Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-02-13
2003-11-18
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S113000, C164S312000
Reexamination Certificate
active
06648055
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a die and to a process for producing a component which is locally reinforced by a porous ceramic insert.
To reduce the component mass, efforts are currently being made to produce relatively large individual components from light metals, for example from aluminum or magnesium, using the pressure die-casting process. This applies in particular to the automotive industry, in which the gear casing and the engine block of motor vehicles are increasingly being manufactured from light metals. However, when using light metals the strength, the resistance to creep and the wear resistance of mechanically loaded partial areas of the components are unsatisfactory in particular in areas which are subject to relatively high temperatures. Consequently, the mechanical load-bearing capacity of light metal components of this type is limited.
A process of the generic type is known from German Patent Document DE 197 10 671 C2. This document discloses a process in which a porous sacrificial body made from a ceramic material (insert) is placed in a defined position in a die and is infiltrated with a molten metal (casting metal) under pressure. The infiltration of the insert with the casting metal leads to the formation of a metal-ceramic composite material (reinforcing element) at the location of the insert. Then, the cast component is heated, so that a reaction takes place between the ceramic material and the casting metal within the reinforcing element, resulting in a composite material comprising ceramic and intermetallic material phases which is superior even to the reinforcing element in terms of its resistance to wear and its strength. However, particularly in the case of local reinforcements, the heating of the component can only be achieved with high technical outlay and high manufacturing costs. Furthermore, process conditions mean that bending stresses may cause damage to the insert during the infiltration.
Japanese Patent Document JP 60130460 A describes a process for producing a composite component which is produced using the centrifugal casting process. A core made from ceramic fibers is placed into a centrifugal die and is supported by holding elements. The holding elements divert the flow of a casting metal past the core, so that after solidification a tube of layered structure is formed, including the core of ceramic fibers and comprising metal at the surfaces. However, a process of this type is not suitable for the infiltration of porous ceramic inserts, since there is not sufficient pressure acting on the insert.
Therefore, the object of the present invention is to provide a die and a further improved process of the above type, so that it is possible to produce light metal components with an improved mechanical load-bearing capacity, in particular an improved resistance to creep, easily and at low cost.
The solution to the object consists in a device (die) having fixing elements for positioning an insert allowing forces which act on the insert to be compensated for by corresponding collinear forces and shielding elements by which the insert is shielded from a principle propagation flow of a casting metal during a casting operation and a process for producing a component with a local reinforcing element made from a metal-ceramic composite material comprising producing a porous ceramic insert from ceramic precursor products; locally positioning the insert in a die which has a runner, a gate, and an impression; filling the die with a casting metal by way of a casting plunger and simultaneously infiltrating the insert at elevated pressure in order to form the local reinforcing element, wherein a preliminary section comprises the filling of the runner and the filling of at least 10% of the impression with the casting metal and wherein a velocity of the casting plunger during the preliminary section is lower than during a filling movement.
The device according to the invention, as described in a preferred embodiment, is distinguished by the fact that, in the die, there are fixing elements which position the insert in a defined way. The fixing elements are designed in such a way that the bending moments which act on the insert are minimized. According to the invention, this is achieved by the fact that forces which act on the insert are compensated for by collinear forces by means of the fixing elements. This means that the force lines of opposite forces lie on a straight line. In addition to the fixing elements according to the invention, the insert is positioned in an impression in such a way that it does not lie directly in the propagation flow of a casting metal. To achieve this, shielding elements are used. Ideally, these shielding elements are components of the impression contour, such as for example edges or walls, which are predetermined by the component geometry. However, it is also possible to design additional fixing elements in such a way that they shield the flow of the casting metal with respect to the insert. Together, the fixing elements and the shielding elements prevent damage to the ceramic insert and thereby reduce the scrap rate in series production of reinforced light metal components.
The insert is preferably positioned in a side of the die which is fixed with respect to a casting machine, since this means that it does not undergo any movement when the die is being closed, which could cause its position to shift. If the geometry of the component and/or the geometry of the die require, it is possible for the insert to be positioned in a moveable side of the die or on a slide. Furthermore, it is possible to position a plurality of inserts in the die, and these inserts may be located in the fixed side and/or the moveable side and/or on a slide.
To minimize the bending moments which act on the insert, it is useful for the insert to be positioned on a wall of the impression. In this case, it is important for the insert to fill up the surface of the die wall in an accurately fitting manner. The die wall is ideally a planar surface.
The definitive fixing of the insert takes place during closing of the die. For this purpose, lugs, pins, edges and/or shielding elements (fixing elements) can be inserted in the tool side which lies opposite the insert (moveable side if the insert is positioned in the fixed side) or on slides.
If the insert is positioned in an accurately fitting manner against the wall of the impression, it is important that no casting metal should penetrate between the insert and the impression wall. This would lead to the insert being lifted off and, together with the action of forces of the fixing elements, would lead to bending moments which would destroy the insert. This can be prevented if, for example, the contact surface between the insert and the impression wall is sealed by edges of the opposite mould side.
In various components, it is necessary for the inserts to be positioned freely in the chamber of the impression. In this case, the fixing is likewise provided by fixing elements. After the impression has been completely filled, the infiltration of the insert takes place uniformly from all sides, i.e. isostatically. Isostatic infiltration has the advantage that the bending moments which act on the insert are reduced to a minimum.
As an alternative and/or to assist the externally acting fixing elements, it is possible to provide the insert with bores and to position it accurately on pins which are located on the fixed side or the moveable side or on a slide. This is advantageous if the design of the component which is to be produced does not locally allow any fixing elements, which are reflected as cavities in the component, to be present in the impression.
The cross section of a casting plunger which delivers the casting metal is generally larger than the cross section of the opening of the impression (gate). The result is that the casting metal is accelerated when it enters the impression at a constant casting-plunger velocity. To protect the insert from the casting metal, i
Haug Tilman
Rauscher Steffen
Rebstock Kolja
Scheydecker Michaael
Walters Markus
Crowell & Moring LLP
Daimler-Chrysler AG
Elve M. Alexandra
Tran Len
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