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畢業(yè)設(shè)計(jì)任務(wù)書
課題：柴油機(jī)齒輪室蓋鉆鏜專機(jī)總體及主軸箱設(shè)計(jì)
專 業(yè) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
學(xué) 生 姓 名 聞 志 祥
班 級(jí) B機(jī)制023
學(xué) 號(hào) 0210110316
指 導(dǎo) 教 師 劉 道 標(biāo)
專 業(yè) 系 主 任
發(fā) 放 日 期 2006年3月 6 日
一、設(shè)計(jì)內(nèi)容
課題來(lái)源于生產(chǎn)。為保證ZH1105W柴油機(jī)齒輪室蓋孔加工及保證相應(yīng)的位置精
度，需設(shè)計(jì)一臺(tái)鉆鏜組合機(jī)床。在完成“三圖一卡”的基礎(chǔ)上，主要完成其右主軸箱設(shè)計(jì)。
二、設(shè)計(jì)依據(jù)
ZH1105W柴油機(jī)齒輪室蓋材料為HT250，其硬度是HB190-240，該專機(jī)左側(cè)鉆
ZH1105W柴油機(jī)齒輪室蓋圖紙上，6－M6－6H孔至￠5，右側(cè)鉆6－￠9孔（深38）
及3－￠9孔（深78）至尺寸。后側(cè)鏜￠45H8孔至￠43.5，倒孔口角至￠46.6。生產(chǎn)按
兩班制進(jìn)行，每班工作6小時(shí)，年產(chǎn)量130000件。
三、技術(shù)要求
1、機(jī)床應(yīng)能滿足加工要求，保證加工精度；
2、機(jī)床應(yīng)運(yùn)轉(zhuǎn)平穩(wěn)，工作可靠，結(jié)構(gòu)簡(jiǎn)單；
3、裝卸方便，便于維修、調(diào)整；
4、盡量使用通用件，以便降低制造成本；
5、各動(dòng)力頭分別由電機(jī)拖動(dòng)，可單獨(dú)控制。
四、畢業(yè)設(shè)計(jì)物化成果的具體內(nèi)容及要求
1、設(shè)計(jì)說(shuō)明書1份，達(dá)1萬(wàn)字以上，且要符合規(guī)范要求；
2、設(shè)計(jì)圖樣全部用AutoCAD繪制，總的繪圖量達(dá)3張A0以上；
3、具體設(shè)計(jì)的圖樣有：
（1）機(jī)床聯(lián)系尺寸圖、被加工零件工序圖、加工示意圖、生產(chǎn)率計(jì)算卡
（2）主要部件和零件的工程圖
可附其他實(shí)物及實(shí)驗(yàn)要求
五、畢業(yè)設(shè)計(jì)進(jìn)度計(jì)劃
起訖日期
工作內(nèi)容
備 注
06.03.06—06.03.07
布置任務(wù)
下達(dá)任務(wù)書
06.03.06—06.03.17
調(diào)查研究，收集資料，熟悉課題,畢業(yè)實(shí)習(xí)
06.03.18—06.03.31
總體設(shè)計(jì)，方案論證
06.04.01—06.05.10
部件、零件設(shè)計(jì)階段
06.05.11—06.06.04
編寫說(shuō)明書
06.06.05—06.06.07
畢業(yè)設(shè)計(jì)預(yù)答辯
06.06.08—06.06.11
修改整理
06.06.12—06.06.13
復(fù)查材料
評(píng)閱
06.06.14—06.06.16
畢業(yè)答辯
06.06.17—06.06.08
材料整理裝袋
六、主要參考文獻(xiàn)：
1、葉偉昌主編.機(jī)械工程及自動(dòng)化簡(jiǎn)明設(shè)計(jì)手冊(cè)(上冊(cè)).北京：機(jī)械工業(yè)出版社，2001
2、葉偉昌主編.機(jī)械工程及自動(dòng)化簡(jiǎn)明設(shè)計(jì)手冊(cè)(下冊(cè)).北京：機(jī)械工業(yè)出版社，2001
3、胡家秀主編.機(jī)械零件設(shè)計(jì)實(shí)用手冊(cè).北京：機(jī)械工業(yè)出版社，1999．10
4、李益民主編.機(jī)械制造工藝設(shè)計(jì)手冊(cè).北京：機(jī)械工業(yè)出版社，1995．10
5、艾興等主編.金屬切削用量手冊(cè).北京：機(jī)械工業(yè)出版社，1996、10
