Induction heating device for molding small parts

Abstract

The invention relates to a mold suitable for molding small parts, comprising a casing adapted to be mounted on a platen (101, 102), the casing comprising a housing adapted to receive an insert (350) adapted to be integrated into the casing, the insert comprising a housing for a die comprising a molding surface (121, 122) of the part; a device for heating the die, the heating device comprising rods (131, 132) made of a material susceptible to induction heating, the rods being adapted to heat the insert (350) and the heating device comprising a housing for a die comprising a molding surface (121, 122) of the part; The rod is mounted in a mold (350), one end of which is in contact with the mold (die), and the molding surfaces (121, 122) are at the center of the rod; coils (141, 142) made of a conductive material surrounding the rod are connected to high-frequency current generators (151, 152), and when a current is supplied to the coils, an induced current is generated in the rods (131, 132), which heats the rods and transmits the heat to the mold (die), and the outer diameter (235) of the rods is the same as or larger than the outer diameter (225) of the molding surfaces (121, 122).

Description

Technical Field

[0001] The present invention belongs to the field of molding methods, and more specifically relates to the molding of small parts.

[0002] As a non-limiting example, the present invention is used for molding lenses for cameras of smartphones.

[0003] The present invention is equipped with a device for rapid heating and cooling, and relates to a tool suitable for mass production of this type of part.

Background Art

[0004] In the large-scale molding of glass or plastic parts called organic glass, the casting temperature is relatively high, and the heating and cooling times of the mold have a great influence on the manufacturing cycle time.

[0005] In fact, the mold needs to be heated to a temperature that ensures sufficient fluidity of the molded material to ensure uniform filling of the cavity, and then cooled to a sufficient solidification temperature of the used material so that it can be removed without damaging the parts thus manufactured. Depending on the molded material, these temperatures are determined, for example, in relation to the melting temperature and the solidification temperature of the material and / or corresponding to the glass transition temperature of the material or the crystallization (crystallization temperature / rate) of the material.

[0006] Generally, the mold is larger than the manufactured parts, and its mass is several orders of magnitude larger than the mass of the molded parts.

[0007] Therefore, the concept of rapid heating and rapid cooling is essentially applied to the mass of the mold.

[0008] Induction heating techniques combined with cooling by fluid circulation are disclosed, for example, in U.S. Patent No. 7,679,036 or U.S. Patent No. 10,232,530, and allow for the concentration of heating on the mold surface in contact with the molding material while ensuring a uniform heating temperature on these surfaces.

[0009] Therefore, by limiting the volume of material being heated and cooled, and by utilizing the high heating power enabled by induction heating, these conventional techniques allow for a reduction in heating and cooling cycle time. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 7679036 [Patent Document 2] U.S. Patent No. 10232530 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0011] However, when the size of the manufactured part is small, for example, a lens with a diameter of less than 10 mm, more commonly less than 2 mm, and when the part is also thin, for example, between 0.1 mm and 0.3 mm thick, and when the part must be manufactured with high precision to be optically compatible, prior art cannot be used, even when considering molds with multiple impressions.

[0012] Furthermore, even with the implementation of these conventional technologies, volume and mass under thermal cycling remain important factors regarding the quantity of parts manufactured. [Means for solving the problem]

[0013] The present invention aims to solve the shortcomings of the prior art, and for this purpose, provides a mold suitable for molding small parts, comprising a casing adapted to be mounted on a platen (mounting plate), the casing having a housing configured to accommodate (receive) an insert; the insert having a housing for a die, configured to be integrated with the casing, and having a molding surface for the part. The device for heating the mold (die) comprises a rod made of an induction-heatable material, the rod is mounted inside an insert, one end is in contact with the mold (die), and the molding surface is substantially at the center of the rod. A coil made of conductive material surrounds the rod and is connected to a high-frequency current generator. When current is supplied to the coil, an induced current is generated within the rod. This induced current heats the rod, which then transfers heat to the mold (die). The outer diameter of the rod (235) is the same as or larger than the outer diameter of the molding surface (225).

[0014] In other words, the mold of the present invention rapidly heats the molding surface to a high temperature using only a small amount of power, and by combining a rod and a coil, it becomes possible to concentrate the heating of the molding surface.

[0015] The present invention can be carried out according to the embodiments and modifications disclosed below, which are considered individually or in technically effective combinations.

[0016] Advantageously, the casing is configured to include a circuit for circulating heat transfer fluid to cool the insert and the mold (die).

[0017] As a result, forced cooling becomes possible, shortening the cycle time.

