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一、論文題目 :CA6140車床手柄座工藝規(guī)程及夾具設(shè)計(jì)
題目來(lái)源
生產(chǎn)實(shí)踐
二、試驗(yàn)研究(調(diào)查)的目的意義:
研究(調(diào)查)的目的:
畢業(yè)之前進(jìn)行這次設(shè)計(jì)是為了給我們將要畢業(yè)的大學(xué)生一次進(jìn)一步學(xué)習(xí)和鍛煉的機(jī)會(huì),在整個(gè)畢業(yè)設(shè)計(jì)中提高了我們的設(shè)計(jì)能力,具體設(shè)計(jì)目的如下:
(1)培養(yǎng)我們解決機(jī)械加工工藝問(wèn)題的能力
(2)進(jìn)一步培養(yǎng)我們識(shí)圖、制圖、運(yùn)用和編寫技術(shù)文件等基本技能
(3)培養(yǎng)我們熟悉并運(yùn)用有關(guān)手冊(cè)、規(guī)范、圖表等技術(shù)資料的能力
研究(調(diào)查)的意義:
機(jī)械加工工藝與夾具設(shè)計(jì)是全面地綜合運(yùn)用有關(guān)專業(yè)課程的理論和實(shí)踐知識(shí)進(jìn)行加工工藝及夾具結(jié)構(gòu)設(shè)計(jì)的一次重要實(shí)踐。通過(guò)該畢業(yè)設(shè)計(jì),綜合所學(xué)專業(yè)知識(shí),熟練的運(yùn)用機(jī)械制造工藝學(xué)的基本理論和夾具設(shè)計(jì)原理的知識(shí),正確地解決一個(gè)零件在加工中的定位,夾緊以及合理制訂工藝規(guī)程等問(wèn)題的方法,培養(yǎng)編制機(jī)械加工工藝規(guī)程和機(jī)床夾具設(shè)計(jì)的能力,同時(shí)培養(yǎng)分析問(wèn)題和解決問(wèn)題的能力,加深理論知識(shí)的理解,強(qiáng)化生產(chǎn)實(shí)習(xí)中的感性認(rèn)識(shí)。設(shè)計(jì)過(guò)程也是理論聯(lián)系實(shí)際的過(guò)程,能培養(yǎng)理論聯(lián)系實(shí)際的設(shè)計(jì)思想,并學(xué)會(huì)使用手冊(cè)、查詢相關(guān)資料等,提高分析和解決工程實(shí)際問(wèn)題的獨(dú)立工作能力,能鞏固、加深和擴(kuò)展有關(guān)機(jī)械加工工藝與夾具方面的知識(shí),為以后的實(shí)際工作奠定堅(jiān)實(shí)的基礎(chǔ)。
三、國(guó)內(nèi)、外研究概況和應(yīng)用前景(附參考文獻(xiàn)):
1 機(jī)械加工工藝技術(shù)的研究現(xiàn)狀
如今,企業(yè)為了增強(qiáng)市場(chǎng)競(jìng)爭(zhēng)力和快速響應(yīng)市場(chǎng)的變化而采用多種新技術(shù)的環(huán)境下,革新傳統(tǒng)的工藝設(shè)計(jì)手段,采用以計(jì)算機(jī)為工具的現(xiàn)代化工藝設(shè)計(jì)和管理方式是企業(yè)上水平、上臺(tái)階的關(guān)鍵之一,也是企業(yè)發(fā)展的必由之路。隨著科學(xué)技術(shù)的發(fā)展,特別是計(jì)算方法和計(jì)算機(jī)的迅速發(fā)展,大大地推動(dòng)了機(jī)械加工工藝的進(jìn)步。計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)即CAPP,通常指機(jī)械產(chǎn)品零件制造工藝過(guò)程的計(jì)算機(jī)輔助設(shè)計(jì)與文檔編制。它是為了解決手工設(shè)計(jì)工藝規(guī)程中存在的效率低下、工藝質(zhì)量不穩(wěn)定、不便于管理、柔性差等問(wèn)題而提出的。應(yīng)用CAPP技術(shù),可以使工藝人員從繁瑣重復(fù)的事務(wù)性工作中解脫出來(lái),迅速編制出完整而詳盡的工藝文件,縮短生產(chǎn)準(zhǔn)備周期,提高產(chǎn)品制造質(zhì)量,進(jìn)而縮短整個(gè)產(chǎn)品的開(kāi)發(fā)周期。
2 夾具設(shè)計(jì)技術(shù)的研究現(xiàn)狀
國(guó)際生產(chǎn)研究協(xié)會(huì)的統(tǒng)計(jì)表明,目前中、小批多品種生產(chǎn)的工件品種已占工件種類總數(shù)的85%左右?,F(xiàn)代生產(chǎn)要求企業(yè)所制造的產(chǎn)品品種經(jīng)常更新?lián)Q代,以適應(yīng)市場(chǎng)的需求與競(jìng)爭(zhēng)。然而,一般企業(yè)都仍習(xí)慣于大量采用傳統(tǒng)的專用夾具,一般在具有中等生產(chǎn)能力的工廠里,約有數(shù)千甚至近萬(wàn)套專用夾具;另一方面,在多品種生產(chǎn)的企業(yè)中,每隔3-4年就要更新50%-80%左右的專用夾具,而夾具的實(shí)際磨損量?jī)H為10%-20%左右。特別是近年來(lái),數(shù)控機(jī)床、加工中心、成組技術(shù)、柔性制造系統(tǒng)等新加工技術(shù)的應(yīng)用,對(duì)機(jī)床夾具提出了如下新的要求:
