In this research, formability of two layer sheet metals of Al1050 and St12 in single point incremental forming (SPIF) has investigated using numerical and experimental approaches. In order to study the sheet metal formability in this process, the tool paths defined in ABAQUS and CNC machine so that an increasing wall angle is created until the sheet metal reaches its maximum allowable angle and fracture is occurred. Since in this process, the tool exerts local stresses on the sheet metal, 3D simulation of the process is needed. In order to study the effect of process parameters, the analysis is done in three levels of tool radius and vertical step size. In order to derive fracture depth of sheet metal, the force diagram is considered in simulations. It is shown that the outer sheet subjected to higher plastic strains and therefore failure occurred initially at the outer layer. Results also showed that increasing the tool radius and vertical step size speed up process but they have inverse effect on the forming limit angle. For experimentally study and also to validation of simulation results, full factorial experiments with respect to forming speed up to three levels designed and carried out. The difference between FEM and experimental results is about %2.1 in forming limit angle.

Incremental forming of metal sheets is one of the new methods of forming, in which the local exertion of forming forces and the absence of a matrix enhances the forming limit of the sheet and extends the flexibility of process in producing of complex geometries. In this research, the forming limit of aluminum/copper bilayer sheets in the single-point incremental forming of different geometries was studied. Considering the instability mechanism of the sheet, the Xue-Wierzbicki damage criterion was used in the form of the VUMAT subroutine of Abaqus in the numerical prediction of the growth and damage initiation of bilayer sheets. Experimental tests showed that the type of geometry has influences on the forming height limit due to the different induced stress and strain states on the sheet. The prediction of the numerical model of the forming height limit on average for different geometries with difference of 8% compared to the experimental tests, which indicates the validity of the numerical model. Accordingly, using the numerical model, the effect of changes in equivalent plastic strain and triaxial stress as crucial variables on the distribution of surface strains and damage was analyzed. Also, cyclic and nonlinear loading in this process was shown by plotting the strain path for different geometries.

Incremental sheet metal forming is one of the promising sheet forming processes, in which local nature of the applied forming forces and independency of the process on the die, induces higher formability in the sheet and increases flexibility of the process in producing intricated geometries. In current study, from damage mechanics window, one of the prominent features of the process, i.e. forming limits of AA5052 sheets has been investigated. For this purpose, firstly, Bao-Wierzbicki damage model is coded and implemented into Abaqus finite element program via VUMAT subroutine. The constants of the damage model, hardening model and Hill48 yield model have been obtained utilizing the uniaxial tensile experiments in three directions of 0º, 45º and 90º with respect to rolling direction. To examine the formability, truncated cone and pyramid geometries with variable increasing wall angles have been considered and the experimental tests and simulation of the process were conducted. Using the stress and strain distribution, fracture phenomena and onset of fracture were described. The results show that the sheet metal fractures before it reaches the designed final height, so that for the geometries of truncated pyramid and truncated cone, the fracture height is obtained 19.9 mm and 16.9 mm, respectively. Considering the sheet anisotropy properties in the process simulation, the fracture height of specimens was predicted with an average accuracy of 9%, and the results reveal that with excluding the anisotropy properties of the sheets, the prediction accuracy decreases. Also, an acceptable agreement was obtained in predicting the fracture location.

Single point incremental forming is a cost-effective process with high flexibility and as a result, would be a proper selection for low-batch and high-customized production compared to traditional processes such as pressing. The target market of this process usually consists of medical, automotive, and aerospace industries in which metals with high strength to weight are highly in demand. These materials are usually formed at elevated temperatures due to their low formability at room temperature. In this study, the AA6061 aluminum sheet was homogeneously heated at 25-400° C. In addition, the effects of important process variables of heat-assisted SPIF including temperature, vertical pitch, feed rate, and three types of lubricants were investigated on formability of truncated cones with various wall angles. According to the results, despite the inability of local heating in enhancing the formability of the AA6061 sheet (37% improvement of formability under optimal conditions), the homogenous heating approach which was used in this article leads to a significant improvement in formability (528%). Temperature is the most important parameters effective on the formability, while lubricant and vertical pitch are ranked as the second and third parameters, respectively and the effect of feed rate is negligible. The critical wall angle increases from 60 to 65 degrees with increasing the temperature from 25 to 400° C. In order to choose a suitable set of parameters, the surface roughness should be taken into account, which may alter the results from 1. 18 to 4μ m as the best and worst surface conditions, respectively. Furthermore, a truncated cone with a wall angle of 65 degrees was successfully formed to 44mm depth using an appropriate combination of process parameters. This demonstrates an outstanding improvement in formability.

