Method of controlling distortion during material additive applications

The present application claims priority to U.S. Provisional Patent Application No. 62/135,893 filed on Mar. 20, 2015, the contents of which are included herein by reference.

The present application relates towards a method of direct material deposition onto a workpiece. More specifically, the present application relates toward a method of performing direct metal deposition upon thin walled sections of the workpiece.

Direct material deposition such as, for example, direct metal deposition is gaining broader acceptance as an approved manufacturing method for creating complex three-dimensional structures. Typically, an energy beam known to provide a sufficient amount of heat energy is infused with a powder metal alloy, causing the alloy to become molten at which time the alloy is deposited upon the workpiece. In addition, the energy beam creates a melt pool of molten workpiece substrate material into which the infused powder metal alloy is joined. While this process has proven technically feasible and commercially viable for many applications, its use has been limited due to temperature differential of the workpiece upon creation of a melt pool.

For example, one application for direct material deposition that has not been feasible is material deposition upon a thin wall or thin metal member of a larger workpiece. In this situation, the thin metal is known to warp while cooling during and/or after the deposition process. As such, necessary dimensional accuracy and stability has proven elusive. Therefore, there is a strong need to develop a process of direct material deposition upon thin walled members, and the like, where dimensional stability is maintained both while generating the melt pool and cooling the workpiece after deposition.

A method of performing material deposition on a thin wall element of a workpiece is disclosed. A source of heat energy and a source of material while performing a material additive process upon the thin wall member of the workpiece is provided. A fixture is located relative to the thin wall element. A source of heat energy is used to form a joining member between the workpiece and the fixture to fixedly secure the fixture to the workpiece. The fixture prevents the thin wall member from deforming when subject to the heat energy and when cooling. A material additive process is performed upon a thin wall member, adding material to the thin wall member to enhance material characteristics of the thin wall member. The joining member is mechanically removed from the workpiece after the workpiece cools. The portion of the material added to the thin wall member is also mechanically removed to achieve a predetermined dimensional configuration.

Fixedly securing the fixture to the workpiece relative to the thin wall member of the workpiece ensures dimensional stability beyond that of merely using a fixture. Therefore, a melt pool can be generated upon the thin wall member and material added from material deposition process providing dimensional and material enhancements to the thin wall member. For example, a more durable material having desirable physical properties can now be deposited upon the thin wall member. The fixture prevents the thin wall member from warping even if the rate of the expansion and contraction of the deposited material differs from that of the substrate definite the substrate and the thin wall member because the joining member prevents differing rates of expansion and contraction resulting from the direct material deposition.

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detail description when considered in connection with the accompanied drawings, wherein:

FIG. 1 shows a process of direct material deposition onto a substrate;

FIG. 2 shows a flowchart of the method of the present invention;

FIG. 3 shows a fixture being located relative to a thin wall member of a workpiece;

FIG. 4 shows an energy beam applying stitching to a seam of a workpiece and a fixture;

FIG. 5 shows direct material deposition onto the thin wall member of a workpiece; and

FIG. 6 shows a dimensionally accurate thin wall member of a workpiece reinforced with a layer of direct material deposition.

Referring to FIG. 1 , a direct material deposition onto a substrate is generally shown at 10 . A nozzle 12 of the type disclosed in U.S. Pat. No. 6,423,926, the contents of which are incorporated herein by reference, is used for the direct material deposition onto a workpiece 14 . The nozzle focuses a laser beam 16 generated by a laser 18 onto the workpiece 14 to generate a melt pool 20 . It should be understood that any energy beam that generates heat energy in addition to a laser 16 , including but not limited to an electron beam, a gas tungsten arc, a plasma transfer arc, or equivalents is included within the scope of this invention. Therefore, although a laser beam 16 will be referred to throughout this application each of these energy beams is included as alternative embodiments.

The nozzle 12 infuses powdered material 22 into the laser beam 16 toward the melt pool 20 . The powdered material 22 includes metal alloys, combinations of different metal alloys, ceramics, and any other material that provides enhanced physical characteristics onto a workpiece 14 at desired locations. Therefore, the powdered material 22 becomes molten at a laser beam 16 upon contact with the melt pool 20 , fusing with the substrate defining a workpiece 14 and forming a direct material deposition (DMD) bead 24 upon the workpiece 14 . It should be understood by those of ordinary skill in the art that multiple passes of the nozzle 12 over a DMD bead 24 is within the scope of this invention such as, for example, disclosed in U.S. Pat. No. 6,925,346, the contents of which are included herein by reference. However, for clarity, description of multiple passes of the nozzle 12 will not be discussed further herein.

