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Three Out of Two PUBLIC ACCESS

Three-dimensional CAD may be the Norm for Bigger Players, but now Smaller Shops can get in on Solid Modeling.

[+] Author Notes

Associate Editor

Mechanical Engineering 123(09), 60-63 (Sep 01, 2001) (4 pages) doi:10.1115/1.2001-SEP4

This article reviews computer-aided design (CAD) software that is meant to function as more than a drawing tool; design offices and general contractors are still learning how to take advantage of its full potential even as the software systems mature. CAD systems are used to sell products before they are produced, to warehouse past designs in a central library, and to describe an intended design to a parts supplier. Traditional wisdom holds that 2D CAD systems are best suited to products with simple geometries that can be easily represented without considerable interpretive errors, products such as the nozzles. Often, 2D drawings can be ambiguous and are open to errors in interpretation, especially in cases of complex designs, according to the Queensland Manufacturing Institute (QMI) report. Century Tool wanted to use the 3D CAD software to check for interferences in the design of a part a customer had charged Century Tool with building.

Computer-aided design software is meant to function as more than a drawing tool; design offices and general contractors are still learning how to take advantage of its full potential even as the software systems mature. CAD systems are used to sell products before they’re produced, to warehouse past designs in a central library, and to describe an intended design to a parts supplier.

Many manufacturing and engineering companies— mainly small ones—still use two-dimensional drafting or a two-dimensional CAD package strictly for design. But as software prices drop, along with the training time needed to master a program, some of these companies are turning to 3-D design software. Once the programs are implemented, the companies generally find a number of unexpected uses.

For instance, Husky Corp. of Pacific, Mo., a maker of small gasoline-line nozzles, recently installed a design package after years of what Thomas Mitchell, senior design engineer, said were long calculations that the engineers carried out when a part design had to be changed. Because the company essentially produces the same nozzles again and again, engineers eventually learned how to tweak the design to correct any problems that might come up.

The company makes vapor-recovery nozzles, which are placed in the gasoline hose between the gas pump and the underground tank to prevent vapors from escaping. Husky also makes a small valve that sits in the gas hose close to the gas pump handle and easily breaks off should the driver take off with the hose still attached to the car. The release valve limits damage to the gas pump in those situations, Mitchell said.

Because the small nozzles and valves aren’t very complex in design, Husky hadn’t really investigated a move to 3-D CAD design, Mitchell said. Engineers saw no need for it. If they wanted to change a design, they simply altered the 2-D design by hand.

The nozzles are produced by sand castings, which are machined. Often, however, the clamp that held the part for machining would break or bend the delicate casting.

“The casting needs to be held to be machined,” Mitchell said. “You’ve got to grab the casting, but you don’t want to ruin it. If you squeeze it too hard, you can bend it out of shape.”

Two-dimensional drawings can often be ambiguous, but 3-D CAD solid models, such as the one above from Micro-Matic Tool, let designers study motion and check for interferences in three dimensions.

So engineers started thinking about how the nozzles could be fully reconfigured to give them additional strength. The machinists and engineers had been guessing about how much force they could apply while machining. When they realized that a simple change in design might mean far fewer destroyed castings, the engineers at Husky decided that 3-D design might serve a purpose for the company after all. Husky implemented Pro/Engineer CAD software from PTC of Waltham, Mass.

“For years, everyone was working in two dimensions, but 3-D CAD is faster,” Mitchell said. “You know what you’ve got because you can see it on the screen.”

Instead of sketching the nozzle design, then producing and testing a prototype to ensure that it was strong enough to withstand the machine clamps, designers worked on their computer screens, making sure the nozzle design depicted there aligned with the design they sought. The engineers figured that the grooves on the nozzle would have to be changed so the nozzle would fit better into the machine clamps. They experimented with the CAD design, putting the grooves in different places.

