Laser fillet welding

A metal article and a method for welding the metal parts to form the metal article, where the method comprises feeding filler material to an intersection of the metal parts, and melting the filler material with a laser beam to form a weld between the metal parts at the intersection.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority of Singapore Patent Application No. 200608084-0, filed on Nov. 21, 2006, and entitled “LASER FILLET WELDING”.

BACKGROUND OF THE INVENTION

The present invention relates to methods for welding. In particular, the present invention relates to methods of welding metal parts, such as parts for aerospace and aviation applications, with the use of laser welding techniques.

In gas turbine engines, it is important to cool the turbine airfoils to preserve the integrity of the airfoil structure and also to attain high engine performance by operating the turbine at optimum temperature levels. It is also important to avoid utilizing more cooling air than is necessary to minimize the overall penalty that occurs with the use of engine air for purposes other than generating thrust or horsepower.

One method of optimizing the use of cooling air is to employ meter plates to restrict the flow entering into the blade roots of each of the airfoils. Meter plates are typically secured to the blade roots of the airfoils with laser seam welding operations. To ensure that the meter plates remain secured to the blade roots during engine operation, the welds between each meter plate and blade root are required to have a minimum weld leg length. However, with laser seam welding, increasing the weld leg length correspondingly increases the weld penetration depth. This undesirably extends the heat-affected zone of the weld, which may form porous regions and cracks in the weld. Additionally, laser seam welds are difficult to visually evaluate if the meter plate is properly welded to the blade root. As such, there is a need for a welding process that provides good welds between metal parts (e.g., meter plates and blade roots), which are also easy to inspect.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a welded metal article and a method for welding metal parts to form the welded metal article. The method includes forming an intersection between a first metal part and a second metal part, feeding filler material to the intersection, and melting the filler material with a laser beam. This allows the melted filler material to fuse to the first metal part and the second metal part to form a weld at the intersection.

DETAILED DESCRIPTION

FIG. 1is a flow diagram of method10for welding first and second metal parts with a laser fillet welding operation. As shown, method10includes steps12-18, and initially involves forming a corner intersection between at least two overlapping metal parts (step12). This is performed by positioning a first metal part having an edge portion (e.g., a meter plate) on top of a surface of a second metal part (e.g., a blade root) such that the first metal part is flush with the surface of the second metal part. This forms a corner intersection between the edge portion of the first metal part and the surface of the second metal part. The corner intersection may extend around the entire perimeter of the first metal part or around a portion of the perimeter of the first metal part. Prior to laser welding, the first metal part may be manually resistance tack welded to the second metal part using standard techniques to ensure proper contact between the metal parts.

A laser beam is then generated and positioned such that it focuses at the corner intersection (i.e., a focal point of the laser beam is located at the corner intersection) (step14). Filler material is then fed to the corner intersection such that the laser beam focuses on, or adjacent to, the filler material (step16). The filler material is a supply of a metal material used to fuse the edge portion of the first metal part to the surface of the second metal part. The filler material may be supplied in a variety of media, such as powders, granules, wire stock, and rod stock. Suitable materials for the filler material and for the metal parts include laser-weldable metals, such as aluminum, steel, iron, titanium, nickel, cobalt, and alloys thereof.

The laser beam is then used to laser weld the filler material and the metal parts (step18). The energy from the laser beam is absorbed by the filler material, which melts the filler material and allows the melted filler material to fuse to the edge portion of the first metal part and the surface of the second metal part. This forms a laser fillet weld at the corner intersection, thereby securing the metal parts together. The laser beam is then moved around the entire perimeter of the first metal part while filler material is continuously fed to the laser beam at the corner intersection. This forms a final welded structure where the first metal part is welded to the second metal part around the entire perimeter of the first metal part.

In one embodiment, the filler material is fed to the corner intersection through a nozzle of a laser system. In this embodiment, steps14-18of method10are performed in a substantially simultaneous manner. The laser beam melts the filler material as the filler material is continuously fed from the nozzle to the corner intersection. As the melted filler material is deposited at the corner intersection, the melted filler material fuses to the edge portion of the first metal part and the surface of the second metal part, thereby forming the laser fillet weld at the corner intersection.

