Die Casting and Die Casting Metal
What is die casting?
Die casting is a manufacturing process for producing metal parts by forcing molten metal under high pressure into a die cavity. As a kind of advanced precision molding technology with high efficiency and less cutting, it is originated from movable type manufacturing in the 1920s. With less than 200 years of history, it is younger than traditional casting technology, but it develops rapidly in metal processing technology and applied to all walks of life. This article we show you some important about die casting and die casting metal.
(1) The history of
die casting manufacturing
(2) Three elements
of die casting production
(3) The die casting
(4) 6 advantages of
(5) The 3 most
common Die Casting alloys
The history of die casting manufacturing
There are many opinions about the origin of die casting, but according to literature, it was originally used for the printing Industry. As early as 1822, Dr. Willam Church made a die casting machine (as picture 1) with daily output 12,000 to 20,000 Pb words. It has shown the big potential of this process. In 1849, J.J.Sturgiss designed and manufactured the first manual piston hot chamber die casting machine, and obtained a patent in the United States. In 1885, Mersen-thaler researched the previous patents and invented the printing die-casting machine. It was only used to produce low-melting lead and tin alloy castings. By the 1860s, it was used to produce zinc alloy die-casting parts.
Die casting is widely used in industrial production only at the beginning of the last century, in the production of cash register, phonograph and bicycle products. In 1904, the Franklin Company of the United Kingdom began to use die-casting to produce automobile connecting rod bearings, setting a precedent for the application of die casting parts in the automotive industry. In 1905, Doehler successfully developed a die-casting machine for industrial production, which can make zinc, tin and copper alloy castings. Wagner then designed the gooseneck type pneumatic die casting machine (as picture 2) for aluminum alloy castings. In 1927, Czech engineer Jesef Pfolak designed a cold-casting chamber die-casting machine. Since the crucible storing molten alloy was separated from the injection chamber, the injection pressure could be significantly increased, making it more suitable for industrial production. It overcomes the shortcomings of the hot-press chamber die-casting machine, thus making the die casting technology a big step forward.
At the beginning of the 19th century, due to the growth of high output in various industries, the huge demand for commercial die castings increased. This movement opened many different markets for the die casting industry to expand into many different businesses. During this period, aluminum and zinc replaced the initial metals tin and lead because of the higher quality of these products. Due to modern surface treatment and efficient production factors, the original process of low-pressure injection molding has been changed to a high-pressure casting method. Throughout history, all major products have been manufactured through die casting processes and have focused on saving companies a great deal of money in production. Consumers can meet their commercial and industrial needs with consistent results, long service life, and reliable finished castings based on demand.
Three elements of die casting production - Die casting equipment, die casting molds and die casting metal
1. Die casting equipment
There are two main types of die casting machines - hot chamber machines, which is used for alloys with low melting temperatures, such as zinc, and cold chamber machines that is used for alloys with high melting temperatures, such as aluminum.
(1) Hot chamber die casting machine
Hot chamber machines are used for alloys with low melting temperatures, such as zinc, tin, and lead. The temperatures required to melt other alloys would damage the pump, which is in direct contact with the molten metal. The metal is contained in an open holding pot which is placed into a furnace, where it is melted to the necessary temperature. The molten metal then flows into a shot chamber through an inlet and a plunger, powered by hydraulic pressure, forces the molten metal through a gooseneck channel and into the die. Typical injection pressures for a hot chamber die casting machine are between 1000 and 5000 psi. After the molten metal has been injected into the die cavity, the plunger remains down, holding the pressure while the casting solidifies. After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit. Prior to the injection of the molten metal, this unit closes and clamps the two halves of the die. When the die is attached to the die casting machine, each half is fixed to a large plate, called a platen. The front half of the die, called the cover die, is mounted to a stationary platen and aligns with the gooseneck channel. The rear half of the die, called the ejector die, is mounted to a movable platen, which slides along the tie bars. The hydraulically powered clamping unit actuates clamping bars that push this platen towards the cover die and exert enough pressure to keep it closed while the molten metal is injected. Following the solidification of the metal inside the die cavity, the clamping unit releases the die halves and simultaneously causes the ejection system to push the casting out of the open cavity. The die can then be closed for the next injection.
