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外 文 翻 譯 專 業(yè) 機械設(shè)計制造及自動化 學 生 姓 名 孫 道 德 班 級 BMZ 機制 031 學 號 0361440120 指 導 教 師 劉 必 榮 1 附 件 1 機 床 基 礎(chǔ) 范云漲 著 孫道德 譯 摘 要 在許多情況下初步加工成型的產(chǎn)品必須在尺寸和表面光潔度方面經(jīng)過進一 步的加工以滿足設(shè)計要求 為了滿足這么高要求的尺寸 去除少量的材料是必需的 機床通常用于執(zhí)行這樣的操作 關(guān)鍵字 機床 車床 機床介紹 機床加工作為產(chǎn)生形狀的一種方法是所有制造過程中最普遍使用的并且 是最重要的方法 機床加工是一種成型的過程通過電機驅(qū)動 材料以切屑的形式被 去除 大多數(shù)的機床加工是通過既支承工件又支承刀具的裝備來完成 盡管在某些場 合 工件無支承情況下 使用移動式裝備來實現(xiàn)加工 小批量生產(chǎn)低費用 機床加工在制造過程中有兩個方面 對于鑄造 鍛造和壓 力加工 每一個要生產(chǎn)的具體工件形狀 即使是一個零件 幾乎都要花費高額的加 工費用 靠焊接來產(chǎn)生的結(jié)構(gòu)形狀 在很大程度上取決于有效的原材料的形狀 一 般來說 通過利用貴重設(shè)備而又無需特種加工條件下 幾乎可以從任何種類原材料 開始 借助機床加工把原材料加工成任意所要求的結(jié)構(gòu)形狀 只要外部尺寸足夠大 那都是可能的 因此對于生產(chǎn)一個零件 通常選擇機床加工甚至于當零件結(jié)構(gòu)及要 生產(chǎn)的批量大小上按理都適于用鑄造 鍛造或壓力加工來生產(chǎn)的 高的精度和良好表面光潔度 機械加工的第二方面用途是建立在高精度和可能 的表面光潔度基礎(chǔ)上 許多零件 如果用別的其他方法來生產(chǎn)屬大批量生產(chǎn)的話 那么在機械加工中則是屬低公差且又能滿足要求的小批量生產(chǎn)了 另方面 許多零 件靠較粗的生產(chǎn)加工工藝提供其一般表面形狀 而僅僅是在需要高精度的且選擇過 的表面上才進行機械加工 例如內(nèi)螺紋 除了機械加工之外 幾乎沒有別的加工方 法能進行加工 再如已鍛工件上的小孔加工 也是在被鍛后進行機械加工才完成的 在美國材料切削業(yè)是一個很大的產(chǎn)業(yè) 費用每年超過 36 109美元 包括材 料 勞動力 管理費 機床裝運費等所花的費用 由于 60 機械和工業(yè)工程以及技 2 術(shù)等級評定工作都跟機床加工工業(yè)有某些關(guān)系 或者通過買賣 設(shè)計或者機器車間 中操作或在有關(guān)工業(yè)企業(yè)中加工 因此 對于工程專業(yè)學生來說 在他的學習計劃 中集中一段時間去學習研究材料切削和機床是個明智的做法 機床為通過切削工具使工件成型以達到所需的尺寸提供了方法 機床通過其基 礎(chǔ)構(gòu)件的功能作用 以控制相互關(guān)系方式支持 夾緊工具和工件 現(xiàn)將基本結(jié)構(gòu)部 件列舉如下 a 床身 構(gòu)架或機架 這是一個主要部件 該部件為主軸 拖板箱等提供一個 基礎(chǔ)和連接中介 在負載作用下 它必須使變形和振動保持最小 b 拖板箱和導軌 機床部件 如拖板箱 的移動 通常是在精確的導軌面約束 下靠直線運動來實現(xiàn) c 主軸和軸承 角位移是圍繞一個旋轉(zhuǎn)軸線發(fā)生的 該軸線的位置必須在機床 中極端精確的限度內(nèi)保持恒定 而且是靠精密的主軸和軸承來提供保證 d 動力裝置 電動機是為機床所普遍采用的動力裝置 通過對各個電機的合適 定位 使皮帶和齒輪傳動裝置減少到最少 e 傳動連桿機構(gòu) 連桿機構(gòu)是個通用術(shù)語 用來代表機械 液壓 氣動或電動 機構(gòu)的 這些機構(gòu)與確定的角位移和線性位移相關(guān)聯(lián) 加工工藝主要有兩個組成部分 a 粗加工 粗加工 金屬切除率高 因而往往切削力也大 但所要求的尺寸精 度低 b 精加工 精加工 金屬切除率低 因而往往切削力也小 但所要求的尺寸精 度和表面光潔度高 由此可見 靜載荷和動載荷 例如由不平衡的砂輪引起的動載荷 在精加工中 比粗加工中有著更為重要的意義 任何加工過程所獲得的精度通常將受到由于力的 作用引起發(fā)生的變形量的影響 機床座架一般是用鑄鐵制造的 然而有些也可能用鑄鋼或中碳鋼來制造 選用 鑄鐵是因為它便宜 剛性好 受壓強度高 并且有減弱機床操作中產(chǎn)生的振動的能 力 為了避免床身鑄件碩大斷面 精心地設(shè)計筋條構(gòu)架以便提供最大的抗彎曲和抗 扭轉(zhuǎn)應(yīng)力的能力 筋條的兩種基本類型是 箱型結(jié)構(gòu)和片狀斜支撐式 箱型結(jié)構(gòu)便 于生產(chǎn) 箱壁上有孔口便于使型芯定位和取出 片狀斜支撐筋條有較大的抗扭剛度 亦能使截面上的碎屑掉落 它常常用于車床床身 機床的拖板箱和導軌是支撐和引 3 導彼此相對運動的零部件 通常是改變刀具相對于工件的位置 運動一般以直線運 動的方式 但也有時是轉(zhuǎn)動 例如對應(yīng)于工件的螺紋上的螺旋角方向而使萬能螺紋 磨床上的砂輪頭轉(zhuǎn)動一個角度 拖板箱構(gòu)件的基本的幾何結(jié)構(gòu)形狀是平的 V 型槽 形 燕尾槽形和圓柱形的 這些構(gòu)件可根據(jù)用途 以各種方法分別使用或結(jié)合使用 導軌的特性如下 a 運動精確 于此拖板是要按直線移動的 這直線必定是由兩個相互垂直的 平面形成而且拖板必定不存在轉(zhuǎn)動 機床導軌的直線度公差是每米 0 0 02 毫米 在水平面上這個公差可以進行處理 以使得到凸形表面 這樣就抵消導軌下凹的作 用 b 調(diào)整手段 為了便于裝配 維護精度和在發(fā)生磨損后便于限制移動構(gòu)件之 間的 竄動 有時在拖板內(nèi)裝入扁條 這扁條被叫做 鋃條 通常該鋃條用穿過 長孔的沉頭螺釘支住 而用平頭螺釘調(diào)整好后用鎖緊螺母上緊 c 潤滑 導軌可用以下兩種裝置進行潤滑 1 間歇潤滑 通過潤滑脂嘴或油嘴進行 這是一種適于運動速度低而不頻繁場 合的方法 2 連續(xù)潤滑 例如通過計量閥和管道將潤滑油泵送到潤滑點 用這種方法引入 兩表面間的油膜必定是很薄的 目的是避免使拖板 浮起 如果滑移表面似鏡面平 滑 油就會被擠出而導致表面粘貼 因而在實踐上 拖板滑移表面是用凹面砂輪的 刃進行磨削或進行刮研 兩種工藝都可產(chǎn)生微小的表面凹痕 它就成為存油凹陷 相配合的零件就不會處處因 浮起 而發(fā)生分離 這樣使拖板確定保持接觸導軌 d 防護 為了維護導軌處于良好狀態(tài) 