Process and apparatus for heat forming of materials

An apparatus 1 for use in the preheating and forming of a material object about at least one mold 12 or die thereon. The apparatus has a primary platform 4 for supporting a length or sheet of material 13 thereon, a heating station 2 having a mechanism 8 for heating the object 13 laid on the primary platform 4 a mechanism for isolating the heating mechanism 8 form the object 13. The apparatus 1 also converts the heating station 2 to a forming station 3 which has associated therewith the mold 12. The forming station may either have an envelope 11 for creation of a vacuum seal or a second mold 17 for the purpose of forming object 13.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the heat bending of sheet 
materials and also relates to an apparatus for effecting such bending. 
More particularly, the invention relates to a method of bending and forming 
sheet materials into a predetermined shape by the utilisation of vacuum 
forming and/or molding techniques following preheating of the material in 
or on an apparatus containing means to enable the said preheating, vaccuum 
forming and/or moulding techniques. 
The invention is particularly adaptable for use in bending a sheet material 
such as that known under the trademark CORIAN. This is a material which, 
due to its physical properties, including its stiffness and brittleness 
when one face is placed under tension and another under compression as a 
result of bending, will fail. 
Sheet materials generally and more particularly so CORIAN, even though they 
often possess significant elasticity especially when in large lengths or 
in large sheets do not have a physical property enabling small radius 
curves to be placed in the material without damage to the material. 
There are in existence a number of heat forming processes whereby materials 
are preheated to enable a subsequent forming process to be carried out on 
the heated material. 
One such process involves preheating of films for subsequent vacuum forming 
about a mold, whereby the preheated material conforms to the shape of the 
mold under vacuum conditions. Many variations of such a process have been 
in existence for some time, however, it has not hitherto previously been 
known to bend a stiff material such as CORIAN about a mold and under a 
vacuum following preheating treatment to a critical temperature to thereby 
enable the provision of curves and bends in the material having radii 
which are relatively small. It has also not been previously known in this 
context to use preheating, thence molding of the preheated material such 
as CORIAN to produce a curve or bend without the use of a vacuum. 
It has been previously known to preheat CORIAN in an oven in an attempt to 
subsequently produce a curve in the material however, such trials have not 
been successful due to difficulties in handling of the CORIAN after 
preheating, difficulties in obtaining and maintaining an even heat 
distribution prior to and during bending of both small and large sheets, 
and difficulties in establishing an optimum heating time commensurate with 
the size and thickness of the material. Problems have also been 
experienced with cracking of the material, crazing of the material surface 
and reduced impact resistance of the material when adopting prior art 
forming methods. 
As CORIAN is weakened by improper bending conditions due to the 
shortcommings of the prior art techniques and due to the particular 
physical nature of CORIAN and like materials it is desirable to provide an 
improved method and apparatus for the handling of CORIAN during the 
bending process from the preheating stage to the final bending stage. 
Where a small radiused curve is to be placed in a thick sheet material such 
as CORIAN, bending to achieve this purpose under room temperature 
conditions would, due to the brittleness of the material under the bending 
conditions, result in the destruction of the material. 
Previously, where it has been desired to form curves in such materials the 
effect was achieved by tedious machining and gluing of the material or by 
using the above described oven techniques. The purpose of the curves 
formed therein is primarily for functional and aesthetic value and to 
eliminate joins in fascia areas. 
The bending of the material is facilitated by heating of the material to a 
critical temperature so that it achieves sufficient pliability to enable a 
vacuum forming operation to be performed in conjunction with a forming 
mold on the heated article. Alternatively, the vacuum may be eliminated in 
favour of mold forming only. 
The critical heating of the article alters the physical and mechanical 
properties of the material matrix to enable small radius curves to be 
produced by bending about a mold without a failure in the material. 
SUMMARY OF THE INVENTION 
The present invention therefore seeks to provide an improved method for 
bending or forming of inherently stiff materials by preheating and vacuum 
mold forming techniques utilising an apparatus comprising essentially a 
preheating station and a molding station. 
In an alternative embodiment of the forming method the vacuuming step may 
be substituted by die form bending and/or complementary sandwich molding 
following heating of an article which is to be die formed or moulded. 
There are therefore two aspects of the invention, a method aspect and an 
apparatus aspect. 