Because a substantial amount of the energy of the laser beam is absorbed by the filler material, the depth of penetration of the weld into the surface of the second metal part is reduced. As a result, the heat-affected zone of the weld is correspondingly reduced, thereby reducing the formation of cracks and large porous regions in the weld. Furthermore, the resulting weld is easy to inspect for proper fusion along the weld path because the weld is located at the corner intersection of the metal parts. This is in contrast to laser seam welds, which are more difficult to inspect because the welds are located between metal parts rather than at a corner intersection. Accordingly, laser fillet welding the filler material at the corner intersection of the metal parts provides a secure weld that is suitable for use in a variety of application, such as aerospace and aviation applications. Examples of suitable applications for method10include meter plate/blade root welding operations, turbine vane cover installations, and other welding applications that are typically laser seam welded.

FIGS. 2-4illustrate a suitable application of method10for producing laser fillet welds with turbine airfoil components.FIG. 2is a bottom perspective view of blade root20, which is a turbine blade root that is insertable into a dovetail slot (not shown) of a supporting rotor disk (not shown). As shown, blade root20includes end wall22, inlet apertures24a-24c, meter plate26, lobed walls28, and front face30. End wall22is a wall segment extending at the base of lobed walls28and front face30. Inlet apertures24a-24care openings within blade root20for receiving cooling air during operation.

As further shown, meter plate26is disposed over end wall22and inlet aperture24b. When meter plate26is secured to end wall22, meter plate26extends over inlet aperture24bfor restricting the flow of air through inlet aperture24bduring operation. As discussed below, meter plate26is secured to end wall22with the laser fillet welding operation of method10(shown inFIG. 1). This secures meter plate26to end wall22with a laser fillet weld, which reduces penetration depths within end wall22, has a reduced heat-affected zone, and is easy to inspect.

While blade root20is shown with a single meter plate26being secured over inlet aperture24b, meter plates may also be secured over one or more inlet apertures (e.g., inlet apertures24aand24c) in a similar manner, and each meter plate may cover one or more inlet apertures. Additionally, while meter plate26is shown inFIG. 1as being secured to end wall22, a similar arrangement may be used with blade roots having inlet apertures in front face30. In this embodiment, meter plate26is secured to front face30with the laser fillet welding operation of method10, which correspondingly reduces penetration depths within front face30, has a reduced heat-affected zone, and is easy to inspect.

FIGS. 3 and 4are expanded side views of end wall22and meter plate26, which illustrate the laser fillet welding operation of method10(shown inFIG. 1).FIG. 3shows end wall22and meter plate26prior to welding, where meter plate26includes edge portion32. Pursuant to step12of method10, edge portion32is disposed on end wall22such that edge portion32forms corner intersection34with end wall22. While only a section of edge portion32is shown inFIG. 3, edge portion32extends around the entire perimeter of meter plate26.

Pursuant to step14of method10, laser beam36is generated from a laser system (not shown), and is positioned such that laser beam36focuses at corner intersection34. Examples of suitable laser systems for use with the present invention include solid-state laser systems and gas laser systems (e.g., Nd:YAG and CO2lasers).

Pursuant to step16of method10, filler material38is fed onto end wall22at corner intersection34, such that laser beam36focuses on filler material38. Depending on the intensity of laser beam36, laser beam36may focus on, or adjacent to, filler material38. As shown inFIG. 3, filler material38is fed to laser beam36in a continuous manner, where laser beam36melts filler material38as filler material38reaches corner intersection34. This may be performed with a laser system that includes a nozzle (not shown) for depositing filler material38. For example, filler material38may be fed through the nozzle of the laser system in a continuous manner. This allows laser beam36to melt filler material38as filler material38exits the nozzle.

The energy from laser beam36is absorbed by filler material38, which heats up and melts filler material38. The energy of laser beam36also results in localized melting of end wall22and edge portion32, thereby causing the molten metals of end wall22, edge portion32, and filler material38to mix and fuse together. Laser beam36is then moved around the entire perimeter of meter plate26, and filler material38is continuously fed to laser beam36, thereby forming a laser fillet weld around the entire perimeter of meter plate26.

FIG. 4shows end wall22and meter plate26after the laser fillet welding operation. As shown, end wall22and edge portion32of meter plate26are fused together at welded joint40. Welded joint40is a laser fillet weld that includes a fused agglomerate of metals from end wall22, edge portion32, and filler material38. This secures meter plate26to end wall22over inlet aperture24bfor restricting the flow of air through inlet aperture24bduring operation. As shown inFIG. 4, welded joint40has a weld leg length (referred to as leg length42) extending from edge portion32of meter plate26, and a penetration depth (referred to a penetration depth44) extending into end wall22.

