NL1040965B1

NL1040965B1 - Die casting method with associated product and apparatus.

Info

Publication number: NL1040965B1
Application number: NL1040965A
Authority: NL
Inventors: Bosman Michiel
Original assignee: Rubitech Heating B V
Priority date: 2014-09-22
Filing date: 2014-09-22
Publication date: 2016-09-29

Abstract

Method for die casting where multiple pre-cast sections are positioned in a main mould, which when closed, forms a gap between at least a portion of the outer surfaces of the pre-cast sections and an inner surface of the main mould. In a following step, a molten metal is injected into the gap through a gate opening in the main mould for at least partially encapsulating the pre-cast sections. The molten metal is then cooled for solidifying, to form a metallic layer for holding the pre-cast sections as an integrated die cast product. The product is then released from the main mould. The product and the apparatus associated with this method for the die casting are also disclosed. The method particularly enables die casting of products that comprise internal channels or hollow regions having curvature(s) and/or undercut(s).

Description

DIE CASTING METHOD WITH ASSOCIATED PRODUCT AND APPARATUS FIELD OF THE INVENTION

The invention relates to formation of products by die casting method, particularly when the product includes an internal channel or hollow region having curvatures and or undercuts.

BACKGROUND

Die casting is a metal casting method that is well known in the art, for forming metal products in various shapes and sizes. Herein, molten metal is injected under high pressure into a mould cavity and cooled for solidifying. The mould cavity is commonly created by two hardened metallic dies (mould assembly or main mould) which have been machined into shape to work like the mould cavity during the casting method. Die casting of products having an internal channel or hollow region having curvature(s) and/or undercut(s), is however, difficult.

Methods are known where a hollow insert is enclosed within a mould assembly and a light-metal casting alloy is injected under pressure into the mould assembly, as shown by patent publications EP0585136 and W02008/059329. Upon cooling and solidification, the hollow insert gets embedded within the alloy, forming a hollow region. Disadvantageously, the hollow insert that is embedded is a simple hollow tube, sleeve or the like and is likely to limit the geometry of the internal channel or hollow region.

Curved internal channels or passages are known being made by using retractable cores, which can be retracted after the molten metal that is injected under pressure in the die casting process, is solidified. This is shown in patent publications GB1465486 and GB2236556. The use of retractable cores makes the mould very complex, expensive and sensitive to wear. Besides, the use of the retractable cores means that it limits the geometry of the internal channel or hollow region.

Patent publication number JP55153650 is directed towards producing a hollow casting by gravity casting (pouring). Two parts of a thin-walled hollow object are e.g. respectively manufactured through die-casting. The parts are combined and brazed to form a thin-walled hollow object, which is then positioned in a mould assembly. Molten metal is then poured between the thin-walled hollow object and the two metal dies of the mould assembly. After the molten metal has solidified, both metal dies are opened and the hollow casting is taken out. Brazing the parts, the necessary preparation therefore, and subsequently casting by pouring the molten metal into the mould assembly is likely to make the process slow and expensive.

SUMMARY OF THE INVENTION

The embodiments of the present invention particularly, though not exclusively, enable die casting of products that comprise internal channels or hollow regions having one or more curvatures and/or undercuts. The associated method and product are also disclosed. The proposed method is potentially suitable for high volume and low cost production.

According to a first aspect of the invention, a method for die casting products with an internal channel having curvatures and undercuts is disclosed. The method comprises the following steps: - placing preformed, interlocking and matching-one-another, hollow sections, -whereby the inner surfaces of said preformed sections, in cooperation, define an internal channel - in a main mould (mould assembly), such that a gap is formed between at least a portion of corresponding outer surfaces of the preformed sections and an inner surface of the main mould, - injecting, under pressure, a molten metal - through at least one opening - into said gap in the main mould for at least partially encapsulating the preformed sections such that after cooling, an integrated die cast product is obtained with an internal channel. This method of die casting is particularly suitable for forming products with internal channels of complex geometry.

According to another embodiment of the first aspect of the invention, said sections are interlocked at least partially in a step form, preferably in a trapezoidal form. The preformed sections are interlocked at their edges during the positioning, by interlocking means, to avoid movement of the preformed sections and/or flashing of the molten metal into the internal channel or hollow region.

According to yet another embodiment of the first aspect of the invention, said method further comprises the steps of: releasably securing at least one of the preformed sections within the main mould, while the positioning and securing occurs, by means of at least one releasable securing means, which securing means comprises a first element that is provided in the main mould, and a second element that is provided on the outer surface of at least one of preformed section, wherein the first element is further used to eject the product for releasing form the main mould.

According to another embodiment, a compressive force is provided by the main mould on the preformed sections by means of a plurality of protrusions disposed on the outer surfaces of said preformed sections. To this end, at least one of the protrusions is slightly, preferably 1 mm, longer than the width of the gap between outer surfaces of said sections and the inner surface of the mould.

