Pressing Forward

evo•lu•tion (noun): a process of continuous development; the progression from a simple form to one of greater complexity and capability

Using high-pressure hydraulic fluid in a flexible rubber bladder (diaphragm) to shape sheet metal against a single tool – known as the sheet hydroforming process – has been in use for decades. However, in recent years, new developments from the Pryer Technology Group (PTG), Tulsa, OK, look to catapult this dark art into a controllable, repeatable, and useful process for forming a range of sheet metal parts for aerospace, as well as a broad range of industries.

Limited Availability
Up until 2008, when PTG began manufacturing Triform presses, aerospace manufacturers wanting to implement sheet hydroforming equipment for the manufacture of aircraft components had two options, with neither being tremendously appealing.

First, manufacturers could source used equipment. Since manufacturing of the majority of these was originally between the 1950s and 1970s, the hydraulic and controls systems were long outdated. Readily available technical support for such dinosaurs was also difficult to find, resulting in high maintenance costs and increased downtime. In addition, as is often typical of decades-old equipment, most used sheet hydroforming presses were extremely large and heavy, making the transportation and installation of such equipment an expensive proposition. Once this equipment was in place, it stayed in place. Battling through this range of negative attributes, manufacturers still sought out these used sheet hydroforming presses because of the capabilities inherent with the process and the edge those capabilities delivered to aerospace component manufacturers.

If the first option was not enough of an obstacle, the second option was often equally unappealing. Manufacturers could purchase a new sheet hydroforming press from a European supplier who, depending on the time of the purchase, was often the only company in the world manufacturing new equipment. Because of this exclusivity and the complex nature of the equipment, the price for new sheet hydroforming equipment was usually significant and often beyond the reach of many manufacturers interested in obtaining sheet hydroforming machines. 

 

Left: This 16" Fluid Cell Model features an 8-second fast-cycle and 5,000psi forming capacity. Center: Before Triform, manufacturers faced the installation and maintenance of this type of hydroforming equipment, which is no small challenge Right: Here are a range of the various products successfully produced on the new Triform Sheet Hydroforming presses.

Answering Needs
Scott Pryer, president, PTG, having decades of experience in both the aerospace parts and the custom hydraulic press manufacturing business, saw the need existing for new, technology-driven sheet hydroforming solutions.

Since 2008, we have been manufacturing Triform presses in the United States for some of the world’s most notable aerospace manufacturing companies,” Pryer explains. “For low volume sheet metal forming, Triform Sheet Hydroforming provides users with a great competitive advantage, allowing companies to not only complete existing projects with greater efficiency but to go out and compete for new projects they previously could not pursue due to the lack of technological capabilities.”

Triform Sheet Hydroforming presses are engineered with high-performance sheet metal forming in focus, while maintaining value in terms of the up-front capital expenditure. Offering a dramatic reduction in tooling costs and tooling lead-time, implementating these machines is resulting in lower manufacturing costs for a wide variety of forming applications.

“Another competitive advantage Triform owners gain with our technology-focused solutions involves the industry’s changing labor force. By implementing our metal forming technology, companies are not as dependent on highly skilled labor in an era where there is an aging skilled manufacturing labor force,” Pryer notes. “Training, new part development, and production are all easier with new, computer driven controls and accurate, repeatable hydraulic systems. This offers manufacturers the ability to form complex geometric shapes with greater consistency without having to rely on those few experienced employees who know the ‘magic formula’ for successfully formed parts.”
 

16" x 48" Tray Press at 10,000psi Forming Capacity

Fluid Cell
Many parts with shallow features are well suited to the simple downward action of a fluid cell sheet hydroforming press.

Sometimes referred to as bladder-only forming, fluid cell sheet hydroforming uses only the flexible rubber bladder or diaphragm to shape sheet metal against a single tool or form block. This unsecured form block is placed on the flat surface of the press bed, allowing the downward pressure of the bladder to form the material around the tool.

“When using this process, multiple parts can run during a single cycle, as long as the tools and blanks fit within the working areas of the press,” Pryer explains. “Fluid cell presses are often considered a high-performance alternative to traditional rubber pad forming. However, while pad forming sheet metal over a form block typically places a maximum pressure of approximately 1,250psi on the part, sheet hydroforming presses yield between 5,000psi and 20,000psi on the part, depending on the specific model.”

Moreover, unlike traditional pad forming pressure, which varies across the surface of the part, sheet hydroforming places uniform pressure on every square inch of the part’s surface, resulting in net shape part production with better definition, reduced handwork, and fewer finishing hammers.

Deep Draw
How does fluid cell forming differ from deep draw sheet hydroforming? For applications that require a controlled flow of the material, such as deep drawn parts or those with curved geometries, which have the potential to wrinkle during the forming process, deep draw sheet hydroforming presses are the ideal solution.

“Utilizing a computer-controlled deep draw process the downward-acting bladder primarily acts to hold the material during pressurization, as the tool extends atop a hydraulic punch cylinder,” Pryer says. “This draws the material into the bladder, allowing it to flow as needed, eliminating wrinkles that would occur during fluid cell or rubber pad press forming, and allowing for much greater part height.

