Education: What is die casting? advantages and disadvantages

In previous sections, we provided a brief introduction to various casting techniques and molding simulation software. For those who have read these, you likely now have a general understanding of casting. If you haven’t yet read those sections, you can check them out via the link below.

• Education: What is Casting and Molding Simulation?

Now, we will move on to introduce “Die casting”, which falls under the category of “Non-expendable mold casting”, as well as its advantages and disadvantages.

What is die casting?

“Die casting” is a casting technique in which molten metal is injected into a precise mold under high pressure, allowing for the production of a large number of high-quality finished products in a very short period. Products manufactured using the die casting process are also referred to as diecasts. “Die” refers to the mold, and “cast” refers to the casting itself.

The origins of die casting can be traced back to 1838, when American inventor David Bruce (1802-1892) developed a hand-operated pivotal type caster, known as the Bruce Casting Machine. Although its history is relatively short compared to traditional casting techniques, which can be traced back to bronze casting in 3200 BC, die casting has undeniably laid the foundation for the later development of industrial technology and the widespread availability of industrial products.

Compared to other casting techniques, die casting has distinct characteristics, such as excellent dimensional accuracy, smooth and polished product surfaces, robust metal structures, high strength, ease of mass production, and the reduction of machining costs. Due to these advantages, die casting is widely applied in modern society for the production of components and structural parts in various fields, such as automobiles, motorcycles, household appliances, and building materials.

Comparison of Die Casting with Other Casting Techniques

As mentioned in other sections, there are various casting techniques with different applications. The most representative casting methods include “Sand casting”, “Precision casting”, “Metal mold casting”, “Low-pressure die casting”, and “Die casting”. Each casting technique has its own advantages and disadvantages, and in practical production, the choice of casting method depends on the product being manufactured and the casting material used.

Below is an overview of the key characteristics and advantages/disadvantages of each casting technique, as illustrated in the diagram.

• Sand casting

  Sand casting is a casting technique in which molten metal is poured into a mold made of sand to form the desired shape. Although a new mold must be created for each casting process, the cost of making the mold is low, and it requires relatively simple equipment, making sand casting very economical. A wide range of metals can be used in this method, including cast iron, cast steel, copper alloys, aluminum alloys, and more. Representative sand casting methods include “Green sand casting” and “Self-hardening casting”, among others.

  (*引用自プロセスX頻道)

• Precision casting

  This is a method in which molten metal flows into a mold made of wax or resin models coated with refractory powder or ceramics, or a plaster mold and is formed. Precision casting is widely used for producing complex products due to its ability to achieve excellent dimensional accuracy and smooth surface finishes. This method is applied in a broad range of industries, from jewelry to aerospace components. Representative precision casting techniques include “Lost-wax casting” and “Plaster mold casting”, among others.

  (*引用自ArmstrongMold頻道)

• Metal mold casting

  Metal mold casting, also known as “Gravity die casting”, is a casting technique in which molten metal is poured into a mold made of heat-resistant steel or cast iron using gravity. Common casting materials include aluminum alloys, magnesium alloys, and copper alloys. Compared to sand casting, metal mold casting produces products with higher dimensional accuracy, smoother surfaces, and superior mechanical properties. This method is often used to manufacture products that require high pressure resistance or strength.

  (*引用自プロセスX頻道)

• Low Pressure Die Casting (LPDC)

  Low Pressure Die Casting (LPDC) is a casting technique similar to metal mold casting, where molten metal is poured into a metal mold to form a shape. However, unlike metal mold casting, which relies on gravity, LPDC uses air pressure (typically 0.01 to 0.1 MPa) to fill the mold. The molten metal is injected into the mold from a sealed, temperature-controlled furnace. Once the metal solidifies, the air pressure is released, and any remaining unsolidified metal is returned to the furnace.

  (*引用自THORS eLearning Solutions頻道)

• Die casting

  Also known as “High Pressure Die Casting (HPDC)”, die casting is a technique in which molten metal is injected into a precise mold under high pressure, typically around 30 to 80 MPa, to form the desired shape. This method is characterized by excellent dimensional accuracy, smooth and polished product surfaces, solid metal structures, and high strength.

  (*引用自リョービ株式会社頻道)

Common Metal Materials for Die Casting

The metal materials used in die casting technology are primarily Non-ferrous metals, including aluminum alloy, zinc alloy, magnesium alloy, copper alloy, etc.

