CN104759954A - Prestress grinding method for revolved body workpiece - Google Patents

Abstract

The invention discloses a prestress grinding method for a revolved body workpiece. The method includes the following steps that (1) the workpiece to be machined is well clamped on a grinding machine; (2) tool setting operation is conducted, a grinding wheel and the workpiece are made to be in a low speed state first, the position of the grinding wheel is adjusted step by step, the linear speed of the grinding wheel is adjusted to be in an ultra high speed state of vs>=150 m/s after sparks just appear on the surface of the workpiece, and the rotating speed of the workpiece is adjusted to be in an ultra high speed centrifugal state; (3) abrasive machining is carried out according to a certain radial amount of feed; after machining is completed, the grinding wheel and the workpiece are separated first, and then the grinding wheel and the workpiece are decelerated to be zero. According to the prestress grinding method for the revolved body workpiece, there is no need to use a special force application mechanism to apply prestress to the workpiece, only the rotating speed of the workpiece in the machining process needs to be controlled, and residual compressive stress can be obtained on the surface of the workpiece after machining is completed; due to the fact that the rotating speed of the workpiece can be adjusted flexibly, different magnitudes of residual compressive stress can be obtained by controlling the rotating speed of the workpiece, so that the using requirements of different parts are met.

Description

A kind of revolving body workpieces pre-stressed grinding method

Technical field

The present invention relates to a kind of machining process, be specifically related to a kind of pre-stressed grinding method.

Background technology

Grinding carries out accurately machined a kind of conventional machinery processing method to workpiece, comprises flat surface grinding and cylindricalo grinding.In grinding, increase substantially grinding speed, can working (machining) efficiency be improved, and make workpiece obtain higher machining accuracy.Such as, German grinding expert Carl.J.Salomom proposes " superhigh speed grinding " on the basis of " heat channel " theory, and its emery wheel refers to that linear velocity is greater than 150m/s, can realize the high efficiency Precision Machining to workpiece.In " superhigh speed grinding " theory, to the rotating speed not special requirement of workpiece, usually require workpiece rotational frequency v _w>=500r/min.In order to improve working (machining) efficiency further, prior art basis proposes " high efficiency deep grinding " theoretical, such as, at the end of the seventies, there is reasonability in Germany professor's P.G.Werner prophesy " high efficiency deep grinding ", and develop First high efficiency deep grinding grinding machine in the world in nineteen eighty-three, keeping emery wheel ultrahigh speed to rotate on the basis of (being greater than 150m/s), suitably improve workpiece rotational frequency (v _w=1kr/min, and grinding depth is larger, value is less) and increase grinding depth.

In many application scenarios, the behaviour for precision component and heavily loaded parts depends on their surface state to a great extent, and this is because part finished surface state directly affects its fatigue strength, corrosion resistance, wearability and dimensional stability etc.Research and practice shows, by adjusting and controlling to make machined surface have suitable residual compressive stress, can improve the fatigue resistance of part, extend its service life.In prior art, the processing methods such as usual employing annealing in process, roll extrusion, shot-peening, ironing and laser-impact make surface of the work produce residual compressive stress, but these methods exist apparatus expensive, surface of the work can be made easily to produce flow harden, reduce the defects such as its impact flexibility.In order to solve this problem, " residual stress of Pre-stress hard cutting and configuration of surface " [South China Science & Engineering University's journal (natural science edition), the 36th volume the 4th phase, in April, 2008 version; 6-9 page] disclose in a literary composition and carry out at pre-stressed state the method that hard turning obtains residual stress, its general principle is: apply the prestressing force in an elastic range to workpiece in advance before cutting, in working angles, workpiece machining surface can produce plastic deformation, this prestressing force of release after cutting, because the elasticity of matrix is recovered, machined surface can produce residual compressive stress.The advantage that prestressing force cuts is only surface of the work just to be made to produce residual compressive stress by machining, and can not cause extra Surface hardened layer.In order to obtain prestressing force, usually before carrying out machining, by force application mechanism, active force being applied to workpiece in prior art, and in process, remaining this force state; Such as, Pre-stress hard cutting is carried out for the inner ring raceway of bearing and outer ring outer round surface in above-mentioned " residual stress of Pre-stress hard cutting and configuration of surface " literary composition, adopt large to the endoporus swelling support of bearing ring in advance, then make in bearing ring, to produce circumferential pre-tensile stress by the mode of radial loaded.But, obtain prestressed method in prior art and have the following disadvantages:

1, need to use special force application apparatus to exert a force to workpiece, make work piece holder structure more complicated, operation bothers more; Such as, and the workpiece when machining is needed to the occasion rotated, when carrying out cylindricalo grinding, in order to ensure obtaining the prestressing force continued, force application mechanism must rotate together along with workpiece, thus adds overall inertia, reduces stability, affects machining accuracy.

2, for specific processing parts, usually need to design specific force application apparatus, cost is high.

3, prestressed size is not easy to control, and especially in process, the prestressing force on workpiece cannot regulate as required in real time.

Summary of the invention

The object of the invention is to overcome the deficiencies in the prior art, a kind of revolving body workpieces pre-stressed grinding method is provided, the method can allow workpiece obtain prestressing force in Grinding Process without the need to adopting force application mechanism, and in process this prestressed large I flexible modulation.

The technical scheme that the present invention solves the problems of the technologies described above is:

A kind of revolving body workpieces pre-stressed grinding method, comprises the following steps:

(1) clamping workpiece to be processed on grinding machine;

(2) carry out aim at tool operation, first allow emery wheel and workpiece be in lower-speed state, progressively adjust emery wheel position, until after surface of the work just occurs spark, grinding speed is adjusted to ultrahigh speed state v _s>=150m/s, is adjusted to ultracentrifugation state by workpiece rotational frequency, make workpiece produce centrifugal bulking effect, obtains prestressing force;

(3) grinding is carried out by certain radial feeds; After completion of processing, first emery wheel is separated with workpiece, then is decelerated to zero separately.

Preferably, in step (2), described workpiece rotational frequency v _w>=8kr/min.

Preferably, in step (2), described workpiece rotational frequency 8kr/min≤v _w≤ 10kr/min.

Preferably, in step (3), described radial feeds a _p=10 ~ 100 μm/kr.

By workpiece maximum speed is controlled in the scope being less than 10kr/min, can prevent because workpiece ultrahigh speed is rotated and grinding machine spindle stability is impacted, also can slow down because workpiece ultrahigh speed is rotated the impact that wheel life produces simultaneously.Along with the development of technology, the stability of grinding machine spindle under ultrahigh speed state can be become better and better, and under the prerequisite that therefore main shaft stability is enough good when grinding machine works, workpiece rotational frequency also can be greater than 10kr/min.

Preferably, in step (3), emery wheel is by setting radial feeds feeding and after starting grinding, workpiece is or/and emery wheel carries out grinding with speed change state; After emery wheel stops radial feed entering the tarry matter stage, workpiece or emery wheel carry out tarry matter with speed change state, be separated by emery wheel and be decelerated to zero separately after tarry matter with workpiece.

