This article contains information regarding die casting and its use.
Here is what you will learn:
Die casting is a high-pressure metal casting process that injects molten metal into a mold. This method yields dimensionally accurate, precision metal parts with a high-quality finish. Its capability to produce intricate details makes it ideal for mass production. Die castings are typically made from non-ferrous metals such as zinc, copper, aluminum, magnesium, lead, pewter, and tin.
The two methods of die casting are hot or cold chambers. The process that is used depends on the type of metal and the part. The cold chamber method is used with metals that have a high melting point such as alloys of aluminum, brass, or copper. Hot chamber die casting is limited to metals that won’t dissolve when heated such as zinc, lead, and magnesium alloys.
The die casting process is efficient and economical, offering a wide range of shapes and components. The resulting parts are durable and can be made to be visually appealing, providing designers with significant advantages and benefits.
The high speed of die casting allows for the production of complex shapes with close tolerances, eliminating the need for post-production processing. Additional tooling or shaping is unnecessary. The final parts are heat resistant and possess high tensile strength.
Depending on the feature and its size, tolerances of +/-.002" can be held in aluminum with tolerances of +/-.0005" in zinc.
Die casting and forging are two distinct metal forming processes with notable differences.
Die casting involves injecting molten metal into a mold cavity at high pressure, producing intricate and detailed shapes with excellent dimensional accuracy. This process is ideal for creating complex, thin-walled parts with a smooth surface finish, making it suitable for applications such as automotive components and consumer electronics.
Forging involves shaping metal by applying compressive forces through hammering or pressing at high temperatures. This process enhances the material's strength and grain structure, producing robust and durable parts commonly used in heavy machinery, aerospace, and construction equipment. While die casting offers precision and complexity, forging excels in strength and structural integrity.
The type of metal used in die cast depends on its final use. Aluminum is used for automobile and truck parts because of its light weight and corrosion resistance, while medical instruments are made from stainless steel.
Metals used for casting must retain their properties and characteristics during and after the melting process. The types include:
More information on each of the metal types is below.
Zinc is an excellent and often overlooked die casting alloy due to its versatility and performance. However, it is 2.3 times heavier than aluminum, making aluminum a preferred choice for larger die castings where weight and material costs are significant factors.
Zinc is the easiest metal to cast. It has high ductility, impact strength, and can easily be plated. The strength of zinc comes from its alloyed metals. Parts cast from zinc have very close tolerances. Zinc alloyed parts have higher impact resistance than cast aluminum, plastics, and grey cast iron.
The exceptional casting fluidity of ZAMAC alloys allows for thin-wall castability, with thicknesses as small as 0.025 inches (0.65 mm). This results in smaller, lighter, and cost-effective components.
The low casting temperature of zinc minimizes thermal shock, extending the lifespan of die casting tools to over ten times that of aluminum dies.
Zinc alloys are rigid, with elastic moduli greater than those of aluminum, magnesium alloys, and engineering plastics. Combined with their strength, this reduces the volume of casting, saving both space and weight.
Bushing and wear inserts in component designs can be eliminated thanks to zinc's superior bearing properties, which outperform bronze in heavy-duty industrial applications.
Zinc has a relatively low melting point, approximately 419°C (786°F), compared to other metals used in die casting, such as aluminum and magnesium. This limitation can restrict the use of zinc die casting in high-temperature applications.
While zinc die castings can achieve good surface finishes, they may not exhibit the same level of corrosion resistance as materials such as aluminum or stainless steel. Proper post-processing and coatings may be necessary to enhance their corrosion resistance.
Aluminum is lightweight, making it ideal for applications where weight reduction is crucial, such as in the automotive and aerospace industries. Its low density contributes to improved fuel efficiency and performance.
Despite being lightweight, aluminum offers a high strength-to-weight ratio, providing excellent structural integrity while maintaining low overall component weight.
Aluminum's excellent thermal conductivity makes it well-suited for applications where efficient heat dissipation is essential, such as in electronic enclosures and heat sinks.
Aluminum has a relatively high shrinkage rate when it cools after being cast. This can lead to dimensional inaccuracies in the finished parts, which may require additional machining or post-processing to meet tight tolerance requirements.
