WO2005051627A1

WO2005051627A1 - Method of producing rapid moulds which are used for plastics processing, and mould thus obtained

Info

Publication number: WO2005051627A1
Application number: PCT/ES2004/000509
Authority: WO
Inventors: Ibon Mitxelena Fernandez
Original assignee: Moldkar Teknolayer, S.L.
Priority date: 2003-11-28
Filing date: 2004-11-16
Publication date: 2005-06-09
Also published as: ES2233210B1; ES2233210A1

Abstract

The invention relates to a method of producing rapid moulds. The inventive method combines rapid prototyping techniques and precision plaster mould casting and makes use of aluminium or an aluminium matrix composite-type material having a low thermal expansion coefficient which provides greater dimensional precision during the production of the mould (9). The invention also imparts good abrasion resistance, thereby increasing the service life of the mould. According to the invention, the mould (9) is produced from a prototype (2) which is made from an inflammable material that is heated in a furnace using a thermal cycle which bakes the prototype and defines a hollow into which the aluminium or the aluminium matrix composite-type material is poured until the mould is obtained (9).

Description

PROCEDURE FOR THE MANUFACTURE OF QUICK MOLDS USED FOR TRANSFORMATION OF PLASTIC AND MOLD AS OBTAINED D E S C R I P C I O N

OBJECT OF THE INVENTION

The present invention relates to a method of manufacturing fast molds of the type that are used for obtaining pieces of plastic material, as well as the mold itself obtained by this process.

The object of the invention is the method used to manufacture the so-called fast molds by combining rapid prototyping techniques, precision casting in plaster mold, and using aluminum or a composite material of aluminum matrix having a low expansion coefficient. thermal that entails greater dimensional accuracy during obtaining the mold, and which also shows great resistance to abrasion that increases the service life of the mold.

It is also the object of the invention the mold obtained in aluminum or in composite material of aluminum matrix.

BACKGROUND OF THE INVENTION

Different technologies are used to manufacture molds used to obtain and / or transform plastic, among which the processes of direct competition technology and the processes of indirect competition technology are worth mentioning. The processes of direct competition use rapid prototyping and high-speed machining techniques of aluminum that give rise to an estimated manufacturing time of a mold less than three weeks, and have an estimated life defined by the manufacture normally of no more than 30,000 plastic pieces.

Among the processes based on rapid prototyping technology, a distinction can be made between the processes that give rise to rapid metal molds and the processes that give rise to rapid plastic molds.

In the case of fast metal molds there are limitations in terms of mold size and surface finish derived from the characteristics of the machine and the material. As for the fast plastic molds, they show some limitations of use because they can only be used for the transformation of small series of plastic parts.

Indirect competition processes use electro-erosion and conventional machining techniques to obtain molds, which are used for long series production, due to their laborious manufacturing process and high cost.

DESCRIPTION OF THE INVENTION

The manufacturing process of rapid molds used for the transformation of plastic parts that is the object of the present invention, is mainly based on the manufacture of the prints of the rapid mold by combining a rapid prototyping technology with the technique Precision casting in plaster mold

(or also called plaster casting) of an aluminum or a material of Aluminum reinforced with silicon carbide particles called aluminum matrix composite that has a low coefficient of expansion that ensures high dimensional accuracy, and shows great abrasion resistance. In this way, the service life of the mold is increased.

First, the mold design is carried out, using 3D CAD computer design techniques, and the cavities of the plastic transformation mold are defined according to the geometry of the plastic part to be obtained.

The 3D CAD data of the mold cavities are then transformed into a tessellated file and transferred to the rapid prototyping machine where the file is sectioned in parallel horizontal planes. In this way the rapid prototyping machine has all the necessary instructions to physically reproduce the mold cavities in a burnable material.

Next, a plaster casting or plaster cast iron casting process is used, which consists of adding to each prototype, its feed and filling system obtained in burnable material, also manufactured in burnable material, such as wax, and introducing all of it. inside a metal cylinder in which plaster is poured until coated, leaving the filling cup out of the plaster to allow the waxing or evacuation of the wax.

The set thus defined is introduced into a furnace in which a thermal cycle of heating and stabilization is followed at different temperatures that lead to the setting of the plaster, drying of the plaster, dewatering and subsequent burning of the burnable material. When the burnable material is calcined and evacuated, a cavity with the prototype geometry is defined. The plaster mold is then removed from the oven and the aluminum or aluminum matrix composite is poured between 600-730 ° C through the feed channels into this cavity. To improve the quality of aluminum, a cooling system is used that enables rapid and direct solidification of the aluminum towards the filling cup.

Once the aluminum or aluminum matrix composite has solidified, the piece obtained from which the feed channels are cut is demoulded. The aluminum or aluminum matrix composite mold is thus defined.

