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The development of rapid prototyping methods has been very drastic in recent years. One of these methods, with a nature similar to sheet-forming processes, is the incremental forming method. In the last two decades, this technique has attracted much attention in industrial applications. The incremental forming process has been able to play a major role in advancing industrial projects in the production of low-volume prototypes. This process is a suitable alternative to conventional forming processes in the single production of conical geometries because of the low cost of machinery, equipment, and tools. In this paper, the two-point incremental forming of conical parts by three multi-point matrix designs, including single, double, and three-step cylinders, were investigated. For this purpose, the feed rate (400-1000 mm/min) and the penetration step of the tool (0.5-1.1 mm) were investigated in three levels to form the aluminum sheets with a thickness of 0.5 mm. In the following, the effect of the input parameters on the limiting height of the formed specimens, thickness distribution, surface roughness, and geometric accuracy of longitudinal cut specimens was assessed. According to the results, using the multi-point matrixes, despite increasing the final geometric accuracy, friction was reduced compared to the conical matrix. Using a two-step matrix, deeper pieces were formed by increasing the formability of the sheet, in which the average height was improved by an average of 12%. However, no significant change was observed in the roughness of the samples formed by all three types of matrixes. Therefore, the design of the proposed matrix had almost no tangible effect on the final surface roughness output. From the view of geometric accuracy, the matrix design with three steps created the highest geometric accuracy, as well as the least deviation relative to the planned path.

Uneven thickness distribution was the main reason for affecting product performance and forming quality when single-point incremental forming the thin-walled parts with complex shapes. Hydraulic supporting was introduced into the single-point incremental forming process, and a hydraulically supported single-point incremental forming process was proposed, uniform distribution of thickness was promoted by adding flexible support to the overhanging sheets. Conical parts with different wall angles were formed by single-point incremental forming of All060 sheets under the auxiliary supports of hydrostatic and variable pressure, the effects of hydrostatic parameters and variable pressure schemes on the thickness distribution and the critical angle of thickness uniformity were quantitatively analyzed through numerical simulations and experimental studies. The results show that the favorable hydrostatic pressure range is as 0 ~ 0.18 MPa for the critical angles of uniform thickness distribution, and the most favorable hydrostatic pressure value is as 0.17 MPa. Compared with unsupported single-point incremental forming, the hydraulically-supported single-point incremental forming process may increase the critical angle of thickness uniformity by 7°, which effectively improves the uniformity of thickness distribution and forming performance of the sheets. [ABSTRACT FROM AUTHOR]

The incremental forming technology has enormous potential in manufacturing sheet parts. However, non-un8iform thickness distribution is a common technical existing issue in forming thin-walled parts using this technology. The use of hydraulic supports has been a realistic, promising solution to this issue. Based on hydraulically-supported incremental forming technology, a variety of strategies were proposed in this article for hydrostatic and variable pressure supports respectively. For each supporting strategy, the thickness distribution and materials flow laws in various forming regions were explored. Experimental and simulation results indicate that when the hydraulic pressure is less than 1.8 bar, the thickness distribution of the hydrostatic-supports is significantly better than that of conventional incremental forming, and the thickness distribution of the variable-pressure supports may be better than that of the hydrostatic-support. The hydraulically-supported incremental forming technology has an potential of enhancing enhance the thickness distribution performance and forming performance of thin-walled parts. [ABSTRACT FROM AUTHOR]

Single point incremental forming is a flexible sheet forming process that does not require a dedicated punch and die for making products for various applications. However, forming parts at steep wall angles, closer to 90°, using this process poses difficulties due to excessive thinning. The motivation behind this study is to overcome the challenges associated with forming parts at steep wall angles using the single point incremental forming process. Controlling the thickness distribution is a significant challenge that needs to be addressed. Excessive thinning leads to disqualification of design criteria, thereby restricting the process' industrial applicability. In the present work, an improved clamping mechanism along with a multi-stage forming approach is employed to address the issue of excessive thinning. Two strategies were evolved; in strategy 1, an improved clamping mechanism was developed for single stage single point incremental forming, while strategy 2 consists of the improved clamping strategy along with a multi-stage forming approach for a single point incremental forming process. The improved clamping was based on the deep drawing process' blank holding type clamping mechanism in both these strategies. The study aimed to compare the formed components' forming depth and thickness distribution using the two strategies. The result revealed that strategy 2 was more effective, resulting in better thickness distribution in the formed component. The thickness distribution improvement resulted from metal flow from the flange region, owing to the improved clamping strategy, during the single and multi-stage forming at steep wall angles. [ABSTRACT FROM AUTHOR]

