CD1型3T電動(dòng)葫蘆壓繩板工藝分析及沖裁模具設(shè)計(jì)-落料沖孔復(fù)合模含7張CAD圖
CD1型3T電動(dòng)葫蘆壓繩板工藝分析及沖裁模具設(shè)計(jì)-落料沖孔復(fù)合模含7張CAD圖,cd1,電動(dòng)葫蘆,壓繩板,工藝,分析,模具設(shè)計(jì),沖孔,復(fù)合,cad
外文出處：《Handbook of Die Design》 Ivana Suchy
Copyright 2006 ISBN 0-07-146271-6
72th pages-77th pages
1．外文資料翻譯譯文（約3000漢字）：
1． 外文資料翻譯譯文
模具設(shè)計(jì)手冊(cè)
伊凡娜·蘇奇
原文書號(hào) ISBN 0-07-146271-6
出版時(shí)間 2006年
譯文內(nèi)容節(jié)選自第72-77頁
2-3 對(duì)零件的外部影響及其對(duì)塑性變形的影響
影響金屬材料塑性變形過程的因素主要有以下幾個(gè)方面：影響金屬材料塑性變形的程度；影響金屬材料塑性變形過程的實(shí)際可行性。這些因素中的許多都與成形過程本身緊密相連，因此它們與成形過程密不可分，但它們的存在可能會(huì)導(dǎo)致成形過程的徹底失敗。
眾所周知的影響因素是材料的硬度，厚度及其變化，化學(xué)分析以及是否存在有害或有益元素。這些因素可以在成型或拉伸過程開始很長(zhǎng)時(shí)間之前進(jìn)行評(píng)估。但是，有些影響難以計(jì)劃或預(yù)測(cè)，因此很難事先進(jìn)行評(píng)估。
對(duì)零件的基本影響之一是與成形，拉伸或切割工具的接觸。在這里，材料的類型，表面光潔度，工具的磨損以及零件表面的磨損會(huì)極大地影響該特定操作的最終結(jié)果。加上金屬成型過程的速度，使用的潤(rùn)滑劑或不存在的潤(rùn)滑劑，工具功能表面之間的間隙，僅舉幾例，就會(huì)出現(xiàn)整個(gè)“雜亂無章的”變量，準(zhǔn)備攻擊制造過程和產(chǎn)生的產(chǎn)品。
事實(shí)是，僅通過成形，切割或拉伸過程就能夠在工具與材料之間的接觸區(qū)域產(chǎn)生變化，而這種變化可以通過改變材料內(nèi)部的應(yīng)力分布，材料的尺寸來進(jìn)一步增強(qiáng)。成型的零件，其他更改也不一定總是有幫助。
2-3-1 溫度
要考慮的重要外部影響之一是制造過程的溫度。零件的晶體結(jié)構(gòu)在塑性變形過程中發(fā)生改變的事實(shí)觸發(fā)了晶體能量的增加。正如先前通過實(shí)驗(yàn)證實(shí)的那樣，這種能量支出中只有大約 10％到 25％與成形過程本身背道而馳。其余的轉(zhuǎn)化為熱量。
因此，成型過程中金屬的溫度升高，這本身就可以將成型過程分為
? 冷成型
? 半熱成型
? 熱成型
所有這些變化都是在特定溫度范圍內(nèi)發(fā)生的。例如，將物體加熱到
0.2Tm≤Tw≤0.3Tm (2-12)
其中 Tm為熔化溫度，Tw為工作溫度；并保持此溫度范圍較長(zhǎng)的時(shí)間，然后進(jìn)行冷卻，會(huì)導(dǎo)致子結(jié)構(gòu)發(fā)生變化，從而導(dǎo)致材料的機(jī)械性能發(fā)生變化，例如硬度降低，剪切強(qiáng)度降低以及可塑性提高。
不會(huì)造成材料硬度隨后損失的變形稱為冷變形，可以在Tw≤0.3Tm的溫度下觀察到它的發(fā)生。
熱量的額外增加，直到Tw ≤ 0.4Tm 并保持在這樣的溫度水平在較長(zhǎng)的時(shí)間段內(nèi)，隨后緩慢冷卻可以在一定程度上恢復(fù)該材料的晶體結(jié)構(gòu)并產(chǎn)生新形成的晶體結(jié)構(gòu)。此過程稱為再結(jié)晶。
在溫度為0.5Tm≤Tw≤0.7Tm的半溫成形中，材料硬度的降低是明顯的，隨后松弛并改變其晶體結(jié)構(gòu)，或者再結(jié)晶。
在熱成形時(shí)，或在Tw ≥0.7Tm時(shí)，金屬材料會(huì)失去所有硬度，并且抗變形性幾乎完全消失。
2-3-2 成型速度
成型過程的速度是另一個(gè)重要方面，可以影響材料并在最終結(jié)果中產(chǎn)生變化。冷成型過程中的緩慢變形將對(duì)材料的成型阻力產(chǎn)生顯著影響。隨著溫度的升高和成型速度的提高，成型阻力通常降低。
然而，冷成型期間成型速度的突然增加可能會(huì)增加材料的成型阻力。
2-3-3 成型零件尺寸的變化
在成型過程中，不僅零件發(fā)生結(jié)構(gòu)變化，而且可以觀察到零件尺寸的變化。這些變化取決于尺寸和幾何結(jié)構(gòu)變形區(qū)域的形狀，隨使用的工藝過程而變化。這種變化的最佳指標(biāo)是長(zhǎng)寬關(guān)系，即長(zhǎng)寬關(guān)系。
