Method of and apparatus for vacuum shaping a glass sheet

A method of deforming a plastic glass sheet from a generally two-dimensional shape into a generally three-dimensional shape at first supports the plastic glass sheet with its two-dimensional upper face juxtaposed underneath the three-dimensional lower face of a vacuum-forming die. The sheet and die are then relatively displaced vertically toward each other so that one portion of the sheet face engages a respective portion of the die face. The two portions are secured together by suction so that the sheet adheres at the one portion of its face to the respective portion of the die face. Finally, the sheet and die are relatively displaced with deformation of the sheet to press the rest of the sheet face and die face together and adhere the faces entirely together by suction. The sheet is supported on a planar conveyor that is rocked about a horizontal axis to engage the faces together. This conveyor and the die can be relatively rocked about a horizontal axis, or even about two transverse horizontal axes.

FIELD OF THE INVENTION 
The present invention relates to the shaping of a planar glass sheet into a 
three-dimensional shape. More particularly this invention concerns a 
vacuum-shaping operation that uses a deep-drawing die. 
BACKGROUND OF THE INVENTION 
It is standard practice to deform a semifinished sheet of glass while it is 
still very hot and somewhat plastic from its invariably substantially 
two-dimensional planar shape into a more complex three-dimensional shape. 
This procedure must be carried out while avoiding point stress which would 
mar the workpiece so that portions of it would be weakened and form 
optical distortions. 
It is possible as suggested in German Pat. No. 1,010,245 to simply press a 
flat plastic sheet workpiece between two matching nonplanar dies, but such 
a procedure invariably mars the surfaces of the workpieces and therefore 
cannot be used for high-quality glass items. Hence suction is used to hold 
the workpiece on the forming die, as this style of holding is extremely 
gentle, the holding force being spread perfectly uniformly over the entire 
surface of the face of the sheet. Thus the surface of the workpiece will 
normally remain perfectly smooth, and the workpiece thickness will remain 
perfectly uniform, giving it good optical properties. 
German patent document No. 3,109,149 describes a vacuum die that is used 
for this purpose. It has a face formed as a plurality of adjacent and 
outwardly open recesses or cells defining compartments opening at the 
face. These compartments can be individually evacuated. In addition the 
entire mold can be deformed from a start position in which the face of the 
mold is substantially planar to a finish position in which the face has 
the shape that is to be imparted to the workpiece. 
Thus the die in the start position is applied normally down against the 
planar top face of the workpiece, which is held in a forming station on a 
conveyor, and the compartments are evacuated. This action pulls the glass 
sheet into tight contact with the still planar die face. Then the die is 
lifted to pick the workpiece up off the conveyor, and is deformed into the 
finish position, drawing the workpiece into the desired shape. The glass 
is given some time to harden in this finish position, then the vacuum is 
cut and the workpiece is freed from the die, which is then returned to its 
start position for another shaping operation. 
Such dies can work on several workpieces at the same time, in which case 
they must normally be subdivided transversely as well as longitudinally 
into separate compartments. Thus the loss of suction at the gap between 
adjacent workpieces will not cause one of them to be dropped. 
The main problem with such an apparatus and method is that the die is an 
extremely complex piece of equipment and is very hard to control 
accurately. It is in fact impossible to form certain shapes as the die 
cannot physically be deformed from the planar start position into some 
shapes. In addition in some arrangements the workpiece is stretched at the 
joints between adjacent relatively movable die portions, creating weakened 
regions that form optical distortions. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
system for shaping a glass sheet. 
Another object is the provision of such a system for shaping a glass sheet 
which overcomes the above-given disadvantages, that is which uses 
relatively simple equipment that operates in a simple manner, and that can 
nonetheless produce very complex shapes. 
SUMMARY OF THE INVENTION 
A method of deforming a plastic glass sheet from a generally 
two-dimensional shape into a generally three-dimensional shape according 
to the invention at first supports the plastic glass sheet with its 
two-dimensional upper face juxtaposed underneath the three-dimensional 
lower face of a vacuum-forming die. The sheet and die are then relatively 
displaced vertically toward each other so that one portion of the sheet 
face engages a respective portion of the die face. The two portions are 
secured together by suction so that the sheet adheres at the one portion 
of its face to the respective portion of the die face. Finally, the sheet 
and die are relatively displaced with deformation of the sheet to press 
the rest of the sheet face and die face together and adhere the faces 
entirely together by suction. 