(1) 能迅速而方便地裝備新產(chǎn)品的投產(chǎn),以縮短生產(chǎn)準(zhǔn)備周期,降低生產(chǎn)成本;
(2) 能裝夾一組具有相似性特征的工件;
(3) 能適用于精密加工的高精度機(jī)床夾具;
(4) 能適用于各種現(xiàn)代化制造技術(shù)的新型機(jī)床夾具;
(5) 采用以液壓站等為動(dòng)力源的高效夾緊裝置,以進(jìn)一步減輕勞動(dòng)強(qiáng)度和提高勞動(dòng)生產(chǎn)率;
(6) 提高機(jī)床夾具的標(biāo)準(zhǔn)化程度。
隨著先進(jìn)制造技術(shù)的發(fā)展和市場(chǎng)競(jìng)爭(zhēng)的加劇,傳統(tǒng)的夾具設(shè)計(jì)方式已成為企業(yè)中產(chǎn)品快速上市的瓶頸,企業(yè)迫切需要提高夾具設(shè)計(jì)的效率。因此,快速實(shí)現(xiàn)夾具設(shè)計(jì)已成為企業(yè)的迫切要求,將計(jì)算機(jī)輔助設(shè)計(jì)技術(shù)應(yīng)用到夾具設(shè)計(jì)的過(guò)程是解決這一問(wèn)題的必然選擇。隨著計(jì)算機(jī)技術(shù)的發(fā)展和應(yīng)用,計(jì)算機(jī)輔助夾具設(shè)計(jì)即 CAFD 在理論和應(yīng)用上都得到了迅速發(fā)展,大大提高了夾具的設(shè)計(jì)效率,對(duì)保證產(chǎn)品質(zhì)量,提高生產(chǎn)率,減輕勞動(dòng)強(qiáng)度,縮短產(chǎn)品生產(chǎn)周期等都具有重要意義。同時(shí)工件夾具供應(yīng)商們采用一種合作伙伴方式與用戶工作,開(kāi)發(fā)動(dòng)力系統(tǒng)以提高精度,研究新的材料并開(kāi)發(fā)舊夾具的新處理方法,并發(fā)明了監(jiān)控夾具性能的方法。
3.機(jī)械加工工藝的研究方向
近年來(lái),隨著現(xiàn)代集成制造系統(tǒng)、并行工程等先進(jìn)制造系統(tǒng)的發(fā)展,無(wú)論從廣度上還是從深度上,都對(duì)CAPP 的應(yīng)用提出了更新更高的要求。從先進(jìn)制造技術(shù)發(fā)展戰(zhàn)略出發(fā),CAPP的發(fā)展應(yīng)在符合技術(shù)發(fā)展趨勢(shì)的前提下,更加強(qiáng)調(diào)市場(chǎng)需求,從系統(tǒng)化角度對(duì)面向產(chǎn)品(以整個(gè)產(chǎn)品為對(duì)象)的CAPP集成化(包含工藝信息管理)、智能化、工程化技術(shù)進(jìn)行深人研究,研究CAPP系統(tǒng)體系結(jié)構(gòu)、基于知識(shí)的工藝快速設(shè)計(jì)、工藝管理等基礎(chǔ)性技術(shù)問(wèn)題,滿足制造企業(yè)工藝信息集成系統(tǒng)的需要。
同時(shí)企業(yè)為了提高競(jìng)爭(zhēng)能力,必須進(jìn)行結(jié)構(gòu)調(diào)整和技術(shù)改造,采用新的生產(chǎn)技術(shù)和裝備,發(fā)展新產(chǎn)品,并調(diào)整市場(chǎng)戰(zhàn)略。機(jī)械加工工藝技術(shù)的發(fā)展有以下兩個(gè)最佳化的趨勢(shì):(1)為達(dá)到通過(guò)增加產(chǎn)量來(lái)提高生產(chǎn)率以便提高經(jīng)濟(jì)效益的目的,可以采取不同的措施和方法,其中包括對(duì)新型加工方法和新型刀具的研究。(2)加工技術(shù)的優(yōu)化越來(lái)越多地考慮環(huán)保的因素,例如不再采用冷卻潤(rùn)滑液,依靠科技進(jìn)步,減少?gòu)U物排放,在制造業(yè)實(shí)施綠色制造已勢(shì)在必行。通過(guò)對(duì)新制造技術(shù)的研究,從而達(dá)到合理利用資源及原材料、降低零件制造成本。
4.機(jī)械加工工藝與夾具設(shè)計(jì)技術(shù)的發(fā)展前景
4.1機(jī)械加工工藝技術(shù)的發(fā)展前景
CAPP對(duì)機(jī)械制造業(yè)技術(shù)進(jìn)步主要表現(xiàn)在適應(yīng)當(dāng)前日趨自動(dòng)化的現(xiàn)代制造業(yè)的需要,為實(shí)現(xiàn)計(jì)算機(jī)集成制造系統(tǒng)建立了必要的集成技術(shù)基礎(chǔ),為企業(yè)管理信息系統(tǒng)提供了技術(shù)基礎(chǔ)數(shù)據(jù)源。縱觀CAPP發(fā)展的歷程,可以看到CAPP的研究和應(yīng)用始終圍繞著兩個(gè)方面的需要展開(kāi):一是不斷完善自身在應(yīng)用中出現(xiàn)的不足,二是不斷滿足新的技術(shù)、制造模式對(duì)其提出的新要求。因此,未來(lái)CAPP的發(fā)展,將在應(yīng)用范圍、應(yīng)用的深度和水平等方面進(jìn)行拓展,表現(xiàn)為以下幾個(gè)方面的發(fā)展趨勢(shì):(1)面向產(chǎn)品全生命周期的CAPP系統(tǒng),(2)基于知識(shí)的CAPP系統(tǒng),(3)基于三維CAD的CAPP系統(tǒng),(4)基于平臺(tái)技術(shù)、可重構(gòu)式的CAPP系統(tǒng)。