可以說，摩擦的多重因素包括零件應(yīng)力范圍的變化、變形影響的變化以及材料硬度的變化。
在成形過程中影響的基本要素之一是成形力（即成形強(qiáng)度），因?yàn)槌尚瘟νㄟ^工具傳遞到材料中。當(dāng)成形力完全被成形材料吸收時(shí)，如在拉伸，成形和擠壓過程中發(fā)生的那樣，這種影響可以表示為：
(2-13)
P =PrA
其中P=形成力
Pr=成形阻力（可使用以下公式）
A=接觸面積
材料的抗變形能力可以表示為： (2-14)
Pr ＝Ps+ Fo+Fi
其中Ps=材料的變形強(qiáng)度。它基于成形材料的特性、應(yīng)力/變形狀態(tài)、變形程度、速度和溫度。
Fo=由于材料的外摩擦而產(chǎn)生的應(yīng)力，這與所用潤(rùn)滑劑的類型、工具和材料的表面狀況、溫度、成形工具和材料接觸區(qū)域內(nèi)的成形應(yīng)力分布有很大關(guān)系；
Fi=內(nèi)（補(bǔ)充）摩擦力，取決于變形區(qū)域的幾何參數(shù)和成形力傳遞到材料中的類型。
2-3-4 變形和應(yīng)變硬化程度
應(yīng)變硬化是在較低溫度下形成金屬時(shí)可能遇到的現(xiàn)象。在此，操作本身使成形材料的晶體變得更細(xì)化，同時(shí)在成形力的方向上延伸。彈性降低，硬度增加。
初始變形將始終阻礙零件成形或變形的所有后續(xù)嘗試。金屬材料的每次變形，以及零件形狀或厚度的預(yù)期變化，都會(huì)產(chǎn)生抵抗這種變形的能力。這種阻力稱為應(yīng)變硬化，并且由于低溫不足以保持材料結(jié)構(gòu)的彈性，因此在冷加工時(shí)會(huì)對(duì)材料產(chǎn)生更大的影響。
某些工藝（例如拉伸）必須在一定數(shù)量的拉伸加工通過后采用緩解工藝（即退火）。否則，材料結(jié)構(gòu)對(duì)其他變化的內(nèi)在抵抗力將使現(xiàn)有的工具（通常是現(xiàn)有的工具）失去作用。換句話說，材料硬度將超過其成形能力。
一旦應(yīng)變硬化，零件就需要增加成形力以實(shí)現(xiàn)額外的成形。的確，有時(shí)零件的熱加工可以部分減輕應(yīng)變硬化的影響，但這可能并不總是有益的。此過程可能會(huì)導(dǎo)致材料表面變形，內(nèi)部應(yīng)力分布不均勻（尤其是在局部加熱中）以及精度降低。
除了在圖紙中，應(yīng)變硬化有時(shí)被認(rèn)為對(duì)產(chǎn)品有益，因?yàn)樗鼤?huì)影響零件的有用硬度，并隨之增加拉伸強(qiáng)度。通常，這種影響可能證明使用劣質(zhì)材料是合理的，并依靠冷加工使它們達(dá)到要求的或預(yù)期的硬度和強(qiáng)度水平。
沿著這些路線，壓彎工具和也許其他彎曲工具很少進(jìn)行淬火，因?yàn)榇慊鸩僮鳎礋崽幚恚⑹顾鼈兊男螤钭冃尾⑶夷サ糇冃慰赡懿⒉豢偸橇钊藵M意。尤其是在使用過于復(fù)雜的沖頭和模具的情況下，這是正確的，因?yàn)樗鼈兊拈L(zhǎng)度增加了問題的復(fù)雜性。取而代之的是，在這種工具的使用過程中，通過材料的加工硬化或應(yīng)變硬化來開發(fā)其必要的硬度。
通常，應(yīng)變硬化會(huì)增加材料的硬度和拉伸強(qiáng)度，而延展性會(huì)下降。甚至翻滾和振動(dòng)拋光也可以使零件表面硬化，而不是說噴砂或噴丸處理。后兩個(gè)過程不僅通過產(chǎn)生類似于表面硬化的效果來改變材料的硬度，而且還改變了零件的視覺外觀。
2-3-5 外部影響的疊加
并非所有的材料都易于成型，有些甚至很難成型。這些材料通常具有令人印象深刻的硬度和較差的彈性模量，無法使用傳統(tǒng)的制造方法進(jìn)行更改。為此，已經(jīng)開發(fā)了一些新型的成型應(yīng)用，即
? 在很高的壓力下形成
? 超塑成型
? 循環(huán)變形
2-3-5-1 在非常高的壓力下成型
即使幾乎不存在這種性質(zhì)，這種類型的成型也是用于增強(qiáng)材料彈性的良好有效方法。大多數(shù)情況下，使用靜液壓成型。在成型階段，零件在極高的壓力范圍內(nèi)受到液體的影響。這種力減小了所形成的材料內(nèi)的位錯(cuò)的密度，同時(shí)迫使它們保持在下部結(jié)構(gòu)形成晶粒的壁的緊密附近。這使他們沒有機(jī)會(huì)聚在一起，同時(shí)成功地阻礙了微裂紋的發(fā)展。
除了成形應(yīng)用之外，這種成形方法還可以用于其他用途。例如，在存在材料鼓脹的情況下，或遇到油罐效應(yīng)和其他與應(yīng)力有關(guān)的變形時(shí)，在高壓下形成，或者在高壓下變平或施膠時(shí)，可以充分緩解材料，使其無應(yīng)力。然而，使用這種成形方法并不總是可行的，因?yàn)檫@與設(shè)備的高成本有關(guān)。
2-3-5-2 超塑成型
