Process Based on Layer Manufacture

Sheet dieless digital forming is a new sheet metal dieless forming technology. This paper introduced the fundamentals of the Sheet dieless digital forming process. Based on the principle of “layered manufacture” in rapid prototype technology, this process resolves the intricate three-dimensional geometry information of the workpiece into a series of two-dimensional data, which can be used by an NC system to control a forming tool to make a curvilinear movement over the raw sheet metal layer by layer until the component wanted is formed. This paper introduced the Sheet dieless digital forming system and metal digital forming technology.

Significant Parameters for the Surface Roughness in Incremental Forming Process

The features of the incremental sheet forming (ISF) process allow it to meet a wide array of customer preferences. In this paper, the variation of surface roughness (SR) in a negative ISF process was systematically studied. The variation was investigated by means of four different process parameters, namely, the vertical step size, forming tool diameter, spindle speed, and feed rate. By using Taguchi analysis with the help of design of experiment and analysis of variance (ANOVA), the effects of the above four process parameters have been studied to optimize parameter levels to realize minimum SR. The results illuminated which parameters have the greatest effect on SR variation, namely, tool size and vertical step size. The confirmation test also showed that the response tables and graphs from Taguchi analysis and ANOVA constitute effective and efficient methods for determining each design parameter's optimal level to produce the minimum value of the SR.

Surface and Microstructure Considerations in High Speed Single Point Incremental Forming of Ti6Al4V Sheets

Flexible sheet metal forming processes represent a big challenge, which involved a number of researchers all over the world in the last decades. Among these, Incremental Sheet Forming (ISF) process is one of the most investigated and promising due to its simplicity, cheapness and applicability. Furthermore, the possibility to increase the process velocity makes the ISF more suitable than in the past; as a consequence, its application potential is surely increased. It was already highlighted that high speed significantly raises the process temperature, improving the workability of Titanium alloys. In this process configuration, no further heating source is strictly required because the temperature increase is generated due to the plastic deformation and the friction conditions at the interface between the punch and the sheet. While the process feasibility has been already investigated, a lack of knowledge in the literature is present focusing on the analysis of the process impact on the material properties. Accordingly, an experimental campaign on Ti6Al4V sheets has been performed, considering a punch speed two orders of magnitude higher than the conventionally used one. The obtained surfaces have been compared to sheets worked by traditional velocity in order to accurately analyze the impact of high speed. Furthermore, microstructural analyses have been carried out confirming the high speed suitability. All the details are reported in the manuscript

Study on Step Depth for Part Accuracy Improvement in Incremental Sheet Forming Process

Incremental Sheet Forming (ISF) is a new-emerging sheet forming process well suited for small batch production or prototyping because it does not need any dedicated dies or punches. In this forming process, sheet metal parts are formed by a smooth-end tool in a stepwise way, during which plastic deformation is highly localized around the tool end. The part geometric accuracy obtained in the current ISF process, however, has not met the industry specification for precise part fabrication. This paper deals with a study on step depth, a critical parameter in ISF, for improving the geometric accuracy, surface quality and formability. Two sets of experiments were conducted to investigate the influence of step depth on part quality. Dimensional accuracy, surface morphology and material fracture of deformed parts were compared and analysed. An optimum value of step depth was suggested for forming a truncated cone. The present work provided significant fundamental information for the development of an advanced ISF control system on tool path control and optimization.

Analytical and experimental investigations on deformation mechanism and fracture behavior in single point incremental forming

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. The characteristic of localized deformation is significantly different from conventional sheet metal forming process. To understand the fundamental material deformation mechanism during the ISF process is of great importance for ISF process design and optimization in achieving improved material formability, accuracy and more uniform thickness distribution. In this paper, an analytical model for single point incremental forming (SPIF) process has been developed to describe the localized deformation mechanism. With the consideration of both bending effect and strain hardening, the stress and strain states in the deformation zone are described. Analytical evaluation reveals that the deformation occurs not only in the contact zone, but also in the neighboring wall which has been already formed in the vicinity of the contact zone. In addition, the results also suggest that the fracture tends to appear at the transitional zone between the contact area and the formed wall. In order to validate the analytical results, SPIF simulation and experiments both have been conducted with good agreement obtained.

