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南昌航空大學(xué)科技學(xué)院學(xué)士學(xué)位論文
畢業(yè)設(shè)計（論文）外文文獻(xiàn)翻譯
題目 升降式路邊停車系統(tǒng)機械部分的設(shè)計
專 業(yè) 名 稱 機械設(shè)計制造及其自動化
班 級 學(xué) 號 078105120
學(xué) 生 姓 名 王飛翔
指 導(dǎo) 教 師 熊麗娟
二O一一年 三 月
刀具和刀夾
想順利的加工工件，就必須做到：
1． 刀具或刀片的種類要恰當(dāng)。
2． 刀夾的類型要合適。
3． 刀具的切削刃要鋒利。
4． 刀具要安裝或調(diào)整到適當(dāng)?shù)奈恢煤透叨取?
刀具的材料
制造車床上使用的刀片的基本材料有以下六種：水淬硬化鋼，高速鋼，硬鑄有色合金，燒結(jié)硬質(zhì)合金，陶瓷和金剛石。使用材料的選擇取決于許多因素：刀具成本，刃磨費用，刀具的尺寸和類型，金屬切削速率，使用時間的長短，零件的光潔度和公差，以及機床的條件和性能。由于有著許多因素，選擇材料常常是根據(jù)一般的經(jīng)驗而不是精確計算。然而，對各種不同刀具材料的某些一般特性是應(yīng)該有所了解的。
水淬硬化鋼
這一類包括高碳工具鋼（即普通碳鋼或加入了少量鉻，釩或鎢的碳鋼）。在美國鋼鐵協(xié)會的分類制中，把各種鋼號的水淬工具鋼都?xì)w為W鋼。用這種材料制造的刀具經(jīng)過適當(dāng)?shù)臒崽幚恚淝邢魅斜惴浅ｄh利，光滑。它們適用于切削速度較低的有限車削，或使用于老式的，低轉(zhuǎn)速設(shè)備，如平皮帶車床上。
用水淬工具鋼制造的刀具其主要的缺點是在刃磨或切削時，切削刃溫度如果超過華氏300~400度，刀具就會軟化。另一個缺點是刃口的耐磨性很低。
高速鋼
高速鋼在切削效率方面同水淬工具鋼相比有很大的改進(jìn)。用高速鋼制成的刀具甚至當(dāng)?shù)毒邷囟冗_(dá)到華氏1050度時，還能保持足夠的硬度進(jìn)行高速切削。即使熱的變成暗紅色，它們還能使用。冷卻至室溫后，這種鋼原來的硬度也不改變。
高速鋼的抗磨性比碳鋼或合金鋼的抗磨性要好的多，這是由于它的含碳量高，尤其在合金成分較高的高速鋼里更是如此。高速鋼由于充分淬火，比碳鋼或硬鑄合金有更高的抗沖擊強度。
美國鋼鐵協(xié)會分類制規(guī)定的有兩種主要的高速鋼，一種是M鋼，一種是T鋼?？梢再I到由這些材料制成的，刃磨成各種形狀的刀條。未經(jīng)刃磨的刀條叫做刀坯，也是可以購買到的。這類刀坯都制成標(biāo)準(zhǔn)尺寸以適應(yīng)普通車床使用。常見的尺寸是3/16英寸見方乘1英寸，1/4英寸見方乘2英寸長，5/16英寸見方乘2。5英寸長，和3/8英寸見方乘3英寸長。高速鋼刀條是校辦機加工車間里最常見的。
硬鑄合金
這類材料不含有足夠的鐵，因而不能算作鋼。相反它們主要是鈷，鉻，鎢和為了特殊用途而加一些其它元素的合金。它們在鑄造狀態(tài)下，不用熱處理，即可達(dá)到充分的硬度。它們在鑄造后，必須磨削至應(yīng)有的尺寸。就其耐熱性，耐磨性，抗沖擊性幾生產(chǎn)成本而言，鑄合金可排在高速鋼和硬質(zhì)合金之間。
硬鑄合金的抗拉強度比較差而且比高速鋼更脆，因而不適用于強烈的沖擊載荷。它們在商業(yè)上的名稱是司太立鎢鉻鈷合金，銳克斯鎢鉻鈷合金和坦塔鎢鉻鈷合金。
燒結(jié)硬質(zhì)合金
要進(jìn)行高效和高速車削，使用燒結(jié)硬質(zhì)刀片形狀合金刀可以得到最佳效果。市場上買到的硬質(zhì)合金有的做成整體形狀，有的做成刀片形狀焊接在刀桿上，或著我卡緊在刀桿上。裝卡的刀片其形狀通常是圓的，方的或三角行的，它上面所有的切削刃都是預(yù)磨好的。這類刀片能夠轉(zhuǎn)動，所以隨時可得到鋒利的切削刃。使用現(xiàn)代化的機床和級別適當(dāng)?shù)臒Y(jié)硬質(zhì)合金刀有可能采用比高速鋼車刀要快10~30倍的切削速度。
