Low CTE slush molds with textured surface, and method of making and using the same

Abstract

A rotomolding tool having a textured surface is provided. The tool comprises a shell having a body portion and an upper mold surface having a grain texture, at least the body portion comprising a nickel-iron alloy having a coefficient of thermal expansion of at most 5.O10.sup.6 in/in/ F. at temperatures between 100 and 500 F.

Claims

1. A rotomolding tool having a textured surface, the tool comprising: a shell having a body portion and an upper mold surface having a grain texture with a depth of 0.005 to 1.0 mm, at least the body portion comprising a nickel iron alloy, wherein the nickel iron alloy comprises: nickel in an amount ranging from 30 wt. % to 38 wt. %; up to 6.0 wt. % of one or more elements selected from the group consisting of cobalt, silicon, aluminum, copper, manganese, sulfur, chromium, zirconium, and titanium; from 0 wt. % to 0.07 wt. % carbon; and iron being the balance; provided that the nickel iron alloy comprises at least one of: aluminum in an amount of at least 0.3 wt %; copper; chromium in an amount of at least 0.7 wt %; zirconium in an amount of at least 0.8 wt %; or titanium in an amount of at least 0.5 wt %; wherein the upper mold surface has undergone a nitriding treatment.

2. The tool of claim 1, wherein the nickel iron alloy has a composition comprising at least 0.05 wt. % aluminum, and 0.01 wt. % chromium.

3. The tool of claim 1, wherein the nickel iron alloy has a composition comprising at least 0.05 to 0.75 wt. % aluminum, and 0.01 to 1.5 wt. % chromium.

4. The tool of claim 1, wherein the body portion has a first hardness having a Vickers hardness (HV) of at least 100 and the upper surface has a second hardness that is higher than the first hardness and a thickness of at most 1.5 mm.

5. The tool of claim 4, wherein the first hardness is 100 to 350 HV and the second hardness is a microhardness of 500 to 2,000 Knoop hardness (HK).

6. The tool of claim 1, wherein the upper mold surface comprises a nickel iron alloy that has undergone an aluminizing treatment prior to the nitriding treatment.

7. The tool of claim 1, wherein the nickel iron alloy has a coefficient of thermal expansion of 0.1810.sup.6 m/m/ C. (0.110.sup.6 in/in/ F.) to 7.210.sup.6 m/m/ C. (4.010.sup.6 in/in/ F.) at temperatures between 37.7 C. (100 F.) and 260 C. (500 F.).

8. The tool of claim 1, wherein the upper mold surface comprises a nitride coating.

9. The tool of claim 1, wherein the tool has a thickness of 3 to 10 mm.

10. The tool of claim 1, wherein the nickel iron alloy has a composition comprising at least 0.1 wt. % aluminum, and 0.25 wt. % chromium.

11. The tool of claim 1, wherein the nickel iron alloy has a composition comprising at least 0.1 wt. % aluminum, 0.1 wt. % zirconium, and 0.1 wt. % titanium.

12. The tool of claim 1, wherein the nickel iron alloy has a composition comprising zirconium.

13. The tool of claim 1, wherein the nickel iron alloy has a composition comprising 0-6.0 wt. % cobalt, 0.05-0.3 wt. % silicon, 0.05-0.2 wt. % aluminum, 0-0.1 wt. % copper, 0.3-0.6 wt. % manganese, 0-0.07 wt. % carbon, 0.005-0.03 wt. % sulfur, 0.01-0.4 wt. % chromium, 0-0.1 wt. % zirconium, and 0-0.1 wt. % titanium.

14. The tool of claim 1, wherein the nickel iron alloy has a composition comprising 0-6.0 wt. % cobalt, 0.05-0.3 wt. % silicon, 0.05-0.75 wt. % aluminum, 0-0.1 wt. % copper, 0.3-0.6 wt. % manganese, 0-0.07 wt. % carbon, 0.005-0.03 wt. % sulfur, 0.01-1.5 wt. % chromium, 0-1.5 wt. % zirconium, and 0-2.0 wt. % titanium.

