Hydro forming is a relatively new process, which uses water pressure to form complex shapes from sheet or tube material. Design studies suggest that automobiles can be made much lighter by using hydro formed components made of steel. Structural strength and stiffness can be improved and the tooling costs reduced because several components can be consolidated into one hydro formed part.
As the automobile industry strives to make car lighter, stronger and more fuel efficient, it will continue to drive hydro forming applications. Some automobile parts such as structural chassis, instrument panel beam, engine cradles and radiator closures are becoming standard hydro formed parts.
The capability of hydro forming can be more fully used to create complicated parts. Using a single hydro formed item to replace several individual parts eliminate welding, holes, punching etc... Hydro forming simplifies assembly and reduce inventory.
The process is quite simple - a blank with a closed-form, such as a cylinder, is internally pressurized using fluid. The fluid is frequently water. The applied pressure is usually in the range 80-450 MPa. Its resultant plastic expansion is confined in a die of the desired shape.
Fig. Equipment for hydro forming
Hydro forming equipment consists of a hydraulic hydro forming press, pressure intensifiers, hydro form water system, and a hydro forming unit
Fig. Hydro formed components
Fig . Hydro formed automobile fig . Hydro formed bellows, beginning
Component with cylinders
Fig. Hydro formed handle bar fig. Hydro formed T-junction
Fig. The high pressure hydro forming machine in
Use at British Steel
2. METHODS OF HYDRO FORMING
There are two types of Hydro forming
1. Tube Hydro forming
2. Sheet Hydro forming
Sheet hydro forming converts the irregular shaped material into a finished and uniform thickness sheet. The tube hydro forming process is used to form parts in materials such as steel tubes and aluminum extrusions by applying hydraulic pressure.
2.1. TUBE HYDRO FORMING
Tube hydro forming is a kind of soft-tool forming technology and developed rapidly in the past decades. For taking tubes as processing blanks and liquid as flexible punch, it is more suitable for manufacturing special tubular components, such as different kinds of hollow shafts, discharge pipe of automobile & aeroplanes, sectional pipes etc..
Tubes were placed in the die and sealed on the end. Then under the co-action of compressive axial force and internal pressure, it is forced to deform from elastic stage to plastic stage. With the increasing of the applied load, the deformation increased correspondingly. Finally, under the extremely high pressure, the tube assumed the internal contour of the die precisely. In tube hydro forming, a cylinder is pressurized internally with 80 to 450 MPa pressure by a fluid like water.
Compared with traditional processing technology, tube hydro forming always manufactures components at one step. So it can enhance part quality, such as
tighter tolerance and increase rigidity, and lower production costs and reduction in production cycle. In this method the tube is placed in die and as press clamps the die valves, low pressure fluid is introduced into tube to pre form it. One the maximum clamping pressure is achieved, the fluid pressure inside the tube is increased so that tube bulges to take internal shape of the die. Simultaneously additional cylinders axially compress the tube to prevent thinning and brushing swing expansion. It is possible that some parts of the component thin excessively during hydro forming. This can sometimes be rectified, in the case of tube hydro forming, by applying axial pressure to feed material into the bulges, thereby reducing bulging.
Fig. Schematic illustration of the hydro forming of a bulge in a tube
fig. Tube Hydro Forming
2.11. TUBE HYDRO FORMING PROCESS
The hydro forming process varies slightly depending on the component, but hereâ„¢s a general look at the overall procedure.
1. First, a computer-controlled machine cuts a length of straight Ëœmetal tubingâ„¢, also called a blank, to the proper size and feeds it into a machine, where it is pre-bent into the approximate contour of the finished part.
2. Next, the blank is inserted into the die, which is pumped full of highly pressurized water.
3. The water fills the blank, which conforms to the die walls. The water shapes the blank into the desired form.
4. At the same time, the machine compresses the ends of the blank, which eliminates thin spots on the outer wall of the blank, and prevents wrinkling on the inner wall, as well.
5. The component is then removed from the hydro forming press, the ends are
trimmed and mounting holes are pierced with lasers and cutting torches.
