發(fā)動機曲軸箱銑主軸孔卡瓦槽夾具設(shè)計

資源目錄里展示的全都有，所見即所得。下載后全都有,請放心下載。原稿可自行編輯修改=【QQ：401339828 或11970985 有疑問可加】 附錄 Residual Stresses A residual stress is one that exists without external loading or internal temperature differences on a structure or machine. It is usually a result of manufacturing or assembling operations. Sometimes it is called initial stress, and the operations, prestressing. When the structure or machine is put into service, the service loads superimpose stresses. If the residual stresses add to the service-load stresses, they are detrimental; if they subtract from the service-load stresses they are beneficial. In the plastic deformation the external force does the merit turns into outside the heat except the majority of extensions, but also some small part by the distortion can the form stores up in the deformation material. This part of energy named storage energy. The storage can the concrete manifestation way is: Macroscopic residual stress, microscopic residual stress and lattice distortion. According to the residual stress balance scope difference, usually may divide into it three kinds: (1) First kind of internal stress, also called the macroscopic residual stress, it is causes by the work piece different part macroscopic distortion nonuniformity, therefore its stress balance scope including entire work piece. For example, serves with Jin Shubang the curving load, then above is pulled elongates, under receives the compression; The distortion surpasses when the limit of elasticity has had the plastic deformation, after then the external force elimination by elongated one side on the existence compressed stress, the leg of right triangle is the tensile stress. This kind of residual stress corresponds the distortion can not be big, only accounts for always stores up can about 0.1%. (2) Second kind of internal stress, also called the microscopic residual stress, it is produces by between the crystal grain or the subgrain distortion nonuniformity. Its sphere of action and the crystal grain size quite, namely maintain the balance between the crystal grain or the subgrain. Sometimes this kind of internal stress may achieve the very great value, even possibly creates the micro crack and causes the work piece destruction. (3) Third kind of internal stress, also calls the lattice distortion. Its sphere of action is several dozens to several hundred nanometers, it is because the work piece forms in the plastic deformation the massive lattice flaw (for example vacancy, interstitial atom, dislocation and so on) cause. In the distortion metal the storage can the major part (80%~90%) uses in forming the lattice distortion. This part of energy enhanced the distortion crystal energy, causes it to be at the thermodynamics non-steady state, therefore it has one kind to make the distortion metal to restore to the free enthalpy lowest stable structure condition spontaneous tendency, and causes the plastic deformation metal in heating time reply and the recrystallization process. Only a few examples of detrimental residual stresses will be given here .One, in the assembly of machinery, occurs when two shafts are not in line or are a few thousandths