螺桿空氣壓縮機的設(shè)計含13張CAD圖

螺桿空氣壓縮機的設(shè)計含13張CAD圖,螺桿,空氣壓縮機,設(shè)計,13,cad 計算機輔助設(shè)計的簡要歷史 在我們講述CAD的基本理論之前,先說說他的簡史是比較合適的。CAD是計算機時代的產(chǎn)品.它從早期的計算機繪圖系統(tǒng)發(fā)展到現(xiàn)在的交互式計算機圖形學(xué).兩個這樣的系統(tǒng)包括:麻省理工學(xué)院的Sage Project及Sketchpad。Sage Project旨在開發(fā)CRT顯示器及操作系統(tǒng). Sketchpad是在Sage Project下發(fā)展起來的.CRT顯示和光筆輸入用于與系統(tǒng)進行交互操作.CAD與初次出現(xiàn)的NC和APT(自動編程工具)碰巧同時出世.后來,X-Y繪圖儀作為計算機繪圖的標(biāo)準(zhǔn)硬拷貝輸出裝置使用,一個有趣的現(xiàn)象是X-Y繪圖儀與NC鉆床具有相同的基本機構(gòu),除了繪圖筆NC機床上的主軸刀具替代之外。 開始，CAD系統(tǒng)僅僅是一個帶有內(nèi)置設(shè)計符號的繪圖編輯器，供用戶使用的幾何元素只有直線、圓弧、以及兩者的組合。自由曲線及其曲面的發(fā)展，如昆氏嵌面、貝塞爾嵌面以及B-樣條曲線，使CAD系統(tǒng)可用于復(fù)雜曲線與曲面設(shè)計。三維CAD系統(tǒng)允許設(shè)計者步入三維設(shè)計空間。由于一個三維設(shè)計模型包含了NC刀具路徑編程所需的足夠信息，所以能夠開發(fā)CAD與NC之間聯(lián)系的系統(tǒng)。所謂交鑰匙的CAD/CAM系統(tǒng)便是根據(jù)這一概念開發(fā)的，并從20世紀(jì)70年代至80年代流行起來。 20世紀(jì)70年代，三維實體建模的發(fā)明標(biāo)志著CAD一個新時代的開始。過去的三維線框模型僅用其邊界來表達(dá)一個物體。這在某種意義上是模糊的，一個簡單的模型可能有幾種解釋。同時也無法獲得一個模型的體積信息。實體模型包含完整的信息，因此，它們不僅可用于生成工程圖，而且也可在同一模型上完成工程分析。后來，開發(fā)了許多商業(yè)系統(tǒng)和研究系統(tǒng)。這些系統(tǒng)中相當(dāng)多的是基于PADL和BUILD系統(tǒng)。盡管它們在表達(dá)上是強有力的，但仍然存在許多缺陷。例如，這種系統(tǒng)要有極強的計算能力和內(nèi)存需求，非常規(guī)的物體建模方式以及標(biāo)注公差能力的缺乏，這一切已阻礙了CAD應(yīng)用。直到20世紀(jì)80年代中期，實體建模開始介入設(shè)計環(huán)境。今天實體建模的應(yīng)用如同繪圖和線框模型應(yīng)用一樣普遍。 在個人計算機上，CAD已走向大眾化。這種發(fā)展使CAD應(yīng)用面廣并且很經(jīng)濟。CAD原本作為一種工具僅被航空和其它主要工業(yè)企業(yè)使用。諸如AutoCAD、VersaCAD、CADKEY等個人機CAD軟件包的引入，使小型公司乃至個人可以擁有并使用CAD系統(tǒng)。到1988年為止已銷售10萬個以上的PC CAD軟件包。今天，基于個人計算機的實體建摸的PC CAD易于獲得，并且銷售變得更為普及。由于微型計算機的迅速發(fā)展使得個人計算機能夠承受實體模型需要的大量計算負(fù)荷，所以如今許多實體模型在PC機上運行，并且作為平臺 已不成為一個問題。隨著標(biāo)準(zhǔn)圖形用戶界面的發(fā)展，CAD系統(tǒng)可以很容易地從一臺計算機傳送，大多數(shù)CAD系統(tǒng)都能在不同平臺上運行。在大型計算機、工作臺和基于個人計算機的CAD系統(tǒng)之間幾乎沒有區(qū)別。 計算機輔助設(shè)計的結(jié)構(gòu) 一個CAD系統(tǒng)包含三個主要部分： （1）硬件 計算機及輸入/輸出裝置。 （2）操作系統(tǒng)軟件。 （3）應(yīng)用軟件 CAD軟件包。 硬件主要用于支持軟件功能。在CAD系統(tǒng)中使用著種類繁多的硬件。操作系統(tǒng)軟件是CAD應(yīng)用軟件與硬件之間的界面。操作系統(tǒng)軟件管理著硬件運行并提供許多諸如創(chuàng)建 和取消操作任務(wù)、控制任務(wù)的進程、在任務(wù)間分配硬件資源、提供通向軟件資源，如文件、編輯器、編譯和應(yīng)用程序的通道等基本功能。這不僅對CAD軟件很重要，而且對非CAD軟件也很重要。 應(yīng)用軟件是CAD系統(tǒng)的核心。它由二維和三維建摸、繪圖、工程分析等程序組成。一個CAD系統(tǒng)的功能便建立在應(yīng)用軟件中。正是應(yīng)用軟件使一種CAD軟件包區(qū)別于另一種，通常應(yīng)用軟件是依賴于操作系統(tǒng)的。要把在一個操作系統(tǒng)上運行的CAD系統(tǒng)移到另一個操作系統(tǒng)上，并不像編譯軟件那樣微不足道。因此也必須注意操作系統(tǒng)。 計算機輔助設(shè)計 計算機輔助設(shè)計給了設(shè)計者去嘗試幾個可行的解決方案的能力。通常還需要某些形式的設(shè)計分析計算，而為了這一任務(wù)已經(jīng)編寫了許多程序。計算機為設(shè)計者對所建議的各種結(jié)構(gòu)設(shè)計的分析和為最終設(shè)計準(zhǔn)備正式繪圖提供了強有力的工具。 在二維繪圖領(lǐng)域中，計算機方法能夠提供比傳統(tǒng)的紙和筆的方法更有意義、更大成本節(jié)約的優(yōu)點，但是一個CAD系統(tǒng)并不僅是一個電子繪圖板。計算機繪圖系統(tǒng)可使設(shè)計者設(shè)計出既快又準(zhǔn)確的圖形，并且很容易修改。在涉及到重復(fù)性工作時，會戲劇性產(chǎn)生復(fù)制產(chǎn)品，因為標(biāo)準(zhǔn)圖形只要一次構(gòu)建成功，就可以從圖庫中取出。剪切和粘貼技術(shù)作為節(jié)約勞動力的輔助工具被使用。當(dāng)幾個分項目設(shè)計人員從事同一個工程時，要建立中心數(shù)據(jù)庫，使得由某一個人繪的細(xì)節(jié)圖可以很容易地合并到其它不同的裝配圖中。中心數(shù)據(jù)庫也可作為標(biāo)準(zhǔn)參考零件庫使用。 有限元是一項成熟的應(yīng)力分析技術(shù)，它多被土木工程和機械工程所采用。它由將結(jié)構(gòu)劃分成有限個的小單元所組成，并計算每一個單元之間的作用力。如果被分割的單元足夠小，就能對一個結(jié)構(gòu)或?qū)嶓w的內(nèi)部應(yīng)力獲得一個好的估計。這些計算機設(shè)計慣用于大型結(jié)構(gòu)物的設(shè)計，諸如船體、橋梁、飛機機身和海面油井平臺。汽車工業(yè)也使用類似的方法來設(shè)計和制造車身。 二維繪圖 CAD使多視圖的二維繪圖成為可能，視圖空間可以從微米到米的比例范圍內(nèi)無限變化。