Simulation and Experimental Observations of Effect of Different Contact Interfaces on the Incremental Sheet Forming Process

Incremental sheet forming (ISF) is a promising forming process perfectly suitable for manufacturing customized products with large plastic deformation by using a simple moving tool. Up to now, however, the effects of contact conditions at the sheet interface are not well understood. The aim of this work is to study the effect of tool type and size on the formability and surface integrity during the forming process. Experimental tests were carried out on aluminum sheets of 7075-O to create a straight groove with four different tools (ϕ 30,ϕ25.4,ϕ20 andϕ10mm). One tool tip was fitted with a roller ball (ϕ 25.4mm) while the other three were sliding tips. The contact force, friction and failure depth were evaluated. A finite element (FE) model of the process was set up in an explicit code LS-DYNA and the strain behavior and thickness distribution with different tools were evaluated and compared with the experimental results. This study provides important insights into the relatively high formability observed in the ISF process. Microscopic observations of the surface topography revealed that a rolling tool tip produced better surface integrity as compared with a sliding tool tip, wherein, distinct scratch patterns in the tool traverse direction were evident.

Comparative Study between Programming Systems for Incremental Sheet Forming Process

Incremental Sheet Forming (ISF) is a method developed to form a desired surface feature on sheet metals in batch production series. Due to a lack of dedicated programming system to execute, control and monitor the whole ISF, researchers tried to utilize programming systems designed for chip making process to suits for ISF. In this work, experiments were conducted to find suitability and quality of ISF parts produced by using manual CNC part programming. Therefore, ISF was carried out on stainless steel sheets using Computer Numerical Control (CNC) milling machines. Prior to running the experiments, a ball-point shaped tool made of bronze alloy was fabricated due to its superior ability to reduce the amount of friction and improve the surface quality of the stainless steel sheet metal. The experiments also employed the method of forming in negative direction with a blank mould and the tool which helped to shape the desired part quickly. The programming was generated using the MasterCAM software for the CNC milling machine and edited before transferring to the machine. However, the programming for the machine was written manually to show the differences of output date between software programming and manual programming. From the results, best method of programming was found and minimum amount of contact area between tool and sheet metal achieved.

Strain Induced Martensite in Incremental Forming - Formation, Effect and Control

Stainless steels are increasingly today applied in industrial use. The metastable structure of austenitic stainless steels enables strain induced martensite formation during plastic deformation. Thus, in order to effectively apply these steels in incremental sheet forming (ISF), it is essential to know their α-martensite transformation tendency in the process. For the four different austenitic stainless steels in the present study, the transformation was found to be very sensitive to the applied process parameters. The martensite formation was more profound with the unstable grades, however, with external heating the martensite formation could be diminished. By optimizing the ISF process, the amount of transformed martensite can be controlled and products with exceptional property combinations can be produced. The novelty of the present paper is to, first, provide information on the influence of strain induced martensite on the incremental forming process and product properties. In addition, based on the observations, propose means to control the transformation. Furthermore, the paper establishes that ISF favours a moderate rate of martensite transformation for extreme formability.

Study on the ISF Procedure of the Throttle Pedal Fixed Plate Based on the Numerical Simulation

Incremental Sheet Forming (ISF) is a new sheet metal forming process characterized by higher formability, product independent tooling and greater process flexibility. A large amount of research work has been spent on ISF process in the last years, but industrial applications are not spreading accordingly. In this paper, numerical simulation, combined with FLD, was performed to analyze the formability of a practical production. Additionally, an actual experiment was done to test and verify the accuracy of numerical simulation analysis results. The high similarity between the analytical prediction values and the measured values indicates it is feasible to predict the formability of the ISF production.

Application of ISF Process for the Throttle Pedal Fixed Plate

Incremental Sheet Forming (ISF) is an emerging process. As a sheet metal forming process, it allows manufacturing components without the development of complex tools in comparison with stamping process. Although existing technical research achievements are plenty, it remains to be improved to make an industrially suitable process. This work is dedicated to the incremental forming of the throttle pedal fixed plate to analyze and figure out the reasonable practical procedure of ISF process, and helpful to promote the industrial applications of ISF.

