GB2104810A - Squeeze casting apparatus - Google Patents

Abstract

The apparatus comprises a die formed by male (10) and female (11) die parts. In a disengaged position the female die part is charged with molten metal and the die parts are then moved to an engaged position in which a casting cavity is formed. As the metal solidifies in the cavity, the die parts are then moved to an advanced position to apply pressure to the metal in the cavity. One die part (the female die part) is provided with an overflow passage from the die cavity for molten metal displaced as the die parts move to the engaged position. An overflow closure (28) is provided for closing the die cavity when the volume of the die cavity reaches a predetermined value. Thus a precise predetermined amount of molten metal is present in the cavity at each casting operation. <IMAGE>

Description

SPECIFICATION Casting apparatus The invention relates to squeeze casting apparatus for casting molten metal.

A previously proposed squeeze casting apparatus comprises a die formed by male and female die parts relatively movable from a disengaged position for allowing the female die part to be charged with molten metal to an engaged position in which a casting cavity is formed, the die parts then being movable to an advanced position for applying pressure to the solidifying metal in the cavity. In such apparatus, as the male die part is inserted into the female die part containing the molten metal, molten metal is displaced up and around the male die part and flows out of the female die part until the engaged position is reached when the fit between the die parts is such to prevent further flow.When this occurs, a closed casting cavity is formed and continued movement of the male die part into the female die part to the advanced position compresses the solidifying molten metal to produce, on complete solidification, a cast metal article having reduced porosity in comparison with the castings made by casting processes in which no such pressure is used.

It is desirable that when the die parts reach the engaged position and then start to apply pressure to the molten metal, that is, when the molten metal can no longer flow between the dies, the amount of molten metal remaining in the die cavity has a predetermined volume to ensure that there is sufficient metal to form the required casting. It is a problem with previously proposed squeeze casting apparatus that this volume cannot be accurately controlled. It is an object of this invention to mitigate or overcome this problem.

According to the invention, there is provided a squeeze casting apparatus comprising a die formed by male and female die parts relatively movable from a disengaged position for allowing the female die part to be charged with molten metal to an engaged position in which a casting cavity is formed, the die parts then being movable to an advanced position for applying pressure to the solidifying metal in the cavity, one die part being provided with an overflow for the passage from the die cavity of molten metal displaced as the die parts move to the engaged position, an overflow closure being provided for so closing the overflow that a closed die cavity is formed when the volume of the die cavity reaches a predetermined value.

The overflow is preferably provided on the female die part and in this case the overflow closure may be carried on the male die part.

The overflow is preferably formed by one or more apertures in the female die part and extending downwardly from an upper edge of the female die part. There may, for example, be two apertures arranged on opposite sides of the female die part.

The overflow closure preferably comprises a plug for each aperture carried on the male die part, the or each plug progressively covering the associated aperture as the die parts move towards said engaged position and closing the associated aperture when the die cavity volume reaches said predetermined value.

The or each aperture may extend downwardly from an upper edge of the female die part and be formed with a guide slot extending parallel thereto on the side of the aperture opposite to the interior of said female die part with each plug moving with a sliding fit in the slot of the associated aperture as the die parts approach the engaged position.

In this case, the or each slot may terminate at the lower end thereof in a seat on which a base of the associated plug rests when the plug closes the associated aperture.

The or each plug is preferably spring biassed for movement relatively to the male die part to allow continued relative movement of the die parts to the advanced position after the or each plug has closed the associated aperture.

A reservoir may be provided adjacent the overflow for receiving molten metal.

Preferably the male die part has a die forming portion whose die cavity defining surface is spaced from a die cavity defining surface of the female die when the die parts are in the engaged position and has a step defining an upper end of the die cavity and connecting said die forming portion to a die closure portion which, in the engaged position, is a close fit within the female die part, the overflow closure being so arranged that the overflow is completely closed thereby as the step reaches the lowermost point of the overflow The following is a more detailed description of one embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:: Figure 1 is a verticai cross-section through a squeeze casting apparatus showing, in the righthand half, two die parts in an advanced position, and in the left-hand part, the two die parts in an engaged position, before the advanced position; Figure 2 is a view on the line Il-Il of Figure 1 with the male die part removed; Figures 3 and 4 are a side elevation and a plan view respectively of a plug of the apparatus of Figures 1 and 2.

