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DEVICE FOR TRANSFORMING MATERIALS BY INDUCTION HEATING
The present invention relates to a device and method
using induction heating, especially with the aim of
transforming or molding materials, especially thermoplastic
matrix composite materials or thermosetting materials.
To achieve the molding of plastics parts or composite
parts, prior art induction heating methods have the
drawback of heating a major part of a mold casing
The invention limits induction heating to a surface,
in order to localize the heating at the mold/material
interface, thus limiting energy consumption and therefore
improving the energy efficiency of the device. The
productivity is also increased with reduced heating and
cooling times because a very small fraction of the volume
of the mold is subjected to induction heating.
The invention is also aimed at reducing the cost of
tooling.
The invention thus relates to a device for the
transformation, especially by molding, of materials,
especially thermoplastic matrix composite materials or
thermosetting materials, comprising:
- two mold casings that are mobile relative to each
other, made out of electrically conductive material, each
including a molding zone designed to be in contact with the
material to be transformed, and
- induction means for generating a magnetic field with
a frequency F enveloping the casing of the mold,
- the faces of at least one of the two mold casings
situated so as to be facing induction means, except for the
molding zones, being coated with a shielding layer made of
a non-magnetic material preventing the magnetic field from
penetrating into the mold casings,
the mold casings being electrically insulated from
each other during the molding phase so that the faces of
the two mold casings demarcate an air gap wherein flows the

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magnetic field that induces currents at the surface of the
molding zone of each mold casing, thus localizing the
heating at the interface between the molding zone and the
material to be transformed.
According to one embodiment, the two mold casings are
coated with a shielding layer.
According to one embodiment, the mold casings comprise
a magnetic compound, preferably having high relative
magnetic permeability and resistivity, for example a
nickel-based, chrome-based and/or titanium-based steel.
According to one embodiment, only one mold casing is
coated with a shielding layer, the other mold casing
comprising a non-magnetic material, preferably with low
resistivity, for example aluminum.
According to one embodiment, the mold casing coated
with a shielding layer comprises a magnetic compound,
preferably having high relative magnetic permeability and
resistivity, for example a nickel-based, chrome-based
and/or titanium-based steel.
According to one embodiment, the shielding layer also
overlaps a part, not constituting a molding zone, of at
least one of the two mutually facing faces of the two moid
casings.
According to one embodiment, the shielding zone also
comprises a metal sheet fixed to the magnetic mold casing,
this metal sheet being for example soldered or screwed in.
According to one embodiment, the shielding layer
comprises a deposit of material, especially an electrolytic
deposit.
According to one embodiment, the thickness e of the
shielding layer is at least equal to:
e = 50* (p/F)1/2
p being the resistivity of the non-magnetic material,
and F the frequency of the magnetic field.

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According to one embodiment, the frequency F is at
least equal to 25 KHz and preferably at most equal to
100 KHz.
According to one embodiment, the shielding layer
comprises a non-magnetic material of low electrical
resistivity, for example copper or aluminum.
According to one embodiment, an electrically
insulating layer is applied to the molding zone of at least
one mold casing to perfect the electrical insulation of
these casings, especially when the material to be
transformed is conductive.
According to one embodiment, the inductive means
comprise two parts, each one fixedly joined to one of the
mold casings to enable the opening of a device, and being
capable of being shifted with the respective mold casing.
According to one embodiment, the two parts of the
inductive means are electrically connected by means of at
least one electrical contactor enabling contact to be
maintained during the relative shift of one mold casing
relative to the other one during the transformation phase.
The invention also relates to a method for the
manufacture of parts, especially in large batches, making
use of the device defined here above.
Other features and advantages of the invention shall
appear from the following description, made by way of a
non-restrictive example with reference to the appended
drawings, of which:
- Figure 1 shows a device according to the invention,
- Figure 2 shows the device of Figure 1 during the
transformation of a material,
- Figures 3a and 3b show two different arrangements of
inductors for the device shown in Figure 1, these figures
corresponding to views along the line 3-3 of Figure 2,
- Figure 4 shows a variant of the device, and
- Figure 5 shows a second variant.

