Process Control Method and Apparatus

The subject matter disclosed herein relates to a process control method and apparatus without the need for additional sensors. More particularly, the subject matter discloses a process control method and apparatus that controls optimum feed rates without the need for sensors to process parameters related to captured power output.

Silicon carbide is a synthetically produced crystalline compound of silicon and carbon (SiC) that can be used to form a ceramic matrix composite (CMC) by combining a SiC matrix phase with a SiC fiber phase using various processing methods. SiC/SiC CMCs have high thermal, mechanical, and chemical stability while at the same time having a high strength to weight ratio.

The hardness of a SiC/SiC CMC is second only to that of diamond tooling. In addition, the SiC fiber reinforced phase adds anisotropy and heterogeneity material properties to the compound. Thus, it is challenging to develop a high quality, efficient and cost-effective way to machine a SiC/SiC CMC.

Ultrasonic impact grinding (UIG) has been used to drill diffuser-type holes and slots in CMCs.

Therefore, it is necessary to develop a machining strategy and method to meet the targeted requirement.

An ultrasonic impact grinding system is disclosed. The ultrasonic impact grinding system includes an ultrasonic vibration tool having a tool tip. The ultrasonic impact grinding system also includes a slurry having a slurry nozzle to deliver a slurry having abrasive particles in an area of the tool tip. The tool tip of the ultrasonic vibration tool engages the abrasive particles to machine a workpiece. The ultrasonic impact grinding system also includes an ultrasonic power supply to provide power to the ultrasonic vibration tool. The ultrasonic impact grinding system also includes a controller to receive captured power output by the ultrasonic vibration tool and to control a feed rate to the ultrasonic vibration tool from the ultrasonic power supply. The power output includes a vibration amplitude as the tool tip engages the abrasive particles. The controller is configured to determine when the captured power output based on the vibration amplitude reaches a specified level. The controller also is configured to modify the feed rate to the ultrasonic vibration tool based on reaching the specified level.

A method is disclosed. The method includes machining a workpiece using an ultrasonic vibration tool to engage abrasive particles in a slurry. The method also includes capturing power output from the ultrasonic vibration tool. The power output is related to a vibration amplitude of a tool tip of the ultrasonic vibration tool. The method also includes receiving the captured power output at a controller connected to an ultrasonic power supply that supplies power to the ultrasonic vibration tool. The method also includes determining the captured power has reached a specified level. The method also includes modifying power to the ultrasonic vibration tool by a control signal from the controller to the ultrasonic power supply.

A method is disclosed. The method includes repetitively determining a magnitude of a power output signal used to power an ultrasonic vibration tool used in an ultrasonic impact grinding machine to generate a corresponding data signal. The method also includes repetitively determining an x-y-z position of the ultrasonic vibration tool during a grinding operation to generate a corresponding position signal. The method also includes adaptively processing the corresponding data signal and the corresponding position signal to generate a control signal for controlling an operation of a drive feed system for the ultrasonic vibration tool.

Before explaining at least one embodiment of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. In the following detailed description of the embodiments of the inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. It will be apparent to one skilled in the art, however, having the benefit of the instant disclosure that the inventive concepts disclosed herein may be practiced without these specific details.

As used herein, a letter following a reference numeral is intended to reference an embodiment of the feature or element that may be similar, but not necessarily identical, to a previously described element or feature bearing the same reference numeral, such as,, or. Such shorthand notations are used for purposes of convenience only, and should not be construed to limit the inventive concepts disclosed herein in any way unless expressly stated to the contrary.

Moreover, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of the “a” or “an” are employed to describe elements and components of embodiments of the instant inventive concepts. This is done merely for convenience and to give a general sense of the inventive concepts, and “a” and “an” are intended to include one or at least one and the singular also includes plural unless it is obvious that it is meant otherwise. It will be further understood that the terms “comprises” or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

As used herein, any reference to “one embodiment,” “alternative embodiments,” or “some embodiments” means that particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the inventive concepts disclosed herein. The appearances of the phrase “in some embodiments” in various places in the specification are not necessarily all referring to the same embodiment, and embodiments of the inventive concepts disclosed may include one or more of the features expressly described or inherently present herein, or any combination or sub-combination of two or more such features, along with any other features that may not necessarily be expressly described or inherently present in the instant disclosure.

