Grinding of hard fragile data machines the theoretical analysis of mechanism

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Summary: Pass pair of hard fragile data (glass) cutting experiments, built the grinding model of hard fragile data, the plasticity that discussed hard fragile data to fall in the action that wear bead is out of shape and rupture behavior. The 1 foreword development as science and technology and production, hard fragile data (wait like project pottery and porcelain, optical glass) application is wide with each passing day. Because the brittleness of hard fragile data is bigger, add man-hour to issue easy happening to rupture in the action that wear bead, because this its treatment mechanism compares metallic data,machine more complex. Machine the theory of mechanism to study still insufficient development and maturity to hard fragile data at present, the research that begins this side actively has important sense to coaching production is carried out. The article passes hard to the model fragile data -- , vitreous cutting experiments, to the grinding of hard fragile data treatment mechanism undertook theoretical analysis, the choice of dosage of the cutting when hard to treatment fragile data has its conclusion to coach certainly meaning. Graph 1 hard fragile data (glass) grinding model pursues the 2 pressure when grinding bead to press plane distributing the circumstance pursues 3 stress distinguish cloth pursues of model of grinding of 2 hard fragile data build odd grain diamond is used to fly on accurate grinder mill plant undertakes to glass. Use high speed cinematograph to observe diamond grain cutting is fragile the dynamic process of hard data; Use observation of scanning report lens to be machined the groove cross section of material and groove form appearance. Through be opposite cutting experiments process and be analysed by the observation of treatment glass surface, the hard fragile data that if the graph is shown 1 times,builds (glass) grinding model. Considerable in cutting experiment examine goes to 3 tests result and the model sexual behavior that discuss hard fragile data to fall in action of the extruding that wear bead, should cut deep lesser when (namely grinding is initiative level) , of hard fragile data be out of shape expression is out of shape for plasticity. From the angle analysis of stress field, hard fragile data is being surrounded only pressure enough big when, ability shows good plasticity like metallic stuff, surround pressure bigger, plasticity is better. Because any upright ministries that wear bead all have certain circular arc radius, can regard ministry of the end that wear bead a radius to be the sphere of R approximately consequently. When should grinding bead to be pressed to vitreous surface below action of perpendicular force P, the interface brim of its and glass is a circle. This circle radius distributings for the pressure on A=[3(1-µ2)PR]½2E(1) interface usable Q expresses to be (2) Q=3P(a2-r2)½2pa3(2) seeing a picture by the graph 2 visible, distributing in the pressure of pressure area brim for 0, and in pressure area center (R=0 is in) pressure distributings the biggest, state with Q0 this center handles pressure, by type (2) can get Q0=3P2pa3(3) to be below the action of distributinging force Q, the stress inside glass can divide the area that it is Ⅰ and Ⅱ area, if pursue,3 are shown. Inside Ⅰ area, glass gets of each direction control stress function; Inside Ⅱ area, glass is controlled stress and the integrated function that play stress. In symmetrical axis (Z axis, be located in Ⅰ area) on, the formula of sea Er Ci of stress is {sr | R=0=sq | R=0=-(Hu)q0(1-zarctana)+q0a2az2z2+a2sz | The stress in R=0=-q0a2r2+a2(4) type all gives priority to stress, minus expresses to press stress. As with pressure area (Z axis) the accretion of the distance, sr, Sq, Sz all is reduced, and Sr=sq is reduced more quickly than Sz. When Z=0, have {sr | R=0=sq | R=0=-1+2uq02sr | If R=0=-q0 is chosen inside U=0 of coefficient of friction.

3, criterion of pressure area center press stress to be {sr | R=0=sq | R=0=-0.

8q0sr | R=0=-q0 this shows, be surrounded in the material of pressure area center press P=0.

Q=0 of 8q0, bias voltage.

The action of 2q0, adjacent at reducing position equably severally, surrounding pressure multiple fall at the circumstance of bias voltage, material happens scarcely destroy. After leaving center, material gets surround press and bias voltage all is reduced, but surround pressure ratio bias voltage to reduce faster, for example, be in in Z=a/2 and Z=a (the stress condition of R=0) is {sr respectively | R=0=sq | R=0=-0.

18q0(z=a/2)sr | R=0=-0.

8q0{sr | R=0=sq | R=0=-0.

029q0(z=a)sr | R=0=-0.

