Asymmetrical fluidic oscillator and a method to control superplastic forming

Abstract

An asymmetrical load-type fluidic oscillator, for providing oscillatory pressure to a chamber, comprising converging and diverging nozzles where fluid passing through forms an accelerated jet, a feedback flow channel connected to the diverging nozzle and to a feedback tank, an exhaust flow channel connected to the diverging nozzle and to the chamber, and a release flow channel connected to the feedback flow channel and to the chamber. The jet from the diverging nozzle enters the feedback flow channel to pressurize the feedback tank. An increase in tank pressure causes the path of the jet to divert to the exhaust flow channel. Fluid is subsequently discharged through the release flow channel, enabling the path of the jet to be diverted back to the feedback flow channel to recharge the feedback tank. Cyclic movement of the jet between the exhaust flow and feedback flow channels causes periodic pressure increases in the chamber.

Description

TITLEAsymmetrical Fluidic Oscillator and a Method To Control Superplastic FormingFIELD OF INVENTION

[0001] This invention relates generally to an asymmetrical fluidic device design that generates gas oscillations and its application in a superplastic forming process. In one aspect, the invention pertains to the fields of fluid dynamics and metal forming, with potential applications in a wide range of technologies where gas flow oscillations may be beneficial. In one embodiment, the invention focuses on the production of automotive and aerospace panels or components through superplastic blow forming, using controlled gas oscillations to enhance the manufacturing process.BACKGROUND

[0002] Superplastic forming (SPF), which may include superplastic blow forming, can be used to create a wide variety of different products, including many parts or components used in the automotive, aerospace, medical, and architectural industries. Typically, a SPF process is carried out through (i) clamping a metallic alloy sheet, which is often relatively thin, within a sealed and heated SPF tool, (ii) heating the sheet to a point of superplasticity (where the metallic sheet is typicallyheated to a temperature higher than one half of its melting point), and (iii) introducing pressurized gas within a chamber of the SPF tool, and to one side of the metallic sheet (forming material), to force it "elongate", "stretch" or "flow", and to take the shape of the SPF tool surface. The gas pressure applied to the forming material is generally referred to as the gas forming pressure Pforming (ie. gas pressure inside the SPF tool pressurized chamber). In the automotive industry, magnesium alloy (for example, AZ31B) and aluminum alloy (for example, AA5083) sheets are commonly heated and superplasticly blow formed, in a temperature range of approximately 450 to approximately 480 degrees Celsius, to create body components such as doors, fenders, bodysides, lift gates, roofs, etc. In the aerospace industry, titanium alloy sheets can be heated and superplastically blow formed in a temperature range of approximately 700 to approximately 900 degrees Celsius to create a variety of different geometrically complex aerospace panels. Multi sheet forming may also occur. In multi sheeting forming a SPF process is combined with diffusion bonding to create intimate contact between two materials at high temperature and specific gas pressure, and to then form and bond multiple sheets together in an inert gas environment. Multi sheet forming can offer additional process benefits, including high stiffness, and may include, for example, honeycomb components.

[0003] Typically, SPF processes are relatively slow, primarily due to the inability of the forming material to achieve a high degree of elongation at highstrain rates without developing tears or cracks. A complex automotive component, for instance, formed from an aluminum or magnesium alloy sheet using a conventional SPF process, can require as much as 3 to 30 minutes to manufacture. Similarly, a complex aerospace component, formed from a titanium alloy sheet through conventional SPF, can require as much as 45 minutes to 10 hours to manufacture. As a result, the use of conventional SPF is often limited to producing high value parts.

[0004] There is therefore a need for an improved SPF process where components can be manufactured at higher production speeds, and that may also, in some instances, allow for the production of more geometrically complex components at a more economical cost with a more uniform thickness variation.SUMMARY

[0005] Further aspects of the invention will become apparent from the following description taken together with the accompanying drawings.

[0006] In an aspect the invention provides an asymmetrical load-type fluidic oscillator for providing oscillatory pressure to a chamber, the asymmetrical loadtype fluidic oscillator comprising a converging nozzle fluidly connected to a diverging nozzle, wherein fluid passing through the converging nozzle subsequently passes through and exits the diverging nozzle forming an accelerated jet of fluid, afeedback flow channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to a feedback tank, wherein the accelerated jet of fluid exiting the diverging nozzle is allowed to pass through the feedback flow channel and into the feedback tank, pressurizing the feedback tank, an exhaust flow channel with a first end fluidly connected to the diverging nozzle and a second end fluidly connected to a chamber; and a release flow channel with a first end fluidly connected to the feedback flow channel and a second end fluidly connected to the chamber, wherein an increase in pressure within the feedback tank causes the path of the accelerated jet of fluid to divert from the feedback flow channel to the exhaust flow channel and into the chamber, wherein fluid from the feedback flow channel and / or the feedback tank is subsequently discharged through the release flow channel, enabling the path of the accelerated jet of fluid to be diverted back to the feedback flow channel for recharging the feedback tank, wherein a cyclic movement of the passage of the jet of fluid between the exhaust flow channel and the feedback flow channel causes periodic pressure increases in the chamber.