For assuring better contact with the inner surface of the main mould, at least one of the protrusions is at least partially resilient, for forming a more efficient contact with said inner surface of the main mould. Preferably, at least one of the protrusions is conical in shape.

According to another embodiment of the invention, said preformed sections and the molten metal are made at least partially by the same metal. Preferably, the metal comprises at least one of metals aluminium and magnesium.

According to a second aspect of the invention, a die cast product with an internal channel is disclosed. The product comprises a plurality of preformed, interlocking and matching-one-another, hollow sections that are integrated by a metallic layer that at least partially encapsulates these preformed sections, whereby the inner surfaces of said preformed sections define, in cooperation, an internal channel.

According to another embodiment of the second aspect of the invention, said preformed sections have at least partially a general C- form cross-section.

According to another embodiment of the second aspect of the invention, said internal channel contains at least one curvature.

This way, products could be made with an internal channel that is curved and/or has one or more undercuts.

According to another embodiment of the second aspect of the invention, said preformed sections are interlocked at least partially in a step form, preferably in a trapezoidal form.

According to another embodiment, said preformed sections comprise a plurality of protrusions which define the distance between outer surfaces of said preformed sections and the inner surface of the main mould.

To this end, the protrusions are slightly, preferably 1 mm, longer than the width of the gap between the castings and the inner surface of the mould.

According to another embodiment, at least one of the protrusions is at least partially resilient for assuring better contact with the inner surface. Preferably, at least one of the protrusions is conical in shape.

According to another embodiment of the invention, said preformed sections and the molten metal consist at least partially of the same metal. Preferably, the metal comprises at least one of metals aluminium and magnesium.

Such die cast products are in particular used in heat exchangers such as in domestic central heating systems consisting of burner and heat-exchanger for heating up the house in the winter and for making hot water. The preformed sections themselves may be produced by a die casting process.

The present invention consists of certain novel features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings and particularly pointed out in the appended claims; it being understood that various changes in the details may be possible without departing from the scope of the invention or sacrificing any of the advantages of the present invention

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings, same reference numbers generally refer to the same parts throughout. The drawings are not necessarily to scale; instead emphasis is placed upon illustrating the principles of the invention. The various embodiments and advantages of the present invention will be more fully understood when considered with respect to the following detailed description, appended claims and accompanying drawings wherein: FIG. 1A illustrates a transverse cross-sectional view of two pre-cast sections positioned within a main mould to form a hollow product, according to an embodiment of the invention. FIG. IB illustrates the hollow product formed as shown in FIG. 1A and after being released from the main mould. FIG. 1C and FIG. ID illustrate enlarged views of two types of arrangements for interlocking means shown in FIG. 1A, for interlocking said pre-cast sections at their edges. FIG. IE illustrates an enlarged view of a releasable securing means between a pre-cast section and the main mould, as shown in FIG. 1 A. FIG. 2A and FIG. 2B illustrate longitudinal cross-sectional views of two pre-cast sections that can be positioned within a main mould for forming a product, according to an embodiment of the invention. FIG. 2C illustrates a longitudinal cross-sectional view of a product when released from the main mould, and formed with the two pre-cast sections illustrated in FIGs. 2A and 2B. FIG. 3 illustrates a longitudinal cross-sectional view of the product where two pre-cast sections are completely encapsulated by the solidified metal.

DETAILED DESCRIPTION

For an improved method, during the step of injecting the main mould is maintained at a temperature of about 250 -280 degrees Celsius and/or the molten metal is maintained at a temperature of about 610 - 640 degrees Celsius.

The following description presents several preferred embodiments of the present invention in sufficient detail such that those skilled in the art can make and use the invention.

Before describing in detail embodiments that are in accordance with the present invention, it should be noted that all of the figures are drawn for ease of explanation of the basic teachings of the present invention only. The extension of the figures with respect to the number, position, relationship and dimension of the parts of the preferred embodiment will be within the skill of the art after the following teachings of the present invention have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength and similar requirements will likewise be within the skill of the art after the following teachings of the present invention have been read and understood.