This can be achieved according to this invention by holding the die 
substantially stationary and moving the glass sheet up toward it to engage 
the faces together. The sheet is supported at a plurality of locations 
underneath the die and the locations can move relative to each other and 
move from general coplanarity to the same shape as the lower face of the 
die. Thus the planar glass sheet is held on the planar upper surface of 
the conveyor which in one continuous stroke moves up and presses the sheet 
against the die, with complementary deformation of the conveyor. 
In accordance with another feature of this invention the sheet is supported 
on a planar conveyor that is rocked about a horizontal axis to engage the 
faces together. This conveyor and the die can be relatively rocked about a 
horizontal axis, or even about two transverse horizontal axes. Similarly 
the conveyor can have a nonplanar upper surface to start with, as for 
instance by forming it of rollers of hyperboloidal shape. 
It is also possible according to this invention for the die face to be 
annular. In this case, after the faces are entirely suctionally adhered 
together, a force is applied to the sheet within the annular die face to 
deform the sheet therewithin. This force can be applied pneumatically by 
forming a pressure differential across the sheet at the region within the 
annular die face. Thus the space within the annulus where the sheet and 
die are adhered together can be pressurized or depressurized. This 
procedure is excellent for forming goggle lenses, windshields, and the 
like as the central region is stretched uniformly so it will have 
excellent optical properties, while the border remains the right shape for 
holding in a frame. 
It is also within the scope of this invention to deform the die after the 
two faces are entirely adhered together by suction. This can be done as 
described in the above-cited German patent document by hinging the die 
together so at least one region of it can flex or pivot relative to the 
rest of the die. 
It is also possible to achieve different effects, virtual surface sculpting 
by varying the pressure between portions of the die face. In this manner 
mounting tabs and the like can be provided for, or scrap pieces of the 
sheet can be held with great force as marring them is not important. 
The sheet according to this invention normally is supported on a conveyor 
and moved horizontally as it is engaged with the die. The die also can be 
moved horizontally synchronously with the sheet as it engages same. 
Usually, however, the sheet is supported on a conveyor comprised of an 
array of rollers rotatable about horizontal axes perpendicular to the 
conveyor transport direction. With this arrangement the conveyor is 
horizontally reciprocated while engaging the die and sheet faces with each 
other and while holding the die and sheet against horizontal displacement 
in the transport direction. Such constant movement of the rollers prevents 
them from marring the under surface of the sheet. For extremely gentle 
handling of the plastic glass sheet, the rollers are rotated jointly at 
the same peripheral speed to displace the sheet in the transport direction 
into a position under the die prior to vertical engagement of the faces 
with each other and thereafter they are rotated at a speed related to the 
conveyor reciprocation speed such that the rollers roll and do not slip on 
the sheet. In other words, the reciprocation speed of the roller array is 
independent of the rotation rate of the rollers, and the peripheral speed 
of the rollers is always identical to that of the workpiece. 
The die according to this invention is normally wholly rigid, although it 
is possible to make it partially flexible as described above. Its die face 
is downwardly convex, at least in the systems where the conveyor and die 
are relatively rocked.

SPECIFIC DESCRIPTION 
As seen in FIGS. 1, 2, 3, 7, and 8, a normally planar glass sheet 1 is 
supported on a standard roller-type conveyor 2 underneath a rigid 
suction-forming die 3 that can be displaced vertically by a cylinder 8 and 
that can be rocked bout a horizontal axis 7 by a motor 13. The bottom face 
of the die 3 is here shown to have three flat portions 3a, 3b, and 3c that 
extend in planes parallel to the axis 7 but not parallel to or coplanar 
with each other, forming a downwardly convex bottom face 3a, 3b, 3c. 
The conveyor 2 comprises a frame 14 that is horizontally reciprocal 
parallel to a transport direction d in a stationary guide or support 15 
(FIG. 8) and that carries an array of identical cylindrical rollers 4 
centered on horizontal respective axes 4A parallel to the axis 7 and 
perpendicular to the direction d. Each such roller 4 is associated with a 
respective gear 11 that meshes with teeth 12 of a toothed drive belt or 
chain 9 carried on sprockets 16 and driven by a motor 5. Thus this motor 5 
can rotate the rollers 4 synchronously at the same peripheral speed to 
displace the workpiece 1 in the direction d. The partial circle TK of the 
sprockets 11 is identical to the roll diameter D, so that in effect the 
workpiece 1 will move at the same rate as the chain 9. 
