Patent Application
20240181523
The present disclosure relates to ultra-large die castings, more particularly, to insert pins and a method of using the same for high pressure die-casting of ultra-large vehicle components.
High pressure die casting (HPDC) is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity having a predetermined shape of a desired casting. Modern vehicles, especially those of hybrid and electric vehicles, are moving toward simpler vehicle body designs that use ultra-large die cast panels and components. Ultra-large castings formed of an aluminum casting alloy allow vehicle bodies to be lighter and less complex to manufacture by replacing the large number of stamped panels required to form the vehicle body with fewer ultra-large single-piece castings. These ultra-large castings are often referred to as mega-castings or giga-castings due to the huge size of the die casting machines used to make these castings. As an example, an ultra-large single-piece casting can have a width of at least 0.8 meter (m), a length of at least 1 m, and a height of at least 0.25 m.
Individual castings may be assembled and joined by bolting the castings together. Load bearing members such as bosses are designed into the castings to the receive bolts or studs. A boss is typically a cylindrical protrusion extending from a wall of a casting and has a thicker cross-section than that of the wall. The thicker cross-section enables the boss to function as a load bearing member. The bolt holes are drilled and tapped to provide internal threads after the casting has solidified and ejected from the mold. The bolt holes may be through-holes extending completely through the boss or blind-holes extending partially through the bosses.
Thus, the current ultra-large castings having bosses with internal threaded bolt holes achieve their intended purpose for joining separate castings together with bolts or studs, there is a continued need to improve the strength and robustness of these bosses while increasing the manufacturing efficiency of the ultra-large castings.
According to several aspects, a system for casting a vehicle component is disclosed. The system includes an insert pin having a first portion with external threads and a second portion extending from the first portion. The system also includes a mold having an interior surface defining a mold cavity and a bore in communication with the mold cavity. The second portion of the insert pin is receivable in the bore such that the first portion of the insert pin extends into the mold cavity. A portion of the mold cavity defines a boss shaped cavity, and the first portion of the insert pin extends into the boss shaped cavity
In an additional aspect of the present disclosure, the first portion of the insert pin includes a distal end. The external threads taper from a first thread depth to a second thread depth lesser than the first thread depth in a direction toward the distal end. The second thread depth is 50% to 75% of the first thread depth. The first portion of the insert pin includes a nitride coating and the second portion of the insert pin includes an end surface defining a key pocket have a predetermined shape.
In another aspect of the present disclosure, the system further includes a sleeve having internal threads fastenable onto the external threads of the first portion of the insert pin. The sleeve includes an external surface defining at least one of an indent, a protrusion, and a spine.
In another aspect of the present disclosure, the insert pin further includes a collar integrally connecting the first portion and the second portion, wherein the collar includes an annular surface facing toward the second portion. The mold further includes an annular seat surface surrounding the bore opening and facing the mold cavity, wherein the annular seat surface cooperates with the annular surface of the collar to limit the insertion of the insert pin into the bore from the mold cavity. The bore is configured to receive an application of a vacuum sufficient to fix the second portion of the insert pin in the bore.
In another aspect of the present disclosure, the insert pin includes an annular shoulder facing the first portion. The bore includes an interior opening and an exterior opening. The mold further includes an interior annular surface in the bore facing toward the exterior opening and configured to abut the annular shoulder of the insert pin in response to the insert pin received in the bore from the exterior opening.
According to several aspects, a die casting system having a mold with an interior surface defining a boss shaped cavity and a bore in communication with the boss shaped cavity. The system further has an insert pin including a first portion having external threads and a second portion extending from the first portion, wherein the second portion is receivable in the bore such that the first portion extends into boss shaped cavity.
In an additional aspect of the present disclosure, the insert pin includes an annular shoulder facing the first portion. The bore includes an interior opening in direct communication with the boss shaped cavity and an exterior opening opposite the interior opening. The mold further includes an interior annular surface in the bore facing the exterior opening, a sealing plate for selectively sealing the exterior opening of the bore, and a biasing member disposed in the bore. The biasing member urges the insert pin, when received in the bore, in a direction toward the interior opening such that the annular shoulder of the insert pin abuts the interior annular surface of the bore.
In another aspect of the present disclosure, the insert pin further includes a collar integrally connecting the first portion and the second portion. The collar includes an annular surface facing toward the second portion. The interior surface of the mold further defines an annular seat surface surrounding the bore opening. The annular seat surface cooperates with annular surface of the collar to limit the insertion of the insert pin into the bore from the boss shaped cavity.
