The present invention relates to an improvement in methods and tools for the injection moulding of ar¬ ticles which include at least one hollow or cavity which is formed by injection moulding at least one removable core, for instance from a readily melted or liquid-dissolvable material, and by injecting a differ- ent material, product material, around or adjacent the core, this last mentioned material being the material from which the finished article is comprised.

In known methods of this kind, there is first moulded in an injection moulding machine from readily removable material a core whose shape corresponds to the shape of the hollow or cavity to be formed in said article, this injection moulding machine being intended to work solely with core material. The resultant core is then transferred to an injection moulding machine which works with the material from which the desired article is to be produced, and is placed in a mould tool of appropriate configuration for moulding the article con¬ cerned. There is formed between the core and the wall of the mould cavity of the tool, a cavity which cor¬ responds to the outer shape of the desired article.

The product material from which the article is formed is injected into the cavity and when the material has set, the core and said article are removed from the tool in the form of a composite unit. This unit is then heated, preferably in liquid, to a temperature which exceeds the melting point of the core material but which is beneath the melting point of the material from

which the article is formed. When the composite is heated, the core material floats-off leaving a hollow of desired shape in the finished article. When the core material is a liquid-soluble material, the core is dissolved in a liquid bath.

Thus, the known methods require the use of two in¬ jection moulding machines, each of which operates with a respective material and a respective mould tool. The methods also require the core to be transported from the core moulding machine and placed in the tool of the article moulding machine. This method is both time consuming and expensive.

The object of the present invention is to avoid these drawbacks and to provide a quick and inexpensive method which will enable articles of still more complicated configuration and incorporating several hollows or cavities to be produced in a simple fashion, and also to provide a mould tool by means of which the method can be carried into effect.

This object is achieved in accordance with the present invention by configuring one single injection moulding tool with mould cavities for injection moulding both core material and product material, and by injection- moulding core material and product material alterna¬ tively in one or more successive steps, each step comprising two part stages in which core material is injected into one mould cavity in one part stage of the method, said one mould cavity either being empty so as to produce a core which corresponds to the shape of the mould cavity, or being partially filled with a product article or a composite unit comprising core material

and product material, so as to coat the unit with an external layer of core material corresponding to the shape of the empty part of the mould cavity, and by injecting in said second part stage product material into a mould cavity which is either empty, so as to produce a product article from product material in the shape of said mould cavity, or is partially filled with a core or a unit comprising core material and product material, such as to coat the unit externally with a layer of product material corresponding to the shape of the empty part of the mould cavity.

In accordance with a second method, in one part stage of the method core material is injected into an empty cavity to produce a core in the shape of the mould cavity, whereafter in the second part stage product material is injected into a mould cavity which is partly filled by the core, such as to coat said core, either completely or partially, with a layer of pro- duct material, corresponding to the shape of the un¬ filled part of the mould cavity.

In a third method, in said one part-stage core material is injected into a mould cavity which is partly filled by composite unit comprising an inner part in the form of a core and an outer layer of product material which embraces said core either completely or partially, such as to produce around said unit a layer of core material which corresponds to the shape of the unfilled part of the cavity, and by subsequently injecting in said second part-stage product material into a larger mould cavity which is partly filled by said unit, so as to produce around said unit, either totally or partially, a layer of product material which corresponds to the

shape of the unfilled part of the mould cavity.

In a fourth method, the product material is injected into a first mould cavity to produce a product article, whereafter core material is injected into a second, larger mould cavity such as to surround the product article either completely or partially, whereafter product material is injected into a third, still larger mould cavity so as to surround, either totally or partially, the composite produced in the preceding stages.

In a fifth method, the part stages are carried out cyclicly in the mould cavities of the injection-mould- ing tool, with alternate injection-moulding of core material and product material.

The inventive tool by means of which the method can be put into effect includes a tool body and at least two tool-parts which are movable in relation to said body and the mould cavities of which parts form in a first position the mould cavity in which a hollow-forming core is moulded, said mould cavity being provided with recesses which form core-anchorages. The tool body is configured to hold the hollow-forming core to the anchorages subsequent to moulding said core, while the tool-parts are intended to adopt another position in relation to one another and to said core, so that the mould cavity will have a larger volume and correspond . to an outer shape of the article to be moulded; and in that the tool is provided with ejector means operative to eject from the tool the composite unit composed of core and product material.

In accordance with a second tool-embodiment, the tool is constructed so that injection moulding can be effected in further positions of the tool-parts, wherein moulding is effective alternatively with core material and product material.

In accordance with a third tool-embodiment, the tool includes a pair of movable tool-parts, which can be moved apart so as to successively increase the volume of the mould cavity.

In accordance with a fourth tool-embodiment, the tool includes two pairs of movable tool-parts, of which the first pair includes a mould cavity for core material and the other pair includes a larger mould cavity for accommodating the core and for injection moulding product material around said core, either completely or partially, subsequent to moving the core from the first to the second mould cavity with the aid of a rotatable tool body which engages anchorages formed on the core.

