Spreaders for Die Casting and Methods of Making the Same

This application claims the benefit of Chinese Patent Application No. 202410683031.5 filed on May 29, 2024. The entire disclosure of the application referenced above is incorporated herein by reference.

The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The present disclosure relates to die casting systems, and more particularly to spreaders of dies used in die casting.

Non-ferrous metals and metal alloys used to manufacture parts of consumer products may be shaped via die casting processes. In die casting, a volume of molten nonferrous metal referred to as a “shot” is forced through a sprue bush and into a cavity in a die via a plunger. The molten metal is allowed to cool and solidify within the cavity prior to removal of the casted part from the die. In some casting processes (e.g., high pressure die casting processes), molten metal is forced into the cavity under high pressure (e.g., 1,500-25,400 pounds per square inch (psi)).

A die casting system can include a die with a first die half and a second die half, which are moved relative to each other during a die cast process. During die casting, the die halves are brought together and molten metal is pushed through a sprue bush towards a spreader. The spreader is fixed at the center of the die cavity of the mold. When the molten metal enters the mold, the molten metal flows over the sprue spreader at the tail end of the main flow passageway and then fills the die cavity. The molten metal flows to open areas between the plunger and the spreader and between the die halves. The open areas include a biscuit area, a gate system area, and a die cavity. The molten metal fills the open areas and then cools and hardens to form a biscuit, a gate system, and a resultant part. The biscuit and the gate system are cut away from the part after casting and recycled or discarded.

A spreader configured to be implemented in a die of a die casting system is disclosed. The spreader includes: a substrate; a hardening layer and an oxide layer. The hardening layer includes: a nitride and carbide layer disposed on the substrate and increasing hardness; and a white layer disposed on the nitride and carbide layer. The oxide layer includes: an inner transition layer disposed on the white layer and increasing resistance to oxidation; and an outer iron oxide layer disposed on the inner transition layer and increasing resistance to soldering during die casting of a part in the die casting system.

In other features, the substrate includes at least one of martensite, bainite, and ferrite.

In other features, the substrate includes nanoprecipitation having size less than 50 nm.

In other features, thermal conductivity of the substrate is greater than 38 watt per meter-kelvin (W/mK).

In other features, the hardening layer has a hardness of greater than or equal to 65 HRC.

In other features, the spreader includes a body including: a first disc; a second disc; and a channel cut into the first disc and the second disc. The channel includes a guide surface for guiding molten metal during a die casting process of the part.

In other features, a thickness of the outer iron oxide layer is 0.5-10.0 μm.

In other features, a thickness of the inner transition layer is 0.1-5.0 μm.

In other features, the outer iron oxide layer mainly includes by weight 70-74% iron, 25-30% oxygen, and 1-5% aluminum.

In other features, oxide in the inner transition layer includes by weight 70-78% iron, 20-25% oxygen, and 1-5% aluminum.

In other features, metal in the inner transition layer includes by weight 4-20% nickel and 1-5% copper.

In other features, a thickness of the white layer is 0.5-2.0 μm and a thickness of the nitride and carbide layer is 80-300 μm.

In other features, a chemical composition of the substrate includes by mass 0-0.2% carbon, 0.2-6% copper, 3-10% nickel, 0.5-3% aluminum, 0.2-1.5% manganese, 0-1.5% chromium, 0-2.5% molybdenum, 0-1.5% tungsten, and 0-0.2% vanadium.

In other features, the inner transition layer includes a sawtooth structure.

In other features, a die casting system including: the spreader of claim; and the die including a first half and a second half. The spreader is attached to the first half and guides molten metal from a sprue bush into a gate system area and a cavity of the die during the die casting process.

In other features, a method of forming a spreader for a die casting system is disclosed. The method includes: providing a forged block of tool steel; machining the block of tool steel to form a preliminary spreader; austenitizing the preliminary spreader; subsequent to austenitizing preliminary spreader, cooling the preliminary spreader to room temperature; subsequent to cooling the preliminary spreader, machining the preliminary spreader to form a final spreader; and subsequent to machining the preliminary spreader, form a hardening layer and an oxide layer by i) nitrocarburizing the spreader and oxidizing the nitrocarburized spreader or ii) oxy-nitrocarburizing the spreader. The hardening layer includes a nitride and carbide layer disposed on a substrate and a white layer disposed on the nitride and carbide layer. The oxide layer includes an inner transition layer disposed on the white layer, and an outer iron oxide layer disposed on the inner transition layer.

In other features, the method further includes, subsequent to machining, nitrocarburizing the preliminary spreader and oxidizing the nitrocarburized spreader to form the hardening layer and the oxide layer.

In other features, the method further includes, subsequent to machining, oxy-nitrocarburizing the preliminary spreader to form the hardening layer and the oxide layer.

