US20020025270A1

US20020025270A1 - Heat-exchanging forming tool and method of making

Info

Publication number: US20020025270A1
Application number: US09/790,080
Authority: US
Inventors: Robert McDonald; William Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-04-07
Filing date: 2001-02-21
Publication date: 2002-02-28

Abstract

A method of making a heat-exchanging forming tool for use in shaping articles of manufacture, said method comprising the steps of:

forming a non-porous metallic shell of generally uniform thickness having an outer contoured shaping surface of predetermined configuration corresponding to the desired shape to be imparted to the article by the tool on the opposite backside surface inversely contoured to that of the shaping surface;

supporting the shaping surface of the shell face down on an insulating support member such that the backside surface of the shell faces upwardly;

arranging a container over the shell;

introducing a plurality of discrete metallic elements into the container to provide a packed mass of such elements in contact with each other and with the backside surface of the shell and surrounding walls of the container, the elements being shaped such that when packed together the elements provide a network of interconnected open spaces throughout the packed mass of the elements; and

heating the elements and shell sufficiently to metallurgically bond the packed metallic elements to one another and to the shell while preserving the network of interconnected open spaces between the elements thereby obtaining a one-piece structure comprised of the non-porous metallic shell backed by an integrated porous metallic support body through which a heat exchanging fluid may be passed to conduct heat to or from the shaping surface of the shell.

Description

CROSS REFERENCE TO RELATED CASES

This application claims the benefit of the filing of provisional application Ser. No. 60/043,069, filed Apr. 8, 1997, and a continuation of U.S. Ser. No. 09/056,511, filed Apr. 7, 1998, incorporated herein by reference.[0001]

TECHNICAL FIELD

The present invention relates to the construction and method of making forming tools for use in shaping articles of manufacture and more particularly to such tools having heat-exchanging characteristics.

BACKGROUND OF THE INVENTION

Forming tools, such as metal molds and dies, are employed in many processes to impart a desired shape to an article of manufacture. For example, metal molds and dies are used to produce cast metal articles having the shape of the casting cavity of the tool. Metal dies are also used in other metal forming operations such as stamping, pressing, coining, drawing, extruding, forging, etc., to impart a desired shape to a metal sheet or billet. In the plastics and glass making industry, metal dies are used to shape various plastics, resins, composites, and glass to produce various shaped articles from these materials.

In many of these forming operations, such as for example the casting of molten metal or the molding of hot plastics or glass, there is a considerable amount of heat that must be dissipated in order to cool the article sufficiently to render the material from which the article is made from stable, allowing it to be released from the forming tool. It is of course desirable in many of these operations that the heat be dissipated as quickly and uniformly as possible since often the rate limiting step of a given forming cycle is the time it takes to extract the heat from the article and product quality is related to the uniformity by which heat is removed from the part. As such, heat transfer efficiency and uniformity of thermal control of the forming tool used to shape the articles are key to the product quality and manufacturing economics of the articles made from the tools. In addition to these advantages, a high efficiency forming tool reduces tooling and manufacturing costs as fewer tools are needed to support a given production schedule or schedules can be fulfilled more promptly with the tools on hand.

In accordance with one known practice, the manufacture of a forming tool, such as a metal mold, begins with a solid block of metal into which a contoured shaping surface is machined having a configuration corresponding to the shape to be imparted to the article being formed by the tool.

In an effort to improve the heat transfer efficiency of the solid metal mold, it is common to bore fluid passages into the mold beneath the shaping surface through which water, gas or other heat-transferring fluids may be passed to draw heat from the mold tool and hence the article. The drilling of cooling passages, however, adds to the time and cost of making the tool and further is limited in its effectiveness since it is not always practical or possible to uniformly extend the passages into all areas of the mold where they are required in order to achieve the desired cooling characteristics. Inadequate or nonuniform cooling of the forming tool may distort the desired shape of the article made by the tool.

