機(jī)床上下料機(jī)械手設(shè)計(jì)【三自由度】【圓柱坐標(biāo)式】
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車(chē)床及其切削加工
車(chē)床主要是為了進(jìn)行車(chē)外圓、車(chē)端面和鏜孔等項(xiàng)工作而設(shè)計(jì)的機(jī)床。車(chē)削很少在其他種類(lèi)的機(jī)床上進(jìn)行，而且任何一種其他機(jī)床都不能像車(chē)床那樣方便地進(jìn)行車(chē)削加工。由于車(chē)床還可以用來(lái)鉆孔和鉸孔，車(chē)床的多功能性可以使工件在一次安裝中完成幾種加工。因此，在生產(chǎn)中使用的各種車(chē)床比任何其他種類(lèi)的機(jī)床都多。
車(chē)床的基本部件有：床身、主軸箱組件、尾架組件、溜板組件、絲杠和光杠。
床身是車(chē)床的基礎(chǔ)件。它通常是由經(jīng)過(guò)充分正火或時(shí)效處理的灰鑄鐵或者球墨鑄鐵制成。它是一個(gè)堅(jiān)固的剛性框架，所有其他基本部件都安裝在床身上。通常在床身上有內(nèi)外兩組平行的導(dǎo)軌。有些制造廠對(duì)全部四條導(dǎo)軌都采用導(dǎo)軌尖頂朝上的三角形導(dǎo)軌(即山形導(dǎo)軌)，而有的制造廠則在一組中或者兩組中都采用一個(gè)三角形導(dǎo)軌和一個(gè)矩形導(dǎo)軌。導(dǎo)軌要經(jīng)過(guò)精密加工，以保證其直線度精度。為了抵抗磨損和擦傷，大多數(shù)現(xiàn)代機(jī)床的導(dǎo)軌是經(jīng)過(guò)表面淬硬的，但是在操作時(shí)還應(yīng)該小心，以避免損傷導(dǎo)軌。導(dǎo)軌上的任何誤差，常常意味著整個(gè)機(jī)床的精度遭到破壞。
主軸箱安裝在內(nèi)側(cè)導(dǎo)軌的固定位置上，一般在床身的左端。它提供動(dòng)力，并可使工件在各種速度下回轉(zhuǎn)。它基本上由一個(gè)安裝在精密軸承中的空心主軸和一系列變速齒輪——類(lèi)似于卡車(chē)變速箱一所組成。通過(guò)變速齒輪，主軸可以在許多種轉(zhuǎn)速下旋轉(zhuǎn)。大多數(shù)車(chē)床有8-18種轉(zhuǎn)速，一般按等比級(jí)數(shù)排列。而且在現(xiàn)代機(jī)床上只需扳動(dòng)2-4個(gè)手柄，就能得到全部轉(zhuǎn)速。一種正在不斷增長(zhǎng)的趨勢(shì)是通過(guò)電氣的或者機(jī)械的裝置進(jìn)行無(wú)級(jí)變速。
由于機(jī)床的精度在很大程度上取決于主軸，因此，主軸的結(jié)構(gòu)尺寸較大，通常安裝在預(yù)緊后的重型圓錐滾子軸承或球軸承中。主軸中有一個(gè)貫穿全長(zhǎng)的通孔，長(zhǎng)棒料可以通過(guò)該孔送料。主軸孔的大小是車(chē)床的一個(gè)重要尺寸，因?yàn)楫?dāng)工件必須通過(guò)主軸孔供料時(shí)，它確定了能夠加工的棒料毛坯的最大尺寸。
尾架組件主要由三部分組成。底板與床身的內(nèi)側(cè)導(dǎo)軌配合，并可以在導(dǎo)軌上做縱向移動(dòng)。底板上有一個(gè)可以使整個(gè)尾架組件夾緊在任意位置上的裝置。尾架體安裝在底板上，可以沿某種類(lèi)型的鍵槽在底板上橫向移動(dòng)，使尾架能與主軸箱中的主軸對(duì)正。尾架的第三個(gè)組成部分是尾架套筒。它是一個(gè)直徑通常大約在51—76mm(2-3英寸)之間的鋼制空心圓柱體。通過(guò)手輪和螺桿，尾架套筒可以在尾架體中縱向移人和移出幾英寸。
車(chē)床的規(guī)格用兩個(gè)尺寸表示。第一個(gè)稱(chēng)為車(chē)床床面上最大加工直徑。這是在車(chē)床上能夠旋轉(zhuǎn)的工件的最大直徑。它大約是兩頂尖連線與導(dǎo)軌上最近點(diǎn)之間距離的兩倍。第二個(gè)規(guī)格尺寸是兩頂尖之間的最大距離。車(chē)床床面上最大加工直徑表示在車(chē)床上能夠車(chē)削的最大工件直徑，而兩頂尖之間的最大距離則表示在兩個(gè)頂尖之間能夠安裝的工件的最大長(zhǎng)度。