In another aspect of the present disclosure, the first portion of the insert pin includes a nitride coating comprising at least one of Titanium Nitride (TiN), Titanium Aluminum Nitride (TiAlN), Titanium Carbonitriden (TiCN), and Aluminum Titanium Nitride (AlTiN).
In another aspect of the present disclosure, the system further includes a metallic sleeve having internal threads complementary to the external threads of the first portion of the insert pin such that the metallic sleeve is fastenable to the first portion of the insert pin. The metallic sleeve includes an exterior surface comprising a coating of at least one of a Zinc (Zn), Nickel (Ni), and an Al-12% Si eutectic alloy.
According to several aspects, a method of casting a vehicle component is disclosed. The method includes providing a mold having an interior surface defining a mold cavity and a bore having an interior opening in direct communication with the mold cavity; providing an insert pin having a first portion and a second portion, wherein the first portion includes external threads; inserting the second portion of the insert pin into the bore such that first portion extends into the mold cavity; filling the mold cavity with a molten metal, wherein the molten metal encapsulates the first portion; cooling the molten metal to a solidified casting; and removing the insert pin from the solidified casting by unfastening the insert pin.
In an additional aspect of the present disclosure, the mold cavity includes a portion defining a boss shaped cavity; and the first portion of the insert pin extends into the boss shaped cavity
In another aspect of the present disclosure, the method further includes cooling the molten metal to about 300° C. to 500° C. to form a solidified casting and unscrewing the insert pin at about 300° C. to 500° C.
In another aspect of the present disclosure, the first portion includes a distal end and the external threads taper from a first thread depth to a second thread depth. The second thread depth is 50% to 75% of the first thread depth.
In another aspect of the present disclosure, the method further includes fastening a sleeve onto the first portion of the insert pin before filling the mold cavity with a molten metal. The molten metal encapsulates the sleeve. The sleeve includes a textured outer surface having a predefined pattern or shapes such as dimples, bumps, and duck tail shaped extensions to improve the joining of the sleeve to the casting.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. The illustrated embodiments are disclosed with reference to the drawings, wherein like numerals indicate corresponding parts throughout the several drawings. The figures are not necessarily to scale, and some features may be exaggerated or minimized to show details of particular features. The specific structural and functional details disclosed are not intended to be interpreted as limiting, but as a representative basis for teaching one skilled in the art as to how to practice the disclosed concepts.
Aluminum-silicon based alloys are typically used for die casting vehicle body components due to the alloys' lightweight, superior moldability, mass producibility, and high strength. These aluminum-silicon ultra-large castings can have intricate details and varying thicknesses throughout the cross-sectional areas of the castings. Load bearing members, such as bosses are commonly designed in aluminum castings. For the purpose of this disclosure, a boss is any raised or protuberant part of a casting. A boss may include a bolt hole having internal threads for receiving a threaded bolt or stud. The bolt hole may be a through-hole that extends completely through the cross-section of the boss or a blind-hold that extends partially through the cross-section of the boss.
Traditionally, after a solidified casting is ejected from the die casting mold, Computer Numerical Control (CNC) machining is used to drill and tap a boss. As bosses are usually heavy with much larger cross-sections compared with typical casting wall thickness, a significant number of hot spots and amount of shrinkage porosity are generated in the bosses during casting solidification. The increasing in porosity is not conducive for forming robust internal threads by traditional drilling and tapping. The following disclosure provides a smart insert pin and a method of utilizing the same for casting thicker load bearing members, such as bosses, with bolt holes having robust internal threads. The smart insert pin eliminates the need for CNC machining of the bosses to form the bolt holes and internal threads.
The mold 102 is typically formed of two pieces 102a, 102b, in which one is a stationary piece 102a and the other is a removable piece 102b configured to facilitate the removal of the solidified casting. A portion of the mold cavity defines a shape of a boss 124. At least one of the mold pieces 102a, 102b defines a bore 120 for receiving a smart insert pin 122, which is described in detail below. The bore 120 is in direct communication with the portion of the mold cavity defining the boss 124.
The ultra-large casting 200 is manufactured by casting an aluminum-silicon (Al—Si) based alloy using the die casting system 100. The molten aluminum-silicon based alloy is injected by the plunger mechanism 108 through the shot sleeve system to fill the mold cavity 106, including the portion of the mold cavity defining the boss 124, within a prescribed time and pressure. The molten metal is cooled to solidification in the mold 102 and ejected from the mold 102. The ejected solidified casting 200 is then machined to design dimensions and tolerances, and heat treated as necessary to desired specifications. The boss 224, bolt hole 226, and internal threads 228 are formed during the die casting process.
