Experimental Investigation on Geometric Error …
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accuracy, and (iii) final accuracy of formed part. Further, Micari et al. [8] subdivided
the shape accuracy as (a) bending of sheet along the clamped edges from where the
plastic deformation initiates, (b) spring-back in formed part after tool/punch is raised
after forming operation, and (c) pillow effect. If a simple truncated conical shape
is to be deformed, these three different errors can be detected on it after forming
operation. Bending of sheet along the clamped edges is normally solved simply by
the use of backing plate. Secondly, when the tool/punch is relaxed after forming the
deformed sheet, metal part slightly rises upward and the final forming depth of part
is lesser than target depth. Finally, pillow defect can be seen as central undeformed
concave region.
Worldwide researchers have made efforts to improve geometric accuracy and
proposed various different strategies for enhancing it. For example, Ceretti et al. [9]
proposed SPIF process with and without full die to form some complex part shapes.
They reported that considerable improvement in geometric accuracy of part was
achieved by using die as compared to the part formed without die. They suggested
to fabricate the die using cheap and easily available material to reduce the tooling
cost. Hirt et al. [10] focused on two main process limitation, namely maximum
formable wall angle and poor geometrical accuracy. It was observed that multi-stage
forming approach is capable of forming steep flanges of the order of 81° while
an improvement algorithm helps to reduce profile deviation. Ambrogio et al. [11]
studied the influence of process parameters, namely tool diameter, step size, wall
angle, forming depth, and sheet thickness on profile deviation of the truncated cone
formed by SPIF process. It was observed that the profile deviation measured along
the corners was mainly influenced by thickness of sheet and forming depth while
pillow effect which was at the middle of the base was majorly influenced by the
size of tool and forming depth. Ambrogio et al. [12] have made efforts to improve
industrial suitability of SPIF process by studying influence of high feed rate on
geometric accuracy. Higher forming time was identified as major limitation and it
was suggested that it can be overcome by using high feed rates. It was found that
with smaller tool diameter good geometrical precision is obtained. Bambach et al.
[13] have formed sheet metal fender of car using SPIF process. They used multistage forming process to improve the accuracy of asymmetrical component. They
suggested that the geometric error of formed part could increase if the part is trimmed
after forming operation due to presence residual stresses. To overcome this limitation,
stress-relief annealing combined with multi-stage forming process was used. It was
observed that multi-stage forming results in higher accuracy as compared to singlestage forming process. But accordingly, the forming time is increased, making multistage forming slower than single-stage forming. Ziran et al. [14] have investigated
tool geometry (hemispherical and flat ended tool) on profile accuracy (or geometric
error) in SPIF process. It was reported that with flat-end tool, low geometric error
is observed and lower forming force is recorded as compared to hemisphericalended tool. Gottmann et al. [15] proposed new setup for laser-assisted SPIF process.
Two main limitations of asymmetric incremental sheet forming (ASIF) (i.e., low
geometrical accuracy and low formability) at room temperature were studied. It is
reported that formability and profile deviation of formed component of Ti grade
83
accuracy, and (iii) final accuracy of formed part. Further, Micari et al. [8] subdivided
the shape accuracy as (a) bending of sheet along the clamped edges from where the
plastic deformation initiates, (b) spring-back in formed part after tool/punch is raised
after forming operation, and (c) pillow effect. If a simple truncated conical shape
is to be deformed, these three different errors can be detected on it after forming
operation. Bending of sheet along the clamped edges is normally solved simply by
the use of backing plate. Secondly, when the tool/punch is relaxed after forming the
deformed sheet, metal part slightly rises upward and the final forming depth of part
is lesser than target depth. Finally, pillow defect can be seen as central undeformed
concave region.
Worldwide researchers have made efforts to improve geometric accuracy and
proposed various different strategies for enhancing it. For example, Ceretti et al. [9]
proposed SPIF process with and without full die to form some complex part shapes.
They reported that considerable improvement in geometric accuracy of part was
achieved by using die as compared to the part formed without die. They suggested
to fabricate the die using cheap and easily available material to reduce the tooling
cost. Hirt et al. [10] focused on two main process limitation, namely maximum
formable wall angle and poor geometrical accuracy. It was observed that multi-stage
forming approach is capable of forming steep flanges of the order of 81° while
an improvement algorithm helps to reduce profile deviation. Ambrogio et al. [11]
studied the influence of process parameters, namely tool diameter, step size, wall
angle, forming depth, and sheet thickness on profile deviation of the truncated cone
formed by SPIF process. It was observed that the profile deviation measured along
the corners was mainly influenced by thickness of sheet and forming depth while
pillow effect which was at the middle of the base was majorly influenced by the
size of tool and forming depth. Ambrogio et al. [12] have made efforts to improve
industrial suitability of SPIF process by studying influence of high feed rate on
geometric accuracy. Higher forming time was identified as major limitation and it
was suggested that it can be overcome by using high feed rates. It was found that
with smaller tool diameter good geometrical precision is obtained. Bambach et al.
[13] have formed sheet metal fender of car using SPIF process. They used multistage forming process to improve the accuracy of asymmetrical component. They
suggested that the geometric error of formed part could increase if the part is trimmed
after forming operation due to presence residual stresses. To overcome this limitation,
stress-relief annealing combined with multi-stage forming process was used. It was
observed that multi-stage forming results in higher accuracy as compared to singlestage forming process. But accordingly, the forming time is increased, making multistage forming slower than single-stage forming. Ziran et al. [14] have investigated
tool geometry (hemispherical and flat ended tool) on profile accuracy (or geometric
error) in SPIF process. It was reported that with flat-end tool, low geometric error
is observed and lower forming force is recorded as compared to hemisphericalended tool. Gottmann et al. [15] proposed new setup for laser-assisted SPIF process.
Two main limitations of asymmetric incremental sheet forming (ASIF) (i.e., low
geometrical accuracy and low formability) at room temperature were studied. It is
reported that formability and profile deviation of formed component of Ti grade