硬質(zhì)合金刀適用于大多數(shù)的機加工作業(yè)，如單刀刃車削，鉆削，洗削，螺紋車削和鉸削。只有當(dāng)硬質(zhì)合金刀能夾持得很牢固而且機床具有合適的功率與轉(zhuǎn)速使其能發(fā)揮有效作用時才應(yīng)采用硬質(zhì)合金刀。
金屬陶瓷
除了工業(yè)用金剛石以外，金屬陶瓷刀片是現(xiàn)有的最硬，最強有力的刀片。他們抗磨損，抗碎裂，抗斷折。這類刀片用在剛性良好的床子上，對夾持牢固的工件能發(fā)揮最好的作用。在大多數(shù)加工情況下，不需要切削液。
金剛石
當(dāng)需要極高質(zhì)量的表面光潔度時，可采用工業(yè)用金剛石作精加工。這種金剛石具有圓形或小平面的切削刃。盡管使用別種刀具材料能取得很光滑的光潔度，但金剛石車削可在公差很小的情況下，提供更加光滑的光潔度。
刀夾
刀夾在切削加工時可使刀具夾持牢固。常用的夾具有以下四種：
1． 帶有標(biāo)準(zhǔn)刀夾的刀架
刀架由支架，螺桿，墊圈，套圈，調(diào)整墊板組成。墊圈嵌在上滑塊槽內(nèi)。套圈和調(diào)整墊板可是刀尖上升或下降。螺桿則將刀夾固定就位。
高速工具刀條的標(biāo)準(zhǔn)刀夾有三種常見的形狀：直刀夾，右偏刀夾和左偏刀夾。用手拿住固定螺釘?shù)囊欢?，便可判斷刀夾是右偏還是左偏。如果刀把偏向右，就是右偏刀夾。如果刀把偏向左，便是左偏刀夾。
直刀夾可用于大多數(shù)加工活兒。當(dāng)需要接近卡盤或雞心夾卡箍進(jìn)行切削時，便可使 用左偏夾。右便刀夾是當(dāng)朝著尾架方向進(jìn)給時使用的。在這三種刀夾上，刀條均以14到16。5的角度固定。這便是所謂刀夾角度。
硬質(zhì)合金刀頭的刀夾也有三種形式，在外表面上與上述高速鋼的刀夾類似。但是夾持刀片的孔和刀夾的底邊是平行的。
2． 開口刀架或稱重型刀架一次可以夾持一把刀，它上面有一個帶T形槽的壓板，一個C型塊，和兩個或多個刀具價緊螺絲。因為這種裝置非常牢靠，它尤其適用于重切削。刀條可以直接裝卡于這種刀架內(nèi)，也可以使用某種類型的硬質(zhì)合金刀夾。
3． 轉(zhuǎn)塔刀架或稱方刀架有一回轉(zhuǎn)塊，車刀可以裝于其中。常見的轉(zhuǎn)塔刀架可以裝四把刀。每把刀都能很快地回轉(zhuǎn)至切削位置并價緊。某些轉(zhuǎn)塔架具有八個刀位。通常，為了增加一個附加的加工工序，可在橫向流板的后部安裝一開口型刀架。采用這種安排，可裝上5~9把不同類型的刀具，就可以按順序?qū)χ貜?fù)型零件進(jìn)行車外圓，成形，車端面，滾花和切斷等工序。
4． 速換型刀具系統(tǒng)一次只夾持一把刀具，但它的三個不同的側(cè)邊均可以用來裝置刀具。它有一個帶夾緊桿的快速換刀架，可安裝一系列的刀夾作車外圓，車端面，鏜孔，切斷，攻絲，滾花和車螺紋。
單刃切削刀具
刀具的各個部分
在認(rèn)磨刀條之前，必須熟悉表明刀具各不同部分的一些術(shù)語
1．頂面 是刀條的頂部，它是當(dāng)切削的一部分從工件上切下時刀條被切下的這一部分切屑所緊貼著的那個表面。
2．切削刃是刀條實際進(jìn)行切削的那一部分。
3．刀尖是側(cè)切刃和端切刃所形成的夾角或圓弧。
4．側(cè)面是切削刃以下的表面。
5．刀頭是刀片上構(gòu)成切削刃和頂面的那一部分。
刀具的角度
用于一切單刃切削刀具的重要刀具角度如下：
1． 橫向后角是刃磨表面和刀條在刃磨之前的垂直側(cè)邊之間的夾角。這個角度以前叫橫向隙角，現(xiàn)在許多機工仍然采用這個術(shù)語。橫向后角是工件的切削表面和刀具側(cè)面之間的隙角。刀具的磨損會使有效橫向隙角變小，如果這個交度太小，刀具就會摩擦，生熱。如果這個角度太大，切削刃就會變鈍，而刀具就易扎進(jìn)工件里。
