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 1. Can I get a concise overview of what CAD is, what it is good for and what to look for in a system? Outline of Answer
Design for Efficiency CAD systems are powerful tools for designers. However, too frequently CAD is considered to be simply automated drafting, a gross underassessment. CAD is a tool for design; designers realize its greatest advantages, but its benefits pervade the entire manufacturing process. It can help the designer do his job faster, better, and more consistently, thus making the entire process more productive, with better design quality, at lower overall manufacturing costs. However, CAD is not simple to implement. To begin with, the successful implementation of CAD frequently requires fundamental organizational changes. Even after implementation, significant further development work with the system may be required before any productive benefits will be seen, and there are some kinds of design tasks for which CAD is not cost-effective.
Evaluating Systems Research at the Industrial Technology Institute (ITI) indicates that within limits, the specific system selected is not the important issue. What is important is how the system will be implemented and used after selection. CAD systems can be viewed as analogous to programming languages. Each has its advantages, but it is really not critical which one you select, because the success or failure is really in what you do with it, not the language itself. Obviously, some system selection effort is required. If the need is surface description, for example, a system that can define surfaces is in order. However, CAD systems can be grouped based on a few broad classifications, and within the groups, the system selected is not that important. How it will be used, however, is vitally important, so the selection process must focus on defining the broad characteristics of the required system, how it will be used, and what further development and organizational changes will be needed to successfully use the system. CAD is capable of revolutionizing certain industries and crippling those who have not mastered it. In other industries, its effect is marginal or negligible. However, CAD is the wave of the future; and even companies whose design tasks are minimal will have to understand CAD, despite having little hands-on need for it themselves.
CAD System Types CAD has developed differently on the two types of platforms. Mainframe CAD vendors have taken their CAD systems and ported them to engineering workstations. PC CAD systems have been started by new companies with typically no history in mainframe CAD. Thus, there, is little or no functional differences between mainframe CAD systems and engineering workstation CAD systems, but there is still quite a gulf between PC CAD systems and engineering workstation systems. The difference stems from both the limitations of the PC hardware and the historical development of CAD. Some large companies still run mainframe CAD systems because they do have some advantages. For instance, there is a single database, which makes database management much easier. Second, security is better, and centralized backups can be made. On the other hand, if the central processor is down, everyone is down. And mainframe systems are usually expensive on a per-user basis, particularly if there are only a few users. In the final analysis, however, a mainframe and terminal system lacks the features for efficient CAD. Engineering workstations combine a powerful CPU, ample memory, a multi-tasking operating system (almost all now are UNIX), a large, fast hard disk, a high-resolution screen (typically 1000 x 800), and fast internal data transfer between components. More powerful versions also perform many graphics operations in hardware, which not only reduces the load on the CPU, but speeds up the system considerably. Engineering workstations also have broad networking capabilities that allow for powerful database functions and the maintenance of a single CAD database for everyone on the system. Engineering workstations provide all the advantages of mainframe systems with none of the drawbacks. Workstations can be added without slowing the system; the price per seat is the same whether there is one or 100 seats and the malfunction of one does not affect any others. Typical workstations available are Sun, Hewlett Packard, Silicon Graphics Iris, and DEC VAXStations. PCs are rapidly closing in on the low end of workstations, and in fact, the prices have overlapped, although there are still significant performance differences. In fact, some workstations are built around the same CPUs found in PCs. The biggest limitation and difference at present is the operating system. MS-DOS, the PC operating system, does not allow multi-tasking nor can it address more than 640 kilobytes of memory. PCs also usually have lower resolution screens, slower and smaller hard disks, and slower internal data transfer rates.
General Concepts The second purpose is drafting, which is the creation of documents that will be used for verification, ordering, or manufacturing. The third purpose is for manufacturing assistance, primarily to create the part geometry for computer-aided manufacturing (CAM), where the geometry is used to create CNC command files. Because it is important to have some comprehension of these purposes to understand CAD system application and selection, more detailed descriptions are needed. Although a company may have some work in all three of the areas, many will find most of their work in only one or two. Further, different groups within a company may each fall in different areas and thus have considerably different requirements for a CAD system. In general, it is recommended that each different group within a company be considered separately.
