CN108326634A - A kind of cutting force measurement apparatus and method in situ towards ultrasonic vibration assisted machining - Google Patents

A kind of cutting force measurement apparatus and method in situ towards ultrasonic vibration assisted machining Download PDF

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Publication number
CN108326634A
CN108326634A CN201810008116.8A CN201810008116A CN108326634A CN 108326634 A CN108326634 A CN 108326634A CN 201810008116 A CN201810008116 A CN 201810008116A CN 108326634 A CN108326634 A CN 108326634A
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stress
amplitude
cutting force
amplitude transformer
force
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CN108326634B (en
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宋乐
李美怡风
宫虎
郑叶龙
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Tianjin University
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Tianjin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
    • B23Q17/09—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool
    • B23Q17/0952—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0061—Force sensors associated with industrial machines or actuators
    • G01L5/0076—Force sensors associated with manufacturing machines

Abstract

The cutting force measurement apparatus and method in situ towards ultrasonic vibration assisted machining that the invention discloses a kind of, include to the vibration frequency and the laser interferometer that is measured in real time of vibration amplitude at tool nose, monitor the high speed camera of cutter and workpiece contact condition, to the PVDF piezoelectric membranes that the stress in amplitude transformer is measured in real time, the piezoelectric force platform that stress propagation characteristic equation is modified；The PVDF piezoelectric membranes are pasted onto the pattern measurement region of amplitude transformer, and the piezoelectric force platform is arranged in the end of amplitude transformer.The present invention is using ultrasonic vibration assisted machining process as research object, its stress wave propagation is studied, by establishing vibrocutting dynamic impulsion mathematical model, the final cutting force value in situ obtained in processing, further to disclose the power mechanism of transmission in Vibration Cutting Process, it is quantitative study cutting force to the affecting laws of machining surface integrity, and further promotes machined surface quality and provide fundamental basis.

Description

A kind of cutting force measurement apparatus and method in situ towards ultrasonic vibration assisted machining
Technical field
The present invention relates to Precision Machining and cutting force measurement, more particularly to a kind of original position towards ultrasonic vibration assisted machining Cutting force measurement apparatus and method.
Background technology
In field of machining, traditional processing method is difficult to realize to difficult-to-machine material, peculiar part and thin-wall part Deng progress Precision Machining, therefore there are Precision Machining and special processing technology, ultrasonic vibration assisted machining is one of method, Have many advantages, such as not available for traditional diamond-making technique, such as reduce cutting force and power attenuation, reduces chip deformation, cutting temperature Degree is substantially reduced, and improves the using effect of cutting fluid, reduces surface roughness, improves machining accuracy and surface quality so that cut It considers to be worth doing disposable, increases actual shearing angle, reduce tool wear, extend the service life of cutter, greatly improve production efficiency etc..
And cutting force as influence cutting effect, tool wear, at bits an important factor for, be always ultrasonic vibration auxiliary plus Research emphasis in work.Cutting force measurement method is realized by placing dynamometer on knife rest pedestal mostly at present, however by Fluctuation to high-frequency vibration influences, force value that dynamometer is obtained and the cutting force in situ at point of a knife there are relatively large deviation, from And authentic data support can not be provided to promote processing quality and technique.For this purpose, under the inspiration of stress wave propagation principle, pass through It chooses sensor appropriate and measurement method, obtains from exciting source, the amplitude transformer complete stress wave propagation situation to from point of a knife again, The final cutting force in situ obtained at point of a knife, this has the propagation characteristic of stress wave and the research of vibrocutting important Practice significance.
Invention content
The purpose of the present invention is overcoming deficiency in the prior art, a kind of original position towards ultrasonic vibration assisted machining is provided Cutting force measurement apparatus and method, the present invention are using ultrasonic vibration assisted machining process as research object, to its stress wave propagation Process is studied, by establishing vibrocutting dynamic impulsion mathematical model, the final cutting force value in situ obtained in processing, with Just the power mechanism of transmission in Vibration Cutting Process is further disclosed, is influence of the quantitative study cutting force to machining surface integrity Rule, and further promote machined surface quality and provide fundamental basis.
The technical solution adopted in the present invention is：A kind of cutting force measurement in situ dress towards ultrasonic vibration assisted machining It sets, includes that cutter and work are monitored to the vibration frequency and the laser interferometer that is measured in real time of vibration amplitude at tool nose The high speed camera of part contact condition, to the PVDF piezoelectric membranes that the stress in amplitude transformer is measured in real time, to stress propagation spy The piezoelectric force platform that property equation is modified；The PVDF piezoelectric membranes are pasted onto the pattern measurement region of amplitude transformer, described Piezoelectric force platform is arranged in the end of amplitude transformer；The PVDF piezoelectric membranes, laser interferometer, high speed camera and piezoelectric force Platform is connected to host computer.
