CATIA A级曲面基本设计

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catiaClass-A知识解读

开瑞汽车工程研究院 KAERI
A-class 包括多方面评测标准 , 比如说反射是不是好看、顺眼等等。当然，G2可以说是一个基本要求,因为 g2以上才有光顺的反射效果。但是, 即使 G3 了，也未必是 a-class, 也就是说有时虽然连续，但是面之间出现褶皱，此时就不是 a-class 通俗一点说，class-A就必须是G2以上连接。 G3 连续的面不一定是 CLASS-A 曲面。汽车业界对于 a class要求也有不同的标准， GM 要求比 TOYOTA ， BMW 等等要低一些，也就是说 gap 和 angle 要求要松一些。关于 A-class surfaces ，涉及曲面的类型的二个基本观点是位置和质量。位置——所有消费者可见的表面按 A-Surface 考虑。汽车的 console （副仪表台）属于 A-surf ，内部结构件则是B-surf。
开瑞汽车工程研究院 KAERI
曲线连续
开瑞汽车工程研究院 KAERI
曲面连续
开瑞汽车工程研究院 KAERI
高光表现
开瑞汽车工程研究院 KAERI
前风挡玻璃，曲率连续（对称面要求）
开瑞汽车工程研究院 KAERI
开瑞汽车工程研究院 KAERI
开瑞汽车工程研究院 KAERI
B、切向连续
开瑞汽车工程研究院 KAERI
1、根据造型特征拆分曲面，分块要合理，曲面在UV方向都保证曲率的连续性及变化趋势的合理。面的分块应该将主模型作为一个整体来考虑，整体的思想可保证整个面的和谐统一 2、建议采用尽可能少的面片，曲面使用单段面和低阶面，一般少于6阶。 3、基本曲面应该建立到或超过理论的相交区域，这提供了更大的自由度，用来对过渡面变化调整和高光线控制。曲面应该产生预期的延伸，延伸没有任何不正常结果（例如猴尾巴和螺旋），这允许下游的建模者产生延伸用来满足实体建模、工艺补充面、钻模和夹具需要。 4、曲面应该修剪到内部边界并且能够缝合，要提供生成修剪实体的理想数据。

