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3-D CAD.

To those uninitiated in using computers to design and produce plastic parts, three-dimensional computer-aided design (3-D CAD) might seem like a hornet's nest. Not so. The experts describe it as more like an adventure full of opportunities than one with perilous, unseen technical and intellectual hazards.


Russell Stay, product manager, Manufacturing, Software Products Marketing Div., SDRC, says that 3-D CAD users need to understand clearly their immediate as well as potential future needs. A moldmaker who builds molds to spec, for example, could get by with automated drafting and numerical control capabilities. A mold designer, by contrast, could benefit from drafting capability, mold-base databases, finite-element analysis (FEA), flow/cooling analysis, and possibly solid assembly modeling of the proposed tool. The resin supplier with technical services would include anything ranging from product design with 3-D CAD to production. The OEM'S computerization level would depend largely upon the degree of in-house effort and vendor relationships.

Stay anticipates new software capabilities for blowmolding and compression molding, thermoforming design and simulation, analysis of thermosetting plastics, thick parts, creep modeling, improved predictability of fiber-filled materials, and laminar/composite structural parts.

Challenges also include increased system integration, automatic analysis modeling from solids, and growth of artificial intelligence for decision making.

Stay advises to buy now rather than be concerned about rapid obsolescence. "The cost savings by waiting for hardware prices to fall or capabilities to increase are offset by loss of added productivity and quality 3-D CAD systems can provide."

Today's integrated software offers a comprehensive functional capability. An advanced user can define a complex problem highly accurately. A novice or casual user, on the other hand, might be confused by a maze of options. Stay says that to avoid this problem, but still allow the advanced user full functionality, SRDC's I-DEAS software permits a user to mask unneeded prompts and features until his familiarity with the system increases.


Daniel L. Schuder, plastics product manager, Graftek, Inc., a subsidiary of Unisys Corp., Inc., adds that documentation, interface, and training programs have shortened the learning curve. Sparked by the increase in power of the platforms, the CAD/CAM industry has advanced from a mainframe-based to a desktop computer-based technology. With the declining price structure of hardware and software, smaller firms are finding that the technology is affordable.

Pricing for an entry level system in the single station market can range from $10,000 to $15,000. Pricing for software programs can range from $500 for an individual PC-based program, which can provide simple drafting capabilities, to as much as 90,000 for a fully integrated design and analysis system that includes solids modeling, production drafting to ANSI standards, finite element analysis, mold simulation, and numerical control.

The technology has been in constant flux, especially the availability of computer power per dollar. Twenty years ago, a popular mainframe computer, such as an IBM 360, could handle 100 users. Ten years later, the DEC VAX 11781 minicomputer handled ten users but had four times more capability per user than the mainframe. Currently, the SPARC single user workstation offers fifty times more power per user than the mainframe of twenty years ago. The future for workstation development? The trend is toward doubling of computing power every twelve to eighteen months, largely through continued advances in microelectronics.

Schuder also mentions the concurrent advances in software. "About five years ago, I first started running design and analysis programs on a terminal connected to a mainframe computer. Response time on the screen depended upon how many other users were on the system and upon the applications being run. Soon after, each time a more powerful workstation became available, something even faster was right on its heels."


Computerized 3-D design offers the solid-model dimensional base for a "one-stop-shopping" approach to plastic design verification by finite-element analysis, mold simulation, and automated mold manufacturing. Having the design in 3-D up front reduces work and time downstream. Information for drafting of detailed layouts and assembly drawings, numerical control operations, technical manuals, and even sales and marketing brochures, is simply extracted from the 3-D database. Any orthogonal or auxiliary views can be generated automatically from the 3-D model. Dynamic rotation of the 3-D image helps the user conceptualize the design. With the 3-D model defined, stress, thermal, and plastic flow analysis can be done without having to interpret the part's three dimensionality from two-dimensional drawings.

Once the 3-D finite-element analysis model is created, data can be transferred into the American Standard Code for Information Interchange (ASCII) format and downloaded to a plastic flow and cooling analysis program for the mathematical calculations relating to the filling, packing, and cooling stages of injection molding.

