There are a number of geometric characteristics that must be taken into account when creating a parametric model of a die casting:.

Contenido

Hay dos tipos básicos de máquinas de fundición a presión: Las máquinas de cámara caliente y las máquinas de cámara fría.[14]​ Se clasifican según la fuerza de sujeción que pueden aplicar. Los valores típicos están entre 400 y 4000 st (2540,1 y 25 401,2 kg).[8]​.

hot chamber casting

Hot chamber die casting, also known as gooseneck machines, relies on a pool of molten metal to feed the die. At the beginning of the cycle, the machine's piston retracts, allowing molten metal to fill the "gooseneck." The pneumatically or hydraulically actuated piston then forces the metal out of the gooseneck into the die. The advantages of this system are the speed of the cycles (approximately 15 cycles per minute) and the convenience of melting the metal in the casting machine. The disadvantages of this system are that it is limited to use with low melting point metals and that aluminum cannot be used because it picks up some of the iron while it is in the melting bath. Therefore, hot chamber machines are mainly used with alloys based on zinc, tin and lead.[14]​.

Cold chamber casting

They are used when the casting alloy cannot be used in hot chamber machines; Among them are aluminum, zinc alloys with a large composition of aluminum, magnesium and copper. The process for these machines begins with melting the metal in a separate furnace.[15]​ A precise amount of molten metal is then transported to the cold chamber machine, where it is introduced into an unheated injection chamber (or injection cylinder). This injection is then introduced into the matrix using a hydraulic or mechanical piston. The biggest disadvantage of this system is the slower cycle time due to the need to transfer the molten metal from the furnace to the cold chamber machine.[16]​.

Two dies are used in die casting; one is called the "covering half array" and the other "ejection half array." The point of union is called separation zone. The coating die contains the sprue (for hot chamber machines) or injection port (for cold chamber machines), which allows molten metal to flow into the dies; This feature matches the injector nozzle on hot chamber machines or the injection chamber on cold chamber machines. The ejector die contains the ejector pins and usually the runner, path from the sprue or injection port to the mold cavity. The cap die is fixed to the front platen of the casting machine, while the ejector die is fixed to the moving platen. The mold cavity is cut into two cavity inserts, which are separate pieces that can be replaced relatively easily and are screwed to the die halves.[17]​.

The dies are designed so that the finished casting slides out of the die cap half and remains in the ejector half when the dies are opened. This ensures that the casting will be ejected each cycle because the ejector half contains the ejector pins to push the casting out of that half of the die. The ejector pins are driven by an ejector pin plate, which precisely drives all the pins at the same time and with the same force, so as not to damage the casting. The ejector pin plate also retracts the pins after ejecting the casting to prepare for the next shot. There must be enough ejector pins so that the total force of each pin is low, since the casting is still hot and can be damaged by excessive force. The pins still leave a mark, so they should be located in places where these marks will not hinder the purpose of the casting.[17]​.

Other components of the matrices are the cores and the slides. Cores are components that typically produce holes or openings, but can also be used to create other details. There are three types of cores: fixed, mobile and loose. Fixed cores are those that are oriented parallel to the direction of pull of the dies (i.e. the direction in which the dies open), so they are fixed, or permanently attached to the die. Mobile cores are those that are oriented in any way other than parallel to the direction of traction. These cores must be removed from the die cavity after the injection solidifies, but before the dies open, using a separate mechanism. Slides are similar to moving cores, except that they are used to form sub-countercut surfaces. The use of moving cores and slides greatly increases the cost of dies.[17] Loose cores, also called pick-outs, are used to cast intricate features, such as threaded holes. These loose cores are introduced into the die by hand before each cycle and then ejected with the part at the end of the cycle. The core must then be removed by hand. Loose cores are the most expensive type of core, due to the additional labor and increased cycle time.[11] Other features of the dies are water cooling passages and vents along the parting line. These vents are typically wide and thin (approximately 0.005 in.) so that when molten metal begins to fill them the metal solidifies quickly and waste is minimized. Risers are not used because the high pressure ensures a continuous feed of metal from the gate.[18]​.

