Republic of Iraq
Academic
Teaching
and Training
Development
Center
Ministry
of Higher
Education
and Scientific
Research
University of Kufa
Materials Engineering Department /College of Engineering
Incremental sheet metal Forming
B.SC Students of Materials Engineering
University of Kufa / College of Engineering
Maythem_saad@yahoo.com
Dec.2014
Contents
1. Aims of this Lecture
2. Introduction
3. Incremental Sheet Metal Forming(ISMF)
4. Application of Incremental Sheet Metal Forming
5. Variant of Incremental Sheet Metal Forming Process
5.1 Single point incremental forming (SPIF)
5.2 Two point incremental forming (TPIF)
6. Description of SPIF Process
7. Basic Process Parameters
8. Tools & equipment’s
9. Forming Tool Path
10. Advantages and Disadvantages of the SPIF Process
11. Summary
12. References
1. Aim of the lecture
The aim of this lecture is:
 Student knowledge on the modern forming process such incremental sheet
metal forming process, types this process, working principle, tools and
equipment required to carry out this process as well as identify the most
important factors associated with the success of this process, which should
be observed to produce high-accuracy product.
 Knowledge the applications of this process
 Learning the geometric modeling and tool path generation mechanism and
engineering programs used to achieve it
 Knowledge the advantages and disadvantages of this process.
2. Introduction
Nowadays, many industrial sections use traditional forming processes like
deep drawing and stamping in order to manufacture sheet metal components with
high productivity by using dies and punches that depend on the dimensions of the
component. These processes need large initial investments and long diepreparation times, with specific dies for each part, particularly when the parts have
complex shapes or are only needed in small series, as it is the case with unique
aeronautic and automotive parts. Because of the high cost of dies and punches, the
conventional manufacturing method is adequate only for mass production
Due to the recent diversification of the customer's demand and fast
development of the manufacturing automation technology, new manufacturing
methods for a small-size production need to be developed. By the early nineties
research efforts succeeded in the development of a new non-conventional sheet
metal forming process, namely Incremental Sheet Metal Forming (ISMF), as a new
promising technology.
3. Incremental Sheet Metal Forming (ISMF)
The incremental sheet metal forming is a highly flexible method, which does
not require expensive tools for manufacturing of complex shaped parts, and the
forming equipment is suitable for large variety of products without matched tool or
expensive investments. This process can be carried out on CNC milling machine,
which doesn’t require any high capacity press machine and a specific shaped die.
Parts can be formed directly from CAD data; therefore, it is suitable for rapid
prototyping or small volume production. This possibility also leads to the benefits
of flexible and fast design changes.
In the ISF process, the localized deformation is one of the outstanding features
of this novel technology, which enhances the formability and flexibility of the
sheet metals. Therefore, it is suitable for a wide range of sheet metal materials.
4. Application of Incremental Sheet Metal Forming
Incremental sheet metal forming (ISMF) is the process characterized by high
flexibility; for this reason, it is suggested for rapid prototyping and customized
products. The ISMF applications can be separate in two different main areas:
 Rapid prototyping for automotive industry
Reflexive surface for headlights.
Automotive heat/vibration shield
 Medical applications
Cranial plate.
Ankle support
Dental plate
5. Variant of Incremental Sheet Metal Forming Process
Incremental sheet metal forming can be divided essentially into two major
types, depending on the number of contact points between sheet, tool in addition
die (when present) as shown in figure(1.1). Single point incremental forming
(SPIF), where the sheet is deformed only by the tool, and no support is present,
while in the two point incremental forming (TPIF), where the sheet is deformed by
means of a tool and a local support or a regular die.
Figure (1.1): Process variants in ISF.
5.1 Single point incremental forming (SPIF)
Single Point Incremental Forming (SPIF) is an innovative flexible sheet metal
forming process, which can be used to produce complex shapes from various
materials. Due to its flexibility, it attracts a more and more attention in the recent
decades. SPIF process was developed from sheet metal spinning, sheet metal shear
flowing and hammering with included CNC technique to control the forming tool
movement. This technique allows a relatively fast and cheap production of
prototypes or small series of sheet metal parts. Also, the process is capable to
manufacture a variety of irregular-shaped and axisymmetric components and
highly customized medical products in small batches.
In single point incremental forming, the sheet is placed on CNC machine table by
means of a simple frame, able to clamp the sheet during the process. A sheet metal
part is formed in a stepwise fashion by a CNC controlled; rotating, spherical tool
without the need for a supporting (partial) die. Figure (1.2) illustrates the basic
incremental single point forming process.
Figure (1.2): The basic SPIF process.
5.2 Two point incremental forming (TPIF)
TPIF is based on the presence of a partial or full dies, which supports the sheet
during the deformation. When using TPIF, the sheet is deformed in two points: the
contact points between tool and sheet and between sheet and die as shown in figure
(1.3). This method of sheet deformation can cause a decrease of sheet formability
in comparison with SPIF, but it allows increasing the geometric accuracy reachable
in a single pass. Using this sheet incremental forming technique, it is possible to
obtain a good dimensional accuracy of the part geometry (reduced spring back)
and it makes TPIF more interesting than SPIF for the industrial application in
realizing complex shape prototypes.
