Mold for hot forming of sheet materials

Abstract

A mold for hot forming of materials in the form of a sheet is disclosed having a first half-shell bearing a die and a second half-shell, between which a chamber for forming the plate is provided. The second half-shell is provided with channels and respective holes for feeding a pressurized gas into the chamber. Inside the die there is at least one ventilated chamber, equipped with heating assemblies and ventilation assemblies for the circulation of hot air inside a ventilated chamber.

Claims

1. A mold for a hot forming of a sheet of material, the mold comprising a first half-shell bearing a die, a second half-shell, and a chamber formed between said first half-shell and said second half-shell for forming of said sheet, the second half-shell being provided with channels and respective holes for feeding a pressurized gas into said chamber, wherein inside said die at least one ventilated chamber is provided, and said at least one ventilated chamber is equipped with heating assemblies and ventilation assemblies for circulation of hot air inside said at least one ventilated chamber.

2. The mold according to claim 1, wherein said heating assemblies include electric resistors mounted from outside of the mold and passing through to said at least one ventilated chamber.

3. The mold according to claim 2, further comprising a pocket adapted to receive said electrical resistors.

4. The mold according to claim 2, further comprising additional heaters, on ends of said mold, to further improve temperature uniformity of the mold.

5. The mold-according to claim 1, wherein said ventilation fan assemblies and said heating assemblies are arranged so that said circulation of hot air is a convective circulation.

6. The mold according to claim 1, wherein said-air circulation of hot air touches an internal surface of said die.

7. The mold according to claim 1, wherein said second half-shell is provided with at least one chamber, said at least one chamber of said second half-shell being equipped with respective heating assemblies and ventilation assemblies for said circulation of hot air inside said at least one chamber of said second half-shell.

8. The mold according to claim 1, further comprising additional infrared heating assemblies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and advantages result from the following description of some preferred embodiments of the mold of the invention illustrated by way of non-limiting example in the figures of the attached drawing tables.

(2) In these:

(3) FIG. 1 is a sectional view of a first embodiment of the mold of the invention in the open position;

(4) FIG. 2 illustrates the mold of FIG. 1 in the closed position;

(5) FIG. 3 is a sectional view of a variant of the mold of the invention in the open position; and

(6) FIG. 4 illustrates the mold of FIG. 3 in the closed position.

DETAILED DESCRIPTION OF THE INVENTION

(7) With particular reference to the numerical symbols of the aforementioned figures, the mold of the invention, indicated as a whole with the reference number 1, comprises a first half-shell 2 equipped with the die 5 of the mold, and a second half-shell 3, which identifies a sealing ring 9 suitable for forming a forming chamber 4 (FIG. 2), by cooperation with the first half-shell 2 of the mold in the closed position. Advantageously, the external walls of the half-shell 2 and of the half-shell 3 are thermally insulated, so as to avoid heat being dispersed.

(8) In turn, inside the die 5, made of metal material such as steel or cast iron and bearing the templates or shapes 13 to be impressed on the sheet 11 to be molded, one or more ventilated chambers 6 are provided, arranged on its side opposite the second half-shell 3. Arranged inside these ventilated chambers 6 are heating assemblies 7, preferably electric resistors, and also fan assemblies 8 suitable for heating by convection the air present in the chambers 6.

(9) Advantageously, the electric resistor assembly 7 of one or more ventilated chambers 6 is mounted from the outside of the half-shell 2 and passes through to the aforementioned ventilated chambers 6.

(10) Arranged above the shapes 13 of the die 5 is the sheet 11 to be molded, which is made of metallic material such as for example aluminum, magnesium and their alloys, or of plastic material and the like. The sheet 11 is deformed under heat against the same shapes 13 due to the combined action of heating of the die 5, by means of the resistor assemblies 7 and the fan assemblies 8, and of the pressure generated on the surface of the sheet 11 opposite the die 5 by a pressurized gas, such as for example nitrogen or argon, fed into the forming chamber 4 of the mold 1 through channels 14 which run through the half-shell 3 to corresponding discharge holes 12.

(11) According to the present invention, the fan assembly 8 and the resistor assembly 7, arranged in the underlying part of the die 5, create a convective air flow, capable of heating the surface of the shapes 13 of the same die 5 which receive the corresponding deformation of the sheet 11. In fact, the air circulating in the chambers 6 touches the surface of the die 5 below the shapes 13, thus achieving a homogeneous and controlled heating of the entire useful surface of the die which receives the sheet 11.

(12) This heating technique allows the amount of work required to introduce the heaters into the mold to be reduced, also allowing a quick and in process maintenance, by removing the resistor 7 coupled to the fan assembly 8 of the heated compartment 6 and replacing it with a new one, thanks to the application by means of a corresponding pocket 10 passing laterally through the half-shell 2 and the same die 5 of the mold 1.

(13) Homogeneity of the temperature on the useful surface of the mold is useful for solving the production problem, especially during the mold's start-up phase.

(14) With the present invention, the possibility of heating or preheating the mold off-line is maintained, as the heating system is linked to the single mold.

(15) According to a further aspect of the invention, additional heaters are provided, for example flat heaters, such as strip heaters, on the ends of the mold, to further improve uniformity of the temperature of the mold itself.

(16) For this purpose, the addition is envisaged of local heating modes, by means of cartridge heaters or by combining a heating system, of the heated platens type, with the present invention.

(17) According to a further aspect of the invention, the heater assembly can be made by means of infrared heaters and/or hybrid systems combined with cartridges, oven press, etc.

(18) In the embodiment described above, the mold of the invention has two half-shells 2,3 which between them define a forming chamber 4. However, without departing from the scope of the invention, the part called die, that is the part that contains the shape of the piece to be molded, is not necessarily the lower one. In this type of processing, the influence of gravity is in fact negligible, or in any case not very significant, so that the die can also be provided in the upper half-shell.

(19) According to the variant illustrated in FIGS. 3 and 4, the mold of the invention, indicated as a whole with the reference number 15, has its second half-shell 3 also provided with at least one chamber 16, heated and ventilated with the same principle as the embodiment shown in FIGS. 1 and 2.

(20) This embodiment offers the advantage, not so much of uniformity of temperature, since the sheet 11 is not directly in contact, but rather of providing heat by radiation from the surface of the half-shell 3, which does not contain the die, towards the sheet 11 itself.

(21) It has been seen in practice that this invention accomplishes the intended aim and objects.

(22) In fact, a structure has been provided which clearly differs from the devices of the prior art, which heat the mold by convection.

(23) Although heating by forced convection with hot air is mentioned in U.S. Pat. No. 6,835,254B2, in this document the heating mode is dedicated to the sheet and not to the mold, as in the device object of the present invention, and not aimed at ensuring uniformity of temperature all through the process.

(24) According to what is described in U.S. Pat. No. 6,835,254B2, the type of heating is a preheating of the sheet only, in order to control its superplastic properties, and takes place before forming in the mold, which must be heated in any case, with all the problems described above.

(25) One of the advantages of the present invention, with respect to all of the prior art mentioned above, is constituted by the improved maintainability of the molds for hot forming.

(26) Naturally the materials used, as well as the dimensions, can be any according to the needs.