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无论是手工编程还是自动编程，在编程前都要对所加工的零件进行工艺分析，拟订工艺方案，选择合适的刀具，确定切削用量。在编程中，对一些工艺问题（如对刀点，加工路线等）也需要做一些处理。因此，数控编程的工艺处理是一项十分重要的工作。 一数控加工的基本特点：数控加工的工序内容比普通机加工的工序内容复杂。数控机床加工程序的编制比普通机床工艺规程的编制复杂。这是因为在普通机床的加工工艺中不必考虑的问题，如工序内工步的安排、对刀点、换刀点及走刀路线的确定等问题，在编制数控加工工艺时却要认真考虑。二数控加工工艺的主要内容选择适合在数控上加工的零件，确定工序内容。分析加工零件的图纸，明确加工内容及技术要求，确定加工方案，制定数控加工路线，如工序的划分、加工顺序的安排、非数控加工工序的衔接等。设计数控加工工序，如工序的划分、刀具的选择、夹具的定位与安装、切削用量的确定、走刀路线的确定等等。调整数控加工工序的程序。如对刀点、换刀点的选择、刀具的补偿。分配数控加工中的容差。处理数控机床上部分工艺指令。三常用数控加工方法平面孔系零件常用点位、直线控制数控机床（如数控钻床）来加工，选择工艺路线时，主要考虑加工精度和加工效率两个原则。若考虑效率，则上述零件采用图的路线比图好，因为经过计算前者刀具空行程路线短。若考虑精度，则采用图3的路线比图4差，因为后者消除了反向间隙。旋转体类零件常用数控车床或磨床加工。（）考虑加工效率：在车床上加工时，通常加工余量大，必须合理安排粗加工路线，以提高加工效率。实际编程时，一般不宜采用循环指令（否则，以工进速度的空刀太大）。比较好的方法是用粗车尽快去除材料，再精车。（）考虑刀尖强度：数控车床上经常用到低强度刀具加工细小凹槽。图的b采用斜向进刀，不宜崩刃，a则易崩刃。平面轮廓零件常用数控铣床加工。应注意：（）切入与切出方向控制：图左图的径向切入，工件表面留有凹坑；右图切向切入、切出，工件表面光滑。（）一次逼近方法选择：只具有直线和圆弧插补功能的数控机床在加工不规则曲线轮廓时，需要用微小直线段或圆弧段去逼近被加工轮廓（其误差称为一次逼近误差），逼近时，应该使工件误差在合格范围同时程序段的数量少为佳。立体轮廓零件（）考虑工件强度及表面质量：图b，该形状的工件受力后，强度较a差，c的表面质量最好。（）考虑机床的插补功能：加工飞机大梁直纹扭曲面时，若加工机床三轴联动，只好用效率较低的球头铣刀；若机床为四轴联动，则可以选用效率较高的圆柱铣刀铣削（图）。less of is the manual programming or programs automatically, all must to the components which processes carry on the craft analysis before the programming, drafts the craft plan, chooses the appropriate cutting tool, the determination cutting specifications.In the programming, to some craft question (for example to knife spot, processes route and so on) also to need to make some processing.Therefore, numerical control programming craft processing is an extremely important work. One. Numerical control processing essential feature: 1. numerical control processing working procedure content is more complex than the ordinary machining working procedure content.2. numerical control engine bed processing procedure establishment is more complex than the ordinary engine bed technological process establishment.This is because does not need to consider in the ordinary engine bed processing craft the question, like in the working procedure a labor step arrangement, to knife, trades knife and feeds the route indeed to grade the question, when establishment numerical control processing craft must consider earnestly actually.Two. Numerical control processing craft primary coverage1. choices suits the components which processes in the numerical control, definite working procedure content.2. analysis processing components blueprint, is clear about the processing content and the specification, the determination processing plan, the formulation numerical control processing route, like working procedure division, processing order arrangement, non-numerical control processing working procedure engagement and so on.The design numerical control processing working procedures, like the working procedure division, the cutting tool choice, the jig localization and the installment, the cutting specifications determination, feeds route determination and so on.3. adjustment numerical control processing working