Referring first to Figure 1 , the squeeze casting apparatus comprises a male die part 10, and a cooperating female die part 11 both arranged with their aligned axes vertical. The female die part has an interior surface divided into an upper portion 1 2 for engagement with a portion of the male die part 10 and a die forming portion 13 defining the die cavity. As best seen in Figure 2, the female die part 11 is provided with two apertures 14 extending downwardly from an upper edge of the female die part 11 and arranged diametrically opposite one another. The apertures 14 together form an overflow and have their lowermost edges 1 5 arranged at the same distance above the lowermost point of the female die part 11.

As also best seen in Figure 2, a guide slot 1 6 extends parallel to each aperture 14 on the side of each aperture 14 opposite the interior of the female die part 11. Each guide slot 1 6 is provided with opposed guide surfaces 1 7 which are arcuate about the same axis and whose radius decreases in a downward direction from the upper edge of the female die member. The lower end of each guide slot is formed with a seat 1 8.

A reservoir 1 9 is provided below the level of each seat 1 8.

The male die part 10 comprises a die forming portion 20 whose outer surfaces 21 defines the die cavity in co-operation with the die forming portion 13 of the female die part 11. A step 22 connects the die forming portion 20 of the male die part 10 with a die closure portion 23 whose outer surface 24 is a close fit within the upper portion 12 of the female die part 11 in the engaged position of the die parts shown in the right-hand portion of Figure 1. The male die part 10 also includes a mounting 25 for connection of the male die part 10 to a piston (not shown) of a hydraulic ram (not shown).

Two holes 26 extend through opposite flanged parts of the mounting 25 and the die closure portion 23 of the male die part 10. A threaded rod 27 extends through each hole and engages at a lower end with a plug 28, shown more clearly in Figures 4 and 5.

Each plug 28 has a surface 29 which is generally frusto-conical in shape for co-operation with the curved surfaces 1 7 of an associated slot 1 6. A part of the frusto-conical surface 29 is, however, cut away to form a surface 30 having the same radius of curvature as the radius of curvature of the upper portion 12 of the female die part 11. Each plug 28 is formed with a flat base 31.

A compression spring 32 acts on an end of each rod 27 opposite to the associated plug 28 to urge the associated plug downwardly but to allow relative movement between the rods 27 and plugs 28 and the male die part 10.

In use, the apparatus operates as follows:- The hydraulic ram (not shown) is actuated to retract the male die part 10 to a disengaged position in which it is clear of the female die part 11. The female die part 11 is then filled with molten metal and the hydraulic ram reversed to move the male die part 10 towards the female die part 11.

As the die forming portion of the male die part 10 dips into the molten metal, the molten metal is displaced and rises up the female die part 11 to flow out of the female die part through the apertures 14. This excess molten metal collects in the reservoirs 1 9.

At the same time, the two plugs 28 enter the slots 16, are held by them with their curved surfaces in the apertures 14 and are guided by the curved walls 1 7 of the slots in downward movement. The curved surfaces 30 of plugs 28 gradually close the apertures 14 as the die parts 10, 11 continue their movement towards one another.

As the die closure portion 23 of the male die part 10 enters the female die part 11, the die parts eventually reach an engaged position and a sealing fit is formed between the die closure portion 23 and upper portion 12 of the female die part 11, which prevents molten metal escaping between the parts. While the apertures 14 are open, however, both molten metal and air can escape through the apertures 14.