2． 縱向后角是切削刃末端和一垂直線之間的形成的夾角。以前這個角叫前向隙角。縱向后角是工件的已加工表面和刀具之間的間隙。如果這個角度太小，刀具將在已加工表面上摩擦從而產(chǎn)生不良的表面光潔度。磨損會使這一角度變小。如果著這一角度太大，刀具可能扎進(jìn)工件，引起顫動，并由于崩刃而無法切削。對于鋼制刀具，這一角度建議采用8~15度，硬質(zhì)合金刀具建議用6~8度。如果刀具安裝的高于旋轉(zhuǎn)中心，就會使有效隙角變小。在選擇合適的角度時，必須考慮到這一點。
3． 端刃角是刀具和工件已加工表面之間的夾角。如果這個角太小，就會造成顫動。然而為了形成光滑的表面光潔度，在精加工時，采用大約6度的小角度是合適的。
4． 側(cè)刃角可將切屑從已加工表面卷走。角度最好在5~15渡之間。
5． 刀尖半徑可使刀具不致有脆弱的尖角，可以延長刀具的壽命并改進(jìn)表面光潔度。對于高強度的粗切刀，半徑可大一些，而對于輕量進(jìn)給則可以小一些。只要沒有顫動產(chǎn)生，刀尖半徑越大，光潔度就越好。對于精加工，刀尖半徑建議采用0。010到0。030英寸或更大，對于粗加工是1/32到1/2英寸。
6． 為了有助于形成切削刃和頂面，必須在刀條上刃磨出兩個前角來。從垂直面或水平面上傾斜就形成前角。當(dāng)?shù)稐l頂面是平的或水平是，它沒有前角。這兩個前角就是縱向前角和橫向前角/
縱向前角，在向側(cè)面單刃進(jìn)給時，可將切削從已加工的工件上卷走，同時使刀具有一種切片的作用?？v向前角為零時，易形成蝸旋形切削，而當(dāng)縱向前角大于零時，它易于使蝸旋形切削伸展為螺旋形切屑/使用5~15度的縱向前角可防止切削刮到工件上。高速鋼刀條通常都刃磨成正前角。然而硬質(zhì)合金刀具可能具有正的或負(fù)的前角。負(fù)前角可使形成切削的剪角增大，造成良好的表面光潔度。負(fù)前角刀具一般可在高速，大走刀的重型車床上使用。
橫向前角指的是刀具的頂面和刀具刃磨前從摸端看過去代表其頂部的那根線之間的夾角。橫向前角可控制機加工時所產(chǎn)生的切屑的形狀以及切屑的移動方向。橫向前角小的刀具比前角大的刀具所產(chǎn)生的切屑要短一些。
7． 刀尖角是側(cè)切刃和端切刃之間的夾角。
單刃切削刀具的分類
為了進(jìn)行某些機加工工序需要不同形狀的刀條，大多數(shù)刀條都刃磨成只朝一個方向切削。其常見的類型現(xiàn)在叫做有切刀和左切刀。以前叫做右偏刀和左偏刀。
右切單刃刀是一種當(dāng)頂面朝上，從刀尖方向看過去切削刃的右邊的刀具。這種刀條裝在車床上，它的切削刃就在左邊。這種刀條是從右向左，即從尾架那一端朝車床的床頭方向切削的。
左切刀是當(dāng)頂面朝上，從刀尖方向看過去切削刃在左邊的刀具。這種刀具都刃磨成從左向右切削的，即朝車床的尾架方向切削的。
常用的刀條類型有以下幾種：
1． 粗車刀是一種用來進(jìn)行重切削，把工件直徑切至接近尺寸的刀具。因為在粗 加工時，表面光潔度是不重要的，這樣的刀條可以刃磨成幾乎是鋒利的到尖。不過，這樣的刀尖通常要稍微磨成圓弧狀以防止崩刀。
2． 精車刀有磨的很鋒利的切削刃，這種切削刃經(jīng)油石研磨可產(chǎn)生非常光滑的光潔度。精車刀通常具有比粗車刀更大的圓弧尖。
3． 圓頭刀是一種可以用于多種類型的通用刀具。當(dāng)頂部磨平時，它既能用于右切也能用于左切，還能車削黃銅。它也可以用來在軸肩角處切削半徑。圓頭刀可用來作精車刀具。
4． 方頭刀只用于工件末端的切削。它用來倒角和粗車以加工方形肩。
5． 切斷刀只用于工件末端的切削，可用來切斷裝卡在卡盤上的棒料或工件。
6． 端面偏刀即通常所謂的偏刀，用來把工件的端部精車成與母線成直角的光滑的端面。右切端面偏刀總是用語精車軸的端部。左切端面偏刀可以用來精車軸肩的左側(cè)。
斷屑槽
為了解決切屑延續(xù)不斷的這一難題，常?？梢栽诟咚黉摰都馍先心コ鲆粋€斷屑槽。斷屑槽能夠在一般磨刀砂輪上刃磨出來，而槽形的斷屑槽則能由一個裝在平面磨床上的薄砂輪刃磨出來。另一種單獨的斷屑器常用于裝卡式硬質(zhì)合金刀上。
切削作用
當(dāng)車床車削時，有三個基本切削力，即：工件的縱向力，作用于刀具的側(cè)面；工件的徑向力，作用于刀具的前端；工件的切向力，作用于刀具的頂部。其中切向力比其他兩個力要大的多，它對切削作用的影響也最大。這一巨大的作用力是加在切削刃上的。在大型金屬切削機床上的測量表明，每平方英尺上的壓力可達(dá)到25萬磅。假如刀具形狀不合適或裝卡角度不合適，刀具很快就會變鈍。