5q0 by the above-listed 4 type are knowable, further from pressure area center, material gets surround pressure smaller, because this material is more possible,in pressure area lower part certain distance place happens above all destroy, craze direction is parallel at the biggest control stress direction () of Z axis direction, this crackle is namely medium a crackle (MC) . In can't arising when pressure when crackle, around pressure area center the material of area will produce apparent plasticity to be out of shape, other everywhere material holds stretch position. In interface brim (graph 3 in Ⅱ area) , sz=0, sr=-sq=[(1-2u)/3]q0, pull stress to reach maximum right now, the crackle that causes by Sr is hertz crackle namely (CC) . In the area that area of Ⅱ area and Ⅰ , Ⅱ borders, because be not had,surround layering high, because this material did not show plasticity. This shows, hard fragile data is being cut deep very hour, had good plasticity to be out of shape condition, form the furrow phase in grinding process thereby. Although be in brittleness cutting phase, still show good plasticity to be out of shape with the material surface of the contact that wear bead (but lower level material happened to destroy) . Hard fragile data is grinding what bead elbow action falls to rupture behavior brittleness material (like glass) with plasticity material (like the metal) in odd axis drawing, when turning round rupture formal contrast sees next tables. Visible, of the metal rupture direction is parallel at the greatest shearing stress direction, accord with the greatest shearing stress criterion; And of glass rupture direction is perpendicular at the biggest play stress way, accord with the biggest press stress standard. Express hard fragile data and metallic stuff rupture formal contrast ruptures drawing of material of brittleness of formal metal stuff is turned round rupture direction is parallel at the greatest shearing stress perpendicular at the biggest pull stress to accord with criterion the greatest shearing stress standard is the oldest pull stress criterion to consider to make clear, metallic stuff still accords with principle of the greatest stress in odd axis or the destruction when many axis is compressed, and the destruction of brittleness material mechanism up to now still very not clear. Nearly one, research of 20 years makes clear, be compressed in odd axis or surround pressure when compressing, brittleness crackle always tends cut the way with the smallest load (press the directional) with the greatest stress namely, most crackle is piece of sex; As outside the accretion of stress, micro-crack amount increases ceaselessly, a large number of micro-crack mutual crisscross join, cause brittleness material to happen to be destroyed completely. In the meantime, as surround the accretion that press, the plasticity of material also increases, the patulous direction of micro-crack deviate the biggest control stress direction. Right now, of one part micro-crack expanding is piece of sex, another share cuts a gender; Should surround pressure very tall when, basically produce shear failure. The case getting power that hard fragile data leaves in the action that wear bead is more complex, simple end is piece of sex to rupture or cannot cut rupture. Around needle of the blade that wear bead, material gets very tall surround pressure, because this will main generation cuts shift (furrow) or the close-grained nucleus that shear failure forms; In the area that is far from needle of the blade that wear bead, basically produce chunk piece sexual collapse is broken. Material and grind a two side contact to because get,be in very great tensile stress and produce craze, form the hoof shape flaw that the graph shows 4 times (HC) . The hertz crackle of the generation when hoof shape crackle and sphere are invaded is identical substantially. When hoof shape crackle patulous direction and cutting direction become older point of view (if be close to 90 ° ) when, because get ahead obstruction, the tensile stress that makes hoof shape crackle expand is very fast damply, make hoof shape crackle stops to expand. When hoof shape crackle expands direction and cutting direction become lesser angle, press stress to make hoof shape crackle ceaseless expand and tend gradually with press stress parallel, bring about groove thereby two side direction produce breach; Arrive when the cutting that wear bead when the brim, it is approximately as a result of S1 0, because crackle of this hoof shape can keep expanding to two side, generate collapse margin thereby. Hoof shape crackle goes to expanding is piece of sex from generation. Graph sketch map of crackle of 4 hoof shape pursues sketch map of 5 crackle stress is grinding an action to fall, brittleness material does not produce hoof shape crackle only. In fact, wearing bead all round craze all may happen anyplace inside area of action of whole strong stress. Because numerous crackle crosses follow in a continuous line each other, just make cut bits to show smash shape and rather than is rectified piece, be being machined at the same time material surface leaves a lot of crackle. When cutting deepness and cutting width all very hour, brittleness material does not produce craze, form smooth plasticity groove only, its action mechanism can show factor of structural stress intensity 5 times to explain with the graph. If the graph is shown 5 times, there is a diameter to be the round hole of D in the flat of infinity, even pressure P bears inside aperture, aperture both sides has length to be the crackle of A. The stress intensity factor of crackle thinks for KI=FPp(D+a)½2(5) D of round hole diameter and width of the cutting that wear bead are equal approximately, pressure P and the osculatory stress that wear bead arris face and stuff are equal, the crackle that is length A regards material as medium natural crackle, criterion by type (5) is knowable, in osculatory pressure and natural crack length particular case falls, cutting width is smaller, intensity factor KI is smaller. Be less than some when KI when critical value KIC, rupture to won't happen. Right now, KIC is the fracture toughness of material. 4 conclusion pass pair of hard fragile data (glass) cutting experiments, the analysis discussed what hard fragile data falls in strength effect to be out of shape the rule. Think to should be cut deep place of very small, stuff suffers surround pressure enough big when, hard fragile data can produce plasticity to be out of shape; Of hard fragile data rupture behavior and metallic stuff are having substaintial distinction. Hard fragile data forms very polyphase each other to hand in the crackle of be linked together in grinding process, make cut bits to show smash shape, be in be left by cutting surface a lot of crackle. CNC Milling CNC Machining