MXPA06007037A - Method and apparatus for manufacturing strong thin-walled castings - Google Patents

Abstract

Method and apparatus for forming good quality strong webs having a minimum dimension of 3 mm or less between iron liners in aluminum engine blocks by utilizing pre-formed metallic inserts conjoined with the outer water jacket core, preferably having cooling liquid passages in such inserts bridging the outer water jacket and preferably shaped to fill the interliner gap and formed of the same alloy as the remainder of the block.

Description

FIELD OF THE INVENTION The invention relates generally to the art of manufacturing thin-walled castings and is particularly useful for the manufacture of aluminum blocks for automobile engines with very thin walls between cylinder liners.

BACKGROUND OF THE INVENTION The description of the invention will be made mainly in terms of its application to the manufacture of engine blocks where there is a constant pressure to increase the ratio of power to weight, which has resulted in a desire to use a minimum amount of weight materials light and with small dimensions, but maintaining its strength and integrity, and therefore, its effectiveness and reliability.

In recent years, for the manufacture of engine blocks, particularly for automotive applications, several processes are available; among which you can list (1) the sand pack filled either by gravity or by low pressure, where a sand mold comprising sand cores that define cavities of predetermined shapes, is filled with a liquid aluminum alloy, the which after its solidification forms the motor block, or (2) semi-permanent low pressure molds, or (3) metal molds filled by gravity with sand cores to form the inner geometry of the biock.

The design of the engine blocks has changed over time with a tendency to increase the power of the engines. The dimensions of the engine blocks tend to be fixed by the dimensions of the body of the car. The blocks need to accommodate cylinders of a greater volume, which implies larger diameters, within the same volume of the block. These designs present a challenging problem for block manufacturers, because cylinder liners (usually made of iron) need to be so close to each other that the aluminum wall formed as a thin wall in the space between them Cylinder liners have to be made increasingly thin (less than about 3 mm).

Since the space between adjacent cylinder liners is so thin, the volume of liquid aluminum that must fill such a cavity between said liners is relatively small and rapidly loses heat upon contact with said iron liners and consequently solidifies prematurely thereby obstructing the cavity and preventing the liquid aluminum fills the rest of said cavity.

It has also been found that increasing the pressure in the aluminum alloy source furnace does not solve the problem mentioned above because the space through which the liquid aluminum must flow is too small.

This uncontrolled solidification occurs even when the iron jackets are preheated to a temperature close to that of the liquid aluminum alloy.

U.S. Patent 5,421, 397 issued June 6, 1995 to Robert K. Hembree et al, mentions this same problem and teaches an elaborate system for not only pre-heating the shirts, but also using a plug 14 to form the cylinder hollow mold having a fluid pd therethrough at a temperature controlled by a computer to delay the premature solidification of the thin walls between the jackets. But even this proposal, which is probably not economical, does not eliminate the internal stresses that develop in the thin walls that are particularly vulnerable to these effects due to the simultaneous cooling of different materials in cohesive contact with one another (iron and aluminum). ).

In other words, even when the aluminum is forced to fill the small cavities between the sleeves, another problem arises, which is that the thin aluminum wall between the cylinder linings fails or develops cracks due to the thermal stresses developed by the rapid transfer of heat from the relatively small amount of aluminum alloy between the shirts and the relatively higher and colder mass of said shirts.

Thus, where the walls have been thinned by design considerations to measure only a few millimeters, this cooling occurs when in contact with the shirts that have different coefficients of expansion and contraction. This causes stress on the thin aluminum walls between the adjacent iron sleeves of the cylinder block, where those thin walls crack when cooled, or later when machined, or when the finished motor is in service. This can cause the oil to leak, pressure leaks and other major engine failures.

Even when premature cooling does not obstruct the cavity between jackets, the control of the cooling rate however is adversely and unpredictably affected and can result in unwanted differences in the crystalline structure of the already cold part.