In the present work, the effect of different forming strategies on material flow in incremental forming of hemi-spherical dome shaped components is investigated. During single stage forming strategy the part has failed at 10 mm depth from the entrance of hemi-spherical dome due to steep wall angle. To overcome this problem, the sheet is deformed by adopting two different multistage forming strategies. Both these strategies have four stages with different intermediate shapes. In the first strategy, the intermediate shapes are modelled as cones with different heights and wall angles. In the second strategy, the intermediate shapes are modelled as domes with different radius of curvature and height. Even though the sheet is formed successfully in both multistage forming strategies, it is found that the intermediate shapes have significant effect on forming limits, geometric accuracy and manufacturing time. The accuracy of dome formed using first strategy is found to be deviating from the desired shape due to formation of stepped features, which has overcome by implementation of second strategy. In addition, a new theoretical model is proposed to predict the thickness of the sheet during the multi-stage forming based on the volume consistency approach. The FE simulations are also performed to study the forming behaviour in both single stage and multi-stage forming. Various quality parameters found from FE simulations such as thickness distribution, forming forces and geometrical accuracy are in agreement with the experimental results.

Single point incremental forming is a method which has the capability of sheet forming by a semispherical tool without the necessity of using specific die. In the present study, Forming Limit Diagrams (FLD) of explosively-welded CP-Ti/St12 bimetal sheet have been evaluated. The effects of process parameters and layer arrangements (St-Ti and Ti-St) were investigated on the FLD and thickness variations. For this purpose, standard circular pattern was carved on the sheets. The changes of strain at the carved pattern and thickness distribution were measured using Video Measuring Machine (VMM). The diagrams of FLD and thickness distribution were achieved using the obtained points and related relationships. Also, the single point incremental forming process was simulated using ABAQUS finite element software to evaluate rupture moment and thickness distribution. According to the experimental results, the sheet formability increased to 30% in the layer arrangement of Ti-St in comparison to St-Ti and the error between finite element and experimental result was about 15%. The effects of layer arrangement, vertical step down, and spindle speed on thickness distribution were about 45, 17, and 12%, respectively. [ABSTRACT FROM AUTHOR]

Based on numerical simulation and experimental studies the process parameter optimization on the formability using a 1 mm thickness Drawing Quality Steel(CR2) in Single Point Incremental Forming (SPIF)was studied. The sample shape chosen was the hayperbolic cone and fabricated using different parameter leveles. A model of numeric simulation was developed in ABAQUS explicit and then experimentally verified using a CNC milling machine. The influence of three significant control factors, namely tool radius, feeding rate, and step depth on the formability was studied. Optimization of process parameters was conducted using the L9 Taguchi orthogonal array. For optimal formability, to assess the optimum combination of process parameters, a signal noise (S/N) ratio was used. The percentage contribution of the method parameters to formability was determined by the Study of Variance (ANOVA). The findings of the study indicated that the depth of the step followed by feed rate and tool radius, was the dominant factor influencing formability. Furthermore, a good agreement (<8% error) between the numerical simulation and experimental study was seen. The study based on the Taguchi configuration of the study shows that at a feed rate (A2) 1000 mm/min, with tool radius (B1) 8 mm, and with step depth (C2) 0.8 mm, the optimal conditions for maximum formability were achieved. [ABSTRACT FROM AUTHOR]