如何使CAFD系統(tǒng)更加實(shí)用是當(dāng)前CAFD研究者們最為關(guān)注的問(wèn)題。CAFD系統(tǒng)將繼續(xù)朝著集成化、標(biāo)準(zhǔn)化、并行化和智能化的方向發(fā)展,同時(shí)各方向間相互交叉、互相促進(jìn)是CAFD系統(tǒng)發(fā)展的必然方向。
4.2 夾具設(shè)計(jì)技術(shù)的發(fā)展前景
機(jī)床夾具是機(jī)械加工不可缺少的部件,機(jī)床技術(shù)向高速、高效、精密、復(fù)合、智能、環(huán)保方向發(fā)展,在其帶動(dòng)下,夾具技術(shù)正朝著高精、高效、模塊、組合、通用、經(jīng)濟(jì)方向研究。
(1) 高精化:高精機(jī)床加工精度提高,降低定位誤差,提高加工精度對(duì)夾具制造精度要求,機(jī)床夾具精度已提高到微米級(jí),世界知名夾具制造公司都是精密機(jī)械制造企業(yè)。誠(chéng)然,適應(yīng)不同行業(yè)需求和經(jīng)濟(jì)性,夾具有不同型號(hào),以及不同檔次精度標(biāo)準(zhǔn)供選擇。
(2) 高效化:提高機(jī)床生產(chǎn)效率,雙面、四面和多件裝夾夾具產(chǎn)品越來(lái)越多。減少工件安裝時(shí)間,各種自動(dòng)定心夾緊、精密平口鉗、杠桿夾緊、凸輪夾緊、氣動(dòng)和液壓夾緊等,快速夾緊功能部件不斷推陳出新。新型電控永磁夾具,夾緊和松開(kāi)工件只需1-2秒,夾具結(jié)構(gòu)簡(jiǎn)化,為機(jī)床進(jìn)行多工位、多面和多件加工創(chuàng)造了條件。
(3) 模塊、組合化:夾具元件模塊化是實(shí)現(xiàn)組合化的基礎(chǔ)。利用模塊化設(shè)計(jì)系列化、標(biāo)準(zhǔn)化夾具元件,快速組裝成各種夾具已成為夾具技術(shù)開(kāi)發(fā)基點(diǎn)。省工、省時(shí),節(jié)材、節(jié)能,體現(xiàn)各種先進(jìn)夾具系統(tǒng)創(chuàng)新之中。模塊化設(shè)計(jì)為夾具計(jì)算機(jī)輔助設(shè)計(jì)與組裝打下了基礎(chǔ),應(yīng)用CAD技術(shù),可建立元件庫(kù)、典型夾具庫(kù)、標(biāo)準(zhǔn)和用戶使用檔案庫(kù),進(jìn)行夾具優(yōu)化設(shè)計(jì),為用戶三維實(shí)體組裝夾具。
(4) 通用、經(jīng)濟(jì)化:夾具通用性直接影響其經(jīng)濟(jì)性。采用模塊、組合式夾具系統(tǒng),一次性投資比較大,夾具系統(tǒng)可重組性、可重構(gòu)性及可擴(kuò)展性功能強(qiáng),應(yīng)用范圍廣,通用性好,夾具利用率高,收回投資快,才能體現(xiàn)出經(jīng)濟(jì)性好。德國(guó)戴美樂(lè)公司孔系列組合焊接夾具,僅用品種、規(guī)格很少的配套元件,即能組裝成多種多樣焊接夾具。元件功能強(qiáng),使夾具通用性好,元件少而精,配套費(fèi)用低,經(jīng)濟(jì)實(shí)用,很有推廣應(yīng)用價(jià)值。
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[7] 張亞明.機(jī)床夾具的分類與構(gòu)成.[J].科技資訊.2008年第4期
四、主要試驗(yàn)研究?jī)?nèi)容
(一)本課題主要的設(shè)計(jì)內(nèi)容包括
(1)零件的分析;
(2)零件二維圖形及三維圖形的繪制;
(3)工藝規(guī)程設(shè)計(jì);
(3)夾具設(shè)計(jì);
(4)進(jìn)行工藝計(jì)算、填寫工藝文件;
(5)完成指定的工序夾具的設(shè)計(jì)工作,撰寫設(shè)計(jì)說(shuō)明書一份;
(6)設(shè)計(jì)并繪制夾具裝配圖一套(包括二維和三維);
(二)研究方法
(1)分析研究零件圖紙,熟悉設(shè)計(jì)對(duì)象。
(2)設(shè)計(jì)工藝規(guī)程,形成工藝過(guò)程綜合卡片。
(3)設(shè)計(jì)鉆夾具,繪制夾具裝配圖,完成夾具三維造型。
(4)撰寫設(shè)計(jì)論文,闡述設(shè)計(jì)依據(jù),說(shuō)明設(shè)計(jì)內(nèi)涵。根據(jù)已經(jīng)得到的設(shè)計(jì)結(jié)果,闡述其中設(shè)計(jì)的方法和依據(jù),整理成文。
