Tsch?tsch H., Koth A. Metal Forming Practise: Processes - Machines - Tools
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14.16 Tube hydroforming (internal high-pressure forming, IHF) 181
A B
C
Figure 14.38 Examples of tube hydroforming
(A í tube fittings;
B í exhaust system for six-cylinder BMW M3;
C í roll bar for Porsche Boxster
(Photographs from Schuler Hydroforming GmbH
& Co. KG works)
A B
Figure 14.39 Example of a hydroformed structured part and schematic diagram of a tu
b
e hydroforming
die
(A í integral automobile engine mount (NAFTA region) (manufactured on 50,000-kN tube
hydroforming unit); B í schematic diagram of a tube hydroforming die (lower die) for auto-
mobile engine mounts incl. axial forming cylinder) (Source: Siempelkamp Pressen Systeme,
Krefeld, Germany)
182 14 Deep drawing
Presses for tube hydroforming are often designed as four-pillar presses, to ensure easy access
from all sides. The tooling dimensions, the position of the horizontal cylinder, the number of
controlled hydraulic axles, the processing medium system and last but not least the closing
force required for the particular press design are all designed specially for tube hydroforming,
i.e. tailored to fit the range of workpieces planned for.
Figure 14.40, for example, shows a tube hydroforming press with 50,000 kN closing force for
forming large-area hydroformed parts.
Figure 14.40 50,000-kN tube hydroforming press at the Fraunhofer Institute for Machine Tools and
Forming Technology in Chemnitz (Photograph: Schuler Hydroforming GmbH & Co. KG works)
To produce hydroformed parts of the very precise shape and size required, achieved by the
high internal pressure at the end of the process (sizing pressure), the tube hydroforming tooling
must meet very high standards.
Figure 14.41 shows a tube hydroforming die used to produce elements for exhaust manifolds.
14.16 Tube hydroforming (internal high-pressure forming, IHF) 183
Figure 14.41
Tube hydroforming die for exhaust manifolds
(photograph from Schuler Hydroforming
GmbH & Co. KG works)
Figure 14.42 Schematic diagram of a full tube hydroforming unit (source: Siempelkamp Pressen Sys-
teme, Krefeld, Germany)
1 Production of semis
2 heat and surface treatment
3 trimming
4 storage
5 washing
6 bending, pre-forming
7 checking, handling
8 applying lubricant
9 feed-in
pre-forming
forming
punching
removal
preparing the processing me-
dium
10 sawing
11 punching; finishing
12 marking
13 cleaning
14 packing
15 process control
184 14 Deep drawing
The disadvantage of the sometimes relatively long cycle compared with competing processes,
which affects the number of parts which can be produced economically, is often balanced out
by the superior qualities of the tube hydroformed components. The cost-effective production of
IHF parts is only possible when the process is seen as a whole, from the pre-treatment of the
starting stock, to heat and surface treatment, up to finishing.
Figure 14.42 shows an example of a complete tube hydroforming unit.
14.16.3 Advantages of tube hydroforming
The crucial advantages of tube hydroforming are:
– the production of complicated components which could previously only be produced from
several separate parts,
– very precise sizing and shaping of components,
– increase in strength due to work hardening,
– low weight with optimum strengh,
– high rigidity,
– high fatigue strength,
– fewer welding joints for complex components,
– low flow resistance (exhaust systems).
14.17 Exercise on Chapter 14
1. What kind of forming process is deep drawing?
2. Name typical workpieces which are produced using this process.
3. What are “characteristic triangles” and how are they formed?
4. Why can it be assumed that the surface of the workpiece and blank is equal when determin-
ing the blank dimensions?
5. Name the most important elements of deep drawing tooling.
6. How is the drawing tooling for the first draw different to that for the second draw?
7. What happens when the blank holder pressure is too low and what happens when it is too
high?
8. Name the most important advantages of sheet hydroforming.
9. What main areas of application for sheet hydroforming do you know? Name their eco-
nomic limits.
10. Explain the priniple of the tube hydroforming (IHF) process.
11. Name typical workpieces which are produced using these processes.
12. How can the process factor of closing force be roughly calculated?
13. Name the most important advantages of tube hydroforming (IHF).
14. What typical defects occur with tube hydroforming?
15 Deep drawing without a blank holder; metal spin
15.1 Deep drawing without a blank holder
When deep drawing without a blank holder, the die assembly is simpler as the blank holder is
not used. What is more, deep drawing without a blank holder can be carried out on any single-
action press.
15.1.1 Deep drawing limits without a blank holder
The permissible limits for the deep drawing steels St 12 – St 14 are around:
Table 15.1 Permissible drawing ratios
Drawo lst draw 2nd draw
perm
D
d
E
1.8 1.2
D/s
58 60
15.1.2 Deep drawing die shape when deep drawing without a blank holder
The optimum drawing ratios which can be achieved are with a drawing die whose curve is an
involute (Figure 15.1b).
