評估刀架在高強(qiáng)度車床上的可靠性 摘要 可靠性是指一部分的設(shè)備在一段時間內(nèi)達(dá)到給定功能的能力。一個機(jī)械系統(tǒng)或者結(jié)構(gòu)比如一臺機(jī)床要運(yùn)動需要所有的組成部分連接在一起。因此，構(gòu)成整體的部分系統(tǒng)的可靠性決定了整體的可靠性。刀架是一個旨在為加工機(jī)床提供必要功能的設(shè)備。部分用在高硬度機(jī)床上的刀架必須要由更高的可靠性。為了本研究的目的，刀架的可靠性評估，采用了故障率最高的機(jī)床系統(tǒng)的進(jìn)行評估。為了進(jìn)行給定刀架的可靠性評估，使用了失敗率數(shù)據(jù)庫，弱點(diǎn)分析，生產(chǎn)可靠性測試，和可靠性測試計(jì)算和定量計(jì)算。通過這么做，可以計(jì)算故障率，MTBF（平均故障間隔時間）和其他的因素。此外，通過使用建議的評估方法，該研究結(jié)果還可以應(yīng)用于車床的其他部分或者子系統(tǒng)的可靠性評估。 關(guān)鍵詞：可靠性評估，可靠性預(yù)測，失敗率數(shù)據(jù)庫，刀架，平均故障間隔時間，失敗率 1 介紹 最近采用了可靠性概念的生產(chǎn)方式被采用了，而不是簡單的設(shè)計(jì)和生產(chǎn)所有工業(yè)領(lǐng)域都關(guān)注的工程。(Saleh, 2006)可靠性是指一部分的設(shè)備在一段時間內(nèi)達(dá)到給定功能的能力。根據(jù)這種生產(chǎn)方法生產(chǎn)的產(chǎn)品同時滿足用戶需求的質(zhì)量和功能。特別是一個機(jī)械系統(tǒng)或者結(jié)構(gòu)比如一臺機(jī)床要運(yùn)動需要所有的組成部分連接在一起。因此，每個部分的可靠性是很重要的。刀架是一個旨在高效，自動的為加工機(jī)床提供必要功能的設(shè)備。這種裝置的核心單元的精度最終決定了生產(chǎn)出的產(chǎn)品的精度。根據(jù)相關(guān)分析，刀架是眾所周知的失效率最高的機(jī)床子系統(tǒng)的組成部分之一。（RAC，1999）特別是刀架需要連接處理系統(tǒng)—這需要很高的剛度。正如高硬度的機(jī)床需要更高的可靠性一樣。（Kim，2005年）。一般來說，電子零件的可靠性評估是根據(jù)假設(shè)的失效率進(jìn)行分析的。（根據(jù)經(jīng)常使用的bath—tub失效率曲線）在電子零件使用壽命時間內(nèi)是相同的。（Lee，2001，Lee，2006）然而，盡管這樣會增加故障率，但是從機(jī)械零件上獲得盡可能多的可靠性信息是有必要的。之所以這么做是因?yàn)槲覀兡壳皼]有很多關(guān)于機(jī)械零件可靠性的信息(Wang, 1999; Lee, 2003)。在這項(xiàng)研究中,對可靠性評估中使用的刀架車床,使用了定量計(jì)算的可靠性和機(jī)械零件的可靠性信息的計(jì)算進(jìn)行了預(yù)測他們的可靠性通過分析他們的弱點(diǎn)使用機(jī)械部件的故障率;制造可靠性測試工具的可靠性測試后,進(jìn)行測量的可靠性測試等功能的剛度、重復(fù)和角分辨率;可靠性和計(jì)算定量標(biāo)準(zhǔn),等等。 2 可靠性預(yù)測 可靠性預(yù)測指的是努力提高產(chǎn)品在市場上的競爭力,并防止意外事故引起的損失,主要是檢查產(chǎn)品的可靠性的設(shè)計(jì)根據(jù)設(shè)計(jì)預(yù)測其發(fā)展?fàn)顟B(tài)或原型的可靠性，從而在生產(chǎn)開始之前提高其可靠性(Moasoft Inc .,2002)?？煽啃灶A(yù)測方法包括FMEA(失效模式和效果分析)、FTA(故障樹分析),最壞情況分析、性能評估和現(xiàn)場數(shù)據(jù)的方法(客戶服務(wù)數(shù)據(jù)),和故障率數(shù)據(jù)庫方法,等等。為了有效地進(jìn)行可靠性預(yù)測,數(shù)據(jù)(關(guān)于失敗率的信息)每個部分的失敗都是可取的。與電子零件不同,機(jī)械零件的可靠性評估沒有明確定義的故障模式和已知的機(jī)械零件的可靠性數(shù)據(jù)。因此,在這項(xiàng)研究中,我們進(jìn)行了可靠性預(yù)計(jì)使用NPRD95(沒有電子零件的可靠性數(shù)據(jù)部分),NPRD95是一個數(shù)據(jù)庫,其中包含的信息機(jī)械部件的故障率(李,2003)。NPRD95數(shù)據(jù)庫,收集和編輯數(shù)據(jù)從1974年到1994年的數(shù)據(jù),是對機(jī)械部件的故障率唯一的信息來源。這些失敗率遵循一個指數(shù)分布(RAe,1995)。為了尋找有關(guān)可靠性的數(shù)據(jù)，首要要做的是將系統(tǒng)模型化。模型化的基礎(chǔ)數(shù)據(jù)是組成部分的清單，材料和畫圖的費(fèi)用等等。建模完成后,失敗率的可靠性信息應(yīng)該添加進(jìn)入數(shù)據(jù)庫。為了查詢可靠性信息，用戶應(yīng)選擇使用環(huán)境下的故障率的選擇部分,一部分一部分得子分子類型。圖1顯示了一個示例的一個搜索連接器使用NPRD95失敗率銷。工具,如圖2所示,由一個六角頭的工具安裝,支持炮塔的主軸,夾緊部分修復(fù)工具的轉(zhuǎn)動,齒輪(驅(qū)動軸)旋轉(zhuǎn)的工具,傳輸能量和電子接近開關(guān)等傳感器部分。六角頭圖3。分析分部裝配和刀架的主要部分。圖4，可靠性隨時間變化的刀架。傳動齒輪,其失效時間是42.411000百萬小時,同時發(fā)現(xiàn)故障率最低的電力部分,其失效時間是19.687800百萬小時。與失敗率成反比的MTBF的指數(shù)分布,結(jié)果證明，傳動齒輪的平均故障間隔時間最短，電力部分有效時間最長。圖3說明了裝配刀架失敗率的分部和弱點(diǎn)和失敗的主要部分。每個空白的百分比表示每個分部裝配的失敗率時假定刀架的失敗率是100%。這時皮帶、皮帶輪、傳動齒輪的徑向軸承,故障率最高,因?yàn)槭÷屎芨?所以可以當(dāng)成薄弱的部分。因?yàn)樗麄円灿休^高的失敗率,接近開關(guān),Quad-Ring(X-Seal),12把刀具可以插入和安裝在3種類型的刀座中。因?yàn)榇蠖鄶?shù)機(jī)械產(chǎn)品的組件是由螺栓和螺母連接的,我們將刀架分級來進(jìn)行可靠性預(yù)測?？煽啃孕畔?yīng)該根據(jù)標(biāo)準(zhǔn)的規(guī)格,材料,和使用環(huán)境的組成部分來尋找。為了查找關(guān)于材料的規(guī)范,我們可以查找KS規(guī)范手冊0430灰口鑄鐵產(chǎn)品和KS 03709鎳鉻鉬鋼材料,而對于相關(guān)的規(guī)格,我們可以查閱KS內(nèi)部規(guī)范和規(guī)范標(biāo)準(zhǔn)。因?yàn)槲覀儾⒉荒芤恢钡玫剿璧氖褂铆h(huán)境和規(guī)范的組成部分機(jī)械部件,所以我們咨詢了設(shè)計(jì)師，選擇最相似的部分(使用環(huán)境、材料和規(guī)格)?？煽啃钥驁D可靠性計(jì)算方法,表示能量的流動,物質(zhì)和信息顯示系統(tǒng)(王,2004)。在這項(xiàng)研究中,該工具的主要的功能是旋轉(zhuǎn)刀架,主要部分是一系列的傳動系統(tǒng)。為了得出預(yù)測結(jié)果,將刀架的MTBF估計(jì)為8590小時,失效時間估計(jì)為116.408200百萬小時。涉及的可靠性預(yù)測條件有操作溫度30°C GB(地面開始)和GC(地面控制)環(huán)境。關(guān)于分部裝配,最高的失敗率在傳動齒輪,其失敗率是42.411000百萬小時,同時發(fā)現(xiàn)故障率最低的電力部分,其失效時間是19.687800百萬小時。與失敗率成反比的MTBF的指數(shù)分布,結(jié)果證明，傳動齒輪的平均故障間隔時間最短，電力部分有效時間最長。圖3說明了裝配刀架失敗率的分部和弱點(diǎn)和失敗的主要部分。每個空白的百分比表示每個分部裝配的失敗率時假定刀架的失敗率是100%。這時皮帶、皮帶輪、傳動齒輪的徑向軸承,故障率最高,因?yàn)槭÷屎芨?所以可以當(dāng)成薄弱的部分。圖4說明了改變刀架和組成裝配工作的可靠性。分部裝配可靠性大幅下降是傳動齒輪,因?yàn)槠鲃育X輪相對故障率高于其他地區(qū)。此外,我們發(fā)現(xiàn)分部裝配的可靠性幾乎等于來自客戶服務(wù)數(shù)據(jù)失敗的實(shí)際分配率。 3 制造的可靠性和可靠性測試 3.1 刀架的可靠性測試 刀架的失效是索引和夾緊的失效這是最重要的功能。這被認(rèn)為是由于接近傳感器的故障,由于夾緊或泄漏造成的密封部件的磨損。此外,損壞的主軸,有缺陷的零件組裝、部件的磨損，由于重復(fù)加載,和負(fù)載不對稱引起的反彈，由于有偏見的工具安裝，都會導(dǎo)致失效。因此,角分辨率、重復(fù)度、剛度和刀架的平面度對于可靠性是非常重要的元素。表1顯示了可靠性的評估項(xiàng)目的評估工具。引用數(shù)據(jù)是由機(jī)床制造商提供的。角分辨率由一個角度編碼器測量重復(fù)測量,如果值超出參考價值,然后彎曲的耦合磨損,0環(huán)磨損和油壓降低預(yù)期。在穿的弧形耦合,刀架的剛度下降。對于這個測量,弧形耦合可以通過負(fù)載單元測量,可以將造成的負(fù)荷測量轉(zhuǎn)換成價值和剛度的變化。