所謂超塑性，是指金屬材料在不造成任何物理或結(jié)構(gòu)損壞的情況下，其長(zhǎng)度可擴(kuò)展至其原始大小的 100％甚至 1000％的能力。超塑性變形不會(huì)導(dǎo)致材料破裂或破裂，有時(shí)甚至現(xiàn)有的裂縫也不會(huì)進(jìn)一步傳播。
從結(jié)構(gòu)上講，超塑性可以定義為材料在高溫下同時(shí)具有受控變形量的同時(shí)具有極高拉伸伸長(zhǎng)率的能力。
金屬材料在變形過程中通常不能承受高應(yīng)變。隨著過程中熱量的增加，應(yīng)變硬化的有害作用減弱，從而產(chǎn)生超塑性。
一些合金的超塑性表現(xiàn)相當(dāng)快。這些是鋅鋁，鋁銅，錫鉛，甚至是鐵鉻鎳系列的某些合金。
當(dāng)前，公認(rèn)的超塑性有兩種：
1. 基于外部條件的超塑性。
2. 基于材料的內(nèi)部結(jié)構(gòu)的超塑性。
第一種超塑性僅適用于多形材料，可在特定溫度范圍內(nèi)觀察到，即1560-1670℉（850-910℃）和非常緩慢的變形，成形力范圍為290 psi（2兆帕）。
令人感興趣的是第二種超塑性。這種情況只能發(fā)生在具有非常細(xì)晶粒微觀結(jié)構(gòu)的材料中，其中晶粒尺寸僅在幾個(gè)微米（即1–5μm）附近。變形機(jī)制包括沿晶粒輪廓的滑移和晶界的位移，同時(shí)也可以觀察到晶粒內(nèi)部位錯(cuò)的滑移。
不幸的是，用于這種工藝的工具帶來了一個(gè)問題，因?yàn)闆]有太多的工具材料能夠長(zhǎng)時(shí)間承受高溫。因此，有時(shí)將帶有選擇性冷卻部分的工具與耐熱鋼和陶瓷材料一起使用。
由于某些材料在變形結(jié)束后無法停止超塑性行為而產(chǎn)生了另一個(gè)問題。它們甚至在此后仍保持部分超塑性，并在以后顯示出明顯的蠕變趨勢(shì)。
2-3-5-3 循環(huán)變形
周期性變形是在間歇壓力或?qū)Τ尚尾牧鲜┘幽撤N其他振動(dòng)影響下進(jìn)行的。它用于必須消除表面摩擦的有害影響的情況。適用于成型的周期性變形的類型可分為
1. 脈沖，頻率小于每秒10個(gè)脈沖
2. 振動(dòng)，每秒10至15,000 個(gè)脈沖
3. 超聲波，每秒使用超過15,000個(gè)脈沖
當(dāng)材料承受由于成型引起的張力時(shí)，冷成型時(shí)脈沖振動(dòng)疊加在金屬材料上，似乎會(huì)降低材料內(nèi)部的屈服應(yīng)力。材料晶體的位錯(cuò)似乎遵循線性缺陷的模式，這被認(rèn)為是塑性變形的主要原因。摩擦的減小使材料在其整個(gè)表面上具有均勻的屈服強(qiáng)度。這樣就可以增加拉深的深度（深拉深可達(dá) 37％），并可以在低的多的壓力下成型。
最常用的方法是低頻振動(dòng)成型，每秒10到300個(gè)（有時(shí)是1000個(gè)）周期。與所有類型的循環(huán)成型一樣，該方法的特征還在于接觸摩擦的明顯變化。摩擦系數(shù)大大降低，有時(shí)降低到其原始值的一小部分。另外，改善了表面條件，減輕了材料內(nèi)的應(yīng)力，并減小了剪切強(qiáng)度。
第二個(gè)使用是超聲波成型或超聲波。已經(jīng)證明，以高頻振動(dòng)的形式施加超聲波能夠減小所需的成形力，同時(shí)增加每次通過的變形量。發(fā)現(xiàn)質(zhì)量和表面光潔度得到改善，同時(shí)零件的尺寸穩(wěn)定性更高，并且減少了摩擦。
例如，在拉絲過程中，超聲波的影響通常指向模具，在此處可以同軸或垂直方式施加超聲波。
在同軸應(yīng)用中，拉力的最大減少是在實(shí)例中實(shí)現(xiàn)的，在這種情況下，線本身開始與其工具一起共振。通過垂直施加超聲波，觀察到模具在尺寸上周期性地收縮和膨脹，使最終產(chǎn)品呈略微橢圓形。在這種應(yīng)用中，應(yīng)力的大幅度降低是常見的，尤其是當(dāng)振動(dòng)作用于導(dǎo)線和工具時(shí)。鋼和鋁的應(yīng)力降低率分別達(dá)到45%和35%。
用超聲攪拌潤(rùn)滑劑繪圖是另一種性質(zhì)類似的方法。在這里，不僅工具和成型材料暴露在超聲波下，而且潤(rùn)滑劑也暴露在超聲波下。超聲波對(duì)潤(rùn)滑劑的影響使其在給定區(qū)域的分散性得到改善，從而產(chǎn)生幾乎理想的流體動(dòng)力潤(rùn)滑。同樣，這種方法降低了拉拔道次的數(shù)量，同時(shí)保持模具不受拉伸材料沉積的影響。改善了零件表面，降低了工裝的磨損。
在鈑金成型中，還發(fā)現(xiàn)由于施加超聲波降低了成型摩擦，從而減少了成型工具的磨損。觀察到所需的成型/拉伸力有所降低，零件的公差范圍得到了改善。
這些過程的缺點(diǎn)雖然不多，但影響很大。首先，必須評(píng)估聲波裝置的成本，包括其高功率消耗和高能量損耗的數(shù)量。只有訓(xùn)練有素的人員才能使用這類設(shè)備，這是另一個(gè)缺點(diǎn)，而不是談?wù)撘粋€(gè)問題的答案：“超聲波如何影響操作這類設(shè)備的人員？”
