Principle of Cold Drawing

Purpose of Cold Drawing

Cold drawing is the process of drawing materials at room temperature. During the drawing process, the material passes through the die. And through the extrusion of the material by the die, the cross-section of the material can be changed according to the different shapes of the die.

The cold drawing of the material needs to ensure that the material can be pulled, so the drawing force of the cold drawing must be higher than the yield strength of the material. At the same time, cold drawing should also ensure that the material will not break, so the drawing force of cold drawing needs to be less than the tensile strength of the material.

Effect of Cold Drawing on Alloys

Size

The biggest function of cold drawing is to control the size of the material. During cold drawing, the die squeezes and deforms the material. Manufacturers can control the size of the material after cold drawing through different dies. It should be noted that if the size of the finished product is too different from the size of the material before cold drawing, cold drawing will be difficult to pull. In this case, the material should be cold drawn several times.

At the same time, since the cross-section of the material is reduced during cold drawing, the length of the material after cold drawing will increase.

Shape

Another effect of cold drawing is to change the shape of the cross section of the alloy material. The difference in shape is determined by the difference in the die. For example, if the die is square, the cross-section of the material after cold drawing will be square. If a round bar is cold drawn in this way, a square bar is obtained after cold rolling. It should be noted that if the material is to be deformed and cold drawn, it is necessary to ensure that the size of the material before and after cold drawing is similar.

Surface

The third effect of cold drawing on the alloy is the surface. As the material passes through the die, impurities on the surface of the material are removed due to friction between the die and the material. This will give the material a polish-like effect. For black rods, it becomes bright rods after cold drawing. But we generally continue to polish or grind the material after cold drawing.

Mechanical Properties

Cold drawing also affects the mechanical properties of the alloy. In previous articles we mentioned that metals will work hardening during deformation. Cold drawing is a cold deformation process, which also produces work hardening. In some cases, cold drawing can serve to control the strength of the alloy. Of course, the work hardening caused by the cold drawing process can be removed by heat treatment.

Cold Drawing of Different Alloy Products

Cold Drawn Bars

For rods, cold drawing can control the size and shape.

For round bars above 50mm, hot rolling or forging are generally used to control the size. For rods below 50mm, the size needs to be controlled by cold drawing.

The strength of the rods after cold drawing is relatively high, but the toughness is relatively poor at the same time. The alloy needs to be softened by heat treatment. For the material after heat treatment, the cold drawn rods still have higher strength.

Round bars can be cold drawn into flat bars, square bars and hexagonal bars. In the manufacturing process, it is still necessary to first cold draw the material with a circular die to reduce the diameter. In the last step of cold drawing, the round bars are cold drawn into other shapes with different shapes of dies. Bars produced in this way still require heat treatment.

Figure 2

Cold Drawn Pipes

Cold drawing is a process required in the production of seamless pipe & tube, coil tube and capillary tube. Its main function is to control the size of the pipes. During the cold drawing process of the pipes, the inner wall is also controlled by the mandrel.

For seamless pipe & tube, cold drawing and cold rolling have similar effects. All these processes are to reduce the outer diameter or wall thickness of the pipe. Compared with cold rolling, cold drawing can make the material stronger. In addition, for large-diameter seamless pipes, more cold-drawing processes are used. In order to make the cold drawing process smoother, the seamless pipe & tube needs to be dusted before cold drawing.

Coil tube and capillary tube are small in size and do not need to be dusted before cold drawing. Therefore, they all have a bright finish after cold drawing. The next step requires bright annealing. Among them, the surface of the capillary can be further polished.

Figure 5

Cold Drawn Wires

Wire can only be manufactured by cold drawing. Cold drawing can control many aspects of the wire.

First of all, the most important thing in cold drawing is to control the diameter of the wire. The smaller the diameter of the wire, the more cold drawing it needs to go through. Likewise, the smaller the diameter of the wire, the longer the length after cold drawing.

Second, cold drawing can change the surface of the wire. The wire is cold drawn from wire rod, which generally has an pickled surface. Cold drawing can make the surface of the wire bright.

Finally, cold drawing can increase the strength of the wire. The more cold drawing the wire undergoes, the higher its tensile strength. For some solid solution strengthened alloys, cold drawing is the only way to increase the strength of the wire. After cold drawing, the wire can obtain different mechanical properties according to different heat treatment regimes. The strength of the wire is the highest if the wire is not heat treated. This wire, also called spring wire, can be used to make springs. If the wire is bright annealed, the wire can obtain a semi-hard state or a soft state depending on the annealing temperature and time. Most of the welding wire is in the soft state.

Figure 7

Cold Drawing VS Cold Rolling

The following table is a comparison of the advantages and disadvantages of cold drawing and cold rolling:

Conclusion

Cold drawing is a cold working process of metal materials. It can change the size, shape, surface and mechanical properties of metals.

Pipes, bars and wires can be produced by cold drawing. Among them, wires can only be produced by cold drawing.

We produce high quality nickel alloy cold drawn rods, cold drawn pipes and cold drawn wires. Please don't hesitate to contact us if you have any needs.