**4. Aluminum alloy behavior during incremental forming**

Incremental sheet forming (ISF) is a flexible process in which a sheet of metal is formed by a progression of localized deformation. This process does not require any specialized tool; a simple tool moves over the surface of the sheet metal by which localized plastic deformation is initiated. Hence, many shapes can be formed by designing a proper path to a tool. The main motto of this process is to form a sheet metal without any manufacturing of specialized dies [38]. **Figure 3** shows an example of the incremental forming. In this **Figure 3**, according to computer numerical control (CNC) machine program instructions, the ball tool moves on the sheet to form the required shape. Hence, the process is in CNC machine; the program can be edited as per the requirement. From the shown **Figure 3**, the hollow and square in cross section will be formed [39].

A few observations are made and discussed on incremental forming process. Incremental forming behavior of 6111-T4 an alloy was investigated for exterior body panel applications. Tensile testing data were used to simulate the incremental forming

**Figure 3.** *Incremental forming of an aluminum sheet on CNC milling machine [34].*

process. The heat treat regimen developed for uniaxial testing was then applied to a series of plane strain tests using a hemispherical punch [40]. The formability of AA-2024 sheets was investigated in the single-point incremental forming (SPIF) process. The process parameters, specifically step size, tool radius, and forming speed, of the SPIF process were varied over wide ranges. The formability was quantified through a response surface method. It was found that the interaction of step size and tool radius was very significant on the formability. The formability of pre-aged AA-2024 sheet decreases with the increase in the forming speed. Additionally, the annealed sheet shows higher formability than the pre-aged sheet [41].

AA7075-O aluminum alloy sheet forming was investigated using experimental campaign and the forming process mechanism was understood. Tensile tests were carried out to characterize the mechanical properties with three different thicknesses. To illuminate the formability of AA7075-O aluminum alloy sheet, the effects of tool path with different incremental steps and the part height were evaluated. To understand the design limits for strain, a fracture forming limit diagram was developed. The influence of different draw angles, sheet thicknesses, step-down sizes, and sheet orientations was considered to analyze forming forces. The part draw angle and incremental steps of the tool path were more effectible on the formability as concluded from the experimental results. The influences of process parameters on tool forces provide further insights into the deformation mechanics of AA7075-O sheets [42]. The formability of AA5052 aluminum alloy at room temperature was studied through truncated square pyramid and cone formed using a CNC machine. For both the shapes, the forming limit diagram (FLD) and thickness distribution were predicted and compared. The FLD obtained through this process and conventional FLD were different. Comparison of FLD and thickness distribution showed that cone had higher forming limit than square cup and the thickness after forming was better in cone shapes than in square cups [43]. An investigation was made on the deformation characteristic of embossed aluminum sheet in the incremental sheet forming process in which the surface quality of tool path along outward and inward movement was compared and noted as surface quality is better in the outward movement. Using ABAQUS software, a finite element simulation, the experimental results and detailed forming mechanism of the 3D structured sheet were reviewed [44].

Formability of friction welded blank made of aluminum 6061 was studied experimentally. Formability was evaluated through FLD, dome height, minimum thickness, and thickness distribution. Many experiments were conducted to know which joining direction caused higher formability and desired forming limit curve. Joints were prepared in three different rollings (0, 45, and 90°) and tested for formability test and compared with FLD, dome height, minimum thickness, and thickness distribution. From the formability comparison, the best joining direction was identified. Using the response surface methodology, the effect of welding process parameters such as rotational speed, plunge depth, and travel speed on formability of welded blanks was analyzed. After finding the effects, welded blanks with optimal parameter combination were fabricated and the effect of incremental forming parameters, that is, spindle speed, feeding rate, and axial step on thickness distribution was analyzed. From the results, it was obtained that joints with diagonal direction caused higher value of bowl height [45]. The effect of longitudinal ultrasonic vibrations on the performance of the incremental forming process of aluminum-1050 sheet was studied. In this technique, ultrasonic vibrations with high frequency and low amplitude were axially added to the movement of forming tool. This system is arranged with different parts including a mechanism attached into the chuck of CNC machine and ultrasonic power to the vibratory tool. Parameters like forming force and sheet formability were examined through straight groove

**159**

*Aluminum Alloys Behavior during Forming DOI: http://dx.doi.org/10.5772/intechopen.86077*

sonic assistance [46].

mental sheet forming [47].

the response surface method.

test in both conventional and ultrasonic-assisted incremental forming process. The results showed that formability increased and forming force decreased with ultra-

Using the finite element method, the behavior of the state of stresses and strains in the hot incremental sheet forming of 1050 aluminum alloy was evaluated, with and without pre-heating. With the assistance of RADIOSS software, numerical simulation was performed. The results were presented a deterioration in the force during electric hot incremental sheet forming compared to the electric hot incre-