[0007] In another aspect the invention provides an asymmetrical load-type fluidic oscillator for providing oscillating fluidic pressure to a chamber, the asymmetrical load-type fluidic oscillator comprising a converging nozzle fluidly connected to a diverging nozzle, wherein fluid passing through the converging nozzle subsequently passes through the diverging nozzle forming a supersonic jet of fluid, a feedback flow channel having a first end fluidly connected to thediverging nozzle and a second end fluidly connected to a feedback tank, a release flow channel with a first end fluidly connected to the feedback flow channel and a second end fluidly connected to the chamber; an exhaust flow channel with a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber; a control channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber; and a splitter separating the feedback flow channel and the exhaust flow channel at their point of fluid connection with the diverging nozzle; wherein an initial passage of fluid through the converging and diverging nozzles causes at least a portion of the resulting supersonic jet of fluid to pass through the feedback flow channel and into the feedback tank, pressurizing the feedback tank, at least a portion of the fluid also passing through the release flow channel; wherein an increase in pressure within the feedback tank subsequently forces the path of the jet of fluid to divert from the feedback flow channel to the exhaust flow channel and into the chamber, wherein a subsequent reduction in pressure in the feedback tank causes a diversion of the path of the jet of fluid from the exhaust flow channel to the feedback channel, resulting in a re-pressurization of the feedback tank, wherein a cyclic movement of the passage of the jet of fluid between the exhaust flow channel and the feedback channel causes periodic pressure increases in the chamber.

[0008] The invention also provides a method of controlling a superplastic forming process wherein a sheet of material is subjected to superplastic formingwhile retained within a chamber of a superplastic forming apparatus having fluidly connected thereto the asymmetrical load-type fluidic oscillator of any one of claims 1 to 7, the method comprising determining a minimum boundary limit for a ratio of a supply pressure (Piniet) applied to the asymmetrical load-type fluidic oscillator relative to a forming pressure (PForming) within the chamber of the superplastic forming apparatus, wherein the application of supply pressure to the asymmetrical load-type fluidic oscillator in a manner that maintains the ratio of Piniet / PForming above the minimum boundary limit causes the asymmetrical load-type fluidic oscillator to generate continuous and uninterrupted gas oscillations, with a supply pressure sensor, detecting a pressure of gas supplied to the asymmetrical load-type fluidic oscillator and transmitting the detected supply pressure to a pressure controller, with a forming pressure sensor, detecting the forming pressure within the chamber and transmitting the detected forming pressure to the pressure controller, and operating the pressure controller to maintain the pressure of gas supplied to the asymmetrical load-type fluidic oscillator such that the ratio of the detected supply pressure to the detected forming pressure is maintained above the minimum boundary limit.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way ofexamples, to the accompanying drawings which show exemplary embodiments of the present invention in which:

[0010] Figure 1A is a schematic view of an example of an asymmetrical load type supersonic fluidic oscillator with a release port.

[0011] Figure IB is a schematic view similar to Figure 1A demonstrating the structure of the asymmetrical load-type supersonic fluidic oscillator in a plane that is 90 degrees that of Figure 1A.

[0012] Figure 2 is a schematic view of an embodiment of a waveform generated by the supersonic fluidic oscillator of Figure IB and by subsonic fluidic oscillator of Figure 3B in its feedback tanks.

[0013] Figure 3A is a schematic view of an example of an asymmetrical load type subsonic fluidic oscillator.

[0014] Figure 3B is a schematic view similar to Figure 3A demonstrating the structure of the asymmetrical load-type subsonic fluidic oscillator in a plane that is 90 degrees that of Figure 3A.

[0015] Figures 4, 5, 6 are successive schematic views demonstrating the flow through the supersonic fluidic oscillator of Figure IB along three different flowpaths.

[0016] Figures 7 and 8 are successive schematic views of an embodiment of a SPF assembly process, demonstrating the principal stages for forming a single component in a SPF tool.

[0017] Figure 9 is a schematic view of an embodiment of a single chamber SPF tool, similar to Figures 7 and 8, demonstrating forming a component through a SPF process.

[0018] Figure 10 is a graph showing an exemplary baseline pressure curve of the gas inside a pressurized chamber of a SPF tool during a typical SPF cycle.

[0019] Figure 11 is a non-scale representation of a pressure-time curve, depicting an example relationship between a baseline gas pressure and a fluctuating gas forming pressure inside a pressurized chamber of a SPF tool.

[0020] Figure 12 is a graph showing a relationship between gas pressure in a pressurized chamber of a SPF tool, and gas supply pressure entering a supersonic fluidic oscillator or a subsonic fluidic oscillator, illustrating a minimum ratio of those pressures, above which the supersonic fluidic oscillator or the subsonic fluidic oscillator generates continuous, uninterrupted, gas oscillations.DESCRIPTION

[0021] The present invention may be embodied in several different forms. The specification and drawings that follow describe and disclose some of the specific forms of the invention.

[0022] In the field of fluid dynamics, an emerging topic of interest is the study of fluidic diverter actuators for flow control. Two papers describing such research were published by NASA in 2010 and 2011, and are entitled "Numerical Studies of a Supersonic Fluidic Diverter Actuator for Flow Control"1and "Numerical Studies of an Array of Fluidic Diverter Actuators for Flow Control"2. The papers describe the oscillatory behavior of flows through fluidic diverter actuators, also known as fluidic oscillators. Some such oscillators are known as supersonic fluidic oscillators. Recently, fluidic devices utilizing liquids as the working fluid have found application at the micro-level in drug administration and lab-on-a-chip devices3.

[0023] Bi-stable (symmetrical) supersonic fluidic oscillators are one form of fluidic device which can provide oscillatory flow outputs for steady flow inputs.1Gokoglu, S., Kuczmarski, M., Culley, D., and Raghu, S., "Numerical Studies of a Supersonic Fluidic Diverter Actuator for Flow Control," Presented at the 5thFlow Control Conference 2010, Chicago, Illinois, USA, June 28 - 1 July 2010Gokoglu, S., Kuczmarski, M., Culley, D., and Raghu, S., "Numerical Studies of an Array of Fluidic Diverter Actuators for Flow Control," Presented at the 41st Fluid Dynamics Conference and Exhibit sponsored by the American Institute of Aeronautics and Astronautics, Honolulu, Hawaii, USA, June 27-30, 20113Jayamohan, H., Sant, J., H., Gale, K., B., "Application of Microfluidics for Molecular Diagnostics," Microfluidic Diagnositics, P305-334, Human Press, Totowa, NJ, USA, 2013Such oscillators make use of a jet flow that attaches to one of two sidewalls as a result of a phenomenon known as the Coanda Effect4. Any of several types of flow switching mechanisms may be used to switch the jet flow between the two sidewalls of the oscillator. That is, bi-stable fluidic oscillators require a "switching mechanism" to move the flow from an "attached" channel side to an opposite channel, and back, repeating continuously. Typically, one or more of three types of switching mechanisms may be used. Those switching mechanisms comprise (i) momentum switching (ii) pressure (recirculation) switching, and (iii) load switching.

