Method for wire bending in three dimensions

Method, applicable to two-dimensional wire bending machines for extension of their operation in bending to form three-dimensional wire frames, which is characterised by the application of a torsional moment along the axis of the wire and before the bending region, causing a permanent plastic deformation of the wire, by twisting it beyond the elastic region, with eventual result any bending action already occured in the regular plane of the two-dimensional bending macnine to be positioned a new plane, which form an angle with the regular plane equal to the remaining due to plastic deformation angle of twist.

The invention refers to a method allowing wire bending machines to form 
three dimensional wire frames, characterised by the application of a 
torsion along the axis of the wire, causing a permanent plastic 
deformation of the wire, by twisting it beyond the yield point. 
STATE-OF-THE-ART 
The applicant is aware of the following cited references: 
______________________________________ 
Patent No. Date Name 
______________________________________ 
1,272,552 7/1918 Spencer 
3,052,277 9/1962 Stegman 
3,857,272 12/1974 Gott. et al. 
4,020,669 5/1977 Gott. et al. 
4,662,204 5/1987 Saegusa 
4,653,301 3/1987 Meliga 
4,735,075 4/1988 Saegusa 
______________________________________ 
U.S. patent application No. 07/505,682 Anagnostopoulos, filed Apr. 9, 1990, 
now U.S. Pat. No. 5,088,310, issued Feb. 18, 1992. 
The general comments on these inventions are: 
There is a great variety of wire bending machines, manually operated, 
semi-automatic and fully automatic for the formation of two-dimensional 
plane wire frames. The construction, however, of machines, especially 
fully automatic, for the formation of three-dimensional wire frames, 
offers much greater difficulties. 
For the formation of three-dimensional wire frames the following methods 
have been used: 
(A) The Bending Head, already used for the formation of two-dimensional 
wire frames is movable, able to rotate about axis which coincides with the 
axis of feeding of straightened wire (U.S. Pat. No. 4,735,075). 
(B) One additional Bending Head is used, which is placed after the regular 
Bending Head for the formation of two-dimensional wire frames and which, 
in the non-operational mode, is placed below the plane of two-dimensional 
formation of wire frames. 
In the operational mode, the additional Bending Head comes out of the 
plane, engages the wire and bends it at a plane which forms a specific 
angle with respect to the regular two-dimensional plane of the machine 
(U.S. Pat. No. 07/505,682). 
(C) Instead of rotating the Bending Head about the axis of the wire, the 
rotation of the wire about its axis. This method assumes the bending of 
straight portions of wire and usually it is in application, in tube 
segments (U.S. Pat. No. 4,662,204). 
The main problems of these methods for the formation of three-dimensional 
frames are the following: 
(a) The rotation of the Bending Head requires additional complicate 
mechanisms. 
(b) The rotation of the Bending Head sets several restrictions regarding 
the dimensions and the shapes of the three-dimensional frame to be formed, 
caused by the space requirements for the rotation of the Head. 
(c) If an additional Bending Head is to be used, the resulting disadvantage 
is the fact that the plane of additional bending is at certain angle with 
respect to the initial bending plane. 
(d) If an additional Bending Head is to be used, additional backward and 
forward movements of the wire to be bent are required for the application 
of the additional Bending Head at the exact point on the wire. In 
practice, the two Bending Heads are placed at a specific unaltered 
distance one from the other. If the wire is to be bent by the two heads, 
alternatively, at two points of distance less than the distance of the two 
bending heads, additional movements are required for the application of 
the Bending Heads at the exact points. 
(e) If additional Bending Head is to be used, the regular plane for the 
two-dimensional wire frames formation sets restriction in the shapes of 
3-d frames to be formed. This plane allows the additional Bending Head to 
bend between 0.degree. and 180.degree. only, while the regular Bending 
Head is allowed to bend from -180.degree. to +180.degree. . 
(f) Finally, the additional Bending Head requires complicate mechanisms for 
its exit and entrance out and in the regular Bending plane. 