The rotating ratio that the object of carrying out speed change in Grinding Process is effectively to suppress grinding machine spindle flutter, reduces forced vibration and change emery wheel and workpiece; For the grinding stage, surface of the work integrality can be improved and extend emery wheel service life, for the tarry matter stage, can reach and alleviate the effect that surface of the work produces " corner angle " phenomenon.In existing tarry matter technology, generally keep during tarry matter emery wheel and workpiece rotational frequency constant, thus form constant velocity ratio, the now vibration of grinding machine is in a kind of regular state, a kind of regular dynamic relative position relation is remained between workpiece and emery wheel, thus form regular non-equivalent grinding at surface of the work, affect workpiece surface quality, occur " corner angle " phenomenon; And adopt method for changing speed in grinding and tarry matter process after, the velocity ratio of emery wheel and workpiece is constantly changed, not only can imitate and suppress grinding machine spindle flutter, reduction forced vibration, and make the vibration of grinding machine be in a kind of irregular state, also a kind of irregular dynamic relative position relation is remained between workpiece and emery wheel, each position of such surface of the work can obtain uniform grinding, improves surface of the work integrality, and alleviates the problem that surface of the work produces " corner angle " phenomenon.In speed-change process, if emery wheel is without the need to axial feed, then emery wheel retainer shaft carries out speed change to invariant position; If emery wheel needs axial feed, then emery wheel carries out axial feed, while carry out speed change.

When speed change, no matter be grinding stage or tarry matter stage, the object of speed change can be workpiece or emery wheel, or both are speed change simultaneously, the form of speed change can be accelerate also can be slow down, and the mode of speed change can be continuous change, also can be staged speed change.

As a kind of preferred version, in the grinding stage, described workpiece is or/and the speed change state of emery wheel is: holding workpiece rotating speed is constant, improves grinding speed; In the tarry matter stage, described workpiece is or/and the speed change state of emery wheel is: keep grinding speed constant, reduce workpiece rotational frequency.This preferred version is adopted suppress main shaft flutter, reduction forced vibration except in order to realize and change emery wheel with except workpiece rotational frequency ratio, its reason is: in the grinding stage, by improving grinding speed, the heat importing workpiece into can be made to reduce further on the one hand, grinding temperature reduces, abrasive particle quantity on the other hand owing to acting on same grinding area increases, and can alleviate and make because improving workpiece rotational frequency the problem that its surface roughness increases; In the tarry matter stage, because emery wheel stops radial feed, emery wheel only contacts in " corner angle " of surface of the work, affect not quite on the formation of surface of the work residual stress, by reducing workpiece rotational frequency, the grinding thichness that is not out of shape of single abrasive particle reduces (for tarry matter stage reduction grinding speed), is conducive to the surface roughness improving workpiece.

As a kind of preferred version, when adopting continuous change mode, in the grinding stage, emery wheel is with 2m/s ²~ 5m/s ²linear acceleration accelerate; In the tarry matter stage, workpiece is with 800 π rad/s ²~ 1200 π rad/s ²angular acceleration slow down.

When adopting staged gear shift mode, in the grinding stage, emery wheel is with 6m/s ²~ 8m/s ²linear acceleration to accelerate after 6m/s ~ 10m/s at the uniform velocity 1 ~ 2s, this process is considered as one and accelerates ladder, circulate 3 ~ 5 times; In the tarry matter stage, workpiece is with 1200 π rad/s ²~ 1600 π rad/s ²angular acceleration deceleration 500r/min after at the uniform velocity 1 ~ 2s, this process is considered as a deceleration ladder, circulates 2 times.

As an example, described workpiece is the bearing inner race be made up of GCr15 material, and when carrying out ultracentrifugation grinding, workpiece initial speed is 8kr/min; In the grinding stage, emery wheel is with 2m/s ²~ 5m/s ²linear acceleration is accelerated continuously; In the tarry matter stage, workpiece is with 800 π rad/s ²~ 1200 π rad/s ²angular acceleration slows down continuously, when workpiece rotational frequency drops to 7kr/min, is separated by emery wheel and is decelerated to zero separately with workpiece.In the tarry matter stage, workpiece speed change lower limit is defined as 7kr/min, and its reason is: after tarry matter is about 2s, and the surface integrity of workpiece and tarry matter time have nothing to do, and determine workpiece speed change lower limit, can ensure working (machining) efficiency.

In process, concrete linear acceleration when concrete angular acceleration during workpiece speed change and emery wheel speed change can be determined according to following two conditions:

(1) rotation speed change amplitude should be beated in the range of speeds of control at electro spindle circle.Circle in the main shaft range of speeds to be beated by dynamic balancing technique and is controlled in an accurate scope by the electro spindle of present stage, and the circle of all the other ranges of speeds is beated relatively large.Suppose that the electro spindle normal revolution driving workpiece to rotate is 8kr/min, pass through dynamic balancing technique, the circle of the rotating speed of this electro spindle within the scope of 6kr/min ~ 10kr/min can be beated controls between 0.5um ~ 1um, the circle of all the other section of rotating speed is beated and is greater than 1um, and therefore the change of rotating speed should in the range of speeds of setting.

(2) time of speed-change process was determined by process time, and this process time is then by total grinding depth and radial feeds a _pdetermine.

Comprehensively above-mentioned two conditions, after determining speed change amplitude and shifting time, just can calculate and choose rational angular acceleration and linear acceleration, make workpiece and emery wheel can justify at respective electro spindle the range of speeds internal speed-changing beated and control.

Operation principle of the present invention is: by the rotating speed of workpiece is risen to ultracentrifugation state, makes workpiece produce centrifugal bulking effect, thus obtains prestressing force; Under pre-stressed state, grinding is carried out to workpiece, make the surface of the work after completion of processing can obtain the residual compressive stress of needs.

The present invention compared with prior art has following beneficial effect:

1, without the need to using special force application mechanism to workpiece Shi Hanzhang, the rotating speed that only need control workpiece in process can make surface of the work obtain residual compressive stress after completion of processing, simplifies clamp structure, reduces cost, easy and simple to handle; And can not to rotate together with workpiece because of prestressing force force application mechanism and affect stability.

2, because the rotating speed of workpiece can flexible modulation, and workpiece rotational frequency is higher, final acquisition residual compressive stress is larger, therefore the residual compressive stress of different size can be obtained by the rotating speed controlling workpiece, with the instructions for use of satisfied different part, this regulative mode flexibly, conveniently, and can regulate in real time.

3, in grinding process, improve workpiece rotational frequency, the time that in emery wheel, single abrasive particle acts on same grinding area shortens, the heat importing workpiece into reduces (grinding burn and crackle are difficult problems grinding field being difficult to overcome always), grinding temperature reduces, thus the residual tension that workpiece surface is harmful is reduced.

4, under the condition not changing grinding depth, workpiece rotational frequency is improved, improve than material removal rate (weighing the parameter of grinding efficiency) on the one hand, on the other hand because workpiece rotational frequency increases substantially, strain rate improves, the mechanical property of workpiece surface material changes, and grinding energy ratio (weighing the parameter of capacity usage ratio) is reduced.

5, workpiece rotational frequency significantly improves, and has good ground effect to high-ductility and difficult grind material, and more effectively can realize ductile regime grinding to hard brittle material.

Even if the gyroscopic effect that 6, Work piece high-speed rotation produces makes the direction of workpiece rotary middle spindle under larger normal grinding force effect still remain unchanged, create favorable conditions for workpiece carries out ultracentrifugation grinding.

7, due to after workpiece rotational frequency increases substantially, possesses the operation can carrying out speed governing in grinding process, pass through variable speed operation, effectively can suppress flutter (the periodicity self-excited vibration exciting feedback to produce by internal system, be called flutter, under occurring in the condition of certain abrasion of grinding wheel area of plane rate), thus improve surface of the work integrity degree and extend emery wheel service life.

