Die casting is a metal casting process widely employed for the mass production of high-quality, durable parts. It is known for its ability to produce components with high dimensional accuracy, making it ideal for industries that require precise and consistent parts, such as automotive, aerospace, and consumer electronics. Whether you’re looking to manufacture complex shapes or achieve smooth surface finishes, die casting is an efficient solution for producing large quantities of metal parts while maintaining tight tolerances and exceptional performance.
Die casting is prized for its ability to produce parts with a smooth surface finish and precise dimensions. In addition, this process is relatively fast and cost-effective, making it an attractive option for many applications.
The die casting process involves several steps, including mould design, metal preparation, injection, casting, and finishing.
The initial step in the die casting process is creating a mould called a die. This mould is usually made from steel or aluminium and is designed to withstand the high temperatures and pressures of the die casting process.
The mould design begins with developing a CAD design of the required mould. This design is then used to create a mould by CNC machining, which is further used in the casting process.
The next step is to prepare the metal for injection. This metal is typically an alloy, such as aluminium, magnesium, or zinc. The metal is melted in a furnace and then poured into a ladle.
Once the metal is in a liquid state, it is injected into the mould under high pressure. The molten metal fills the mould cavity and cools to create the desired shape.
After the metal has cooled and hardened, the mould is opened, and the part is ejected. Ensure that the part has cooled entirely before handling to avoid any potential injuries.
The final step in the process is to finish the part. Surface finishing plays a vital role in die casting, as it can impact the durability and function of the part. Standard finishing processes include anodizing, powder coating, wet plating, and many more.
Die casting encompasses several distinct processes, each designed to meet specific manufacturing needs based on factors like material type, production speed, and part complexity. The most common die casting methods are hot and cold chamber die casting, but there are additional variations such as vacuum, gravity, high-pressure, and low-pressure die casting. Below is an overview of the key types of die casting, including their suitable materials and typical applications.
Cold chamber die casting is a process in which molten metal is manually ladled into an unheated injection chamber, then injected into the die at high pressure using a hydraulic piston. The cold chamber process is typically used for metals with higher melting points, such as aluminum, magnesium, and copper alloys, as these metals could damage the machinery used in hot chamber die casting.
In hot chamber die casting, the machine contains a built-in furnace that melts the metal, which is then injected directly from the furnace into the mold. A gooseneck mechanism submerged in the molten metal fills with the material and then injects it into the die under pressure. The hot chamber process is ideal for metals with lower melting points, such as zinc, tin, and lead alloys, because the molten metal is continuously supplied to the machine.
Vacuum die casting is a variation of the high-pressure die casting process where the air is evacuated from the die cavity before the molten metal is injected. The vacuum reduces or eliminates trapped gases in the final casting, which leads to improved part density and mechanical properties. The vacuum process also helps reduce porosity, making it an ideal choice for parts subjected to high stress or pressure.
Gravity die casting, also known as permanent mold casting, involves pouring molten metal into a metal mold (or die) using only the force of gravity. The metal flows into the mold and fills the cavity before cooling and solidifying. No external pressure is applied, and the metal flows into the mold purely by gravity. This process is typically used for simpler parts and offers better mechanical properties than sand casting.
High-pressure die casting is one of the most widely used die casting processes. In this method, molten metal is injected into the die at very high pressure (usually 10-175 MPa) using a piston or plunger. This high pressure ensures that the molten metal fills all areas of the mold, resulting in highly precise and detailed parts with smooth surface finishes. The process is fast, highly automated, and suitable for large production runs
Low-pressure die casting is a process where molten metal is slowly forced into the mold under low pressure (0.1 to 1 MPa) from a holding furnace located below the die. The metal is pushed into the mold through a riser tube, ensuring a smooth and controlled filling of the cavity. This process minimizes turbulence and gas entrapment, resulting in higher-quality parts with fewer defects. Low-pressure die casting is commonly used for large components like aluminum wheels, engine components, and structural parts, where structural integrity and dimensional accuracy are crucial.
