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題目 鈦合金攻螺紋技術(shù)及絲錐改進(jìn)
專 業(yè) 名 稱 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
班 級(jí) 學(xué) 號(hào) 078105235
學(xué) 生 姓 名 曾 威
指 導(dǎo) 教 師 王細(xì)洋
填 表 日 期 2011 年 3 月 12 日
鈦合金攻螺紋技術(shù)及絲錐改進(jìn)
【摘要】鈦合金是一種比重小、強(qiáng)度高、耐腐蝕和耐熱等特性的金屬結(jié)構(gòu)材料。鈦合金攻螺紋切削時(shí)刀具極易磨損，刀具壽命很短。通過對(duì)鈦合金攻螺紋過程受力分析，將絲錐直槽變?yōu)槁菪?，可以使切削熱和切削力不至于過分集中于切削刃附近，改善散熱條件，也可加強(qiáng)切削刃，減少崩損。
【關(guān)鍵字】鈦合金、攻螺紋、金屬結(jié)構(gòu)材料、熱處理強(qiáng)化、絲錐直槽、螺旋槽
鈦合金是一種比重小、強(qiáng)度高、耐腐蝕和耐熱等特性的金屬結(jié)構(gòu)材料。TA7屬單相組織的型鈦合金，不能熱處理強(qiáng)化，通常在退火狀態(tài)下使用，具有良好的熱穩(wěn)定性和熱強(qiáng)性。TC4屬雙粗組織的型合金，有較高的力學(xué)性能和高溫變形能力，良好的韌性和塑性，能進(jìn)行各種熱加工和熱處理強(qiáng)化。鈦合金在100~150仍有很高的強(qiáng)度，被廣泛應(yīng)用于火箭發(fā)動(dòng)機(jī)外殼、航空發(fā)動(dòng)機(jī)氣機(jī)盤、葉片、結(jié)構(gòu)鍛件等。
1.鈦合金攻螺紋切削過程特點(diǎn)
鈦合金是一種難切削材料，突出特點(diǎn)是刀具極易磨損，刀具壽命很短。主要體現(xiàn)在：
（1）切削層變形小由于鈦合金的塑性低和鈦的化學(xué)活潑性高，在高的切削溫度下化學(xué)親和性很強(qiáng)，容易與大氣中的氧、氮等元素化合，從而脆性降低，切削變形小。
（2）切削溫度高鈦合金導(dǎo)熱性很差，導(dǎo)熱系數(shù)只相當(dāng)于45鋼的1/5~1/7切削熱不容易傳出，集中在切削區(qū)和切削刃附近較小范圍內(nèi)。
（3）冷硬現(xiàn)象嚴(yán)重一是切削過程中產(chǎn)生的塑性變形，另一方面在高的切削溫度下，鈦很容易吸收空氣中的氧和氮形成硬而脆的外皮，冷硬現(xiàn)象不僅會(huì)降低零件的疲勞強(qiáng)度，而且能加劇刀具磨損程度。
（4）刀具容易磨損主要有機(jī)械磨損：毛坯余量和組織不均勻，硬皮與刀具表面接觸發(fā)生強(qiáng)烈的機(jī)械摩擦，使刀具受到不均勻的負(fù)荷造成崩刃現(xiàn)象。此外切削過程中已加工表面較大的彈性恢復(fù)，也使刀具磨損。粘接磨損：鈦合金對(duì)刀具材料的親和性很強(qiáng)，在切削溫度高和切削力大的條件下，很容易與刀具中的某些元素如C、Ti、Co等粘附在一起，隨切屑的流出帶走刀具材料中的質(zhì)點(diǎn)。
2．鈦合金攻螺紋過程受力分析及改善措施
（1）切削層變化帶來的絲錐受力不均勻絲錐攻螺紋過程屬于半封閉式多刃薄切削過程，與車削螺紋相比較，切削條件惡劣。在工件底孔內(nèi)切出的螺紋，是由絲錐切削刃瓣上的各切削牙逐層切削而成的。不難看出，絲錐或工件旋轉(zhuǎn)一周后，每個(gè)切削牙都前進(jìn)一個(gè)螺距，并分別從工件上切除一層金屬。用機(jī)用絲錐攻螺紋時(shí)，隨著絲錐切入孔中，切削層總面積逐漸增加。當(dāng)切削錐全部進(jìn)入孔中工作時(shí)，切削層總面積達(dá)到最大值。當(dāng)絲錐再繼續(xù)前進(jìn)時(shí)，由于校準(zhǔn)部不起切削作用，所以切削層總面積不再增加。對(duì)于鈦合金來說，因切削層巨大的摩擦力和塑性變形給運(yùn)動(dòng)中的絲錐受力帶來了波動(dòng)。一個(gè)最有效的改變辦法是將螺紋孔底孔直徑增加到所允許的上限，最大程度地減小切削層厚度。
（2）“陷切”造成的絲錐受力惡化攻螺紋時(shí)，作用在絲錐各切削刃上的切削力可分解為軸向力、徑向力和切向力。切向力直接決定攻螺紋扭距的大小，其他兩個(gè)分力則影響攻螺紋的切削過程。從圖2中可以看出，開始攻螺紋時(shí)，絲錐依靠在工件上切出的JI螺紋側(cè)面被引導(dǎo)前進(jìn)。但因JI面太小，加之鈦合金塑性變形，承受不了絲錐對(duì)工件的軸向力而產(chǎn)生接觸變形，使絲錐的軸向前進(jìn)量不足，各刃瓣滯后并在螺紋表面一側(cè)切出階臺(tái)而造成“陷切”現(xiàn)象。攻螺紋繼續(xù)進(jìn)行時(shí)，在由KJ、GH、GF、CD等側(cè)刃、頂刃切削時(shí)產(chǎn)生的軸向力合力Fa(-)和由JI、EF、AB等側(cè)刃切削時(shí)產(chǎn)生的軸向力合力Fa(+)未趨平衡以前，“陷切”現(xiàn)象將繼續(xù)發(fā)生。但隨著絲錐與工件相接觸的螺紋引導(dǎo)表面的增大，“陷切”量將逐漸減??；攻螺紋的“陷切”現(xiàn)象直接影響螺紋一側(cè)面的正確成形，并使其表面粗糙度值高，嚴(yán)重時(shí)足以啃住絲錐，使之處于抱死狀態(tài)。