CAD Used for Design Concept Design - CAD systems intended for concept design are used by the designer to create a simulated prototype. The designer uses this type of system to visualize the part, study part geometry, study clearance and fit problems, and allow others in the design team to check that the part meets all design requirements, including those for design concept and artistic requirements. The designer may also use it to check kinematic relationships or interface with other programs to study a variety of different properties such as dynamic response, material stresses, or deflections. The use of CAD for concept design may actually increase total design time, but should result in significantly reduced prototype time, fewer manufacturing problems, and a better quality product with greater initial lifetime performance. The benefits of using CAD in this way can usually only be seen when using a life-cycle view of a product - looking beyond the benefits to design, per se, and recognizing the impact that design has on the total life cycle of the product, including manufacturing, sales, and service. A CAD system used for concept design usually requires excellent surface modeling capabilities and may require solid modeling capabilities. It may also require the ability to do simple analyses such as weight, volume, surface area, and interface to more complex computer-aided engineering programs such finite element analysis. Repetitive Design - Many designs are principally compilations of some standard parts or have large sections that are similar from design to design. In these cases, the design is either so similar to existing designs or uses geometry that is so well understood by the designer that the use of the CAD system for understanding the spatial relationships of the parts is largely, though not entirely, unnecessary. The function of the CAD system in repetitive design includes checking the geometric and spatial relationships to confirm what the designer is reasonably certain about and to begin the process of documenting the design, which is generally finished by a draftsman. The goal of this type of CAD use is to improve productivity by helping the designer define the design in detail much faster than could be done manually. Concept Design vs. Repetitive Design - Most manufacturing firms do some kind of design. When selecting CAD systems, the manufacturer must determine where his design effort falls on a line between repetitive and concept design as end-points. Note that this determination is not a function of how a firm intends to use the CAD system; instead, how a CAD system is used (and what kind of CAD system is best) is a function of where the design effort falls on this line. In general, the greater the potential for using standard parts, parametric parts programs, group technology, and pieces of old designs, the closer to the repetitive design end of the line. Conversely, with greater potential for the ``original'' work, the closer a firm is to the conceptual design end. Note the word potential. Because they have simply automated old design processes, many firms use few standard parts and have yet to use group technology or parametric programming. Thus, the failure to use these techniques is not an indicator that the firm lacks the potential to do so. Note also that for many firms it is not meaningful to plot just one location on that line.
Data Transfer There are two levels of CAD-to-CAD data transfer problems. The first is the problem of translating CAD data from one kind of system to another and is a function of how the two systems store data and the mathematics used to represent the data. The second type of problem is based on how the data are stored in the CAD system. If some care is not given to this problem, the data in the CAD system can be created in ways that make it useless to other groups. This issue should be resolved by considering the different uses of the data and the requirements of each use. More detailed comments on this issue appear in the section on Interfaces to Other Systems. CAD-to-CAD data transfer can be a complex problem, because most CAD/CAM systems store design data in a form most convenient for retrieval for that particular system. Transferring CAD data from one CAD system to another is simpler if the systems are identical and can be difficult if different. There are many fundamentally different ways in which a CAD system can organize and define data, so the translation problem becomes analogous to translating between languages. One CAD system can have concepts and data structures that do not exist in another, thus making translation quite difficult. Native to Native - transferring product data from one system to another of the same format. No translation or conversion is necessary. Both parties need to support identical systems. Native to Neutral - transferring product data from one system to another of a different format. The data is translated into a neutral format, such as IGES, STEP or DXF. The receiving system will than translate this data from a neutral format into their own proprietary format. Direct Conversion - transferring product data from one system to another of a different format. . The receiving system will use a conversion tool (direct translator) that will translate the sending systems proprietary format into the receiving systems proprietary format. An additional problem arises when a vendor releases a new version of their software, thus forcing the modification of preprocessors in all the resident systems to adapt to changes in the data structure. This type of file transfer can be cost-effective only when there are just a few CAD systems that are connected. Physical File Transfer between Facilities - Companies often need to transfer CAD files between facilities. Several different tasks must be completed to accomplish this. The CAD files must first be in a format that the receiving company can read. (See the section on CAD-to-CAD data transfer). Next is the problem of physically transmitting the CAD files, the subject of this section. CAD files are frequently quite large, with some getting as big as 20 to 30 megabytes in size. Size is the factor. Several options are open to the user; Magnetic tape, Floppy Disk, Modems, email and the internet. CAD Selection Criteria Five major scales help define the type or types of CAD system a company will use.