Graphic displays can depict, for example, temperature, shear rates, and velocity profiles during any part of the molding cycle, allowing determination of where proper mold filling may be affected as a result of wall thickness changes. Factors such as volumetric shrinkage and gate freeze-off also can be visualized.

In the future, it is expected that the software will be able to interpret different analysis results. Also, the ability to download molding parameter data to the injection molding machine can shrink the window of error in the cycle.

The "associativity" of the 3-D model also permits the user to work in one view while the computer displays multiple views. Software programs permit the sketching of a moldbase around a pregenerated cavity layout, estimating mold cost, including cavities and cores, and automatic generation of a bill of materials. The mold design program can reduce design time by up to 50%.

Even more significant savings can be realized, using the 3-D database, if numerical-controlled (NC) machining produces the mold. With an NC programmer, tool paths can be created to accurately machine the cavities and cores from the 3-D solid model surface or wireframe data.


Tom Hayden, design engineering manager, Huron Plastics Group, attributes at least half of the company's average growth rate of 20% for each of the last three years to its 3-D CAD system. Because of the computer, he says, the company has a much broader range of projects.

Three years ago, the company was basically a supplier of injection molds and a processor of small parts such as clips and brackets. CAD capability started with two workstations, built to three, and two more are expected to be added soon. The 3-D operations are built around an integrated turnkey software system supplied by Unisys Corp. The database generated for design of the solid model prototype can be transferred for generating FEA, mold simulation models, and cutting tool paths for producing molds. I

Hayden says that 3-D CAD was the driving force in opening new markets for the company with a more diversified range of products. Almost totally in automotive, its designs now include armrest and door assemblies, interior trim components, and structural parts. "We are now perceived as a more high-tech company with a wider range of services," Hayden comments. o



D & L Inc. designs and manufactures components for moldmakers and molders and also customizes and integrates CAD/CAM systems for designers. "I always emphasize practicality and ease of implementation when configuring hardware and software solutions for plastics engineers and mold designers," says Glenn Starkey, vice president, Engineering. "Rather than install a complex system to cover every facet of the plastics industry, I customize the system for the intended applications. A medium-sized mold builder who feels he needs 3-D CAD and Computer-Aided Manufacturing (CAM) might not want to add the personnel and equipment to perform mold cooling and filling analysis. I'll install Cadkey, for example, to provide the needed 3-D power, and CK/Mold Design to provide an on-line catalog of mold bases and components."

Starkey says that SmartCam and MasterCam both have proven to be excellent choices for machining software, and both packages can directly communicate to and from 3-D PC-based software. This saves the user from having to use the International Graphics Exchange Specification (IGES) or two-dimensional DXF (Data Exchange Format) protocols for file transferring.

Starkey emphasizes the importance of receiving feedback from the mold designer before the 3-D model is completed. "I 4 have seen many cases in which a designer has painstakingly prepared a 3-D wireframe or solid model only to have it completely redrawn by the mold designer in order to represent the different parting lines and drafts on the actual part. If the model does not include the appropriate draft angles, it is essentially useless. If we are going to use the logic that the 3-D model is the bible, then communication between the part engineer and mold designer is critical."


Geoffrey Engelstein, director of CAD services, GR Technical Services, says that designing in 3-D makes determining clearances much easier, especially when parts with different draft angles have to mesh. The company performs mold filling and cooling analysis on almost all its designs. Engelstein says that once the model is entered in the computer, beginning the analysis procedure is relatively simple. I

Performing a mold cooling analysis includes a 3-D layout of the cooling lines around the part. Seeing the cooling lines three-dimensionally, rather than needing to decipher the mold drawings, makes it easier to envision how the part will cool and where any hot spots might turn up.

"Apart from a few downsides, we are extremely pleased with the increased productivity 3-D CAD has given our design group," Engelstein comments. "However, it takes time to adjust to the new way of thinking. Draftsmen normally look at 2-D drawings and envision them as 3-D models. With 3-D CAD, you start with the model and decompose it into 2-D views for drawings. It takes time for people to make the adjustment.

