Mold , method for manufacturing a mold and method for manufacturing a
plastic or composite material product by means of said mold
5 The present invention relates to a mould more particularly intended for
manufacturing products in plastic or composite material, without however being limited
thereto.
It is known that it is highly favorable to use a molding method applying heating
by electromagnetic induction, notably for rapidly and efficiently heating plastic or
10 composite materials which have to be shaped, but also for heating parts in metals or
metal alloys before stamping them and quenching them in the tool.
According to such an induction-heating method, the molding device comprises
inductors through which flows a medium frequency current igen delivered by a power
generator and generating a variable electromagnetic field over time. This variable field
15 is at the basis of the well known phenomenon of electromagnetic induction: when
applied to a current conducting material, it creates a variable magnetic flux over time
and an induced voltage in the conducting material, which in turn generates induced
currents at the surface of the conducting metal, over a depth called the skin thickness
b and given by the relationship:
wherein p is the magnetic permeability of the material with p = po.pr, ci is the electric
conductivity of the material (reciprocal of the electric resistivity Rel), w is the angular
frequency and is equal to 2.rr.f wherein f is the frequency of the excitation current and
of the generated magnetic field.
25 When the conducting material is not ferromagnetic, the value of pr is close to I and the
skin thickness is given by the relationship:
8u,„ag„ =500
Re/
For this purpose, the material induction-heating method is known from
30 FR 2 867 939 which describes a mold with which the precursor material which will
assume its definitive properties after heat treatment, may be received in a cavity.
Supplying the inductor with a medium frequency electrical current generates induced
2
currents in the skin thickness of an intermediate part in contact with the material to be
heated, which limits the volume of the part of the mold , which has to be heated.
Moreover, inside this intermediate element, blocks of inserts made from
materials having distinct electric resistivities or magnetic permeabilities may be
5 positioned in order to obtain different surface temperatures.
However, the present inventors have observed that the dimensioning and the
placement of the blocks of inserts in the mold is a delicate operation which does not
allow very fine adjustment of the surface temperatures.
Further, even when this placement is performed in a very fine way, which takes
10 considerable time, it is observed that certain surface areas are subject to an
overheating or subheating phenomenon , which are detrimental to good manufacturing
of the molded product by generating hardness heterogeneities , for example.
Regardless of the geometry of these parts, temperature undulations are further
observed at heat transfer areas which will further worsen the overheating and
15 subheating phenomena described earlier.
The object of the invention is to find a remedy to these drawbacks by proposing
a mold for easier manufacturing and for which these molding temperature
heterogeneities may be attenuated , as well as a method for manufacturing such a
mold with which the targeted magnetic and/or thermal performances may easily be
20 modulated.
For this purpose , the first object of the invention is a mold comprising at least
one lower portion and one upper portion defining a cavity inside which a molding
material is to be brought to a temperature Ttr greater than 20 °C, which is introduced
and then shaped by contact with said lower and upper portions of the mold which are
25 heated by the action of an induced current generated by at least one electromagnetic
inductor, at least one of said lower and upper portions having a heat transfer area with
said molding material , said heat transfer area comprising at least a sub-area for heat
transfer consisting of at least one ferromagnetic material having a Curie point Tc
comprised between 20 and 800°C, which is in contact with said molding material
30 and/or with a coating consisting of a non-ferromagnetic material with heat conductivity
greater than 30 W.m "' K"', itself in contact with said molding material.
Within the scope of the present invention , by heat transfer area , is meant the
area(s) of the 'mold through which flows an induced current generated by the
electromagnetic inductor. As this was seen earlier , the thickness of this area depends
3
on the average electric resistivity of the material of the mold and on the frequency f of
the excitation current and is in all cases at most equal to bamagn.
It is preferred that this heat transfer area be in a single piece i.e. this is a bulk
area of a single piece, which does not result from an assembly of elements and which
5 cannot be disassembled. This term however does not exclude the presence of one or
several coatings forming a body with a base substrate.
In a preferred embodiment, said heat transfer comprises at least two heat
transfer sub-areas having magnetic permeability different from each other in the
vicinity of said temperature Ttr, at least one of said sub-areas consisting of a
10 ferromagnetic material having a Curie point Tc comprised between 20 and 800°C,
each of said sub-areas being in contact with said material to be molded and/or with a
possible coating consisting of a non-ferromagnetic material having heat conductivity of
more than 30 W.m'K', itself in contact with said molding material.
In an alternative of this preferred embodiment, the transfer sub-areas have
15 identical Curie points but consist of different proportions of magnetic compounds.
In another alternative of this preferred embodiment of the mold according to the
second object of the invention, the heat transfer sub-areas have different Curie points,
which may consist of two iron-nickel alloys of different composition or else further of an
iron-nickel alloy of identical composition but of different crystallographic structure.
20 The molds according to the invention may further incorporate the following
features, taken individually or as a combination:
- the cavity has at least one angle area , at least one heat transfer sub-area
surrounding this area,
- the coating in non-ferromagnetic material consists of aluminium, copper, tin
25 or alloys thereof,
- the Curie point is comprised between 60 and 350°C,
- the ferromagnetic material consists of an iron-nickel alloy, preferably
comprising at least 25% by weight of nickel, from 0.001 to 10% of
manganese as well as inevitable impurities resulting from the elaboration
30 and which may contain up to 15% by weight of chromium, up to 15% by
weight of cobalt, up to 15% by weight of copper, up to 10% by weight of at
least one element selected from silicon, aluminium, vanadium,
molybdenum, tungsten or niobium, and may further comprise at least one
element selected from sulfur, boron, magnesium or calcium.
