汽車缸套專用鏜床設計
汽車缸套專用鏜床設計,汽車缸套專用鏜床設計,汽車,專用,鏜床,設計
英文翻譯原文:
(一)BORING AND BORING MACHINES
As carried out on a lathe, boring produces circular internal profiles in hollow work-pieces or on a hole made by drilling or another process, Boring is done with cutting tools that are similar to those used in turning. Because the boring bar has to reach the full length of the bore, tool deflection and, therefore, maintainance of dimensional accuracy can be a significant problem.
The boring bar must be sufficiently stiff—that is, made of a material with high elastic modulus, such as tungsten carbide –to minimize deflection and avoid vibration and chatter. Boring bars have been designed with capabilities for damping vibration.
Although boring operations on relatively small work-pieces. Can be carried out on a lathe, boring mills are used for large work-pieces. These machines are either vertical or horizontal, and are capable of performing operations such as turning, facing, grooving, and chamfering. A vertical boring machine is similar to a lathe but has a vertical axis of work-piece rotation.
The cutting tool (usually a single point made of M-2 and M-3 high-speed steel and C-7 and C-8 carbide) is mounted on the tool head, which is capable of vertical movement (for boring and turning) and radial movement (for facing), guided by the cross-rail. The head can be swiveled to produce conical (tapered) surfaces.
In horizontal boring machine, the work-piece is mounted on a table that can move horizontally in both the axial and radial directions. The cutting tool is mounted on a spindle that rotates in the headstock, which is capable of both vertical and longitudinal movements. Drills, reamer, taps, and milling cutters can also be mounted on the machine spindle.
Boring machine are available with a variety of features. Although work-piece diameters are generally 1 m-4 m(3ft-12ft),work-piece as large as 20 m(60ft) can be machined in some vertical boring machines. Machine capacities range up to 150 kw (200hp).these machines are also available with computer numerical controls, which allow all movements to be programmed. With such controls, little operaror involvement is required and consistency and productivity are improved. Cutting speeds and feeds for boring are similar to those for turning.(For capabilities of boring operations)
Jig borers are vertical boring machines with high –precision bearings. Although they are available in various sizes and used in tool rooms for making jigs and fixtures, they are now being replaced by more versatile numerical control machines.
Design considerations for boring. Guidelines for efficient and economical boring operations are similar to those for turning. Additionally, the following factors should be considered：
a. Whenever possible, through holes rather than blind holes should be specified.(The term blind hole refers to a hole that does not go though the thickness of the work-piece )
b. The greater the length –to –bore-diameter ratio, the more difficult it is to hold dimensions because of the deflections of the boring bar due to cutting forces.
c. Interrupted internal surfaces should be avoided.
（2）Fundamentals of Machine Tools
In many cases products form the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications. To meet such precise tolerances the removal of small amounts of material is needed. Usually machine tools are used for such operation.
In the United States material removal is a big business-in excess of $ per year, including material, labor, overhead, and machine-tool shipments, is spent. Since 60 percent of the mechanical and industrial engineering and technology graduates have something connection with the machining industry either through sale, design, or operation of machine shops, or working in related industry, it is wise for an engineering student to devote some time in his curriculum to studying material removal and machine tools.
A machine tool provides the means for cutting tools to shape a workpiece to required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members, which are as follow:
(a) Bed, Structure or Frame. This is the main member which provides a basis for, and a connection between, the spindles and slides; the distortion and vibration under load must be kept to a minimum.
(b) Slides and Sideways. The translation of a machine element (e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surfaces (the slideway).
(c) Spindles and Bearings. Angular displacements take place about an axis of rotation; the position of this axis must be constant within extremely fine limits in machine tools, and is ensured by the provision of precision spindles and bearings.
(d) Power Unit. The electric motor is the universally adopted power unit for machine tools. By suitably positioning individual motors, belt and gear transmissions are reduced to a minimum.