普通車(chē)床是生產(chǎn)中最經(jīng)常使用的車(chē)床種類(lèi)。它們是具有前面所敘述的所有那些部件的重載機(jī)床，并且除了小刀架之外，全部刀具的運(yùn)動(dòng)都有機(jī)動(dòng)進(jìn)給。它們的規(guī)格通常是：車(chē)床床面上最大加工直徑為305-610mm(12-24英寸)；兩頂尖之間距離為610—1 219mm(24-48英寸)。但是，床面上最大加工直徑達(dá)到1 270mm(50英寸)和兩頂尖之間距離達(dá)到3 658mm(12英尺)的車(chē)床也并不少見(jiàn)。這些車(chē)床大部分都有切屑盤(pán)和一個(gè)安裝在內(nèi)部的冷卻液循環(huán)系統(tǒng)。小型的普通車(chē)床——車(chē)床床面最大加工直徑一般不超過(guò)330mm(13英寸)——被設(shè)計(jì)成臺(tái)式車(chē)床，其床身安裝在工作臺(tái)或柜子上。
雖然普通車(chē)床有很多用途，是很有用的機(jī)床，但是更換和調(diào)整刀具以及測(cè)量工件花費(fèi)很多時(shí)間，所以它們不適合在大量生產(chǎn)中應(yīng)用。通常，它們的實(shí)際加工時(shí)間少于其總加工時(shí)間的30％。此外，需要技術(shù)熟練的工人來(lái)操作普通車(chē)床，這種工人的工資高而且很難雇到。然而，操作工人的大部分時(shí)間卻花費(fèi)在簡(jiǎn)單的重復(fù)調(diào)整和觀察切屑產(chǎn)生過(guò)程上。因此，為了減少或者完全不雇用這類(lèi)熟練工人，六角車(chē)床、螺紋加工車(chē)床和其他類(lèi)型的半自動(dòng)和自動(dòng)車(chē)床已經(jīng)很好地研制出來(lái)，并已經(jīng)在生產(chǎn)中得到廣泛應(yīng)用。
普通車(chē)床作為最早的金屬切削機(jī)床中的一種，目前仍然有許多有用的和為人們所需要的特性?，F(xiàn)在，這些機(jī)床主要用在規(guī)模較小的工廠中，進(jìn)行小批量的生產(chǎn)，而不是進(jìn)行大批量的生產(chǎn)。
在現(xiàn)代的生產(chǎn)車(chē)間中，普通車(chē)床已經(jīng)被種類(lèi)繁多的自動(dòng)車(chē)床所取代，諸如自動(dòng)仿形車(chē)床，六角車(chē)床和自動(dòng)螺絲車(chē)床?，F(xiàn)在，設(shè)計(jì)人員已經(jīng)熟知先利用單刃刀具去除大量的金屬余量，然后利用成型刀具獲得表面光潔度和精度這種加工方法的優(yōu)點(diǎn)。這種加工方法的生產(chǎn)速度與現(xiàn)在工廠中使用的最快的加工設(shè)備的速度相等。
普通車(chē)床的加工偏差主要依賴(lài)于操作者的技術(shù)熟練程度。設(shè)計(jì)工程師應(yīng)該認(rèn)真地確定由熟練工人在普通車(chē)床上加工的試驗(yàn)零件的公差。在把試驗(yàn)零件重新設(shè)計(jì)為生產(chǎn)零件時(shí)，應(yīng)該選用經(jīng)濟(jì)的公差。
對(duì)生產(chǎn)加工設(shè)備來(lái)說(shuō)，目前比過(guò)去更著重評(píng)價(jià)其是否具有精確的和快速的重復(fù)加工能力。應(yīng)用這個(gè)標(biāo)準(zhǔn)來(lái)評(píng)價(jià)具體的加工方法，六角車(chē)床可以獲得較高的質(zhì)量評(píng)定。
在為小批量的零件(100—200件)設(shè)計(jì)加工方法時(shí)，采用六角車(chē)床是最經(jīng)濟(jì)的。為了在六角車(chē)床上獲得盡可能小的公差值，設(shè)計(jì)人員應(yīng)該盡量將加工工序的數(shù)目減至最少。