4
A second object of the invention is formed by a method for manufacturing a
mold according to the first object of the invention , wherein an upper portion and a
lower portion of a mold are fed , delimiting a cavity and at least one of said lower and
upper portions of which have a heat transfer area comprising a ferromagnetic metal
5 alloy, and then a layer of a non-ferromagnetic material is deposited having a heat
conductivity of more than 30 W.m-'K-' over all or part of the portion of said heat
transfer area consisting of said ferromagnetic alloy. Preferably, the metal or metal alloy
layer having a heat conductivity of more than 30 W . m-'K-1 consists of aluminium,
copper, tin or alloys thereof, in particular alloys of copper and of nickel.
10 A third object of the invention is formed by a method for manufacturing a mold
according to the second object of the invention , wherein an. upper portion and a lower
mold portion are fed , delimiting a cavity and at least one of said lower and upper
portions of which has a heat transfer area comprising a ferromagnetic alloy, and a
non-ferromagnetic metal or alloy layer is deposited on all or part of the portion of said
15 heat transfer area consisting of said ferromagnetic alloy and said metal or alloy layer is
diffused by localized heat treatment, said metal or alloy being selected so as to cause
precipitation of amagnetic phases by its diffusion , thereby forming a heat transfer subarea,
the proportion of magnetic compounds of which is different from all or part of the
remainder of the heat transfer area. Preferably , the heat transfer area initially
20 comprises an austenitic or austeno -ferritic or austeno-martensitic iron-nickel alloy
comprising at least 25% by weight of nickel, from 0 . 001 to 10% of manganese as well
as inevitable impurities resulting from the elaboration and which may contain up to
15% by weight of chromium, up to 15% by weight of cobalt, up to 15% by weight of
copper, up to 10% by weight of at least one element selected from silicon , aluminium,
25 vanadium , molybdenum , tungsten or niobium and which may further contain at least
one element selected from sulfur, boron, magnesium or calcium, and the nonferromagnetic
metal consists of aluminium.
A fourth object of the invention is formed by a method for manufacturing a mold
according to the second object of the invention, wherein an upper portion and a lower
30 portion of a mold are fed , delimiting a cavity and at least one of said lower and upper
portions of which has a heat transfer area comprising a ferromagnetic alloy, and then it
is preceded with localized heat treatment on at least one portion of said heat transfer
area consisting of said alloy , so as to form a heat transfer sub-area, whereof the
crystallographic structure and therefore the Curie point are different from all or part of
5
the remainder of the heat transfer area . Preferably the heat transfer area initially
comprises an austenitic or austeno-ferritic or austeno -martensitic iron-nickel alloy
comprising at least 25% by weight of nickel , from 0.001 to 10% of manganese as well
as inevitable impurities resulting from the elaboration and which may contain up to
5 15% by weight of chromium , up to 15% by weight of cobalt, up to 15% by weight of
copper, up to 10% by weight of at least one element selected from silicon , aluminium,
vanadium , molybdenum , tungsten or niobium, and which may further contain at least
one element selected from sulfur, boron , magnesium or calcium , and said localized
heat treatment consists in rapidly cooling said heat transfer area portion , thereby
10 causing transformation of all or part of the austenite into martensite.
A fifth object of the invention is formed by a method, for manufacturing a mold
according to the second object of the invention, wherein an upper portion and a lower
portion of a mold are fed , delimiting a cavity and at least one of said lower and upper
portions of which has a heat transfer area comprising a ferromagnetic metal alloy, and
15 a layer of a non-ferromagentic alloy or metal is deposited on all or part of the portion of
said heat transfer area consisting of said alloy and said non -ferromagnetic metal or
alloy layer is diffused by localized heat treatment , said metal or alloy being selected so
as to locally modify the Curie point by its diffusion thereby forming a heat transfer
sub-area, the Curie point of which is different from that of all or part of the remainder of,
20 the heat transfer area. Preferably, the heat transfer area initially comprises an ironnickel
alloy comprising at least 25% by weight of nickel as well as inevitable impurities
resulting from the elaboration and which may contain up to 10% by weight of
chromium, up to 10% by weight of cobalt and up to 10% by weight of copper, and said
metal deposited on at least one portion of the heat transfer area is copper.
25 -. A sixth object of the invention is formed by a device for induction-molding
comprising a mold according to the invention and at least one electromagnetic
inductor.
A seventh object of the invention is formed by a method for manufacturing a
product in plastic or composite material by means of a mold according to the invention,
30 wherein said plastic material or said composite materials, are introduced inside the
cavity of said mold and then shaped by contact with said lower and upper portions of
the mold, at least one of which is brought to a homogeneous temperature within plus
or minus 8°C , and preferably within plus or minus 5°C, and comprised between 60°C
6
and 350°C by the action of an induced current generated by said electromagnetic
inductor.
Within the scope of the present invention, by the term of plastic are notably
designated thermoplastic compounds, thermosetting compounds, elastomers,
5 vulcanizable compounds.
Moreover, by the term of composite, is meant any combination of the plastic
materials cited above with an element such as glass, carbon, an oxide, a metal or a
metal alloy. This additional element may be incorporated in the form of dispersed
fibers, or in the form of a woven or non-woven network, or else further in the form of
10 one or several facings adhering to the plastic material so as to form a sandwich or
bilayer structure, or else further a cell structure such as a honeycomb structure for
example.