[0018] According to a particular embodiment, the insert includes a circuit for circulating a heat transfer fluid, which is connected to the fluid circulation circuit of the casing.

[0019] In addition to faster cooling of the mold (die) and shortening of the cycle time, this circuit also enables temperature control by simultaneously using induction heating and fluid circulation cooling for applications that require it.

[0020] According to a particular embodiment, the casing and the insert have separate cooling circuits. According to this embodiment, different heat transfer fluids can be circulated within the casing and within the insert, and said fluids can be adapted to the temperatures respectively reached during the molding operation.

[0021] According to one embodiment, the cooling circuit of the insert comprises a baffle (baffle, regulating plate, baffle plate). Such a baffle promotes turbulent flow of the cooling fluid within the conduit and convective (conduction) exchange using the walls.

[0022] Advantageously, the mold comprises a thermocouple housed inside the rod, and the hot junction is near the end of the rod.

[0023] The information obtained by the thermocouple makes it possible to control both heating and cooling in order to optimize the manufacturing cycle.

[0024] According to a preferred embodiment, the outer diameter of the perimeter defining the outside of the molding surface is less than 5 mm, preferably less than 2 mm.

[0025] According to an advantageous embodiment, the coil that generates the induction (current) is made of copper and comprises an annular part surrounding a second part of the rod and stems for connection to a high frequency alternating current power supply, and the sections of the stems and the annular part are 10 mm 2 are as follows. Thus, the reduction of the cross-section of the coil limits its electrical resistance and heating under the influence of the alternating current, and there is no need to implement a forced cooling device for the coil.

[0026] In a preferred embodiment, the die comprises a molding portion having a molding surface made of steel that is easily subjected to induction heating, and a technical portion made of a highly thermally diffusive material. This embodiment facilitates both rapid heating and rapid cooling.

[0027] Advantageously, the molding surface of the die is made of nickel. This embodiment is particularly suitable for molding optical components.

[0028] Therefore, this mold is advantageously used in plastic injection presses for mass production of small camera lenses.

[0029] This mold is particularly suitable for manufacturing lenses with a thickness between 0.1 mm and 0.3 mm. [Brief explanation of the drawing]

[0030] The present invention is implemented according to preferred embodiments, which are shown in Figures 1 to 5 below, but is not limited thereto:

[0031] [Figure 1] This is a schematic front view of an injection molding assembly with the mold according to the present invention mounted on it;

[0032] [Figure 2] This shows an exploded perspective view of an exemplary embodiment of a rod and die mounted in a mold according to the present invention;

[0033] [Figure 3] A partial front view showing a partial cross-section of some exemplary embodiments of the mold of the present invention.

[0034] [Figure 4]Figure 3 shows an exemplary embodiment of a duct equipped with baffles (adjustment plates, baffle plates) for circulating and cooling a heat transfer (exchange) fluid within an insert, with a section AA defined therein.

[0035] [Figure 5] This is a perspective view of an exemplary embodiment of a baffle (adjustment plate, baffle plate). [Modes for carrying out the invention]

[0036] According to the exemplary embodiment shown in Figure 1, the apparatus for mounting the mold of the present invention comprises a plastic injection press, and the two opposing parts (111, 112) of the mold are assembled on platens (101, 102).

[0037] One platen (mounting plate) (101) is movable toward and away from the other platen (mounting plate) (102). Thus, when the two parts of the mold (111, 112) are joined and held toward each other by the opening and closing means of the press, they form a plurality of sealed cavities into which liquid or paste-like molding material is injected.

[0038] The material conforms to the molding surface of the sealed cavity, and then the mold cools and the material solidifies.

[0039] Next, the mold is opened by separating the platens (mounting plates) of the press from each other, and the parts manufactured in this way are removed.

[0040] Therefore, according to this exemplary embodiment, the first part (111) of the mold comprises a die with a raised molding surface (121), and the opposing part (112) of the mold comprises a die with a recessed molding surface (122).

[0041] Once the mold is closed and the two parts (111, 112) are held together, the molding cavities are partitioned and fixed by the molding surfaces (121, 122) of these two parts.

[0042] The die, which has these molding surfaces (121, 122), is set in contact with rods (131, 132) that are held by each part of the mold.

[0043] The rods are made from ferromagnetic alloys, such as martensitic tooling steel, which are susceptible to induction heating.

[0044] According to one embodiment, the molded surface is made of nickel and polished to optical quality. The nickel is deposited on the molded surface by any plating or coating technique.