The apertures 14 and the plugs 28 are so arranged that the plugs 28 close the apertures 14 completely to form a closed die cavity to prevent further escape of molten metal when the volume of molten metal remaining in the female die part 11 is at a predetermined value. This predetermined volume is chosen to give an optimum cast.

As seen in the left-hand part of Figure 1. this full closure of the apertures 14 by the plugs 28 is arranged to occur when the step 22 reaches the level of the lowermost point of the apertures 14.

As the plugs 28 close the apertures 14, the bases 31 of the plugs 28 rest on the seat 18 and the curved surfaces 30 of the plugs 28 form a continuation of the upper portion 12 of the female die 11 and thus are a sealing fit with the trailing end 23 of the male die part 10.

Next, downward movement of the male die part 10 is continued to an advanced position to apply required pressure to the solidifying molten metal in the die cavity, as shown in the right-hand part of Figure 1. During this movement, the male die part 10 moves relatively to the plugs 28 and this movement is accommodated by the sliding of the rods 27 in the holes 26. The springs 32 ensure that the plugs 28 are urged down on to the seats 1 8 to maintain the apertures 14 fully closed.

Once the metal has solidified, the male die part is retracted to allow removal of the casting. After the dies and reservoirs 1 9 have been cleared and cleaned, the casting operation can be repeated to produce cast articles on a continuous basis.

The squeeze casting apparatus described above with reference to the drawings can be used to produce cast articles of any required shape. They may, for example, be used for casting pistons for internal combustion engines or compressors and in this case the molten metal used may be aluminium or an aluminium alloy.

It will be appreciated that inserts of any suitable material could be included in the finished casting and can be inserted into the female die part before the molten metal is poured into the female die part 11.

Claims (10)

1. A squeeze casting apparatus comprising a die formed by male and female die parts relatively movable from a disengaged position for allowing the female die part to be charged with molten metal to an engaged position in which a casting cavity is formed, the die parts then being movable to an advanced position for applying pressure to the solidifying metal in the cavity, and wherein one die part is provided with an overflow for the passage from the die cavity of molten metal displaced as the die parts move to the engaged position, an overflow closure being provided for so closing the overflow that a closed die cavity is formed when the volume of the die cavity reaches a predetermined value.

2. An apparatus according to claim 1, wherein the overflow is provided on the female die part and the overflow closure is carried on the male die part.

3. An apparatus according to claim 2 wherein the overflow is formed by one or more apertures in the female die part and extending downwardly from an upper edge of the female die part.

4. An apparatus according to claim 2 or claim 3, wherein the overflow closure comprises a plug for each aperture carried on the male die part, the or each plug progressively covering the associated aperture as the die parts move towards said engaged position and closing the associated aperture when the die cavity volume reaches said predetermined value.

5. An apparatus according to any one of claims 1 to 4 wherein the or each aperture extends downwardly from an upper edge of the female die part and is formed with a guide slot extending parallel thereto on the side of the aperture opposite to the interior of said female die part wich each plug moving with a sliding fit in the slot of the associated aperture as the die parts approach the engaged position.

6. An apparatus according to claim 5 wherein the or each slot terminates at the lower end thereof in a seat on which a base of the associated plug rests when the plug closes the associated aperture.

7. An apparatus according to claim 6 wherein the or each plug is spring biassed for movement relatively to the male die part to allow continued relative movement of the die parts to the advanced position after the or each plug has closed the associated aperture.

8. An apparatus according to claim 7 wherein a reservoir is provided adjacent the overflow for receiving molten metal.

9. An apparatus according to any one of claims 1 to 8 wherein the male die part has a die forming portion whose die cavity defining surface is spaced from a die cavity defining surface of the female die when the die parts are in the engaged position and has a step defining an upper end of the die cavity and connecting said die forming portion to a die closure portion which, in the engaged position, is a close fit within the female die part, the overflow closure being so arranged that the overflow is completely closed thereby as the step reaches the lowermost point of the overflow.

10. A squeeze casting apparatus substantially as hereinbefore described with reference to the accompanying drawings.