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A new fast, three-dimensional concept modeler for the design engineer's office is yet another entry into the burgeoning desktop rapid-prototyping field.

Industry is using rapid-prototyping technology for product development at an ever-increasing rate. One million physical models are now fabricated each year, and with more than a million engineering workstations installed, the trend is expected to continue. The business of rapid prototyping (RP) is predicted to grow to nearly $800 million by 1998, according to a market analysis by Frost and Sullivan.

Meanwhile, new RP products are targeting increasingly better-defined niche applications. The recent rise of the desktop RP machine for the design engineer's office is the most prominent example (see "Rapid Concept Modelers," January 1996), but manufacturing-oriented RP technologies aimed at metal casting and other production uses are not being ignored by system vendors.

The design engineer's uses for rapid-prototyping equipment seems to be determined primarily by the stage of the product design cycle - early, middle, late - to which he or she is assigned. Replying to a June 1994 survey of the primary uses for RP systems, conducted by Cincinnati-based consultants Schweiter & Associates, respondents pointed to a wide range of tasks: concept modeling (29 percent); engineering verification (17 percent); pattern production for castings (16 percent); manufacturing prototyping (16 percent); form, fit, and function testing (10 percent); concept proofing (6 percent); and vendor/customer samples (6 percent).

Stratasys Corp. in Eden Prairie, Minn., has opted to address the entire spectrum of those diversified needs with three new RP products, according to Scott Crump, president and chief executive officer.

For quick iterations of concepts early in the design cycle and easier communication among the members of product-development teams, Stratasys engineers have developed Genisys, a $55,500 office tool that produces reasonably accurate "check models" or "rough drafts" designers can pass around.

For greater precision and wider flexibility in materials and build styles, the offering is the $100,000-range FDM 1650, which runs three times as rapidly as the company's current FDM (fused deposition modeling) machines, the workhorses of the Stratasys product line.

For fast fabrication of large precision prototypes (in several materials) that can serve as casting patterns and production masters, the company is developing the Stratasys 8000. Expected in the fourth quarter of 1996, the Stratasys 8000 will provide a spacious build envelope (20 inches by 17 inches by 24 inches), which is said to cover about 80 percent of the large parts modeled by the automotive and aerospace industries. Incorporating technology from both the Genisys and FDM product lines, the new machine will cost from $250,000 to $300,000, Crump said. The 8000 will feature an improved controller, perhaps a new x-y table, and software enhanced with artificial-intelligence capabilities so it can run six times quicker than today's FDM systems.

DESKTOP MACHINE

Early consideration of all potentially problematic aspects of an engineering design when it is just a concept is key to speeding product development. And time certainly is crucial, for one-third of potential gross profits are lost when a new product is late to market by six months, according to a study by the Gallup Organization. Comprehensive design optimization early in the process is the best way to avoid these costly delays. Smaller product design offices have typically been forced to employ RP service bureaus for this purpose, but the new and more affordable desktop machines offer an alternative that could save time and money.

Stratasys, which has addressed the issue to some extent with its FDM systems, has now targeted this segment of the design engineering community with its introduction of a fast single-material system that allows a designer to "print" concept iterations directly from the workstation on the design desk. Desktop systems enable the design engineer to have confidence that the part displayed on the CAD screen is the right choice.

Genisys, which sets up as a printer on the computer network and features a simple user interface that automatically sets modeling parameters, prints three-dimensional models in layers from standard STL files in minutes. The user simply removes the part when it is done and breaks away the supports, and it is ready for use. If needed, the operator can drill, machine, sand, and mark the model, which is of a durable P2000 nylon-poly thermoplastic.

Crump claimed that the Stratasys material is more thermally resistant and robust than the "wax" material used in Multi-Jet Modeling technology from 3D Systems Corp., Valenica, Calif. The company recently announced the trade name, price, and commercial availability of the Multi-Jet Modeling system as the Actua 2100 concept modeler, which will cost $60,000 per unit. Beta tests of the Actua 2100 were conducted at Ford Motor Co., Motorola, Pratt & Whitney, and Texas Instruments.

With a moderately large footprint (36 inches by 32 inches by 29 inches) and a weight of 185 pounds, Genisys does manage to fit onto a table. It is quiet, emitting only 58 decibels of sound when operating. It also features low ambient build temperatures. Power to the print head cuts off automatically when the unit's door is opened.

Genisys is based on technology acquired from IBM in January 1995, Crump said. The work-piece envelope is 8 inches in each dimension. Part accuracy is [+ or -]0.014 inches, and the bead width of the extruded modeling material is 0.013 inches. The Genisys unit's head speed is clocked at 4 inches per second, which Crump claimed to be the fastest in the RP industry. During building, the actual model moves in the y-direction, while the print head operates in the x-direction, according to Jon Cobb, vice president for channel sales.

A dozen easy-to-load cassettes that look like foot-long Pez candy dispensers hold 52 thermoplastic biscuits each, containing up to 12 pounds of 3-D printing material. "The 12 cassettes can produce a week of queued parts," he said.