As this will have been understood, the definition of the mold according to the
invention is based on the modulation of the characteristics of use of the heat transfer
15 area, thereby giving the possibility of attenuating the heterogeneities of surface
temperature of this mold. Indeed, it was seen in a new and surprising way that
obtaining a homogeneous temperature at the functional surface of the mold required
heterogeneity of the characteristics of use of the heat transfer area.
In particular, it was seen that overheatings had notably occurred in.
20 concentration areas of induced currents and subheatings in areas where the induced
currents do not flow. These phenomena notably depend on the geometry of the parts
to be manufactured, the angular areas with an acute angle ranging up to a right angle
being the center of current concentrations by a spiking effect, while the obtuse angle
angular areas are short-circuited and do not see the induced current.
25 Within the scope of the present invention, by angular area or angle area is
meant an area at which the general direction of the surface of the molding cavity
changes substantially.
Thus, if reference is made to Fig. 1, a sectional view of an exemplary mold 1
according to the prior art may be seen therein, in two upper 2 and lower 3 portions
30 defining in their air gap, a cavity entirely filled with plastic material 4 during molding.
The mold 1 is entirely made in a magnetic material having a Curie point To close to the
transformation temperature Ttr of the molding material. The manufactured object, here
a basin, includes two horizontal side edges 5 and 6 connected to a bottom 7 through
two vertical side walls 8 and 9.
7
The figure also includes the indication of the orientation of the magnetic field H
to which the mold is subject under the effect of one or several electromagnetic
inductors (not shown) through which flows an electric current of frequency f. The
electromagnetic inductors are preferably integrated into the lower portion and into the
5 upper portion of the body of the mold, as this may be seen in Fig. 1 of FR 2 867 939.
The figure also includes circulation lines of induced currents generated by the action of
the magnetic field H and illustrated by two dotted lines in each of the portions 2 and 3
of the mold. Finally it includes an illustration of the skin areas of the portions 2 and 3
delimited by a dotted line with an alternation of dashes and dots.
10 In the case of this basin 1, the areas in which significant sub-heating was
observed , are located in the vicinity of the areas ab2, bcl , cdl and ed2 which are also
areas where it is seen that the induced currents pass far away from the material during
molding, these currents passing through the shortest way in order to cross the skin
area. These areas may be defined as areas in which the angle extending from a first
15 portion of the basin to a second portion is obtuse.
As regards now the overheating areas, they were observed in the vicinity of the
areas ab1 , bc2, cd2 and ed1 which are also areas where it is seen that the induced
currents concentrate by a spiking effect. These areas may be defined as areas
wherein the angle extending from a first portion of the basin to a second portion is
20 acute.
Now, when the intention is to increase the power injected into a usually subheated
area, it was established that the relevant local area should have greater
magnetic permeability than the value of the surrounding areas, in the vicinity of the
relevant operating temperature, i.e. in an interval of + or - 10 ° C around this operating
25 temperature , which amounts to operating on inhomogeneous heat transfer
permeability areas.
Conversely, when the intention is to reduce the power injected into a usually
overheated area , the relevant local area must have a smaller magnetic permeability
than the value of the surrounding areas, at the relevant operating temperature, i.e. in
30 an interval of + or - 10 °C around this operating temperature.
Of course, it is particularly advantageous to place the areas with modified
permeabilities in the vicinity of the angular areas of the molding cavity, depending on
the type of relevant angle. In particular stronger permeability areas may be positioned
8
in sub-heated areas and reduced permeability areas in overheated areas, as they
have been defined above.
One of the main alternatives of the invention consists of making available a
mold having heat transfer sub-areas for which the magnetic permeabilities differ
5 because they consist of magnetic materials for which the Curie points are different.
The adjustment of the Curie point may in particular be obtained by adjusting
the composition of the relevant materials.
This may also be obtained by retaining a homogeneous chemical composition
but by modifying the crystallographic structures of the materials depending on the
10 relevant areas. Indeed, the Curie point of a material greatly depends on the
crystallographic structure and may completely change when passing from an
austenitic structure to a martensitic structure for example. Such a change in structure
is itself easy to obtain since localized heat treatment may be sufficient for achieving it,
whether this is a more or less rapid heating (such as an austenitization for example)
15 and/or cooling step.
If a material area becomes amagnetic before another surface area of the mold
because its temperature exceeds its Curie point, less than that of an adjacent area,
the permeability of the area decreases from very high values to the value 1 and the
injected power strongly decreases. Self-regulation of the temperature around the Curie.
20 point of the low Curie point area is then obtained, thus allowing fine adjustment of the
temperature adjustments.
Another alternative of the invention consists of making available a mold having
heat transfer sub-areas, the magnetic permeabilities of which differ although they
consist of magnetic materials having identical Curie points. This local decrease in the
25 permeability may in particular be obtained by depositing and then precipitating certain
non-ferromagnetic elements, which do not have any influence on the Curie point, with
magnetic elements of the initial magnetic alloy, so that the non-ferromagnetic phases
are formed and therefore decrease the permeability of the relevant sub-area.
Nickel-iron alloys lend themselves well to these deposition and diffusion
30 methods and in particular transformation temperatures comprised between 60 and
350°C may be reached, fully compatible with the transformation temperatures of most
plastics and composites, when they contain more than 25% by weight of nickel.