When starting your die casting project, one of the most critical decisions is selecting the right material. The material must be capable of withstanding the high temperatures and pressures inherent in the die casting process, while also meeting the functional and performance requirements of your end-use application. Additionally, it’s crucial to select a material that is compatible with the specific die casting method you plan to use, as different processes may suit particular metals better.
Given the complexity of these factors, working with an experienced die-casting partner can help ensure that you make the best decision based on your project’s unique needs. Among the wide range of materials available, aluminum, magnesium, and zinc alloys are the most commonly used due to their strength, lightweight properties, and versatility.
Below is a comparison of these commonly used die casting materials, along with key characteristics and common applications.
When it comes to mass-producing metal parts, die casting is one of the most efficient and cost-effective methods. It’s a process that has been around for centuries, but its popularity has grown in recent years as manufacturers seek ways to reduce production costs.
Here are some of the advantages of die casting:
Die casting is used in a variety of industries and applications. Some of the most common uses for die casting include:
Many other industries use die-casting processes for medical, construction, and toy industries. It is a versatile process that can be used to create various parts and products.
Die casting is a manufacturing process that has been around for centuries and continues to be popular because of its versatility and ability to create complex shapes. The process can be used to create metal parts for a variety of industries, including automotive, aerospace, furniture, and appliance manufacturing.
Through our extensive network of manufacturers, Xometry Europe offers die casting services for several dozens of materials including aluminium, magnesium and zinc alloys. Simply head over to our Instant Quoting Engine to upload your model and receive a quote to order parts.
Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high-volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small- to medium-sized castings, which is why die casting produces more castings than any other casting process.[1] Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.
Die casting equipment was invented in for the purpose of producing movable type for the printing industry. The first die casting-related patent was granted in for a small hand-operated machine for the purpose of mechanized printing type production. In Ottmar Mergenthaler invented the Linotype machine, which cast an entire line of type as a single unit, using a die casting process. It nearly completely replaced setting type by hand in the publishing industry. The Soss die-casting machine, manufactured in Brooklyn, NY, was the first machine to be sold in the open market in North America.[2] Other applications grew rapidly, with die casting facilitating the growth of consumer goods, and appliances, by greatly reducing the production cost of intricate parts in high volumes.[3] In ,[4] General Motors released the Acurad process.[5]
The main die casting alloys are: zinc, aluminium, magnesium, copper, lead, and tin; although uncommon, ferrous die casting is also possible.[6] Specific die casting alloys include: zinc aluminium; aluminium to, e.g. The Aluminum Association (AA) standards: AA 380, AA 384, AA 386, AA 390; and AZ91D magnesium.[7] The following is a summary of the advantages of each alloy:[8]
As of , maximum weight limits for aluminium, brass, magnesium, and zinc castings are estimated at approximately 70 pounds (32 kg), 10 lb (4.5 kg), 44 lb (20 kg), and 75 lb (34 kg), respectively.[9] By late-, press machines capable of die casting single pieces over-100 kilograms (220 lb) were being used to produce aluminium chassis components for cars.[10]
The material used defines the minimum section thickness and minimum draft required for a casting as outlined in the table below. The thickest section should be less than 13 mm (0.5 in), but can be greater.[11]
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Metal Minimum section Minimum draft Aluminium alloys 0.89 mm (0.035 in) 1:100 (0.6°) Brass and bronze 1.27 mm (0.050 in) 1:80 (0.7°) Magnesium alloys 1.27 mm (0.050 in) 1:100 (0.6°) Zinc alloys 0.63 mm (0.025 in) 1:200 (0.3°)There are a number of geometric features to be considered when creating a parametric model of a die casting:
There are two basic types of die casting machines: hot-chamber machines and cold-chamber machines.[14] These are rated by how much clamping force they can apply. Typical ratings are between 400 and 4,000 st (2,500 and 25,400 kg).[8]