在車床上切削時，就會從正在加工的材料上擠下片狀的切屑。即連續(xù)的金屬帶。在軟的，韌性材料上，這種楔擠作用是連續(xù)進(jìn)行的。再較硬的材料上，楔擠力使金屬受壓縮。壓縮一直延續(xù)到剪斷為至。于是被擠壓的金屬就與工件脫離。在切削加工中始終重復(fù)這一過程。
刀具的形狀比切削刃的實際鋒利程度更加重要的多。刀具沒有后角就會使刀具在工件上磨蹭。這樣加大了對切削刃的壓力，從而影響刀具的性能。后角太大會使刀具脆弱無力，不能很好支撐切削刃。這樣刀口就會迅速折斷或磨損。
刃磨高速工具鋼刀條
1． 使刀具具有銳利的切削刃。
2． 使刀條為特定的工序提供正確的或最好的形狀。
3． 使刀條的前端留有隙角。
4． 使刀條的側(cè)面留有隙角。
5． 使切屑能在刀條頂面順利滑過，并脫離切削刃。
刃磨右切圓刀頭的正確程序如下：
1． 檢查砂輪，看砂輪表面是否修整好。再不平的或有溝的砂輪上刃磨出好的切削刃是困難的。應(yīng)在刃磨切削刀具的專用臺式磨床或立式砂輪機上進(jìn)行刃磨。在這種砂輪機的一邊應(yīng)安裝一個氧化鋁粗砂輪另一邊裝一個細(xì)砂輪。使用粗砂輪把刀條粗磨成一定的形狀。然后用細(xì)砂輪精磨刀條。
2． 刀具砂輪機應(yīng)具有刃磨支架，把雙手?jǐn)R在支架上，以控制刀條的運動。握緊刀條，使它不能在砂輪上跳動。但不要握的太緊，以致難于移動刀條。
3． 手握刀條在砂輪上刃磨出橫向后角，以便磨成側(cè)刃角。這個角度在切削軟鋼時應(yīng)大約6度。手握刀條貼在砂輪上，使刀條底部向內(nèi)傾斜即可得到這種角度。當(dāng)刃磨時，應(yīng)將刀條在砂輪面上橫向來回移動，而不改變其位置。這有利于較快的磨好刀條并防止在砂輪上磨出溝槽來。當(dāng)?shù)稐l發(fā)熱時就把它浸在水里使其冷卻。初學(xué)者經(jīng)犯上下移動的錯誤。這會在刀條側(cè)面形成許多不同的角度，從而使它變的形狀怪異。要避免出現(xiàn)這種情況，就應(yīng)該使刀條固定在砂輪的一個位置上。要來回移動而決不要上下移動。
4． 在對側(cè)刃磨出橫向后角以把刀條磨成應(yīng)有的形狀。
5． 刃磨縱向后角，要握著刀使端部向上。成半圓形地擺動刀柄。力圖使端部圓弧與兩側(cè)均勻的光滑的連接起來。在刃磨刀片的圓弧時，一定要減輕壓力。不做到這一點，磨出的圓頭刀就會大于所要求的形狀。
6． 刃磨右切刀的橫向前角，應(yīng)使刀條的頂面即頂部與砂輪的右側(cè)成直角。使刀片底部向內(nèi)傾斜。使刀具保持這一位置，直到砂輪將整個頂面磨到切削刃時為止/刃磨左切刀的橫向前角。要用手握住刀條于砂輪左側(cè)。讓刀條底部向內(nèi)傾斜。讓砂輪將整個頂面磨至切削刃。沒有理由在刀條前端刃磨低于刀柄的頂面。這樣會浪費昂貴的刀條并使刀具外形受到損害。
7． 用油石研磨精加工的刀條是一個很好的習(xí)慣。選擇一個中細(xì)的油石。再油石上蘸一點煤油或豬油。使切削刃在油石上來回磨動。一定要把刀條拿平，以便不致使它的各種角度有任何改變。
只要稍加實踐，就能夠正確的刃磨刀條。記住，一個磨得很好的刀條應(yīng)具有恰當(dāng)?shù)?刀具角度和磨的很勻稱的平整表面。
車床的維護(hù)
在任何時候都要保持車床的清潔和潤滑良好。同任何精密機械一樣，車床也要認(rèn)真維護(hù)。只要操作者對床子進(jìn)行恰當(dāng)?shù)木S護(hù)，它就能運轉(zhuǎn)正常，加工精確。不要犯依賴別人給床子加油和維修的錯誤。操作者的人身安全取決于他保持床子安全運轉(zhuǎn)的能力。車床的正常維護(hù)包括清理，加油，調(diào)整和小修等工作。
清理車床
在每一個工作日后要徹底清理車床。如果切屑和臟物留在導(dǎo)軌，傳動裝置和其它運行部件上時，它的表面就會變粗糙并出現(xiàn)凹坑。這會導(dǎo)致迅速磨損以致使這些部件難于操縱。建議按下述步驟清理車床：