Additions, of chromium, cobalt and copper may range up to 15% by weight
notably allowing finer adjustment of the Curie points:
9
- for example an austenitic alloy with 56% by weight of nickel (remainder = iron)
by weight sees its Curie point pass from 530 to 300°C when the molybdenum
percentage passes from 0 to 11 % by weight.
- for example, an austenitic alloy with 40% by weight of nickel (remainder =
5 iron) by weight sees its Curie point pass from 360 to 100°C when the chromium
percentage passes from 0 to 15% by weight.
- for example an austenitic alloy containing 30 to 32% by weight of nickel and 2
to 8% by weight of chromium (remainder = iron) by weight has a continuous
distribution of Curie points in the range from -20°C to 170°C, and this for each of these
10 compositions, the Curie point may be increased by 10 to 15°C per percent by weight of
addition element which are copper or cobalt.
Addition of 0.01 to 10% by manganese allows improvement in the hot shape
ability of the alloy.
The preferred alloy according to the invention may further contain up to 10% by
15 weight of at least one element selected from silicon, aluminium, vanadium,
molybdenum, tungsten or niobium.
All these elements (Cr, Cu, Co, Mo, Si, Al, Nb, V, W), have the advantage of
allowing adjustment of the Curie point to different values, while having different actions
of these elements on important properties here such as electrical resistivity pei, or heat.
20 conductivity 5th.
Thus, in austenitic alloys Fe-Ni-Mo, molybdenum significantly increases
electrical resistivity: for example the alloy Fe-56%Ni sees its electric resistivity pass at
room temperature from 30pO.cm to 100pO.cm when the molybdenum percentage
passes from 0 to 9% by weight.
25 In austenitic alloys Fe-Ni-Cr, chromium significantly increases electrical
resistivity: for example the alloy Fe-45%Ni sees its electric resistivity pass at room
temperature from 45p0.cm to 90p0.cm when the chromium percentage passes from 0
to 6% by weight.
In austenitic alloys Fe-Ni-Cu, copper significantly decreases electrical
30 resistivity: for example the alloy Fe-30%Ni sees its electrical resistivity pass at room
temperature from 88p0.cm to 78p0.cm when the copper percentage passes from 4 to
10% by weight.
Also Si, Al, Nb,V and W more or less substantially low the Curie point Tc and
increase the electrical resistivity.
10
Finally, this alloy may further comprise at least one element selected from
sulfur, boron, magnesium or calcium. In particular it is preferred to limit the
accumulated content of sulfur and boron to an interval from 2 to 60 ppm, while the
accumulated content of magnesium and calcium will preferably be limited to an interval
5 from 10 to 500ppm. These elements notably allow improvement in the machine ability
of the grade.
Moreover, regardless of the geometry of these parts, temperature undulations
have further been observed at the heat transfer areas. Without intending to be bound
by a theory, it is assumed that these undulations may come from the structure of the
10 inductors which appear as turns and would be at the origin of induced "mirror" currents
with respect to their location and to their shape.
It was seen that it was possible to considerably attenuate these undulations by
covering all or part of the heat transfer area with a non-ferromagnetic material which
conducts heat particularly well. Such a material apparently gives the possibility of
15 playing the role of a heat wave diffuser, which attenuates the temperature differences
in significant proportions. This type of regulation may in particular make sense on nonangular
areas such as the areas c1 and c2 of the basin of Fig. 1.
Generally, the thickness of such coatings will be smaller than that of the heat
transfer area and preferably less than one tenth of the skin thickness.
20 It is obvious that the different measures proposed within the scope of the
invention for homogenizing the surface temperature of the mold may be combined
insofar that they are compatible with each other.
The molds of the invention may be obtained by simply machining bulk blocks of
magnetic materials or else by machining blocks of amagnetic materials, or even of
25 non-metal materials, followed by deposition of a layer of magnetic materials by any
suitable process, such as plating, deposition by plasma, by sputtering, or else further
by projection. In all the cases, once a surface has been obtained with suitable
geometrical dimensions and with suitable magnetic properties, it is possible to apply
the method for manufacturing a mold according to the invention. This method in
30 particular gives the possibility of simply obtaining a heat transfer area as one piece,
without adding any insert.
For this purpose, all the alternatives described earlier may be used, which
more particularly.apply to the manufacturing of a mold, at least one portion of the heat
transfer area of which comprises, or even consists of a iron-nickel matrix which will be
11
modified at the locations identified as having to be adapted for ensuring good final
temperature homogeneity.
The invention will now be described in more detail but in a non-limiting way and
illustrated by examples.
Examples
A series of molds is made in different materials which will be described in each
example. These molds all have a shape identical with the one of the mold of Fig. 1 for
manufacturing a basin.
10 In a first series of examples, the plastic material to be molded making up the
product is a thermoplastic composite with glass fiber and polypropylene matrix which
has a transformation point at a temperature of 200°C.
In a second series of examples, the plastic material to be molded making up
the product is a plastic which has a transformation point at a temperature of 125°C.
15 Unless indicated otherwise, the indicated percentages of the alloyed
compositions are expressed by weight and all the compositions according to the
invention contain 0.1 % of manganese and of usual inevitable impurities resulting from
the elaboration.
20 Counterexample 1
In order to be able to compare the performances of the invention with those of
the prior art, it was proceeded with a first molding test by means of a mold including
added metal parts called inserts.
