View of CAD technology

 Views on the CAD technology
Chen Boxiong
to autodesk Mechanical Desktop R4 as the representative of three-dimensional design platform has been installed in many computer designers, autodesk Inventor R2 started using the three-dimensional conceptual design to practical application of the field just around the corner. technological innovation made the situation a new technology development requirements, and therefore the design and the understanding and use of three-dimensional modeling techniques, is now necessary to discuss and clarify the basic issues. The following software features and design needs from the start, I would like to make some view to discuss with you.
1.
1.1 design and drawing should be drawing all the design is inevitable, but always very strange
design drawing, is inevitable, is compelling. an engineer can not remember their design (even a relatively simple) in the full details of the graphical representation is the only possible way. These figures look first to the designers themselves: to remember, research and design their own ideas with Minato. Second is to give other engineers to see, in order to discuss the exchange of each other, work together to complete the design. and finally to the manufacturer to see, in order to design intent into a real part in the manufacturing plant. in the design of the entire process, the idea of the original impulse is three-dimensional concept, There is no doubt; design and implementation of the result is three-dimensional solid, which no doubt; However, in the traditional design, in the transmission of information between the two is actually two-dimensional graphical representation of the whole. This Britain came in the fall we are all accustomed to the phenomenon of the past, and seems to be right and proper. Comparison of perfection in order to do this, many scholars also effort, we have developed engineering drawings for the expression of standards in schools, with 200 hours training students, three-dimensional description of the human habit of forget to re-establish two-dimensional projection of the new presentation rules, and in the design process to further strengthen the technology of these statements. placed the original three-dimensional concept not readily available to single people to develop two-dimensional projection rules, which is not very strange?
1.2 drawing software, is inevitable, but also very strange
CAD technology in the infant stage at yesterday, the three-dimensional modeling ability is poor, not enough to express most of the design concept, with AutoCAD R9 intervention following software design, that is, instead of hand-drawing, it is inevitable. But now, software has been a qualitative leap, but most users there mention of CAD, people still thought of it first hand instead of drawing, rather than effective overall aided design. that many of the leading mechanical design department asked me, drawing paper past, we now use a computer, both of which are different? from the design process point of view, really is not much different. on paper easy to get things, and still easy to get; drawing paint specification, beautiful, and design quality has not improved much; only from the drawing point of view, to improve a number of efficiency, taking into account the investment in hardware and software, daily consumables investment, the efficiency of this seems to be not enough, you know this is hard to say how long the payback period of investment, whether the depreciation in the system before the expiration of a profit technology ... So, just computer-aided drawing, not to improve the design quality to solve the key problems in technological innovation. However, many people in the computer graphics (or so-called analysis, and I certainly am very surprised, like, how they had?
1.3 design problems in two-dimensional drawing
Indeed, the two-dimensional computer graphics technology for the popularization of CAD has played an important role, but also to enter higher level applications, is the necessary technical preparations. However, CAD application results should be: to improve the design quality, dissemination and preservation of design experience, improve design efficiency and reduce trial costs and improve design management ... in short, the source in the traditional design than the traditional design. The truth is that until now, two-dimensional mechanical CAD computer design technology could not solve several problems in the most awkward. In other words, if a mechanical engineer, the ability to feel inadequate graphics , need someone helped the drawing, I would like to ask the engineer: of design quality, and most in need of some assistance to several problems? may have the following number of common:
1> complex projection line generation problems
parts for rough castings and forgings, designers often draw quite a headache when the two-dimensional working drawings. intersecting lines and intersecting lines drawn do not understand, or even have to look for wood-based work plan approval. In fact this part in his head how many times I do not know want to, long to be through, that is, expression do not understand. For some details (such as casting on some cross-line fillet) is not easy in the minds of thinking clearly, would like to assist with the draw obtained two-dimensional projection map and more difficult to solve. So often this things, the designer after the success of new product trial, facing the real part in turn modify their design.
2> Drain standard size, leakage is drawing the line after a few people question
revision, leakage Standard size things still occur. and designers in the design of the more unique places, revision of the idea of people more familiar with this design, leak size, the more difficult to prevent leakage Chart. is: Do not know true colors, just because in the mountain.
3> body geometry and motion analysis of the relationship between the issues discussed
planar motion mechanism if it is, things are still better, even if the size of the map location is not quasi- , there is always an effective qualitative analysis, the space motion, there is no good solution. To get around this problem, people are always the first consideration in the design easy to design the plane body, while trying to avoid the space agency, although in many design in, knowing that space agencies may be more subtle, more optimized.
