Patent Application
20150174636
This invention relates generally to manufacturing and in particular to a method and apparatus for processing metal components by performing shot peening on metal components.
Shot peening operates by the mechanism of plasticity that entails impacting a metal surface with shot (round metallic, glass or ceramic particles) with a force sufficient to create plastic deformation. With shot peening, a surface of a metal material may be impacted with shot to produce a compressive residual stress layer and improve mechanical properties of the metal. The impact of the shot occurs with a force sufficient to create plastic deformation. Experience shows that it is most desirable to apply shot penning to critically stressed parts to improve fatigue life of metals and/or to provide protective compressive stresses to combat stress and corrosion related to material failures. In particular, the fatigue life of metallic aircraft parts are enhanced by subjecting the structural parts to a shot peening process which converts surface stress to positive compressive stresses in order to improve the life of the metal parts.
In the present invention, a cast steel shot, high hardness conforming to AMS4231 is used in the apparatus or machine practicing the method and process to impart the compressive stresses to the aircraft part. The shot size used in the machine conforms to ASH 230, which is continuously screened for uniformity and condition in a closed loop system that allows sphere, spheroid or ellipsoid shapes but generally is capable of sorting out marginal shapes that are nodulated, elongated or twins. Also, unacceptable shapes such as teardrop, broken or jagged are further eliminated from the process automatically.
Shot peening is generally performed using large booths or houses with rolling worktables or beds on rails or the like that are controlled by computerized systems such as programmable controls and variable speed AC drive to control the motors for the rolling worktable in the system. This type of shot peening using the method and apparatus of the present invention is referred to as an automated shot peening operation. Certain aircraft parts that are too large or irregular in shape for the booths are then often done by manual shot peening. Furthermore, manual shot peening is sometimes performed as a touch-up in addition to automated shot peening to process an area or portion of a part surface that was not shot peened by the automated system.
More recently, it has been discovered that for longer, thinner components, like wing stringers, chords, webs, etc. that metallic aircraft parts do have changes in shape, contour and length during the peening process. This is a common occurrence thereby leaving a need for a better method and apparatus for the peening process application in order to control and to better apply more uniformity and compressive stresses across the surface of an aircraft part even at lower intensity levels. The present invention accomplishes the task by controlling the angle of impingement on all surfaces of the part at approximately a 45° angle to produce the desired uniformity. This approach is considered optimal for all parts of any size or shape and has been validated by Almen tests and by the aircraft industry.
This new peening process of the present invention and the new machine design is proven by the Almen tests done on the smaller parts and now provides a method and apparatus for longer, thinner parts. The same angle of impingement applied to longer, thinner components will minimize distortion from peening, reduces the need for rework, peen-forming, etc., and thereby reduces the cost and energy needs by 40% to 50% over existing peening methods and apparatus required to perform the shot peening operation.
U.S. Pat. No. 3,669,912 teaches a centrifugal shot throwing wheel that may be used to obtain limited saddleback formation by shot peening only on one side of an aircraft wing to obtain a curvature.
U.S. Pat. No. 2,701,408 teaches a method of providing a curved surface by shot peening one side of a part as it passes through the shoot peening booth.
U.S. Pat. No. 5,460,025 teaches a method and apparatus for controlling a shot peening operation that includes the measurement of pressure at the nozzle to direct the shot unto the work piece where the conveying medium is generally compressed air.
U.S. Pat. No. 4,329,862 utilizes shot peening of an aircraft part so the part takes on the compound curvature of an aircraft wing surface.
U.S. Pat. No. 7,669,449 utilizes a method of sending shot into an inlet of a nozzle where the shot is redirected to form a plurality of streams of shot within the nozzle.
However, none of these prior art references teach the novel method and apparatus of the present invention to improve the overall uniformity of the shot peening process to ensure quality metallic aircraft parts.
Accordingly the present invention provides an improved method and apparatus to provide uniform intensity across all part surfaces of a metallic part at approximately a 45° degree angle. This means that inter-surface connections radii/corner are shot peened at 90° degrees also optimizing the intensity application to the most highly stressed zones between vertical and horizontal areas of an aircraft part. This optimizes the method or process application to best possible approach proved by Almen strip tests of the geometric shot path by the control design.
The process or method for achieving the uniformity and coverage control of the part to be peened is found in a method for improving the shot peening of a part, the method comprising: mounting a rotary peening head on a stationary surface; moving a worktable with the part thereon parallel to the stationary surface; positioning the rotary peening head at 45° angle on the stationary surface from the axis of the worktable direction of travel; and directing a fan shaped shot path across the part at a 45° angle as the part moves beneath the stationary surface on the worktable. This method provides complete coverage of all part surfaces that heretofore was missing in other shot peening machines.
