The wire drawing process is carried out on the sheet metal drawing machine. Under the action of tension, the metal material, such as copper wire rod with a large cross-sectional area passes through the wire drawing die hole, so as to obtain the required cross-sectional shape and size. Compared with other processes, the drawing process has the advantages of high precision, simple operation and strong adaptability.

Common drawing materials include wire, thin round bar, and some special-shaped parts. Today, we focus on copper wire rod drawing. For the drawing of copper wire rod, PCD drawing die and CVD diamond coating drawing die are the most suitable. PCD wire drawing die and CVD diamond coating wire drawing die have the advantages of high hardness, good wear resistance, high precision, high finish, and can ensure the surface finish and accuracy of wire rod in the long-time wire drawing process. However, if the drawing process of copper wire rod is not mature, manufacturers need to be particularly familiar with the wire breakage of copper wire. This is helpful for the drawing factory to make a reasonable and objective analysis and judgment on the causes of copper wire breakage in the production process.

Four common copper wire rod breaks

• Central burst

The copper wire is broken from the center, with a sharp cone at one end and a sharp hole at the other end. The burst hole in the center is most likely to be mistaken for a broken bubble. It can be found that the tearing of the concave material in the center of the hole itself can be amplified by the bursting force of the concave material. Therefore, it may be the central burst caused by excessive oxygen content in the copper rod (greater than 6000ppm), or the central burst caused by inclusions, and the central burst caused by poor wire drawing equipment.

• Bubble break

The cross section of the broken copper wire is in the shape of a hole. In the enlarged picture, the hole surface is very smooth without bulge or cracking. The cause of bubble breakage is due to improper hydrogen control during casting and shrinkage caused by poor cooling. If the hole is small, it may be closed in the subsequent hot working process. If the hole is large, it cannot be closed, resulting in bubble disconnection.

• Tension break

This is a common thread break during stretching. The wire-breaking feature is that the broken head is in cup cone shape or sharp cone shape. The wire breaking is caused because the tensile force is greater than the tensile strength of the copper wire itself. The causes are poor lubrication during copper wire drawing; Improper angle of eye mold; Excessive surface reduction rate and improper speed matching.

• Copper powder break

There is a considerable amount of copper powder in the wire drawing lubricant. During wire drawing, copper powder will accumulate at the entry angle of the eye mold, so that the copper wire is clamped in the eye mold, resulting in wire breakage. In addition, the peeling and accumulation of copper thorns in front of the eye mold will also cause wire breakage.

In order to avoid the above situation, manufacturers need to pay attention to four suggestions.

• The surface of wire blank shall be properly treated before drawing, such as pickling, homogenization, etc.
• In order to eliminate the defects such as ash inclusion, pricking and pit on the surface of wire blank and obtain high-quality finished wire rod, the wire blank shall be peeled. Before peeling, it shall be stretched to make the section of wire blank round and the surface with certain hardness.
• The processing rate of wire rod shall be determined according to the plasticity of metal, production efficiency, deformation conditions, equipment capacity, die quality, lubrication conditions, etc. On the premise of not affecting the quality and performance of finished products, the greater the total processing rate, the better.
• The choice of lubricant should consider two aspects: cooling and cleaning. According to the different materials, drawing processes and quality requirements of wire rod, choose lubricants with different varieties, concentrations and composition ratios. For example, in the rough drawing stage, the speed is generally low and the deformation is large, so the emulsion can be used as the lubricating coolant; During fine drawing, due to high speed and high surface requirements, high-grade lubricating oil needs to be selected.

The above is about the common breakage of copper wire drawing and preventive measures. If you still have questions about the choice of wire drawing die, the following video will help you.