US20160296997A1

US20160296997A1 - Die-casting system with a refractory metal alloy surface

Info

Publication number: US20160296997A1
Application number: US14/682,411
Authority: US
Inventors: Lim Yuan Kwang; Tan Yong Sheng Andrew; Muhammad Azzli Bin Mahmood; Loh Yan Seng
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 2015-04-09
Filing date: 2015-04-09
Publication date: 2016-10-13
Also published as: SG10201602797SA

Abstract

A die-casting mold, includes a die insert including a mold surface with a refractory metal alloy layer and a method of manufacturing a die-casting mold, including machining a mold surface of a die insert such that the mold surface is a near net shape with respect to a workpiece and applying a refractory metal alloy layer onto the die insert.

Description

BACKGROUND

The present disclosure relates to die-casting and, more particularly, to a die-casting mold with an undersized cavity pattern with a refractory metal alloy layer.
A die-casting mold typically contains steel die cavity inserts within a steel housing. Some die-casting molds utilize cavity inserts manufactured of relatively thick layer of refractory metals backed by a steel plate bolted in countersunk manner. Although effective, the refractory metal is necessarily of a thickness to allow the mold pattern to be machined into the refractory metal, hence rendering little practical cost savings. This may also be relatively expensive, as refractory metal alloys, and ceramics, may be difficult to machine. This typically may result in a long fabrication lead-times.

SUMMARY

A die-casting mold, according to one disclosed non-limiting embodiment of the present disclosure can include a die insert including a mold surface with a refractory metal alloy layer.
A further embodiment of the present disclosure may include, wherein the mold surface is undersized with respect to a workpiece.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer is sized to form the workpiece.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer includes Anviloy.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer includes Tungsten (W).
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer is W90Ni4Mo4Fe2.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer is manufactured from a compositionally homogeneous powder mixture that is utilized in a laser cladding operation to produce the refractory metal alloy layer.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the compositionally homogeneous powder mixture includes tungsten (W) powder of less than about 44 microns particle size and other powders of less than about 74 microns particle size.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the other powders include Nickel (Ni), Molybdenum (Mo,) and Iron (Fe) powder.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the refractory metal alloy layer is about 0.010″ in thickness.
A further embodiment of any of the foregoing embodiments of the present disclosure may include a die housing, the die insert at least partially receivable into the die housing.
A method of manufacturing a die-casting mold, according to another disclosed non-limiting embodiment of the present disclosure can include machining a mold surface of a die insert such that the mold surface is a near net shape with respect to a workpiece; and applying a refractory metal alloy layer onto the die insert.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the die insert is manufactured of steel.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein applying the refractory metal alloy layer includes a laser cladding operation with a compositionally homogeneous powder mixture.
A further embodiment of any of the foregoing embodiments of the present disclosure may include performing a post-clad machining operation to finalize the mold surface with respect to the workpiece.
A further embodiment of any of the foregoing embodiments of the present disclosure may include ball milling a powder mixture to form the compositionally homogeneous powder mixture.
A further embodiment of any of the foregoing embodiments of the present disclosure may include ball milling a powder mixture including tungsten (W) powder of less than about 44 microns particle size, and other powders of less than about 74 microns particle size to form the compositionally homogeneous powder mixture.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the other powders include Nickel (Ni), Molybdenum (Mo,) and Iron (Fe) powder.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein a powder mixture forming the compositionally homogeneous powder mixture includes tungsten (W) powder of about 325M.
A further embodiment of any of the foregoing embodiments of the present disclosure may include, wherein the powder mixture includes other powders of about 200M.
The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a schematic cross-sectional view of a die casting mold;

FIG. 2 is a block diagram illustrating a method to manufacture the die-casting mold;

FIG. 3 is a schematic cross-sectional view of a laser cladding process for the die casting mold to apply a refractory metal alloy layer;

FIG. 4 is a schematic cross-sectional view of thermal distribution provided by the die casting mold;