procedure procedure.If to knife, trades a knife choice, the cutting tool compensation.In 4. assignment numerical control processing tolerance.On 5. processing numerical control engine bed partial craft instruction.Three. The commonly used numerical control processing method 1. even faces are the components commonly used spot position, the linear control numerical control engine bed (for example numerical control drilling machine) process, when choice craft route, mainly considers the processing precision and the processing efficiency two principles.If consideration efficiency, then above components use Figure 1 route compared to Figure 2 well, because the process calculates the former cutting tool spatial traveling schedule route to be short.If consideration precision, then uses Figure 3 routes compared to Figure 4 the difference, because the latter eliminated the reverse gap.2. solid of revolution class components commonly used numerical control lathe or grinder processing.(1) consideration processing efficiency: Processes when the lathe, usually processes the remainder to be big, must arrange the rough machining route reasonably, enhances the processing efficiency.When actual programming, (otherwise not suitably uses the circulation instruction generally, enters speed by labor run-out too to be big).Is removes the material as soon as possible compared with the good method with the roughing, again lathe finishing.(2) consideration knife point intensity: On the numerical control lathe uses the low intensity cutting tool to process the tiny scoop channel frequently.Figure 5 b uses the diagonal feed, not suitable breaking, a then easy breaking.3. plane outline components commonly used numerical control milling machine processing.Should pay attention: (1) cuts into with cuts the directional control: Figure 6 left chart radial directions cut into, the work piece surface leaves leeway the pit; The figure to the right tangential cuts into, cuts, the work piece surface is smooth.(2) (2) one time approaches the method choice: Only has the straight line and the circular arc interpolation function numerical control engine bed when the processing irregular curve outline, needs to use the small tangential path or the round segmental arc approaches is processed the outline (its error to be called a time approximate error), when approaches, should cause the work piece error segment quantity to be short good for while the qualified scope.(3) 4. three-dimensional outline components(4) (1) consideration work piece intensity and surface quality: Chart 7b, after this shape work piece stress, the intensity compares a difference, the c surface quality is best.(5) (2) considers the engine bed the interpolation function: When processing airplane summer beam straight burr distortion surface, if the processing engine bed three axle linkage, has to use an efficiency low ball milling cutter; If the engine bed is four axis linkages, then may select the efficiency high column milling cutter milling (Figure 8).