同樣,接近傳感器支架振動和溫度升高引起的連續(xù)操作可以使用一個加速度計(jì)測量傳感器和熱電偶。為了測量上述項(xiàng)目,我們做了一個可靠性測試器的結(jié)構(gòu),如圖5所示。測試人員將其分為傳動部分、測量部分、控制部分和支撐部分。傳動部分由刀架伺服電動機(jī)驅(qū)動,液壓裝置和潤滑裝置,測量數(shù)據(jù)處理的電腦。平板的支承部分由刀架的安裝可靠性測試器,和一個支架的傳感器是固定的,在這項(xiàng)研究中,我們還用表面安裝板的阻尼器。圖6顯示了刀架可靠性測試,實(shí)際上是為本研究研究的刀架。3.2 對刀架的性能評估 我們測試了刀架的性能以確定可靠性測試的最佳操作條件。以便于通過長時間的操作測試性能來定義失效。 3.2.1油壓和剛度/重復(fù)性 刀架的徑向方向的剛度是由油壓的變化在彎曲的耦合。油壓在這項(xiàng)研究中的應(yīng)用是20 ~ 70公斤/ em”和強(qiáng)度造成負(fù)載單元400 n .在測試,下面油壓中的剛度明顯降低40公斤/ em和保持固定的油壓超過40公斤/ em”。此外,對重復(fù)性油壓也有很大的影響。如果油壓過低,重復(fù)性的下降是因?yàn)榛⌒螉A緊力低的耦合。然而,過高的使用油壓在結(jié)構(gòu)方面是不可取的。圖8顯示了根據(jù)油壓的變化可重復(fù)性。如果我們考慮可重復(fù)性，油壓最可取的是50公斤/ern。 3.2 角速度的分辨率和熱膨脹角速度 角分辨率很難建立模型，很難進(jìn)行評估和重復(fù)性精度比較。圖9顯示了通過測量每個指數(shù)的角度不斷的操作后8小時指數(shù)的平均值誤差。鑒于編碼器值的偏移的基本指數(shù)作為測量結(jié)果,我們可以看到一個索引錯誤的0.03°。此外,鑒于錯誤不發(fā)生在只有一個方向,我們可以看到,錯誤不是由不平衡引起的彎曲的耦合。我們?yōu)榱俗袷馗鶕?jù)角分辨率的影響測量了影響旋轉(zhuǎn)索引3和9多次。振動測量的酸度計(jì)安裝在支架用于修復(fù)接近傳感器。圖10所示,我們可以看到,索引的夾緊所造成的影響。 4 可靠性評估 4.1 可靠性測試 通過可靠性試驗(yàn),獲得的結(jié)果可能取決于測試條件。在這項(xiàng)研究中,進(jìn)行性能評估的基礎(chǔ)上,進(jìn)行了可靠性試驗(yàn)。 油壓下60公斤/crr,這被認(rèn)為是保持固定和可重復(fù)性。雖然有其他方法,包括偏心荷載,空載和一致的加載方法等,,我們采用了空載連續(xù)操作的可靠性測試建立刀架的負(fù)載情況,因?yàn)樗呛茈y加速的。我們進(jìn)行了操作重復(fù)刀架的旋轉(zhuǎn)和反彈指數(shù)序列的1 ~ 7 - - > 4 - > 10,操作時間的周期大約是8秒,為了獲得更快的測試結(jié)果。我們測量了編碼器數(shù)據(jù)和傳感器數(shù)據(jù)的差距1000次后(即測量經(jīng)過4000次的索引)為了定量分析測試結(jié)果,并進(jìn)行了100000次的連續(xù)操作。可靠性測試的結(jié)果,總共三個故障發(fā)生。第一次失敗,刀架駐扎本身完全與重復(fù)性約190萬周期后迅速下降后約160萬周期。我們檢查機(jī)油壓力的液壓馬達(dá)提供夾緊力來確定故障的原因,但它是工作得很好,接近開關(guān)也工作正常。雖然第一次失敗的原因不存在,似乎是最可能的原因的振動支架用于修復(fù)接近開關(guān)。開始操作第一次暫停后,沒有在第一次手術(shù)中,但是我們繼續(xù)測試,因?yàn)樗冀K是在基本價值。在第二次失敗,操作120萬次后停止,恢復(fù)正常運(yùn)行后支架修復(fù)接近開關(guān)的搬遷,如第一次失敗。在這方面,我們進(jìn)行了一項(xiàng)惡化接近開關(guān)的測試,但是,生活和接近開關(guān)的性能沒有受到600萬/偏移的影響。因此夾緊的異常操作肯定會造成支架修復(fù)接近開關(guān)的轉(zhuǎn)換。刀架停止大約在一百萬周期調(diào)整接近開關(guān)后。由于失敗的原因的分析,液壓馬達(dá),這是旨在提供夾緊力,不是工作,因?yàn)橛蛪菏?公斤/cm。假設(shè)這是一個液壓系統(tǒng)的問題,我們拆卸工具后,發(fā)現(xiàn),分析后,o形環(huán),旨在傳播夾緊力,已經(jīng)損壞。圖二和圖12顯示了o形環(huán)。 5 結(jié)論 在這項(xiàng)研究中,我們提出一個方法來預(yù)測和評估的可靠性定量刀架通過可靠性預(yù)測、可靠性測試和分析車床刀架用于困難。結(jié)果的基礎(chǔ)上,我們建議的方法努力提高可靠性的車床刀架。結(jié)果區(qū)域:(I)的基礎(chǔ)上我們進(jìn)行了可靠性預(yù)測的可靠性數(shù)據(jù)的組成部分,刀架和結(jié)果符合可靠性測試和客戶服務(wù)研究。(2)我們使用NPRD95失敗率數(shù)據(jù)庫進(jìn)行了可靠性預(yù)測,房屋信息機(jī)械部件的故障率,并預(yù)測平均是8590小時。雖然這是不到10000小時的目標(biāo)生活的工具,它被認(rèn)為是一個錯誤,由于資料的缺乏,機(jī)械零件的可靠性(故障率)和應(yīng)用程序類似的部分比較方法根據(jù)信息的缺乏。(3)我們獲得的數(shù)據(jù)在三個使用可靠性測試失敗,失敗都發(fā)生在傳動部分?？煽啃苑治龅慕Y(jié)果,一個刀架的失敗被發(fā)現(xiàn)是最好的解釋為魏牛分布、和MTBF被魏牛分布在13433小時計(jì)算。(4)然而,以確保一個更可靠的測試的可靠性,增加可靠性的數(shù)量將是明智的測試。我們增加了支架的厚度,從0.7噸到1.0噸,接近開關(guān),建議提高可靠性的方法,如更換薄弱部分,即Quad-Ring和o形環(huán)。 開題報告 動力刀架設(shè)計(jì) 開題報告 1、 綜述 1 研究的意義 目前，在世界機(jī)床制造和機(jī)械加工領(lǐng)域，復(fù)合加工技術(shù)是處于領(lǐng)先地位的技術(shù)。實(shí)現(xiàn)車銑復(fù)合加工，有許多可行方案，而臥式車床床身搭載轉(zhuǎn)塔動力刀架就是其多種方案中應(yīng)用最廣泛的一個。其中，數(shù)控轉(zhuǎn)塔刀架是實(shí)現(xiàn)復(fù)合加工的核心功能部件，不僅可以像普通刀架裝配多把普通車刀，并且能夠同時提供動力驅(qū)動動力刀具，完成銑、鉆、攻絲、鉸孔等加工。 在當(dāng)今市場單件小批量和快速生產(chǎn)的需求的刺激下，催生出了復(fù)合加工。在眾多領(lǐng)域中，車銑復(fù)合加工發(fā)展目前來說已經(jīng)具有一定規(guī)模。在一般的機(jī)械加工領(lǐng)域中,加工主要分為以下兩種方式：第一，工件轉(zhuǎn)動，這種加工方式是車削加工；第二，刀具轉(zhuǎn)動，這種加工方式是加工中心加工。這兩種加工方式的結(jié)合就是車銑復(fù)合加工,它既能夠完成車削功能,同時又能夠完成銑、鏜、鉆、鉸、擴(kuò)等功能。車銑復(fù)合加工不僅是機(jī)械加工的發(fā)展方向之一，同樣也是當(dāng)今世界機(jī)床技術(shù)發(fā)展的大潮流。銑刀旋轉(zhuǎn)、工件旋轉(zhuǎn)、銑刀軸向進(jìn)給和徑向進(jìn)給，在這四個車銑復(fù)合加工機(jī)床的基本運(yùn)動中，要完成這銑刀旋轉(zhuǎn)的動作就需要使用到動力刀架。在引入動力數(shù)控刀架后，車銑復(fù)合加工中心基本實(shí)現(xiàn)了如下幾個目標(biāo): ⑴縮短制造工藝鏈和物流長度;⑵減少裝夾次數(shù)以及工裝夾具數(shù)量;⑶減小使用占地面積，降低了成本。實(shí)現(xiàn)了在確保質(zhì)量的前提下，提高生產(chǎn)率和自動化的程度。 步入新世紀(jì)以來，我國的數(shù)控機(jī)床行業(yè)發(fā)展勢態(tài)愈發(fā)迅猛，主機(jī)技術(shù)向著高速、智能、復(fù)合、環(huán)保方向不斷發(fā)展。動力刀架作為數(shù)控機(jī)床及加工中心重要部件之一，它的性能優(yōu)劣關(guān)系到整臺機(jī)床的性能，甚至深刻影響著我國制造業(yè)整體水平的高低。當(dāng)前市場中，動力刀架技術(shù)已經(jīng)趨近成熟完善，國外很多著名刀架生產(chǎn)商都已設(shè)計(jì)研發(fā)并推廣出自己的系列化產(chǎn)品，國內(nèi)也已有較為完善的生產(chǎn)機(jī)制。但是絕大部分仍然是模仿國外的產(chǎn)品，缺乏自主創(chuàng)新能力，它與國外的先進(jìn)水平相比較，在精度等方面還存在著一定的差距，在一定程度上這會制約機(jī)床發(fā)展。所以，在動力數(shù)控刀架的設(shè)計(jì)上，提高反復(fù)多次定位的精度和降低刀架出現(xiàn)故障的概率意義重大。 2 研究的現(xiàn)狀 動力刀架最早出現(xiàn)于1980年。經(jīng)過30多年的發(fā)展，隨著伺服刀架的出現(xiàn)，動力刀架由最初的外加動力刀具驅(qū)動模塊的形式發(fā)展為現(xiàn)今伺服動力刀架。伺服刀架又分為雙伺服動力刀架以及單伺服動力刀架。 