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The molding device shown in Figures 1 and 2 comprises
two mold casings 10 and 20 moving relative to each other.
The mold casings 10, 20 are made up out of a magnetic
material, one part of which constitutes a molding zone,
respectively 12 for the mold casing 10 and 22 for the mold
casing 20. The molding zones 12, 22 are situated on two
mutually facing faces of the mold casings.
A network of inductors 30, electrically connected in
parallel or in series to a current generator, is positioned
about the mold casings. Each inductor 30 comprises a
conductive turn and comprises two separable parts 32, 34,
each one being fixedly joined to a mold casing, 10, 20
respectively.
One part of the external surface of each mold casing
10, 20, except for the molding zones 12, 22, is lined with
a shielding layer 14, 24. In the example, the shielding
coats the external faces of the mold casings situated so as
to be facing the inductors 30 and one part of the mutually
facing faces of the two mold casings. However, it is not
necessary for the external faces of the mold casings that
are not facing an inductor (i.e. the faces parallel to the
plane of Figure 1) to be coated with a shielding layer
because the magnetic field generated has very limited
influence on these faces.
Figure 1 shows the two mold casings at a distance from
each other before molding and Figure 2 is similar to that;
of Figure 1 and shows the two mold casings during the
molding operation.
During the transformation of a material 40, as shown
in Figure 2, this material is gripped and held under
pressure between the molding zones 12, 22 of the two mold
casings. The material then provides the electrical
insulation between these two mold casings 10, 20. Through
this electrical insulation, the space demarcated by the
facing surfaces of /the two mold casings constitutes an air

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gap 42 enabling the circulation of a magnetic field in this
space.
When the inductor means comprising conductive turns 30
are crossed by alternating electrical currents Ii with a
frequency F, for example ranging from 25 to 100 KHz, the
inductors generate a magnetic field that envelops the mold
casings 10, 20.
The magnetic field thus generated crosses the mold
casings and also circulates in the air gap, i.e. between
the mold casings.
The magnetic field induces currents in directions
opposite to the directions of the currents Ii and the
presence of the air gap enables the generation of the
induced currents Icl and Ic2 which flow on the surface of
each of the two mold casings.
The shielding layer prevents the magnetic field from
reaching the mold casing, except for the molding zones.
These induced current Icl and Ic2 therefore have thermal
action chiefly on the surface of the molding zone which is
therefore the main zone heated by the action of the
inductors. Since the shielding is non-magnetic, it is very
little heated by induction.
In order that the device may work efficiently, the
shielding layer must have a thickness greater than the
penetration depth of the magnetic field (skin thickness).
Thus, the magnetic field is prevented from reaching the
mold casing and heating it in places other than the molding
zone.
To determine the thickness of the shielding layer
required, the following formula is used:
e = 50*(p/F.ur)1^2
where p is the resistivity of a non-magnetic field, jir is
the relative magnetic permeability of the material, and F
the frequency of induction currents. For a non-magnetic
material, we take: jar = l,and the formula becomes :e = 50* (p

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/F)1/2 In order that the magnetic shielding may be
effective, the thickness of the layer of non-magnet i.c
material must be greater than the skin thickness with the
frequency mentioned here above, ranging from 25 KHz to
100 KHz, the skin thicknesses are less than one millimeter.
The device of the invention is especially efficient as
the presence of the air gap 42 has the effect of
concentrating the magnetic flow within it, thus further
increasing the action of the magnetic field at the molding
zones and hence the inductive energy contributed to the
surface of the molding zones.
One device according to the invention therefore has
the advantage of locally heating the molding zone, directly
at the molding zone/material interface and not in the
thickness of the mold casing. This amounts to a
substantial saving of energy. A device of this kind also
has the advantage of being simple and costing little to
manufacture.
The air gap also has the effect of limiting the
influence of the geometry and/or the distribution of the
inductors on the resultant heating because the air gap 42
(Figures 3a and 3b) "smoothens" the energy provided by the
inductors. Thus, inductive turns 30'i to 30'4 (Figure 3b)
evenly distributed on the length of the mold have
practically the same effect as the same number of inductor
turns 30]_ to 3O4 (Figure 3a) distributed on a shorter
length. This arrangement makes it possible to choose the
distribution of the inductive turns at will.
The fixing of the layer of non-magnetic material on
the mold casing may be done in various ways, for example by
fixing a sheet metal or by depositing material, for example
by an electrolytic deposition.
The non-magnetic material used to 'form the shielding
preferably has low resistivity so as to limit energy
losses. The material is, for example, copper or aluminum.

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The magnetic material used for the mold casing is a
magnetic compound which may have a Curie temperature as
well as an electrical resistivity that is greater than that
of copper, as is the case for example with nickel-based,
chrome-based and/or titanium-based steel alloys. High
electrical resistivity of the mold casing is an advantage
because it enables more efficient induction heating.
However, it must be noted that the magnetic permeability of
the material constituting the mold casing also influences
the efficiency of the induction heating. Indeed, if we
refer to the formula mentioned here further above, high
relative magnetic permeability leads to a lower penetration
depth of the magnetic field, and a same quantity of energy
is therefore distributed on a more restricted zone and the
result thereof is greater heating.
When the material has a Curie point, at a temperature
close to this Curie point the material of the mold casing
loses its magnetic properties and the induction heating
diminishes greatly, thus enabling the heating temperature
to be regulated around the Curie point.
The device shown in Figures 1 and 2 is provided with a
cooling system to enable the making or transformation of
parts by heating at a high rate, the cooling being
implemented between two processing operations. To this
end, in each mold casing, there is provided a network of
channels 18, 28 enabling a cooling liquid to be made to
flow in the vicinity of the molding surfaces 12, 22. The
cooling thus obtained performs very well firstly because
the metal mold casing is thermally highly conductive and
secondly because the channels may be laid out as closely as
possible to the molding zones 12, 22.
In the case of the molding of a composite material,
after the heating and shaping cycle, the cooling is used to
fix the composite material in its definitive form.