Geometric complexity - is a measure of how difficult it is to understand the object being designed. Higher levels of geometric complexity require a more complete description of the object to be included in the drawing or CAD database, i.e. high complexity results in a need for higher levels (e.g. 3-D. surfaces) of CAD application. In addition, high geometric complexity may be an indicator that CAD/CAM is needed - some parts are so complex they can only be made accurately using CAD/CAM. Newness-of-design concept - is a measure of how different the design is from previous designs. Three inquiries help measure ``newness''. First, is the final design a small revision of previous designs? Second, does the final design include many parts that are common to previous designs? Third, is the design similar in concept, even if different in detail, to previous designs? For each component, the difference between typical designs and previous designs is determined. The combination of scores for the three components provides an overall measure of ``newness''. Designs that are low on this newness score will usually benefit from such CAD features as parametric parts programming or a library of standard parts that will require the company to apply group technology to its designs. Documentation – is a measures the level of drafting required, drafting being the production of drawings as documents rather than as ``data'' or for the development of design concepts. Documentation covers both traditional drafting and technical publications such as manuals or process plan sheets. The components of this scale are the number of drawings, the dimensioning and text needs of each drawing, and the number of technical manuals needed. Manufacturing processes - is a measure of the need to develop CAD to help control CNC machines in manufacturing. It is measured by considering the degree to which CNC machines are used in the manufacturing process to control motion in two or three dimensions. There are two ways to score this: one is to use the current processes; the other is to estimate potential for CNC and CAD/CAM based on product characteristics. It is best to do both. By so doing, you should get a score for the present operations and a score for potential CNC use. For example, there may be a plant doing many of the relatively small production runs on screw machines which might better be done using CNC machines. This plant would have a low score for current CNC use but a high score for potential CNC use. Externally caused revisions - is a measure of the kind of interface required with other groups or outside companies. This measures the number and frequency of revisions caused in the design by groups outside the design team. For example, if you are making a subassembly that fits into a product made by an outside company and that outside company changes the shape of the mating surface or some specifications on the operating parameters of the subassembly, that is an externally caused revision. High numbers of externally caused revisions indicate a CAD system because CAD systems can make the revisions quickly and efficiently. Other Considerations After you have defined the capabilities you need in a system and have narrowed your search to a few systems that fit the requirements defined, you should consider the following items when making your final system selection.
To select a CAD system, follow these steps:
In summary, to get the most out of your CAD system, follow these guidelines.
Stage: Awareness Training, Business Analysis | Product Data Exchange Questions 2. I have a specific question about CAD that needs an expert and probably won’t show up in standard reference materials. How can I get to the people who may know the answer? Your first tactic should be to turn to experts with whom you already have a relationship. This is a useful first approach because technical questions are seldom straightforward. Upon getting the answer, you may discover that you asked the wrong question. Or it may turn out that once a question is answered, related questions pop up. Thus it is useful to work with people who can help you work through a process, rather than with people who can only provide specific answers to specific questions. There are times, however, when a specific answer is called for, or when you may not have access to the necessary experts. In these cases it may prove useful to use the wide variety of newsgroups and listservs that are dedicated to CAD, and CAD related issues. "Resources" provides an index to these newsgroups and listservs. Stage: All | Product Data Exchange Questions 3. Can I send diagrams, pictures or CAD files using EDI, E-mail, or the Web? Yes. The X-12 EDI protocol has an 841 transaction which serves as an "envelope" in which any kind of data can be transmitted. A word of caution though. Value Added Networks often charge based on the amount of data sent by a subscriber, and CAD or graphics drawings can get quite large. CAD and graphics can be sent by any email system that allows attachments. Be forewarned though, that many e-mail systems have trouble with attachments when they are used for transmitting very large files. If you have such data transmission needs it may be worthwhile to use the Internet’s File Transfer Protocol (FTP), which allows one to easily copy files from remote computers In order to send CAD or graphics files via the Web the people transmitting the files have to mount the file on their server, and then configure the server to recognize the file format as one that others can download. The person receiving the file has two choices. One possibility is to set up his browser to recognize the file format and automatically download it. The other is to bring up a dialogue box which will query the user as to how and where the file should be saved. Finally, remember that whatever method of transmission is used, receivers of a message can only read files for which they have appropriate software. As an example anyone with the ability to use attachments and a copy of Excel can transmit an Excel spreadsheet. But the receiver needs to have Excel in order to read the attachment. Stage: Awareness Training | Product Data Exchange Questions 4. I’m thinking of taking on business that will require me to accept CAD files from my customer. How can I do this, and does it make business sense to do so? The technology of accepting CAD files is relatively straightforward, as discussed in question #2. The real question is whether it makes business sense to do so. What are the implications of "accepting CAD files"? The simplest possibility is that you already get graphics from your customer, and this is simply a more convenient way of getting the graphics that you have always used. On the other hand "accepting CAD files" may be part of a whole new form of business, e.g. doing some form of design work that is new for your company. In terms of assessing the technology you need, the resources attached to this question will be of