Abstract:
A vibration damping system for machining parts uses magneto rheological radial squeeze film damper technology to reduce part vibration, enhance tool lifecycles, and to improve part surface finish. In the described embodiment, the damping system includes a pair of damping cylinders affixed to a machine tool fixture, each cylinder containing a solid core concentrically situated within an internal sleeve portion of the cylinder. Rheological fluid contained within a radial space between the core and sleeve defines a radial squeeze channel for the fluid. Fluid stiffness is controlled in real time by varying an electric current to modulate a magnetic field passing through the fluid to dampen vibrations in accordance with at least one predetermined algorithm. As material is removed from the part during machining, the fluid damping characteristics are actively managed by a machine tool controller as a function of a combination of dynamically changing and predetermined algorithmic inputs.

Description:
FIELD 
     The present disclosure relates generally to damping vibrations induced via tool machining of a workpiece, and more specifically to magneto rheological damping fixtures configured to provide real-time vibration control. 
     BACKGROUND 
     Metal machining involves vibratory forces that result from interactions of a cutting tool with a workpiece or part to be machine finished. Vibrations induced by such interactions create adverse effects on cutting tool life cycles, are deleterious to workpiece or part surface quality, and may produce hazardous noise pollution. Magneto rheological technology is known to reduce cutting tool vibration and associated tool chatter during machining processes involving workpieces held within fixtures. Known magneto rheological damping systems utilize electric currents to modify magnetic fields to produce variable stiffness of rheological fluids for damping effect. As such, rheological fluids are able to effectively and dynamically shift frequency ranges in-situ during machining of workpieces by automatically varying viscosities of a particular rheological damping fluid being used. 
     Although sophistication levels of damping systems have continued to advance, there remain certain deficiencies and/or limitations. For example, some damping systems require the placement of weights on workpieces or machine tool structures during the machining process. Since the weights must be physically removed, replaced, and/or shifted about as the machining progresses, workers are required to enter and exit the machine environment. 
     In addition, most magneto rheological damping systems involve only linear damping capabilities, thus providing damping along a single axis, such as only along either a lateral or a side-to-side axis. Further, since volume or mass of a part or workpiece is reduced during its actual machining, levels of stiffness of the rheological fluid are not adjusted in real time to fully accommodate changing workpiece vibration characteristics. 
     It is therefore desirable to provide improved magneto rheological fixture damping systems. 
     SUMMARY 
     In accordance with one aspect of the present disclosure, a modular machining fixture damping system uses rheological fluid to dampen vibrations during machining of a workpiece. The fixture damping system includes a plurality of radial squeeze film dampers containing magneto rheological fluid, which are configured to provide damping in at least two dimensions. 
     In accordance with another aspect of the present disclosure, a machine controller is configured to modulate the virtual density or dynamic stiffness of the magneto rheological fluid in accordance with a predetermined algorithm for providing real-time adjustments of a magnetic field therethrough via modulation of an electric current passing through one or more electromagnets. 
     In accordance with another aspect of the present disclosure, a machine tool controller utilizes the algorithm to modulate the magnetic field to control dynamic stiffness of the rheological fluid. 
     In accordance with yet another aspect of the present disclosure, the machine tool controller employs the algorithm to achieve a given dynamic stiffness of the rheological fluid as a function of reduction in mass of the workpiece during the machining process. 
     In accordance with a still further aspect of the present disclosure, the modular machining fixture damping system includes a modular machining fixture, a block for holding a workpiece, and a cradle for supporting the block, all integrated within a machining tombstone. 
     The features, functions, and advantages disclosed herein can be achieved independently in various embodiments or may be combined in yet other embodiments, the details of which may be better appreciated with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a modular machining fixture that may be used in the magneto rheological damping system of the present disclosure. 
         FIG. 2  is a cross-sectional view of the modular machining fixture of  FIG. 1 , taken along lines  2 - 2  of  FIG. 1 . 
         FIG. 3  is a combination perspective and cross-sectional view of a damper that may be used in the magneto rheological damping system of the present disclosure. 
         FIG. 3A  is a cross-sectional, perspective view showing an enlarged portion of the damper shown in  FIG. 3 . 
         FIG. 4  is a top view of a portion of the modular machining fixture of  FIGS. 1 and 2 . 