The amplitude transformer uses horn,stepped, and the pattern measurement region of the amplitude transformer is horn,stepped 5 stress value particular points on small end：The starting point of stress amplitude, the terminal of stress amplitude, the peak of stress amplitude, stress amplitude It is worth two equal branches of distance between peak and stress amplitude terminal.
One group of PVDF piezoelectric membrane is pasted on the pattern measurement region of each amplitude transformer to answer in amplitude transformer to measure The curve that power is propagated, every group of PVDF piezoelectric membranes stickup includes three PVDF piezoelectric membranes evenly distributed in the circumferential direction.
A kind of measurement method of the cutting force measurement device in situ towards ultrasonic vibration assisted machining based on above-mentioned, including with Lower step：
Step 1：Assemble a kind of above-mentioned cutting force measurement device in situ towards ultrasonic vibration assisted machining；
Step 2：Laser interferometer monitors a certain radial vibration frequency and amplitude at point of a knife, and high speed camera monitors cutter With the contact condition of workpiece, and using vibration frequency, amplitude and contact the period as the input condition of finite element simulation, obtain luffing Bar FEM Numerical Simulation determines pattern measurement region；
Step 3：PVDF piezoelectric membranes are pasted onto pattern measurement region, obtain the distribution of amplitude transformer upper stress, and be fitted stress Propagation characteristic equation；
Step 4：Piezoelectric force platform obtains the cutting force of pedestal, is modified to stress propagation characteristic equation；
Step 5：Integrate amplitude transformer upper stress propagation characteristic equation.
Step 3 is specially：Five groups of PVDF piezoelectric membranes are distributed on horn,stepped, every group is be spaced 120 ° three A PVDF piezoelectric membranes obtain the stress propagation situation in entire amplitude transformer, and decoupling is acquired to PVDF piezoelectric membrane signals, Obtain five groups of three-dimensional stress value σx、σy、σz；Obtain stress value variation and relationship of the measurement point at the amplitude transformer abrupt change of cross-section：σx1 =axz2+bxz+cx, σy1=ayz2+byz+cy, σz1=azz2+bzz+cz, wherein ax、bx、cxThe respectively directions x cutting force FxEffect Two-term coefficient, Monomial coefficient and the constant term coefficient of lower stress propagation property fitting equation；ay、by、cyThe respectively directions y Cutting force FyTwo-term coefficient, Monomial coefficient and the constant term coefficient of the lower stress propagation property fitting equation of effect, az、bz、cz The respectively directions z cutting force FzTwo-term coefficient, Monomial coefficient and the constant term of the lower stress propagation property fitting equation of effect Coefficient.
Step 4 is specially：By piezoelectric force stage+module on pedestal, according to measurement gained three-dimensional cutting force calculating pair Stress value is answered, is further compared with stress propagation characteristic equation, and corrects stress propagation characteristic equation：σx2=kxσx1+bx, σy2=kyσy1+by, σz2=kzσz1+bz, wherein kx、bxRespectively piezoelectric force platform measurement is to the directions x cutting force FxEffect The first order correction factor and constant term correction factor of lower stress propagation characteristic equation, ky、byRespectively piezoelectric force platform measuring Value is to the directions y cutting force FyThe first order correction factor and constant term correction factor of the lower stress propagation characteristic equation of effect, kz、bz Respectively piezoelectric force platform measurement is to the directions z cutting force FzThe first order correction factor of the lower stress propagation characteristic equation of effect With constant term correction factor.
Step 5 is specially：First, a certain radial vibration frequency at point of a knife when obtaining cutwork using laser interferometer Rate and vibration amplitude monitor the contact condition of point of a knife and tool with high speed camera, and vibration frequency, amplitude and contact period are made For the condition of finite element analysis, the pattern measurement region of amplitude transformer is obtained according to Finite element analysis results；Then PVDF is pasted In pattern measurement region, decouples and fit amplitude transformer upper stress propagation characteristic conic section；Finally, using piezoelectric force platform Stress propagation characteristic equation is modified, more accurate stress propagation characteristic equation is obtained.
The beneficial effects of the invention are as follows：The present invention proposes that a kind of stress wave for during ultrasonic vibration assisted machining passes Broadcast the apparatus and method that characteristic carries out real-time and accurate measurement, that is, set up based on PVDF piezoelectric membranes, with laser interferometer and Supplemented by high speed camera, in conjunction with the stress wave measurement chain of piezoelectric force platform composition.The it is proposed of the measuring device and method, Ke Yiwei Stress wave Analysis on Mechanism provides experimental demonstration in vibrocutting, is conducive to theoretical development and perfection.Meanwhile it being tied according to measuring Fruit provides possibility so that vibration is more effectively transferred to for more rational exciting mode and energy transmission system optimization Material plasticity deformed area provides fundamental basis for the further development of ultrasonic vibration assisted machining technology, promotes the surface of processing Quality and integrality.