Based on numerical simulation and experimental studies the process parameter optimization on the formability using a 1 mm thickness Drawing Quality Steel(CR2) in Single Point Incremental Forming (SPIF)was studied. The sample shape chosen was the hayperbolic cone and fabricated using different parameter leveles. A model of numeric simulation was developed in ABAQUS explicit and then experimentally verified using a CNC milling machine. The influence of three significant control factors, namely tool radius, feeding rate, and step depth on the formability was studied. Optimization of process parameters was conducted using the L9 Taguchi orthogonal array. For optimal formability, to assess the optimum combination of process parameters, a signal noise (S/N) ratio was used. The percentage contribution of the method parameters to formability was determined by the Study of Variance (ANOVA). The findings of the study indicated that the depth of the step followed by feed rate and tool radius, was the dominant factor influencing formability. Furthermore, a good agreement (<8% error) between the numerical simulation and experimental study was seen. The study based on the Taguchi configuration of the study shows that at a feed rate (A2) 1000 mm/min, with tool radius (B1) 8 mm, and with step depth (C2) 0.8 mm, the optimal conditions for maximum formability were achieved. [ABSTRACT FROM AUTHOR]

Incremental forming method with lower cost and more flexibility can be a suitable alternative for traditional methods of the hole-flanging. In this study, the possibility of square hole-flanging of AL1050 aluminum sheet using incremental forming method has been investigated and the quality of the pyramid flange has been compared with conical flange. The final shape of the flange is defined so that wall angle increases with raising height. The process simulation was performed using Abaqus software and an experimental test was done to validate the simulation results. After performing the experimental tests, flange features such as the final size of the hole, flange height, and wall thickness were measured. The results showed that at the created flange around the circular hole, there is less spring back and more dimensional accuracy, however, it can be flanged a square hole by incremental approach with consideration of the height and hole size. The dimensional measurements showed that the final size of the hole will increase after the hole-flanging. By investigation of the various holes, it was found that in the larger initial hole, increasing the hole size after the flanging will be lower. [ABSTRACT FROM AUTHOR]

Multi-Point Incremental Forming (MPIF) process is a new hybrid process that combines two common manufacturing methods. These are Multipoint Forming (MPF) and Incremental Sheet Forming (ISF) processes. In this study, an experimental set-up, based on a MP reconfigurable die, was designed and manufactured to explore the flexibility of this innovative process and its potentialities to produce complex parts using the same tools. The obtained results have indicated that this novel technique, that doesn’t require costly equipments, is an effective approach to manufacture multitude of parts with different shapes. Moreover, it has been shown that the parts geometrical accuracy as well as thickness distribution are enhanced compared to the conventional ISF process and that the geometrical defects, called ‘dimples’ and caused by the pins’ ends, are significantly reduced and almost eliminated after the insertion of a rubber piece between the reconfigurable die and the blank sheet. On the other hand, the effect of the size and geometry of the rectangular pins on the geometrical accuracy and the dimpling defect has been studied using a finite element analysis. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the effect of process parameters on maximum formable wall angle in incremental forming of 0.5 mm thickness extra deep drawing steel sheets. For this purpose, four important process parameters namely, tool diameter (A), feed rate (B), part geometry (C) and step depth (D) have been correlated with maximum wall angle. Experiments have been conducted on CNC milling machine in accordance with Taguchi L9 orthogonal array. The statistical methods, signal to noise (S/N) ratio and Pareto ANOVA have been used to find out the optimum process settings and percentage of contribution of different process parameters on maximum wall angle. A linear regression model was also proposed to predict the wall angle as a function of process parameters. Based on the studies, the optimum conditions were found to be A1B2C1D1 (A = 6 mm, B = 1500 mm/min, C = VWACF, and D = 0.7 mm). It was also found that the tool diameter has significant effect on maximum wall angle followed by feed rate, shape and step depth. Furthermore, wall thickness distribution of formed parts under different process conditions has been studied through experiments and finite element simulations using LS-DYNA. A good correlation was found between experimental results and numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, the single point incremental forming (SPIF) of friction stir welded (FSWed) 5083 aluminum alloy sheets are investigated experimentally and numerically. The aluminum sheets with 2mm thickness are friction stir welded with the same FSW parameters. In order to obtain the effect of FSW on the formability of SPIF, the base sheets and FSWed sheets are formed to conical shapes with different forming angles and then the limiting wall angles are determined for each condition. The experimental results indicate that the limiting forming angle of FSWed sheet is not so much different than the base sheet and FSW does not have a negative effect on the sheet metal formability in SPIF. To study the effect of SPIF and FSW in mechanical and microstructural properties of the formed parts, the effects of these process on the grain size and micro-hardness is investigated. Furthermore, the incremental forming is numerically simulated using the ABAQUS software and the sheet thickness distribution, obtained from the simulation, is compared with the experimental results. After verification of the numerical simulation model, the effect of FSW on the thickness distribution and strain distribution in SPIF is studied. The results indicate that in weld region and base metal region, the distributions of thickness and major strain are uniform while the distribution of minor strain is nonuniform. [ABSTRACT FROM AUTHOR]