隨著車削中心和車銑復(fù)合機(jī)床模塊化設(shè)計(jì)的發(fā)展以及對功能部件性能參數(shù)和可靠性要求的逐漸提高，在單伺服動力刀架的基礎(chǔ)上衍生出下列動力刀架產(chǎn)品： （1） 內(nèi)置電主軸的直驅(qū)動力刀具刀架結(jié)構(gòu) 這種動力刀架采用內(nèi)置的電主軸直接驅(qū)動動力刀具代替伺服電機(jī)通過傳動系統(tǒng)驅(qū)動刀具，是動力刀具的最大轉(zhuǎn)速得到了提升，可達(dá)到10000r/min。同時刀盤和動力刀座采用了BMT接口，提高了重復(fù)定位精度。此項(xiàng)技術(shù)最先由德國Sauter公司申請專利。 （2） 力矩電機(jī)直驅(qū)式動力刀架 這種動力刀架大幅度減少傳動系統(tǒng)的復(fù)雜性，省去大量零件，使刀架體積變小，性能與功能與原來的伺服電機(jī)驅(qū)動刀盤的動力刀架。但是因?yàn)楹喕藗鲃酉到y(tǒng)，因此可靠性大幅度提升。 （3） 帶Y軸、B軸的動力刀架 目前國外動力刀架的研究均已成熟，德國，日本，意大利，英國等發(fā)達(dá)國家均有成熟的產(chǎn)品運(yùn)用于生產(chǎn)。國外的生產(chǎn)商如德國肖特公司（sauter），意大利巴拉法蒂（baruffaldi）、杜普瑪?shù)峡耍╠uplomatic）等著名的生產(chǎn)商。 世界上最著名數(shù)控轉(zhuǎn)塔刀架生產(chǎn)企業(yè)是德國的Sauter公司和意大利Baruffaldi公司。 這兩家企業(yè)刀架的性能指標(biāo)如表1所示: 表1 國外廠家生產(chǎn)的刀架的技術(shù)參數(shù) 國內(nèi)的動力刀架技術(shù)仍處于發(fā)展階段，目前國內(nèi)動力刀架生產(chǎn)較為著名的生產(chǎn)商有：常州市宏達(dá)機(jī)床數(shù)控設(shè)備有限公司、常州市新墅數(shù)控設(shè)備有限公司、煙臺環(huán)球機(jī)床附件集團(tuán)有限公司、沈陽精誠數(shù)控機(jī)床附件廠。這些廠家中技術(shù)規(guī)格參數(shù)指標(biāo)較高的是沈陽機(jī)床數(shù)控刀架分廠和煙臺環(huán)球機(jī)床附件廠。表2是國內(nèi)兩個廠家生產(chǎn)的兩種型號的轉(zhuǎn)塔刀架的技術(shù)參數(shù)。 表2 國內(nèi)廠家的刀架技術(shù)參數(shù) 圖1 國內(nèi)產(chǎn)品 圖2 國外產(chǎn)品 圖1，圖2分別為國內(nèi)和國外生產(chǎn)的產(chǎn)品 從上面兩表的數(shù)據(jù)就可以看出國外生產(chǎn)的刀架轉(zhuǎn)位速度快，在實(shí)際加工時有較高的效率。45°轉(zhuǎn)位并加緊時間這項(xiàng)種煙臺環(huán)球機(jī)床附件廠生產(chǎn)的刀架的用時是德國肖特公司的一倍。而且兩家國內(nèi)生產(chǎn)廠家的技術(shù)還是從意大利Baruffaldi公司引進(jìn)的。由此可見，國內(nèi)的刀架生產(chǎn)技術(shù)與國外的先進(jìn)水平仍有很大差距。 3 已有成果 目前煙臺環(huán)球機(jī)床附件廠生產(chǎn)的動力刀架均有不錯的性能具體參數(shù)見圖3 圖3 煙臺環(huán)球機(jī)床附件廠的動力刀架參數(shù) 目前，我校研究生在楊慶東教授的指導(dǎo)下也研制出了國內(nèi)首創(chuàng)的力矩電機(jī)直驅(qū)刀架。 力矩電機(jī)直驅(qū)刀架大幅度簡化了刀盤的傳動系統(tǒng)，使刀架體積大幅度減小，由于傳動系統(tǒng)的簡化，刀架的精度以及可靠性也得到了提升。 2、 研究內(nèi)容 1 研究方向 作為大學(xué)生的畢業(yè)設(shè)計(jì)對于動力刀架的設(shè)計(jì)以及研究，要緊跟國內(nèi)外先進(jìn)水平，在了解先進(jìn)動力刀架結(jié)構(gòu)的同時，設(shè)計(jì)出符合畢業(yè)設(shè)計(jì)要求的動力刀架。根據(jù)導(dǎo)師指導(dǎo)建議，設(shè)計(jì)單伺服電機(jī)驅(qū)動動力刀架。 2 研究內(nèi)容 1、 進(jìn)行數(shù)控車削中心動力刀架總體研究，并進(jìn)行整體布局設(shè)計(jì)； 2、 研究各種電機(jī)，為動力刀架選擇合適的電機(jī)； 3、 研究出一種動力切換的可行方案 4、設(shè)計(jì)刀架結(jié)構(gòu)、動力驅(qū)動，完成關(guān)鍵部件的設(shè)計(jì)計(jì)算； 5、完成動力刀架的二維設(shè)計(jì)和三維設(shè)計(jì) 。 3、 實(shí)現(xiàn)方法及預(yù)期目標(biāo) 基礎(chǔ)參數(shù) 動力刀架中心高 120mm 刀位 12 動力到頭最高速度 6000r/min 相鄰刀具轉(zhuǎn)位時間 0.2s 1 實(shí)施的初步方案 動力刀架基本結(jié)構(gòu)：（1）轉(zhuǎn)位驅(qū)動系統(tǒng)(2)動力驅(qū)動系統(tǒng)（3）冷卻裝置（4）精定位裝置（5）裝刀裝置（6）數(shù)控刀架換刀動作。 驅(qū)動方式方案 方案一：采用雙伺服電機(jī)驅(qū)動 雙伺服電機(jī)驅(qū)動的動力刀架是最基礎(chǔ)的動力刀架，技術(shù)成熟，成本相對其他刀架較小。簡圖如圖3 圖3 雙伺服動力刀架簡圖 采用兩個伺服電機(jī)驅(qū)動，伺服電機(jī)1通過液壓機(jī)構(gòu)驅(qū)動刀盤粗分度，再由端齒盤壓緊確定精確分度，伺服電機(jī)2通過齒輪傳動驅(qū)動動力刀具。 方案二：單伺服電機(jī)驅(qū)動動力刀架 簡圖如圖4 圖 4 單伺服電機(jī)驅(qū)動動力刀架簡圖 單伺服動力刀架只采用一個伺服電機(jī)來驅(qū)動刀盤轉(zhuǎn)動和動力刀具，減小了動力刀架的體積，節(jié)省了空間，減少了功率損失。同時比起雙伺服電機(jī)驅(qū)動，單電機(jī)驅(qū)動刀盤和動力刀具，有一個動力切換的問題，難度相對大一些。 方案三：力矩電機(jī)直驅(qū)刀架和電主軸動力模塊 簡圖如圖5 圖 5 力矩電機(jī)直驅(qū)刀架為我校自助研發(fā)的刀架，直驅(qū)刀盤沒有傳動系統(tǒng)精度更高，且電機(jī)在刀盤內(nèi)部，極大減小了刀盤的體積，但是這種技術(shù)還不太成熟，實(shí)現(xiàn)的難度較大。 方案四：力矩電機(jī)外置加上電主軸驅(qū)動動力刀具 簡圖如圖 6 圖 6 力矩電機(jī)外置為安裝動力模塊提供了空間，減小了方案三的難度，但同時也增大了整個刀架的體積。 根據(jù)導(dǎo)師的建議以及本人的能力水平?jīng)Q定采用方案二。采用液壓與齒輪的配合切換動力。單伺服電機(jī)驅(qū)動節(jié)省了較多空間，使刀架體積變小，且只采用一個電機(jī)，提高了功率利用率。 精定位機(jī)構(gòu) 刀具在切削時需要很高的剛性和定位精度，因此刀架選用端齒盤做精定位元件。如圖 7 圖 7 夾緊機(jī)構(gòu) 壓直接鎖緊機(jī)構(gòu)是由液壓油紅直接控制動齒盤的松開和鎖緊,刀架結(jié)構(gòu)簡單且刀盤鎖緊力大,縮短了傳動鏈,提高了傳動效率。為了完成快速剎緊和得到大的剎緊力,松幵和剎緊一般選用液壓和機(jī)械等來實(shí)現(xiàn)。這種機(jī)液結(jié)合的方法可以簡化刀架的結(jié)構(gòu),能夠迅速換向,傳動平穩(wěn),縮短換刀的時間,數(shù)控刀架執(zhí)行動作簡單且刀盤鎖緊力大,提高刀架的分度速度外,同時也使刀具壽命得到提高。 裝刀裝置 裝刀裝置包括刀盤、刀夾及夾刀裝置。目前刀盤有2種模式:歐式VDI刀盤和日式 槽刀盤。 動力刀座選擇 目前在市場上有多種動力刀座如：DIN1809接口類型、DIN5480與DIN5480P接口類型、DIN5482接口類型和梅花式接口類型。 各種類型接口如圖4 圖4各種動力刀座接口 各種接口特點(diǎn)如表3 表3 在此畢業(yè)設(shè)計(jì)中選擇DIN1809接口作為動力刀座的接口。 2 重點(diǎn)、難點(diǎn) 1) 伺服電機(jī)的選擇 2)液壓機(jī)構(gòu)及控制系統(tǒng)的結(jié)構(gòu)設(shè)計(jì) 3)刀盤的旋轉(zhuǎn)定位與精確定位 4）輪系的設(shè)計(jì) 5）整個刀塔系統(tǒng)的運(yùn)動仿真。 6）單伺服電機(jī)驅(qū)動刀盤和動力刀具的協(xié)調(diào)問題 3 擬解決方案 1.參考機(jī)床動力學(xué)常規(guī)建模方式進(jìn)行建模，然后根據(jù)方程進(jìn)行動力學(xué)仿真。然后根據(jù)仿 真結(jié)果，再重新優(yōu)化建模方式。 2.參考實(shí)驗(yàn)室其他實(shí)驗(yàn)平臺的搭建方法，在此基礎(chǔ)上做合理的方法改進(jìn)與技術(shù)的引用。 3.向刀架生產(chǎn)廠家專業(yè)人員請教、研討測試的相關(guān)事宜。 4.通過網(wǎng)絡(luò)和圖書館以及電子圖書館查閱相關(guān)專業(yè)性文獻(xiàn)資料。 5.定期向?qū)焻R報階段性的科研成果，提出階段性的問題，與導(dǎo)師共同商討并解決實(shí)際 問題。 