great help. However, we suggest that before you worry about technology you carefully consider business implications. First make the business case, then worry about the technology. Stage: Awareness Training, Business Analysis | Product Data Exchange Questions 5. What is the best way to manage incoming data when different customers insist that I use their CAD system? Or in an alternate forms: 4a- If I want to exchange CAD files with a trading partner, what special problems do I have to watch out for? 4b- I should be able to translate my customer’s CAD files into the system I use, but it never works out quite right. How can I identify the problem and solve it? Stage: Business Analysis, Requirements Analysis, Design, Implementation | Product Data Exchange Questions What is the request: Same system or reliable data transfer? If your customer insists that you use a particular CAD system, you should clarify what is meant by that demand. Does the customer want to be able to ship and receive usable CAD files, or does he really want you to use a particular system? If the real issue is compatible files you need to explore the possibility of reliable translation, probably through the standard called IGES (Initial Graphics Exchange Standard). The problem with IGES is that it does not provide foolproof translation from system to system. Thus it is necessary to see if there is a variant of IGES that will provide reliable translation for your particular purposes. Eventually CAD products will conform to the new product data exchange standard, STEP. Once these products become common (probably in a few years) translation among systems will be much more reliable. Some STEP conformant products are now on the market, so in addition to looking at IGES, you should see if there are STEP products which can help. The essence of the problem is that CAD data transfer is tricky because the files are complex, and even small incompatibilities in hardware or software can cause problems. Often the only solution is systematic trouble-shooting by an expert. The resources listed for this question will help you develop much of that expertise. Process for finding a solution Your first action should be to contact your customer’s CAD expert, the one who is most likely to know exactly how the files were constructed and what was done with them. A second tactic would be to discuss the matter with your CAD vendor, who might also understand the nuances of the systems involved, and who has a vested interest in your satisfaction with the CAD system you bought. Third, the resources which go with this question may provide the help you need. Finally, if all else fails, there is always the possibility of hiring a specialized consultant. Business considerations If the customer really wants you to use a particular CAD system, technology can’t help. You have to make the business decision as to whether it is worth it to obtain and maintain an additional CAD system, or to change the CAD system you currently use. What is the account worth, and what might it be worth in the future? What expertise resides within your company? If you devoted technical resources to the new CAD system, how what would happen to other accounts and other customers? These are the kinds of questions that become important. 6. I’m beginning to think in terms of purchasing a CAD application. How can I find out who the vendors are and what they offer? For an extensive list of vendors see the resources associated with this question. Stage: Requirements Analysis, Design | Product Data Exchange Questions 7. I have trouble keeping up with the engineering change notices sent out by my customers. Is there an effective way of solving this problem? Or in alternate form: 7a. When I get diagrams or CAD files from my customer, I can’t be sure that what I have is the most up-to-date version. Can I do anything about this? The key to the solution is to maintain an indexing system with all the major data elements needed to track versions. Examples of these data elements include version, date, and author. It may well be that your trading partner already has such a system in place that you could implement. If this is not the case, you and your trading partner should work one out. When doing so focus on what data elements are needed for version control in your particular case. Maintaining these systems takes some work and dedication, so the trick is to get the simplest one that will meet your needs, and not the best possible system. Stage: Requirements Analysis, Design | Product Data Exchange Questions 8. My customer ships me poor quality CAD data. Sometimes the model is too complex and my computer can’t handle the analyses I need to do. Sometimes there is duplicate data and my CAM systems crash. Sometimes the data is incomplete and I can’t do CAD to CAM translations. Sometimes the data is wrong. Is there anything I can do to solve these kinds of problems? This problem has been of major concern to the Automotive Industry Action Group (AIAG), and they have devoted quite a bit of time to dealing with it. For directions to their publications on this topic see the resources attached to this question. In brief, their approach to the problem is to begin with the following definition of CAD data quality:
Based on this definition, AIAG recommends that companies do the following:
Stage: Design, Implementation | Product Data Exchange Questions 9. We can’t use e-mail attachments reliably to receive CAD files. It seems to depend on the e-mail systems at both ends and the type of CAD files, but sometimes we can read the attachments and sometimes we can’t. How can we fix this problem? Problems with receiving CAD file attachments are the same as found for any email attachment. First, make sure you have an application that can read the attached file. If for example, someone sent you an Access data base and you did not have Access on your computer, you could not read the file. Assuming you have an appropriate application your problem is likely to be incompatibility between the encoding method of the sender and the decoding method of the receiver. Most older UNIX e-mail systems use UUencode and UUdecode to send attachments. Most newer e-mail systems use MIME to encode and decode attachments. In addition there are Mac systems that use BinHex. Most newer e-mail systems can handle a variety of encoding systems. If you can discover (either through experimentation or by asking the sender) how an attachment was encoded, you will be able to read the attachment. A problem you may encounter is that older e-mail systems may not be able to understand an attachment sent in the newer MIME format. Should you encounter this problem three solutions are possible. First, change your e-mail system. (If it is old enough you may want to do this in any case). Second, obtain a special interpreter. Third, see if the sender of the message can retransmit it in a format your system can understand. Stage: Maintenance | Product Data Exchange Questions |