8, due to after workpiece rotational frequency increases substantially, possesses the operation can carrying out speed governing in grinding process, pass through variable speed operation, can alleviate because of system forced vibration under constant velocity-ratio (be subject to system outer periodic disturbance produce, as unbalanced emery wheel or axle) and " corner angle " phenomenon that workpiece machining surface is produced, thus improve workpiece surface quality.

Accompanying drawing explanation

Fig. 1 is the grinding model figure of abrasive grain cutting sword.

Fig. 2 is superhigh speed grinding conceptual schematic view.

Fig. 3 is that the internal stress under workpiece centrifugal effect analyzes schematic diagram.

Fig. 4 is the graph of a relation between the rear surface compress residual stresses obtained of workpiece rotational frequency and processing.

Fig. 5 is workpiece rotational frequency and circumferential stress graph of a relation.

Fig. 6 and Fig. 7 is the assembly relationship model figure of main shaft and bearing.

Fig. 8 is that bearing and main shaft (rotor) wear surface are radially expanded deformation relationship curve map.

Fig. 9 be bearing shaft to radial rigidity and speed of mainshaft graph of relation.

Figure 10 is the speed of mainshaft and bearing contact angle graph of relation.

Figure 11 is the speed of mainshaft and bearing touch power graph of relation.

Figure 12 is experiment and the simulation result figure of relation between the speed of mainshaft and axis system intrinsic frequency.

Figure 13 is that workpiece is ground the formation mechenism figure of superficial layer residual stress.

Figure 14 is the stress-strain curve diagram at different strain rate and temperature.

Figure 15 is the effect diagram of speed change amplitude to chatter growth rate.

Figure 16 is speed change forward spindle system emery wheel and Workpiece vibration signal graph.

Figure 17 is axis system emery wheel and Workpiece vibration signal graph after speed change.

Detailed description of the invention

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited thereto.

See Fig. 1 ~ Figure 17, for the periphery grinding of the bearing inner race be made up of GCr15, revolving body workpieces pre-stressed grinding method of the present invention comprises the following steps:

(1) clamping workpiece to be processed on grinding machine;

(2) carry out aim at tool operation, first allow emery wheel and workpiece be in lower-speed state, progressively adjust emery wheel position, until after surface of the work just occurs spark, grinding speed is adjusted to fast state v _s>=150m/s, is adjusted to ultracentrifugation state 8kr/min by workpiece rotational frequency;

(3) a pressed by emery wheel _p=10 ~ 100 μm/kr sets radial feeds feeding and after starting grinding, carries out grinding with speed change state, and specifically in the grinding stage, holding workpiece rotating speed is constant, and emery wheel is with 2m/s ²~ 5m/s ²linear acceleration accelerate continuously; After emery wheel stops radial feed entering the tarry matter stage, carry out tarry matter with speed change state, specifically keep grinding speed constant, workpiece is with 800 π rad/s ²~ 1200 π rad/s ²angular acceleration slow down continuously, when workpiece rotational frequency drops to 7kr/min, emery wheel be separated with workpiece and be decelerated to zero separately, completion of processing.

Below the operation principle of revolving body workpieces pre-stressed grinding method of the present invention is explained in detail, to verify technique effect of the present invention.

First the ABC of grinding is described, for principle analysis is below provided fundamental basis.

1, grinding general principle

(1) the irregular abrasive particle of countless size is randomly dispersed in wheel face, each abrasive particle can regard a little steel knife as, compared with conventional cutting, grinding is just equivalent to have many pocket knife continuous cutting surface of the work, but not all abrasive particle can play shear action when grinding;

(2) abrasive grain cutting experiences three processes: swiping (elastic deformation), cultivated plough (plastic deformation) and cutting, and make surface form thermal stress and distortional stress, model as shown in Figure 1;

(3) maximumly grinding thichness h is not out of shape _gmax(grinding core formula)

$h_{g\max }=\frac{1}{A_{g_1}^p}{\left[\frac{2}{c_1{k}_s}\right]}^{\frac{1}{p+1}}{\left[\frac{v_w}{v_s}\right]}^{\frac{1}{p+1}}{\left[\frac{a_p}{d_e}\right]}^{\frac{1}{2(p+1)}}$

In formula, A _g1-with the proportionality coefficient of static sharpening number

K _s-the coefficient relevant with grinding-wheel grinder tooth shape shape

C ₁-the coefficient relevant with emery wheel sharpening density

V _w-workpiece alignment speed

V _s-grinding speed

A _p-grinding depth (radial feeds)

D _e-emery wheel equivalent diameter

From the above, after emery wheel type is determined, v _w, v _sand a _pdirectly affect h _gmax.

And be not out of shape thickness of cutting and have larger impact to grinding process, as follows:

1. the grinding force of influence on abrasive particle, thus affect abrasive particle and normally to work required bond strength;

2. grinding energy ratio e is affected _ssize;

3. affect grinding area temperature, thus affect the character of abrasion of grinding wheel and surface layers residual stress, size and distribution situation;

4. machined surface roughness is affected.

2, plain grinding

Grinding dosage (v _w, v _sand a _p) impact on grinding force, grinding temperature and surface roughness.

(1) grinding force

1. speed of grinding wheel v _sduring increase, the total abrasive particle number participating in cutting in the unit interval increases, and what make every abrasive particle is not out of shape grinding thichness h _maxreduce, thus make grinding force reduce;

2. grinding depth a _pduring increase, what not only make every abrasive particle is not out of shape grinding thichness h _gmaxincrease, time also, the Grinding Contact arc length of emery wheel and workpiece lengthens, and the abrasive particle number of simultaneously working increases, and grinding force is increased;

3. workpiece rotational frequency v _wduring increase, every abrasive particle be not out of shape grinding thichness h _gmaxincrease, grinding force is increased.

(2) grinding temperature

1. along with grinding depth a _pincrease, workpiece surface temperature raise.This is because increase a _pafter, every abrasive particle is not out of shape grinding thichness h _gmaxincrease, make the relation that in grinding process, abrasive dust deformation force and frictional force increase;

2. along with workpiece rotational frequency v _wincrease, workpiece surface temperature may reduce to some extent.This is because workpiece rotational frequency v _wduring increase, though make heat source strength increase, thermal source translational speed is on the surface of the workpiece accelerated, and makes the cause of thermal source time shorten when surface of the work effect;

3. along with speed of grinding wheel v _sincrease, workpiece surface temperature raise.This is because work as v _safter increase, the work abrasive particle number in the unit interval increases, and grinding thichness (is not out of shape grinding thichness h _gmaxreduce) thinning, namely abrasive dust is split thinner, and abrasive dust deformation energy increases.Produce the abrasive particle number ploughing plough and swiping effect to increase simultaneously, friction is aggravated.

(3) surface roughness

1. speed of grinding wheel v _sduring increase, the total abrasive particle number participating in cutting in the unit interval increases, and what make every abrasive particle is not out of shape grinding thichness h _gmaxreduce, thus make surface roughness R _areduce;

2. grinding depth a _pduring increase, what not only make every abrasive particle is not out of shape grinding thichness h _gmaxincrease, also make the Grinding Contact arc length of emery wheel and workpiece lengthen, the abrasive particle number of simultaneously working increases, and grinding force increases, and thus makes surface roughness R _aincrease;

3. workpiece rotational frequency v _wduring increase, every abrasive particle be not out of shape grinding thichness h _gmaxincrease, thus make surface roughness increase;

4. surface roughness and grinding force have certain functional relation, and namely grinding force is larger, and surface roughness is larger, otherwise less.