一.数控机床编程的方法数控机床程序编制的方法有三种：即手工编程、自动编程和CAD/CAM 。 1手工编程由人工完成零件图样分析、工艺处理、数值计算、书写程序清单直到程序的输入和检验。适用于点位加工或几何形状不太复杂的零件，但是，非常费时，且编制复杂零件时，容易出错。 2自动编程使用计算机或程编机，完成零件程序的编制的过程，对于复杂的零件很方便。3CAD/CAM利用CAD/CAM软件，实现造型及图象自动编程。最为典型的软件是Master CAM，其可以完成铣削二坐标、三坐标、四坐标和五坐标、车削、线切割的编程，此类软件虽然功能单一，但简单易学，价格较低，仍是目前中小企业的选择。二.数控机床程序编制的内容和步骤1.数控机床编程的主要内容分析零件图样、确定加工工艺过程、进行数学处理、编写程序清单、制作控制介质、进行程序检查、输入程序以及工件试切。 2.数控机床的步骤分析零件图样和工艺处理 根据图样对零件的几何形状尺寸，技术要求进行分析，明确加工的内容及要求，决定加工方案、确定加工顺序、设计夹具、选择刀具、确定合理的走刀路线及选择合理的切削用量等。同时还应发挥数控系统的功能和数控机床本身的能力，正确选择对刀点，切入方式，尽量减少诸如换刀、转位等辅助时间。数学处理 编程前，根据零件的几何特征，先建立一个工件坐标系，根据零件图纸的要求，制定加工路，在建立的工件坐标系上，首先计算出刀具的运动轨迹。对于形状比较简单的零件（如直线和圆弧组成的零件），只需计算出几何元素的起点、终点、圆弧的圆心、两几何元素的交点或切点的坐标值。编写零件程序清单 加工路线和工艺参数确定以后，根据数控系统规定的指定代码及程序段格式，编写零件程序清单。程序输入 程序校验与首件试切三.数控加工程序的结构程序的构成：由多个程序段组成。O0001；（FANUC-O,AB8400-P,SINUMERIK8M-%）机能指定程序号，每个程序号对应一个加工零件。N010 G92 X0 Y0；分号表示程序段结束N020 G90 G00 X50 Y60；.；可以调用子程序。N150 M05；N160 M02；程序段格式：（）字地址格式：如N020 G90 G00 X50 Y60；最常用的格式，现代数控机床都采用它。地址为程序段号，地址和数字构成字地址为准备功能，.。（）可变程序段格式：如B2000 B3000 B B6000；使用分割符各开各个字，若没有数据，分割符不能省去。常见于数控线切割机床，另外，还有编程等格式。（）固定顺序程序段格式：如00701+02500-13400153002；比较少见。其中的数据严格按照顺序和长度排列，不得有误，上面程序段的意思是：N007 G01 X+02500 Y-13400 F15 S30 M02；One. The numerical control engine bed programs the method numerical control engine bed programming method has three kinds: Namely manual programming, automatic programming and CAD/CAM. 1. manual programming by completes the components pattern analysis, craft processing, the value computation, the written procedure detailed list artificially until the procedure input and the examination.Is suitable in the position processing or the geometry shape not too complex components, but, extremely time-consuming, when also establishment complex components, easy to make a mistake. 2. automatic programming use computer or Cheng Bianji, completes the components procedure the establishment process, is very convenient regarding the complex components.3.CAD/CAM uses the CAD/CAM software, the realization modelling and the image automatic programming.The most typical software is Master CAM, its may complete the milling two coordinates, three coordinates, four coordinates and five coordinates, the turning, the line cutting programming, although this kind of software the function is unitary, but simple easy to study, the price is low, was still the present small and medium-sized enterprise choiceTwo. The numerical control engine bed programming content and the step 1. numerical control engine bed programs the primary coverage analysis components pattern, the determination processing technological process, carries on mathematics processing, the compilation procedure detailed list, the manufacture control medium, carries on the program check, the input routine as well as the work piece tries to cut. 2. numerical control engine bed step. The analysis components pattern and the craft processing basis pattern to the components geometry shape size, the specification carries on the analysis, is clear about the