When it comes to die casting, there are two main techniques — hot chamber and cold chamber. The technique you choose depends on your project specifications and the type of results you seek to achieve. In this guide, we’ll discuss the former method, including how it works, which metals are used and what advantages this process offers over its cold chamber counterpart.
What Is Hot Chamber Die Casting?
Die casting refers to a permanent mold manufacturing process pioneered in the early 20th century that uses large amounts of pressure to push molten metal through a mold. Due to the significant amount of pressure applied, this method can produce castings with a great degree of surface detail, excellent dimensional accuracy and extremely thin walls — sometimes as small as half a millimeter.
Industrial metal castings vary greatly in size, ranging from extremely tiny to 50 or so pounds. Parts manufactured using this process include tools, machine components, carburetors, motors, various housings and toys.
Hot Chamber Die Casting
In hot chamber die casting, metal heats up in an attached casting machine. These casting machines, also known as gooseneck machines, feature a built-in furnace that heats metal until it achieves a molten state. This process uses a hydraulic-powered piston, which forces molten metal from the furnace and into the die. This type of die casting is a relatively quick process. The hot chamber die casting process is used for high-productivity applications that require substantial output.
In cold chamber casting, casting machines don’t heat the metal. Instead, a molten metal must be poured into the chamber either manually with ladles or with an automatic ladle system. Once the metal is poured in, a hydraulic piston forces the molten metal into the die at high pressure.
Materials Used in Hot Chamber Die Casting
Because hot chamber die casting features an internal melting pot, hot chamber die casting machine manufacturers recommend that metals with lower melting points be used. This is so the metals won’t dissolve or erode the machine’s metal when heated or put under high pressure. For example, machine parts like the plunger are continuously submerged within the molten metal. If the metal has too high of a melting point, it can cause the plunger to sustain damage and lose its functionality. This could warrant costly replacements.
Materials like aluminum have higher melting points. This metal melts at 1,220 degrees Fahrenheit compared to a material like zinc, which melts at 786 degrees. Therefore, aluminum is not appropriate for the hot chamber die casting process. The most suitable materials to use for hot chamber die casting are zinc and magnesium alloy, which we will discuss in further detail below.
Zinc, which possesses exceptional hardness and strength, lends itself to many applications and serves as a great alternative to pressed, machined, fabricated and stamped components. Zinc also has good structural integrity and wear resistance, which makes it ideal for highly complex, multifaceted shapes used in the electronics and automotive safety industries. Other advantages of zinc alloy include:
- Good electrical conductivity
- Affordable raw material
- Good hardness and strength
- Great thermal conductivity
- Excellent stability and dimensional accuracy
- Great thin wall capabilities
- Ability to cold form, which facilitates joining
- Outstanding resistance to corrosion
- Full recyclability
- High-quality finishing characteristics
Magnesium is the most lightweight of the die cast alloys but has a great strength-to-weight ratio. It also has excellent radiofrequency interference (RFI) and electromagnetic interference (EMI) shielding properties, which is great for electrical housings and connectors. It’s also used for laboratory and medical equipment to protect against interfering signals. Other advantages of magnesium include:
- High thermal and electrical conductivity
- Ability to withstand high operating temperatures
- Extremely thin wall capabilities
- Great dimensional accuracy and stability
- Excellent finishing characteristics
- Great resistance to environmental corrosion
- Full recyclability
For more information on the properties of these alloys, refer to our alloy properties page.
Hot Chamber Die Casting Process
In the hot chamber die casting process, the molten metal supply is connected to the die casting machine and serves as an important component in this type of operation. We’ll explain the process step-by-step below:
- The hot chamber fills up with liquid metal: The shot cylinder, which powers the injection stroke, is located above the molten metal supply. This shot cylinder connects to a plunger rod, which connects to the plunger. The plunger makes contact with the molten material, and at the beginning of a casting cycle, this plunger is at the top of the hot chamber. When in this position, liquid metal can enter the chamber via intake ports, filling it up.
- The plunger goes down: As the cycle starts, the shot cylinder pushes the plunger down, causing it to travel past the intake ports, which prevents the liquid metal from entering the hot chamber. At this point, the right amount of molten metal is in the hot chamber for the shot, which will fill the mold and make the casting.
- The plunger goes down further: Then, the plunger is pushed down further, which forces the liquid metal into the die. In hot chamber die casting, the pressure that must be exerted on the molten metal to fill the die typically ranges from 700 to 5,000 pounds per square inch (psi). This pressure is held for as long as needed for the casting to solidify.
- The plunger returns to its original position: To prepare for the next cycle, the plunger reverses and returns to its original position at the top of the hot chamber. This once again exposes the intake ports, allowing molten metal to come in and fill the chamber.
Advantages of Hot Chamber Die Casting
Hot chamber die casting offers many advantages over cold chamber die casting, with the most important benefit perhaps being the much faster cycle time. This allows die casting companies to create more products in less time, which improves their efficiency and productivity — plus client satisfaction. This process also provides the following additional advantages:
- More environmental friendliness due to less wasted metal
- More efficiency due to the machine containing an internal melting pot
- Reduced porosity
- Longer machinery life because only low-melting-point metals are used
Contact Premier Engineered Products for Hot Chamber Die Casting Services
Premier is a U.S.-based, family-owned die casting company that offers a wide range of die casting services, including consulting services for numerous die casting projects. Whether you require help with assembly improvements or product design, we can assist you. If you have any questions about our services, feel free to fill out our contact form. We look forward to speaking with you and helping you with your die casting project needs!