Published International Application No. WO-96/17716, which is commonly assigned to the assignee of the present invention, discloses a forming tool designed to dissipate heat more efficiently and uniformly than the traditional approach described above. Disclosed is a manufacturing process for making a heat-exchanging forming tool in which a porous heat-transferring body, such as a block of foamed metal, is machined in much the same manner as that of the solid block described above to provide a contoured surface. Particles of molten metal are then thermally sprayed onto the contoured surface of the porous block to develop the non-porous shaping surface of the tool. The open metal network of the porous body defines a tortuous flow path for cooling fluid to pass to provide rapid, uniform cooling of the shaping surface and thus the article being formed by the tool.

Although the porous body forming tool described in the previous paragraph is considered to be a tremendous advancement over traditional solid block forming tools, the method described still involves machining a contoured surface into a block of material, albeit porous, which is also a costly and time consuming process. The described multi-layer thermal spraying process for building the non-porous shaping surface is also costly and requires specialized equipment and skilled operators.

A principle object of the present invention is to improve on these early developments in heat-exchanging forming tools by simplifying the construction and method of making high efficiency heat exchanging forming tools.

SUMMARY OF THE INVENTION

In a broad sense, the invention involves the pre-forming of a non-porous metallic shell having an outer contoured surface that serves as a shaping surface of the forming tool to be made. Once the shell is formed, a porous support body is built off the back side of the shell to provide the tool with the desired heat-exchanging characteristics.

The primary/fundamental concept of mold design and construction is fulfilled, namely design and construct one piece molds having an open, internal structure beneath the molding surface thus providing for:

a uniform and short path for thermal energy flowing from the molded part to the heat transfer fluid; a 10-15 fold increase over non-porous molds in the surface area of the fluid side contact with the heat transfer fluid; turbulent flow of the heat transfer fluid at all normal flow rates; and structures which will handle up to 10,000 psi in compression for aluminum and greater than 10,000 psi for other construction materials such as steel or titanium.

The development of the porous support body begins with a plurality of discrete metallic elements that are capable of being bonded metallurgically to one another and to the shell. The elements are packed together against the backside surface of the shell and are shaped such that when packed, the elements provide a network of interconnected open spaces extending throughout the packed mass of elements. The elements and shell are united as a one-piece metallic structure by heating the elements and shell sufficiently to generate metallurgical bonds at the points of contact between contiguous elements and the shell, while retaining the network of interconnected open spaces throughout the mass of bonded elements.

The invention has several advantages over conventional forming tools of the solid block type described above and the early heat-exchanging tools disclosed in the aforementioned published application. One principle advantage is that the support body is as-formed to the shape of the preformed shell, eliminating the costly and time consuming process of machining a contoured shaping surface from a solid or porous metal support body block.

The preforming of the metallic shell further dispenses with the multi-step process of thermal spraying metallic particles onto the machined contoured surface of the porous support body. In accordance with the present invention, the metallic shell can be preformed by any of a number of processes, including casting, stamping, powder metal forming, forging, and even thermal spraying if desired, thereby offering a wide variety of options, some of which may be more suitable than others for any given manufacture. Stamping the shell, for example, provides a very quick, cost efficient way of producing the non-porous shaping surface of the forming tool, as opposed to machining the surface into a solid block or developing the surface by thermal spraying molten particles of metal onto a contoured surface of a porous metal block.

The use of the metallurgically bondable metallic elements to form the support body also has several advantages over the machine support blocks (solid and porous) described above. One principle advantage is that the elements are able to conform as a mass readily to the desired shape of the support body and particularly to the backside surface of the preformed shell. This eliminates the need to machine a contoured surface in the support body. Rather, the contour is as-formed with the formation of the support body.

Another advantage that the metallic elements provide is that when packed together, the mass is substantially porous. Throughout the mass there exists a network of interconnected open spaces or channels. When bonded together according to the invention, the porous network is preserved, providing a more efficient, less costly approach to producing a porous support body than that of a machine porous block as disclosed in the aforementioned published application.