先用刷子掃除全部切屑。
注意 大部分切屑鋒利如刀，因此決不可以用手去清理。
用一把2英寸的漆刷或小臺刷來清理切屑是方便的。這時應(yīng)把尾架移到床身的右端。
1． 用一塊干凈的布或棉絲擦拭所有的油漆表面。否則留在油漆表面的油跡會變硬和污染油漆。
2． 用同樣的布或棉絲擦去所有機加工表面的油污和油脂。
3． 刷掉切屑盤里所有的切屑，然后把它擦干凈。
4． 在安裝卡盤以前，先用一鐵絲作成的螺紋清除器將其內(nèi)螺紋清除干凈。再把主軸螺紋擦拭干凈。滴上一，兩滴油。
5． 把頂尖錐柄裝入主軸孔之前，先把主軸孔和頂尖錐柄擦拭干凈。如果頂尖錐柄上有毛刺或粗糙的疵點，在裝入主軸孔之前，要用挫或油石將毛刺或粗糙疵點除掉。
6． 有時，可用一根繩來擦拭絲杠上的螺紋槽。把繩繞在絲杠上。調(diào)整傳動位置，使絲杠以中速轉(zhuǎn)動。開動車床，隨著絲杠的轉(zhuǎn)動，當(dāng)繩子沿著絲杠螺紋往前走時，來回拉動繩子。
7． 當(dāng)給車床加油時，要擦拭掉任何可能益處和滴在油漆表面上的油。
8． 開始工作前，一定要確保在導(dǎo)軌上保持有一層薄薄的油膜。
9． 調(diào)整橫向進(jìn)給和復(fù)合流板的鑲條螺釘，以消除部件之間的松動狀態(tài)即間隙。如果用手握住刀架并來回晃動就能使橫向進(jìn)給移動，這就說明。鑲條螺釘太松了。調(diào)整每個鑲條螺釘，直到橫向進(jìn)給手柄得到平滑運動為止。當(dāng)螺釘調(diào)整好以后，推拉倒架就不可能使橫向進(jìn)給移動。
10． 決不要把刀具或工件放在車床導(dǎo)軌上。這樣做就會損壞經(jīng)過精密刮研的表面精度/可把工具放在車床的木板上。
11． 當(dāng)使用刀架磨頭時，一定要保護(hù)車床的機加工表面，要把它們覆蓋起來。如果在磨削加工時這些表面沒有覆蓋好，從砂輪上掉下來的沙礫就會嵌入支撐面，從而很快破壞車床的精度。
12． 每星期一次，用蘸有煤油的干凈布，把車床整個擦拭一遍。先擦干凈油漆表面，然后擦機加工表面。擦干后就在所有的加工表面薄薄的涂上一層清潔的油。
車床的加油和潤滑
車床的恰當(dāng)潤滑是很重要的。每臺車床都帶有一張潤滑圖。所使用的潤滑油和潤滑脂的等級，品種一定要符合圖中的要求。要養(yǎng)成每天開始工作之前給車床加油的習(xí)慣。有些部件要每天加油。另一些部件按圖表規(guī)定要每周或每月加油一次。幾個人使用同一臺車床，常常是人人相互依賴，結(jié)果是沒人給機床加油和維護(hù)。
CUTTING TOOLS AND TOOLHOLDERS
To machine a workpiece successfully you must have :
1. the correct kind of cutting tool or tool bit
2. the right type of toolholder
3. a tool with a sharp cutting-edge
4. the cutting tool set or adjusted to the correct height and position.
Cutting-tool materials
Tool bits used on the lathe are made form one of six basic materials: water-hardening steels,high-speed steels,hard-cast,nonferrous alloys,sintered (cemented) carbides,ceramics,and diamonds. The selection of the material used depends upon many factors including:tool cost,size and design of tool ,metal-removal rate ,length of run ,finish and tolerance of