Patent Application
20120107546
This invention pertains to methods of holding and confining a layer of vibration damping material against a selected surface area of a vibratile metal article to reduce mechanical vibrations generated by or transmitted in the article by effecting coulomb damping and/or viscous damping of at least the adjacent portion of the article. More specifically, one or more relatively thin layers of the vibration damping material are placed over the surface area, or in a suitable shallow recess in the surface area, and covered by an overlying sheet layer of suitable metal composition. The periphery of covering sheet layer is securely joined to the article surface by ultrasonic welding so that the covering layer confines the vibration damping material in interfacial contact with the surface area.
Automotive vehicle body structures, components, and propulsion devices are examples of many articles of manufacture that experience mechanical vibrations in their structure. The vibrations may, for example, occur in a wall or housing or partition structure, or in a shaft, or other structure susceptible to vibrating or passing vibrations. Often such operational or imposed vibrations are of a frequency that, if coupled with the surrounding atmosphere in a manner that makes them audible, can produce distressing noise to a user of the vehicle or other article. Further, vibrations in structures may lead to decreased fatigue life, if the amplitude, frequency, and mode structure are not controlled. Automotive vehicles have many body structures, motors, engine components, power transmission components, brakes, and the like that are designed to serve many functions in addition to operating at an acceptable vibrational or noise level. Still, there remains a need for practices of reducing vibrations and noise output from many such vibratile vehicle parts and other articles of manufacture.
At least in the case of automotive vehicles, such practices are needed both in the design of new vehicle parts for quiet operation and in the modification of existing vehicle parts for reduced broadcasting of noise and minimizing vibrational amplitude.
A vibratile article of manufacture is often characterized by one or more shaped body portions and corresponding surface layers. In accordance with embodiments of the invention, a method is provided for incorporating one or more thin layers of unattached, but confined, vibration damping material on or within the body portion of a metallic article at or below a finished surface of the article. In some embodiments of the invention the vibration damping material may be in the form of one or more thin metal sheets or foils of a composition like that of the body of the article, or compatible with the body composition. The thickness of each such metal layer is suitably in the range of about 0.05 millimeters (50 micrometers) to about 0.5 millimeters (500 micrometers). In many embodiments the total thickness of the metal sheet or sheets will be from fifty micrometers up to about two thousand micrometers. Such sheets serve as coulomb dampers when they are in frictional engagement against an adjacent metal body surface. In other embodiments of the invention, the damping material may, for example, be thin layers of polymer material, which serve as viscous, energy absorbing layers that lie against a metal body surface and dampen vibrations originating in the adjacent body portion or being transported through it.
The layers of coulomb damping material are generally of uniform thickness and shaped to lie with their major surfaces in close contact with an adjacent body surface to provide interfacial contact for frictional vibration damping of the body portion. The layers of viscous damping material are generally of uniform thickness and shaped to lie with their major surfaces in close intimate contact with an adjacent body surface to provide vibration damping of the body portion. Typical viscous damping materials include rubber or rubberlike materials and polymers that exhibit strong hysteretic damping; that is, they form a large hysteresis loop in stress-strain space when deformed at a frequency of interest. Examples of such materials would include butyl rubber, neoprene, polyurethane, and other polymers, such as vinyls or nylons. The plan-view shape of the damping layer is designed to cover an area of the body to achieve a suitable interfacial vibration damping effect. Where two or more layers of damping materials are applied to a body portion, both layers may be used to achieve coulomb damping or viscous damping or a combination of both damping mechanisms. The thickness of the viscous damping material will usually be in the range of about twenty-five micrometers to about one thousand micrometers.