The inventive concepts may be described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams or flowchart illustration, and combinations of blocks in the block diagrams or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

Inventive concepts may be implemented as a computer process, a computing system or as an article of manufacture such as a computer program product of computer readable media. The computer program product may be a computer storage medium readable by a computer system and encoding computer program instructions for executing a computer process. When accessed, the instructions cause a processor to enable other components to perform the functions disclosed below.

A method and system are disclosed. The method and system set and control optimum feed rates for ultrasonic impact grinding of CMCs without any additional sensors. The term “sensorless” or “sensor less” may refer to the feature of not adding sensors to an existing system. In other words, additional sensors may not be needed to enable the functionality disclosed herein. Instead of the pre-programmed feed rates of the current methods, the disclosed method utilizes the power data from an ultrasonic generator to adaptively adjust the feed rate the UIG's Computer Numerical Control (CNC) controller. It has been found that for a given vibration frequency, the power level in the ultrasonic generator is a good indicator of the average force on the tool. The disclosed method uses this power to set the appropriate feed rate to maintain a desired force. The force level needed for a particular tool design, slurry composition, and CMC material may be determined using modeling.

depicts an ultrasonic vibration toolaccording to the disclosed embodiments. Ultrasonic vibration toolincludes a transducer, an energy-forming horn, an ultrasonic tool tip, and a tool tip edge. The electrical energy input to transduceris converted to mechanical vibrations at a high frequency (usually at 20-40 kHz) along longitudinal axisof tool. The excited vibration is subsequently transmitted through energy-focusing hornto tool tipin order to amplify the vibration amplitude which is delivered to tool tip edge. Toolis located directly above the workpiece (not shown in) and vibrates along its longitudinal axisat a desired amplitude.

Ultrasonic vibration toolis used to machine a CMC component such as to form holes, slots, and the like. Toolis attached to a work fixture (not shown) using a suitable fastener. Toolalso includes back portion, flangeand front portionthat enhance delivery of the mechanical vibrations from tool tipto horn. These features may be arranged in various configurations to achieve the functionality disclosed above.

depicts a machining process implemented by ultrasonic vibration toolaccording to the disclosed embodiments. Tool tipis vibrated toward and away from a surfaceof workpiecein a directionthat is, for example, perpendicular to the surface of the workpiece. In some embodiments, tool tipmay be vibrated toward and away at other angles related to workpiece. Workpiecemay be a substrate that is part of the CMC component. An abrasive slurryis constantly fed into machining areaby slurry source. Slurrycontains abrasive particles, made of abrasive material, such as diamond, boron carbide, and the like, that is suspended in water, oil, or other solutions. Slurryalso flushes away debris from machining area.

The vibration of tool tipcauses abrasive particlescontained in slurrylocated between the tool tip and workpieceto impact surfaceand subsequent surfaces, thereby the removal of material by microchipping as generally indicated by reference numberin. Because the actual machining is carried out by abrasive particles, tool tipmay be softer than the workpiece. Thus, the UIG process can be treated as a micro scale material fracture process using abrasive particlesas the cutting edges.

The fracture toughness of a SiC matrix may be increased by its fiber reinforcement. The removal process of fibers, however, does not always occur simultaneously with the SiC matrix. This condition indicates that the failure mechanisms vary between machining the SiC matrix and the fibers.

The fracture mechanism of a SiC matrix is relatively uniform. Fiber fracture forms may be related to fiber orientation and density. SiC fibers are first de-bonded from the SiC matrix due to extrusion by tool. One or more of a bending-induced fracture, a compression-induced fracture and a shear-induced fracture occur in different orientations of the SiC fibers.

Material removal rate mainly depends on vibration amplitude, applied static pressure, abrasive concentration, and size distribution of the abrasive particles. Once the slurry solution is selected to be used, primarily only vibration amplitudeand feed rates can be adjusted to achieve the desired material removal. Vibration amplituderefers to the peak-to-peak amplitude at tool edgeof tool tip. Tool edgevibrates in direction. The amplitude of this vibration, or vibration amplitude, varies as tooloperates.