自動(dòng)螺絲車(chē)床通常被分為以下幾種類(lèi)型：?jiǎn)屋S自動(dòng)、多軸自動(dòng)和自動(dòng)夾緊車(chē)床。自動(dòng)螺絲車(chē)床最初是被用來(lái)對(duì)螺釘和類(lèi)似的帶有螺紋的零件進(jìn)行自動(dòng)化和快速加工的。但是，這種車(chē)床的用途早就超過(guò)了這個(gè)狹窄的范圍?，F(xiàn)在，它在許多種類(lèi)的精密零件的大批量生產(chǎn)中起著重要的作用。工件的數(shù)量對(duì)采用自動(dòng)螺絲車(chē)床所加工的零件的經(jīng)濟(jì)性有較大的影響。如果工件的數(shù)量少于1 000件，在六角車(chē)床上進(jìn)行加工比在自動(dòng)螺絲車(chē)床上加工要經(jīng)濟(jì)得多。如果計(jì)算出最小經(jīng)濟(jì)批量，并且針對(duì)工件批量正確地選擇機(jī)床，就會(huì)降低零件的加工成本。
因?yàn)榱慵谋砻娲植诙仍诤艽蟪潭壬先Q于工件材料、刀具、進(jìn)給量和切削速度，采用自動(dòng)仿形車(chē)床加工所得到的最小公差不一定是最經(jīng)濟(jì)的公差。
在某些情況下，在連續(xù)生產(chǎn)過(guò)程中，只進(jìn)行一次切削加工時(shí)的公差可以達(dá)到±0．05mm。對(duì)于某些零件，槽寬的公差可以達(dá)到±0．125mm。鏜孔和采用單刃刀具進(jìn)行精加工時(shí)，公差可達(dá)到±0．0125mm。在希望獲得最大產(chǎn)量的大批量生產(chǎn)中，進(jìn)行直徑和長(zhǎng)度的車(chē)削時(shí)的最小公差值為土0．125mm是經(jīng)濟(jì)的。
金屬切削加工在制造業(yè)中得到了廣泛的應(yīng)用。其特點(diǎn)是工件在加工前具有足夠大的尺寸，可以將工件最終的幾何形狀尺寸包容在里面。不需要的材料以切屑、顆粒等形式被去除掉。去除切屑是獲得所要求的工件幾何形狀，尺寸公差和表面質(zhì)量的必要手段。切屑量多少不一，可能占加工前工件體積的百分之幾到70％—80％不等。
由于在金屬切削加工中，材料的利用率相當(dāng)?shù)?，加之預(yù)測(cè)到材料和能源的短缺以及成本的增加，最近十年來(lái)，金屬成形加工的應(yīng)用越來(lái)越多。然而，由于金屬成形加工的模具成本和設(shè)備成本仍然很高，因此盡管金屬切削加工的材料消耗較高，在許多情況下，它們?nèi)匀皇亲罱?jīng)濟(jì)的。由此可以預(yù)料，在最近幾年內(nèi)，金屬切削加工在制造業(yè)中仍將占有重要的位置。而且，金屬切削加工的自動(dòng)生產(chǎn)系統(tǒng)的發(fā)展要比金屬成形加工的自動(dòng)生產(chǎn)系統(tǒng)的發(fā)展要快得多。
在金屬切削加工中，信息的傳遞是通過(guò)剛性傳遞介質(zhì)(刀具)實(shí)現(xiàn)的。刀具相對(duì)工件運(yùn)動(dòng)，機(jī)械能通過(guò)刀具作用于工件。因此，刀具的幾何形狀和刀具與工件的運(yùn)動(dòng)方式?jīng)Q定了工件的最終形狀。這個(gè)基本過(guò)程是機(jī)械過(guò)程：實(shí)際上是一個(gè)剪切與斷裂相結(jié)合的過(guò)程。
如前所述，在金屬切削加工中，多余的材料由剛性刀具切除，以獲取需要的幾何形狀、公差和表面光潔度。屬于此類(lèi)加工方法的例子有車(chē)削、鉆削、鉸孔、銑削、牛頭刨削、龍門(mén)刨削、拉削、磨削、珩磨和研磨。
大多數(shù)切削加工(或稱(chēng)機(jī)械加工)過(guò)程是以?xún)删S表面成形法為基礎(chǔ)的。也就是說(shuō)，刀具與工件材料之間需要兩種相對(duì)運(yùn)動(dòng)。一種定義為主運(yùn)動(dòng)(決定切削速度)，另一種定義為進(jìn)給運(yùn)動(dòng)(向切削區(qū)提供新的加工材料)。
車(chē)削時(shí)，工件的回轉(zhuǎn)運(yùn)動(dòng)是主運(yùn)動(dòng)；龍門(mén)刨床刨削時(shí)，工作臺(tái)的直線運(yùn)動(dòng)是主運(yùn)動(dòng)。車(chē)削時(shí)，刀具連續(xù)的直線運(yùn)動(dòng)是進(jìn)給運(yùn)動(dòng)；而在龍門(mén)刨床刨削中，刀具間歇的直線運(yùn)動(dòng)是進(jìn)給運(yùn)動(dòng)。