This paper focuses on the formability and thickness distribution in incremental sheet forming (ISF) of extra-deep drawing steel (EDD). In ISF, the formability of the material is primarily measured by the maximum formable wall angle and maximum allowable thinning. The maximum wall angle is generally obtained by forming frustum of cones and square pyramids having different wall angles till fracture, which requires a large number of experiments. Therefore in the present study, a continuously varying wall angle conical frustum (VWACF) was used to predict the maximum wall angle to minimize the number of experiments. VWACF is generated using circular, parabolic, elliptical and exponential generatrices. In order to get the maximum allowable thinning, the thickness of the formed geometry has been measured at various points along the depth. In addition, the thickness distribution has been computed theoretically based on the sine law and also using finite element code LS-DYNA. Theoretical and simulated thickness values have been compared with measured thickness values. It was found from the results that the finite element model was more accurate than theoretical model in predicting thickness distribution.

The use of metamodelling techniques in process design has become indispensable to perform faster solutions reducing time to market. This approach allows the implementation of decision support tools which are easier to use than the conventional numerical simulations. In this paper, a robust metamodelling technique has been designed and its feasibility has been validated for the crucial problem of localised thinning in sheet metal forming process. The proposed methodology is based on the innovative integration between the Design of Experimental statistical method and the Kriging one. This approach, in fact, allows to analyse contemporary the continuous and categorical factors and, as a consequence, to define a single tool for changing process conditions (i.e., material and product shape). To test the reliability of the mathematical approach, the same was performed for the case study of Incremental Sheet Forming, a process strongly affected by the not homogeneous distribution of the thickness. Taking advantage of this strategy, a wide experimental investigation has been performed to build the base of knowledge of the problem both for the metamodelling design and for the validation of the decision support tool; moreover, the experimental data were utilized to set and validate a numerical model, which was subsequently used to enrich the dataset. The proposed metamodel, suitably modified according to each process peculiarities, can be generally adapted for sheet thickness prediction. [ABSTRACT FROM AUTHOR]

Although multi-stage incremental sheet forming has always been adopted instead of single-stage forming to form parts with a steep wall angle or to achieve a high forming performance, it is largely dependent on empirical designs. In order to research multi-stage forming further, the effect of forming stages ( n) and angle interval between the two adjacent stages (Δ α) on thickness distribution was investigated. Firstly, a finite element method (FEM) model of multi-stage incremental forming was established and experimentally verified. Then, based on the proposed simulation model, different strategies were adopted to form a frustum of cone with wall angle of 30° to research the thickness distribution of multi-pass forming. It is proved that the minimum thickness increases largely and the variance of sheet thickness decreases significantly as the value of n grows. Further, with the increase of Δ α, the minimum thickness increases initially and then decreases, and the optimal thickness distribution is achieved with Δ α of 10°. Additionally, a formula is deduced to estimate the sheet thickness after multi-stage forming and proved to be effective. And the simulation results fit well with the experimental results. [ABSTRACT FROM AUTHOR]