Next, the cavity will be placed in a mold holder, adding the accessory elements to perform the injection, whether injection nozzles, ejectors, guides and other conventional elements used to obtain plastic parts.

The mold obtained by casting in aluminum or aluminum matrix composite will be of the hollow type, it will have the cavity (outer face) that reproduces the shape of the plastic piece to be obtained and the opposite part (inner face) to the cavity will be emptied and will incorporate inner ribs to provide stiffness.

The thickness of the walls that define the mold will be increasing towards its inner face in the direction of its cavity (from the outside to the inside), just as the thickness of the defined ribs will be equally progressively increasing towards the inner face of the mold.

The mold obtained by casting will incorporate: defined anchor points on its inner face on which the clamping plate that closes the mold will fit, holes that serve as a guide for the ejectors, a hole for the introduction of the injection nozzle, some winds consisting of through holes used to evacuate the air trapped in the mold and cooling channels consisting of hollow turns for entry and exit of the liquid / gas refrigerant. The diameter of each of them will vary depending on the geometry of the piece.

These same elements will have been previously defined in the prototype, also taking into account that said prototype will have been oversized with respect to the aluminum or composite mold with matrix <of aluminum as a result of the contraction that occurs during the solidification and cooling of the latter , considering a contraction factor of between 0.50% and 1.50%.

On the other hand, another correction factor of plastic injection contraction must be taken into account, which will vary depending on the type of plastic and must be applied to adequately oversize the prototype.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, it has been represented:

Figure 1.- Shows a sequential representation of the different phases of the manufacturing process of the rapid mold used for the transformation of plastic.

Figure 2.- Shows a perspective view of the injection side of the aluminum matrix composite mold obtained by the process object of this invention and where its inner face is shown.

Figure 3.- Perspective sample of the injection side of the aluminum matrix composite mold obtained by the process object of the invention and where its outer face is shown.

Figure 4.- Shows a perspective view of the ejection side of the aluminum matrix composite mold obtained by the process object of the invention and where its outer face is shown.

PREFERRED EMBODIMENT OF THE INVENTION

In view of the figures, the manufacturing process of a rapid mold used for the transformation of plastic is described below, of the type that uses a prototyping machine (1) for reproduction (III) in a prototype (2) of burnable material, preferably wax, to the design (I) corresponding to the mold (10) that has been preferably made with the aid of a computer (3). The computer also performs the transformation (II) of the design commands into orders to be executed by the prototyping machine (1).

By means of the prototyping machine, a prototype (2) is obtained in burnable material, to which the feeding system (4) is added (IV). Then, the connection (V) of the cup of the feeding system (4) to a metal or wooden sheet (5) is carried out by means of glue wax, continuing with the coupling (VI) of a cylinder (6) ) hollow and perforated steel that rests on the sheet (5) surrounding without touching the prototype (2), and then sealing (Vil) of the cylinder holes (6).

Next, the empty plaster (VIII) is poured and under vibration for 1 to 10 minutes until the prototype is covered with a minimum thickness of security between the prototype and the surface of the plaster mold from 1 to 5.5 cm, the plaster having been previously obtained from the powder mixture of CaSO ₄ and water, in a vacuum and by stirring and under vibration for 1 to 10 minutes.

It is then allowed to stand so that hydration (IX) of the plaster occurs between 60 and 240 minutes. The heating (X) is then carried out in the oven with the filling cup facing down, after previously removing the sheet (5), according to a thermal cycle that burns the prototype (2), burns it and dehydrates the plaster, being defined a cavity (7) of configuration coinciding with that of the prototype (2). The thermal cycle runs according to the following temperatures and times:

(i) Maintain Ti = 100-200C for 1 to 6 hours, (ii) rise from T ^ to T ₂ = 500-750 ° Cen 2 to 14 hours., (iii) maintain T ₂ for 5 to 48 hours, (iv) lower from T ₂ to T ₃ = 150-400 ° C in 2 to 10 hours (v) maintain T ₃ for 1 to 5 hours

Subsequently, the casting (XI) of aluminum or an aluminum matrix composite material into the cavity (7) is carried out, after having previously removed the plaster mold (8) from the oven and placing it on a plate, pouring the material at a temperature of 600 to 730 ° C at the same time that the vacuum is performed below said plate.

Once the mold has been filled with the aluminum or the aluminum matrix composite, the cooling system (8), inserted inside the plaster mold, is connected and allows Get a better metallurgical quality.

Finally we proceed to the demoulding (XII) of the piece of aluminum or composite material of aluminum matrix once the plaster mold has solidified and cooled, cutting the feed channel and obtaining the mold (9) of aluminum or matrix composite material of aluminum.

