Hot chamber and cold chamber die casting are both metal casting methods. But they work in different ways. Hot chamber die casting uses a built-in furnace. It works faster and makes parts from low-melting-point metals like zinc. Meanwhile, cold chamber casting uses a separate furnace to melt metal. It can produce parts from moderate to higher melting point metals like aluminum but does not work fast.
The selection decision lies in the metal types and complexity of the part. Read this article to discover their different aspects, alloys, applications, and processes.
Hot Chamber Die-Casting
The process is called hot chambers because of the submerged injection system (gooseneck system and plunger) in the molten metal inside a furnace. It operates more quickly using an automated technique to make metal parts.
The manufacturer forces molten metal into a reusable steel mold under high pressure. Zinc, tin, and lead-based alloys are the primary metals it uses. This process works with lower melting points of metal (below 450°C / 842°F) to avoid injection system damage. However, lead alloys are restricted in many industries due to their toxicity.
Metal Injection: The Gooseneck System
The gooseneck systems in hot chamber die-casting work for pumping molten alloys into the die cavity. It is submerged in a furnace to improve metal flow. Wherein a hydraulic or pneumatic plunger driven by oil/gas at 7–15 MPa / 1,000–2,200 psi forces metal into the die and up the gooseneck. This design is ideal for mass production, allowing 2-5 injections per minute.
Key Challenges:
Some impurities like oxidized metal can accumulate in the gooseneck, forming dross. They block flow and reduce part quality as a result. So, proper cleaning systems need to avoid this.
Additionally, constant exposure to molten alloy deteriorates the plunger and gooseneck over time. This requires replacement every 50,000–100,000 cycles.
Die Materials and Durability
Dies are made with stronger and harder materials like steel (e.g., H13 grade). These dies tend to stand up against intense pressures and heat. However, tiny cracks form inside the die when heat is above 400°C and cools. Any die can last 100,000–500,000 cycles before undergoing repair.
Speaking about its cost, it remains high, ranging from $20,000 to $50,000 per die. That alternatively becomes affordable when used for mass production. Regular maintenance, coatings, and temperature management inevitably increase its lifespan.
Cycle Time Breakdown
- Filling: It takes 0.1–0.5 seconds to insert molten metal into the die. Speed usually depends on plunger force and metal viscosity.
- Solidification: The molten metal cools and hardens in 2–10 seconds. Thicker parts need longer, while thin-walled parts (e.g., 1–3 mm) cool down soon enough.
- Ejection: Ejector pins make this process easy, removing the part in 1-3 seconds. Additionally, using lubricant spray on the die (e.g., graphite) avoids sticking.
Temperatuurregeling
To get consistent casting quality, picking a precise temperature is valuable. Therefore, the furnace maintains molten zinc at 410–430°C (770–806°F). This means changes in temperature of even 10°C can cause defects.
During casting, electric resistance heaters or gas burners heat the furnace. Meanwhile, thermocouples observe temperature the entire time. This is because poor control (too hot) degrades metal, and too cold causes dross. Likewise, premature solidification does not fill gaps or cause cracks.
Ejection System
The part becomes ready for removal when its metal is fully solid. The manufacturers open the die using ejector pins that push the part out.
Additionally, hydraulic actuators control the force and avoid damage. Meanwhile, angled pins smoothly release complex shapes. You can also use a lubricant mist to cool the die and stop sticking. All this means that well-functioning ejection systems perform highly efficiently.
Voordelen
- This process is 3–4x faster than cold chamber die casting.
- Inbuilt furnaces use 20–30% less energy than those that melt metal separately.
- It makes parts with tight tolerances (±0.1 mm) and smooth surfaces.
- Hot chamber casting is ideal for mass production (10,000+ parts).
- It is widely used in automotive hinges or electronic housings.
Nadelen
- This technique is not suitable for aluminum or magnesium spuitgieten. Because they have a higher melting point, which would damage the gooseneck.
- Temperature deviation from frequent cycling stresses the gooseneck, and cracks occur as a result.
- Requires skimming of impurities to avoid dross.
Koud Kamer Die Casting
The cold chamber casting isn’t like a hot chamber; it has a separate furnace to melt metal. Instead, manufacturers shift molten metal through a ladle into the shot sleeve. Wherein the hydraulic plunger forces it into the mold cavity. The rest process is almost similar. This process works well with moderate to high melting temperatures of metals like aluminum, magnesium, and copper-based alloys.
Metal Ladling and Injection
You can transfer heated metal toward the machine using either a manual or automated ladle.
- Manual ladling is slower and not very consistent. It is used to pour molten metal into the shot sleeve. Variations in part quality occur as a result.
- Automated ladling refers to a robotic arm. That accurately measures and inserts the heated metal. It fills the gaps properly and reduces human error. This process helps improve production rates around 10–20%. Additionally, it removes defects like air entrapment and incomplete fills.
Shot Sleeve and Plunger
Short sleeves are part of injection systems. This is the point from where molten metal is poured before being injected into the die. Manufacturers make them using harder materials like steel so they can handle intense temperatures and pressures.
Whereas the plunger is like a rod powered by a hydraulic cylinder. It forces the molten alloy into the mold. Usually, this can be of two types: flat and tapered.
A flat plunger works for simpler parts with constant wall thickness. Meanwhile, tapered plungers are useful for tough designs, stopping turbulence and air entrapment.