它提供給機械設(shè)計師放大的功能，即使在恰當(dāng)配合的裝配零件中最小的零件也能看清楚，設(shè)計程序甚至能自動辨認(rèn)CAD裝配圖中的潛在問題。針對具有不同特征的零件，如運動的或靜止的，在顯示時可以被指定成不同的顏色。為了有利于工程設(shè)計的變化，可使用帶有自動尺寸變化的系統(tǒng)對零件進行尺寸標(biāo)注。 三維繪圖 隨著三維建模的出現(xiàn)，設(shè)計者具有了更多的自由度。他們可以生成三維零件圖并且可以無限制地修改以獲得所需的結(jié)果。通過有限元分析，應(yīng)力加到計算機模型上，并且以圖形化的方式顯示其結(jié)果，在產(chǎn)品物理模型真正產(chǎn)生之前，對設(shè)計中的任何內(nèi)在問題給設(shè)計者一個快速的反饋。 三維模型可用線框、曲線或?qū)嶓w方式生成。在線框模型中，直線和圓弧構(gòu)成了模型邊界。結(jié)果是一個可以從任何位置觀察的三維模型，但仍只是一個框架形式。創(chuàng)建曲面猶如在骨架上包上皮。一旦這樣生成后，模型就可以被渲染，使得圖形看上去更逼真。曲面模型普遍用于構(gòu)建板金的展開和重疊以用于制造。 實體模型是最復(fù)雜的建模層次，并且用于建立實體模型的程序在一段時期內(nèi)只用在大型計算機上。只有近年來微型計算機才達(dá)到這個能力水平，也可以運行復(fù)雜的算法，生成實體模型。計算機“認(rèn)為”實體模型是一種具有實體質(zhì)量的模型，所以它可被“鉆孔”“加工”“焊接”，好象它是一個實際的零件。它能夠由任何材料構(gòu)成并呈現(xiàn)其材料特性，因此，能夠進行質(zhì)量計算。 計算機輔助繪圖的好處 用計算機完成繪圖及設(shè)計任務(wù)的好處是令人難忘的：提高速度、提高準(zhǔn)確性、減少硬拷貝存儲空間及易于恢復(fù)信息、加強信息傳輸能力、改善傳輸質(zhì)量和便于修改。 速度 工業(yè)用計算機能以平均每秒3300萬次完成一項任務(wù)；更新的計算機其速度更快。用計算機計算零件的變形量是一個重要功績。當(dāng)理論上的載荷力加到零件上時、通過計算機進行有限元分析或者在監(jiān)視器上顯示一個城市的整體規(guī)劃時，這兩者都是既費時又計算量大的任務(wù)。AutoCAD軟件可根據(jù)需要多次復(fù)制所需模型的形狀和幾何尺寸，快速自動地進行剖面填充及尺寸標(biāo)注。 準(zhǔn)確 AutoCAD程序依靠操作系統(tǒng)及計算機平臺每點具有14位的精度。這在用數(shù)學(xué)計算諸如一個圓的線段數(shù)、程序必須圓整線段時是十分重要的。 存儲 計算機能夠在物理空間中存儲上千幅圖，這空間能夠存儲上百幅手工圖。而且計算機能夠很容易地搜索和找到一幅圖，只要操作者擁有正確的文件名。 傳輸 由于計算機的數(shù)據(jù)是以電子形式存儲，它能被送到各種位置。最明顯的位置是監(jiān)視器。計算機可以在屏幕上以不同的方式顯示數(shù)據(jù)，如圖形，并能方便地將數(shù)據(jù)轉(zhuǎn)換成可讀圖形。這些數(shù)據(jù)也可被傳送給繪圖機，打印出常見的圖紙，通過直接連接到計算機輔助制造機床或由電話線傳到地球的任何地方。你可以不再冒損失或丟失的危險去郵寄圖紙，現(xiàn)在圖紙可以通過電信網(wǎng)立即發(fā)送到目的地。 A Brief History of?。茫粒? Before we present the basics of CAD ,it is appropriate to give a brief history . CAD is a product of the computer era. It originated from early computer graphic systems to the development of interactive computer graphics. Two such systems include the Sage Project at the Massachusetts Institute of Technology (MIT) and Sketchpad. The Sage Project was aimed at developing CRT displays and operating systems. Sketchpad was developed under the Sage Project. A CRT display and light pen input were used to interact with the system. This coincidentally happened at about the same time that NC and APT(Automatically Programmed Tool)first appeared. Later, X-Y plotters were used as the standard hard-copy output device for computer graphics. An interesting note is that an X-Y plotter has the same basic structure as a NC drilling machine except that a pen is substituted for the tool on NC spindle. In the beginning, CAD systems were no more than graphics editor with some built-in design symbols. The geometry available to the user was limited to lines, circular arcs, and the combination of the two. The development of free-form curves and surfaces, such as Coon’s patch, Bezier’s patch, and B-spline, enable a CAD system allow to be used for sophisticated curves and surface design. Three-dimensional CAD system allow a designer to move into the third dimension. Because a three-dimensional model contains enough information for NC cutter-path programming, the linkage between CAD and NC can be developed. So called turnkey CAD/CAM systems were developed based on this concept and became