What are common methods of tube cold drawing?

Hollow tube profile drawing  The cross-section is hollow, such as for drawing of tubes and hollow profiles.

There are several drawing methods as below.

1. Empty pulling: During the pulling process, no plugs is placed inside the tube billet. After the pulling, the wall thickness changes slightly. The main purpose is to reduce the diameter, also known as reduction pulling.

2. Fixed short plug pulling: During the pulling process, a plug is placed inside the tube billet and is fixed by a core rod. After the pulling, the tube billet can achieve reduction and thinning. This is the most widely used method in practice.

3. Floating plug pulling: During the pulling process, a plug is placed inside the tube billet, but the core head is not fixed. It stabilizes in the deformation zone by its own shape. This method enables the production of spiral tubes.

4. Long core rod pulling: The tube billet is placed on a surface-polished core rod, and during the pulling process, the core rod and the tube billet pass through the die hole together.

Combination method: The core rod is inserted into the tube billet with a bottom, and the core rod and the tube billet are pushed out of the die hole together. This method is used in the production of refractory metals and precious metal short tubes, and is also suitable for the production of large-diameter tubes (diameter > 300mm).

Expansion pulling: It is a method for producing large-diameter products using small-diameter tube billets. There are two methods: pressing expansion and pulling expansion.

Fixed short plug pulling

1) Deformation process

The deformation is divided into three sections: AB section: empty pulling zone, mainly radial reduction deformation, the wall thickness generally increases, also known as reduction zone. The characteristics of stress and strain are the same as those during empty pulling.

BC section: reduction wall thinning zone, in this stage, the outer diameter decreases, the inner diameter remains unchanged, and the wall thickness decreases. The characteristics of stress and strain are the same as those during bar pulling.

CD section: constant diameter zone, it is an elastic deformation zone.

Floating plug pulling

1) Deformation process

AB section: Empty pulling zone, the tube billet reduces in diameter and thickness

BC section: radial reduction zone, the tube billet undergoes a large radial reduction while the wall thickness remains unchanged. The wall thickness reduction amount is approximately equal to the wall thickness increase amount during free-end pulling.

CD section: secondary empty pulling zone, due to the change in the pulling stress direction, the inner wall of the tube billet slightly leaves the surface of the plug.

DE section: wall thinning zone, the outer diameter decreases, the inner diameter remains unchanged, achieving wall thinning.

EF section: constant diameter zone