Description of the drawings
Fig. 1：The structural schematic diagram of in situ cutting force measurement device of the present invention towards ultrasonic vibration assisted machining；
Fig. 2：One PVDF piezoelectric thin-film structure schematic diagrames of the embodiment of the present invention；
Fig. 3：One amplitude transformer schematic diagram of the embodiment of the present invention；
Fig. 4：One amplitude transformer upper stress variation diagram of the embodiment of the present invention；
Fig. 5：One signal acquisition process block diagram of the embodiment of the present invention；
Fig. 6：One PVDF piezoelectric membrane force analysis figures of the embodiment of the present invention；
Fig. 7：The entire block diagram of one cutting force measurement chain of the embodiment of the present invention.
Attached drawing marks：
1, amplitude transformer；2, cutter；3, main shaft；4, workpiece；5, laser interferometer；6, high speed camera；7, PVDF piezoelectric membranes； 8, piezoelectric force platform；9, charge amplifier；10, data collecting card.
Specific implementation mode
The invention will be further described below in conjunction with the accompanying drawings.
In the present invention, it is contemplated that the impact characteristics and measurement characteristic area feature of ultrasonic vibration assisted machining, it is used Sensor need to have enough accuracy, sensitivity, flexible degree, dynamic characteristic and anti-interference ability, therefore propose with PVDF Based on (Polyvinylidene Fluoride, Kynoar) piezoelectric membrane, supplemented by laser interferometer and high speed camera, and The distributed measurement chain scheme constituted in conjunction with piezoelectric force platform.
During actual ultrasonic vibration assisted machining, due to percussion, the vibration frequency of cutter 2, vibration amplitude All with pumping signal difference, here, measuring a certain radial vibration frequency and width at point of a knife in advance using laser interferometer Value, and using the contact condition of high speed camera acquisition cutter 2 and workpiece, item is inputted using measured value as the load of finite element analysis Part, to obtain accurate pattern measurement region.PVDF piezoelectric film sensors are good with degree of flexibility, Hz-KHz is big, sensitivity The features such as high, is reference with characteristic area, multigroup measuring node is arranged in amplitude transformer, and essence is carried out to the communication process of stress wave Locating tab assembly obtains stress propagation characteristic curve.Intend configuring piezoelectric force platform in amplitude transformer end in measurement scheme, in order to test The accuracy of stress wave characteristic equation is demonstrate,proved, and it is modified, to obtain more complete fluctuating stress equation.
Ultrasonic vibration corresponding to a kind of cutting force measurement device in situ towards ultrasonic vibration assisted machining of the present invention is auxiliary Cutting apparatus is helped as shown in Figure 1, the ultrasonic vibration auxiliary cutting device includes amplitude transformer 1, cutter 2 and main shaft 3, workpiece 4 is solid It is scheduled on the main shaft 3.
As shown in Figure 1, a kind of cutting force measurement device in situ towards ultrasonic vibration assisted machining of the present invention, including to knife Have the laser interferometer 5 that a certain radial vibration frequency and vibration amplitude measure at 2 points of a knife, monitoring cutter 2 and workpiece 4 The high speed camera 6 of contact condition, to the PVDF piezoelectric membranes 7 that the stress in amplitude transformer 1 is measured in real time, to stress propagation spy The piezoelectric force platform 8 that property equation is modified；The laser interferometer 5 and 6 measured value of high speed camera are used for finite element analysis Load input；The PVDF piezoelectric membranes 7 are pasted onto the pattern measurement region of the amplitude transformer 1, the piezoelectric force platform 8 It is arranged in the end of the amplitude transformer 1；The laser interferometer 5, high speed camera 6, PVDF piezoelectric membranes 7 and piezoelectric force platform 8 are connected to host computer.
Wherein, the amplitude transformer 1 uses horn,stepped, the vibration width at the point of a knife that laser interferometer 5 is surveyed It is worth, load input condition of the contact condition of 6 surveyed tool work piece of vibration frequency and high speed camera as finite element analysis, obtains The pattern measurement region of amplitude transformer.
Wherein, the pattern measurement region of the amplitude transformer 1 is that 5 stress values on horn,stepped small end are special Point：The starting point of stress amplitude, the terminal of stress amplitude, the peak of stress amplitude, stress amplitude peak and stress amplitude Two equal branches of distance between terminal.It is thin that one group of PVDF piezoelectricity is pasted on the pattern measurement region of each amplitude transformer 1 For film 7 to measure the curve of amplitude transformer upper stress propagation, every group of stickup of PVDF piezoelectric membranes 7 includes three along the circumferential direction uniform cloth The PVDF piezoelectric membranes 7 set.
