Patent Application
20070068648
The present invention relates to the repair of die-cast dies, and more particularly, to methods of using amorphous alloys to repair die-cast dies and/or injection molds.
Die-cast dies have been widely used to manufacture a variety of machine parts. For example, automobile parts, such as transmission housings, are typically cast from die-cast dies. Generally, these types of dies are made of a tool steel, such as H-13 tool steel, or comparable material, and are used in a number of casting operations.
Over time, the die-cast die may become worn from repeated exposure to mechanical erosion and/or chemical attack. Additionally, the die cast-die may experience physical and thermal stresses, which may cause surface cracking. Consequently, the die-cast die may need to undergo a repair process to restore its original configuration and dimension, and to improve its metallurgical integrity.
Several die-cast die repair techniques exist. For example, Tungsten-Inert-Gas (“TIG”) welding and Plasma-Arc welding (“PAW”) techniques have conventionally been used to repair die-cast dies. However, these conventional welding repair processes typically expose the die-cast dies to high temperatures, which may cause the dies to crack in and/or near repaired areas or to be distorted. Additionally, a large area of the dies under welding zone may be unnecessarily exposed to the heat. Thus, die-cast dies that have been repaired using conventional welding techniques may not retain their original functionality and may need to be serviced more often after repair.
Hence, there is an ongoing need to provide improved methods for repairing die-cast dies. It is desirable for the method to be compatible with existing manufacturing methods and to be relatively inexpensive to perform. It is also desirable for the repair method to have cost and performance advantages over existing repair methods and over the option of replacing worn parts with new ones. The present invention addresses one or more of these needs.
Methods are provided for repairing a worn surface of a steel die-cast die. In one embodiment, and by way of example only, the method comprises depositing an amorphous material onto the worn surface, where the amorphous material formulated to form an amorphous layer after being heated to a predetermined temperature and cooled. The method also includes heating the amorphous material to the predetermined temperature with a laser beam to form a repair layer of the amorphous alloy over the worn surface. Additionally, the method includes allowing the heated amorphous material to solidify to thereby form the amorphous layer.
In another embodiment, and by way of example only, the method includes heating a solid amorphous material with a laser beam to a predetermined temperature to form a liquid, where the amorphous material formulated to form an amorphous layer after being heated to the predetermined temperature and cooled. Additionally, the method includes the step of depositing the amorphous material onto the worn surface to form a repair layer of the amorphous layer thereover. The method also includes allowing the liquid to cool to form the amorphous layer.
In still another embodiment, and by way of example only, a die-cast die having a repaired area is provided. The die-cast die includes a matrix layer comprising steel and a repair layer disposed over the matrix layer, wherein the repair layer comprises an amorphous alloy.
Other independent features and advantages of the method for repairing die cast dies will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Referring now to
In some cases, the workpiece has a surface that is corroded or eroded, and includes an impurity buildup or other contamination that may interfere with laser welding. Thus, the workpiece is preprocessed and prepared for welding repair thereon, step 204. In one exemplary embodiment, the work piece is machined and degreased to remove the contamination. In another example, the workpiece is grit blasted with an abrasive material such as aluminum oxide.
The repair layer 104 is then formed, step 206. In one exemplary embodiment of step 206, the repair layer 104 is formed by depositing amorphous material over the worn surface. The amorphous material is heated using a laser-welding process and transformed into an amorphous layer. It will be appreciated that any one of numerous materials may be used that are suitably formulated to produce an amorphous layer which can better withstand environments in which die-cast dies typically operate than materials previously used to repair dies. The amorphous material may be a powder, or any other form suitable for use in a laser welding technique. In an example in which the amorphous material is a powder, the powder material is laser deposited onto the worn surface. In another exemplary embodiment of step 206, the repair layer 104 is formed by heating a solid amorphous material into a liquid using a laser beam and forming the amorphous layer onto the worn surface after cooling.
In any case, the amorphous material is preferably selected to yield an amorphous layer having a relatively high hardness, high wear resistance and high corrosion resistance. For example, the amorphous layer preferably has a Rockwell hardness value of between about Rc 65 to about Rc 73. In another example, the amorphous alloy is preferably more resistant to wear than polycrystalline materials, due to high hardness and fine boride distributions. In still another example, the amorphous alloy is more resistant to corrosion than polycrystalline materials, due to an absence of grain boundaries. Examples of suitable materials include LMC-C and LMC-M both available from Liquidmetal Technologies of Lake Forest, Calif. More preferably, the chemical compositions of the preferred amorphous layer by weight percent includes between about 40 and about 50% of chromium, between about 5% and about 7% of boron, between about 1% and about 3% of silicon, up to about 1% of carbon, and balance iron.
Next, the amorphous material is laser-welded and transformed into an amorphous alloy. It will be appreciated that one of various types of lasers suitable for welding may be used, such as, for example, a welding torch described in U.S. Pat. No. 6,593,540, which is commonly assigned to the assignee of the present invention, Honeywell International, Inc., an Yttrium Aluminum Garnet (YAG) laser that includes a doping material, such as Neodymium (Nd), or a direct diode, a fiber, or a CO2 laser generator.
During laser welding, the laser preferably has a power output of about 50 watts or higher. The laser beam is directed onto the amorphous material and energy from the laser beam melts the material. It will be appreciated that welding parameters, such as laser power output, powder feed rate, traverse speed and shield gas flow rate, and the like may be manipulated to eliminate or minimize hot cracking on the workpiece. After the melted material cools, it solidifies to form an amorphous layer having a Rockwell hardness of between approximately Rc 65 and Rc 73.
It will be appreciated that step 206 may be repeated several times to achieve a desired thickness and dimension of the repair layer 104, or to cover a desired surface area. After the repair layer 104 is formed, the repair area may be machined to restore original contour and dimension of the repaired workpiece 100, step 208. Any one of various conventional machining techniques may be used. One suitable technique includes a CNC controlled milling and/or grinding process that is used to machine the workpiece or surface of the workpiece to a desired dimension or contour.
Optionally, the repaired workpiece may be heat treated, step 210. In one exemplary embodiment, the heat treatment is performed below the re-crystallization temperature to relieve welding stress while avoiding crystal growth. In another exemplary embodiment, the repaired workpiece is heat treated at a temperature of between approximately 800 to approximately 1400 degrees F. for about 1 hour. Subsequently, the repaired workpiece may be inspected, for example, by an FPI (fluorescent penetration inspection), to determine whether it can be returned to service, step 212.
There has now been provided a method for repairing a die-cast die that substantially eliminates cracking, reduces part distortion, and minimizes the area of a heat-affected zone of the dies by using a laser welding process. In the laser welding process, the laser power output and welding parameters such as beam spot size, powder feed rate, traverse speed and shield gas flow rate, and the like are controlled. Also, the amorphous layer provides excellent wear-resistance, while maintaining bulk hardness at a level sufficient to provide a tough support structure. This allows the welded material to withstand repeated thermal cycling without spallation and prolongs the service lives of the repaired die-cast dies thereof.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