• Aluminum alloy

  With a specific gravity of approximately 2.7 g/cm³, aluminum alloy is actively utilized across various fields due to its excellent corrosion resistance, lightweight properties, and ability to maintain dimensional accuracy over long periods. It accounts for about 97.9% of the overall die casting production process, making it the most widely used die casting material. For example, it is used in the cylinder structure of automobiles and motorcycles, brake levers, gas stoves, and other applications.

• Zinc alloy

  With a specific gravity of approximately 6.6 g/cm³, zinc alloy is characterized by impact resistance, excellent mechanical properties, high dimensional accuracy, and ease of surface coating. It is suitable for producing thin-walled complex structural components. However, due to its heavier weight, it is not ideal for lightweight products. In applications, it is commonly used in car door handles, PC connectors, and car radiator grill covers.

• Magnesium alloy

  With a specific gravity of approximately 1.8 g/cm³, magnesium alloy is the lightest material among practical metals, being one-fourth that of iron (Fe) and aluminum (Al). It possesses characteristics such as dent resistance and vibration absorption, making it widely used in the structural frames of electronic products like smartphones and computers.

• Copper alloy

  With a specific gravity of approximately 8.9 g/cm³, copper alloy features excellent thermal and electrical conductivity, high strength, and corrosion resistance. It is mainly applied in construction materials such as water faucet nuts, room door handles, and hinges.

  

Structure of Die Casting Equipment

The structure of die casting machines can vary depending on the die casting technology used. However, from a structural perspective, they can be divided into three main components: the “Clamping unit”, which controls the opening and closing of the mold; the “Injection unit”, which injects the molten metal into the mold; and the “Ejector unit”, which ejects the cooled castings from the mold.

• Clamping unit

  The clamping unit is a mechanism that controls the opening and closing of the mold, which is mounted on the movable template and the fixed template. It provides sufficient mold clamping force to counteract the mold opening force generated when the molten metal is injected into the mold.

• Injection unit

  The injection unit is responsible for injecting the molten metal from the filling tube into the cavity of the mold. Structurally, it consists of several components, including the injection sleeve, injection plunger, injection cylinder, accumulator, and others.

• Ejector unit

  The ejector unit is a mechanism that removes the product from the movable die after the molten metal has cooled and solidified within the mold. It is composed of parts such as the ejector pin, ejector plate, ejector cylinder, and others.

  

Die Casting-Related Technologies

In modern die casting technology, various principles or techniques serve as the core to develop different derivative technologies, similar to casting technology. These related technologies can be broadly classified into two categories: “General die casting”, which refers to the basic technology, and “Special die casting”, which refers to derivative technologies.

• General die casting

  In common general die casting technology, die casting machines can be categorized based on the type of injection structure they employ, distinguishing between “Cold chamber die casting” and “Hot chamber die casting”.

  • Cold chamber die casting

    In terms of structure, the die casting machine is set up separately from the melting and holding furnace. The injection mechanism’s chamber is exposed to air, leading to the cooling of the molten metal. Equipment using this technique is referred to as a cold chamber die casting machine. During the injection process, it employs a two-stage injection method consisting of low-speed and high-speed injection. The low-speed injection typically operates at a speed of about 0.1 to 0.7 m/s, while high-speed injection operates at around 2 to 3 m/s. However, with advancements in technology, equipment capable of high-speed injection up to 10 m/s has recently emerged in the market.

    (*引用自North American Die Casting Association頻道)

  • Hot Chamber die casting

    Unlike the structure of cold chamber die casting machines, the injection mechanism and the melting and holding furnace are designed as an integrated unit. The most significant feature is that the injection mechanism’s chamber is immersed in a dedicated melting and holding furnace. During production, the molten metal from the melting furnace is injected into the mold through a goose-neck. Equipment that utilizes this technique is referred to as a hot chamber die casting machine. During the injection process, the injection occurs at a speed of approximately 1 to 2 m/s.

    (*引用自North American Die Casting Association頻道)

• Special die casting

  Special die casting refers to various specialized techniques developed to improve common defects found in general die casting technology, such as misrun, cold shut, shrinkage cavity, and others.