part,and condition and capability of the machine tool . Because of these factors ,material selection is more often based on general experience than on precise evaluation . There are, however ,certain general characteristics of the different cutting-tool materials you should understand.
Water-hardening Steels.These include the high-carbon tool steels (either plain carbon or those with minor additions of chromium , vanadium,or tungsten) .The different grades of water-hardening tool steels are classed as W steels in American Iron and Steel Institute’s system of classification . Tools made from these materials have very sharp ,smooth cutting-edges when properly heat-treated. They are adequate for limited turning at a relatively low cutting speed or when old ,low-speed equipment ,such as a flat-belt lathe , is used .
The main limitation of tools made form water-hardening steels is that they soften if the cutting-edge temperature exceeds approximately 300-400F during sharpening or cutting .A second disadvantage is low resistance to edge wear .
High-speed Steels. High-speed steels offer great improvement in cutting efficiency over water-hardening tool steels .Tools made from high-speed steels retain enough hardness to machine at rapid rates even when the tool temperature reaches 1050F . They can be used even though they become dull red with heat . Upon cooling to room temperature , the original hardness of these steels does not change .
Wear resistance of high-speed steels is much better than that of the carbon or alloy steels . This is due to the high carbide content ,especially in the higher-alloy types of high-speed steel . Fully hardened , high-speed steels have greater resistance to shock than carbides or hard-cast alloys .
