Physics of influence treatment surface is mechanical the element of function

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In machining process, because workpiece gets the action of cutting force, heat in metal cutting, its surface and base material function have very big different, in physics mechanical performance side produces bigger change. One, those who machine exterior layer is cold in making sclerotic 　 machine a process in cutting or grinding, if machine the plasticity that expresses layer generation to be out of shape,make the generation between crystal cuts slippage, crystal lattice is serious and screwy, produce grain spin, broken change with fiber, cause the appearance that the intensity of exterior layer and hardness improve, call cold make sclerotic appearance. The sclerotic degree of exterior layer depends on generation plasticity metabolic force, be out of shape speed reachs the temperature when be out of shape. Power is greater, plasticity is out of shape bigger, the sclerotic rate of generation is older also. Be out of shape speed is jumped over big, plasticity is out of shape more inadequate, the sclerotic degree of generation also is reduced accordingly. The temperature when be out of shape affects plasticity deformation, high sclerotic rate reduces temperature. (One) influence surface layer is cold the 1 of element 　 　 that makes sclerosis. Of face of the knife after the point round part of cutting tool cutting tool is mixed wear away of pair of surface layers cold make sclerosis have very big effect, the wear extent of face of the knife after point round part is mixed is bigger, cold the hardness that makes sclerotic layer and deepness are bigger also. 2. Cutting dosage 　 is in cutting dosage, the impact is bigger is cutting speed V C and feed F. When V C increases, express the sclerotic degree of facing and deepness to be reduced somewhat. As a result of,this is on one hand cutting speed adds congress to make temperature heighten, conduce to cold the return that makes sclerosis; On the other hand the accretion as a result of cutting speed, cutting tool and workpiece contact time are short, make the plasticity deformation of workpiece is reduced. When feed F increases, criterion cutting force increases, plasticity deformation also increases, what express facing accordingly is cold make sclerotic appearance serious also. But when F is lesser, as a result of the point circle of cutting tool horn is machining apparently extruding number increase, what express facing accordingly is cold make sclerotic phenomenon also can increase. 3. Be jumped over by the hardness of treatment material by treatment material 　 low jump over with plasticity big, criterion what after cutting is machined, its express facing is cold make sclerotic appearance more serious. (2) reduce exterior layer cold the 1 of measure 　 　 that makes sclerosis. The geometrical parameter of logical choice cutting tool, use bigger before the horn after horn is mixed, reduce radius of round part of its cutting point as far as possible when blade is ground; 2. When use cutting tool, should reasonable limitation ever since of knife face wear away degree; 3. Dosage of logical choice cutting, use higher cutting rate and lesser feed; 4. Add man-hour to use effective cutting liquid. 2, the 　 of 　 of metallographic organization change of exterior layer (one) the element 　 that the metallographic organization that affects exterior layer changes when machining, the heat energy of energy majority translate into that cutting place wastes and make treatment surface occurrence temperature elevatory. Lift when temperature when exceeding metallographic to organize critical point of change, with respect to the change that can produce metallographic to organize. General cutting is machined, because unit cutting is sectional,the power that consumes is not too big, the phenomenon that organization of reason generation metallographic changes is less. But because cutting rate is high,grinding is machined, a few times the heat in metal cutting of generation is bigger than common cutting treatment, parts of these quantity of heat by cut bits to take away, very small one part passes into emery wheel, if cooling result is bad, will pass into workpiece surface partly greatly very much, make the metallographic organization of workpiece surface layer produces change, the hardness that causes exterior layer and intensity drop, generation remains stress is caused even show micro-crack, this kind of phenomenon calls grinding burn. Accordingly, appear grinding treatment is a kind of model easily the treatment method that machines exterior metallographic to organize change. According to the temperature when grinding burn different, can divide for: 1.

Temper burn quenchs when grinding when steel, if grinding area temperature exceeds martensite transition temperature, criterion the temper troostite that the martensite organization with workpiece former surface will change into hardness to reduce or organization of body of all alone family name, this says for temper burn. 2.

Grinding of injury of baked wheaten cake of temper by dipping in water quenchs when steel, if grinding area temperature exceeds,become critical temperature, in the urgent cold action of cutting fluid, make workpiece surface the outerest metallic change quenchs for 2 martensite is organized. Its hardness is taller than original temper martensite, but hard fragile, and the temper organization that its lower level still reduces slower for hardness because of cooling rate, the baked wheaten cake is temper by dipping in water that this kind of phenomenon weighs is hurt. 3.