         FIG. 4A  is an enlarged inset portion of  FIG. 4 . 
         FIG. 5  is an elevational view of an exemplary machine tool configuration utilizing the magneto rheological fixture damping system of the present disclosure. 
         FIG. 6  is a flowchart depicting exemplary functions of a machine tool controller that may be utilized in the magneto rheological fixture damping system of the present disclosure. 
     
    
    
     It should be understood that the drawings are not to scale, and that the disclosed embodiments may be illustrated only schematically. It should be further appreciated that the following detailed description is only exemplary, and not intended to be limiting. As such, although the present disclosure is, for purposes of explanatory convenience, depicted and described in only illustrative embodiments, the disclosure may be implemented in numerous additional embodiments, and within or as part of various additional systems and environments not shown or described herein. 
     DETAILED DESCRIPTION 
     The following detailed description is intended to provide examples of both apparatus and methods for carrying out the disclosure. Actual scope of the disclosure is as defined by the appended claims. 
     Referring initially to  FIG. 1 , a modular machining fixture  10  includes a rigid base  12 , and a pair of end clamps  14 ,  16 , spaced along a longitudinal axis “a-a”. The end clamps  14 ,  16  are releasably secured to the base  12  by vertically disposed bolts  18 . Situated on the base  12  between the end clamps  14 ,  16  is a dovetail block  20  configured for holding a workpiece (not shown in  FIG. 1 ), as later described. The dovetail block  20  includes a plurality of spaced, laterally extending, dovetail surfaces  22  for supporting the workpiece, as will be appreciated by those skilled in the art. A plurality of side clamps  28  are secured on one side of the block  20  to a vertically or upstanding cradle wall  32 , while a plurality of opposing side clamps  30  are secured to a similar opposite cradle wall  34 . The side clamps  28 ,  30  are secured to the spaced cradle walls  32 ,  34 , respectively, by laterally extending bolts  36  (shown only with respect to side clamps  30 ). 
     In the embodiment disclosed, a pair of laterally spaced elongated cylindrical magneto rheological dampers  40  and  42  pass through respective sets of apertures  44 ,  46  of respective side clamps  28  and  30 , as shown, each of the dampers  40  and  42  having their ends supported within apertures  38  of end clamps  14  and  16 . Each of the dampers  40 ,  42  includes an axially oriented threaded port  54 ,  56 , respectively, for receiving magneto rheological fluid within the cylindrical dampers, as further described below. 
     Referring now to  FIG. 2 , a cross-sectional view of the machining fixture  10  reveals each of the elongated cylindrical magneto rheological dampers  40 ,  42 . Each damper  40 ,  42  includes an exterior cylindrical damper sleeve  50  that houses a solid metal core  52  configured to incorporate electromagnets (not shown) for reaction with a rheological fluid contained between the sleeve  50  and the core  52 . A channel  60 , defined by the radial space between the elements of sleeve  50  and core  52 , contains a reactive rheological fluid which responds dynamically to changes in magnetic fields, as those skilled in the art will appreciate. To generate and modulate a magnetic field through the fluid, an electrical current may be applied between the sleeve  50  and the core  52  by connecting each to respective positive and ground electrical leads, the current then passing through the electromagnets of the core  52 . Since the rheological fluids incorporate magnetic particles suspended in a carrier fluid, such as a type of oil, when the magnetic particles are subjected to a magnetic field, the fluid viscosity or stiffness will change as a function of magnetic field intensity, up to the point of becoming a viscoelastic solid at full magnetic saturation. Any discussion of specific characteristics of such magneto rheological fluids is, however, beyond the scope of this disclosure. 
     Continuing reference to  FIG. 2 , it will be noted that the dovetail block  20  is supported on a cradle base  48 , and that each of the vertical cradle walls  32 ,  34  is integrally fixed to the cradle base  48 , as shown. As noted, the side clamp  28  is secured to the vertical wall  32 , while the side clamp  30  is secured to the vertical wall  34 . As such, the side clamps may be configured to be adjustable for tuning bending moments of the dampers  40 ,  42  by virtue of the previously described laterally extending bolts  36  ( FIG. 1 ), as those skilled in the art may appreciate. 