processing the content and the request, decided the processing plan, the determination processing order, designs the jig, chooses the cutting tool, the determination reasonable feeds the route and the choice reasonable cutting specifications and so on.Simultaneously also should display the numerical control system the function and the numerical control engine bed itself ability, the correct choice to the knife spot, cuts into the way, reduces as far as possible such as trades the knife, indexing and so on the non-cutting time. Before mathematics processing programming, according to the components geometry characteristic, establishes a work piece coordinate system first, according to the components blueprint request, the formulation processing road, in the establishment work piece coordinate system, first calculates the cutting tool the path.Regarding the shape quite simple components (for example straight line and circular arc composition components), only must calculate the geometry element the beginning, the end point, the circular arc center of circle, two geometry element point of intersection or the tangential point coordinate figure. Compilation components procedure detailed list processing route and after craft parameter determination, stipulates according to the numerical control system assigns the code and the segment form, the compilation components procedure detailed list. Procedure input . The program check tries with first to cutThree. Numerical control processing procedure structure 1. procedure constitutions: Is composed by many segments.O0001; O(FANUC-O, AB8400-P, SINUMERIK8M-%) function assigns the procedure number, each procedure number corresponds processing components.N010 G92 X0 Y0; The semicolon expressed the segment finished N020 G90 G00 X50 Y60; ; May transfer the subroutine.N150 M05; N160 M02;2. segment forms: (1) word address format: If N020 G90 G00 X50 Y60;The most commonly used form, the modern numerical control engine bed all uses it.Address N is the segment number, address G and the digital 90 constitution character address is the preparation function,.(2) invariable segment form: If B2000 B3000 B B6000;Use minute tally B opens each character respectively, if does not have the data, divides the tally not to be able to omit.Common in numerical control line cutting engine bed, moreover, but also has forms and so on 3B programming.(3) fixed smooth segment form: If 00701+02500-13400153002;Quite rare.Data strictly according to the order and the length arrangement, acts without fail, above segment meaning is: N007 G01 X+02500 Y-13400 F15 S30 M02;尽管对高速加工的研究已有多年，但现在对高速加工还缺少一个明确简洁的定义和解释。高速加工的基本出发点是高速低负荷状态下的切削可较低速高负荷状态下切削更快地切除材料。低负荷切削意味着可减轻切削力，从而减少切削过程中的振动和变形。使用合适的刀具，在高速状态下可切削高硬质的材料。同时，高速切削可使大部分的切削热通过切屑带走，从而减少零件的热变形。 上述这些优点仅在合适的加工策略的情况下才能实现。如果使用了不适当的加工策略，轻则会导致刀具寿命的降低，重则可能导致更加可怕的结果。有一点必须记住，这就是高速加工并不是简单地使用现有刀具路径，通过提高主轴转速和进给率实现。高速加工刀具路径高速铣削刀具路径有多种限制，当将这些限制逐一列出后，则之所以需要这些限制的原因就一目了然。 1. 刀具不能和零件产生碰撞2. 切削负荷必须在刀具的极限负荷之内3. 残留材料不能大于指定极限4. 应避免材料切除率的突然变化5. 