[0045] Each rod is surrounded by a coil (141, 142) made of a conductive material such as copper, to prevent mechanical contact.

[0046] The coils are connected to high-frequency current generators (151, 152), whose high frequencies typically range between 10 kHz and 200 kHz.

[0047] If the rod is made of a material with high magnetic permeability, when a high-frequency current is supplied to the coil, the current induced within the rod heats it up. The rod then conducts that heat to the mold (die).

[0048] As shown in the cross-sectional view in Figure 1, each mold part (101, 102) has a structure with two molds (dies) located at the ends of two rods, and each set of rods, molds (dies), and coils is identical in the same mold part (101, 102), but is not limited to this particular configuration.

[0049] In alternative embodiments, the die is integrated with the rod by machining the end of the rod, or the die is assembled to the end of the rod by mechanical assembly, welding or brazing, or the die is formed directly on the tip of the rod by additive manufacturing.

[0050] In this embodiment, thermocouples (161, 162) are attached to each rod, making it possible to measure the temperature of the rod ends closest to the molding surface.

[0051] Each molded part is equipped with conduits (171, 172) for circulating heat transfer fluid.

[0052] In one embodiment, the heat transfer fluid is water, and the conduit is connected to a pumping and cooling unit (175) that circulates the heat transfer fluid within molded conduits (171, 172) for cooling.

[0053] According to other exemplary embodiments, depending on the molding temperature, the mold, and the mass of the molded part, the heat transfer fluid is oil or gas, and the circulation of the fluid is carried out in a closed or open circuit.

[0054] The system of the present invention is advantageously equipped with a control bay (190) that controls, in particular, the opening and closing of a press, a high-frequency generator, power supply to a coil, and circulation of a heat transfer fluid, in accordance with measurements obtained from a thermocouple set on a rod.

[0055] Therefore, the system is controlled to provide reproducible injection and temperature cycles.

[0056] As shown in Figure 2, according to an exemplary embodiment, the rod (131, 132) essentially comprises three functional parts.

[0057] According to an exemplary embodiment, the first part (231) allows for its centering and placement in the mold.

[0058] Advantageously, the mold includes an insert, which is mounted within the casing. According to this embodiment, the rods (131, 132) are then mounted within the insert, and the first portion (231) allows the rods to be positioned within the insert.

[0059] According to this embodiment, the second portion (232), which is continuous with and integrated with the first portion (231), is substantially cylindrical and forms a region that is mainly subjected to electromagnetic induction.

[0060] For this purpose, the rod cylindrical The second part (232) is made of a material that is easily subjected to induction heating, preferably a material with high magnetic permeability such as ferromagnetic steel.

[0061] In another embodiment, the portion of the rod exposed to the induced magnetic field of the coil consists of a coating susceptible to induction heating. In a non-limiting example, the rod may be made of copper or a copper alloy, or more generally, a material with high thermal conductivity, and the region exposed to the magnetic field generated by the coil may be coated with a material such as nickel. The thickness of the coating is selected according to the penetration depth of the induced current.

[0062] Induction (current) is in the rod cylindrical It is generated by a coil (141, 142) comprising an annular part (241) surrounding a second part (232) and a stem (242) for connecting the coil to a high-frequency AC power supply.

[0063] As a non-limiting example, the high-frequency current source is a 25kW generator that produces alternating current with frequencies ranging from 35kHz to 70kHz. This type of generator can power up to four devices according to the present invention.

[0064] The stem (242) is in electrical contact with the annular part (241), and according to this embodiment, it is integral with the annular part, and this set is made of a conductive material such as copper.

[0065] Advantageously, the cross-section of the coil (245) limits the heating of the rod as the high-frequency AC generated by the generator flows through it, so 10mm 2 It is formed to be less than [a certain size].

[0066] In a favorable embodiment, the coil is insulated from the rod by an insulating ring (243) made of an electrically insulating material that allows a magnetic field to pass through and is resistant to the temperature generated in the second portion of the coil (141) of the rod.

[0067] The temperature here can reach 450°C, but the insulating ring, rod, and coil are exposed to such temperatures for only a very short time, well less than a second.

[0068] As a non-limiting example, the insulating ring (243) may be made of ceramic, or the ring may be made of a plastic material, whether reinforced or not, that can withstand such temperatures for a very short period of time.

[0069] The insulating ring (243) ensures that the coil is centered and held relative to the rod.

[0070] The third portion of the rod (233) is in contact with the die, more specifically with the molding portion (221) of the die.

