Siemens Sinumerik 840D Operating Turning page 42

Section 5
Programmable presettings
Notes
When starting a part program the basic settings as defined by the manu-
facturer will be activated. These depend on the individual machine specifi-
cation and apply thereafter for the whole of the program run (modal) unless
they are changed by the operator by programming.
This section describes just a few of the possible selections for turning- and
milling machines that deserve highlighting
(Codes that have already been dealt with are no longer included).
Continuous path behaviour:
*
Exact stop Code G9 block-by-block Code G60 modal
In order to reach the final position precisely the path velocity is reduced at
the end of the block towards zero. This is useful, for instance, to obtain
relatively sharp edges when machining around contour corners.
However, it must be borne in mind that, if there are too many positioning
sequences, it will result in increased machining and cannot be neglected.
Continuous control operation Code G64
In this case the tool moves as much as possible with constant velocity
without deceleration at the end of a block. Hence the machining time is
less than under the continuous path status "Exact stop".
The corners of contours are machined without any relief and therefore the
corners are not so sharply defined.
With this function the control works with a speed control taking into ac-
count several blocks ahead (Look ahead).
The even speed in this instance results in better cutting conditions and
also a better surface quality.
The following image compares the frequent braking and accelerating se-
quences between the individual blocks in case of G60 and the constant
speed in case of G64.
*
Usual preset starting status
Feed rate
G64 Continuous operation
with look ahead
Programmed feed rate
G60 Exact stop
Block path
B501
B501
Page 6 840D/828D SINUMERIK Operate