切削速度和加速度必须在机床能力范围内6. 切削方向（顺铣/逆铣）应保持恒定7. 应避免切削方向的突然变化8. 尽量减少空程移动9. 切削时间应减少到最短然而，在实际零件的刀具路径编制过程中，很难全部满足上述要求。事实上，在加工复杂形状的零件时，也根本无法全部满足上述要求。在这种情况下，应尽可能地满足这些要求，同时，在必要的情况下可忽视一个或多个限制。在上述限制中，有些限制相对其它限制来说显然更加重要，应首先满足这些限制。上述的这些限制是大致按其重要性而顺序列出。精加工为高速加工提出了一个特殊的问题，即刀痕问题。由于零件形状的限制，对切削条件的妥协常常会在加工后的零件表面上留下可见刀痕。当然，可通过抛光的方法来消除这些刀痕，但这样就违背了我们使用高速加工的初衷。可很容易地对粗加工和半精加工进行优化处理，因为在进行过这些操作后，CAM操作者有多种选择来修改零件的形状，刀痕可通过随后的精加工来消除。编程能力好的高速加工程序在机床上执行得非常快，但它的产生却需花费很长的时间和大量的精力。在如模具制造这样的单件加工领域，因等待加工程序而导致机床停机的现象非常普遍。如果简单地将这种压力强加给CAM操作者，让他们更快地产生刀具路径，常常会迫使他们走捷径。其结果是所编制的程序并不经济、有效。尽管机床在继续运转，但加工速度却大打折扣。 显然，使用这种策略进行高速加工是不明智的。要得到最好的高速加工结果，必须提供足够强大的CAM能力，以能得到高质量的加工程序，保证机床能全负荷地进行工作。为此需： 使用具备自动高速加工功能的CAM软件。这样可减少操作者优化程序的工作量。 使用能快速计算出无过切刀具路径的CAM软件。批处理功能可将复杂程序的计算留在夜间进行。 使用高性能的计算机并经常更新配置。确保计算机具有足够内存，以提高其运行效能。 确保每台机床都配备有足够多的CAM编程人员。培训机床操作者，使他们能直接在车间进行加工编程，这样可最大限度地发挥他们的加工技能。 确保对操作者进行了适当的高速加工编程培训。安排加工顺序除最简单的零件外，高速加工总是牵扯到多个加工步骤。在高速加工编程中，最重要的是选取正确的加工顺序。Delcam所遇到的用户问题，有很大一部分都是策略的使用顺序问题，而不是策略本身的使用问题。尽管CAM软件如PowerMILL的自动化水平日益提高和增强，但它最终代替不了用户自己对加工零件和加工策略的理解和经验。在这里我们无法详细讨论如何安排加工顺序，在此，仅给出几条安排加工顺序的基本原则： 永远同时考虑欲切除的材料，而不是仅仅考虑要加工成形的几何形状。 尽可能地将加工步骤减少到最少。 尽可能地使用连续策略，例如，偏置路径通常比平行路径好。 在可能情况下应尽量避免垂直下刀，尽量从材料外部切入材料。 在零件的一些临界区域应尽量保证不同步骤的精加工路径不重叠。这些区域如果出现路径重叠，势必会出现刀痕。 尽量不换刀，使用单个刀具精加工临界区域。刀具设置错误常常导致精加工后加工表面出现刀痕。 尽可能使用短刀具。长刀具更容易磨损。如有可能，应考虑重新定位零件方向，使用短刀具来加工不容易加工的区域。结论：高速加工对加工工程中的每个环节的要求都很苛刻。使用正确的物理设备是进行高速加工的基本要求，可精确指定这些物理设备的参数。很难具体指定高速加工中需要什么样的CAD和CAM功能，而CAD和CAM对高速加工的质量和稳定性具有显著影响。 供高速加工使用的CAD模型必须能精确地表达要加工出的模型形状，这意味着两点，其一，模型精度必须大于加工公差；其二，在可能的情况下，应将不需要进行铣削加工的模型特征从模型中删除或遮盖。昂贵的高速加工设备必须配备以足够的CAM编程人员，以保证机床使用的是最好的程序。让机床加工人员在车间编制加工程序是提高编程质量的一个途径。确保CAM操作者和机床操作人员进行过良好的高速加工技术培训。仔细安排加工顺序至关重要。适当使用CAM系统所提供的加工策略是获得良好高速加工结果的最有效途径。Although had many years to the high speed processing research, but also lacks an explicit succinct definition and the explanation now to the high speed processing.The high speed processing basic starting point is under the high speed low load condition cutting may compare under the low speed high load condition to cut excises the material quickly.The low load cutting meant may reduce the cutting force, thus in reduced cutting process vibration and distortion.Uses the appropriate cutting tool, may cut the high flinty material under the high-speed run.At the same time, the high-speed cutting may cause the majority of cuttings to carry off hotly through the scrap, thus reduced components thermal deformation. The above these merits only can realize in the appropriate processing strategy situation.If has used not the suitable processing strategy, light can cause the cutting tool life depression, the heavy piece possibly causes a more fearful result.Some point must remember that, this is the high speed processing uses the existing cutting tool way simply, through enhances the main axle rotational speed and to feed rate realization.High speed processing cutting tool wayThe high speed milling cutting tool way has many kinds of limits, after lists one by one these limits, then the reason that needs these limits the reason to be clear. 