The mold (9) of aluminum or aluminum matrix composite material obtained according to the described procedure is hollow, it will have the cavity (10) that reproduces the shape of the plastic piece to be obtained and will incorporate interior ribs ( 11) to provide stiffness, provided that the thickness of the walls that define the mold are between 1 and 15 mm, as well as the thickness of the inner ribs (12) will be between 4 and 7mm and this will progressively increase inwards ( 13) of the mold.

Likewise, the mold will incorporate anchor points (13) defined on its inner face (12) on which the clamping plate that closes the mold will be coupled, holes (15) to introduce the ejectors, a central hole (14) for the introduction of the injection nozzle, bolts (16) for guiding the mold in the injection part, holes (17) for guiding the mold in the ejection part, winds for evacuating the air trapped in the mold and some refrigeration channels consisting of hollow turns for refrigerant inlet and outlet.

Claims

1.- Manufacturing process of a rapid mold used for the transformation of plastic, of the type that uses a prototyping machine (1) to obtain a prototype (2), of burnable material, preferably wax, corresponding to the design (I) of the mold (9) made with the help of a computer (3), and that also transforms (II) the design commands into orders to be executed by the prototyping machine (1), provided that the prototype obtained is Add your feeding system (4), also in burnable material, essentially characterized in that it proceeds according to the following stages:

- Connection (V) of the feeding system cup (4) to a metal or wooden sheet (5) by means of glue wax, - coupling (VI) of a hollow and perforated cylinder (6) of steel that supports on the sheet (5) surrounding without touching the prototype (2), - sealing (Vil) of the cylinder holes (6), - pouring (VIII) of the gypsum in vacuum and under vibration for 1 to 10 minutes until covering the prototype with a minimum thickness of security between the prototype and the surface of the plaster cast of 1 to 5.5 cm, - hydration (IX) of the plaster for 60 to 240 minutes, - heating (X) in the oven with the filling cup oriented downwards after previously removing the sheet (5), according to a thermal cycle that burns the prototype (2), calcines it, and dehydrates the plaster, being defined a cavity (7) of configuration coinciding with that of the prototype (2 ), the thermal cycle proceeding according to the following temperatures and times:

(vi) Maintain T-ι = 100-200 ° C for 1 to 6 hours, (vii) rise from Ti to T ₂ = 500-750 ° Cen 2 to 14 hours., (viii) maintain T ₂ for 5 a 48 hours, (ix) lower from T ₂ to T ₃ = 150-400 ° C in 2 to 10 hours (x) keep T ₃ for 1 to 5 hours

- casting (XI) of aluminum or an aluminum matrix composite material in the cavity (7), after having previously removed the plaster mold from the oven and placing it on a plate, pouring the material at a temperature between 600 and 730 ° C at the same time that the vacuum is made below said plate, - placement of the cooling system (8), inserted into the plaster mold, - demoulding (XII) of the aluminum part or of the aluminum matrix composite material Once the plaster mold has solidified and cooled, cutting the feed channel and obtaining the aluminum mold (9) or the aluminum matrix composite material.

2. Manufacturing process of a mold quickly used for plastic processing according to claim 1, wherein the cooling system (8) of the casting process is placed on the inner face (12) of the mold and comprises a tube copper diameter between 2 and 4 mm and that runs through the entire inner part (12) of the mold, the two ends of the tube and the inlet and outlet of the cooling air that once traveled inside the mold will be out of the plaster mold, cooling being carried out by introducing liquid or refrigerant gas through the inlet.

3.- Manufacturing process of a rapid mold used for the transformation of plastic according to claim 1 characterized in that the plaster that is poured into the prototype is obtained from the mixture of CaSO ₄ powders and water in vacuum and by agitation and low vibration for 1 to 10 minutes.

4.- Manufacturing process of a rapid mold used for the transformation of plastic according to claim 1 characterized in that the prototype (2) from which it is obtained is oversized with respect to the mold (9) of aluminum or metal matrix composite between 0, 5% and 1.5%.

5. Cast aluminum or composite aluminum matrix obtained according to the procedure described in claim 1, characterized in that a hollow mold which has a cavity (10) reproducing the shape of the plastic part to obtain and incorporate inner ribs (11) to provide stiffness, provided that the thickness of the walls defining the mold are between 1 and 15 mm, as well as the thickness of the inner ribs (11) will be between 4 and 7mm and this will progressively increase towards the inside (12) of the mold, with the mold (9) being provided to incorporate anchor points (13) defined in its inner face (12) on which the clamping plate that closes the mold will be attached, about holes (15) for inserting the ejectors, a central hole (14) for the introduction of the injection nozzle, some bolts (16) for guiding the mold in the injection part, some holes (17) for guiding the mold in l In addition to ejection, winds to evacuate the air trapped in the mold and cooling channels consisting of hollow turns for entering and leaving the refrigerant.