March 2014
219
Tracto-Technik GmbH & Co KG
Article
Tracto-Technik GmbH & Co KG
– Germany
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The key issue is to consider the changing distances between
the alterable inside diameter of the tube and the outside
diameter of the mandrel, which supports the tube during the
bending process and prevents the bend from collapsing. Much
more complex is the bending of “tailored profiles”, because in
that case special adaptations of all bending tools have to be
applied.
Due to high competitive pressure the quality of the finished
bending parts is crucially important to succeed in the global
market. Special quality criteria ensure that the tendency
towards constant rise of customer and quality requirements is
taken into account when selecting a specific bending process
[10, p.433]
. The criterion shape and positional tolerances defines
the permissible deviation of the bending part compared
with its reference geometry. Category 1 allows considerable
deviations, which could probably be realised by most of
the bending methods. Category 2 presupposes closer
tolerances, which are usually obtainable by all semi-finished
parts whose tolerances are within the standards. Category
3 describes high dimensional accuracies with adherence
to very close tolerances. This category therefore requires a
thorough evaluation of the eligible bending method(s) as well
as selection of semi-finished parts which meet the highest
demands where tight tolerances regarding the geometrical
dimensions are concerned. After the bending products of
category 3 need often a hydroforming calibration.
Semi-finished parts with high-quality surfaces are crucially
important particularly in terms of tube and profile assembling
as visible parts. In order to consider this when selecting
a bending method, the surface factor describes allowable
damages or deviations of the bending part’s surface. The
surface factor is also classified into three categories, starting
with allowable deviations from the reference surface quality
(eg deep scratches and grooves as well as geometrical
deviations at the inside curve) over minor deviations without
any technical or functional losses up to a flawless surface.
Commercialisation and follow-up
of the research results
The criteria for categorisation of bending performances
introduced above allow a sufficiently clear description of
tube and profile bending parts in regard to their production
complexity. During the course of the project the criteria are
being further developed and refined. Based on these criteria
it is possible to pre-select an optimum bending method for a
certain bending part, taking into account the bending part’s
geometry and the manufacturing limitations of the bending
method at the same time.
Suggestions and validation of the criteria by industry are
considered. By transferring the research results of this
project into a national or international standardisation process
the criteria should become industry standards. Overall
acceptance of the standards is the prerequisite and can be
used for increasing the application possibilities of tube and
profile bending parts. Actual and future work deals with the
categorisation of the big range of different bending processes
and their variations and tool setups. The design of a detailed
catalogue which includes the performance of each process is
now worked out.
This project receives financial support by the German Federal
Ministry of Economics and Technology according to a decision
of the German Federal Parliament.
References
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Torsion factor 1
Torsion factor 2
Torsion factor 3
Figure 4: The torsion factor describes the component’s geometry with regard to deformation due to torsion
[6]