In other features, the method further includes, subsequent to forming the oxide layer, machining the final spreader.

In other features, a chemical composition of the block of tool steel includes by mass 0-0.2% carbon, 0.2-6% copper, 3-10% nickel, 0.5-3% aluminum, 0.2-1.5% manganese, 0-1.5% chromium, 0-2.5% molybdenum, 0-1.5% tungsten, and 0-0.2% vanadium.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

In the drawings, reference numbers may be reused to identify similar and/or identical elements.

During each time die casting a part, a surface layer of a spreader of a die is contacted with high temperature molten metal. The same die and spreader are used to die cast multiple parts. This causes a surface layer of the spreader to softened because of increasing temperature, which reduces erosion resistance. Each time after opening the mold, it is needed to blow and spray compressed air and lubricating coating on the surface of the spreader to rapidly cool the spreader. As such, the surface layer of the spreader is subjected to periodic thermal stress and corrosion action, formation and expansion of surface microcracks are caused, and finally, a thermal fatigue phenomena of cracking and stripping occurs. At high temperatures, iron is easy to be corroded by molten metal. The chemical and mechanical reaction between molten metal and substrate of the spreader can induce surface corrosion and soldering on the spreader. For the above reasons, the sprue spreader will be scrapped due to hot melting loss.

Die casting is performed at high temperatures, for example, the molten metal that is pushed into a die to form a part can be at temperatures greater than 500° C. As an example, the molten metal may be molten aluminum (Al). A spreader of the die is exposed to the molten metal and can thermally fatigue failure, erode and/or washout over time. The spreader is exposed to consistently high temperatures, periodic thermal stress and is flushed by molten metal at excessive velocities. The spreader can also experience soldering/or corrosion, where tiny portions (or bits) of the molten can harden onto the spreader and thus alter the shape and degrade the performance of the spreader. The spreader can be referred to as a sprue spreader and a distributor. The spreader may be in the form of a single unitary structure and/or include multiple distributor rings. During operation, molten metal is pushed towards the spreader from a sprue bush, fills a biscuit area, and is guided to and through a gate system area and into a die cavity. The molten metal in the biscuit area, the gate system area, and the die cavity are cooled during a cooling stage to form a biscuit, a gate system and a part.

The resultant biscuit, which is formed due to solidification of molten metal in the biscuit area, can have a thickness of 20-35 millimeters. The biscuit is designed to ensure the flow of molten (or liquid) metal (e.g., aluminum alloy) and to ensure integrity and mechanical properties of parts. Due to the size and thickness of the biscuit, the biscuit last to solidify during the cooling stage. The solidification rate of the biscuit thus determines the corresponding ejection time and production time of the part being formed. The cooling of the biscuit tends to be the “bottleneck” in the production process.

The examples set forth herein include spreaders and methods of forming the same. The spreaders have improved thermal fatigue resistance, wear resistance, and corrosion resistance. The spreaders have high thermal conductivity properties and thus fast cooling rates. The spreaders have a fast heat removal rate and thus a shorter total cycle time for improved production efficiency and reduced corresponding costs. The spreaders also have high hardness levels and are resistant to erosion/or washout. The spreaders are less susceptible to corrosion and soldering during molten metal filling operations. The spreaders are thermal fatigue, corrosion, erosion and washout resistant and thus have a higher service life expectancy.

In some embodiments, spreaders are provided for high pressure aluminum die casting that exhibit improved cooling and solidification rates as well as tool service life. The spreaders are made of a tool steel having a unique composition, as disclosed herein, that provides particular attributes including a fast-cooling rate and high resistance to corrosion, erosion, washout, and soldering. The spreaders also exhibit high thermal conductivity, which is attributed to their nano-copper (Cu) particles and coherent interfaces between precipitates and substrate matrices. This facilitates a reduction in surface temperatures of the spreaders and an increase in heat removal rates of the spreaders and biscuits being formed. The increase in heat removal rates of the biscuits increases the corresponding solidification rates and thus shortens the solidification times of the biscuits. Each of the spreaders includes i) an anti-sticking iron oxide layer that enhances corrosion and soldering resistance from molten Al, and ii) a hardening layer formed of carbides and nitrides and is disposed between the anti-sticking iron oxide layer and a substrate and improves surface hardness of the spreader. The spreaders increase production efficiency, reduce cost of applications and maintenance, and have a longer service lifetime than traditional spreaders.

shows a die casting systemthat includes a diehaving a first halfand a second half. The diesits in and is held by a mold base set. Portions of the mold base setare held by a movable platenand a fixed platen. The movable platenis moved by a first motor assemblyvia a control module. The first motor assemblyincludes a motorthat moves a shaftconnected to the movable platen. The movable platemoves on rails. A parting linebetween the die halves,and portions of the mold base setis shown. A sprue bushextends through the fixed platenand towards a spreader, which is attached and/or held by the die half. Molten metalis supplied to the sprue bushvia a ladleor other device.

