The New Charge In Hydroforming
A custom-designed intensifier helps speed the process with a pre-charged, nitrogen gas pressure tank that provides water pressures of up to 58,000 within a matter of seconds.
Just a few years ago, much was being written about the process of hydroforming: its advantages and the fact that it was being promoted as the panacea for achieving global competitiveness. The advantages of hydroforming, which include dramatic reductions in part weights, reduction in the number of components and assembly operations required, lower in-process inventories and labor costs, and improved strength and quality, were what every manufacturer was looking for.
Unfortunately, many found the reality of developing the hydroforming process and implementing it into their production strategies to be not as straightforward as anticipated. In some cases, it created as many problems as it was supposed to solve. This was due, in part, to the fact that North America did not have many experienced suppliers that were totally in tune with hydroforming methods. Also, hydroforming requires in-depth pre-development analysis of final product strength versus raw material yield and tensile strength, bending and pre-forming steps, tooling designs, and tolerances, plus finding the equipment capable of producing parts in a production-volume environment.
Some automotive builders are now using hydroforming for frame rails, engine cradles, and in door assemblies, while aerospace firms are finding that hydroformed tubing can be used effectively in fuel systems. The home appliance industry is also discovering uses, such as cabinet strengthening and even some exterior features like door handles.
Speeding the Transition to Hydroforming
For over thirteen years, 3-Dimensional Services of Rochester Hills, Michigan, has been helping these companies and industries make the transition to hydroforming a little easier-and significantly faster. The company combines an expansive list of rapid prototyping capabilities with the additional resources of its subsidiary company, Urgent Design & Manufacturing. As a result, the two firms are able to produce rapid prototype hydroformed parts 50% to 70% faster than traditional prototype shops, and up to 90% faster than production companies. According to Mike Finta, Director of Engineering at 3-Dimensional Services, a major contributor to the time savings has been the reduction of the typically long intervals to make dies, which he estimates at up to 36 weeks at most production firms.
"We use CAD/CAM networking and CNC machining centers to produce the accurate tooling," notes Finta. "Usually, we're able to make tool steel dies within a six-week time frame, while, for some applications, we've used aluminum alloys for the dies. These can take as little as one week to finish because of the increased machining speeds and feeds afforded by the 'soft' material."
A second, more recent contributor to the firms' fast hydroforming capabilities has been the acquisition of a U.S.-built, patent-pending intensifier that is custom designed to 3-Dimensional Services' specifications. Along with pumps, the intensifier uses a series of hydraulic cylinders and a pre-charged, nitrogen gas pressure tank to provide the water pressuresup to 58,000 psithat the hydroforming operation requires. Importantly, the intensifier-type operation is quick: working pressures up to the 58,000-psi maximum are achieved in as little as two seconds. As a result, cycle times for hydroforming parts are fast and economical, and they simulate what can be expected in actual production environments.
"This acquisition was an important step for us and our clients," says Finta. "Our first hydroforming system was one which we had built and jury-rigged ourselves. While it was able to produce quality prototype parts, it could take up to a half-hour to complete a cycle. It was critical that our efforts more accurately reflect what could be expected in production. This new system not only produces the parts, it provides our clients with the production-like data that assures both a successful implementation and launch, plus continued quality at the higher, production volumes. We are not only establishing the integrity of the prototype design, but also the confidence in the production process."
Tracing Hydroforming's Advantages
Briefly, hydroforming consists of the high-pressure clamping of a piece of tubing into a die, sealing the ends of the tubing, and introducing high water pressures in the I.D. of the tube. The pressure elongates and stretches the tube to the shape of the machined die cavity; structural modifications and work hardening, which can develop higher strength properties in the formed part, also occur. Because the pressure is applied to the workpiece in all directions at once, stress is also equally applied. Therefore, unlike in other forming operations, there is no spring back to compensate for. Thus, whereas a typical forming operation might require up to ± 4mm tolerance, the hydroforming operation can achieve tolerances as tight as ± 0.5mm.
Prior to the hydroforming process, tube sections may be bent to required shapes, and pre-forming operations may be necessary or desirable to make the hydroforming step easier and faster. "Because each of these operations will typically work-harden the piece and add strength, a thorough knowledge of the metallurgy of the raw material and how it will be affected is required, so that the required finish product specifications are met," remarks Finta.
But it is just this strength-increasing characteristic of the hydroforming process that makes it a valuable manufacturing tool. "In most applications, we can start with a lighter-weight tubing and develop the strengths, in specific areas, without the need for additional support components or bracing, without the need for welding, and without using heavier materials," says Finta.
As part of their rapid prototype hydroforming services, the companies provide both low-pressure (10,000 to 15,000 psi) and high-pressure (over 15,000 to 58,000 psi) application capabilities, along with static and axial feed forming. In axial feed forming, the ends of the tubing are pushed into the die cavity simultaneously as water pressure is applied, thus providing additional material to 'flow' (under the high pressure). This permits deeper draw configurations and more expansion in localized areas, in addition to maintaining optimum, consistent wall thickness throughout the part.
In addition to the intensifier system, 3-Dimensional Services can utilize either a 5000-ton press with 6-ft x 12-ft bed, or a 7000-ton press having a 6-ft x 12-ft bed to mount the dies used to clamp and secure the tubing. Also part of their hydroforming capabilities are a CNC tube bender with up to 3.5-inch tube diameter capacity, and a wide selection of hydraulic and mechanical presses for any pre-forming steps that may be required. Complementing the production capabilities are full engineering services that include part design and analysis for manufacturing intent, and a fully in-house prototype-to-production tool and die build area.
Just how fast can the rapid prototype hydroforming process provide parts? Mike Finta provides an answer. "We were working with one customer, developing hydroformed substitutes for automotive suspension components," Finta began. "While they (the customer) were still trying to complete their computer simulation and analysis of the virtual part, we were able to finish actual parts. In another instance, one client's computer analysis indicated that their part could not be made by hydroforming. When we completed the part in question, they went back into their computer program and changed the analysis parameters to match the finished part (reverse engineering analysis). The potential for hydroforming is still being explored and realized, but now we can do it in practice as well as in the virtual world."
3-Dimensional Services, Urgent Design & Manufacturing, and a third sister company, Urgent Plastic Services, provide rapid prototyping for other processes in addition to hydroforming. These include machined, mold and injection mold, cast, stamped and formed fabrications, high-definition stamping (intricate shapes and maximum elongation) of super alloys, and assembly operations.
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