Which method involves injecting molten plastic into a die to create shapes?

The method that involves injecting molten plastic into a die to create shapes is known as plastic injection molding. This process is characterized by its efficiency in producing complex and intricate shapes with high precision. During injection molding, plastic material is heated until it melts and is then injected under pressure into a closed mold. Once the material cools and solidifies, it takes the shape of the mold cavity.

Plastic injection molding is widely used in various industries due to its ability to produce a large number of identical parts quickly and with minimal waste. The use of a die or mold allows for very specific designs and can accommodate a vast range of product sizes and forms, making it an ideal choice for manufacturing components in automotive, electronics, consumer goods, and more.

The other options, such as polymer molding, thermoforming, and compression molding, represent different manufacturing processes that do not specifically utilize the injection of molten plastic under pressure into a die to form shapes. For example, thermoforming involves shaping plastic sheets using heat and pressure without the injection process, while compression molding involves placing plastic material into a heated mold and then applying pressure to shape it, without the injection technique used in injection molding.