四、對進(jìn)度的具體安排 周次 任務(wù) 5-6 根據(jù)老師的意見對自己的方案進(jìn)行修改；選定各種部件型號， 設(shè)計(jì)整體方案計(jì)算主要參數(shù)，畫出草圖； 7-8 關(guān)鍵零件設(shè)計(jì)計(jì)算強(qiáng)度校核，刀塔總裝配草圖設(shè)計(jì)，動力刀部 分設(shè)計(jì)； 9-10 完成動力部分設(shè)計(jì) 11-12 完成總裝配圖，零件圖，及三維模型 13-14 修改改進(jìn)設(shè)計(jì)及其圖紙 15 完成設(shè)計(jì)說明書 16 準(zhǔn)備答辯，上交論文 五、參考文獻(xiàn) [1] 王家興，馬仕龍.動力刀架的發(fā)展趨勢和應(yīng)用分析[J].機(jī)械工程師，2010，(12). 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[16]蔣宏生.數(shù)控車削中心動力刀架的計(jì)算機(jī)輔助設(shè)計(jì).碩士學(xué)位論文,哈爾濱工業(yè)大學(xué). [17]駱鳴.數(shù)控機(jī)床刀具夾緊系統(tǒng)的改進(jìn)設(shè)計(jì)[J].天津理上大學(xué)學(xué)報,2009(4):85-88. [18]王懷棟. 數(shù)控車床自動回轉(zhuǎn)刀架控制系統(tǒng)簡介.數(shù)字技術(shù)與應(yīng)用2011年 03期? [19]賈德峰. 動力刀架結(jié)構(gòu)參數(shù)優(yōu)化及綜合性能檢測研究.大連理工大學(xué) [20]吉濤; 劉乘.多工位轉(zhuǎn)塔刀架的數(shù)控實(shí)現(xiàn).機(jī)床與液壓 2006年 09期??? 指導(dǎo)教師：（簽署意見并簽字） 年 月 日 督導(dǎo)教師：（簽署意見并簽字） 年 月 日 領(lǐng)導(dǎo)小組審查意見： 審查人簽字： 年 月 日 1 Abstract Reliability refers to the ability of a part,device or system to conduct an intended function in a given condition for a certain period of time.Amechanicalsystemorstructuresuchasamachinetoolexercisesthecapacity of the entire system with regard to the various constituent parts that are connected to each other; as such, the reliability of the parts constituting the system determines the reliability of the entire system. A tool post is a device designed to efficiently provide the tools necessary for the processing of a turning machine:the parts used in a hard turning machine which requires higher stiffness must provide greater reliability. For the purposes of this study, the reliability of a tool post, which has the highest failure rate of a turning machine system, was assessed. In order to conduct a reliability assessment of a given tool post,reliability prediction using a failure rate database,weak point analysis, the manufacture of a reliability tester and the calculation of reliability testing and quantitative reliability criteria were also carried out. By so doing, the failure rate, the MTBF (Mean time between failures) and other factors could be calculated. Furthermore,the results can also be applied to otherpartsoftheturningmachineortoareliabilityassessmentofasubsystem by using the suggested assessment method. Keywords: Reliability assessment; Reliability prediction; Failure rate database; Tool post; Mean time between failures; Failure rate 1. Introduction A production method to which the concept of reliability is applied has recently been used, rather than simple design and production focusing on the functions in all industrial fields (Saleh, 2006). Reliability refers to the ability of a part, device or system to conduct an intended function in a given condition for a certain period of time. Products that are produced according to such a method meet the customers' requirements in terms of both quality and function. In particular, a mechanical system or structures like a machine tool which exercises the capacity of an entire system in which the many constituent parts are connected to each other; as such, the reliability of the parts constituting the system determines the reliability of the entire system. Therefore the reliability of each part is very important (Lee, 2006). A tool post is a device that efficiently and automatically provides the tools necessary for the processing of a turning machine, and the precision of such a device is the core unit that ultimately determines the precision of a processed product. According to the relevant analyses, a tool post is known to have the highest failure rate among the subsystems that constitute a turning machine system (RAC, 1991).In particular,a tool post used in relation to processing in a processing system - which requires high stiffness, such as that provided by a hard turning machine-requires higher reliability (Kim, 2005). In general, the reliability assessment of the electronic parts is conducted on the assumption that the failure rate (according to the bath-tub failure rate curve which is generally used) remains the same during the useful life of the electronic parts (Lee, 2001; Lee, 2006). However, although the failure rate of the mechanical parts tends to increase, it is an essential to obtain as much information on the