CATIA软件曲面建模技巧

CATIA软件曲面建模技巧Catia软件是一款广泛应用于工程设计和制造领域的三维建模软件。

曲面建模是Catia软件中的一个重要功能，通过灵活运用曲面建模技巧可以实现更为精细和复杂的设计。

本文将介绍一些Catia软件曲面建模的技巧和方法。

一、曲面建模简介在Catia软件中，曲面建模是基于曲面定义的模型构建方式。

通过创建和编辑曲面，我们可以构建出各种复杂的产品形状和曲线。

曲面建模相比于实体建模，可以更加自由地表达设计者的想法和要求，提供更大的设计灵活性。

二、基本曲面绘制1. 创建曲面在Catia软件中，我们可以通过多种方法创建曲面。

例如，可以使用曲线工具绘制曲线然后利用曲线来创建曲面，也可以使用曲面工具直接绘制曲面。

在创建曲面时，可以根据设计需求选择合适的绘制方法。

2. 编辑曲面Catia软件提供了丰富的曲面编辑工具，可以对已有的曲面进行修改和调整。

例如，可以使用平移、旋转、缩放等操作来调整曲面的大小和位置，也可以使用修剪、填充、切割等操作来改变曲面的形状和结构。

三、曲面拟合技巧1. 拟合曲面在实际设计过程中，我们常常需要根据已有的曲线或曲面来生成新的曲面。

Catia软件提供了曲面拟合工具，可以通过选择已有的曲线或曲面进行拟合操作。

拟合曲面时，可以指定曲面的类型和度数，从而达到更好的设计效果。

2. 曲面平滑曲面平滑是提高产品外观质量的重要技巧之一。

在Catia软件中，我们可以通过调整曲面的节点和控制点，使用曲率连续性工具，来使曲面在过渡处更加平滑。

通过合理运用曲面平滑技巧，可以消除因曲面变化导致的不连续性，提高产品的美观性和舒适度。

四、曲面修剪和联接1. 修剪曲面有时候，我们需要对曲面进行修剪，以满足设计要求。

在Catia软件中，可以使用曲面修剪工具对曲面进行修剪操作。

通过选择修剪边界和修剪刀具，可以将曲面进行精确的修剪。

2. 曲面联接曲面联接是将两个或多个曲面进行无缝连接的技巧。

在Catia软件中，可以使用曲面联接工具将曲面进行联接。

Catia_A级曲面设计

CLASS ‘A’ SURFACING‘A'Class surfacing and its importance:A class surfaces are those aesthetic/free form surfaces,which are visible to us(interior/exterior),having an optimalaesthetic shape and high surface quality.Mathematically class A surface are those surfaces which arecurvature continuous while providing the simplest mathematical representation needed for the desiredshape/form and does not have any undesirable waviness.Curvature continuity:It is the continuity between thesurfaces sharing the same boundary.Curvature continuitymeans that at each point of each surface along the commonboundary has the same radius of curvature.Why Class A is needed:We all understand that today products are not only designed considering the functionality but special consideration aregiven to its form/aesthetics which can bring a desire in onesmind to own that product.Which is only possible with high-class finish and good forms.This is the reason why in designindustries Class A surface are given more importance.UNDERSTANDINGUnderstanding for Class A surfaces:1. The fillets -Generally for Class A, the requirement is curvature continuous and Uniform flow of flow lines from fillet to parent surface value of 0.005 or better (Position 0.001mm and tangency to about 0.016 degrees).2. The flow of the highlight lines -The lines should form a uniform family of lines. Gradually widening or narrowing but in general never pinching in and out.3. The control points should form a very ordered structure -again varying in Angle from one Row to the next in a gradual manner (this will yield the good Highlights required).4. For a Class A model the fillet boundary should be edited and moved to form a Gentle line -and then re-matched into the base surface.5. Matched iso-params in U & V direction are also a good representation of class A.6. The degree (order) of the Bezier fillets should generally be about 6 (also for arc Radius direction) sometimes you may have to go higher.7. Also you have to take care of Draft angle, symmetry, gaps and matching of surfaces Created with parent or reference surfaces.8. Curvature cross-section needles across the part -we make sure the rate of Change of curvature (or the flow of the capping line across the top of the part) is Very gentle and well behaved.The physical meaning:Class A refers to those surfaces, which are CURVATURE continuous to each other at their respective boundaries. Curvature continuity means that at each "point" of each surface along the common boundary has the same radius of curvature.This is different to surfaces having;Tangent continuity -which is directional continuity without radius continuity -like fillets.Point continuity -only touching without directional (tangent) or curvature equivalence.In fact, tangent and point continuity is the entire basis most industries (aerospace, shipbuilding, BIW etc ). For these applications, there is generally no need for curvature.By definition:Class A surface refers to those surfaces which are VISIBLE and abide to the physical meaning, in a product. This classification is primarily used in the automotive and increasingly in consumer goods (toothbrushes, PalmPC's, mobile phones, washing machines, toilet lids etc). It is a requirement where aesthetics has a significant contribution. For this reason the exterior of automobiles are deemed Class-A. BIW is NOT Class-A. The exterior of you sexy toothbrush is Class-A, the interior with ribs and inserts etc is NOT Class-A. QUESTION:What is Body_in_white?What is class A surface?Are the interior trim (A,B,C pillar, dash board, center console, handles) of a car using class A surface? Anybody using the basic design bundle of UG for class A surfacing? UG\Shape Studio?How does it compare with Catia?Ans:1A class A surface is anything that you the customer sees. i.e. exterior panels and interior surfaces.A ClassB surface is something that is not always visible i.e. the underside of a fascia that you would have to bend down to see.A Class C surface is the back side of a part of a surface that is permanently covered by another part.BIW is stuff like the body side etc..Ans:2Actually 'body in white' is the term used to describe the whole vehicle body after it has been welded/bolted together before it is painted or any parts are attached on the fit up line.Ans:3We also use it to mean after it has been painted -I always assumed that the white bit refers to primer. Next step is to fit the windscreen and backlight, when it becomes the glazed body in white, or BIW+G.ANS: 4BIW -Some surfaces are Class A, i.e. body side, roof, sill appliqué.I heard some time ago from a old designer that the term BIW comes from when cars were built from wood, they were painted white as it gives the frame a uniform color so imperfections were easily visible.Ans:5BIW meaning Body In White is so called due to its appearance after the application of the primer to the entirely Body panel assembled vehicle just before going into the painting process.Usually the primer is white or silver grey which gives the so called name.ANS: 6Catia is mostly used for BIW design (Ford switching to catia, and Toyota). Is this because itcould easily create quintic surfaces? With UG with Design bundle only, most of the surfaces created are cubic.-------------------------------------------------------------------ANS: 7A class surface means -it is not just seen surface and unseen surface In normal no technical words,A class surface meansIt is smooth looking reflective surface with no distortion of light highlights, which moves in a smooth uniform designer intended formations.when you create -car body panel, due to their complex shapes it not possible to create the surface with one single face /patch so you make multiple face/patch ( surface is a group of face/patch added together.)when these things are added, at the boundary of joining you need to have connectivity and continuation of minimum order two.for exampleIn case one, at the connecting boundary of two patches you have common boundary but it is sharp corner. this does not qualify as A class surface.In case two -at the connecting boundary of two patches have common boundary and no sharp corner -but you have tangent continuity, this also does not qualify as A class surface.In case two -at the connecting boundary of two patches have common boundary and no sharp corner -you have tangent continuity and curvature continuity this does qualify as A class surface. ( sine curve is good example for curvature continuity. but you can not call it a A class surface )reason is very simple the real requirement of aesthetic and good looking and designer intended shape is not there.ANS:8For obtaining Class-A surfaces,CATIA is more commonly used due to its inherent ability to model very high quality surfaces in general.But,any engineering software(CATIA,UG,IDEAS,Pro-E,etc)cannot develop a Class-A surface.This being due to engineering calculations involved in any surface generated by such softwares.For pure Class-A surfaces you would need styling softwares like Alias,Studio,etc.The use of any software would depend on the level of expectations placed on you.If your projects need only the modeling of the trim,generic engg softwares will do,but if you intend to go down right from styling,you would need Studio,etc.-------------------------------------------------------------------ANS:9IHO,Catia V4has added a tool called Blend surf that is able to obtain virtual curvature continuity.Previously, even styling was comfortable with models-and hence tools-defining fillets with conics,and many OEMs still accept this for Class-A surfaces.Catia V5has GUI interfaces to impose curvature continuity the same way that Alias-Wave front Studio Tools(Auto Studio)does.They are both based on piece-wise polynomial equations,for what its worth.While a conic fillet is not technically curvature continuous,there are many vehicles,including luxury models,that have utilized them for Class-A surfaces and downstream-parts.Considering the tolerances in creating molds and dies and then producing parts from them....a sheet metal panel is not a math model.