Hot-chamber die casting, also known as gooseneck machines, rely upon a pool of molten metal to feed the die. At the beginning of the cycle the piston of the machine is retracted, which allows the molten metal to fill the "gooseneck". The pneumatic- or hydraulic-powered piston then forces this metal out of the gooseneck into the die. The advantages of this system include fast cycle times (approximately 15 cycles a 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 aluminium cannot be used because it picks up some of the iron while in the molten pool. Therefore, hot-chamber machines are primarily used with zinc-, tin-, and lead-based alloys.[14]
These are used when the casting alloy cannot be used in hot-chamber machines; these include aluminium, zinc alloys with a large composition of aluminium, magnesium and copper. The process for these machines start with melting the metal in a separate furnace.[15] Then a precise amount of molten metal is transported to the cold-chamber machine where it is fed into an unheated shot chamber (or injection cylinder). This shot is then driven into the die by 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 "cover die half" and the other the "ejector die half". Where they meet is called the parting line. The cover die contains the sprue (for hot-chamber machines) or shot hole (for cold-chamber machines), which allows the molten metal to flow into the dies; this feature matches up with the injector nozzle on the hot-chamber machines or the shot chamber in the cold-chamber machines. The ejector die contains the ejector pins and usually the runner, which is the path from the sprue or shot hole to the mould cavity. The cover die is secured to the stationary, or front, platen of the casting machine, while the ejector die is attached to the movable platen. The mould cavity is cut into two cavity inserts, which are separate pieces that can be replaced relatively easily and bolt into the die halves.[17]
The dies are designed so that the finished casting will slide off the cover half of the die and stay in the ejector half as the dies are opened. This assures that the casting will be ejected every cycle because the ejector half contains the ejector pins to push the casting out of that die half. The ejector pins are driven by an ejector pin plate, which accurately drives all of the pins at the same time and with the same force, so that the casting is not damaged. The ejector pin plate also retracts the pins after ejecting the casting to prepare for the next shot. There must be enough ejector pins to keep the overall force on each pin low, because the casting is still hot and can be damaged by excessive force. The pins still leave a mark, so they must be located in places where these marks will not hamper the casting's purpose.[17]
Other die components include cores and slides. Cores are components that usually produce holes or opening, but they can be used to create other details as well. There are three types of cores: fixed, movable, and loose. Fixed cores are ones that are oriented parallel to the pull direction of the dies (i.e. the direction the dies open), therefore they are fixed, or permanently attached to the die. Movable cores are ones that are oriented in any other way than parallel to the pull direction. These cores must be removed from the die cavity after the shot solidifies, but before the dies open, using a separate mechanism. Slides are similar to movable cores, except they are used to form undercut surfaces. The use of movable cores and slides greatly increases the cost of the dies.[17] Loose cores, also called pick-outs, are used to cast intricate features, such as threaded holes. These loose cores are inserted into the die by hand before each cycle and then ejected with the part at the end of the cycle. The core then must be removed by hand. Loose cores are the most expensive type of core, because of the extra labor and increased cycle time.[11] Other features in the dies include water-cooling passages and vents along the parting lines. These vents are usually wide and thin (approximately 0.13 mm or 0.005 in) so that when the molten metal starts filling them the metal quickly solidifies and minimizes scrap. No risers are used because the high pressure ensures a continuous feed of metal from the gate.[18]
The most important material properties for the dies are thermal shock resistance and softening at elevated temperature; other important properties include hardenability, machinability, heat checking 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] The dies used in die casting are usually made out of hardened tool steels, because cast iron cannot withstand the high pressures involved, therefore the dies are very expensive, resulting in high start-up costs.[18] Metals that are cast at higher temperatures require dies made from higher alloy steels.[19]