4> update and modify the design of the traditional two-dimensional design problems
is one-shot deal. If you want to update or modify, we must re-drawing, the general provisions can not be patched (the majority of the requirements of the design department is the case). especially the multi-view part, in the modified design, part of the expression and its relevant design parameters can not be completely put together, of course, no direct correlation, these technologies maintaining and updating the data is very troublesome. Although the two-dimensional graphics in AutoCAD, the changes are more convenient method, but because the expression is cumbersome, quite unreliable.
5> design engineering management
mentioned here is the management of the design, not just on the drawing management. CAD good use of some of our units, there are already several thousands DWG files, and continues to grow. These documents, in addition to graphical information, there will be a large number of design parameters and other non-graphic information, their level of relations by assembling a complex and orderly association. Can the traditional design The management model used in the CAD system? two-dimensional graphics to solve the above problems, said it was impossible to solve, it seems too much, but at least it is very difficult. This is because the two-dimensional map of the data structure, there is not enough of the original full data, can not organize and use the data. you know, two-dimensional engineering drawings express a complete idea of expression is not designed, nor is it true expression of design ideas. This pattern must be professionally trained people (memorize the expression of rules) when reading, data extraction Picture stories of the people must be interpreted in accordance with many rules, he can understand the meaning of drawing people. That is, the generation of two-dimensional engineering drawings and to recognize and read, the total can not be separated . The ultimate goal of computer applications is not the limitations of two-dimensional parametric two-dimensional parameter is for
above analysis, once popular for a time solution. remember that developers will be two-dimensional graphics software parameters of hot speculation, but there are many software commercial introduction of a number of two-dimensional graphical parameters of foreign software to sell. It seems two-dimensional parameter is an effective solution for CAD applications, an attempt to make such a generic two-dimensional graphics parameter to solve the contradictions discussed earlier. This technique The core objectives of the program are: training in computer applications, such as engineers attempt to make her generation and to recognize and read the same two-dimensional drawings. However, designers of these programs overlook the most critical issues: The computer will never be the computer. forever! open a joke, perhaps Hong Kong and Taiwan to the computer called the PC, thus affecting their right. By the way, engineering drawings, vector scanning processing software designers, have made the same mistake. from the generation of two-dimensional engineering drawings for , a view of the overall parameters of the already very difficult (of course not referring to the keyway, spline, step shaft of such a simple graphics), if the establishment of linkages between multi-view parameters, the more difficult. In this way, with a finite number of parameters drives the parts diagram, that is done is extremely difficult, and in the process, the equivalent of a designer can only mouth, commanding a mapping tool will be used only Silly boy, drawing his design. D Parametric Technology , the association between multiple views must be done Di; the same time the system must be able to identify on the basis of user error, such as user requirements into the inner hole diameter is greater than the time when the outer circle. only done these can be achieved the real parameters of two-dimensional engineering drawings. In fact, I see this type of software, no one can be up to do.
2.2 availability of two-dimensional parametric
course, if the problem is reduced to: generation and management of the use of professional design, the parameters of the two-dimensional standard parts library, the situation is really much better, because the data structure of such problems is limited and defined. fit to do a lot of topics, such as: portfolio machine tool design, fixture design, gage design and so on. Practice has proved that the idea is correct, on-site use is also very good. Unfortunately, most people have is that put forward this view at least eight years, and did not see that developers to do it seriously. even qualified (I say qualified, not just CAD) of the GB used parts library you can not find the mark. If and back to a two-dimensional parametric point of view, that is, the dimensional set of professional design parameters of the generated map achieve . In many of the design department of FAW, so the professional software is widely used to generate and effectively improve the design efficiency, reduce errors, improve design quality. shows that the technology of two-dimensional graphical model parameters, has her useless, and has made a clear effect. But this is a What is the goal? This is a very long history, involving a number of leadership and authority of their argument: But this is the whole process of designing a small part of the engineers most familiar with is difficult, at least in part, is not the most need someone to help a part. so the D should be a CAD Design. Why is this problem a long time debating? Main The reasons are:
1> who participate in this discussion, site design capabilities and design experience in the end what? really are mature and experienced designer? or mechanical engineering graduate, but did not complete the design of the quasi-independent Engineer?
