Metal founding – Process – With measuring – testing – inspecting – or condition determination
Reexamination Certificate
2002-09-12
2004-11-23
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
With measuring, testing, inspecting, or condition determination
C164S113000, C164S492000, C164S250100, C164S312000
Reexamination Certificate
active
06820679
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of primary forming a material in which a metal is re-shaped in a primary forming operation.
Primary forming methods of this type comprise, inter alia, casting methods such as pressure-diecasting, gravity-diecasting and sand-casting methods, and also forging and drop-forging methods, in which a metal is re-shaped.
In such primary forming methods, the temperature development of the metal is important for better workability and desired microstructural formation. In particular in the case of casting methods in which a liquid metal or (in the case of thixo casting or solid state melting) pasty or softened solid metal solidifies in the primary mold, it is advantageous to control the temperature variation of the metal. For controlling the temperature variation, it is known, for example from DE 195 45 177 A1, to supply heat to the workpiece or metal inductively by an electromagnetic field which is variable over time. In this way, a defined amount of heat can be introduced into the workpiece, it being possible for the locational and temporal distribution of the inductive field to be varied. The changing of the electromagnetic field can in this case be made dependent on the re-shaping state of the workpiece.
Such inductive heating of a workpiece is already enough to avoid local solidification and undesired premature cooling of the workpiece. However, the inductive coupling-in of the electromagnetic waves can be problematical when relatively large molds are used, for example of a relatively large pressure diecasting installation with metallic mold halves, since the electromagnetic field that changes or oscillates over time has the effect of also inducing eddy currents in the mold halves.
SUMMARY OF THE INVENTION
The invention is based on the object of providing improvements over the prior art and, in particular, of providing novel primary forming methods with which heat can be supplied relatively easily to a metal in a desired way, it advantageously being possible for the supply of heat to be varied in terms of space and time.
This object is achieved according to the invention by a conductively generated voltage being applied to parts of the primary forming device during a filling operation before the primary forming operation and/or during the primary forming operation and/or during a subsequent treatment in the primary mold after the primary forming operation, in such a way that a closed circuit is formed and thermal energy is supplied to the metal conductively, with the closed circuit running through the metal.
According to the invention, the metal is consequently heated conductively, i.e. an electric current is passed through the metal. For this purpose, according to the invention, a voltage is applied to parts suitable for this of the molds between which the metal is located or the primary forming device used.
Conductive heating of this type can be achieved with relatively simple apparatus in comparison with inductive heating, by connecting a current source suitable for this to the desired parts of the device. A welding current source which can deliver the desired high current intensities of, for example, greater than/equal to 100 A at the desired voltage of, for example, less than/equal to 100 V may be used for example as the current source.
According to the invention, the voltage can be input in particular at components which have a large contact surface with the metal, such as for example in the case of a casting device the casting plunger, the casting chamber or mold halves, so that a relatively uniform supply of heat to the metal can be achieved. Since, with increasing temperature, the electrical resistance of the metal likewise increases, a natural inverse feedback occurs in the metal, so that, when there is stronger heating of some regions of the metal, the resistance increases and the current flows more through other, cooler regions of the metal.
The voltage can be applied in principle in all regions of the primary forming device. If metallic components are used, in the case of a pressure diecasting device, for example, the casting plunger, the casting chamber, the anvil, the mold halves or a slide, the voltage can be connected directly to these components. Furthermore, it is possible to provide in the components concerned electrodes for the connection of the voltage source, which according to the invention represent parts of the primary forming device. Use of electrodes may, for example, be meaningful in mold halves which have a ceramic insulation with respect to the mold cavity.
The current may be supplied differently in individual phases of the method. In the case of a pressure diecasting method, a voltage can be advantageously applied between the casting plunger and the anvil during the filling phase, in which the molten or pasty metal is filled into the casting chamber, so that a current is generated through the metal over the length of the casting chamber.
In this way it is possible in particular for the temperature of the metal to be kept constant; furthermore, it is possible to increase the temperature of the metal in the casting chamber, so that an unnecessarily great amount of energy is not used up in a melting phase before filling. Later heating is meaningful in particular in the case of thixo-casting methods or SMS (Solid State Melting) methods, in which a slug of a merely softened or slightly pasty metal is introduced, since unnecessary heating of the slug or keeping-warm of preheated slugs before filling can consequently be at least partially prevented.
During mold filling, a voltage can be applied in particular between the mold halves, so that the metal located in the mold cavity is heated directly between the mold halves. If the mold halves are covered on their inner side to a relatively great extent with a ceramic insulator, electrodes can be additionally used for this purpose. Metallic cooling elements fitted in the mold halves may also be used, for example, as electrodes, so that it is unnecessary for further electrodes to be fitted in existing devices. Furthermore, a current can also be generated between the casting plunger or casting chamber and one or both mold halves, so that the metal still in the casting chamber and in the gate is also heated. If slides are used for producing desired pressure diecasting molds, these can also be used as a connecting point for voltage with respect to another slide, one or both mold halves or, in particular, the casting plunger and/or casting chamber.
In the solidifying phase after mold filling, it may be advantageous in particular to keep the butt of material between the casting plunger and the anvil liquid, in order that a pressure continues to be exerted on the metal located in the mold cavity, in order to ensure good compaction or dense feeding of the metal in the mold cavity. Furthermore, it is possible, for example by a voltage between the casting plunger or casting chamber and the mold halves, or an electrode fitted in them or a slide fitted in them, to keep clear the gate which joins the space inside the casting chamber to the mold cavity, in order that the pressure exerted on the butt of material acts for a longer time on the metal located in the mold cavity.
Furthermore, by suitable current conduction in the metal, it is possible to achieve directional solidification in the mold cavity, in that cooling initially occurs in the regions of lower current intensity and then spreads from these regions into the mold cavity. Since, where there is cooling, the metal is detached from the walls of the mold halves, a sudden change in resistance occurs, which further intensifies this effect. Consequently, a detachment of the metal in the solidified regions from the mold halves and directional solidification can be gradually achieved.
After the solidifying process, a further thermal treatment, in which thermal energy is conductively supplied to the material in desired regions in a desired way, can be carried out without further aids to improve the microstructure
DRM Druckguss GmbH
Lin Kuang Y.
Whitham Curtis & Christofferson, P.C.
LandOfFree
Method of primary forming a material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of primary forming a material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of primary forming a material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3321607