reliability of mechanical parts as possible, all the more so because we don't currently have much information on the failure rate of mechanical parts (Wang, 1999; Lee, 2003). In this study, with regard to the reliability assessment of the tool post used in a hard turning machine, the quantitative calculation of reliability and the calculation of the reliability information of the mechanical parts were conducted by forecasting their reliability and analyzing their weak points using the failure rate of the mechanical parts;manufacturing a reliability tester for the reliability testing of a tool post; carrying out a reliability test for the measurement of such functions as stiffness, repetition and angular resolution; and calculating the quantitative reliability criteria, and so forth. 2. Reliability prediction Reliability prediction refers to the efforts made to enhance the competitive power of a product in the market and to prevent losses caused by unexpected accidents, mainly by checking the reliability of the product's design according to its development state or by forecasting the reliability of a prototype, thereby enhancing its reliability before production starts (Moasoft Inc., 2002). The reliability prediction methods include FMEA (Failure Mode and Effect Analysis), FTA (Fault Tree Analysis), Worst Case Analysis, performance assessment and the field data method (Customer Service Data), and the failure rate database method, and so on. To conduct reliability prediction effectively,data (information on the failure rate) on the failures of each part is desirable. Unlike electronic parts, there is no clear definition of the failure mode and known reliability data for mechanical parts. Therefore, in this study,we conducted a reliability prediction using the NPRD95 (Nonelectric Part Reliability Data 95), a database containing information on the failure rate of mechanical parts(Lee, 2003). The NPRD95 database, which holds collected and edited data accumulated from 1974 to 1994, is the only source of information on the failure rate of mechanical parts. These failure rates follow an exponential distribution (RAe, 1995). In order to search for information on reliability,modeling of the system is required first of all.The basic data for modeling are the parts list,bills of materials and drawing, and so on. Once modeling has been completed, the reliability information should be entered using the failure rate database. For reliability information, the user chooses the failure rate under the usage environment in the part selection set to part, part sub-type. Figure 1 shows an example of a search of the Connector Pin for the failure rate by using the NPRD95. A tool post, as shown in Fig. 2, is composed of a turret head to which the tools are mounted, a main shaft that supports the turret, a clamping part to fix the rotation of the tool, gears (drive shaft) to transmit power for the rotation of the tool, and electrical sensor parts such as a proximity switch. The turret head has a Fig. 3.Analysis of the sub-assembly and main parts of the tool post. Time Fig. 4.. Reliability change of the tool post and sub-assembly over time. drive-gear, whose failure rate is 42.411000 failures/ million hours, while the lowest failure rate is found in the electricity parts, whose failure rate is 19.687800 failures/million hours. The failure rate being in inverse proportion to the MTBF in an exponential distribution, the result means that the mean time between failures of the drive gear is shortest and the failure rate of the electricity parts is longest. Figure 3 illustrates the failure rate of the sub-assembly of the tool post and the weak points and failure rate of the main parts. The percentage of each blank indicates the failure rate of each sub-assembly when it is assumed that the failure rate of the tool post is 100%. The Timing Belt, Pulley and Radial Bearing of the Drive Gear, which has the highest failure rate, have a high failure rate and therefore can be expected to be weak parts. As they also have a high failure rate, the Proximity Switch, Quad-Ring (X-Seal), 3 piece type holder into which 12 tools