三维机械设计及三维标注英文版课件.pptx

Fundamentals of 3D Computer-Aided Mechanical Design 3D Mechanical Designand 3D Annotation Using UG NXFundamentals of 3D Computer-Aided Mechanical Design The objective of this module is to help students to understand the fundamentals of computer-aided design(CAD)concepts and become familiar with the operations in CAD modeling so as to effectively use CAD approaches for mechanical product design.The commercial CAD system,UG NX is employed as the platform for CAD environment.In Chapter 1,the brief introduction to the development process of 3D modeling techniques in CAD and its applications to mechanical design are given.Following this introduction,important topics in product modeling using UG NX,including the basics of UG NX,sketch,part modeling,assembly modeling,drawing and 3D annotation are provided.Fundamentals of 3D Computer-Aided Mechanical Design Teaching hours:32(10 hours for laboratory exercise);Module Point:2Reference:1.3D Mechanical Design and 3D Annotation Using UG NX(UG NX 三维机械设计及三维标注)M.北京：铁道出版社，20192 CHANG KUANGHUA.Product Design Modeling using CAD/CAE M.Elsevier Science,2014.Fundamentals of 3D Computer-Aided Mechanical Design Chapter 1 Introduction to CAD in Mechanical Engineering车辆车辆工程系工程系 Fundamentals of 3D Computer-Aided Mechanical Design Main points This chapter aims at introducing the development history of CAD technology and its application in mechanical design,the advantages of 3D mechanical design and the data exchange standard of CAD.The main aspects of this chapter are:(1)Master development of CAD technology;(2)Understand the advantages of 3D mechanical design;(3)Understand CAD data exchange standards.Fundamentals of 3D Computer-Aided Mechanical Design 1.1 Development History of CAD TechnologyThe first computer graphics system was invented by the United States in the 1950s,then a passive computer-aided design techniques with simple plot output capabilities was developed.At the beginning of 1960s,surface modeling in computer-aided design(CAD)application became a reality,and commercial computer graphics equipment was introduced in the mid-1960s.In 1970s,a complete CAD system began to form.Fundamentals of 3D Computer-Aided Mechanical Design People wished to use this technology to eliminate the traditional manual sketching that is cumbersome,time-consuming and low in drawing accuracy.At that time,the starting point of CAD technology is to use the traditional three-view method to express the parts and use 2D engineering drawings produced on paper as media for technical communication.This technology is known as two-dimensional(2D)modeling technology.The meaning of CAD at this time is only a substitute for the drawing boardFundamentals of 3D Computer-Aided Mechanical Design Figure 1-1 Development history of CAD technology Fundamentals of 3D Computer-Aided Mechanical Design 1.1.1 Wireframe models wireframe model:The construction of 3D solids with wireframes and polygons.This modeling method describes objects with a set of edges formed entirely by vertices just like the frame made by the wire.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.1 Wireframe modelsAdvantages:brings accessibilities for the production of engineering drawings such as a simple structurelow requirements on computer performancerepresent three-dimensional data of basic objectscan generate arbitrary viewscan maintain a correct projection relationship between viewscan generate trimetric views and perspective viewsFundamentals of 3D Computer-Aided Mechanical Design 1.1.1 Wireframe modelsDisadvantages:inconclusive for the reality of the object in a wireframe because all the curves are displayedimpossible to represent the nonpolygon surface due to the lack of surface geometric informationmiss the relationship information between edges and faces,faces and faces in the data structureFundamentals of 3D Computer-Aided Mechanical Design 1.1.1 Wireframe modelscannot construct a solid entitycannot identify the face and bodycannot distinguish the inside or outside of a solid objectnot able to support a finite element mesh for structural analysis of a physical object other than beam or truss structures.cannot effectively express the topological relationship between geometric data Due to the lack of surface information of the model both CAM and CAE cant be realizedFundamentals of 3D Computer-Aided Mechanical Design 1.1.2 Surface models The Bzier algorithm was proposed by Pierre Bzier,which provided the designer to deal with surface and curve problems with a computer.A surface can be thought of as an infinitely thin shell stretched over a wireframe.Based on the data structure of the wireframe model,surface models represent a shape by its surface geometry.A surface model includes information about the faces and edges of a part and can express the topology between the edge and the face.