In accordance with a fifth tool-embodiment, the tool includes three pairs of movable tool-parts which include successively larger mould cavities intended to accommodate a composite of core and/or product material moved from a preceding mould cavity.

In accordance with a sixth tool-embodiment, the tool includes four pairs of movable tool-parts which present successively larger mould cavities intended to accom¬ modate a composite of core and/or product material moved from a preceding mould cavity.

The invention will now be described in more detail with

reference to exemplifying embodiments thereof illustra¬ ted in the accompanying drawings, in which Figure 1 is a sectional view of an injection moulding tool and shows the tool in a core-moulding position; Figure 2 is a sectional view similar to Figure 1 but shows the core in an article-moulding position; Figure 3 illustrates another embodiment of the inven¬ tive tool having two fixed mould cavities, seen in the direction of the arrow III in Figure 4; Figure 4 illustrates the tool in Figure 3 from one side and in an open position;

Figure 5 illustrates a tool which has three fixed mould cavities; Figure 6 illustrates a double-tool having two pairs of fixed mould cavities;

Figure 7 illustrates a tool provided with four mould cavities for alternate injection of core material and product material; and Figure 8 illustrates a method which is commenced by injection moulding an article-part.

The reference numeral 1 in Figure 1 identifies gene¬ rally an injection moulding tool which comprises a fixed tool-body 2 and two tool-parts 3 and 4 which can be moved towards and away from one another in said tool body, as illustrated by respective arrows 5 and 6. The tool-parts 3 and 4 function to define a mould cavity, generally referenced 7, which comprises cavity-parts 8 and 9 formed in the tool-body 2 and mutually opposing cavity-parts 10 and 11 formed in the tool-parts 3 and

4. The reference 12 identifies a gate by means of which core material is injected into the mould cavity 7 from an injection unit 13. Injection of core material into the mould cavity 7 results in the formation of a core

In Figure 2, the tool is shown in a position in which the two movable tool-parts 3 and 4 have been moved apart in the directions of arrows 5 and 6 through a distance 14 such as to form a cavity or void between the core 7' and the wall surfaces defining the cavity- parts 10 and 11. The core 7' is held in place within this enlargement of the mould cavity, created by moving the tool-parts 3, 4 away from one another, by means of the core-parts formed in the cavity-parts 8 and 9 provided in the tool body 2. As shown, product material which is intended to form an article or product 15 has been injected into the mould cavity through a gate (not shown), such as to surround the core T .

The composite unit 7', 15 consisting of core and pro¬ duct material has been obtained in one and the same tool and in one and the same injection moulding machine. In accordance with the invention, this machine is equipped with two injection units, i.e. one unit for core material and one unit for product material. Thus, time and transport-costs have been saved, by using a mould tool which has a mould cavity whose volume can be enlarged in one step. When the core 7' is removed from the composite, there is obtained a moulded article 15 which includes a commensurate hollow.

Figure 3 illustrates a tool embodiment which includes two inserts 16 and 17 mounted on a tool body 18, which can be rotated or swung through 180°, in the direction of double-arrow 19. A core 20 is formed in the inserts for the purpose of producing the hollow in a 90° tube- bend 23. The core is configured with two anchoring

beads 21 and 22 on the ends of said core. When the tool and its inserts 16 and 17 are opened, as described in more detail below with reference to Figure 4, the core will be held firmly by the anchoring beads 21, 22 while being moved to the tool insert 17. The tool is then closed. The mould cavity of the tool insert 17 has a larger volume than the cavity of the insert 16 and has the configuration of the outer shape of the tube bend 23. Injection of product material through a gate 24 results in the formation of the tube-bend 23, which forms a composite unit together with the core 20. When the tool is again opened, the composite unit is ejected from the mould, at the same time as the tool-body 18 is rotated through 180° and a further core, held by its anchoring beads 21, 22, is moved from the tool-insert 16 to the tool-insert 17.

Figure 4 shows the tool of Figure 3 in an open posi¬ tion. Those parts of the Figure 4 illustration which are also shown in Figure 3 are identified in Figure 4 by the same reference numerals. In the Figure 4 illustration, the reference numeral 25 identifies a center part which can be rotated in the direction of arrow 19 and displaced in the direction of the arrow 26. The center part is fixedly connected to the rotate- able body 18 of the tool, which can thus also be dis¬ placed in said direction 26 and rotated in said direc¬ tion 19, together with the center part 24. The Figure shows the pipe-bend 23 and the core 20, said core being supported in the tool body 18 by the anchoring parts or beads 21, 22 on said core.

