Laser beam stop sensor and method for automatically detecting the presence of laser beam stop material using a laser beam stop sensor

#The present invention is related generally to laser machines used for welding and machining of articles, and specifically to device that assures protection for portions of an article adjacent to the work area, such as a turbine airfoil, undergoing an operation by a laser machine from damage as a result of the by-products of the operation or from malfunction of the laser machine and a method for assuring that portions of the article are protected prior to and during an operation.

#Laser machines are commonly used for welding and machining of articles. In the modem manufacturing environment, this equipment is used with increasing frequency in situations in which precision is required and speed is important. This equipment can be used to lower costs by increasing output while reducing rates of scrap.

#These laser machines are increasingly used for manufacturing operations in which large numbers of identical parts must be made with great precision, and the costs of the materials for such parts is high, so that scrappage of the parts is undesirable. Because of the repetitive nature of these precision operations, these laser machines typically include well-known controllers that can be programmed to perform a series of operations with minimum input by the operator. One area in which these laser machines have found use is in the manufacture of airfoils for gas turbine engines. These airfoils are expensive, intricate articles that usually are manufactured to near final form by investment casting. Not only is the casting process expensive, but the airfoils can be made of expensive super alloy material or titanium alloy material. However, because of the intricacy of these airfoils, it is not possible for the investment casting operations to always provide a finished product. For example, it may be necessary to drill fine holes through the airfoils, or to provide a fluid connection from a passageway manufactured into the airfoil by the investment casting process to the airfoil surface. Alternatively, it may be necessary to add a different material to the airfoil surface. This cannot be accomplished by casting, but can readily be accomplished by laser welding. It may also be desirable to refurbish an airfoil removed from service or damaged during a manufacturing operation by repair welding. This can be accomplished using the same material as the base material, or material different than the original base material.

#Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

#FIG. 1 is a front elevation view of the present invention, showing the spatial relationship among the laser nozzle, the workpiece, the fixture, the beam stop material and the sensor of the present invention, with the sensor engaged;

#FIG. 2 is top view of the beam stop material in position adjacent to predetermined work areas of a work piece, but not located in the fixture;

#Whenever possible, the same reference numbers will be used throughout the figures to refer to the same parts.

#The present invention is directed to a method for preventing a laser machine from performing operations on a workpiece unless a suitable beam stop material is in place in areas adjacent to the locations at which the preselected operations are to be performed. The method finds particular use in turbine airfoil manufacturing, in which the expensive workpiece is in the form of a turbine airfoil. The method and the apparatus of the present invention improve upon the current methods of protecting areas adjacent to the locations where laser operations are performed. Currently, protection of these areas is dependent upon operator diligence for proper placement and location of the beam stop material.

#Beam stop material can be any suitable material that can be used to absorb sufficient energy from the laser beam so as to render the laser beam ineffective as an energy source capable of performing an operation on a workpiece. As the laser beam is directed onto a workpiece, the laser beam strikes the workpiece to accomplish a specific work operation. This work operation may be a welding operation or a metal removal operation, such as a hole drilling operation or a trimming operation. However, during welding operations, a laser beam or a portion of a laser beam can reflect from the surface of the workpiece onto an adjacent area next to the area undergoing the operation with sufficient energy to cause collateral damage to the adjacent area. While these reflections can also occur during metal removal operations, a more prevalent problem is back wall burn, previously discussed. Beam stop materials are well known in the art, and are used in the adjacent areas subject to collateral damage to absorb laser energy. Different beam stop materials are used for different types of laser beams. Beam stop materials may also vary from one workpiece to the another, as more energy may be required to remove sufficient energy from a laser beam, or reflections of a laser beam, to prevent damage to a workpiece made of one type of material than from a workpiece made of a different type of material. While the primary purpose of the beam stop material is to prevent back wall strikes and to absorb reflections from the laser beam, or at least sufficient amounts of energy so as to render the reflected beam ineffective, the beam stop material provides the added advantage of protecting the surfaces adjacent to the preselected locations at which preselected operations are to be performed from molten material spattered or ejected from the location undergoing the laser operations. Beam stop materials may be held in place by the workpiece, or may be made in such a manner so as to be assembled to the workpiece and be held in place on the workpiece. However, the diligence of the operator in placing and removing the beam stop material is still required.