(三)技術(shù)路線
零件的分析—毛坯制造形式選擇—基準(zhǔn)選擇—工藝路線方案制定—相關(guān)分析計(jì)算—夾具設(shè)計(jì)—對(duì)零部件造型
(四)可行性分析
根據(jù)我在大學(xué)期間系統(tǒng)的學(xué)習(xí),包括機(jī)械制造工藝學(xué)、機(jī)械課程設(shè)計(jì)等相關(guān)專業(yè)課程和金工實(shí)習(xí)、生產(chǎn)實(shí)習(xí)等相應(yīng)實(shí)習(xí)課程。在硬件方面,工程訓(xùn)練中心和學(xué)校圖書館提供了良好的學(xué)習(xí)、設(shè)計(jì)環(huán)境,實(shí)習(xí)中看到的機(jī)床實(shí)際造型及在網(wǎng)上搜索到的與設(shè)計(jì)相關(guān)的技術(shù)資料和文獻(xiàn),這些都能夠使我更加直觀,方便的進(jìn)行設(shè)計(jì),同時(shí)還有指導(dǎo)老師的引導(dǎo)和幫助,相信我一定能夠順利按時(shí)完成設(shè)計(jì)。
五、試驗(yàn)(調(diào)查)研究進(jìn)度和預(yù)期結(jié)果
(一)時(shí)間進(jìn)程:
12月底 拿到設(shè)計(jì)題目,熟悉題目和要求
1月~2月初 練習(xí)CAD,Pro/E繪圖軟件,建立零件的實(shí)體造型
2月~3月初 分析零件,進(jìn)行工藝規(guī)程設(shè)計(jì)
3月~4月初 第6道鉆工序夾具結(jié)構(gòu)設(shè)計(jì),繪制裝配圖和三維實(shí)體圖
4月~6月初 整理和撰寫設(shè)計(jì)論文,形成終稿,送審、答辯、修改并裝訂。
(二)預(yù)期結(jié)果
1、零件二維圖形及三維建模
2、手柄座加工工藝工序卡片及過(guò)程綜合卡片
3、第6道鉆工序夾具裝配圖與三維圖
4、設(shè)計(jì)論文
六、指導(dǎo)教師意見(jiàn):
指導(dǎo)教師簽字:
年 月 日
評(píng)議結(jié)果:
所在系(教研室)簽字:
年 月 日
教學(xué)院部意見(jiàn):
系主任簽字:
年 月 日
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題 目:CA6140車床手柄座加工工藝規(guī)程及夾具設(shè)計(jì)
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工學(xué)院畢業(yè)論文(設(shè)計(jì))外文翻譯
題 目:CA6140車床手柄座加工工藝規(guī)程及夾具設(shè)計(jì)
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原文:
20.9 MACHINABILITY
The machinability of a material usually defined in terms of four factors: 1、Surface finish and integrity of the machined part; 2、Tool life obtained; 3、Force and power requirements; 4、Chip control. Thus, good machinability, good surface finish and integrity, long tool life and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone. Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, tool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.
20.9.1 Machinability of Steels
Because steels are among the most important engineering materials (as noted in Chapter 5), their machinability has been studied extensively. The machinability of steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels. Resulfurized and Rephosphorized steels. Sulfur in steels forms manganese sulfide inclusions (second-phase particles), which act as stress raisers in the primary shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels. Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, with built-up edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability. Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant (Section 32.11) and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels. When the temperature is sufficiently high-for instance, at high cutting speeds and feeds (Section 20.6)—the lead melts directly in front of the tool, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means “l(fā)ow carbon,” a condition that improves their corrosion resistance.) However, because lead is a well-known toxin and a pollutant, there are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels). Consequently, there is a continuing trend toward eliminating the use of lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels. Calcium-Deoxidized steels. An important development is calcium-deoxidized steels, in which oxide flakes of calcium silicates (Casco) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear. Temperature is correspondingly reduced. Consequently, these steels produce less crater wear, especially at high cutting speeds. Stainless steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. However, ferrite stainless steels (also 300 series) have good machinability. Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool materials. The effects of other elements in steels on machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels. Carbon and manganese have various effects on the machinability of steels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die steels are very difficult to machine and usually require annealing prior to machining. Machinability of most steels is improved by cold working, which hardens the material and reduces the tendency for built-up edge formation. Other alloying elements, such as nickel, chromium, molybdenum, and vanadium, which improve the properties of steels, generally reduce machinability. The effect of boron is negligible. Gaseous elements such as hydrogen and nitrogen can have particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; 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 embitterment of steels (liquid-metal embitterment, hot shortness; see Section 1.4.3), 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.