Following the flowchart set forth in FIG. 2 , and referring now to FIG. 3 , the inventive method of the present application will now be discussed further. In this embodiment, the workpiece 14 defines a thin wall member 26 , previously performing DMD upon a thin wall member 26 of the workpiece has not been feasible, because generating a melt pool upon a thin wall member 26 in subsequent cooling caused warpage of the thin wall member 26 beyond that which is desirable of a workpiece 24 requiring dimensional accuracy. To prevent warpage, a fixture 28 is located relative to the thin wall member 26 .

In this embodiment, the thin wall member 26 includes a first element 30 extending away from the workpiece 14 and a second element 32 extending in a generally lateral direction from the first element 30 . The fixture 28 is configured to provide a net or near net engagement between an upper surface 34 of the workpiece 14 , the first element 30 and the second element 32 . While this configuration is only one example, it should be understood by those of skill in the art that the fixture is designed to provide a net or near net engagement with the thin wall member 26 to prevent the thin wall member 26 from migrating from its design intent as will be explained further herein below.

Referring to FIG. 4 , a joining member 36 is formed between the workpiece 14 and the fixture 28 by the nozzle 12 . In this embodiment, the joining member 36 bridges a seam 38 defined between the thin wall member 26 and the fixture 28 for fixedly securing the fixture 28 to the workpiece 14 . The nozzle 12 directs the energy beam 16 , in this non-limiting embodiment, a laser, to form a plurality of stitches formed from the powdered material 22 . Each stitch 40 bridges the seam 38 defined between the thin wall member 26 and the fixture 28 . However, it should be understood by those of ordinary skill in the art that some or all of the stitches 40 may also bridge an alternative seam defined between the workpiece 14 and fixture 28 .

Once the fixture 28 has been secured to the workpiece 14 in a manner that maintains the net or near net shape of the thin wall member 26 , the DMD process is performed upon the thin wall member 26 as represented in FIG. 5 . As such, powdered material 22 is directed by the nozzle 12 into the energy beam 16 and melt pool 20 formed on the thin wall member 26 . As a result, the DMD bead 24 is formed upon the thin wall member 26 , optionally with a build-up of material thickness to substrate thickness ratio of 0.4 to 0.5. It can be appreciated that the DMD process performed upon the thin wall member 26 softens the thin wall member as a result of the formation of a melt pool 20 . Therefore, absent the fixture 28 , the thin wall member 26 is likely to become deformed from its net or near net disposition. It should be further appreciated that multiple passes of the nozzle 12 providing a plurality of layers of DMD bead 24 is within the scope of this invention, which is likely to cause various temperature gradients to occur between the thin wall member 26 and the plurality of layers of DMD bead 24 . This is most likely to occur upon cooling and solidifying of the DMD bead 24 .

It is further within the scope of this invention that the material used to “stitch” the fixture 28 to the workpiece 14 be different than that used to deposit the DMD bead 24 . For example, the DMD bead 24 may require deposition of expensive or exotic alloys, including ceramics or other non-metallic content not required to achieve desirable performance characteristics. Because the joining member 26 is only temporary, the material used to form the joining member 26 need not be expensive or exotic. The material need only withstand radiant heat generated by the energy beam 16 or dissipating from the melt pool 20 through the thin wall member 26 . Thus, a lower cost material is selectable for forming the joining member 26 .

It is further contemplated by the inventors that the ratio between spacing of adjacent stitches 40 and length of the DMD bead 24 along the thin wall member 26 is between about 0.003 and 0.006. It is believed that the spacing provides optimal resistance to deformation of the thin wall member 26 during the DMD process and subsequent cooling step.

Once sufficiently cooled, the DMD bead 24 is subject to mechanical reshaping such as, for example, machining to reshape the DMD bead 24 to a support element 42 as best represented in FIG. 6 . As set forth above, the support element 42 includes different and beneficial mechanical properties to that of the substrate defining the thin wall member 26 . During the machining step, the stitches 40 are mechanically removed simultaneously with forming the support element 42 . In the inventive method set forth above, the thin wall member retains its intended dimensional configuration while providing beneficial DMD mechanical properties to enhance the performance of the workpiece 14 .

It is further contemplated by the inventors that the fixture 28 provides additional benefits to that of maintaining the thin wall member 26 at its net or near net disposition. For example, the fixture 28 can provide accelerated cooling of the thin wall member 26 and the DMD bead 24 to reduce manufacturing cycle time. This is achievable by either selecting rapid cooling materials to form the fixture 28 , or design features that further increase the rate of cooling by the fixture 28 of the thin wall member 26 and DMD bead 24 . Alternatively, the fixture 28 can be designed to slow the cooling process of the thin wall member 26 to reduce a possible propensity to warp.

The invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention as possible in light of the above teachings. The invention can be practiced otherwise then as specifically described within the scope of the appended claims period.