(e) Transmission Linkage. Linkage is the general term used to denote the mechanical, hydraulic, pneumatic or electric mechanisms which connect angular and linear displacements in defined relationship.
There are two broad divisions of machining operations:
(a) Roughing, for which the metal removal rate, and consequently the cutting force, is high ,but the required dimensional accuracy relatively low .
(b) Finishing, for which the metal removal rate, and consequently the cutting force, is low, but the required dimensional accuracy and surface finish relatively high .
It follows that static loads and dynamic loads, such as result form an unbalanced grindingwheel, are more significant in finishing operations than in roughing operations, The degree of precision achieved in any machining process will usually be influenced by the magnitude of the deflections, which occur as a result of the force acting.
Machine tool frames are generally made in cast iron, although some may be steel casting or mild-steel fabrications. Cast iron is chosen because of its cheapness, rigidity, compressive strength and capacity for damping the vibrations set-up in machine operations, To avoid massive sections in castings, carefully designed systems of ribbing are used to offer the maximum resistance to bending and torsional stresses. Two basic types of ribbing are box and diagonal. The box formation is convenient to produce, apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing provides greater torsional stiffness and yet permits swarf to fall between the sections; it is frequently used for lathe beds.
The slides and slideways of a machine tool locate and guide members which move relative to each other, usually changing the position of the tool relative to workpiece .The movement generally takes the form of translation in a straight line, but is sometimes angular rotation, e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding which the helix angle of the workpiece thread. The basic geometric elements of slides are flat, vee, dovetail and cylinder. These elements may be used separately or combined in various ways according to the applications . Features of slideways are as follows :
(a) Accuracy of Movement. Where a slide is to be displaced in a straight line, this line must lie in two mutually perpendicular planes and there must be no slide rotation. The general tolerance for straightness of machine tool slideways is 0~0.02mm per 1000mm; on horizontal surfaces this tolerance may be disposed so that a convex surface results, thus countering the effect of "sag" of the slideway.
(b) Means of Adjustment. To facilitate assembly, maintain accuracy and eliminate "play" between sliding members after wear has taken place, a strip is sometimes inserted in slides. This is called a gibstrip. Usually, the gib is retained by socket-head screws passing through elongated slots；and is adjusted by grub-screws secured by lock nuts.
(c) Lubrication. Slideways may be lubricated by either of the following systems：1)Intermittently through grease or oil nipples, a method suitable where movements are infrequent and speed low．
2) Continuously e.g. by pumping through a metering valve and pipe-work to the point of application; the film of oil introduced between surfaces by these means must be extremely thin to avoid the slide “floating”．If sliding surfaces were optically flat oil would be squeezed out，resulting in the surfaces sticking. Hence in practice slide Sill"faces are either grourld using the edge of a cup wheel，or scraped. Both processes produee minulte surface depressions，which retain‘‘pocket” of oil, and complete separation of the parts may not occur at all points.
(d) Protection．To maintain slideways in good order, the following conditions must be met：
1) Ingress of foreign matter，e．g．swarf，must be prevented. Where this is no possible，it is desirable to have a form of slideway，which does not retain swarf，e.g. the inverted vee.