[0024] A bi-stable load switched supersonic fluidic oscillator relies on a load switching mechanism to divert flow utilizing feedback tanks. As the flow travels through narrow flow channels, the feedback tanks fill, which results in an increase in pressure that propagates upstream towards the jet exit. When the pressure at a splitter tip reaches a sufficiently high value, the jet "switches" to the other channel. This process then repeats itself through use of a second feedback tank, causing oscillation.

[0025] Fluidic Oscillators can be generally categorized into subsonic and supersonic types. A key distinction lies in the flow velocity of the gas, with supersonic fluidic oscillators achieving speeds equal to or beyond Mach 1 (speed of sound), while subsonic fluidic oscillators operate at lower velocities or below Mach 14Lubert, Caroline (2011), "On Some Recent Applications of the Coanda Effect", International Journal of Acoustics and Vibration, Vol.16, No.3(and at times significantly below Mach 1). The supersonic variant has the capacity to produce substantially higher oscillation pressure amplitudes, which may make it advantageous for specific manufacturing processes, such as SPF.

[0026] Bi-stable load-type supersonic fluidic oscillators, with dual exhaust ports and dual feedback tanks, as outlined in US Patent No: US 10,875,072 B2, exhibit the capability to produce large gas pressure oscillation amplitudes when each exhaust port is linked to an individual chamber. Conversely, connecting a Bistable load-type supersonic fluidic oscillator, with both of its dual exhaust ports connected to a single chamber, can result in a significantly reduced gas oscillation amplitude making it somewhat less attractive under certain conditions or situations. A paper describing such research was published in 2023, and is entitled "An Investigation of a Newly Developed Bistable Load-Type Supersonic Fluidic Oscillator for Generating Large-Amplitude Pressure Pulsations"5.

[0027] With reference to Figures 1A and IB there is shown, schematically, a unique asymmetrical load-type fluidic oscillator 41 constructed in accordance with an embodiment of the invention. The asymmetrical load-type fluidic oscillator utilizes a single exhaust port designed to connect to a single chamber (for example, as is commonly found in superplastic forming tools). In the particular embodiment of the invention shown in the attached drawings, fluidic oscillator 41 is an5Xu, S., Ryzer, E., and Rankin, G.W., 2023, "An Investigation of a Newly Developed Bistable Load-Type Supersonic Fluidic Oscillator for Generating Large-Amplitude Pressure Pulsation," J. Fluids Eng., 145(5)asymmetrical load-type supersonic fluidic oscillator. Such can be distinguished from the symmetrical supersonic fluidic oscillators currently known in the art. The structure of asymmetrical load-type supersonic fluidic oscillator 41 will be described in greater detail below. A typical waveform of an oscillator is depicted in Figure 2, which shows a general triangular shaped plot occurring inside the feedback tank of the oscillator.To provide a better understanding of how supersonic fluidic oscillator 41 functions, reference is made to the exemplary embodiment shown in Figures 1A and IB. Here, an exhaust port 52, a control port 57, and a release port 72 are each connected to the same single part forming chamber 60. Throughout this specification "fluidly connected" is used to signify that respective parts or components are in "fluid communication" such that fluid can flow between them. Chamber 60 may be an enclosed chamber or may be open to the atmosphere. Fluid enters oscillator 41 through an inlet or inlet channel 42 (demonstrated by the solid arrow in Figure 1A) and fills a supply reservoir 43. The ensuing or resulting jet of fluid (not shown) passes through a converging nozzle 44, is accelerated to sonic speed, and then further accelerated to supersonic speed as it passes through a diverging nozzle 45. A Coanda effect results in the supersonic jet of fluid initially "attaching" to the feedback flow channel side wall 49 when it exits diverging nozzle 45, as shown in Figure 4. As the jet of fluid passes along flow channel side wall 49, it will tend to entrain fluid from chamber 60 through control port 57 and into acontrol channel 62, which will tend to help stabilize the wall "attachment" of the supersonic jet. The supersonic jet at this point will substantially flow through a feedback flow channel 48 and will begin to charge a feedback tank 70 (see Figure 1A) through a feedback port 56. Part of the jet's flow may also pass through a release flow channel 74 and exit into chamber 60 at port 72. Backpressure within the feedback flow channel 48 (largely created by a pressurization of feedback tank 70 as it is filled with fluid) will eventually become great enough to force the supersonic jet to "switch" to pass through an exhaust flow channel 64 and to flow along an exhaust flow channel side wall 65, exiting through exhaust port 52 into chamber 60, as shown schematically in Figure 5. When the jet of fluid flows through exhaust flow channel 64, the previously stored fluid in feedback tank 70, as well as the fluid in channels 48 and 74, will start to be released through port 72 into chamber 60, as shown generally in Figure 6. The entrained flow from control channel 62 will tend to help to stabilize the attachment of the supersonic jet on or along wall 65.It will be appreciated that initially, when fluid is flowing back from feedback tank 70 and along feedback flow channel side wall 49, while it may be possible for some of that fluid to exit through channel 64 and exhaust port 52, the majority of the fluid will flow through channel 74 and release port 72 into chamber 60. With fluid flowing along exhaust flow channel side wall 65, as the pressure in feedback tank 70, and hence channel 48, begins to decrease the transverse forceimmediately downstream from diverging nozzle 45 tending to keep the jet flow positioned along exhaust flow channel side wall 65 will also begin to decrease and part of the jet flow will begin to be diverted by a splitter 46 back into channel 48. Once the supersonic jet attaches to the splitter, the fluid from feedback tank 70 will primarily be discharged through channel 74 and release port 72. The discharge process of feedback tank 70 continues until flow is once again substantially established through channel 48 and into feedback tank 70. That is, the supersonic jet will sweep back from exhaust flow channel side wall 65 toward feedback flow channel side wall 49. As the flow begins to "switch", the jet of fluid will move past splitter 46 and toward flow channel side wall 49, at which time flow will again be directed to feedback tank 70, and a portion of the fluid may be released through flow channel 74. In other words, as the pressure within feedback tank 70 and channel 48 is dissipated, the jet of fluid will eventually switch back to feedback flow channel 48, due to the Coanda Effect and the described process will be repeated. That process repeats itself continuously to create a continuous oscillation of the jet of fluid between the two primary flow paths.