15. The tool of claim 1, wherein the nitriding treatment comprises ion nitriding.

16. A rotomolding tool having a texture surface, the tool comprising: a shell having a body portion and an upper mold surface having a grain texture having a depth of 0.005 to 1.0 mm in the upper mold surface, at least the body portion comprising a nickel iron alloy, the nickel iron alloy having a composition comprising nickel in an amount ranging from 30 wt. % to 38 wt. %, 0.05 to 0.75 wt. % aluminum, 0.01 to 1.5 wt. % chromium, up to 6.0 wt. % of one or more elements selected from the group consisting of cobalt, silicon, copper, manganese, sulfur, zirconium, and titanium, from 0 wt. % to 0.07 wt. % carbon, and iron being the balance, provided that the nickel iron alloy comprises at least one of: aluminum in an amount of at least 0.3 wt %, copper, chromium in an amount of at least 0.7 wt %, zirconium in an amount of at least 0.8 wt %, or titanium in an amount of at least 0.5 wt %; the body portion having a second hardness that is higher than the first hardness with the tool having a thickness of 3 to 10 mm, wherein the upper mold surface has undergone a nitriding treatment.

17. The tool of claim 16, wherein the nickel iron alloy has a composition comprising zirconium in the amount of at least 0.1 wt. %.

18. The tool of claim 16, wherein the nitriding treatment comprises ion nitriding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a molding tool in accordance with an embodiment of the present invention;

(2) FIG. 2 is a view similar to FIG. 1 illustrating another embodiment of the present invention;

(3) FIG. 3 is a view similar to FIG. 2 illustrating yet another embodiment of the present invention;

(4) FIG. 4A is a view similar to FIG. 1 illustrating still yet another embodiment of the present invention;

(5) FIG. 4B is a view similar to FIG. 1 illustrating still yet another embodiment of the present invention;

(6) FIG. 5 is a flow chart illustrating an exemplary technique for making one embodiment of the present invention;

(7) FIG. 6 is a flow chart illustrating the manufacture of yet another embodiment of the present invention; and

(8) FIG. 7 is similar to FIG. 6 illustrating yet another embodiment of the present invention.

DETAILED DESCRIPTION

(9) As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

(10) Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word about in describing the broadest scope of the invention.

(11) It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular aspects or embodiments of the present invention and is not intended to be limiting in any way.

(12) It must also be noted that, as used in the specification and the appended claims, the singular form a, an, and the comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.

(13) Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.

(14) Referring to FIG. 1, in at least one embodiment, the present invention provides a slush molding tool 10. The slush molding tool 10 has a body portion 12 and an upper mold surface portion 14. In at least one embodiment, the upper mold surface portion 14 has a grained texture, shown schematically as 16. The molding tool 10 is usable in any suitable slush molding process.

(15) In certain embodiments, the grain 16 will have a depth or texture of 5 to 1,000 microns, in other embodiments of 50 to 600 microns, and in yet other embodiments of 100 to 400 microns. While the molding tool 10 can have any suitable thickness, in certain embodiments the mold tool 10 will have an average thickness of 3 to 10 mm and in other embodiments of 3.5 to 4.5 mm with the body portion 12 comprising the majority of the thickness. In one embodiment, the molding tool 10 has a substantially uniform thickness, wherein uniform means that no portion of the tool has a thickness that varies by more than 0.1 mm from any other portion of the tool. In certain embodiments the upper mold surface portion 14 has a thickness of 0.002 to 1.5 mm, in other embodiments of 0.2 to 1.0 mm, and in yet other embodiments of 0.4 to 0.6 mm.

(16) The tool 10 shown in FIG. 1 is schematically illustrated to have a relatively unique shape, however, it should be understood that the shape of the tool 10 in FIG. 1 is for illustrative purposes only and should not be construed to limit the side or shape of the molding tools in accordance with the present invention in any way, shape or form.

(17) In that regard, molding tools 10 of the present invention can be used to make automotive parts of any suitable shape or size. Without being limited, some examples of suitable parts to be made by the tools of the present invention include, but are not limited to instrument panels, door panels, consoles and other parts such as headliners and seats. Typical parts molded from the tools of the present invention are PVC or other suitable polymeric material such as polyurethane, and have thicknesses of 0.5 to 3 mm and have lengths and widths between 2 inches and 8 feet. In some embodiments, the molded parts may have lengths and/or widths of 2 to 6 feet.

(18) The molding tool 10 is made of a material having a low coefficient of thermal expansion (low CTE) in the molding process temperature range. In at least one embodiment, the molding material comprises a nickel-iron alloy having a coefficient of thermal expansion of no more than 510.sup.6 in./in./ F. at temperatures between 100 and 500 F. In another embodiment, the nickel-iron alloy has a coefficient of thermal expansion of 0.110.sup.6 to 4.010.sup.6 in./in./ F. at temperatures between 100 and 500 F., in other embodiments of 0.2510.sup.6 to 2.510.sup.6 in./in/ F. at temperatures between 100 and 500 F., and in yet other embodiments of 0.510.sup.6 to 1.510.sup.6 in./in./ F. at temperatures between 100 and 500 F. In at least one embodiment, the nickel-iron alloy has a Vickers hardness of at least 100 HV as measured by ASTM Test Method No. E-384. In other embodiments, the nickel-iron alloy has a Vickers hardness of 200 HV to 350 HV, in other embodiments of 200 to 325 HV and in yet other embodiments of 250 to 300 HV, as measured by ASTM Test Method No. E-384.

