茶杯塑件塑料注射模具設(shè)計(jì)
茶杯塑件塑料注射模具設(shè)計(jì),茶杯,塑料,注射,模具設(shè)計(jì)
洛陽理工學(xué)院畢業(yè)論文
CAD/CAM
Computer technology has risen in an exponential curve. Only a generation ago computers were not really needed for NC control. Except for relatively few five-axis machines. NC was point to point, which was easily accomplished with manual programming.
With the advent of two-dimensional profiling, hower, a need arose for numerous calculations to generate the curved profile. At that point the computer was looked upon as a useful tool in manufacturing engineering. After some development, it was found that punched or magnetic tape could be dispensed with entirely in favor of computer programs that controlled the machines directly. Then came the minicomputers, which when operating with the central processor brought about the first real concept of the automatic factory.
All of these developments were important steps in the advance of technology. The computer is no longer viewed as a remote piece of hardware used primarily in accounting and engineering departments, but instead as an important tool to be used increasingly in CAD and CAM.
Today CAD and CAM have become closely linked for complete processing from design to production. The desin engineer can now create the desired design on a CRT screen that is linked to a computerized graphics plotter. The same system can be used to determine the viability of the design by analyzing stresses and deflections that will take place under loading conditions. The functioning of mechanical linkages may also be checked. After the design is complete, the production group can draw on the information developed in CAD for computer-aided manufacture. Thus the unified CAD-CAM team has been developed to bring the product from the design concept through manufacture.
CAD Functions
Initially CAD systems were primarily automated drafting stations in which computer plotters produced engineering drawings. The systems were later linked to graphic display terminals, which allowed the user to communicate with the computer in pictures instead of raw columns of numbers. Now advanced systems have added analytical capabilities. CAD functions may be grouped into four major categories: geometric modeling, engineering analysis, kinematics, and automated drafting.
Geometric Modeling Traditionally, engineers do the sketching and drafts-men the drafting. Engineers then discover needed changes or improvements and draftsmen draft what is required. Moving a bracket 2 in, to the left causes an entree chain reaction throughout a complete set of drawings.
Now the computer has opened up a new way to meet design engineering needs with speed and reliability in products ranging from high-performance aircraft to complex, integrated circuits. The designer can sketch directly on the screen of a graphics terminal. Lines and contours are defined by pressing keys and positioning a light pen, and the computer displays what is expressed.
Curve fitting, or reducing the design to a set of control equations is done at the terminal, eliminating coding, card punching, punching, and repeated computer batch runs;then CAD converts the preliminary design to a dimensional drawing with auxiliary views.
If the drawing reveals a problem of compatibility with a subassembly, the pieces can be moved around with the light pen. The computer then converts this pictorial representation to a mathematical model stored in the computer data base for later use. The model may be used or other CAD fuctions or it may be recalled and refined by the engineer at any point in the design process.
Geometric modeling is often considered to be the most important feature of a CAD system because so many other design functions in the system depend heavily on the model. The geometric model may be used to create a finite element model of a structure for stress analysis. The model may also serve as an input for automated drafting to produce engineering drawings. If CAD/CAM systems are interfaced, the geometric model can be used to create NC tapes for fabricating the part.
Most modeling is done with a wire frame that represents the part shape with interconnected line elements .
Analysis After the geometric modeling is done, the CAD system allows the designer to move directly to analysis. With simple keyboard instructions, the computer is asked to calculate weight, volume, surface area, moment to inertia, or center of gravity of a part. However, the most powerful method of analyzing a part is by the finite element method. In this technique the structure is broken down into a network of simple element that the computer uses to determine stresses, deflections, and other structural characteristics. Such analysis requires the tremendous computational power of a mainframe computer.
Kinematics Many CAD system have kinematic features for plotting or animating the motion of simple, hinged parts such as doors or cranks. Such analysis can ensure that moving components do not impact on other parts of the structure. The design of an automobile hood linkage, for example, requires only a few minutes of interaction with a computer, whereas hundreds of hours of hours can be required for manual design of the same part.
Experts believe that in the future computers and programs will be available to completely synthesize a complex mechanical system based solely on its intended function.