Figure 15.1 Shapes of the drawing die when deep drawing without a blank holder
Drawing dies of c shape have also proved themselves, as the lubricant adheres well. How-
ever, they are more expensive to manufacture.
The a shape conical drawing die, with a 60° cone angle (Figures 15.1a and 15.2) is the most
useful drawing die. It is easy to produce and can achieve maximum drawing ratios.
ning
186 15 Deep drawing without a blank holder; metal spinning
Figure 15.2
Conical deep drawing die
Table 15.2 Permissible drawing ratios depending on d
M
/d
K
for D/s = 40
d
M
/d
K
0.6 0.7 0.8
E
perm
1.9 1.6 1.5
The lower the quotient of d
M
by d
K
(mean values are around 0.6 – 0.8), the higher the permis-
sible drawing ratio is.
15.1.3 Calculation of force and mechanical work
The calculation of force and mechanical work is carried out as shown in Chapter 14.7.1 and
14.9.
15.1.4 Exercises on Chapter 15:
1. What are the advantages of this process?
2. What are the limits of its application?
15.2 Metal spinning
15.2.1 Definition
Metal spinning is when tensile and compressive forces are used to form pre-cut, round sections
of sheet or hollow blanks into axisymmetric (rotationally symmetric) hollow parts with various
kinds of outlines. This is done with roller tools which indent points, or occasionally lines, on
workpieces which are generally rotating. There is no intention to change the thickness of the
sheet.
The shear and tube spinning processes, often used in conjunction with spinning, are processes
for producing rotationally symmetric hollow parts, with a change in the wall thickness in-
tended.
15.2 Metal spinning 187
15.2.2 Application of the process
The spinning process can boast a long historical development. In spinning, the rotating sheet
metal blank is gradually fed against the spinning mandrel, the opposing tool which provides
the shape, by controlled pressure from a spinning tool. Today, easily formable materials for
handcrafts and art purposes are still spun manually. There has been a huge upswing in the
industrial use of the process since the introduction of modern CNC machines. The low tooling
costs compared to deep drawing and the high flexibility when CN controls are used are only
some of the factors responsible for this.
Figure 15.3 Spun shells (Photographs from the hdm-Metalldrückmaschinen GmbH works, Ahlen,
Germany)
15.2.3 Description of the process
As in deep drawing, tangential compressive stresses and radial tensile stresses occur in the
deformation zone, which is highly localised.
The movement of the tools along the surface of the workpiece created is carried out manually
or is mechanised, using a template device or CNC.
Figure 15.4 The principle of spinning
1 spinning roller
2 round blank
3 spinning mandrel
4 tailstock
5 initial state
6 intermediate state
7 final state
188 15 Deep drawing without a blank holder; metal spinning
Figure 15.5 Experimental set-up for CNC spinning on a turning lathe (Dresden University of Applied
Sciences, Germany; photographer: Sebb) (1 í spinning roller, 2 í blank, 3 í spinning man-
drel 4 í tailstock
For simple parts, the movements of the spinning roller can be easily adapted to suit each work-
piece shape using the CNC program. In the following example, carried out on the experimental
equipment in Figure 15.5, the photographs depict the steps required to gradually feed the sheet
material onto the spinning mandrel.
In industrial practice, the spinning machines generally used have a “playback” system, i.e. the
feed movements of the spinning rollers are carried out on the machine without a workpiece by
an experienced operator using a joystick; these movements are saved in the CNC system. The
saved feed movements can then also be edited on a graphic interface.
Figure 15.7 shows a high-performance spinning machine with an MC 2000 playback control
system based on a Siemens SINUMERIK CNC system of type 840D.
The machine stands out for the high repeatability of the saved values starting at 0.001 mm,
features fully automatic contour measurement by means of a specially-developed sensor head
scanning process, and can take up to eight tools. Figure 15.8 shows the working area.
15.2 Metal spinning 189
Spinning process steps Photographs of the spinning process
Initial state:
The round blank is clamped tight by the tail-
stock. The spinning roller is in the starting
position.
Intermediate state 1:
The blank rotates with a rotation speed of
1000 rpm and the spinning roller starts to form
the blank. Wrinkling occurs due to the tangen-
tial compressive stresses
Intermediate state 2:
The material is gradually fed onto the mandrel
by the controlled movement of the roller. The
wrinkles are removed by being rolled over.
Final state:
A cup with flange is produced.
Figure 15.6 Spinning process steps (photographer: Sebb, Dresden University of Applied Sciences,
Germany)
190 15 Deep drawing without a blank holder; metal spinning
Figure 15.7 High-performance hdm 45/90 spinning machine (Photograph: hdm-
Metalldrückmaschinen GmbH works, Ahlen, Germany)
Figure 15.8 Working area of the HDM 45/90 (Photograph: hdm-Metalldrückmaschinen GmbH works,
Ahlen, Germany)