6、范云漲等主編.金屬切削機(jī)床設(shè)計(jì)簡(jiǎn)明手冊(cè).北京：機(jī)械工業(yè)出版社，1993．8
7、孟憲椅等主編.機(jī)床夾具圖冊(cè).北京：機(jī)械工業(yè)出版社，1991．4
8、韓敬禮等主編.機(jī)械電氣設(shè)計(jì)簡(jiǎn)明手冊(cè).北京：機(jī)械工業(yè)出版社，1994．5
9、謝家瀛主編.組合機(jī)床設(shè)計(jì)簡(jiǎn)明手冊(cè).北京：機(jī)械工業(yè)出版社，1999．10
10、楊培元等主編.液壓系統(tǒng)設(shè)計(jì)手冊(cè).北京：機(jī)械工業(yè)出版社，1995．10
11、大連組合機(jī)床研究所編.組合機(jī)床設(shè)計(jì).北京：機(jī)械工業(yè)出版社，1986
12、大連組合機(jī)床研究所編.組合機(jī)床設(shè)計(jì)參考圖冊(cè).北京：機(jī)械工業(yè)出版社，1986
13、李云.機(jī)械制造工藝及設(shè)備設(shè)計(jì)指導(dǎo)手冊(cè).北京.機(jī)械工業(yè)出版社. 1996
14、薛源順.機(jī)床夾具設(shè)計(jì).北京.機(jī)械工業(yè)出版社.2000
15、李益民.機(jī)械制造工藝設(shè)計(jì)簡(jiǎn)明手冊(cè). 北京.機(jī)械工業(yè)出版社.1993
七、其他
4
外文翻譯
專 業(yè) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化
學(xué) 生 姓 名 聞 志 祥
班 級(jí) B 機(jī) 制 023
學(xué) 號(hào) 0210110316
指 導(dǎo) 教 師 劉 道 標(biāo)
鉆削與鏜削
Addison-Wesley pub.Co.
聞志祥 譯
摘要：通過驅(qū)動(dòng)刀具能在工件上鉆出通孔或盲孔，鉆刀是正對(duì)著工件繞著自己的軸線旋轉(zhuǎn)。當(dāng)然，刀具從其軸線向外的切削距離應(yīng)和需加工的孔的半徑相等。在實(shí)際生產(chǎn)中，是采用關(guān)于同一軸線對(duì)稱的兩切削刀刃的刀具。鉆削既可被應(yīng)用于手工也可用于鉆床中。鉆床在尺寸和結(jié)構(gòu)上有所不同。然而，當(dāng)工件被牢固地安裝好后，鉆刀總是繞著自己的軸線旋轉(zhuǎn)。這是和在車床上鉆孔是相反的。鏜孔是擴(kuò)大以前鉆削或鏜削好了的孔。鏜孔能夠消除鉆空加工時(shí)孔所產(chǎn)生的偏心，使孔擴(kuò)大到需鉸削的尺寸。下面是對(duì)鉆削、鉆床分類和鏜孔的簡(jiǎn)要介紹。
關(guān)鍵詞：鉆削、鏜削、鉆床、鉆削刀具、鏜刀、鉆床的分類
鉆削刀具
在鉆削操作中，采用的是一種柱形的螺旋式刀具，被稱之為鉆刀。鉆刀有一條或兩條切削刃和相應(yīng)的出屑槽，出屑槽呈直線或螺旋線形。出屑槽的作用是為在鉆削過程中產(chǎn)生的切屑提供一個(gè)通道，同時(shí)也是便于潤(rùn)滑劑和冷卻劑到達(dá)鉆刀的切削刃和工件的被加工表面。以下是普通刀具的概括論述：
鉆體
柄舌
刃帶
刀刃
出屑槽
后刃面
刃帶
刀刃
出屑槽
柄部
頸部
螺旋角
出屑槽
頂角
死頂尖
楔邊
圖4.1
麻花鉆。麻花鉆是最普通的一類鉆刀。麻花鉆有兩條切削刃和兩條螺旋線形的出屑槽，出屑槽連續(xù)地圍繞分布在整個(gè)鉆體上（如圖4.1）。鉆刀除了鉆體部分，還有鉆頸和鉆柄，鉆柄可以是圓柱形，也可以是錐行。在后者的情況下，鉆柄是通過柄舌的楔形作用安裝在主軸的錐形鉆套中，柄舌是安裝在主軸鉆套的狹槽中，這樣鉆刀和主軸形成一個(gè)整體來(lái)傳遞旋轉(zhuǎn)運(yùn)動(dòng)。在另一方面，圓柱形鉆柄是被安裝在鉆夾頭里，然后，以安裝錐形鉆柄的方法將其安裝進(jìn)主軸的鉆套中。
從圖4.1 可以看出，兩條切削邊被稱為刀刃，兩條切削刃是通過楔子連接在一起。麻花鉆還有兩條刃帶，其能在鉆削操作中對(duì)刀具起正確的導(dǎo)向和定位的作用。兩條刀刃形成鉆刀的頂角，頂角大小的選擇是依據(jù)被加工材料的特性。工業(yè)生產(chǎn)中經(jīng)常使用的鉆刀的頂角是118°，其適合鉆削低碳鋼和鑄鐵。對(duì)于硬度和剛度較高的金屬，譬如，硬剛，黃銅和青銅，宜選用稍大頂角（130°或140°）的鉆刀。常用麻花鉆的出屑槽的螺旋角是范圍是在24°-30°之間。當(dāng)在鉆削銅或軟塑材料時(shí)，推薦使用螺旋角較大的刀具（35°-45°之間）。