Wherein, the PVDF piezoelectric membranes 7 are connected to charge amplifier 9, and host computer is connected to by charge amplifier 9 Data collecting card 10.
Based on the measurement method of the above-mentioned cutting force measurement device in situ towards ultrasonic vibration assisted machining, including following step Suddenly：
Step 1：Assemble a kind of above-mentioned cutting force measurement device in situ towards ultrasonic vibration assisted machining.
Step 2：In advance using a certain radial vibration frequency and amplitude at laser interferometer measurement point of a knife, high speed camera The contact condition of cutter and workpiece is monitored, and using institute's vibration measuring dynamic frequency, amplitude and contact period as the load of finite element simulation Input condition obtains 1 FEM Numerical Simulation of amplitude transformer, determines pattern measurement region；
Step 3：PVDF piezoelectric membranes 7 obtain the distribution of amplitude transformer upper stress, and are fitted stress propagation characteristic equation.
Be distributed five groups of PVDF piezoelectric membranes 7 on horn,stepped 1, every group be spaced 120 ° three PVDF piezoelectricity it is thin Film 7 obtains the stress propagation situation in entire amplitude transformer 1, is acquired decoupling to 7 signal of PVDF piezoelectric membranes, obtains five groups Three-dimensional stress value σx、σy、σz；Obtain the relationship of stress value variation and measurement point between position of tool tip：σx1=axz2+bxz+ cx, σy1=ayz2+byz+cy, σz1=azz2+bzz+cz, wherein ax、bx、cxThe respectively directions x cutting force FxThe lower stress propagation of effect Two-term coefficient, Monomial coefficient and the constant term coefficient of property fitting equation；ay、by、cyThe respectively directions y cutting force FyMake With the two-term coefficient of lower stress propagation property fitting equation, Monomial coefficient and constant term coefficient, az、bz、czThe respectively side z To cutting force FzTwo-term coefficient, Monomial coefficient and the constant term coefficient of the lower stress propagation property fitting equation of effect.
Step 4：Piezoelectric force platform 8 obtains the cutting force of pedestal, is modified to stress propagation characteristic equation.
Piezoelectric force platform 8 is mounted on the base, corresponding stress value is calculated according to gained three-dimensional cutting force is measured, into one Step is compared with stress propagation characteristic equation, and corrects stress propagation characteristic equation：σx2=kxσx1+bx, σy2=kyσy1+by, σz2=kzσz1+bz, wherein kx、bxRespectively piezoelectric force platform measurement is to the directions x cutting force FxThe lower stress propagation of effect is special The first order correction factor and constant term correction factor of property equation, ky、byRespectively piezoelectric force platform measurement cuts the directions y Cut power FyThe first order correction factor and constant term correction factor of the lower stress propagation characteristic equation of effect, kz、bzRespectively piezoelectricity is surveyed Power platform measurement is to the directions z cutting force FzThe first order correction factor of the lower stress propagation characteristic equation of effect and constant term amendment Coefficient.
Step 5：Integrate 1 upper stress propagation characteristic equation of amplitude transformer.
First, using laser interferometer 5 obtain cutwork when point of a knife at a certain radial vibration frequency and vibration amplitude, The contact condition of point of a knife and tool is monitored with high speed camera 6, and using vibration frequency, amplitude and contact period as finite element analysis Load input condition, according to Finite element analysis results obtain amplitude transformer pattern measurement region；Then PVDF is pasted onto spy Measured zone is levied, decouples and fits amplitude transformer upper stress propagation characteristic conic section；Finally, right using piezoelectric force platform 8 Stress propagation characteristic equation is modified, and obtains more accurate stress propagation characteristic equation.
The present invention is described further with reference to specific embodiments and the drawings.
Embodiment one
(1) measurement method based on the cutting force measurement device in situ towards ultrasonic vibration assisted machining, with PVDF piezoelectricity Based on film 7, supplemented by laser interferometer 5 and high speed camera 6, and the combined type measurement method of piezoelectric force platform 8 is combined.
Piezoelectric force platform 8 is that the most widely used cutting force measurement method is carried out with it herein both at home and abroad at present The comparative analysis of 7 measurement result of PVDF piezoelectric membranes.And PVDF piezoelectric membranes 7 are pasted onto pattern measurement region, realize to stress Dynamic real-time measurement.Laser interferometer 5 measures a certain radial vibration frequency and amplitude at point of a knife, and high speed camera 6 monitors knife The contact condition of tool and workpiece 4 carries out finite element analysis and determines pattern measurement region；In conjunction with piezoelectric force platform 8, PVDF piezoelectricity Film 7 and laser interferometer 5, high speed camera 6, constitute from vibration source to knife bar, then arrive whole measurement chain of point of a knife.