In the overheated areas identified earlier the material of the mold is locally
25 replaced with these inserts consisting of non-magnetic materials such as austenitic
stainless steel.
The inserts are placed in the concentration areas of the induced currents,
which gives the possibility of locally reaching a highly increased penetration depth of
the power. This means that the induced currents are no longer concentrated on the
30 extreme surface of the bend but are spread out on the surrounding bend area thus
dissipating less energy on the actual exchange surface of the bend.
In this case, one manages to limit the temperature difference between the mold
and the product to an interval of the order of 20-30°C which may be sufficient but
requires a higher cost for building the molds, does not allow adjustment and perfect
12
insert/mold heat transfer and does not allow the manufacturing of certain products with
a complex geometry such as shapes with a funnel or a very deep bowl.
Counter-example 2
5 It was then proceeded with a second test according to the prior art by making a
mold for which the heat transfer area consists of a single ferromagnetic alloy.
The molds were machined in austenitic alloys FeNi or FeNiCr known for
allowing easy adjustment of the Curie point by the composition. Indeed , it is well
known that if a Curie point Tc is selected close to the desired plateau temperature
10 (here for the shaping of plastics or composite), a temperature self-regulation
phenomenon is obtained around Tc (the magnetic losses and currents disappear for a
major part upon approaching the Curie point) and finally a rebalancing of the
subheated and overheated areas.
With the solution using a FeNiCr alloy having Tc=210°C, one obtains:
15 - thermal inhomogeneity around the marked angles of the product : 4Tan9,e= 15°C
- thermal inhomogeneity at the bottom of the basin ATbas;,, = 20°C
- thermal inhomogeneities reflecting the inductor turns AT;nducr„rns= 20°C.
Thus, therefore , the temperature self-regulation effect around the Curie point is
mainly effective on the temperature homogeneity of the areas with an acute angle,.
20 reducing it to 15°C instead of 20 to 30°C with inserts and much more without any
insert. The other types of thermal inhomogeneities are on the other hand little
improved.
Example 1
25 An austenitic FeNiCr alloy is used, for which the Curie temperature Tc is in the
vicinity of 210°C - which may for example be Fe-35%Ni or Fe-37%Ni-6%Cr or Fe-
50%Ni-11.5%Cr alloy - as a precursor to the homogeneous bulk condition under
which the 3D shape of the plastic or composite product will be machined so as to be
shaped by induction-heating.
30 In this example, after machining the heat transfer surfaces, an aluminium sheet
of the order of 50pm is flattened so that this sheet actually covers the functional
machined surface of the mold, i.e. both surfaces facing the two parts of the mold.
Next, by laying both of these covered mold parts in an oven while keeping the
aluminium sheet on the upper face of the mold, a heat treatment for melting/plating the
13
aluminium on the surface is applied by bringing the mold part to a temperature above
600°C, for at least a few minutes but only allowing negligible diffusion of the aluminium
into the FeNiCr alloy . The purpose of this heat treatment is actually only close
adhesion of the aluminium onto the FeNiCr alloy (metal-metal bond).
5 It is then proceeded with a molding test by means of the obtained mold. One
then obtains:
- thermal inhomogeneity around the marked bends of the product ®Tangie = 12°C
- ®Tdottom= 20°C.
- thermal inhomogeneities reflecting the inductor turns ATinducturns = 8°C
10 Thus, therefore , the temperature self-regulation effect around the Curie point is
mainly effective on the temperature homogeneity of the areas with an acute angle and
is reinforced by the thin aluminium conducting coating , reducing it to 12°C instead of
15°C without aluminium and from 20 to 30°C with inserts and much more without any
insert.
15 Further, the thin aluminium layer plays an interesting role as a heat diffuser
even at these high frequencies and in relatively short heat transfer times (of the order
of one minute) since the thermal heterogeneity resulting from the direct effect of
localization of the turns of the inductor on the functional surface ATinducturns is brought
back to 8°C instead of 20 ° C without the aluminium layer. The temperature of the.
20 bottom of the basin remains also far from the goal , which in certain cases of plastic or
of product specifications may be accepted.
EMM le 2
Example no. 1 is reproduced but with another precursor alloy since the aim
25 hereis to obtain in a plastic material as shaped above, a temperature of 125°C during
heating by induction.
Different FeNiCrCu alloys having a Curie point very close to 125°C were
successfully tested here:
- Fe-32%Ni
30 - Fe-30 .3%Ni-2%-Cr
- Fe-36.5%Ni-9%Cr-0.2%Mn
- Fe-29%Ni-2%Cr-3.5%Co
- Fe-40%Ni-13%Cr-2%Co
- Fe-30%Ni-2%Cr-3%Cu
14
- Fe-28%Ni-2%Cr-5.5%Cu
Each alloy is supplied in the condition of a block in which the 3D shape of the
plastic material to be shaped by induction-heating will be machined.
After machining the functional heat transfer surfaces, a 50pm aluminium sheet
5 is applied so that this sheet actually covers the functional machined surface of the
mold, i.e. both surfaces facing both parts of the mold. Next, laying these two covered
mold parts in an oven while keeping the aluminium sheet on the side of the upper face
of the mold, a heat treatment for melting/plating aluminium is applied on the functional
surface by bringing the mold parts to a temperature above 600°C during at least a few
10 minutes but only allowing negligible diffusion of the aluminium into the FeNiCr alloy.