2.12. HOW CAN TUBE HYDRO FORMING BENEFIT
THE AUTO MANUFACTURER
1. Increased strength to weight ratios
2. Improved stiffness torsion and bending rigidly
3. Improvement in NHV Factor
4. Incorporation of hole punching, slot making, embosses swing hydro forming process.
5. Reduction in number of manufacturing stages, hence tooling.
6. Reduction in welding, hence distortion and subsequent heat treatment.
7. Reduction in production cost
8. Reduced floor area
2.2. SHEET HYDRO FORMING
Sheet hydro forming involves forming of sheet with application of fluid pressure. During the sheet hydro forming process, the hydraulic pressure varies in the range equal to or less than 100 MPa A sheet metal blank informed by hydraulic counter pressure generated by punch drawing sheet into pressurized water chambers. The water pressure effectively punches the sheet firmly against punch to form required shape.
The major advantage of fluid forming is increased drawing ratio. The process take place in two stages performed during one press stroke. The sheet is performed by applying low fluid pressure while it is clamped firmly by a blank holder pressure. Performing achieves on evenly distributed strengthening in the component center. In next step fluid pressure increased gradually and blank holder pressure is controlled relative to sheet reformation.
Fig. Sheet hydro forming
2.21. NEW CONCEPT IN SHEET HYDRO FORMING
Double Sheet Hydro Forming
Structural component with closed components are formed by this process. Some advantages of this process are:-
Integration of more parts, further reduction of components & thus steps.
Stiffness increase and reduction in overall spring back due to closed box section & continuous weld section.
A complete component is made in one single hydro forming step, with only top and bottom die.
Fig. Double sheet hydro forming
2.22. THE APPLICATION SPECTRUM
1. There are numerous automotive components well suited to hydro forming of sheets.
2. This is especially true in area of outer skin with its extreme demand of surface quality and dimensional accuracy.
3. Longer outer skin parts for passenger cars, utility vehicles and truck such as goods, doors and tender as well as complex structural components can be formed.
4. Low capital cost. Fewer and simpler dies.
5. Better NHV (noise, vibration and harshness factors) factors.
6. Reduction in weight.
7. High process capability.
8. Reduction in cost of component.
Fig. Schematic View of Advantages
3. FORMING LIMIT DIAGRAM
During hydro forming process failure occurs due to thinning, this is due to the excessive deformation in a given region. A quick and economical analysis of deformation in a forged part is analyzed from forming limit diagram.
The ability to detect point to point variation in strain distribution generally requires circle diameter between 2.5 to 5 mm. The sheet is then deformed, converting circles in to ellipse, and the distorted pattern is then measured and evaluated. Regions where the area has expanded are locations of sheet thinning Regions where area has contracted have undergone sheet thickening. Using the ellipse on the deformed grid, the major (Strains in the direction of larger radius) and associated minor strains (Strains perpendicular to the major) can be determined for variety of locations and values can be plotted on the forming limit diagram.
If both major and minor strains are positive deformation is known as stretching, and thinning will possible.
Fig. Forming Limit Diagram
4. HYDRO FORMING PROCESS CONTROL
A typical hydro forming system would include a press capable of developing necessary forces to clamp the die valves together when internal pressure acts on fluid; a high pressure water system to intensify water pressure for forming component, looking including aerial cylinder and punches, depending on component and a control system for process monitoring.
Since the entire process of operation takes place inside a closed die, one cannot see what actually happens during forming. Therefore the controller plays a vital role in displaying, monitoring and controlling the different parameters of forming in real time.
Fig: Schematic Diagram of Tube Hydro forming and Process Control
5. HYDRO JOINING
Usually after hydro forming, additional joining operations are required to form assemblies. To reduce manufacturing time and number of process steps, joining operation are being integrated into hydro forming process. This also reduces tool cost. Two approaches to hydro joining are punch riveting hydro clinching.
In punch riveting, pressurized fluid acts on one sheet while a moving punch acts on other sheets from opposite sheet. Punch is moved against rivet and under the fluid counter pressure; it spreads to form a solid, visually attractive joint.
In hydro clinching, high pressure fluid action the punch. The prescribed fluid presses the material to be hydro formed part through a note in sheet to be joined.
During the last 12 years, general awareness of hydro forming has grown steadily. Although interest in hydro forming is wide ranging, the vast majority of application are in automobile industry.
Hydro Forming is not solution for manufacturing all automotive parts. The benefits of automotive light weight resin and weight reduction achieved by hydro forming can be measured in kilogram. It cannot be applied to every components, one has to study inability of hydro forming the part and the economic and technical payback.
Just like transistor revolutionized the electronic industry, hydro forming has taken the vehicle manufacturing industry a step up to evolutionary ladder, allowing auto component for vehicle. Although hydro forming has not taken off rapidly as it should have, is only matter on time before this technology is absorbed in the industry.
1. The Machinist Journal (October Edition)