Ironing is a metalworking process that is commonly used in the manufacturing of drawn cups. It is a cold working operation that involves reducing the wall thickness of a drawn cup while maintaining its diameter. The correct answer to this question is option 'c', which states that ironing is used to decrease the wall thickness of the drawn cup.

Explanation:

1. What is ironing?
Ironing is a metal forming process that is typically performed after deep drawing to achieve the desired final shape and dimensions of a drawn cup. It involves compressing the walls of the drawn cup between a punch and a die, resulting in a decrease in wall thickness.

2. Purpose of ironing:
The primary purpose of ironing is to achieve a uniform wall thickness in the drawn cup. By reducing the wall thickness, the cup becomes more rigid and can withstand higher internal pressures without failure. Additionally, ironing helps to improve the surface finish and dimensional accuracy of the cup.

3. Ironing process:
During the ironing process, the drawn cup is placed on a die, and a punch is pressed against the cup's open end. As the punch moves downward, it causes the cup's walls to flow radially inward and reduce in thickness. The material is redistributed from the thicker regions to the thinner regions, resulting in a more uniform wall thickness.

4. Ironing parameters:
Several factors influence the ironing process, including the material properties, lubrication, punch and die design, and process parameters such as pressure and stroke length. These parameters need to be carefully controlled to ensure the desired reduction in wall thickness is achieved without causing defects or material failure.

5. Benefits of ironing:
Ironing offers several benefits in the manufacturing of drawn cups. It allows for the production of cups with precise dimensions and a consistent wall thickness, ensuring uniform performance and quality. It also helps to improve the cup's mechanical properties, such as strength and rigidity, making it suitable for various applications.

In conclusion, ironing is a metalworking process used to decrease the wall thickness of a drawn cup. By compressing the cup's walls between a punch and a die, the material flows radially inward, resulting in a more uniform wall thickness. Ironing plays a crucial role in achieving the desired final shape, dimensions, and mechanical properties of drawn cups.