     Referring now to  FIG. 3 , one of the dampers, damper  40  is shown in greater detail; the dampers  40 ,  42  are essentially identical, except for their relative positions, i.e., one is positioned on each side of the axis a-a. As earlier noted, each damper  40 ,  42  contains an exterior cylindrical sleeve  50  have threaded fluid ports in each end ( FIG. 3 ). Each of the threaded ports  54 ,  56  communicates with an interior axial fluid port  57 , which in turn communicates with a plurality (for example three) of radially oriented, interior fluid ports  58  collectively configured to supply magneto rheological fluid directly into the channel  60 . The described porting arrangement can permit constant flow and/or exchanges of fluid in order to maintain consistent temperatures, to the extent that rising fluid temperatures may deleteriously affect density of the fluid and thus damping capability of the dampers  40 ,  42 . Such described system of ports  54 ,  56 ,  57 , and  58  may offer capability for real time transfers of fluid to and from a fluid cooling unit (not shown). 
     Continuing reference to  FIG. 3 , it will appreciated by those skilled in the art that the damper core  52  may be configured as an inner solid metal rod fitted within the outer sleeve  50 , and that the various interior ports  54 ,  56 ,  57 , and  58  will all enable the passage of magneto rheological fluid through the central core, formed as an inner rod, as shown and described. It will further be appreciated that the outer sleeve  50  and the damper core  52  may be press-fitted and welded together at their respective ends. As such, a central portion  53  of the fed damper core  52  may be of a reduced diameter to provide the channel  60  for containing magneto rheological fluid, as further described below. 
     Referring now also to  FIG. 4 , a view of the end clamps  14 ,  16 , includes the cylindrical magneto rheological damper  40  supported therebetween, but depicted without the side clamps  28 . Those skilled in the art will appreciate that vibrations will be transferred from a workpiece (not shown) that is secured to the dovetail block  20  into the entire modular machining fixture  10 , including the end clamps  14 ,  16 , as well as into the side clamps  28 , which have been removed for clarity of discussion. Thus, assuming for sake of simplicity that the loads on site clamps  28  can be represented by the loads on the end clamps  14 ,  16 , it will be appreciated that any vibratory forces, shown as arrows  62 , transmitted into the clamps  14 ,  16  will be reacted by equal and opposite countervailing forces  66 ,  68  on the damper  40 . As such, the damper  40  will tend to vibrate with the workpiece. The magneto rheological fluid can however be controlled via modulation of an electrically induced magnetic field to react to reduce and/or minimize such vibrations as the fluid, represented by a rotary arrow  70  in  FIG. 4A , is squeezed between the elements of the damper sleeve  50  and core  52  while moving within the channel  60 . This manner of magneto rheological fluid control is referred to as radial squeeze film damping, and may be effectively utilized in a radial squeeze film damping system, as more fully described below. 
     Those skilled in the art will appreciate that the damper core  52 , built as a solid cylindrical structure, is theoretically configured to be secured as a stationary structure, while the portion of the damper sleeve  50 , radially surrounding the central portion  53  of the damper core  52 , is configured to bend radially outwardly from the core under vibratory forces. As such, in the disclosed modular machining fixture  10 , at least two dimensional damping capability can be provided via the reactive behavior of the magneto rheological fluid  70  within the channel  60 ; i.e. vertically and laterally. In the disclosed embodiment, the dynamically collapsible channel  60  may have a dimension that ranges from 0.005 to 0.08 inch between the sleeve  50  and the core  52 . 
     The disclosed modular machining fixture  10  has the capability of providing both dynamic and static stiffness for damping workpiece vibrations. The clamps  28 ,  30  configured to retain the cylindrical dampers  40 ,  42  to the cradle walls  32 ,  34 , respectively, may be adjusted to increase or decrease static stiffness. As such, the laterally extending bolts  36  are adjustable to provide for desired bending moments on the respective dampers  40 ,  42  for controlling static stiffness. Conversely, dynamic stiffness control may be simultaneously provided via real-time dynamic reactions of the magneto rheological fluid  70  to changes in viscosity. Finally, it will be apparent that the radial design of the damper allows damping a vibration along multiple axes, and particularly in the more desirable vertical and lateral directions/dimensions. However, additional arrays of such dampers (not shown) may be combined with the disclosed dampers  40 ,  42  to provide damping even along a longitudinal (i.e. an end-to-end) dimension, if and wherein tooling requirements may dictate. 