(2) laser interferometer 5, high speed camera 6 provide load parameter for finite element analysis, determine pattern measurement region
In the present embodiment, the horn,stepped 1 for selecting magnification ratio larger selects No. 45 steel of material, amplitude transformer 1 intrinsic Frequency is set as 20kHz, selects outside diameter for D1=50mm, end diameter D2=22mm, according to quarter-wave amplitude transformer 1 The equation of motion and boundary condition etc. calculate the length of amplitude transformer 1, be used in combination Workbench to carry out emulation adjustment, obtain amplitude transformer 1 Big end length is 12mm, and small end length is 55mm.
After building ultrasonic vibration auxiliary cutting device, a certain radial vibration frequency of point of a knife is measured using laser interferometer 5 And amplitude, high speed camera 6 monitor cutter and workpiece 4 contact condition, and using institute's vibration measuring dynamic frequency, amplitude and contact the period as The load input condition of Finite Element Simulation Analysis.
If there is radial load to act on amplitude transformer 1, when the effect for not considering stress wave, it is equivalent to cantilever beam, then is become Each point stress value is directly proportional at a distance from force position on 1 same busbar of width bar.And in practical situations, cutting force is in amplitude transformer Stress wave is generated in 1, and reflection is overlapped mutually between stress wave, and complicated stress distribution is formed in amplitude transformer 1.It is single when having When radial force effect, Transient is carried out to bar, obtains the stress amplitude of 1 small end of amplitude transformer as shown in figure 4, simultaneously, emulation is sent out Existing, under frequency and action time identical other two direction active force, the distribution situation of stress amplitude is identical, and only amplitude has Variation.Therefore, select 5 stress value particular points on small end (starting point of stress amplitude, the terminal of stress amplitude, stress amplitude Peak, two equal branches of distance between stress amplitude peak and stress amplitude terminal) it is used as pattern measurement region,
(3) PVDF piezoelectric membranes 7 measure the communication process of stress wave
The driving frequency of ultrasonic vibration assisted machining is higher, and working frequency is up to 20kHz or more.PVDF piezoelectric membranes 7 Have many advantages, such as that piezoelectric modulus is big, frequency response is wide, acoustic impedance is easy to matching, mechanical strength is big, light weight and impact resistance, for convenience The whole process for measuring stress wave propagation selects PVDF piezoelectric membranes 7 as the sensor for measuring stress wave propagation.
1. the measuring principle of PVDF piezoelectric membranes 7
Piezoelectric effect：When being reinforced to certain dielectrics along certain orientation and make its deformation, generated on certain surface Charge returns to non-charged state again after external force is removed, this phenomenon is known as direct piezoelectric effect.
Introduce piezoelectric stress constant dij, under effects of strain, generated charge density can indicate PVDF piezoelectric membranes 7 For：
Wherein, dijSubscript i=1,2,3, as shown in Fig. 2, indicating that the polarization direction of PVDF piezoelectric membranes 7 and machinery are answered respectively Force direction (shearing force is indicated with 4,5,6), σ indicate the stress intensity of all directions.
2. 7 type selecting of PVDF piezoelectric membranes and stickup
7 type selecting of PVDF piezoelectric membranes：Since 7 purpose of PVDF piezoelectric membranes is to obtain the cutting stress value at particular point, Therefore, the PVDF piezoelectric membranes for selecting sensing area small as far as possible；Secondly, for ease of measuring, the big PVDF piezoelectricity of piezoelectric constant Film has more advantage, furthermore, there are the PVDF piezoelectric membranes of shielding measure that can reduce the influence of interference when measuring.
PVDF piezoelectric membranes 7 mount：5 feature locations selected by above-mentioned steps 2,5 groups of PVDF piezoelectricity of arrangement are thin Film 7, as shown in Figure 4.At 5 pattern measurement regions, at interval of 120 ° of stickups, 1 PVDF piezoelectric membrane 7, subsequently to carry out The decoupling of three axis force.Using double faced adhesive tape or epoxide-resin glue, PVDF piezoelectric membranes 7 are pasted onto in amplitude transformer 1, for anti-anti-avulsion It falls, can again be fixed with adhesive tape；Meanwhile the stickup of PVDF piezoelectric membranes 7 need to prevent electrode from being contacted with measured object, in order to avoid cause The two is connected, and signal is wrong.
3. Data collection and signal analysis
Since 7 thickness of PVDF piezoelectric membranes only has tens μm, therefore electrode is generally in upper and lower surface, when PVDF piezoelectric membranes 7 Impression strain, generated is charge, can be exported by upper/lower electrode.Fig. 5 show signal acquisition process block diagram, PVDF pressures The charge signal of conductive film 7 is amplified by charge amplifier 9, is converted into voltage signal, by data collecting card 10, in entrance Position machine, and it is acquired and is handled.