-------------------------------------------------------------------ANS:10It is true that it is tough to make good curvature continuous surface in UG,but not impossible.Remember one thing A-class doesn't mean just curvature continuity.and smooth reflections on CAD surface.it is lot more than that.Imagine.what happens to your A class surface in case pressed sheet metal body panel. and molded plastic components.They have to retain there intended smoothness and other characteristics to remain A class.to achieve this lot of other things has to be taken care while designing A class surfaces.For example:1-Line features on body side external panel and feature on hood panel which is very common,are to be designed to avoid skidding while they are pressed.like wise2-Flange width and other things are to be taken care while designing fenders wheel arch area for avoiding bulging effect and skidding effect.3-Fuel lid opening area,plunged flange for bulge effect.4-Panel stretching needs to be taken care.Lot many other things go in designing A class sheet metal panels for door,roof etc.5-In case of plastic,sink marks and other things.ANS:11In Europe a'A'class surface is generally taken to be the visible side of any component/assembly-a'B' class surface generally relates to the opposite(or inside)face of an'A'surface-i.e.the surface which defines the thickness of the part,and is where the mounting and reinforcing detail tends to be located.'B' class surfaces can also be referred to as'engineering surfaces.I have not personally heard of any surface being referred to as a'C'type.Catia,while it is ok for surfacing tends to be more used for generating engineering surface detail and solid models-software packages like ICEMSURF tend to be more used for generating visual quality surfaces.-------------------------------------------------------------------ANS:12True A-class surfacing-especially on vehicle exteriors goes further than G2or"curvature"continuity.G3is often sought on the more major block surfaces.G3deals with curvature"acceleration",i.e.the rate of change of curvature across a boundary.G2means as has been described before that the curvature value is the same across a boundary.G3means that the surface curvature leading to the boundary is changing shape at the same rate.Its like driving a car round a bend,you start off straight then gently add steering lock to the point where you need no more,then you gently wind off the steering until you're straight again.If you look at the curve your car made,this would be G3.A-Class and B-class would refer to surface quality required for the component which is different to A-side and B-side which refers to which is the visible/non visible part of a component.ICEM surf is considered the best tool for speedy A-class surfacing due to the sophistication of its real-time diagnostics.The consequence:The consequence of these surfaces apart from visually and physically aesthetic shapes is the way they reflect the real world. What would one expect to see across the boundary of pairs of point continuity, tangent continuity and curvature continuity surfaces when reflecting a straight and dry tree stump in the desert????Point Continuity (also known as G0 continuity) -will produce a reflection on one surface, then at the boundary disappear and re-appear at a location slightly different on the other surface. The same reflective phenomenon will show when there is a gap between the surfaces (the line markers on a road reflecting across the gap between the doors of a car).Tangent Continuity (also known as G1 continuity) -will produce a reflection on one surface, then at the boundary have a kink and continue. Unlike Point continuity the reflection (repeat REFLECTION) is continuous but has a tangent discontinuity in it. In analogy, it is "like" a greater than symbol.Curvature Continuity (also known as G2 continuity, Alias can do G3!) -this will produce the unbroken and smooth reflection across the boundary.To achieve the same Class 'A' surfaces that automotive manufacturers demand, consumer product manufacturers have availed themselves of the same advanced surface modeling tools. What is a Class 'A' surface? The simple answer is that it is a perfectly smooth surface with no anomalies, in which all adjoining surfaces have curvature continuity. This means that where two surfaces meet, the graduation of one into the other is achieved without discernible abrupt transitions. The techniques used to create Class 'A' surfaces typically reside in top level surface modeling software developed for the motor industry, rather than mid-range mechanical CAD packages that have evolved from 3D solid modeling for mechanical assemblies.Analyzing A Class SurfaceHighlight plot :Highlight is the behavior of the form orShape of a surface when a light ornature reflects on it. This reflection oflight or nature gives you anunderstanding about the quality ofsurface. This reflection required shouldbe natural, streamline and withuniformityDesigner Fillets:If you take two adjoining2D lines,or a couple of tangential surfaces,the intersection between them can be turned into an arc(2D)or a fillet(3D),each of which is inserted with a constant radius.However the transition from each line or surface can often be too abrupt for the design.According to Mike Lang,Technical Director of VX,fillets should look simple-you shouldn't see a fillet line in a model.They should also be simple to create."Achieving tangent and curvature continuity in complex shapes on other systems is hard work.A reduction in the weight of a curve will allow it to retain its tangency,but sharpen the change in curvature. This can be seen most effectively by reducing the weight almost to zero.Fairings-the shape of the curve-can be influenced by energy,variation,jerk,bend or tension-each of which will produce a subtle difference in the mathematical fit through the curve.Echo Attributes:Part of the process of obtaining Class'A'surfaces is being able to see what's happening to the curve or the surface as it is being developed.Increasing the scale of the iso lines allows designers to pick up smaller imperfections in surfaces.Where blue iso lines lose their curve they change to white.The shifting colors of Gaussian shading are also particularly adept at detecting subtle blemishes.Echo Attributes also has numerous other modifiable elements,including the ability to apply colors to lines and surfaces,and to alter the transparency of the surface.Curvature plots on non-designer fillets show regular arcs,unlike designer fillets that show the weighting of the curve at each point."good design work relies on good wire frame technology.If you don't have basic curve geometry,you won't be able to produce a good surface”.Designers must always go through the routine of checking curves,especially if the design has come in from an outside source-perhaps containing older style Bezier curves with lots of points.The following describes the mathematics for the so called Bezier curve.It is attributed and named after a French engineer ,Pierre Bezier ,who used them for the body design of the Renault car in the 1970's.They have since obtained dominance in the typesetting industry.Consider N+1control points pk (k=0to N)in 3space.The Bezier parametric curve function is of the form.B (u)is a continuous function in 3space defining the curve with N discrete control points P k .u=0at the first control point (k=0)and u=1at the last control point (k=N).Notes:•The curve in general does not pass through any of the control points except the first and last. From the formula B (0) = P 0and B (1) = P N .•The curve is always contained within the convex hull of the control points, it never oscillates wildly away from the control points.•If there is only one control point P 0, i.e.: N=0 then B (u) = P 0for all u.•If there are only two control points P 0and P 1, i.e.: N=1 then the formula reduces to a line segment between the two control points.•the term shown below is called a blending function since it blends the control points to form the Bezier curve.Bezier Curves•The blending function is always a polynomial one degree less than the number of control points. Thus 3 control points results in a parabola, 4 control points a cubic curve etc.•Closed curves can be generated by making the last control point the same as the first control point. First order continuity can be achieved by ensuring the tangent between the first two points and the last two points are the same.•Adding multiple control points at a single position in space will add more weight to that point "pulling" the Bezier curve towards it.•As the number of control points increases it is necessary to have higher order polynomials and possibly higher factorials. It is common therefore to piece together small sections of Bezier curves to form a longer curve. This also helps control local conditions, normally changing the position of one control point will affect the whole curve. Of course since the curve starts and ends at the first and last control point it is easy to physically match the sections. It is also possible to match the first derivative since the tangent at the ends is along the line between the two points at the end.Second order continuity is generally not possible.