A multipass incremental sheet forming strategy of a car taillight bracket

Incremental sheet forming (ISF) satisfies the increasing demand for the production of small batch products or customized parts. Up to now, however, there are little studies or applications on the ISF process of geometrically complex products as a result of the long processing time and the difficulty in generating an appropriate tool path. In this study, an attempt was made to process a car taillight bracket which had several intricate geometrical characteristics, especially the nearly straight-wall region and the groove region. It was firstly verified that cracks and wrinkles are prone to be brought about in the two crucial regions of the target product if a traditional multipass forming was employed. Thus, a multipass strategy, based on a detailed area division which considered the processing depth, was approached. And this strategy required only one transitional model so as to shorten the manufacturing cycle. In this way, associated with each region was a corresponding tool path which can be easily modified. Based on the proposed multipass design, the taillight bracket was successfully processed without evident forming defects. And the thickness thinning rate approximately met the conventional requirement of less than 25 %. Then, as the transitional model plays an important role in the forming performance of the final product, the design of the addendum surface of the aforementioned two critical areas was discussed. It was verified that a regular transitional surface which is geometrically nearer to the final shape is able to obtain a satisfying forming quality.

Brass 70/30 and Incremental Sheet Forming Process

This work addresses through bibliographies and experiments the behavior of sheet brass 70/30 for Incremental Sheet Forming process - ISF, based on the parameters: wall angle (), step vertical (ΔZ) strategy and the way the tool. Experiments based on the method called Single Point Incremental Forming - SPIF. For execution of practical tests, we used the resources: software CAD / CAM, CNC machining center with three axles, matrix incremental, incremental forming tool and a device press sheets. Furthermore, measurement was made of the true deformation () and thickness (s1). Practical tests have shown that the spiral machining strategy yielded a greater wall angle, compared to the conventional strategy outline.

Evaluation of Geometric Accuracy and Thickness Variation in Incremental Sheet Forming Process

Abstract The aim of this study is to evaluate dimensional conformity and thickness variation of a pyramid geometry obtained by negative single point incremental sheet forming. DC04 mild steel, which has been widely used in automotive and numerous applications due to high formability, was used for experimental investigations. Dimensional accuracy of whole geometry and surface roughness are investigated under the influence of toolpath parameters such as tool diameter, feed rate and vertical step down. In this paper, geometric accuracy and thickness are evaluated by production tolerances of conventional methods and results show that thickness reduction of formed sheet and geometrical deviation of side faces are out of tolerance for all cases.

Feature-based tool path generation approach for incremental sheet forming process

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Although tool path plays an important role in the ISF process, there is only limited development in the tool path generation strategy and the conventional contour based strategies have been proven to cause problems in surface quality and geometric accuracy. This paper presents a new feature-based tool path generation algorithm for incremental sheet forming process. In this algorithm, tool paths are generated according to the specified critical edges. To obtain a better understanding of forming mechanism using the new tool path generation method, the thickness distribution, geometric accuracy and surface quality of the ISF formed shapes by using the feature-based tool path approach are compared with the traditional ISF tool path method based on three case studies including a truncated cone with double bottoms, a non-symmetrical cone and a car fender. The results suggest that the new tool path stretches the sheet in a different way and results in different thickness distributions. The results of these case studies also demonstrate the advantages of the feature based tool path generation especially in surface quality, geometric accuracy and forming time.

Analysis of the Influence of Geometrical Parameters on the Mechanical Properties of Incremental Sheet Forming Parts

Incremental Sheet Forming (ISF) process may be classified within the field of sheet metal forming processes, more specifically in the asymmetric incremental deformation process. Some studies have been carried out on the influence of different parameters in the process. However, there are few publications that evaluate the influence of these parameters using design of experiments by finite element modelling. This study provides a better understanding of the process, which will enable an optimization of the ISF process and its comparison with other metal forming processes. Furthermore, this study will be the basis for determining the development of the equipment necessary to carry it out.

Robust Design of Incremental Sheet forming by Taguchi's Method

Although the competitiveness of Incremental Sheet Forming process can be recognized by the literature review, some intrinsic aspects penalize its industrial application. In particular, even if the idea to take advantage from the bigger formability appears of great interest, on the other hand the not homogeneous thickness distribution reduces the industrial suitability. However, a significant improvement in the thickness distribution can be obtained by using an “artificially modified” tool trajectory. In fact, previous experimental investigations carried out by the authors showed that it is possible to influence the thinning phenomenon by applying a proper tool trajectory. The present study was executed with the aim to design a robust procedure able to highlight how to modify the tool trajectory in order to improve the thickness distribution along the profile. More in particular, the study is based on the coupled use of the numerical analysis and the Taguchi's method. All the results are widely discussed in the paper.

