Cold chamber vs. warm chamber vs. hot chamber

Cold chamber vs. warm chamber vs. hot chamber die casting

Cold chamber vs. warm chamber vs. hot chamber die casting are manufacturing processes used to produce parts and components found in nearly every industry worldwide. Die castings are made from non-ferrous metals, and it is the metal choice that will dictate which method is used.

Die casting is the preferred manufacturing process for large runs of complex metal parts because of its reliability, accuracy, and versatility. Both cold chamber and hot chamber methods follow the same general approach, but they differ in machinery setup and molten metal delivery.

While the hot chamber process has lower cycle times, it cannot accommodate metals with higher melting points. The cold chamber process allows for the production of higher density parts but, with the wrong partner, if the process is not optimized, metal can cool too quickly in the chamber resulting in defects.

Many production efficiencies and benefits associated with cold chamber vs. warm chamber vs. hot chamber casting are dependent on the manufacturing partner and die quality.

Choosing the right method will depend on if the project is a one-time part development, the part’s application, and which metal will satisfy the manufacturer’s needs.

This article discusses each process in detail, where they diverge, and how to take advantage of each method.

 

Quick Overview of Die Casting

Die casting is a manufacturing process that creates complex non-ferrous metal (alloys that are not iron-based) parts with reusable dies. Differences between hot chamber and cold chamber casting are minimal. They use the same primary process, and we will cover the basic steps first.

Four steps create the foundation of any die casting run.

  1. Preparation: The mold cavity is first sprayed with lubricant. This helps control the temperature of the die and helps when it comes time to remove the part.
  2. Filling: Metal is then injected into the mold under high pressure. The pressure is maintained until the metal hardens.
  3. Ejection: Dies are drawn apart, and the cast part is ejected from the mold.
  4. Shakeout: The cast part is separated from the runners, gate, flash, and sprues using either additional machinery, sawing, or grinding.

Regardless of the cold chamber or hot chamber method, or using zinc or aluminum, the manufacturing process will still follow these steps. It is helpful though that ‘cold’ and ‘hot’ help differentiate between each method.

 

Cold Chamber Casting Method Overview

The name ‘Cold Chamber Casting’ sometimes suggests that cold or solid metal is forced into the mold -that is not the case.

Cold chamber die casting is used for metals with high melting points in applications worldwide. With cold chamber casting, the machine that houses the die and chamber is separate from the furnace.

Metals such as aluminum, brass, and copper alloys require a robust furnace to reach higher melting points and get to a pourable form.

With cold chamber die casting, metal is heated in a separate furnace then transferred into the casting machine. Molten alloys are ladled into a cold chamber then injected into the die using a high-pressure plunger.

 

What Types of Metals are Used for Cold Chamber Casting?

  • Aluminum: This is the most commonly cast metal globally and has become popular for its unique combination of lightweight and strength. Aluminum die-cast parts can withstand higher operating temperatures and have more surface finishing options than other non-ferrous metals. Most aluminum die-cast parts are 95% post-consumer recycled material making them both affordable and eco-friendly. It is also conductive, corrosion-resistant, and has excellent RFI and EMI shielding properties.
  • Brass/Copper Alloys: Of all die-cast parts, brass/copper alloys have the highest corrosion resistance. They also display high hardness and some of the highest mechanical properties of non-ferrous metals. Yellow brasses are subject to metallurgical processes most often. Cast brass/copper alloys display good finishing options, excellent dimensional stability, accurate dimensional control, and have strength that approaches that of steel parts. This is also the highest cost of all die-cast alloys.

 

Hot Chamber Casting Method Overview

The metal used in hot chamber casting is heated in a furnace that is connected to the casting machine. Once it reaches the appropriate temperature, molten metal travels from the furnace via a gooseneck and is forced into the die using a hydraulic piston. The process happens quickly and can last between 15-20 minutes.

Hot chamber casting is limited to metals that will not dissolve or erode the machine metal components when under high pressure.

 

What Types of Metals are Used for Hot Chamber Casting

  • Zinc alloys: This alloy enjoys some of the fastest production rates among all die-cast metals. Zinc has closer tolerances than other metals and even molded plastic. Zinc’s superior strength, stiffness, and fluidity make it an ideal choice for parts with thin walls. Its properties allow for design flexibility, lower fabrication costs, and even reduced part cost. Zinc die-cast parts are more dimensionally stable, tougher, and stronger than injection molded parts.
  • Tin alloys: Tin is among the oldest metals used by people. It is known for its low melting point and fluidity. Because of its formability and softness, it is often added to other metals to make alloys. During casting, there is little to no shrinkage upon solidification resulting in dimensionally sound parts. Using tin for casting has added cost benefits. Tin has a low melting point, so rubber or carbon steel molds can be used. It is more expensive than other metals, but its properties make it perfect for casting. Tin is also non-toxic, solderable, and does not tarnish easily.
  • Lead alloys: Lead alloys work best in applications that require less than 8000 pounds of tensile strength per square inch. Popular applications include fire-safety equipment and bearings. Compared to other metals, lead is an affordable option and prized for its corrosion resistance. Because of its toxicity, it cannot be used in applications that require close contact with food.
  • Magnesium: Magnesium provides the perfect combination of rigidity, lightweight, and resistance to wear, making it an excellent option for diverse part applications. Because it is produced from brines, seawater, and magnesium-bearing minerals, it is an affordable option for casting. Magnesium is 75% lighter than steel, 33% lighter than aluminum, and nearly equal to most plastic polymers. It is also a good choice for manufacturers who want eco-friendly parts because it is 100% recyclable. This is an ideal choice for applications that require high performance, high strength-to-weight ratio, and magnesium parts have a cast net shape.