•Except for the redundant cases of 2 control points (straight line), it is generally not possible to derive a Bezier curve that is parallel to another Bezier curve.A circle cannot be exactly represented with a Bezier curve.It isn't possible to create a Bezier curve that is parallel to another,except in the trivial cases of coincident parallel curves or straight line Bezier curves.Bezier curves have wide applications because they are easy to compute and very stable. There are similar formulations which are alsocalled Bezier curves which behave differently, in particular it ispossible to create a similar curve except that it passes through the control points. See also Spline curves.Examples: The pink lines show the control point polygon, the grey lines the Bezier curve.1.The degree of the curve is one less than the number of controlpoints, so it is a quadratic for 3 control points. It will always besymmetric for a symmetric control point arrangement.2.The curve always passes through the end points and is tangent tothe line between the last two and first two control points. Thispermits ready piecing of multiple Bezier curves together with first order continuity.3.The curve always lies within the convex hull of the control points.Thus the curve is always "well behaved" and does not oscillatingerratically.4.Closed curves are generated by specifying the first point the sameas the last point. If the tangents at the first and last points match then the curve will be closed with first order continuity.. Inaddition, the curve may be pulled towards a control point byspecifying it multiple times. 1 2 3 4The Bezier surface is formed as the Cartesian product of the blending functions of two orthogonal Bezier curves.Where P i,j is the i,jth control point. There are N i+1and N j+1control points in the i and j directions respectively. The corresponding properties of the Bezier curve apply to the Bezier surface. -The surface does not in general pass through the control points except for the corners of the control point grid. -The surface is contained within the convex hull of the control points. Along the edges of the grid patch the Bezier surface matches that of a Bezier curve through the control points along that edge.Closed surfaces can be formed by setting the last control point equal to the first. If the tangents also match between the first two and last two control points then the closed surface will have first order continuity. While a cylinder/cone can be formed from a Beziersurface, it is not possible to form a sphere.BEZIER SURFACEA little history of Surface Modeling A little historySurface modeling was developed in the automotive and aerospace industries in the late1970s to design and manufacture complex shapes.Nurbs--nonuniform rational B-splines--and cubic-surface formats appeared early and remain the primary spline and surface formatsused throughout the CAD industry.Nurbs and cubics are supported byIGES(Initial Graphics Exchange Specification),a neutral file format for exchanging data between CAD systems.Nurbs and cubic formats are represented in a computer by polynomial equations generated by a CAD system,and onscreen through thelocation and shape of curves and surfaces.For example,the equationof a line,a first-degree polynomial,has this formY=ax+bThe equation for a parabola,a second-degree polynomial,has the formY=ax2+bx+cAnd the equation of a cubic spline,a third-degree polynomial,looks likeY=ax3+bx2+cx+dThe more terms in the polynomial equation,the more"shape"thecurve or surface has.The data structure of a Nurbs curve or surface is comprised of points, weights,and parameter values that define a control net which istangent to the curve or surface.The control net on a Nurbs surface is a rectangular grid of connected straight-line elements which define thetangency of the surface at positions along the control net.The points inthe database which describe the control net are not actually on the surface,they are at the vertices of the control net.Weights in theNurbs data structure determine the amount of surface deflectiontoward or away from its control point.Cubic data structures use third-degree polynomials that describe pointsactually on the curve or surface.Therefore,the Nurbs control net is an abstraction of the underlying surface,whereas the cubic equation is the surface.Nurbs and cubic formats each have advantages and disadvantages.Nurbs equations model more complex shapes by increasing the degree of the exponents in the polynomial,thus increasing the memory required to store and evaluate the equation.Cubic equations,on the other hand,require less storage and can capture complex shapes by adding more cubic segments to the spline or surface.Nurbs and cubic equations are said to be"piecewise"and"parametric,"which means the curve or surface is a sequence of connected segments that use parametric u and v values ranging from0to1or0to n(number of segments)to calculate points along the curve or surface.Nurbs and cubic formats each have advantages and disadvantages.Nurbs equations model more complex shapes by increasing the degree of the exponents in the polynomial,thus increasing the memory required to store and evaluate the equation.Cubic equations,on the other hand,require less storage and can capture complex shapes by adding more cubic segments to the spline or surface.Nurbs and cubic equations are said to be"piecewise"and"parametric,"which means the curve or surface is a sequence of connected segments that use parametric u and v values ranging from0to1or0to n(number of segments)to calculate points along the curve or surface.Ultimately,a good CAD system shields users from having to know too much about the mathematics that represent the underlying surfaces.In addition,surface modelers should:Provide enough tools to completely define any feature on the part using surfaces.Have many functions for defining the different shapes of surfaces including ruled,revolved,lofted,extruded, swept,offset,filleted,blended,planar boundary,and drafted.Each of these functions have further variations. For example,offset surfaces should allow for constant or tapered offsets.Draft-surface functions should let users input curves to define the draft surface,or allow using curves on a surface whereby the draft angle is referenced off a surface-normal vector at points along the curve.The lofted surface should allow for the input of cross-section curves or for the input of curves both along and across the surface.Support functions such as surface trimming,extending,intersecting,projecting,polygon tessellation,IGES translation,coordinate-system transformations,and editing.Allow extracting surface data such as flow curves,vectors,and planes,among other functions.Have a set of tools for defining points,planes,vectors,and splines used with surface modeling.Most surface creation functions need user inputs to define surfaces.Two useful surface-modeling functions are the controlled sweep and the draft surface.A controlled sweep forces a profile curve to remain perpendicular to the sweep path by using a control surface.Without a control surface in the construction of a swept surface,the profile curve typically wants to lay down or spin around the sweep path.A properly defined control surface solves the problem.A draft surface is similar to a controlled sweep in that it uses curves lying on one surface to create another.The resultant draft surface passes through the input curve and is composed of straight-line elements radiating from the reference surface at an angle to the surface normal vectors taken at points along the input curve.A draft-surface function can build one surface perpendicular to another,along a curve.A Comparison Between Solid-Surface Modeling:While surface modelers excel at defining complex shapes,solid modeling is good at quickly building primitive geometry.Primitive geometry consists of basic surfaces such as planes,cylinders,cones, spheres,and tori.Surface modeling is not as fast at creating simple part geometry,but if your solid modeler can't easily model a feature,such as a fillet,surface modeling can almost always finish the part. And for every solid-modeling function there is a counterpart in surface modeling.Nurbs surfaces can be incorporated into an existing solid model by"stitching"the Nurbs surface to the solid model.Some parts can be completely defined by a solid modeler as a collection of primitive surfaces,while other parts require Nurbs surfaces to fully define the geometry.Most parts manufactured with tooling require some kind of Nurbs surface to support production.Reverse engineering is heavily dependent on Nurbs surfaces to capture digitized points into surfaces.In addition,Nurbs-surface files generated over the last20years are circulating in IGES format between vendors and subcontractors.These files support the design of parts in one system and manufacturing in another.Solid modeling will not replace Nurbs-surface modeling because the two work hand in hand to complete part geometry.TYPES OF CONTINUTYContinuity is a measure of how well two curves or surfaces "flow" into each other.•POSITION (G0)This type of continuity between curves implies that the endpoints of the curves have the same X,Y, and Z position in the world space. This is the minimum requirement for obtaining G0.•TANGENT (G1)This type of continuity between curves implies that the tangent CVs must be on one line.•CURVATURE (G2)This continuity type impacts the third CV of the curve. All three CVs have to be considered in order to maintain a smooth curvature comb.If a curvature comb does not have a smooth transitional line. In order to improve the curvature comb, manually modify the position of the three CVs that constitute the G2continuity.。

