Patent Publication Number: US-H2285-H

Title: Automatic airfoil root prep machine and associated method

Description:
BACKGROUND 
     The present invention relates to an apparatus and method for preparing airfoil roots through polishing or cleaning. 
     In many situations it is desirable to polish or otherwise clean or prepare a workpiece. For example, in some applications, portions of airfoils for gas turbine engines are desired to be polished to remove oxidation to allow for electrical contact for a plating operation. In such situations, it is desired to remove oxidation to provide electrical contact at a bottom of a root of the airfoil. The plating operation can then be performed, such as for a Turbo Tip™ application where material is plated onto a tip of the airfoil to facilitate cut-in seal formation at the airfoil tip when installed in a gas turbine engine. 
     In the prior art, polishing operations were performed manually with an operator manually holding a blade root in contact with a rotating polishing brush. This manual process presents a number of ergonomic and safety concerns because the operator must perform repetitive tasks and place his or her hands near the rotating brush. Moreover, manual polishing can result in undesirable variation between polishing operations due to operator actions that are not identical for all polishing operations. 
     Thus, an improved method and apparatus for workpiece polishing or cleaning is desired. 
     SUMMARY 
     An apparatus for polishing an airfoil root according to the present invention includes a fixture for holding the airfoil, an actuation cylinder assembly for moving the fixture holding the airfoil, a brush, a motor for rotating the brush, a switch, and control circuitry. The actuation cylinder assembly is configured to move the fixture holding the airfoil toward the brush to trigger the switch, and the control circuitry is configured to run a timer when the switch is triggered to control contact between the airfoil and the brush for polishing. In another aspect, the present invention includes an associated polishing method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an airfoil polishing machine according to the present invention. 
         FIG. 2  is a perspective view of the machine of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram of an airfoil polishing machine  10 , and  FIG. 2  is a perspective view of the machine  10 . In the illustrated embodiment, the machine  10  includes a brush  12 , a motor  14 , a fixture  16 , an actuation cylinder  18 , a switch  20 , a control valve  22 , a limit switch  24 , control circuitry  26 , operator controls  28 , a hood  30 , a proximity sensor  32  and a vent system  34 . A workpiece  36  and an optional workpiece mask  38  can be engaged with the machine  10  for polishing, buffing, abrasive cleaning or other preparation procedures. As used herein, the term “polishing” is intended to encompass all polishing, buffing, abrasive cleaning or other similar procedures. 
     The brush  12  can be an abrasive polishing brush, such as a 10 inch (25.4 cm) outer diameter aluminum oxide grit wheel brush, available from Weiler Corp., Cresco, Pa. The particular characteristics of the brush  12  can vary as desired for particular applications. Moreover, in alternative embodiments, a polishing, buffing or cleaning implement other than a brush could be used. The motor  14  is used to rotate the brush  12 . In one embodiment, the motor is a 1 horsepower (746 watt) rotary buffer, available from Baldor Electric Co., Fort Smith, Ark. 
     The fixture  16  is used to movably hold the workpiece  36 . In the illustrated embodiment, the fixture  16  includes a workpiece holder slot  16 - 1  that can accept and retain the workpiece  36  (along with the mask  38 , if present) as well as a linear track  16 - 2  for guiding the workpiece along a linear path that extends toward the brush  12 . 
     The actuation cylinder  18  can be a fluidically-actuated cylinder that produces substantially linear actuation, such as a pneumatic cylinder or a hydraulic cylinder. Fluid can be supplied from a fluid supply  40  through a suitable control valve  22  to pressurize the actuation cylinder  18  to induce movement. The fluid supply  40  can be incorporated within the machine  10 , or can be an external supply such as a pneumatic shop air system connected to the control valve  22  and the actuation cylinder  18  through suitable conduits, hoses, pipes, etc. The fixture  16 , specifically the holder  16 - 1 , is engaged with the actuation cylinder  18  such that the actuation cylinder can move the fixture (carrying the workpiece  36 ) toward or away from the brush along the linear path. 
     The switch  20  is configured to sense when the fixture  16  has moved the workpiece  36  to a given point sufficient to bring the workpiece  36  into contact with the brush  12 . When the switch  20  is triggered, a timer is activated by the control circuitry  26  to regulate the cleaning operation. 
     The limit switch  24  is configured to detect excessive movement of the holder  16 - 1  of the fixture  16  toward the brush  12  beyond a given point. The limit switch  24  is generally located closer to the brush  12  than the switch  20 . Triggering (i.e., “faulting out”) the switch  24  can indicate that the brush  12  is worn or otherwise in need of replacement, or that a workpiece  36  is not present in the fixture  16 . Moreover, triggering the switch  24  can generate a suitable indication to an operator via the control circuitry  26  that action is needed. 