[0071] According to an exemplary embodiment, the die comprises a molding section (221) having a molding surface for a manufactured part, and the molding section is a rod cylindrical The technical section (222) is integral with the second section (232) and is formed to be assembled and positioned in the center of the molding section (221).

[0072] According to the alternative embodiment, the molded part (221) is connected to the rod by mechanical assembly, welding, or brazing.

[0073] The molding surface of the die is the rod cylindrical It fits and is mounted within a circle (225) having a diameter smaller than the diameter (235) of the second part (232).

[0074] This configuration allows the rod to operate despite the reduced power consumption. cylindrical Local induction heating occurs in the second section (232), making it possible to heat the molded surface (221) quickly and uniformly.

[0075] This apparatus has an outer footprint diameter (225) of the molding surface that is less than 5 mm, preferably less than 2 mm, and is particularly suitable for manufacturing small parts with recesses or protrusions of similar size. Therefore, the mold of the present invention is particularly suitable for molding small optical lenses, such as those found in mobile phone cameras, webcams, miniature surveillance cameras, or miniature optical aiming devices, but is not limited thereto.

[0076] The die's technical section (222) specifically enables the realization of the cavity's dividing surface (product), provides a sealing function and a function for introducing material into the cavity, and promotes the cooling of the molding section (221) by diffusing heat to the cooling means of the mold.

[0077] According to an exemplary embodiment, the forming section (221) is made of tool steel that is susceptible to induction heating. Advantageously, the forming surface of the die is made of nickel and is polished.

[0078] Therefore, when high-frequency alternating current is supplied to the coils (141, 142), a certain degree of heating effect occurs on the mold (die). However, the coil configuration is such that its annular portion (annular part) (241) is on the rod cylindrical Since it surrounds the second part (232), most of the heating effect is on the rod. cylindricalThis means that the heat is concentrated in the second part, and this heat is then transferred to the mold (die) by conduction over a short distance.

[0079] According to this exemplary embodiment, the rod will have one or more housings (260) that extend along its entire length or in part to accommodate a thermocouple therein.

[0080] These thermocouples, advantageously, measure the temperature closest to the molded portion (221).

[0081] According to an exemplary embodiment, the technical section (222) is made of the same tool steel as the forming section, but according to other variations, it is made of a steel or other material that is less susceptible to induction heating and has a high thermal diffusivity, such as a copper alloy that can withstand the processing temperature of the forming material.

[0082] The thermal diffusivity of a material is defined by the ratio λ / ρc, where λ is the thermal conductivity of the material, ρ is the density of the material, and c is the specific heat capacity. In the present invention, a high thermal diffusivity is 50.10 -6 m 2 Greater than / s, preferably 100.10 -6 m 2 It is thought to be greater than / s.

[0083] In this final embodiment, the mold (die) can be cooled more rapidly after the injection of the material being molded.

[0084] According to an exemplary embodiment shown in Figure 3, the mold of the present invention comprises a casing (310) capable of receiving one or more inserts (350), each insert carrying (capable of holding) its own die and heating device, which can be connected to a high-frequency AC generator by appropriate connecting means (340).

[0085] Therefore, the insert holds a mold (die) consisting of a molding section (221) and an engineering section, a rod, and a heating means comprising a coil, means for connecting to a high-frequency generator, and a conduit for circulating a heat transfer fluid.

[0086] Therefore, the mold of the present invention is modular, and the molding section can be replaced simply by changing the rod, without having to rework the casing or insert.

[0087] Advantageously, the casing (310) includes a circuit for circulating heat transfer fluid to cool the casing, the insert, and the mold (die).

[0088] Therefore, according to one embodiment, one or more first circuits enable circulation between an inlet (371) and an outlet (372) in order to circulate the heat transfer fluid within the casing around the insert.

[0089] One or more other circuits include an inlet (375) and an outlet (376) for the circulation of heat transfer fluid passing through the casing (310) and the insert (350) as close as possible to the rod. According to this exemplary embodiment, the insert (350) includes an internal circuit for circulating the heat transfer fluid, which connects to the circuit of the casing when the insert is installed in the casing. For this purpose, the insert includes sealing means (not shown) adapted to secure this connection.

[0090] In other embodiments, the insert features its own cooling circuit that uses a different heat transfer fluid from that of the casing as needed.

[0091] Therefore, the casing is cooled, for example, by the circulation of water, and the insert and, if applicable, the rod are also cooled by the circulation of gas, such as air, argon, nitrogen, carbon dioxide, or helium, but are not limited to these examples.

