Hydroforming heats up

New techniques and equipment push industry forward

The Tube & Pipe Journal December 2003
January 13, 2004
By: Eric Lundin

Hydroforming was one of the fastest-growing metal forming technologies during the 1990s. Most of U.S. industry cooled down during and after the recession of 2001, but things have been heating up lately, and the world of hydroforming is no exception. The North American Hydroforming Conference and Exhibition (Sept. 29 – Oct. 1 in Dayton, Ohio), which was sponsored by the Tube & Pipe Association, International® (TPA), and the Society of Manufacturing Engineers (SME), showcased new techniques, equipment, and applications that are moving the industry forward.

Hydroforming at Higher Temperatures

The majority of hydroforming knowledge is based on steel. Steel's characteristics make it a favorable choice for many products, and steel has been the dominant material in many industries, especially automotive, for decades. Lately, though, hydroformers are finding that less afformable materials such as aluminum are good potential candidates when formed at elevated temperatures.

At room temperature, aluminum elongates just 12 to 15 percent before it fails. By contrast, steel is much more formable; some stainless steel alloys elongate up to 50 percent before failure.

In a recent project involving an aluminum side member for a rear suspension, however, Siempelkamp Pressen Systeme GmbH & Co. KG (SPS) achieved more than 66 percent elongation. The company also is experimenting with a valve cover made from sheet aluminum. The process is similar to deep drawing, but it uses just one die and forms the part in one shot.

"For both applications, the temperature is 350 degrees Celsius," said Klaus Heimerl, manager of project planning for SPS.

Bernd Sent, Ph.D., a member of Schuler AG's board of directors, attended the conference and delivered the keynote address at the welcoming reception and special-event dinner, which were sponsored by Schuler.

Schuler Hydroforming Inc. is working with a major automotive company on a more ambitious project—hot hydroforming of aluminum elbows, T fittings, and an automotive space frame.

"The elbows and T's are hydroformed, then joined to straight sections of tubing. The entire frame then is put into a huge die and hydroformed a second time," said Tim Werding, general manager of the company.

Taylan Altan, Ph.D., director of the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) at The Ohio State University, concurs that higher temperatures have great potential. The ERC/NSM is working in a temperature range between 250 and 300 degrees C. Experimentation revealed, however, that the forming medium boiled at less than 250 degrees. The experiments also showed that the heat, which was provided by cartridge heaters inside the dies, wasn't distributed as evenly as necessary.

"We're working on a closed system so we can keep the forming medium under pressure and raise its boiling point," Altan said. "It will circulate the oil so the temperature of the part is consistent and stable."

While he anticipates higher temperatures will increase the use of aluminum, he also is confident that this will boost the use of magnesium too.

"Magnesium has a higher strength-to-weight ratio than aluminum, but it is more expensive," Altan said, "Magnesium castings are used for many applications, but high-temperature processes should increase the use of formed magnesium parts."

Michael Treude of Schuler Hydroforming Inc. and Murray Mason of F & P Manufacturing Inc. attended the welcoming reception. F & P Manufacturing America Inc. sponsored a tour of its factory in nearby Troy, Ohio, where attendees saw its hydroforming line.

Another technology, hot metal gas forming, uses ceramic dies and induction heating to elevate the temperature of the part to be formed. Hot Metal Gas Consortium Inc. has been using this process in research on several metals, including 5000- and 6000-series aluminum alloys and high-strength steel, according to Bill Dykstra of Temper Inc.

New Approaches in Press Technology

Noticing that hydroforming press design had evolved from stamping press design, the design team of AP&T Schfer Technologie GmbH tried to avoid the stamping perspective when it developed its latest press, according to Dale Nichols, president of AP&T North America Inc.

"We didn't even call it a press. We called it a 'device' to get away from the press mindset," said Nichols.

"The core requirement is to hold the tool closed when the hydroforming process achieves maximum pressure," said Colin Macrae, director of AP&T Schfer Technologie GmbH.

"A press really is a big clamp," explained Nichols, "so that's how we approached it. We just asked ourselves, 'What are the basic functions this device needs to perform?'"

Using this strategy, the company designed a press that is smaller and has less stringent installation requirements than a typical press. It stands 5.1 meters high and can be installed on a 6-inch-thick concrete floor. It does not need an elaborate foundation, and it doesn't need a pit, according to Macrae.

Don Clouser of Staub Laser Cutting (right) discusses hydroformed parts with Don Hockin of Ultrafit Manufacturing Inc.

Schuler, SPS, and AP&T all have developed mechanical locking systems that hold presses closed during the hydroforming process. This eliminates the need for hydraulic pressure to hold the press closed, which eliminates the time needed for the hydraulic system to build the necessary pressure. In other words, a mechanical locking system can cut a significant amount of time from a hydroforming cycle.