This design is conceived to optimize that processes application and to reduce the energy demands for large parts while promoting continuous cost improvement for the end user and helping to contain process costs for improved profits. Thus the invention is describes as a shot peening machine, comprising: a loading station for placing parts on a movable worktable connected to a rail car riding on a pair of rails and driven by a motor; a staging area for beginning the shot peening operation having a control panel cabinet housing start and stop pushbuttons to start and end the shot peening operation and further including electrical controls for controlling motors and sensors in the shot peening system such as the motors for an elevator, an auger, a dust collector system including a dust collector and a dust shaker, shot pit shakers; shot feeder and other electrical controls in the shot peening system like the valves on shot hoses between a shot hopper feeding the peening process; a shot peening chamber having rotary shot heads driven by a motor, the rotary shot heads mounted on a stationary roof of the shot peening chamber and angled at 45 degrees with respect to the axis of travel of the worktable, hoses with valves for controlling the shot fed from the shot hopper to the rotary shot heads; a containment chamber connected to the exit opening of the shot chamber for collecting the dust from the peening operation; a dust collection system including a dust box connected to an opening at a floor level of the containment chamber, a dust collection house having the dust collector motor and the dust shaker motor and a dust hopper for collecting the dust from the peening operation and a pipe extending from the dust box to the dust collection house for sucking the dust out of the containment chamber; and a shot pit located below a grate supporting the rails and pit shot hoppers below the grate for collecting used shot in the shot peening process and channeling it into pit shakers that move the shot to a deeper pit connected to an elevator with buckets for carrying the used shot out of the deeper pit to an auger above the shot chamber to carry the shot into a shot hopper that feeds the rotary shot heads mounted on the roof surface of the shot chamber through a series of hoses with valves controlling the shot fed into the rotary shot heads to control the intensity of the shot within the shot chamber
It is, therefore, an object of this invention to provide a shot peening application improvement which is capable of providing shot peening over a wide range of different metallic part materials like aircraft stringers.
It is another object of the present invention to provide a shot penning application capable of providing substantially uniform distribution of shot along a relative great flow area simply and inexpensively.
It is a further object of this invention to provide a shot peening application, which can achieve shaping of parts over a wide range of types of parts than heretofore known air pressure or gravity shot peening devices.
A still further object of the present invention is to provide a shot peening application in which substantially uniform distribution of propelled shot is achieved in an inexpensive manner.
Yet another object is to do multiple and volume amount of aircraft parts spread across an angled worktable with the perfect angle to monitor the proper intensity of the shot peening process.
The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings.
Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of a new shot peening machine 10 for carrying out the method of a shot peening process for aircraft parts through a new machine apparatus as shown in the perspective view of the shot peening machine 10 in
Shot peening of a surface in the shot peening machine 10 causes change in the mechanical properties of the aircraft stringers. The shot peening of the present invention is performed to relieve tensile stresses that builds up in various components and replaces those stresses with beneficial compressive stresses. Shot peening is capable of being performed on various surfaces of aircraft parts such as, for example, without limitation, a stringer, a wing, a tail, a fuselage, or parts thereof, or some other surface or portion of a surface of an aircraft part.
The first section of the machine 10 is a parts loading and unloading zone 11 where the aircraft stringers 10 or any other parts are loaded onto worktable 15 of the rail car 14. The rail car 14 moves upon on a pair of rails 16 that extend the length of the machine 10 and through its various chambers to be described in detail later. The rail car 14 is generally comprised of four main components.
The second section of the machine 10 is a rail car 14 staging area chamber 36 where a fully loaded worktable 15 generally passes through a clear slotted plastic curtain (not shown) hanging down over an opening to the entrance of staging area chamber 36 and the curtain is configured to conform to the outline of the rail car 14 and its worktable 15 to ride up and across the length of the worktable 15 as it moves from the staging area where the process of shot peening starts and ends as the worktable 15 with the parts passes into and back out of a third section called a shot peening chamber 38 for processing the aircraft parts 12 passing therethrough. The clear curtain also serves as a visual for an operator of the machine 10 in controlling the rolling rail car in the process. The intensity of the shot peening operation in this chamber 38 will be described in greater detail later. Another unique aspect of the machine 10 is that the steel shot used in the shot peening operation is collected in all three previously described sections as it falls to the floor of the machine 10.
