Introduction
To keep a competitive edge in the ever-changing metal fabrication market different processes have to be explored. One of these processes is called hydroforming, which has been around for some time but with recent developments could prove to be profitable.
Hydroforming Process
Hydroforming consists of two divisions, tube and sheet metal forming. The two divisions are processed using similar techniques that are developed to accommodate the different products. The basic principals for the different techniques are to utilize fluid pressure to form a part. Hydroforming differs from conventional deep drawing processes in that it replaces the die tool with a rubber diaphragm that is backed with fluid pressure to form the part to the punch tool. Relating this concept to a tubular part, the tube is placed in a die then the tube is filled with a fluid pressure to form the part to the die. Standard hydroforming techniques start with a CNC bent tube or sheet of metal. The part is then placed in the tool, followed by the cycling of the press to clamp the tool shut. From this point I will focus on the forming of tubes for clarity. Knowing the different techniques can also apply to sheet forming. The tube is filled with a “low-pressure” fluid that forms the part to the die. Resulting is a part that conforms to the general shape of the die. “Low pressure” forming is ideal for parts with large radii, simple cross sections and parts with flat surfaces. If a “high pressure” is used the part will conform to complex cross sections with small radii. The drawback to high pressure forming is that due to friction the part will have non-uniform thickness. The latest buzz word in the hydroforming industry is a process called “active hydroforming”. In active hydroforming the part is placed in the tool. However, before the tool is cycled shut a fluid pressure is applied to expand the part while holding a uniform thickness. From here the press is cycled and the part is formed. The resulting part will have uniform thickness and form to complex cross sections. Active hydroforming takes the strong points from high and low pressure hydroforming and combines it to one process. Let’s lead the market in this advanced hydroforming process. Chamber pressure and part lubrications are critical parameters in the hydroforming process and requires some part testing to develop the right mix for the two. The forming press must be able to overcome the die separation force that is generated by the pressure in the tube. Die separation force can be calculated knowing force = pressure * area, where area is equal to the die cross sectional area.
Hydroforming Benefits
Hydroforming has benefits in part characteristics and process flow compared to conventional forming techniques. The hydroforming process allows close control of perimeters (ie. fluid pressure and lubrication) to prevent wrinkling and tearing of parts. Deeper draws are also possible using this procedure. The process yields itself to a higher quality part that is stiffer, more resistant to buckling and less likely to have surface defects. With hydroforming, advantages of hollow tube forming techniques can replace the conventional box section stamping assemblies which are costly and require large assembly areas and massive amounts of welding. This leads to part integration and forming techniques that will lend nicely to design for assembly. Improved process flow comes from decreased die wear because it is not metal on metal forming, it is metal on fluid forming. Tooling costs are reduced by up to 40% because only half of the tool has to be purchased the other half is accommodated by the fluid. Equipment requirements are similar to that of conventional forming with similar press sizes. There are machines out there that can hydroform and perform standard stamping operations. This lends itself to a very flexible operation The final benefit to hydroforming is an expanding market. Magna International landed a $367 million annual sale to GM for light truck frames to be hydroformed. Magna won the bid against conventional forming techniques and traditional suppliers. The big news is not that GM switched suppliers but switched processes. They must have been impressed with Magna’s hydroforming technology to adapt a relatively new process on such a critical component in the trucks make up. Magna’s executive vice president said, “We think the market for hydroforming products could be as high as $6 billion.” This is a great security blanket when looking at investing in the hydroforming process. It is estimated that 15 years ago 10% of steel in a typical North American built vehicles was tubular, where in today’s vehicles it is closer to 16% resulting in an expanding hydroforming market.
Hydroforming Risks
With every process there are risks. Hydroforming is no exception. Hydroforming does not lend itself to low volume runs, there needs to be a high volume of parts to spread the tooling costs. There are also a couple of specific drawbacks which relate directly to the process. Pierced holes have small deflections around the area of impact. For tube forming the tube has to take a shape that is workable by the tube bender. The risks show that hydroforming is not the cure all but has great potential in the right market.
Conclusion
Hydroforming is a process that should be looked at in order to keep on top of this every-changing industry. The proof is out there that the process is advancing. Lets not miss the chance to lead the industry into the future, marketing this process.
References
Hard Print
1) English, Bob. "GM shifts technology suppliers for '98 trucks." Automotive News Apr. 29, 1996: 1+.
2) Kapakjain, Serope Manufaturing Engineering and Technology, Third Edition New York: Addison-Wesley PC, 1995.
3) Mason, Murray. "Exploring Tube Hydroforming Methods." The Fabricator Oct. 1996: 38-40.
4) "One Hydrulic Press; Three Forming Techniques." Manufacturing Engineering Dec. 1996: 18.
Internet
5) "Hydroforming" American iron & Steel Institute.
6) "Hydroforming of a Square Box" Abaqus.