2) Lubricating oil must be retained．The adhesive property of oil for use on vertical or inclined slide surface is important; oils are available which have been specially developed for this purpose. The adhesiveness of oil also preverts it being washed away by cutting fluids．
3) Accidental damage must be prevented by protective guards．
譯文:
(一)鏜削加工和鏜床
像車床加工零件一樣，鏜床能在中空的工件或由鉆削加工或其它工藝所加工的孔上進行內(nèi)輪廓圓的加工。鏜削是由那些類似車削的刀具完成的。因為鏜頭必須達到鏜桿的全長，刀具將發(fā)生彎曲，因此，尺寸精度的保持性成為了一個重大問題。
鏜桿必須有足夠的剛度——刀桿是由較高彈性模量的材料制造的，比如碳化鎢（硬質(zhì)合金）——去減小彎曲和避免搖動和振動。鏜桿被設計有減振的能力。
鏜床既能加工在車床上加工的較小工件，鏜銑床又能加工巨大的工件。這類機械既有立式的又有臥式的并且能夠完成如：車削、車端面、切槽、和倒角。一臺立式的鏜床類似一臺車床，但它有一根垂直的工件旋轉(zhuǎn)軸。
刀具（通常用于切削的單獨切削點是由M-2和M-3高速鋼和C-8硬質(zhì)合金制造的）被安裝于能垂直運動（用于鏜削和車削）和徑向運動（用于車端面）并由十字導軌導向的刀頭上。刀頭能夠旋轉(zhuǎn)去加工圓錐形表面。
在臥式鏜床上工件被裝夾在能在水平面內(nèi)兩個軸向和徑向上移動的工作臺上，刀具被安裝于能做垂直和縱向兩方向上運動的主軸箱上。鉆頭、鉸刀、螺紋刀和銑刀都能安裝于機床主軸上。
鏜床具有許多優(yōu)良的性能，它所加工工件的直徑是1m-4m(3ft-12ft)，工件尺寸達到20m(60ft)的可在專用的立式鏜床上加工。機床功率范圍可達到150kw(200hp)。這些可用于所有運動都能編程的數(shù)字控制加工。利用這些控制，只需要很少的相關操作，并且穩(wěn)定性和生產(chǎn)率大大提高了。鏜床的切削速度和進給速度和車床比較相似。
坐標鏜床是屬于具有較高精度支撐的立式鏜床。盡管它們可用于各類尺寸的工件加工和擁有夾緊合安裝的刀具空間。它們正被多功能的數(shù)控機床取代。
鏜床的設計要求：導軌的效率，類似于車削的經(jīng)濟型操作，另外，應該考慮以下因素：
a.無論何時，應盡可能注意是加工通孔而并盲孔。（盲孔系列是指那些沒有穿國工件厚度的孔）
b.應該控制徑向進給速率，很難去支撐徑向，因為切削力引起鏜桿的彎曲變形。
c.應該避免交叉的內(nèi)表面加工。
（2）機床基礎
為了滿足規(guī)定的設計規(guī)格，大多數(shù)情況下初步加工的產(chǎn)品都必須再經(jīng)過進一步的尺寸和表面的精加工。要達到這樣的精確規(guī)定公差的要求，少量材料需要被切除掉，而機床通常就是用于此種操作。
在美國，材料切除是一項大業(yè)務——每年這方面的支出超過36×109美元，包括材料、勞力和機床運輸。60%的機械工程和工業(yè)工程畢業(yè)生都通過貿(mào)易、設計、機械修理工廠，或通過在相關行業(yè)工作而與機械工業(yè)密不可分，因而如果他們花費一定的時間精力來學習這個領域中的材料切除和機床技術的話會是很明智的選擇。
機床提供切割工具的方式，以使工件成型，達到規(guī)定的尺寸；此種機器依靠其基礎部件的運作來掌握工具和工件之間的聯(lián)系。其基礎部件的運作如下：