of an inch out of parallel, and they are forced into connection by rigid couplings. The resulting stresses in the shafts become reversing stresses when the shafts are rotated. The correction, when perfect alignment cannot be economically attained, as is frequently the case, is to use flexible couplings of a type necessary for the degree of misalignment. The preceding case occurs with elastic stresses only, and the residual stresses are maintained by bearing constraints. In applications where mechanical work causes plastic yielding .stresses remain when the constraints are removed. For example, the forging of shafts and crankshafts and the cooling after forging may induce residual stresses, the equilibrium of which id changed in machining, causing some warping of the shafts. It is then common practice to straighten the shafts in a press before the final machining operation. Straightening requires a bending moment large enough to cause permanent set or yielding. Detrimental residual stresses commonly result from differential heating or cooling. A weld is a common example, The weld metal and the areas immediately adjacent are, after solidification, at a much higher temperature than the main body of metal. The natural contraction of the metal along the length of the weld is partially prevented by the large adjacent body of cold metal. Hence residual tensile stresses are set up along the weld. In general, local or shallow heating which would expand the region or surface, if it were free, a distance well beyond that which the adjacent larger volume will allow causes yielding and upsetting of the heated material, This readily occurs because of the reduced yield strength at elevated temperatures. The same cooler volume prevents the upset, heated region from fully contracting during its cooling, and tensile general rule is that the “l(fā)ast to cool is in tension,” although there is an exception if certain transformations of microstructure occur. Methods for minimizing or reversing these stresses include annealing for stress relief and hammer or shot peening of the weakened surface. Annealing requires heating mild steel to 1100~1200F, followed by slow cooling, Some preheating of the parts to be joined may minimize the tensile stresses in welds. A thin but highly effective surface layer of compressive stress may be induced by cold-rolling, coining, and peening processes. It is seen that these processes work-harden an outer layer, thus causing compressive stresses to remain, together with minor tensile stresses in adjacent interior layers. Since the compressive layer is readily obtained all around, these processes are suitable for reversing loads and rotating components where the stress varies between tension and compression. The processes must be carefully controlled in respect to roller pressures and feeds, shot size and speed, etc., for which extensive information is available in engineering books and periodicals. Cold-rolling is applied primarily to cylindrical and other shapes that can be rotated, such as threads and shaft fillets. The shape, size, and pressure of the roller and the yield strength of the shaft determine the depth of