popular in the 1970s and 1980s. The 1970s marked the beginning of a new era in CAD-the invention of three-dimensional solid modeling. In the past, three-dimensional, wire-frame models represented an object only by its bounding edges. They are ambiguous in the sense that several interpretations might be possible for a single model. There is also no way to find the volumetric information of a model. Solid models contain complete information; therefore, not only can they be used to produce engineering drawing, but engineering analysis can be performed on the same model as well. Later many commercial systems and research systems were developed. Quite a few of these systems were based on the PADL and BUILD systems. Although they are powerful in representation, many deficiencies still exist. For example, such systems have extreme computation and resource (memory) requirements, an unconventional way of modeling object and a lack of tolerance capability have all hindered CAD applications. It was not until the mid-1980s that solid modelers made their way into the design environment. Today, their use is as common as drafting and wire-frame model applications. CAD implementations on personal computers (PCs) have brought CAD to the masses. This development has made CAD available and affordable. CAD originally was a tool used only by aerospace and other major industrial corporation. The introduction of PC CAD packages, such as, AutoCAD, VersaCAD, CADKEY, and so on, has made it possible for small companies and even individuals to own and use CAD systems. By1980, more than 100,000 PC CAD packages had been sold. Today PC-based solid modelers are available and are becoming increasingly popular. Because rapid developments in microcomputers have enabled PCs to carry the heavy computational load necessary for solid modeling, many solid modelers now run on PCs, and the platform has become less of an issue. With the standard graphics user interface (GUI), CAD systems can be ported easily from one computer to another , Most major CAD systems are able to run on a variety of platforms. There is little difference between mainframe, workstation, and PC-based CAD systems. The Architecture of CAD A CAD system consists of three major parts: (1)Hardware computer and input/output(I/O)devices. (2)Operating system software. (3)Application software CAD package. Hardware is used to support the software functions. A wide range of hardware is used in CAD systems. The operating system software is the interface between the CAD application software and the hardware. It supervises the operation of the hardware and provides basics functions such as creating and removing operation tasks, and providing access to software resources such as files, editors, compilers and utility programs. It is important not only for CAD software, but also for non-CAD software. The application software is the heart of a CAD system. It contains of programs that do 2-D and 3-D modeling, drafting, and engineering analysis. The functionality of a CAD system is built into the