2> PC CAD software is relatively immature system, its capability is weak, in fact, really old version of AutoCAD will draw two-dimensional graphics. as did a very poor job of science, too little new knowledge dissemination channel , job training opportunities for engineers are also quite small.
3> value-added software developers in the hands of the main developers is the lack of experience in engineering design students, can not tell exactly how the design process. But do not underestimate the experience round and simple geometric patterns. in such materials under the guidance of the students, not to mention design experience, there are problems with the basic concepts.
4> mechanical design is the most troublesome of various design, the most difficult standard, it seems what can be obtained is drawn into the two-dimensional drawings.
5> a lot of the promotion of applied technology or training teachers who did not really figure out the problem, but also design their own lack of experience, with its sleepy, how can make Visible. designing, there are two main modes: design innovation into the design and retrieval. only to create the conditions into the design-based, is our own product development and design patterns before it becomes competitive, to be clearly economic benefits. The retrieval system is mainly in mature design based on the increase, which is the main mode of class design tooling. complete record into the design of the secondary, the direction is the use of CAD system, is a clear cost-effective way. from the traditional design process, the map does have copied elements, but the main content of the work is to create a new two-dimensional expression. For example, a grinding spindle design, the idea in the beginning, naturally, that unclear with a couple of steps, each long, but have a rough idea, probably in the future design process, the parameters of this initial concept has been modified beyond recognition. until the end of the design, this root axis parameter is clearly down to a formal two-dimensional drawings. Therefore, in the general design, the total program to go through the sketches, assembly drawings, component diagram, a formal assembly diagram, the formal part drawing drawing several rounds of such work h Few unfinished drawings or assembly drawings of parts to get away down the situation. So, to say Parametric two-dimensional graphical approach is not supporting graphics-aided design. and for a mechanical engineer, to draw his two-dimensional engineering drawings special skill, or to use computer-aided really does not matter. In this sense, with the drawing board or computer, there is no essential difference. But, AutoCAD software in two-dimensional diagram of this processing, a unique, strong geometric design function, the accuracy is also very reliable. If the design of AutoCAD as a limited database to use in mastering the operation of the skill or assistance with the procedures look too complex, we can solve many difficult to solve analytical method for solving engineering or professional design simulation data that CAD really needs to effectively improve the quality of design. If you want to be in two-dimensional graphics in real-aided design, this model is really a way of CAGD. such as the author in 1989 as the main design and development of the power head CAD system credibility. This is the AutoCAD R9 to complete the work. can be seen, the establishment of two-dimensional design of the database, in the context of two-dimensional drawing is also useful potential applications.
3. From the beginning three-dimensional design is the inevitable trend
3.1 D design also two-dimensional design
part in the design of the original impulse is when the three-dimensional, there is a color, material, hardness, shape, size, location, related parts, manufacturing processes, and associated with the concept of three-dimensional solid, even with a very complex relationship between the movement of three-dimensional solid. only because of the limited means before, people have mutually agreed in the first quadrant (the United States is the third quadrant) the expression of parallel projection of two-dimensional view of the rules associated with the finite two-dimensional projection of three-dimensional expression of their ideas. This expression is very incomplete information, and drawing, Picture stories people have to go through special training in order to ; error. it is easy to rapidly expand aid the whole process, the design process can use all the uniform data, which was developed CAD today, tomorrow our computer CAD. From the beginning the design of three-dimensional, two-dimensional works in drawing still comply with the requirements of traditional design, because the processing and assembly site still can not install the computer system. In this way, support software must be generated from two-dimensional three-dimensional working drawings, and the ability to bi-directional association; order to scrape together in the design and modify the size and shape distribution, support software must also have three-dimensional entity with overall size constraints and characteristics of modified capacity. would then be possible to establish full and complete design database and on this basis, further stress and strain analysis, part quality attribute analysis, space motion analysis, assembly interference analysis, NC control machinability analysis, high accuracy two-dimensional drawing generation, Evaluation of the appearance of colors and shapes, commercial advertising generated a series of modeling and animation are able to fully meet the demand, this is the whole process of design effective assistance, this is a clear technical and economic benefits of CAD. If you do this, the work of the traditional two-dimensional graph-based design data management will become a three-dimensional design data for the conservation and management, and engineering University of mechanical drawing class can dramatically cut removed, to preserve the original concept of three students, two-dimensional drawing of the painting should be followed greatly simplified. In our country, in the near future as the full realization of the Boeing 777 digital design is not possible, but in three-dimensional mechanical system concepts from the beginning of the implementation, conditions for PC-based CAD is available, you can expect to solve the traditional design of the difficulties listed earlier. This will significantly improve the design to make sure the quality, followed by a improve the design speed.