In the broadest form of the method aspect of the invention the invention 
comprises: 
a method for the preheating and subsequent die or mold forming of a 
material comprising the steps of: 
a) Placing a length or sheet of the material to be formed about the die or 
mold on a support apparatus having means to provide at least a heating 
station and a material forming station, 
b) causing heating elements at said heating station to come into direct or 
indirect contact with or, in close proximity to the said sheet material, 
c) allowing at least a portion of said material to be heated to a 
predetermined temperature, by said elements, 
d) isolating said heating elements away from said material, or isolating 
said material away from said heating elements, in order to remove the 
influence of the heating elements on the material, 
e) locating said material when heated on a material forming station at, 
adjacent or near said heating station, 
f) placing the material on a first forming mold or die of a predetermined 
shape and configuration, 
g) creating a seal via an envelope about said material so that said 
material and said mold is contained wholly within said envelope, 
h) applying a vacuum to the inside of said envelope so that the material 
which remains in the heated condition is caused to conform at least in 
part to the shape of at least a portion of said mold or die, 
i) allowing said material to cool so that the said shape is maintained in 
said material. 
According to an alternative embodiment of the method aspect, the invention 
comprises: 
a method for the preheating and subsequent die or mould forming of a 
material comprising the steps of: 
a) Placing a length or sheet of the material to be formed about the die or 
mould on a support apparatus having means to provide at least a heating 
station and a material forming station, 
b) causing heating elements at said heating station to come into direct or 
indirect contact with or in close proximity to the said sheet material, 
c) allowing at least a portion of said material to be heated to a 
predetermined temperature by said elements, 
d) isolating said heating elements away from said material, or isolating 
said material away from said heating elements so as to remove the 
influence of said heating elements, 
e) locating said material when heated on the forming station which is at, 
adjacent or near said heating station, 
f) placing the material on a first forming mold or die of a predetermined 
shape and configuration, 
g) bringing a second forming mold or die which is complementary to said 
first forming mold into contact with said material so that said material 
to be formed is sandwiched between said molds or dies so as to conform to 
the profiled shape of at least a portion of one or both of said molds, 
h) allowing said material to cool so that the shape so formed is maintained 
in said material. 
According to the preferred embodiment, the heating elements are disposed 
either above, below or above and below the material to be formed. 
According to the apparatus aspect of the invention, there is provided an 
apparatus for use in the preheating and vacuum forming of a material 
object about at least one mold or die said apparatus comprising: 
a primary platform for supporting a length or sheet of material thereon, 
a heating station having means for heating an object laid on said primary 
platform, 
means for isolating the heating means from the object; 
means for conversion of the heating station to a forming station or for 
locating said object at a forming station, 
said forming station having associated therewith a mold or die to which 
said material will conform at least in part, 
said apparatus also comprising means to envelope at least said object and 
said formation station so that when a vacuum is applied to the inside of 
the envelope at least a part of the object is forced by virtue of said 
vacuum to conform to the shape of at least a portion of the said mold or 
die. 
According to another embodiment of the apparatus aspect of the invention 
the invention comprises: 
an apparatus for use in the preheating and mold or die forming of a 
material object about a mold or die said apparatus comprising; 
a primary platform for supporting a length or sheet of material thereon; 
a heating station having means for heating an object laid on said primary 
platform, 
means for isolating the heating means from the object means for conversion 
of the heating station to a forming station or locating said object at a 
forming station, 
said forming station having associated therewith a first mold or die and a 
second mold or die having a profiled shape which is complementary to said 
first mold or die so that when said material is placed on said first mold 
or die said second mold or die which is vertically, pivotally, 
rotationally or laterally adjustable is brought into contact with said 
material causing at least a part of said material to be deformed or bent 
about said first mold or die and thereby causing said part to conform to 
the shape of said second and/or said first mold or die. 
According to the preferred embodiment of the apparatus aspect of the 
invention, the primary platform comprises a table having associated 
therewith an optionally moveable array of heating elements configured such 
that the elements exist above and below the object when the object is 
placed in the heating station. The platform in combination with the 
heating elements form the heating station. In one embodiment the elements 
are contained in a housing or housings which are vertically adjustable to 
enable raising and lowering of the elements according to heating 
requirements. The housings also act in controlling the temperature of the 
material to be heated. The heating elements may also be located in the 
platform i.e. underneath the material being worked on. 