Figure 5 illustrates a tool embodiment which includes three tool inserts 27, 28 and 29, which are mounted on

a rotatable body 30 and which are spaced apart at an angle of 120°. The tool insert 27 corresponds fully with the tool insert 16 of the Figure 3 embodiment. When the tool is opened, the body 30 is rotated through an angle of 120°, therewith moving the core 20 to the tool insert 28. This tool insert has no gate, but merely functions as a core-cooling station. Cooling of the core can be advantageous in the case of certain combinations of core material and product material, in order to obtain a more rapid production cycle.

Figure 6 illustrates a tool embodiment comprising two pairs of tool-inserts 31, 31' and 32, 32', respective¬ ly. When core material is injected into the tool, two cores are obtained simultaneously, one in each of the respective inserts 31 and 31'. The tool is opened and the tool-body 33 carrying the tool-inserts is rotated through 90 ^β , such as to bring the two cores simultan¬ eously into respective tool-inserts 32 and 32', in a manner similar to that described with reference to

Figure 3 and 4. Product material is then injected into said inserts, so as to produce a composite unit 20, 23, in the afore-described manner. This method results in a very rapid production cycle.

Figure 7 illustrates a method of injection-moulding an article which incorporates complicated hollows, by injecting core material and product material alterna¬ tively, and in sequence, into different, successive mould cavities having successively increasing volumes. The same core material is used in both injection pro¬ cesses in the method illustrated in the Figure. This also applies to the product material. The use of one and the same core material and product material is not

necessary, however, since up to four mutually different materials can be used in each mould-injection opera¬ tion.

Injection moulding in one part-stage of the first moulding step is effected with core material in the tool part 35, in which a curved core 36 having a pro¬ jection 37 is produced. The tool is opened and the core, held firmly by its anchoring parts, is moved to the tool-part 39, by rotation through 90° in the direc¬ tion of the arrow 38. The tool-part 39 has a larger mould cavity than said tool-part 35, and product ma¬ terial is injected through the gate 24 in the second part-stage of said first step, so as to produce a pipe- bend 40.

The tool is again opened and rotated through 90° in the direction reference 38, such as to move the composite unit 36-40 to a tool-part 41 which has a still larger mould cavity. In the first part-stage of the second step, core material is injected through the gate 43, which forms a connection between the tool-parts 35 and 41, such as to produce a Z-shaped core-part 42. In¬ jection moulding of core material is thus effected simultaneously in the tool-parts 35 and 41.

The tool is then opened again and rotated through 90°, so as to move the composite unit 36-40-42 to a last tool-part 44 which has a cavity of still larger volume. Product material is injected into the last tool-part 44 in the second part-stage of the second step, such that the knee-part 42 of the bend will be partially sur¬ rounded by product material. Because the gate 24' communicates with the gate 24, injection of product

material into the tool-parts 39 and 44 will take place simultaneously.

The tool-parts 35, 39, 41, and 44 are moveably con- nected to the tool-body and are moved in mutually unchanged positions. The progressively more complicated composite unit of core and product material is moved between the mould cavities of respective tool-parts with the aid of a rotatable tool-body which, in prin- ciple, is configured and functions in the same manner as the tool-body 18 described with reference to Figure 4. The described method provides a cyclic manufacturing process which is highly effective and which can be carried out in a rational manner. The method is also cost-saving, since it avoids time-consuming and expen¬ sive transfer of the injection moulded composite unit between different tools located in different injection moulding machines. Subsequent to removing the core material from the composite unit, there is obtained a product of complicated shape consisting of said product material and incorporating various hollows.

Figure 8 illustrates a method which differs in prin¬ ciple from the methods described with reference to Figures 1-7 in which a core is produced first. In the method illustrated in Figure 8, the first step is one of injecting product material through the gate 24 so as to mould a product-detail 46 in a tool-part 45. The tool is then opened and the tool-body rotated through 120° in the direction of the arrow 49, such as to bring the product-detail 46, supported by its anchoring parts, into a tool-part 47. An approximately spherical core 48 is then injection moulded around the product- detail 46, in the manner afore-described. The tool is

then again opened and the tool-body rotated through 120°, so as to bring the composite unit into the mould cavity of the tool 49. Product material is then in¬ jected through the gate 24, so as to form an approxima- tely shperical wall 50, which in the moulding process is joined to the original product-detail 46. The in¬ jection of product material through the gate 24 and into respective tool-parts 45 and 49 takes place simul¬ taneously. This method also enables articles to be produced cyclicly and effectively.

The core material mentioned in the afore-described embodiments may be a readily melted metal alloy of low melting point, and the product material may be a syn- thetic resin of high melting point. It will be under¬ stood, however, that the method is not limited to the use of these specific materials, since the only necess¬ ary criterion is that the two materials will have mutually different melting points that possess the afore-described mutual relationship. The core may also be formed from a material which is soluble in acid, or even in water. Other modifications are conceivable within the scope of the following claims. Neither is the injection moulding tool restricted to the described and illustrated embodiments thereof, since changes and modifications can be made thereto within the scope of the following claims.