3, superhigh speed grinding

The conclusion about " grinding dosage is on the impact of grinding force and surface roughness " of plain grinding is still applicable to superhigh speed grinding, but grinding dosage, on the impact of grinding temperature, the change of essence has occurred.

The superhigh speed grinding that Germany cutting object neo-confucian Carl Salomon proposes is theoretical: raise different with the increase of cutting speed from cutting temperature in conventional cutting velocity interval, after cutting speed increases to a certain critical speed relevant with the kind of workpiece material, along with the increase of cutting speed, cutting temperature and cutting force reduce on the contrary (heat channel is theoretical), as shown in Figure 2.

Theoretical application: when superhigh speed grinding, because grinding speed is very high, the translational speed of abrasive particle on grinding area is fast several times, and the time compole of single chip formation is short.On the one hand, under the temperature lag of strain rate response, even if heat source strength increases, but heat does not also have enough time to import workpiece into is just taken away by abrasive dust, thus surface of the work grinding temperature is decreased, and can cross the region that fire damage easily occurs; On the other hand, high strain-rate (can the grinding speed be approximately equal to) forming process of the abrasive dust completed in this very short time, surface of the work elastically deformed layer will be made to shoal, the bump height got along because of Plastic Flow in grinding groove mark both sides diminishes, the cultivated plough of chip formation and swiping distance are diminished, and workpiece surface is hardened and the reduction of residual stress tendency.

In addition, find in the research about high efficiency deep grinding, on the basis keeping emery wheel ultrahigh speed to rotate, along with workpiece rotational frequency v _wincrease, workpiece surface temperature reduces to some extent; Along with grinding depth a _pincrease, workpiece surface temperature raise.

Under regard to technique effect of the present invention relevant operation principle be described in detail.

One, workpiece is rotated by ultrahigh speed and obtains prestressed principle

1, centrifugal effect produces prestressing force

Object is when being rotated, capital produces centrifugal effect, this centrifugal effect can impel object to have the trend of outwards motion, from the microstructure of interior of articles, each minute cells body of composition object has the trend of outwards escaping, and this trend can impel the tension producing radial direction between the cell cube of interior of articles, meanwhile, the cell cube with outside escaping tendency forms a kind of swelling state, and this swelling state can allow between cell cube and produce tangential stress.As shown in Figure 3, tangential stress meets in the internal stress analysis of workpiece in rotary course along workpiece rotational frequency direction (circumferential stress ) and vertical direction (radial stress σ _ρ) be tension, and radial stress σ _ρcompare circumferential stress little.As can be seen here, there is certain prestressing force in the workpiece itself rotated, but in the prior art, the rotating speed of workpiece is usually all relatively low, the workpiece maximum (top) speed of general superhigh speed grinding is 0.3 ~ 0.5k r/min, and the rotating speed of the workpiece of high efficiency deep grinding also only reaches 1k r/min; And because the stability of the too high meeting of workpiece rotational frequency to grinding machine spindle impacts, so more high-revolving workpiece in prior art, can not be adopted to carry out grinding.And the workpiece under ordinary rotational speed is in Grinding Process, the prestressing force produced because of centrifugal action is very limited, does not therefore substantially produce effect to forming residual compressive stress after completion of processing, usually needs to obtain residual compressive stress by other follow-up processing methods.

2, workpiece produces the rate request of effective prestress

When not considering clamping workpiece fixture workpiece is applied pretightning force time, the stress formula that workpiece produces because of centrifugal effect is:

In formula, υ-Poisson's ratio

P-density of material

ω-corner of workpiece speed

A-workpiece inner circle radius

B-excircle of workpiece radius

Arbitrary radius in ρ-sagittal plane

σ _ρ-workpiece radial stress

-workpiece circumferential stress

Displacement expression formula (workpiece radial expansion volume) expression formula is:

$u_{\mathrm{\ρ}}=\frac{(3+\mathrm{\υ})(1-\mathrm{\υ})}{8E}p{\mathrm{\ω}}^2\mathrm{\ρ}[a^2+b^2+\frac{(1+\mathrm{\υ})a^2{b}^2}{(1-\mathrm{\υ}){\mathrm{\ρ}}^2}-\frac{(1+\mathrm{\υ}){\mathrm{\ρ}}^2}{3+\mathrm{\υ}}]$

In formula, E-elastic modelling quantity

U _ρ-radial expansion volume

According to above-mentioned formula, can calculate and not consider under pretightning force condition, the internal stress that workpiece produces because of centrifugal effect and radial expansion volume.Due to the Poisson's ratio υ < 1 of most of material, make if consider the pretightning force that fixture applies workpiece again, circumferential stress can be made (reference can be increased further computing formula), and radial stress is contrary with pre-tight stress direction, play negative function (generally pre-tight stress can be greater than radial stress), therefore in ultracentrifugation grinding process, the circumferential stress that workpiece produces because of centrifugal effect plays a leading role to plastic deformation, and leading role is played in the formation of this circumferential stress to residual compressive stress.

As can be seen here, square being directly proportional of the circumferential stress of workpiece and the rotating speed of workpiece; And the circumferential stress of workpiece is larger, more favourable to the residual compressive stress obtained after processing; Therefore workpiece rotational frequency is higher in theory, is more conducive to the residual compressive stress after obtaining processing.Through experiment, for general metal parts, relation between workpiece rotational frequency and the residual compressive stress finally obtained as shown in Figure 4, as can be seen from Figure 4, along with the raising of workpiece rotational frequency, surface of the work residual compressive stress (representing by negative value in figure) also constantly increases, and when workpiece rotational frequency is elevated to more than 8kr/min, the amplitude of variation of surface of the work residual compressive stress becomes comparatively mild, therefore, when workpiece rotational frequency reaches more than 8kr/min, the residual compressive stress obtained after grinding is ideal.

Such as, using 6203 bearing inner races of GCr15 material as object, design parameter is as shown in the table:

Do not considering that the situation of pretightning force calculates, the circumferential stress of the workpiece surface material (i.e. ρ=b) that different workpieces rotating speed is corresponding can drawn according to formula, obtaining the curve of workpiece rotational frequency and circumferential stress relation as shown in Figure 5.As can be seen from the figure, when workpiece rotational frequency is greater than 6kr/min, workpiece circumferential stress is just more than 1MPa; When workpiece rotational frequency is greater than 8kr/min, circumferential stress ascendant trend is more obvious, close to 2MPa, obtains prestressed better effects if, so determine that workpiece rotational frequency is that more than 8kr/min is comparatively reasonable.

Yes require emphasis, in the present invention, the workpiece rotational frequency rotating speed 1kr/min reached in 8kr/min and " high efficiency deep grinding " of the prior art theory has difference in essence, not only there is fundamental difference from putting forward high-revolving object, and numerically see from the concrete of rotating speed the difference also having internal, about 8 times of workpiece rotational frequency in " high efficiency deep grinding " of the prior art theory to the requirement of workpiece rotational frequency in the present invention, on the basis of the workpiece rotational frequency 1kr/min of " high efficiency deep grinding ", because the object improving workpiece rotational frequency is different, even if the basic general knowledge of those skilled in the art in conjunction with this area and the experiment of limited number of time, also the workpiece rotational frequency being greater than 8kr/min that the present invention limits cannot be obtained.