The formability of the AA2024-O aluminum alloy sheet material was evaluated with respect to the impact of forming tool shape, tool diameter, wall angle, step size, sheet thickness, and tool rotation. Forming depth was measured by scanning the components using a noncontact 3D scanner. Wall angle and step size had proved more significant factors which affect the formability greatly [48]. An attempt was made to optimize the incremental forming parameters (spindle speed, tool feed, and step size) for surface roughness to be least and wall thickness to be larger using

The formability of AA5052 alloy sheets at room temperature was checked with pre-cut holes at the center with different diameters. In the forming operation, coneshaped parts were formed with the optimized values. Formability was compared with sheet with smaller holes and larger holes and it was observed that smaller holes had better formability. Also, the thickness of the formed part wall without hole is less. As the diameter of the hole increases, the wall thickness also increases [49]. To evaluate deformation behavior of AA-6061 aluminum alloy sheet, the single point incremental forming (SPIF) process was chosen. To form the sheet into the desired conical shape, the SPIF experiments and finite element method simulation were performed and to measure the major and minor strains, the digital image correlation (DIC) method was used. The major and minor strains in post deformation results were compared with FEM results for AA6061 thin sheet material. An experimental fracture forming limit diagram was assessed using the punch stretching test. Consequently, the effective plastic strains at the onset of fracture were predicted and compared with experimental data. In order to get insight into forming behavior and surface roughness, the microstructural examination on the truncated dome fabricated using optimized parameters was carried out through micro-texture analyses [50]. By using the electric hot incremental forming process (EHIF), the dimensional accuracy of parts has got more improvement compared to single-stage forming and double-stage forming at room temperature. The effect of EHIF process parameters, such as tool diameter, feed rate, step size, and current, on temperature was studied. For a cone of AA 1060, the maximum temperature, the average temperature, and the maximum temperature difference were measured. Besides, the response surface method and Box–Behnken design were employed, and they

established corresponding models to predict targeted values [51].

AA 7075-O sheets were formed into variable angle funnels and 45° wall angle cones by SPIF. The same material was deep drawn and a bulge test part was formed to compare with SPIF. Moreover, the formed parts were sectioned and characterized for texture and surface finish at equivalent strains. To compare the strain paths of SPIF and deep drawing, finite element models were used [52]. For AA 1050 sheet metal, the deformation characteristics, forming behavior, and deformation mechanism of the SPIF process were evaluated. For process deformation characteristics such as dimensional accuracy, thickness distribution, true surface strain, von Mises stress, and equivalent plastic strain, evolved at different forming stages, were estimated through experimental investigation and finite element analysis. Analysis was carried out to identify the reason of typical failure under biaxial strain mode [53].

#### *Aluminum Alloys Behavior during Forming DOI: http://dx.doi.org/10.5772/intechopen.86077*

*Aluminium Alloys and Composites*

process. The heat treat regimen developed for uniaxial testing was then applied to a series of plane strain tests using a hemispherical punch [40]. The formability of AA-2024 sheets was investigated in the single-point incremental forming (SPIF) process. The process parameters, specifically step size, tool radius, and forming speed, of the SPIF process were varied over wide ranges. The formability was quantified through a response surface method. It was found that the interaction of step size and tool radius was very significant on the formability. The formability of pre-aged AA-2024 sheet decreases with the increase in the forming speed. Additionally, the

AA7075-O aluminum alloy sheet forming was investigated using experimental campaign and the forming process mechanism was understood. Tensile tests were carried out to characterize the mechanical properties with three different thicknesses. To illuminate the formability of AA7075-O aluminum alloy sheet, the effects of tool path with different incremental steps and the part height were evaluated. To understand the design limits for strain, a fracture forming limit diagram was developed. The influence of different draw angles, sheet thicknesses, step-down sizes, and sheet orientations was considered to analyze forming forces. The part draw angle and incremental steps of the tool path were more effectible on the formability as concluded from the experimental results. The influences of process parameters on tool forces provide further insights into the deformation mechanics of AA7075-O sheets [42]. The formability of AA5052 aluminum alloy at room temperature was studied through truncated square pyramid and cone formed using a CNC machine. For both the shapes, the forming limit diagram (FLD) and thickness distribution were predicted and compared. The FLD obtained through this process and conventional FLD were different. Comparison of FLD and thickness distribution showed that cone had higher forming limit than square cup and the thickness after forming was better in cone shapes than in square cups [43]. An investigation was made on the deformation characteristic of embossed aluminum sheet in the incremental sheet forming process in which the surface quality of tool path along outward and inward movement was compared and noted as surface quality is better in the outward movement. Using ABAQUS software, a finite element simulation, the experimental results and detailed forming mechanism of the 3D structured sheet

