US20040151611A1

US20040151611A1 - Method for producing powder metal tooling, mold cavity member

Info

Publication number: US20040151611A1
Application number: US10/354,840
Authority: US
Inventors: Kerry Kline; Gary Pyle; Barbara Lyke; Tom Stuart; Michael Bellis; Daniel Swart
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2003-01-30
Filing date: 2003-01-30
Publication date: 2004-08-05

Abstract

A method of producing a mold cavity insert using powder metals includes the steps of providing a master die having a pattern with a shape that defines a mold cavity, applying powder metal in the master die, and compacting the powder metal within the master die with a press assembly to form a compacted part. The method further includes the steps of removing the compacted part from the master die, placing the compacted part in a furnace, and heating the compacted part in the furnace to an elevated temperature to cure the part and provide a mold cavity insert that may be employed in a mold.

Description

TECHNICAL FIELD

The present invention generally relates to the production of tooling dies and molds and, more particularly, relates to a method of producing mold cavity members from powder metals.

BACKGROUND OF THE INVENTION

Conventional techniques for fabricating mold cavity inserts generally require highly skilled tool and mold makers using complex machinery. Hence, the conventional fabrication of a mold cavity insert for use in a mold is rather time consuming and expensive. Due to the market demand for reduced cycle time, several processes have been developed which are generally categorized as rapid tooling. The rapid tooling techniques generally utilize a rapid prototype pattern in a metal fabrication process to create a mold cavity insert. Some rapid tooling methods employ a metal fabrication process referred to as investment casting. Using an expendable pattern as a guide, investment casting generally creates a ceramic shell into which molten metal is poured to form the final part. Investment casting-based techniques have achieved reduced cycle time and cost as compared to more sophisticated conventional machined approaches. However, many investment casting techniques result in reduced quality surface finish, geometry limitations of the ceramic shell and the investment casting process, and extreme hardness of the cast mold cavity inserts.

Other rapid tooling approaches have been proposed based on a metal shell approach in which a metal shell is first formed onto a rapid prototype pattern, the shell is subsequently removed from the pattern, and is then reinforced to form a mold cavity insert. A high strength ceramic is typically used to bond the metal shell to a standardized pocketed mold base. Mold cavity inserts manufactured according to such prior techniques generally exhibit poor thermal conductivity, and are susceptible to rapid wear and, hence, a short useful life, and have process related geometry limitations.

Powder metal-based rapid tooling methods also exist which form powder metal and binder into a mold cavity insert. The powder metal is loaded into a pattern and is heated in a furnace to remove the binder and sinter the metal powders together. The resultant part is densified via infiltration with a low melting point metal, such as copper. One example of a powder metal-based rapid tooling method is disclosed in U.S. Pat. No. 5,956,561, which utilizes powder metal and hot iso-static pressure to produce die and mold surfaces in a generally rough state. This process uses loose fill powder metal loaded into a canister surrounding a machined pattern prior to applying the hot iso-static pressure. The approach set forth in the aforementioned patent produces a net shape on the cavity surface, but does not necessarily produce a finished sized insert ready to fit into a mold or die base/housing. The resultant die or mold manufactured according to such an approach may be damaged or destroyed in the process, and involves a rather slow process.

Accordingly, it is therefore desirable to provide for a rapid tooling method for forming a mold cavity insert with reduced cycle time, and which offers the ability to use a master pattern to repeatedly form multiple mold cavity inserts.

SUMMARY OF THE INVENTION

The present invention provides for a method of producing a mold cavity member using powder metals. The method includes the steps of providing a master die having a pattern with a shape that defines a mold cavity, applying powder metal in the master die, and compacting the powder metal within the master die with a press assembly to form a compacted part. The method further includes the steps of removing the compacted part from the master die, placing the compacted part in a furnace, and heating the compacted part in the furnace to an elevated temperature to cure and provide a mold cavity member. The method of producing the mold cavity member is a low cost technique which reduces the tooling fabrication cycle time. Further, multiple mold cavity members may be produced repeatedly with the same-master die and press assembly.