Woven reinforced materials such as CMCs may include three different constituents: fibers, matrix, and porosities. Particularly in CMCs, due to the complex manufacturing method followed and especially during the stage of Chemical Vapor Infiltration (CVI), big porosities can be found within the material and therefore need to be considered to get an in-depth understanding of the machining mechanism.

depicts a typical microstructure of a workpiececomprised of CMC materialhaving fiber towsandwhich are formed of CMC fiber, and are interwoven. Workpiecemay be an intermediate product being machined to form a component, such as a blade outer air seal, a static vane, a turbine blade, other components for gas turbine engines, and other components for other applications. CMC materialalso includes a CMC matrix such as shown at, as well as pores or voids in the matrix.

Accordingly, a CVI CMC structure may include the fiber-rich region, matrix-rich region and porosities, and their relative content can be expressed as:

depicts how the relative content of fiber (λ) and matrix (v) changes along the hole and depending on where a holeis machined within the CMC workpiece. Holemay refer to a slot, an indentation, and the like. Referring to, as workpieceis being machined, tool tipand tool tip edgemay initially encounter tow. One can appreciate that the relative content of towsand(fibers) as well as the matrix and porosity is changing along hole axis Y. It also may vary depending on where holeis machined. More than one hole may be machined into workpiece. Thus, variation may be encountered between the content of workpieceat the distinct area. For example, directly to the left of hole axis Y, the respective materials of workpiecewould differ in order.

Referring to, tool tipencounters a tow, with a slight bit of matrixhaving porosity. As may be appreciated, tool tip edgemoves further along tool axis Y. This further movement along tool axis Y may result in a greater vibration amplitudefor tool tip. Referring to, a subsequent step shows where tool tipis machined through towand is again encountering matrixhaving porosity at area. In a subsequent step, tool tipwill have moved through areaof matrixwith porosities and will again encounter a portion of tow. These steps also result in further movement of tool tip edgealong tool axis Y, which may result in an increased vibration amplitudefor tool tip.

As depicted in, the relative content of fiber, matrix and porosity is changing along tool axis Y, and it also varies depending on where the hole is machined. Therefore, two stochastic variables are defined to describe the structure of the material; the relative content of fiber is defined as λ while the relative content of matrix as v. Hence, the total relative content of material at a specific instant of the drilling process (t) or drilling depth (d) for a certain size of a tool(s) can be defined as:

One may appreciate that, depending on how the material is distributed along the drilling path, toolmight encounter different resultant axial loads. Due to the stochastic nature of λ and v, a probabilistic approach defining how the resultant cutting load tends to fluctuate depending on the cutting depth (d), can offer an understanding of how the heterogeneous material property affects the level of dynamics of the system.

depicts a graphof measured machining loads of CMCs, which have different magnitude due to the heterogeneous nature. This is due to the different material constituents (fibers, matrix and porosities), which are in contact with the tool tip at each instant of the machining process. Graphincludes axis, which provides values for the machining depth of toolin millimeters. Graphalso includes axis, which provides values for machining loads in Newtons. As shown in, after every 9-11 mils, one or more peak loadsmay be observed, which correlates to the depth of each tow/ply, and the pattern is repeatable. From machining perspective, the fluctuated loads are not desirable for creating precision features and can cause overloading of tooling for some cases. Thus, it is desirable to perform adaptive control of axial loads to improve process efficiency.

Without a precise follow-up control of frequency and amplitude of the electric signal feeding the ultrasonic stack, the output power of a power supply for toolwill fluctuate strongly during machining process resulting in bad quality of the process. In the UIG process, the average power P can be estimated with the following equation:

In addition to the CMC materials and the distribution of SiC fibers, the average load also depends on the feed rate along the machining direction, or tool axis Y.depicts graphhaving axisproviding values for time in seconds and axisproviding values for force in Newtons. When the feed rates are suitable to the material removal capability of the process, the average load tends to be small and stable other than a few peak loadsthat occur where the area has higher ratio of SiC fibers as shown in graph.

On the other hand, when feed rates are beyond, or exceeds, the material removal capability of the process, the cutting load increases quickly, and sometimes it can cause tool breakage and deflection if the applied load is over its yield strength. Thereafter it is necessary to monitor and control the power output to avoid overloading the tool.