3.2 is the only real sense of three-dimensional design, creating as many two-dimensional design CAD
Parametric software vendors told me, with two-dimensional parameter, You are free to modify the parts shape and size, complete design update, how good it. But I never believed such views. changes the size of parts is easy, the question is how do I dare to change. to dare to change, at least, mechanical analysis must be carried out otherwise broken link how to do this? us learn workers who have learned full force and material force of reason, after three to five years after the design work, how much you have left this knowledge? do not often use the knowledge to forget, not without reason is not often used, but too much trouble: as a check of the shaft torsion still make do, you try to analyze the engine cylinder head. not to mention the high quality of design, many of the problem in this analysis. see the thin compact design abroad, and our black thick lump of similar design, but the stiffness is not good, because who will say: the key is not used local materials. Where is the key component of most needed materials? Can not find this site, the design is still the silly big black thick. shows stress and strain analysis is extremely important in CAD content. Only three-dimensional design, be possible to set up the finite element analysis of the raw data, then the part geometry optimal design. otherwise, it is traditional design methods: the bench several times and even prototype assessment test, the high cost, long cycle, is a modern market economy can not be tolerated. the opportunity is fair to each designer in demand determined, whoever designed, the first to create successful, will come to be the market, there are economic benefits. often such a situation, according to the shape of disposable lighters abroad, we re-create one of the injection is complete, at a glance different. why? you did not release sufficient injection mold shrinkage local. In this issue, there is no way the traditional two-dimensional design. under discussion in the assembly part design, so that each engineer has a dream. D design can only be done locally on the force, while the three-dimensional design must be able to realize this dream.
3.3 you can directly enter the three-dimensional design
have a similar discussion, we present electronic professional teaching, the principle is the semiconductor Let's talk about, followed by diodes, transistors, single-tube amplification, complex amplification, small-scale integrated circuit h in this order about hardware. and from the binary, the conversion of various binary, machine instructions, to the general programming talk about this order h software. emphasis here is on a not necessarily graduate. because the , still can use a good computer. for the purpose of computer applications is the do not know and has been involved in this process. and if the computer can not take over more and more the work of humans has confirmed the process of automation, there will be more and more computer systems in use. Therefore, the computer software application features : the use of software features, depending on your subject requirements to complete want to do. As for the software, what is done internally, there is no need to worry about. as long as you really clear what to do (in fact this is not easy) . in the software application, the software capabilities how strong your application results of a number of good, do not have to like that in college, by learning from the binary. visible, skip the stage of two-dimensional engineering graphics software applications, directly from the three-dimensional design start, no problem. Of course, in the three-dimensional modeling of two-dimensional graph to use to line generation technology, or must master. For a mature designer, the biggest obstacle to enter the three-dimensional design software application is not technology, but their own way of thinking. accustomed to two-dimensional engineering drawings over the years because the expression of a set of rules used to Picture stories in the use of three-dimensional model for describing the various types and characteristics of the relationship between the thinking has been estranged from. In this On the one hand, and even as a new college graduate students receiving capacity. his own mode of thinking, One under the guidance of experienced teachers, will soon meet the requirements.
4. All parameters of three-dimensional model of the necessary drive and can only be
4.1 model-driven design parameters, it makes sense to design model
The establishment of the database is populated with data design process. to establish a database aims to scrape together in the future the process of design with reference and modify data, and finally to complete the design. it is not three-dimensional model parameter-driven, not much in the design purposes. just do assembly relation, location, relationships and even movement relationship.
4.2 Design parameters of the model-driven design model for the possibility of
divided into two categories. something I call the . the other I call limited parameters can be fully constrained, and this is the basic concept of parameter. for mechanical design, the geometric model accounts for the vast majority of our design objects. Thus, our design can be used almost all parameters can be expressions of the three-dimensional model . Autodesk's MDT and Inventor are typical of such software. MDT is a typical parametric modeling software, the parameters of the technical features of the constraints and engineers are still some differences between the idea that this distinction is probably always there the idea because the software is always behind the idea of human beings.
constrained model parameters are divided into two categories:
1> geometric constraints. For example: parallel, concentric with each other, the two lines of equal length h such constraints is to determine their geometric relationship, and this geometric relationship in the future design remain the same.