(19) While any suitable material can be used to make the molding tool, provided that the resulting tool has a coefficient of thermal expansion of no more than 510.sup.6 in./in./ F. at temperatures between 100 and 500 F. and a Vickers hardness of at least 100, one particularly suitable material comprises a nickel-iron alloy. In one embodiment, the nickel-iron alloy has the following composition:

(20) TABLE-US-00001 Elements Wt. % Nickel 30-38 wt. % Cobalt 0-6.0 wt. % Silicon 0.05-0.3 wt. % Aluminum 0.05-0.2 wt. % Copper 0-0.1 wt. % Manganese 0.3-0.6 wt. % Carbon 0-0.07 wt. % Sulfur 0.005-0.03 wt. % Chromium 0.01-0.4 wt. % Zirconium 0-0.1 wt. % Titanium 0-0.1 wt. % Iron balance

(21) In another embodiment, the nickel-iron alloy has the following weight percent:

(22) TABLE-US-00002 Elements Wt. % Nickel 31-37 wt. % Cobalt 0-5.75 wt. % Silicon 0.07-0.28 wt. % Aluminum 0.06-0.1 wt. % Copper 0-0.09 wt. % Manganese 0.35-0.55 wt. % Carbon 0-0.06 wt. % Sulfur 0.01-0.02 wt. % Chromium 0.02-0.3 wt. % Zirconium 0-0.1 wt. % Titanium 0-0.1 wt. % Iron balance

(23) In yet another embodiment, the nickel-iron alloy has the following weight percent:

(24) TABLE-US-00003 Elements Wt. % Nickel 36 wt. % Silicon 0.25 wt. % Aluminum 0.1 wt. % Manganese 0.5 wt. % Sulfur 0.02 wt. % Chromium 0.25 wt. % Zirconium 0.1 wt. % Titanium 0.1 wt. % Iron balance

(25) While any suitable nickel-iron alloy having the above-identified properties can be used, in at least one embodiment, Invar has been found to be particularly suitable. Furthermore, Invar No. 36 and Super Invar have been found to be particularly suitable and are available from Carpenter company of Wyomissing, Pa.

(26) Turning to FIG. 2, in another embodiment, a molding tool 20 is provided having a body portion 22 and an upper mold surface portion 24. Body portion 22 has a composition and properties similar to those of body portion 12 described with reference to FIG. 1. In at least one embodiment, the upper mold surface portion 24 will have graining represented schematically by 26. In certain embodiments, the grain 26 will have a depth or texture of 5 to 1,000 microns, in other embodiments of 50 to 600 microns, and in yet other embodiments of 100 to 400 microns. While the molding tool 20 can have any suitable thickness, in certain embodiments the mold tool 20 will have an average thickness of 3 to 10 mm and in other embodiments of 3.5 to 4.5 mm with the body portion comprising the majority of the thickness. In one embodiment, the molding tool 20 has a substantially uniform thickness, wherein uniform means that no portion of the tool has a thickness that varies by more than 0.1 mm from any other portion of the tool. In certain embodiments the upper mold surface portion 24 has a thickness of 0.002 to 1.5 mm, in other embodiments of 0.2 to 1.0 mm, and in yet other embodiments of 0.4 to 0.6 mm.

(27) In the embodiment illustrated in FIG. 2, the upper mold surface portion 24 has a higher hardness than the hardness of the body portion 22 of the mold tool 20. In this embodiment, the body portion 22 has a Vickers hardness in the range of 100 to 350 as measured by ASTM Test Method No. E-384 and the upper surface portion 24 has a microhardness in the range of 350 to 2,000 HK and in yet other embodiments of 400 to 1,500 HK, in yet other embodiments of 600 to 1,000 HK, and in yet other embodiments of 700 to 900 HK as measured by ASTM Test Method No. E-384. The increased hardness of the upper mold surface portion 24 can be provided by surface treating the upper mold surface portion 24. The upper mold surface 24 is also referred to as a case hardened surface.