2．外文資料原文（與課題相關(guān)，至少1萬印刷符號(hào)以上）：
2．外文資料原文
Handbook of Die Design
Ivana Suchy
Original ISBN 0-07-146271-6
Published in 2006
Excerpt from page 72-77
2-3 EXTERNAL INFLUENCES ON THE PARTAND THEIR IMPACT ON PLASTIC DEFORMATION
Several factors may affect the process of plastic deformation of metal material by influ- encing the extent of deformation and the actual feasibility of the forming process along the given guidelines. Many of these factors are so tied to the forming process itself that they are inseparable from it, and yet their presence may bring about a total failure of that oper- ation.
Widely known factors of influence are the hardness of the material, thickness and its variations, chemical analysis, and absence or presence of harmful or beneficial elements. These factors can be assessed long before the forming or drawing processes begin. However, there are influences that are difficult to ascertain, difficult to plan or predict, and therefore difficult to evaluate beforehand.
One of the basic influences on the part is the contact with the forming, drawing, or cut- ting tooling. Here, the type of material, the surface finish, the wear and tear of the tooling, and that of the part’s surface can immensely affect the final result of that particular oper- ation. Add the speed of the metal-forming process, the lubricant used or its absence, clearance between the functional surfaces of the tooling, to name but a few, and a whole “jungle” of variables emerge, ready to attack the manufacturing process and the result- ing product.
The fact, that the process of forming, cutting, or drawing alone is capable of producing changes in the areas of contact between the tooling and the material can become further enhanced by changes in the distribution of stresses within that material, changes in the size of the formed part, and other changes does not always help either.
2-3-1 Temperature