Most metals are less dense as a liquid than as a solid, therefore the castings may shrink upon cooling as the molten metal solidifies. The thicker portions of the casting, such as the boss 224, shrink proportionally greater than the comparatively thinner portions of the casting, such as the wall 266. To account for non-desirable formation of porosity due to shrinkage of the casting during the cooling and solidification stage, a portion of the insert pin 122 is disposed in the cavity of the mold defining the boss 224 before the molten metal is poured into the cavity 106. The insert pin 122 decreases the volume of molten alloy required to cast the boss 224 and functions as a heat sink to form a casting skin 229 on the internal surface 229 of the bolt hole 226, the internal threads 228, and the immediate sublayer beneath the surface of the bolt hole. The casting skin 229 has less porosity than the core of the casting and thus provides a more robust internal threads 228 than the internal threads manufactured by the traditional drill and tap method. Based on laboratory fatigue strength testing, test samples of castings having the casting skin 229 intact exhibits a 10 to 15% increase in fatigue strength as compared to test samples of castings in which the casting skin is removed.
The first portion 402 includes a distal end 418 spaced from the collar 406. The external thread 404 is tapered from the collar 406 to the distal end 418, in which the external threads 404 proximal to the distal end 418 includes a thread depth of 50% to 75% of the thread depth proximal to the collar 406. The thread depth is defined as the distance between the crest 420 and the root 422 of a thread which is measured normal to the longitudinal axis-A extending through the length of the insert pin 400. The tapered threads help the insert pin 400 removal from the solidified casting 200 and enhance bolt engagement and load retention.
A removable end plate 728 is provided for selectively sealing the exterior opening 726 of the bore 720. The end plate 728 may be fixed to mold by removable bolts 730 or screws 730. A biasing member 732, such as coiled springs 732, is disposed between the end surface 614 of the second portion 608 of the insert pin 600 and the end plate 728. The biasing member 732 urges the annular shoulder 610 of the insert pin 600 against the interior annular surface 722 of the opening, thus limiting the insert pin 600 from fully entering the cavity 706.
Referring to
Molten metal is cast onto the exterior surfaces 804, 904 of the sleeves 800, 900. Once the casting has solidified, the insert pins 400, 600 are unscrewed, or unfastened, from the sleeves 800, 900 leaving the sleeves 800, 900 in the solidified casting 200. The sleeves 800, 900 with the internal threads 82, 902 remain as part of the casting. While the outer surfaces 804, 904 of the sleeves 800, 900 are shown to be cylindrical in shape, it should be appreciated that the outer surface 804, 904 may define any other shapes that may provide an improved metallurgical bond and/or mechanical locking to the casting.
Referring to
Moving to Block 1304, the method includes providing an insert pin having at least a first portion and a second portion. The first portion includes external threads. Inserting the second portion of the insert pin into the bore such that the threaded first portion extends in the portion of the cavity defining the load bearing member. A nitride coating may be applied on at least the first portion of the insert pins to prevent soldering or metallurgical bonding with the casting. The nitride coating may be applied by ion/plasma nitriding and controlled gas nitriding. Examples of nitride coating includes Titanium Nitride (TIN), Titanium Aluminum Nitride (TiAlN), Titanium Carbonitriden (TiCN), and Aluminum Titanium Nitride (AlTiN).
Moving to Block 1306, filling the mold cavity with a molten metal, wherein the molten metal encapsulating the threaded first portion, and cooling the molten metal to a predetermine temperature in which the molten metal has solidified.
Moving to Block 1308, the method ends by removing the insert pin from the solid casting by unfastening the insert pin. Referring to
The optimal timing for the removal of the smart insert pins from the casting may be determined with sophisticated casting solidification and residual stress simulations. The casting should be solidified and cooled down to a temperature of about 300° C. to 500° C. to have sufficient strength to be able to remove the pin. However, the removal of the pin can be difficult if the casting is cooled down to room temperature as the aluminum will shrink causing more compressive residual stress to be developed around the insert pin. The optimal timing for the removal of the smart insert pins from the casting may be determined based on casting solidification and residual stress simulations for a specific casting.
Computer Numerical Control (CNC) machining of bosses, particularly in ultra-large or giga castings can be very difficult and expensive. The above disclosed smart insert pins produce threaded internal diameter holes in the bosses. The smart insert pins also enable cast-in-place metal inserts with internal threaded holes in the bosses. The smart insert pins reduce or eliminate the requirement of CNC machining for forming the bolt holes with internal threads. It should be appreciated that the insert pins, together with the sleeves, are not limited to high pressure die casting. The insert pins may be also used in other casting process including, but not limited to squeeze casting, low pressure casting, and semi-permanent mold casting.
The description of the present disclosure is merely exemplary in nature and variations that do not depart from the general sense of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.