鉆柄
鉆頸
鉆體
倒棱
頂角
圖4.2
空心鉆。 空心鉆是由倒棱，鉆體，鉆頸和鉆柄組成，如圖4.2所示。此類的空心鉆有三條或四條出屑槽和相應(yīng)數(shù)量的刃帶保證良好的導(dǎo)向來(lái)獲得高的加工精度 。從圖4.2還可以看出空心鉆有一平斷，倒棱可能有三條或四條切削邊，或稱為刀刃，頂角可在90-120范圍內(nèi)變化。空心鉆是用來(lái)擴(kuò)大先前已有的孔，它不是用來(lái)鉆削新的孔的?？招你@有高的生產(chǎn)率，高的加工精度和能鉆削出高質(zhì)量的表面的特性。
槍孔鉆。槍孔鉆是用來(lái)加工深孔的。所有的槍孔鉆的出屑槽都是直的，只有一單條切削刃。在槍鉆的鉆體上有一個(gè)孔，其起著導(dǎo)管的作用，冷卻劑在較的壓力下通過該孔流到槍鉆的頂尖部位。
現(xiàn)有兩種槍鉆，即，用來(lái)加工盲孔的中心鉆和套筒鉆。套筒鉆的中心有一個(gè)圓柱形孔，鉆孔時(shí)可在工件上形成一個(gè)芯子，當(dāng)鉆頭連續(xù)進(jìn)給進(jìn)行鉆孔時(shí)，芯子對(duì)鉆起導(dǎo)向作用。
平鉆。平鉆是用于鉆削大于7/2英寸的孔（90mm）乃至更大的孔。該類的鉆易于磨削。
鏜刀
鏜孔是擴(kuò)大以前鉆削或鏜削好了的孔。鏜孔能夠消除鉆空加工時(shí)孔所產(chǎn)生的偏心，使孔擴(kuò)大到需鉸削的尺寸。
平底擴(kuò)孔是指擴(kuò)大一個(gè)鉆孔的末端。這個(gè)擴(kuò)大的孔的底部是平的，它與原來(lái)的孔是同軸的。刀具與導(dǎo)向銷一起使用，導(dǎo)向銷裝進(jìn)已鉆好的孔中，用于切削刃對(duì)中。平底擴(kuò)孔主要用于在上面安裝螺栓下面安裝螺釘?shù)目椎募庸?。在一個(gè)已加工好的孔上加工一個(gè)小的平面，該面稱之為刮孔平面。在粗糙的表面上為螺栓提供平滑的沉頭座的操作是很普遍的。如果把一個(gè)已加工控切成斜邊以便適合一個(gè)平底螺栓的圓錐座，該操作稱為锪錐面。
刀具用于臥式鏜床或是被安裝在一個(gè)大型桿上或是作一個(gè)鏜前頭，它們依次排布在 機(jī)床的主軸上。絕大多數(shù)鏜孔操作是使用具有一個(gè)單齒的鏜刀，如圖4.3所示，因?yàn)樗麄円子诎惭b和維修。鏜桿的作用是將來(lái)機(jī)床自軸的動(dòng)力傳遞到刀具上和保持在切削過程中的剛性，在加工過程中，工件通常不動(dòng)，刀具在孔中作旋轉(zhuǎn)進(jìn)給運(yùn)動(dòng)。如圖所示，通常需給鏜桿提供附加支撐。鏜桿必須足夠的長(zhǎng)以達(dá)到末端支撐和為機(jī)床操作提供一定的縱向空間。
工作臺(tái)
鏜刀
鏜刀
鏜桿
床頭箱
主軸
工件
鏜桿
端部支承
圖4.3
在銑床、坐標(biāo)鏜床、或鉆床上進(jìn)行精密鏜削時(shí)，有必要使用一種帶有千分尺調(diào)整的工具。這種工具安裝在刀具頭上并作旋轉(zhuǎn)運(yùn)動(dòng)。因此任何孔徑的增加必須通過調(diào)整工具半徑來(lái)獲得。圖4.3b所示的是最常見的組合式雙鏜刀布置形式,他包括兩個(gè)相對(duì)的刀具夾在溝槽中。螺柱是用來(lái)在指定位置鎖緊刀具和調(diào)整他們的位置。整體裝進(jìn)一個(gè)矩形狹槽中,且鎖在固定位置。刀具固定在滑行刀架里,且與頂尖成一條直線。刀具的精度取決與刀具車間的全體人員而不是操作者.
圖4.4
通常用于小型機(jī)床譬如車床的鏜刀是單齒鏜刀，他是被以其能進(jìn)入孔內(nèi)的方式支承著。圖4.4a所示刀具的末端事實(shí)鍛造的，然后通過磨削成型。它是安裝在一個(gè)單獨(dú)的支承桿上，該支承桿是安裝在車床的刀架上。對(duì)于轉(zhuǎn)塔車床所用的是類似于圖4.4b所示的刀具，只是刀桿稍有不同。刀具的修改是鏜桿部分，如圖4.4c所示，它被設(shè)計(jì)成在鏜桿的末端擁有一個(gè)小型高速鋼刀具。鏜桿的剛度強(qiáng)，其長(zhǎng)度可根據(jù)孔的長(zhǎng)度作相應(yīng)的調(diào)整。盡管這些刀具的間隙、斜度和切削角應(yīng)該接近那些在車床操作中推薦使用的相近，但如果孔較小的話，這些角度是不能使用的。