can be inserted and installed. Because most mechanical products are composed of components that are linked to each other by rings, bolts and nuts, we classified the composition of the tool post to a single level for reliability prediction. The reliability information should be searched for according to the standards of the specifications, materials, and usage environment of the constituent parts. For the material-related specifications, we referred to the specifications manual of KS 0430I gray cast iron products and KS 03709 nickel chrome molybdenum steel materials, while for parts-related specifications, we referred to the KS specifications and in-house specifications standard. Because the desired usage environment and specifications of the constituent mechanical parts are not always available, we selected the most similar parts (usage environment, materials and specifications) in consultation with the designer. A reliability block diagram is a method for calculating failure rate-related reliability by expressing the flows of energy,matter and information shown by the system (Wang, 2004). In this study, where the tool rotation of the tool post is regarded as the main function, the main parts were put together by series connection. For the prediction results, the MTBF of the tool post was estimated at 8,590 hours and the failure rate at 116.408200 failures/million hours. The reliability prediction conditions involved an operation temperature of 30°C in a GB (Ground Begin) and GC (Ground Controlled) environment. With regard to the sub-assembly, the highest failure rate is found in drive-gear, whose failure rate is 42.411000 failures/ million hours, while the lowest failure rate is found in the electricity parts, whose failure rate is 19.687800 failures/million hours. The failure rate being in inverse proportion to the MTBF in an exponential distribution, the result means that the mean time between failures of the drive gear is shortest and the failure rate of the electricity parts is longest. Figure 3 illustrates the failure rate of the sub-assembly of the tool post and the weak points and failure rate of the main parts. The percentage of each blank indicates the failure rate of each sub-assembly when it is assumed that the failure rate of the tool post is 100%. The Timing Belt, Pulley and Radial Bearing of the Drive Gear, which has the highest failure rate, have a high failure rate and therefore can be expected to be weak parts. As they also have a high failure rate, the Proximity Switch, Quad-Ring (X-Seal), 3 piece type curvic coupling and the Proximity Sensor of the electric parts are expected to break down during actual operation. Figure 4 illustrates the change in the reliability of the tool post and the constituent sub-assembly over time.The sub-assembly that reliability declines sharply is drive gear because the failure rate of the timing belt of the drive gear has a relatively higher failure rate than the other parts. In addition, we found that the reliability of the sub-assembly was almost equal to the failure distribution rate derived from actual customer service data. 3. Manufacture of a reliability tester and reliability testing 3.1 Tool post reliability tester The failure of a tool post is the failure of indexing and clamping, which are the most important functions of a tool post.This is thought to be the result of a malfunction of the proximity sensor, which senses clamping or leaks caused by wear and tear of the sealing parts. In addition, damage to the main shaft, the defectiveness of parts assembly,the wear of parts due to the repetition of loads, and the backlash caused by loads asymmetry due to biased tool installation also lead to failure. Therefore, the angular resolution, repetition degree, stiffness and flatness of a tool post are very important elements of function and reliability. Table 1 shows the assessment items for a reliability assessment of a tool post. The reference data are made by machine tools maker. Angular resolution and repetition are measured using an angle encoder, and if the values fall outside the reference value, then curvic coupling