Formability of friction welded blank made of aluminum 6061 was studied experimentally. Formability was evaluated through FLD, dome height, minimum thickness, and thickness distribution. Many experiments were conducted to know which joining direction caused higher formability and desired forming limit curve. Joints were prepared in three different rollings (0, 45, and 90°) and tested for formability test and compared with FLD, dome height, minimum thickness, and thickness distribution. From the formability comparison, the best joining direction was identified. Using the response surface methodology, the effect of welding process parameters such as rotational speed, plunge depth, and travel speed on formability of welded blanks was analyzed. After finding the effects, welded blanks with optimal parameter combination were fabricated and the effect of incremental forming parameters, that is, spindle speed, feeding rate, and axial step on thickness distribution was analyzed. From the results, it was obtained that joints with diagonal direction caused higher value of bowl height [45]. The effect of longitudinal ultrasonic vibrations on the performance of the incremental forming process of aluminum-1050 sheet was studied. In this technique, ultrasonic vibrations with high frequency and low amplitude were axially added to the movement of forming tool. This system is arranged with different parts including a mechanism attached into the chuck of CNC machine and ultrasonic power to the vibratory tool. Parameters like forming force and sheet formability were examined through straight groove

annealed sheet shows higher formability than the pre-aged sheet [41].

**158**

were reviewed [44].

test in both conventional and ultrasonic-assisted incremental forming process. The results showed that formability increased and forming force decreased with ultrasonic assistance [46].

Using the finite element method, the behavior of the state of stresses and strains in the hot incremental sheet forming of 1050 aluminum alloy was evaluated, with and without pre-heating. With the assistance of RADIOSS software, numerical simulation was performed. The results were presented a deterioration in the force during electric hot incremental sheet forming compared to the electric hot incremental sheet forming [47].

The formability of the AA2024-O aluminum alloy sheet material was evaluated with respect to the impact of forming tool shape, tool diameter, wall angle, step size, sheet thickness, and tool rotation. Forming depth was measured by scanning the components using a noncontact 3D scanner. Wall angle and step size had proved more significant factors which affect the formability greatly [48]. An attempt was made to optimize the incremental forming parameters (spindle speed, tool feed, and step size) for surface roughness to be least and wall thickness to be larger using the response surface method.

The formability of AA5052 alloy sheets at room temperature was checked with pre-cut holes at the center with different diameters. In the forming operation, coneshaped parts were formed with the optimized values. Formability was compared with sheet with smaller holes and larger holes and it was observed that smaller holes had better formability. Also, the thickness of the formed part wall without hole is less. As the diameter of the hole increases, the wall thickness also increases [49].

To evaluate deformation behavior of AA-6061 aluminum alloy sheet, the single point incremental forming (SPIF) process was chosen. To form the sheet into the desired conical shape, the SPIF experiments and finite element method simulation were performed and to measure the major and minor strains, the digital image correlation (DIC) method was used. The major and minor strains in post deformation results were compared with FEM results for AA6061 thin sheet material. An experimental fracture forming limit diagram was assessed using the punch stretching test.

Consequently, the effective plastic strains at the onset of fracture were predicted and compared with experimental data. In order to get insight into forming behavior and surface roughness, the microstructural examination on the truncated dome fabricated using optimized parameters was carried out through micro-texture analyses [50]. By using the electric hot incremental forming process (EHIF), the dimensional accuracy of parts has got more improvement compared to single-stage forming and double-stage forming at room temperature. The effect of EHIF process parameters, such as tool diameter, feed rate, step size, and current, on temperature was studied. For a cone of AA 1060, the maximum temperature, the average temperature, and the maximum temperature difference were measured. Besides, the response surface method and Box–Behnken design were employed, and they established corresponding models to predict targeted values [51].

AA 7075-O sheets were formed into variable angle funnels and 45° wall angle cones by SPIF. The same material was deep drawn and a bulge test part was formed to compare with SPIF. Moreover, the formed parts were sectioned and characterized for texture and surface finish at equivalent strains. To compare the strain paths of SPIF and deep drawing, finite element models were used [52]. For AA 1050 sheet metal, the deformation characteristics, forming behavior, and deformation mechanism of the SPIF process were evaluated. For process deformation characteristics such as dimensional accuracy, thickness distribution, true surface strain, von Mises stress, and equivalent plastic strain, evolved at different forming stages, were estimated through experimental investigation and finite element analysis. Analysis was carried out to identify the reason of typical failure under biaxial strain mode [53].
