Of high-speed steel cutting tool wear away mechanism

  • Time:
  • Click:44
  • source:XIMENG CNC Machining
Foreword is in metallic cutting treatment, high temperature of pressure of the tall cutting force that by difficult treatment material creates, tall contact, cutting, acuteness chemistry eroded substandard bound condition to raise extremely tall requirement to cutting tool and cutting tool material. In addition, the cutting condition such as fluid of quantity of penetration of a cutting tool of appearance of cutting tool geometry and sharp cutting blade, loop, cutting also increased the astringent sex of treatment. Cutting cutting tool often is to be close to its to be able to bear or endure get these bear (especially thermal stress and mechanical stress) the job below ultimate position. Although material of high-powered cutting tool -- if CVD is mixed,PVD coating hard alloy, cermet, pottery and porcelain, cubic nitrogen changes boron (CBN) with diamond -- use increasingly grow in quantity, but high-speed steel (HSS) remain material of commonly used metallic cutting cutting tool. High-speed steel is opposite taller tenacity, and can the possibility that economic ground makes complex form cutting tool, the use in making its are machined in a lot of cutting still has rationality. Heat with electric broken bits (ESH) technology and deposit of physical gas phase (PVD) of the name of pulverous metallurgy high-speed steel that coating technology photograph links introduce, improved the cutting performance of high-speed steel cutting tool further. Since on 70 time evening introduced the century successfully since PVD-TiN coating, on the coating stuff with consider to be centered in development all the time better to the learning of cutting tool of cutting of high-speed steel metal and deposit technology. The article is right high-speed steel cutting tool (include not coating and coating cutting tool) wear away the mechanism undertook brief comment, discussed the character of material of mechanism of invalidation of metallic cutting process, cutting tool, high-speed steel and its coating in detail. Metallic cutting process for understanding metal cutting wear away mechanism, be necessary brief understanding in cutting tool / the osculatory state that place of workpiece material interface takes dominant place. Common orthogonal cutting model applies to any cutting operations, include turning, milling, sawing, auger cut, tap, broaching. The plasticity that passes workpiece data is cut, and the slippage of face of the knife before face of the knife after workpiece material is provided relative to Yu Dao is mixed, can build curve of character of a group of temperature. Main heat source is located in those who cut bits to form advocate cut area and cut what attrition contacts between bits and cutting tool is deputy cut an area, accordingly, be in what have a paragraph of space with cutting blade before the meeting on knife face reachs highest temperature. Should clarify it is not easy that action has the cutting force on cutting blade and mechanical stress at the knife, because these force are mixed as cutting craft of cutting parameter differ and have very big change. In the interrupted cutting that uses onefold cutting blade, cutting tool from cut workpiece to arrive quit work, its suffer strength condition to be widely divergent possibly also. Generally speaking, total cutting force F and cutting speed and feed are relevant. Use low attrition coating to be able to reduce cutting force, drop cutting blade temperature thereby, can improve productivity in order to use low attrition coating. We the type from mechanism of cutting tool invalidation is knowable, high-speed steel cutting tool uses those who be close to his to succumb meet when the limit and fracture stress limit invalidation. When workpiece material interior is being cut forcibly like the chock that expands ceaselessly like when cutting blade, be maintained by it " interstitial " two surfaces appear it is the metal with chemical very tall active. In fact, as a result of external oxygen or cutting fluid cannot enter this area, mean won't form oxidation film or hold the post of how the secondary floor that he can have protective effect. Accordingly, edge also is exposed fall in very abominable condition. Cutting tool material is characteristic (1) cutting tool of cutting of metal of high temperature intensity must can maintain tall hardness at the same time below cutting high temperature (or tall succumb intensity) and tall rupture intensity. When interrupted cutting, latter especially important. Rate of tall heat conduction also is a character that cutting tool should have, because it can reduce cutting tool material the tendency of local hot bate. The tall hear resistance of carbide, nitride and