ANS:D - Hollow ram is used for indirect extrusion.

Among the given statements, the true statement regarding the extrusion of metals is: Hollow ram is used for indirect extrusion. In indirect extrusion, also known as back extrusion, a hollow ram is used. The metal billet is placed inside the hollow ram, and pressure is applied to force the billet through the die. This process allows for more complex shapes to be extruded compared to direct extrusion, where the billet is placed outside the ram. The other statements are not accurate:

• The speed of the extruded material may not necessarily be the same as that of the ram speed. It depends on various factors such as the material being extruded, the design of the extrusion setup, and the desired properties of the extruded product.
• Redundant work is not specifically a function of the die angle in extrusion. Redundant work refers to the unnecessary deformation or energy loss during a metal forming process, which can occur due to factors such as friction, improper tool design, or improper process parameters.
• Relative motion between the billet surface and the container wall may or may not be present in extrusion, depending on the specific setup and conditions. In direct extrusion, the billet moves relative to the container wall, while in indirect extrusion, the billet moves relative to the ram.