3, the restriction of workpiece rotational frequency

From the above analysis, the rotating speed of workpiece is higher in theory, is more conducive to forming residual compressive stress, but too high rotating speed, can occur with other problems, therefore must restrict the maximum speed of workpiece.Through further investigation and the exploration of applicant, find that workpiece rotational frequency is too high and mainly can bring following problem.

(1) grinding machine spindle stability is impacted

Under ultrahigh speed state, centrifugal expansion phase is produced seemingly with above-mentioned workpiece, grinding machine spindle and the bearing on it all can produce centrifugal bulking effect under ultracentrifugation state, and this centrifugal bulking effect can have an impact to bearing rigidity and the matching relationship between main shaft and bearing, thus affect the stability of main shaft work.

Explore below by " the centrifugal expansion of high-speed main spindle is on the impact of bearing dynamic characteristic " experiment and improve the speed of mainshaft to the impact of bearing dynamic characteristic.The assembly relationship model of main shaft and bearing as shown in Figure 6 and Figure 7.

(1.1) centrifugal bulking effect has an impact to the matching relationship between main shaft and bearing

Under normality, be interference fit relation between bearing inner race and main shaft, therefore need to consider the impact of pretightning force on main shaft and bearing inner race swell increment, on this basis, in conjunction with the swell increment computing formula of workpiece under above-mentioned centrifugal effect, main shaft swell increment u can be derived _s(ρ) with bearing inner race swell increment u _b(ρ) computing formula, specific as follows:

$u_s\left(\mathrm{\&rho;}\right)=\frac{(3+\mathrm{\&upsi;})(1-\mathrm{\&upsi;})}{8E(1-\mathrm{\&upsi;})}p{\mathrm{\&omega;}}^2\mathrm{\&rho;}[(1-2\mathrm{\&upsi;})(a^2+b^2)+\frac{a^2{b}^2}{{\mathrm{\&rho;}}^2}]-\frac{(1+\mathrm{\&upsi;})(1-2\mathrm{\&upsi;})}{8E(1-\mathrm{\&upsi;})}{\mathrm{p\&omega;}}^2{\mathrm{\&rho;}}^3+\frac{1+\mathrm{\&upsi;}}{E}\frac{{\mathrm{Fb}}^2}{b^2-a^2}(1-2\mathrm{\&upsi;}+\frac{a^2}{{\mathrm{\&rho;}}^2})$

In formula, F-pretightning force

A-main shaft inner circle radius, i.e. r ₁

B-main shaft exradius, i.e. r ₂

$u_B\left(\mathrm{\&rho;}\right)=\frac{3+\mathrm{\&upsi;}}{8E}p{\mathrm{\&omega;}}^2\mathrm{\&rho;}[(1-\mathrm{\&upsi;})(a^2+b^2)+(1+\mathrm{\&upsi;})\frac{a^2{b}^2}{{\mathrm{\&rho;}}^2}]-\frac{{(1-\mathrm{\&upsi;})}^2}{8E}p{\mathrm{\&omega;}}^2{\mathrm{\&rho;}}^3+\frac{{\mathrm{Fa}}^2\mathrm{\&rho;}}{(a^2-b^2)E}[1-\mathrm{\&upsi;}+\frac{b^2}{{\mathrm{\&rho;}}^2}(1+\mathrm{\&upsi;})]$

In formula, F-pretightning force

A-bearing inner race inner circle radius, i.e. r ₂

B-bearing inner race exradius, i.e. r ₃

As ρ=r ₂time, main shaft and bearing fit face diameter can be simulated to the change curve (each parameter derive from high-speed main spindle 715 model CNC milling machines on) of dilatancy with rotating speed by above-mentioned formula, result as shown in Figure 8:

As shown in Figure 8, along with the rising of rotating speed, the swell increment distortion of bearing is far away from main shaft, and therefore, the centrifugal expansion of main shaft can not affect the change of Bearing inner radial clearance.Under high-speed cruising state, the magnitude of interference between bearing inner race and main shaft reduces, and contact stress diminishes, and the stress of suit when becoming 0 corresponding rotating speed be called separate speed, after rotating speed reaches separate speed, the interference between bearing with main shaft is connected will lose efficacy, and be situation about must avoid.Particularly, when rotating speed is greater than 8kr/min, bearing expansion amplitude is obvious gradually; When rotating speed is greater than 10kr/min, reach the half of initial interference; When rotating speed is greater than 18kr/min, there is de-pine in main shaft and bearing.

Therefore consider from the angle of the matching relationship safety between main shaft and bearing, the rotating speed of main shaft is advisable to be no more than 10kr/min.

(1.2) centrifugal bulking effect is on the impact of bearing rigidity

The stability of rigidity to main shaft of bearing has material impact, explores the relation between the speed of mainshaft and bearing rigidity, can judge the impact of rotating speed on main shaft stability.Here test by being installed in CNC milling machine by experiment high-speed main spindle, observe the relation between the speed of mainshaft and bearing rigidity, result as shown in Figure 9.As can be seen from Figure 9, bearing axial rigidity and radial rigidity all reduce with the rising of rotating speed, and particularly, when rotating speed is greater than 5kr/min, bearing rigidity starts on a declining curve, but fall is slow; When rotating speed is greater than 8kr/min, fall is more obvious; When rotating speed is greater than 10kr/min, rigidity is downward trend substantially linearly.As can be seen here, the speed of mainshaft is limited in the scope being not more than 10kr/min, can guarantees that bearing rigidity meets instructions for use.

In order to verify the relation between the above-mentioned speed of mainshaft and bearing rigidity, also can explore from the relation between the speed of mainshaft and bearing contact angle, contact force, its reason is to have substantial connection between bearing rigidity and contact angle, contact force.Test by experiment high-speed main spindle is installed in CNC milling machine equally, obtain the relation between main shaft and bearing contact angle, contact force, respectively as shown in Figure 10 and Figure 11.As can be seen from the figure, along with the raising of the speed of mainshaft, the contact angle of bearing inner race increases, contact force reduces, the contact angle of bearing outer ring reduces, contact force increases, and its reason is positioned at, during high-speed cruising, ball makes bearing inner race contact angle increase under centrifugal action, and contact force reduces; And outer ring contact angle reduces, contact force increases, thus causes the decline of bearing axial rigidity and radial rigidity.Thus the relation demonstrated between the speed of mainshaft and bearing rigidity.In addition, compared with not considering the situation of bearing inner race radial centrifugal force bulking effect, when considering this bulking effect, the contact angle of the inside and outside circle of bearing and ball will reduce, and contact force increases.When the rotating speed of testing high-speed main spindle is 1.5kr/min, the centrifugal dilatancy of bearing inner race makes inner ring contact angle reduce 3.6%, and outer ring contact angle reduces 2.9%; Make inner ring contact force add 3.5%, outer ring contact force adds 2.8%, and therefore, bearing radial rigidity increases relative to when not considering the centrifugal expansion of inner ring.