Tool path optimization for single point incremental sheet forming using response surface method

Incremental sheet forming (ISF) process is based on localized plastic deformation in a thin sheet metal blank. It consists to deform progressively and locally the sheet metal using spherical forming tool controlled by a CNC machine-tool. Although it is a slow process compared to conventional forming technique such as stamping. The cost reduction linked to the fact that punches and dies are avoided which makes it a very attractive process for small batch production and rapid prototyping. However, ISF process depends strongly on the forming tool path which influences greatly the part geometry and sheet thickness distribution. A homogeneous thickness distribution requires a rigorous optimization of the parameter settings, and an optimal parameterization of the forming strategy. This paper shows an optimization procedure tested for a given forming strategy, in order to reduce the manufacturing time and homogenize thickness distribution of an asymmetric part. The optimal forming strategy was determined by finite element analyses (FEA) in combination with response surface method (RMS) and sequential quadratic programming (SQP) algorithm.

A Numerical Simulation of Incremental Forming Process for Polymer Sheets

The incremental sheet forming (ISF) technology has recently received considerable interest due to pre-eminence advantages for low-batch, high-quality, and customized products. Regarding the manufacturing of polymeric materials, this technology could be considered as potential candidate to satisfy growing requirements of low batch and customized products in very short development and production lead-times. In this paper the numerical simulation of ISF process with a cone shape in 45° wall angle, hemispherical-head tools and helical tool-paths is presented. A finite element model, implementing a viscoelasticity material model, is used to examine the deformation of ISF on polymer sheets. The simulated results were utilized to predict variances in thickness of deformed polymer sheet and geometric accuracy. Finally, the comparison between the results from numerical simulations and laboratory experiments carried out on a CNC machine is also presented.

On the use of Back-drawing Incremental Forming (BIF) to improve geometrical accuracy in sheet metal parts

Industrial interest about Incremental Sheet Forming (ISF) process is growing in the last years. Up to a few years ago, two main investigation ways were proposed, the former aimed at analysing the process mechanics, the latter at reproducing some “case study” geometries. In industrial applications, if the long cycle-time can be neglected in small batches manufacturing, geometrical accuracy represents a relevant drawback, especially when the product has to be coupled to one another. For this reason, in the opinion of the authors, the low accuracy is the most relevant defect of ISF processes today. Among the techniques already set-up to reduce inaccuracy, the use of different material supports or the use of “arbitrarily modified” tool trajectories are probably the most known. In this paper a simple approach is proposed, based on the process self capability to correct inaccuracy when different steps of Incremental Sheet Forming are carried out on both the part surfaces. In particular, it is demonstrated that a relevant increasing in accuracy is obtainable at the second repeated step, while new ones do not reduce the inaccuracy sensitively. The above approach builds a new scenario since it allows to keep the basic equipment (without any support) and does not require any further knowledge concerning the material behaviour after the punch action. These aspects are deeply discussed in the next chapters.

Tool Directionality in Contour-Based Incremental Sheet Forming: an Experimental Study on Product Properties and Formability

The Incremental Sheet Forming (ISF) process offers a large variety in tool path strategies to obtain a particular final product shape. As fundamental understanding of the relevant deformation modes in ISF is growing, the selection of the tool path strategy may be shifted from trial-and-error towards more fundamentally based knowledge of the process characteristics. Truncated cones and pyramids have been fabricated by both unidirectional (UD) and bidirectional (BD) contour-based tool path strategies, considering different wall angles and materials (Mn-Fe alloyed aluminum sheet and low carbon steel sheet). It is shown that the induced through-thickness shear along the tool movement direction is clearly non-zero for UD, in which case the sense of tool movement is the same for all contours, while it is close to 0 for BD, due to the alternating tool sense during consecutive contours. Furthermore, the heterogeneity in product thickness, as observed for the UD strategy in [1,2], is avoided by using the BD strategy. It is verified that this difference in deformation may affect the mechanical properties in the walls of pyramids by means of tensile testing, but the results are material-dependent. For the aluminum alloy, the re-yield stress along the tool movement direction is smaller for BD in comparison to UD, and the fracture strain in large wall angle products is higher. For the steel, no statistically significant differences in mechanical properties between UD- and BD-processed parts are observed. Finally, for both materials a (slightly) higher limiting wall angle has been repeatedly measured using the BD tool strategy. In light of these results, the bidirectional tool path strategy is to be preferred over the unidirectional one, as thickness distribution and formability are more favorable, while both strategies require similar resources and processing time.