Metal deforming – By extruding through orifice – With metal-deforming other than by extrusion
Reexamination Certificate
2002-08-05
2004-04-06
Tolan, Ed (Department: 3725)
Metal deforming
By extruding through orifice
With metal-deforming other than by extrusion
C072S263000, C072S467000, C072S468000
Reexamination Certificate
active
06715330
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a device and a method for continuous pressing of a plastically deformable blank, for example made of a metal, into a three-dimensional section with a predetermined cross-sectional area, comprising a fixed die with an opening formed in the die, through which the plastically deformable blank is intended to be pressed, and at least one rotary die arranged, adjacent to the opening, around an axis extending transversely of the pressing direction, the die having one or more recesses in its peripheral surface for forming the blank into a three-dimensional section with transverse sectional parts during the rotation of the rotary die.
TECHNICAL BACKGROUND
In continuous pressing of a plastically deformable blank, for example a heated metal such as aluminium, so-called extrusion, the blank passes an opening with a desired cross-sectional area, thereby forming a section whose longitudinal cross-section is constant. There is a great need for continuous manufacture of sections with transverse sectional parts, such as racks, hollow sections, etc.
International Patent Specification WO97/12745 discloses a method and a device invented by the present inventor, which aim at allowing extrusion of sections with sectional parts protruding transversely of the section. According to this publication, a rotating die is arranged to constitute part of the opening through which the blank is pressed. As the cross-sectional area of the blank is being reduced, the rotating die simultaneously forms it. The rotating die can be designed to produce transverse bars in the section, or to form a raised or embedded company name in the section.
The difference compared to various types of die stamping with rotating elements is to be noted, illustrated for example in DE 42101746, where only a very limited forming of the blank takes place. When shaping according to the above technique, as referred to by the present invention, the rotating die forms part of the actual extrusion process.
The application of this technique in existing, largely standardised, press facilities such as hydraulic pressing plants, screw extruders, conform extrusion machines, etc, was previously impossible. Facilities of said type usually comprise a tool arrangement of the type shown in
FIG. 2
, with a support
5
for a substantially cylindrical tool
3
comprising a fixed die
1
. There is not much space around this tool, and the forces generated during the pressing are very strong.
Furthermore, it is very important that the number of production stoppages be reduced, since the cost of unexploited machine capacity is very high. It is, therefore, desirable that tools can be changed rapidly according to pressing needs.
Since Patent Specification WO97/12745 was published, the need for sections with a cross-sectional area that varies longitudinally has arisen, i.e. a section having not only transverse sectional parts such as bars, but also a varying cross-section or material thickness along the continuous section.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the above problem, and permit extrusion of sections with longitudinally varying material thickness.
This object is achieved by means of a device and a method of the type described by way of introduction, wherein the rotary die has a varying pitch radius as seen from the axis, which allows pressing of sections with varying cross section.
The term “pitch radius” is used here in the same way as in the description of a gear wheel, i.e. the average radius of the whole die or parts of the die. Accordingly, the pitch radius takes up a peripheral surface in which various kinds of recesses or protrusions have been made to form the sections. A varying pitch radius may be achieved by a non-circular die (for example an oval die), or by the rotary die being slightly offset relative to said axis. This would result in a section, whose continuous material thickness would vary cyclically, which is desirable when manufacturing a beam with varying strength.
According to a preferred embodiment, the device further comprises means for varying the cross-sectional area immediately upstream of the rotary die. In other words, the fixed die is arranged to have an opening with a variable cross section. Thus, the amount of material pressed towards the rotary die may be varied, suitably according to the shape of the rotary die. The means for varying the cross-sectional area are suitably synchronised with the rotary die and may consist of supporting surfaces moveable transversely of the pressing direction.
According to a second aspect of the invention, the rotary die is arranged to be lockable in a predetermined position. Thus, the rotary, moveable die may be locked, and thereby essentially converted into a fixed die. Pressing may now take place, either by passing one rotary die or by passing one or more fixed dies, which offers improved possibilities of varying the pressed sections.
The rotary die may suitably have smooth sectors, which in the locked position face the blank, so that, in this position, the blank passes the locked die for forming a smooth sectional segment. By orienting a smooth sector so that it faces the blank when locking the rotary die, the forces acting on the rotary die in the locked position are minimised. Locking the rotary die in a position where recesses or protrusions are oriented so that they face the blank would in fact require a great locking force and would, in addition, mean a risk of loose pieces forming in the cavities of the die during pressing.
According to a third aspect of the invention, the rotary die is arranged immediately downstream of said opening, whereby the blank is reduced when passing through said opening down to substantially the predetermined cross-sectional area, and then formed when passing said rotary die, so that the final shape of the three-dimensional section is determined.
Unlike prior art, the area of the blank is in this case reduced down to substantially its final cross-sectional area upstream of the rotating die, whereby the forces acting on the rotating die can be minimised. This results in manageable bearing forces, which allows the bearings of the rotary die to be contained in the fixed die. The expression “substantially down to” means primarily down to between 100% and 130% of the final predetermined cross-sectional area.
The blank meets with the rotating die radially within its average radius (the pitch radius). In this way, some area reduction still takes place at the rotating die, and thus a certain acceleration of the blank occurs during this passage while at the same time the material fills cavities in the rotating die.
The expression “immediately downstream of” means that the rotary die is located so close to the opening that the pressure of the pressing is used in the shaping done by the rotating die. If the distance is too long, for example several times the across corner dimension of the section, the blank will self-lock adjacent to the rotating die because of the friction caused upstream against the supporting surfaces when the rotating die is in a pressing phase.
The rotary die is preferably mounted in bearings in a transverse cavity formed next to the opening, thereby being rotatable around an axis extending transversely of the pressing direction.
This design of the fixed die allows a space-efficient location of the rotary die within the machine. Furthermore, this construction means that the rotary die is easily accessible, since it is relatively easy to loosen and remove the tool in a normal compression moulding machine. Thus, the device can be designed so as to be compatible with conventional extruding machines in order to allow rapid changing of tools without the need for expensive production stoppages.
By forming a cavity in the fixed die, the space is used as much as is possible, and, in addition, a smaller amount of toughened material is needed for the fixed die, which reduces the cost.
The rotary die is preferably mounted in bearings with a certain axial play. This pla
Burns Doane Swecker & Mathis L.L.P.
Markram Development AB
Tolan Ed
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