chamber die casting machine
Cold chamber machines are used for alloys with high melting temperatures that can not be cast in hot chamber machines because they would damage the pumping system. Such alloys include aluminum, brass, and magnesium. The molten metal is still contained in an open holding pot which is placed into a furnace, where it is melted to the necessary temperature. However, this holding pot is kept separate from the die casting machine and the molten metal is ladled from the pot for each casting, rather than being pumped. The metal is poured from the ladle into the shot chamber through a pouring hole. The injection system in a cold chamber machine functions similarly to that of a hot chamber machine, however, it is usually oriented horizontally and does not include a gooseneck channel. A plunger, powered by hydraulic pressure, forces the molten metal through the shot chamber and into the injection sleeve in the die. The typical injection pressures for a cold chamber die casting machine are between 2000 and 20000 psi. After the molten metal has been injected into the die cavity, the plunger remains forward, holding the pressure while the casting solidifies. After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit. The clamping unit and mounting of the dies are identical to the hot chamber machine.
2. Die casting molds
The dies into which the molten metal is injected are the custom tooling used in this process. The quality of die-casting molds has a decisive effect on the quality and efficiency of die castings production. The dies are typically composed of two halves - the cover die, which is mounted onto a stationary platen, and the ejector die, which is mounted onto a movable platen. This design allows the die to open and close along its parting line. Once closed, the two die halves form an internal part cavity which is filled with the molten metal to form the casting. This cavity is formed by two inserts, the cavity insert and the core insert, which are inserted into the cover die and ejector die, respectively. The cover die allows the molten metal to flow from the injection system, through an opening, and into the part cavity. The ejector die includes a support plate and the ejector box, which is mounted onto the platen and inside contains the ejection system. When the clamping unit separates the die halves, the clamping bar pushes the ejector plate forward inside the ejector box which pushes the ejector pins into the molded part, ejecting it from the core insert. Multiple-cavity dies are sometimes used, in which the two die halves form several identical part cavities.
(1) Die channels
The flow of molten metal into the part cavity requires several channels that are integrated into the die and differs slightly for a hot chamber machine and a cold chamber machine. In a hot chamber machine, the molten metal enters the die through a piece called a sprue bushing (in the cover die) and flows around the sprue spreader (in the ejector die). The sprue refers to this primary channel of molten metal entering the die. In a cold chamber machine, the molten metal enters through an injection sleeve. After entering the die, in either type of machine, the molten metal flows through a series of runners and enters the part cavities through gates, which direct the flow. Often, the cavities will contain extra space called overflow wells, which provide an additional source of molten metal during solidification. When the casting cools, the molten metal will shrink and additional material is needed. Lastly, small channels are included that run from the cavity to the exterior of the die. These channels act as venting holes to allow air to escape the die cavity. The molten metal that flows through all of these channels will solidify attached to the casting and must be separated from the part after it is ejected. One type of channel that does not fill with material is a cooling channel. These channels allow water or oil to flow through the die, adjacent to the cavity, and remove heat from the die.
(2) Die Design
In addition to these many types of channels, there are other design issues that must be considered in the design of the dies. Firstly, the die must allow the molten metal to flow easily into all of the cavities. Equally important is the removal of the solidified casting from the die, so a draft angle must be applied to the walls of the part cavity. The design of the die must also accommodate any complex features on the part, such as undercuts, which will require additional die pieces. Most of these devices slide into the part cavity through the side of the die, and are therefore known as slides, or side-actions. The most common type of side-action is a side-core which enables an external undercut to be molded. Another important aspect of designing the dies is selecting the material. Dies can be fabricated out of many different types of metals. High-grade tool steel is the most common and is typically used for 100-150,000 cycles. However, steels with low carbon content are more resistant to cracking and can be used for 1,000,000 cycles. Other common materials for dies include chromium, molybdenum, nickel alloys, tungsten, and vanadium. Any side-cores that are used in the dies can also be made out of these materials.
(3) Die casting metal
Not all alloys can be used to produce die casting parts, the currently widely used die-casting alloys are non-ferrous metals. Due to the high melting point of ferrous metals, the service life of die-casting molds is extremely low. Therefore, die-casting processes are rarely used to produce ferrous metal castings. Generally, non-ferrous die-casting alloys are divided into two categories: high melting point such as Aluminum alloy and low melting point alloys such as Zinc alloy.