(28) The upper mold surface portion 24 can be case hardened by ion nitriding the surface. Ion nitriding is generally known in the art and will not be explained in great detail here. Generally, the tool is exposed to a ion nitriding process to provide the desired hardness of the upper surface portion 24. Generally, the tool 20 is heated and in a chamber with nitrogen being introduced into the chamber. A voltage is biased on the tool 20 to accelerate nitrogen particles toward the tool. When nitrogen particles hit the aluminum, chromium, zirconium, silicon, or titanium in the tool 20, the nitrogen reacts with the element to form aluminum nitride, chromium nitride, zirconium nitride, silicon nitride, or titanium nitride respectively, in the surface of the tool 20. The aluminum nitride, chromium nitride, zirconium nitride, silicon nitride, or titanium nitride have a higher hardness than the nickel-iron alloy that forms the remainder of the body portion 22.

(29) It should be understood that the ion nitride will cause nitride formation that extends or diffuses somewhat into the body of the tool, such as up to 1.5 mm into the body. The hardness of the nitrided portion of the tool 20 will decrease as the case hardening depth extends further into the body portion 22 such that typically the hardest portion of the tool will be just at the upper mold surface 24 of the tool 20. In that regard, when mentioning microhardness of the upper mold surface portion 24 of the tool 20, it should be understood that the measurements are being taken just at the upper mold surface and that the entire nitrided portion of the molding tool does not necessarily have the same hardness as that of the upper surface and thus the present invention and claims are not to be limited as such. It should also be understood that those experienced in the art of nitriding can incorporate other elements such as carbon during nitriding to produce nitride materials such as titanium carbo nitride (TiCN) and silicon carbide (SiC). In some embodiments, a substantial portion or the entire body surface will be subjected to the nitriding process, resulting in case hardening of a substantial portion or the entire body surface, not just the upper mold surface.

(30) In one embodiment, the nickel-iron alloy has a higher level of nitriding elements, such as aluminum, chromium, zirconium, silicon, and/or titanium to provide even yet a harder surface portion to the tool. In this embodiment, the nickel-iron alloy has the following composition:

(31) TABLE-US-00004 Elements Wt. % Nickel 30-38 wt. % Cobalt 0-6.0 wt. % Silicon 0.05-0.3 wt. % Aluminum 0.05-0.75 wt. % Copper 0-0.1 wt. % Manganese 0.3-0.6 wt. % Carbon 0-0.07 wt. % Sulfur 0.005-0.03 wt. % Chromium 0.01-1.5 wt. % Zirconium 0-1.5 wt. % Titanium 0-2.0 wt. % Iron balance

(32) In yet another embodiment, the nickel-iron alloy has the following composition:

(33) TABLE-US-00005 Elements Wt. % Nickel 31-37 wt. % Cobalt 0-5.75 wt. % Silicon 0.07-0.28 wt. % Aluminum 0.06-0.6 wt. % Copper 0-0.09 wt. % Manganese 0.35-0.55 wt. % Carbon 0-0.06 wt. % Sulfur 0.01-0.02 wt. % Chromium 0.02-1.3 wt. % Zirconium 0-1.0 wt. % Titanium 0-1.0 wt. % Iron balance

(34) In yet another embodiment, the nickel-iron alloy has the following composition:

(35) TABLE-US-00006 Elements Wt. % Nickel 36 wt. % Silicon 0.25 wt. % Aluminum 0.3 wt. % Manganese 0.5 wt. % Sulfur 0.02 wt. % Chromium 0.7 wt. % Zirconium 0.8 wt. % Titanium 0.5 wt. % Iron balance

(36) In yet another embodiment, the nickel-iron alloy has the following composition:

(37) TABLE-US-00007 Elements Wt. % Nickel 36 wt. % Silicon 0.25 wt. % Aluminum 0.5 wt. % Manganese 0.5 wt. % Sulfur 0.02 wt. % Chromium 0.8 wt. % Iron balance

(38) In other embodiments, an optional pre-treatment step can be done prior to the ion nitriding to increase the amount of aluminum in the surface area of the mold tool. In this embodiment, the mold tool 20 can undergo aluminization prior to ion nitriding. Aluminizing is well known and as such will only be generally described here. Generally, aluminizing is a high temperature chemical process whereby aluminum vapors diffuse into the surface of the base metal forming new metallurgical aluminized alloys. The aluminide alloys formed at the surface can contain up to 20% aluminum. Also, aluminizing can be performed by hot dipping. While the tool may be aluminized in any suitable manner, in one embodiment, the tool is exposed to vapor diffusion of aluminum on the surface of the tool. With the amount of available aluminum for nitriding increased via the aluminum process, the resulting ion nitrided tool 20 will have a higher surface hardness than those similarity treated but having lesser amounts of aluminum. In these embodiments, the surface harness will be 500 to 2,000 HK and in other embodiments 600 to 1,500 HK and in yet other embodiments 700 to 1,000 HK.