1. The cutting tool cannot produce with the components collides 2. The cutting load must within the cutting tool limit load 3. The residual material cannot be bigger than assigns limit 4. Should avoid the material excision rate changing 5 suddenly. The cutting speed and the acceleration must in the engine bed area of competence 6. The direction of cut (down milling/up milling) should maintain constant 7. Should avoid the direction of cut changing 8 suddenly. Reduces the spatial regulation to move 9as far as possible. The cutting time should reduce short toHowever, in the actual components cutting tool way establishment process, very difficult to satisfy the above request completely.In fact, when processing complex shape components, also is unable to satisfy the above request completely radically.In this case, should satisfy these requests as far as possible, simultaneously, may neglect or many limits in the essential situation.In the above limit, some limit relative other limits are obviously more important, should first satisfy these limits.But the above these limits are press its importance the order to list approximately.The precision work asked a special question for the high speed processing, namely slash question.As a result of the components shape limit, to cuts the condition the compromise to be able to leave behind the obvious slash frequently on the processing components surface.Certainly, may eliminate these slashes through the polishing method, but has like this violated the original intention which we use process high speed.May very easily carries on optimized processing to the rough machining and the semi-finishing, because after has carried on these operations, the CAM operator has the multiple options to revise the components the shape, the slash may eliminate through afterwards precision work.The programming ability good high speed processing procedure carries out extremely quickly on the engine bed, but its production must spend the very long time and the massive energy actually.Makes such single unit processing domain in like the mold, causes the engine bed engine off because of the waiting processing procedure the phenomenon to be extremely common.If imposes simply this pressure on the CAM operator, lets them have the cutting tool way quickly, can force them frequently to walk the shortcut.Its result is the procedure which establishes is uneconomical, is effective.Although the engine bed is continuing to revolve, but the processing speed greatly sells at a discount actually. Obviously, uses this kind of strategy to carry on the high speed processing is wise.Must obtain the best high speed processing result, must provide the enough formidable CAM ability, by can obtain the high grade processing procedure, guaranteed the engine bed can the capacity load carry on the work.Needs for this:Forever simultaneously considered wants to excise the material, but is not considered merely must process formed the geometry shape. Processes