Forming with Fluids
- August 29, 2019
If you’re looking for a way to cut forming die costs in half, you’ve come to the right place.
Skeptical about cutting die costs in half? It’s actually an understatement. Quite possibly, a big one. That’s according to Caleb Dixon, sales engineer and hydroforming expert at St. Louis-based Beckwood Press Company. Dixon says the company’s Triform line of sheet hydroforming presses not only reduces die costs by 50 to 90 per cent compared to traditional press tooling, but often improves part quality as well, offering a handful of customer examples as proof.
Notes from the field
Steelville Manufacturing Co. is a leading aerospace supplier that has used traditional forming methods for decades to supply metal parts to companies such as Boeing, Lockheed Martin and Sikorsky. After switching to hydroforming, Steelville cut the time needed to produce dies in half, while also eliminating a fair amount of the buffing and polishing on the 34 part numbers transferred from the company’s press brakes.
A large aerospace job shop in Thailand, Jinpao Precision Industry Co. Ltd., has found that the complex parts it was producing on its stamping machines can be made “significantly faster” on a hydroformer. Setup time is now minutes vs. hours, parts no longer have the tooling marks, wrinkles, and scratches common to mechanical forming methods, and cycle time has been reduced thanks to hydroforming’s ability to form multiple parts in a single cycle.
Aerosud Holdings, which manufactures wing components for the Airbus 320, was forced to anneal parts a total of six times in order to draw a 114 mm (4.5 in.) diameter aluminum canister 165 mm (6.5 in.) deep. Despite these time-consuming steps, scrap rates remained high, and downstream welding processes were impacted. By switching to hydroforming, however, annealing is no longer necessary. Production costs were lowered by an estimated 25 per cent. And because hydroforming generates more uniform pressure, engineers were able to move from 2 mm (0.080 in.) to 1.6 mm (0.063 in.) thick material, reducing raw material costs by 20 per cent.
Nor is today’s advanced hydroforming technology limited to newcomers; many Triform customers have been using it for decades, Dixon notes, augmenting the capabilities of their larger, aging presses with newer, more nimble equipment. Aside from significantly prolonging the life and uptime of their legacy machine tools, they were able to bring cycle times of 90 to 120 seconds down to 20 seconds or less on the new machines. Similarly, tool changes went from 30 minutes or longer to just seconds. “Because of this success, many companies have moved a large majority of their overall production to a Triform press,” he says.
Dixon can offer additional examples, but by this point, you might be wondering how hydroforming works and whether it’s a good fit for your shop. For starters, hydroforming isn’t for everyone. Car bumpers and quarter panels are a stretch, primarily because of the high volumes associated with such automotive work. Nor will computer chassis or any parts by the millions be hydroformed anytime soon. On the contrary, hydroforming is ideally suited to high-mix, low-volume manufacturers in the aerospace, defense and medical industries, especially those trying to gain a competitive edge through increased flexibility, improved part quality, lower tooling costs and shorter setup times.
Interested? Dixon says there are several things you should know. First, hydroforming is a loosely-defined term used across a variety of industries, and includes both tube and sheet forming. This article discusses only the latter. “In our case, we offer two distinct sheet hydroforming processes: fluid cell and deep draw.” The first is best suited for relatively shallow parts and parts with open corners. Many aerospace suppliers use it to produce structural components, ribs, panels and brackets, for example. Deep draw works as the name describes. It’s typically used to produce hemispheres, canisters and many complex engine components. This process can also be used for shallow parts with curved flanges where wrinkling might be a problem.
Both processes rely on a universal diaphragm, or membrane, that varies in thickness depending on part requirements. It is positioned above the workpiece where the ram would sit in a conventional press; think of it as the upper die half of a traditional forming die. This diaphragm is the workhorse of the system, offering pressures up to 20,000 psi and acting as a universal die half for any forming block, female cavity or punch tool.
With fluid cell hydroforming, setup is simple: place a male forming block, female cavity, or even multiple, dissimilar dies onto the machine bed, and position a net-shape blank on top of each die. The circular or rectangular ram containing the diaphragm is then pressurized while it extends over the bed and encloses the die. Depending on the machine and forming pressure required, complete parts can be formed anywhere from 15 seconds to over two minutes.
Deep draw hydroforming, on the other hand, requires a male punch tool and a draw ring or opening in the bed. A blank is placed over the draw ring,
and as the punch is driven upward through the opening, the material begins to lock on to the punch using low pressure to allow for material slide. As the material drives upward into the diaphragm, the punch height and forming pressure increases. In this process, the punch heights and pressures are fully programmable to allow for enhanced part quality and reduced scrap.
Reaping the benefits
That’s it in a nutshell. Dixon notes that the process itself is nothing new, although modern technology has greatly improved part accuracy and consistency compared to the hydroformers of yore. “Our processes mimic those of the old Cincinnatis and Versons developed back in the 1940s and 50s,” he says. “Many of those machines are still in existence and are still making parts every day, but they are manually operated and require a skilled craftsman in most cases to form a good part. Triform has removed the guesswork and process variability with an automated control system and advanced electronics.”
Dixon notes several additional advantages of hydroforming. “The diaphragm provides even pressure on every square inch of the part’s surface. This results in reduced wrinkling, thinning and tearing and allows for the ability to form complex part geometries with inexpensive tooling and little to no secondary finishing afterwards.”
That said, hydroforming isn’t for everyone. The cycle times are admittedly slower compared to mechanical forming methods, and hydroforming isn’t well-suited for box-shaped parts, where hard tooling might be needed to generate tight corner radii. But unlike legacy hydroforming equipment and traditional draw forming presses, a modern sheet hydroforming machine can form any size part that fits within its work envelope.
Finally, there’s lower tooling cost. The reason for the advertised 50 to 90 per cent reduction should be clear by now—only one die is required, and there’s no need for springs, guide pins, strippers and all the other accoutrements of forming work. “Instead of spending hundreds of thousands on a progressive forming die, a company might spend $10,000 or less—often much less,” says Dixon. “Some of our customers are even 3D-printing their own tools in-house.”
Changeover time is also much faster, Dixon adds. “This is one of the biggest reasons why hydroforming is ideal for high-mix, low-volume production. Imagine forming multiple workpieces in a single operation by simply placing a tool or tools on the machine table, loading a blank and pushing cycle start. If you are looking at an annual part volume of 75,000 or less for a single part, then hydroforming is a very strong contender; if you’re making a variety of parts in smaller quantities, hydroforming is a slam dunk.” SMT