THE PRESENT INVENTION 
It offers a very simple method for the formation of three-dimensional wire 
frames by already existing two-dimensional, plane, Bending Machines. The 
method uses for the formation of three-dimensional wire frames, as 
additional elaboration of the wire, the "torsion" and not the "bending" of 
the wire already used by common three-dimensional Wire Bending Machines. 
For the formation, in the present invention, of the third dimension shape, 
the wire is not bent in the plane of this third dimension, either by means 
of an additional Bending Head or by means of rotation of already existing 
Bending Head, but rather after its regular two-dimensional plane bending 
the wire is forced to twist by an additional torsional mechanism, about 
its initial straight axis, at an angle of twist exceeding its yield point 
strain. A permanent plastic deformation is caused, in such a way that the 
already applied bending action to refer to plane at angle equal to 
twisting, remaining plastic deformation, angle. The applied torsion on the 
wire is of such value that the remaining after plastic deformation, angle 
of twist, corresponds to angle of the additional bending plane. 
The resulting advantages of the present method are the following: 
(a) The mechanism for the application of torsion is very simple and does 
not require complicate or combined operations. 
(b) It does not set any restriction in the formed three-dimensional wire 
frame because it is placed before the Bending Head at the straight portion 
of the wire. 
(c) The angle of the additional bending plane may be arbitrary. 
(d) No additional forward and backward movements of the wire are required 
for the application of the Bending Heads at the exact points. 
(e) No additional mechanism is required to exit and enter the additional 
Bending Head from the regular bending plane. In fact, the mechanism for 
the application of the torsion is permanently installed below the bending 
plane. 
(f) The predetermination of applied torsion is easy, allowing the 
programming of torsion as well as bending actions with result in ability 
of process automation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The plane (1) which coincides with the figure plane, is the regional 
bending plane for 2-D or plane wire frames and represents the plate of 
bending of a 2-D Bending Machine. 
The wire enters the machine from the left and moves to the right following 
the axis X--X until the Bending Head (6). Mechanism (2) straightens the 
wire. Mechanism (3) measures the length of the wire as it is progressed. 
Mechanism (4}applies the torsion on the wire, which is used for the 
formation of three-dimensional wire frames, in a way described below. Wire 
guide (5) guides the wire to the Bending Head (6), which Head bends the 
wire on plate (1). The cutter (7) is used for cutting of the ready wire 
frame out of the advancing wire from coil. 
For the formation of a plane frame (i.e. of H shape) the following 
consecutive progressions, by mechanism (2), and bendings, by Bending Head 
(6), are required: progression of predetermined length--bending at 
specific angle--additional progression of predetermined length--additional 
bending at specific angle. 
If, at the end of the additional progression and before the additional 
bending, the wire is forced to a torsion by mechanism (4), in a direction 
forcing the already formed frame to move away from plate (1), then the 
additional bending will create a frame not on the plane of the machine but 
a three-dimensional one. 
The description of the mechanism for the application of the "torsion" 
(Mechanism 4) follows: The basic parts of the mechanism are the immovable 
gripper (8) and the rotating gripper (9) of the wire. In both grippers the 
hydraulic pistons (10) press the movable jaws (11) on immovable jaws (12) 
forcefully engaging the wire between them. The jaws are of selected length 
and of semi-cylindrical cross-section in such a way that no transverse 
normal plastic deformation to occur at the surface of the wire during the 
gripping action. 
The hydraulic fluid enters the pistons by the steady tube through the hole 
(13). In the rotating gripper (9) the hydraulic fluid comes with steady 
tube to hole (14) and fills the cylindrical space (15) which seals with 
the two sealing rings (16). Finally through the hole (17) it arrives to 
piston (10). The rotating gripper rotates by means of sprocket (18), being 
supported on bushing (19). The sprocket (18) is driven by sprocket (20) 
through chain (21). 