Die and component material and hardness for various cast metals Die component Cast metal Tin, lead & zinc Aluminium & magnesium Copper & brass Material Hardness Material Hardness Material Hardness Cavity inserts P20[note 1] 290–330 HB H13 42–48 HRC DIN 1. 38–44 HRC H11 46–50 HRC H11 42–48 HRC H20, H21, H22 44–48 HRC H13 46–50 HRC Cores H13 46–52 HRC H13 44–48 HRC DIN 1. 40–46 HRC DIN 1. 42–48 HRC Core pins H13 48–52 HRC DIN 1. prehard 37–40 HRC DIN 1. prehard 37–40 HRC Sprue parts H13 48–52 HRC H13The main failure mode for die casting dies is wear or erosion. Other failure modes are heat checking and thermal fatigue. Heat checking is when surface cracks occur on the die due to a large temperature change on every cycle. Thermal fatigue is when surface cracks occur on the die due to a large number of cycles.[20]
Typical die temperatures and life for various cast materials[21] Zinc Aluminium Magnesium Brass (leaded yellow) Maximum die life [number of cycles] 1,000,000 100,000 100,000 10,000 Die temperature [°C (°F)] 218 (425) 288 (550) 260 (500) 500 (950) Casting temperature [°C (°F)] 400 (760) 660 () 760 () ()The following are the four steps in traditional die casting, also known as high-pressure die casting,[5] these are also the basis for any of the die casting variations: die preparation, filling, ejection, and shakeout. The dies are prepared by spraying the mould cavity with lubricant. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting. The dies are then closed and molten metal is injected into the dies under high pressure; between 10 and 175 megapascals (1,500 and 25,400 psi). Once the mould cavity is filled, the pressure is maintained until the casting solidifies. The dies are then opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins. Finally, the shakeout involves separating the scrap, which includes the gate, runners, sprues and flash, from the shot. This is often done using a special trim die in a power press or hydraulic press. Other methods of shaking out include sawing and grinding. A less labor-intensive method is to tumble shots if gates are thin and easily broken; separation of gates from finished parts must follow. This scrap is recycled by remelting it.[14] The yield is approximately 67%.[22]
The high-pressure injection leads to a quick fill of the die, which is required so the entire cavity fills before any part of the casting solidifies. In this way, discontinuities are avoided, even if the shape requires difficult-to-fill thin sections. This creates the problem of air entrapment, because when the mould is filled quickly there is little time for the air to escape. This problem is minimized by including vents along the parting lines, however, even in a highly refined process there will still be some porosity in the center of the casting.[23]
Most die casters perform other secondary operations to produce features not readily castable, such as tapping a hole, polishing, plating, buffing, or painting.
After the shakeout of the casting it is inspected for defects. The most common defects are misruns and cold shuts. These defects can be caused by cold dies, low metal temperature, dirty metal, lack of venting, or too much lubricant. Other possible defects are gas porosity, shrinkage porosity, hot tears, and flow marks. Flow marks are marks left on the surface of the casting due to poor gating, sharp corners, or excessive lubricant.[24]
Water-based lubricants are the most used type of lubricant, because of health, environmental, and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all minerals from it, it will not leave any by-product in the dies. If the water is not properly treated, then the minerals can cause surface defects and discontinuities.
Today "water-in-oil" and "oil-in-water" emulsions are used, because, when the lubricant is applied, the water cools the die surface by evaporating, hence depositing the oil that helps release the shot. A common mixture for this type of emulsion is thirty parts water to one part oil, however in extreme cases a ratio of one-hundred to one is used. Oils that are used include heavy residual oil (HRO), animal fat, vegetable fat, synthetic oil, and all sorts of mixtures of these. HROs 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, e.g. graphite, aluminium, mica. Other chemical additives are used to inhibit rusting and oxidation. In addition emulsifiers are added to improve the emulsion manufacturing process, e.g. soap, alcohol esters, ethylene oxides.