One of the important external influences to consider is the temperature of the manufactur- ing process. The fact that the crystalline structure of the part is being altered during plastic deformation triggers a rise in the crystalline energy. As previously confirmed by experi- ments, only about 10 to 25 percent of this energy outlay goes against the forming process itself. The rest of it is transformed into heat.
For this reason, the temperature of metals during the forming process is increased, which in itself allows for a division of forming processes into,
? Cold forming
? Half-warm forming
? Warm forming
All of these variations are taking place during specific temperature ranges. For example, heating an object to
0.2Tm ≤ Tw≤ 0.3Tm (2-12)
where Tm is the melting temperature and Tw is the working temperature; and keeping such temperature range for a prolonged time, which is followed by cooling produces changes in the substructure and ensuing changes in mechanical qualities of the mater- ial, such as lowering of hardness, lowering of the shear strength, and enhancement of plasticity.
Deformation with no subsequent loss of hardness of the material is called a cold deformation and its occurrence can be observed at temperatures of Tw ≤0.3Tm.
Additional increase of heat, up to Tw≤0.4Tm and remaining at such temperature level for extended period of time, which is followed by a slow cooling can somewhat revive the crystallographic structure of the material and give rise to newly-formed crystalline struc-tures. This process is called recrystallization.
At half-warm forming, which occurs at temperatures of 0.5Tm ≤Tw≤0.7Tm, the lower- ing of the hardness of material is obvious with subsequent relaxation and changes in its crystalline structure, or recrystallization.
With warm forming, or at Tw ≥0.7Tm, the metal material loses all its hardness and the resistance to deformation disappears almost totally.
2-3-2 Forming Speed
Speed of the forming process is another important aspect that can affect the material and produce variations in the final outcome. Slow deformation during the cold forming process will have a noticeable influence on the material’s resistance to forming. With increase in temperature and with increase in forming speed, the resistance to forming is often lowered.