The most important material properties for dies are resistance to thermal shock and softening at elevated temperature; Other important properties are hardenability, machinability, heat check resistance, weldability, availability (especially for larger dies) and cost. The longevity of a die is directly dependent on the temperature of the molten metal and the cycle time.[17]​ Dies used in die casting are typically made of hardened tool steel, as cast iron cannot withstand the high pressures involved, so the dies are very expensive, resulting in high start-up costs.[18]​ Metals that cast at higher temperatures require higher melting temperature alloy steel dies.[19]​.

The main cause of failure of casting dies is wear or erosion. Other failure modes are heat checking and thermal fatigue. Thermal control is when cracks occur on the surface of the die due to a large temperature change in each cycle. Thermal fatigue is when surface cracks occur in the matrix due to a large number of cycles[20].

Los siguientes son los cuatro pasos de la fundición a presión tradicional, también conocida como fundición a alta presión,,[5]​ estos son también la base de cualquiera de las variantes de fundición a presión: preparación de la matriz, llenado, expulsión y sacudida. Las matrices se preparan rociando la cavidad del molde con lubricante. El lubricante ayuda a controlar la temperatura de la matriz y también facilita la extracción de la colada. A continuación se cierran las matrices y se inyecta metal fundido en ellas a alta presión; entre 10 y 175 megapascales (1450,4 y 25 381,6 psi). Una vez que se llena la cavidad del molde, se mantiene la presión hasta que la fundición se solidifica. A continuación, se abren las matrices y la inyección (las inyecciones se diferencian de las coladas porque puede haber varias cavidades en una matriz, lo que da lugar a varias coladas por inyección) es expulsada por los pasadores eyectores. Por último, el sacudido consiste en separar la chatarra, que incluye la compuerta&action=edit&redlink=1 "Compuerta (fundición) (aún no redactado)"), el corredor&action=edit&redlink=1 "Canal (fundición) (aún no redactado)"), el chatarra&action=edit&redlink=1 "Bebedero (fabricación) (aún no redactado)") y el flash&action=edit&redlink=1 "Flash (fabricación) (aún no redactado)"), de la inyección. Para ello se suele utilizar un troquel especial de recorte en una prensa mecánica o hidráulica. Otros métodos para sacudir son el aserrado y el esmerilado. Un método menos intensivo en mano de obra es el volteo de las granadas si las compuertas son finas y se rompen con facilidad; a continuación hay que separar las compuertas de las piezas acabadas. Esta chatarra se recicla refundiéndola.[14]​ El rendimiento es aproximadamente del 67%.[22]​.

La inyección a alta presión conduce a un rápido llenado de la matriz, que es necesario para que toda la cavidad se llene antes de que cualquier parte de la fundición se solidifique. De este modo, se evitan las discontinuidades, aunque la forma requiera secciones finas difíciles de rellenar. Esto crea el problema del atrapamiento de aire, porque cuando el molde se llena rápidamente hay poco tiempo para que el aire salga. Este problema se minimiza incluyendo rejillas de ventilación a lo largo de las líneas de separación, sin embargo, incluso en un proceso muy refinado seguirá habiendo cierta porosidad en el centro de la pieza fundida.[23]​.

La mayoría de los fundidores realizan otras operaciones secundarias para producir características que no son fácilmente moldeables, como tapping") un agujero, pulir, chapar, pulir o pintar.

Inspection

After shaking the laundry, it is inspected for defects. The most common defects are errors and cold closures. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of ventilation, or too much lubricant. Other possible defects are gas porosity, shrinkage porosity, hot breaks, and flow marks. Flow marks are marks left on the surface of the casting due to misguidance, sharp corners, or excess lubricant.[24]​.

Lubricants

Water-based lubricants are the most used type of lubricant, for health, environmental and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all the minerals it contains, it will not leave any byproducts in the dies. If water is not treated properly, minerals can cause surface defects and discontinuities.