CATIA CATIAA级曲面检查规范说明

重庆南方摩托车技术研发有限公司CATIA A 级曲面检查规范北京迅利创成科技有限公司日期：2011年12月7日目录1.规范描述............................... 错误!未定义书签。

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设置建模精度......................... 错误!未定义书签。

曲面间的间隙/重叠.................... 错误!未定义书签。

曲面间的连续性....................... 错误!未定义书签。

光顺性要求........................... 错误!未定义书签。

脱模................................. 错误!未定义书签。

配合间隙............................. 错误!未定义书签。

输出格式............................. 错误!未定义书签。

4规范内容 ............................... 错误!未定义书签。

高光连续性检查....................... 错误!未定义书签。

连续性检查.......................... 错误!未定义书签。

曲率梳连续性检查..................... 错误!未定义书签。

两零件搭接关系检查................... 错误!未定义书签。

A级曲面的间距离检查................. 错误!未定义书签。

(整理)Catia--曲面设计.

第一章曲面设计概要1、曲面造型的数学概念：（1）、贝塞尔（Bezier）曲线与曲面：法国雷诺的Bezier在1962年提出的，是三次曲线的形成原理。

这是由四个位置矢量Q0、Q1、Q2、Q3定义的曲线。

通常将Q0，Q1，…，Qn组成的多边形折线称为Bezier控制多边形，多边形的第一条折线与最后一条折线代表曲线起点和终点的切线方向，其他折线用于定义曲线的阶次与形状。

（2）、B样条曲线与曲面：与Bezier曲线不同的是权函数不采用伯恩斯坦基函数，而采用B样条基函数。

（3）、非均匀有利B样条（NURBS）曲线与曲面：NURBS是Non-Uniform Rational B-Splines的缩写。

Non-Uniform（非统一）指一个控制顶点的影响力的范围能够改变。

当创建一个不规则曲面的时候，这一点非常有用。

同样，统一的曲线和曲面在透视投影下也不是无变化的，对于交互的3D建模来说，这是一个严重的缺陷。

Rational（有理）指每个NURBS物体都可以用数学表达式来定义。

B-Spline（B样条）指用路线来构建一条曲线，在一个或更多的点之间以内差值替换。

（4）NURBS曲面的特性及曲面连续性定义：NURBS曲面的特性：NURBS用数学方法来描述形体，采用解析几何图形，曲线或曲面上任何一点都有其对应的坐标（x,y,z），据有高度的精确性。

曲面G1与G2连续性定义：Gn表示两个几何对象间的实际连续程度。

●G0：两个对象相连或两个对象的位置是连续的。

●G1：两个对象光滑连接，一阶微分连续，或者是相切连续的。

●G2：两个对象光滑连接，二阶微分连续，或者两个对象的曲率是连续的。

●G3：两个对象光滑连接，三阶微分连续。

●Gn的连续性是独立于表示（参数化）的。

2、检查曲面光滑的方法：①、对构造的曲面进行渲染处理，可通过透视、透明度和多重光源等处理手段产生高清晰度的、逼真的彩色图像，再根据处理后的图像光亮度的分布规律来判断出曲面的光滑度。

CATIA曲面设计理念全剖析(A面,B面,C面)

CATIA曲面设计理念全剖析（A面，B面，C面）2009-05-04 19:47关于做曲面，谈谈一点心得。

我觉得无论是CATIA或则其它软件，做曲面前规划曲面很重要，不能画到哪里是哪里，先构建基面和大过度面等，再添加细微特征和圆角特征等。

我们都会发现一般国外过来的数据都十分轨整，即使打上UV线，UV线的流向都十分整齐，而一般国外的数据都常常保留理论交线，这都是具备完整规划的曲面才可以做出类似“铁线尖角”模型通常经过规划的曲面模型，其曲面质量肯定是比较好。

最忌讳的是利用一个曲面来表现很多特征，无论是数据交换还是曲面质量一定会遇到不少麻烦。

实体也有同样的道理，先规划大轮廓，再做挖取部分，不要想起挖个洞就挖一个洞，想起补一块再补一块。

我从v4生成的exp文件中拖出了的model文件在五版本中打开时，如果是二维图，则提示说没有没有prj.model文件。

（我已经在option中设置了prj.model的路径了）请问如何在斯版本中声称这个文件？在五版本中读取四版本中的model文件有没有其它好办法？Top-Down 的思路已是欧美工程师的作业习惯了，除了设变的好处之外，当然在协同设计同步工程上也有相关的机制存在的，使用top-down 的观念从事设计工作最重视事前的规划，忌讳想到那里做到那里，而且要避免循环参考的问题，故有以下几点建议︰1.规划出共享的线架构及曲面的档案，即Layout Part, 将其放在总组立的第一个零件，所有零件皆以此为准2.先行插入共享零件及外购标准件，其定位点当然也是置于LayOut Part 中，以便日后进行设变单一化3.规划出几个大的次组件，在次组件中插入新零件进行零件的设计4.在零件数量渐渐变多时，仅量保持新零件参考旧零件的原则，避免循环参考的现象5.适当发布组件以利后续使用以上是一个大约的概念，若有不足请补充！以此法设计虽说是分成很多零件，但在零件设计时的方式也和在同一零件设计时方法一样并无特别的地方，当然要避免循环参考，若有发生这种现象时CATIA 会提醒你的，只要找出相关的父子关系就以解决这现象了ps : 在选项中的零件设计下要启动"与选取对象保持关联" 的选项！设计的基本方法即：自上而下或自下而上自上而下：1、可以构造骨架零件（在属性中将这个零件不显示在BOM 表中），然后将参考参数（点、线、面、控制变量等）发布（publish）;同时，我们在主骨架的控制下，可以构造子装配的骨架；在进行详细设计时，我们可以选择只关联发布元素，这样可以避免过多的参考，非关键元素在关联设计时生成的是只有子关系而没有父关系的元素，在进行大装配时，不致与造成系统崩溃；同时可以使用DMU的功能，在设计的同时检查设计的合理性，而这些检查皆可以挂在目录树中，使得我们可以重复的利用这些资源，我们只需要更新即可，而不必每次都从新选择等。

