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Printing In Three Dimensions PUBLIC ACCESS

Office Printers that Produce Designs Rapidly as Solid Objects Reduce the Time From Thought to Reality.

[+] Author Notes

Associate Editor

Mechanical Engineering 123(05), 58-60 (May 01, 2001) (3 pages) doi:10.1115/1.2001-MAY-3

This article discusses that a starch printer, commonly referred to as a three-dimensional printer, serves as a way to make physical models from 3D CAD files. The rapid engineering and 3D printing methods are frequently used in conjunction with a host of compatible technologies, notably a scanning technology that brings physical objects—including items produced by a 3D printer—back into the digital realm. Engineers make use of this form of scanning technology to digitize a complex item that they would have a hard time reverse engineering any other way. Others might use it to digitize 3D artwork such as sculptures to capture a long-term, digital archive of important cultural artifacts. Rapid prototyping at DaimlerChrysler takes place in the vehicle engineering operations mock-up department, among other places. The group builds physical models of parts for the engineers who designed them. Models might range from an individual part to a full-scale mock-up of the entire vehicle.

For Dave Fish, the CAD work team leader at Wescast Industries, a method of printing a computeraided design model in three dimensions has helped to slash modeling costs and development time by 50 percent at his company.

Wescast, based in Wingham, Ontario, makes exhaust manifolds for automobiles and light trucks by pouring iron into sand molds. The company designs the manifolds on a CAD system and then puts them through a rigorous analysis, using computer-aided tools that test for strength and manufacturability. After analysis, Wescast used to produce a handmade prototype for physical testing.

But the company found that it needed to shorten that cycle. As an auto parts supplier, Wescast found the entire design-to-production process too lengthy.

Suppliers are uniquely beholden, after all, to the customers whose parts they design. Frequently, the automotive companies would request that Wescast make a change to the exhaust design after it had already reached the prototype stage. Obviously, the company found it expensive to trash the prototype and restart the process from scratch.

The answer, Fish said, was what he called a starch printer, but what is commonly referred to as a three-dimensional printer, which serves as a way to make physical models from 3-D CAD files. The system Wescast uses, like many on the market, prints the part layer by layer from a starch-based material until it resembles a 3-D model of the CAD file. This process, sometimes called fused deposition modeling, is comparable to the rapid prototyping done on larger machines. The 3-D printers can be situated in an office, according to Fish. Employees don’t need to take special precautions around the starch- based printing materials that his company’s printer uses.

“This is cost efficient; we can easily pop out a bunch of models,” Fish said. “It’s making a significant impact in the prototyping area, where time and cost were previously prohibitive.

“A customer will call us and say, ‘I need this in a week. Can you do it?’ ” Fish added. He said the printer gives him the ability to model a part quickly and to physically show it to the customer.

A model made by lengthier traditional means—for example, from clay, foam, or wood—might be obsolete even before it can be made. And since the printer is following the computer’s instructions, there’s a one-to-one correlation between the model and the file.

In essence, Fish said, the 3-D printer gives his company a way to carry out low-cost rapid prototyping without the expense or environmental hazards of a larger system. In some cases, the starch-based model produced on the printer is strong enough to serve as the mold used, in turn, to make the sand-cast model that will hold the iron used to make the exhaust manifolds.

The rapid prototyping and 3-D printing processes, however, are two separate animals, and companies select the process they need. A rapid prototyping machine builds solid models from plastic or other material, using CAD output. The models are often used all the way through the product-development process. The rapid prototyping process is additive—that is, models are built layer by layer. On the other hand, 3-D printing normally refers to a modeling process performed by a similar machine that is often faster and less expensive, but is typically used earlier in the design stage for testing concepts, rather than perfecting a product model prior to its manufacture.

Rapid prototyping systems, a technology now about a decade old, replicate the part exactly, but, for some companies, the machines are too costly. Starting costs usually are $100,000 and can range upward. Operators must be specifically trained to run the machine, and the plastic or other materials used to produce objects can be expensive, as can maintenance costs.

Because Wescast produces fairly easy-to-print parts, the 3-D printer is applicable, Fish said. He has found that designers can print a CAD file on a 3-D printer faster than they can with a rapid prototyping machine, which allows them to print a model quickly, study it for accuracy, make a change to the CAD file, and print another model. This methodology, Fish said, gives CAD designers easier and more immediate access to physical prototypes of the designs they make on their computers.

Three-dimensional printing systems print a part from a CAD file layer by layer from a starch-based material until it resembles a 3-D model of the CAD design. Color prints are also available.

Grahic Jump LocationThree-dimensional printing systems print a part from a CAD file layer by layer from a starch-based material until it resembles a 3-D model of the CAD design. Color prints are also available.

At Wescast, the printer has helped to cut in half a design cycle that formerly took about one year, from modeling through virtual and physical testing and validation, tooling, customer approval, and production, Fish said. It also allows the company to make about 30 to 35 models a month, which is about double the number that were made when the company produced handmade prototypes of each product. Each prototype made on the 3-D printer costs about $30 for the materials used, Fish said.

Wescast uses a 3-D printer from Z Corp. in Burlington, Mass. Fish has found that the printed models serve another purpose separate from prototyping.

“We first bought this for verification of nonvirtual prototypes, but now it’s a way to correlate with the customers and the original equipment manufacturers that what we’re making is what they want,” Fish said. “Now, they ask regularly to see the printed models because they want to see the look and feel of the part.”

The rapid engineering and 3-D printing methods are frequently used in conjunction with a host of compatible technologies, notably a scanning technology that brings physical objects—including items produced by a 3-D printer—back into the digital realm. Engineers make use of this form of scanning technology to digitize a complex item that they would have a hard time reverse engineering any other way. Others might use it to digitize 3-D artwork such as sculptures to capture a long-term, digital archive of important cultural artifacts.