以下條件必須滿足 1 必須防止外面物質(zhì) 如碎屑進入 具有某一形狀的導軌那是所期望的 在這 種場合 是不可能進入雜物的 例如是倒 V形的導軌時 那就不可能保存碎屑雜物 在導軌上 2 必須保存潤滑油 在垂直或傾斜的導軌面上使用的油要有粘性 那很重要 為了這種使用目的已經(jīng)專門研制出多種有用的潤滑油 油的粘性也要保護 以免被 切削液沖毀 3 必須用防護罩來防止意外的破壞 車床 一臺機床有三個主要功能 1 牢固地支持工件或者刀架和刀具 2 在工 4 件和刀具之間提供相對運動 3 提供一定的走刀和切削速度范圍 以去除切屑形 式來加工金屬的機床一般被分為四大類 使用單點刀具切削的機床 使用多點刀具 切削的機床 使用隨機點刀具切削的機床 磨削 和考慮用于特殊場合的機床 機床本質(zhì)上使用單點刀具切削包括 1 普通車床 2 塔式車床 3 仿 形車床 4 單軸自動車床 5 多軸自動車床 6 牛頭刨床和龍門刨床 7 鏜床 使用多點刀具切削的機床包括 1 鉆床 2 銑床 3 拉床 4 鋸 床 5 齒輪切割機床 使用隨機點刀具切削的機床包括 1 外圓磨床 2 無心磨床 3 平面 磨床 普通車床是基本的旋削機床 從這點出發(fā) 已經(jīng)研制出其他旋削機床 驅(qū)動電 機裝在床身基礎(chǔ)上并通過齒輪 皮帶相結(jié)合來驅(qū)動主軸 以提供每分鐘 25到 1500 轉(zhuǎn)的轉(zhuǎn)速 主軸是一根堅固的空心軸 裝在重型軸承之間 其前端用來安裝驅(qū)動盤 花盤 以便把確定的運動傳到工件 該驅(qū)動盤可借助螺紋 凸輪鎖緊機構(gòu)或借助一個螺紋墊圈和鍵固定在主軸上 車床的床身是鑄鐵件 它提供精確的磨削的滑動表面 導軌 其上放有拖板 該車床拖板是 H型的鑄件 而刀具就安裝在拖板上的刀架上 溜板箱裝在拖板前面 并裝有移動刀具的齒輪機構(gòu) 而拖板順著導軌或橫過導軌以提供所希望的刀具的運 動 拖板上面的小刀架能使刀夾回轉(zhuǎn)所要求的任意角度 為使刀具作線性運動 在 小刀架上裝有手輪和絲桿 以手輪和使小刀架垂直于車床導軌移動的絲桿來提供橫 向進給 溜板箱中的齒輪系可為拖板沿著導軌和橫跨導軌提供動力進給 進給箱齒 輪將運動傳給拖板并控制刀具相對于工件的運動速度 典型的車床進給范圍是主軸 每轉(zhuǎn)從 0 002到 0 160英寸 大約有 50級轉(zhuǎn)速 由于進給箱的移動運動是由主軸齒 輪驅(qū)動的 因此進給量直接與主軸速度有關(guān) 進給箱齒輪傳動機構(gòu)也用于加工螺紋 并能加工每英寸 4到 224扣螺紋 進給箱和車床溜板箱之間的連結(jié)軸是光桿和絲桿 許多車床制造商把這兩桿結(jié) 合成一桿 實際上那就以精確的開支減少機器的費用 進給桿 光桿 用于提供刀 具的運動 它對于精確的工件和好的表面光潔度是很重要的 螺紋導桿 絲桿 用 于提供精確的 螺紋 導程 這對于螺紋切削是必需的 光桿是通過摩擦離合器來 驅(qū)動的 那樣在刀具切削超載情況下能夠打滑保護 這一安全裝置不能裝在絲桿上 5 因為螺紋加工是不允許打滑的 由于螺紋全深很難一次走刀加工完成 因此裝設(shè)一 螺紋指示盤作為下幾次走刀加工時重新對刀用 車床裝有尾座 它具有一精確的軸 該軸有一錐孔 以便安裝鉆頭 鉆夾 鉸 刀和車床頂針 尾座可以沿著車床導軌移動以適應(yīng)工件的不同長度以及加工錐體或 錐形表面 轉(zhuǎn)塔車床基本上是具有某種附加特性的普通車床 提供作為半自動加工和減少 人工操作誤差的機會 轉(zhuǎn)塔車床的拖板設(shè)有 T形槽以便在車床導軌兩端安裝夾刀裝 置 當轉(zhuǎn)塔轉(zhuǎn)入到合適位置時 要正確地裝設(shè)刀具以便進行切削 拖板也裝設(shè)有自 動停機裝置以便控制刀具行程和提供良好的切削的再生產(chǎn) 轉(zhuǎn)塔車床的尾座是六角 形結(jié)構(gòu) 在六角頭中可以裝六把刀具 雖然裝刀和加工準備要花大量時間 但轉(zhuǎn)塔 車床一次裝刀以后無需熟練工人就可以連續(xù)地重復地操作加工 直到刀具變鈍并需 更換為止 這樣轉(zhuǎn)塔車床僅就生產(chǎn)工作在經(jīng)濟上是可行的 合理的 于此 根據(jù)所 制造零件的數(shù)量 為加工準備需要花一定數(shù)量的時間那是合理的 無可非議的 單軸自動車床使用一個立式轉(zhuǎn)塔和兩個橫向溜板 工件通過機床主軸孔被送入 卡盤 而刀具是靠凸輪來自動操作控制 多軸自動車床裝有四 五 六或八根主軸并且在每根主軸中裝一個工件 各主 軸圍繞著一根中心軸來轉(zhuǎn)換位置 以主刀具溜板去接近各主軸 每根軸位上都裝有 一側(cè)向可以獨立操作的刀具滑板 由于各刀具滑板都是靠凸輪操作的 因此加工準 備可能花幾天時間 因而至少需要 5000 件的批量生產(chǎn) 它的使用才是合理的 這種 機床的主要優(yōu)點就是所有的刀具同時工作 并且一個工人可以看管幾部機床 對于 相對簡單的零件而言 多軸自動車床可以以每五秒鐘一件的速度生產(chǎn)加工出成品來 6 附 件 2 Fundamentals of Machine Tools Abstract In many cases products from the 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 Key words machine tools Lathes Introduction of Machining Machining as a shape producing method is the most universally used and the most important of all manufacturing processes Machining is a shape producing process in which a power driven device causes material to be removed in chip form Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported workpiece Low setup cost for small Quantities Machining has two applications in manufacturing For casting forging and press working each specific shape to be produced even one part nearly always has a high tooling cost The shapes that may he produced by welding depend to