oxide, showed they regard protection as the potential of PVD or CVD scumble layer, and when them when the material of cutting tool of formal consist in with little grain is medium, also have distinct aggrandizement effect. However, they regard material of workpiece of aggrandizement element consist in as medium circumstance very common also, below this kind of circumstance, of cutting tool of their meeting aggravate grind bead to wear away. (2) rupture tall hardness of intensity and hardness and tall brittleness are contacted together, undertake aggrandizement to metallic stuff (if pass martensite temper by dipping in water,obtain high-speed steel dispersion of grain of hard, horniness) meet those who bring about material to rupture normally intensity is reduced. The common workpiece stuff that high-speed steel cutting tool fits to machine generally speaking, the macroscopical hardness of the workpiece data that processes with cutting of high-speed steel cutting tool wants under cutting tool hardness. However, a few part that include in a lot of workpiece material (like carbide, nitride and oxide) hardness (HV1500 - 3000) want matrix of cutting tool of prep above high-speed steel with hear resistance, can accelerate cutting tool invalidation through abrasion. In cutting bits to fashion a process, the tall tenacity of workpiece material, big rupture percentage elongation (extend a gender) can bring about generation cutting high temperature with treatment hardening capacity. And the intensity that high temperature can reduce high-speed steel cutting tool, return the chemical reaction between meeting aggravate cutting tool and workpiece material at the same time, increase the possibility that forms the photograph between the metal. This will increase the attrition between cutting tool and workpiece material, thereby this plants farther aggravate adverse state. When the mechanical performance that compares cutting tool material and workpiece data, another fact that must consider is, the formation that cuts bits is to be in normally extremely tall cut what happen below rate. Consider very tall meet an emergency is led, workpiece material curve can rise, the RT hardness that makes carbolic steel corresponding thereby can work in its with cutting blade the hardness below temperature matchs well. When interrupted cutting, when temperature very tall cutting blade cuts cold workpiece material suddenly when, need special attention this kind of circumstance. Type of cutting tool tatty regards research as the model with orthogonal cutting, common characteristic includes tatty of high-speed steel cutting tool crescent moon wears away depression, hind knife face wears away, point of a knife wears away, point collapse blade, score wears away etc. The cutting function of cutting tool basically depends on material of parameter of cutting means, cutting, workpiece and cutting tool material, it still can be worn away by point of a knife, hind knife face wears away, crescent moon wears away depression, point collapse blade or these elements are common of action restrict. Depend on same these parameter, cutting tool wears away or happen in order to grind bead tatty way gradually; Perhaps wear away through producing plasticity metabolic felt means; Perhaps rupture through disperse mechanism, create cutting tool material more and more dispersing lose; Perhaps carry the integrated action of these mechanisms. Below, the scanning electron microscope that we use a few has used high-speed steel hob respectively (SEM) with optical microscope (OM) metallograph, illustrate is of all kinds wear away mechanism. Not of coating cutting tool wear away mechanism (1) grind bead to wear away grind bead to wear away in blade of cutting of high-speed steel milling cutter hind knife face wears away and crescent moon is depression there is dominant effect in wearing away. Wear away photograph of the horniness in the scratch action that groove is grain of the horniness in workpiece material and cutting tool material resists scraping protects action to be formed jointly. It is at the back of the carbide with cutting tool older stuff, from the flow that cut bits direction can see, existence can remove the typical field ditch that protects action to cutting tool material. Extremely tiny dominant effect has in grinding bead to wear away in cutting tool, and horniness carbide can be only counteractive wear away. Of high-speed steel tall succumb intensity (tall hardness) can enhance its resistance to grind bead tatty ability with more carbide content. Nextpage (2) when felt wears away to issue observation in inferior enlarge multiple, of milling cutter tooth basically wear away the mechanism is to grind bead to wear away it seems that, namely workpiece material (carbolic steel) in the plough action of horniness