(b)
support
Figure (1.3): Two point incremental forming
(a) TPIF with partial die and (b) TPIF with full die.
6. Description of SPIF Process
Single point incremental forming (SPIF) is a process that uses principles of
layered manufacturing. It transforms the complicated geometry information into a
series of parameters of two-dimensional layers, and then the plastic deformation is
carried out layer-by-layer through the computer numerically controlled movements
of a spherical forming tool to get complex-shaped parts.
In this method, the CAD model is horizontally sliced throughout passing
horizontal planes in the CAD model as shown in figure (1.4). The number of these
planes is responsible for the product accuracy.
Figure (1.4): The layered manufacturing concept used to form the part using ISMF.
The tool path can automatically be generated for each slice by following the
contour of that slice using ISMF technique as shown in figure (1.5).
a
b
c
d
Figure (1.5): Steps and tool traveling for each layer of SPIF.
Since ISF process is carried out on 3-axis CNC milling machines, the process
can be successfully automated and CAD/CAM system can be truly integrated by
converting the 3D CAD model to CAM system and then post processed by
programming system to generate the required G-cod according to the forming
requirements of the sheet. These trends make the
repeatability an easy task and
open unexpected scenarios in the industry.
7. Basic Process Parameters
Several parameters as shown in figure (1.6) affect the process mechanics in
single point incremental forming and therefore play a role on accuracy, forming
time, surface finish and thickness variation such as:
1. Forming tool path (FTP)
2. Tool diameter (d)
3. Z- incremental value (∆Z)
4. Spindle speed rpm (ω)
5. Feed rate (F)
6. Sheet thickness (t)
Tool Path
Figure (1.6): Basic process parameters.
In particular, the accuracy of the final geometry mainly depends on the chosen
Z-increment and tool diameter: at increasing of Z-increment a greater thinning and
heavier stretching condition are obtained together to a worst surface quality while
larger tool diameter improves the surface quality, but reduces material formability,
due to the larger contact surface.
8. Tools & equipment’s
1) 3-axis CNC Machine
3) Forming tools
2) SPIF clamping system
4) Lubrication condition
9. Forming Tool Path
The tool path is the path that forming tool follows its way through space to
produce the desired geometry of the product.
ISMF process depends strongly on the Forming Tool Path (FTP) which
influences greatly the part geometry and sheet thickness distribution. Tool path
generation became key topic in incremental sheet forming. It is essential to develop
dedicated tool paths to improve the efficiency of this process. The part geometry
can be generated using MATLAB programming system or any programming
system contains CAD system as shown in (Fig. 1.7), and then transferred to CAM
system to generate the required G-code through post-processed.
Figure (1.7) show geometric modeling and generated tool path
Figure (1.8) Scheme illustrates the CAD / CAM Integration of manufactured parts
10. Advantages and Disadvantages of the SPIF Process
 The main advantages are:
 Production of parts directly from the CAD file;
 Inexistence of full or partial die;
 Design changes can be easily and quickly performed;
 Increase of material formability;
 Can be performed in a conventional CNC machine;
 Due to the incremental nature of the process, forces are small;
 Good surface finish quality can be achieved.
 The main disadvantages are:
 Longer forming time compared with conventional Deep Drawing Process;
 Limited to small size production batches;
 The forming of right angles must be achieved by multi-stage strategies;
 Difficult to form sharp corner & edge because crack easily occurs.
 Geometrical errors occur such as Spring back, pillow effect and sheet bending
as shown in figure (1.9)
Figure (1.9): Geometrical errors during the SPIF process.
11. Summary
 The incremental sheet metal forming is a highly flexible method and does
not require expensive tools for manufacturing of complex parts.
 SPIF less cost compare with conventional forming.
 SPIF is suitable for rapid prototyping or small volume production.
 SPIF has high formability.
 ISF has some limitations including long processing time, low accuracy.
 Tool path generation is a key topic in incremental sheet forming.
12. References
1. S.H.Wu, Ana Reis, F.M. Andrade Pires, Abel D. Santos, A. Barata da Rocha “Study of tool
trajectory in incremental forming” Advanced Materials Research Vols. 472-475 pp (15861591), 2012.
2.
Mohamed Azaouzi , NadhirLebaal “Tool path optimization for single point incremental
sheet forming using response surface method“ Simulation Modeling Practice and Theory ,
pp.(49–58),2012.
3. S. B. M. Echrif and M. Hrairi, “Research and Progress in Incremental Sheet Forming
Processes”. Materials and Manufacturing Processes, pp.(1404–1414), 2011.
4. S. Dejardina, S. Thibaudb, J.C. Gelina, G. Michela. “Experimental investigations and
numerical analysis for improving knowledge of incremental sheet forming process for sheet
metal parts”, Journal of Materials Processing Technology Vo. 210, Issue 2, pp. (363-369),
2010.
5. R.B. Patil “ CAD/CAM & Automation”, Department of Mechanical
pune,India,2008.
Engineering,