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Unfolding |
General
remarks
An unfolding is
an equal-area projection of a 3D-surface to a plane. This transformation is
necessary, because the source material for lots of workpieces like tubes,
funnels nozzles, transition fits are based on planar sheets, boards or panels of
synthetics. Metal sheet constructors , plumbers, shipbuilders, roofers,
carpenters, model constructors are daily confronted with the problem to unfold
difficult bodies. Whereas it is relative easy to unfold cylindric and prismatic
bodies, it is very difficult to unfold rotation-surfaces, screwing-surfaces and
surface-penetrations. Free-Form-Surfaces. e.g. spanned synthetics,
boat-frames etc., are a particular challenge for every engineer. Using
classic drawing tools either it's not possible to unfold them or only by making
huge time and constructive efforts.
Before using the computer as a consequence thereof the CAD-Technic, but also
still today, the scriber supplies the basis of any unfolding. His spatial
imaginative power, accurate working and not at all his many years of experience
are necessary to generate the unfolding basing on the ready workpiece and to
draw the 2D-cutting-sheets.
After cutting the material the required parts can be produced by bending,
soldering, welding and adherence. Considering the workflow from all aspects
the 2D-cutting sheet is one of the most important. An incorrect cutting-sheet
requires always a costly reworking. According to the "try and
error"-principle at this point isn't effective. Before the cutting can
start an accurate drawing must be there.
In industry and crafts precise unfolding is the key-competence to meet the
requirements of modern production. Getting the 2D-cuttings-sheets fast and
correct is crucial factor for production.
Triangulation
In
mathematics you can find methods for some special cases (like pipe-bends,
T-pieces, Y-branch pipes etc.) to find templates for the cutting. These methods
are often implemented in CAD-programs. But if in praxis constructions differ
from this methods (e.g. free-form-surfaces, transition-fits, pipe-penetrations,
letters, geographical reliefs ) you really need innovative solutions. Unfolding
such things is only possible by dismantling in triangles. The surfaces to unfold
is divided in lathy triangles, which will be laid together in the x-y-plane.
Using this "triangulation" you can unfold most complexe bodies and
surfaces. But in practise this method is only suitable to a limited extend
without an computer because you can only get a limited numbers of triangles
using the manual method and complex 3D-curves (splines) are hardly controllable.
Innovative
Solution BLACK CAD V.6
Excatly for
this "triangulation-method" we compiled a program running under
AutoCADŽ / BricscadŽ. The only conditions is that the surface to unfold
got an upper and lower edge, which are linear-conform and the position of a
welding seam is defined in the 3D-model. So you can get 2D-cutting-sheets for
very complex bodies, created by transition-fits with the volume-modelling in
AutoCADŽ / BricscadŽ .