However, a sudden increase in the forming speed during cold forming may increase the forming resistance of the material.
2-3-3 Changes in the Size of the Formed Part
During forming, not only the structural changes occur in the part, but additionally, modifica- tions of the part’s size can be observed. These changes depend on the size and geometrical
shape of the deformed areas, which varies with the technological process used. The best indicator of such changes is the relationship of the length and width or, l/w.
Naturally, friction is an influential factor in this scenario and it can be said that the mul- tiplying element of friction consists of the changes in the stress range in the part, changes of deforming influences, as well as changes in the hardness ofmaterial.
One of the basic elements of influence in the forming process is the forming force (i.e., forming intensity), as it is being transferred into the material by the tooling. Where such forming force is being completely absorbed by the formed material, as it happens in draw- ing, forming, and extruding, such influence can be expressed as:
P = Pr A (2-13)
where P= forming force
Pr= forming resistance (formula below can be used) A=area of contact
The material’s resistance to deformation can be expressed as:
Pr =Ps +Fo +Fi (2-14)
Where Ps=deforming strength of the material. It is based on the properties of the formed material, on the stress/deformation state, on the degree of deformation, its speed, and temperature.
Fo= amount of stress due to the outer friction on the material, which is heavily influ-enced by the type of lubricant being used, the surface condition of the tool and that of the material, temperature, distribution of forming stresses in the areas of contact between the forming tooling and the material;
Fi=inner (complementing) friction, dependent on the geometric parameters of the area of deformation and on the type of transmission of the forming forces into the material.
2-3-4 Extent of Deformation and Strain Hardening
Strain hardening is a phenomenon that can be encountered during forming of metals at lower temperatures. Here the operation itself causes the crystals of the formed material to become more refined, while extending themselves in the direction of the forming force. The elasticity decreases and the hardness increases.
The initial deformation will always hinder all subsequent attempts at forming or deforming of a part. Every deformation of metal material produces, alongside the intended changes in the part’s shape or thickness, a resistance against such deformation as well. This resistance is called strain hardening and it exerts greater influence on mate- rial with cold working, since the low temperature is not adequate to keep the material structure elastic.
Some processes, such as drawing, must utilize a relieving process (i.e., annealing) after certain number of drawing passes. Otherwise the inner resistance of the material structure to additional changes will render the existing tooling and often the existing tool force, use- less. In other words, the material hardness will exceed its formingcapacities.
Once strain-hardened, the part requires an increase in forming force to achieve additional forming. True, sometimes the influence of strain hardening can be partially alleviated by heat working of the part, which may not be always beneficial. This process may produce distortion of the material surface, and uneven distribution of inner stresses (especially in localized heating) coupled with a diminished accuracy.
Other than in drawing, strain hardening is sometimes considered beneficial to the product becauseof its effect on thepart’s useful hardness, with subsequentincrease in tensilestrength. Often such influences may justify the use of materials of inferior qualities and count on cold working to bring them up to required or expected levels of hardness and strength.
Along these lines, press-brake tooling and perhaps some other bending tools, are rarely ever hardened, for the hardening operation (i.e., heat treatment) will distort their shape and grinding the distortion away may not always prove satisfactory. This is true especially where a too complicated punch and die are being utilized, their length adding to the com- plexity of a problem. Instead, the necessary hardness of such tooling is developed during its use, through work hardening or strain hardening of the material.
Generally, strain hardening increases the hardness and tensile strength of the material, while the ductility is decreased. Even tumbling and vibratory finishing can harden the sur- face of parts, not talking about sand blasting or shot peening. The latter two processes totally alter not only the material hardness by creating an effect similar to the case-hardening, but the visual appearance of the part as well.
2-3-5 Superimposition of Outer Influences
Not all materials are easily formable and some can hardly be formed, if ever. These mate- rials, usually of impressive hardness and poor modulus of elasticity, cannot be altered using the traditional manufacturing methods. For these, some new types of forming applications have been developed, namely
? Forming at very high pressures
? Superplastic forming
? Cyclic deformation
2-3-5-1 Forming at Very High Pressures. This type of forming is a good and effective process used to enhance elasticity in the material even where such property is nearly nonex- istent. Most often, hydrostatic forming is being used. During the forming stage the part is subjected to the influence of a liquid at extremely high ranges of pressure. Such force diminishes the density of dislocations within the formed material, while forcing them to remain in the close proximity of the walls of the substructure-forming grain. This gives them no chance at grouping together, while it is successfully hindering the development of microcracks.