A plunger (or piston)pushes the molten metaltowards the spreader, which guides the molten metal into runner channelsin a gate system area, which has a gate. The molten metal fills a die cavity. Depending on an amount of molten metal supplied, the molten metal may at least partially fill an overflow area. A plungeris moved by a shaft, which is driven by a second motor assemblyvia the control module. The second motor assemblyincludes a motorthat moves the shaft.

The die casting systemfurther includes an ejector back plate, an ejector plate, and ejector pins. The plates,and ejector pinsare moved via a third motor assemblyvia the control module. The third motor assemblyincludes a motorthat moves a shaftthat is connected to the back plate.

The die casting systemmay perform various operations during a die casting process, which may include the use of one of the spreaders disclosed herein. The operations may include opening the die(separating the die halves,), lubricating the die halves,, closing the die(bringing the die halves,together), supplying molten metal at high pressure (e.g., 20-120 mega-pascals (Mpa)) and filling the die cavitywith the molten metal, cooling the molten metal in the die cavityto form a part, and releasing the part from the die cavity. The supplying of the molten metal may be done manually or automatically by a robot or machine. The molten metal may include Al and/or one or more other nonferrous metals, such as magnesium (Mg), zinc (Zn), and Cu. The molten metal may include one or more alloys of Al, Mg, Zn, and Cu. The die halves,may have cooling channels extending though the die halves,for cooling the part. Cooling fluid is circulated through the channels.

Subsequent to solidification, the dieis opened and the die halves,are separated and the solidified shot including the casted part, the gate system and the biscuit are ejected from the dieat the same time by the ejector pins. The gate system and biscuit are formed in the gate system areaand a biscuit area, which is between the spreaderand the plungerwhen the plungeris fully deployed (or pused) into the sprue bush. The shot is then removed from the die cavity area by hand or robot. The gate system and the biscuit are removed from the part. This may also include removal of one or more other unwanted portions, such as an overflow portion formed in the overflow area.

Examples of the spreaderand methods of forming the same are described below with respect to. Two example spreaders are shown in. These spreaders and other spreaders may be formed using the methods disclosed herein.

shows a spreaderthat includes a body. The bodymay be a solid body or a hollow body. The bodymay include an outer (or base) ring or disc, an inner ring or disc, a planar surface, and a guide surface. When the bodyis solid, the guide surfacemay be notched into the discs,, as shown. The guide surfaceextends along a notched sideof the inner discand into an end portionof the outer disc. The guide surfaceguides molten metal into runner channels (or areas) of a gate system area. The guided surfaceis a complex surface that may direct molten metal in multiple directions, for example, towards and into two runner areas.shows a gate systemincluding a biscuitand two runners.

shows another spreaderthat includes a body. The bodymay be a solid body or a hollow body. The bodymay include an outer (or base) ring or disc, an inner ring or disc, and a guide surface. When the bodyis solid, the guide surfacemay be notched into the discs,including into an end surfaceof the inner disc, as shown. The guide surfaceincludes three portions,,. Each of the portions,,includes a bottom surface and side surfaces to guide molten metal. The first portionextends along an end surface (or ledge)of the base disc. The second portionextends along a portionof the inner disc. The third portionextends along the top surface. The guide surfaceguides molten metal into one or more runner areas of a gate system area. The guide surfaceis a complex surface that may direct molten metal in one or more directions, for example, towards one or more runner areas.

The spreaders disclosed herein are formed using the methods disclosed herein and have chemical compositions disclosed herein.shows a plot of resistance versus thermal conductivity for different spreader materials. A first regionis associated with spreader H13 steel, a second regionis associated with three-dimensional (3D) printed spreader material, and regions,are associated with spreader tool steel for examples disclosed herein. The regionis associated with spreaders formed of tool steel disclosed herein that has been austenitized and age hardened. The regionis associated with spreaders formed of tool steel disclosed herein that has been surface treated after austenitized and age hardened.