The forming station in the preferred embodiment comprises the primary 
platform and means thereon to receive and support a mold or die. The 
station is adapted to enable the creation of an envelope about the forming 
station which in turn enables an airtight space to be formed enabling a 
negative pressure to be applied to the space. The forming station has 
means to enable sealing of and adjustment of the position of the envelope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 there is shown a plan view of a material forming 
apparatus 1 comprising a primary platform 2 and a vacuum assisted forming 
platform 3. The platform 2 and the forming platform 3 are supported by a 
support table 4 (see FIG. 2). 
The platform 2 has disposed above it an array of heating elements 5 
arranged in a housing 6. The housing 6 is adapted to be moved vertically 
to enable the elements to be moved close to the object 13 to be heated 
thence to be moved away from the object when the required temperature has 
been reached. 
A further array of heating elements 7 is contained in well 8 so that the 
object can be heated also from underneath where required. The object which 
is placed in passage 9 overlies these heating elements so that in 
conjunction with heating elements 5 the object 13 can be evenly heated on 
both sides until the required degree of heating of the object is achieved. 
In one embodiment the molding platform 3 comprises a mainframe structure 10 
for supporting a silicone envelope 11 which envelopes mold 12 and object 
13 when placed on top of mold 12. When the object to be operated on is 
placed on mold 12 following heating on heating platform 2 the envelope 11 
is then brought downwards either manually or automatically so that sealing 
of the envelope is effected at interphase 14. The mainframe 10 slidable 
moves in an upward and downward direction along guide posts 15, either 
manually, or under the assistance of hydraulic means (not shown). The 
sealing creates an airtight seal thus enabling an applied vacuum to cause 
the object 13 to conform to the profiled shape of mold 12. Using this 
process sheet materials and indeed materials of other shapes can be formed 
with a large variety of radiused curves or bends particularly at their 
extremities thereby eliminating the need for other machining and or 
joining methods to form such bends. 
In an alternative embodiment the aforementioned vacuuming step is not used. 
In this case rather than relying on vacuuming to cause the desired 
profiled bend to be formed in the material a second mold is used. The 
second mold has a complementary shape which squeezes the heated CORIAN 
material between the molds. The CORIAN then conforms to the shape of at 
least the first mold 12. The first mold acts as a die about which the 
CORIAN bends to conform to the predetermined shape. 
In this alternative embodiment of the invention the forming station is 
adapted with a second die or mold 17 (see FIG. 4) which sandwiches the 
object 13 between the die or mould 12. According to this embodiment the 
mold 17 may be pivotally attached to either platform 14 or to mold 12. The 
use of the second mold 17 provides an alternative to the use of vacuum 
forming about mould 12. 
The heating temperatures and times are critical to the effective bending of 
the material using the above described process and apparatus. The heating 
temperature and time varies according to the thickness of the material. A 
typical case is a 13 mm sheet which would require a temperature of 
approximately 180.degree. C. for 31/2 minutes. A 19 mm sheet may require 
51/2 minutes heating at 180.degree. C. 
The material to be formed would preferably fall within the thickness range 
of 8 mm to 20 mm. Preferably the material is heated for a period between 2 
and 4 minutes and at a temperature of approximately 180.degree.. 
Generally, the thinner the sheet to be formed, the shorter the time 
required to achieve the requisite plasticity in the sheet. Preferably the 
heating range is 160.degree. to 200.degree. C., and it has been found that 
180.degree. C. is an optimum temperature to achieve the required 
plasticity. 
Preferably the sheets which are formed by the apparatus and methodology of 
the present invention are provided with a radiused edge along the 
longitudinal length of the sheet. Ideally the radius of curvature of the 
radiused edge would fall within the range 12 mm to 150 mm however, this is 
not to be construed as limiting of the feasible radii that may be achieved 
using this method. 
The process is suitable for use with many acrylic products preferably in 
sheet form. To control temperature and assist in heat retention and even 
distribution a housing 16 is utilised to house the heating elements. 
Although the invention has been described in relation to the bending of 
CORIAN, it is conceivable that the process is useful for bending other 
materials which may be brittle at room temperature but which may become 
pliable under heat treatment. 
It will be recognised by persons skilled in the art that numerous 
variations and modifications can be made to the invention as hereinbefore 
described and with reference to the accompanying illustrations.