The selection of a material for die casting is based upon several factors including the density, melting point, strength, corrosion resistance, and cost. The material may also affect the part design. For example, the use of zinc, which is a highly ductile metal, can allow for thinner walls and a better surface finish than many other alloys. The material not only determines the properties of the final casting, but also impacts the machine and tooling. Materials with low melting temperatures, such as zinc alloys, can be die cast in a hot chamber machine. However, materials with a higher melting temperature, such as aluminum and copper alloys, require the use of a cold chamber machine. The melting temperature also affects the tooling, as a higher temperature will have a greater adverse effect on the life of the dies.
The die casting process cycle
The die casting process cycle consists of 5 main phases, as described below. The total cycle time is very short, usually between 2 seconds and 1 minute.
(1) The clamping phase
-The first step is to prepare and clamp the die halves. Each half mold is first cleaned from the last injection and then lubricated to facilitate the discharge of the next part. The lubrication time increases with the size of the part, the number of cavities and side cores. In addition, depending on the material, lubrication may not be required after each cycle, but may be required after 2 or 3 cycles. After lubrication, the two half dies connected in the die casting machine are closed and firmly clamped together. When injecting metal, enough force must be applied to the mold to make it close firmly. The time required to close and clamp the die depends on the machine - larger machines (machines with higher clamping forces) will take more time. This time can be estimated according to the dry cycle time of the machine.
(2) The injection phase
-The molten metal is held at a set temperature in the furnace and then transferred to a chamber where it can be injected into the mold. The method of transferring molten metal depends on the type of die casting machine, whether it is a hot chamber die casting machine or a cold chamber die casting machine. Differences in this equipment will be detailed in the next section. Once transferred, the molten metal is injected into the mold under high pressure. A typical injection pressure range is 1000 to 20000 psi. During solidification, this pressure holds the molten metal in the mold. The amount of metal injected into the mold is called a projectile. Injection time is the time required for the molten metal to fill all channels and cavities in the mold. This time is very short, usually less than 0.1 seconds, to prevent any part of the metal from setting prematurely. The proper injection time can be determined by the thermodynamic properties of the material and the wall thickness of the casting. Larger wall thickness requires longer spraying time. In the case of a cold chamber die casting machine, the injection time must also include the time to manually pack the molten metal into the shot peening chamber.
(3) The cooling phase
-Once the molten metal injected into the mold enters the cavity, it begins to cool and solidify. When the whole cavity is filled and the molten metal solidifies, the final shape of the casting is formed. After the cooling time is over and the casting solidifies, the mold can be opened. The cooling time can be estimated according to the thermodynamic properties of the metal, the maximum wall thickness of the casting and the complexity of the die. Larger wall thickness requires longer cooling time. The geometric complexity of the mold also requires a longer cooling time because of the additional resistance to heat flow.
(4) The ejection phase
-After a predetermined cooling time, the half mold can be opened, and the injection mechanism can push the casting out of the mold cavity. The time to open the mold can be estimated based on the dry cycle time of the machine, the injection time is determined by the size of the casting shell, and it should include the time when the casting falls off the mold. The ejecting mechanism must exert a certain force to eject the parts because the parts will shrink and adhere to the mold during the cooling process. Once the casting is ejected, the mold can be clamped for the next injection.
(5) The trimming phase
-During cooling, the material in the mold channel will solidify and adhere to the casting. Excess material and any resulting flash must be cut from the casting by cutting or sawing or by hand using a trimming press. The time required to trim excess material can be estimated based on the size of the casting shell. The scraps from this finishing can either be discarded or reused during the die casting process. Recycled materials may need to be readjusted to the proper chemical composition before they can be combined with non-recycled metals and reused during the die casting process.
6 advantages of die casting
(1) Die casting is fast
Die casting can be produced in seconds each part and quantities of hundreds to thousands of metal parts each day.
(2) Near net shape
Die casting are produced “near net shapes” no matter how complex the shape is how tight the tolerances are.
(3) Lighter weights
Die casting are stronger because of the material surface skin not the thickness of materials so parts can weigh less with thinner casting wall thicknesses.
(4) Die casting is versatile
Many more part shapes and sizes can be produced using the die casting manufacturing process.
(5) Die castings are durable
Die-castings parts are metal and have a long service life.
(6) Die castings are inexpensive
Die castings are fast to produce and useless material. Die casting are typically less expensive than most other metal parts manufacturing processes.
3 most common Die Casting Metal - Aluminum Alloy, Magnesium Alloy and Zinc Alloy
1. Aluminum Alloy
Aluminum Alloy is superior to other die casting alloys and it has rich sources. Therefore, it plays an important role in the production in various countries, and its consumption is far more than other die-casting alloys.
