Process for die-casting light-weight metals

Details Process for die-casting light-weight metals Process for die-casting light-weight metals

2000-02-10

2001-10-30

Dunn, Tom (Department: 1725)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S066100, C164S113000, C164S312000, C164S457000, C164S253000

Reexamination Certificate

active

06308766

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a process for die-casting light-weight metals, in particular aluminum and aluminum alloys, in which the molten metal is charged into a filling chamber and injected from the filling chamber into a hollow mold cavity by means of a piston.
In a known die-casting process molten metal is introduced into a filling chamber and, by means of a piston, injected from the filing chamber into a hollow mold cavity of a die-casting machine. The greater part of the gases such as e.g. air or water vapor is expelled from the mold cavity by the metal injected into the mold. In variants of this process, the mold cavity is evacuated in advance down to a residual pressure of approx. 200 to 500 mbar and, in special vacuum die-casting processes, even to a residual pressure of less than 100 mbar.
Molds for die-casting thin walled and large surface area or complex shaped die-cast parts exhibit narrow regions which hinder the melt and make it practically impossible to remove the gases from the mold cavity. On evacuating the mold before filling it is not possible to achieve a high vacuum, because of the lack of air tightness and due to the cost and time involved. Although the occlusion of gases in the form of pores or blisters is much less pronounced with vacuum die-casting than with conventional die-casting, the number of these defects in the die-cast part is still too high for the use of such parts as safety components in automobile manufacture, because of inadequate mechanical properties.
In a die-casting process for casting aluminum parts known by the name Pore Free Die-casting (PFD), before injecting the metal into the mold cavity, the latter is flooded with oxygen, to a pressure above atmospheric pressure so that the gases in the mold cavity are replaced by oxygen. The oxygen fed to the mold cavity flows through narrow gaps and regions and, after a certain duration of flooding, the greater part of the gases previously in the mold cavity are expelled from the mold cavity and it is possible to prevent atmospheric gases from re-entering the mold. On subsequently injecting of molten aluminum into the mold, the aluminum reacts with oxygen to form Al
2
O
3
which remains as a dispersion of fine particles in the die-cast part without noticeably altering its properties.
It has been found, however, that even on maintaining a pressure in the mold cavity above the atmospheric pressure, it is practically impossible to completely remove the gases from the interior of a die-casting mold by flooding it with oxygen. Residual gases often remain for an extended period in regions that are difficult to flood. Water-based separating agents require, for example, a certain amount of time until they dry up completely under relatively high atmospheric pressure. In the case of die-casting molds for manufacturing die-cast pacts of relatively complicated shape, some regions are difficult to reach with oxygen with the result that residual gases such as air or water vapor are not replaced by oxygen, but remain as such in the mold cavity. During die-casting, these residual gases and water vapor form separating agents remaining in the mold cavity and become trapped in the metal form pores there and, as a result of subsequent heat treatment such as e.g. solution treatment lead to blisters at the surface. Due to these blisters, many die-casting parts cannot be heat treated.
Accordingly, it is a principle object of the present invention to provide a process for die-casting as described above wherein the occlusion of gases is reduced considerably and as a result the above mentioned problems of formation of pores and blisters in die-cast parts can be prevented.
SUMMARY OF THE INVENTION
The foregoing object is achieved by way of the present invention wherein the mold cavity is evacuated in advance, hereinafter referred to as pre-evacuating, then flooded with oxygen and before injecting with the molten metal, the mold is again evacuated and finally the molten metal is injected into the mold cavity.
The essential aspect of the invention lies in the combination of the known vacuum die-casting process with the PFD process. In accordance with the process of the present invention, the above mentioned disadvantages of the individual processes can be eliminated in a simple manner. By pre-evacuating the mold cavity the residual amount of air and water vapor can be substantially reduced, so that the subsequent flooding of the mold cavity with oxygen leads to practically complete removal of the residual gases. With the process according to the invention excellent results are obtained even with relatively low vacuum.
In order to achieve optimum results with respect to the formation of pores and blisters, the pre-evacuation of the mold cavity, prior to flooding with oxygen, effects a residual pressure of less than 100 mbar.
On flooding the mold cavity with oxygen, a pressure above atmospheric pressure is usefully maintained.
In order to prevent gases and water vapor from flowing back into the mold cavity, it may be useful to maintain an oxygen atmosphere around the die. In this way, should any leaks occur, oxygen instead of air and water vapor would be sucked back into the mold cavity.
With the process according to the invention two versions are possible:
1. The steps of pre-evacuation and flooding with oxygen are performed before filling the filling chamber with molten metal.
2. The molten metal is poured into the filling chamber and the filling opening closed off with the piston. Subsequently all three steps that is, pre-evacuation, flooding with oxygen and again evacuating the mold cavity are carried out one after the other during a first filling phase which lasts until the molten metal enters the mold space. This second version can be employed especially with large die-casting machines as these facilitate longer first filling phases.
With the process according to the invention it is possible to manufacture die-cast parts out of aluminum or an aluminum alloy with a content of enclosed gases of less than 1 cm
3
enclosed gases per 100 g aluminum. Such die-cast parts have excellent mechanical properties and may be employed for functional structure parts such as safety parts in automobile manufacture. Furthermore, the die-cast parts manufactured according to the invention can be heat treated or welded without danger of blisters forming due to enclosed gases.
A particularly advantageous application of the process according to the invention is achieved by the combination of the MFT or HQC process i.e. with the die-casting process and devices such as described in patent documents EP-A-0759825 and DE-C-3002886.


REFERENCES:
patent: 3382910 (1968-05-01), Radtke et al.
patent: 3744546 (1973-07-01), Miki et al.
patent: 4431047 (1984-02-01), Takeshima et al.
patent: 4463793 (1984-08-01), Thurner
patent: 5076344 (1991-12-01), Fields et al.
patent: 6024158 (2000-02-01), Gabathuler et al.
patent: 6176294 (2001-01-01), Kuramasu et al.
patent: 55-8382 (1980-01-01), None
patent: 55008382-A (1980-01-01), None
patent: 58-3766 (1983-01-01), None
patent: 1134289-A (1985-01-01), None
patent: 1134289 (1985-01-01), None
Patent Abstracts of Japan, vol. 004, No. 033 (M-003), Mar. 21, 1980.
Patent Abstracts of Japan, vol. 007, No. 074 (M-203), Mar. 26, 1983.
Database WPI Section Ch, Week 8532, Derwent Publications Ltd., London, GB; Class M22, AN 85-195087 XP002110421.

Affiliated with

Also associated with

Rating

Process for die-casting light-weight metals does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for die-casting light-weight metals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for die-casting light-weight metals will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2578489