Metal molds are used in various manufacturing processes for shaping and forming materials. In the context of the given options, metal molds are used in the die casting process.

Die casting is a manufacturing process that involves injecting molten metal into a mold cavity under high pressure. The metal solidifies and takes the shape of the mold, resulting in a finished part or product. This process is widely used in the production of complex-shaped metal components with high precision and accuracy.

Here is a detailed explanation of the die casting process and the use of metal molds:

**Die Casting Process:**
1. Mold Preparation: The metal mold, also known as a die, is prepared by machining two halves that fit together to form a cavity. The mold is typically made of a durable material such as steel or iron.

2. Molten Metal Injection: The molten metal, usually an alloy of aluminum, zinc, or magnesium, is heated to its melting point and injected into the mold cavity. The injection is performed under high pressure to ensure the metal fills the mold completely and accurately.

3. Cooling and Solidification: Once the metal is injected, it rapidly cools and solidifies within the mold cavity. Cooling channels within the mold help in dissipating heat and achieving uniform cooling.

4. Mold Opening and Ejection: After the metal solidifies, the mold halves are separated, and the finished part is ejected from the mold cavity. The mold is then closed again for the next cycle.

**Advantages of Metal Molds in Die Casting:**
- Durability: Metal molds are capable of withstanding high temperatures and pressures, making them suitable for the die casting process.
- Precision and Repeatability: Metal molds can maintain tight tolerances, allowing for the production of complex and intricate parts with consistency.
- Surface Finish: Metal molds can produce parts with smooth surface finishes, reducing the need for additional finishing operations.
- Longevity: Metal molds have a longer lifespan compared to other mold materials, making them a cost-effective choice for high-volume production.

In conclusion, metal molds are used in the die casting process. This process involves injecting molten metal into a mold cavity under high pressure to produce complex-shaped metal components with precision and accuracy. Metal molds offer durability, precision, and longevity, making them suitable for high-volume production.