①． 床身、構(gòu)造和框架。這三種主要的部件為錠子和滑移的基礎，并將它們聯(lián)系起來；操作中的變形和震動必須盡量避免。
②． 滑移與滑軌。機械部件（如滑移）的轉(zhuǎn)換通常是通過在精密的指導表面（滑軌）的控制下做直線運動而完成的。
③． 錠子與軸承。角位移是圍繞一個旋轉(zhuǎn)軸線發(fā)生的；這個轉(zhuǎn)軸的位置必須一直處于嚴格精確的限制之中，并由精密錠子和軸承提供保障。
④． 動力儀器。電動機是被廣泛應用于機床的動力儀器。通過將各電動機放置于合適的位置，傳輸帶和齒輪運輸會被降低到最低限度。
⑤． 傳輸聯(lián)接。聯(lián)接是一個通常用來指機械驅(qū)動的、水壓驅(qū)動的、氣壓驅(qū)動的和電力驅(qū)動的機械裝置，將有角移置和直線移置聯(lián)系起來，使其符合規(guī)定。
加工操作大體上分為兩類：
① . 粗加工。其金屬切除率高且由此導致的切除力較大，但規(guī)定的尺寸精度相對較低。
② . 精加工。其金屬切除率低且由此導致的切除力較小，但規(guī)定的尺寸精度相對較高。
靜載荷及動載荷，如處于非平衡狀態(tài)的砂輪所導致的結(jié)果，自然在精加工方面比在粗加工操作方面更為重要。任何加工過程所達到的精確度通常會受到偏差大小的影響，這種影響是是操作動力的結(jié)果。
機床框架通常由鑄鐵制造，雖然有些機床可能為鋼鑄件或低碳鋼結(jié)構(gòu)。選擇鑄鐵是因為其價格、硬度、耐壓強度及減少加工操作中的震動的能力。為了避免鑄件出現(xiàn)輕重不均的部分，精心設計的肋材構(gòu)架系統(tǒng)被采用，最大可能地抵抗造成彎曲和變形的壓力。
兩種肋材構(gòu)架分別為箱形和對角線形。箱形結(jié)構(gòu)便于生產(chǎn)，因為壁上的孔徑允許核心的定位和抽取。對角線楞條配置則提供更大的抗紐剛度并允許金屬屑從部件當中的孔隙落出，因此經(jīng)常被用于機床。
車床的滑移和滑軌指引并且為相互影響運動的部件定位，通常根據(jù)工件更改車床的位置。運動一般采取直線運動的形式，但有時是旋轉(zhuǎn)，例如，對應于工件的螺紋螺旋角方向而轉(zhuǎn)動萬能螺紋磨床上的砂輪頭的一個角度?；镜膶ΨQ滑移部件為扁平、V形、燕尾槽形及汽缸形。這些部件既可單獨使用又可根據(jù)用途以不同方式組合使用?；壍奶卣魅缦拢?
1 如果滑移要在一條直線上移動位置，這條直線必須位于兩個相互垂直的平面之間且必須沒有滑動旋轉(zhuǎn)。
2 機床滑軌的直線性規(guī)定公差一般介于0～0.02mm/100mm之間；在水平表面此公差可以被處理以得到凸形表面這樣就可以抵消滑軌下沉的作用。
3 潤滑油?；壙赡鼙灰韵聝煞N系統(tǒng)中的任何一種潤滑：
1． 間歇通過油脂或油嘴潤滑。這種方法適合運作不頻繁和速度不高的情況。
2． 持續(xù)潤滑，如通過計量閥和管道根據(jù)需要抽??；通過這些方法操作的表面之間的潤滑油薄膜必須非常薄，以避免滑移漂浮。如果滑移表面是鏡平面，油就會被擠出，使表面粘接。因此實際操作中滑移表面不是被杯狀輪邊緣壓平，就是被刮去。兩種操作過程都會產(chǎn)生微小的表面凹痕，這種凹痕會導致少量潤油存留，而且零件的完全分離可能不會總是發(fā)生；因此，滑移的正確定位得到保留。
4 保護。為了維護滑軌，使其正常工作，必須滿足如下條件：
1． 必須避免外來物質(zhì)如鐵屑的進入。如果這種條件不可能滿足，則應該采用不會滯留鐵屑的，如倒V形的滑移。
2． 潤滑油必須保留。潤滑油在垂直的或傾斜滑移表面上的粘性特質(zhì)非常重要；特制的潤滑油市場有售。潤滑油的粘性同時能防止其被切削液沖走。
3． 必須防止由保護裝置導致的意外損壞。
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