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Unlike known systems, the device of the invention
concentrates the action of the magnetic field and the
thermal effects in the vicinity of the molding zones. As a
consequence, since the heating is more localized, there is
less thermal energy to be dissipated during the cooling
which is therefore faster. Thus, the cycle time of the
device is reduced and the productivity is therefore
significantly increased.
Figure 1 identifies the boundary f between each mo .Id
casing 10, 20 and the layer of non-magnetic material that
lines it. The position of this boundary f relative to the
molding zone 12, 22 has an influence on the quality of the
heating and hence on the molding. With the device of the
invention, it is easy, by adding or removing material, to
modify the position of the boundary f, thus providing great
flexibility in the designing of the tooling. Indeed, it
becomes possible to adjust the position of the boundary
after the processing tests, especially molding, in real
conditions.
Since the inductors are made up of two separable parts
32, 34 fixedly joined to the mold, the separation of the
two mold casings is easy. This enables fast extraction of
the part 4 0 after molding and therefore contributes to
manufacturing at a high rate. During the transformation of
a material, the electrical continuity between the two parts
32, 34 of the network of inductors is ensured by electrical
contactors 36. This contactor permits a relative shift of
the two parts 32, 34 of the network of inductors because
the transformation of the materials is generally done at
constant pressure but leads to a reduction of thickness of
the material and therefore a reduction of the distance
between the two mold casings 10, 20.
The transformation of the electrically conductive
composite materials necessitates the use of a variant of
the device. Indeed, with conductor materials such as for

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example carbon-fiber-based materials, the electrical
insulation between the two mold casings is not always
perfectly ensured and short circuits may occur locally,
generating electrical arcs that may affect the surface of
the material to be transformed and/or the surface of the
molding zones. To improve the electrical insulation and
thus prevent any risk of shorting, an electrical insulating
layer is deposited on at least one of the two molding zones
12, 22. Such a layer comprises for example Teflon,
amorphous carbon, glass fiber or again ceramic-based
materials. This layer must have temperature worthiness and
adapted mechanical resistance with a thickness of about one
micrometer.
Conventionally, mechanical means (not shown) for
ejecting the manufactured part are also planned.
The manufacturing method thus implemented therefore
comprises chiefly four phases:
- positioning of the material or materials of the part.
to be processed on the lower mold casing of a device,
- heating of the two molding zones, and pressurizing
of the material between the two molding zones for a given
period of time,
- implementing the cooling of the mold casing in order
to cool the parts;
- raising the upper mold casing and ejecting/removing
the part.
The method thus implemented benefits extensively from
the advantages provided by the device according to the
invention, especially in terms of productivity: the local
heating related to the molding zone minimizes the cycle
times.
The easy adjustment of the heated zone by the adding
or removal of portions of the shielding layer provides
great flexibility: it is easy to modify the tooling as a
function of the results obtained during the first tests.

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Finally, the tooling is economical to produce because
the shielding layer 14, 24 does not necessitate any complex
or costly manufacture.
One variant shown in Figure 4 of the device according
to the invention makes it possible to obtain a simpler
tooling, especially in the context of the transformation of
very fine parts, especially parts with a thickness of less
than a millimeter. Indeed, such thicknesses are used to
limit the heating to only one face of the part. The
invention uses a device in which one of the two mold
casings is not lined with a shielding layer, this mold
casing (70) comprising a non-magnetic material. Thus, this
mold casing (70), which is not transparent to the magnetic
field, always make available an air gap wherein there IJows
the magnetic field created by the induction network (74) .
The induction heating is therefore done chiefly at the
molding zone of the mold casing 72 which is coated with a
shielding layer. Such a device is less costly to make
because the mold casing (70) does not include any shielding
layer. In the example of Figure 4, the mold casing 7 0 is
devoid of any cooling circuit.
Another variant (Figure 5) provides for only one mold
casing 50 around which inductive turns 52 are arranged. In
this configuration, the shielding layer that surrounds the
mold casing localizes the heating on the molding zone 60
without any presence of an air gap. The absence of this
air gap makes such a device more sensitive to the geometry
of the network of inductors, but the heating is chiefly
localized on the surface of the molding zone through the
shielding layer.