  • Vacuum die casting

    Vacuum die casting is a technique that forcibly removes any residual air or gases from the filling tube and the mold cavity, expelling them outside the mold during the casting process. By ensuring that air and gases are removed, this technique enhances the fluidity of the molten metal and reduces the likelihood of defects such as gas porosity in the internal structure of the casting. To maintain the vacuum state during the casting process, the equipment must be modified for airtightness at various components, including the mold parting surface, ejector pins, filling tubes, and plunger tips. Additionally, it is crucial to select mold lubricants and plunger lubricants that produce minimal gas during the casting process.

    (*引用自リョービ株式会社頻道)

  • Low speed filling die casting

    Low speed filling die casting involves filling the mold cavity with molten metal at a low speed, allowing the molten metal to flow smoothly without generating turbulence during the filling process. This gradual filling helps to expel gases from the cavity, thereby reducing the likelihood of air entrapment defects. Because it avoids turbulence, this method is also referred to as “Laminar flow die casting”. Related techniques that have emerged include “Squeeze casting process”, “Horizontal low-velocity die casting process”, and the “New injection die casting process”.

    • Squeeze casting process

      Unlike common cold chamber and hot chamber die casting machines, which have a horizontal injection mechanism, squeeze casting machines are designed with a vertical injection structure. During the casting process, the filling tube is tilted along with the injection structure to allow the molten metal to be smoothly injected into the filling tube. After the pouring operation is complete, the injection structure returns to its original position, aligning the filling tube with the mold before injecting the molten metal into the mold cavity to form the casting.

      (*引用自North American Die Casting Association頻道)

    • Horizontal Low-velocity die casting process

      The horizontal low-velocity die casting process is a derivative technology developed from cold chamber casting. Unlike traditional cold chamber die casting, this method injects molten metal into the mold cavity at a low speed (0.03 to 0.06 m/s) during the injection process. However, due to the low injection speed, it is necessary to install heaters at the filling tube to prevent the molten metal from cooling down within the tube. Additionally, insulating plunger lubricants with good thermal resistance must be selected. To reduce the occurrence of shrinkage cavities in thick sections of the casting, the mold should also incorporate a structure for localized pressure casting.

      

    • New Injection Die Casting Process (NI Casting Process)

      The new injection die casting process involves using air pressure to inject molten metal into the mold cavity, followed by the application of pressure using a pressure bar to shape the casting. In addition to requiring specialized injection mechanisms, this method also necessitates the application of a powdered release agent in the runner and cavity to inhibit heat transfer during the injection of the molten metal into the mold cavity.

      

  • Local squeeze die casting

    In local squeeze die casting, when the molten metal has completely filled the mold cavity and begins to solidify, a pressure pin positioned on the mold applies localized pressure to the thicker sections of the casting. This helps to supplement any insufficient molten metal in areas where shrinkage cavities might form, preventing defects. Typically, the pressure applied by the pressure pin is about 1.5 times the casting pressure. However, if the timing of applying the pressure is incorrect, the desired results may not be achieved.

    

  • Pore Free Die Casting (PF Method)

    Also known as the PF method, pore free die casting involves closing the mold in advance and positioning the plunger rod at the filling port. Next, active gas, specifically oxygen (O₂), is filled into the mold cavity. After the filling is complete, the plunger rod is retracted, and the molten metal is poured into the filling tube. The molten metal is then injected into the mold cavity at high speed to form the casting. Due to the high-speed injection, the atomized molten metal reacts with the oxygen inside the cavity, creating a momentary vacuum environment, which significantly reduces the occurrence of porosity defects in the casting.

    

  • Semi-solid metal casting

    Semi-solid metal casting utilizes a slurry state where both liquid and solid phases coexist, taking advantage of the semi-solidified or semi-molten condition of the metal for the die casting process. Related technologies include “Rheocasting”, which involves transitioning from a liquid to a solid-liquid coexistence state, and “Thixocasting”, which transitions from a solid to a solid-liquid coexistence state.

    (*引用自Lincoln Electric Automation, Columbus頻道)

  • Integrated die casting

    Unlike conventional die casting techniques that require multiple sets of molds to produce small to medium-sized structural components (such as motorcycle brake levers, automotive wheels, and engine parts), integrated die casting allows for the production of large and complex structural components in a single operation (such as automotive chassis and battery enclosures). Due to the clamping force used exceeding 6,000 tf, this method is also referred to as “Giga casting”.

    (*引用自Idra Group頻道)

With this explanation, I believe everyone now has a general understanding of die casting. In the next unit, we will delve deeper into the fundamental principles and concepts of die casting, introducing more detailed examples for a better understanding.

Until then, see you next time.