wear, 0Ring wear and oil pressure decrease are forecast. In the case of wear of the curvic coupling, the stiffness of the tool post decreases. For this measurement, the wear of the curvic coupling can be measured by inflicting loads with a load cell, measuring the transformation value and the stiffness change. Equally, the proximity sensor bracket vibration and temperature increase caused by continual operation can be measured using an accelerometer sensor and thermocouple. In order to measure the aforementioned items, we made a reliability tester for the structure, as shown in Fig. 5. The tester is divided into a drive part, measurement part, control part and supporting part. The drive part is composed of a servomotor to drive the tool post, a hydraulic device and lubricating device; the measured data are processed in the PC. The supporting part is composed of a surface plate on which the tool post reliability tester is installed, and a bracket to which the sensor is fixed, In the study, we also used a surface plate on which a damper is installed.Figure 6 shows the tool post reliability tester which was actually made for this study. 3.2Assessmentofthe performance of the tool post We measured the performance of the tool post in order to determine the optimum operational conditions for reliability testing. This was conducted so as to define a failure by consecutively measuring performance in a long operation. 3.2.1 Oil pressure and stiffness/repeatability The stiffness of the radial direction of the tool post is determined by the change of the oil pressure on the curvic coupling. The oil pressure applied in this study is 20~70 kg/em' and the strength inflicted by the load cell is 400 N. In the test, the stiffness decreased noticeably in oil pressure below 40 kg/em' and remained fixed for oil pressure of more than 40 kg/em'. Figure 7 illustrates the change in stiffness according to the change in oil pressure. The optimum stiffness for maintaining the stiffness of a tool post requires oil pressure ofatleast40kg/em'. Moreover, oil pressure also has a great impact on repeatability. If oil pressure is too low, repeatability declines because of the low clamping force of the curvic coupling. However, the use of too high a level of oil pressure is not desirable in the structural aspect either. Figure 8 illustrates the change of repeatability according to oil pressure. Oil pressure proved most desirable at 50 kg/ern" if we consider repeatability; because repeatability meets the basic value in oil pressure over 50 kg/ern' and fails to meet the basic value in oil pressure below 50 kg/ern', 3.2.2Angularresolution and thermal expansion Angular resolution, for which the absolute basis is difficult to establish, is harder to assess in comparison with repeatability precision. Figure 9 shows the average value of index errors by measuring the angles of each index after incessant operation for 8 hours. As shown in Fig. 9, the basic index is 9, but the indexing error does not show a consistent tendency. Given the offset of the encoder value by the basic index as a result of measurement, we can see an indexing error of about O.03°s. In addition, given that the error does not occur in only one direction, we can see that the error is not caused by the lopsided curvic coupling. We measured the impact by rotating indexes 3 and 9 repeatedly in order to observe the impact according to the angular resolution. Vibration was measured by an acidometer installed on the bracket used to fix the proximity sensor. As Fig. 10 illustrates, we can see that the impact caused by the clamping of the indexingindexing of3isnearly 10times higherthan that ofthe indexing of 9, which supports the findings of the angular resolution test above. If the indexing is conducted incessantly, thermal expansion occurs in the tool post. Thermal expansion can be measured with a gap sensor installed in the radial axial direction. Thermal expansion was found to be 0.5 um in the radial direction and l.Oum in the axial direction after 72 hours of operation. In the following consecutive operation, no more thermal expansion occurred. Therefore, the failure ofatoolpostcanbedefined as follows; (1) oil pressure isbelow 60 kg/ern', (2) the repeatability is over 0.005°, (3) the thermal expansion is over l.Oum in the radial or axial direction, (4) tool post is stopped. That is, one of the mentioned items leadsto failure ofthetoolpost. 