Aluminum alloys can exhibit more brittleness compared to materials like zinc or magnesium. This brittleness may result in issues such as cracking or breakage under heavy loads or impact, which can make aluminum die castings less suitable for applications requiring high durability.
Brass naturally resists corrosion, making it an ideal choice for components exposed to moisture or harsh environmental conditions. Its ability to resist rust and tarnish helps prolong the lifespan of die-cast parts.
Brass also boasts high thermal conductivity, which is advantageous for components requiring efficient heat dissipation, particularly in electrical and electronic applications.
Melting of brass can be a complex and an involved process. Die casting has to be constantly monitored and labor intensive. Improperly inserted lubricants can burn the casting. Scaling is common as well as porosity (small voids or holes) and die defects.
Brass features a lower melting point compared to some other die-casting materials, which may restrict its use in high-temperature applications. This can lead to parts deforming or failing under extreme heat conditions.
TThe most common types of die casting are hot and cold chamber die casting. In hot chamber die casting, metals are heated directly in the casting machine, whereas in cold chamber die casting, metal is preheated in a furnace and then transferred to the casting machine as molten metal. Both processes yield complex shapes with tight tolerances, offering heat resistance and high tensile strength with minimal requirements for additional tooling and shaping.
Hot chamber die casting uses alloys with a low melting temperature. Dies have two sections – movable and fixed. The fixed half is the covered die and is mounted on a stationary platen aligned with the gooseneck that connects to the chamber for inserting the molten metal. The movable die is the ejector die.
Molten metal is held in an open holding pot that is connected to the combustion area or furnace from which the molten metal enters the holding pot. With the plunger, that drives the molten metal up the gooseneck into the mold, in the up position the molten metal flows into the shot chamber. Once the metal is present, the plunger moves down forcing the molten metal up the gooseneck into the die.
The two halves of the mold are forced together under great pressure to close the mold. The plunger remains down until the molten metal in the die cools. After solidification, an ejection system pushes the casting out from the two die halves.
Cold chamber refers to the temperature of the chamber when the molten metal is introduced. With hot chamber casting, the chamber is filled with molten metal prior to beginning the casting process. In the cold chamber process, the chamber is at room temperature before the molten metal is poured.
High melting temperature metal alloys are used for cold chambered die casting. The molten metal is heated in a separate furnace and ladled or poured through a pouring hole into the shot chamber that encloses a ram for pushing the molten metal into the die. The parts of the die are the same with movable and fixed sections. The cold chambered method forces the molten metal in vertically.
As the ram moves vertically toward the die, the molten metal is forced forward at pressures between 2000 psi or 2 ksi to 20,000 psi or 20 ksi. The pressure is held by the ram until the molten metal cools and solidifies to be ejected.
The basic steps for high pressure die casting are listed below. They vary depending on the chosen process of a manufacturer. (from https://www.thediecasting.com/the-die-casting-process-step-by-step/)
Step one – Preparation of the Die: To prepare the die for casting, it is sprayed with a lubricant or releasing agent. Lubricants allow for clean part release by placing a film over the part. To make application easy, the lubricating agent is mixed with water that evaporates when sprayed on the heated steel die.
Step two – Clamping the Die: The halves of the die are clamped together under high pressure. The amount of force is determined by the machine.
Step three – Cooling: Cooling time depends on the type of metal and the temperature at which it will solidify. The geometry and wall thickness of the part are also factors.
Step four – Ejection: The halves of the mold are separated, and an ejection mechanism forces the part out of the die. The amount of force for removal has to be carefully monitored.
Step five – Trimming: Flashing (a thin portion of metal around the edge of a casting) is removed, known as deflashing, which is excess material such as metal that may have seeped between the die halves or runners.
(from www.kineticdiecasting.com)
Die casting design geometry determines how parts fill and cool as well as how their geometry affects stress, grain, and porosity. The grain structure and level of stress are determined by the type of metal.
The examples in the above diagram are a sampling of the types of geometric features produced by die casting.
Drafting is a draft angle that varies depending on the type of wall and surface, the depth of the surface, and the selected metal. A mathematical formula determines the angle.
Fillet radii makes a part stronger by redirecting stress concentration at sharp interior corners by distributing it over the broader volume of the fillet to lessen weak points. It prevents cracking during straightening.
