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Technological & Economical Aspects Page 3:
1.) Part design determines
production costs: Example engine cradle
3. Hydroforming processes and die design for high volume production
The tool is still the key element of every cold and warm forming process and machinery and therefore an important aspect of the
A common comment heard within the industry is: For hydroforming you just need a good machine and a simple tool which is mainly made by two die halves similar to the outer shape of the component and some axial cylinders. Unfortunately this is wrong and you should know before you start using hydroforming in mass production. The mentioned "one die = two halves" - procedure might work for some prototyping samples but is far away from mass production application. A few aspects of this point of view will be discussed.
Die Design in
Fig 3.5: Selected basic elements for a mass production hydroform die with inserts (square section)
Axial Forming Cylinder Units
One general difference of hydroform tools in comparison to other forming tools is the requirement of axial forming cylinders. In Fig. 3.6 the Allform-method of connecting theses cylinders to the hydroform tool is shown in comparison to the so-called "plate design fixture". The advantages of the sketched system B) are:
The mass production proven Allform axial forming cylinder system is available up to forces of 50.000 kN. It is equipped and delivered with a small hydraulic unit to fix the system to the tool with the correct torque.
Fig 3.6 A: Fixture of Axial Cylinders A) Plate Design
Fig 3.6 B: Fixture of Axial Cylinders B) ALLFORM Design
Hydropiercing, which means piercing within the hydroform process, requiring integrated piercing units within in the hydroform tool, has several advantages:
In general hydropiercing is possible piercing outward with means of internal pressure or inward by means of a piercing unit. In most applications the piercing is done into the part by piercing units by using a hydraulic cylinder.
The piercing itself follow the calibration stage of the hydroforming process; therefore the cycle time is slightly increased by about 1 to 1,5 seconds. In Fig. 3.7 three mass production proven methods are shown for hydropiercing: All methods have in common designs which avoid the separation of the slug after piercing to avoid any risk of tool damage caused by uncontrolled slugs within the die.
Typical method i.e. for painting holes; slug connected
for part lifetime.
Fig 3.7: Mass production proven methods of hydropiercing
The necessary piercing force can be calculated by the sum of two parts:
In Fig. 3.8 the necessary piercing unit force is shown for a circular hole with different diameters, assuming an UTS of 400 MPa, tube thickness of 2,5 mm and a piercing pressure of 160 MPa. It shows that typical piercing forces are in a range of 500 kN up to 2000 kN. The magnitude of this force can lead to the problem of piercing holes next to each other when piercing of multiple holes with one piercing unit is not possible (example Fig. 3.9).
Fig 3.8: Example: Necessary force of hydrulic piercing unit depending on hole diameter
Fig 3.9 (a) Example of "coined" (see Fig 3.7) holes within the hydroform process
Fig 3.9 (b) Example of "coined" (see Fig 3.7) holes within the hydroform process
As a solution SPS offers ultra-compact piercing units which also satisfy other principle requirements for hydroforming piercing units:
As an example such a 500 kN - piercing unit is shown in Fig. 3.10. They are only used for mentioned reasons and not used in standard applications where less sophisticated solutions are more applicable.
Fig 3.10: Ultra-compact hydropiercing unit in die split plane
It is also possible to pierce holes without slug; an example is shown in Fig 3.11
Fig 3.11: Hydropiercing / Example: Index hole
The necessary piercing pressure also depends on the necessary piercing quality; two aspects are shown in Fig. 3.12: The rollover height sA and the influence of the rollover area (Diameter De) are reduced when applying higher internal pressure during piercing. By increasing the piercing pressure the necessary force of the piercing unit increases; this leads not only to a bigger size of the piercing unit but also to higher clamping and press force. Normally the piercing pressure is lower than the final (and highest) calibration pressure for a part and the press system should decrease the internal pressure to the necessary piercing pressure automatically.
If the piercing pressure is higher than the calibration pressure the economy of hydropiercing has be checked carefully. This leads to the fact that hydropiercing can be in some cases uneconomic and each single application should be checked for viability.
Fig 3.12: Selected quality aspect of hydropiercing and influence of internal pressure during piercing
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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