4. the decoupling of three-dimensional cutting force
It takes and is spaced 120 ° of three PVDF piezoelectric membranes 7 on a certain section of horn,stepped and analyzes it, Amplitude transformer is equivalent to a cantilever beam, as shown in fig. 6, PVDF piezoelectric membranes 7, under X, Y, Z three-dimensional force effect, deformation divides Analysis is as follows：
In Z-direction cutting force FzUnder effect, cantilever beam is in axial tension or compression, is had according to Hooke's law：
σFzFor stress value, ε (z) is FzStrain caused by effect, E are the elasticity modulus of amplitude transformer, FzIt is answered caused by effect Become：
ε (z)=Fz/S (3)
Wherein, S represents the small end area of section of amplitude transformer.Therefore, in FzIt cuts under force effect, on the same section of amplitude transformer The stress value experienced of three PVDF piezoelectric membranes 7 be identical.That is σz1=σz2=σz3。
In Y-direction cutting force FyUnder, symmetric curvature occurs for equivalent cantilever beam, according to curved axis approximate differential equation：
ω is amount of deflection, and M (y) is FyThe lower moment of flexure of effect, I represent the moment of inertia of circular section shape, and strain size and Relationship between amount of deflection is：
ε (y) is FyThe strain that the equivalent a certain position of cantilever beam generates under effect, HyiFor PVDF piezoelectric membranes shown in Fig. 67 with Vertical range between Z axis.
In summary (4) (5) two formula can obtain strain stress relation formula：
LzFor the Z-direction distance between 1 small end end face of PVDF piezoelectric membranes 7 and amplitude transformer, D is 1 end diameter of amplitude transformer.
Then for the stress value at three PVDF piezoelectric membranes 7 on same section, with HyiIt is directly proportional, i.e.,
ε1(y), ε2(y), ε3(y) it is FyUnder effect, stress value is corresponded at three PVDF piezoelectric membranes 7；Hy1,Hy2, Hy3For The vertical range corresponding to Z axis at three PVDF piezoelectric membranes 7.
Similarly, for FxIt cuts under force effect, it is similar with above formula (5) (6) (7) (8) derivation, by curved axis approximate differential side Relational expression between journey and ess-strain charge can be obtained by cutting force FxAct on the strain generated at PVDF piezoelectric membranes 7 For：
ε (x) is FxThe strain generated under cutting force effect, HxiFor the vertical range between PVDF piezoelectric membranes 7 and X-axis.
Then for the stress value at three PVDF piezoelectric membranes 7 on same section, with HxiIt is directly proportional:
ε1(x), ε2(x), ε3(x) it is FxUnder effect, stress value is corresponded at three PVDF piezoelectric membranes 7；Hx1,Hx2, Hx3For The vertical range corresponding to X-axis at three PVDF piezoelectric membranes 7.
For three PVDF piezoelectric membranes 7 (1,2,3), HyiAnd HxiIt is different：
Wherein θ=90 °, θ1=0 °, θ2=120 °, θ3=240 °.
And it can be obtained according to the relationship between formula (1) (10) (11) (12) (13) PVDF piezoelectric membranes charge and strain：
Qi=kxiεx+kyiεy+kziεz (14)
QiCharge is generated for i-th of PVDF piezoelectric membrane 7,kzi= S0E0d31(S0And E0Respectively represent the sensing area and Young's modulus of PVDF piezoelectric membranes 7), εxFor FxUnder effectInstituteWhat is generated answers Become, εyFor FyStrain caused by effect is lower, εzFor FzStrain caused by effect is lower.
And then the relationship obtained between the charge and three axis force of each group of PVDF piezoelectric membrane 7 generation can be indicated with matrix For：
Formula (14) can be converted following form：
Formula (15) equivalent-simplification at
Ax=β (17)
Wherein,
It is calculated according to matrix
R (A)=R (A | β)=3 (18)
The two order is equal, and is equal to unknown number εx、εy、εzNumber, therefore unique solution can be obtained.That is PVDF piezoelectricity is thin Strain on 7 three directions of film：εx1、εy1、εz1。
PVDF piezoelectric membranes 7 are pasted onto five feature locations, there is five groups of strains or stress value σx、σy、σz, carry out secondary Curve matching, it is assumed that the equation after conic fitting is as follows：
The equation of fitting is F in amplitude transformerx、Fy、FzThe lower stress propagation characteristic curve of effect.