the step to reduce few as far as possible to. Uses the continual strategy as far as possible, for example, the bias way is usually better than the parallel way. To be supposed to avoid the vertical under knife as far as possible in the possible situation, as far as possible cuts into the material from the material. In components some critical regions should guarantee as far as possible the different step the precision work way does not overlap.If these regions appear the way to overlap, will be able to appear the slash inevitably. Does not trade the knife as far as possible, the use single cutting tool precision work critical region.The cutting tool establishment wrong causes the precision work postprocessing surface to appear the slash frequently. Uses the short cutting tool as far as possible.The long cutting tool is easier to wear.If has the possibility, should consider locates the components direction, uses region which the short cutting tool processes not not easily to process.Conclusion: The high speed processing to processes in the project each link request very to be all harsh.Uses the correct physical equipment is carries on the high speed processing the basic request, but assigns these physical equipment precisely the parameter.Very difficult to assign in the high speed processing to need any type specifically CAD and the CAM function, but CAD and CAM have the remarkable influence to the high speed processing quality and the stability. Must be able precisely to express the model shape for the high speed processing use CAD model which must process, this meant two, its one, the model precision must be bigger than the processing common difference; Second, in the possible situation, to be supposed not to need to carry on the milling processing the model characteristic to delete from the model or the cover.The expensive high speed processing equipment must provide by the enough CAM programmers, guaranteed the engine bed uses is the best procedure.Let the engine bed process the personnel is improves the programming quality in the workshop establishment processing procedure a way.Guarantees the CAM operator and the engine bed operator has carried on good high speed processing technology training.The careful arrangement processing order is very important. Uses the processing strategy which the CAM system provides is suitably obtains the good high speed processing result the most effective way.计算机辅助设计的简要历史 在我们讲述CAD的基本理论之前,先说说他的简史是比较合适的。CAD是计算机时代的产品.它从早期的计算机绘图系统发展到现在的交互式计算机图形学.两个这样的系统包括:麻省理工学院的Sage Project及Sketchpad。Sage Project旨在开发CRT显示器及操作系统. Sketchpad是在Sage Project下发展起来的.CRT显示和光笔输入用于与系统进行交互操作.CAD与初次出现的NC和APT(自动编程工具)碰巧同时出世.后来,X-Y绘图仪作为计算机绘图的标准硬拷贝输出装置使用,一个有趣的现象是X-Y绘图仪与NC钻床具有相同的基本机构,除了绘图笔NC机床上的主轴刀具替代之外。 开始，CAD系统仅仅是一个带有内置设计符号的绘图编辑器，供用户使用的几何元素只有直线、圆弧、以及两者的组合。自由曲线及其曲面的发展，如昆氏嵌面、贝塞尔嵌面以及B-样条曲线，使CAD系统可用于复杂曲线与曲面设计。三维CAD系统允许设计者步入三维设计空间。由于一个三维设计模型包含了NC刀具路径编程所需的足够信息，所以能够开发CAD与NC之间联系的系统。所谓交钥匙的CAD/CAM系统便是根据这一概念开发的，并从20世纪70年代至80年代流行起来。 20世纪70年代，三维实体建模的发明标志着CAD一个新时代的开始。