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Hydroforming
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Hydroforming (or hydramolding) is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces.
One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.
Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die.
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Encyclopedia
Hydroforming (or hydramolding) is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces.
One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.
Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die. To hydroform aluminum into a vehicle's frame rail, a hollow tube of aluminum is placed inside a negative mold that has the shape of the desired end result. High pressure hydraulic pistons then inject a fluid at very high pressure inside the aluminum which causes it to expand until it matches the mold. The hydroformed aluminum is then removed from the mold.
Hydroforming allows complex shapes with concavities to be formed, which would be difficult or impossible with standard solid die stamping.
Hydroformed parts can often be made with a higher stiffness to weight ratio and at a lower per unit cost than traditional stamped or stamped and welded parts.
This process is based on the 1950s patent for hydramolding by Milton Garvin of the Schaible Company of Cincinnati, OH. It was originally used in producing kitchen spouts. This was done because in addition to the strengthening of the metal, hydramolding also produced less "grainy" parts, allowing for easier metal finishing.
Process schematic
Sheet hydroforming
In sheet hydroforming there is Bladder forming (where there is a bladder that contains the liquid, no liquid contacts the sheet) and hydroforming where the fluid contacts the sheet (no bladder). A work piece is placed on a draw ring (blank holder) over a male punch then a hydraulic chamber surrounds the work piece and a relatively low initial pressure seats the work piece against the punch. The punch then is raised into the hydraulic chamber and pressure is increased to as high as 15000 psi which forms the part around the punch. Then the pressure is released and punch retracted and hydraulic chamber lifted and the process is complete.
Tube hydroforming
In tube hydroforming there are two major practices: high pressure and low pressure:
Under high pressure the tube is fully enclosed in a die prior to presurization of the tube. In low pressure the tube is slightly pressurized to a fixed volume during the closing of the die (used to be call the Variform process).
In tube hydroforming pressure is applied to the inside of a tube that is held by dies with the desired cross sections and forms. When the dies are closed on the tube the ends are sealed and the tube is filled with hydraulic fluid the internal pressure causes the tube to conform to the die. Punches may also be incorporated in the forming die to punch holes in the work piece during the forming process.
Explosive hydroforming
Industrial hydroforming machines use a piston to generate pressure in the hydraulic fluid used in hydroforming, but an experimental alternative is the use of explosives to generate the pressure. Called explosive hydroforming, this method places an explosive charge, with or without an additional working fluid, on the high pressure side of the material. When the explosive is detonated, the pressure forces the working material into the die, at pressures of up to millions of pounds per square inch. See also explosive welding, which allows metals of different types to be bonded at a microscopic level. Since both explosive hydroforming and explosive welding use similar techniques, it is possible to combine the two methods to both shape and weld metals simultaneously.
Setup and equipment:
Tools and punches can be interchanged for different part requirements.
Typical tools
One advantage of hydroforming is the savings on tools. For sheet metal only a draw ring and punch or male die is required. The bladder of the hydro form itself acts as the female die eliminating the need to fabricate a matching female die. This allows for changes in material thickness to be made with usually no necessary changes to the tool. However dies must be highly polished and in tube hydroforming a two-piece die is required to allow opening and closing.
Geometry produced
Another advantage of hydroforming is that complex shapes can be made in one step. In sheet hydroforming with the bladder acting as the female die almost limitless geometries can be produced. Tube hydroforming can produce many geometric options as well but is limited by a few factors: Forming pressure, tube wall thickness, material yield strength and die design.
Tolerances and surface finish
Hydroforming is capable of producing parts within tight tolerances including aircraft tolerances where a common tolerance for sheet metal parts is within thirty thousandths of an inch. Sheet metal hydroforming also allows for a smoother finish as draw marks produced by the traditional method of pressing a male and female die together are eliminated.
Effect on work material
When a blank is hydroformed the metal flows around the die rather than stretching, which produces less material thinning, and also reduces the rate of work hardening which helps eliminate the need for an annealing process on some parts that might otherwise require further forming operations.
Examples
Notable examples include:
- Satellite antennas up to 6 metres in diameter, such as those used in the Allen Telescope Array.
- The brass tube of Yamaha saxophones.
- The process has become popular for the manufacture of aluminium bicycle frames. The earliest commercially manufactured one being that of the Giant Manufacturing Revive bicycle first marketed in 2003.
- Many motor vehicles have major components manufactured using this technology, for example:
- The technique is widely used in the manufacture of engine cradles. The first mass produced one was for the Ford Contour and Mystique in 1994. Others from a long list include the Pontiac Aztek, the Honda Accord and the perimeter frame around the Harley Davidson V-Rod motorcycle's engine.
- As well as engine cradles, the main automotive applications for hydroforming are suspension, radiator supports and instrument-panel support beams. The first mass produced automotive component was in 1990 with the instrument panel support beam for the Chrysler minivan.
- Various vehicle bodies and body components, the earliest mass produced one being the 1997 Chevrolet Corvette. A selection from many examples are the Ford F-150, 2006 Pontiac Solstice and the steel frame inside the John Deere HPX Gator Utility Vehicle.
Controversy
Hydroforming is also used in the construction of non-transportation items. Notable among these is a patent controversy in the use of the process to produce steel drums. A pair of US inventors applied for a patent using this process, but it is accepted that Trinidad and Tobago Instruments Ltd. had used this process previously in the production of steel drums.
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