The embodiments of the invention disclose, a die casting method and the associated product. Herein, two or more precast sections are positioned in a main mould when the main mould is open. The arrangement is such that when the main mould is closed, a gap is formed between at least a portion of corresponding outer surfaces of the precast sections and an inner surface of the main mould. A molten metal is then injected into the gap through at least one gate opening in the main mould, for at least partially encapsulating the precast sections. After cooling and solidifying the molten metal, a metallic layer is formed that holds the precast sections as an integrated die cast product, which can be released from the main mould. Advantageously, the embodiments of the present invention enable die casting of products that comprise hollow regions or internal channels having curvature(s) or undercut(s). FIG.1A illustrates a transverse cross-sectional view of two pre-cast sections 102 and 104 positioned within a main mould 106, to form an integrated die cast product 108, as shown in FIG. IB, according to an embodiment of the invention. In this embodiment, the pre-cast sections 102 and 104 form a hollow region 110, after the positioning and forming the product 108. Although only two pre-cast sections 102 and 104 are shown, the embodiments can have more than two as well. The main mould 106 is shown to be closed, when a gap 112 is formed between the outer surfaces 116 of the pre-cast sections 102 and 104 and an inner surface 114 of the main mould 106. A molten metal 118 is injected into the gap 112 through a gate opening 120 in the main mould 106. The gate opening widens towards the pre-cast sections. Though only one gate opening 120 is shown, according to another embodiment more than one gate openings 120 may be used. Upon cooling, the molten metal 118 solidifies to form a metal layer 122, which holds the pre-cast sections 102 and 104 together to form the integrated die-cast product 108. In this embodiment, the gap 112 is continuous along the transverse cross-section and encapsulates the pre-cast sections 102 and 104. According to other embodiments, the encapsulation may be partial as well.

According to another embodiment (not shown), the gate opening(s) 120 is/are structured to prevent destruction or deformation of the pre-cast sections 102 and 104 during the injection. The pre-cast sections 102 and 104 can be preformed by a step of die casting in their corresponding moulds (not shown), before said positioning in the main mould 106. According to an embodiment, the main mould 106 further includes a cooling means or a cooling system (not shown) for cooling the molten metal 118 after the injection, such as at a pre-determined cooling rate or to a pre-determined temperature. In this embodiment, a compressive force is provided on the outer surfaces 116 when the main mould 106 is closed. The compressive force is provided by multiple protmsions 124 on the outer surfaces 116. The protrusions compressively rest against the inner surface 114 for holding the pre-cast sections 102 and 104 together, while maintaining the gap 112. The protrusions 124 in this embodiment are likely to be fully embedded in the metal layer 122. Otherwise, any excess materials of the protrusions 124, which remain partially exposed through the metallic layer 122 or those which remain fully exposed with no metallic layer 122 formed over them, can be removed from the product 108. In this embodiment, the protrusions 124 are conical in shape. Other shapes may also be used in other embodiments.

The protrusions 124 may be resiliently flexible, for forming a more efficient contact with the inner surface 114. One releasable securing means 128 is shown for securing the pre-cast section 102 within the main mould 106 during the positioning. According to this embodiment, the securing means 128 has a first element 128a that is provided in the main mould 106 and a second element 128b that is provided on the pre-cast section 102, wherein the first element 128a is releasably secured to the second element 128b. Once the product 108 is formed, according to this embodiment, a part of the second element 128b is likely to remain exposed from the metallic layer 122. This exposed part can be removed if desired, preferably after releasing the product 108 from the main mould 106.

More of such securing means 128 may be used, as required and based on the structure of the pre-cast sections 102 and 104. Each pre-cast section 102 or 104 may be provided with at least one second element 128b, along with a corresponding first element 128a on the main mould 106. The first element 128a may also be usable to eject the product 108 for releasing from main mould 106. Interlocking means 126, for interlocking said precast sections 102 and 104 at their edges, are also shown.

Two types of arrangements for the interlocking means 126 are shown by the enlarged views at FIG. 1C and FIG. ID. Other types of arrangements may also be used in other embodiments. Such interlocking helps avoid or at least reduce flashing of the molten metal 118 into the hollow region 110. FIG. IE illustrates an enlarged view of the releasable securing means 128. In other embodiments, other types of arrangements for the securing means 128 may equally be used.

According to an embodiment, the pre-cast sections 102 and 104 and/or the molten metal 118 comprise aluminium and/or magnesium, as these metals are suitable material for this method of die casting.

According to another embodiment, FIG. 2A and FIG. 2B illustrate longitudinal cross-sectional views of two pre-cast sections 102 and 104 respectively, that can be positioned within the main mould (not shown) for forming a hollow product 108, according to an embodiment of the invention. Their respective open ends 202 and 204 are shown. FIG. 2C illustrates a longitudinal cross-sectional view of the product 108 that is formed with the two pre-cast sections 102 and 104 as illustrated in FIGs. 2A and 2B. In this embodiment, the product 108 is a hollow and a free-form channel that is curved along the longitudinal direction. The metallic layer 122 partially encapsulates the pre-cast sections 102 and 104 for holding them together at the two junctions 206 (as highlighted by the two dashed circles), to form the integrated die cast product. FIG. 3 illustrates a longitudinal cross-sectional view of the product 108 formed with two pre-cast sections 102 and 104, according to another embodiment. Like in the embodiment illustrated in FIG. 2C, in this embodiment, the product 108 has a free-form internal channel that is curved along the longitudinal direction. However, in this embodiment, the two pre-cast sections 102 and 104 are not only completely encapsulated by the metallic layer 122, but the metallic layer 122 is also extended beyond the two pre-cast sections 102 and 104.