And the change of bearing rigidity also can be verified by experiment on the impact of the stability of main shaft, the intrinsic frequency by testing high-speed spindle system reflects the stability of main shaft, and the intrinsic frequency of axis system is higher, and stability is better.Test by experiment high-speed main spindle is installed in CNC milling machine equally, carry out analog simulation simultaneously, obtain the experiment of relation between the speed of mainshaft and axis system intrinsic frequency and simulation result as shown in figure 12, as can be seen from the figure, along with the raising of the speed of mainshaft, the intrinsic frequency of axis system is on a declining curve, when the speed of mainshaft is greater than 10kr/min, and the intrinsic frequency substantially linearly downward trend of axis system.

As can be seen here, consider from centrifugal bulking effect the angle of the impact of bearing rigidity, the rotating speed of main shaft is advisable to be no more than 10kr/min.

(2) on the impact of wheel life

According to Principle of Grinding and Cutting, when workpiece rotational frequency increases, the grinding thichness that is not out of shape of every abrasive particle increases, and thus makes grinding force increase.When grinding force significantly rises, easily cause abrasive particle heavy wear, even come off, and abrasive wear or come off and can grinding force be made further to increase, thus formation vicious circle, not only seriously constrain the service life of emery wheel, axis system also can be made to produce high vibration, directly affect workpiece machining surface integrality.

As can be seen here, considering from affecting wheel life angle, also needing to limit the maximum speed of workpiece.

No matter need ben, be from grinding machine spindle stability (essence is processing safety), and the aspects such as emery wheel service life or workpiece machining surface quality control are considered, all need to limit the workpiece rotational frequency of ultracentrifugation grinding.Because emery wheel service life and workpiece machining surface quality improve by various approach, but processing safety must ensure, thus when running at high speed main shaft stability requirement as restriction workpiece rotational frequency principal element.

In sum, workpiece rotational frequency 8kr/min≤v is determined _w≤ 10kr/min is comparatively preferred scheme.

Two, the explanation that workpiece rotational frequency makes grinding temperature reduce is improved

Grinding thichness h is not out of shape according to maximum _maxcomputing formula is known, as workpiece rotational frequency v _wincrease, h _maxincrease, illustrate that grinding thichness increases.Grinding thichness increases, and grinding total amount of heat also can increase, but increases substantially due to workpiece rotational frequency, and the time that grinding is formed shortens, even if total amount of heat increases, but has little time to import workpiece into and is just taken away by abrasive dust, thus cause surface of the work grinding temperature to reduce further.

After grinding temperature reduces, the impact of grinding temperature on residual stress can be improved.In grinding process (in plain grinding and superhigh speed grinding, the affecting laws of grinding temperature to residual stress is similar), reach very high-temperature at the instantaneous grinding skin that makes, and in the depths from surface 0.05 ~ 0.10mm, will room temperature be in.Therefore, when top layer is heated and cool, internal stress can change, and process is as follows:

In grinding process, after by mill, superficial layer is heated, temperature along the distribution of the degree of depth as shown in Figure 13 (a), θ _prepresent temperature when metal enters perfect plasticity flow regime, when metal reaches and more than θ _ptime, metal can free wxpansion, can not produce internal stress.θ _srepresent the temperature of certain layer of metal under metal surface, metal heated distortion under this temperature action and the internal stress produced exceedes yield limit, just start to produce plastic deformation, therefore, θ _sit is the division temperature of metallic elastic distortion and plastic deformation area in top layer.θ _splastically deforming area time (region 2) above, θ _spure elasticity Bian Hang district time (region 3) below.θ _hrepresent room temperature, top layer is not by the impact of grinding heat at this temperature.

The variation relation of the temperature of a certain depth in grinding top layer t is in time as shown in Figure 13 (a) upper right corner.When temperature reaches maximum temperature θ instantaneously from 0 ₁time, if most skin temperature has exceeded θ _p, region 1 is Plastic Flow state completely, does not produce internal stress, as shown in Figure 13 (b).At θ _p~ θ _hregion 2 and 3, metal level is in expanded by heating state, creates compression.At θ _p~ θ _sregion 2, due to transition of flowing from elastoplasticity to perfect plasticity, therefore compression stress reduces gradually; At θ _s~ θ _hregion 3, because metal is still in elastic stage, still have elastic compression to be out of shape, produce compression, but to diminish gradually.θ _hfollowing because of metal keeps room temperature constant, can not produce elastic deformation, but under the impact of outer thermal expansion metal, will produce the tension balanced with it.

When wheel grinding stops, the moment begun to cool down, as shown in Figure 13 (c), outer surface cooling velocity is greater than endosexine, the stressless plastic flow layer of original surface cools rapidly and shrinks, owing to being subject to the obstruction of lower floor, thus produce tension, make the compression scope in region 2,3 increase further simultaneously.This internal surface temperature is inconsistent and stress distribution that is that cause is extexine tension constantly increases, and the compression of endosexine reduces gradually, be performed until internal and external temperature consistent till.When workpiece cools completely, when endosexine temperature reaches unanimity, as shown in Figure 13 (d), plastic compression deformation is there occurs after the two-layer expanded by heating in region 1,2, cooled physical length is shorter than the raw footage before being heated, thus the tension in region 1 rises further, and region 2 is also become by compression along with cooling carrys out tension.Region 3,4 two-layerly produces compression due to stress equilibrium.Therefore, the thermal stress distribution of Figure 13 (d) for producing under grinding temperature effect.

Grinding skin temperature and thermograde larger time, residual tension is larger.In ultracentrifugation grinding process, workpiece rotational frequency increases substantially, and the grinding time in single abrasive particle unit are reduces, and workpiece temperature reduces, i.e. maximum temperature θ ₁reduce.Owing to being constant by the formation mechenism of mill superficial layer residual thermal stress, when workpiece temperature gradient (temperature that different depth is corresponding different) reduces, the degree of depth being in perfect plasticity flowing under surface of the work reduces, even there is not Plastic Flow state, same experience expanded by heating and cooling after, the degree of depth that the degree of depth forming residual tension under not only making surface of the work reduces, formed residual compressive stress increases, and residual tension also can be made to reduce.

Three, the explanation of the impact of workpiece rotational frequency contrast material removal rate and grinding energy ratio is improved

(1) material removal rate is compared

Than material removal rate Z ' _wrefer to material volume worn on unit interval unit grinding wheel width, computing formula is as follows:

Z′ _w＝v _wa _p/b _s

In formula, b _s-grinding wheel width

In ultracentrifugation grinding process, grinding depth a _pconstant, workpiece rotational frequency v _wsignificantly promote, the contact arc length of emery wheel and workpiece increases, and improves than material removal rate.In same time, the worn amount of metal increases, and grinding efficiency improves.

(2) grinding energy ratio

Grinding energy ratio refers to the energy removed unit volume workpiece material and consume, and what the importance of this parameter was that various abrasive particle and workpiece interfere all must meet principle of conservation of energy, and it depends on grinding condition.

$e_s=\frac{P}{V_W}=\frac{v_s{F}_t}{v_w{a}_p{f}_a}$

In formula, the grinding power of P-system consumption

V _wthe volume of-removal material

F _t-tangential grinding force

F _a-axial feeding (during cylindricalo grinding=1)

Because workpiece rotational frequency improves, tangential grinding force F _tequally also can change, so the influence degree of workpiece rotational frequency to tangential grinding force first need be analyzed.