The parting line is where the two halves of the die meet, defining the inside and outside surfaces, as well as determining which side of the die serves as the cover and which side serves as the ejector.
Bosses are mounting points, stand offs, and are designed to maintain uniform wall thicknesses to eliminate after casting machining.
Ribs facilitate the complete filling of the die casting with molten metal. They create pathways for the molten metal and streamline the ejection process, thereby enhancing efficiency and speed.
Holes and windows necessitate the highest degree of drafting because they connect directly with the die surface, potentially impeding ejection and obstructing the flow of molten metal.
Holes can be seen in this die cast plunger lock from Window Repair Parts.
There are several variations of die casting, each offering unique characteristics and advantages. These variations are selected based on factors such as material choice, part geometry, production volume, and quality standards. Manufacturers meticulously evaluate these factors to determine the most suitable die casting method for a particular application.
The variations described below have been developed to address flaws, errors, deformities, and other challenges encountered in die casting operations.
Prior to injecting or pouring the molten metal, the die cavity is filled with oxygen. When the hot metal enters the cavity, the oxygen chemically combines with it to prevent gas bubbles eliminating trapped gas pores. In the diagram below, note the opening for active gas in this cold forging process.
Acurad is an anagram for accurate, reliable, and dense. It combines stable fill and directional solidification to create fast cycle times. It includes thermal analysis, flow and fill modeling, heat treatable castings, and indirect squeezing. Double pistons increase the pressure when the shot is partially solidified.
Molten metal is poured directly into a permanent die, completely filling it, which minimizes turbulence, oxidation, and foaming. The die can be vertical, horizontal, or tilted, resulting in parts with high quality, strength, and mechanical characteristics, as well as stiffness.
Investment or lost wax casting, is labor intensive process involving shaping of the mold from a wax prototype dipped in liquid ceramic. When the ceramic hardens, the wax is melted away. Molten metal is poured into the ceramic cavity. After solidification, the ceramic mold is broken away and the metal casting removed.
The die is enclosed within an airtight housing. Pressure is applied to the die cavity, drawing in molten metal which solidifies before being ejected.
Semi-solid metal, in a semi-solid or slurry state, is agitated, poured, and directed into a shot sleeve to be forcefully injected into the mold cavity under pressure. This process results in parts with excellent surface finishes, tight dimensional tolerances, and a favorable microstructure.
Low Pressure the chamber with the molten metal is below the die, as can be seen in the diagram. It is pushed up through an intake port into the die chamber. The pressure is maintained until the molten metal solidifies.
Die castings are crafted from steel alloys and consist of two sections: the fixed or cover half and the ejector or removable half. A sprue hole, typically round and tapered, serves as the entry point for molten metal into the die cavity. The ejector half features a runner or passage, along with a gate or inlet, to direct the molten metal into the die cavity. The two halves are secured together using ejector pins.
The die has an opening for a coolant or lubricant, which helps in releasing the part from and keeping the temperature even. Lubricant improves the finish and prevents the part from sticking to the die cavity. The most common form of lubricant is water mixed with oil.
A die can last through several thousand parts, which depends on the amount of stress it endure, maintains, and cared. Die casting dies are expensive and can add to the cost of the final part.
Several types of dies have been developed and continue to evolve due to the dynamic nature of die casting technology. New dies are regularly introduced to enhance capabilities and efficiency.
Below is a description of a few of the common ones.
This process produces a single unit and is compatible with machines designed for one die, considering factors like shot height, locking force, and die size. It is particularly beneficial for low-volume production runs, center gating (the entry point for molten metal), and intricate parts with multidirectional features.
Multiple cavity dies are designed to produce multiple identical parts in a single casting operation.
Combination dies, a type of multiple cavity die, produce different parts that fit together instead of casting identical parts. The diagram illustrates examples of the parts that can be produced from a single die casting.
Unit dies can be inserted into larger dies where the larger die remains fixed, allowing flexibility to create various components with the unit die. However, there are constraints related to the size and weight of the unit die, determining its feasibility for insertion.
Die casting is the quickest and most economical of production processes. Hundreds of thousands of parts can be produced from one mold producing dimensionally accurate and precision parts. Listed below are the advantages and disadvantages of die casting.