grain. But, the discovery when observation plays in taller enlarge multiple, say well and truly, its wear away is to grind bead to wear away as joint as felt tatty action. The felt that has dominant effect wears away (call slight felt to wear away normally) be material of surface layer high-speed steel is torn off to cause by tall shearing force, and this kind of shearing force is mix by the slow daggle of surface layer material cutting material of bits flow direction cut broken those who form. If cutting tool is used below the upper limit temperature of its hear resistance, cause serious felt possibly to wear away, flow of plasticity of large-scale surface material is formed in direction of the flow that cut bits. If cutting blade reachs very high temperature (when be being machined with speed of very tall cutting namely) , criterion hind knife face wears away and crescent moon wears away depression will wear away with felt give priority to. When cutting chemistry when the workpiece stuff with more expensive aggressivity, felt wears away will farther aggravate. High-speed steel material basically is what fall in high temperature through its is tall succumb intensity (Gao Gong rigid) will resistance is spent gently and spend felt to wear away again. (3) big range plasticity is out of shape sometimes, bear of susceptive of point of high-speed steel cutting tool exceeded his to succumb intensity, cause big range plasticity to be out of shape, bring about point passivation thereby. (4) exhaustion and rupture of whole cutting tool macroscopical rupture to be able to happen likely, but it is small probability incident however. Commonner is the local collapse blade of cutting tool point. Need attention, collapse blade is it seems that from what grind mark parallelly to begin with point. Of coating cutting tool wear away mechanism since on since coating of TiN of 70 time evening applies the century at cutting tool of cutting of high-speed steel metal, PVD coating already became cutting tool to wear away defended standard measure, and the layer of scumble of pottery and porcelain that the coating center nowadays can provide all sorts of kinds for high-speed steel cutting tool. Ply is 1 - the PVD scumble layer of 10µm basically protects blade of cutting tool cutting with two kinds of means: ① serves as resist abrasive wears away and covering layer of slight felt tatty; ② is passed reduce the attrition between cutting tool and workpiece material, cut especially bits and before the attrition between knife face, will drop cutting tool temperature. The hardness with this kind of very will expensive coating (tall wearability) react with relatively as inferior as metallic stuff chemistry active (low but dissolve is spent) union is together, and latter can prevent to wear away as felt the generation of the fusion welding mechanism of precondition. Accordingly, the coating of most commonly used PVD nowadays is to pass exhaustion and come off discontinuously / fall off and invalidation, is not to pass slow wear away gradually by purify. Once exterior coating by purify, of coating cutting tool wear away mechanism becomes with not coating cutting tool is identical, and the cutting parameter that uses normally as a result of coating cutting tool is more severe exacting, accordingly its wear away degree is more acuteness also. (1) because matrix preparation is undesirable,cause coating to fall off undesirable and main likelihood has preparation of matrix of high-speed steel cutting tool two kinds of circumstances: In kibble / when essence of life grinds treatment, matrix surface temperature exceeded austenite to change temperature, formed brittleness thereby bigger not layer of temper martensite surface; Or cause matrix appearance too coarse. When high-speed steel regards PVD coating as matrix, grinding high temperature forms not layer of surface of temper martensite brittleness will make the adherent force of coating is reduced. The PVD coating of high-speed steel cutting tool has quantitative class to be 1 - the interior of 5GPa presses stress. Normally, deposit is had in the TiN coating on high-speed steel about the transverse remains of 4GPa presses stress. This kind presses stress to be helpful for enhancing the adhesion of coating interior, but have adverse effect to the adhesiveness of coating and matrix however. Press stress exorbitantly to add rough matrix surface, may bring about fall in the circumstance that does not have any exterior load, coating proper motion is broken away from. Its reason is, in coating transverse press stress to add coarse matrix, will be in whole coating / the generation on matrix interface pulls stress. If this system gets the action of exterior load, coating is very easy along help the area with the largest stress (go up along cutting tool namely