The purpose of this heat treatment is actually only close adhesion of the aluminium
onto the FeNiCr alloy (metal-metal bond).
It is then proceeded with a molding test by means of the obtained mold.
One then obtains:
15 - a thermal inhomogeneity around the marked bends of the product
ATange= 10°C
a bottom = 16°C
thermal inhomogeneities reflecting the inductor turns ATinduoturns = 6°C
The same advantages of performances (reduction of thermal heterogeneities).
20 are thus verified as in Example 2 on the same complex product shape but with
different heating temperatures and precursor alloy.
Example 3
An austenitic Fe-30%Ni-2%Cr-3%Cu alloy is used here, for which the Curie
25 temperature Tc is in the vicinity of 125°C for rapid shaping of a plastic material after
induction heating.
This alloy is supplied in the condition of a block in which the 3D shape of the
product to be shaped will be machined. After machining the functional heat transfer
surfaces; a 50pm aluminium sheet is applied so that this sheet actually covers the
30 functional machined surface of the mold, i.e. both surfaces facing both parts of the
mold.
Next, laying both covered mold parts in an oven while keeping the aluminium
sheet on the upper side of the upper face of the mold, a heat treatment for
melting/applying the aluminium is applied on the functional surface while bringing the
15
mold parts to a temperature above 600°C during at least a few minutes but only
allowing negligible diffusion of the aluminium into the FeNiCrCu alloy. The purpose of
this first heat treatment is only close adhesion of the aluminium onto the alloy (metalmetal
bond). At this stage, the heat transfer surface is compliant and similar with those
5 of the preceding Examples 1 and 2.
In a new heat treatment step, well differentiated from the preceding one,
certain surfaces of the mold are heated with different known means (torch, localized
inductor, pre-heated metal parts and contact, supply of energy by radiation...) so as to
cause diffusion under the surface of aluminium applied beforehand, then generating
10 precipitation of a non-magnetic secondary phase and significant lowering of the
permeability pr.
The faces subject to this intense supply of surface heat are necessarily the
faces al, a2, b1, b2, dl, d2, el, e2, i.e. all the faces of the heat transfer surface
except those of the bottom of the basin (c1 and c2). For the deposited aluminium, the
15 heat supply should cause the surface temperature to be raised to at least 500°C,
preferably at least 600°C so as to cause diffusion of the aluminium into the subsurface
without too high overmelting of the aluminium degrading the homogeneity of
the deposit.
It is then proceeded with a molding test by means of the obtained mold. One.
20 then obtains:
- a thermal inhomogeneity around the marked bends of the product ATangie = 12°C
- a i bottom = 8°C
- thermal inhomogeneities reflecting the inductor turns AT inductums = 11 °C
Thus, therefore, the temperature self-regulation effect around the Curie point is
25 mainly effective on the temperature inhomogeneity of the areas with an acute angle
and is reinforced by the thin aluminium conducting coating, reducing it to 12°C instead
of 15°C without aluminium and to 20-30°C with insert and much more without any
insert. Further, the thin aluminium layer plays a very interesting role of a heat diffuser
even at these high frequencies and within also short heat transfer times (of the order
30 of one minute) since the thermal heterogeneity resulting from the direct effect of
localization of the turns of the inductor on the functional surface ®Tnductums is brought
back to 11 °C instead of 20°C without the aluminium layer.
Further, in this case of forced diffusion of aluminium into a sub-surface of
certain faces of the mold, the bottom bowl temperature is substantially raised to 6°C
16
from the goal , demonstrating the advantage of controlling the temperature
heterogeneities with calibrated heterogeneities of properties in a heat transfer subarea.
5 Example 4
An austenitic and ferromagnetic FeNiCrCu alloy is used here at room
temperature after hot and then cold transformations followed by recrystallization and
cooling annealing of 5°C/h to 5,000°C/h down to room temperature and with 25 to
36%Ni. Indeed, in this composition domain, having such an austenitic alloy (or
10 possibly austeno-ferritic in certain composition cases) pass into liquid nitrogen,
completely transforms it into martensite for which the Curie point is much higher at
shaping operating temperatures aimed by the invention (<350°C). By localizing this
transformation effect to liquid nitrogen in sub-heated areas, the temperature of these
areas is raised.
15 A transfer surface is used made from the alloy of Example 3 with a Curie point
in the vicinity of 125°C on the precursor alloy with one of the following alloys:
- Fe-32%Ni
- Fe-30.3%Ni-2%Cr
- Fe-29%Ni-2%Cr-3.5%Co
20 - Fe-30%Ni-2%Cr-3%Cu
- Fe-28%Ni-2%Cr-5.5%Cu
and then an aluminium sheet is applied by a first heat treatment on the surface, and
then diffused into a sub-surface by a second heat treatment on the faces other than
the bottom of the bowl. Finally, the protruding edges (ab2, bcl, cdl, ed2) of the
25 transfer surface suffering from chronic sub-heating are locally treated with nitrogen in
order to locally induce a martensitic structure and a strong local increase in Tc.
It is then proceeded with a molding test by means of the obtained mold. One
then obtains:
- a thermal inhomogeneity around the marked bends of the product Mangle= 7°C
30 - ATbottom = 9°C.
- thermal inhomogeneities reflecting the inductor turns ATinducturns= 10°C.