20.9.2 Machinability of Various Other Metals
Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulus. Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment. Cast gray irons are generally merchantable but are. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are merchantable with hard tool materials. Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds. Wrought copper can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine, especially with the addition of lead (leaded free-machining brass). Bronzes are more difficult to machine than brass. Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is hydrophobic). Molybdenum is ductile and work-hardening, so it can produce poor surface finish. Sharp tools are necessary. Nickel-based alloys are work-hardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels. Tantalum is very work-hardening, ductile, and soft. It produces a poor surface finish; tool wear is high. Titanium and its alloys have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; 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 coolant-type cutting fluid, however, because of the explosion and fire.
20.9.3 Machinability of Various Materials
Graphite is abrasive. It requires hard, abrasion-resistant, 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 work piece. Tools should be sharp. External cooling of the cutting zone may be necessary to keep the chips from becoming “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or water-soluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be annealed for a period of time at temperatures ranging from C°80 to C°160 (F°175 to F°315), and then cooled slowly and uniformly to room temperature. Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics. Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing, pulling, and edge delaminating are significant problems; they can lead to severe reduction in the load-carrying capacity of the component. Furthermore, machining of these materials requires careful removal of machining debris to avoid contact with and inhaling of the fibers. The machinability of ceramics has improved steadily with the development of nanoceramics (Section 8.2.5) and with the selection of appropriate processing parameters, such as ductile-regime cutting (Section 22.4.2). Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the properties of the individual components, i.e., reinforcing or whiskers, as well as the matrix material.
20.9.4 Thermally Assisted Machining