[0028] It will be appreciated that care must be given to the dimensioning and the design of release flow channel 74 and its release port 72 in order to avoid an equilibrium state where the pressure load at feedback tank 70 is not accumulated and an oscillation is not triggered. The design of release flow channel 74 and its release port 72 may vary between oscillators depending on a range of factors thatmay include: the material from which the oscillator is constructed, the temperature of the manufacturing process within which the oscillator is used, the cross sectional area and length of the release flow channel, the size of the release port, the type of gas flowing through the oscillator, the surface roughness of flow channels, the location of the release flow channel vis-a-vis feedback flow channel 48, etc. It will also be appreciated that the "direction" of release flow channel 74 may vary by being in the opposite direction or at an angle to that shown in the attached drawings. With release channel 74, and its release port 72, appropriately designed, there will be a sufficient resistance to flow during feedback tank charging to result in oscillation of the supersonic jet. The supersonic jet flowing through feedback flow channel 48 will largely by-pass release flow channel 74, with release flow channel 74 only significantly venting gas to chamber 60 while the supersonic jet is forced to the exhaust flow channel 64 and exit at exhaust port 52 to chamber 60 (ie. during feedback tank 70 discharging).

[0029] From a thorough understanding of the invention, one of skill in the art will appreciate that, after passing through the convergent-divergent nozzle 44 / 45, fluid flow is accelerated to supersonic speed. The supersonic jet will flow out from diverging nozzle 45 and will entrain fluid from the surrounding regions, causing local vacuum pressures at those locations. Although downstream pressure waves (pressure signals), moving at sonic speeds, cannot be well transmitted back through the supersonic jet, the direction of the supersonic jet outwardly fromdiverging nozzle 45 can be altered by the transverse pressure force under Coanda effect.

[0030] It will also be understood that control channel 62 effectively enables a "communication" between exhaust port 52 and what will largely be an area of "still" fluid at one side of the supersonic jet. Flow within control channel 62 will at least initially be subsonic. As mentioned, if the jet of fluid flowing into feedback tank 70 is supersonic, a "pressure signal" (or pressure wave) will not effectively pass through the supersonic flow and there will be no effective "communication" with control channel 62. If the jet flow into feedback tank 70 is subsonic then a pressure "signal" can pass.

[0031] It will be appreciated that the release of pressure through release port 72 will tend to create the formation of a vacuum pressure near control channel 62, leading to an inflow through exhaust port 52, tending to reduce the vacuum condition that has formed, and tending to intensify the transverse pressure bias on the supersonic jet such that it will tend to prefer the feedback path through channel 48 rather than the exhaust path through channel 64. It will be appreciated that the supersonic jet will initially bypass the release channel 74 and release port 72 due to the flow momentum. When feedback tank 70 has been sufficiently filled and pressurized such that it adds resistance to the flow of fluid though feedback flow channel 48, release port 72 will allow for a pressure release such that the flowthrough feedback channel 48 will drop to a subsonic state, effectively permitting a "communication" between the feedback channel / tank and control channel 62. The supersonic jet will then overcome the transverse pressure bias and "switch" to exhaust flow channel 64 (ie. the exhaust path). After the flow switches to exhaust flow channel 64, the "communication" between the high-pressure feedback tank 70 and chamber 60 leads to discharge flows through exhaust flow channel 64 and port 52 and release channel 74 and port 72. As the pressure load in the feedback tank decreases, the supersonic jet starts to transversely swing back from exhaust flow channel 64 to feedback channel 48. When the flow swings back and attaches splitter 46, the discharge flow through exhaust channel 64 and port 52 is (pressure wave or pressure signal) blocked and fluid from feedback tank 70 can only be released through release channel 74 and port 72. The discharge from feedback tank 70 continues until the feedback pressure load eventually reaches a level which is too small to counter the transverse pressure bias on the jet, at which point the supersonic jet will "switch" back to channel 48. The inventor has discovered that without release flow channel 74, the pressure "communication" between feedback tank 70 and exhaust port 52 may eventually be blocked by the supersonic jet, and consequently, an equilibrium may occur without oscillation or with oscillations of low amplitudes.

[0032] The applicant has also discovered that smaller oscillation amplitudes may be possible through the use of an asymmetrical load-type subsonic fluidicoscillator 80, shown schematically in Figure 3.