（3）攻螺紋過程中的擺動(dòng)容易使絲錐單向嵌入工件基體中在絲錐正常工作的條件下，如前所述，由于同時(shí)工作的絲錐各切削牙切削寬度不等，使前面切削牙的切削面積大于后面切削牙的切削面積，所以，作用在絲錐各刃瓣上的徑向力不等，也使徑向力的合力不等于零（）。顯然，在攻螺紋時(shí)，絲錐將偏向徑向力小的一邊，絲錐的軸線相對(duì)于孔的軸線將發(fā)生偏移，導(dǎo)致被加工的螺孔擴(kuò)大同時(shí)也使絲錐緊貼在一邊。當(dāng)絲錐的切削錐長度較短，即導(dǎo)角較大時(shí)，各刃瓣上切削牙的切削寬度差別愈大，中徑擴(kuò)大的可能性越大，故絲錐的切削錐長度不宜太短。
（4）攻螺紋扭矩的非穩(wěn)定性攻螺紋的扭矩由三個(gè)部分組成，即切削扭矩、絲錐與已加工螺紋間的摩擦扭矩和由于切屑堵塞在容屑槽內(nèi)產(chǎn)生的扭矩。在正常切削的條件下，攻螺紋扭矩主要是切削扭矩，后一種扭矩所占的比重一般很小，可忽略不計(jì)。絲錐在通孔中攻螺紋時(shí)扭矩的變化情況。隨著絲錐切入底孔，進(jìn)行切削的牙數(shù)增加，攻螺紋扭矩增大。當(dāng)切削錐全部進(jìn)入底孔時(shí)，扭矩達(dá)到最大值。當(dāng)絲錐的切削錐從孔的另一端露出時(shí)，攻螺紋扭矩開始減小。顯而易見，攻螺紋扭矩基本上與絲錐切削層總面積成正比，攻螺紋扭矩的變化規(guī)律與絲錐切削層總面積的變化規(guī)律大致相同。為了避免在扭矩最大值時(shí)用力過猛，必須掌握所施加扭矩大小及緩急程度。另外還可以通過以下途徑來有效地減小攻螺紋扭矩：1、增大前角使攻螺紋扭矩減小，例如前角為時(shí)，假設(shè)扭矩為100%，那么當(dāng)前角變?yōu)闀r(shí)，則扭矩就減小到70%，前角時(shí)扭矩僅達(dá)到原來的53%，但是增大前角會(huì)使絲錐強(qiáng)度降低，也不利于散熱，這一點(diǎn)應(yīng)注意。
一．選擇盡可能少的絲錐刃瓣數(shù)即槽數(shù)，這是因?yàn)椴蹟?shù)的增加，一方面使切削厚度變薄，難以切削，另一方面增加了絲錐與工件摩擦面積，使絲錐扭矩變大，一般的四槽比三槽約增加8%的扭矩。
二．選擇對(duì)口的切削液，減小摩擦。如濃度較大的硫化油，添加15%~20%的四氯化碳，可降低表面粗糙度值和減小絲錐咬死的可能性。
3．絲錐前面導(dǎo)向部分的導(dǎo)角既不能過大也不能太小，導(dǎo)角過大，切削層厚度大，受力容易崩牙咬死，切屑也不易卷曲，但導(dǎo)角過小，切屑過薄，在硬化層上摩擦，加劇絲錐磨損。另外絲錐校準(zhǔn)部分不宜過長，否則和螺紋孔壁摩擦將會(huì)加劇，一般為4~5個(gè)螺距。
4．絲錐改進(jìn)實(shí)例由于鈦合金材料在加工過程中容易產(chǎn)生表面加工硬化，特別是加工小直徑螺紋孔，成了難題。攻螺紋時(shí)由于縮孔，攻上幾扣，就抱住絲錐，切削力特別大，普通絲錐容易折斷，使工件無法繼續(xù)加工。基于上述受力分析過程，將絲錐的大徑、中徑、小徑磨小并分為四個(gè)等級(jí)，每只絲錐相差0.1mm，以期減少切削力帶來的影響，但是由于切削量小，工件又容易產(chǎn)生加工硬化，加工起來比較費(fèi)勁，效率很低，攻上幾個(gè)螺紋孔就不能繼續(xù)使用了。后來我從改變切削的角度入手，經(jīng)過多次反復(fù)實(shí)驗(yàn)，將絲錐直槽變?yōu)槁菪郏丛谠邢餮郎习绰菪嵌饶ト?~2扣，以減小絲錐與切屑的接觸面積。前角由原來的減少至，使切屑與前刀面的接觸長度小，既可以增加切屑與前刀面的接觸面積，使切削熱和切削力不至于過分集中于切削刃附近，改善散熱條件，也可加強(qiáng)切削刃，減少崩損。
參考文獻(xiàn):
[ 1] 高鐘锍.機(jī)電控制工程[M].北京:清華大學(xué)出版社,2002.
[2] 張建民.機(jī)電一體化系統(tǒng)設(shè)計(jì)[M].北京:北京理工大學(xué)出版社,2002.
[ 3] 王貴明.數(shù)控實(shí)用技術(shù)[M].北京:機(jī)械工業(yè)出版社,2000.
The alloy of titanium attacks whorl technology
and screwtap to improve