A fourth section is the shot peen containment chamber 40 where the shot used in the operation of the machine falls free through a rail grate system 42 that extends through all four sections of the machine 10. The rails 16 are spaced apart a predetermined distance and parallel to one another and rest upon a grate 44 with small openings 46 so that the ASH 230 steel shot used in the process is able to pass through the openings 46 along the length of the grate 44 to be collected in hoppers located below the grate surface to be collected in a series of pit hoppers 48 located beneath the grate 44 running the length of the machine 10 from the first section to the fourth section. Thus the steel shot is collected, recycled and reused in the overall process as will be described in greater detail later.
And a fifth and last section is an opening 42 at the end of the fourth section shot containment chamber 40 having a clear slotted curtain hanging down (not shown) over the opening 42 to allow the proper airflow into the chamber 40 of the system for superior dust control and media cleansing as well as a visual for an operator of the machine 10.
Turning now to
Inside the control panel cabinet 50 are three Cerus Titan P Series variable frequency drives (“VFD) of predetermined horsepower ratings for controlling several of the eleven motors rated at 480 volts, 3-Phase used by the shot peening machine 10. The VFDs are soft starters (not shown) for controlling motors M1, M2 and M3 that drive corresponding motor wheel heads 52, 54 and 56 for the shot peening machine 10. Another VFD controls motor M4 for the rolling rail car 14. The control panel cabinet 50 further includes the electrical controls and switches for operating a motor M5 for an elevator 58, a motor M6 for a shot feeder and motors M7, M8 and M9 for shot pit shakers 1, 2 and 3, respectively. Also, electrical controls for a dust collector system includes a dust collector motor M10 and a dust collector shaker motor M11 that are also housed within a NEMA 12 enclosure.
An important further feature of the invention is that the control circuits of the dust collector and dust collector shaker motors M10 and M11, respectively, are interlocked with the controls circuits of the motors within the peening machine to prevent the operation of shot peening or any of the wheel heads operating that might cause dust unless the dust collector system is energized and operating properly.
Further, VFDs provide many advantages when used instead of electro-mechanical contactors to control 3-phase AC induction motors. However, there are other electrical control configurations with AC variable speed drives that may be used in place of the VFDs to control the eleven AC induction motors used in this shot peening machine 10. Therefore, this invention is not limited to just this particular set of electrical controls as described herein.
Turning now again to
In short, the control panel cabinet 50 contains all of the necessary controls to operate the peening machine 10. The operator is able to view important aspects of the process by looking at the control panel 60 containing the gauges and operator pushbuttons for the peening machine. The control panel 60 on one of the exterior cabinet doors nearest the staging area includes the following items: an emergency stop button with the button in red surrounding by a yellow circle to highlight its location, three start/stop pushbuttons and light indicators for the three motor wheels 52, 54 and 56 energized by the corresponding motors M1, M2 and M3; a rolling worktable 15 start button with light indicator, an RPM indicator for the three synchronous motor wheels; start/stop pushbuttons and indicator lights for the elevator shot bucket, shot feeder and pit shakers 1, 2 and 3; and indicator displays with dome pushbuttons thereon for each of the three MagnaValves to control the flow rate of the shot for process uniformity and coverage control of the shot peened part. These controls on the control panel 60 allow the intensity of the fan shot path to be controlled to optimize shot peening of all the part surfaces in the process. Also, the emergency button when pushed by the operator or other person, completely stops the entire process and cuts power to all eleven motors in the systems whereby the rolling worktable 15 and all other moving parts stop immediately. This function is to assure the safety of personnel operating or coming into contact with the peening machine as safety becomes an important aspect in the design of the peening machine in the present invention
Next as shown in
Meanwhile, the shot wheel blaster heads 52, 54 and 56 are capable of wheel speeds up to 1500 RPM but in the present invention operating at approximately 1200 RPM provides the low intensity shot peening that achieves the best results. The steel shot pattern that fans out across the parts 12 in the shot chamber 38 then the shot falls free to the pit hoppers 48 below the first four sections of the machine 10. A underground shot pit 72 of approximately ten 10′ deep runs below the entire length of the rail grate 44 with the pair of rails 16 thereon. Excess used steel shot is continuously falling into the pit hoppers 48 and directed to a underground floor channel 74 running below the pit hoppers 48 with at least one pit shaker 76 to move the shot along to a shot collection pit 78 approximately three feet lower than the floor channel 74 below the pit hoppers 48.