The company took the software upgrade one step further by linking the new CAD package with analysis software, called Pro/Mechanica, also from PTC. Engineers at Husky exported the CAD design to the analysis software, which told them how much pressure a part could withstand as designed. That way, they saw whether or not the clamp would crush a part before they produced it.

“It’s good to be able to simulate the part and make sure you can clamp it tight enough without destroying it, instead of having to fix something after you get it out the door,” Mitchell said.

“Previously, we’d actually make the part and we’d just see what happened once we machined it,” he added.

Traditional wisdom holds that 2-D CAD systems are best suited to products with simple geometries that can be easily represented without considerable interpretive errors, products such as the nozzles Husky makes.

But as systems become more commonplace and inexpensive and include features that can easily be used by small companies, many engineers are discovering that 3-D CAD can be relevant for them.

Originally, CAD systems were no more than electronic drawing boards. And indeed 2-D CAD systems can still be thought of as electronic drawing boards, according to a report issued by the Queensland Manufacturing Institute in Brisbane, Australia, a research and technical training plant set up by a number of Australian companies. The QMI wants to encourage its manufacturing members in the use of CAD technologies because its research shows CAD can save a company money.

Three-dimensional CAD systems, such as this one from Thinkdesign of Santa Clara, Calif., allow engineers to make precise changes to models.

Grahic Jump LocationThree-dimensional CAD systems, such as this one from Thinkdesign of Santa Clara, Calif., allow engineers to make precise changes to models.

Often, 2-D drawings can be ambiguous and are open to errors in interpretation, especially in cases of complex designs, according to the QMI report. Still, the systems are useful because electronic sketches allow engineers to start editing and copying designs quicker than they could with draft sketches. Also, 2-D CAD data can be sent to computer-aided manufacturing software to generate 2-D toolpaths.

With 3-D solid modeling software—which defines the interior volume, mass, and exterior surface of an object—engineers can cut cross-sections through the digitized parts to show internal details. They can study the action of moving parts and check for interferences in three dimensions. Also, they can compute weight, moment of inertia, and center of gravity from the solid model.

CAD packages that make use of surface modeling define the outside of a model; they don’t define the inside.

Husky found yet another benefit of a 3-D CAD model. Because the model depicts an animated version of how the part will look when produced, salespeople can use the CAD file to market the product before it’s made.

“You can just take a computer on the road and go out and sell the thing,” Mitchell said.

Companies continue to discover additional uses for 3-D CAD, particularly for the systems that include solid modeling capability.

Micro-Matic Tool, a Youngstown, Ohio, shop that designs and builds plastic injection molds for customers, upgraded its 3-D CAD package from a surface to a solid modeling package more than a year ago.

Century Tool and Gage of Fenton, Mich., uses 3-D Thinkdesign software to clean up designs that have been submitted by its customers.

Grahic Jump LocationCentury Tool and Gage of Fenton, Mich., uses 3-D Thinkdesign software to clean up designs that have been submitted by its customers.

“We still need to see things in 2-D,” said Lou Vitullo, engineering manager. “When we do a part, there’s still a lot of 2-D work like waterlines and bolt holes that goes into the design.”

When customers sent images of the part for which they needed Micro-Matic to create a mold, they almost always transmitted them as 3-D CAD files. Though Micro-Matic could translate any CAD file into its surface-modeling CAD software, engineers then had to turn the 3-D CAD file into a 2-D file in order to get necessary 2-D information. But the surface-modeling package failed to delineate hidden lines when Vitullo translated a 3-D into a 2-D view.

“As a result, you’d get lines over lines over lines and it’d take you a long time to clean it up,” he said.

The company upgraded to a solid-modeling package called Thinkdesign from Think3 in Santa Clara, Calif. After experimentation, Micro-Matic engineers find it easiest to translate a customer’s surface-modeled CAD image into the Thinkdesign surface program, then create a solid model from the surface model in order to check for surface gaps. They then create 2-D and section views from the solid model and pass those views to the computer-aided machining department.

Vitullo has found another use for the CAD program as well.