Schuler has tweaked the hydroforming process at the beginning of the cycle too. In an installation at F & P Manufacturing America Inc. in Troy, Ohio, one of the company's presses uses a technique Schuler calls "quick filling."

"It floods the part with fluid before the press is closed," Werding said. "This saves one or two seconds per cycle. That doesn't sound like a lot, but it is when it's multiplied by 450,000 parts per year."

Lubricants Ease Downstream Processes

ss="bodytext">Lubricant manufacturers are continuing to improve lubricants for the hydroforming industry. Whether a lubricant is intended for bending or hydroforming, it has to meet several criteria in addition to facilitating successful forming. Hydroformers look for lubes that are compatible with hydroforming fluids and downstream processes such as welding and laser cutting.

"For bending, gels are generally better than liquids," according to Paul Brownback, technical coordinator of D.A. Stuart Co. "Gels drip less, so there's less waste, and they don't contaminate the pressure lubricant. Also, they wash off during hydroforming and supply alkalinity to the hydroforming system, which is an additional benefit for hydroforming operations." The company also is continuing to develop pastes, which can be good alternatives to gels.

Don Clouser of Staub Laser Cutting (right) discusses hydroformed parts with Don Hockin of Ultrafit Manufacturing Inc.

Metal Mates Inc. also is developing gel lubricants. The company has a gel-type product that has a consistency similar to that of mayonnaise, according to Keith Karbum, the company's vice president of sales. The product currently is in the final stages of testing for compatibility with laser operations, including welding and cutting.

Doing More With More

The UltraLight Steel Auto Body Advanced Vehicle Concept (ULSAB-AVC) project has done more for the potential use of steel tubing in automotive applications than was initially anticipated.

ULSAB-AVC is the culmination of the ULSAB program, which was initiated in 1994 to demonstrate steel's continuing viability in automotive applications. Related projects include UltraLight Steel Auto Closures (ULSAC), which encompasses doors, hoods, deck lids, and hatches, and UltraLight Steel Auto Suspension (ULSAS), which focuses on suspension components. These projects resulted in two vehicle designs: a two-door model and a four-door sedan.

Originally the amount of tube was 5 percent of the mass of the project automobile. Through the life of the project, it rose to more than 16 percent of the car's mass, according to Paul Schurter, manager of automotive market development and product applications for Dofasco Inc. Main project results, compared to the benchmark average in 1995, include 25 percent less mass, 80 percent more torsional rigidity, 52 percent more static bending rigidity, and 58 percent improvement in first vibrational mode. In addition, it meets or exceeds crash requirements and costs 3 percent less than other body structures in its class.

Fuh-Kuo Chen, director for the Manufacturing Automation Technology Research Center (MATRC) of the National Taiwan University (right), discusses metal forming technology with Chi-Mou Ni, principal engineer, General Motors Body Engineering Center.

These results were achieved by using a variety of advanced materials and technologies and unusual approaches to vehicle design. One hundred percent of the materials are high-strength steels; 80 percent of these are advanced high-strength steels. Tubes appear in the frameless door structure, and several tubular structures—hydroformed and otherwise—appear in the suspension of the concept vehicles. All told, tube accounts for 16.6 percent of the mass of the four-door version. This includes hydroformed tube (7 percent of the vehicle's mass) and tailored hydroformed tube (6 percent).

The results of this project show that not only do advanced steel alloys have strong potential for future growth, but so does one of the hottest advanced metal forming technologies—hydroforming.

AP&T Schfer Technologie GmbH and AP&T North America Inc., www.apt.se.
D.A. Stuart Co., www.dastuart.com.
Dofasco Inc., 1330 Burlington St. East, Hamilton, ON L8N 3J5, www.dofasco.ca.
Engineering Research Center for Net Shape Manufacturing (ERC/NSM) at The Ohio State University, http://nsm.eng.ohio-state.edu.
F & P America Manufacturing Inc., www.fandp.com.
Metal Mates Inc., www.metalmates.net.
Schuler Hydroforming Inc., www.schulergroup.com.
Siempelkamp Pressen Systeme GmbH & Co. KG, www.sps-pressen.de.
Temper Inc., P.O. Box 755, Rockford, MI 49341, 616-293-1349.
Tube & Pipe Association, International, www.tpatube.org.
ULSAB, www.ulsab.org;
ULSAB-AVC, www.ulsab-avc.org;
ULSAC, www.ulsac.org;
ULSAS, www.ulsas.org.
Eric Lundin

Eric Lundin

FMA Communications Inc.
2135 Point Blvd
Elgin, IL 60123
Phone: 815-227-8262

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