Casting of metals

Abstract

A segmented die assembly for the casting of a metal object, the die assembly incorporating chill segments that are cooled using oil and/or water and/or air, the segments being interconnected and moved by actuators under the control of a Fuzzy logic module, wherein in use the assembly ensures that the chill maintains contact with the surface of the casting as it solidifies.

Description

TECHNICAL FIELD

This invention relates to the sand casting of metals, particularly aluminium and more particularly to the casting of aluminium products requiring desired mechanical properties.

This is particularly so in the casting of aluminium cylinder blocks for automotive engines. Recent developments in aluminium cylinder block design have resulted in a requirement for high mechanical properties in the bulkhead sections of the casting. The rapid cooling of a casting results in increased hardness and other properties in the casting, or selected areas of the casting. The rapid cooling can be achieved by oil and/or water and/or air-cooling of the mould, particularly in the use of metal moulds. However in sand cast moulds, the cooling can be achieved by a metal insert or chill in the mould, the chill having the capacity of conducting the heat into itself, thus cooling the molten metal and solidifying the casting.

BACKGROUND ART

While chilling processes have been used in the area of the bulkheads of the cylinder block, they have caused many production related problems in existing facilities using moulds made from sand.

It is an object of this invention to provide for the rapid cooling of a cast metal object to produce the desired mechanical properties of the object.

A further object of the invention is to provide for the rapid cooling of the bulkhead section of a casting thereby producing the desired mechanical properties in the sand cast aluminium alloy.

A still further object of the invention is to provide movable die portions or segments, with each segment containing the chill.

A still further object of the invention is to maintain the chill in contact with the casting as it shrinks during solidification.

A still further object of the invention is to allow the chill to move with the bulkhead section thus reducing residual stresses and potential cracking of the casting as it shrinks during solidification.

DISCLOSURE OF THE INVENTION

Thus there is provided according to the invention a segmented die assembly for the casting of a metal object, the die assembly incorporating chill segments to be retained in contact with the molten metal during solidification of the casting, characterised in that the one or more of the segmented die segments are movable to maintain the chill in contact with the surface of the casting as it solidifies.

Preferably, there is a central chill segment and an outer die segment on opposite sides of the casting.

Preferably, the die segments are interconnected, and movable by an actuator.

Preferably, the chills are cooled, using oil and/or water and/or air.

Preferably, each actuator is controlled by a Fuzzy logic module.

Preferably, the Fuzzy logic module controls the actuators independently in response to inputs from devices measuring casting solidification parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings in which:

FIG. 1 is an end view of a segmented die cope;

FIG. 2 is a top view of the segmented die cope in FIG. 1; and

FIG. 3 is a detail view of two segments illustrating the degree of contraction of the cylinder block.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description the invention is described as casting a cylinder block 1 of an internal combustion engine, but it is to be realized by a person skilled in the relevant art however, that the invention can be applied to the casting of any article whether it is cast in aluminium or another metal.

The figures show a design for a segmented die assembly having an interconnected chill segment 2 and outer segment 4 on each side of the cylinder block 1. The chill segment 2 and outer segment 4 are interconnected by a coupling 6, the coupling ensures that the chill returns with the outer segment when it is retracted by the actuator (not shown). The coupling comprises a ‘T’ shaped projection stemming from the chill segment 2, the head 8 of the coupling being received in a recess in the outer segment that is shaped and adapted to receive the male portion of the coupling. This assembly produces the bulkhead section of the cylinder block, and can form a part of the clamping system of the chill machine. The design shown cools the half round and sides of the bulkhead resulting in a faster and more uniform cooling of the bulkhead section.

As discussed above, the contraction of the block from the solidus is a problem with any chill that is produced as a one-piece assembly. Tightening on the inside surfaces of the chill 2 will result in the casting 1 locking onto the chill. The total movement required by the actuator is increased as the segments follow the casting, and any clearance C between the couplings 6 that interconnect the segments can be used to control at what point and how much the chill 2 moves. An actuator under the control of a controller moves each die assembly, the actuators pushing the respective die to the centre section, which is fixed.

Each chill 2 is cooled by cool water, air or oil passing through the chill. Sensors such as thermocouples monitor the temperature of the cooling medium entering the chill and the outgoing cooling medium from the chill. Also the temperature of the molten metal is monitored and together with the difference in temperature between the ingoing and outgoing water these parameters are fed to a Fuzzy logic module whereby the amount of actuator movement required is calculated. The Fuzzy logic module controls the actuators independently in order to ensure that the chills are in contact with the casting as it cools and contracts.

At the end of the casting cycle the actuators pull the chills back to their default position and the casting is removed from the casting machine.

The development of the segmented die assembly will result in a cost effective method of producing the mechanical properties required in modem engine block design.

Although one form of the invention has been described it is to be noted that variations and modifications can be made falling within the spirit and scope of the invention.

Claims

1. A segmented die assembly for the casting of a metal object, the die assembly incorporating chill segments to be retained in contact with the molten metal during solidification of the casting, characterised in that the one or more of the segmented die segments are movable to maintain the chill in contact with the surface of the casting as it solidifies.

2. The segmented die assembly as set forth in claim 1, further characterized in that there is a central chill segment and an outer die segment on opposite sides of the casting.

3. The segmented die assembly as set forth in claim 1, further characterized in that the die segments are interconnected, and movable by an actuator.

4. The segmented die assembly as set forth in claim 1, further characterized in that the chills are cooled, using oil and/or water and/or air.

5. The segmented die assembly as set forth in claim 3, further characterized in that each actuator is controlled by a Fuzzy logic module.

6. The segmented die assembly as set forth in claim 5, further characterized in that the Fuzzy logic module controls the actuators independently in response to inputs from devices measuring casting solidification parameters.

7. (canceled)

8. A die assembly for casting of a metal object, comprising a center section in which molten metal solidifies to form a casting of the metal object, and die segments on opposite sides of the casting; wherein each die segment comprising an outer segment and chill segment interconnected with the outer segment; wherein the chill segments are each positioned for contact with the surface of the casting and the outer segment are each positioned radially outward from its interconnected chill segment; and wherein one or more of the die segments are movable to maintain the chill segments in contact with the surface of the casting as it solidifies.

9. A die assembly as set forth in claim 8, wherein the center section is fixed.

10. A die assembly as set forth in claim 8, wherein the center section has a shape corresponding to a cylinder block.

11. A die assembly as set forth in claim 8, wherein the chill sections cool bulkhead sections of the cylinder block.

12. A method of casting a metal object with the die assembly of claim 8, said method comprising the steps of: moving each die segment inward to the center section; contacting the chill segment with the casting