There are two main types of high-speed steels designated in the American Iron and Steels Institute system , M steels (molybdenum base and T steels tungsten base . Tool bits made from these materials can be purchased already ground to various shapes . Unground tool bits called tool-bit blanks can also be purchased . These tool-bit blanks are made in standard size to fit the commonly used lathes . The common sizes are 3/16in square by 1 in long ,1/4in square by 2in long ,5/16in square by 2-1/2in long ,and 3/8in square by 3in long . High-speed steel tool bits are the type most used in the school machine shop .
Hard-cast Alloy . These materials do not contain sufficient iron to be classed as steels . Rather , they are mainly alloys of cobalt , chromium , and tungsten with other elements added for special purpose . They reach full hardness in the as-cast condition , without heat treatment . The must be ground to size after casting . In terms of resistance to heat , wear ,shock ,and initial cost , cast alloys rank between high-speed steels and carbides .
Hard-cast alloys are weaker in tension and more brittle than high-speed steels and thus are not suitable for severe shock loads . They are known by such commercial names as stellite , Rex alloy ,and tantung .
Sintered Carbides . For efficient and high-speed machining ,best results can be obtained with sintered carbide tools . Carbide tools are available in solid form and as inserts which are either brazed or clamped in toolholders . Clamped inserts are usually round , square , or triangular in shape and have all edge is always available . These inserts can be rotated so that a sharp edge is always available . With modern machine tools and the proper grade of cemented carbide , it is possible to use cutting speeds 10 to 30 time faster than those feasible with high-speed steels .
Carbides are suitable for most machining operations such as single-point turning , drilling ,milling , thread cutting, and reaming . Carbides should be used only when they can be supported rigidly and when the machine tool has adequate power and speed to enable their efficient use .
Ceramic . With the exception of industrial diamonds , ceramic inserts are the hardest and strongest inserts available . They resist abrasive wear , chipping , and breakage . These inserts work best on very rigid machine tools and on well-supported workpieces . For most operations , cutting fluids are not needed .
Diamonds . Industrial diamonds that have either circular or faceted cutting-edges are used for light finishing cuts when an extremely high-quality surface finish required . Although a very smooth finish can be achieved using other cutting-tool materials , diamond turning can provide even smoother finishes with very small tolerances .
TOOLHOLDERS
The toolholder holds the cutting tool rigid during cutting operations . Four types of toolholders are in general use .
1 . The tool post with standard toolholders . The tool too post is comprised of the post , screw , washer , collar , and rocker . The washer fits the top slidee piece slot . The collar and the rocker elevate or lower the point of too . The screw clamps the toolholder in place .
The standard toolholder for high-speed steel cutter bits comes in three common shapes : straight , right-hand offset or shank , and left-hand offset or shank . You can identify right-hand and left-hand offset holders by holding the setscrew end in your hand . If the shank bends to the right , it is a left-hand offset holder .
The straight toolholder is fused for most work . The left-hand toolholder is used when you need to cut close to the chuck or lathe dog . The right-hand holder is used when feeding toward the tailstock of the lathe . The cutting-tool bit is held in each of these toolholders at an angle of 14 to 16.5 degrees . This is called the toolholder angle .
Carbide toolholders also come in three styles and are similar in appearance to those mentioned above . The hole for the cutter bit , however , is parallel to the bottom edge of the holder .
2. The open-side or heavy-duty tool block holds one tool at a time and consists of a T-slot clamp , a C-shaped block , and two or more tool clamping screws . Because this unit is very rigid , it is especially useful for heavy cuts . A tool bit can be mounted directly in the tool block or some type of carbide tooolholder can be used .
3. The turret tool block or four-way toolholder consists of a swiveling block in which the tools are clamped Common turret block hold four tools . Each can be quickly swiveled into cutting position and clamped in place . Some turret blocks have eight tool stations . Frequently ,an open-side-type tool block is also mounted on the rear of the cross slide to add one additional cutting operation . With this arrangement , anywhere form five to nine different kinds of tools can be mounted and operated in sequence for turning , forming ,facing ,knurling , and cutting off duplicate parts .
4. The quick-change-type tool system holds only one tool at a time , but three different sides can be used to position the tool . It consists of a quick-change tool post with a clamping lever and a series of toolholders for turning , facing , boring , cutting off , threading , knurling , and thread cutting .