Drafting With automated drafting, detailed engineering drawings may be produced automatically from a data base. In addition, most drafting systems have automatic scaling and dimensioning features.
A typical CAD system with automated drafting can generate up to six views on the screen. Any design change made on one view is automatically added to the others.
CAM Functions
CAM functions center around four main areas: numerical control, process planning, robotics, and factory management.
Numerical control As stated previously, NC uses coded information to control machine tool movements.
The computer can now generate a NC program directly from a geometric model of a part. Automatic capillaries are generalities linked to highly symmetric geometric and other specialized shapes.
Process Planning Process planning is involved with the detailed sequence of production steps from start to finish. Essentially, the process plan describes the state of the workplace at each workstation. The use of computers as an aid to process planning is comparatively recent and has led to a rebirth of what is known as group technology (G T). Group technology is based on organizing all similar parts into families to allow standardization of fabricating steps.
Currently under development is process planning system that is able to produce process plans directly from the geometric model database with almost no human assistance. In this system ,the process planner would review the impact from the design engineer via communication and then enter this input into the CAM system, which would generate a complete set of process plans automatically.
Robotics Many advances are being made to integrate robotics into CAM. One of these efforts is the U.S. Air Force Integrated Computer-Aided Manufacturing (ICAM) project, of which the goal is to organize every step of manufacturing around computer automation. As part of this program, a robot is used to drill sheet metal aircraft parts. The robot selects drill bit from a tool rack, drills a set of holes to 0.005 in tolerance, and machines the perimeter of any one of 250 types of parts. Production rates are four times faster than conventional manual fabrication.