[Abstract] Titanium is of small specific gravity , high strength, strong corrosion resistance and heat resistance ,which are the characteristics of metallic structural materials. Titanium is a kind of material easily tapped cutting tool wear, shorting its using time . Titanium is tapping on stress analysis, tapping directly into the spiral groove that can make cutting heat and force without being unduly concentrated in the vicinity of the cutting edge ,not only improve heat dissipation, but also strengthen the cutting edge, in order to reduce losses collapse.
[Key word] Titanium, Gewinde scheiden, metal structural materials, heat resistance, Straight Fluted Taps, spiral chute
Titanium alloy is a kind of metal structural material , with characters of small proportion , high intensity, strong corrosion-resisting and heat-resisting and so on . TA7 belongs to the organized single-phase type of titanium alloy , which can't be strengthen under the heat treatment, used under the condition of putting out the fire in common situation , with good performence of hot stability and intensity . TC4 belongs to organized double-thick of type titanium alloy , which has higher mechanics performance and the ability of deformed under high temperature, good toughness and plasticity, which can work with all kinds of heat process and strengthen treatment. Titanium alloy still has very high intensity under. It is widely used in the outer shell of rocket engine, aviation engine chassis, blade, structural forging,etc..
1. The characteristics of the titanium alloy’s Gewinde scheiden whorl cut the process:
The titanium is a material which is very hard to cut. The outstanding characteristic is that the cutting tool is very easy to be polish and its life-span is very short . Main reflects are as following :
(1)Cut layer can transfigure small because Titanium alloy is plasticity lowness and the titanium chemistry is activity . Under the high temperature of cutting that have strong affine of chemistry and easy combination with element chemical such as oxygen , nitrogen easy to hit the target with atmosphere. It is brittleness lessening , cutting deformation are minor.
