Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
1999-10-12
2001-07-10
Beck, Shrive (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S140000, C427S405000, C427S456000, C219S076100, C219S076120, C219S076140, C228S119000, C228S208000, C228S261000
Reexamination Certificate
active
06258402
ABSTRACT:
BACKGROUND OF THE INVENTION
Co-pending application entitled “Method For Repairing Steel Spray-Formed Tooling With TIG Welding Process” by Pergande and Hussary having Ser. No. 09/415,974 is filed together herewith and assigned to the same assignee.
FIELD OF THE INVENTION
This invention relates in general to spray-formed steel tooling produced by thermal spray processes and more particularly to a method for repairing of such spray-formed steel tooling.
DESCRIPTION OF THE RELATED ARTS
Spray-formed tooling is fabricated by first creating a pattern of the desired tool using a free form fabrication technique. The pattern is then used to create a ceramic mold that is the inverse of the tool to be produced. The resulting ceramic mold is the receptor into which metal is sprayed to form a deposit in the shape of the desired tool.
At least one spray forming process is wire-arc spraying. In wire-arc spraying, electric current is carried by two electrically conductive, consumable wires with an electric arc forming between the wire tips. A high-velocity gas jet blowing from behind the moving wires strips away the molten metal that continuously forms as the wires are melted by the electric arc. The high-velocity gas jet breaks up or atomizes the molten metal into finer particles in order to create a fine distribution of molten metal droplets. The atomizing gas then accelerates the particles away from the electrode tips to the substrate surface where the molten particles impact the substrate to incrementally form a deposit in the shape of the tool.
The completed tool is then mounted and used to produce parts just like any other stamping, die casting, or molding process. There is concern about fatigue life because the porosity of the tool produced is five percent or more, but preliminary estimates of the fatigue life of these parts under load is 10,000 or more cycles which is acceptable for prototype tool applications.
Spray-forming of steel is used for rapid production of prototype and production steel tooling at considerable cost savings over the conventional production by machining and heat treatment of steel tooling for such applications as injection molding and stamping. Typically small sets of prototype permanent tooling can take from four to five months to fabricate, while large prototype tooling can take up to one year to fabricate. Spray-formed steel tooling has been produced in one month at costs substantially less than for permanent tooling.
Such spray-formed steel prototype tooling however, has a limited lifetime than its conventional machined steel counterpart, due, in part to the more granular nature of the thermally-sprayed steel, and generally lower overall strength of the sprayed material. Thus, spray-formed steel tooling may be expected to incur a greater need for repair during its useful lifetime and subsequent extension of lifetime through advanced surface repair processes. Typical tool repair involves arc welding new material on the tool, then machining and polishing the material to match the tool. However, the non-homogeneous nature of thermal spray-formed steel does not allow for the practice of common welding techniques used on tool steel unless the thermal spray-formed steel is heated to approximately 200° C. before welding and then cooled slowly to reduce cracking.
U.S. Pat. No. 5,302,414 entitled “Gas-Dynamic Spraying Method for Applying A Coating” was issued to Alkhimov et al. on Apr. 12, 1994. The method introduces particles of a powder into a gas. The particles are a metal, alloy, or a polymer. The gas and the particles are formed into a supersonic jet having a temperature low enough to prevent thermal softening of the particles. The jet is directed against an article of another material such as a metal, alloy or dielectric where the particles coat the article.
SUMMARY OF THE INVENTION
It is a principle advantage of the present invention to repair spray-formed steel tooling economically and without the need for highly experienced welding personnel.
It is another advantage of the present invention to be able to weld spray-formed steel tooling by conventional welding processes.
It is yet another advantage to avoid any gas release during repair from the spray-formed steel tooling that operates to weaken the repair.
These and other advantages are inherent in the following method for repairing thermal spray-formed tooling such as die pieces. The method has the steps of first cleaning the surface area to be repaired of dirt and impurities. Once the surface area is cleaned, it is then prepared to accept cold-gas spray coatings. Once the surface is cleaned and prepared, an intervening layer of low-carbon steel is deposited onto the repair surface by the process of cold spraying or cold gas-dynamic spraying to a predetermined thickness on the surface area to be repaired. Once the surface has a finite layer of cold-sprayed steel on the surface, a weldment is deposited on the surface by an electric welding process and the weldment is then finished to the desired surface by conventional machining, grinding and polishing.
REFERENCES:
patent: 5201455 (1993-04-01), Reynolds, Jr. et al.
patent: 5302414 (1994-04-01), Alkhimov et al.
patent: 5571431 (1996-11-01), Lantieri et al.
patent: 5831241 (1998-11-01), Amos
patent: 5915743 (1999-06-01), Palma
patent: 5956845 (1999-09-01), Arnold
A method of “cold” gas-dynamic deposition. Authors A.P. Alkhimov, V.V. Kosarev, and A.N. Papyrin; Dec. 1990; Sov. Phys. Doki 35(12).
Hussary Nakhleh
McCune Robert Corbly
Pergande Paul Earl
Beck Shrive
Kolb Jennifer
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