Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
2000-12-29
2002-05-07
Nguyen, Nam (Department: 1722)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S113000, C164S900000
Reexamination Certificate
active
06382302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention concerns a diecasting machine for production of mouldings from thixotropic metal billets, containing a sprue system which connects a cylindrical casting chamber cavity with a moulding cavity, where the sprue system has a cylindrical sprue cavity immediately adjacent to the casting chamber cavity and contains at least one sprue, and all sprues lead laterally away from the generated surface of the sprue cavity, and each sprue has a concentric center line and at its end facing towards the moulding cavity has an inlet opening for introduction of the thixotropic metal alloy into the moulding cavity, and the sprue system is connected to the casting chamber cavity by a passage perpendicular in relation to a concentric longitudinal axis of the cylindrical casting chamber cavity, and the inlet openings are arranged in relation to the passage opening such that the surface normals of the inlet openings do not coincide with the longitudinal axis of the cylindrical casting chamber cavity.
2. Background and Prior Art
Diecasting machines for production of mouldings from thixotropic metal billets are known in themselves. Such diecasting plants essentially contain a casting chamber to hold the diecasting alloy or thixotropic metal billet, a ram moving in the longitudinal direction in the casting chamber for applying pressure to the diecasting alloy or thixotropic metal billet, at the end of the casting chamber opposite the ram a casting chamber opening, and a sprue system comprising essentially a sprue to transfer the diecasting alloy or thixotropic alloy paste from the casting chamber opening into the moulding cavity.
EP-A 0 718 059 describes a horizontal diecasting machine for production of mouldings from a thixotropic alloy paste, where the diecasting machine has an oxide scraper which is located between a semi-cylindrical area of the casting chamber, suitable for insertion of a thixotropic metal billet, and the moulding cavity, and which serves to prevent oxide inclusions in the alloy structure of the moulding.
DE-OS 40 15 174 describes a diecasting machine with a two-part mould for casting of plastic or metal, where between the two mould halves is fitted a specially shaped casting holding device which can assume a changing passage cross section and in its closing position delimits a tapering cross section which is smaller than the predetermined cross section of the casting chamber opening.
The process for production of mouldings from thixotropic i.e. part solid/part liquid metal billets is known as thixoforming. The metal billets are all billets of a metal which can be transformed into a thixotropic state. In particular the metal billets can consist of aluminium, magnesium or zinc or alloys of these metals.
Thixoforming utilizes the thixotropic properties of part liquid and part solid metal alloys. The phrase “thixotropic behaviour of a metal alloy” means that a correspondingly prepared metal behaves as a solid when not under load, but under a thrust load its viscosity reduces to the extent that it behaves in a similar way to a metal melt. This requires heating of the alloy in the setting interval between the liquid and solid temperature. The temperature must be set such that for example a structure proportion of 20 to 80 w. % is melted but the rest remains in solid form.
In thixoforming, part solid/part liquid metals are processed into mouldings in a modified diecasting machine. The diecasting machines used for the thixoforming differ in relation to diecasting machines for diecasting metal melts for example by a longer casting chamber to hold the thixotropic metal billet and a larger ram stroke required as a result, and for example a mechanically reinforced design of the parts of the casting machine guiding the thixotropic metal alloy due to the higher pressure loading of these parts during thixoforming.
Thixoforming takes place for example with a horizontal diecasting machine. In this machine the casting chamber which holds the thixotropic metal billet lies horizontal. In thixoforming a thixotropic metal billet is inserted in such a horizontal casting chamber of a diecasting machine and, by application of pressure from a casting ram, is introduced at high speed and under high pressure into a casting mould usually consisting of steel, in particular hot worked steel, i.e. it is introduced or injected into the moulding cavity of the casting mould where the thixotropic metal alloy sets. The pressure applied to the thixotropic metal billet is typically 200 to 1500 bar and in particular between 500 and 1000 bar. The resulting flow speed of the thixotropic alloy paste is for example 0.2 to 3 m/s and in particular 0.3 to 2 m/s.
The casting structure forming during setting of the thixotropic metal alloy in the casting mould essentially determines the properties of the moulding. The structure formation is characterised by the phases such as mixed crystal and eutectic phases, the casting grains such as globulites and dendrites, segregations and structure faults such as porosity (gas pores, micropores) and contamination, for example oxides.
The metal billets used for thixoforming of part solid alloys have a process-induced fine grain which—if no grain coarsening occurs during pretreatment of the thixotropic metal billets i.e. during heating of the billets and their transport into the diecasting machine—recurs in the alloy structure of the mouldings. A fine grain generally improves the material properties, increases the homogeneity of the alloy structure and helps avoid structural defects in the moulding. Thixoforming of part solid alloys in comparison with diecasting of metal melts also has further substantial advantages. These include a significant energy saving and shorter production times as firstly the thixotropic metal billets, in comparison with diecasting of metal melts, need be heated to a lower temperature and thus for a shorter time before thixoforming, and secondly, in the casting mould they cool or return to a solid state more quickly, which contributes to a reduction in grain coarsening. The energy saving arises in particular because a majority of the melt heat and the entire superheating heat, i.e. the heat additionally supplied to the metal alloy to achieve a temperature increase above the melt point to ensure the liquid state of the metal alloy, and the energy for keeping the melt warm, are no longer required. A further advantage is also the better dimensional precision due to the lower shrinkage and production of mouldings close to the final dimensions, whereby the machining steps are reduced and alloy material saved. Also, the processing temperature is around 100° C. lower and reduces the temperature change stress on the individual components of the diecasting machine, which extends the tool life. The lower processing temperature in thixoforming than in diecasting of metal melts allows the processing of alloys with a low iron content, as no alloying of the tool from contact melting occurs. Thixoforming also allows a better mould filling with fewer air inclusions.
In diecasting machines which are known from the state of the art, a metal billet in the thixotropic state, usually a thixotropic aluminium billet, is inserted into a casting chamber (or more precisely into a casting chamber cavity inside the casting chamber) and by means of pressure application is pressed through a usually cylindrical constriction at one end of the casting chamber known as the passage opening. The thixotropic material is thus sheared. The sheared thixotropic material, starting from a sprue cavity lying next to the passage opening, is deflected into trapezoid sprues and reaches the moulding cavity of a mould. Normally the sprues are arranged at approximately right angles to the concentric center axis of the passage opening. The arrangement between the casting chamber and moulding cavity is referred to below as the sprue system. The sprue system is used to introduce the thixotropic alloy paste in the casting chamber into the moulding c
Alusuisse Technology & Management Ltd.
Bachman & LaPointe P.C.
Lin I.-H.
Nguyen Nam
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