 

Is There a Warm Chamber Die Casting Method?

Hot chamber casting is sometimes inaccurately called warm chamber casting. Other forms of die casting have intermittent steps to eliminate defects, increase efficiencies, or create parts with greater complexity.

Most manufacturing partners will use the proper terms cold chamber and hot-chamber casting to differentiate between each process.

 

Differences Between Hot and Cold Chamber Process

The differences between hot and cold chamber processes are few and far between. Both methods follow the same primary steps of the die casting process. They also use high pressure; not gravity die casting methods.

Furnace location and strength are the primary differences between hot and cold chamber processes.

Each metal alloy has a different melting point, and metals with lower melting points are cast using the hot chamber method. To make the process more efficient, hot chamber machines are constructed with the furnace attached to the die assembly. This way, alloys can be heated and quickly injected into the die cavity.

Metals with higher melting points require a robust furnace to reach the proper temperature. These higher temperatures can also damage machine components, so it’s best to keep the two separate.

Molten metal is then ladled into the machine’s chamber then injected into the die cavity. If this molten metal were used in a hot chamber machine, it would destroy the parts.

Cold chamber machines can cast 50 to 90 times per hour, and hot chamber machines can cast 400 to 900 times per hour.

 

Die casting steps are different for Hot vs. Cold

Preparation: Mold cavity lubricated – This where both techniques briefly diverge, then come back to step 2.

  • Hot chamber metals melted in the connecting furnace.
  • Cold chamber metals melted in a separate furnace.
  • Higher pressure is required for the cold chamber method.
  • Cold chamber cavities were built to create multiple parts in one mold at once.

Filling: Metal is injected into the mold.

Ejection: The cast part is ejected.

Shakeout: The cast part is separated from non-essential components.

 

Advantages and Disadvantages of Hot Chamber Die Casting

Like any process, hot chamber die casting comes with a unique set of advantages and disadvantages.

A primary advantage of hot chamber casting is fast cycle time. An average cycle time for this method is about 15 casts per minute. The process is more efficient than cold chamber because metal is melted in a portion of the machine then fed directly into the chamber.

Hot chamber casting also enjoys longer die life due to lower molten metal temperatures of cast products. While the hot chamber method has many advantages, the main disadvantage is its limited use in metals with lower melting points.

 

Advantages and Disadvantages of Cold Chamber Die Casting

The most significant advantage of the cold chamber method is its ability to make higher density cast parts. 

The added density is attributed to the increased pressure used during the metal injection process. The cold chamber method also allows for low cost-effective production of non-ferrous metal parts compared to other methods.

Injector components in cold chamber casting machines enjoy a longer machine life. Because metal is ladled in, there is limited contact between the machine’s injector components and molten metal.

Disadvantages include slower production cycles, often due to metal needing to be ladled into the chamber. If the process is not optimized, molten metal can cool significantly if it sits in the chamber too long and causes defects or porosity.

 

Die Casting General Advantages and Disadvantages

As a whole, die casting offers excellent flexibility in creating large numbers of complex metal parts. It comes with significant cost and design advantages but is limited to non-ferrous metals and not well suited for small runs. 

 

Die Casting Advantages
  • High dimensional accuracy or cast parts and components.
  • Fast production once dies are created, and machines are optimized.
  • Thinner walls are achievable when compared to other casting methods (0.6mm -0.8mm).
  • Wide range of part shape and complexity.
  • Simplified assembly (external threads can be cast, or holes cored to internal tap drill size).
  • Good finish (1 μm – 2.5 μm) (depending on the purpose, not all parts will require extra finishing).

 

Die Casting Disadvantages
  • High initial cost (cost of molds and machine set up).
  • A large production volume is required to make the process cost-effective.
  • Some porosity is common with die casting.
  • Die casting is limited to non-ferrous metals (Zinc, Aluminum, Magnesium, Copper, Lead, and Tin).

 

Hot Chamber vs. Cold Chamber Summary

  • Most steps in the cold and hot chamber die casting process are the same.
  • The desired metal type and part application will dictate which method to use.
  • Cold chamber die casting works best for metals with high melting points such as aluminum, brass, and copper.
  • Hot chamber die casting works best for metals with lower melting points such as magnesium, tin, lead alloys.
  • Metal is heated in a separate furnace with the cold chamber method.
  • A furnace that is connected to the chamber via a gooseneck heats metal in the hot chamber process.
  • Trying to heat high melting point metals in a hot chamber setup could damage the machine’s parts.

 

How to Find the Right Partner

Selecting the right manufacturing partner could mean the difference between producing high-performance parts that withstand the tests of time and stress and lack-luster parts that fail too soon.

A manufacturing partner must understand the part’s application, your desired materials, and timeline. Redstone Manufacturing has steel foundries in Vietnam, China, and India. We can provide competitive quotes, so you get the best-delivered cost for hot chamber or cold chamber die-cast parts.

If you need help with this process, contact our sales team.

 

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