The high speed milling of aviation engine mould

  • Time:
  • Click:105
  • source:KOMANG CNC Machining
Blade is the main part of aviation engine, its characteristic expression is appearance and load circumstance very complex, and dimension size six to one. Generally speaking, the treatment workload of blade occupies whole platform engine to machine the 30%~40%[1] of workload. The cent of main workmanship process of blade is made for semifinished product and machining two large stage. The production of blade semifinished product has commonly cast and forging 2 kinds. Foundry technology is multi-purpose at turbine job lamina and guider lamina, especially hollow lamina, at present already by common cast development for fusible pattern nicety. Forging the dominant position with the largest lamina is blade intensity tall, but forging the treatment difficulty of the mould is great, cost is high. Blade forgings craft also already by half essence forge work up is forge of essence of life. Forging without surplus nicety blade becomes the development climate that compressor lamina will create henceforth. This shows, blade nicety mould and accurate forging die are the main tool that blade makes. Of mould of essence of life and precision forging die model antrum curved surface and conjugate of blade curved surface, form is complex; Sort is much, batch is small; The machinability of material is poor, especially forging die. According to statistic, the design of blade mould occupies whole aviation engine to design the 30%[2] of production cycle with production cycle, periodic to the production quality of engine, production, production cost has immediate effect. High speed cutting has efficient, high accuracy, can cutting is tall quality of surface of hard data, workpiece is advanced a series of advantages. Although the one-time investment in respect of machine tool, cutting tool is higher, but the manufacturing efficiency that considers blade pattern integratedly, n, service life and the reparability after wearing away, high speed milling still is to solve mould of aviation engine lamina the most effective method of production issue of efficient, low cost. Heretofore, technology of high speed cutting applies in industry of aviation manufacturing industry, automobile manufacturing industry, mould succeed most extensively most. In the application of aviation manufacturing industry, basically center in plane whole structural member and aviation engine spare parts of tall hard alloy (basically be blade) on high speed cutting, and the technology of high speed milling of lamina of compressor of concerned aviation engine and turbine lamina mould and craft, the person that pay close attention to is not much. Craft of blade mould machining analyses 1 material to analyse blade material to have alloy of aluminium alloy, titanium and stainless steel, its essence mould is provided or forging of the mould model body and model core, material is alloy steel commonly and pass hard processing of temper by dipping in water (namely hard steel of temper by dipping in water) , be like 5CrNiMo. The steel that hard steel of temper by dipping in water points to to the course quenchs and the hardness after temper achieves HRC 50 above commonly [3] . The hardness of material of hard steel of temper by dipping in water is tall, wearability is good, plasticity is poor; Heat conduction performance is poor, coefficient of thermal conductivity is the 1/7 of 45 steel about. The hardness of material of hard steel of temper by dipping in water and intensity depend on the quantity containing carbon of the martensite in the organization. These elements of blade mould material bring the following difficulty to cutting treatment: (1) unit cutting muscularity, treatment is difficult, and the smooth stability of cutting process is poorer; (2) material coefficient of thermal conductivity is small, cutting temperature is high, make cutting tool wears away serious, and the petty carbide aggravate that dispersion shows to distributing after the temper in the organization of cutting tool wear away; (3) workpiece hardness and cutting speed are the main factor that affects the configuration that cut bits, below fixed rate condition, easy generation is dentate when cutting of hard steel of temper by dipping in water cut bits, cause the circular commutation of cutting force and high frequency vibration, workpiece surface quality is poor. The milling of groovy speed processes hard steel of temper by dipping in water directly hard, aux used to uses electric spark treatment and grinding treatment, efficiency is low. High speed milling can machine hardness HRC60, more expensive even workpiece stuff, can machine the mould after temper by dipping in water is hard directly, because [4] : (1) as a result of cutting mechanism different, force of the cutting when high speed cutting is reduced, treatment is easy, and cutting is out of shape small; (2) when high speed cutting, cut bits with very tall speed eduction, take away many heat in metal cutting, the quantity of heat that passes workpiece and cutting tool decreases substantially; (3) the job is smooth, vibration is little, the treatment surface quality of the spare parts is high, the reason has 2 sides: When high speed cutting, of the machine tool stimulate Zhen Pin rate is high, was far from the natural frequency of machining complex, avoided flutter; Cutting force is the main and incentive source in cutting process, cutting force is reduced make incentive source is reduced. Use high speed cutting, not only can improve productivity substantially, and can reduce cutting tool effectively to wear away, improve the exterior quality that the spare parts machines. 2 craft analysis because aviation engine foliaceous body face is by base yuan blade profile is pressed accumulate the dimensional curved surface that fold regular accumulating and becomes certainly [1] , form is complex (see figure below) , because of this its nicety mould and forging die model antrum curved surface also is complex free curved surface [5] . Model appropriate of antrum curved surface uses method of milling of numerical control much axis to undertake machining. The blade mould that lamina of aviation engine turbine pursues traditional machines a course to be: Semifinished product anneal - thick mill - half essence mill - quench and temper - kibble - electric spark machines special place (model antrum, pointed horn) - essence of life is ground - clamp is repaired. In this technological process, after quenching, can undertake grinding treatment and electric spark are machined only, heat treatment arises be out of shape also must have repair by electric spark or handiwork. What manual handling time wants to occupy whole treatment cycle is very major, manufacturing efficiency is low. If use method of high speed milling, criterion its technological process is: Semifinished product anneal - thick mill - half essence mill - quench and temper - high speed milling - clamp is repaired. Different treatment method and machine tool, different workpiece material, limits of corresponding speed of high speed cutting is different, give a certain numerical value very hard to the speed limits of high speed cutting so. The research result that covers hypothesis of high speed cutting and mechanism of high speed cutting according to Sa the name of a river in Shaanxi and Henan provinces, inside limits of speed of high speed cutting, cutting force drops, the temperature rise of workpiece is inferior, heat is out of shape lesser, the durability of cutting tool rises. General, workpiece material hardness is smaller, rate of high speed cutting is higher. Provide steel to die of temper by dipping in water, speed of high speed cutting should be 300m/min left and right sides. When die of temper by dipping in water of high speed milling provides steel, after achieving fixed cutting rate, the temperature of osculatory area will maintain cutting tool and workpiece to be controlled in 700 ℃ , continue to lift no longer; The average temperature of workpiece maintains between ℃ of 190 ℃ ~225 [3] . This can use very high cutting rate, inferior every tine feed and cutting deepness the important basis of steel of strong pattern of temper by dipping in water of milling of direct high speed. High speed milling besides improve cutting efficiency besides, still can bring following advantages: Nextpage (1) treatment fare is low. High speed milling replaces electric spark treatment, can machine the mould after temper by dipping in water is hard antrum directly. Such already leave out process designing of treatment of electrode material, electrode and treatment, saved electrode to machine process place to require cost again. Material purify rate can be rivalled with electric spark treatment, even more actor, can acquire better exterior quality. For example, hardness of material of some forging die is as high as HRC54, model if antrum finish machining is finished entirely by high speed cutting, handling time is 88min. If according to the craft previously, from production treatment of electrode, electric spark needs 17h about to polishing. (2) mould life is lengthened. High speed cutting avoided electric spark treatment to leave white hard layer in treatment surface (recast layer) blemish. White hard layer is right mould life, mix in Die Casting especially forging waiting for the pattern that uses below tall stress condition is very harmful. Of mould life rise to still have another reason, in conventional treatment technology, of purify of electric spark treatment model antrum surplus is larger. The temper by dipping in water of mould material appears a gender poorer, mould core and outside hardness differ bigger, when the surplus that should machine is larger, the outside face after inferior place became mould core hardness to machine, bring about the place intensity and hardness to drop, service life drops. (3) reduced workload of manual rest and reorganization. Because quantity of cutting of high speed milling is reduced, the milling cutter that can use smaller diameter is mixed to small round horn radius the detail of mould structure undertakes machining, saved partial treatment and manual clamp to trim the job. The decrease and produces craft to simplify to produce cycle to shortening contribution of manual nap time exceeded speed of high speed cutting to increase brought value even. Acquisition exterior surface roughness can achieve Ra0.

5, can rival with grinding. (4) high speed milling also makes mould rehabilitate more convenient. After blade mould is using period of time, the area distributing a model that leaving model line can appear cave in, bring about product quality to drop, build a model with respect to need at this moment, in order to maintain the quality of the product and the service life that prolong a mould. Building a model in the past basically is to pass a cave in to be in filling solder again electric spark treatment will finish, or burnish of labour of filling solder defensive position. When filling solder, the mould is put in stress concentration, easy the craze when bringing about a mould to use. Accordingly, after electric spark is machined, still must increase go stress anneal, the time building a model of the mould is longer. After using high speed to machine, need to reduce the cent of the mould range only, use the program of NC finish machining when be being machined so directly, need not new process designing, rose to repair modular efficiency. And can raise the exterior surface roughness of mould antrum, the blemish such as the chap of the generation in the process that purify mould uses, make mould service life is lengthened. The place on put together is narrated, make in the efficient, low cost of blade mould in, high speed mill is sold can produce main effect. Cutting tool and cutting tool material are to make high speed mill is sold in mould treatment the advantage that produces efficient, low cost, must logical choice cutting tool and cutting tool material. A when technology of cutting of high speed of block up of material of 1 cutting tool develops main obstacle once was cutting tool material is high temperature resistant with wear-resisting damage issue. Cutting tool wears away mechanism considers to make clear, when high speed cutting, temperature of point of a knife will exceed 900 ℃ , right now of cutting tool wearing away is mechanical attrition wears away not only (wear away with face of the knife after cutting tool give priority to) , still have stick receive wear away, diffuse wear away and oxidation wears away (with cutting tool point wears away and crescent moon wears away depression for main form) . Material of cutting tool of high speed cutting needs taller hardness and heat-resisting, wearability. Appear of new material, new technology ceaselessly, make cutting tool material develops pottery and porcelain, diamond, CBN, PCBN by inchoate high-speed steel, hard alloy (Polysrystallinecubic Born Nitride, get together nitrogen of brilliant cubic metre changes boron) with material of cutting tool coating. The in high speed milling application of PCBN cutting tool and cutting tool of hard alloy coating in blade mould is most wide. PCBN is the much brilliant material that will imperceptible below high temperature high pressure CBN material agglomeration combines together. Because suffer CBN to produce technical limitation, the CBN of the big grain that is used at cutting cutting tool directly at present still very difficult, consequently PCBN got developing more quickly. Because PCBN cutting tool has the hardness with close of diamond cutting tool, the thermal stability that has prep above diamond again is mixed the tall chemical stability of elements of pair of iron a group of things with common features, the application in the high speed cutting that provides steel in die of temper by dipping in water consequently is wide. PCBN cutting tool is unfavorable cutting undertakes below low speed, because it is in order to lose before the high fever that produces when horn and high speed cutting is in those who make workpiece material bate undertakes cutting is machined ceaselessly inside limits of cutting area iota, and the iron with unfavorable also soft cutting a group of things with common features material, did not quench steel and aluminium alloy, because easy generation accumulates bits tumour, cause cutting force to fluctuate, make be worsened by treatment surface, lower cutting tool life. Although material of hard alloy cutting tool has tenacity it is good, good to fight concussion, versatility wait for an advantage, but hardness of its high temperature and wearability still cannot satisfy need of high speed cutting. Technology of cutting tool coating is developing of technology of hard alloy cutting tool a main turning point. Coating hard alloy is to use method of gas phase deposit, on better in tenacity hard alloy matrix, tu Fuyi layer or multilayer the material of tall hardness, tall wearability, obtain the cutting tool stuff that already tall tenacity has tall wearability again thereby. Coating material can divide it is 2 kinds big: One kind is " hard " coating material, wait like TiC, TiN, Al2O3, the advantage is hardness tall, wearability is good. Another kind is " soft " coating material, wait like MoS2WS2, the characteristic is the surface attrition factor is low, cutting force is small, cutting temperature is low. To improve the cutting performance of coating cutting tool, new-style coating material and coating method emerge in endlessly. Compound coating and multilayer coating material, for example, tiAlN, TiCrAlN, TiSiN and TiAlSiN, the application in the high speed cutting in hard steel of temper by dipping in water is wide [6] . Compound coating is the structure that forms by all sorts of different functions or characteristic coating film, its model coating is current hard coating + soft coating, every film has different feature each, make coating has better integral performance thereby. Multilayer coating is by a variety of function the filmy overlay of each different and into, composition of every film chemistry is basic and constant [7] . Among them, tiAlN coating has hardness temperature of tall, oxidation is tall, hot rigid is good, adherent force small, heat conduction leads factor of strong, attrition low and good character, apply to the tall hard data such as alloy of tall alloy steel of high speed cutting, stainless steel, titanium, nickel alloy especially. In the requirement the circumstance of tall wearability falls, what show in place of field of high temperature capability in view of TiN coating is insufficient, tiAlN hopeful part or replace TiN[8-9] completely. Carry out a proof, razor blade of coating hard alloy is compared not the life of coating razor blade rises severalfold [10] . In addition, versatility of coating razor blade is good, a kind of razor blade can be replaced a variety of not coating razor blade, simplified to cutting tool manages and reduce cutting tool cost greatly. Type of 2 cutting tool and structure are in process of milling of blade mould high speed, integral type establishs milling cutter application most extensive. Milling cutter of milling of blade mould high speed has 3 kinds big: Head of knife, ball stands smooth De Lixi milling cutter and but dislocation milling cutter. Easy invalidation of very easy damaged, cutting tool, curved surface machines the point of a knife of flat bottom milling cutter precision is low. Because mould antrum is free curved surface, and precision and exterior quality demand are high, consequently ball head stands milling cutter application most, and point of a knife of milling cutter of flat bottom of unlike of point of a knife of ball head milling cutter is fragile in that way, and edge appearance is helpful for cutting blade go up of load distributing equably. But the production of ball head milling cutter is more difficult than making the same score bottom milling cutter, the cutting speed that ball heart manages is 0, make treatment surface diminution of quality. To small size model antrum, unfavorable use but dislocation milling cutter. What Nextpage needs special attention is, milling cutter high speed stands to add man-hour in coating of hard alloy of whole form of characters or letters, because point of a knife often is in treatment process,contact workpiece first, and milling cutter point of a knife is in rigid difference, easy happening damaged of point of a knife. The coating near the point of a knife after cutting tool damaged is easy be destroyed and may appear fall off. The hardness after workpiece quenchs rises greatly, be like material of the workpiece after quenching to pledge not all, have flaw, machinability can be reduced greatly, when choosing the place to the local horniness after quenching when treatment, cutting force can greaten suddenly, appear easily collapse blade phenomenon. The generation of life of quality of the means breaking bits of the geometrical parameter of blade of cutting tool structure, cutting and cutting tool efficiency to high speed cutting, surface, cutting tool and quantity of heat in metal cutting have very big effect. When high speed milling, the horn after appropriate cutting tool and reasonable feed rate, can arise enough the big ply that cut bits, take away quantity of heat, avoid cutting sclerosis. The horn before edge is the important parameter that affects load of cutting tool cutting, should logical choice; The feed of every cutting blade concerns cutting load and cutting tool. Generally speaking, the geometrical angle of high speed cutting tool and traditional cutting tool have corresponding concern mostly. Choose appropriate cutting tool parameter, besides make cutting tool holds cutting blade sharp with enough strength outside, very main purpose is can form enough ply cut bits, make cut bits to become the carbon fin of cutting process, take away as far as possible much quantity of heat. Milling dosage and milling means are machined to the mould, choose correctly and optimize cutting parameter, it is to make sure high speed cutting can achieve the top period effect, important segment that avoids machine tool flutter. Current, high speed treatment still does not have complete craft parameter list and database of high speed cutting, cannot undertake choosing through cutting manual. Also still decide to cutting tool of avery kind of without specific formula first-rate cutting parameter is combined. Dosage of high speed milling basically includes deepness of milling rate, milling (include axial milling deepness and flank milling deepness) , of feed speed or every tine feed and milling cutting tool dangerous extend length to wait. The factor that affects dosage of high speed milling is very much, among them the mainest is workpiece material and milling cutter material match a relation. In actual production, can wait according to feature of workpiece material, cutting tool material, working procedure, will decide first-rate cutting speed and feed through experiment or emulated method. At present investigator of quite a few selects an issue in what pay close attention to dosage of high speed cutting. Provide steel to die of temper by dipping in water, rate of high speed milling should be inside 300~6000m/min limits. The cutting plan that adopts normally is: Tall cutting speed, medium feed and small cutting deepness. But in be being machined actually, not be cutting speed taller, the effect is better. Want integrated to workpiece, cutting tool and equipment consideration, formulate machines plan reasonably. What need points out is, small to blade mould radius, narrow model antrum or outline treatment, to achieve tall outline precision, still need older feed rate, especially to tall hard quench rolled steel expects. If feed rate is too low, milling cutter may lose cutting ability because of heating up overload. When high speed milling, answer to choose the treatment that arrange mill as far as possible, because be when suitable mill, the ply cutting bits that cutting tool just cut workpiece to arise is the biggest, reduce gradually subsequently. When going against mill, the ply cutting bits that cutting tool just cut workpiece to arise is the smallest, add gradually subsequently thick, increased the attrition of cutting tool and workpiece so, a large number of heat produce on edge, when the quantity of heat that produces in going against mill so arranges mill than be in a lot of more, radial load also increases greatly. It is at the same time in suitable mill, the crucial point is main press press stress, and in going against mill edge suffers pull stress, condition getting power is more abominable, lowered the service life of cutting tool. When milling antrum curved surface, cutting tool can be Z to perpendicular into / retreat a knife, curved surface law to into / retreat a knife, curved surface to with enter reversely / retreat knife and inclined to or screw type is entered / retreat a knife to wait [9] . In be machined actually, what can use curved surface is tangential feed or better screw type feed. And when screw type feed cuts material, if treatment area is,go up big small, radius can reduce helix to arrive with feed subsequently appoint deepness. If blade antrum contains n, answer right now as far as possible from material outside take a knife, with the cutting state of modal analysis material. And of handsome to doing not have antrum close area, use helix feed means, cut in local district. What high speed cutting wants to assure cutter track is directional, when change of curved surface curvature is big, answer to serve as optimal way taking a knife with direction of radius of the biggest curvature; Hour of change of curved surface curvature, curvature radius is abate to taking the effect of knife direction, appropriate alternative is only a knife path is mean the way taking a knife with the longest length. Below the premise that assures to machine precision, should reduce empty time taking a knife, increase cutting time as far as possible the scale in whole workpiece, in order to improve treatment efficiency. At present the treatment of high speed cutting of domestic aviation industry basically uses loop cutting, decide cutting process and cutting tool way through bos namely, reduce cutting tool cut and cut a number, in order to obtain the cutting process of stable, efficient, high accuracy. Can use annulus to cut, helix cutting, perhaps divide pace annulus to cut a law to take a knife. Dentate cutting bits is the type cutting bits that material of hard steel of temper by dipping in water of high speed milling often produces constantly. Dentate the intermittent cycle commutation that cuts the generation of bits to be able to create cutting force and high frequency vibration, affect cutting tool life, make cutting tool premature invalidation. To dentate the generation mechanism that cuts bits, at present existence heat insulation is cut and periodic brittleness ruptures 2 kinds of academic systems. Document [3] thinks, when cutting rate raises certain and critical cost, as a result of the material that temperature lifts and brings about hot bate action is more than deformation aggrandizement action, the configuration that cut bits by successive and banding what change takes even interval to distributing to cut is dentate cut bits. Dentate the treatment that the deformation that cuts bits decided to die of temper by dipping in water provides steel greatly is difficult easy degree. Material hardness is taller, the configuration that cut bits by successive and banding change is jumped over for dentate cutting speed low. Be aimed at the workpiece material of different hardness, machine conditional combination through optimizing feed of cutting speed, every tine and cutting deepness to wait, can control the configuration that cut bits to be successive and banding. Conclusion (1) the production of blade nicety mould and accurate forging die is the job of vital technology preparation that aviation engine lamina creates. Because high speed milling can process oil hard data directly, replaced the electric spark treatment in conventional technology and grinding treatment thereby, reduced clamp to trim the job, prolonged mould life. (2) PCBN cutting tool and material of cutting tool of coating hard alloy apply in milling of blade mould high speed more, among them TiAlN coating material has its distinct advantage, applied potential is great. Integral type makes the same score a bottom to establish milling cutter and ball head milling cutter, agree with the treatment of blade mould face. (3) the main factor that parameter of high speed milling is precision of influence workpiece treatment and efficiency, its choose to still rely on experience at present. Milling means suggests to use suitable mill. Model when antrum curved surface is machined, feed of choose of Ying Shen reelect / document of the means that retreat a knife [3] thinks, when cutting rate raises certain and critical cost, as a result of the material that temperature lifts and brings about hot bate action is more than deformation aggrandizement action, the configuration that cut bits by successive and banding what change takes even interval to distributing to cut is dentate cut bits. Dentate the treatment that the deformation that cuts bits decided to die of temper by dipping in water provides steel greatly is difficult easy degree. Material hardness is taller, the configuration that cut bits by successive and banding change is jumped over for dentate cutting speed low. Be aimed at the workpiece material of different hardness, machine conditional combination through optimizing feed of cutting speed, every tine and cutting deepness to wait, can control the configuration that cut bits to be successive and banding. CNC Milling CNC Machining