If when cutting fluid undertakes working grinding, anneal burn need not exceed the critical temperature that changes, because air of workpiece metal surface layer is cold cooling rate is slower, make hardness of the intensity after grinding, surface drops quickly, produced anneal burn. When grinding burn, the surface can appear the burn such as yellow, brown, violet, blueness is lubricious. This is the oxidation film color that workpiece surface produces below instantaneous high temperature, level of burn of face of different burn colour appearance is different. Deeper burn layer, although machining later period to use,can get rid of without feed grinding burn color, but burn layer did not get rid of however, make the hidden trouble in be being used in the future. (2) the 1 of 　 of technology measure 　 that prevents grinding burn. 　 of dosage of logical choice grinding reduces grinding deepness to be able to reduce the temperature of workpiece surface, reason is helpful for reducing burn. Increase workpiece speed and feed, because time of heat source effect decreases, make metallographic organization has not enough time to change, can reduce burn consequently, but can bring about exterior surface roughness the value increases. Use commonly raise emery wheel speed and wider emery wheel to make up for. 2. 　 of seasonable nap is like logical choice emery wheel the granuality of emery wheel jumps over fine, hardness to jump over tall Shi Zili the gender is poor, criterion grinding temperature also heighten. Bits is ground to jam when emery wheel organization is too close together emery wheel, easy occurrence burn. When emery wheel passivation, great majority is ground bead squashs in treatment surface only and chafe and do not have cutting effect, make grinding temperature heighten, reason should seasonable nap emery wheel. 3. Improve cooling method 　 to use cutting fluid to be able to take away the quantity of heat of grinding area, avoid burn. Commonly used cooling method effect is poorer, when rotating as a result of emery wheel high speed, circumferential direction generates powerful air stream, make cutting fluid enters grinding area very hard, because this cannot drop in temperature effectively. To improve cooling method, can adopt a plan 5, 4 show inside cooling emery wheel. Cutting fluid is connected from the center, rely on centrifugal force effect, from emery wheel through the space of emery wheel interior the brim all around is swung piece, because this cutting fluid can enter grinding area directly, cooling effect is very good. But must use tailor-made poriferous emery wheel, ask lest jam,cutting fluid course filters carefully emery wheel. 3, the classics of workpiece of leftover stress 　 of exterior layer after machining, its express facing to be put in leftover stress. The wearability that remains presses stress to be able to improve workpiece appearance and bear the fatigue intensity when pulling stress, the effect just in time that remains plays stress is contrary. When the fatigue intensity limit that if pull stress to be worth,exceeds workpiece material, make workpiece surface produces crackle, quicken the attaint of workpiece. The cause that causes leftover stress has the following 3 respects: (One) cold plasticity is out of shape the leftover stress 　 that cause is below cutting strength effect, already machined the surface to be out of shape by intense cold plasticity, the plasticity that faces the extruding that already machined the surface and attrition generation with the knife after cutting tool among them is out of shape most outstanding, right now base metal is affected and be in flexibility to be out of shape condition. After cutting force eliminate, base metal incline to restores, but the limitation that already was arisen layer of plasticity metabolic surface, restore to be less than original state, produce remains to press stress in exterior layer consequently. (2) thermoplastic be out of shape the work of leftover stress 　 that cause machines the surface to produce heat to expand below action of heat in metal cutting, base metal temperature is right now inferior, because metal of this surface layer produces hot pressing stress. When cutting process ends, exterior temperature drops faster, reason systole is out of shape be more than li of layer, because surface layer is out of shape,get the limitation of base metal, so generation remains pulls stress. Cutting temperature is higher, thermoplastic be out of shape bigger, remains pulls stress bigger also, produce crackle even sometimes. What arise when grinding is thermoplastic be out of shape more apparent. (3) the metallographic that the high temperature of the generation when the cutting of 　 of leftover stress <DIV Align=left> that metallographic organization change causes can leave exterior layer organizes change. Different metallographic organization has different density, exterior layer metallographic organized metabolic result to cause the change of bulk. When exterior layer bulk expands, because get the limitation of matrix, arose to press stress; Conversely, arise pull stress. </DIV> CNC Milling CNC Machining