在加工工件中，普遍使用多切削刃的鏜刀。如圖4.4f，這些表面類似筒形絞刀的刀具，但具有鑲齒銑刀，它們被調(diào)整成補(bǔ)償磨損和直徑變化。這種類型的鏜刀比單刃刀具有較長(zhǎng)的壽命，因此在加工中更經(jīng)濟(jì)。如圖4.4e 所示的帶有導(dǎo)向銷的以保證同軸度的平底擴(kuò)孔刀具是用來(lái)擴(kuò)大孔的末端。
鉆床的分類
便攜式的小機(jī)床上可實(shí)現(xiàn)鉆削操作，一般的機(jī)床上也可以實(shí)現(xiàn)鉆削操作。一般的機(jī)床在形狀和尺寸上不同于便攜式小機(jī)床，但它們也有共同的特征。例如，它們都擁有一根或更多根的麻花鉆，當(dāng)在加工以被固定裝好了的工件時(shí)，每根麻花鉆繞著自己的軸作旋轉(zhuǎn)運(yùn)動(dòng)。這和在車床上工件被夾緊并隨著卡盤作旋轉(zhuǎn)運(yùn)動(dòng)而進(jìn)行的鉆削是相反的。下面是對(duì)一些普通式鉆床的概述。
臺(tái)式鉆床。臺(tái)式鉆床通常是被放在工作臺(tái)上的普通加工用途的小型機(jī)床。這種鉆床包括一個(gè)動(dòng)力來(lái)源的電動(dòng)機(jī)，動(dòng)力是通過滑輪和皮帶傳遞到裝有刀具的主軸上。進(jìn)給運(yùn)動(dòng)是通過降低操縱桿，由操縱桿帶動(dòng)主軸的下降（或上升）來(lái)實(shí)現(xiàn)的。臺(tái)鉆的主軸在套筒內(nèi)自由旋轉(zhuǎn)（套筒由操縱桿通過齒輪齒條系統(tǒng)驅(qū)動(dòng)，但不隨主軸一起旋轉(zhuǎn)）。
加工工件時(shí)，工件是被放在機(jī)床的工作臺(tái)上，有時(shí)需要一個(gè)特殊的花鉗來(lái)固定。被加工工件的最大厚度是受機(jī)床主軸與工作臺(tái)之間的間隙限制。
立式鉆床。立式鉆床可被用于輕度、中等、甚至相對(duì)重負(fù)荷強(qiáng)度的工作，這主要取決于立式鉆床的尺寸。
立式鉆床與臺(tái)式鉆床基本相似，主要的不同點(diǎn)是里是立式鉆床的底座上裝有一較長(zhǎng)的圓柱形支柱。在支柱上附加安裝了一個(gè)可以鎖定在任一想要高度的滑動(dòng)工作臺(tái)。當(dāng)立式鉆床用于中等強(qiáng)度的工作時(shí)，其所需的動(dòng)力要比臺(tái)式鉆床的多。
在立式鉆床里有比較的的鉆床。因此，這大的鉆床有一個(gè)箱柱和較高的動(dòng)力，以此滿足重負(fù)荷。此外，它是采用齒輪箱為主軸提供不同的旋轉(zhuǎn)速度和軸向進(jìn)給量，通過齒輪箱可以預(yù)先設(shè)置任何想要的主軸轉(zhuǎn)速和進(jìn)給速率。
多軸鉆床。多軸鉆床的結(jié)構(gòu)堅(jiān)固，其工作時(shí)需要很強(qiáng)的動(dòng)力，每臺(tái)多軸鉆床能同時(shí)鉆削很多孔。為滿足加工要求，不同的刀具是可以調(diào)整的，同時(shí)根據(jù)需要，整個(gè)床頭箱部分（帶有主軸和刀具）是可以傾斜的。
這類的鉆床主要用于批量生產(chǎn)且擁有很多孔的零件的加工。例如汽缸體。
排式鉆床。當(dāng)幾個(gè)獨(dú)立的鉆頭（每個(gè)都有一個(gè)單獨(dú)主軸）排列在一個(gè)單獨(dú)的普通的工作臺(tái)上，此時(shí)，該機(jī)床被稱之為排式鉆床。這種機(jī)床特別地適用于幾種需連續(xù)進(jìn)行的操作。
圖4.5
絲桿
鉆床的床頭箱
搖臂
主軸
底座
立柱
電動(dòng)機(jī)
搖臂鉆床。搖臂鉆床，特別地適合那些不便于安裝在立式鉆床上的大型和重型工件進(jìn)行鉆孔。在圖4.5可以看出，搖臂鉆床有一安裝在底座上的立柱。搖臂鉆床的搖臂帶著鉆床的床頭箱主軸和刀具移動(dòng)，該搖臂能夠沿立柱上升或下降，并可以鎖緊在任一所需的位置上。床頭箱沿著搖臂滑動(dòng)并使主軸作旋轉(zhuǎn)運(yùn)動(dòng)和軸向進(jìn)給運(yùn)動(dòng)。此外，搖臂能夠擺動(dòng)，因此刀具可移動(dòng)到圓柱坐標(biāo)系統(tǒng)的任一位置。