a large degree on the shapes of raw material that are available By making use of generally high cost equipment but without special tooling it is possible by machining to start with nearly any form of raw material so tong as 7 the exterior dimensions are great enough and produce any desired shape from any material Therefore machining is usually the preferred method for producing one or a few parts even when the design of the part would logically lead to casting forging or press working if a high quantity were to be produced Close accuracies good finishes The second application for machining is based on the high accuracies and surface finishes possible Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process On the other hand many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed Internal threads for example are seldom produced by any means other than machining and small holes in press worked parts may be completed In the United States material removal is a big business in excess of 36 X 109 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 follows 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 Slideways The translation of a machine element e g 8 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 relatively high It follows that static loads and dynamic loads such as result from an unbalanced grindingwheel are more significant in finishing operations than in roughing operations The degree of precision achieved in anymachining 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 restance to bending and torsional stresses Two basic 9 types of ribbing are box and diagonal The box formation is convenient to produce a apertures in walls permitting the positioning and extraction of cores Diagonal ribbing provides grater 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 more relative to eachother usually changing the position of the tool relative to the 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 with 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 according to the applications Features of slidewys 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 sffsct 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 the slides This is called a gibstrip Usually the gib is retained by socket head screws passing through elongated slots and is adjusted by grud screws secured by lock nuts c Lubrication Slideways may be lubricated by either of the following systems 1 Intermittently though grease or oil nipples a method suitable where morements are infrequent and speed low 2 Continuously e g by pumping though a metering valve and pipe work 10 to the point of application the film of oil introduced between surfaces by these means must be extremely thin to avoid the slid floating If sliding surfaces were optically flat oil would be squeezed out resulting in the surfaces sticking Hence in practice slide surfaces are either ground using the edge of a cup wheel or