Sometimes a design is also required that provides more effective engine cooling passages in the spaces between jackets, because there is now less material to dissipate the heat of the cylinders, even maintaining uniform cooling speeds becomes increasingly difficult to as the space between shirts becomes smaller. The current designs now have aluminum wall thicknesses between sleeves of approximately 2 to 3 mm. Consequently, the formation of a cooling passage reduces the thickness of the aluminum wall in said passages to only about 1 mm.

Previous art techniques, such as piercing passages in the wall between shirts do not work in such small dimensions (because tools of small diameter and relatively large lengths can be expensive, easy to break, and difficult to control without changing their direction. it should be mentioned that a round hole to form the cooling passages would have a diameter of only about 1 mm and would provide insufficient flow.To obtain sufficient flow, several passages are needed and / or the vertical height requires several times the horizontal width.

Some current proposals for providing said cooling passages comprise special heart-making techniques, either using sand or other fragile materials such as glass. These processes are not ideal, because they are typically expensive and can be dangerous.

Other current practices include emptying a solid section between the cylinder liners and then opening or machining a very thin space in the thin wall between the jackets, the upper part of this space is closed and then welded (thus forming a cooling passage) . This procedure requires expensive equipment and tools to cut / machine.

OBJECTIVES OF THE INVENTION The present invention overcomes the disadvantages of the prior art by introducing a pre-formed insert, with the shape required to fit in the narrowest space between adjacent cylinder liners, at least in those spaces where the thickness is 3 mm or less. less. This insert is preferably made of aluminum of the same alloy, or optionally of a different alloy, or also of some other suitable material (such as bronze or copper) and positioned at the desired location at the same time the sand core is produced which defines the water jacket of the block.

This insert can have an hourglass shape similar to the preformed heart described in US Patent No. 6,298,899 and similarly has the advantage of avoiding the "tilting angle" mentioned therein. Although similar in form due to its position, the heart of the '899 patent has a very different purpose and involves a different concept.

The pre-formed insert of the invention is significantly different and has more advantages. The heart of the '899 patent is a non-permanent sand core, whereas in contrast the pre-formed insert of the invention is a permanent solid structure that effectively remains in place as part of the manufactured part after it is removed. the heart that forms the water jacket.

The pre-formed insert of the invention can be totally solid, or can additionally have a passage formed integrally therein. The tube or passage in said insert allows to have an effective and stable passage for the cooling fluid through the ultra-thin space between the sleeves.

It is therefore an object of the invention to provide a method for manufacturing engine blocks of aluminum alloys, the method eliminates the problems of unfilled spaces, stresses, and / or uncontrolled cooling speeds in the walls between shirts between pairs of shirts positioned very close to each other (or in any other piece of cast iron, automotive or not, where it is required to empty a portion with a strong and thin wall which otherwise would have problems of fluidity, cooling, and / or differential stresses), while preferably also providing a suitable passage for the cooling fluid.

It is another object of the invention to provide an engine block for automotive applications made of aluminum alloys where the inter-cylinder jacket wall is formed by a pre-formed insert relatively free of stress and having a shape that fills the space and a suitable content to function as part of the final piece and to bond well chemically, (including the option of some surface melting occurring, possibly aided by an agent such as zinc) and / or mechanically with the rest of the piece and with the shirts, preferably if they are of the same aluminum alloy that forms the rest of the piece.

It is another object of the invention to provide a method for manufacturing a motor block of aluminum alloys where a cooling passage is formed in the narrow space between jackets of said block by supplying a pre-formed insert having a cooling passage formed previously in said insert, which is made of a material and form suitable for being assembled in said space between jackets, and wherein said passage is located in such a way that it maintains a flow communication with the separated zones of the cooling fluid jacket of said block.

In one embodiment of the present invention, there is provided a method of manufacturing a casting product comprising pre-formed solid elements having at least a thickness dimension of less than about 3 mm and then separately melting the remainder of the product with a metal liquid having the pre-formed elements already in place to form the final casting product.