Rapid prototyping and 3-D printing are used with other technologies. Chrysler engineers use CAD and 3-D printing as part of the overall design process.

Grahic Jump LocationRapid prototyping and 3-D printing are used with other technologies. Chrysler engineers use CAD and 3-D printing as part of the overall design process.

For instance, in 1998 and 1999, a team of researchers from Stanford University in Stanford, Calif., and the University of Washington in Seattle traveled to Italy to scan Michelangelo’s sculptures and architecture in order to create such an archive.

The team was led by Mark Levoy, a Stanford computer science professor, who said the project marked his first attempt to capture data on a sculpture as large as Michelangelo’s David. The scanned artwork can serve many purposes, he said. The digital files could help reconstruct the works of art if they were ever to suffer harm. Also, some damaged works of art can be virtually restored, Levoy said. That is, the computer file can be tweaked to show how a damaged piece might have looked originally.

Levoy and his team used custom-made scanners from Cyberware of Monterey, Calif., and by Faro Technologies in Lake Mary, Fla., and 3D Scanners of London. But Stanford’s computer graphics laboratory has developed another software technology that converts 3-D scanned data into a non-uniform rational B-spline, or NURBS, model, a mathematical basic used in CAD programs. The scanned-in models can then be adjusted and worked on in the user’s CAD program. The technology is now being produced commercially by Paraform of Santa Clara, Calif.

“There are times when manipulation of the model in the digital domain makes sense,” said Brian Kissel, Paraform’s chief executive officer. “However, if anything is complex and organic in nature, it’s easier to do that manipulation with a physical model. But after you’ve changed the physical model, how do you get it back into the computer to make the changes that will produce the part?”

The 3-D scanning technology comes into play by scanning the part back into the computer, in essence letting engineers make a CAD file of a part already produced in three dimensions, Kissel said. The technology can be combined with a 3-D printer to fine-tune a design, he added.

In such cases, an engineer could produce a design that, when printed, proves to need more work. The printed design is then worked on in three dimensions, which is sometimes easier, particularly with complex parts, than tweaking the CAD model because the part can be seen and handled, Kissel said. The altered design is then scanned back into the computer so the adjustments made on it in the real world are mirrored in the CAD file.

“In the auto industry, they take a 3-D model and if they find an assembly problem or a constraint problem, they modify the physical model and then read that back into the computer,” Kissel said.

The 3-D printers are also frequently used in the custom engineering realm, Kissel added. In that case, the engineers start with a common design—for sunglasses, say— and modify it according to each user’s request. The modified designs are then printed so engineers can quickly view results. They’re sometimes then changed and scanned back into the CAD programs.

Custom engineering of models is also used in medical applications, such as fitting hearing aids or the new, invisible braces that adhere to the wearer’s teeth. In such cases, engineers make a 3-D printed mold of the design to ensure that it fits the wearer exactly.

DaimlerChrysler in Detroit uses 3-D prints of models in another fashion. The automaker uses printed versions of 3/8-scale models of its vehicles for wind-tunnel testing, saving as much as 90 percent in model-building time compared with the previous method of hand-building the parts used in each test model.

Rapid prototyping at DaimlerChrysler takes place in the vehicle engineering operations mock-up department, among other places. The group builds physical models of parts for the engineers who designed them. Models might range from an individual part to a full-scale mock-up of the entire vehicle.

The department implemented 3-D printing technology, in this case from Stratasys of Eden Prairie, Minn., to cut the amount of time designers spent waiting for the department to model their parts in three dimensions. The department had been experiencing frequent backlogs when it built prototypes by hand, according to Dennis Pircer, a senior engineer at DaimlerChrysler.

Printing a CAD model of a part in three dimensions lets engineers handle parts, see what their designs look like in real life, and possibly make changes.

Grahic Jump LocationPrinting a CAD model of a part in three dimensions lets engineers handle parts, see what their designs look like in real life, and possibly make changes.

The automaker had been using scale models for decades, as have most of its competitors. Designers began using them as a visual review tool. The smallest model that designers found they could build, while maintaining key elements of the design, was 3/8 scale. In the middle 1960s, Chrysler’s aerodynamicists began using those hand-built models for wind-tunnel testing.

One mock-up department member might build 3/8- scale models of vehicle underbodies and engines. The underbody and engine models are then assembled with the outer body surface of the vehicle, which is usually made of clay, for wind-tunnel testing of the complete 3/8-scale vehicle model. Then the 3-D printed models of the parts are incorporated into the scale vehicle that will go into the wind tunnel.

Because surface finish and durability are critical during wind-tunnel testing, the department had to be able to sand and glue prototyped parts. The prints are sturdy enough to allow this, Pircer said.

“We’re using 3-D printing for an increasing number of assembly parts,” Pircer said. “Our 3/8-scale engine models are 100 percent 3-D prints and our full-scale models contain 3-D prints of some of the smaller components as well.”

The department has also modeled entire engines, transmissions, exhaust manifolds, master cylinders for the brake system, and upper and lower radiator cross members on the 3-D printer.

To make the parts for full-scale models, however, the department usually uses a rapid prototyping machine.

Pircer credits the printer with cutting as much as 90 percent from the typical 13 to 15 weeks previously used by the department to hand-build models for wind-tunnel testing.

As Pircer and Fish point out, their departments have found that a 3-D printer, once purchased, can be used for a variety of purposes, including showing prototyped parts to customers and tweaking prototyped parts in real life and, in Fish’s case, sometimes using them as a mold to make parts.

Copyright © 2001 by ASME
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