In some embodiments of the invention the layer(s) of damping material is applied to an unaltered surface of the body portion, or into a shallow recess formed in the surface for the purpose of receiving the damping material. It is generally preferred to provide a shallow recess in the body surface that is shaped or configured to receive and laterally confine the one or more layers of vibration damping material. The inserted damping material, placed in the recess, may lie flush-with or above the surrounding surface of the body. In most embodiments of the invention, a recess having a depth up to about one thousand micrometers and less than the total thickness of the vibration damping material will be suitable. In each such embodiment a thin metal sheet is placed over the vibration damping material so as to confine it in interfacial contact with the underlying surface. The periphery of the metal cover sheet is ultrasonically welded to the surrounding surface of the metal body of the article. In each embodiment, the layer of damping material is entirely covered with a thin sheet of metal, preferably of the same composition as the adjoining body of the article. The shape of the covering metal sheet is such that it may be ultrasonically welded around its entire periphery to trap and contain the vibration damping layer in interfacial contact against the body portion of the article. In most embodiments a thickness of the covering metal sheet of up to about three hundred micrometers will be suitable.
In some embodiments of the invention the vibration damping material may be introduced into an unfinished body portion of the article as the body portion is being made. In other embodiments of the invention, some part of a previously-made body portion may be adapted for placement and covering of vibration damping material by methods of this invention. The surface of the body portion or layer within the body portion may be substantially flat or contoured. After the layer or layers of damping material have been confined on or within the body portion of the article by ultrasonic welding of the covering metal layer, the surface of the article may be finished in any desired manner for the appearance, use, and performance of the article.
The selection of the damping material or materials and the locations of the materials in or on the body of the article are determined by trial or experience to provide a desired vibration damping effect in a vibratile article of manufacture.
Other objects and advantages of the invention will be apparent from a description of illustrative examples which follow below in this specification. The examples are intended for illustration of practices of the invention but not as limitations on the scope of the invention.
Embodiments of this invention are useful in damping vibrations in articles of manufacture having one or more metallic portions or structural elements in which mechanical vibrations are produced or transmitted. Many such vibratile articles are used, for example, in automotive vehicles. The article may have at least one structural element which is formed of a metal composition such as an aluminum alloy, a steel alloy, a magnesium alloy, or other metal alloy composition. Since an automotive vehicle comprises many parts and components and is intended to be used in motion, many such components are subjected to, or are susceptible to fatigue-causing and/or noise-making vibrations.
Practices of the invention will be illustrated as applied to at least one structural element of an article, such as a metal housing for an electronic device for controlling the operation of an electric motor for driving one or more wheels of a vehicle. For example, such a housing component may be die cast from an aluminum casting alloy, such as alloy 380.
The design of article 10 has taken into consideration that it may generate or transfer mechanical vibrations as it is being used in its location on a vehicle. Further the structure and shape of the article have been tested and/or analyzed to identify a region of the article in which such vibrations might be damped by application of thin layers of suitable damping materials to one or more surfaces 14 of a body portion. In some embodiments of the invention, it is suitable to apply a layer of damping material directly to a region of a surface 14. However, it is often preferred to provide a strategically-located, receptacle volume or recess in the body portion to better confine the vibration damping material.
As a result of such determinations and in this illustrative embodiment, a shallow recess 16 has been formed in surface 14. In
The outline of recess 16 and the dimension(s) of its walls 22 are predetermined to receive one or more layers 20 of vibration damping material. In
In
In still other embodiments of the invention, the total thicknesses of one or more layers of vibration damping material may be substantially the same as the height of walls 22. And, as stated, one or more layers of vibration material may be inserted in a recess 16 or on a surface 14 of body portion 12.
In some embodiments of the invention, the coulomb damping materials consist of a stack of layers that are each about 50 to about 500 micrometers in thickness. And depending on how many layers of damping material are placed in a recess 16 (or directly on a surface 14) the depth of a recess, as measured by side walls 22, is up to several hundred micrometers or so.
In other embodiments of the invention, coulomb damping material consists of a single layer that is about 50 to about 2000 micrometers in thickness. Viscous damping material may suitably consist of a single layer that is about 25 to about 1000 micrometers in thickness.