[0033] That is, the applicant has surprisingly discovered that by removing release port 72 from supersonic fluidic oscillator 41, subsonic fluidic oscillator 80 will be able to generate a stable oscillation with a subsonic jet. In the case of subsonic fluidic oscillator 80, if the jet that exits diverging nozzle 45, and that extends into channel 48, is subsonic, the fluid stored in feedback tank 70 may be continually released through exhaust flow channel 64 and exhaust port 52, meaning that there may be no need for a release port 72 to reduce the stored pressure load at feedback tank 70. It has also been discovered that a release port 72 may cause problems for the load switch of a low-velocity jet from feedback flow channel 48 to exhaust flow channel 64. When a low-velocity jet is flowing through feedback flow channel 48, it may not bypass a release port 72 as it would in the case of a supersonic jet. The low-velocity jet could then directly exit through the release port to chamber 60 without oscillating. However, by removing release port 72, the applicant has discovered that subsonic fluidic oscillator 80 will oscillate, in a similar manner as described above with respect to supersonic fluidic oscillator 41, albeit at smaller oscillation amplitudes.

[0034] One of skill in the art, having an appreciation of the above discussion, will understand that subsonic fluidic oscillator 80 will function generally similar to supersonic fluidic oscillator 41, with a primary exception being that release flowchannel 74 and release port 72 may not be required in the case of subsonic fluidic oscillator 80 and that the switching of the flow in the subsonic fluid oscillator may be achieved at smaller oscillation amplitudes.

[0035] Alterations to oscillators 41 and 80 are contemplated while remaining within the broad scope of the invention. For example, while asymmetrical load-type supersonic fluidic oscillator 41 with release port 72, and asymmetrical load-type subsonic fluidic oscillator 80 without a release port, are specifically discussed and shown in Figures 1A, IB, 3A, and 3B, the geometry and location of exhaust flow channel 64, control channel 62, and feedback flow channel 48 may vary slightly, while the length of the exhaust flow channel 64, control channel 62 and feedback flow channel 48 may vary considerably. It should also be noted that the location of exhaust port 52, control port 57, and feedback tank port 56 may vary slightly, and that the geometry and length of exhaust port 52, control port 57, and feedback tank port 56 may vary significantly. Further, the "direction" of the exhaust flow channel 64, exhaust port 52, control channel 62, control port 57, feedback tank port 56 may vary considerably from the depicted Figures 1A, IB, 3A, and 3B by being in the opposite direction or at an angle. Still further, the geometrical shape and the volume of the feedback tank 70 could vary by being in the opposite "direction" or at an angle to that generally depicted in the drawings. Various shaped configurations (including, but not limited to, cubic, cuboid, or cylinder shaped) are also contemplated or feedback tank 70. Feedback tank 70 may alsoincorporate support structures that are relatively small compared to the overall volume of the feedback tank 70, and that are positioned at various locations. It will be appreciated that the volume of the feedback tank will be specifically designed to target a particular range of operating frequencies, or a specific operating frequency generated by the oscillator (41 or 80). It is expected that in some cases the construction of oscillators 41 / 80 may include machining flow passageways and channels (48, 62, 64, 74), nozzles 44 and 45, splitter 46, and / or feedback tank 70 into a block of material and / or through securing layers of materials together (with a gas tight seal therebetween) to form such structures. It is also expected that in some cases ports 52, 56, 57, and / or 72 may be formed through various machining operations, through drilling a block of material, or through securing layers of materials together (with a gas-tight seal therebetween) to form such ports. Regardless, one of skill in the art will appreciate that the "depth" of the oscillator 41 / 80 (ie. in a direction perpendicular to the plane of the pages which contain Figures 1 and 3-6) will be designed to provide a desired gas mass flow rate or a desired filling time into chamber 60, and may vary considerably from that in the depicted Figures (which are schematic in nature and not meant to be of scale). The applicant has found that, in general the "depth" of the oscillator 41 / 80 may typically be equal to or greater than the smallest "throat" opening at converging nozzle 44 and diverging nozzle 45. However, there may also be situations where the "depth" of the oscillator could be smaller.

[0036] Figures 7, 8, and 9 show an embodiment of an SPF apparatus 100 for forming a single component. Apparatus 100 is generally comprised of a chamber portion (upper) 120 and a tool portion (lower) 140, which together form opposed tool portions that are clamped or pressed together about a sheet of forming material 220, that is to be formed into a desired part or article. Tool portion 140 includes a tool forming surface 200. When chamber portion 120 and tool portion 140 are clamped together, a sealed chamber 240 is formed. Chamber portion 120 may include one or more gas forming pressure sensors 160, which measure pressure within chamber 240 (also referred to as the forming pressure). Sensors 160 can alternatively be located at a distance away from apparatus 100 and can be connected to apparatus 100 through a conduit, tube, or piping. Chamber portion 120 may include an oscillator 41 / 80. An injection or supply pressure sensor 280, for detecting the gas pressure that is directed into oscillator 41 / 80, may reside in gas flow inlet channel 42. Alternatively, sensor 280 may be located remote and connected by a tube that can transmit gas pressure. Still further, sensor 280 may reside in a gas pressure controller 300. Gas pressure controller 300 may be coupled upstream of injection pressure sensor 280 and gas pressure sensor 160. Tool portion 140 includes a tool forming surface 200.

[0037] As shown in Figure 9, pressurized gas (the solid arrow) may be introduced into sealed chamber 240, via oscillator 41 / 80. The pressurized gas establishes a baseline pressure within sealed chamber 240. Pressure sensor 160measures the gas pressure within sealed chamber 240 during the SPF process. In order to maintain a desired pressure / time curve or relationship during the SPF process, and to maintain the desired gas fluctuations or oscillations, a feedback mechanism is formed whereby pressure controller 300 monitors the pressure within the chamber 240 via pressure sensor 160 and, in conjunction with injection pressure sensor 280, controls or regulates the amount (or pressure) of gas supplied to the oscillator 41 / 80, and effectively how much gas is injected into chamber 240.