In the present invention there are at least three pit shakers 76 that move the shot along to the shot collection pit 78. The steel shot is then moved by the bucket conveyor 62 up the elevator 58 as shown in
The shot blaster wheels 52, 54 and 56 are shown angled approximately 45° to the axis of the rail car 14 and worktable 15 travel direction on a slanted roof portion 84 of the chamber 36 and the roof 84 is approximately parallel to the worktable 15. The hopper 64 is elevated above the roof 84 where the shot wheel blaster heads 52, 54 and 56 are mounted upon. There is a natural gravity feed of the steel shot in the hopper 64 to the wheel blaster heads 52, 54 and 56 through the control MagnaValves inline with the hoses 66-68. The operation of the auger 80 feeding the hopper 64 with recycled shot in turn is connected to the bucket conveyor 62 within the elevator 58. The elevator 58 is then connected via the belted bucket conveyor 62 to the deeper shot collection pit 78 approximately three 3′ foot lower than a pit floor 86 of the deep pit 72 along with the pit hoppers 48 just below the steel rail grate 44 with the steel rail tracks 16.
Moreover, a pit shaker motor M7 is located in the deep pit 72 or in the underground floor channel 74 below the first section 11 of the machine 10. A pit shaker motor M8 is located below the containment chamber 40 while a pit shaker motor M9 is in the underground floor channel 74 below the right side of the containment chamber 40 and runout rail tracks 16 and rail grate 44 on the right hand side of the machine 10. The shaker motors M7, M8 and M9 drive the shakers 76 become the way that shot is moved from the underground shot pit 72 to the deep shot collection pit 78 for collecting the shot into the buckets of the bucket conveyor 62 in the elevator 58 to return the spent process shot to the shot hopper 64 for reuse.
This is the ideal configuration of the shot wheel heads 52, 54 and 56 in triflow configuration. The intensity desired results from the shot peening are achieved at all angles at 45° to all part surfaces and 90° to all corner and fillet radii. To optimize the application of the shot peening process for all part configurations subject to warpage such as stringers, wing skin chords and webs during peening. Controlling peening intensity on all part surfaces to the smallest variation possible is achieved by peening all accessible vertical and horizontal surfaces at 45°. Most important is intensity on corner fillet radii will be peened at 90°, which is best practice leaving all peening between 45° on all surfaces of the part and 90° in corner radii. In Almen tests and trials with the machine 10, there was no better application geometry found, which proved this is the optimum angle for shot peening of the aircraft parts.
To further prove out that the best angle for the shot path from the wheel blasters on the roof 84 Almen test strips were placed on the worktable 15 with the shot path control fixed at 45° to the travel direction of the worktable 15. Through a series of Almen test strips receiving the shot path at 45°. Then the Almen test strips were run at other angles. The surfaces on the parts that had shot peening on all accessible surfaces of any component configuration mounted on the worktable 15 proved through the Almen test strip tests that the 45° angle was the correct geometry for quality shot peening of all part surfaces.
Now in operating the shot peening machine 10, there are many considerations to take into account. First, the dust collector system 90 and a dust collector shaker driven by motor M11 (not shown) are electrically interlocked to prevent the operation of any rotary wheel heads 52, 54 and 56 unless the dust collector system 90 is energized and operating. This prevents any potential environmental problems because the shot peening process creates a large amount of dust. Further the rotary wheel heads 52, 54 and 56 connected to motors M1, M2 and M3 operate in conjunction with the speed and cycles of the rolling worktable motor M4. The rolling worktable motor M4 is capable of reversing and repeating operating cycles both manually and automatically as operated by the end user or as programmed in the programmable logic controller (PLC). An operating cycle is determined when the rolling worktable 15 has traveled to an end limit or the X axis and returned to the “Starting Point” of the X axis. The rolling worktable 15 will automatically reverse direction when reaching the end limit switch and will automatically stop when returning to the “Start Point” of the staging area. Whenever the rolling worktable 15 returns to the Start Point in the operating cycle, the cycle ends and all motors including the collection system will become de-energized and shut down the peening system and its apparatus. The end limit sensor for the rolling worktable 15 is determined by the function of a photoelectric sensor or mechanically actuated by a limit switch. This function will energize the reversing coil “R” and the direction of the rolling worktable 15 will reverse and return to the Start Point. The “Repeat” command is performed manually or programmed into the PLC. This function will energize the reset coil “RS” and the rolling worktable 15 and the process will reset and begin at the Start Point. These statements recall some of the operating sequences of the peening system incorporated into the new peening machine 10
The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use or uses contemplated.