“We keep a few seats of it on the floor so that people can see what the part is supposed to look like,” he said. “Those seats are used strictly as a viewer. It’s kind of like looking at the part on a TV screen, except that you can rotate it.”

Century Tool and Gage of Fenton, Mich., which manufactures compression molds and secondary tooling for the automotive, heavy truck, aerospace, and personal watercraft industries, switched to Thinkdesign software from a 2-D system.

Century Tool wanted to use the 3-D CAD software to check for interferences in the design of a part a customer had charged Century Tool with building.

“Using the software, I normally pull in the surface data of the part itself,” said Tim Cummings, a member of the company’s 15-person design and engineering team. “If the data comes from another CAD system, it’s either converted to ICES or we have converters here for CATIA and Unigraphics systems.

“Then, we download the data into Thinkdesign and we clean up anything that isn’t a closed solid,” he added.

The data allow the design and engineering team to make sure toolpaths can be run that will properly machine the mold.

When Century Tool was an exclusive 2-D company, employees sometimes didn’t build molds exactly according to the submitted design because the 2-D design didn’t portray the interior of what would eventually become a very complex mold, Cummings said. Fixing those mistakes slowed the production line.

“Working in 2-D didn’t allow us. to catch errors deep within the mold,” he said. “We simply couldn’t see them. To keep our customers happy, we often absorbed the additional costs incurred due to mistakes and production bottlenecks.”

Century Tool and Micro-Matic are both relatively small shops. Implementing a 3-D CAD program across a distributed, giant corporation can be another story altogether, said Erwin Pfister, who knows whereof he speaks. His employer, Rieter Group, recently moved from its eight disparate 2-D CAD systems to the Unigraphics system from UGS of Cypress, Calif. Pfister is part of a team working on the project.

Headquartered in Winterthur, Switzerland, Rieter Group is organized into two divisions: Rieter Textile Systems and Rieter Automotive Systems.

Rieter Textile Systems makes huge pieces of machinery that convert fibers and plastics into yarns and make manmade fibers. Rieter Automotive Systems makes automotive noise control equipment as well as thermal insulation products and interior trim for vehicles. With factories in more than 20 countries, Rieter sought to bring all employees into a common corporate culture as well as to keep CAD designs within one common system by rolling out one software system to unite all sites.

Micro-Matic frequently has to turn 3-D files submitted by customers back into 2-D files in order to get needed manufacturing information.

Grahic Jump LocationMicro-Matic frequently has to turn 3-D files submitted by customers back into 2-D files in order to get needed manufacturing information.

The project, which started in 1999 and is still under way, includes linking the sites via a product-data management system call Iman, also from UGS. But sometimes change is a hard sell, even if executives see it as being for the better, Pfister said.

“Even if working in 3-D is so much nicer than working in 2-D, our engineers were used to 2-D, and they don’t want to change,” he said.

When the upgrade is complete, Rieter will have a repository for every design it has created. Rather than keep them in disparate systems at each site and pass them back and forth, which, of course, created hassles, lost designs, and paperwork, the company now keeps 12,000 designs in the CAD system and has plans to increase that number to 30,000, Pfister said. This parts library is unified under a newly created numbering system, he said.

Rieter has addressed the problems involved in such a large-scale implementation by creating a centralized standards-setting body that will draw up specifications on how part designs will be numbered, stored, created, and accessed. The standards will also pertain to PDM use.

Still, Rieter Group faces a challenge that the job shops don’t have: tying employees together via a common language. At almost every Rieter site, employees speak a different language. And, in some ways, employees don’t like to feel part of a vast corporation, which can be a side effect of standards setting, because they feel anonymous or small. But Rieter won’t be skimping on training costs, which Pfister said helps to address some of the hesitancy employees face.

Like Husky and the other small companies, executives at Rieter found that, although they originally implemented CAD for quicker, easier design, the tool serves a number of additional purposes, some of which will no doubt be discovered well after full implementation.

Copyright © 2001 by ASME
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