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Technological & Economical Aspects Page 2:
1.) Part design determines
production costs: Example engine cradle
2. How to reduce the number of production steps: Examples
One point of view to achieve an economic production is to reduce the necessary numbers of production steps which often leads to a reduction of capital investment for dies and machinery, production costs and reduces the technological risk as well. In the following three examples are shown to achieve this for hydroforming applications:
Integrated End Forming within the Hydroforming
In the past it was a standard to seal the circular tube ends, expand all other square sections according to the part design by hydroforming and finally to cut the tube ends if a non-circular end section is needed for further functions or assembly. This leads to scrap material, which can be avoided for most applications in using the integrated end forming in the hydroforming procedure (Fig. 3.1).
A computer simulation using the finite element method shows the necessary steps and principle die design (Fig. 3.2):
First the hydroform die is closed and the tube end is flattened. A non-circular punch expands the flattened tube end and moves forward forming the tube ends until the tube end is calibrated and sealed. Now the normal hydroform process starts. The part can be produced with the required end square section calibrated outside and inside similar to known end forming tolerances; any scrap is avoided. An end area of a component is shown in Fig. 3.3
Fig 3.3 a
Fig 3.3 b
Fig 3.3 End areas of hydroforming components produced without end scrap.
The disadvantages of the described procedure are the slightly higher costs of the non-circular axial forming punches.
Integrated Tube End Detection
This method is used in high volume hydroforming production since 1991 for stainless steel and copper applications /1/. For a safe hydroform production a safety sealing procedure during hydroforming is necessary. This leads to different requirements according to the tube end quality and especially the end length tolerance. Even during comparatively simple bending procedures the tube end length after bending can vary within a range of 1 up to 3 mm. To avoid a cutting process between bending and hydroforming, the integrated tube end detection within the standard ALLFORM control system is recommended.
To detect the tube end, an increase of pressure within the axial hydraulic cylinders is detected whilst the axial cylinders are moving forward. If the pressure increases steeply axial stroke/axial pressure relationship, the tube end is reached. The system starts the hydroform process itself now "knowing" the tube end. As in all hydraulic systems the minimum force to move forward during this phase of "searching the tube ends" is about 5 .. 10% of the maximum force of the hydraulic cylinder. Therefore the system limit is the risk of buckling the tube ends or sections caused by this minimum measurable axial force. For said reason the axial cylinders should not be more powerful for the component beeing produced.
As a first check whether this method works for a known application, the buckling stability of the tube end area can be compared with the minimum necessary sealing force for hydroforming, which is about 10 .. 20 % higher than the theoretical one in industrial applications /2/.
Naturally the hydroform system needs some time to "search" the tube ends. The increase of cycle time during hydroforming by using this system depends mainly on the tolerances of the tube end length. With tolerance of about 1 up to 3 mm in end length, the cycle time increases by up to 1,5 seconds.
Integrated forming of bushes
Fig. 3.4 shows a computer simulation (FEA) of a method to avoid the further use of bush assembly for structural parts i.e. cross members or engine cradles /3/. The shown method saves costs for bushes and further welding.
The method is only possible in comparatively flat part sections and with tube materials with high elongation (>40%)
With permission of
Siempelkamp Pressen Systeme / Germany.
update: Januar 12, 2000
Letzte Änderung: 12 Januar 2000
© 1998-2000 Hydroforming.net by Boerries Burkhardt.
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