These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [0008]
FIG. 1 is a partial cross-sectional view taken through the center of a master die illustrating the application of powder metal in the cavity of the die; [0009]
FIG. 2 is a partial cross-sectional view taken through the master die illustrating a press assembly compressing the powder metal; [0010]
FIG. 3 is a partial cross-sectional view taken through the master die illustrating further compression of the powder metal via the press assembly; [0011]
FIG. 4 is a partial cross-sectional view taken through the master die illustrating opening of the press assembly; [0012]
FIG. 5 is a partial cross-sectional view taken through the master die further illustrating release of the compacted part from the die; [0013]
FIG. 6 is a schematic diagram of a hipping furnace illustrating the application of hot iso-static pressure to compacted parts according to a first embodiment; [0014]
FIG. 7 is a perspective view of a vacuum furnace illustrating the sintering of compacted parts according to a second embodiment; and [0015]
FIGS. 8A and 8B are top views of two sides of a mold incorporating mold cavity inserts manufactured according to the present invention. [0016]

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. [0017] 1-5, a sequence of steps for forming a compacted powder metal part 20 is generally illustrated in accordance with a method of making a mold cavity insert according to the present invention. The compacted powder metal part 20 is formed using a master die 10 having inner wall 16 forming a cavity defining a pattern having a desired shape. The inner wall 16 of master die 10 generally defines a shape that is to be formed into the compacted powder metal part 20. The master die 10 is a prefabricated master die which may be fabricated, machined or otherwise formed of steel or other hard metals that may be repeatedly used to form a plurality of compacted powder metal parts. Master die 10 may be molded of a single material or may include multiple laminated layers of materials, as shown.
The steps for forming the compacted powder metal part also employ the use of a press assembly. The press assembly includes a [0018] first hob 12 and a second hob 14. The second hob 14 is a stationary hob having a surface that engages an opening within the inner wall 16 of master die 10 and remains stationary relative to the supporting ground. The first hob 12 is a movable hob (press) that is actuated via an actuating mechanism (not shown) which moves the hob 12 toward and away from stationary hob 14. The movable hob 12 has a contacting surface for contacting the upper open end of inner wall 16 of master die 10. The press assembly operates by actuating movable hob 12 towards stationary hob 14 to compress powder metal 20 a within a cavity formed by inner wall 16 of master die 10 and the upper surface of stationary hob 14 and the lower surface of movable hob 12.
With particular reference to FIG. 1, the [0019] powder metal 20 a is applied within the cavity formed by inner walls 16 of master die 10 during an initial loading stage. In doing so, the powder metal 20 a rests on top of the upper surface of stationary hob 14. The powder metal 20 a may include any of a number of known powder metals including, but not limited to, ferrous and non-ferrous structure alloys, having a suitable binder. Powder metals are well-known and generally include a material such as steel, and a binder such as, but not limited to, plastic, wax, and/or lubricants such as stearic acid, lithium stearate, or iron stearate. The binder is heat activated to bind together the powder metal particles to form a semi-solid compacted structure.
The powder metal may include any of a number of known powder metals including tool steels, nickel, alloys, and other materials that are useful for forming a mold cavity insert. The selection of the type of powder metal may depend upon the tooling application, as should be evident to those in the art. It should also be appreciated that the powder metal and/or the [0020] inner wall surface 16 of master die 10 and contacting surfaces of hobs 12 and 14 may include a release coating to prevent the powder metal from bonding to any of the master die 10 and press assembly hobs 12 and 14. A suitable release coating may include yttrium oxide, according to one example. Other examples of release agents may include aluminium oxide, zirconium oxide, silicon dioxide, manganese oxide, titanium oxide, thorium oxide, titanium carbide, titanium nitrite, and moron nitrite.
Once the [0021] powder metal 20 a is completely applied (loaded) within the master die 10, the press assembly is actuated to close during the compression stage. During the compression stage, the movable hob 12 is forcibly actuated downward and into contact with the powder metal 20 a as shown in FIG. 2. In this position, the powder metal 20 a is formed into a partially compacted part 20 b. As the movable hob 12 is forcibly actuated downwaurd towards the stationary hob 14, the master die 10 also begins to move downward. The movable hob 12 continues to move to a fully compressed position as shown in FIG. 3 in which the powder metal 20 a is formed into a fully compacted part 20.
In forming the compacted [0022] powder metal part 20 during the compression stage, the method of making the tooling die insert according to the present invention further includes the step of heating the master die 10 and the press assembly hobs 12 and 14 to an elevated temperature of at least one hundred and seventy-five degrees Fahrenheit (175° F.), according to one example. It should be appreciated that at least one, and preferably all, of the master die 10, movable hob 12, and stationary hob 14 are heated to an elevated temperature so as to cause the binder to partially cure and hold the compacted part 20 together in a semi-solid state.