FIG. 5 is a block diagram illustrating a method for powder processing to form a compositionally homogeneous powder mixture feedstock for the refractory metal alloy layer of the die-casting method of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a die-casting mold 20. Although only one side of the die-casting mold 20 is illustrated, the other side will be generally equivalent. The die-casting mold 20 includes a die housing 22 and a die insert 24 at least partially received into the die housing 22. The die insert 24 includes a mold surface 26 with a refractory metal alloy layer 28. That is, the undersized aspect of the die insert 24 is brought up to proper size to form the workpiece by the refractory metal alloy layer 28. In one disclosed example, the die housing 22 is manufactured of 4340 steel, the die insert 24 may be manufactured of tool steel, and the refractory metal alloy layer 28 may be manufactured of a relatively thin Anviloy®, tungsten alloy, molybdenum or other refractory metal alloy that forms a final mold surface layer 30 and is about 0.010″ in thickness. Anviloy® is a machinable tungsten-based material developed primarily for die-casting, aluminum permanent mold, and difficult extrusions.
With reference to FIG. 2, a method 100 to manufacture the die insert 24 initially includes machining the mold surface 26. The mold surface 26 is first undersized—with respect to the desired final dimensions of a workpiece to be die-cast—but close to near net shape (step 102). Next, a compositionally homogeneous powder mixture feedstock for the refractory metal alloy layer 24 is manufactured (step 104) as further described below.
Next, the compositionally homogeneous powder mixture feedstock is utilized in a laser cladding operation (step 106) to produce the refractory metal alloy layer 28 on the die insert 24. In one example, Anviloy® type powder may be utilized, but the powder is not limited to Anviloy® or tungsten alloy powders as the choice of powder may be achieved to select the application and properties desired. The laser process facilitates the rapid solidification of the refractory metal alloy layer 28 onto the mold surface 26 with metallurgical bonding for the production of a high hardness.
In one embodiment, the compositionally homogeneous powder mixture feedstock is communicated through cladding nozzles onto the mold surface 26 and laser beam rastered onto the powder to create a melt pool that is allowed to solidify rapidly under a protective Argon (Ar) atmosphere (FIG. 3). The refractory metal alloy layer 28 then solidifies onto the mold surface 26.
Next, post-clad machining is performed (step 108) to finalize the desired mold surface layer 30. Minimal post-clad machining results in a die surface of a desired roughness to perform the die cast. In general, a die insert with high hardness, toughness and tunable thermal conductivity is conducive to prolong tool life that readily produces acceptable die castings with low porosity.
Thus, the relatively thin layer of the refractory metal alloy layer 28 has a relatively high thermal conductivity (region of ˜128 W/m-K) fabricated onto a relatively lower thermal conductivity (an order of magnitude lower) steel substrate surface (with minimal or no post clad machining required). This allows the die insert 24 to advantageously distribute the heat on the surface yet be durable (FIG. 4.) The laser surface engineered also facilitates repair of the die insert 24 since only the mold surface 26 is treated with the refractory metal alloy layer 28. Further, the die insert 24 steel substrate affords the toughness to withstand the punishing cyclic rigors of the die cast process that repeatedly and dynamically squeezes the rapidly solidifying molten mass of the high temperature superalloy workpiece within the die insert 24.
With reference to FIG. 5, a method 200 for powder processing to form the compositionally homogeneous powder mixture feedstock for the subsequent laser melting initially includes selection of a Tungsten (W), Nickel (Ni), Molybdenum (Mo) and Iron (Fe) powder (steps 202, 204) prior to mixture thereof (step 206).
The tungsten alloy powder provides an extremely high melting range of about 2597-6170° F. and high thermal conductivity of about 128 W/m-K to withstand the molten superalloy (reported 2300-2437° F. for IN718). The tungsten alloy powder for superalloy die-cast application can be of a composition that is equivalent, or similar, to Anviloy, i.e., W90Ni4Mo4Fe2. In one example, the tungsten (W) is about 90% by weight of the mixture.
The mixture of Tungsten (W), Nickel (Ni), Molybdenum (Mo), and Iron (Fe) powders include a distribution of particle sizes with the lower weight percent elements having coarser particle size distributions, whilst tungsten (W) is at finer particle size distribution. Hence, in one example, −325M (−325 mesh equivalent to less than 44 microns particle size) of tungsten (W) powder, and −200M (equivalent to less than 74 microns particle size) of the other powder is utilized. That is, a micron particle size ratio of the tungsten (W) powder to the other powders is about 44:74. In one example, the tungsten (W) is about 80%-90% by weight of the mixed powder. In another example, the tungsten (W) is about 90% by weight of the mixed powder, the Nickel (Ni) is about 4%, the Molybdenum (Mo) is about 4%, and the Iron (Fe) is about 2%.
The mixed powder is then ball milled (step 208) such as via a tubular blender, to produce the compositionally homogeneous powder mixture feedstock with effective powder distribution and chemical homogeneity for subsequent processing (step 210, 212). The ball milling ensures homogeneity in the mechanically alloyed powder so as to produce a homogenous powder for the laser melting onto the steel substrate (step 106; FIG. 2). It should be appreciated that various powder mixing may alternatively or additionally be provided.
The method 100 for manufacture of the die insert 24 advantageously reduces cost as the fabrication of an entire die insert is not manufactured from refractory alloys, as well as permits versatility in the die insert fabrication. The method 200 for powder processing to form the compositionally homogeneous powder mixture feedstock permits the adjustment of the powder composition, so as to produce a specifically tailored physical surface to include tunable thermal conductivity. In principle, a high thermally conductivity material experiences less thermal strain on the material and prolong die life. Coupled with a high melting point alloy, it is then possible to die cast high temperature superalloys without chemical alloying the surfaces. The laser melting process also allows adjustment as to the rate of solidification to control the hardness via control of fine microstructure in the refractory alloy layer. Whilst high thermal conductivity favors less thermal strain and hence longer die life through less thermal fatigue cracks, the high thermal conductivity also negatively impacts die cast-ability of superalloys with a too rapid freezing rate. Hence, a relatively thin layer of refractory metal is preferred
The use of the terms “a,” “an,” “the,” and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.
Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.
It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.
The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be appreciated that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.