Dimensional accuracy typically ranges within 0.1 mm for the first 2.5 cm and 0.02 mm for each additional centimeter.
Surface finishes of 1 – 25 μm. (from website https://firstratemold.com/advantages-and-disadvantages-of-die-casting/).
The production rate depends on cavitation, which refers to the number of cavities in a mold. A single mold can achieve between 200 to 300 shots per hour. For smaller parts, this rate can increase to the thousands per hour.
Reproduces any design down to the finest details with thin walls and structures.
Threaded inserts, bearings, and addons can be easily included.
Parts have tensile strengths of 60,000 psi or a 415 MPa.
Hydraulic and pneumatic equipment are commonly used for efficiency and lower cost.
Produces complex parts with extremely close tolerances.
Every mold has to be individually precision manufactured, which requires hours of crafting, shaping, and forming.
Furnaces have to burn into the 1000‘s of degrees consuming costly energy that produces pollutants that have to be air filter controlled.
Molding and shaping equipment is precision designed to withstand the stress of the heating process.
Only metals with high fluidity can be used, which influences the types of parts to be produced.
The process requires careful monitoring and management, particularly during the cooling phase.
Dies are made of hardened steel and cannot be adjusted or changed. They are very expensive and costly.
Porosity, shrinkage, and metal pouring are common defects.
Requires very long lead times.
Aluminum casting is a method used to produce high-tolerance, high-quality parts by injecting molten aluminum into a meticulously designed and precision-engineered die, mold, or form. This efficient process enables the production of complex, intricate, and detailed parts that precisely match the specifications of the original design.
Zinc die casting is a process in which molten zinc is injected into a steel die cavity that matches the shape, size, and dimensions of the part or component being manufactured. The resulting cast zinc product exhibits...
The casting process is an ancient art that dates back several thousand years to the beginning of written history. Archaeological finds document the use of casting over 6000 years ago, around 3000 BC or BCE...
Investment casting is a metalworking process that involves creating a ceramic shell over a wax pattern to produce parts with exceptionally uniform and smooth surfaces. The wax pattern is typically created using an aluminum die. The final products of investment casting are free from parting lines, mold half marks, or other deformities.
An iron casting is a durable product made by combining iron with carbon. It can be easily cast into a mold and generally contains a higher proportion of carbon than steel, typically ranging from 2 to 4.3 percent.
Lost wax casting, also known as precision casting, is a process that uses a wax pattern to form a ceramic mold for creating intricate part or product designs. This method is renowned for its accuracy in reproducing parts with precise tolerances over the years.
Permanent mold casting is a process that utilizes robust, reusable molds to manufacture parts and components from molten metals. These molds are typically constructed from steel or...
Sand casting is a manufacturing process where liquid metal is poured into a sand mold, which holds a hollow cavity of the desired shape until it solidifies.
Aluminum forging is a method used to process aluminum alloys, employing pressure and heat to create high-strength, durable products. This process involves pressing, pounding, and...
Cold forging is a metal shaping & manufacturing process in which bar stock is inserted into a die and squeezed into a second closed die. The process, completed is at room temperature or below the...
Copper and brass forging involves shaping copper and brass to create complex and intricate forms. The forging process meticulously controls the temperature at which copper and brass are worked, ensuring precise results and...
Forging is a metalworking process that involves manipulating, shaping, deforming, and compressing metal to achieve a desired form, configuration, or appearance as specified in a metal processing design or diagram...
In this article, essential terms associated with both open and closed die forging are discussed, emphasizing the importance of comprehending their definitions. Forging, a manufacturing process involving pressing, hammering, or shaping metal...
Rolled ring forging is a metalworking technique wherein a thick, solid, round metal piece is punched to form a hole, creating a donut shape. Subsequently, the donut shape is squeezed and pressured to transform it into a thin ring...
Forging steel is a manufacturing process that shapes steel through localized compressive forces, such as hammering, pressing, and rolling. This method is extensively employed to produce high-quality steel products...
The ancient craft of forging can be categorized into two main types – hot and cold forging. Hot forging has a long history spanning centuries, whereas cold forging emerged during the 19th century industrial revolution. Despite their distinct origins,...