Hard turning technology

00011 inches surface is bright and clean degree, 0.

000009 inches of circularity and ± 0.

Public errand of 0002 inches of diameters, such precision is undertaking to the workpiece before temper by dipping in water is hard " soft turning " can achieve likewise on identical machine tool, thereby utmost land increases utilization rate of equipment and installations. However some of factory is chosen impoliticly at first improper (saying exactly is cheaper) bit, whether does another some of factory perhaps have very tall tigidity, enough to bear to connect the pressure of turning to did not hold at general doubly to their machine tool. With a ha hold out a company (the applied engineer TomSheehy of Hardinge) told about this company a few proposals to hard turning and understanding. It is 8 when when the factory evaluates hard turning seriously, must remember well main process factors below. Workpiece although the initial drop that 45Rc material is hard turning, but hard turning often undertakes on the workpiece of 60Rc above hardness. Hard turning material includes tool steel, bearing steel, cementite steel and chromic ferronickel alloy normally, be able to bear or endure corrode heat-resisting nickel base the special material such as cobaltic alloy of chromium of alloy, tungsten. According to the viewpoint of metallurgy, cutting deviation of the hardness inside deep limits small (the material that is less than 2 Rc) shows best process to be able to forecast a gender. Sometimes, the dimension of workpiece or geometrical feature do not agree with completely hard turning, most agree with the spare parts of hard turning has lesser length / diameter (L/D) comparing; Say commonly, do not have L/D of the workpiece that prop up than not be more than 4:1, of L/D of the workpiece that prop up than not be more than 8:1. Although long and thin spare parts has rear push frame to be being propped up, but cutting pressure still causes Dao Zhen likely greatly too. Stiffness of machine tool machine tool decides the treatment precision of hard turning, the machine tool that 15~20 makes inside year recently has very good tigidity almost, enough copes with utility of certain hard turning. Below a lot of circumstances, the overall condition of the machine tool is more fundamental than using fixed number of year on older rate, safeguard excellent hand to move what old lathe can make hard turning even to await choose a target. Anyhow, because be opposite spare parts public errand and surface are bright and clean degree of requirement is stricter and stricter, machine tool stiffness will be a simple question no longer. Increase tigidity and damp character to give hard turning utility, ha Ting brought into a lot of features turning center, include polymer composite material to strengthen baseplate, area among them pinchcock head (make main shaft is propped up approach work) direct formula main shaft and static press slideway. Systematic tigidity is the biggest change mean reduce all impending, cutting tool as far as possible outspread extend with the spare parts, cancel shift unoccupied place piece with washerbed down the livestock, its target is to maintain all thing to be close to as far as possible turn tower tool carrier. Bit has some of factory to oppose square nitrogen changes boron at first (the high price of CBN) razor blade flinchs, although CBN razor blade is most agree with hard turning. CBN razor blade can hold fixed position in interrupted cutting process changeless, safe cutting tool wear rate is offerred in successive cutting process. When using proper hard turning technology, CBN razor blade besides it is beyond grinding of be not a patch on of respect of control diameter public errand, other function is the first of all. Pottery and porcelain is inferior to CBN wear-resisting, because this is general,need not be less than ± at tolerancepublic errand 0.