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CLAIMS
1. Device for the transformation by heating,
especially for molding, in particular of thermoplastic
matrix composite materials or thermosetting materials,
comprising:
- two mold casings (10, 20) that are mobile relative
to each other, made out of electrically conductive
material and including a molding zone (12, 22) designed
to be in contact with the material to be transformed, and
induction means (30) for generating a magnetic
field with a frequency F enveloping the casing of the
mold,
- the faces of at least one of the two mold casings
(10, 20) situated so as to be facing induction means,
except for the molding zones, being coated with a
shielding layer (14, 24) made of a non-magnetic material,
preventing the magnetic field from penetrating into the
mold casings (10, 20),
the mold casings being electrically insulated from
each other during the molding phase so that the faces of
the two mold casings demarcate an air gap (42) wherein
flows the magnetic field that induces currents at the
surface of the molding zone (12, 22) of each mold casing
(10, 20), thus localizing the heating at the interlace
between the molding zone and the material to be
transformed.
2. Device according to claim 1, wherein the two mold
casings (10, 20) are coated with a shielding layer (14,
24) .
3. Device according to claim 2, wherein the mold
casings (10, 20) comprise a magnetic compound, preferably
having high relative magnetic permeability and
resistivity, for example a nickel-based, chrome-based
and/or titanium-based steel..
4. Device according to claim 1, wherein only one
mold casing (72) is coated with a shielding layer, the

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other mold casing (70) comprising a non-magnetic
material, preferably with low resistivity, for example
aluminum.
5. Device according to claim 4, wherein the mold
casing coated with a shielding layer comprises a magnetic
compound, preferably having high relative magnetic
permeability and resistivity, for example a nickel-based,
chrome-based and/or titanium-based steel.
6. Device according to one of the claims 1 to 5,
wherein the shielding layer (14, 24) also overlaps a
part, not constituting a molding zone, of at least one of
the two mutually facing faces of the two mold casings..
7. Device according to one of the claims 1 to 6,
wherein the shielding zone also comprises a metal sheet
fixed to the magnetic mold casing, this metal sheet being
for example soldered or screwed in.
8. Device according to one of the claims 1 to 7,
wherein the shielding layer (14, 24) comprises a deposit
of material, especially an electrolytic deposit.
9. Device according to one of the above claims,
wherein the thickness e of the shielding layer is at
least equal to:
e = 50* (p/F)1/2
p being the resistivity of the non-magnetic material,
and F the frequency of the magnetic field.
10. Device according to one of the above claims wherein
the frequency F is at least equal to 25 KHz and preferably at
most equal to 100 KHz.
11. Device according to one of the above claims wherein
the shielding layer (14, 24) comprises a non-magnetic material
of low electrical resistivity, for example copper or aluminum.
12. Device according to one of the above claims, wherein
an electrically insulating layer is applied to the molding
zone of at least one mold casing to improve the electrical
insulation between the mold casings, especially when the
material to be transformed is conductive.

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13. Device according to one of the above claims, wherein
the inductive means (30) comprise two parts (32, 34), each one
fixedly joined to one of the mold casings, and being capable
of being shifted with the respective mold casing.
14 Device according to claim 13, wherein the two parts
(33, 34) of the inductive means are electrically connected by
means of at least . one' electrical contactor (36) enabling
contact to be maintained during the relative shift of one mold
casing (10, 20) relative to the other one during the
transformation phase.
15. Method for the manufacture of parts, especially in
large batches, making use of a device according to one of the
above claims, and comprising the following steps:
- positioning the material or materials of the part to
be processed on the lower mold casing (10) of the device,
heating the two molding zones (12, 22) , and
pressurizing the material (40) between the two molding zones
for a given period of time

The present invention concerns a device for the
transformation, especially by molding, of materials,
especially thermoplastic matrix composite materials or
thermosetting materials, comprising:
- two mold casings (10, 20) that are mobile relative
to each other, electrically conductive material and
including a molding zone (12, 22) designed to be in
contact with the material to be transformed, and
induction means (30) for generating a magnetic
field,
- the faces of one of the two mold casings (10, 20)
situated so as to be facing induction means, except for
the molding zones (12, 22), being coated with a shielding
layer (14, 24) made of a non-magnetic material preventing
the magnetic field from penetrating into the mold casings
(10, 20),
the mold casings being electrically insulated from
each other during the molding phase so that the faces of
the two mold casings demarcate an air gap (42) wherein
flows the magnetic field that induces currents at the
surface of the molding zones (12, 22), thus localizing
the heating at the interface between the molding zone and
the material to be transformed.