[0038] Pressure controller 300 may be separate from oscillator 41 / 80 and may be located outside forming apparatus 100. Injection gas pressure sensor 280, while shown to be outside the forming apparatus 100, may alternatively be located within forming apparatus 100, so long as injection pressure sensor 280 is downstream from pressure controller 300 and upstream from oscillator 41 / 80.

[0039] As oscillator 41 / 80 injects gas into sealed chamber 240 to create and generally maintain a desired baseline pressure, the oscillator also injects, then holds, and then withdraws very small amounts of gas into and out of sealed chamber 240, thereby generating pressure fluctuations. The pressure fluctuations applied by oscillator 41 / 80 cause the actual or overall gas pressure within sealed chamber 240 to fluctuate or oscillate relative to the baseline pressure. Any gas that is withdrawn from sealed chamber 240 by oscillator 41 / 80, as noted above, tends to be minute in comparison to the gas that is injected into the sealed chamber.

[0040] The forming gas pressure of the described structure is thus a combination of the baseline gas pressure (shown graphically in Figure 10) and the fluctuating gas pressure. Figure 11 is a non-scale graphical representation of a gas pressure vs time curve, depicting a relationship between the baseline gas pressure and the forming gas pressure a sealed chamber. The baseline pressure is indicated by a dashed line that begins at the x-y axis junction. The forming or actual gas pressure is depicted by the solid line.

[0041] Different manners of constructing and fluidly connecting oscillator 41 / 80 and SPF apparatus 100 are contemplated. In an embodiment of the invention, oscillator 41 / 80 is constructed and is integral with the SPF apparatus itself. It is contemplated that oscillator 41 / 80 may be formed by machining flow channels or passageways within separate components that are fabricated through various machining operations, including but not limited to CNC machining, Wire and Sink EDM (Electrical Discharge Machining), Additive manufacturing, and 3-D printing. The individual components can then be gasketed, epoxied, welded, bolted, diffusion bonded, or otherwise secured to each other to achieve a gas tight seal therebetween, and to form dedicated flow channels, feedback tanks, supply reservoir(s), supply inlet 42, exhaust flow port 52, control flow port 57, and release port 72. The oscillator can then be secured within SPF tool chamber 240 and connected to the incoming gas supply line by welding, bolting, screwing, etc, as shown schematically in Figure 9. In many instances it is expected that the channelsor passageways of oscillator 41 / 80 will have rectangular or generally rectangular cross-sections, however, other cross-sectional shapes are contemplated, provided that appropriate flow calculations are conducted to account for the impact that different cross sectional shapes may have on flow. The components may be manufactured from various materials, including, but not limited to, different types of metal alloys or steel alloys (including Stainless and Inconel), ceramics, plastics, composite materials, and other materials that are capable of accommodating the temperatures, pressures, and working environment to which they will be exposed.

[0042] The applicant has found that a relationship exists between the gas pressure at inlet 42 (measured, for example, by pressure sensor 280, and referred to as Piniet) of oscillator 41 / 80 and the forming gas pressure (measured, for example, by pressure sensor 160, and referred to as PForming). In particular, it has been found that maintaining the ratio ( Rratio) of Piniet / PForming (where Piniet and PForming are absolute pressures) above a defined minimum boundary limit allows oscillator 41 / 80 to generate continuous uninterrupted gas oscillations of various amplitudes and frequencies within sealed chamber 240. A ratio Rratio below a minimum boundary limit (illustrated by the dashed lines in Figure 12) will result in a ceasing of oscillation, or inconsistent or interrupted oscillation. Thus, regulating the gas supply pressure Piniet provided to oscillator 41 / 80 to achieve a desired gas pressure ratio Rratio of Piniet (measured with gas pressure sensor 280) vs Ptorming (measured at gas pressure sensor 160) above the minimum boundary limit allows oscillator 41 / 80to generate continuous, uninterrupted, gas oscillations within pressurized chamber 240. In one embodiment of the invention the ratio of Piniet to PForming is above 1.9 for supersonic flow and below 1.9 for subsonic flow when the fluid is air. It will be appreciated that this ratio may be adjusted for different working gases.

[0043] The applicant has also found that there is no practical maximum boundary limit, or that the maximum boundary limit is extremely large, that allows oscillator 41 / 80 to maintaining a relatively large range of ratios ( Rratio) of Piniet / PForming with values greater than 100 where Piniet and PForming are absolute pressures above a defined minimum boundary limit to generate continuous, uninterrupted, gas oscillations within pressurized chamber 240. Having the minimum boundary limit as the only limit for generating gas oscillation and not having maximum boundary limit allows significantly greater operating range for oscillator 41 / 80, compared to the typical bi-stable load-type supersonic fluidic oscillator with dual exhaust ports and dual feedback tanks.

[0044] In an embodiment of the invention, control channel 62, exhaust flow channel 64, and release flow channel 74, together with their associated ports (57, 52, and 72, respectively) are fluidly connected, or "open", to chamber 60. In this manner supply pressure provided to the oscillator can be controlled while measuring the pressure inside the chamber, such that the ratio of Piniet / PForming can be maintained to achieve and / or maintain a desired oscillation frequency (orfrequencies in a narrow operating range).

[0045] The applicant has determined that a graph similar to that illustrated in Figure 12 can be created for a particular geometrically shaped oscillator 41 / 80 following routine testing or calibration of the oscillator, and that such a graph can be used to control the operation of the SPF process for a particular application.