In another embodiment of the present invention, there is provided a method for manufacturing an aluminum alloy engine block with cylinder liners comprising supplying a mold for melting said engine block; inserting pre-formed solid elements, each between a pair of shirts of said cylinders and filling said mold with liquid aluminum alloy to form said motor block.

In still another embodiment of the present invention, there is provided an engine block made of aluminum alloy, comprising pre-formed solid elements relatively free of stress between said cylinder liners and the remainder of said block being melted from said alloy of aluminum that forms an integral block after its solidification of said piece.

In still other embodiments of the invention, the solid elements may incorporate a cooling fluid passage tube, or the preformed solid insert may have a cooling passage already formed therein (optionally with a removable core in said insert ) BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an isometric view of the heart of a mold to form the water jacket (i.e., the cooling passages) of an aluminum block incorporating three pre-formed solid aluminum inserts (in accordance with a preferred embodiment of the present invention), wherein said inserts have a cooling passage and where each is incorporated by means of the bridge heart with the heart of the cooling jacket in a respective position of the space between the jackets.

Figure 2 shows a schematic view from above of a cylinder engine block with an iron cylinder liner assembled just in each of the cylinder spaces and a solid aluminum insert (without passages therein) positioned in the cylinder. space between shirts of each pair of shirts in a finished block (thus showing the relationship between the parts of the engine in which the invention can be practiced effectively).

Figure 3 shows a schematic vertical section taken along the line A-A of Figure 2.

Figure 4 shows a schematic top view similar to Figure 2, but in accordance with a different preferred embodiment of the present invention where the pre-formed inserts each incorporate a connection passage with the cooling fluid flow (shown with lines dotted).

Figure 5 shows a schematic vertical section taken along the line A-A of Figure 4.

Figure 6 is an isometric view of a pre-formed solid insert showing two connecting cores, which pass through and extend beyond the ends of the upper portion of the pre-formed insert (in accordance with the preferred embodiment of the invention). Figures 2 and 3) placed in the space between shirts.

Figure 7 is an isometric view showing two iron jackets mounted on the heart of a mold with a preformed solid insert (in accordance with the preferred embodiment of Figures 2 and 3) which is placed in the space between jackets. " DETAILED DESCRIPTION OF A PREFERRED MODALITIES OF THE INVENTION.

The solution to the problems of filling with liquid aluminum a casting mold of a motor block 8 having thin walls 9 between jackets comprises incorporating a solid insert 10 made of a suitable material, for example from the same aluminum alloy as will form the rest of the cast block. Other materials that can be used for the preformed insert include, for example, bronze, copper and alloys and equivalents thereof. The pre-formed insert (designated generally by the reference numeral 10) can be forged or extruded.

The pre-formed insert 10 is placed between the cylinder liners 12 before introducing the liquid aluminum into said mold. The insert 10 is contained and fixed in place by the liquid aluminum which solidifies to form the remainder of block 8. In a preferred embodiment, the pre-formed insert (see inserts 10a or 10b) has grooves 14 to be assembled with the liquid aluminum, thus providing a better union between the insert and the aluminum when the liquid aluminum cools and solidifies. Bonding can also occur through the surface melting of the insert 10 during the casting of the piece. This can be helped by the addition of a binding agent such as zinc having a low melting point.

In a preferred embodiment, because the coefficients of expansion and cooling are the same or similar between the pre-formed insert 10 and the liquid aluminum alloy used to empty the block in the casting mold, one of the advantages of this invention is that the pre-formed inserts 10 do not have a residual stress.

Additionally, even though the inserts 10 are not made of the same alloy, very little thermal stresses are induced or induced in the pre-formed inserts 10 due to aluminum shrinkage or due to the expansion of iron liners 12 (since that the inserts 10 are already cold and are in a solid form free of stress). This way cracks are minimized or eliminated. In addition, the block of the invention withstands with advantages the stresses or cracks caused by the post-machining processes such as drilling. .