Metals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heat—a torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arc—is forces, (b) increased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter. It may be difficult to heat and maintain a uniform temperature distribution within the work piece. Also, the original microstructure of the work piece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of high-strength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride. SUMMARY Machinability is usually defined in terms of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of process variables.
譯文:
20.9 可機(jī)加工性
一種材料的可機(jī)加工性通常以四種因素的方式定義:1、分的表面光潔性和表面完整性。2、刀具的壽命。3、切削力和功率的需求。4、切屑控制。以這種方式,好的可機(jī)加工性指的是好的表面光潔性和完整性,長(zhǎng)的刀具壽命,低的切削力和功率需求。關(guān)于切屑控制,細(xì)長(zhǎng)的卷曲切屑,如果沒(méi)有被切割成小片,以在切屑區(qū)變的混亂,纏在一起的方式能夠嚴(yán)重的介入剪切工序。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。在制造廠里,刀具壽命和表面粗糙度通常被認(rèn)為是可機(jī)加工性中最重要的因素。盡管已不再大量的被使用,近乎準(zhǔn)確的機(jī)加工率在以下的例子中能夠被看到。
20.9.1 鋼的可機(jī)加工性
因?yàn)殇撌亲钪匾墓こ滩牧现唬ㄕ绲?章所示),所以他們的可機(jī)加工性已經(jīng)被廣泛地研究過(guò)。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。從而得到了所謂的易切削鋼。二次硫化鋼和二次磷化鋼,硫在鋼中形成硫化錳夾雜物(第二相粒子),這些夾雜物在第一剪切區(qū)引起應(yīng)力。其結(jié)果是使切屑容易斷開(kāi)而變小,從而改善了可加工性。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。化學(xué)元素如碲和硒,其化學(xué)性質(zhì)與硫類似,在二次硫化鋼中起夾雜物改性作用。鋼中的磷有兩個(gè)主要的影響。它加強(qiáng)鐵素體,增加硬度。越硬的鋼,形成更好的切屑形成和表面光潔性。需要注意的是軟鋼不適合用于有積屑瘤形成和很差的表面光潔性的機(jī)器。第二個(gè)影響是增加的硬度引起短切屑而不是不斷的細(xì)長(zhǎng)的切屑的形成,因此提高可加工性。含鉛的鋼,鋼中高含量的鉛在硫化錳夾雜物尖端析出。在非二次硫化鋼中,鉛呈細(xì)小而分散的顆粒。鉛在鐵、銅、鋁和它們的合金中是不能溶解的。因?yàn)樗牡涂辜魪?qiáng)度。因此,鉛充當(dāng)固體潤(rùn)滑劑并且在切削時(shí),被涂在刀具和切屑的接口處。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)。當(dāng)溫度足夠高時(shí)—例如,在高的切削速度和進(jìn)刀速度下—鉛在刀具前直接熔化,并且充當(dāng)液體潤(rùn)滑劑。除了這個(gè)作用,鉛降低第一剪切區(qū)中的剪應(yīng)力,減小切削力和功率消耗。鉛能用于各種鋼號(hào),例如10XX,11XX,12XX,41XX等等。鉛鋼被第二和第三數(shù)碼中的字母L所識(shí)別(例如,10L45)。(需要注意的是在不銹鋼中,字母L的相同用法指的是低碳,提高它們的耐蝕性的條件)。然而,因?yàn)殂U是有名的毒素和污染物,因此在鋼的使用中存在著嚴(yán)重的環(huán)境隱患(在鋼產(chǎn)品中每年大約有4500噸的鉛消耗)。結(jié)果,對(duì)于估算鋼中含鉛量的使用存在一個(gè)持續(xù)的趨勢(shì)。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。一個(gè)重要的發(fā)展是脫氧鈣鋼,在脫氧鈣鋼中矽酸鈣鹽中的氧化物片的形成,這些片狀,依次減小第二剪切區(qū)中的力量,降低刀具和切屑接口處的摩擦和磨損。溫度也相應(yīng)地降低。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。不銹鋼,奧氏體鋼通常很難機(jī)加工。振動(dòng)能成為一個(gè)問(wèn)題,需要有高硬度的機(jī)床。然而,鐵素體不銹鋼有很好的可機(jī)加工性。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。經(jīng)沉淀硬化的不銹鋼強(qiáng)度高、磨蝕性強(qiáng),因此要求刀具材料硬而耐磨。 鋼中其它元素在可機(jī)加工性方面的影響,鋼中鋁和矽的存在總是有害的,因?yàn)檫@些元素結(jié)合氧會(huì)生成氧化鋁和矽酸鹽,而氧化鋁和矽酸鹽硬且具有磨蝕性。這些化合物增加刀具磨損,降低可機(jī)加工性。因此生產(chǎn)和使用凈化鋼非常必要。根據(jù)它們的構(gòu)成,碳和錳鋼在鋼的可機(jī)加工性方面有不同的影響。低碳素鋼(少于0.15%的碳)通過(guò)形成一個(gè)積屑瘤能生成很差的表面光潔性。盡管鑄鋼的可機(jī)加工性和鍛鋼的大致相同,但鑄鋼具有更大的磨蝕性。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。大多數(shù)鋼的可機(jī)加工性在冷加工后都有所提高,冷加工能使材料變硬并且減少積屑瘤的形成。其它合金元素,例如鎳、鉻、鉗和釩,能提高鋼的特性,減小可機(jī)加工性。硼的影響可以忽視。