Nowadays, "water in oil" and "oil in water" emulsions are used, since, when applying the lubricant, the water cools the surface of the matrix as it evaporates, depositing the oil that helps release the grit. A common mixture for this type of emulsion is thirty parts of water to one of oil, although in extreme cases a proportion of one hundred to one is used.[25] Among the oils used are heavy residual oil, animal fat, vegetable fat, synthetic oil, and all types of mixtures of these. HRO are gelatinous at room temperature, but at the high temperatures found in die casting, they form a thin film. Other substances are added to control the viscosity and thermal properties of these emulsions, for example, graphite, aluminum, mica. Other chemical additives are used to inhibit oxidation and rust. In addition, emulsifiers are added to improve the emulsion manufacturing process, for example, soap, alcohol ester, ethylene oxide.[26]​.

Historically, solvent-based lubricants such as diesel and kerosene were often used. These were good at releasing the part from the die, but a small explosion occurred during each shot, causing a buildup of carbon on the walls of the mold cavity. However, they were easier to apply evenly than water-based lubricants.[27]​.

Advantage

Advantages of die casting:[11]​.

Disadvantages

The main disadvantage of die casting is its high capital cost. Both the necessary casting equipment and the dies and related components are very expensive, compared to most other casting processes. Therefore, for die casting to be an economical process, a large production volume is needed. Other disadvantages are:

Acurad

Acurad was a die casting process developed by General Motors in the late 1950s and 1960s. The name is an acronym for precise, reliable and dense. It was developed to combine stable filling and directional solidification" with the fast cycle times of the traditional die casting process. The process pioneered four innovative technologies for die casting: thermal analysis, flow and filling modeling, high-integrity, heat-treatable die castings, and indirect die casting (explained later).[5]​.

Thermal analysis was the first performed for any foundry process. It was done by creating an electrical analogue of the thermal system. A cross section of the arrays was drawn on Teledeltos paper and then the thermal loads and cooling patterns were drawn on the paper. The water lines were represented with magnets of different sizes. Thermal conductivity was represented by the reciprocal of the resistivity of the paper.[5]​.

The Acurad system employed a bottom fill system that required a stable flow front. Logical thinking and trial and error processes were used because computerized analysis did not yet exist; however, this modeling was the precursor to computerized flow and fill modeling.[5]​.

The Acurad system was the first die casting process that could successfully cast low-iron aluminum alloys such as A356 and A357. In a traditional die casting process, these alloys would be welded to the die. Additionally, Acurad castings could be heat treated and met US military specification MIL-A-21180-D.[5]​.

Finally, the Acurad system employed a patented double-shot piston design. The idea was to use a second piston (located within the primary piston) to apply pressure after the shot had partially solidified around the perimeter of the casting cavity and shot sleeve. Although the system was not very effective, it led the manufacturer of the Acurad machines, Ube Industries, to discover that it was just as effective to apply sufficient pressure at the right time later in the cycle with the primary piston; This is indirect pressure casting.[5]​.

No porosity

When no porosity is allowed in a casting, the poreless casting process is used. It is identical to the standard process, except that oxygen is injected into the die before each shot to purge air from the mold cavity. This causes small dispersed oxides to form as the molten metal fills the matrix, virtually eliminating gas porosity. An added advantage is the increased resistance. Unlike standard die casting parts, these parts can be heat treated and welded. This process can be carried out in aluminum, zinc and lead alloys.[16]​.

Vacuum assisted high pressure casting

In vacuum-assisted high-pressure casting, also known as vacuum-assisted high-pressure casting (VHPDC),[33] a vacuum pump removes air and gases from the die cavity and metal supply system before and during injection. Vacuum die casting reduces porosity, allows for heat treatment and welding, improves surface finish, and can increase strength.

Direct injection into the heated mold

Heated manifold direct injection die casting, also known as direct injection die casting or manifoldless die casting, is a zinc die casting process in which molten zinc is forced through a heated manifold and then through heated mini nozzles leading to the molding cavity. This process has the advantages of lower cost per part, thanks to reduced scrap (by eliminating sprues, gates and slides) and energy savings, and better surface quality thanks to slower cooling cycles.[16]​.

Semisolid

Semi-solid metal casting uses a metal that is heated between its liquidus and its solidus "Solidus (thermodynamics)") or its eutectic temperature, so that it is in its "soft region". This allows for more complex pieces and thinner walls.