[0046] Through the use of oscillator 41 / 80, applying pressurized gas at a baseline pressure to a surface of forming material 220, when the forming material is received within a heated SPF tool chamber 240 created when chamber portion 120 and tool portion 140 are clamped together, while also maintaining a Rratio value that is higher than the minimum boundary limit required for the generation of continuous gas oscillations, results in pressure oscillations where each oscillation (i) deforms the material, and (ii) subsequently allows for a partial stress relief of the material. Figure 12 illustrates three examples of different Rratio paths (labelled "Path 1", "Path 2", and "Path 3") within the "oscillation region" that could be followed to permit the formation of continuous, uninterrupted, gas oscillations of various amplitudes and frequencies. It will be appreciated that the straight line of Path 2 represents a constant frequency. Other Rratio paths are possible and are contemplated.

[0047] Control of the SPF process may include programming a pressurecontroller 300 (or a PLC or other microprocessor control connected to pressure controller 300) to operate in a manner that maintains Rratio above the minimum boundary limit, as determined from a plot similar to that shown in Figure 12, and as determined for the particular oscillator 41 / 80 and forming material 220 and SPF apparatus 100 in question. Through the measurement of gas pressures with sensor 160 and sensor 280, controller 300 can determine Rratio and make adjustments to the input pressure if needed to maintain Rratio above the minimum boundary limit at any point during the SPF process. Further, controller 300 may be programmed or otherwise operated such that Rratio follows a particular desired and predefined path (for example Path 1, Path 2, or Path 3 shown in Figure 12) during the SPF process. It is expected that in many cases it will be desirable to maintain a constant frequency of oscillations, to the extent that the precision of the components, and in particular controller 300, are capable of producing a constant frequency. In practice, small variations in straight line Path 2 are expected on account of manufacturing and operational limitations associated with controller 300 and other component parts.

[0048] Each pressure fluctuation generated by oscillator 41 / 80 will subsequently allow the pressure within sealed chamber 240 to "alternate" between two states of pressurization (increased and generally relatively constant). For example, when the forming pressure within sealed chamber 240 is increased beyond the baseline pressure, (as depicted by the dashed arrows in sealed chamber240 shown in Figure 9) the rate of deformation of material 220 will tend to be enhanced. This is followed by a period where the forming pressure within sealed chamber 240 is held relatively constant allowing forming material 220 to undergo a state of relaxation. This allows for a period of partial stress relief of material 220 during the SPF process. The applicant has found that this "switching" of the forming pressure, where the forming pressure is increased above the base line pressure and then returned to baseline pressure during each cycle as shown in Figure 11, permits a deformation of material 220 in a manner that allows for successive periods of a partial relief of stresses within forming material 220, that can arise when the forming material 220 undergoes deformation during a superplastic forming process.

[0049] The applicant has found that in a particular embodiment of the invention, a pressure fluctuation frequency of from about 0.1 to about 500 Hz can be achieved within sealed chamber 240 and oscillator 41 / 80 feedback tank 70. The applicant has also found that an amplitude pressure fluctuation of between 0.01 psi and 100 psi is achievable within oscillator 41 / 80, feedback tank 70, and that amplitude pressure fluctuation of between 0.001 psi and 10 psi are achievable within sealed chamber 240.

[0050] In one embodiment, the pressure fluctuations created by the invention may be continuous and of a generally uniform frequency throughout the formingprocess. In another embodiment, the pressure fluctuations may be continuous, and of both a generally uniform frequency and a generally uniform amplitude throughout the forming process. In other embodiments, the frequency and / or the amplitude of the pressure fluctuations may be discontinuous and / or varied during the forming process. One of ordinary skill will understand that in this context "uniform" does not necessarily mean precisely and exactly identical, and that variations are contemplated.

[0051] A further advantage realized through the employment of the invention is that through use of oscillator 41 / 80, pressure fluctuations are created without the need for moving parts within the oscillator. Given the relatively high temperatures at which an SPF apparatus typically operates, moving parts may expand, warp and / or break-down during a forming cycle or during repetitive forming cycles. Oscillator 41 / 80, on the other hand, does not use or require moving parts. The oscillator has no moving parts that can break down under high operating temperatures or as a result of sudden shock or vibration. The frequency and amplitude characteristics of the gas exiting the oscillator can be influenced by a number of factors, which may include the design of the internal geometry of the oscillator, the design of feedback tank 70, feedback tank port 56, feedback flow channel 48, converging nozzle 44, diverging nozzle 45, control port 57, control channel 62, exhaust flow channel 64, exhaust port 52, release flow channel 74, release port 72, the inlet gas pressure , the gas pressure within chamber 240, thegas pressure supply to the oscillator, the gas temperature, and / or the type of gas flowing through the oscillator. Varying one or more of these factors and / or one or more design parameters permits a customization of the oscillator and its operation for a specific or particular application.

[0052] It will be understood by those of skill in the art that the above described structures and processes are, in an embodiment, applicable to a superplastic forming process (such as may be applied to metallic materials that may be exposed to temperatures ranging from 400 to 900 degrees Celsius), the described structures and processes may in alternate embodiments be employed in other manufacturing processes, including but not limited to the blow forming of plastic and other "stretchable" materials at considerably lower temperatures (eg. 150 to 300 degrees Celsius).

[0053] It is to be understood that what have been described are the preferred embodiments of the invention. The scope of the claims should not be limited by the preferred embodiments set forth above, but should be given the broadest interpretation consistent with the description as a whole.

Claims

CLAIMS1. An asymmetrical load-type fluidic oscillator for providing oscillatory pressure to a chamber, the asymmetrical load-type fluidic oscillator comprising: a converging nozzle fluidly connected to a diverging nozzle, wherein fluid passing through the converging nozzle subsequently passes through and exits the diverging nozzle forming an accelerated jet of fluid, a feedback flow channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to a feedback tank, wherein the accelerated jet of fluid exiting the diverging nozzle is allowed to pass through the feedback flow channel and into the feedback tank, pressurizing the feedback tank, an exhaust flow channel with a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber; and a release flow channel with a first end fluidly connected to the feedback flow channel and a second end fluidly connected to the chamber, wherein an increase in pressure within the feedback tank causes the path of the accelerated jet of fluid to divert from the feedback flow channel to the exhaust flow channel and into the chamber, wherein fluid from the feedback flow channel and / or the feedback tank is subsequently discharged through the release flow channel, enabling the path ofthe accelerated jet of fluid to be diverted back to the feedback flow channel for recharging the feedback tank, wherein a cyclic movement of the passage of the jet of fluid between the exhaust flow channel and the feedback flow channel causes periodic pressure increases in the chamber.

