Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-07-12
2003-02-18
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S113000, C164S098000
Reexamination Certificate
active
06520242
ABSTRACT:
BACKGROUND AND SUMMARY OF INVENTION
This application claims the priority of German Application No. 100 25 489.6, filed May 23, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a device for producing metal/ceramic composite materials and to a process for producing such materials.
DE 197 50 599 discloses a process for producing a metal/ceramic composite material, in which a porous ceramic preform is placed into a pressure die-casting die and is infiltrated with liquid aluminium using the pressure die-casting process. In this process, however, the ceramic preform has to be produced, machined, and placed into a pressure die-casting die in a complex way. This may lead to flexural stresses in the preform if the geometric match between the pressure die-casting die and the preform is inadequate. During the infiltration of the preform as part of the pressure die-casting operation, these flexural stresses may cause the preform to fracture and the component to be scrapped.
Accordingly, the present invention is based on the object of providing a device and a process through which the production of a metal/ceramic composite material is simplified and the process reliability is increased.
The object is achieved by a device and a process according to the present invention.
The device according to the present invention is integrated in a pressure die-casting machine or in a squeeze-casting machine, referred to below as “casting machine” to simplify matters. This device has an injection plunger, a casting chamber with an opening, and a die with a runner and a die cavity. The opening of the casting chamber is suitable for filling the casting chamber (1) with a ceramic precursor product for producing a ceramic preform and (2) with a liquid casting metal. This has the resultant advantage that the preform is produced directly in the mold cavity in which it is subsequently infiltrated with the casting metal, so that no further significant remachining is required. The infiltration results in the production of a metal/ceramic composite material or a component made from the composite material. The term “ceramic precursor product” means a ceramic powder or a ceramic powder mixture which may contain further organic or inorganic auxiliaries.
The powder is transferred, via the opening into the casting chamber, and from there into the runner and the mold cavity, where it is compressed to form the preform. In this context, the term “pressing” is understood as meaning compacting of the powder which, depending on the pressure applied, may express itself as a self-supporting structure of intermeshing powder grains or in the form of a loose powder bed. For this operation, a high pressure is required, which can be produced with minimum technical outlay by a shot head. The term shot head is understood as meaning a device which presses pulverulent dry or moist material into a mold by gas pressure and/or mechanical pressure.
The shot head is mounted movably with respect to the opening and can be exchanged for a casting ladle, which is likewise mounted movably with respect to the opening. The casting ladle is used to fill the casting chamber with the liquid casting metal. This device enables the casting chamber to be used to fill the die cavity with different media in succession.
Further, a suction or blowing device can be fitted onto the opening, which device sucks or blows residual powder, in particular which remains in the casting chamber after the powder has been pressed into the mold cavity, out of the casting chamber. In the process, contamination of the casting metal with the powder is prevented, since this would impair the casting performance and the infiltration performance of the casting metal.
In the runner, the die has a blocking slide which, after the die cavity has been filled with the powder, prevents the powder from dropping back into the casting chamber. The closure device of the slide is coupled to the drive of the injection plunger, enabling the slide to be opened when the casting metal is pressed into the runner by the injection plunger.
In conventional pressure die casting, the runner of the die serves, inter alia, to provide further casting metal for recompression after the die cavity has been filled with the casting metal. The device according to the present invention also causes the ceramic powder to be recompressed. In terms of bulk density, this powder takes up a greater volume than a liquid casting metal. For this reason, the runner of the die of the device according to the present invention is designed with a larger volume than is the case with a conventional die. According to the present invention, the volume is between 10% and 30% of the volume of the die cavity, thus ensuring that there is always sufficient powder available for recompression of the preform.
In a further embodiment, a device according to the present invention comprises a die with a mold cavity and a runner which, through a notch, has an opening leading to the die cavity. The die is integrated in a casting machine and, unlike a conventional die, includes at least two openings for filling with material. One opening is used to convey a pressurized powder into the mold cavity and thus to produce a porous ceramic preform in the die cavity. The second opening comprises the notch of the runner and is used to fill the die cavity with a liquid casting metal. With the aid of this device, it is possible to produce the porous ceramic preform directly in the mold cavity and then for this preform to be infiltrated with the casting metal so as to produce a composite material. The opening for filling with powder can be arranged at the most suitable point on the die. The position of this opening depends on the design of the die and of the casting machine. It may be arranged in such a way that the distance which the powder has to cover from the opening into the die cavity is as short as possible.
The powder can be pressed into the die cavity by a shot head. The shot head of a conventional core-shooting machine is recommended for this purpose. This head is usually mounted in a fixed position at the opening of the die, which is advantageous for metering of the powder. Furthermore, the short conveying path allows a relatively high pressure to be applied to the powder, with an associated high degree of compacting.
It is expedient for the die cavity to be closed off from the runner by a blocking slide, in order to ensure a counter-pressure for compacting the powder to form the preform. Furthermore, after the die cavity has been filled with the powder, the opening to the shot head can be closed by a blocking slide. This prevents the casting metal from escaping from the die cavity while it is filling the latter.
To prevent outlet valves that vent the di e cavity from becoming blocked, the device has a filter channel, which is illustrated in FIG.
3
and narrows conically, in front of each of the outlet valves. The passage opening is designed to be sufficiently narrow, as a function of the condition of the powder, for it to become blocked according to the present invention by powder but to be permeable to gaseous media. Furthermore, the filter channel is applied in such a way that its center axis lies in a parting plane between two parts of the die. This has the advantageous effect that the filter channel is cleaned after opening of the die and ejection of the component.
It is possible to place an insert, which fills up certain regions of the mold cavity, in a fixed position in the mold cavity. These regions are not filled while the powder is pressed in and are not represented in the form of a preform. If the geometry of the insert avoids undercuts, as is necessary when designing dies, the insert can be removed after production of the preform. The regions which are now clear and have not been filled by the preform are thus filled by the casting metal alone. As has been described, the preform is infiltrated with the casting metal, so that the composite material is formed, the assumptio
Crowell & Moring LLP
Daimler-Chrysler AG
Lin Kuang Y.
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