There are a number of geometric characteristics that must be taken into account when creating a parametric model of a die casting:.

Contenido

Hay dos tipos básicos de máquinas de fundición a presión: Las máquinas de cámara caliente y las máquinas de cámara fría.[14]​ Se clasifican según la fuerza de sujeción que pueden aplicar. Los valores típicos están entre 400 y 4000 st (2540,1 y 25 401,2 kg).[8]​.

hot chamber casting

Hot chamber die casting, also known as gooseneck machines, relies on a pool of molten metal to feed the die. At the beginning of the cycle, the machine's piston retracts, allowing molten metal to fill the "gooseneck." The pneumatically or hydraulically actuated piston then forces the metal out of the gooseneck into the die. The advantages of this system are the speed of the cycles (approximately 15 cycles per minute) and the convenience of melting the metal in the casting machine. The disadvantages of this system are that it is limited to use with low melting point metals and that aluminum cannot be used because it picks up some of the iron while it is in the melting bath. Therefore, hot chamber machines are mainly used with alloys based on zinc, tin and lead.[14]​.

Cold chamber casting

They are used when the casting alloy cannot be used in hot chamber machines; Among them are aluminum, zinc alloys with a large composition of aluminum, magnesium and copper. The process for these machines begins with melting the metal in a separate furnace.[15]​ A precise amount of molten metal is then transported to the cold chamber machine, where it is introduced into an unheated injection chamber (or injection cylinder). This injection is then introduced into the matrix using a hydraulic or mechanical piston. The biggest disadvantage of this system is the slower cycle time due to the need to transfer the molten metal from the furnace to the cold chamber machine.[16]​.

Two dies are used in die casting; one is called the "covering half array" and the other "ejection half array." The point of union is called separation zone. The coating die contains the sprue (for hot chamber machines) or injection port (for cold chamber machines), which allows molten metal to flow into the dies; This feature matches the injector nozzle on hot chamber machines or the injection chamber on cold chamber machines. The ejector die contains the ejector pins and usually the runner, path from the sprue or injection port to the mold cavity. The cap die is fixed to the front platen of the casting machine, while the ejector die is fixed to the moving platen. The mold cavity is cut into two cavity inserts, which are separate pieces that can be replaced relatively easily and are screwed to the die halves.[17]​.

The dies are designed so that the finished casting slides out of the die cap half and remains in the ejector half when the dies are opened. This ensures that the casting will be ejected each cycle because the ejector half contains the ejector pins to push the casting out of that half of the die. The ejector pins are driven by an ejector pin plate, which precisely drives all the pins at the same time and with the same force, so as not to damage the casting. The ejector pin plate also retracts the pins after ejecting the casting to prepare for the next shot. There must be enough ejector pins so that the total force of each pin is low, since the casting is still hot and can be damaged by excessive force. The pins still leave a mark, so they should be located in places where these marks will not hinder the purpose of the casting.[17]​.

Other components of the matrices are the cores and the slides. Cores are components that typically produce holes or openings, but can also be used to create other details. There are three types of cores: fixed, mobile and loose. Fixed cores are those that are oriented parallel to the direction of pull of the dies (i.e. the direction in which the dies open), so they are fixed, or permanently attached to the die. Mobile cores are those that are oriented in any way other than parallel to the direction of traction. These cores must be removed from the die cavity after the injection solidifies, but before the dies open, using a separate mechanism. Slides are similar to moving cores, except that they are used to form sub-countercut surfaces. The use of moving cores and slides greatly increases the cost of dies.[17] Loose cores, also called pick-outs, are used to cast intricate features, such as threaded holes. These loose cores are introduced into the die by hand before each cycle and then ejected with the part at the end of the cycle. The core must then be removed by hand. Loose cores are the most expensive type of core, due to the additional labor and increased cycle time.[11] Other features of the dies are water cooling passages and vents along the parting line. These vents are typically wide and thin (approximately 0.005 in.) so that when molten metal begins to fill them the metal solidifies quickly and waste is minimized. Risers are not used because the high pressure ensures a continuous feed of metal from the gate.[18]​.