切削速度v是主運(yùn)動(dòng)中刀具(在切削刃的指定點(diǎn))相對(duì)工件的瞬時(shí)速度。車(chē)削、鉆削和銑削等加工方法的切削速度可以用下式表示：
V= m／min
式中v為切削速度，其單位為m／min；d是工件上將要切削部分的直徑，其單位為m；n是工件或主軸的轉(zhuǎn)速，單位為rev／min。根據(jù)具體運(yùn)動(dòng)方式不同，v、d和n可能與加工材料或工具有關(guān)。在磨削進(jìn)，切削速度通常以m／s為單位度量。
在主運(yùn)動(dòng)之外，當(dāng)?shù)毒呋蚬ぜ鬟M(jìn)給運(yùn)動(dòng)f時(shí)，便產(chǎn)生重復(fù)的或連續(xù)的切屑切除過(guò)程，從而形成所要求的加工表面。進(jìn)給運(yùn)動(dòng)可以是間歇的，或者是連續(xù)的。進(jìn)給速度vf定義為在切削刃的某一選定點(diǎn)上，進(jìn)給運(yùn)動(dòng)要對(duì)于工件的瞬時(shí)速度。
對(duì)于車(chē)削和鉆削，進(jìn)給量f以工件或刀具每轉(zhuǎn)的相對(duì)移動(dòng)量(mm／rev)來(lái)表示；對(duì)于龍門(mén)刨削和牛頭刨削，進(jìn)給量f以刀具或工件每次行程的相對(duì)移動(dòng)量(mm／stroke)來(lái)表示。對(duì)于銑削，以刀具的每齒進(jìn)給量fz (mm／tooth)來(lái)表示，fz是相鄰兩齒間工件的移動(dòng)距離。所以，工作臺(tái)的進(jìn)給速度vf (mm／min)是刀具齒數(shù)z，刀具每分鐘轉(zhuǎn)數(shù)n與每齒進(jìn)給量人的乘積(vf=nzfz)。
包含主運(yùn)動(dòng)方向和進(jìn)給運(yùn)動(dòng)方向的平面被定義為工作平面，因?yàn)樵撈矫姘瑳Q定切削作用的兩種基本運(yùn)動(dòng)。
車(chē)削時(shí)的切削深度α(有時(shí)也被稱(chēng)為背吃刀量)是刀具切削刃切進(jìn)或深人工件表面內(nèi)的距離。切削深度決定工件的最終尺寸。在車(chē)削加工中采用軸向進(jìn)給時(shí)，切削深度可以通過(guò)直接測(cè)量工件半徑的減少量來(lái)確定；在車(chē)削加工中采用徑向進(jìn)給時(shí)，切削深度等于工件長(zhǎng)度的減少量。在鉆削中，切削深度等于鉆頭直徑。對(duì)于銑削，切削深度定義為側(cè)吃刀量αe，它等于銑刀徑向吃刀深度，而銑刀軸向吃刀深度(背吃刀量)被稱(chēng)為αp。
未變形狀態(tài)時(shí)的切屑厚度h，就是在垂直于切削方向的平面內(nèi)垂直于切削刃測(cè)量得到的切屑厚度。切削后的切屑厚度(即切屑實(shí)際厚度h2 )大于未變形時(shí)的切屑厚度，也就是說(shuō)切削比或者切屑厚度比r=h1/h2總是小于1。 ‘
未變形狀態(tài)的切屑寬度b，是在與切削方向垂直的平面內(nèi)沿切削刃測(cè)得的切屑寬度。
對(duì)于單刃刀具切削加工，切削面積A是未變形的切屑厚度h1和切屑寬度b的乘積(即A=h1b)。切削面積也可以用進(jìn)給量f和切削深度α表示如下：
H1=fsink 及 b=a／sink
式中x為主偏角(即切削刃與工作平面形成的夾角)。
因此，可以由下式求出切削面積
A=fa
附錄2：
Lathes And It’s Cutting Process
Lathes are machine tools designed primarily to do turning, facing,and boring. Very little turning is done on other types of machine tools,and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the workpiece. Consequently, more lathes of various types are used in manufacturing than any other machine tool.
