Metal deforming – With indication of condition or position of work – product,... – Including deformation by simple bending
Reexamination Certificate
2000-08-02
2003-04-01
Jones, David (Department: 3725)
Metal deforming
With indication of condition or position of work, product,...
Including deformation by simple bending
C072S031110, C072S389300, C072S702000
Reexamination Certificate
active
06539763
ABSTRACT:
TECHNICAL FIELD AND PRIOR ART
The invention relates to a press brake used in particular for bending metal sheets.
An example of a press brake, as known in the prior art, is shown schematically in
FIGS. 1 and 2
.
It comprises an upper beam
1
placed above a lower beam
2
. The latter is a fixed beam, bearing on its ends, while the upper beam
1
is a moving beam and is actuated in a vertical plane by drive members located also at its two ends.
The drive members deliver the force needed to bend the metal sheets or plates.
More specifically, the beams
1
,
2
are mounted in a frame formed from two side plates
9
a
and
9
b
joined together especially by a bracing beam (not shown).
The upper beam
1
and the lower beam
2
are contained in the same vertical plane and the upper beam slides with respect to the side plates
9
a
and
9
b
with the aid of guiding means
8
a
and
8
b
consisting, for example, of two hydraulic rams.
Working edges of these two, upper and lower, beams bear a bending punch P and a corresponding die M, respectively.
As may be seen in
FIG. 2
, the lower part
4
of the lower beam
2
is fastened, by welding or by any other means, at its ends to the side plates
9
a
and
9
b
forming the frame of the press brake.
FIG. 3
shows a sheet
10
placed on the die M in which a “V”, which will allow the bending, is formed. A force F is exerted along the axis of the “V”, and at the extreme tip
12
of the punch P, in order to bend the sheet.
The bend angle of a metal plate or sheet depends on the extent of penetration of the punch P into the die M.
A press brake may, in general, carry out three types of bending.
The relative movement of the punch may be stopped at the stage shown in FIG.
4
. This represents a first type of bending, called “3-point air bending”.
This type of bending is obtained by limiting the stroke of the beam
1
during the set-up of the machine.
If, on the contrary, the penetration is increased, the sheet
10
descends into the “V” up to a limit defined by the bottom of the V (FIG.
5
). This represents the technique called “semi-coining”. This technique has furthermore the following characteristics:
the radius Ri of the sheet, or plate,
10
, internal to the bent zone, is in general equal to or slightly greater than the thickness of the sheet;
when the pressure of the punch is released, reopening of the bend occurs, due to the residual elasticity of the sheet
10
.
Finally, if the force is again increased, the tip
12
penetrates the sheet
10
and “swages” the bend radius (FIG.
5
). This represents so-called “coining” bending which has the following features:
the inside radius Ri is less than the thickness of the sheet; it is determined by the radius of the punch;
the bend angle is equal to that of the “V” of the die M and of the punch, the elasticity of the sheet having disappeared.
In the case of 3-point air bending, since the side walls of the bend, of the punch and of the die are never in contact with one another, the shape of the die is of little importance. It may, moreover, be a U.
Compared with bending to the bottom of the “V” and coining, air bending is that requiring the least force and the metal remains highly elastic.
These elements mean that this bending shape is the most sensitive to angular variations and requires particular attention in carrying it out.
In particular, in “3-point” bending, experience shows that a mechanical difference of {fraction (1/10)} of a millimeter, measured for example between two 12-tip elements of two punches, results in an angular variation of 2° in bending a 2 mm sheet performed in a V of 12 (i.e. 6 times the thickness).
In general, and still in the case of “3-point” bending, using a width corresponding to 8 to 12 times the thickness of the sheet
10
to be bent allows partial bending to be carried out with a tolerance of ±1°.
This is the optimum precision obtained with air bending.
A method making it possible to help in carrying out bending operations with optimum precision consists in using a protractor
16
, mounted as illustrated in FIG.
6
: the sheet
10
can bear on the arm
18
of the protractor, said arm being mounted on the die M.
When the edge of the sheet
10
is parallel to the arm of the protractor, the pressure on the punch is reduced to the minimum with the aid of the power control so as to allow the sheet to release the elastic bending stress. The angle A of this elasticity is determined with respect to the desired angle indicated by the protractor.
Next, the pressure is increased so as to increase the depth of bending of the elasticity angle, mentioned above (angle A).
The technique of “semi-coining” also results in springback of the sheet. Consequently, tooling with an 88° apex angle, for example, is chosen for 90° bending. This 88° angle may be reduced to 85° for thick sheets.
The bending precision, under optimum conditions, allows a tolerance of ±30 minutes of angle to be achieved.
The coining bending is that which allows the highest angular precision to be achieved, the elasticity of the sheet being eliminated. However, this type of bending requires it to be possible to increase, during the 2
nd
phase of the bending, the force applied to the punch so as to bring the sheet edges back onto the side walls of the V of the die. The angle of the tooling is then the desired bend angle. The tools used must therefore be very accurate in order, in turn, to form the sheet to their specific characteristics.
The angular precision obtained with this type of bending may at best be 15 minutes of angle.
Consequently, it is apparent that the question of the precision of a press brake is a critical problem which, in most cases, is difficult to solve.
Moreover the bending precision is all the more difficult to obtain the thinner the sheet
10
.
For heavy plate, unlike thin sheet, the imperfections become negligible compared with the unitary penetration for 1°.
There are also numerical control presses in which an operator enters a desired angle. The control then calculates the penetration and the force that are needed to obtain the desired angle. The calculation is performed with the aid of a known formula or with one developed by the user.
However, this formula can only be an approximation of reality and is not in general applicable to all cases or in the various types of bending, or does not have the same precision in all cases and in the various types of bending.
The problem arises as to how to make the bending machines more precise.
In particular, the problem arises of how to obtain a more precise calculation, or a more precise evaluation or indication, of the bending penetration. Document JP-60-247 415 describes a press brake provided with a means for measuring distances between a lower tool and an upper tool and with a computing means for calculating an effective bend angle of a workpiece as a function of the distance measurements made. The effective bend angle is compared with the bend angle to be attained, and a correction to the descent of the tool is determined. A memory stores information relating to the relationship between the effective bend angle and the bend angle to be attained, and the bend angles and the level of descent of the tool.
The device described in that document involves a step of calculating the effective angle from measured distances and determines a correction to the descent of the tool according to these measured distances.
The precision obtained with this type of device is not satisfactory. This is because the calculation made during the calculation step is necessarily limited in its precision and its validity.
Furthermore, this method does not make a distinction according to the various types of bending carried out. An angle calculated for one measured distance and for one given type of bending is not necessarily valid, or does not necessarily have the same type of precision, for another type of bending.
SUMMARY OF THE INVENTION
The subject of the invention is firstly a numerical control system for a bending machine, comprising:
means for input
Amada Europe
Jones David
LandOfFree
Precision press brake does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Precision press brake, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Precision press brake will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3009751