Claims

1. A die-casting mold, comprising:

a die insert including a near net shape mold surface with a refractory metal alloy layer, wherein the refractory metal alloy layer is manufactured from a compositionally homogeneous powder mixture that is utilized in a laser cladding operation to produce the refractory metal alloy layer.

2. The mold as recited in claim 1, wherein the mold surface is undersized with respect to a workpiece.

3. The mold as recited in claim 2, wherein the refractory metal alloy layer is sized to form the workpiece.

4. The mold as recited in claim 1, wherein the refractory metal alloy layer includes Anviloy®.

5. The mold as recited in claim 1, wherein the refractory metal alloy layer includes Tungsten (W).

6. The mold as recited in claim 1, wherein the refractory metal alloy layer is W90Ni4Mo4Fe2.

7. The mold as recited in claim 1, wherein the refractory metal alloy layer is manufactured from a compositionally homogeneous powder mixture that is utilized in a laser cladding operation to produce the refractory metal alloy layer.

8. The mold as recited in claim 7, wherein the compositionally homogeneous powder mixture includes tungsten (W) powder of less than about 44 microns particle size and other powders of less than about 74 microns particle size.

9. The mold as recited in claim 8, wherein the other powders include Nickel (Ni), Molybdenum (Mo,) and Iron (Fe) powder.

10. The mold as recited in claim 1, wherein the refractory metal alloy layer is about 0.010″ in thickness.

11. The mold as recited in claim 1, further comprising a die housing, the die insert at least partially receivable into the die housing.

12. A method of manufacturing a die-casting mold, comprising:

machining a mold surface of a die insert such that the mold surface is undersized with respect to a desired near net shape with respect to a workpiece;

applying a refractory metal alloy layer onto the die insert to form a near net shape wherein the refractory metal alloy layer is manufactured from a compositionally homogeneous powder mixture that is utilized in a laser cladding operation to produce the refractory metal alloy layer; and

performing a post-clad machining operation to finalize the near net shape mold surface with respect to the workpiece.

13. The method as recited in claim 12, wherein the die insert is manufactured of steel.

14-15. (canceled)

16. The method as recited in claim 12, further comprising ball milling a powder mixture to form the compositionally homogeneous powder mixture.

17. The method as recited in claim 12, further comprising ball milling a powder mixture including tungsten (W) powder of less than about 44 microns particle size, and other powders of less than about 74 microns particle size to form the compositionally homogeneous powder mixture.

18. The method as recited in claim 17, wherein the other powders include Nickel (Ni), Molybdenum (Mo,) and Iron (Fe) powder.

19. The method as recited in claim 12, wherein a powder mixture forming the compositionally homogeneous powder mixture includes tungsten (W) powder of about 325M.

20. The method as recited in claim 19, wherein the powder mixture includes other powders of about 200M.

21. The mold as recited in claim 1, wherein a hardness is controlled by a fine microstructure in the refractory alloy layer.

22. The method as recited in claim 12, further comprising adjusting a rate of solidification via the laser cladding operation to control the hardness by control of a fine microstructure in the refractory alloy layer.