     The control circuitry  26  acts as the central control for most of the functions of the machine  10 . The control circuitry  26  can include suitable circuits, processors, memory and other subcomponents as necessary or desired for particular applications. The operator controls  28  are provided to allow an operator to activate and control the machine  10 . In one embodiment, the operator controls  28  include a pair of operator buttons, switches or other suitable controls for activating the machine  10  to perform a polishing operation, with the pair of operator controls configured as “dead man” switches such that all (i.e., both) must be triggered to activate the machine  10  to perform a polishing operation. In this way the operator controls  28  help ensure that an operator must place both hands at the controls  28  and away from the brush  12  during polishing, to promote operator safety. The operator controls can include other functionality, such as suitable indicators or displays as desired. 
     The hood  30  can cover portions of the machine  10  during operation for operator safety purposes and to help contain dust and debris. The hood  30  can be pivotal, to allow access inside when needed. When closed, the hood  30  can cover the brush  12 , the motor  14 , and at least portions of the fixture  16 , the workpiece  36  and the mask  38 . The hood  30  can include an opening  30 - 1  to allow the workpiece  36  to be inserted into the holder  16 - 1  of the fixture  16  with the hood  30  closed, and for the workpiece  36  and the fixture  16  to be moved toward the brush  12  during a polishing operation while the hood  30  remains closed. The proximity sensor  32  can be positioned adjacent to the hood  30  to detect when the hood  30  is open. An open hood condition can be indicated to the control circuitry  26 , and can prevent a polishing operation from beginning, that is, operations of the motor  14  and the actuation cylinder  18  can be prevented and actuation of the operator control  28  overridden. The vent system  34  can be operably connected to the hood  30  to evacuate dust and debris. 
     The machine  10  can be used with a variety of types of workpieces  36 . In one embodiment, the workpiece  36  is an airfoil for a gas turbine engine, and includes a root portion. The workpiece  36  can be made of a nickel-based superalloy or other materials. The machine  10  can be used to help remove oxidation from the workpiece, in particular to remove oxidation from a bottom portion of the root of an airfoil to allow for electrical contact at the root for a later plating operation. 
     In order to perform a polishing operation, an operator can first position the mask  38 , if used, on the workpiece  36 . The workpiece  36  and the mask  38  are then placed in the holder  16 - 1  of the fixture  16  (with the root facing toward the brush  12  if the workpiece  36  is an airfoil), which is initially in a “home” position spaced from the brush  12  and accessible from outside the hood  30 . The hood  30  is closed if it is open. The operator then triggers the operator controls  28  to initiate polishing—the operator should not be touching the workpiece  36  at this point. The control circuitry  26  responds to the operator input by rotating the brush  12  with the motor  14 . The actuation cylinder  18  moves the fixture  16  and the workpiece  36  toward the rotating brush  12  along the linear path. The workpiece  36  (i.e., the root of the airfoil) comes into contact with the rotating brush  12 , which can abrasively remove oxidation on the workpiece  36 . The actuation cylinder  18  advances the fixture  16  holding the actuation cylinder  18  the workpiece  36  toward the brush  12  at given pressure within the actuation cylinder  18 , such as approximately 14 psi (96.53 kPa). The pressure within the actuation cylinder  18  can correspond to a force of the brush  12  against the workpiece  36  of approximately 5-6 lbs (22.24-26.69 N) in some embodiments. When the actuation cylinder  18  moves the fixture  16  far enough the trigger the switch  20 , a timer is initiated by the control circuitry  26 . The control circuitry  26  governs operation of the actuation cylinder via the control valve  22 , and maintains contact between the workpiece  36  and the brush  12  for a given time period established by the timer, such as 1-2 seconds in one embodiment. In this way, movement of the holder  16 - 1  and the workpiece  36  toward the brush  12  is not to any particular fixed spatial location, but can correspond to a variety of spatial locations of the holder  16 - 1  and the workpiece  36  relative to the brush  12 . The actuation cylinder  18  will continue to advance the fixture  16  as long as pressure is supplied to do so, with the corresponding travel distance of the workpiece  36  able to vary depending upon factors such as the amount of wear of the brush  12 . The limit switch  24  detects excessive movement of the fixture  16  which can indicate that the brush  12  is worn and in need of replacement. After the given time period, during which polishing is accomplished due to abrasive contact between the brush  12  and the workpiece  36 , the control circuitry  26  caused the actuation cylinder  18  to move the fixture  16  and the workpiece  36  away from the brush  12  and back to the home position. The operator can then remove the polished workpiece  36 , and can optionally insert a new workpiece to begin another polishing operation. The control circuitry  26  can let the motor  14  continue to run and rotate the brush  12  after the fixture  16  has returned to the home position for a period of time, such as two minutes, to reduce on/off cycling of the motor  14  between successive polishing operations. Operation of the motor  14  can be stopped during such a time period if the proximity sensor  32  detects that the hood  30  has been opened. 
     Those of ordinary skill in the art will recognize that the present invention provides numerous advantages and benefits. For example, reliable and repeatable polishing can be provided despite brush wear over time that can reduce the diameter of the brush or variations in individual workpieces. Moreover, the need for complex brush actuation equipment with complex positioning and sensors is reduced, which results in greatly reduced capital costs for the polishing equipment. 
     While the invention has been described with reference to an exemplary embodiment(s), 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(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.