coarse field ditch) happen fall off. These field ditch are grinding craft too extensive or grinding parameter choice are undeserved cause. Another case that causes coating invalidation by appearance of matrix surface form also makes clear, the surface layer that may spread to high-speed steel material in the crackle that forms in coating is the following. Pass fatigue effect, these crackle may cause blade of cutting blade collapse and serious point rupture subsequently. (2) the temperature standard that because matrix heats up the coating that bate causes to once high-speed steel base material was achieved,fall off,can produce excessive bate, cannot bear the brittleness that contacts pressure and coating ruptures. Contrast of darker light and shade of acid etching section made clear coating lower part to produce hot bate because of excessive temper. Next, this kind of coating ruptures and individual fragment is decomposed to be pettier fragment again. Cutting blade tatty distributings to wear away with what evolve into above description the mechanism will bring about cutting tool finally wear away to grind blunt differentiate standard more than (given perhaps hind knife face, before knife face wears away width, or somehow point becomes blunt) . Fashion a process depression with tooth of an a solar month of 31 days (be by treatment material carbolic steel) for exemple, this kind of final meeting restricts cutting tool life wear away produce advanced knife face to go up. Original, hob tooth suffers the collapse blade with finite degree. Meanwhile, the cutting tool material that produces advanced knife range heats up bate (the contrast of light and shade with adjacent coating darker place announces the indication that gives excessive temper) the carrying capacity that reduced coating, make coating is mixed because of burst brittleness ruptures and invalidation. Once coating by purify, because acuteness felt wears away,meet, form tooth of an a solar month of 31 days quickly on the high-speed steel tooth that loses protection depression. Of initiative phase wear away to often can pass slight burst (collapse blade) make point of a knife becomes blunt, subsequently and those who come is wear away with felt with abrasive the linear stable state that give priority to wears away mechanism. The point of a knife of advance gradually type becomes blunt is one of reasons that cutting blade temperature lifts continuously, final, be out of shape through point burst or serious plasticity, achieve wear away quickly condition. The sharp sex of the flowing sex that improves cutting tool appearance and point can prolong cutting tool life. The application of coating is farther aggrandizement this kind of action. However, will raise wearability through coating, often be to improve productivity, is not to acquire longer cutting tool life. Normally, cutting tool can suffer two kinds or a variety of wearing away the joint action of the mechanism, but should judge which kind of wearing away action of the dominant since the mechanism may be quite difficult. The way that improves performance of high-speed steel cutting tool (1) the high-speed steel cutting tool that improves high-speed steel material to be described from above wears away mechanism, we can conclude: Hardness, hear resistance (hot rigid) and rupture tenacity -- include macroscopical with microcosmic level -- it is the precondition that cutting tool acquires tall cutting property. In recent years, the uniformity that the technology of high-speed steel develops to basically be centered in high-speed steel and clean are spent completely on. Pass pulverous metallurgy (PM) technology, can acquire fine grain all pledge structure. However, the author thinks, the hardness that still improves high-speed steel further likely / tenacity comparing. Through using accept rice technology, reduce the size of matrix grain and horniness photograph grain accept rice scope further inside, make completely likely function of high-speed steel cutting tool " more superstratum building " . (2) another kind of way that raises exterior integrality to improve performance of high-speed steel cutting tool further is to improve cutting tool appearance bright and clean degree, avoid to bring about material of high-speed steel surface layer because of producing overmuch heat in metal cutting to worsen namely. The macroscopical intensity of high-speed steel cutting tool and function of the blade that fight collapse are very sensitive to the exterior blemish of the generation when exterior preparation, accordingly, shift to an earlier date to avoid cutting tool invalidation, must undertake preparation to surface of cutting tool point. Slick cutting tool surface conduces to resist micro-crack, avoid coating to fall off prematurely. CNC Milling CNC Machining