轉(zhuǎn)塔鉆床。歸屬于轉(zhuǎn)塔鉆床類的機(jī)床，或是半自動(dòng)或是全自動(dòng)控制的。轉(zhuǎn)塔機(jī)床的一個(gè)普遍的設(shè)計(jì)特征是用轉(zhuǎn)塔代替原來(lái)機(jī)床的主軸，轉(zhuǎn)塔上裝有幾把鉆削、鏜削
和螺紋切削刀具。因此，幾種連續(xù)的操作只需要在一次初安裝下就可以完成，在兩種操作之間不需要再次裝夾工件。
如今，由數(shù)字或計(jì)算機(jī)控制系統(tǒng)控制的自動(dòng)轉(zhuǎn)塔鉆床是相當(dāng)?shù)钠毡榱?。在這種情況下，人的工作只是對(duì)工件進(jìn)行初安裝和對(duì)其進(jìn)行監(jiān)控。這類機(jī)床就空間要求（機(jī)床的物理尺寸）和工件裝夾次數(shù)而言比排式鉆床有優(yōu)越性。
長(zhǎng)孔鉆床。長(zhǎng)孔鉆床是一類特殊的被用作鉆削長(zhǎng)孔的機(jī)床，譬如，槍管的長(zhǎng)孔就是用此類機(jī)床加工。通常長(zhǎng)孔鉆在使用時(shí)對(duì)工件的進(jìn)給速度是較慢的。這類機(jī)床在工作時(shí)，工件作旋轉(zhuǎn)運(yùn)動(dòng)，而刀具不作旋轉(zhuǎn)運(yùn)動(dòng)。長(zhǎng)孔鉆床有立式結(jié)構(gòu)也有臥式結(jié)構(gòu)。然而，這兩種結(jié)構(gòu)的共同特征是在鉆削過程中工件的精確導(dǎo)向和剛性支承。
坐標(biāo)鏜床。這類機(jī)床是為獲得高的精確性和精密性而特別設(shè)計(jì)的。這類機(jī)床不但鉆孔而且能夠給孔定位，因?yàn)楣ぷ髋_(tái)的運(yùn)動(dòng)由電子測(cè)量裝置監(jiān)控著。
DRILLING AND BORING
Addison-Wesley pub.Co.
Abstract: Drilling involves producing through or blind holes in a workpiece by forcing a tool, which rotates around its axis, against the workpiece. Consequently, the range of cutting from that axis of rotation is equal to the radius of the required hole. In practice, two symmetrical cutting edges that rotate about the same axis are employ. Drilling operations can be carried out by using either hand drills or drilling machine. The latter differ in size and construction. Nevertheless, the tool always rotates around its axis while the workpiece is kept firmly fixed. This is contrary to drilling on a lathe. Boring is enlarging holes previously drilled or bored. Drilled holes are frequently bored to eliminate any possible eccentricity and to enlarge the hole to a reaming size. Following is a survey of drilling, drilling machine tool and boring.
Keyword: drilling boring drilling machine tool classification of drilling machine cutting tool for drilling operations cutting tool for boring operations
CUTTING TOOL FOR DRILLING OPERATIONS