(4) piezoelectric force platform 8
Piezoelectric force platform 8 is current main cutting force value measurement method both at home and abroad.In the present invention, it is surveyed using piezoelectricity Main correction means of the power platform 8 as stress propagation characteristic equation.Known from above, the stress that PVDF piezoelectric membranes 7 are fitted passes It is σ to broadcast characteristic equationx1=axz2+bxz+cx, σy1=ayz2+byz+cy, σz1=azz2+bzz+cz, enable 8 place of piezoelectric force platform Position is z=-12mm, and stress value at piezotable can be calculated by substituting into equation, and the actual measured value of dynamometer is Fx2, Fy2,Fz2, it is quotient with face area and obtains stress value σx2,σy2,σz2, it is assumed that σx2,σy2,σz2With a model to σx1,σy1,σz1It is bent Line equation is modified, and k is Monomial coefficient, and b is constant term coefficient, then has σx2=kxσx1+bx, σy2=kyσy1+by, σz2=kz σz1+bz.Therefore finally obtain accurate stress wave propagation property curve.
(5) laboratory facilities
As shown in fig. 7, being formed with laser interferometer 5, high speed camera 6, PVDF piezoelectric membranes 7 and piezoelectric force platform 8 One complete cutting force measurement chain.Obtain the characteristic curve of stress wave propagation.
1. laser interferometer, high speed camera provide load parameter for finite element analysis, pattern measurement region is determined
After building ultrasonic vibration auxiliary cutting device, a certain radial vibration frequency at laser interferometer measurement point of a knife is used And amplitude, high speed camera monitor the contact condition of cutter and workpiece, and using institute's vibration measuring dynamic frequency, amplitude and contact period as having The load input condition of the first simulation analysis of limit.1 FEM Numerical Simulation of amplitude transformer is obtained, 5 features of amplitude transformer small end are selected Measure position.
2. PVDF piezoelectric membranes 7 obtain the distribution of 1 upper stress of amplitude transformer, and are fitted stress propagation characteristic equation
Five groups are distributed on horn,stepped, every group is three PVDF piezoelectric membranes 7 for being spaced 120 °, obtains entire become Stress propagation situation on width bar is acquired decoupling to 7 signal of PVDF piezoelectric membranes, obtains five groups of three-dimensional stress value σx、σy、 σz.Obtain the relationship of stress value variation and measurement point between position of tool tip:σx1=axz2+bxz+cx, σy1=ayz2+byz+ cy, σz1=azz2+bzz+cz。
3. piezoelectric force platform 8 obtains the cutting force F of pedestal2
Piezoelectric force platform 8 is mounted on pedestal, calculates corresponding stress value according to gained three-dimensional cutting force is measured, further It is compared with stress propagation equation, and update equation again, i.e. σx2=kxσx1+bx, σy2=kyσy1+by, σz2=kzσz1+bz。
4. integrating 1 upper stress propagation characteristic equation of amplitude transformer
Build ultrasonic vibration auxiliary cutting device, using laser interferometer 5 measure 2 point of a knife of cutter at vibration frequency with shake Dynamic amplitude be used in combination high speed camera 6 to monitor contact condition and the time of contact of cutter 2 and workpiece 4, with vibration frequency, vibration amplitude, Load input parameter of the time of contact as finite element analysis obtains 5 pattern measurement positions of 1 small end of amplitude transformer.In feature It measures position and pastes PVDF piezoelectric membranes 7, measured value is decoupled and fits 1 upper stress propagation characteristic conic section of amplitude transformer. Finally, using the method for piezoelectric force platform 8, stress propagation characteristic equation is modified, it is special to obtain final stress propagation Property equation.
So far, during ultrasonic vibration assisted machining, stress propagation characteristic side can be combined by piezoelectric force platform 8 Journey is conducive to the further promotion of ultrasonic vibration assisted machining processing effect to obtain more accurately cutting force value in situ.
Although the preferred embodiment of the present invention is described above in conjunction with attached drawing, the invention is not limited in upper The specific implementation mode stated, the above mentioned embodiment is only schematical, be not it is restrictive, this field it is common Technical staff under the inspiration of the present invention, without breaking away from the scope protected by the purposes and claims of the present invention, may be used also By make it is many in the form of, within these are all belonged to the scope of protection of the present invention.

Claims (7)

1. a kind of cutting force measurement device in situ towards ultrasonic vibration assisted machining, which is characterized in that including to tool nose The laser interferometer that the vibration frequency and vibration amplitude at place are measured in real time monitors the high speed phase of cutter and workpiece contact condition Machine, to the PVDF piezoelectric membranes that the stress in amplitude transformer is measured in real time, the pressure that stress propagation characteristic equation is modified Electric force plate/platform；The PVDF piezoelectric membranes are pasted onto the pattern measurement region of amplitude transformer, and the piezoelectric force platform setting exists The end of amplitude transformer；The PVDF piezoelectric membranes, laser interferometer, high speed camera and piezoelectric force platform are connected to upper Machine.
