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R. Jagtap et al.
1 Introduction
Incremental forming (ISF) process is a novel, flexible sheet metal forming process.
It is also called as a die-less forming process because it does not require a dedicated
die for forming sheet metal parts [1]. Virtually, any part shape can be formed using
ISF process with minimum tooling setup, as parts using ISF are formed using a
numerically controlled machine such as CNC milling machine or a numerically
controlled robot arm [2]. It has a short setup time as well as lower production cost for
producing small number of different part shapes [3]. It offers many advantages over
conventional sheet metal forming method such as improved material formability,
small forming forces, die-less forming, short changeover time from one part shape
to other and design changes are quickly and easily carried out [4]. ISF has already
been used to form a variety of parts such as aircraft cowling [5], different aerospace
components [6], human prosthesis reconstruction [7], cranial implant [8], knee joint
[9], solar cooker [10], and car exterior skin part [11].
Despite its advantages over conventional sheet metal forming process, ISF is
not popular in industries due to its key shortcomings such as low geometric precision, uneven thickness along walls of formed component, localized thinning and long
forming time. Many researchers such as Ambrogio et al. [12] have studied and investigated the influence of parameters on thinning, formability and surface quality. Some
researchers used techniques such as tool path optimization [13], use of secondary
support [14], use of closed-loop control systems [15] and different tool geometries
[16] etc. to improve the geometric accuracy of formed parts. Researchers such as
Störkle et al. [17] also used robots instead of using CNC machined for forming.
The current ISF process development does not meet the quality of parts which is
acceptable in industries. Hence, some researchers [18, 19] studied and developed a
combined ISF process with some allied process called a HSIF process to improve the
quality of incrementally formed parts. As HISF process is in its early development
stage, only a few researchers such as Araghi et al. [19], Lu et al. [5] and Shamsari
et al. [20] have applied research efforts to study the HISF process comprising SPIF
combined with stretch forming process. It has reported by Araghi et al. [16], Lu et al.
[5], and Kumar and Kumar [21] that the HISF process is capable of improving forming
time, thickness distribution and thinning as compared to SPIF process. Hence, there
is stern need to apply more research efforts to develop a reliable HISF process which
can produce sound parts with uniform thickness distribution and reduced thinning in
short forming cycles.
The present study aims to develop HISF process comprising preforming and SPIF
process. Material flow in ISF and stretch forming are completely different, hence it
can be used to improve the thickness distribution and reduce thinning in formed
parts. Further, stretch forming is considerably faster than SPIF process, hence total
forming time can be reduced using SPIF and stretch forming. Figure 1 illustrates the
schematic representation of the proposed hybrid forming process. A simple and lowcost tooling setup is developed for forming conical frustums using proposed HISF
process. The objectives of the present experimental investigation are as follows:
R. Jagtap et al.
1 Introduction
Incremental forming (ISF) process is a novel, flexible sheet metal forming process.
It is also called as a die-less forming process because it does not require a dedicated
die for forming sheet metal parts [1]. Virtually, any part shape can be formed using
ISF process with minimum tooling setup, as parts using ISF are formed using a
numerically controlled machine such as CNC milling machine or a numerically
controlled robot arm [2]. It has a short setup time as well as lower production cost for
producing small number of different part shapes [3]. It offers many advantages over
conventional sheet metal forming method such as improved material formability,
small forming forces, die-less forming, short changeover time from one part shape
to other and design changes are quickly and easily carried out [4]. ISF has already
been used to form a variety of parts such as aircraft cowling [5], different aerospace
components [6], human prosthesis reconstruction [7], cranial implant [8], knee joint
[9], solar cooker [10], and car exterior skin part [11].
Despite its advantages over conventional sheet metal forming process, ISF is
not popular in industries due to its key shortcomings such as low geometric precision, uneven thickness along walls of formed component, localized thinning and long
forming time. Many researchers such as Ambrogio et al. [12] have studied and investigated the influence of parameters on thinning, formability and surface quality. Some
researchers used techniques such as tool path optimization [13], use of secondary
support [14], use of closed-loop control systems [15] and different tool geometries
[16] etc. to improve the geometric accuracy of formed parts. Researchers such as
Störkle et al. [17] also used robots instead of using CNC machined for forming.
The current ISF process development does not meet the quality of parts which is
acceptable in industries. Hence, some researchers [18, 19] studied and developed a
combined ISF process with some allied process called a HSIF process to improve the
quality of incrementally formed parts. As HISF process is in its early development
stage, only a few researchers such as Araghi et al. [19], Lu et al. [5] and Shamsari
et al. [20] have applied research efforts to study the HISF process comprising SPIF
combined with stretch forming process. It has reported by Araghi et al. [16], Lu et al.
[5], and Kumar and Kumar [21] that the HISF process is capable of improving forming
time, thickness distribution and thinning as compared to SPIF process. Hence, there
is stern need to apply more research efforts to develop a reliable HISF process which
can produce sound parts with uniform thickness distribution and reduced thinning in
short forming cycles.
The present study aims to develop HISF process comprising preforming and SPIF
process. Material flow in ISF and stretch forming are completely different, hence it
can be used to improve the thickness distribution and reduce thinning in formed
parts. Further, stretch forming is considerably faster than SPIF process, hence total
forming time can be reduced using SPIF and stretch forming. Figure 1 illustrates the
schematic representation of the proposed hybrid forming process. A simple and lowcost tooling setup is developed for forming conical frustums using proposed HISF
process. The objectives of the present experimental investigation are as follows: