Cold processing techniques such as Cold Drawing are used to create seamless pipes after they have been extruded. Cold drawing is a slower process that results in a lower reduction ratio of 15-35 percent depending on the alloy, but it produces a very fine and admirable grain structure. Depending on the need, all production processes have advantages.  Cold working has the added benefit of faster instrument adjustments and lower operating costs. Cold drawing is a metalworking technique that involves stretching the metal with tensile forces. It's called cold working when it's finished at room temperature. The principle is equivalent to cold pilgering, in which the pipe is forced between dies to reach the desired size by reducing the lateral dimension, i.e. diameter, and increasing the longitudinal dimension, i.e. volume. Draw Bench is the name of the unit that is used for this purpose.
By cold working on steel, the draw bench uses only friction and no heat to alter the form of the metal. The drawing starts with the acquisition of raw materials, with special attention paid to the material's chemistry and measurements, such as scale, wall thickness, concentricity, and straightness tolerances. The next step is aiming, which entails reducing the diameter of the substance at the tube end so that it can reach the die. Push pointing, rotary swaging, and squeeze points are the most popular techniques. With a backbench, die head, and front part, the draw bench is normally mechanical. The cold drawing reduction method is divided into two types: Rod drawing, which uses a mandrel within the tube, and Sink drawing, which does not.
A hardened steel mandrel is inserted within the shaft, followed by a gripper, in rod drawing. The size of the die determines the pipe's outer diameter, while the size of the mandrel determines the inner diameter. Lubricating oil is pumped on the surface after the tubing is inserted into the die. Rod drawing has the advantage of being able to achieve reasonable drawing rates and a significant reduction ratio. Both the outer diameter and the thickness of the wall are limited here. This is not the case for Sink drawing, in which the pipe is drawn directly from the die without the use of a mandrel or internal support.
This results in a decrease in outer diameter without having a significant impact on wall thickness. This procedure can be used to draw the tube to its final size and as a scaling move after rod drawing. The diameter to wall thickness ratio will determine the correct die angle. The drawn product, also known as cold-drawn tubing, has a bright and polished finish, improved mechanical properties, better machining characteristics, and accurate and uniform dimensional tolerances. Annealing may also be used as heat treatment to remove internal pressures and smooth the substance. The finished product is packaged, shipped, and delivered after all of the processes are completed.

Stainless Steel Seamless Pipe Cold Drawing Process

Sink Drawing

This is the simplest drawing procedure. The tube is drawn through a hardened die made of polished tool steel or, for smaller sizes, an industrial diamond. With the correct lubrication, when the tube surface comes into contact with the polished die surface it is worked smooth. The inside bore surface is not constrained so the wall thickness of the tube will always increase when it’s drawn. Large cross sectional area reductions can be performed using this technique.

Plug Drawing

This is the type of drawing used for the highest quality output. The outside and inside diameters of the tube are worked at the same time. A plug made of high grade tool steel with a polished surface is located precisely in the middle of the outside diameter drawing die. The tube is loaded over the plug attached to a fixed rod. As the tube is drawn through the die the burnishing action of the metal flowing over the stationary plug imparts a high tolerance surface finish inside the tube.

When properly lubricated and prepared the ID will show very few defects and finishes of 0.20 microns Ra are achieved. Therefore, plug drawing is chosen to significantly improve the ID surface condition.