"The common thread in all the things we like about 3-D CAD is not so much the model itself, but what you do with it once you have it. You can look at a hidden-line view, rotate it, shade it, or see how it would look with a woodgrain finish. You can see how it will fill, or cool, or support loads. And you can machine it."


Jeff Delmas, product manager, MCAE, Intergraph Corp., says that although potential users may be put off by a lack of trust in I the technology, and areas of application are overlooked, today's CAD systems can be "amazingly" effective and often pay for themselves in less than a year. He adds that CAD developers must look to broaden the scope of problems that can be solved by computer systems, such as shrinkage and warping evaluation techniques. The trend will be to give users an estimate of the effects certain processes will have on the shape of the part. Also, he says, a single unified approach is needed for better and faster finite-element modeling capabilities, as well as for software packaging and training. Because of the complexity of the analysis, he insists, users cannot afford to spend much time learning how to operate a CAD modeler and a poorly connected third-party solver and support software.

Rather than reinventing the wheel, Mark Pettit, Intergraph's senior product consultant, advocates an aggressive use of standards and proven design solutions to improve mold design cycle time and product quality. Computerized support of this fundamental design strategy," he says, "will see the rise of powerful library-based applications that will have several levels of sophistication, starting with simple selection of standard mold components and automatic generation of drawings. "

In the next level of design support, Pettit continues, the CAD system allows the designer to establish assembly relationships between the parts of the mold and permits automatic reflection of changes to the individual part parameters. "For example," he says, "if a plate thickness is modified, the mold assembly plate stack will adjust accordingly. Features, too, may be modified and the assembly will automatically reflect the change. CAD applications that allow dynamic, three-dimensional parametric mold design are just beginning to appear on the market.

Finally, the designer will soon be able to get additional computerized help in the selection of the appropriate design solution. The well-defined set of mold components and features provides an ideal domain for the application of expert system technology. Rather than selecting standard components and features based on low-level geometric parameters, the designer will be able to specify solution requirements in terms of functional parameters."


By providing the ability to predict the flow and temperature patterns, and the deformed shape, of a molded plastic part prior to prototyping, computer-aided engineering (CAE) tools have helped prevent countless bad parts from ever being produced. Bob Shaefer, general manager, Moldflow, Inc., says that one of the most important trends in CAE today is the move towards diagnostic solutions that pinpoint the specific parameters that may be causing a problem and measure the contribution of each factor to the overall difficulties.

One of the major software contributions is in simplifying control of warpage and residual stress in an injection molded part by varying the part, mold design, and processing conditions. Shaefer says that warpage is basically caused by shrinkage resulting from differences in packing pressure and level of crystallization; temperature variations in the mold during the filling, packing, and cooling phases; and the effects of the polymer and/or filler orientation.

Moldflow's MF/WARP produces separate deformed representations of the part for each of the three causes of shrinkage, Which, when combined, produce the actual deformed shape. The ability to pinpoint the sources of warpage, and which is dominant, permits making changes in the part and/or tool design and the molding conditions. Shaefer says the graphic representations normally provide all the information needed to eliminate warpage; producing a trial part is unnecessary, except as a final verification.


Michael Kmetz, president, IDES, Inc., points out that there are nearly 13,000 different grades of plastic materials on the U.S. market today, encompassing thermosets, thermoplastics, and elastomers. "Ideally, one would like to have access to an extensive comparative plastic material database from within the CAD system. Currently, however, such a system does not exist, but a number of software vendors do have extensive stand-alone systems. Many of the major material suppliers provide systems that contain their materials data."

GE Plastics, for example, makes its Engineering Design Database available to qualified customers of GE resins. This system provides the type of information that designers require, including stress versus strain at various temperatures, creep modulus, and design recommendations.

Another plastic materials selection software system, Selector, by IDES and International Plastics Selector, contains a database that Kmetz says includes essentially every U.S. materials manufacturer and supplier. The system provides all the necessary software capabilities to select, display, and print plastic materials data. Also included is an extensive database of chemical resistance information. The software can interface to PC-based CAD systems by providing information in ASCII text format. Future enhancements will include features to allow Selector to run directly with PC-based CAD systems.