In drilling operations, a cylindrical rotary-end cutting tool, called a drill, is employed. The drill can have either one or more cutting edges and corresponding flutes, which can be straight or helical. The function of the flutes is to provide outlet passages for the chips generated during the drilling operation and also to allow lubricants and coolants to reach the cutting edges and the surface being machined. Following is a survey of the commonly used drills.
Twist drill. The twist drill is the most common type of drill. It has two cutting edges and two helical flutes that continue over the length of the drill body, as shown in Fig.4.1. The drill also consists of a neck and a shank that can be either straight or tapered. In the latter case, the shank is fitted by the wedge action into the tapered socket of the spindle and has a tang, which goes into a slot in the spindle socket, thus acting as a solid means for transmitting rotation. On the other hand, straight-shank drills are held in a drill chuck that is, in turn, fitted into the spindle socket in the same way as tapered shank drills.
Fig.4.1 The twist drill
As can be seen in Fig.4.1, the two cutting edges are referred to as the lips, and are connected together by a wedge, which is a chisel-like edge. The twist drill also has two margins, which enable proper guidance and locating of the drill while it is in operation. The tool point angle (TPA) is formed by the two lips and is chosen based on the properties of the material to be cut. The usual TAP for commercial drills is 118, which is appropriate for drilling low-carbon steels and cast irons. For harder and tougher metals, such as hardened steel, brass and bronze, larger TAPs (130or 140) give better performance. The helix angle of the flutes of the commonly used twist drills ranges between 24 and 30 . When drilling copper or soft plastics, higher values for the helix angle are recommended (between35 and 45).