(2)Cut temperature high titanium alloy heat conductivity very bad, heat conduction coefficient whether 45 steel of 1/5~1/7s cut hot only, in smaller range near concentrating on the cutting area and cutting the edge.
(3)Cold hard phenomenon serious one cut out of shape plasticity that course produce, on the other hand at high cutting temperature, titanium very apt oxygen and nitrogen to absorb air form hard and fragile crust, the hard phenomenon of cold not only will reduce fatigue strength of the part but also can aggravate the cutter and wear and tear the intensity.
(4)The cutter is apt to wear and tear and mainly have machinery that is worn and torn: Blank surplus and organization even, hard skin with cutter surface exposed to, take place strong machinery rub, make the cutter caused and broken out the edge phenomenon by the load not even. Cut course process surface loud elasticity resume, make the cutter wear and tear too already. Sticking wears and tears: Titanium alloy affinity of material very strong to cutter, in cut temperature to be high cutting strength under the heavy terms, it is very easy to seize with some elements in the cutter such as C, Ti, Co,etc. together, with flowing out the particle taken away in the cutter material of smear metal.
2. Titanium alloy attacks the whorl course and is analyzed and improved the measure by strength.
(1)Cut layers of screwtap that change bring specialize in strength even screwtap whorl course belong to semi-closed many edge thin to cut the course, compared with whorl of turning, it is abominable to cut the condition. Whorl that cut out in work piece underport, to cut by screwtap edge every of petal cut tooth chase layers of cut, as shown in Fig. 1. It is easy to find out, after the screwtap or work piece rotates a circle, each one cuts the tooth and advances a pitch, and excise a layer of metal from work piece separately. Specialize in whorl, cut hole with machine with screwtap with screwtap, cut one layer of the whole area increase. When cutting all awls and entering and working in the hole, cut one layer of the whole area and reach the maximum. When the screwtap continues advancing again, do not play a cutting role because of the department of regulating, cut one layer of the whole area to no longer increase. To alloy of titanium, cut layers of enormous frictional force and plasticity deformation give screwtap of sport bring, fluctuate strength. A most effective change method increases underport diameters of hole of the whorl to the upper limit allowed, reduce and cut one layer of thickness to the greatest extent.
(2)" Fall into, cut " screwtap that cause worsen, specialize in whorl, act on in screwtap cutting strength cutting strength at the edge can resolve axial force, radial strength and tangential force into each ", as shown in Fig. 2. Tangential force determine, specialize in whorl size to sprain distance directly, other two component force influence cutting course to specialize in the whorl. Can find out begin specialize in whorl, JI that screwtap rely on at work piece cutting out lead, advance to the side of the whorl in 2 Fig.. But because JI too light, in addition titanium alloy plasticity out of shape, bear screwtap axial force in work piece produce, keep in touch out of shape, make the axial of the screwtap insufficient in advancing amount, every edge one lags behind and cuts out the steps platform and causes the " fall into and cut " phenomenon on one side of the surface of whorl. Specialize in whorl continue go on, by KJ, GH, GF, CD side edge, carry edge axial force that produce join forces cut, join forces Fa by JI, EF, axial force that AB produce when the side edge is cut '), trend towards before such as equilibrium, " fall into and cut " the phenomenon will continue taking place ". But the whorl contacted with the screwtap and work piece guides superficial increase, " fall into and cut " quantity will be reduced gradually "; Attack " falls into and cuts " the phenomenon influences the taking shape correctly of a side of whorl directly "ing of whorl, make surface its roughness enough to gnaw live in screwtap when being value serious high, make it in, embrace state extremely.
(3)Specialize in whorl swing of course apt to make screwtap to be one-way to imbed work piece of the matrices on terms that the screwtap work normally, as noted previously, because the screwtap working at the same time each cuts the tooth and cuts the width, make the cutting area of cutting the tooth above cut the cutting area of the tooth in the back of greater thanning, so, the radial strength of acting on screwtap every edge one makes the resultant of forces of radial strength not equal zero（）As shown in Fig. 3. Obviously, while attacking the whorl, screwtap agree more on radial to be strength little axis axis in hole of screwtap take place skew, cause, expand at the same time making screwtap stick to aside closely spiral shell hole that process. Cutting in screwtap awl length relatively short, lead when angle heavy, every edge cut cutting of tooth width difference loud at the petal, the bigger possibility China expanded directly, so the awl length of cutting of the screwtap should not be too short.