The sprocket (18) is driven by servomotor (22) and gear train speed reducer 
(23), the rotation angle of which is measured by rotary encoder (24). The 
rotary encoder (24) measures that way, by suitable scaling, the rotation 
angle of gripper (9). For the rotation of gripper (9), another means may 
be used as for example rack and pinion connection, where rack may replace 
sprocket (18). The torsional action of mechanism (4) will be described 
below since the operation of a 2-D Bending Machine is considered as known 
state-of-the-art. 
Assume that movable (11) and immovable (12) jaws compress adequately the 
wire between them, as a result of applied hydraulic pressure on pistons. 
Assume that the rotating gripper (9) rotates at an angle 
.DELTA..phi..sub.o, with respect to immovable gripper (8). Then, an outer 
generic straight line of the cylindrical surface of the wire will receive 
a helical shape AB.GAMMA..DELTA. (FIG. 2) of angle between bound radii OA 
and O.DELTA. equal to .DELTA..phi..sub.o. Let l be the total length of the 
jaws. The wire is acted gradually by the torsional moment excerted by the 
jaws, through its surface friction. Let l1 be the required length for 
total torsional moment M.sub.to to be excerted on wire. Naturally l1&lt;&lt;l. 
That way, the total angle of twist .DELTA..phi..sub.o may be divided into 
three portions, referring created 3 helix of an outter generic straight 
line of the cylindrical surface of the wire: 
Angle of twist .DELTA..phi..sub.1 on length l1. 
Angle of twist .DELTA..phi..sub.2 on free length l2. 
Angle of twist .DELTA..phi..sub.3 on length l3. 
We are allowed to assume for geometrically identical jaws of equally 
applied hydraulic pressure that: 
EQU l1=l3 
Assuming perfect contact of jaws and outter surface of the wire, then 
applied force P on jaws (FIG. 3a) creates a uniform contact pressure P, 
according to the relation: 
##EQU1## 
For the applied torsional moment, if .mu. is the coefficient of static 
friction, the following relation holds: 
##EQU2## 
To determine twisting angles .DELTA..phi..sub.1, .DELTA..phi..sub.2, 
.DELTA..phi..sub.3, the external load - external deformation relations, 
valid for torsion in elastic region 
EQU .DELTA..sub.6 =(M.sub.t .multidot.l)/(T.sub.p .multidot.G) 
cannot be used since the developing stress exceeds the yield point. 
Actually, the developing stress in outter portions of the wire varies 
between the yield stress .sigma..sub.B and ultimate stress (corresponding 
to rapture) .sigma..sub.F. Assuming that equivalent shearing stress is 
connected to normal stress with the relation: 
##EQU3## 
for rod heavily loaded in torsion, we assume within an accuracy level, 
that the shearing stress varies linerarly from the center of wire rod to 
some radius R.sub.1 (FIG. 3-.gamma.) from 0 (zero) to the value 
.tau..sub.F and from there again linearly to external radius R from value 
.tau..sub.F to .tau..sub.M. 
The required torsional moment is given by the relation: 
##EQU4## 
equation (3) for steel, heavily loaded in torsion is as follows: 
##EQU5## 
which is 53% higher than the required M.sub.to to set outter shearing 
stress to value .tau..sub.F. 
##EQU6## 
In FIG. 3-.delta., the corresponding picture for the determination of the 
relation between twisting angle .DELTA..sub..phi.2 and length 1.sub.2 for 
a given required of wire rod: 
EQU .epsilon..sub.2 =.DELTA.l.sub.2 /l.sub.2 
Taking into account that twisting angle in elastic range is negligible 
against the twisting angle in plastic region, and the fact that the volume 
of the wire rod remains constant, we have: 
##EQU7## 
Eliminating angle w and expressing .DELTA..phi..sub.2 in degrees we 
receive: 
##EQU8## 
That way, we determine the dimension 1.sub.2 in connection with diameter 
of wire for given twisting angle .DELTA..phi..sub.2 in degrees for desired 
outter normal strain .epsilon..sub.2 of wire. 
For example for .DELTA..phi..sub.2 =90.degree. and .epsilon..sub.2 =10%=0.1