[0092] Accordingly, according to the exemplary embodiment shown in Figure 4, the insert (350) and optionally the rod also include conduits (450) for the circulation of gas under pressurization to ensure gas cooling, and these conduits are advantageously equipped with baffles (adjusting plates, baffle plates) (445) or turbulators (agitators) to promote convective exchange.

[0093] Figure 5 shows exemplary embodiments of baffles (adjustment plates, baffle plates) consisting of straight lines (4451) or twists (4452), the baffles being made of steel, bronze, or polymer materials, but not limited to these examples.

[0094] The advantageous effects of these baffles (adjustment plates, baffle plates) are not limited to gas circulation; they can also promote convective exchange, and therefore, cooling is possible even in the case of heat transfer fluids consisting of liquids such as water or oil.

[0095] Localized induction heating of rods and fluid circulation circuits enables rapid heating and cooling cycles suitable for mass production.

[0096] As a non-limiting example of a typical molding cycle for a mobile phone camera lens, heating the molding surface to a temperature of 260°C begins at a temperature of 130°C, which corresponds to the temperature of the mold (die) after the preceding part has been removed, and is performed in less than 5 seconds, more commonly less than 2 seconds, with an induction power of less than 5KW. Cooling from this temperature to the part removal temperature of less than 190°C is achieved in 10 seconds using a 5mm diameter conduit and a water flow rate of 2.5 liters per minute per cooling circuit, allowing the cycle between two removals to be completed in less than 1 minute.

[0097] The above description and exemplary embodiments demonstrate that the present invention achieves its intended purpose, and in particular, the mold of the present invention enables rapid heating and cooling of the imprint and the components contained therein with low power, making it particularly suitable for the manufacture of thin and small-dimensional components such as optical lenses.

Claims

1. A mold having a configuration suitable for molding small parts, comprising a casing (310) adapted to be mounted on platens (mounting plates) (101, 102), and a housing configured such that the casing accommodates (receives) an insert (350); The insert (350) is configured to be integrated with the casing (310) and includes a housing for a die with molding surfaces (121, 122) having an outer diameter for forming a part. The device for heating the mold (die) is The heating device comprises a rod (131, 132) made of a material easily subjected to induction heating, the rod consisting of a first part and a cylindrical second part, and mounted within an insert (350), the die being integrated at the end of the cylindrical second part, and the molding surface (121, 122) being substantially at the center of the cylindrical second part. The coils (141, 142) made of conductive material surrounding the cylindrical second part are connected to high-frequency current generators (151, 152). When current is supplied to the coils, an induced current is generated within the cylindrical second part, which heats the cylindrical second part, and the cylindrical second part transfers heat to the mold (die). The outer diameter (235) of the cylindrical second portion, surrounded by the coil, is larger than the outer diameter (225) of the molded surface (121, 122). A mold characterized by the following features.

2. The mold according to claim 1, characterized in that the casing (310) comprises at least one circuit (171, 172) for circulating a heat transfer fluid for cooling the insert (350) and the mold (die).

3. The mold according to claim 2, characterized in that the casing (310) and the insert (350) have separate cooling circuits.

4. The mold according to claim 1, characterized in that the cooling circuit of the insert comprises a conduit (440) that is compatible with the circulation of a heat transfer fluid.

5. The conduit (440) for circulating the heat transfer fluid within the insert is a baffle (adjustment plate, baffle plate) (445, 445 １ , 445 ２ The mold according to claim 4, characterized by comprising ).

6. The mold according to claim 1, comprising thermocouples (161, 162) housed inside rods (131, 132), wherein the thermal junctions are located at the ends of the cylindrical second portion.

7. The mold according to claim 1, characterized in that the outer diameter of the circumference (225) is less than 5 mm, preferably less than 2 mm.

8. The coil (141, 142) is made of copper and comprises an annular part (241) surrounding a cylindrical second portion and a stem (242) for connecting to a high-frequency AC power supply, with the cross-section (245) of the stem and annular part being 10 mm ２ The mold according to claim 7, characterized by comprising the following:

9. The mold according to claim 1, characterized in that the die is made of steel that is easily subjected to induction heating and comprises a forming section (221) having forming surfaces (121, 122) and a technical section (222) made of a material with high thermal diffusivity.

10. The mold according to claim 9, characterized in that the molding surfaces (121, 122) of the molding section of the die are made of nickel.

11. The mold according to claim 10, characterized in that it is used in a plastic injection press for mass production of small camera lenses.

12. The mold according to claim 11, characterized in that the thickness of the lens is between 0.1 mm and 0.3 mm.

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