penetration, which can be calculated. A special fixture may be attached to the carriages of a lathe and made to slowly traverse the desired rolling of bolts and screws has long been part of a forming process that not only forms but strengthens the threads by deformation and grain flow around the roots and by inducing compressive residual stresses. Coining of holes, also called ball drifting, is a manufacturing process of forcing a hard, tungsten carbide or AIDI 52100 steel, slightly oversize ball through a hole in a plate, bushing, or tubing to give the holes final size and a fine finish. The length of the hole may be from 1/20 to 10 times its diameter. The machine is often set up for a high production of small parts with unskilled labor. An incidental result is that the process increases hardness, hence wear resistance, and induces around the hole a compressive residual stress that is usually advantageous, as in roller-chain links. The links ate highly stressed in pulsating tension with a concentration of the stress at and near the hole surfaces. With the compressive stress from ball drifting, the net tensile stress in service is decreased, and failure is minimized. Peening is the most widely used method for prestressing by mechanically induced yielding. By the impact of rounded striking objects, the surface is deformed in a multitude of shallow dimples, which in trying to expand put the surface under compression. Hammer peening, usually by air-driven tool with a rounded end, is useful on limited areas, such as a weld in shaft or on areas found weakened by corrosion, decarburization, or minor fatigue damage. With a hard spherical end to the tool, the depth of the compressed layer, which occurs below the surface, is about half the strain-hardened region. Shot peening is done on steels by the high-velocity impingement of small, round, steel or chilled cast-iron shot with diameters from 0.007to 0.175 in.. The compressed layer has a depth from a few thousandths to a few hundredths of an inch, less than with hammer peening, but roughly proportioned to the shot size used and its velocity. Again the residual stress produced is about half of the strain-hardened yield strength. Shot peening is extensively used because it may be applied with minimum cost to most metals and shapes, except some interior ones. On soft metals, glass beads may be used. Helical springs are commonly shot peened, with up to a 60%increase in allowable stress under pulsating loads. Part of the improvement may be due to the removal of the weakening longitudinal scratches left from the wire-drawing operation. Similarly, coarse-machined and coarse-ground surfaces are smoothed and improved by shot peening, which may be a more economical method than producing a final finish by machining or grinding. Peening is not used on bearing and other closely fitting surfaces where high precision is required. A final grinding for accuracy after peening would remove part or all of the residual stress. Machines are available for the automatic and continuous peening of small-and medium-size parts moving on a conveyor or turntable through the blast. 殘余應力 殘余應力是結(jié)構(gòu)或者機器中在沒有外部載荷或者內(nèi)部溫差時存在的一種應力，它通常是在制造或者裝配過程中所產(chǎn)生的。