Single-point Cutting Tools
Tool Parts . Before you can grind a tool bit , you must become acquainted with some of the terms used to describe the various parts of the cutting tool .
1 . The face is the top of the tool bit . It is the surface on which a part of the chip attaches as it is cut away form the workpiece .
2. The cutting-edge is that part of the cutter bit which actually does the cutting .
3. The nose is the corner or are formed by the side and end cutting-edge .
4. The flank is the surface below the cutting-edge .
5. The point is the part of the tool bit which is shaped to form the cutting-edge and face .
Tool Angles .The following are important tool angles used for all single-point cutting tools .
1. The side relief angle is the angle between the ground surface and the vertical side of the tool bit before it is ground . This angle was formerly called side clearance , and many machinists still use this term .The side relief angle provides clearance between the cut surface of the work and the flank of tool . Tool wear reduces the effective side clearance angle .If the angle is too small, the cutter will rub and heat . If the angle is too large , the cutting-edge will be weak and the tool will have a tendency to dig into the workpiece.
2. The end relief angle is the angle formed between the end of the cutting-edge and a vertical line. It was formerly called front clearance. The end relief angle provides clearance between the finished surface of the work and the tool. If this angle is too small, the tool will rub on the finished surface and produce a poor finish. Wear tends to reduce this angle. If the angle is too large , the tool may dig into the work , chatter, and fail through chipping . An angle of 8 to 15 is recommened for steel tools and 6 to 8 for carbide tools .If the tool is set above the center of rotation , the effective clearance angle is reduce . This must be considered in choosing the proper angle .
3. The end cutting-edge angle provides clearance between the cutter and the finished surface of the work .If this angle is too small, it may cause chatter. A small angle of about 6 is desirable on light finishing cuts, however, in order to produce a smooth finish .
4. The side cutting-edge angle turns the chip away form the finished surface .Recommended angles are between 5 and 15 .
5. The nose radius removes the fragile corner of the tool , prolongs tool life , and improves finish . The radius may be large for maximum-strength rough-cutting tools and may be reduced for light feeds . The larger the nose radius ,the better the finish as long as chatter dose not occur .Recommended nose radii are 0.010 to 0.030 in . or more for finishing cuts , and 1/30 to 1/2 in for roughing cuts .
6. To help shape the cutting-edge and face , it is necessary to grind rake angles on a tool bit .Rake is an inclination form the vertical or horizontal .The two rake angles are back rake and side rake .
Back rake , in a single-point feeding to the side , turns the chip away form the finished work and gives the tool a slicing action .A zero back rack tends to make a spiral chip , and a back rake angle greater than zero tends to stretch the spiral chip out into a helix . A back-rake angle of form 5 to 15 is used to keep chips form scratching the workpiece . High-speed steel tool bits are always ground with a positive rake .However , cemented carbide tools may have either a positive or negative rake .Negative rake increases the shear angle at which the chip is formed , providing for a good chip and a good surface finish .Negative rake tools are generally used on a heavy-duty lathe that is operated at high speed with a heavy feed .
Side rake refers to the angle between the face of the tool and a line that would represent the top of the unground tool bit as viewed form the end . Side rake controls the type of chip produced during machining as well as the direction in which the chip will travel .A tool with a small side-rake angle will produce shorter chips than one with a large rake angle .
7 .The nose angle is the angle between the side-cutting edge and the end-cutting edge .
Classes of Single-point Tools
Different shapes of tool bits are needed to do certain machining operations . Most tool bits are ground to cut in one direction only .The two common types are referred to as right cut and left cut .These were formerly called right-hand and left-hand tool bits .
A right-cut single-point tool is one that , when viewed form the point end with the face up , has its cutting-edge on the right side .When the tool bits is placed in the lathe , the cutting-edge is on the left side .This tool bit cuts form the right to the left , or form the tailstock end toward the headstock of the lathe .
A left-cut tool bit has the cutting-edge on the left when viewed form the point end with the face up . This tool bit is ground to cut form the left to the right or toward the tailstock of the lathe .
Commonly used types of tool bits include the following:
1. A roughing tool is a tool bit designed to take heavy roughing cuts to reduce the diameter of a workpiece to approximate size . Because finish is not important w