application software. It is application software that makes one CAD package different form another. Application software is usually operating-system-dependent. To transport a CAD system running in one operating system to another operating system is not as trivial as recompiling the software. Therefore, attention must be given to the operating system as well. Computer Aided Design Computer aided design gives the designer the ability to experiment with several possible solutions. Usually some forms of design analysis calculations need to be done and many programs have been written for this task. The computer provides the designer with a powerful tool for analyzing proposed designs and for preparing formal drawing of the final design. Two-dimensional drawing is one area in which computer methods can off significant, quantifiable cost advantages over traditional paper and pen methods, but a CAD system is not just an electronic drawing board. Computer drawing systems enable designers to produce fast accurate drawings and easily modify them. Draught productivity rises dramatically when repetitive work is involved, since standard shapes are constructed only once and can be retrieved from a library. Cut and paste techniques are used as labor-saving aids. When several detail drawn by one person can be easily incorporated into different assemble drawing. This central database also serves as a library of standard preferred computers. Finite element is a sophisticated stress analysis technique much used by civil and mechanical engineers. It consists of dividing a structure into small, but finite, components and calculating the force between each element. If the elements are small enough, a good estimate of the internal stresses in a structure or solid body can be obtained. These computer techniques are routinely used in the design of large structure such as ship hulls, bridges, aircraft fuselages and offshore oil rig. The motor car industry also uses similar methods for design and manufacture of car bodies. Two-dimensional Drawings CAD makes possible multiview 2D drawing, with an endless possibility of views in range of scales from microns to meters to meters. It gives the mechanical designer the ability to magnify even the smallest of components to ascertain if the assembled components fit properly and even to design programs to identify automatically potential problems in CAD assembly. Parts with different characteristics, such as movable or stationary, can be assigned different colors on the display. Parts can be dimensioned with automatic dimensioning changes, allowing for expedient engineering design changes. Three-Dimensional Drawings Designers have even more freedom with the advent of 3D modeling. They can 3D parts and manipulate them in endless variations to achieve the desired results. Through finite element analysis FEA), stress can be applied to a computer model and the results graphically displayed, giving the designer guick feedback on any inherent problems in a design before the creation of a physical prototype. 