Single point incremental forming is a new and flexible method for 3D parts production of sheet metal.In this way, a hemispherical tool forms incrementally, the sheet being clamped in perimeter. Because of the nature of localized deformation in this process, the formability is higher and forming forces are lower as compared to traditional sheet metal forming process. However, in this method dimensional accuracy is somewhat low due to spring back and bending that occurs in boundaries. Recently, the incremental forming process using frictional heat has been developed. In this research, the experimental effect of generated heat by friction stir of the tool on dimensional accuracy in components of AA3105 sheet has been studied at high rotational speeds. By this method, due to friction movements of tool, the temperature of formation area rises while fixing the general temperature of sheet by spraying cooling liquid. Then, the sheet has low strength in contact region with tool while it has high strength in other areas. As a result, the force imposed on the sheet as well as the undesirable plastic deformation will decrease. Also, by decreasing the yielding stress, elastic strain and spring back decrease as well. An increase in formability because of softening of forming area is another contribution of this strategy. This idea has been studied via production of some parts of truncated-pyramid geometry and changing rotational speed from 1000 to 7000 RPM. The results show that at speed higher than 3000 RPM, formability and dimensional accuracy of the parts increase.

Regarding to the uprising need for production of new components with high efficiency, application of methods that could facilitate the prototyping and minimize the financial and time costs are of high importance. Single Point Incremental Forming, which is a process with no need for die manufacturing, was successful in minimizing the costs and the prototyping period required for design validations. Accordingly, studying this process from different perspectives and obtaining an accurate method for determination of failure in this procedure is important. Some of the benefits of this process are an increase in formability, high flexibility in production of complex shapes and reduction of forming forces. In all available processes that are used for forming of metallic sheets there is a certain limit for formality beyond which typical failures including wrinkle, necking or rupture will occur. Today different experimental and numerical methods are developed for determination of forming limit. In this study in order to obtain the forming limits and to anticipate the failure in Single-Point-Incremental-Forming process, generalized forming limit diagrams are utilized. Initially the Single Point Incremental Forming process is simulated using ABAQUS Software and then resulting strain path of critical elements of the part are compared against the forming limits obtained by generalized forming limit diagrams to study the existence of failure in both simulations and experimental tests.

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.

Incremental forming is considered as one of the rapid prototyping methods and has a high degree of flexibility and cost-effectiveness at low production volume. Meanwhile, the lack of technical knowledge has challenged the use of this method in the industry. One of the things that can help the actual usage of this process is the suitable process window; a window used to determine maximum tearing depth of the sheet with respect to the material, thickness and wall angle. In this study, firstly, the formability of low-carbon steel sheet, St12, with the thicknesses of 1. 25 and 1. 50 mm in single point incremental forming of a truncated pyramid with different constant wall angles has been investigated experimentally. Then, it is compared with the formability of the truncated pyramid with variable wall angles under two different wall geometries. Based on the experimental results, the process windows are presented in terms of the maximum depth and wall angle and compared to each other under different circumstances. The results showed that the critical wall angle for St12 sheet in incremental forming of a truncated pyramid with a fixed wall angle differs from the pyramid with variable wall angle, but doesn’ t depend on the size of the pyramid base. The critical wall angle for the fixed and variable wall angle pyramids was obtained 67⁰ and 75⁰ , respectively. For a pyramid with a fixed wall angle, the thickness distribution of the wall is almost constant, while for a pyramid with a variable wall, it varies along the path.

Incremental forming of metal sheets is one of the new methods of metal forming with high flexibility in batch production of complex geometries. Due to the absence of a matrix and the gradual applying of forming forces, the forming limit in this process is increased compared to conventional ones. In this research, formability, forming, and finally fracture of aluminum/ copper bilayer sheets produced by explosive welding method in the single point incremental forming process are studied. In the numerical prediction of growth and onset of fracture of sheets in this process, the Xue-Wierzbicki damage criterion was used as the VUMAT subroutine in Abaqus software. Using the numerical model, variations of the stress triaxiality and equivalent plastic strain as the variables affecting the damage growth in the incremental forming process were analyzed and explained, and the effect of cyclic and nonlinear loading in this process was shown. Experimental results show a different failure height of various geometries due to different loading conditions. Also, using the verified numerical model, in addition to predicting crack growth location, the fracture height in the formed geometries was predicted by 4. 06% difference with respect to the experimental results.

Welded sheets are made by butt connecting of the base plates in various welding methods. These sheets are called welded sheets, tailor welded blanks (TWBs). Due to their many benefits, they have found many uses in various parts of the industry. In this Research, the formability and effect of weld line of TWBs of St12 and St14 in thicknesses of 1 mm and 1. 5 mm in single point incremental forming in the form of a truncated pyramid has been investigated. At first, the maximum depth that can be shaped in single point incremental forming of a truncated pyramid from each of the base plates for different values of wall angle was obtained and the critical wall angle for each of them was determined. Then, the incremental forming of the truncated pyramid was done using welded sheets at the critical wall angle of the base plates. In this regard, TWBs were considered with different layouts and combinations of base plates. To investigate the effect of weld line on forming depth, each combination was prepared in two weld directions of 0 and 45⁰ relative to the rolling direction. The experiment results showed that the fracture depth of TWBs with 45⁰ was reduced by an average of 14% compared to TWBs in the rolling direction. Furthermore, the average depth of the TWBs at the average critical wall angle of the base plates decreases to about 25% compared to the base plates. Therefore, the TWBs should be formed at their critical wall angles.