Fig.4.2 The core drill
Core drills. A core drill consists of the chamfer, body, neck, and shank, as shown in Fig.4.2.This type of drill may have either three or four flutes and an equal number of margins, which ensure superior guidance, thus resulting in high machining accuracy. It can also be seen in Fig.4.2 that a core drill has flat end. The chamfer can have three or four cutting edges, or lips, and the lip angle may vary between 90° and 120° . Core drills are employed for enlarging previously made holes and not for originating holes. This types of drill is characterized by greater productivity, high machining accuracy, and superior quality of the drilled surfaces.
Gun drills. Gun drills are used for drilling deep holes. All gun drills are straight-fluted, and each had a single cutting edge. A hole in the body acts as a conduit to transmit coolant under considerable pressure to the tip of the drill.
There are two kinds of gun drills, namely, the center-cut dill used for drilling blind holes and the trepanning drill. The latter has a cylindrical groove at its center, thus generating a solid core, which guides the tool as it proceeds during the drilling operation.
Spade drill. Spade drills are used for drilling large holes of 7/2in. (90mm) or more. Their which results in a marked saving in cost of the tool as well as a tangible reduction in its weight, which facilitates its handling. Moreover, this type of drill is easy to grind.
BORING TOOLS
Boring is enlarging holes previously drilled or bored. Drilled holes are frequently bored to eliminate any possible eccentricity and to enlarge the hole to a reaming size.
Counterboring is enlarging one end of a dilled hole. The enlarged hole, which is concentric with the original one, is flat on the bottom. The tool is provided with a pilot pin that fits into the drilled hole to center the cutting edges. Counterboring is used principally to set bolt heads and nuts below the surface. To finish off a small surface around a drilled hole is known as spot facing. This is a customary practice on tough surface to provide smooth seats for bolt heads. If the top of a drilled hole is beveled to accommodate the conical seat pf a flat-head screw, the operation is called countersinking.
Fig.4.3
Tools used in horizontal boring machines are mounted in either a heavy bar or a boring head, which in turn is connected to the main spindle of the machine. Most boring operations use a single-point cutter as shown in Fig.4.3, because they are simple to set up and maintain. The bar serves to transmit power from the machine spindle to the cutter as well as to hold it rigidly during the cutting operation. The workpiece is normally stationary and the rotating cutter is fed through the hole. It is often necessary to provide additional support for the bar as shown in the figure. The bar must be long enough to reach the end support and also must provide the necessary longitudinal traverse for the machining operation.
For precision boring work on milling machines, jig bore, or drill presses, it is necessary to use a tool having micrometer adjustment. Such tools are held in a cutter head and rotate. Hence, any increase in hole size must be obtained by adjusting the tool radially from its center.
The most popular double-cutter arrangement is the block type shown in Fig.4.3b, which consists of two opposing cutters resting in grooves on the block. Screws are provided to lock the cutters in position as well as to adjust them. The entire assembly fits into a rectangular slot in the cutters in position as well as to adjust them. The entire assembly fits into a rectangular slot in the bar and is keyed in place. Cutters are ground while assembled in the block and are held in alignment by the center holes provided. The responsibility for tool accuracy and setup belongs to the toolroom personnel rather than the operator.
Fig.4.4 Types of boring tools
The boring tool commonly use in small machines such as lathes is a single -pointed tool, supported in a manner that permits its entry into a hole. This tool, shown in Fig.4.4a is forged at the end and then ground to shape. It is supported in a separate holder that fits into a lathe tool post. For turret lathes, slightly different holders and forged tools similar to the one shown in Fig.4.4b are used. A modification of this tool is the boring bar shown in Fig.4.4c, which is designed to hold a small high-speed steel tool bit at the end. The bar supporting the tool is rigid and may be adjusted according to the hole length. Although the clearance, rake, and cutting angles cannot be used if the tools should be similar to those recommended for lathe work, these angles cannot be used if the holes are small.