Historically, solvent-based lubricants, such as diesel fuel and kerosene, were commonly used. These were good at releasing the part from the die, but a small explosion occurred during each shot, which led to a build-up of carbon on the mould cavity walls. However, they were easier to apply evenly than water-based lubricants.
Advantages of die casting:[11]
The main disadvantage to die casting is the very high capital cost. Both the casting equipment required and the dies and related components are very costly, as compared to most other casting processes. Therefore, to make die casting an economic process, a large production volume is needed. Other disadvantages are:
Acurad was a die casting process developed by General Motors in the late s and s. The name is an acronym for accurate, reliable, and dense. It was developed to combine a stable fill and directional solidification with the fast cycle times of the traditional die casting process. The process pioneered four breakthrough technologies for die casting: thermal analysis, flow and fill modeling, heat treatable and high integrity die castings, and indirect squeeze casting (explained below).[5]
The thermal analysis was the first done for any casting process. This was done by creating an electrical analog of the thermal system. A cross-section of the dies were drawn on Teledeltos paper and then thermal loads and cooling patterns were drawn onto the paper. Water lines were represented by magnets of various sizes. The 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 thought processes and trial and error were used because computerized analysis did not exist yet; 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 aluminium alloys, such as A356 and A357. In a traditional die casting process these alloys would solder to the die. Similarly, Acurad castings could be heat treated and meet the U.S. military specification MIL-A--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. While the system was not very effective, it did lead 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 squeeze casting.[5]
When no porosity is allowed in a cast part then the pore-free casting process is used. It is identical to the standard process except oxygen is injected into the die before each shot to purge any air from the mould cavity. This causes small dispersed oxides to form when the molten metal fills the die, which virtually eliminates gas porosity. An added advantage to this is greater strength. Unlike standard die castings, these castings can be heat treated and welded. This process can be performed on aluminium, zinc, and lead alloys.[16]
In vacuum assisted high pressure die casting, a.k.a. vacuum high pressure die casting (VHPDC),[33] a vacuum pump removes air and gases from die cavity and metal delivery system before and during injection. Vacuum die casting reduces porosity, allows heat treating and welding, improves surface finish, and can increase strength.
Heated-manifold direct-injection die casting, also known as direct-injection die casting or runnerless die casting, is a zinc die casting process where molten zinc is forced through a heated manifold and then through heated mini-nozzles, which lead into the moulding cavity. This process has the advantages of lower cost per part, through the reduction of scrap (by the elimination of sprues, gates, and runners) and energy conservation, and better surface quality through slower cooling cycles.[16]
Semi-solid die casting uses metal that is heated between its liquidus and solidus (or liquidus and eutectic temperature), so that it is in a "mushy" state. This allows for more complex parts and thinner walls.[citation needed]
Low-pressure die casting (LPDC) is a process developed to improve the consistency and integrity of parts, at the cost of a much slower cycle time.[34] In LPDC, material is held in a reservoir below the die, from which it flows into the cavity when air pressure in the reservoir is increased.[34] Typical pressures range from 0.3 bar (4.4 psi) to 0.5 bar (7.3 psi).[34][35] Somewhat higher pressures (up to 1 bar (15 psi)) may be applied after the material is in the die, to work it into fine details of the cavity and eliminate porosity.[34]
Typical cycle times for a low-pressure die casting process are longer than for other die-casting processes; an engine block can take up to fifteen minutes.[34] It is primarily used for aluminum, but has been used for carbon steel as well.[34]
Integrated die casting[36] refers to the high-level integration of multiple separate and dispersed alloy parts through a large-tonnage die-casting machine, and then formed into 1–2 large castings. The aim is to reduce manufacturing costs through one-time molding, significantly decreasing the number of parts needed for car assembly and improving overall efficiency.[37] Elon Musk's team first proposed this processing method during the Tesla manufacturing process which is Giga Press program.[38]
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