Patent Application
20110168347
1. Field
The embodiments discussed herein relate to a core gas removal device and method and, more particularly, to a core gas extraction method in which cleaning pins attached to an ejector plate remove tar and product gas contaminants from cavities of a die.
2. Description of the Related Art
In an internal combustion engine, the cylinder head is positioned above the cylinders and includes a platform containing part of the combustion chamber and the location of the valves and spark plugs. The cylinder head is important to the performance of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports determines a major portion of the volumetric efficiency and compression ratio of the engine.
A typical cylinder head for an internal combustion engine is formed by casting. A related casting operation is shown in
Because the tight plugs provide locations for core gas venting in a die, if the tight plugs become clogged, the risk of defects related to trapped core gases increase. Therefore, tight plug passages must remain open for venting.
The related processes to clean the tight plugs relied on an operator to manually clean out tar from the tight plugs on every stroke with a rod. However, the amount of reach required for these operators to clean the tight plugs with a rod resulted in safety violations, and was also inefficient due to the amount of time required for an operator to manually clean the tight plugs.
To address the problems with the manual tight plug cleaning process, an automated process was developed in which cleaning pins attached to the ejector plate lowered into the tight plugs during each part ejection cycle. A tar collection box was used as a central location to collect all tar particles extracted by the clean pins from the tight plugs. The tar collection box was located just above the tight plugs such that the clean pins traveled through the tar collection box during each part ejection stroke. However, large tar build-up was observed around the clean pins caused by tar build up in the tar collection box. This occurred because during each cycle, the cleaning pins moved through the excess tar in the tar collection box. As a result, tar build-up was observed on sides of the clean pins at the end of each part ejection/tight plug cleaning cycle. Excess tar accumulation in the tar collection box prevented proper venting of the core gas through the tight plug, resulting in gas related defects such as misruns and “elephant skin” surface defects on the cylinder head.
Therefore, an improved core gas extraction method is desired in order to overcome the above-described problems.
It is, therefore, an object to provide a novel and improved method for clean tight plug bushings of upper dies in a low pressure casting process.
Accordingly, there is provided an apparatus for core gas removal in a low-pressure cylinder head die casting operation which includes an upper die, a lower die, an ejector plate disposed above the upper die to eject a part that has been cast, a plurality of tight plugs fastened into cavities formed in the upper die, and a plurality of clean pins attached to the ejector plate, each clean pin corresponding to a location of one of the tight plugs. The clean pins and the tight plugs have matching geometries so that during a part ejection stroke after a casting cycle is complete, the ejector plate lowers to eject a cylinder head from the upper die such that a portion of the clean pins extend axially into the tight plugs to clean core gas residue formed on inner walls of the tight plugs during the casting cycle.
In one exemplary embodiment, the clean pin includes a clean pin body including a succession of at least two cylindrical stepped portions, such that the stepped portions are arranged in order of decreasing diameter along a longitudinal axis of the clean pin and a circular plate-shaped head arranged along the longitudinal axis at an end of the cylinder adjacent to a stepped portion having a largest diameter.
In another exemplary embodiment, sides of the clean pins have a clearance of 1-2 mm from the inner walls of the tight plugs when the clean pins are lowered into the tight plugs.
The objects and advantages of the described embodiments will be realized and achieved by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
A more complete appreciation of the claimed invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
a is a plan view of a portion of a tight plug according to an embodiment of the invention; and
b a tight plug fastener attached to the tight plug shown in
Low pressure casting is a method to apply pressure on a molten metal surface contained in a sealed crucible and raising the molten metal into a mold. The conventional low-pressure casting apparatus 1 shown in
The casting may be any desired one of well-known low-pressure metal casting processes. The casting process described in U.S. Pat. No. 4,695,329 is useful in various embodiments of the invention and is hereby incorporated by reference. A sand-based cylinder head core (not shown) is inserted between the upper and lower dies 10, 20 and molten metal (not shown) is filled in between the dies 10, 20 to mold the cylinder head (not shown). The molten metal is supplied only as needed for one casting cycle from a sealed crucible (not shown). In the present invention, the metallic cylinder head is preferably formed of an aluminum alloy in order to reduce the weight of an internal combustion engine. The metal used in the casting operation of the present invention is AC2C (per the Japanese Industrial Standard, “JIS”). AC2C is an aluminum casting alloy which includes Cu in an amount of 2 to 4% by weight, Si in an amount of 5 to 7% by weight, Mg in an amount of 0.2 to 0.4% by weight, Mn in an amount of 0.2 to 0.4% by weight, and a balance of Al. However, the cylinder head of the present invention may be cast from any of casting aluminum alloys traditionally used in the casting of cylinder heads for use in internal combustion engines. Some illustrative, non-limiting examples of the aluminum alloys that may be used include:
JIS AC2B alloys (Cu 2.0-4.0 wt %, Si 5.0-7.0 wt %, Mg<0.5 wt %, Zn<1.0 wt %, Fe<1.0 wt %, Mn<0.5 wt %, Ni<0.3 wt %, Ti<0.2 wt %, balance Al),
JIS AC4B alloys (Cu 2.0-4.0 wt %, Si 7.0-10.0 wt %, Mg<0.5 wt %, Zn<1.0 wt %, Fe<1.0 wt %, Mn<0.5 wt %, Ni<0.3 wt %, Ti<0.2 wt %, balance Al), and
JIS AC4C alloys (Cu<0.2 wt %, Si 6.5-7.5 wt %, Mg 0.20-0.4 wt %, Zn<0.3 wt %, Fe<0.5 wt %, Mn<0.3 wt %, Ti<0.2 wt %, balance Al).
