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ture set. The additional clamping takes precedence in most cases.
Regardless of the clamping sequence, it is the main clamping that
is solved prior to the additional clamping.
4.1 General solution concept of main clamping fixture
On a horizontal machining centre in one clamping, a maximum
of four faces of the workpiece are workable. When solving the
main clamping, one must try to find a position for the workpiece
in the workspace a of machining centre in which the machining
of all the connected faces is possible. In this way the greatest
accuracy of the workpiece can be obtained and the accuracy re-
quirement and the complexity of the fixture are the lowest. This
position of the workpiece is called the “technologically ideal
workpiece position”. The fixture determined in this way is the
best possible fixture solution.
However, in several cases the disposition of connected faces
means that the workpiece can not be held in a technologically
ideal workpiece position. In this case, it is necesary to find a pos-
ition of the workpieces in which at least the machining of strictly
connected faces is possible in one clamping. In other words, the
loosely connected faces in this stage are left out of consideration.
In this way, the fixture solution is still “fair”, but the accuracy
requirements refer only to the parallelism, or rather to the per-
pendicularity of any fixture surfaces.
If this attempt is not successful, then one must give up the
idea of machining all of strictly connected faces in one clamp-
ing. There are also cases when not the entire face, but only the
strictly connected features (holes) on the face are workable with
other strictly connected faces in one clamping (see Sect. 4.1.3).
Lastly, when none of these attempts is successful the strictly
tolerance-related features must be machined in separate clamp-
ings. In this case, the accuracy requirements of the fixture are
very high.
Taking into consideration the abovementioned aspects, four
strategies are devised for solving the main clamping.
4.1.1 Technologically ideal clamping
This strategy is aimed at finding the position of the workpiece
in the machine workspace, which would allow machining of all
the connected faces in one clamping. The potential position of
a workpiece in the machine workspace is determined from the
requirement that all connected faces should be machined in one
clamping. Depending on the plane locating type, this can be for-
mulated in the following manner:
• In the case of horizontal plane locating type pos1, the plane
locating face and its opposite face must not be tolerance-
related faces, because it is not possible to machine them
together with other faces in the same clamping.
• For a vertical plane locating type pos2, the plane locating
face, the face which is facing the machine table, and its op-
posite face, must not be tolerance-related faces.
In order to select the workpiece position, it should be satisfactory
for both plane and side locating and clamping (Fig. 7). Since the
horizontal plane locating (pos1) allows machining of four faces
(while pos2 allows only three faces to be machined) and the fix-
ture construction is simpler, the system first attempts to generate
a fixture solution for horizontal plane locating type. If that at-
tempt fails, a second attempt is made at solving the fixture for
vertical plane locating.
Suitability for plane locating. The selected workpiece position
is suitable for plane locating if the plane locating face contains
surfaces which are suitable for plane locating. If the workpiece
position is suitable for plane locating, then in the next step,