scraped Both processes produce minute surface depressions which retain pocket of oil and complete separation of the parts may not occur at all points positive location of the slides is thus retained 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 when 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 prevents it being washed away by cutting fluids 3 Accidental damage must be prevented by protective guardchined following the press working operations Lathes A machine tool performs three major functions 1 it rigidly supports the workpiece or its holder and the cutting tool 2 it provides relative motion between the workpiece and the cutting tool 3 it provides a range of feeds and speeds Machines used to remove metal in the form of chips are classified in four general groups those using single point tools those using multipoint tools those using randompoint tools and those that are considered special Machines using basically the single point cutting tools include 1 engine lathes 2 turret lathes 3 tracing and duplicating lathes 4 single spindle automatic lathes 5 multi spindle automatic lathes 6 11 shapers and planers 7 boring machines Machines using multipoint cutting tools include 1 drilling machines 2 milling machines 3 broaching machines 4 sawing machines 5 boring machines Machines using random point cutting tools include 1 cylindrical grinder 2 milling machines 3 surface grinders Special metal removal methods include 1 chemical milling 2 electrical discharge machining 3 ultrasonic machining The lathe removes material by rotating the workpiece against a cutter to produce external or internal cylindrical or conical surfaces Ti is also commonly used for the production of flat surfaces by facing in which the workpiece is rotated whiled the cutting tool is moved perpendicularly to the axis of rotation The engine lathe is the basic turning machine from which other turning machines have been developed The drive motor is located in the base and drives the spindle through a combination of belts and gears which provides the spindle speeds with the forward end used for mounting a drive plate to impart positive motion to the workpiece The drive plate may be fastened to be the spindle by threads by a cam lock mechanism or by a threaded collar and key The lathe bed is cast iron and provides accurately ground sliding surfaces on which the carriage rides The lathe carriage is a H shaped casting on which the cutting tool is mounted in a tool holder The apron hangs from the front of the carriage and contains the driving gears that move the tool and carriage along or across the way to provide the desired tool motion A compound rest located above the carriage provided for rotation of the tool holder through any desired angle A hand wheel and feed screw are provided on the compound rest for linear motions of the tool The cross feed is provided with a hand wheel and feed screw for moving the 12 