2. The asymmetrical load-type fluidic oscillator as claimed in claim 1 further comprising a control channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber.

3. The asymmetrical load-type fluidic oscillator as claimed in claim 2 having a splitter separating the feedback flow channel and the exhaust flow channel at their point of fluid connection with the diverging nozzle.

4. The asymmetrical load-type fluidic oscillator as claimed in claim 3 wherein the diversion of the flow of the accelerated jet of fluid from the feedback flow channel to the exhaust flow channel causes a flow of fluid from the feedback tank and the feedback flow channel through the release flow channel and through the release port decreasing the pressure in the feedback tank, wherein upon a level of reduction in the pressure in the feedback tank the accelerated jet of fluid moves from travelling throughthe exhaust flow channel to travelling through the feedback flow channel such that the flow of pressurized fluid is diverted from being delivered to the chamber to being delivered to the feedback tank.

5. The asymmetrical load-type fluidic oscillator as claimed in claim 4 wherein the accelerated speed of the fluid is supersonic.

6. The asymmetrical load-type fluidic oscillator as claimed in claim 4 wherein the accelerated speed of the fluid is sub-sonic.

7. An asymmetrical load-type fluidic oscillator for providing oscillating fluidic pressure to a chamber, the asymmetrical load-type fluidic oscillator comprising: a converging nozzle fluidly connected to a diverging nozzle, wherein fluid passing through the converging nozzle subsequently passes through the diverging nozzle forming a supersonic jet of fluid, a feedback flow channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to a feedback tank, a release flow channel with a first end fluidly connected to the feedback flow channel and a second end fluidly connected to the chamber;an exhaust flow channel with a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber; a control channel having a first end fluidly connected to the diverging nozzle and a second end fluidly connected to the chamber; and a splitter separating the feedback flow channel and the exhaust flow channel at their point of fluid connection with the diverging nozzle; wherein an initial passage of fluid through the converging and diverging nozzles causes at least a portion of the resulting supersonic jet of fluid to pass through the feedback flow channel and into the feedback tank, pressurizing the feedback tank, at least a portion of the fluid also passing through the release flow channel; wherein an increase in pressure within the feedback tank subsequently forces the path of the jet of fluid to divert from the feedback flow channel to the exhaust flow channel and into the chamber, wherein a subsequent reduction in pressure in the feedback tank causes a diversion of the path of the jet of fluid from the exhaust flow channel to the feedback channel, resulting in a re-pressurization of the feedback tank, wherein a cyclic movement of the passage of the jet of fluid between the exhaust flow channel and the feedback channel causes periodic pressure increases in the chamber.

8. A method of controlling a superplastic forming process wherein a sheet of material is subjected to superplastic forming while retained within a chamber of a superplastic forming apparatus having fluidly connected thereto the asymmetrical load-type fluidic oscillator of any one of claims 1 to 7, the method comprising: determining a minimum boundary limit for a ratio of a supply pressure ( Piniet) applied to the asymmetrical load-type fluidic oscillator relative to a forming pressure (PForming) within the chamber of the superplastic forming apparatus, wherein the application of supply pressure to the asymmetrical loadtype fluidic oscillator in a manner that maintains the ratio of Piniet / PForming above the minimum boundary limit causes the asymmetrical load-type fluidic oscillator to generate continuous and uninterrupted gas oscillations, with a supply pressure sensor, detecting a pressure of gas supplied to the asymmetrical load-type fluidic oscillator and transmitting the detected supply pressure to a pressure controller, with a forming pressure sensor, detecting the forming pressure within the chamber and transmitting the detected forming pressure to the pressure controller, and operating the pressure controller to maintain the pressure of gas supplied to the asymmetrical load-type fluidic oscillator such that the ratio of thedetected supply pressure to the detected forming pressure is maintained above the minimum boundary limit.

9. The method as claimed in claim 8 further comprising; determining a series of ratios of Piniet / PForming, wherein each ratio lies above the minimum boundary limit, and operating the pressure controller to achieve the predetermined ratios in progression during the superplastic forming process, from a lowest of the ratios through to the highest of the ratios.

10. The method as claimed in claim 8 wherein the ratio of the detected supply pressure to the detected forming pressure is maintained constant, resulting in a constant frequency of gas oscillations.

11. The method as claimed in claim 8 wherein the ratio of the detected supply pressure to the detected forming pressure is progressively adjusted, resulting in a constant or desired amplitude and frequency of gas oscillations.

12. The method as claimed in any one of claims 8 to 11 wherein the frequency of pressure fluctuations within the chamber of the superplastic forming apparatus caused by the asymmetrical load-type supersonic fluidic oscillator is from 0.1 Hz to 500 Hz.

13. The method as claimed in any one of claims 8 to 11 wherein an amplitude of pressure fluctuations within a feedback tank of the asymmetrical loadtype supersonic fluidic oscillator is between 0.01 to 100 psi.

14. The method as claimed in claim 8 wherein the asymmetrical load-type supersonic fluidic oscillator operates to simultaneously apply pressurized gas at a baseline pressure and to generate pressure fluctuations.

15. The method as claimed in claim 8 wherein the ratio of Piniet to PForming is above 1.9 for supersonic flow and below 1.9 for subsonic flow when the fluid is air.