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。氧已經(jīng)被證明了在硫化錳夾雜物的縱橫比方面有很強(qiáng)的影響。越高的含氧量,就產(chǎn)生越低的縱橫比和越高的可機(jī)加工性。選擇各種元素以改善可加工性,我們應(yīng)該考慮到這些元素對(duì)已加工零件在使用中的性能和強(qiáng)度的不利影響。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)1.4.3節(jié)),盡管其在室溫下對(duì)力學(xué)性能沒(méi)有影響。因?yàn)榱蚧F的構(gòu)成,硫能嚴(yán)重的減少鋼的熱加工性,除非有足夠的錳來(lái)防止這種結(jié)構(gòu)的形成。在室溫下,二次磷化鋼的機(jī)械性能依賴于變形的硫化錳夾雜物的定位(各向異性)。二次磷化鋼具有更小的延展性,被單獨(dú)生成來(lái)提高機(jī)加工性。
20.9.2 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。高的切削速度,高的前角和高的后角都被推薦了。有高含量的矽的鍛鋁合金鑄鋁合金也許具有磨蝕性,它們要求更硬的刀具材料。尺寸公差控制也許在機(jī)加工鋁時(shí)會(huì)成為一個(gè)問(wèn)題,因?yàn)樗信蛎浀母邔?dǎo)熱系數(shù)和相對(duì)低的彈性模數(shù)。鈹和鑄鐵相同。因?yàn)樗吣ノg性和毒性,盡管它要求在可控人工環(huán)境下進(jìn)行機(jī)加工?;诣T鐵普遍地可加工,但也有磨蝕性。鑄造無(wú)中的游離碳化物降低它們的可機(jī)加工性,引起刀具切屑或裂口。它需要具有強(qiáng)韌性的工具。具有堅(jiān)硬的刀具材料的球墨鑄鐵和韌性鐵是可加工的。鈷基合金有磨蝕性且高度加工硬化的。它們要求尖的且具有耐蝕性的刀具材料并且有低的走刀和速度。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。黃銅很容易機(jī)加工,特別是有添加的鉛更容易。青銅比黃銅更難機(jī)加工。鎂很容易機(jī)加工,鎂既有很好的表面光潔性和長(zhǎng)久的刀具壽命。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。鉗易拉長(zhǎng)且加工硬化,因此它生成很差的表面光潔性。尖的刀具是很必要的。鎳基合金加工硬化,具有磨蝕性,且在高溫下非常堅(jiān)硬。它的可機(jī)加工性和不銹鋼相同。鉭非常的加工硬化,具有可延性且柔軟。它生成很差的表面光潔性且刀具磨損非常大。鈦和它的合金導(dǎo)熱性(的確,是所有金屬中最低的),因此引起明顯的溫度升高和積屑瘤。它們是難機(jī)加工的。鎢易脆,堅(jiān)硬,且具有磨蝕性,因此盡管它的性能在高溫下能大大提高,但它的機(jī)加工性仍很低。鋯有很好的機(jī)加工性。然而,因?yàn)橛斜ê突鸱N的危險(xiǎn)性,它要求有一個(gè)冷卻性質(zhì)好的切削液。
20.9.3 各種材料的機(jī)加工性
石墨具有磨蝕性。它要求硬的、尖的,具有耐蝕性的刀具。塑性塑料通常有低的導(dǎo)熱性,低的彈性模數(shù)和低的軟化溫度。因此,機(jī)加工熱塑性塑料要求有正前角的刀具(以此降低切削力),還要求有大的后角,小的切削和走刀深的,相對(duì)高的速度和工件的正確支承。刀具應(yīng)該很尖。切削區(qū)的外部冷卻也許很必要,以此來(lái)防止切屑變的有黏性且粘在刀具上。有了空氣流,汽霧或水溶性油,通常就能實(shí)現(xiàn)冷卻。在機(jī)加工時(shí),殘余應(yīng)力也許能生成并發(fā)展。為了解除這些力,已機(jī)加工的部分要在80C°—160C°(175F°—315F°)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。熱固性塑料易脆,并且在切削時(shí)對(duì)熱梯度很敏感。它的機(jī)加工性和熱塑性塑料的相同。因?yàn)槔w維的存在,加強(qiáng)塑料具有磨蝕性,且很難機(jī)加工。纖維的撕裂、拉出和邊界分層是非常嚴(yán)重的問(wèn)題。它們能導(dǎo)致構(gòu)成要素的承載能力大大下降。而且,這些材料的機(jī)加工要求對(duì)加工殘片仔細(xì)切除,以此來(lái)避免接觸和吸進(jìn)纖維。隨著納米陶瓷(見(jiàn)8.2.5節(jié))的發(fā)展和適當(dāng)?shù)膮?shù)處理的選擇,例如塑性切削(見(jiàn)22.4.2節(jié)),陶瓷器的可機(jī)加工性已大大地提高了。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。
20.9.4 熱輔助加工
在室溫下很難機(jī)加工的金屬和合金在高溫下能更容易地機(jī)加工。在熱輔助加工時(shí)(高溫切削),熱源—一個(gè)火把,感應(yīng)線圈,高能束流(例如雷射或電子束),或等離子弧—被集中在切削刀具前的一塊區(qū)域內(nèi)。好處是:(a)低的切削力。(b)增加的刀具壽命。(c)便宜的切削刀具材料的使用。(d)更高的材料切除率。(e)減少振動(dòng)。也許很難在工件內(nèi)加熱和保持一個(gè)不變的溫度分布。而且,工件的最初微觀結(jié)構(gòu)也許被高溫影響,且這種影響是相當(dāng)有害的。盡管實(shí)驗(yàn)在進(jìn)行中,以此來(lái)機(jī)加工陶瓷器如氮化矽,但高溫切削仍大多數(shù)應(yīng)用在高強(qiáng)度金屬和高溫度合金的車削中。小結(jié),通常零件的可機(jī)加工性能是根據(jù)以下因素來(lái)定義的:表面粗糙度,刀具的壽命,切削力和功率的需求以及切屑的控制。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。
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