Using its AutoGen software package, printing the model is as easy as point and click on the Genisys unit. AutoGen orients, scales, slices the part, and inserts supports, all with simple commands. Genisys operates on Sun Microstation, Silicon Graphics, and Hewlett Packard workstations, and will be ported to Windows NT in June 1996. Cobb added that a parts-nesting capability also will be introduced at that time.

Cobb reported that six beta versions of the Genisys system are now being operated by selected users. One of them is Andersen Corp. in Bayport, Minn., a world leader in the manufacture of windows and patio doors for residential and light commercial use.

"Andersen project teams would want a Genisys concept modeler for the same reason they would want a pen plotter - to enhance communication," said Merlyn E. Leslie, CAE technical support manager for the company, which has annual sales of $1 billion. Andersen product-development personnel also use Stratasys' existing FDM technology, which has been upgraded with the new product introductions. "We chose Stratasys because the FDM process is simple and it provides fast, reasonable accuracy and materials properties in an office environment," Leslie said.

NEW FDM MACHINE

The major enhancement embodied by the new FDM 1650 unit is a threefold increase in build speed from the start of the process to its completion, said Jim Fendrick, vice president for international sales. He noted that one-third of that speed boost is due to improved hardware and two-thirds to better software. The FDM 1650 uses a controller developed by originally by IBM, Fendrick added.

The FDM 1650, which is designed for versatility and speed, produces components of acrylonitrile butadiene styrene (ABS), medical ABS, investment casting wax, or polyamide in a workspace with dimensions of 9.5 inches by 9.5 inches by 10 inches. Crump said that other ABS grades are under development, stressing a platable variety. Accuracy is [+ or -]0.005 inches.

The enclosure is 26 inches by 42 inches by 36 inches and weighs 350 pounds. QuickSlice 2.0, the proprietary operating system software, provides PC-like user interfaces.

Andersen Windows has been getting good results from its FDM machines. The company develops many variations of its double-hung and casement windows, so RP makes sense. A double-hung window, for example, can contain 350 wood, vinyl, composite, aluminum, or brass-plated zinc die-cast parts, including detailed items such as locks, keepers, jam liners, grilles, and an innovative pivot component that makes washing easier.

Jim Wyman, CAE technical support engineer at Andersen, is enthusiastic about using RP technology. "RP cuts a lot of time out of the front end of the design process. Being able to produce multiple iterations of a design cheaply enables us to have more confidence in the final design," he said. In fact, the designers can do four times the number of design iterations in half the time it would take to do two without the current process, which includes finite-element analysis and Stratasys' FDM prototyping technology.

"With this system," Leslie said, "we can optimize and test many more design concepts than with traditional methods. Our FDM systems and our testing efforts give us confidence that our design is valid before a part has been constructed from the final product material in an expensive prototyping effort. Without this system we could be spending 85 percent more time verifying some of our designs."

Wyman said that the Stratasys FDM machines, one of which is operated by a former woodworker, helps speed ergonomic and safety evaluations by focus groups by permitting engineers to quickly produce working design models for people to handle. The RP units are also useful in optimizing the wall thicknesses and profiles of vinyl and metal liner structures. "We will do 15 iterations of a single profile," he reported.

Error avoidance is another big benefit. "We produced a temporary spacer of ABS for a piece of window hardware, and found that the hole pattern was off at a time when we were just completing the tooling.

That discovery not only saved us $7,500 but also six weeks in development time," Wyman said.

A particular challenge for one Andersen product-development team was designing a snap cover, a decorative cover that conceals fasteners in a window frame. Snap covers must be lightweight and attractive, yet strong enough to withstand the high stress levels encountered during packaging and installation.

Until recently, Andersen's designers were forced to prototype each design iteration in the end material - the only way to predict performance. Much time was spent in trial and error, optimizing designs to satisfy both strength and appearance criteria. Design and testing periods were long and costs high.

Using FEA software running on the company's Computervision CADDS 5 CAD system, Andersen designers produced a geometric model from the CAD file for the snap cover. They then calculated the surface deflections that would occur when pressure is applied to the structure. Several designs were analyzed with FEA, pinpointing the areas that needed modification.

Once the initial fit trials had been run, the designers generated an ABS model on an FDM machine. After sanding and painting, the components were then tested on an Instron force/deflection measuring machine to calculate the snap force. If the physical results correlated with the FEA predictions, then the FEA model was validated. Wyman said a typical empirically derived force-to-failure number matches within 6 percent of calculated values. Materials property (strength) data previously developed by failure-testing ABS coupons are used in the FEA software.

Designers then inserted the strength properties of the end or final material into the FEA model, which at that point could accurately predict the performance of the final part. This result was then evaluated to determine whether the part's performance characteristics fulfill the design requirements.
COPYRIGHT 1996 American Society of Mechanical Engineers
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Title Annotation:rapid prototyping technology
Author:Ashley, Steven
Publication:Mechanical Engineering-CIME
Date:Mar 1, 1996
Words:1927
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