CATIA软件曲面建模教程

CATIA软件曲面建模教程CATIA是一款功能强大的计算机辅助设计软件，被广泛应用于航空航天、汽车制造、机械制造等领域。

在CATIA中，曲面建模是一项重要的技术，它可以帮助设计师创建复杂的曲面形状，实现更加精确的产品设计。

本教程将介绍CATIA软件中的曲面建模方法和技巧。

第一步：创建曲面基体在CATIA软件中，首先需要创建一个曲面的基体，可以是一个点、线、面或者立体实体。

基体决定了曲面的整体形状和特征。

在创建基体时，需要考虑产品的设计要求和实际需求，选择合适的基体形状和尺寸。

第二步：曲面绘制和修改在CATIA中，有多种方法可以进行曲面绘制和修改。

例如，可以使用控制点曲线绘制曲线形状，然后根据需要进行调整和修改。

同时，还可以利用插值曲线、曲面旋转、拟合曲线等功能来实现更加复杂的曲面形状。

第三步：曲面修饰和加工在曲面建模完成后，通常需要进行一些修饰和加工操作，以满足设计要求。

CATIA提供了多种曲面修饰和加工的工具，如平滑、倒角、变形等。

通过这些操作，可以使曲面更加平滑、美观，并且符合产品设计要求。

第四步：曲面分析和检查曲面建模完成后，需要进行曲面分析和检查，以确保曲面的质量和准确性。

CATIA提供了多种曲面分析和检查工具，如曲面曲率分析、曲面边界检查等。

通过这些工具，可以及时发现和修正曲面建模中的问题，保证产品设计的准确性和可行性。

第五步：导出和应用完成曲面建模后，可以将曲面导出为合适的文件格式，如IGES、STEP等，以便在其他设计软件或者制造设备中应用和使用。

同时，也可以将曲面直接应用于产品设计中，进一步完善产品的形状和功能。

总结：本教程介绍了CATIA软件中曲面建模的基本方法和技巧。

通过学习和实践，设计师可以快速掌握CATIA软件的曲面建模功能，并且灵活运用于实际的产品设计中。

曲面建模的技术和应用是设计师必备的技能之一，掌握CATIA软件的曲面建模方法，将为设计师的工作提供更多的可能性和创造力。

CATIA曲面设计

CATIA曲面设计CATIA是一款由法国达索系统公司开发的三维设计软件，它提供了丰富的工具和功能，使用户能够进行各种设计任务。

其中，曲面设计是CATIA的一个重要功能，它在汽车、飞机、船舶等领域的设计中起着至关重要的作用。

本文将介绍CATIA曲面设计的基本原理和应用。

一、CATIA曲面设计的基本原理曲面是由许多曲线构成的，而曲线是通过连接不同的点所得到的。

在CATIA中，曲线和曲面的创建是基于数学模型的，具体来说，是基于贝塞尔曲线和贝塞尔曲面的原理。

贝塞尔曲线是一种通过给定的控制点，通过插值运算得到的曲线。

在CATIA中，用户可以通过调整控制点的位置、权重和个数，来控制曲线的形状。

通过将多个贝塞尔曲线连接起来，就可以创建复杂的曲面。

贝塞尔曲面则是由多个贝塞尔曲线构成的。

在CATIA中，用户可以通过将贝塞尔曲线进行连接和调整，来创建曲面。

CATIA还提供了多种曲面操作工具，如修剪、切割、偏移等，使用户能够对曲面进行进一步的编辑和优化。

二、CATIA曲面设计的应用CATIA曲面设计在许多领域都有广泛的应用。

以下将介绍其中几个典型的应用案例。

1. 汽车设计在汽车设计中，曲面设计是非常重要的一部分。

汽车外观的美观性和空气动力学性能都与曲面设计密切相关。

CATIA提供了丰富的曲面设计工具，使汽车设计师能够创建出流线型的车身曲面，以提高汽车的空气动力学效果和燃油效率。

同时，CATIA还支持对车身曲面进行模拟和分析，以确保其在不同工况下的稳定性和安全性。

2. 飞机设计在飞机设计中，曲面设计同样具有重要的作用。

飞机外形的流线型设计不仅能减少气动阻力，提高飞行速度，还能提高飞行稳定性和安全性。

CATIA提供了丰富的飞机曲面设计工具，使飞机设计师能够创建出符合气动原理和结构强度要求的曲面结构。

同时，CATIA还支持对飞机曲面进行分析和仿真，以确保其在各种飞行工况下的性能和安全性。

3. 船舶设计在船舶设计中，曲面设计同样扮演着非常重要的角色。

汽车设计-A级曲面(A-Class Surface)模型设计质量规范模板

XX公司企业规范编号xxxx-xxxx汽车设计-A级曲面（A-Class Surface）模型设计质量规范模板A级曲面模型设计质量规范1 范围本规范规定了使用计算机软件（Alias或CATIA V5）构建A-Class Surface曲面数字模型所遵循的质量技术要求。

2 术语和定义下列术语和定义适用于本规范。

曲面Surface数学点的集合，它是在平面（R2）的一个连通子集上定义的连续函数图像。

A级曲面A-Class Surface造型外表面数字模型的一种，满足特定的技术质量要求，用于表示最终冻结的造型外表面。

曲面连续性Surface Continuity在使用多个小块曲面构建大的曲面时，在两个和两个以上曲面进行拼接边界处存在的几何位置关系。

一般用到的有位置连续（G0）、相切连续（G1）、曲率连续（G2）、曲率变化率连续（G3）。

曲线阶数曲线数学表达多项式的最高次幂就是曲线的阶数（Degree），等于该曲线控制点数（Order）减一。

曲线控制点（CV）与控制边（Hull）曲线的直观表达一般用控制点来表示的，两个相邻控制点的连线就是控制边（Hull）。

如图1所示。

曲线Span用来描述曲线特定位置分段数字信息，可以简单的理解为曲线的段。

曲线可以是单段（1 Span）多次的，也可以是多段（N Spans）多次的。

如图1所示，图1中的曲线就是多段（N Spans）多次。

图1 曲线基本信息图曲面块Patch在使用曲线构建曲面过程中，形成曲面的U、V方向上曲线的Span数的乘积就是曲面的Patch数，也相应把曲面分成若干个曲面块（Patch）。