The most important material properties for dies are resistance to thermal shock and softening at elevated temperature; Other important properties are hardenability, machinability, heat check resistance, weldability, availability (especially for larger dies) and cost. The longevity of a die is directly dependent on the temperature of the molten metal and the cycle time.[17]​ Dies used in die casting are typically made of hardened tool steel, as cast iron cannot withstand the high pressures involved, so the dies are very expensive, resulting in high start-up costs.[18]​ Metals that cast at higher temperatures require higher melting temperature alloy steel dies.[19]​.

The main cause of failure of casting dies is wear or erosion. Other failure modes are heat checking and thermal fatigue. Thermal control is when cracks occur on the surface of the die due to a large temperature change in each cycle. Thermal fatigue is when surface cracks occur in the matrix due to a large number of cycles[20].

Los siguientes son los cuatro pasos de la fundición a presión tradicional, también conocida como fundición a alta presión,,[5]​ estos son también la base de cualquiera de las variantes de fundición a presión: preparación de la matriz, llenado, expulsión y sacudida. Las matrices se preparan rociando la cavidad del molde con lubricante. El lubricante ayuda a controlar la temperatura de la matriz y también facilita la extracción de la colada. A continuación se cierran las matrices y se inyecta metal fundido en ellas a alta presión; entre 10 y 175 megapascales (1450,4 y 25 381,6 psi). Una vez que se llena la cavidad del molde, se mantiene la presión hasta que la fundición se solidifica. A continuación, se abren las matrices y la inyección (las inyecciones se diferencian de las coladas porque puede haber varias cavidades en una matriz, lo que da lugar a varias coladas por inyección) es expulsada por los pasadores eyectores. Por último, el sacudido consiste en separar la chatarra, que incluye la compuerta&action=edit&redlink=1 "Compuerta (fundición) (aún no redactado)"), el corredor&action=edit&redlink=1 "Canal (fundición) (aún no redactado)"), el chatarra&action=edit&redlink=1 "Bebedero (fabricación) (aún no redactado)") y el flash&action=edit&redlink=1 "Flash (fabricación) (aún no redactado)"), de la inyección. Para ello se suele utilizar un troquel especial de recorte en una prensa mecánica o hidráulica. Otros métodos para sacudir son el aserrado y el esmerilado. Un método menos intensivo en mano de obra es el volteo de las granadas si las compuertas son finas y se rompen con facilidad; a continuación hay que separar las compuertas de las piezas acabadas. Esta chatarra se recicla refundiéndola.[14]​ El rendimiento es aproximadamente del 67%.[22]​.

La inyección a alta presión conduce a un rápido llenado de la matriz, que es necesario para que toda la cavidad se llene antes de que cualquier parte de la fundición se solidifique. De este modo, se evitan las discontinuidades, aunque la forma requiera secciones finas difíciles de rellenar. Esto crea el problema del atrapamiento de aire, porque cuando el molde se llena rápidamente hay poco tiempo para que el aire salga. Este problema se minimiza incluyendo rejillas de ventilación a lo largo de las líneas de separación, sin embargo, incluso en un proceso muy refinado seguirá habiendo cierta porosidad en el centro de la pieza fundida.[23]​.

La mayoría de los fundidores realizan otras operaciones secundarias para producir características que no son fácilmente moldeables, como tapping") un agujero, pulir, chapar, pulir o pintar.

Inspection

After shaking the laundry, it is inspected for defects. The most common defects are errors and cold closures. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of ventilation, or too much lubricant. Other possible defects are gas porosity, shrinkage porosity, hot breaks, and flow marks. Flow marks are marks left on the surface of the casting due to misguidance, sharp corners, or excess lubricant.[24]​.

Lubricants

Water-based lubricants are the most used type of lubricant, for health, environmental and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all the minerals it contains, it will not leave any byproducts in the dies. If water is not treated properly, minerals can cause surface defects and discontinuities.