001 inches operation. Pottery and porcelain does not agree with interrupted cutting, and should not add cooling fluid, because thermal shock may cause bit rupture. The appearance of geometry of blunt predestined relationship of bit is the inherent characteristic of material of pottery and porcelain, force of cutting of translate into of this one characteristic increases and workpiece surface is bright and clean degree drop. Additional, point of blade of pottery and porcelain ruptures may be disastrous, it may make blade does not have all cutting to be able to be used. Cermet (cubic carbonization titanium) sclerotic to successive cutting cementite material is very effective, although it does not have CBN in that way wearability, fortunately bit falls to be able to wear away into scale ground and do not rupture in most circumstance. Razor blade of the horn before losing gets as a result of its strong cutting blade using normally. To it contrary, before horny razor blade because its cutting force is smaller, just use in tigidity likely hard turning undertakes on not tall machine tool. The best proposal about bit is with tool supplier clasp, be in especially first phase, with achieving optimal cutting rate quickly. Cooling fluid the biggest question about cooling fluid is to be used after all need not cooling fluid. To the interrupted cutting spare parts of gear and so on, had better be " dry move " , otherwise feed and the thermal shock when retreating a knife cause bit rupture probably. As to successive cutting, the pliable but strong of high temperature enough that knife head produces in dry moving process is changed (soften) beforehand cutting area, reduce what material hardness makes to be cut easily thereby. Rate increasing when this phenomenon showed dry cutting is beneficial. In the meantime, have clear cost advantage without type of cooling fluid cutting. In successive cutting utility, cooling fluid may conduce to lengthen cutting tool life and improve the appearance bright and clean degree. The key of the problem is to want refrigerative fluid to be able to reach knife head, high-pressured cooling fluid is the best method that solves this problem, because it is not easy,evaporate below high temperature. In addition, high pressure can reduce the accumulation that cut bits, because cut bits block, cloggy cooling fluid to flow to the opportunity of knife head,decrease thereby. Another method is the coping that releases cooling fluid bit at the same time and bottom, ensure cooling fluid reachs knife head continuously. If use cooling fluid, it must be water radical. Bits is cut in what form in the hard turning course that matchs completely, the quantity of heat that can take away 80~90% (highest temperature can amount to cutting area 1, 700 ° F) . So blazing cut bits in case refrigeration of osculatory low burning point is oily, whole process is completely possible come to naught. If be in,open wide type machine tool aspirant travel hard turning, must increase proper protector, avoid to operate personnel to be cut bits scald. The quantity of heat that craft produces because of hard turning is major by cut bits to take away, treatment around undertakes checking can discovering whether whole process is harmonious to cutting bits. When successive cutting, cut bits to should show blazing orange yellow, be like the ground like a lace elegant and piece. If cut bits,press with the hand after refrigeration rupture basically, making clear the quantity of heat that cuts bits to take away is normal. The white 　 that change a layer " Bai Hua layer (hot influence area) " show may rebarbatively operate in hard turning and grinding in, what form a naked eye to lose sight of in material surface namely is very thin (normally 1 micron) incrustation. Bai Hua layer is formed in hard turning process, because bit passivation causes overmuch quantity of heat to deliver a part,be commonly inside. Change a layer to often be formed on bearing steel in vain, and to bearing circle and so on needs to bear the spare parts of tall contact pressure is very harmful, as the elapse of time, the white likelihood that change a layer comes off and bring about bearing invalidation. Bearing manufacturer almost test on means of provide for oneself, so that be in,this respect is in lead position. As to the plant that just begins to be engaged in hard turning, the head that the proposal is beginning to produce a few undertake selectiving examination randomly inside week, in order to decide every razor blade can turning how many spare parts and do not form Bai Hua layer. Metallurgy company is capable to have these tests. Although a razor blade is a standard with can machining 400 spare partses, after it is machining 300 possibly also, become blunt and begin to make the spare parts produces Bai Hua layer. Bore hole the cutting pressure with very great need of boring oil hard data, because this often is met,twice land increases boring lever susceptive torsional and tangential force. Use before 35 ° or razor blade of radius of 55 ° acute angle, small point of a knife can reduce horny pattern cutting pressure. Raising cutting rate while reduce cut mix greatly feed speed, also be the way that reduces cutting pressure. When boring hole, cutting tool must as homocentric as the spare parts or center of spare parts of summary prep above, the bending that causes because of cutting is out of shape make the position of real center line is reduced. Best clamp form is entire length runs from opposite directions sleeve, it is pinchcock head and collet of only place screw next. Car whorl uses proper bit geometry figure is the key in whorl of the turning on oil hard data, one of best whorl razor blade are the triangular razor blade that is similar to the installation on boring lever. Below correct process parameter, included angle of 60 ° whorl and radius of small point of a knife are very effective. When whorl of the turning on oil hard data, to control cutting pressure is mixed prolong bit life, be necessary to increase knife number and be reduced cut deep. Another kind of choice is to use alternant type flank to cut way, changeable cutting force stands the position causes longer cutting tool life. 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