According to an embodiment, during the step of injecting, the main mould 106 is maintained at a temperature of about 250 -280 degrees Celsius and/or the molten metal 118 is maintained at a temperature of about 610 - 640 degrees Celsius. To avoid abrasion of the pre-cast sections 102 and 104, these temperatures may be adjusted. The design for the gate opening 120 and the other casting parameters such as the pressure of injection of the molten metal 118 may also be adjusted, based on the geometry of the product 108. Generally, an increased exit area for the gate opening 120 is desirable. The gate opening 120 may further be at an angle of about 0-70 degrees to the precast sections 102 and 104. Multiple gate openings 120 are desirable for larger products 108, particularly when the pressure of injection is reduced.

After the injection, there may be a holding phase for the molten metal 118 under reduced or no pressure, before cooling. The combination of the geometry of the main mould 106, the various temperatures and the pressures as discussed above preferably need to be optimised based on the geometry of the product 108 and the materials used for the product 108 and for the molten metal 118. The product 108 may be used for various applications, such as for use in heat exchangers.

As to further discussion of the manner of usage and operation of the present invention, the same should be apparent from the above description. Accordingly, no further discussion relating to the manner of usage and operation will be provided.

While the foregoing description presents preferred embodiments of the present invention along with many details set forth for purpose of illustration, it will be understood by those skilled in the art that many variations or modifications in details of design, construction and operation may be made without departing from the present invention as defined in the claims. The scope of the invention is as indicated by the appended claims and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

Method for injection molding an injection molded product with an internal channel, comprising the following steps: - placing preformed, interlocking and mutually fitting hollow castings - the inner sides of which form a channel in cooperation - in a main mold such that a space is formed between at least a portion of the corresponding outer edges of the preformed castings and an inside of the main mold; - spraying a molten metal under pressure - through at least one opening in the main mold - into said space between the outer edges of the preformed castings and the inside of the main mold, to enclose the preformed castings at least partially in such a way that after cooling an integrated injection molded product with an internal channel.

A method according to claim 1, characterized in that said castings engage at least partially stepwise.

Method according to claim 2, characterized in that said castings engage at least partially in trapezoidal form.

The method according to any of claims 1 to 3, further comprising the steps of: releasably securing at least one of said preformed castings in the main mold, wherein placing and mounting is by means of at least one releasable securing means consisting of a first element that is provided in the main mold and a second element provided on the outside of at least one of the preformed castings, the first element being used to eject the cast product from the main mold.

Method according to any of claims 1 to 4, characterized in that pressure is exerted on the preformed castings by means of the plurality of protrusions present on these castings by the main mold.

A method according to claim 5, characterized in that at least one of said protrusions is up to 1 mm longer than a width of the space formed between the outer edges of the preformed castings and the inside of the main mold.

Method according to claim 5 or 6, characterized in that at least one of said protrusions is at least partially resilient.

A method according to any of claims 5-7, characterized in that at least one of said protrusions is conical in shape.

Method according to any of the preceding claims, characterized in that said preformed castings and the molten metal are at least partially made from the same metal.

Method according to any of the preceding claims, characterized in that the metal comprises at least one of the metal aluminum and magnesium.

An injection molded product with an internal channel comprising: a plurality of preformed, interlocking and mating hollow castings that are integrated by a layer of metal that at least partially encloses these preformed castings, the inner sides of the preformed castings cooperating with it internal channel.

An injection molded product according to claim 11, characterized in that said preformed castings have at least partially a generally C-shaped cross section.

Injection molded product according to claim 11 or 12, characterized in that said internal channel comprises at least one bend.

Injection-molded product according to any of claims 11 to 13, characterized in that said castings interlock at least partially stepwise.

Injection molded product according to claim 14, characterized in that said castings engage at least partially in trapezoidal shape.

Injection molded product according to any of claims 11 to 15, characterized in that the preformed castings have protrusions that define a gap between the castings and an inside of the main mold.

Injection molded product according to claim 16, characterized in that at least one of said protrusions is up to 1 mm longer than a width of the space formed between the outer edges of the preformed castings and the inside of the main mold.

Injection molded product according to claim 16 or 17, characterized in that at least one of said protrusions is at least partially resilient.

Injection molded product according to any of claims 16 to 18, characterized in that at least one of said protrusions is conical in shape.

Injection-molded product according to any of claims 11 to 19, characterized in that the preformed castings and the layer of metal consist at least partially of the same metal.

The injection molded hollow product of claim 20, wherein the metal comprises at least one of the metals aluminum and magnesium.