A still further advantage of the invention is that the metallurgical bonding of the packed elements to the shell unites the support body and shell as one integrated metallurgical structure. As such, a direct, continuous metallurgical and mechanical transition is provided between the non-porous shell and the porous metal support body, uninterrupted by any gaps or interfaces at the transition, for quickly and efficiently conducting heat from the shell to the porous support body.

BRIEF DESCRIPTION OF THE DRAWINGS

Presently preferred embodiments of the invention are disclosed in the following description and in the accompanying drawings, wherein: [0019]
FIG. 1 is a schematic, exploded cross-sectional view of the apparatus and component materials used for constructing a forming tool in accordance with a first presently preferred embodiment of the invention; [0020]
FIG. 2 is an assembly view of the apparatus and components of FIG. 1; [0021]
FIG. 3 is a schematic cross-sectional view of the forming tool produced by the apparatus and material components of FIGS. 1 and 2; [0022]
FIG. 4 is an enlarged schematic cross-sectional view of the [0023] encircled area 4 of FIG. 3;
FIG. 5 is a still further schematic enlargement illustrating in greater detail the metallurgical bond generated between contiguous metallic elements and the shell of the tool; [0024]
FIG. 6 is a schematic cross-sectional view like FIG. 2 but of an alternative embodiment of the invention; and [0025]
FIG. 7 is a cross-sectional view of the forming tool produced by the apparatus and material components of FIG. 6.[0026]