As is known from, for example, German patent documents Nos. K 22,178 X/39A 
and 2,119,699, the support 14 of the conveyor 2 is reciprocated 
horizontally by a motor 6 connected to it via a crank arrangement 10 to 
impart to it a horizontal oscillation at a speed v.sub.R which increases 
and decreases regularly and sinusoidally. The purpose of such oscillation 
is to prevent the rollers 4 from sinking up into the soft sheet 1; they 
are kept moving to distribute the supporting force and maintain the bottom 
face of the workpiece smooth. 
More particularly and as shown in FIG. 8, this arrangement drives the 
rollers both with the angular transport speed w(trans) and the angular 
oscillation speed w(osc). Thus the glass sheet 1 moves relative to the 
conveyor frame 14 with a speed equal to the sum of the velocity component 
Rw(trans) created by the motor 4 and the speed Rw(osc) of the motor 6. 
Meanwhile the frame 14 is moving at a sinusoidally increasing and 
decreasing speed v.sub.R (osc) which determines the angular speed w(osc) 
and which is complementary to the oscillation speed Rw(osc), so that 
v.sub.R (osc)=-Rw(osc). 
Thus as shown in FIGS. 1, 2, and 3, the workpiece 1 is first moved into 
position underneath the die 3, is arrested, and then the actuator 8 moves 
the entire die 3 down, while it is tipped, so that the portion 3a flatly 
lies on the sheet 1. A controller 18 is connected to a suction fan 17 and 
to valves 19 connected between the intake of te blower 17 and the 
respective die-face portions 3a. Meanwhile the conveyor 2 is reciprocating 
underneath the sheet 1, with the rollers 4 rolling on its surface and 
therefore having a peripheral speed directly related to the oscillation 
speed. Another valve 20 is connected between the output side of the blower 
17 and the central section 3b. 
In this position, therefore, the compartments at the portion 3a are 
evacuated so that the sheet 1 is adhered to it. Then, as shown in FIG. 2 
the entire die 3 is simultaneously pivoted and lowered to press the 
central face portion 3b down on the sheet 1. This action bends the sheet 
between the portions 3a and 3b. The blower 17 is then connected to the 
portion 3b to adhere the sheet 1 to it. 
Then as shown in FIG. 3 the die 3 is rocked further back and lifted, and 
its portion 3c is evacuated to engage it flatly against the sheet 1, 
further deforming it. The die 3 can then be lifted up while the sheet 1 
cures and hardens, and the center portion 3b may be discontinued via its 
valve 19 from the intake of the blower 17 and connected via the valve 20 
to its output to bulge out the center portion of the sheet 1, since now 
its ends are firmly secured at the portions 3a and 3c. 
It is also possible as seen in FIGS. 4 and 5 for the rollers 4 of the 
conveyor 2 to be independently vertically displaceable. Thus as the die 3 
is moved down from the position of FIG. 4 to that of FIG. 5 the surface 
defined by the conveyor 2 and holding the workpiece 1 moves from a planar 
one to one complementary to the die 3. Thereafter the entire die 3 can be 
rocked bout a longitudinal axis 21 which is horizontal and perpendicular 
to the pivot axis 7. 
In FIG. 6 an annular die 3' is used. Thus only an annular portion of the 
sheet 1 is adhered to it. In addition in this arrangement the conveyor 2 
can be raised and lowered relative to the die 3' and rocked about a 
horizontal axis 7' to press the sheet 1 against the die 3'. This die 3' 
furthermore may move horizontally with the sheet 1 on the conveyor 2 as 
indicated by arrow 22. An edge portion 3d may also be hinged at 23 on the 
die 3' for further deformation of the sheet 1 once it is picked up. This 
arrangement is particularly useful for goggle lenses, windshields, and the 
like, as the central portion of the sheet never touches the die and 
remains perfectly smooth, and since gravity alone will cause the central 
sheet portion to hang down somewhat, stretching out any minor deformations 
on the underside of the sheet. 
The method and apparatus of this invention are therefore capable of 
producing an extremely high-quality workpiece with a relatively simple 
piece of equipment. Shapes that hitherto have been considered impossible 
to make in glass at a competitive price can be produced relatively easily. 
In fact with the system of this invention a semispherical shape can be 
created simply by nutating a semispherical die about a central axis at an 
ever greater angle.