The essential components of a lathe are the bed, headstock assembly, tailstock assembly, carriage assembly, and the leadscrew and feed rod.
The bed is the backbone of a lathe. It usually is made of well-
normalized or aged gray or nodular cast iron and provides a heavy, rigid
frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one fiat way in one or both sets. They are precision-machined to assure accuracy of alignment. On most modem lathes the ways are surface-hardened to resist wear and abrasion, but precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed.
The headstock is mounted in a fixed position on the inner ways,usually at the left end of the bed. It provides a powered means of rotating the work at various speeds. Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears--similar to a truck transmission--through which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modem lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.
Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy beatings, usually
preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size d this hole is an important dimension of a lathe because it detemtines the maximum size of bar stock that can be machined when the material must be fed through spindle.
The tailstock assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location. An upper casting fits on the lower one and can be movedtransversely upon it, on some type of keyed ways, to permit aligning the tailstock and headstock spindles. The third major component of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76 mm (2 to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a handwheel and screw.
The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways. The second size dimension is the maximum distance between centers. The swing thus indicates the maximum workpiece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of workpieee that can be mounted between centers.
Engine lathes are the type most frequently used in manufacturing. llley are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mtn ( 12 to 24 inches) swing and from 610 to 1 219 mm (24 to 48 inches) center distances, but swings up to 1 270 mm (50 inches) and center distances up to 3 658 mm ( 12 feet) are not tmcommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes--with swings usually not over 330 mm ( 13 inches)--also are available in bench type,designed for the bed to be mounted on a bench or cabinet.
Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the workpiece, they ale not suitable for quantity production. Often the actual chip-production time is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operator's time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing.
The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered.
The engine lathe has been replaced in today's production shops by a wide variety of automatic lathes such as automatic tracer lathes, turret lathes, and automatic screw machines. All the advantages of single-point tooling for maximum metal removal, and the use of form tools for finish and accuracy, are now at the designer's fingertips with production speeds on a par with the fastest processing equipment on the scene today.
Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used.
Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately andrapidly. Applying this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating.
In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations.
Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines.Originally designed for rapid, automatic production of screws and similar threaded pans, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important pm't in the economy of the parts machined on the automatic screw machine.Quantities less than 1 000 parts may be more economical to set up on the turret lathe than on the automatic screw machine. The cost of the pans machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities.
Since surface roughness depends greatly upon material tumed, tooling, and feeds and speeds employed,minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances.
In some cases, tolerances of ±0.05mm are held in continuous production using but one cut. Groove width can be held to ± 0.125mm on some parts. Bores and single-point finishes can be held to ±0.0125mm. On high-production runs where maximum output is desirable, a minimmn tolerance of ± 0. 125mm is economical on both diameter and length of turn.
Metal-cutting processes are extensively used in the manufacturing industry. They are characterized by the fact that the size of the original workpieee is sufficiently large that the final geometry can be circumscribed by it, and that the unwanted material is removed as chips, particles, and so on. The chips are a necessary means to obtain the desired tolerances, and surfaces. The amount of scrap may vary from a few percent to 70% - 80% of the volume of the original work material.