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is broadly related to forming tools of the type used to impart a desired shape to articles of manufacture made from such shapable materials as metal, plastics, resins, glass, composites, etc. Included among the forming tools contemplated are metal molds and dies used in the casting and forming of various metals and their alloys and composites; metal dies used in the injection molding and thermal forming of plastics, resins, glass; and various other shaping tools of the general type disclosed in the aforementioned International Published Application No. WO-96/17716, the disclosure of which is incorporated herein by reference. [0027]
The invention is concerned more specifically with heat-exchanging forming tools employing a manufacturing process in which a porous metallic support body is formed to shape against and metallurgically bonded to a preformed non-porous metallic shell having an outer contoured surface corresponding in configuration to the shape to be imparted to an article of manufacture shaped by the tool. What results from the process is a one-piece metallic structure having a non-porous preformed shell backed by an integrated support body comprised of a plurality of individual metallic elements bonded metallurgically to one another and to the shell in a manner to provide an interconnected network of open pores or channels throughout the body defining a tortuous flow path for the passage of a heat-transferring fluid through the body. [0028]
Such a heat-exchanging forming tool constructed in accordance with a first presently preferred embodiment of the invention is illustrated schematically in FIG. 3 and designated generally by the [0029] reference numeral 10. The tool 10 includes a non-porous preformed metallic shell 12 having an outer contoured shaping surface 14 having a configuration corresponding to that of a predetermined shape to be imparted by the tool to an article of manufacture (not shown). For example, the shaping surface 14 could represent one-half the cavity of a mold or die for shaping molten metal, plastics, glass, etc.
Various techniques can be employed for producing the preformed [0030] shell 12. These include, but are not limited to, casting the shell to shape from molten metal, forming a sheet or plate of metal to shape to provide the desired contour, machining the shell from a block of metal which is contemplated but less preferred due to the cost and time involved, thermal spraying molten metal particles to the desired shape of the shell, or forming the shell to shape using known powder metal forming techniques. The shell 12 is formed to have a generally uniform thickness such that a backside surface 20 of the shell 12 is contoured inversely to that of the shaping surface 14. The material for the metallic shell 12 may be any of numerous metals or their alloys or composites suitable for the application and the forming process employed to produce the shell 12. Suitable materials are given below.
The [0031] shell 12 is backed by a porous heat exchanging metallic support body 16. As shown, the body 16 may include a five-sided metallic enclosure or casing 18 joined to the backside surface 20 of the shell 12 adjacent the perimeter of the shell enclosing space or chamber 22 therebetween. A packed mass 24 of metallic elements 26 are housed within the chamber 22 and joined by metallurgical bonds across points of contact between contiguous elements 26 and at least the backside surface 20 of the shell, and preferably to the walls of the enclosure 18 as well. As such, there is a continuous metallurgical and mechanical transition from one portion of the forming tool to the next, and particularly between the shell 12 and the porous metallic mass 24, providing a direct, uninterrupted flow path for the conduction of heat between the shaping surface 14 of the tool 10 and the porous support body 16, uninterrupted by gaps or transitional interfaces that would deter heat flow.
In addition to there being a direct metallurgical bond between the [0032] shell 12 and support body 16, there is also provided an interconnected network of open pores or channels 28 throughout the packed metallic mass 24 and in communication with the shell 12. In the preferred arrangement, the pores are distributed generally uniformly throughout the support body 16 and particularly in the vicinity of the shell 12 to provide corresponding generally uniform cooling or heating across the shell. The open porous network 28 exposes a large surface area of the support body metal to the open network 28. In this way, the porous metal support body 16 acts likes a radiator and is able to disburse heat at a far greater rate than would a solid metal block lacking such pores. The rate of heat transfer is enhanced still further by the introduction of a heat-exchanging fluid such as water or other well known flowable heating or cooling agents through the porous network 28. The porous network 28 defines a tortuous flow path for the fluid through the body 16, imparting turbulent flow to the fluid as it moves through the body 16 even at low flow rates. Such turbulent flow at low flow rates optimizes the cooling efficiency of the heat-transfer fluid and minimizes the expenditure of energy to attain turbulent flow.
It will be seen in FIG. 3 that [0033] openings 30 are provided in the walls of the enclosure 18 which may serve as inlets and outlets for the heat transfer fluid passed through the support body 16.
FIGS. 1 and 2 illustrate how the [0034] tool 10 of FIG. 3 is produced according to the invention. As shown, a metal container 32 is provided having upstanding side walls 34. At the bottom of the container 32 is a support block 38 having an upper support surface 40. The block 38 is fabricated preferably of an insulating material such as sand or ceramic granules or the like shaped such that the upper support surface 40 presents a contour that duplicates the shape of the article to be formed by the tool 10.
The shaping [0035] surface 14 of the shell is disposed face down on the upper surface 40 of the support block 38. As will be seen in FIG. 2, the shape of the upper surface 40 fully complements that of the shaping surface 14 of, the shell 12 such that there is full surface-to-surface contact between the shell 12 and block 38.