(39) Referring to FIG. 3, a tool 30 is provided having a coating. This embodiment differs from the embodiment described and illustrated with respect to FIG. 2 in that the tool 30 is not surface treated but instead has a surface coating 34 deposited on top of the upper mold surface to create a new top surface of the tool. For instance, the characteristics of the body 32 in FIG. 3 is similar to that of body 22 in FIG. 2. Typically, when the surface coating 34 is provided, the grain 36 will be deeper than those in which the surface is case hardened or diffusion hardened. In this instance, the surface grain texture may be at least 200 microns. In the embodiment illustrated in FIG. 3, the coating 34 has a thickness of 0.1 to 25 microns, and in other embodiments 0.5 to 12 microns, and in other embodiments 1 to 5 microns and in yet other embodiments of 3 to 4 microns. While the molding tool 30 can have any suitable thickness, in certain embodiments the mold tool 30 will have an average thickness of 3 to 10 mm and in other embodiments of 3.5 to 4.5 mm with the body portion 32 comprising the majority of the thickness. In one embodiment, the molding tool 30 has a substantially uniform thickness, wherein uniform means that no portion of the tool has a thickness that varies by more than 0.1 mm from any other portion of the tool.

(40) The coating 34 can be any suitable coating and provided in any suitable manner such that the resulting coating has a microhardness of 350 to 9,000 HK, in yet other embodiments 500 to 4,000 HK, in yet other embodiments 600 to 2,000 HK, and in yet other embodiments 700 to 1,500 HK. The coatings 34 can be provided in any suitable process such as electroplating, electroless plating, physical vapor deposition (PVD), or chemical vapor deposition (CVD). While any suitable coating can be provided, examples of suitable coatings include aluminum nitride, zirconium nitride, silicon nitride, titanium nitride and chromium nitride. The surface coatings 34 can also be in addition to metal, ceramic or high temperature polymers or combinations of these coatings. Metallic and ceramic coatings containing nickel, chromium, titanium, aluminum and other metals and alloys can be used to protect and seal the shell as well as improved mold release properties. Certain coatings, such as electroplating, range in thickness from 1 to 500 microns, in other embodiments from 5 to 200 microns, and in yet other embodiments 10 to 100 microns.

(41) Referring to FIG. 4A, a mold tool 40 is provided comprising a shell 42 having a schematically illustrated reinforcing element 52 and generally rectangular shaped heating/cooling elements cut or cast therein as schematically illustrated by 48. However, it should be understood that heating/cooling elements 48 can have any suitable shape.

(42) Referring to FIG. 4B, a mold tool 41, similar to that shown and described with respect to FIG. 1, is provided. The mold tool 41 comprises a shell 43 having generally circular shaped heating/cooling elements cut or cast therein as schematically illustrated by 49. However, it should be understood that heating/cooling elements 49 can have any suitable shape.

(43) Elements for controlling temperatures such as channel, grooves and fins for heating and cooling can be incorporated into the mold either during the forming process by casting them in (FIG. 4B) or after the mold has been formed by machining, welding, soldering, or brazing them to the back of the shell (FIG. 4A) to improve efficiency.

(44) Referring to FIG. 5, an embodiment for making the molding tool is illustrated. A mass of iron nickel alloy 60 is provided. The alloy can then be machined or cast to shape 70. While any suitable shaping technique can be used, two suitable techniques are CNC cutting and electrical discharge machining (EDM). CNC cutting is well known and generally comprises cutting the metal to the desired shape and geometry. CNC EDM is also well known, and generally comprises removing metal by burning it away with electrical discharge.

(45) Another technique for making the molding tool is to cast the material to a near net shape. After casting, CNC machining can be used to further modify the shape of the tool to the desired geometry and size. After the tool has been shaped, the tool may undergo an optional annealing step 72. After optional annealing, the CTE of the material will be stabilized or improved.

(46) Lastly, the tool has grain provided on the upper mold surface. The graining can be provided in any suitable manner such as by acid etching, laser etching, or mechanical etching. The graining will typically have a depth of 5 to 1,000 microns, in other embodiments of 50 to 600 microns, and in yet other embodiments of 100 to 400 microns.

(47) Referring to FIG. 6, after the tool 10 has been formed, the tool can undergo surface treatment as discussed above wherein the surface is either nitrided or aluminized and then nitrided.

(48) Referring to FIG. 7, the tool 10 after being manufactured can then be coated as described above.

(49) While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.