compound rest perpendicular to the lathe way A gear train in the apron provides power feed for the carriage both along and across the way The feed box contains gears to impart motion to the carriage and control the rate at which the tool moves relative to the workpiece On a typical lathe feeds range from 0 002 to 0 160 in per revolution of the spindle in about 50 steps Since the transmission in the feed box is driven from the spindle gears the feeds are directly related to the spindle speed The feed box gearing is also used in thread cutting and provides from 4 to 224 threads threads per in The turret lathe is basically an engine lathe with certain additional features to provide for semiautomatic operation and to reduce the opportunity for human error The carriage of the turret lathe is provided with T slots for mounting a tool holding device on both sides of the lathe ways with tools properly set for cutting when rotated into position The carriage is also equipped with automatic stops that control the tool travel and provide good reproduction of cuts The tailstock of the turret lathe is of hexagonal design in which six tools can be mounted Although a large amount of time is consumed in setting up the tools and stops for operation the turret lathe once set can continue to duplicate operations with a minimum of operator skill until the tools become dulled and need replacing Thus the turret lathe is economically feasible only for production work where the amount of time necessary to prepare the machine for operation is justifiable in terms of the number of part to be made The single spindle automatic lathe uses a vertical turret as well as two cross slides The work is fed through the machine spindle into the chuck and the tools are operated automatically by cams The multispindle automatic lathe is provided with four five six or eight spindles with one workpiece mounted in each spindles Each spindle position is provided with a side tool slide operated independently Since 13 all of the slides are operated by cams the preparation of this machine may take several days and a production run of at least 5000 parts is needed to justify its use The principal advantage of this machine is that all tools work simultaneously and one operator can handle several machines For relatively simple parts multispindle automatic lathes can turn out finished products at the rate of 1 every 5 sec References 1 Valliere D Computer Aided Designing Manufacturing Prentic Hall 1990 2 Goetsch D L Midern Manufacturing Process Delmar Publishers Inc 1991 3 Goetsch D L Advanced Manufacturing Technology Delmar Publishers Inc 1990 4 Amstead B H Manufacturing Processes 1987 5 Metalforming Digest ASM international 1993 6 Edwards Tr K S McKee R B Fundamentals of Mechanical Component Design McGrawHill 1991 7 Chemov N Machine Tools Mir Publishers 1984 8 Wakil Sherif D E1 Processes and Design for Manufacturing Prentice Hall 1989