Matrijs Materialen
Basically, cold chamber dies include hardened tool steel like H13 or H11. There are already strength-to-weight ratios and wear resistance in this material. That therefore handles high heat (up to 700°C/ 1292°F) and intense injection pressures without deforming.
However, there are some challenges that the die faces. For example, heat checks from constant heat and cooling cause surface cracks. Meanwhile, erosion from high-temperature alloys brings gradual wear.
Therefore, try to focus on regular maintenance, surface treatments, and coating (nitriding or PVD). These can increase the die’s lifespan and improve performance as well.
Koelkanalen
The engineers integrate cooling channels into the mold strategically. This is because these channels regulate the solidification step and decrease cycle times. Placing them near high-heat areas can produce constant cooling. That, therefore, does not cause warping, shrinkage, or internal cracks.
Sprue and Runner System
These components of the cold chamber machine help direct heated alloy from the shot sleeve into the die cavity.
The sprue part tends to be an entry point from where runners distribute metal away. Design them appropriately to remove major defects like air entrapment and block flow.
Ejection System
At the stage of solidified castings removal from the die without damage, ejection systems ensure smooth performance. These systems include the use of ejector pins, lubricant spray, hydraulic actuators, and ejector boxes resembling hot chambers.
Wherein, the part gets cool, the die opens, activating the ejector box and ejector pins push out the cast part.
Voordelen
- It can cast a wider range of alloys like aluminum, magnesium, and copper.
- There is less thermal shock because the shot sleeve and plunger do not face constant molten metal, reducing wear.
- It can make highly sharp, detailed parts with thin walls.
Nadelen
- It is slower than the hot chamber process and takes 20–60 seconds per part.
- It needs more energy and maintenance due to higher temperatures and pressures. That makes it costly.
- The use of manual ladling and maintaining die frequently increases labor requirements.
Comparison of Hot Chamber and Cold Chamber Die-Casting
| Parameter | Warm kamer spuitgietwerk | Koud Kamer Die Casting |
| Typical Alloys | Zinc, tin, lead-based alloys | Aluminum, magnesium, copper-based alloys |
| Metal Temperatures | 400–450°C (752–842°F) | 600–700°C (1112–1292°F) |
| Injection Pressures | 7–15 MPa (1,000–2,200 psi) | 30–150 MPa (4,350–21,750 psi) |
| Cycle Times | 5–15 seconds | 20–60 seconds |
| Die Temperatures | 150–200°C (302–392°F) | 200–300°C (392–572°F) |
| Tooling Costs | Lower (simpler dies, lower maintenance) | Higher (complex dies, frequent maintenance) |
| Production Rates | 300–700 parts/hour | 100–300 parts/hour |
| Afwerking oppervlak | Smooth, minimal post-processing required | Good, it may require additional finishing |
| Tolerance Capabilities | ±0.1 mm | ±0.2 mm |
| Energy Consumption | Uses 20–30% less energy | Requires external melting, increasing energy use |
| Deelcomplexiteit | Handle small to medium-sized parts, simple to moderate complexity | Best for larger, more complex parts |
Casestudies
Manufacturers commonly use hot chamber die casting to make zinc alloy buckles and fasteners. They use this technique because of its ability to produce small-size parts and mass production.
Whereas cold chamber dies, casting produces aluminum engine blocks. This part includes large size, complex geometry, and the need for high strength. Which is why cold chamber casting is best.
Toepassingen en industrieën
Automobiel:
Automotive industries use hot chambers to produce zinc alloy parts like seat belt components, wiper parts, and car audio housings. The impressive properties of zinc give them smooth finishes and high durability.
Conversely, cold chamber die casting helps in making aluminum engine brackets, engine room components, and lighting parts. This is because it can create any difficult designs with high strength.
Ruimtevaart:
You know, hot chamber die casting is rarely used for aerospace parts. That is because its casting metal (zinc, magnesium) has a lower melting point. But it does not mean there is no use of this process in this industry. Many small magnesium aerospace parts, like brackets, housings, and connectors, are made with it. That provides lightweight strength, corrosion resistance, and durability.
However, cold chamber die-casting parts made with magnesium alloys are used in aircraft. For instance, seat frames and cabin components. These parts are lighter and stronger.
Consumptiegoederen:
Manufacturers make products that are popular in fashion and accessories using hot chamber die casting. For example, zinc alloy buckles, zippers, and decorative trims.
Aluminum electronic enclosures and heat sinks are widely used in consumer electronics. They are made with a cold chamber process.
Opkomende toepassingen
Electric Vehicles (EVs):
Die casting is increasingly used to produce lightweight battery housings and structural components for EVs.
The increasing demand for EVs for lightweight parts is the reason behind the wide use of the die-casting technique. This process creates battery housings and structural components that contain less weight than average and are stronger.
5G Technology:
Aluminum and magnesium die-cast have now become important components for 5G infrastructure. For example, antenna housings and heat management systems.
Conclusie
Hot chamber die casting operates quickly and is an affordable option. It deals with lower melting point metals like zinc. On the other side, cold chamber die casting uses more energy as it melts the alloy separately. However, this process is efficient for tough and high melting point materials like aluminum, copper, etc. When choosing, look for their metal suitability, design complexity, and production volume. This way, you will get the desired results.