All the advantages already listed with Example 3 are thereby obtained with
additionally a significant reduction in the temperature heterogeneity between bend
17
areas which then drops to 7°C instead of 10-12°C without any martensitic
transformation,
Example 5
5 An austenitic or austeno-ferritic alloy is used here with 25-34% Ni and
<11%Cu, for which the Curie point is located in the vicinity of 125°C- which may for
example be a Fe-28%Ni-5%Cu alloy - as a precursor to the homogeneous bulk
condition, in which the 3D shape of the product (plastic or composite) will be
machined, to be shaped by induction heating.
10 After machining the heat transfer surfaces, a 50pm aluminium sheet is applied
so that this sheet actually covers the faces of the functional machine surface of the
mold other than the faces of the bottom of the basin, therefore the faces of type a, b, d,
e, f, g on both surfaces facing both mold parts. In a different way from the preceding
examples, the faces of type c (bottom of the bowl) are covered with a thin 40pm
15 copper sheet.
And then the different heat treatments are subsequently successively carried
out:
- melting/application of the aluminium on the heat transfer surface by bringing the mold
parts to a temperature above 600°C for at least a few minutes but only allowing.
20 negligible diffusion of the aluminium into the FeNiCrCu alloy,
- melting/application of copper on the heat transfer surface by raising the mold parts to
a temperature above 1,000°C for at least a few minutes but allowing negligible
diffusion of the copper into the FeNiCrCu alloy. This treatment will preferably be
performed by putting the whole mold in an oven which will then allow diffusion of the
25 aluminium into the sub-surface in order to precipitate secondary and magnetic phases
and adjust the permeability in the relevant sub-surface.
- surface heating of the copper localized at the faces of type c for a sufficiently long
time and at a high temperature so that the copper is mixed with the matrix of the
precursor alloy FeNiCrCu. Thus the Curie point at the surface of type c is increased.
30 Finally, a localized quench is carried out in liquid nitrogen of the protruding
edges of the molding cavity, as described in Example 4, in order to modify the
microstructure of the magnetic alloy.
It is then proceeded with a molding test by means of the obtained mold.
One then obtains:
18
a thermal inhomogeneity around the marked bends of the product ATangJ,=6°C
a bottom=8°C.
thermal inhomogeneities reflecting the inductor turns Alinductums = 8°C
With this method, one therefore also manages to reduce the different thermal
5 heterogeneities very satisfactorily.
As this will have been understood, the present invention proposes several
solutions with which the surface temperature heterogeneities of the heat transfer area
of a mold may be attenuated at most, it being understood that these different solutions
10 may be combined at will depending on the particular geometry of the product to be
obtained and therefore on the corresponding molding cavity,
The description which has just been made more particularly relates to the
molding of plastic material and of composite but is not limited thereto, such a mold
may find uses for shaping other types of products such as glasses, metals or metal
15 alloys for example. In the case of metal products, the shaping of the materials may in
particular be carried out by hot die stamping.
19
CLAIMS
1. A mold comprising at least one lower portion and one upper portion delimiting a
cavity inside of which a material to be molded which has to be brought to a
temperature Ttr of more than 20°C, is introduced and then shaped by contact
5 with said lower and upper portions of the mold which are heated by the action of
an induced current generated by at least one electromagnetic inductor, at least
one of said lower and upper portions having a heat transfer area with said
molding material, said heat transfer area comprising at least one heat treatment
sub-area consisting of at least one ferromagnetic material having a Curie point
10 Tc comprised between 20 and 800°C, which is in contact with said molding
material and/or with a coating consisting of a non-ferromagnetic material with a
heat conductivity of more than 30 VV.mAK"', itself in contact with said molding
material.
2. The mold according to claim 1, wherein said heat transfer area comprises at
15 least two heat transfer sub-areas having magnetic permeability different from
each other in the vicinity of said temperature Tr, at least one of said sub-areas
consisting of a ferromagnetic material having a Curie point Tc comprised
between 20 and 800°C, each of said sub-areas being in contact with said
molding material and/or with a possible coating consisting of a non-.
20 ferromagnetic material having a heat conductivity of more than 30 W.m K"', itself
in contact with said molding material.
3. The mold according to claim 1 or 2, for which said cavity has at least one angle
area , at least one heat transfer sub-area surrounding said area.
4. The mold according to any of claims 1 to 3, for which said coating in
25 -non-ferromagnetic material consists of aluminium, copper, tin or alloys thereof.
5. The mold according to any of claims 1 to 4, for which said Curie point is
comprised between 60 and 350°C.
6. The mold according to any of claims 1 to 5, for which said ferromagnetic material
consists of an iron-nickel alloy.
30 7. The mold according to claim 6, for which said ferromagnetic material comprises
at least 25% by weight of nickel, from 0.001 to 10% of manganese as well as
inevitable impurities resulting from the elaboration and may contain up to 15% by
weight of chromium, up to 15% by weight of cobalt, up to 15% by weight of
copper, up to 10% by weight of at least one element selected from silicon,
20
aluminium, vanadium, molybdenum, tungsten or niobium, and may further
comprise at least one element selected from sulfur, boron, magnesium or
calcium.
8. The mold according to any of claims 2 to 7, for which said heat transfer
5 sub-areas have identical Curie points but consist of different proportions of
magnetic compounds.
9. The mold according to any of claims 2 to 7, for which said heat transfer
sub-areas have different Curie points.
10. The mold according to claim 9, for which said heat transfer sub-areas consist of
10 two iron-nickel alloys of different composition.