Spreaders associated with regionsandhave a higher thermal conductivity (or cooling rate) than spreaders associated with region. Spreaders associated with regionare more resistive to corrosion, erosion, washout and soldering than spreaders associated with regionsand. Spreaders associated with regionmay have a hardness Rockwell C (HRC) scale rating of 45-48. Spreaders associated with regionmay have a HRC scale rating of 43-45. Spreaders associated with regionhave a HRC scale rating of greater than or equal to 42. Spreaders associated with regionmay have a HRC scale rating of greater than or equal to 65. The regionis associated with the herein disclosed tool steel without surface treatment. The regionis associated with the herein disclosed tool steel with surface treatment as disclosed herein. The surface treatment includes i) nitrocarburizing and oxidizing, or ii) oxy-nitrocarburizing.

shows a portionof a spreader. The spreader includes a substrateinto which and on which multiple layers are formed. The substrate is a steel substrate. An example chemical composition of the steel substrate is provided below. A hardening layeris formed on the substrate. The hardening layerincludes a white layerand a nitride and carbide layer. The white layermay be dissociated into the substrateand pearlite (N) formation occurs during the casting process to provide a resulting substrate. The white layermay be discomposed into matric and transformed into pearlite to increase hardening depth. Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5% by weight) and cementite (12.5% by weight). The white layerdissociates into substrateand transforms into pearlite to increase the hardness of the material to resist high temperature softening. The hardening layerprovides nanoprecipitation nitride/carbide strengthening. The hardening layeris formed by nitrocarburizing, which increases a high hot hardness level of the material and enhances erosion and washout resistance.

The hardening layerundergoes an oxidizing treatment to form an oxidizing structureincluding an inner transition layerand an outer layer. The oxidizing structure (or oxidizing layers) improves soldering and corrosion resistance of the spreader. The outer layeris an outer iron oxide layer. The inner transition layerhas a “sawtooth” structure, which is represented by jagged lineinand is enriched with Ni and/or Cu metal. The enrichment of Ni and Cu and “sawtooth” structure improve the bonding between i) oxidizing structureincluding the outer oxide layer, and ii) the hardening layerof the resulting substrateand inhibits internal oxidation.

The spreaders disclosed herein have high thermal conductivity, which is attributed to low carbon, chromium, silicon content and the coherence interface between precipitate and matrix of the corresponding substrates. A coherent interface is formed when there is a good match between lattices of the precipitate and the matrix to provide a continuous structure across the interface. The spreaders have high hardness levels and are highly resistive to corrosion and soldering and high temperature softening.

The substates have a micro-structure that may include martensite, bainite, and/or ferrite. The substrates include nanoprecipitation having a size less than 50 nanometers (nm) with austenite (e.g., less than 2% by volume). After austenitizing spreaders as described herein at high temperatures, the substrate material is quenched and has a hardness of less than or equal to 30 HRC. In an embodiment, the hardness is less than or equal to 28 HRC. After age hardening and surface treatment of the spreaders, surface hardness is greater than or equal to 65 HRC. Thermal conductivity at temperatures of 200-500 Celsius (C) is greater than or equal to 38 watt per meter-kelvin (W mK).

The outer layeris referred to as an anti-sticking layer that is formed on a steel surface (or surface). The inner transition layerhas a sawtooth shape and is at an interface between the outer layerand the hardening layer. The inner transition layer provides interpenetration of the outer layer(or iron oxide layer) and the hardening layer.

In an embodiment, a thickness Tof the outer layeris 0.5-10 micrometers (μm) and a thickness Tof the inner transition layeris 0.1-5 μm. In an embodiment, the outer layerincludes by weight 70-74% Fe, 25-30% oxygen (O), and 1-5% Al. In an embodiment, the chemistry of oxide in the inner transition layerincludes by weight 70-78% Fe, 20-25% O, and 1-5% Al. In an embodiment, the chemistry of metal in the inner transition layerincludes by weight 4-20% Ni and 1-5% Cu. In an embodiment, the white layerhas a thickness Tof 0.5-2 μm and the nitride and carbide layerhas a thickness Tof 80-300 μm.

In an embodiment, the chemical composition of the tool steel used to form the substrate, by mass, includes 0-0.2% carbon (C), 0.2-6% copper (Cu), 3-10% nickel (Ni), 0.5-3% aluminum (Al), 0.2-1.5% manganese (Mn), 0-1.5% chromium (Cr), 0-2.5% molybdenum (Mo), 0-1.5% tungsten (W), 0-0.2% vanadium (V), and other chemical elements for the remaining balance of the chemical composition. This composition is different than the composition of H13 steel, which by mass, includes 4.75-5.5% Cr, 1.1-1.75% Mo, 0.8-1.2% Si, 0.8-1.2% V, 0.32-0.45% C, 0.3% Ni, 0.25% Cu, and 0.2-0.5% Mn. The carbon is included to promote the formation of a hard martensitic microstructure during austenitizing. The chromium is included to provide the steel with high oxidation resistance. For H13 steel, chromium, molybdenum, tungsten, vanadium, and/or manganese may be included to promote the formation of carbide particles within the martensitic microstructure during tempering to increase the hardness and strength of the steel.

In an embodiment, Al content of the tool steel used is greater than or equal to 2% to assure full precipitation of Al and reduce the interstitial Al that cause lattice distortion and reduce thermal conductivity and induced internal oxides during service.