As illustrated in
In accordance with practices of this invention ultrasonic welding is used to bond peripheral portions of a thin metal sheet, strip, foil, or tape to a surface of a metal article or portion of an article so as to confine vibration damping material against a surface of the article. When this welding process is applied to bond a vibration material-covering metal sheet layer to a surface of a metal article, a true metallurgical bond is created over the interface, although no liquid (molten) metal is involved. The ultrasonic consolidation of the metal-metal interface occurs in a solid (non-molten) state environment.
The temperature rise at the interface between the covering layer and the surface of the metal article is below the melting point, typically 35% to 50% of the absolute value of the melting point for most metals, and any heating that occurs is confined to a region a few microns thick. Rapid heat dissipation from the region of bonding ensures that minimal residual stresses arise. As such, post-processing to relieve residual stresses is typically not necessary. Similarly, phase transformation is generally avoided.
The main components of an ultrasonic welding unit are well known and commercially available. An ultrasonic generator or power supply receives main grid electricity at a low frequency, preferably in the range of 50 to 60 Hz, and at a low voltage of 120V or 240V AC. The generator converts the input to an output at a higher voltage, preferably having a frequency in the range of 15 to 60 kHz. A useful working frequency is 20 kHz, which is above the normal range of human hearing of about 18 kHz. Systems employing higher frequencies of 40 kHz to 60 kHz with lower amplitude vibrations are preferably employed for fragile materials, such as very thin foils or substrates which are easily damaged.
The high frequency output of the ultrasonic generator is transmitted to a transducer or converter, which converts the signal to mechanical vibratory energy at the same ultrasonic frequencies. State-of-the art transducers operate on piezoelectric principles and incorporate discs or rings made of piezoelectric material, such as piezoelectric ceramic crystals, which are compressed between two metal sections. An advanced generator features automatic tuning adjustment in relation to the transducer so that constant amplitude of vibration is maintained during the operation of the welding unit.
The vibratory energy of the transducer is transmitted to a booster, which decreases or increases the amplitude of the ultrasonic waves. The waves are then transmitted to the sonotrode (also called a horn), which is a custom-made tool that comes in contact with the workpieces. The sonotrode may be designed as a tool-holder carrying a tool bit, or it may be provided in one integrated piece incorporating specific geometric features. In many embodiments for application of a tape, foil, or strip to a surface of an article, the sonotrode may be formed as a roller with axles for rolling contact with the upper surface of the strip.
In the embodiment of
The methods illustrated in
In the above illustrations of practices of the invention, one or more layers of damping material were confined within a recess formed in a body portion of the article. In other embodiments of the invention, one or more layers of damping material may be covered and confined against a surface of an article without the use of a formed recess. For example, as illustrated in
An example of application of this invention may be to a portion of a power electronics housing as used to contain the power inverter module for a hybrid electric automobile. Such housings may be die cast from a suitable alloy such as aluminum casting alloy 380. The recess may be machined into an inner surface of the housing with damping material positioned within the recess but extending above the electronic component of the housing. A cover sheet would be subsequently welded around its periphery to trap the damping material between the sheet and the casting. In the case of the power electronics housing , the damping treatment is placed on the inside surface of the housing such that once the housing is assembled, the added materials are not visible and they are not exposed to the environment, but rather lie within a sealed enclosure.
In the use of an article made in accordance with this invention, the covered and trapped vibration damping material engages a surface of the article in vibration damping interfacial contact. Where the vibration damping material is a metal sheet or layer, or other non-viscous material, the interfacial contact is frictional and coulomb damping occurs to absorb energy of the vibrations and to mitigate their intensity and effect. Where the vibration damping material is viscous, such as a polymeric material, the damping effect is of a viscous mechanism and nature.
Thus, practices of the invention have been described by some illustrative examples. But the invention is clearly applicable to the incorporation of one or more thin layers of vibration damping material to variously shaped surfaces of many different shapes of metal articles.