2> size constraints. For example: length, height, angle, radius, h such a constraint is to determine their size and relative distance, in the future design, these dimensions may change, may also be other parts reference. MDT and the characteristics of a typical modeling software.
characterized model is divided into three categories:
1> based on contour features: first, two-dimensional constraints are parameterized contour, then the software according to requirements and may generate three-dimensional model characteristics. For example: stretching, turning, setting out the characteristics of h so that Boolean operations can also be combined in the same model .
2> based on existing features of the characteristics: first, there are certain characteristics, based on this modification. For example: rounded corners, the array has been attached to h which is a characteristic feature.
3 > Positioning features: a coordinate control of parametric results, generated face, work axes, work points, or reference coordinate system. These elements are parameterized. MDT for the design of data management, providing design and management of data structure variables functions. Meanwhile, in MDT provided a wealth of data on the design parameters of the structure and management tools, which are traditional design techniques for refining and abstract, is to use the program to simulate the traditional design skills and provides a typical example of the user. to master and use this type of technology, improving the quality of the design will play a direct role.
1> the design variables are used to control the activation of parts of variable. design variables, in order to establish the design size of the auto parts association.
2> design variables can use the data to external databases, such as: Excel table or *. PRM file. In this way, design data will be possible on a larger scale within the means with more control, management and computing. can be seen, from the function, the realization of all parameters of the three-dimensional modeling, MDT already have the necessary and sufficient conditions. These features are actually designed for the traditional knowledge of the procedures treatment, this function is > I think that the computer + application software called mature designers. In fact, the composition of a CAD system should include hardware, software and users, no matter how strong the ability to design software, human action is the effect of the decision to use the software the decisive factor. very clear, with a CAD software, in different hands, there will be quite different the results. For example: AutoCAD in the hands of just some of electronic drawing board, while in other hands has become a very good platform for two-dimensional design.
This may depend on the following conditions:
1> to do the design of their own understanding of how deep in the end?
2> in the modeling data preparation prior to the adequacy of the design of the full?
3> on your own professional design experience and knowledge in the end how wide?
4> use the software features of their grasp in the end how much?
visible effect in the pursuit of software applications, the first should check the adequacy of their preparation . can not imagine a lack of experience in the design of new engineers will complete a proper full-parametric model-driven three-dimensional parts. Even very understanding of software application developers, professional design knowledge may be due to the poor, often in his program ignorance once again, such examples and even quite common. engineers using CAD systems, especially three-dimensional design system, the existing lack of technical preparations for sure, the concept must be modified some of their own, this is the inevitable technological advances. at least you have been your Drawing teacher may read some reference books, and author of a number of taught you inadvertently incorrect application methods, and you shift the point of view these methods as the authority of the h word, and improve their professional design knowledge, to participate in formal training in software applications is to make themselves in the CAD system to play its due role in the key.
There is a point of view: according to the software design software for their own design. In this view the process of CAD application software the main factors not the user. so users need to overcome self, to adapt to the software. I think this is wrong, in the professional design, the highest authority is not software, but the designer. Therefore, in the process of CAD technology, we must we take the initiative. Help you choose a fairly accurate idea of the software.
2> software does not provide a direct function of user requirements. The solution is not conform to the software functionality required to give up this function should be the use of indirect tactics, such as generated in the MDT parameters of the stiffener. This shows that the choice of software is more appropriate.
3> software does not provide the user requested features. outflanking tactics, and professional programs can not be added, which indicates that the software does not fit your design requirements. < br> 4> clear, the user requirements, user requirements or unreasonable. For example: want to draw a few two-dimensional view, requires that the software generates the corresponding three-dimensional model. Another example: the requirements of part 600 of the full parameter The reason why the assembly h is inappropriate for such a request, because in practical engineering design process, or from existing technology and the human mind to discuss the results, it is impossible to achieve such a request, or it is not necessary. Under such circumstances, can only enhance the user's own design skills and theoretical level of the.
In short, the use of any CAD software, must I (mature professional designer) mainly to my design ideas and the original data-based, software will always be subsidiary. learning software functions and operations of the process, just like the process of learning a foreign language, to express the results not change their content, but to change the method of expression. according to the design of software design ideas point of view, the essence of the design will, that is, the creative engineer, has been greatly restricted. Of course, if the only copy maps, the establishment ...