3Dmodels can be created in wire-frame, in surfaces or in solid form. In wire-frame, lines and arcs form edges that generate the model. The result is a 3D form that can be viewed from any location but still only a skeletal form. Creating a surface stretches a skin over the skeleton (Fig.8-1b).Once this is done, the model can be rendered so that it appears more tangible. Surface models are commonly used in the creation of sheet metal developments that can be unfolded for manufacture. Solid models are the most complex level of modeling and while the programs to create them have been available for some time on large mainframe computers, it is only recently that microcomputers have reached a level of power that allows the running of the sophisticated algorithms needed to create solid model（Fig.8-2）. The computer “thinks” the solid is sold mass so it can be “drilled”, “machined,”or “welded” as if it were an actual physical part. It can be made out of any material’s characteristics, thereby allowing calculations of mass to be made. CAD’S Benefits The benefits of computer use in drafting and design tasks are impressive: increased speed, greater accuracy, reduction of hardcopy storage space as well as better recall, enhanced communication capabilities, improve quality and easier modification. Speed A person computer used in industry can perform a task at an average rate of 33 million operations per second; newer computer are even faster. This is an important feat when using it to calculate the amount of deflection of a component, when theoretical physical forces are applied to it, through finite element analysis(FEA) or when displaying an entire city plan on a monitor, both of which are time-consuming and calculation-intensive tasks. AutoCAD software can duplicate any geometry as many times as required and can also perform crosshatching and dimensioning automatically and equally as fast. Accuracy The AutoCAD program has an accuracy of 14 significant digits of precision for each point, depending on the operating system and computer platform. This extremely important when the program must round off numbers during mathematical calculations such as segmenting a circle. Storage The computer can store thousands of drawings in the physical space that it would take to store hundreds of manual drawings. Also, the computer can search and find a drawing with ease, as long as the operator possesses the correct. Communication Because the computer’s data is stored in an electronic form, it cam be sent to s variety of locations. The first obvious location is the monitor. The computer can display the data on the screen in different forms such as graphics, easily converting the data into readable drawing. The data can also be a plotter to produce the familiar paper drawing, via a direct link to a computer-aided manufacturing (CAD) machine or via telephone to anywhere around the globe. You no longer have to mail drawing, risking damage and loss; they can not be at their destination instantly via the telecommunications network.