In plain grinding, utilize the regression analysis in probabilistic method and variance analysis to carry out power multifactorial experiment data processing, establish the grinding force empirical equation of multiple material.In power function relationship between grinding force and grinding dosage, part formula is as follows:

During grinding quenching 45 steel, $F_t=699.94v_s^{-0.60}{v}_w^{0.08}{a}_p^{0.90};$

During the non-Quenched 45 Steel of grinding, $F_t={1903.83v}_s^{-0.89}{v}_w^{0.06}{a}_p^{0.77};$

During grinding titanium alloy TC4, $F_t={141.70v}_s^{-0.47}{v}_w^{0.61}{a}_p^{0.64};$

From above-mentioned grinding force empirical formula, v _wto grinding energy ratio e _simpact compare F _tgreatly (like this equally during superhigh speed grinding), thus grinding energy ratio e _salong with v _wincrease reduce.

Except workpiece rotational frequency increases substantially and can make grinding energy ratio and reduce, in ultracentrifugation grinding process, strain rate ε can remote-effects grinding energy ratio e _s.

How raising about strain rate affects the mechanical property of material, as shown in figure 14, adopts the fracture model of heat-mechanics effect coupling to be described, i.e. so-called Adiabatic Shear or thermoplastic unstability.Two kinds of antipodal processes can be produced to affect material mechanical performance under high strain-rate.On the one hand flow stress improves (hardening process) with the increase of strain and strain rate; Plastic deformation is usually from the slip region of some weakness on the other hand, and the temperature concentrating on these local deformation districts under high strain-rate raises rapidly, thus impels flow stress to decline (softening process).The softening of local impels distortion more to concentrate (local deformation district is narrower), further impels local temperature acutely to raise (even exceeding phase transition temperature) in return.Under such cyclic softening effect, once softening impact exceedes the impact of sclerosis, generation unstability ruptures rapidly by material.During temperature rise △ T wherein in Adiabatic Shear, plastic work done changes into caused by heat energy, and formula is as follows:

$\mathrm{\&Delta;T}=\frac{\mathrm{\&beta;}}{\mathrm{\&rho;}{C}_{v}J}{\&Integral;}_0^{{\mathrm{\&epsiv;}}_{\max }^p}\mathrm{\&sigma;d}{\mathrm{\&epsiv;}}^p$

In formula, ρ-density of material

C _v-specific heat at constant volume

J-mechanical equivalent of heat

The percentage (0.9 ~ 1) of heat is converted in β-plastic work done

ε ^p-plastic strain

Temperature T is the function T=T (ε) of strain, and stress can regard the function of strain and temperature as:

σ＝σ(ε,T)＝σ(ε,T(ε))

So plastic instability condition can be rewritten as

$0\&le;-\frac{\frac{\&PartialD;\mathrm{\&sigma;}}{\&PartialD;\mathrm{\&epsiv;}}}{\frac{\&PartialD;\mathrm{\&sigma;}}{\&PartialD;T}\frac{\mathrm{dT}}{\mathrm{d\&epsiv;}}}\&le;1$

Can analyze from this condition and produce critical strain needed for thermoplastic unstability or critical strain rate, as measurement material to the index of Adiabatic Shear susceptibility.

Owing to producing high strain rate in superhigh speed grinding process, (ε can reach 10 ^-4~ 10 ^-6s ^-1), abrasive dust is formed under Adiabatic Shear state, and material removal mechanism changes (softening impact exceedes hardening effect).Therefore, in ultracentrifugation grinding process, when workpiece rotational frequency increases substantially, strain rate ε improves, softening tendency is larger, abrasive dust thermal insulation is cut more obvious, makes the tangential grinding force needed for cutting unit volume metal on a declining curve, thus affects grinding energy ratio e _ssize.

Need it is clear that, according to the theory calculate in abrasive dust process and summary of experience, workpiece rotational frequency rise, grinding force F can improve.Tangential grinding force needed for cutting unit volume metal mentioned here declines, and not representing total tangential grinding force can reduce because every abrasive particle be not out of shape cutting average thickness increase, so the power needed is larger.

Four, workpiece rotational frequency is improved on the explanation of the impact of materials processing performance

In ultracentrifugation grinding process, workpiece rotational frequency increases substantially, workpiece surface material strain rate improves, softening tendency is larger, abrasive dust thermal insulation is cut more obvious, material is easier to worn, the grinding performance of difficult grind material is improved, and ductile regime grinding is realized to hard brittle material, too increase toughness material at elasticity small deformation stage removed ratio simultaneously.

Five, the Action Specification of the gyroscopic effect that workpiece rotational frequency produces is improved

Centrifugal force when gyroscopic effect refers to that object rotates can make self to keep balance, namely the object be rotating has and have two features as gyro: precession and gyroscopic inertia---when the gyro of High Rotation Speed runs into external force, the direction of its axle can not change along with the direction of external force, but axle is round the precession of a fixed point.

In ultracentrifugation grinding process, workpiece rotational frequency increases substantially, even if under the effect of larger grinding force, workpiece can keep the stability of its axis of rotation relative inertness direction in space because of resistance moment (gyroscopic couple) that gyroscopic effect produces, thus effectively improves the security performance of axis system.

Six, speed change is to the explanation suppressing grinding machine spindle flutter effect

In ultracentrifugation grinding process, workpiece rotational frequency increases substantially, and grinding force increases, when reaching certain grinding force, the abrasive particle partial exfoliation of wheel face, grinding force reduces, make system more easily produce self-excited vibration, not only reduce emery wheel service life, also can affect surface of the work integrality.

In order to surface of the work can be made when grinding to obtain larger residual compressive stress, emery wheel service life and processing work surface integrity being ensured again, on the one hand by studying the relation of grinding speed and emery wheel durability, drawing optimum v _w/ v _svalue; Method on the other hand by the continuous speed change when grinding suppresses flutter.

Whether flutter can be suppressed, by experimental verification by speed change: choose emery wheel cutting speed 0.25mm/min about during grinding; Workpiece rotational frequency 100r/min; The mean speed of emery wheel, within the scope of 1150 ~ 1660r/min, gets one every 30r/min, and altogether in 18 kinds of grinding wheel speed situations, rotation constant speed and variable-speed grinding mode are tested.For investigating speed change amplitude to the affecting laws of chatter growth rate, under given experiment condition, choose speed change amplitude be respectively 0, ± 0.1, ± 0.2; Speed change waveform is sinusoidal wave; Speed change frequency is 0.1Hz, experimental result as shown in figure 15:

According to vibration average growth rate formula:

$\stackrel{\&OverBar;}{\mathrm{\&alpha;}}=\frac{T_s}{2\mathrm{\&pi;}(t_2-t_1)}\ln (A_2/A_1)$

In formula, T _s-emery wheel often turns the time

T ₁, t ₂-time of freely drafting

A ₁, A ₂vibration amplitude under-corresponding two times

It should be noted that, in order to calculate the average chatter growth rate under various grinding condition, carrying out in continuous crush grinding process at emery wheel, record respectively and process and be ground to t ₁=10s, t ₂the vibrating signal in two moment of=40s, just can obtain t ₁, t ₂the flutter amplitude A in two moment ₁, A ₂, thus calculate average chatter growth rate.

Can be obtained by experimental result, as P=0.0, be the equal of constant speed grinding, the vibration growth rate of variable-speed grinding corresponding when the vibration growth rate of its correspondence is obviously greater than P=0.1 and P=0.2, and namely demonstrating variable-speed grinding can suppress flutter effectively; In addition, the growth rate of flutter reduces along with the increase of speed change amplitude, indicates increase speed change amplitude favourable to suppression flutter.Under these experimental conditions, when average chatter growth rate when speed change amplitude is 0.2 is constant speed grinding 40%.