Once the [0023] powder metal 20 a is formed into the fully compacted part 20, the ejection stage begins by retracting the movable hob 12 upward so as to open the press assembly and expose the upper surface of the compacted part, as shown in FIG. 4. The compacted part 20 is then ejected from the master die 10 during the lowering the master die 10 relative to the stationary hob 14, as shown in FIG. 5, to complete the ejection stage. In doing so, the upper surface of stationary hob 14 causes the compacted part 20 to be forced outward from master die 10. It should be appreciated that the movable hob 12 and master die 10 may be actuated by any of a number of known hydraulic, electric, or mechanical actuation devices. It should also be appreciated that additional hobs may be used inside hob 12 and hob 14 or external to hob 12 or hob 14, moving parallel to hob 12 or hob 14. Movement of all components in the press assembly, tooling die, and/or hobs may be actuated via any number of known hydraulic, electric, or mechanical devices.
Once the compacted [0024] powder metal part 20 is formed and removed from the master die 10 and press assembly, the compacted part 20 is heated at an elevated temperature and an elevated pressure in a hipping furnace 22 as shown in FIG. 6 and/or is heated at an elevated temperature in a vacuum in a vacuum furnace 22′ as shown in FIG. 7. Referring to FIG. 6, the hipping furnace 22 includes a housing having an inner volume for holding a plurality of compacted powder metal parts 20. The hipping furnace 22 is shown holding eight compacted parts 20 spaced apart from each other and stacked one layer above another layer via ceramic spacers 26. The ceramic spacers 26 isolate the compacted parts 20 from each other and allow air flow between each of the parts 20. The hipping furnace 22 provides hot iso-static pressure (HIP) and includes a hipping furnace control 24 for controlling the elevated temperature and pressure in the furnace 22. The parts 20 are heated in the hiping furnace 22 at a pressure in excess of 15,000 pounds-per-square inch (psi) and a temperature of at least about two thousand eighty degrees Fahrenheit (2,080° F.). According to one embodiment, the hipping furnace is heated to an elevated temperature of about 2,080° F. and a pressure of about 15,000 psi. It should be appreciated that the time of heating in the hipping furnace 22 and the temperature and pressure in the furnace 22 should be sufficient to sinter the powder metal so that the powder metal pieces form a solid-state atomic transport or liquid phase molecular bond. The furnace temperature should be selected so that the furnace temperature approaches the softening point of the powder metal which is the temperature at which the powder metal transitions from a solid state to a liquid state. Once the compacted parts 20 are fully sintered in the furnace, the resultant mold cavity inserts 20 are removed from the furnace and allowed to cooled.
Referring to FIG. 7, the compacted [0025] powder metal parts 20 are shown heated in a vacuum furnace 22′ and are similarly isolated one from another via ceramic spacers 26. The vacuum furnace 22′ includes a vacuum furnace control 24′ which controls the temperature and vacuum created within the furnace 22′. The vacuum furnace 22′ is heated to a temperature of about two thousand eighty degrees Fahrenheit (2,080° F.), according to one embodiment. In contrast to the hipping furnace 22, a vacuum is created within the vacuum furnace 22′ during the heating stage. According to one embodiment, a vacuum is created within the vacuum furnace 22′ below atmospheric pressure sufficient to pull unwanted gases from the furnace. Once the compacted parts 20 are fully sintered, the resultant mold cavity inserts 20 are removed from the vacuum furnace 22′ and are allowed to cool.
While the compacted [0026] parts 20 are sintered in either a hipping furnace 22 or a vacuum furnace 22′, it should be appreciated that further processing of the mold cavity inserts 20 may occur. In another embodiment, the compacted parts 20 may be sintered sequentially in both the hipping furnace 22 and the vacuum furnace 22′. In a further embodiment, the mold cavity inserts 20 may be subjected to one or more heat treating processes to further harden the resultant inserts 20.
Once the fully sintered mold cavity inserts [0027] 20 are removed from the hipping furnace 22 or vacuum furnace 22′ and are allowed to cool, the individual mold cavity inserts 20 may be inserted into a mold 30 as shown in FIGS. 8A and 8B. According to the example shown, mold cavity inserts 20 may include an insert having a shaped surface to provide a desired shape within the mold 30. The mold 30 may include any of a number of mold cavities which may include one or a plurality of mold cavity inserts 20 arranged to provide a desired mold configuration. The mold 30 is then useful for repeatedly producing shaped parts in an injection molding process or other shaped part forming processes including, but not limited to, vacuum forming, positive pressure thermoforming, reaction injection molding, compression, sheet metal forming, etc.
Accordingly, the method of producing a [0028] mold cavity insert 20 according to the present invention advantageously provides a low cost technique for rapidly forming mold cavity inserts. It should be appreciated that the method of the present invention repeatedly utilizes the master die 10 and press assembly to manufacture many mold cavity inserts 20. This method is able to produce mold cavity inserts having complex geometries with completed cavity dimensions that allow the inserts to be easily incorporated into a mold. It should further be appreciated that the method of the present invention may produce complete, partial or laminated members of mold cavities using members made using other fabrication techniques.
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law. [0029]

