【正文】
。此外,晶粒流動(dòng)方向的控制增加了產(chǎn)品的強(qiáng)度特性。冷加工的主要優(yōu)點(diǎn)是經(jīng)濟(jì)、操作更為迅速、容易,因?yàn)闊o須安排額外的加熱和處理。但是應(yīng)該記住某些材料(如含硫磺的鋼)在提高溫度時(shí)會(huì)變得更脆。只要在熱的狀態(tài)下,就可以加工大件產(chǎn)品和高強(qiáng)度材料,因?yàn)樘嵘臏囟冉档土藦?qiáng)度,進(jìn)而降低了載荷。當(dāng)然,在一些操作(如拉延)中應(yīng)變硬化是可取的,可以提高強(qiáng)度;在這些情況下,熱加工幾乎沒有優(yōu)勢(shì)。在熱加工過程中,因?yàn)榛钴S晶粒在加工溫度范圍內(nèi)會(huì)生長(zhǎng),就有可能適當(dāng)控制晶粒尺寸。熱、冷成形的優(yōu)點(diǎn)與缺點(diǎn)既然我們已經(jīng)談及了各類金屬加工工序,現(xiàn)在我們應(yīng)該給熱加工和冷加工工藝一個(gè)總體評(píng)價(jià)了。但是在該工序中,工件被壓進(jìn)一個(gè)封閉空間迫使材料通過一個(gè)被稱為磨具的適當(dāng)?shù)拈_口處流出。這道工藝由一套設(shè)計(jì)適當(dāng)?shù)耐鼓:桶寄硗瓿伞=饘俦“灞环旁谀ゾ呱侠靡粋€(gè)坯料壓板來避免產(chǎn)品缺陷。當(dāng)截面需要減小很多時(shí),也許有必要通過幾個(gè)階段來完成此操作。根據(jù)情況不同,磨具可以是開式或閉式。這是一種很有用途的工藝,用于生產(chǎn)金屬薄板和各種常用端面,如鐵軌、槽鋼、角鋼和圓鋼。軋制在這一工藝中,通過一個(gè)調(diào)整過的位于兩個(gè)動(dòng)力驅(qū)動(dòng)的軋輥之間的孔利用摩擦來拉伸工件。典型的成形方法有軋制、鍛造、拉延、拉深、彎曲和擠壓。例如。這一點(diǎn)很重要,因?yàn)榇蟮睦渥饔不瘯?huì)使材料變脆。材料的流動(dòng)應(yīng)力在再結(jié)晶溫度之上或之下全然不同。成形工藝可以分為以下兩個(gè)大類,即冷成形和熱成形。這是個(gè)很經(jīng)濟(jì)的方法,因?yàn)榭梢垣@得所需的形狀、尺寸和光潔度而無需使材料有任何大的損失。在此工藝中引起的應(yīng)力大于材料的屈服強(qiáng)度,但小于材料的斷裂強(qiáng)度。英語(yǔ)翻譯FormingForming can be defined as a process in which the desired size and shape are obtained through the plastic deformations of a material. The stresses induced during the process are greater than the yield strength, but less than the fracture strength, of the material. The type of loading may be tensile, pressive, bending, or shearing, or a bination of these. This is a very economical process as the desired shape, size, and finish can be obtained without any significant loss of material. Moreover, a part of the input energy is fruitfully utilized in improving the strength of the product through strain hardening. The forming processes can be grouped under two broad categories, namely, cold forming, and hot forming. If the worki