Multistage forming is usually adopted to form those parts which have steep angles or even vertical walls during incremental sheet forming (ISF) process. In order to study the multistage incremental forming further, based on a finite element method model which was experimentally verified, different forming strategies were adopted to form a frustum of cone with a wall angle of 30° to research the influence of the number of forming stages ( n) and the incremental wall angle between the two adjacent stages (∆ α) on the formability of ISF. The simulation results including the thickness distribution, the equivalent plastic strain, and the magnitude of springback were analyzed in detail. It was found that with the growth of n, the minimum thickness increases largely, and more uniform thickness distribution is achieved, but the quantity of springback becomes larger in contrast with a single-pass process because of the accumulation of springback during each forming stage. Furthermore, an expression to figure out the appropriate value of n was given. In addition, the maximum thickness reduction decreases initially and then increases as the value of ∆ α grows. Meanwhile, it indicates that there is no relation between ∆ α and the quantity of springback. [ABSTRACT FROM AUTHOR]

Sheet incremental forming (ISF) is a promising technology. It is inexpensive and does not require particular dies. Sheet thinning, however, has always been one of the forming defects which impede the process's wide application. Although a multi-stage forming process is supposed to be effective to deal with this problem, it is still uncertain how the process can reduce thickness thinning and there is no applicable rule to determine the favorable number of forming stages. In this work, based on a truncated cone, a finite element method (FEM) model for a double-pass forming was established first. Unlike simplifications in previous studies, with the process of the three-dimensional coordinates in numerical controlled (NC) machining code, the tool trajectory in this simulation model is the same as that in real work. With this approach, it was expected to gain reliability of the simulation result, and then this simulation result and a single-pass forming result were analyzed. The results of the analysis indicate that more uniform thickness distribution in the double-forming process largely benefits from the increase of the total plastic deformation zone. Finally, under the condition of constant volume in deformation, an equation was proposed to work out the right number of necessary forming stages and the rule of this equation was verified with a relatively complex product. [ABSTRACT FROM AUTHOR]

Conventional sheet metal forming operations require component-specific and costly tooling, and their design and fabrication add to the lead time. Incremental forming is one of the technologies that has emerged as an alternative to the conventional sheet-metal forming processes for mass customization, where the necessary part is obtained by gradually tracing its contours on a sheet of required thickness using stepwise tool indents. In this investigation, stainless steel AISI 304 sheets were incrementally formed using a hemispherical tool under varying step depths, spindle speeds and horizontal feeds. The limit of formability and thickness distribution of the formed sheet were characterized. The microstructure of the formed specimens was studied using an optical microscope. [ABSTRACT FROM PUBLISHER]

Abstract: Single Point Incremental Forming (SPIF) is an emerging sheet-metal-forming technology, capable of manufacturing complex parts at low cost for small to medium-batch production. The present paper is focused on presenting an innovative and viable method to test the thinning limits of sheet metals in Negative Incremental Forming along with verification of the Cosine''s law of thickness distribution. The Cosine''s law was verified by comparing the experimentally measured thicknesses of incrementally formed parts with those predicted by the law. To test the thinning limit of a sheet metal, the idea is based on the forming of an axi-symmetric part varying its slope with depth corresponding to varying thinning. An arc of a circle was selected as generatrix to model such an axi-symmetric part. Based on the Cosine''s law, mathematical expressions were derived to predict the thickness distribution along the depth of the part and the thinning limit of the sheet-metal. The Aluminum sheet metal was used as an experimental material. In order to test its thinning limit, the axi-symmetric part, modeled with a generatrix arc, was formed incrementally until it cracked. Thickness of the fractured part was measured at various points along its depth and compared with that predicted by the Cosine''s law. The maximum thinning at a point, at which thickness followed the Cosine''s law, was called the thinning limit of the sheet metal. In order to obtain accurate results, four such parts having the same generatrix design were formed. Based on these results, several axi-symmetric and asymmetric parts were formed at fixed slopes. It was found that the thinning limits obtained from the parts formed at fixed slopes were a little lower than those obtained from the parts modeled with the same generatrix design. As conclusion, a strategy to test the lowest possible thinning limits of sheet metals has been proposed. The proposed method is capable to test the thinning limits of sheet metals at reduced processing time and cost. [Copyright &y& Elsevier]