In another embodiment of the invention, a passage 15 for cooling fluid is preferably formed in or as part of a pre-formed insert 10.; for example, by placing an insert 10b or 10c with a conduit for said cooling fluid having the shape required to be assembled in the space between the cylinder liners. The passage 15 can take the form of a thin-walled tube 17 (made of steel or a similar material), see Figure 1, or it can be formed integrally with the insert using a heart-bridge 16, see Figure 6. For facilitating the connection of the cooling passage in the insert 10b with the rest of the cooling passages of the outer jacket (formed by the heart of the water jacket 6), the connecting heart 16, when used to form the passage 15 in the pre-formed insert 10 b remains in place until after the emptying of the block is finished (and then it is removed with the separation of the heart of the jacket 6). Known examples of similar connecting core materials include salt, carbon or glass (see U.S. Patent No. 6,205,959).

The present invention can be practiced, for example, with the current casting processes and equipment, which may comprise a liquid aluminum alloy source furnace, a source of pressurized gas, typically nitrogen, which is injected into said source furnace to push towards said liquid aluminum alloy above through a suitable conduit connected to an inlet of a mold placed above said source furnace. The liquid alloy is forced to enter all mold cavities and after that mold is filled, liquid flow is stopped by an appropriate device, for example, a slide valve or gate and then the mold is disconnected from the mold. said furnace source and the process is repeated with the next mold to be filled. A mass of heat absorbing material, also known as "chill" (or heat absorbing device) can currently be put in contact with the liquid aluminum alloy, according to a proprietary process of the assignee of this patent, for directional solidification of it in the desired direction to produce good quality parts. This controlled cooling can be interrupted by the small gaps between liners in the aluminum blocks of modern automotive engines, but this problem is overcome using the present invention. A preferred condition for the use of the present invention is that the dimension is less than 3 mm, but the method also applies to dimensions between thicker jackets when there is a need to provide cross sections between jackets with less residual stresses due to the solidification process or for any other of the reasons mentioned above.

Those skilled in the art will recognize, or will be able to determine, without laborious experimentation, some equivalent variant of the numerous embodiments of the invention described herein. All equivalent variants are considered to be within the scope of the present invention and which are encompassed by the claims that follow.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by someone who has average knowledge in the art to which the invention pertains. Although methods and materials similar or equivalent to those described in the practice or tests of the present invention can be used, suitable methods and materials are described herein. All publications, patent applications, patents and other references mentioned herein are incorporated in their entirety by reference. In case of conflict, the present specification, including explanations of terms, will control the meaning. Additionally, the materials, methods and examples are illustrative only and are not intended to be limiting.

Although some preferred embodiments of the present invention and modifications thereof have been described in detail, it should be understood that this invention is not limited to such precise modalities and modifications, and that other modifications and variations may be made by one skilled in the art without departing from it. of the spirit and scope of the invention as described in the appended claims.

Claims (5)

1. A method for manufacturing a cast product comprising pre-formed solid elements having at least one dimension thinner than about 3 mm and melting the remainder of the product with liquid metal to form the final cast product.

2. A method for manufacturing an aluminum alloy engine block comprising cylinder liners wherein said method comprises providing a mold for emptying said block; inserting pre-formed solid elements between said cylinder liners and filling said mold with liquid aluminum alloy to form said motor block.

3. A motor block made of aluminum alloy by a casting process, comprising pre-formed solid elements relatively free of stress between said cylinder liners, and where the rest of said motor block is formed of said aluminum alloy, said elements forming an integral block after the solidification of said casting piece.

4. A method according to claim 1 or 2 wherein the pre-formed elements have at least one passage therethrough.

5. A method according to claim 4, wherein the passage through said inserts is formed by means of a connecting heart through each space between jackets that is between each pair of iron jackets and extending between opposing halves of the jackets. a heart used to form a water jacket and that forms part of the mold of said engine.