In production work, boring cutters with multiple cutting edges are widely used. These cutters, shown in Fig.4.4f resemble shell reamers in appearance but are usually provided with inserted-tooth cutters that may be adjusted radially to compensate for wear and variations of diameter. Boring tools of this type have longer life than single-pointed tools and hence are more economical for production jobs. The counterboring tool shown in Fig.4.4e provided with pilots to ensure concentric diameters. Is designed to recess or enlarge one end of a hole.
CLASSIFICATION OF DRILLING MACHINES
Drilling operations can be carried out by employing either portable small machines or appropriate machine tools. The latter differ in shape and size, although they have common features. For instance, they all involve one or more twist drills, each rotating around its own axis while the work piece is kept firmly fixed. This is contrary to the drilling operation on a lathe, where the work piece is held in and rotates with the chuck,. Following is a survey of the commonly used types of drilling machines.
Beach-type drilling machines. Beach-type drilling machines are general-purpose, small machine tools that are usually placed on benches. This type of drilling machine includes an electric motor as the source of motion, which is transmitted via pulleys and belts to the spindle, where the tool is mounted. The feed is manually generated by lowering a lever handle, which is designed to lower (or raise) the spindle. The latter rotates freely inside a sleeve (which is actuated by the lever through a rackpinion system but does mot rotate with the spindle ).
The workpiece is mounted on the machine table, although a special vise is sometimes used to hold, the workpiece. The maximum height of a workpiece to be machined is limited by the maximum gap between the spindle and the machine table.
Upright drilling machines. Depending upon the size, upright drilling machine tools can be used for light, medium, and even relatively heavy jobs.
It is basically similar to bench-type machines, the main difference being a longer cylindrical column fixed to the basic. Along that column is an additional, sliding table for fixing the workpiece which can be locked in position at any desired height. The power required for this type is more than that for bench-type drilling machines, since this type is employed in performing medium-duty job.
There are also large drilling machines of the upright type. In this case the machine has a box column and a higher power to deal with large jobs. Moreover, gear boxes are employed to provide different rotational spindle speeds as well as the axial feed motion, which can be preset at any desired rate.
Multispindle drilling machines. Multispindle drilling machines have sturdy construction and require high power; each is capable of drilling many holes simultaneously. The positions of the different tools (spindles)can be adjusted as desired. Also, the whole head (which carries the spindles and tools) can sometimes be titled, as required.
This type of drilling machine is used mainly for mass production in jobs having many holes, such as cylinder blocks.
Gang drilling machines. When several separate heads (each with a single spindle)are arranged on a single common table, the machine tool is then referred to as a gang drilling machine. This type of machine tool is particularly suitable where several operations are to be performed in succession.
Fig.4.5 A Sketch of radial drill.
Radial drill. A radial drill is particularly suitable for drilling holes in large and heavy workpiece that are inconvenient to mount on the table of an upright drilling machine. As you can see in Fig.4.5, a radial drilling machine has a main column, which is fixed to base. The cantilever guide arm, which carries the drilling head spindle and tool, can be raised or lowered along the column and clamped at any desired position. The drill head slides along the arm and provides rotary motion and axial feed motion. Again, the cantilever guide arm can be swung, thus enabling the tool to be moved in all directions according to a cylindrical coordinate system.
Turret drilling machines. Machines tools that belong to the turret drilling machines are either semi-or fully automatic. A common design feature is that the main spindle is replaced by a turret, which carries several drilling, boring, reaming, and threading tools. Consequently, several successive operations can be carried out with only a single initial setup and without the need for setting up the workpiece again between two operations.
Nowadays, automatic turret drilling machines that are operated by NC or CNC systems are quite common. In this case, the human role is limited to the initial setup and monitoring. This type of machine tool therefore has advantages over the gang drilling machines with respect to space required (physical size of the machine tool) and the number of workpiece setup.
Deep-hole drilling machines. Deep-hole drilling machines are special machines employed for drilling long holes like those of rifle barrels. Usually, gun-type drills are used; these are fed slowly against the workpiece. In this type of machine tool, it is the workpiece that is rotated, while the drill is kept from rotary motion. A deephole drilling machine may have either a vertical or horizontal construction. However, in both case, the common feature is the precise guidance and positive support of the workpiece during the drilling operation.
Jig-boring machine. These machine tools are specially designed to posses high precision and accuracy. A machine of this type not only drills the holes but also locates them because the table movements are monitored by electronic measuring devices.
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