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.2 Surface modelsIn surface model we can achieve face-to-face intersection,rendering,surface area calculation,hiding and other functionsThe application of the surface model indicates that CAD technology is freed from the three-view mode that simply acts like the engineering drawingsFirst time the main information of the product parts is fully described by the computerA surface model is good for visualizing complex surfaces and supports NC tool path generation.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.2 Surface modelsThe surface model can only represent the surface and boundary of the object and it cannot be cut.The physical properties such as mass,centroid,and moment of inertia of a solid object represented in a surface model is hard to determine,and it is difficult to express complex manufacturing information.Additional information must be added to a surface model in order to specify in/out and top/bottom of the physical object that the surface model represents.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.3 Solid modelsSolid models contain information about the edges,faces,and the interior of the part.The mathematical description contains information that determines whether any location is inside,outside,or on the boundary surface.In terms of mathematically representing a solid object,two major modeling methods1)constructive solid geometry(CSG)2)boundary representation(B-rep)are widely employed by geometric modeling kernels,which are the core of CAD systems.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.3 Solid modelsCSG approach expresses the sequential process of modelingB-rep model specifies connectivity information ofvertex,edge,face,and volume that must be defined to construct the solid model.The solid model theoretically helps to bring together model expressions in CAD,CAE and CAM which brings amazing convenience to the product design the popular application of solid modeling technology marks the second technological revolutionFundamentals of 3D Computer-Aided Mechanical Design 1.1.4 Parametric solid modelParametric is a term used to describe a dimensions ability to change the shape of model geometry as soon as the dimension value is modified.Parametric modeling manipulates parameters to control the geometric shape of a solid objects.Parameters come from dimensions in 2D profiles in sketch,dimensions on 3D solid features and variables in user-defined equationsFundamentals of 3D Computer-Aided Mechanical Design 1.1.4 Parametric solid modelThe core of parametric modeling is to use geometric constraints,engineering equations and relationships to illustrate the shape characteristics of the product model.The parametric modeling technique is also called the dimension-driven geometry technology.It brought the third technological revolution in the history of CAD development.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.4 Parametric solid modelSide effects:the user must follow the intrinsic use mechanism of the software such as never allowing underconstraint and solving in reverse order etc.it is difficult to put all the dimensions when the cross-sectional shape of the part is complicatedIt is difficult to determine which dimensional modification will satisfy the design intentsif an unreasonable parameter is given to cause a feature to interfere with other features,a change in topological relationship is caused.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.4 Parametric solid modelApplicationFrom the application point of view,the parameterization system is particularly suitable for the parts industry where the technology is quite stable and mature.In such an industry,the shape of the part changes little,and often only the analog design is used that is the shape is basically fixed,and only a few key dimensions need be changed to obtain a new serial design result.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.5 Variational modeling technologyvariational geometry extended(VGX),based on parametric technology.The variable technology further distinguishes the size“parameters”defined in the parametric technique into geometry constraints and size-constraints,rather than constraining all geometries by size only as in the parametric technique.it is naturally desirable to allow the existence of under size-constraints in the initial stages of the design.