有時它被稱為初始應力，而這個過程則被成為施加預應力。當這些結(jié)構(gòu)或者機器投入使用時，工作載荷就會與殘余應力相疊加。如果參與應力相加，則這種殘余應力是有害的；如果殘余應力與工作應力相減，則這種殘余應力是有利的。 塑性變形中外力所作的功除大部分轉(zhuǎn)化成熱之外，還有一小部分以畸變能的形式儲存在形變材料內(nèi)部。這部分能量叫做儲存能。儲存能的具體表現(xiàn)方式為：宏觀殘余應力、微觀殘余應力及點陣畸變。按照殘余應力平衡范圍的不同，通?？蓪⑵浞譃槿N： （1）第一類內(nèi)應力，又稱宏觀殘余應力，它是由工件不同部分的宏觀變形不均勻性引起的，故其應力平衡范圍包括整個工件。例如，將金屬棒施以彎曲載荷，則上邊受拉而伸長，下邊受到壓縮；變形超過彈性極限產(chǎn)生了塑性變形時，則外力去除后被伸長的一邊就存在壓應力，短邊為張應力。這類殘余應力所對應的畸變能不大，僅占總儲存能的0.1％左右。 （2）第二類內(nèi)應力，又稱微觀殘余應力，它是由晶?；騺喚ЯＶg的變形不均勻性產(chǎn)生的。其作用范圍與晶粒尺寸相當，即在晶?；騺喚ЯＶg保持平衡。這種內(nèi)應力有時可達到很大的數(shù)值，甚至可能造成顯微裂紋并導致工件破壞。 （3）第三類內(nèi)應力，又稱點陣畸變。其作用范圍是幾十至幾百納米，它是由于工件在塑性變形中形成的大量點陣缺陷（如空位、間隙原子、位錯等）引起的。變形金屬中儲存能的絕大部分（80％~90％）用于形成點陣畸變。這部分能量提高了變形晶體的能量，使之處于熱力學不穩(wěn)定狀態(tài)，故它有一種使變形金屬重新恢復到自由焓最低的穩(wěn)定結(jié)構(gòu)狀態(tài)的自發(fā)趨勢，并導致塑性變形金屬在加熱時的回復及再結(jié)晶過程。 這里僅列舉幾個有害的殘余應力的例子，在機器的裝配過程中，當兩軸不在一條直線上或者在平行度上相差千分之幾英寸時，采用剛性聯(lián)軸器強使他們聯(lián)接在一起。當軸旋轉(zhuǎn)時，軸上所產(chǎn)生的應力就是一個方向不斷改變的應力。在通常情況下無法經(jīng)濟地實現(xiàn)兩軸線之間的精確找正對準時，補救的方法是采用能夠補償一定找正誤差的彈性連軸器。 出現(xiàn)上述情況時僅產(chǎn)生彈性應力，而殘余應力是由于受到軸承約束而得以保存的。在機械加工造成塑性屈服的操作中，當約束去掉后，仍然留有應力。例如，在軸和曲軸的鍛造及隨后的冷卻過程中可能會產(chǎn)生殘余應力，切削加工會改變其平衡狀態(tài)，使軸產(chǎn)生某種程度的翹曲。因此，通常的作法是在進行最終的切削加工之前，在壓床上將軸矯直。矯直時需要采用足以使軸產(chǎn)生永久性變形或者屈服的彎矩。 不均勻加熱或者冷卻通常會產(chǎn)生殘余應力。焊縫是一個最常見的例子。在焊縫凝固后，焊縫金屬和鄰近區(qū)域的溫度要比金屬主體的溫度高的多。金屬沿著焊縫長度的自然收縮將被鄰近的體積較大、溫度較低的金屬限制了一部分。因此沿著焊縫產(chǎn)生了殘余拉應力。 通常，局部或淺表面加熱會使受熱部分和表面膨脹。如果膨脹部分能夠自由移動，其移動距離會大大超過鄰近的較大體積的材料的移動距離，造成了受熱材料的屈服和變厚。由于在高溫時屈服強度會降低，因此，這種現(xiàn)象很容易出現(xiàn)。在冷卻過程中，溫度降低的相同體積的材料能夠阻止受熱變厚區(qū)域完全收縮，結(jié)果產(chǎn)生了拉應力。因此，火焰切割后的表面處于受拉狀態(tài)，其強度降低。一般規(guī)律是“最后冷卻的部位處于受拉狀態(tài)”，但是如果顯微組織發(fā)生某種變化就會出現(xiàn)例外的情況。將這些殘余拉應力減至最小或者使之反向的方法有：通過退火消除應力，對強度降低的表面進行垂擊或噴丸處理。在退火過程中，要求把低碳鋼加熱到1100~1200F，某些合金鋼要加熱到1600F，然后對每英寸厚度保溫一小時，隨后進行緩慢冷卻。對被聯(lián)接零件進行某些預熱可以將焊縫中的拉應力降至最低。 冷壓、擠壓和噴丸強化都會產(chǎn)生一層薄的，但是十分有效的壓應力表面層。可見看出，這些工藝方法使工件外層產(chǎn)生加工硬化，從而產(chǎn)生壓應力，同時在與之相鄰的內(nèi)層中產(chǎn)生較小的拉應力。由于在各處都很容易獲得壓應力層，因此這些工藝方法適用于交變載荷和應力在拉應力與壓應力之間變化的回轉(zhuǎn)類零件。在采用這些工藝方法時，必須認真地控制滾輪的壓力和進給量、噴丸的大小和速度等。對于這些，在工程技術(shù)書籍和期刊中有大量資料可供參考。 冷壓主要用于圓柱形和其他回轉(zhuǎn)類的形狀，諸如螺紋和軸的圓角。滾輪的形狀、尺寸和壓力以及軸的屈服強度決定著穿透深度，這是可以通過計算得到的。一種專用的夾具可以裝在車床的溜板上，使其在軸的預定長度范圍內(nèi)緩慢地往復運動，與之同時軸由床頭箱帶動著旋轉(zhuǎn)。采用滾絲法加工螺栓和螺釘上的螺紋早就已經(jīng)成為一種成形加工方法。這種方法不僅能夠生成螺紋，而且還能通過螺紋根部附近的變形和晶粒流動以及產(chǎn)生的殘余壓應力來增加螺紋的強度。 孔的擠壓，又可以稱為鋼球漲孔，這種加工方法上迫使一個尺寸稍大的堅硬的碳化鎢或AISI52100 鋼球通過板、套筒或者管子上的孔獲得最終尺寸和較高的光潔度?？椎拈L度可以等于其直徑的0.05~10倍。擠壓漲孔機通常由非熟練工人操作，使用于小型零件的大量生產(chǎn)。這種方法能夠提高硬度，因此能提高耐磨性，并且在孔的周圍產(chǎn)生殘余壓應力，這種殘余壓應力通常是有利的。例如在滾子鏈的鉸鏈中，鉸鏈承受很高的脈動拉應力，而且在孔表面上和表面附近有應力集中。采用鋼球擠壓和漲孔可以產(chǎn)生壓應力，這會降低工作中的凈拉應力，將斷裂事故減到最低限度。 噴丸強化是通過采用機械方式引起工件表面屈服而施加預應力的最常用的方法。在圓形打擊物的沖擊下，表面發(fā)生變形并形成許多淺坑，由于這些淺坑有向外擴展的趨勢而使表面受壓。錘擊強化通常采用氣動圓頭工具進行，這種方法可以用于較小的區(qū)域。采用硬的球頭工具時，受壓層深度可達0.3英寸左右，與表面凹坑的直徑大致相等。最大殘余應力出現(xiàn)在表面以下，其大小約為應變硬化區(qū)屈服強度的一半。 噴丸強化時，以直徑為0.007~0.175英寸的小圓鋼丸或者冷硬鑄鐵丸高速沖擊鋼制零件。受壓層的深度從千分之幾英寸到百分之幾英寸，小于錘擊強化時受壓層的深度，大致與所用球丸的直徑和速度成正比。所產(chǎn)生的殘余應力也大約等于應變強化區(qū)的屈服強度的一半。 除了零件的某些內(nèi)部形狀外，噴丸強化可以用于大多數(shù)金屬和形狀，而且成本最低，因此噴丸強化得到了廣泛的應用。對于軟金屬，可以采用玻璃球。螺旋彈簧通常要進行噴丸硬化，可以使其在脈動載荷作用下的許用應力提高60%。強度增加的原因之一可能是由于消除了拔絲時產(chǎn)生的能夠起減低強度作用的縱向擦痕所致。同樣，進行噴丸強化可以改善初加工表面和初磨表面的 質(zhì)量，使其變的光滑，這種方法可能比采用切削加工或者磨削加工的方法進行最終加工更為經(jīng)濟。噴丸強化不能用于軸承和其他精度要求高的精密配合表面。對噴丸強化后的工作進行精磨可能會消除部分或者全部殘余應力?？梢圆捎脟娡铏C對在傳送帶或者轉(zhuǎn)臺上移動的中小尺寸零件進行自動而連續(xù)地噴丸強化。