Net shaped dies and molds and method for producing the same

A method for making dies or molds from powdered metals is disclosed. The method includes the steps of: providing a pattern of a desired shape to define the mold or die cavity configuration; providing a canister; placing the pattern in the canister and filling the canister with a selected powdered metal; hot isostatic pressing the canister and powdered metal to produce a consolidated and densified compact; and sectioning the compact along a plane to enable removal of the pattern and thus providing the desired die or mold cavity in the fully densified powdered metal die or mold set so formed.

BACKGROUND OF THE INVENTION 
The present invention relates to the production of dies and molds made 
directly from powdered metals. The dies, according to the invention, are 
made by placing a specially formed pattern, having the shape of the 
desired die cavity, into a canister and fixing it in an appropriate 
location inside of the canister. The spaces between the pattern and the 
canister are then filled with a selected powdered metal, evacuated and 
sealed. Hot Isostatic Pressing (HIP) is then used to consolidate the 
powdered metal to full density. Separation of the compact along an 
appropriate plane enables the pattern to be removed thereby revealing the 
desired die cavity formed in the consolidated powdered metal. 
Present techniques for the production of dies involve casting ingots of the 
die material which must be reduced in size by rolling and/or forging. 
These steps result in significant yield loss of the material and create 
less than ideal mechanical properties due to the coarse nature of the 
microstructure. Following the rolling or forging, it is necessary to 
machine the cavity into the die. This is a very time consuming and labor 
intensive process which results in substantial expense and in additional 
wasted material. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method of making dies and molds for 
subsequent use in the manufacture of shaped parts, such as by die casting, 
injection molding and the like. The method includes the steps of providing 
a pattern of a desired shape to define the finished mold or die cavity 
configuration; placing the pattern in a canister; filling the interior of 
the canister with a selected powdered metal to surround the pattern 
therein; hot isostatic pressing the canister and powdered metal by the 
application of heat and pressure to consolidate and densify the powdered 
metal surrounding the pattern; and sectioning the canister and densified 
metal along a plane to remove the pattern and thus provide a die or mold 
cavity of desired shape in the densified metal sections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A method of practicing this invention as shown in FIG. 1 involves the 
creation of a steel pattern 4 by classical machining techniques. This 
pattern is the size and shape of the desired cavity to be produced in the 
finished die. The pattern is affixed to the bottom of the canister 8 by 
tack welds 9. A coating of yttrium oxide 5 is applied to the surface of 
the pattern 4. In a separate operation, the fill/evacuation tube 1, top 2 
and central portion of the canister 10 are welded together. This assembly 
is then welded to the bottom segment 8 of the canister. 
Powder of the desired die material is then introduced into the canister via 
the opening 7 in the fill/evacuation tube 1. The powder 6 in this example 
is M4 tool steel and fills the space between the pattern and the internal 
surfaces of the canister. The air is evacuated from the canister through 
the fill/evacuation tube 1 which is then welded closed. The canister 
containing the pattern and the powder is then hot isostatic pressed at 
2175.degree. F. for five hours at a pressure of 15,000 PSI. This process 
consolidates the powder creating a solid compact around the pattern. 
In order to remove the pattern, the consolidated canister is bandsaw cut as 
shown in FIG. 2. Upon removal of the pattern halves from the compact, the 
desired die cavity is revealed, see FIG. 3. 
A presently preferred embodiment of the invention is shown in FIG. 4. In 
this embodiment, a parting plate 11 is placed between the halves of the 
pattern 12. The parting plate 11 may be, for example, 1/2 inch thick 
carbon steel. The parting plate is either integral with the pattern 12 or 
may be pinned or tack welded thereto. The pattern is made slightly 
oversized on each side of the parting plate to accommodate the thickness 
of the parting plate. The assembled pattern and parting plate are coated 
with a parting agent such as boron nitride and are then positioned inside 
the canister 13. Tack welding or mechanical fasteners are used to attach 
the pattern/parting plate to the inside of the canister. The canister is 
then welded closed, incorporating a fill tube. In this example, H13 powder 
is introduced into the canister through the fill tube followed by 
evacuation and sealing of the canister. Hot isostatic pressing at 
2175.degree. for five hours at 15,000 PSI consolidates the powder into a 
solid. 
Removal of the pattern is accomplished by cutting or milling the edges of 
the canister to expose the edges of the parting plate. The die halves are 
then separated from the pattern and the parting plate. The pattern 
assembly may then be used to produce additional dies or molds. 
While the above description is the currently preferred approach, there are 
numerous variations which would be apparent to those of ordinary skill in 
the art. These include, but are not limited to, changing the powdered 
material used for the die. Obviously, this selection would be determined 
by the properties required in the final die or mold. Typical materials 
generally classified as tool steels, nickel alloys, cobalt alloys and 
copper alloys could be used. The consolidation parameters would then be 
selected for the alloy being used. 
Also, the technique used to manufacture the patterns may include forging, 
casting or selected layer sintering. It is also possible to use parts 
which were previously produced from dies made by the present invention. 
Presently, yttrium oxide has been applied to the pattern to act as a 
release coating to prevent the powder from bonding to the pattern during 
the consolidation process. Other choices of release agents or diffusion 
barriers could be equally effective. These may include aluminum oxide, 
zirconium oxide, silicon dioxide, magnesium oxide, titanium oxide, thorium 
oxide, titanium carbide, titanium nitride and boron nitride. It would also 
be possible to create the release layer on the pattern by thermally 
treating the pattern in an oxidizing or nitriding environment. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure. The presently preferred 
embodiments described herein are meant to be illustrative only and not 
limiting as to the scope of the invention which is to be given the full 
breadth of the appended claims and any and all equivalents thereof.