如图2所示。

图2 曲面基本信息图3 A-Class Surface曲面数字模型质量要求3.1公差要求3.1.1曲线间隙：=0mm。

3.1.2曲面间隙：≤0.003mm；3.1.3曲面相切角度偏差：≤0.1Grad（圆角处：≤0.5Grad）。

3.1.4没有边长小于1mm的微小曲面。

CATIA A级曲面全面介绍

A级曲面全面介绍！在整个汽车开发的流程中，有一工程段称为ClassAEngineering，重点是在确定曲面的品质可以符合A级曲面的要求。

所谓A级曲面的定义，是必须满足相邻曲面间之间隙在0.005mm以下（有些汽车厂甚至要求到0.001mm），切率改变(tangencyChange)在0.16度以下，曲率改变(curvaturechange)在0.005度以下，符合这样的标准才能确保钣件的环境反射不会有问题。

a-class包括多方面评测标准,比如说反射是不是好看、顺眼等等。

当然，G2可以说是一个基本要求,因为g2以上才有光顺的反射效果。

但是,即使G3了，也未必是a-class,也就是说有时虽然连续，但是面之间出现褶皱，此时就不是a-class通俗一点说，class-A就必须是G2以上连接。

G3连续的面不一定是CLASS-A曲面。

汽车业界对于aclass要求也有不同的标准，GM要求比TOYOTA，BMW等等要低一些，也就是说gap和angle要求要松一些。

关于A-classsurfaces，涉及曲面的类型的二个基本观点是位置和质量。

位置——所有消费者可见的表面按A-Surface考虑。

汽车的console（副仪表台）属于A-surf，内部结构件则是B-surf。

质量——涉及曲面拓扑关系、位置、切线、曲面边界处的曲率和曲面内部的patch结构。

有一些意见认为“点连续”是C类，切线连续是B类，曲率连续是A类。

而我想更加适当地定义为C0、C1和C2，对应于B样条曲线方程和它的1阶导数（相切=C1）和它2阶导数（曲率=C2）。

因此一个A-surf有可能是曲率不连续的，如果那是设计的意图，甚至有可能切线不连续,如果设计意图是一处折痕或锐边,（而通常注塑或冲压不能有锐边，因此A-suuf一定是切线连续(C1)的）。

第二种思想以汽车公司和白车身制造方面的经验为基础，做出对A-surf更深刻的理解。

他们按独立分类做出了同样的定义。

(整理)Catia--曲面设计.

第一章曲面设计概要1、曲面造型的数学概念：（1）、贝塞尔（Bezier）曲线与曲面：法国雷诺的Bezier在1962年提出的，是三次曲线的形成原理。

这是由四个位置矢量Q0、Q1、Q2、Q3定义的曲线。

（2）、B样条曲线与曲面：与Bezier曲线不同的是权函数不采用伯恩斯坦基函数，而采用B样条基函数。

（3）、非均匀有利B样条（NURBS）曲线与曲面：NURBS是Non-Uniform Rational B-Splines的缩写。

Non-Uniform（非统一）指一个控制顶点的影响力的范围能够改变。

当创建一个不规则曲面的时候，这一点非常有用。

同样，统一的曲线和曲面在透视投影下也不是无变化的，对于交互的3D建模来说，这是一个严重的缺陷。

Rational（有理）指每个NURBS物体都可以用数学表达式来定义。

B-Spline（B样条）指用路线来构建一条曲线，在一个或更多的点之间以内差值替换。

曲面G1与G2连续性定义：Gn表示两个几何对象间的实际连续程度。

●G0：两个对象相连或两个对象的位置是连续的。

●G1：两个对象光滑连接，一阶微分连续，或者是相切连续的。

●G2：两个对象光滑连接，二阶微分连续，或者两个对象的曲率是连续的。

●G3：两个对象光滑连接，三阶微分连续。

●Gn的连续性是独立于表示（参数化）的。

CATIA中A级曲面应用全面介绍精华篇

A级曲面没有十分严格的数学描述也没有十分严格的概念定义。

在汽车行业，所谓A级曲面的定义，是必须满足相邻曲面间的间隙在 0.005mm 以下（有些汽车厂甚至要求到 0.001mm），切率改变 ( Tangency Change ) 在0.16度以下，曲率改变 (Curvature Change) 在0.005 度以下，符合这样的标准才能确保钣件的环境反射不会有问题。

CLASS-A包括多方面评测标准，比如说反射是不是好看、顺眼等等。

当然，G2可以说是一个基本要求，因为G2以上才有光顺的反射效果。

但是，即使G3了，也未必是A级曲面，也就是说有时虽然连续，但是面之间出现褶皱，此时就不是A级曲面了。

通俗一点说，CLASS-A就必须是G2以上连接。

汽车业界对于A级曲面要求也有不同的标准，GM要求比TOYOTA ，BMW等要低一些，也就是说Gap和Angle要求要松一些。

关于A级曲面，涉及曲面类型的二个基本观点是位置和质量。

位置，所有消费者可见的表面按A-Surf考虑，汽车的Console（副仪表台）属于A-Surf，内部结构件则是B-surf；质量，涉及曲面拓扑关系、位置、切线、曲面边界处的曲率和曲面内部的Patch结构。

