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2025-01-15 06:07 本頁(yè)面
【正文】 材料的可機(jī)加工性能不僅取決于起內(nèi)在特性和微觀結(jié)構(gòu)，而且也依賴于工藝參數(shù)的適 當(dāng)選擇與控制。 也許很難在工件內(nèi)加熱和保持一個(gè)不變的溫度分布。（ b）增加的刀具壽命。 金屬基復(fù)合材料和陶瓷基復(fù)合材料很能機(jī)加工，它們依賴于單獨(dú)的成分的特性，比如說(shuō)增強(qiáng)纖維或金屬須和基體材料。纖維的撕裂、拉出和邊界分層是非常嚴(yán)重的問(wèn)題。為了解除這些力，已機(jī)加工的部分要在 CC ?? 16080 —（ FF ?? 315175 — ）的溫度范圍內(nèi)冷卻一段時(shí)間，然而慢慢地?zé)o變化地冷卻到室溫。刀具應(yīng)該很尖。 各種材料的機(jī)加工性 石墨具有磨蝕性。它們是難機(jī)加工的。它的可機(jī)加工性和不銹鋼相同。然而，因?yàn)楦叩难趸俣群突鸱N的危險(xiǎn)（這種元素易燃），因此我們應(yīng)該特別小心使用它。 盡管鑄銅合金很容易機(jī)加工，但因?yàn)殄戙~的積屑瘤形成因而鍛銅很難機(jī)加工。它需要具有強(qiáng)韌性的工具。 鈹和鑄鐵相同。 其它不同金屬的機(jī)加工性 盡管越軟的品種易于生成積屑瘤，但鋁通常很容易被機(jī)加工，導(dǎo)致了很差的表面光潔性。例如，當(dāng)溫度升高時(shí)，鋁會(huì)使鋼變脆（液體 — 金屬脆 化，熱脆化，見(jiàn) 節(jié)），盡管其在室溫下對(duì)力學(xué)性能沒(méi)有影響。氣態(tài)元素比如氫和氮在鋼的特性方面能有特別的有害影響。刀具和模具 鋼很難用于機(jī)加工，他們通常再煅燒后再機(jī)加工。因此生產(chǎn)和使用凈化鋼非常必要。馬氏體鋼易磨蝕，易于形成積屑瘤，并且要求刀具 材料有高的熱硬度和耐月牙洼磨損性。結(jié)果，這些鋼產(chǎn)生更小的月牙洼磨損，特別是在高切削速度時(shí)更是如此。鉍和錫現(xiàn)正作為鋼中的鉛最可能的替代物而被人們所研究。鉛鋼被第二和第三數(shù)碼中的字母 L 所識(shí)別（例如， 10L45）。這一特性已經(jīng)被在機(jī)加工鉛 鋼時(shí)，在切屑的刀具面表面有高濃度的鉛的存在所證實(shí)。在非二次硫化鋼中，鉛呈細(xì)小而分散的顆粒。越硬的鋼，形成更好的切屑形成和表面光潔性。這些夾雜物的大小、形狀、分布和集中程度顯著的影響可加工性。通過(guò)宗教鉛和硫磺，鋼的可機(jī)加工性已經(jīng)大大地提高了。 因?yàn)榧羟泄ば虻膹?fù)雜屬性，所以很難建立定量地釋義材料的可機(jī)加工性的關(guān)系。 切削力和功率的需求。 they can be difficult to machine. Tungsten is brittle, strong, and very abrasive, so its machinability is low, although it greatly improves at elevated temperatures. Zirconium has good machinability. It requires a coolanttype cutting fluid, however, because of the explosion and fire. Machinability of Various Materials Graphite is abrasive。 the higher the oxygen content, the lower the aspect ratio and the higher the machinability. In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquidmetal embrittlement, hot shortness。 Tool life obtained。 Force and power requirements。 see Section ), although at room temperature it has no effect on mechanical properties. Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability. Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a builtup edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are remended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive。 it requires hard, abrasionresistant, sharp tools. Thermoplastics generally have low thermal conductivity, low elastic modulus, and low softening temperature. Consequently, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, and proper support of the workpiece. Tools should be sharp. External cooling of the cutting zone may be necessary to keep the chips from being “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or watersoluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be annealed for a period of
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