Factory management This portion of CAM ties together the other areas to coordinate operations of an entire factory. The management system relies heavily on group technology with its families of similar parts. Computers also perform various management tasks such as inventory control and scheduling in systems that have come to be known as material requirements planning (MRP) systems.
CAD / CAM技術(shù)
計(jì)算機(jī)技術(shù)以指數(shù)曲線的形式上升。僅僅在上一代以前電腦在數(shù)字控制方面還并不是真的需要。除相對(duì)較少為五軸聯(lián)動(dòng)機(jī)。數(shù)字控制是點(diǎn)對(duì)點(diǎn)，這是很容易完成的手工編程。
面對(duì)兩維剖面，然而 ，需要進(jìn)行眾多計(jì)算來產(chǎn)生輪廓曲線。在這一點(diǎn)上，計(jì)算機(jī)在制造工程方面看作是一個(gè)有用的工具。經(jīng)過一番發(fā)展之后，發(fā)現(xiàn)用針刺或磁帶可完全免除對(duì)計(jì)算機(jī)程序的依賴，從而直接控制機(jī)器的正常運(yùn)行。緊接著是微型電腦，它在與中央處理機(jī)的經(jīng)營過程中帶來了自動(dòng)化工廠的第一次真正的概念。
所有這些事態(tài)發(fā)展在技術(shù)進(jìn)步方面都是重要的步驟。計(jì)算機(jī)已不再被看作是一個(gè)硬件而僅用于計(jì)算和工程部門，而是作為一個(gè)重要的工具，被日益廣泛地應(yīng)用于CAD和CAM 中。
今天CAD和CAM已為了能夠完成從設(shè)計(jì)到生產(chǎn)的加工而緊密聯(lián)系在一起?，F(xiàn)在設(shè)計(jì)工程師可以在連接著一臺(tái)計(jì)算機(jī)化的圖形繪圖機(jī)的CRT屏幕上創(chuàng)造理想的設(shè)計(jì)。同一系統(tǒng)可以通過分析應(yīng)力和撓度來確定設(shè)計(jì)的可行性，從而將在加載條件得到證明。運(yùn)轉(zhuǎn)機(jī)械的聯(lián)系，也可以進(jìn)行檢查。在設(shè)計(jì)完成后，制作小組可以借鑒國際上在CAD方面發(fā)達(dá)的信息用于電腦輔助制造。這樣，統(tǒng)一的CAD-CAM小組已經(jīng)研制成功，使產(chǎn)品從設(shè)計(jì)理念過渡到制造。
CAD的作用
最初的CAD系統(tǒng)，主要是通過計(jì)算機(jī)繪圖制作工程圖紙來自動(dòng)監(jiān)測站起草工作。后來，系統(tǒng)和圖形顯示終端連接，使操作者可直接與計(jì)算機(jī)以圖形方式交流，代替了過去用原始數(shù)據(jù)的方式?，F(xiàn)在，先進(jìn)的系統(tǒng)已經(jīng)加入了分析能力。CAD的職能可分為四大類：幾何造型，工程分析，運(yùn)動(dòng)學(xué)和自動(dòng)化起草。
幾何造型 在傳統(tǒng)上，工程師們做素描而制圖人員起草。這時(shí)工程師會(huì)發(fā)現(xiàn)需要進(jìn)行調(diào)整或改進(jìn)的地方，并需繪圖員起草。向左邊移動(dòng)支架2英寸 ，會(huì)因?yàn)橐惶淄暾牟堇L而引起一系列連鎖反應(yīng)。
現(xiàn)在，計(jì)算機(jī)開辟了一條新的途徑，以滿足工程設(shè)計(jì)的需要，它在高性能的飛機(jī)，到復(fù)雜的集成電路這些產(chǎn)品方面具有快速和可靠的特點(diǎn)。設(shè)計(jì)者可以直接在屏幕上素描圖形終端。線和輪廓線的定義是通過按下按鍵和定位輕筆，從而在電腦顯示器上顯示 需要表達(dá)的內(nèi)容。
曲線擬合，或降低設(shè)計(jì)到一套在終端已經(jīng)完成的控制方程，從而消除編碼，卡沖床，沖壓，并重復(fù)電腦的運(yùn)行軌道;這時(shí)CAD把初步設(shè)計(jì)轉(zhuǎn)換成三維輔助制圖。
如果繪畫揭示了一個(gè)與組件的相容性問題，這個(gè)組件就會(huì)圍繞光筆四周轉(zhuǎn)動(dòng)。這時(shí)電腦就會(huì)把這個(gè)有代表性的圖案轉(zhuǎn)換成數(shù)學(xué)模型，從而儲(chǔ)存在電腦資料庫，以便日后使用。該模型也許被用到或在其它CAD 職能中或人們可能還記得，也有可能在任何一點(diǎn)上被工程師在設(shè)計(jì)過程中重新定義。