In sum, in ultracentrifugation grinding process, can effectively suppress main shaft flutter by speed change, the reduction along with system flutter just can reach protection emery wheel and ensure the object of workpiece machining surface quality.

Seven, speed change is to the explanation alleviating the effect of surface of the work generation " corner angle " phenomenon

In ultracentrifugation grinding process, workpiece rotational frequency increases substantially, grinding force increases, axis system dynamic characteristic changes, the forced vibration causing it to cause because of uneven emery wheel or axle is more violent, may be there is the small defect in local or protuberance in the surface of the work under constant velocity-ratio effect, namely create " corner angle " phenomenon, and crudy is difficult to ensure.

Larger residual compressive stress is obtained in order to make surface of the work when grinding, its surface quality can be ensured again, require that on the one hand lathe not only will have the axis system of high rigidity, high strength, high rotating accuracy and high balance quality, and excellent overall dynamics characteristic will be had; On the other hand alleviate by the method for the speed change when grinding " corner angle " phenomenon that surface of the work produces.

Ensure crudy by the speed change when grinding, theory analysis is as shown in the vibration signal function of time of Figure 16.For convenience of description, when not considering that system self-excited vibration and intrinsic frequency cause resonance, suppose that emery wheel and workpiece only produce forced vibration, and initial vibration signal to be amplitude equal with frequency, but the sinusoidal wave x that phase place does not wait _s(t)=Asin (ω ₀and x t) _w(t)=A (ω ₀t+ π).When grinding dosage is constant, if x _s(t) and x _wwhen the phase between () is 0 t, ground effect is the most desirable, if but phase by pi between them time, " corner angle " phenomenon that workpiece machining surface produces is the most serious---work as t=T _owhen/4, emery wheel upwards offsets maximum, and workpiece offsets downward maximum, grinding depth a _pbe decreased to minimum of a value; Work as t=T _owhen/2, emery wheel to being 0 with workpiece variation, grinding depth a _preturn to setting value; Work as t=3T _owhen/4, emery wheel offsets downward maximum, and workpiece upwards offsets maximum, grinding depth a _pincrease to maximum; Work as t=T _otime, emery wheel to being 0 with workpiece variation, grinding depth a _preturn to setting value again.Constantly circulate with this, until completion of processing, thus make surface of the work produce " corner angle " phenomenon.According to vibration principle, when axis system speed changes, the vibration signal of output also changes thereupon.As shown in the vibration signal function of time of Figure 17, when workpiece rotational frequency progressively reduces, the amplitude A in Workpiece vibration signal, circular frequency ω ₀and phase place to correspondingly change, wherein amplitude A and circular frequency ω ₀to reduce.Due to the change of work spindle vibration signal, the degree causing grinding depth to change because of forced vibration will reduce, thus reach the effect alleviating surface of the work generation " corner angle " phenomenon.It should be noted that, in real ultracentrifugation grinding process, because the rotating speed of emery wheel and workpiece is quite high, excited frequency is away from the intrinsic frequency of " lathe-workpiece-grinding tool " process system, so the vibration that axis system produces mainly comprises self-excited vibration and forced vibration, and the vibration signal that emery wheel and workpiece produce is all not identical.Even so, but still the impact of vibration on axis system can be reduced by speed change.

Above-mentioned is the present invention's preferably embodiment; but embodiments of the present invention are not by the restriction of foregoing; change, the modification done under other any does not deviate from Spirit Essence of the present invention and principle, substitute, combine, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.

Claims (10)

1. a revolving body workpieces pre-stressed grinding method, is characterized in that, comprises the following steps:

(1) clamping workpiece to be processed on grinding machine;

(2) carry out aim at tool operation, first allow emery wheel and workpiece be in lower-speed state, progressively adjust emery wheel position, until after surface of the work just occurs spark, grinding speed is adjusted to ultrahigh speed state v _s>=150m/s, is adjusted to ultracentrifugation state by workpiece rotational frequency, make workpiece produce centrifugal bulking effect, obtains prestressing force;

(3) grinding is carried out by certain radial feeds; After completion of processing, first emery wheel is separated with workpiece, then is decelerated to zero separately.

2. revolving body workpieces pre-stressed grinding method according to claim 1, is characterized in that: in step (2), described workpiece rotational frequency v _w>=8kr/min.

3. revolving body workpieces pre-stressed grinding method according to claim 2, is characterized in that: in step (2), described workpiece rotational frequency 8kr/min≤v _w≤ 10kr/min.

4. revolving body workpieces pre-stressed grinding method according to claim 1, is characterized in that: in step (3), described radial feeds a _p=10 ~ 100 μm/kr.

5. the revolving body workpieces pre-stressed grinding method according to Claims 1-4 any one, it is characterized in that: in step (3), emery wheel is by setting radial feeds feeding and after starting grinding, workpiece is or/and emery wheel carries out grinding with speed change state; After emery wheel stops radial feed entering the tarry matter stage, emery wheel, or/and emery wheel carries out tarry matter with speed change state, is separated with workpiece after tarry matter and is decelerated to zero separately by workpiece.

6. revolving body workpieces pre-stressed grinding method according to claim 5, is characterized in that, in the grinding stage, described workpiece is or/and the speed change state of emery wheel is: holding workpiece rotating speed is constant, improves grinding speed; In the tarry matter stage, described workpiece is or/and the speed change state of emery wheel is: keep grinding speed constant, reduce workpiece rotational frequency.

7. revolving body workpieces pre-stressed grinding method according to claim 5, is characterized in that, in grinding stage and tarry matter process segment, described workpiece is or/and the gear shift mode of emery wheel is continuous change or staged speed change.

8. revolving body workpieces pre-stressed grinding method according to claim 7, is characterized in that, when adopting continuous change mode, in the grinding stage, emery wheel is with 2m/s ²~ 5m/s ²linear acceleration accelerate; In the tarry matter stage, workpiece is with 800 π rad/s ²~ 1200 π rad/s ²angular acceleration slow down.

9. revolving body workpieces pre-stressed grinding method according to claim 7, is characterized in that, when adopting staged gear shift mode, in the grinding stage, emery wheel is with 6m/s ²~ 8m/s ²linear acceleration to accelerate after 6m/s ~ 10m/s at the uniform velocity 1 ~ 2s, this process is considered as one and accelerates ladder, circulate 3 ~ 5 times; In the tarry matter stage, workpiece is with 1200 π rad/s ²~ 1600 π rad/s ²angular acceleration deceleration 500r/min after at the uniform velocity 1 ~ 2s, this process is considered as a deceleration ladder, circulates 2 times.

10. revolving body workpieces pre-stressed grinding method according to claim 7, is characterized in that: described workpiece is the bearing inner race be made up of GCr15 material, and when carrying out ultracentrifugation grinding, workpiece initial speed is 8kr/min; In the grinding stage, emery wheel is with 2m/s ²~ 5m/s ²linear acceleration accelerate continuously; In the tarry matter stage, workpiece is with 800 π rad/s ²~ 1200 π rad/s ²angular acceleration slow down continuously, when workpiece rotational frequency drops to 7kr/min, emery wheel be separated with workpiece and be decelerated to zero separately.