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Interior and exterior hydro-forming

Complex hollow body or form components shapes can be fabricated with interior and exterior hydro-forming processes.
For this technology, DUNKES builds interior and exterior hydro-forming plants ranging from 1000 kN to 40,000 kN as frame or 3/4 column presses tailored to customer needs.

Starting with the prototyping and concluding with the implementation of serial production, the company can offer the required press and hydro-forming technology, including the required number of add-on axis. A special software developed for hydro-forming guarantees an ideal basis for creating extensive process programmes. Instead of a compact control with significantly limited application capabilities, which must be individually adjusted for each customer, a modular system is available that can be optimally adjusted to the specific requirement by changing individual components. This approach provides a high degree of modularity and reusability, and therefore also a high quality standard.


Interior hydro-forming

Interior hydro-forming involves forming, e.g. of a pipe by means of pressure applied from the inside.


Process sequence:
Example: Interior hydro-forming fabrication of a T-pipe



Step 1: A pipe open on both ends is inserted into the open interior hydro-forming tool.


Step 2: The pipe is flooded with hydro-forming fluid* and the tool is closed.


Step 3: Sidemounted auxiliary axes seal the pipe faces.


Step 4: Pressure is now applied (fed through opening(s) in the auxiliary pushers) to the pipe using a hydro-forming system (pressure distributor e.g. 3000 bar). the pipe now contacts the tool skins, while a pusher for the neck opening begins to synchronously retract. Due to the high pressure, the material begins to flow by following the retracting pusher. In order to maintain the face seal on the pipe during the process, the two auxiliary pushers are correspondingly readjusted. 



Fs = Closing force of the tool
Fa = Closing force of the auxiliary pushers
Fg = Counterforce of the pusher for the neck opening
P   = Interior pressure


Step 5: The auxiliary pushers move toward the outside after the forming process, and the interior hydro-forming tool is opened. The hydro-forming fluid concurrently drains from the pipe.


Step 6: The formed pipe is removed. Note: A subsequent process step mechanically cuts off and machines (deburring, chamfering, etc.) the closed neck opening


*) hydro-forming fluid is an oil in water emulsion with a water content > 80%. In most cases, work is performed with a water content of > 95%. The benefits of low-cost (mineral oil content) and the low compressibility are contrasted by the disadvantages of low viscosity (leakage losses) and low lubrication. In order to avoid excessive evaporation water loss, the hydro-forming temperature may not exceed 60° C.
In addition to the aforementioned example, there are a host of applications were the hydro-forming process is used. The following itemises several examples.




Exterior hydro-forming
Exterior hydro-forming involves forming, e.g. of a blank by means of pressure applied from the outside. The advantages that only the upper portion of the hydro-forming tool is equipped with the forming contour.


Process sequence:
Example: Exterior hydro-forming fabrication of a closing lid

Step 1: A blank is placed into the lower tool half (counter pressure reservoir) of the opened exterior hydro-forming tool. A circumferential seal is installed along the form contour of the lower tool half.


Step 2: The lower tool half is flooded with hydro-forming fluid. The holddown is concurrently placed onto the blank. The full holddown force is applied when the lower tool half has been fully flooded.


Step 3: The upper form die travels down and displaces the hydro-forming fluid in the lower tool half through the blank. During this process step the blank aligns with the form contour of the form die.


Step 4: When the form die has reached the lower switching point, the final shape of the formed part is attained with actively applied pressure.


Step 5: The form die and die cushion travel upward. The fully shaped workpiece is removed.


Advantage:  The lower tool half does not form.