Nowadays, "water in oil" and "oil in water" emulsions are used, since, when applying the lubricant, the water cools the surface of the matrix as it evaporates, depositing the oil that helps release the grit. A common mixture for this type of emulsion is thirty parts of water to one of oil, although in extreme cases a proportion of one hundred to one is used.[25] Among the oils used are heavy residual oil, animal fat, vegetable fat, synthetic oil, and all types of mixtures of these. HRO are gelatinous at room temperature, but at the high temperatures found in die casting, they form a thin film. Other substances are added to control the viscosity and thermal properties of these emulsions, for example, graphite, aluminum, mica. Other chemical additives are used to inhibit oxidation and rust. In addition, emulsifiers are added to improve the emulsion manufacturing process, for example, soap, alcohol ester, ethylene oxide.[26]​.

Historically, solvent-based lubricants such as diesel and kerosene were often used. These were good at releasing the part from the die, but a small explosion occurred during each shot, causing a buildup of carbon on the walls of the mold cavity. However, they were easier to apply evenly than water-based lubricants.[27]​.

Advantage

Advantages of die casting:[11]​.

Disadvantages

The main disadvantage of die casting is its high capital cost. Both the necessary casting equipment and the dies and related components are very expensive, compared to most other casting processes. Therefore, for die casting to be an economical process, a large production volume is needed. Other disadvantages are:

Acurad

Acurad was a die casting process developed by General Motors in the late 1950s and 1960s. The name is an acronym for precise, reliable and dense. It was developed to combine stable filling and directional solidification" with the fast cycle times of the traditional die casting process. The process pioneered four innovative technologies for die casting: thermal analysis, flow and filling modeling, high-integrity, heat-treatable die castings, and indirect die casting (explained later).[5]​.

Thermal analysis was the first performed for any foundry process. It was done by creating an electrical analogue of the thermal system. A cross section of the arrays was drawn on Teledeltos paper and then the thermal loads and cooling patterns were drawn on the paper. The water lines were represented with magnets of different sizes. Thermal conductivity was represented by the reciprocal of the resistivity of the paper.[5]​.

The Acurad system employed a bottom fill system that required a stable flow front. Logical thinking and trial and error processes were used because computerized analysis did not yet exist; however, this modeling was the precursor to computerized flow and fill modeling.[5]​.

The Acurad system was the first die casting process that could successfully cast low-iron aluminum alloys such as A356 and A357. In a traditional die casting process, these alloys would be welded to the die. Additionally, Acurad castings could be heat treated and met US military specification MIL-A-21180-D.[5]​.

Finally, the Acurad system employed a patented double-shot piston design. The idea was to use a second piston (located within the primary piston) to apply pressure after the shot had partially solidified around the perimeter of the casting cavity and shot sleeve. Although the system was not very effective, it led the manufacturer of the Acurad machines, Ube Industries, to discover that it was just as effective to apply sufficient pressure at the right time later in the cycle with the primary piston; This is indirect pressure casting.[5]​.

No porosity

When no porosity is allowed in a casting, the poreless casting process is used. It is identical to the standard process, except that oxygen is injected into the die before each shot to purge air from the mold cavity. This causes small dispersed oxides to form as the molten metal fills the matrix, virtually eliminating gas porosity. An added advantage is the increased resistance. Unlike standard die casting parts, these parts can be heat treated and welded. This process can be carried out in aluminum, zinc and lead alloys.[16]​.

Vacuum assisted high pressure casting

In vacuum-assisted high-pressure casting, also known as vacuum-assisted high-pressure casting (VHPDC),[33] a vacuum pump removes air and gases from the die cavity and metal supply system before and during injection. Vacuum die casting reduces porosity, allows for heat treatment and welding, improves surface finish, and can increase strength.

Direct injection into the heated mold

Heated manifold direct injection die casting, also known as direct injection die casting or manifoldless die casting, is a zinc die casting process in which molten zinc is forced through a heated manifold and then through heated mini nozzles leading to the molding cavity. This process has the advantages of lower cost per part, thanks to reduced scrap (by eliminating sprues, gates and slides) and energy savings, and better surface quality thanks to slower cooling cycles.[16]​.

Semisolid

Semi-solid metal casting uses a metal that is heated between its liquidus and its solidus "Solidus (thermodynamics)") or its eutectic temperature, so that it is in its "soft region". This allows for more complex pieces and thinner walls.