在老的汽车业有这样一种分类法：A面，车身外表面，白车身；B面，不重要表面，比如内饰表面；C面，不可见表面。

这其实就是A级曲面的基础。

但是现在随着美学和舒适性的要求曰益提高，对汽车内饰件也提到了A-CLASS的要求。

因而分类随之简化，A面，可见（甚至是可触摸）表面；B面，不可见表面。

关于曲面质量的连续理论，有一些意见认为“点连续”是C类，切线连续是B类，曲率连续是A类。

而我想更加适当地定义为C0、C1和C2，对应于B样条曲线方程和它的1阶导数（相切=C1）和它2阶导数（曲率=C2）。

因此一个A-surf有可能是曲率不连续的，如果那是设计的意图，甚至有可能切线不连续，例如设计意图是一处折痕或锐边。

Catia--曲面设计共10页文档

第一章曲面设计概要1、曲面造型的数学概念：（1）、贝塞尔（Bezier）曲线与曲面：法国雷诺的Bezier在1962年提出的，是三次曲线的形成原理。

这是由四个位置矢量Q0、Q1、Q2、Q3定义的曲线。

（2）、B样条曲线与曲面：与Bezier曲线不同的是权函数不采用伯恩斯坦基函数，而采用B样条基函数。

（3）、非均匀有利B样条（NURBS）曲线与曲面：NURBS是Non-Uniform Rational B-Splines的缩写。

➢Non-Uniform（非统一）指一个控制顶点的影响力的范围能够改变。

当创建一个不规则曲面的时候，这一点非常有用。

同样，统一的曲线和曲面在透视投影下也不是无变化的，对于交互的3D建模来说，这是一个严重的缺陷。

➢Rational（有理）指每个NURBS物体都可以用数学表达式来定义。

➢B-Spline（B样条）指用路线来构建一条曲线，在一个或更多的点之间以内差值替换。

曲面G1与G2连续性定义：Gn表示两个几何对象间的实际连续程度。

●G0：两个对象相连或两个对象的位置是连续的。

●G1：两个对象光滑连接，一阶微分连续，或者是相切连续的。

●G2：两个对象光滑连接，二阶微分连续，或者两个对象的曲率是连续的。

●G3：两个对象光滑连接，三阶微分连续。

●Gn的连续性是独立于表示（参数化）的。

CATIA-轿车外形A级曲面设计

家用小型轿车外形A 级曲面设计1轿车外形A 级曲面模型建立1 云点预处理及Mesh 面的建立此次毕业设计，云点的测量是由老师完成的，我只完成模型建立和二维图制作，主要应用CATIA V5软件，在界面内，用命令导入需处理的云点，如图1-1所示：图1-1 由于云点坐标系与车身坐标系不一致，需用命令对其进行调整，如图1-2所示：图1-2 先将云点用（Filter ）进行过滤，参数值设为0.11。

然家用小型轿车外形A 级曲面设计2 后对云点用命令，生成Mesh 面，如图1-3所示：图1-32 顶盖、发动机罩及行李箱盖A 级曲面设计由于整车是一个对称体，所以只需做一半的车身曲面，另一半靠对称完成。

我们在做中间曲面时，就必须保证这些曲面关于ZX 平面对称后两块曲面之间无缝、无重叠，无棱角，并且具有较好的光顺性。

因此，在做顶盖、发动机罩及行李箱盖曲面时，就需注意上述要求，下面介绍两种常用的方法：1 由云点生成线，再由线组成一封闭体，在界面，用命令生成面。

这样作出的曲面比较容易保证光顺性，但此曲面与云点的误差较大，所以这就要求画出的线与云点所在的面结合很好。

2 由云点生成线，再由线组成一封闭体，在界面，用命令截取封闭体内的部分云点，再用命令生成面。

这样作出的曲面与云点的误差较小，但曲面的光顺性不易保证。

这就要求用命令生成面时，结合系数不能选的太小。

下面我将用上述两种方法完成顶盖、发动机罩及行李箱盖A 级曲面的制作。

2.1 应用第一种方法完成顶盖A 级曲面设计首先，在界面，用命令，在ZX 平面上截出一组此平面上的点，如图2-1所示。

在图中看出由ZX 平面截出的是一条线，其实它是由很多的点组成，家用小型轿车外形A 级曲面设计3 并不是线，我们可通过（Cloud Display Options ）命令将这些点稀释，就可看清这条“线”其实是点，如图2－2所示。

图2-1图2-2 用（3D Curve ）画出一条光顺曲线，如图2－3所示：家用小型轿车外形A 级曲面设计4图2-3 通过（Curvature Analysis ）分析曲线的光顺性，如图2-4所示。

最经典Catia曲线曲面设计基本理论

将其写为矩阵表达式则为：
P（t）＝ [ B0,3(t) B1,3(t) B2,3(t) B3,3(t) ] [ P0 P1 P2 P3 ]T
6
⎡− 1 3 − 3 1⎤ ⎡P0 ⎤
[ ] ＝ t 3
t2
t
1
⎢ ⎢
3
−6
⎢− 3 3
⎢ ⎣
1
0
3 0 0
0⎥⎥
⎢ ⎢
P1
⎥ ⎥
0⎥ 0⎥⎦
⎢ ⎢ ⎣
P2 P3
只有四个系数控制曲线的形状。而二维三次曲线的参数表达式为：
有 8 个系数可用来控制此曲线的形状。（3）对非参数方程表示的曲线、曲面进行变换，必须对其每个型值点进行几何变换，不能对其方程变换（因不满足几何变换不变性）；而对参数表示的曲线、曲面可对其参数方程直接进行几何变换。（4）便于处理斜率为无穷大的情形，不会因此而中断计算。
Pz（t）＝ [ B0,3(t) B1,3(t) B2,3(t) B3,3(t) ] [ P0z P1z P2z P3z ]T
注意：上式基函数的计算仅需一次，不必三次。
2．Betnstein 基函数的性质
注意：是基函数的性质，并非曲线的性质。（1）正性
（2）端点性质
（3）权性
由二项式定理可知：
（4）对称性
2
2．基本概念
曲线、曲面的显式、隐式、参数表示曲线、曲面可以用显式、隐式和参数表示。显式：形如 z ＝ f（x，y）的表达式。对于一个平面曲线，显式表示一般形式是：y=f（x）。在此方程中，一个 x 值与一个 y 值对应，所以显式方程不能表示封闭或多值曲线，例如，不能用显式方程表示一个圆。隐式：形如 f（x，y，z）＝ 0 的表达式。如一个平面曲线方程，表示成 f（x，y）=0 的隐式表示。隐式表示的优点是易于判断函数 f（x，y）是否大于、小于或等于零，也就易于判断点是落在所表示曲线上或在曲线的哪一侧。参数表示：形如 x ＝ f（t），y ＝ f（t），z ＝ f（t）的表达式，其中 t 为参数。即曲线上任一点的坐标均表示成给定参数的函数。如平面曲线上任一点 P 可表示为： P(t) = [x(t), y(t)]；空间曲线上任一三维点 P 可表示为： P(t) = [x(t), y(t), z(t)]；如图：

CATIA曲面设计理念全剖析(A面,B面,C面)

CATIA曲面设计理念全剖析（A面，B面，C面）2009-05-04 19:47关于做曲面，谈谈一点心得。

我觉得无论是CATIA或则其它软件，做曲面前规划曲面很重要，不能画到哪里是哪里，先构建基面和大过度面等，再添加细微特征和圆角特征等。

最忌讳的是利用一个曲面来表现很多特征，无论是数据交换还是曲面质量一定会遇到不少麻烦。

实体也有同样的道理，先规划大轮廓，再做挖取部分，不要想起挖个洞就挖一个洞，想起补一块再补一块。

我从v4生成的exp文件中拖出了的model文件在五版本中打开时，如果是二维图，则提示说没有没有prj.model文件。

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