11. The mold according to claim 9, for which said heat transfer sub-areas consist of
an iron-nickel alloy of identical composition but of different crystallographic
structure.
12. The mold according to any of claims 1 to 11, for which said heat transfer area is
15 a one-piece area.
13. A method for manufacturing a mold according to claims 1 to 12, in which an
upper portion and a lower portion of a mold is fed delimiting a cavity and for
which at least one of said lower and upper portions has a heat transfer area
comprising a ferromagnetic metal alloy having a Curie point Tc comprised,
20 between 20 and 800°C, and then a layer of a hon-ferromagnetic material having
a heat conductivity of more than 30 W.m-'K"' is deposited on all or part of the
portion of said heat transfer area consisting of said ferromagnetic alloy.
14. The method according to claim 13, wherein said non-ferromagnetic material
layer having a heat conductivity of more than 30 W.m-'K-1 consists of aluminium,
25 copper, tin or alloys thereof, in particular alloys of copper and nickel.
15. The method for manufacturing a mold according to any of claims 2 to 8, wherein
an upper portion and a lower portion of a mold is fed delimiting a cavity and for
which at least one of said lower and upper portions has a heat transfer area
comprising a ferromagnetic metal alloy, and a layer of metal or of non-
30 ferromagnetic alloy is deposited on all or part of the portion of said heat transfer
area consisting of said ferromagnetic alloy, and said metal or alloy layer is
diffused by localized heat treatment, said metal or alloy being selected so as to
cause precipitation of amagnetic phases by its diffusion, thereby forming a heat
21
transfer sub-area for which the proportion of magnetic compounds is different
from all or part of the remainder of the heat transfer area.
16. The method according to claim 15, wherein said heat transfer area initially
comprises an austenitic or austeno -ferritic or austeno-martensitic iron-nickel
5 alloy comprising at least 25% by weight of nickel, from 0 .001 to 10% of
manganese as well as inevitable impurities resulting from the elaboration and
which may contain up to 15% by weight of chromium , up to 15% by weight of
cobalt, up to 15% by weight of copper, up to 10% by weight of at least one
element selected from silicon , aluminium , vanadium, molybdenum, tungsten or
10 niobium , and which may further contain at least one element selected from
sulfur, boron , magnesium or calcium, and said non-ferromagnetic metal consists
of aluminium.
17. The method for manufacturing a mold according to any of claims 2 to 7, 9 and
11, in which an upper portion and a lower portion of a mold is fed delimiting a
15 cavity and for which at least one of said upper and lower portions has a heat
transfer area comprising a ferromagnetic metal alloy , and it is then proceeded
with localized heat treatment on at least one portion of said heat transfer area
consisting of said alloy, so as to form a heat transfer sub-area for which the
crystallographic structure and therefore the Curie point are different from those.
20 of all or part of the remainder of the heat transfer area.
18. The method according to claim 17, wherein said heat transfer area initially
comprises an austenitic or austeno -ferritic or austeno-martensitic iron -nickel
alloy comprising at least 25% by weight of nickel , from 0.001 to 10% of
manganese as well as inevitable impurities resulting from the elaboration and
25 which may contain up to 15% by weight of chromium , up to 15% by weight of
cobalt, up to 15% by weight of copper , up to 10% by weight of at least one
element selected from silicon , aluminium , vanadium, molybdenum , tungsten or
niobium, and which may further contain at least one element selected from
sulfur, boron, magnesium or calcium, and said localized heat treatment consists
30 of rapidly cooling said heat transfer area portion , thus causing transformation of
all or part of the austenite into martensite.
19. A method for manufacturing a mold according to any of claims 2 to 7 and 9 to 10,
wherein an upper portion and a lower portion of a mold is fed delimiting a cavity
and for which at least one of said lower and upper portions has a heat transfer
22
area comprising a ferromagnetic metal alloy, and a layer of a non-ferromagnetic
metal or alloy is deposited on all or part of the portion of said heat transfer area
consisting of said alloy, and said non-ferromagnetic metal or alloy layer is
diffused by localized heat treatment, said metal or alloy being selected so as to
5 locally modify the Curie point by its diffusion thereby forming a heat transfer subarea
for which the Curie point is different from that of all or part of the remainder
of the heat transfer area,
20. The method according to claim 19, wherein said heat transfer area initially
comprises an iron-nickel alloy comprising at least 25% by weight of nickel as well
10 as inevitable impurities resulting from the elaboration and which may contain up
to 10% by weight of chromium, up to 10% by weight of cobalt and up to 10% by
weight of copper, and said metal deposited on at least one portion of said heat
transfer area is copper. .
21. An induction molding device comprising a mold according to any of claims 1 to
15 12 or of a mold which may be obtained by the method according to any of claims
13 to 20, and at least one electromagnetic inductor.
22. A method for manufacturing a plastic or composite material product by means of
a mold according to any of claims 1 to 12 or by a mold which may be obtained by
the method according to any of claims 13 to 20 or by a molding device according
20 to claim 21, wherein said plastic material or said composite materials are
introduced inside the cavity of said mold and then shaped by contact with said
lower and upper portions of the mold, at least one of which is brought to a
homogeneous temperature to within plus or minus 8°C and comprised between
60°C and 350°C by action of an induced current:. generated by said
25 electromagnetic inductor.
23. The method according to claim 22, for which said temperature is homogeneous
to within plus or minus 5°C.