Owing to the rather poor material utilization of the metal-cutting processes, the anticipated scarcity of materials and energy,and increasing costs, the development in the last decade has been directed toward an increasing application of metal-forming processes. However, die costs and the capital cost of machines remain rather high; consequently, metal-cutting processes are, in many cases, the most economical, in spite of the high material waste, which only has value as scrap. Therefore,it must be expected that the material removal processes will for the next few years maintain their important position in manufacturing.Furthermore,the development of automated production systems has progressed more rapidly for metal-cutting processes than for metal-forming processes.
In metal-cutting processes, the imprinting of information is carried out by a rigid medium of transfer (the tool), which is moved relative to the workpiece, and the mechanical energy is supplied through the tool. The final geometry is thus determined from the geometry of the tool and the pattem of motions of the tool and the workpiece. The basic process is mechanical: actually, a shearing action combined with fracture.
As mentioned previously, the unwanted material in metal-cutting processes is removed by a rigid cutting tool, so that the desired geometry, tolerances, and surface finish are obtained. Examples of processes in this group are turning, drilling, reaming, milling,shaping, planing, broaching, grinding, honing, and lapping.
Most of the cutting or machining processes are based on a tw, dimensional surface creation, which means that two relative motions are necessary between the cutting tool and the work material. These motions are defined as the primary motion, which mainly determines the cutting speed, and the feed motion, which provides the cutting zone with new material.
In turning the primary motion is provided by the rotation of the workpiece, and in planing it is provided by the translation of the table; in turning the feed motion is a continuous translation of the tool, and in planing it is an intermittent translation of the tool.
The cutting speed v is the instantaneous velocity of the primary motion of the tool relative to the workpieee (at a selected point on the cutting edge).
The cutting speed for turning, drilling, and milling processes can be expressed as
v = dn m/min
Where v is the cutting speed in m/min,d the diameter of the workpiece to be cut in meters, and n the workpiece or spindle rotation in rev/min. Thus v, d, and n may relate to the work material or the tool, depending on the specific kinematic pattern. In grinding the cutting speed is normally measured in m/s.
The feed motion f is provided to the tool or the workpiece and, when added to the primary motion, leads to a repeated or continuous chip removal and the creation of the desired machined surface. The motion may proceed by steps or continuously. The feed speed vf is defined as the instantaneous velocity of the feed motion relative to the workpiece (at a selected point on the cutting edge).
For mining and drilling, the feed f is measured per revolution (mm/rev) of the workpiece or the tool; for planing and shaping f is measured per stroke (mm/stroke) of the tool or the workpiece. In mining the feed is measured per tooth of the cutter fz(mm/tooth); that is, fzis the displacement of the workpiece between the cutting action of two successive teeth. The feed speed vf(mm/rain) of the table is therefore the product of the number of teeth z of the cutter, the revolutions per minute of the cutter n, and the feed per tooth(vf=nzfz).
A plane containing the directions of the primary motion and the feed motion is defined as the working plane, since it contains the motions responsible for the cutting action.
In turning the depth of cut a (sometimes also called back engagement) is the distance that the cutting edge engages or projects below the original surface of the workpiece. The depth of cut determines the final dimensions of the workpiece. In taming, with an axial feed, the depth of cut is a direct measure of the decrease in radius of the workpiece and with radial feed the depth of cut is equal to the decrease in the length of workpiece. In drilling, the depth of cut is equal to the diameter of the drill. For milling, the depth of cut is defined as the working engagement ae and is the radial engagement of the cutter. The axial engagement (back engagement) of the cutter is called ap.
The chip thickness hi in the undeformed state is the thickness of the chip measured perpendicular to the cutting edge and in a plane perpendicular to the direction of cutting. The chip thickness after cutting (i. e., the actual chip thickness h2) is larger than the undeformed chip thickness, which means that the cutting ratio or chip thickness ratio r =h1/h2 is always less than unity.
Chip Width The chip width b in the tmdeformed state is the width of the chip measured along the cutting edge in a plane perpendicular to the direction of cutting.
For single-point too! operations, the area of cut A is the product of the undeformed chip thickness h l and the chip width b (i.e., A = h1b). The area of cut can also be expressed by the feedf and the depth of cut a as follows:
H1=f sink and b = a/sink
Where k is the major cutting edge angle (i. e., the angle that the cutting edge forms with the working plane).
Consequently, the area of cut is given by
A =fa
·11·
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