Much of today's materials data deal with physical properties at a specific condition, such as tensile strength at room temperature and 50% relative humidity. More extensive comparative information often is necessary for designers to develop a plastic part. Development is under way to augment Selector with databases of advanced design information. For example, the enhanced system will provide comparative tensile strength data as a function of temperature, humidity, and time for a much wider range of commercially available plastics.

Other systems to augment the CAD design process include those tools that perform routine calculations necessary in the early stages of a design, such as cost estimator and feature design programs. Cost estimating programs use the volume of the part produced by the CAD system, coupled with the price of the plastic material and other factors such as injection cycle time and injection machine cost, to determine an approximate piece cost. Feature design programs such as the IDES's PD-1 system assist with the development of snap-fits, ribs, hollow bosses, and press-fits. These programs can drastically reduce the number of calculations or trial and error redesigns that must be done with the CAD system.


Hoechst Celanese's Engineering Plastics Division uses stereolithography (SLA) equipment at its laboratories in Summit, N.J., to help develop prototypes for customers. Harry Morgan, senior technical service specialist, says that "SLA can save the company's customers anywhere from $5000 to 50,000 in prototype molds and many hundreds of thousands dollars more by shortening the design cycle."

SLA systems use laser and low-viscosity photocurable resins to create 3-D prototypes directly from a 3-D database. When beams of laser light pass over portions of the curable resin, it solidifies. To produce a physical prototype, the 3-D CAD model data is segmented into horizontal slices by computer. This segmented data is used to guide the laser, which builds up the prototype layer by layer. With a layer complete, the part is submerged deep enough for another layer to be built onto it. Small parts can be completed in an hour; larger parts take up to twelve hours to complete. Parts that Hoechst Celanese has helped develop for customers, using the SLA facilities, include motor housings, automotive instrumentation, switches, office equipment, and furniture components.


Since GE Plastics' introduction at ANTEC 1989 of Polymer Inflation and Thinning Analysis (PITA) software for blowmolding and Sheet Thinning Analysis for Thermoforming (STAT) software, the technology has been further developed and applied. The 3-D analytical processes can be used for modeling such parts as bumpers and fascias, instrument panels, and refrigerator liners. (See-PE, January 1990, p. 25.)

Charles A. Taylor, mechanical engineer, Solid Mechanics Program, GE Corporate R&D, relates that some emphasis has been placed on the comparison between numerical predictions and actual experimental data. Taylor reports that the resulting verification of the PITA and STAT software allows engineers to perform analyses with a higher degree of confidence in the predictions.

Taylor adds that the 3-D technology has been applied to dozens of blowmolded and thermoformed applications, including bumpers, instrument panels, refrigerator liners, aircraft parts, and consumer and industrial parts. As an example, a STAT thermoforming analysis was performed on an electrostatic dissipative shield for an AT&T telephone. Thermoforming the complex geometry leads to nonuniform thickness distributions that are directly related to the shield's dissipative characteristics. Multiple 3-D STAT analyses eliminated the need of costly trial and error process modifications to find the best processing technique for the part.

Mark Minnichelli, manager, Advanced Design Engineering, GE Plastics, says that a snap-fit program is now part of the company's Engineering Design Database. Also, Plastics Education and Troubleshooting (PETS) has been added, allowing molders with specific problems to enter the database for help.

Minnichelli reports that an "intelligent" materials selection system is being developed that would permit the user to define an application's requirements, not necessarily in hard numbers. Options then would be provided from among the company's materials. Finite-element analysis and mold-filling programs also complement the company's blowmolding and thermoforming software.


Plastics and Computer Inc.'s new Situation Analysis and Solution System (SASS) is a qualitative software package that fully integrates with the comprehensive quantitative analysis of the company's TMconcept Expert System for Molding. Anne Bernhardt, president, says that SASS guides plant operating personnel in troubleshooting and brings the knowledge base of an expert system to the machine operator on the shop floor. It guides him in analyzing the situation and prompts him to take the most effective and rapid corrective action.
COPYRIGHT 1990 Society of Plastics Engineers, Inc.
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Title Annotation:three dimensional computer aided design
Publication:Plastics Engineering
Date:Oct 1, 1990
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