A plurality of the individual, discrete [0036] metallic elements 26 are then poured into the container 32 where they are packed together (either under their own weight or by applied pressure) against the backside surface 20 of the shell 12 such that the mass of elements are conformed closely to the shape of the backside surface 20. The elements 26 are fabricated of metallic material selected for the ability to bond the elements 26 metallurgically to one another and to the metallic shell 12 and, if provided, to the metallic enclosure 18. It will be appreciated by those skilled in the art that there are numerous metallics capable of bonding metallurgically to one another, including pure metals, their alloys and composites and combinations thereof. The selection of the particular material or materials for the shell 12 and elements 26 will depend in part on the particular end use of the forming tool and may include considerations such as the required strength of the tool, the thermal conductivity requirements of the material, as well as material availability and cost considerations. Also a factor may be the process selected for generating the metallurgical bonds which may include brazing, sintering, soldering, casting etc. The metallic materials contemplated for the shell 12 and elements 26 may include, for example, aluminum, magnesium, copper, stainless steel, tool steel, nickel, nickel-aluminide, titanium, etc., to name a few.
Another characteristic of the [0037] individual elements 26 is that they have predetermined shapes that, when assembled in the packed mass 24, provide the network of interconnected open spaces or pores 28 throughout the mass. Various shapes may be employed depending upon the availability of the material and desired degree of porosity to be provided to the support body 16. Some of the shapes contemplated include, for example balls, beads, rods, jacks, wires, etc., or combinations thereof.
As shown in FIG. 2, the five-sided [0038] metallic enclosure 18 may initially comprise a separate component that is fitted down into the container 32 after the elements 26 has been introduced such that the walls of the enclosure 18 enclose the elements 26. Free ends or edges 42, preferably confront the backside surface 20 of the shell 12 and the walls of the enclosure 18 are preferably dimensioned to pack the elements 26 tightly against the shell 12 such that the elements 26 are in intimate contact with each other and with the shell 12 and enclosure 18.
Once assembled, the [0039] elements 26, shell 12 and enclosure 18 are heated sufficiently to cause the elements 26 to bond metallurgically across contiguous contact points with each other and with the shell 12 and enclosure 18, while preserving the porous network 28 as illustrated schematically in FIGS. 3 and 4. As shown, the metallurgical bonding has the effect of uniting the elements 26, shell 12, and enclosure 18 as one continuous metallic structure.
As mentioned, sintering may be employed as the means of producing the metallurgical bonds. In such case, it may be advantageous to coat the [0040] elements 26 as well as the shell 12 and enclosure 18 with a suitable sintering flux which will act to cleanse the bonding surfaces of impurities, oxides, etc., that may otherwise inhibit the formation of the metallurgical bonds. The flux selected if and as required will be appropriate to the metallic materials involved as those skilled in the art will appreciate. Also, it will be appreciated that the appropriate sintering temperature may vary according to the materials involved but in any case will be heated to such a temperature and for a time sufficient to generate the metallurgical bonds.
Where soldering or brazing is employed as the means of producing the metallurgical bonds, the contact surfaces of the [0041] elements 26, shell 12 and enclosure 18 may be coated with a low melting point metallic material 44 (FIG. 5) having a known fusing temperature that, when heated to such temperature, will meld across contiguous points of contact to generate the bonds. It is preferred that the brazing or soldering be carried out in an evacuated atmosphere. For this purpose, the chamber 22 between the enclosure 18 and shell 12 can be sealed and evacuated to provide such environment.
Various brazing and soldering materials may be employed depending, to a large degree, on the metallic materials to be bonded and particular end use requirements of the forming tool to be made, including the required strength and operating temperatures of the forming [0042] tool 10. During metallurgical bonding, the metallic coating 44 may combine or alloy with the parent metal of the element 26, producing localized alloyed zones 46 at points of contact between contiguous elements and the interior surfaces of the shell 12 and enclosure 18 (See FIG. 5). Examples of suitable material combinations that would bond in such manner include parent material of aluminum or alloys thereof for the elements 26, shell 12, and enclosure 18, and zinc or alloys thereof for the metallic coating 44. In such case, the assembly of the elements 26, shell 12 and enclosure 18 would be heated to a temperature above the melting point of the zinc coating 44, whereupon the zinc would melt and alloy with the aluminum parent material at the points of contact to generate the metallurgical bonds, as illustrated best in FIG. 5. Of course, numerous other parent/coating combinations could be employed, as will be appreciated by those skilled in the art.
A forming tool made in accordance with a second embodiment of the invention is illustrated in FIG. 6 and designated generally by the [0043] reference numeral 110. The forming tool 110 is alike in all respects with the forming tool 10 of the first embodiment except that the enclosure 18 has been omitted. The remaining features are the same and are referred to by the same reference numerals offset by 100.
FIG. 7 schematically illustrates the process for making the forming [0044] tool 110 employing a container 132 similar to that of the container 32 except that the interior of the container 134 has a non-adhering coating or lining 48 applied thereto, such as a ceramic coating or board, to which the metallic elements 126 will not bond. In this way, the porous support body 116 is releasible from the container 132 following the formation of the tool 110. An enclosure similar to that of enclosure 18 can be attached, if desired, in a subsequent joining operation.
The disclosed embodiments are representative of presently preferred forms of the invention, and are intended to be illustrative rather than definitive thereof. The invention is defined in the claims. [0045]