4. Reliability assessment 4.1 Reliability test Through a reliability test, a variety of results may be obtained depending on the test conditions. In this study, on the basis of the performance assessment conducted above, the reliability test was carried out under oil pressure of 60 kg/crrr', which is thought to keep the stiffuess and repeatability fixed. Although there are other methods, including the eccentric loading, non-loading and consistent loading methods and so forth, for establishing the load condition for the tool post, we adopted non-loading continuous operation for the reliability testing because it was difficult to select the accelerating force. we conducted the operation repeating the rotation and backlash of the tool post index in a sequence of 1~7-->4->10, where the operation time of a cycle was approximately 8 seconds, in order to obtain the test results more quickly. We measured the encoder data and gap sensor data once after 1,000 cycles (that is, measured after 4,000 times of indexing) in order to quantitatively analyze the test results, and conducted 100,000 cycles of consecutive operation. As a result of the reliability test, three failures occurred in total. In the first failure, the tool post stationed itself completely after about 1.9 million cycles with repeatability rapidly falling after about 1.6 million cycles. We checked the oil pressure of the hydraulic motor supplying the clamping force to identify the cause of the failure, but it proved to be working well, as did the proximity switch. Although the eause of the first failure was not found,the most probable cause seems to be the vibration of the bracket used to fix the proximity switch. The repeatability of the tool post, which started operation after the first halt, was not as high as in the first operation, but we continued the test because it remained within the basic value. In the second failure, the operation stopped after 1.2 million cycles and normal operation resumed after relocation of the bracket fixing the proximity switch, as in the first failure. In this respect, we conducted a deterioration test of the proximity switch, but the, life and performance of the proximity switch were not affected by 6 million on/offs. Therefore the abnormal operation of clamping is sure to be caused by the transformation of the bracket fixing the proximity switch. The tool post stopped at about the millionth cycle after readjustment of the proximity switch.As a result of the analysis of the cause of the failure, the hydraulic motor, which was intended to supply the clamping force, wasn't working because the oil pressure was 0 kg/ern'. Assuming this to be a problem with the hydraulic system, we disassembled the tool post and found, after analysis, that the O-ring, which was intended to transmit the clamping force, had been damaged, and the quad-ring was worn. Figures II and 12 show the damaged part of the O-ring and wear of the quad-ring. 4.2 Reliability analysis We operated the tool post for about 4.1 million cycles for a reliability test, during which three failures occurred. From this, we reasoned that the life of a tool post is about 1.8 million cycles, that of a hydraulic one is 4.1 million cycles, and that the most frequent cause of failure is not the life of the proximity switch itself but the displacement of the bracket fixing the proximity switch. We analyzed the reliability of the tool post on the basis of the data obtained from there liability test.The data that should be collected for a reliability analysis include failed parts, failure time, failure mechanism, failure mode, usage conditions and the measures taken against failure, and so forth. Of these, the failure time, usage conditions and number of failures are the important elements to be used in an analysis of the failure rate. That is why we calculated th