Aluminum Alloy Characteristics:
*High operating temperatures
*Outstanding corrosion resistance
*Very good strength and hardness
*Good stiffness and strength-to-weight ratio
*Excellent EMI and RFI shielding properties
*High thermal and electrical conductivity
*High dimensional stability
*Good finishing characteristics
*Relatively easy to cast
*Requires use of a cold chamber machine
Composition, Mechanical Properties and Physical Properties for Aluminum Alloy
2. Mechanical Properties
3. Physical Properties
4. Aluminum Die Cast Alloy Equivalents
Advantages of Aluminum Die Casting
Light Weight is one of the most significant benefits of aluminum die casting. It is able to withstand the highest operating temperatures of all die cast alloys and with more surface finishing options than other die cast alloys. Moreover, aluminum casting is versatile, corrosion resistant; it retains high dimensional stability with thin walls and can be used in almost all industries.
Aluminum Die Casting Applications:
Aluminum die casting is widely used in producing Auto parts, motorcycle parts. It can improve automotive fuel efficiency by contributing to weight saving requirements.
Aluminum die casting is used in a broad range of networking and infrastructure equipment in the telecom and computing industries because RF filter boxes and housings require heat dissipation.
Aluminum die casting is also used in handheld devices such as the shell of electric drill. As aluminum castings can provide EMI/RFI shielding, rigidity, and durability with minimal weight
Because of aluminum’s excellent electrical performance and shielding properties, even in high-temperature environments, die cast aluminum is ideal for electronic connectors and housings
2. Magnesium Alloy
Magnesium is strong, rigid, fully recyclable, and is the ideal alloy for saving weight when you don’t want to sacrifice durability.
Magnesium Alloy Characteristics:
*Very low density
*High strength-to-weight ratio
*Excellent machinability after casting
*Use of both hot and cold chamber machines
*High conductivity; electrical, and thermal
*Withstands high operating temperatures
*High dimensional accuracy and stability
*Exceptional thin wall capability
*Good environmental corrosion resistance
*Good finishing characteristics
Composition, Mechanical Properties and Physical Properties for Magnesium Alloy
2. Mechanical Properties
3. Physical Properties
Magnesium Die Cast Alloy Equivalents
Advantages of Magnesium Die Castings
There are many benefits to casting with magnesium alloy. Not only is magnesium the lightest of all the structured materials (Almost as light-weight as plastic) but it has excellent stiffness and strength-to-weight ratios. Additionally, magnesium has the advantage of greater strength and rigidity along with inherent EMI/RFI shielding, durability, heat-dissipation, and full recyclability
Magnesium Die Casting Applications
Magnesium has outstanding EMI and RFI shielding properties, perfect for connectors and electrical housings. It is also utilized for medical and laboratory equipment to provide protection against other interfering signals in a hospital room.
Magnesium Die Casting is also used for m anufacturing thin-wall parts such as auto parts and computer parts.
3. Zinc Alloy
Zinc alloy once played an important role in the development history of die casting. Its high strength and hardness lends itself to many solutions it’s the ideal alternative to machined, pressed, stamped, and fabricated components.
Zinc alloy characteristics:
*Good impact strength
*Excellent surface smoothness allowing for painting or plating
*Easiest to cast
*Can form very thin walls
*Long die life due to low melting point
*High strength and hardness
*Excellent electrical conductivity
*High thermal conductivity
*Low cost raw material
*High dimensional accuracy and stability
*Excellent thin wall capability
*Ability to cold form, which eases joining
*High quality finishing characteristics
*Outstanding corrosion resistance
*Use of a hot chamber machine
Composition, Mechanical Properties and Physical Properties for Zinc alloy
2. Mechanical Properties
3. Physical Properties
Die Cast Alloy Equivalents
Applications for Zinc Die Castings:
Zinc alloy die casting can be used to make parts for structural and decorative purposes.
Structural purposes: such as carburetor, pillar, lock, gear and frame. As a structural part, it requires high mechanical strength, dimensional accuracy and internal quality of castings.
Decorative purposes: such as daily necessities, toys, decorations, lighting, watch shell, mobile phone shell, metal buckle, bathroom accessories, etc. the surface quality of die-casting parts is required to be high, the surface is required to be bright and clean, and it should have beautiful appearance.