It is more efficient to access all process data in real-time. Based on the available information from machine tools and ultrasonic power supplies, an adaptive process control approach is proposed in this invention to improve the machining stability and performance as shown in.

depicts a closed loop adaptive ultrasonic systemaccording to the disclosed embodiments. The system includes an ultrasonic power supply, which receives incoming electrical power at power terminal. Power supplysupplies electrical power to ultrasonic vibration toolvia power terminal. Toolincludes tool tip, which is used to perform a machining operation on workpiece. Workpieceis mounted on machine table, which in turn is driven in x-y-z directions by drive systemunder the control of CNC controller. Ultrasonic power supplymay also supply electrical power to drive systemand CNC controller, or theses elements can be powered from other sources.

When toolis fixed in a stationary position, drive systemcan position workpieceunder tool tipas needed in order to carry out the machining operation under the control of CNC controller. Alternatively, workpiececan remain stationary and toolcan be carried by its own drive system similar to drive systemalso under control of a CNC controller, similar to CNC controller.

The power output from ultrasonic power supplyis captured during the machining operation by data acquisition device and signal processing device. In particular, voltages and currents are captured for processing by control unit, as disclosed below.

After appropriate filtering to remove unwanted artifacts, if necessary, the data signal from deviceis suppled to control unit. Control unitalso controls the operation of CNC controller. The data signal is used by control unitto control the operation of CNC controllerto, in turn, control the feed rates of drive systemto maintain desired loads on tool. Speed and position data from axis encoder scalar unitis also supplied in real time to control unit. Based on all of this data, control unitcan determine the motion and rate of motion along the machining axis of toolrequired in order to achieve the desired and most efficient machining process. This feature allows control unitto CNC controller, accordingly. Control unitcan also control the operation of tool, e.g., turning the tool on and off, controlling various operating parameters, and turning slurry sourceon and off.

Databaseis included in system. During the disclosed processes, all process data, including machining conditions, reference and actual load as well as amplitude profiles are stored in database. The data may be saved for analysis. If the targeted process performance is achieved to meet the quality inspection requirements of parts subject to ultrasonic machining by tool, then the reference process signature and the measured signature may be fused as an adjusted baseline signature. The adjusted baseline signature may be saved to database. In machining subsequent CMC parts, the adjusted baseline signature may be used for process monitoring and control by following the same processes used to machine the previous workpieces.

This iterative process may be repeated until all parts are machined. Over time, with physics-guided machine learning, a reliable historical dataset may be built as an up-to-date representation of the physical operation of system. Thus, a process profile with high fidelity may be built, which can be used to evaluate the current condition. It also may be used to predict future behavior, refine the control of tool, and optimize operations within system.

depicts a flowchartfor controlling ultrasonic vibration toolaccording to the disclosed embodiments. Flowchartmay refer tofor illustrative purposes. Flowchart, however, is not limited by the embodiments disclosed by.

Stepexecutes by providing power to tool. Ultrasonic power supplyprovides power to tool. The power output of ultrasonic power supplymay control a tool speed to maintain a desired load on tool. Stepexecutes by machining a workpieceusing toolto engage abrasive particlesin slurry. Abrasive particlesmachine workpieceand are washed away by slurry.

Stepexecutes by capturing a power output from toolusing data acquisition and signal processing device. The power output is related to a vibration amplitudeof a tool tipof tool. In some embodiments, a larger vibration amplitude may be used to efficiently machine the fiber tow, such as towsand, during operations. Based on Equation 2 disclosed above, a profile for vibration amplitudemay be estimated to overcome nonuniform fracture toughness along the machining path, shown by hole axis Y. A smaller vibration amplitudemay be provided for regions with a higher ration of pores in matrix. A larger vibration amplitudemay be provided for regions with an increased concentration ratio of fiber tows. This estimated amplitude may be used as a reference for adaptive process control of system.

Stepexecutes by receiving the captured power output at a controller, such as control unit, from device. Stepexecutes by determining whether the captured power output received at control unithas reached a specified level. As noted above, a reference amplitude may be used to compare against the captured power output having vibration amplitude. Control unitmay process the power output to determine a vibration amplitudecurrently being experienced by tool.

If stepis no, then flowchartproceeds back to stepto continue machining workpiecewith tool. If the actual feed rate, or vibration amplitude, is within a reasonable range by not reaching a specified level, then the process continues until a peak load condition is observed or machining is completed.