Patent Application
20080241579
The present invention relates generally to a cast component, and more particularly a cast component having localized areas of improved physical properties.
Cast components are often designed to the limit of their mechanical properties to take advantage of strength to weight ratios. The requirement for more stringent emissions is also a contributing factor due to seeking high combustion pressures and temperatures. Because of the physical characteristics of cast materials, specifically gray cast iron in engine applications, the thermal fatigue limit is often reached causing failure in certain areas of the component. When this happens, it is difficult and time consuming to repair castings and other components often resulting in significant downtime and costs for the component owner. Typically repairs to castings involve removing damaged portions of the casting through machining, and subsequently rebuilding the damaged area by welding.
An example of a component that is susceptible to damage is the cylinder head of an internal combustion engine. Because of repeated heating and cooling of the engine, the cylinder heads often reach their thermal fatigue limit and develop cracks near openings, such as valve seats, fuel injector bores, and exhaust ports. Another problem associated with cylinder heads is warping. When warped, the bottom surface of the head becomes uneven and does not seal properly. Some warped cylinder heads can be milled until the fireside surface is again flat. However, milling the surface reduces the thickness of the head, making the head more susceptible to future operating damage. Heads that can't be milled flat are typically scrapped.
One example of producing a casting having localized areas of improved thermal resistance of the cylinder head is U.S. Pat. No. 4,337,736 (the '736 patent) issued to Raush et al. The '736 patent discloses a cast iron cylinder head having a preformed workpiece of a thermal fatigue-resistant alloy material metallically bonded to the cylinder head around the valve bridge area to provide reinforcement in this area. The preformed workpiece has thin fusible sections, which melt when the hot base material is cast over them. Although the disclosure of the '736 patent may provide for localized areas of improved thermal resistance, it may be costly and have limited applicability.
The present disclosure is directed to overcoming one more of the problems set forth above.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
One aspect of the present disclosure is directed to a method of producing a component. The method may include form forming the component to include a void portion, heating the component to a first predetermined temperature, and adding a quantity of molten filler material into the void portion. The molten filler material may then further heat the void portion to chemically bond the filler material to the void portion.
Another aspect of the present disclosure is directed toward the component itself. The component may comprise a first component portion made from a first material and a second component portion made from a molten filler material. The first component portion may be produced with a void portion. The molten filler material may be cast into the void portion such that the second component portion is chemically bonded to the first component portion.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,
a is a sectional view of the cylinder head of
a is sectional view of the first component portion of
b is a sectional view of the first component portion of
c is sectional view of the first component portion of
d is a sectional view of the first component portion of
a is a sectional view of the cylinder head 10 of
Referring now to
In the third control block 204, the component 10 may be preheated to a predetermined temperature. The preheat temperature will vary depending on the type and thickness of material surrounding the void portion 30 and the type and amount of molten filler material 60 being added to the void portion 30. For proper determination of preheat temperature, computer simulation or experimentation may be necessary. It may desirable to preheat the first component portion 15 as much as possible without damaging the component 10. Depending on the component 10, types of damage may include stress relieving and warping caused by overheating or melting of the original surface. On the other hand, failure to preheat the component 10 to high enough of a temperature may cause cracking of the parent material when the melted filler material is poured or lack of bonding between the two materials. In one embodiment, the preheat temperature for a cast iron cylinder head 10 may be in the range of 950° F. to 2000° F. For certain types of cylinder heads 10, a preheat temperature of 1100° F. has been found to reduce stress and warping while reducing the risk of cracking.
In the fourth control block 206, a quantity of filler material 60, or second component portion, is melted and poured into the void portion 30 of the first component portion 15. As the melting point of the first component portion 15 and the second component portion 60 may be the same or may be different, the melting point of the second component portion 60 may be exceeded to cause further heating of the first component portion 15 at the void portion 30. As the molten filler material 60, or second component portion, and the first component portions cool, a metallurgical bond may be formed between the filler material 60 and the first component portion 10 at a bond layer 65. In the final control block 208, the component 10, including the solidified filler material 60, may be machined to a final component shape.
Embodiments of the present disclosure may be applicable to produce a variety of components having localized areas of improved physical properties, such as improved thermal fatigue properties, hardness, and the like. Referring now to
As shown in
b is a sectional view of the first component portion 15 of
As described in the second control block 204, the cylinder head 10 may be preheated in an oven to a first temperature. In one embodiment the first temperature range is in the range of 950° F. to 2000° F., more preferably 1050° F. to 1150° F. From the preheat oven, the cylinder head 10, with the graphite plugs 40 and dams 50 in position, may be moved to a heated and insulated box (not shown) adapted to maintain the first temperature range and allow for addition of the molten filler material 60.
A quantity of filler material 60, such as cast iron, or other material suitable to attain the desired gradient properties in the void portion 30 is prepared by melting. For example, the filler material 60 may be melted in a crucible and held in a furnace at a temperature sufficient to complete a porosity free bond with the parent material. In the case of a cylinder head 10, the temperature may be approximately 2725° F. The filler material 60 may be of a chemical composition similar to that of the cylinder head 10 or component, or it could be quite different depending on the properties desired.
It is envisioned in the present disclosure that it may be necessary to locally heat the void portion 30 of the first component portion 15 to a second predetermined temperature. The second predetermined temperature may vary depending upon the type, mass and wall thickness of the parent material and the volume of filler material 60. The second predetermined temperature range is hot enough to permit bonding of the void portion 30 and filler material 60, but cool enough to prevent the filler material 60 from melting through the parent material of the void portion 30. The lower limit of the range may be determined through simulation and/or experimentation and may account for factors such as material shrinkage, bonding strength, microstructure, and stress associated the parent and/or filler material. Factors that impact bonding point may include type and volume of the parent material, the type and volume of the filler material, the chemistry of the parent component. Additionally, the second preheat temperature may prevent rapid cooling of the filler material 60, in turn maintaining desired mechanical properties. Additionally or alternatively, the molten filler material 60 may be heated beyond its melting point to further increase heating of the first component portion 15.
A quantity of welding flux (not shown) may also be applied to the void portion 30. The flux may act to remove oxidation, other contaminants, and aids in wetability of the filler material 60 onto the void portion 30 after the molten filler material 60 is poured. A typical flux may be manufactured from a borax-based material. With the temperature of the void portion 30 within second temperature range, molten filler material 60 may be removed from the furnace. Slag that may be floating on the surface of the molten filler material 60 may be skimmed from the melted filler material. With the molten filler material 60 substantially free of slag, it is poured into, and fills the void portion 30 as shown in
After addition of the molten filler material 60, the component 10 may then be allowed to cool. In one embodiment, the component 10, or a portion thereof, may be partially cooled using compressed air. A wand (not shown) having a diffuser attached thereto and being attached to a compressed air source may be moved about, over the filler material 60. In one embodiment, to achieve desired mechanical properties, such as hardness and microstructure, it is desired to employ a cooling rate sufficient enough, depending on chemistry, to cool the entire volume of the void portion 30 to achieve desired microstructure, or transformation products, of the matrix structure at a newly formed bond layer 65 between the void portion 30 and the filler material 60. For example using cast iron and dependent on the volume of material affected, it may be desired to bring the temperature of the void portion 30 down to a range of 1100° F. to 1200° F. in a time period of 30 to 180 seconds. After all void portions 30 have been filled, the cylinder head 10 may be cooled, preferably, at a rate slow enough to avoid distortion or cracking of the component. The plugs 40 and dams 50 may then be removed as shown in