幾何造型，往往被認(rèn)為是CAD系統(tǒng)中最重要的一個(gè)功能，因?yàn)楹芏嗥渌脑谙到y(tǒng)上的功能設(shè)計(jì)嚴(yán)重依賴于模型。幾何模型可以被用來創(chuàng)造一個(gè)用于結(jié)構(gòu)應(yīng)力分析的有限元模型。該模型也可作為一項(xiàng)為自動(dòng)化起草制作工程圖紙的投入。如果CAD / CAM系統(tǒng)是接口，幾何模型可以用來產(chǎn)生數(shù)字控制錄音帶編造的那部分。
大部分模型是用有代表部分的形狀與互聯(lián)線元素做成的一個(gè)線框。
分析 幾何造型被完成后， CAD系統(tǒng)就允許設(shè)計(jì)師直接進(jìn)入分析。用簡單的鍵盤指令，使計(jì)算機(jī)計(jì)算重量，體積，表面積，時(shí)刻以慣性，或重心的一個(gè)組成部分。然而，對(duì)零件進(jìn)行分析的最優(yōu)方法是有限元分析。用這種技術(shù)，結(jié)構(gòu)就會(huì)分解成一個(gè)網(wǎng)絡(luò)的簡單成分，然后電腦運(yùn)用它去決定壓力，撓度，和其他結(jié)構(gòu)特征。這樣的分析，需要巨大的計(jì)算能力的電腦主機(jī)。
運(yùn)動(dòng)學(xué) 許多CAD系統(tǒng)在策劃方面都有運(yùn)動(dòng)學(xué)特征或動(dòng)畫的簡單運(yùn)動(dòng)，鉸鏈部位，如門或曲柄。這樣的分析，才能確保運(yùn)動(dòng)部件不影響其他部分的結(jié)構(gòu)。例如設(shè)計(jì)汽車的聯(lián)動(dòng)裝置，用計(jì)算機(jī)設(shè)計(jì)僅需幾分鐘，然而，人工設(shè)計(jì)同樣的部件要花費(fèi)上百個(gè)小時(shí)。
專家認(rèn)為，在未來，計(jì)算機(jī)和程序，將完全基于其預(yù)定的功能可合成一個(gè)復(fù)雜的機(jī)械系統(tǒng)。
自動(dòng)化起草 用自動(dòng)化起草機(jī)構(gòu)，可以從資料庫自動(dòng)產(chǎn)生詳細(xì)的工程圖紙。此外，大部分起草系統(tǒng)具有自動(dòng)縮放及標(biāo)注功能。
一個(gè)帶著自動(dòng)化起草工作的典型的CAD系統(tǒng)，可以在屏幕上產(chǎn)生多達(dá)6個(gè)的觀點(diǎn)。對(duì)某一個(gè)觀點(diǎn)的任何設(shè)計(jì)變更的制作會(huì)自動(dòng)添加給其他人。
CAM的功能
CAM的功能中心主要圍繞四個(gè)領(lǐng)域：數(shù)值控制，工藝設(shè)計(jì)，機(jī)器人和工廠管理。
數(shù)值控制 如前所述，數(shù)字控制用編碼信息來控制機(jī)床運(yùn)動(dòng)。
計(jì)算機(jī)可以將一個(gè)零件的幾何模型直接轉(zhuǎn)換為數(shù)字控制程序。自動(dòng)毛細(xì)血管都是以高度對(duì)稱的幾何和其他專門的形狀泛泛的聯(lián)系在一起。
工藝規(guī)劃 工藝規(guī)劃從開始到結(jié)束涉及到詳細(xì)序列的生產(chǎn)步驟?；旧希に嚪桨冈诿恳粋€(gè)工作站都描述了該區(qū)域的工作場所。使用計(jì)算機(jī)作為輔助工具的過程中的規(guī)劃是比較近的，并已導(dǎo)致了我們所熟悉的成組技術(shù)（ GT ）的重生。成組技術(shù)以組織全體類似零件進(jìn)入某區(qū)域?yàn)榛A(chǔ)，并允許其進(jìn)行標(biāo)準(zhǔn)化的制造步驟。
目前正在開發(fā)的是工藝設(shè)計(jì)系統(tǒng)，它能夠在幾乎沒有任何人的援助下直接從幾何模型數(shù)據(jù)庫中產(chǎn)生進(jìn)程計(jì)劃。在這個(gè)系統(tǒng)中，這一過程規(guī)劃者將從同設(shè)計(jì)工程師通過交流審查其影響，然后再把它輸入到CAM系統(tǒng)中，這樣將產(chǎn)生一套完整的工藝方案自動(dòng)。
機(jī)器人 CAM的許多改進(jìn)得益于智能機(jī)器人技術(shù)的引入。其中的努力，是美空軍計(jì)算機(jī)集成計(jì)算機(jī)輔助制造（沿海）項(xiàng)目，其中的目標(biāo)是組織管理圍繞計(jì)算機(jī)自動(dòng)化生產(chǎn)的每一步。作為這項(xiàng)活動(dòng)的一部分計(jì)劃，機(jī)器人將用于鉆飛機(jī)零部件的金屬板材。機(jī)器人從工具機(jī)架上選擇鉆頭，鉆了一套0.005英寸余量的洞 ，并且組裝了機(jī)器周邊250種零件中的任何一個(gè)。生產(chǎn)率是傳統(tǒng)的手工制作的4倍。
工廠管理 CAM技術(shù)的這部分和其他領(lǐng)域聯(lián)系在一起，用以協(xié)調(diào)整個(gè)一個(gè)工廠的操作。該管理系統(tǒng)在很大程度上依靠于成組技術(shù)及其領(lǐng)域的類似零件。電腦也做好各項(xiàng)管理工作，如庫存控制和調(diào)度系統(tǒng)，已被稱為物料需求計(jì)劃（ MRP ）系統(tǒng)。
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