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.5 Variational modeling technologyAdvantages:Can adopt the design method of the size after shape.The correctness and efficiency of the design can still be guaranteed.The modeling process is a process similar to an engineer thinking about a design in his mind.The design process is relatively free and relaxed.In addition to the general serialized part design,the variable system is especially handy when doing conceptual design,and is more suitable for innovative design such as new product development and old product remodeling design.the fourth technological revolution of CAD developmentFundamentals of 3D Computer-Aided Mechanical Design 1.1.6 Direct modeling and synchronous modeling techniquesThe feature-based parametric modeling system adds the concept of feature tree to CSG.This is the kernel principle of popular mainstream feature-based 3D mechanical CAD systems at this time.The direct modeling core has only B-rep information but doesnt have CSG information,because the order of the modeling is not considered,so designers can quickly define and edit geometry by simply clicking on the model geometry and moving it.Fundamentals of 3D Computer-Aided Mechanical Design 1.1.6 Direct modeling and synchronous modeling techniquesThe synchronization technology is a 3D modeling method and constraint solving technique that combines feature-based modeling and direct modeling to achieve dimension-driven and stretch deformation(Stretch)in a 3D environment.Direct modeling method can retain the solid feature information of the part and implement the design changes.Thus,the history-less modeling and feature-based parameter modeling are perfectly compatible.Synchronous technology advances a large step on top of existing history-based parametric modeling technique.Fundamentals of 3D Computer-Aided Mechanical Design According to the design task and the product characteristics of the design,the designer should determine what kind of modeling method will be employedParametric modeling system that supports specific parametric,feature and history-based modeling emphasizes the integrity and systematicness of the design ensuring that any design changes will update all models.This can achieve more advantages in terms of capturing and reusing design intents,family-based or platform-driven product design.Fundamentals of 3D Computer-Aided Mechanical Design 1.2 Application of CAD Technology in Mechanical DesignInfluence of 3D CAD technology on mechanical designBasic functions of CAD systemCAD Data exchange standardFundamentals of 3D Computer-Aided Mechanical Design 1.2.1 Influence of 3D CAD technology on mechanical design1)improve design quality The comprehensive knowledge is stored in the computer system,which provides a scientific basis for product bine the power of human being and computersthe optimization of certain process parameters and product structures2)save time and increase productivityAutomation of design calculations and modeling greatly reduces design development time.The integration of CAD/CAM can shorten the cycle timethe design efficiency can be increased by 3 to 5 timesFundamentals of 3D Computer-Aided Mechanical Design 1.2.1 Influence of 3D CAD technology on mechanical design3)reduce costs by a large marginThe high-speed operation save labor force greatlyoptimized design brings savings in raw materialsthe production preparation time is shortened4)allows designers to focus on more creative work rather than doing massive calculations and drawing work5)CAD/CAE/CAM integration With 3D CAD technology,mechanical design time has been reduced by nearly 1/3.Fundamentals of 3D Computer-Aided Mechanical Design 1.2.1 Influence of 3D CAD technology on mechanical design(1)CAD technology is more innovative than traditional mechanical design.Traditional mechanical design focuses on practical experience and design methods are mostly based on analogy design.Using CAD technology for mechanical design,it can have a strong 3D effect which can stimulate the designers innovative thinking and design a new more creative product.(2)CAD technology lays the foundation for the mechanical design informatization.CAD technology fully computerizes the entire mechanical design process.Thus,the design defects and deficiencies can be found in time through the 3D design technology before the specific processing and manufacturing,and can be improved in time,which not only shortens the design time but also improves the quality of the design.Fundamentals of 3D Computer-Aided Mechanical Design 1.2.2 Basic functions of CAD systemCAD system is composed of system software,supporting software and application software.At least the following basic functions should be included:(1)Geometric modeling(2)Assembly modeling(3)Engineering drawing(4)Scientific calculation and analysis(5)Data management and exchange(6)Other functionsFundamentals of 3D Computer-Aided Mechanical Design 1.2.3 CAD Data exchange standardWith the continuous development,maturity of CAD technology and the continuous improving of CAD applications in various industries,CAD standardization work has increasingly shown its importance.As part of the high-tech standardization,CAD standardization occupies a very important position in the CAD technology.CAD data exchange problem is an important issue faced by various industries after the widespread application of CAD.Fundamentals of 3D Computer-Aided Mechanical Design 1.2.3 CAD Data exchange standardthe most commonly employed neutral files for CAD model translations mainly are:DXF(Data Exchange File)IGES(Initial Graphics Exchange Specification)STEP(Standard for The Exchange of Product model data)application