“And, through a simple push of a button, the Triform deep draw press quickly transforms to the fluid cell process.”

A step-by-step look at the fluid cell hydroforming process and the progressive increase in PSI.

Old vs. New
Sheet hydroforming presses that are considered outdated, are models featuring manual controls consisting of levers and valves. Controlling these presses is anything but repeatable, so achieving relatively consistent results is not typical.

As is often the case, older hydroforms do not actually achieve the pressure set by the operator. There are attempts to set the target pressure, but those settings are more of a suggestion than a reality. Older equipment has a control switch that lets the operator change (suggest) forming pressure every ½", 1", or 2" throughout the draw, but again, the reality is that even if the operator chooses the finite control setting every ½", the punch cylinder moves past those changes faster than the machine can react. Because of this, everything becomes an estimate, which is exactly why so many companies operating aging sheet hydroforming equipment do so in cooperation with an experienced operator who has learned the touch and feel of the press over decades. However, production is negatively affected when these seasoned individuals take time off.

“Unlike the evolved sheet hydroforming presses of today, the pressure achieved on older hydroforms varied from part to part and even varied throughout the course of the day due to various factors,” Pryer explains. “On many of the more critical jobs, operators would fight the high scrap rates associated with the variation of oil temperature and even air leaks associated with the controls. When starting up the machine in the morning, while the oil was cold, machines operated noticeably differently when compared to its operations later in the day, as temperatures increased.”

In addition, on deep draw sheet hydroforming, a mechanical limit switch controls the punch height when tripped at the desired height. In many cases, the tolerances for the heights were ±0.015", and if the application required greater accuracy, there would be a need to develop special tooling, which was not guaranteed to work in every case.

“Transitioning from the older equipment to the new controls, the customers will truly see reduced set-up time and a dramatic reduction of in-process scrap. Modern Triform sheet hydroforming presses tightly control both the bladder pressure (down to 1% of full scale) and punch position (±0.002") for superior results and near absolute repeatability,” Pryer states.
 

Deep Draw Hydroforming Process

Resurgence in SH
“Perhaps the most significant development to impact sheet hydroforming in recent years involves the control technology now available to part developers and machine operators,” Pryer notes. “Replacing the manual knobs and levers of old are highly refined, yet easy to use CNC control platforms. No longer must a manufacturer rely on the experience and the touch and feel of an artisan. Recipes can now be stored easily through the press HMI, with recall via part number.”

Setup and troubleshooting has never been easier, and once a recipe is proven, it can be stored for future use. In most cases, a repeat job can be setup and the first part successfully made in less than 10 minutes.

Another powerful control feature, reducing new part-development time, is the ability for the operator to pause and open the chamber at a specific point in the forming process. This unique capability enables the visual inspection of the part’s step-by-step progression. From this point, the cycle can be continued or terminated as directed by the operator.

Fluid Cell-Formed Aerospace Part with Tool

“With the open feature, the impact each recipe step value has on the material can be visually verified, with appropriate adjustments made through the human machine interface, reducing part development time,” Pryer explains.

Modern sheet hydroforming presses also benefit from 21st century design technology.

“Today’s engineers have access to modern design software, eliminating much of the guesswork and manual aspects of the design process. Employing finite element analysis (FEA) allows for the simulation of forces eventually applied to the press, enabling the design of structures for infinite life.

Today’s sheet hydroforming presses are smaller, more portable machines, which, in most cases, do not require expensive pits or special foundations. Despite the reduction in size and weight, these machines are well equipped to handle the long-term stresses associated with the technology.”

Finally, aging machine tools are a never-ending headache. Companies previously having worked with aging machine tools, for which service, support, and replacement parts have long since left the building, know how this lack of available replacement parts and service and support resources becomes a major concern.

“Because of these issues, whenever possible, Triform Sheet Hydroforming presses come with standard, off-the-shelf components, often available from local parts suppliers found across the globe,” Pryer states. “Our focus is on selling quality sheet hydroforming equipment; not replacement parts.”

Progression of the Fluid Cell

Present Day
The benefits really are clear.

Specifically engineered to apply consistent, multi-directional force on the part, Triform presses deliver uniform pressure as it draws around the tool, greatly reduces stretching or thinning of the formed areas.

“This technology results in less than 10% variation from the blank to the finished part thickness on deep drawn parts,” Pryer says. “Because of this minimized thinning, starting material thickness can be reduced, in turn allowing for a significant reduction in material costs without sacrificing part strength.

Triform presses reduce the time required for new part development, minimizing scrap and lowering material costs. Sophisticated, yet easy-to-use controls let the operator manipulate the process variables throughout the forming cycle (in up to 30 recipe steps). Both bladder pressure and punch position are programmable for accuracy and repeatability down to 1% of full scale and ±0.002".

With all of the above benefits, together with the reduction or elimination of hand finishing and other labor costs, Triform Sheet Hydroforming has really entered the 21st century.

Triform Sheet Hydroforming
Tulsa, OK and St. Louis, MO
www.triformpress.com