(4)That attacked torsion of whorl is not that the torsion that stability attacks the whorl is made up of three parts, cut torsion, screwtap with process friction torsion of whorl already and because smear metal stop up in torsion that bits produce in the trough of holding. Under the terms of cutting normally, it mainly cuts the torsion to attack the torsion of whorl, the last one proportion that torsion account for generally very light, can ignore. In Fig. 3 is the change of the torsion while attacking the whorl in the open hole of the screwtap. Cut underport with screwtap, tooth cut to go on count, increase, specialize in torsion of whorl increase. When cutting all awls and entering the underport, the torsion reaches the maximum. When the cutting awl of the screwtap emerges from another end of the hole, specializing in the torsion of whorl begins to reduce. Obviously, specialize in whorl torsion cut one layer of the whole area directly proportional to with screwtap basically, specialize in whorl change law and screwtap of torsion cut layers of change of the whole area law roughly same. In order to avoid exerting oneself in the torsion maximum too quicklily, must grasp the torsion size and pressing or otherwise intensity exerted. In addition it come, reduce, specialize in whorl torsion effectively through following route:
One. It is before it increase for horn make specialize in there aren't whorl the torsions,such as before horn, suppose torsion have 100%, angle turn into, torsion reduce get 70% then, the torsion only reaches original 53% when the the previous corner at present then, but the angle will make the screwtap intensity reduce before increasing, unfavorable to dispelling the heat, this should notice.
Two. choose screwtap edge petal that lack as much as possible count the trough is counted promptly, this is because the increase that the trough counted, make, cut thickness thin, difficult to cut, increase screwtaps and work piece rub the area on the other hand on one hand, make the torsion of screwtap large, four general troughs nearly increase 8% of the torsion than three troughs.
3 .Chooses the fitting cutting liquid, reduce the friction. Such as density heavy vulcanization oil, add 15%0% tetrachloromethane, can reduce surface roughness value and reduce possibility that screwtap kill.4~5, Whom screwtap lead partly lead angle can too little either, lead angle to be too big, cut layers of thickness heavy, strength being apt to break out tooth kill, the smear metal is difficult to be curly, but lead horn to be too light, smear metal too thin, rub on hardening layer, aggravate screwtap wear and tear. In addition the calibration part of the screwtap should not be too long, otherwise rub against whorl hole wall and aggravate, it is generally 4 pieces of pitch.
4.The screwtap improves the embodiment and is prone to the work hardening of surface in the course of processing because of the titanium alloy material, especially process the small diameter whorl hole, become the difficult problem. Specialize in whorl, because of contract hole, several deduct attack, embrace screwtap, cut strength to be very much heavy, the ordinary screwtap is easy to break, make the work piece unable to continue processing. Because of described above to receive strength analytic process, large foot-path, hit foot-path, path rub little dividing 4 grades into of screwtap, each screwtap differs by 0.1mm, in the hope of reducing and cutting the influence that strength brings, but because the cutting amount is small, the work piece is prone to the work hardening again, process and stand up more strenuous, efficiency is very low, attack, have several whorl hole can continue and use. Later on I start with changing the angle that is cut, through testing repeatedly many times, turn spiral trough into by frank trough screwtap, in cut tooth rub, go, 1 spike according to spiral angle originally, as shown in Fig. 5, in order to reduce the contact area of screwtaps and smear metal. The previous horn come from original reduction, make smear metal and one hundred sheetses of Taxi contact length little ago, already can increase smear metal and one hundred sheetses of Taxi contact area ago, make, cut hot cutting strength to be unlikely to concentrate on, cut edge while being excessive, improve the heat dissipation condition, can also strengthen and cut the edge, reduce and break out and decrease.
effect of the process parameters on the rim thickness of glass fiber and Wollastonite filled PBT by conventional and microcellular injection-molding process has been conducted.
References:
[1]Gao Zhongshu. The electromechanics controls the project [M]. Beijing: The publishing house of Tsing-Hua University, 2002.
[2]Zhang JianMin. Electromechanics' integrated system is designed [M]. Beijing: Beijing BJ Universithy of Polytech Press, 2002.
[3]Wang GuiMing. Practical technique of numerical control [M]. Beijing: The publishing house of the mechanical industry, 2000.
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