Claims

I claim:

1. A method of making a heat-exchanging forming tool for use in shaping articles of manufacture, comprising:

providing a prefabricated non-porous metallic shell having an outer contoured shaping surface corresponding to the shape to be imparted to the article to be formed by the tool and an opposite backside surface;

providing a plurality of discrete metallic elements metallurgically bondable to each other and to the backside surface of the shell;

assembling the metallic elements against the backside surface of the shell and in contact with one another to provide a packed mass of such elements, the elements being shaped such that when packed together the elements provide a network of interconnected open spaces throughout the packed mass of the elements; and

metallurgically bonding the packed metallic elements to one another and to the shell while preserving the network of interconnected open spaces between the elements thereby obtaining a one-piece structure comprised of the non-porous metallic shell backed by an integrated porous metallic support body through which a heat exchanging fluid may be passed to conduct heat to or from the shaping surface of the shell.

2. The method of claim 1 wherein the metallic elements are packed and bonded within a container extending from the backside surface of the shell such that the structural support body assumes the shape of the interior of the container and the backside surface of the shell.

3. The method of claim 2 wherein the support body is releasable from the container.

4. The method of claim 2 wherein the container includes an insulating base having an upper support surface contoured inversely to that of the shaping surface and side walls extending upwardly of the support surface.

5. The method of claim 4 wherein the shaping surface of the shell is supported face down on the support surface of the base and the side walls of the container are extended upwardly from the backside surface of the shell.

6. The method of claim 5 wherein the side walls are lined with insulating material to prevent bonding of the support body to the side walls.

7. The method of claim 4 wherein the metallic elements metallurgically bond to the walls of the container such that the walls of the container become an integrated portion of the forming tool.

8. The method of claim 7 wherein the mass of metallic elements are encased by the container.

9. The method of claim 1 wherein the metallurgical bonding results from sintering the metallic elements and shell at an elevated sintering temperature.

10. The method of claim 1 wherein the metallic elements are coated with a low melting point metallurgical bonding metal and are heated to a temperature sufficient to fuse the coatings of contiguous metallic elements to one another and to the shell thereby producing the metallurgical bonding of the elements and shell.

11. The method of claim 10 wherein the bonding metal alloys with the metal of the metallic elements and shell.

12. The method of claim 1 wherein the metallic shell comprises a preformed cast member.

13. The method of claim 1 wherein the metallic shell comprises a preformed metal plate member.

14. The method of claim 1 wherein the metallic shell comprises a preformed thermal-spayed member.

15. The method of claim 1 wherein the preformed shell is a machined member.

16. The method of claim 1 wherein the preformed shell is fabricated from powder metal.

17. The method of claim 1 wherein the preformed shell is formed with a generally uniform thickness.

18. The method of claim 1 including supporting the shell shaping surface down on an insulating support member and arranging a five-sided metallic enclosure about the mass of metallic elements with an open end of the enclosure confronting the backside surface of the shell thereby providing a chamber housing the metallic elements, and heating the shell, elements and enclosure sufficiently to bond the elements to one another and to the shell and enclosure.

19. A method of making a heat-exchanging forming tool for use in shaping articles of manufacture, said method comprising the steps of:

arranging a container over the shell;

20. A heat-exchanging forming tool for use in shaping articles of manufacture comprising:

a non-porous preformed metallic shell having an outer shaping surface of predetermined contour corresponding in configuration to the desired shape to be imparted to the article by the tool; and

a porous heat-exchanging support body having a plurality of individual metallic elements packed together and against a backside surface of said shell and bonded metallurgically to one another and to said shell across contiguous points of contact while providing a network of interconnected open spaces throughout the support body defining a tortuous flow path through the support body through which a heat exchanging fluid may be passed to conduct heat to or from the shaping surface of the shell.