As shown in
Once the metal casting process has been completed, the apparatus 1 enters a part ejection stroke whereby the cylinder head is ejected from the apparatus 1. As the upper die 10 rises from the lower die 20 after the casting cycle has been completed, the casted cylinder head “sticks” to the upper die 10. This occurs because cylinder heads for use in internal combustion engines generally have a large size and a complicated shape, resulting in a low cooling rate during the casting.
As illustrated in
As a result of the clean pins, tar collects only on the top surface of the cast cylinder heads. This reduces tar build-up on the clean pins 50, allowing the tight plugs 40 to effectively vent out core gases.
As illustrated in
A clean pin head 52 is located at one end of the clean pin 50 along the longitudinal axis A. At least two stepped portions 51 are required for the clean pin. An embodiment of the present invention includes four stepped portions 51. More than four stepped portions 51 may also be used. Each stepped portion 51 includes a chamfer 53 at an end of the stepped portion 51 furthest from the head 52 such that there is a smooth connection between two adjacent stepped portions. Preferably, the chamfer 53 is at an angle between 15 and 30 degrees from the axis A.
The material used for the clean pin 50 of the present invention is H-13 steel, which is also the same material as the dies 10, 20 and the tight plugs 40. H-13 steel is commonly used as a tooling material used in die casting for casting aluminum alloys, especially for part designs with critical features and/or if high production runs are employed. H-13 steel yields a higher resistance to heat checking, cracking and die wear caused by the thermal shock associated with the die casting process. However, other materials suitable as tooling materials may be used for the clean pins.
Prior to installation in the apparatus 1, the clean pins 50 undergo a heat treatment in order to harden the clean pin 50. The heat treatment may be a T6 heat treatment or the like. After undergoing the heat treatments, the clean pins 50 have a smooth surface and a hardness of HRC 42-45. Additionally, after the heat treatment, the clean pins 50 are also subjected to a nitride treatment to harden the outside surface of the clean pins 50 to improve wear resistance. In an exemplary embodiment, the nitride layer on the surface of the clean pins 50 has a hardness of at least HV700.
After undergoing the heat treatments and nitriding processes, the clean pins 50 are fixedly attached to the ejector plate 30 through a counter bore hole 31 made in the ejector plate 30 corresponding to each clean pin 50. The clean pin head 52 fits in the pocket 32 of the hole and a lid (not shown) holds the clean pins 50 in place in the pocket 32. The clean pins 50 have a length of approximately 250 mm. In a preferred embodiment, the clean pins 50 are pushed downwards approximately 50 mm from the top to the bottom of the part ejection stroke. As a result of the heat treatments and the nitriding treatments, the clean pins 50 are durable and have a long life in the absence of a machine or process malfunction in the overall apparatus 1.
A tight plug 40 into which the clean pins 50 lower into during the part ejection stroke is illustrated in
An example of the present invention is presented below by way of illustration without intent to limit the scope of the claimed invention.
A clean pin was machined using H13 steel containing four stepped portions. The first stepped portion including a chamfered edge had a length of 136.60 mm and a diameter (thickness) of 17 mm. The second stepped portion including a chamfered edge had a length of 37.1 mm and a thickness of 15 mm. The third stepped portion including a chamfered edge had a length of 27.73 mm and a thickness of 9 mm. The fourth stepped portion including a chamfered edge had a length of 43.97 mm and a thickness of 7 mm. Each of the lengths and thicknesses of the stepped portions had tolerances of 0.10 mm. The ends of the stepped portions were chamfered at 15 degrees. The clean pin head had a thickness of 24 mm and a length of 7 mm. The overall length of the clean pin was 252.4 mm. The heat treatment was a T6 treatment and the nitride treatment was a HV 700 treatment.
Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