     Referring now to  FIG. 5 , an exemplary magneto rheological fixture damping system  80  is configured to utilize the earlier described modular machining fixture  10 . The system  80  includes a tombstone  82 , which may be effectively described as a pedestal-style tooling column. A workpiece  84  is secured to the modular machining fixture  10 . The tombstone  82  is supported on a base  86  that may be secured to a fixed structure, such as a floor  88 . Cooperatively spaced laterally from the fixture mounted workpiece  84  is a pedestal style machine tool  90  having a base  92  also secured to a fixed structure, such as the floor  88 . The machine tool  90  includes a motor  94  which drives a tool  96 . Finally, a rigid element  98  supports a machine tool controller  100 , by which all aspects of the disclosed real time damping system  80  may be controlled. 
     Exemplary details of the operation of the machine tool fixture damping system  80  may now be described in reference to the flowchart of  FIG. 6 , which depicts all fundamental operational interactions as managed by the machine tool controller  100 . 
     During machining of the workpiece  84 , all automated vibratory inputs, represented as element  102 , received from fixture  10 , along with any previously established programming parameters, are fed into a machine tool data bank, represented as element  106 . The machine tool data bank  106  represents all cutting parameters along with accelerometer vibration signals. Real-time data from the machine tool data bank  106  is conveyed to a data algorithm analyzer, represented as element  108 , which conducts real-time analysis of received data, and feeds the analyzed data into a controller algorithm, depicted as element  110 . Predetermined target system parameters, represented as element  112 , modulate the data from element  110 , and the two sets of data  110  and  112  are fed into a magneto rheological controller  114 . 
     Simultaneously, and in parallel with the foregoing, direct user inputs, shown as element  104 , are fed into the magneto rheological controller  114  as well. Finally, any programmed machine code, reflected as element  107 , is simultaneously fed into the controller algorithm  110  and to the machine tool controller  100 . Both set of data are fed directly into the magneto rheological controller  114 , which then directly controls/manages the magneto rheological dampers  40 ,  42 . 
     It will be apparent that the ability of the squeeze film damping system  80  to accommodate direct user inputs  104  gives rise to the capacity of real time damping throughout the entire machining process. As such, as material is removed from the workpiece  84 , the natural frequency and resonance of the physical workpiece  84  changes in real time. This translates into a requirement of more or less damping, and the machine tool controller  100  is able to manage and control in real time, at least via elements  104  and  108 , any required amount of damping needed while the workpiece is physically reduced in size during the machining process. 
     Method: 
     A method of using the magneto rheological film damper system  80  to provide vibration damping of a workpiece during machining may include filling a radial space between a sleeve and a cylindrical core of a cylindrical magneto rheological radial squeeze film damper with a magneto rheological fluid; securing the damper to a machine tool fixture; securing the assembled fixture and damper to a tombstone; applying a workpiece to the fixture; placing a machine tool adjacent the workpiece, and configuring a controller to manage a predetermined algorithm to control stiffness of the fluid via application and modulation of an electric current across the fluid to control a magnetic field through the fluid in real time during machining of the workpiece via the machine tool. 
     The method may further include determining and varying the stiffness of the fluid in real time to control vibration damping as a function of reduction of mass of the workpiece. 
     INDUSTRIAL APPLICABILITY 
     The disclosed magneto rheological radial squeeze film damper system  80  may provide improved tooling capabilities across a large range of parts, part sizes, machines, and cutting tools. Offering a broad band damping solution, the system  80  is not limited to use of only tuned mass dampers which require physical application and removal of weights during the machining process as natural frequency of the part or workpiece changes. The system  80 , on the other hand, utilizes a machine tool controller driven by predetermined algorithms that may be adapted and tailored to provide real-time damping adjustments via simple modulation of electric current or voltage to change intensity of a magnetic field. 
     As such, the system  80  may provide improved part surface finish, reduced tool chatter and tool machining cycles, as well as reduced workplace environmental hazards created by sole use of tuned mass dampers. 
     Although only one embodiment may have been depicted or suggested herein, it should be appreciated that the disclosure provided is not intended to be limiting, but intended to be exemplary for purposes of economy and convenience.