Because a substantial amount of the energy of laser beam36(shown inFIG. 3) is absorbed by filler material38, penetration depth44of the welded joint40is reduced, even with large lengths for leg length42. This allows leg length42to be large to secure meter plate26to end wall22, while also reducing the heat-affected zone of welded joint40. Suitable lengths for leg length42range from about 500 micrometers (about 20 mils) to about 1,300 micrometers (about 50 mils). Suitable depths within end wall22for penetration depth32include less than about 25% of the length of leg length42, and particularly suitable depths includes less than about 10% of the length of leg length42.

As discussed above, reducing penetration depth44correspondingly reduces the heat-affected zone of welded joint40. Reducing the heat-affected zone of welded joint40reduces the formation of cracks and large porous regions in welded joint40, thereby increasing the strength and reliability of welded joint40. Furthermore, the welded joint40is easy to inspect for proper fusion along the weld path because welded joint40is located at corner intersection34of end wall22and edge portion32.

EXAMPLES

The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Welded joints of Example 1 and Comparative Example A were each formed at a corner intersection of a meter plate and an end wall of a blade root, which correspond to end wall22and meter plate26(shown inFIGS. 2-4). For the welded joint of Example 1, the blade root was restrained in a fixture mount and the meter plate was then positioned on a surface of the blade root to form a corner intersection. The meter plate was then manually tack welded to the blade root to maintain the meter plate's position and to ensure proper contact between the meter plate and the blade root.

Filler material (powdered PWA 1447 nickel-based alloy) was then deposited at the corner intersection, and a computer numerical controlled CO2laser system (Huffman model HC-205 from Huffman Corporation, Clover, S.C.) was then used to laser fillet weld the entire perimeter of the meter plate. As the laser beam was moved relative to the perimeter of the meter plate, the filler material was continuously fed to the laser beam, thereby forming a laser fillet welded joint around the perimeter of the meter plate.

FIG. 5is a macrograph of a section of the welded joint of Example 1, which corresponds to welded joint40(shown inFIG. 4). The reference numerals provided inFIG. 4are correspondingly used inFIG. 5for ease of discussion. End wall22, welded joint40, and edge portion32of meter plate26can be seen inFIG. 5. The dark portion46shown inFIG. 5is an epoxy mold that encased the sectioned welded joint40. As shown inFIG. 5, welded joint40does not penetrate very far below the surface of end wall22. In fact, penetration depth44of welded joint40is less than 10% of its weld leg length42from edge portion32of meter plate26.

As discussed above, a substantial amount of the energy of laser beam36is absorbed by filler material38, which reduces penetration depth44of welded joint40into end wall22of blade root20. This correspondingly reduces the heat-affected zone of welded joint40. This is evidenced inFIG. 5, where welded joint40is substantially free of cracks and large pores or voids. As such, the resulting welded joint40of Example 1 provides a strong weld between meter plate26and blade root20.

For the welded joint of Comparative Example A, the blade root was also restrained in a fixture mount, and the meter plate was then positioned on a surface of the blade root to form a corner intersection. The meter plate was then manually tack welded to the blade root to maintain the meter plate's position and to ensure proper contact between the meter plate and the blade root. A computer numerical controlled CO2laser system (Huffman model HC-205 from Huffman Corporation, Clover, S.C.), without filler material, was then used to laser seam weld the entire perimeter of the meter plate to the blade root, thereby forming a laser seam welded joint.

FIG. 6is a macrograph of a section of welded joint48of Comparative Example A, which secured end wall50of a blade root to edge portion52of meter plate54. End wall50and meter plate54correspond to end wall22and meter plate26(shown inFIG. 5). End wall50, welded joint48(substantially penetrating into end wall50), and edge portion52of meter plate54can be seen inFIG. 6. The dark portions56shown inFIG. 6are an epoxy mold that encased the sectioned welded joint48.

In contrast to the laser fillet welding operation of Example 1, the laser seam welding operation of Comparative Example A did not include filler material38. As such, the laser beam was positioned above edge portion52of meter plate54, thereby directly welding meter plate54to end wall50of the blade root. This caused welded joint48to penetrate substantially below the surface of end wall50. As shown, welded joint48had a penetration depth58that was almost as deep as its weld leg length60from edge portion52of meter plate54. This increased the heat-affected zone of welded joint48, causing cracks62and a large void64to form in welded joint48. Cracks62and void64accordingly reduced the strength of welded joint48of Comparative Example A.

A comparison of welded joints40and48(shown inFIGS. 5 and 6, respectively) illustrates the benefits of laser welding meter plate26to blade root20with the use of filler material38, where filler material38is fed to corner intersection34of meter plate26and blade root20. Accordingly, the laser fillet welding operation of the present invention provides secure welded joints (e.g., welded joint40) between metal parts that are strong and easy to inspect.