Claims

1. A method of producing a mold cavity member, comprising the steps of:

providing a master die having a pattern with a shape that defines a mold cavity;

applying powder metal in the master die;

compacting the powder metal within the master die with a press assembly to form a compacted part;

removing the compacted part from the master die;

placing the compacted part in a furnace; and

heating the compacted part in the furnace to an elevated temperature to cure the part and provide a mold cavity member.

2. The method as defined in claim 1, wherein the step of compacting the powder metal comprises compressing the powder metal within the cavity of the master die between a first hob and a second hob.

3. The method as defined in claim 2, wherein the step of compacting the powder metal comprises forcibly moving the first hob towards the second stationary hob.

4. The method as defined in claim 1, wherein the step of heating the compacted part comprises heating the compacted part in a hipping furnace at a pressure in excess of 15,000 psi.

5. The method as defined in claim 1, wherein the step of heating the compacted part comprises heating the compacted part in a vacuum furnace.

6. The method as defined in claim 1, wherein the step of heating the compacted part comprises heating the part in the furnace at a temperature of at least 2,080° F.

7. The method as defined in claim 1 further comprising the step of heating at least one of the master die and the press assembly.

8. The method as defined in claim 7, wherein the at least one of the master die and press assembly is heated to a temperature of at least 175° F.

9. The method as defined in claim 1, wherein the mold cavity member comprises a mold cavity insert.

10. The method as defined in claim 9 further comprising the step of placing the mold cavity insert in a mold.

11. A method of producing a mold cavity member, comprising the steps of:

applying powder metal in the master die;

heating at least one of the master die and a press assembly;

compacting the powder metal within the master die with the press assembly having a first hob and a second hob to form a compacted part, wherein the powder metal is compressed within the cavity of the die between the first hob and the second hob;

removing the compacted part from the master die;

placing the compacted part in a furnace; and

12. The method as defined in claim 11, wherein the step of compacting the powder metal comprises forcibly moving the first hob toward the second stationary hob.

13. The method as defined in claim 1 1, wherein the step of heating the compacted part comprises heating the compacted part in a hipping furnace at a pressure in excess of 15,000 psi.

14. The method as defined in claim 11, wherein the step of heating the compacted part comprises heating the compacted part in a vacuum furnace.

15. The method as defined in claim 11, wherein the step of heating the compacted part comprises heating the part in the furnace at a temperature of at least 2,080° F.

16. The method as defined in claim 11, wherein the at least one of the master die and press assembly is heated to a temperature of at least 175° F.

17. The method as defined in claim 11, wherein the tooling member comprises a mold cavity insert.

18. The method as defined in claim 17 further comprising the step of placing the mold cavity insert in a mold.