过去的三维线框模型仅用其边界来表达一个物体。这在某种意义上是模糊的，一个简单的模型可能有几种解释。同时也无法获得一个模型的体积信息。实体模型包含完整的信息，因此，它们不仅可用于生成工程图，而且也可在同一模型上完成工程分析。后来，开发了许多商业系统和研究系统。这些系统中相当多的是基于PADL和BUILD系统。尽管它们在表达上是强有力的，但仍然存在许多缺陷。例如，这种系统要有极强的计算能力和内存需求，非常规的物体建模方式以及标注公差能力的缺乏，这一切已阻碍了CAD应用。直到20世纪80年代中期，实体建模开始介入设计环境。今天实体建模的应用如同绘图和线框模型应用一样普遍。 在个人计算机上，CAD已走向大众化。这种发展使CAD应用面广并且很经济。CAD原本作为一种工具仅被航空和其它主要工业企业使用。诸如AutoCAD、VersaCAD、CADKEY等个人机CAD软件包的引入，使小型公司乃至个人可以拥有并使用CAD系统。到1988年为止已销售10万个以上的PC CAD软件包。今天，基于个人计算机的实体建摸的PC CAD易于获得，并且销售变得更为普及。由于微型计算机的迅速发展使得个人计算机能够承受实体模型需要的大量计算负荷，所以如今许多实体模型在PC机上运行，并且作为平台 已不成为一个问题。随着标准图形用户界面的发展，CAD系统可以很容易地从一台计算机传送，大多数CAD系统都能在不同平台上运行。在大型计算机、工作台和基于个人计算机的CAD系统之间几乎没有区别。 计算机辅助设计的结构一个CAD系统包含三个主要部分：（1）硬件 计算机及输入/输出装置。（2）操作系统软件。（3）应用软件 CAD软件包。 硬件主要用于支持软件功能。在CAD系统中使用着种类繁多的硬件。操作系统软件是CAD应用软件与硬件之间的界面。操作系统软件管理着硬件运行并提供许多诸如创建 和取消操作任务、控制任务的进程、在任务间分配硬件资源、提供通向软件资源，如文件、编辑器、编译和应用程序的通道等基本功能。这不仅对CAD软件很重要，而且对非CAD软件也很重要。 应用软件是CAD系统的核心。它由二维和三维建摸、绘图、工程分析等程序组成。一个CAD系统的功能便建立在应用软件中。正是应用软件使一种CAD软件包区别于另一种，通常应用软件是依赖于操作系统的。要把在一个操作系统上运行的CAD系统移到另一个操作系统上，并不像编译软件那样微不足道。因此也必须注意操作系统。 计算机辅助设计 计算机辅助设计给了设计者去尝试几个可行的解决方案的能力。通常还需要某些形式的设计分析计算，而为了这一任务已经编写了许多程序。计算机为设计者对所建议的各种结构设计的分析和为最终设计准备正式绘图提供了强有力的工具。 在二维绘图领域中，计算机方法能够提供比传统的纸和笔的方法更有意义、更大成本节约的优点，但是一个CAD系统并不仅是一个电子绘图板。计算机绘图系统可使设计者设计出既快又准确的图形，并且很容易修改。在涉及到重复性工作时，会戏剧性产生复制产品，因为标准图形只要一次构建成功，就可以从图库中取出。剪切和粘贴技术作为节约劳动力的辅助工具被使用。当几个分项目设计人员从事同一个工程时，要建立中心数据库，使得由某一个人绘的细节图可以很容易地合并到其它不同的装配图中。中心数据库也可作为标准参考零件库使用。 有限元是一项成熟的应力分析技术，它多被土木工程和机械工程所采用。它由将结构划分成有限个的小单元所组成，并计算每一个单元之间的作用力。如果被分割的单元足够小，就能对一个结构或实体的内部应力获得一个好的估计。这些计算机设计惯用于大型结构物的设计，诸如船体、桥梁、飞机机身和海面油井平台。汽车工业也使用类似的方法来设计和制造车身。 二维绘图 CAD使多视图的二维绘图成为可能，视图空间可以从微米到米的比例范围内无限变化。它提供给机械设计师放大的功能，即使在恰当配合的装配零件中最小的零件也能看清楚，设计程序甚至能自动辨认CAD装配图中的潜在问题。针对具有不同特征的零件，如运动的或静止的，在显示时可以被指定成不同的颜色。为了有利于工程设计的变化，可使用带有自动尺寸变化的系统对零件进行尺寸标注。 三维绘图 随着三维建模的出现，设计者具有了更多的自由度。他们可以生成三维零件图并且可以无限制地修改以获得所需的结果。通过有限元分析，应力加到计算机模型上，并且以图形化的方式显示其结果，在产品物理模型真正产生之前，对设计中的任何内在问题给设计者一个快速的反馈。 三维模型可用线框、曲线或实体方式生成。在线框模型中，直线和圆弧构成了模型边界。结果是一个可以从任何位置观察的三维模型，但仍只是一个框架形式。创建曲面犹如在骨架上包上皮。一旦这样生成后，模型就可以被渲染，使得图形看上去更逼真。曲面模型普遍用于构建板金的展开和重叠以用于制造。 实体模型是最复杂的建模层次，并且用于建立实体模型的程序在一段时期内只用在大型计算机上。只有近年来微型计算机才达到这个能力水平，也可以运行复杂的算法，生成实体模型。计算机“认为”实体模型是一种具有实体质量的模型，所以它可被“钻孔”“加工”“焊接”，好象它是一个实际的零件。它能够由任何材料构成并呈现其材料特性，因此，能够进行质量计算。 计算机辅助绘图的好处 用计算机完成绘图及设计任务的好处是令人难忘的：提高速度、提高准确性、减少硬拷贝存储空间及易于恢复信息、加强信息传输能力、改善传输质量和便于修改。 速度 工业用计算机能以平均每秒3300万次完成一项任务；更新的计算机其速度更快。用计算机计算零件的变形量是一个重要功绩。当理论上的载荷力加到零件上时、通过计算机进行有限元分析或者在监视器上显示一个城市的整体规划时，这两者都是既费时又计算量大的任务。AutoCAD软件可根据需要多次复制所需模型的形状和几何尺寸，快速自动地进行剖面填充及尺寸标注。 准确 AutoCAD程序依靠操作系统及计算机平台每点具有14位的精度。这在用数学计算诸如一个圆的线段数、程序必须圆整线段时是十分重要的。 存储 计算机能够在物理空间中存储上千幅图，这空间能够存储上百幅手工图。而且计算机能够很容易地搜索和找到一幅图，只要操作者拥有正确的文件名。 传输 由于计算机的数据是以电子形式存储，它能被送到各种位置。最明显的位置是监视器。计算机可以在屏幕上以不同的方式显示数据，如图形，并能方便地将数据转换成可读图形。这些数据也可被传送给绘图机，打印出常见的图纸，通过直接连接到计算机辅助制造机床或由电话线传到地球的任何地方。你可以不再冒损失或丢失的危险去邮寄图纸，现在图纸可以通过电信网立即发送到目的地。 A Brief History of 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 Coons patch, Beziers 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 DrawingsCAD 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 D
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