Such method of forming can be used for other than forming applications too. For example, where bulging of the material exists, or an oilcan effect and other stress-related distortions are encountered, forming at high pressures, or rather flattening or sizing at high pressures, can ade- quately relieve the material, leaving it stress free, straight, and even. Yet, the use of such form- ing methods is not always feasible as it is tied to a high cost of an equipment.
2-3-5-2 Superplastic Forming. By superplasticity we mean the ability of metallic materials to extend in length 100 percent and even 1000 percent of its original size, without suffering any physical or structural damage. Superplastic deformation does not cause the material to crack or to fracture and sometimes even existing cracks do not propagate any further.
Structurally, superplasticity can be defined as an ability of the material to develop extremely high tensile elongations at elevated temperatures, while being subjected to the controlled amounts of deformation.
Metal materials generally do not tolerate high strains during deformation. With the addition of heat to the process, the detrimental effect of strain hardening is diminished and superplasticity
can result. Some alloys behave superplastically, rather quickly. These are zinc-aluminum, aluminum-copper, tin-lead, and even some alloys of the iron-chromium-nickel range.
At present, there are two types of superplasticity recognized:
1.Superplasticity based on the outer conditions.
2.Superplasticity based on the inner structure of material.
The first type of superplasticity is reserved to polymorphous materials and it can be observed at certain temperature ranges, i.e., 1560–1670°F (850–910°C) and at very slow deformations, with forming force in the range of 290 psi (2 MPa).
Of interest is the second type of superplasticity. This can occur only in materials with a very finely grained microstructure, where the grain size is in the vicinity of but several micrometers (i.e., 1–5 mm). The mechanism of deformation consists of slippage along the outline of the grain and often a displacement of the grain boundary, while slippage of dislocations inside the grains can be observed as well.
Unfortunately, the tooling for such processes presents a problem, as not many tooling materials are capable of withstanding high temperatures at extended periods of time. For that reason, the tooling with selectively cooled portions is sometimes being used along with heat-resistant steels and ceramic materials.
Additional problem is being created by the inability of some materials to stop behaving superplastically after the deformation has ended. They remain partially superplastic even afterwards and display a marked tendency to creep later on.
2-3-5-3 Cyclic Deformation. Cyclic deformation is performed either with intermittent pressure or with some other kind of vibrating influence upon the formed material. It is used in cases where the detrimental influence of surface friction has to be eliminated. Types of cyclic deformation applicable to forming can be categorized as
1. Pulsing, with frequency of less than 10 pulses per second
2. Vibrating, with 10 to 15,000 pulses per second
3. Ultrasound, using more than 15,000 pulses per second
The superimposition of pulsing vibration on the metal material in cold forming, when the material is exposed to the tensions caused by forming, seems to reduce the yield stress within the material. The dislocations of material crystals seem to follow the pattern of lin- ear defects, which are considered the main causes of plastic deformation. The reduction of friction provides the material with a uniform yield across its surface. This gives a possibil- ity of an increase of the depth of drawing (up to 37 percent for deep drawing) and to form- ing at much lower pressures.
The most often used method is that of low frequency vibrating forming, with 10 to 300 (and sometimes 1000) cycles per second. As with all types of cyclic forming, this method too is characterized by marked changes in contact friction. The coefficient of friction is considerably lowered, sometimes down to a fraction of its original value. Additionally, the surface conditions are improved, the stresses within the material are relaxed, and the shear strength is diminished.
Second in usage comes the ultrasonic forming or ultrasound. It has been proven that the application of ultrasound in the form of high-frequency vibrations is capable of reducing the needed forming force, while increasing the amount of deformation per each pass. The quality and surface finish were found improved along with greater dimensional stability of the part and reduction of friction.
For example, in wire drawing, the influence of ultrasound is often directed toward the die, where it can be applied either coaxially or in a perpendicular fashion. In coaxial applicationt
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