2. a kind of cutting force measurement device in situ towards ultrasonic vibration assisted machining according to claim 1, feature It is, the amplitude transformer uses horn,stepped, and the pattern measurement region of the amplitude transformer is that horn,stepped is small 5 stress value particular points on end：The starting point of stress amplitude, the terminal of stress amplitude, the peak of stress amplitude, stress amplitude Two equal branches of distance between peak and stress amplitude terminal.
3. a kind of cutting force measurement device in situ towards ultrasonic vibration assisted machining according to claim 2, feature It is, pastes one group of PVDF piezoelectric membrane on the pattern measurement region of each amplitude transformer to measure amplitude transformer upper stress biography The curve broadcast, every group of PVDF piezoelectric membranes stickup includes three PVDF piezoelectric membranes evenly distributed in the circumferential direction.
4. a kind of cutting force in situ based on 1 to 3 any one of them of the claims towards ultrasonic vibration assisted machining is surveyed Measure the measurement method of device, which is characterized in that include the following steps：
Step 1：Assemble a kind of cutting force in situ towards ultrasonic vibration assisted machining as described in any one of claims 1 to 3 Measuring device；
Step 2：Laser interferometer monitors a certain radial vibration frequency and amplitude at point of a knife, and high speed camera monitors cutter and work The contact condition of part, and using vibration frequency, amplitude and contact period as the input condition of finite element simulation, obtaining amplitude transformer has The first simulation result of limit, determines pattern measurement region；
Step 3：PVDF piezoelectric membranes are pasted onto pattern measurement region, obtain the distribution of amplitude transformer upper stress, and be fitted stress propagation Characteristic equation；
Step 4：Piezoelectric force platform obtains the cutting force of pedestal, is modified to stress propagation characteristic equation；
Step 5：Integrate amplitude transformer upper stress propagation characteristic equation.
5. a kind of survey based on the cutting force measurement device in situ towards ultrasonic vibration assisted machining according to claim 4 Amount method, which is characterized in that step 3 is specially：Five groups of PVDF piezoelectric membranes are distributed on horn,stepped, between every group is Every 120 ° of three PVDF piezoelectric membranes, obtain the stress propagation situation in entire amplitude transformer, to PVDF piezoelectric membranes signal into Row acquisition decoupling, obtains five groups of three-dimensional stress value σx、σy、σz；Stress value variation is obtained with measurement point apart from the amplitude transformer abrupt change of cross-section The relationship at place：σx1=axz2+bxz+cx, σy1=ayz2+byz+cy, σz1=azz2+bzz+cz, wherein ax、bx、cxThe respectively directions x Cutting force FxTwo-term coefficient, Monomial coefficient and the constant term coefficient of the lower stress propagation property fitting equation of effect；ay、by、cy The respectively directions y cutting force FyTwo-term coefficient, Monomial coefficient and the constant term of the lower stress propagation property fitting equation of effect Coefficient, az、bz、czThe respectively directions z cutting force FzThe two-term coefficient of the lower stress propagation property fitting equation of effect, first order Coefficient and constant term coefficient.
6. a kind of survey based on the cutting force measurement device in situ towards ultrasonic vibration assisted machining according to claim 4 Amount method, which is characterized in that step 4 is specially：By piezoelectric force stage+module on pedestal, cut according to gained three-dimensional is measured It cuts power and calculates corresponding stress value, be further compared with stress propagation characteristic equation, and correct stress propagation characteristic equation：σx2 =kxσx1+bx, σy2=kyσy1+by, σz2=kzσz1+bz, wherein kx、bxRespectively piezoelectric force platform measurement cuts the directions x Cut power FxThe first order correction factor and constant term correction factor of the lower stress propagation characteristic equation of effect, ky、byRespectively piezoelectricity is surveyed Power platform measurement is to the directions y cutting force FyThe first order correction factor of the lower stress propagation characteristic equation of effect and constant term amendment Coefficient, kz、bzRespectively piezoelectric force platform measurement is to the directions z cutting force FzStress propagation characteristic equation is primary under effect Item correction factor and constant term correction factor.
7. a kind of survey based on the cutting force measurement device in situ towards ultrasonic vibration assisted machining according to claim 4 Amount method, which is characterized in that step 5 is specially：First, a certain diameter at point of a knife when obtaining cutwork using laser interferometer To vibration frequency and vibration amplitude, with high speed camera monitor point of a knife and tool contact condition, and by vibration frequency, amplitude and Condition of the period as finite element analysis is contacted, the pattern measurement region of amplitude transformer is obtained according to Finite element analysis results；Then PVDF is pasted onto pattern measurement region, decouple and fits amplitude transformer upper stress propagation characteristic conic section；Finally, using pressure Electric force plate/platform is modified stress propagation characteristic equation, obtains more accurate stress propagation characteristic equation.
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